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April 2

Book recommendations on the history of automotive engines

Hello, Science Reference Desk. I am looking for recommendations on full-length, non-fiction books (or equivalently-detailed internet resources) that review the modern history of automobile engines. I'm looking for a book that goes into considerable depth beyond our articles. For context, this query is prompted by some extensive reading I have already conducted; I've absorbed about everything I can from our articles... This morning on BBC World Service radio, I learned that after switching to 1.6 liter, six cylinder turbocharged hybrid engines, Formula 1 cars are now completing laps faster than when they used ten cylinder, 3.0 liter BMW engines just a few years ago (interview paraphrased in the web news story). This progress seems incredible, and it's no surprise that it's flared some brand rivalry! I'm trying to determine whether these technology results are representative of progress across the entire automotive industry, or if F-1 engines have evolved so far out on their own branch of the technology tree that these improvements cannot translate to ordinary cars - (needless to say, turbo-compound engines used in these racecars look an awful lot like turbocharged aircraft engines!); or if the new race results are consequences of other changes independent of engine performance. Nimur (talk) 16:34, 2 April 2016 (UTC)

doubt you'll find a full-length general interest book specifically about what you're looking for....vaguely related though: this is among the greatest (and best-selling) pop autobiographies ever written and about American auto industry...has all kinds of cool stuff about the creation of the Ford Mustang.. Iacocca: An Autobiography 68.48.241.158 (talk) 19:14, 2 April 2016 (UTC)

I'd second that. It generally takes a while to get good technical books about motor sport, so I don't believe there is detailed information about the latest engines in book form. If you were to buy Autocourse from the last few years, you could start to read some of it. The other issue you'll face is that F1 isn't just about engine power: aerodynamics have a huge part to play, and the influence of changing regulations on the amount of aerodynamic assistance makes a huge effect on lap times. For example, the Coandă effect had a huge influence on F1 design a few years ago, but is pretty much outlawed now. Also, note that unrestricted 1.6 turbo engines would blow 3 litre NA engines into the weeds: in the 1980s both were allowed: the 3L engines produced 5-600 BHP; the 1.5L turbos knocked out well over 1000 BHP in qualifying form. And a final comment: the F1 fraternity does not refer to the current generation as the "engine": they are power plants, comprising an internal combustion engine, a turbo with a heat recovery system (MGU-H) and a kinetic recovery system (MGU-K) with a battery storage system and an electric power unit to boost output. If you read in places like https://www.formula1.com/ some of this will be covered.--Phil Holmes (talk) 19:29, 2 April 2016 (UTC)

Indeed, thank you for the terminology correction! Nimur (talk) 15:25, 3 April 2016 (UTC)

You might want to try a magazine like Popular Mechanics. While not exclusively devoted to car engines, I bet they go into more detail than car magazines, which tend to be very superficial on mechanical details. If you go to a library with those in stock, you can probably find quite a bit of detail on car engines found in issues over the decades. StuRat (talk) 19:25, 2 April 2016 (UTC)

Cough. I'd be a little surprised if Popular Mechanics covered the design parameters of Formula One systems pushing out around 900 BHP from 1.6L power plants. They tend not to be home maintenance projects. The estimate from Bernie Ecclestone today was that Mercedes-Benz spent around $700M developing theirs, so it's a bit more than a garage project.--Phil Holmes (talk) 20:55, 2 April 2016 (UTC)

For Formula One, yes, it's uber advanced, everything custom. Other racing classes can be done in one's garage, one of my neighbors was a race car driver and was always working on his race car. Engines have improved tremendously over the course of my life, with increasing compression, greater efficiency and even transmissions being more efficient in using the energy the engine delivers to them. I wonder at times, just what will the next half century bring?Wzrd1 (talk) 20:59, 2 April 2016 (UTC)

Thanks guys. Nimur (talk) 13:56, 3 April 2016 (UTC)

Do bacterium have feelings/aspirations?

Lets take paramecium for example. Does paramecium have feelings, such as happiness and sadness? Moreover, how do they know what they are doing? Surely they must have aspirations, such as "I must eat 6 pieces of algae today and then reproduce". --FallinggoApartio (talk) 19:51, 2 April 2016 (UTC)

Did you mean to post this yesterday? DrChrissy ^(talk) 19:54, 2 April 2016 (UTC)

No. That would require nerve cells and a brain. Think of a computer program, does it have feelings and aspirations, or does it just do what it is programmed to do, without any thought at all ? StuRat (talk) 19:54, 2 April 2016 (UTC)

StuRat, be careful what you assume to require nerve cells and a brain. Some organisms can surprise you.

"Studies on Physarum have even shown an ability to learn and predict periodic unfavorable conditions in laboratory experiments. Professor John Tyler Bonner, who has spent a lifetime studying slime molds argues that they are "no more than a bag of amoebae encased in a thin slime sheath, yet they manage to have various behaviours that are equal to those of animals who possess muscles and nerves with ganglia – that is, simple brains." --Slime mold#Behavior

--Guy Macon (talk) 06:13, 3 April 2016 (UTC)

Ultimately there is no way to know whether a paramecium has subjective experience, aka qualia. That's what makes it subjective. But it does seem unlikely. --Trovatore (talk) 19:58, 2 April 2016 (UTC)

If you're a materialist I think it's pretty safe to say that single-celled organisms don't have "feelings" or mental "experiences", any more than your skin cells do. Thought requires a brain. --71.110.8.102 (talk) 22:14, 2 April 2016 (UTC)

Yes, materialists would say that, that's true. However materialists really cannot explain the hard problem of consciousness. The extremists among them, the "eliminative materialists", simply deny that it's a problem. --Trovatore (talk) 22:44, 2 April 2016 (UTC)

Given what we know about qualia (nothing), I see absolutely no reason to think that single-celled organisms don't (or do) have qualia, whether or not you're a "materialist". -- BenRG (talk) 04:00, 3 April 2016 (UTC)

• Paramecium lack the portions of the nervous system which are responsible for producing feelings and emotions. --Jayron32 03:27, 3 April 2016 (UTC)

They respond to stimuli. Maybe between stimulus and response there are intermediate states that, once we've figured out what qualia are, we'll recognize as qualia. Maybe not. -- BenRG (talk) 04:00, 3 April 2016 (UTC)

"Paramecium lack"??? I'm almost used to seeing "bacteria" used as a singular noun, but "paramecium" as a plural is new to me. --Trovatore (talk) 04:06, 3 April 2016 (UTC)

Sedan vs. Hatchback

What advantages do sedans have over hatchbacks? Is it just a question of aesthetics? --Llaanngg (talk) 20:41, 2 April 2016 (UTC)

Hatchbacks potentially allow for more storage space than a sedan, given the large hatch access to the storage area and the two-box design that merges passenger and cargo compartments. clpo13_(talk) 20:52, 2 April 2016 (UTC)

I think you read the Q backwards, he was asking for advantages of the sedan. StuRat (talk) 21:00, 2 April 2016 (UTC)

Whoops, you're right. Dunno what I was thinking. clpo13_(talk) 21:03, 2 April 2016 (UTC)

Disadvantages of hatchbacks:

1) They get hot, due to all that extra window surface area, and it being more horizontal than in a sedan. (Could be an advantage in winter, if not covered in snow.) I had a game melt back there (King Oil). Louvers can help here, but they impair visibility somewhat.

2) The contents of the cargo area can be seen, both looking messier and tempting thieves. There can be some type of cover used to prevent this.

3) The opening height can be higher, and the hatch heavier, making it harder for short people to close the hatch.

4) The pneumatic(?) cylinders that hold them open can fail, and if the hatch falls on your head, it could cause serious injury.

5) Smells in the hatch area intrude on the passengers more. Imagine a bag of manure.

6) More window area to clear of ice in winter.

7) The more horizontal hatch is more likely to shatter in a hail storm. StuRat (talk) 21:00, 2 April 2016 (UTC)

What hatches have a more horizontal rear window than a sedan? Iapetus (talk) 13:55, 4 April 2016 (UTC)

Hyundai Accent, for one. Compare that with sedans, many of which have a nearly vertical rear window. StuRat (talk) 14:51, 4 April 2016 (UTC)

• 
  1998-2002 Lincoln Town Car Signature Series

That's two sedans you compare. This is the hatchback version:

• 

Thanks, removed Hyundai Accent Sedan to avoid confusion. The spoiler on the top looks like it would help protect the rear windshield from hail. StuRat (talk) 15:25, 4 April 2016 (UTC)

That's the point, StuRat. I wanted to know why would someone prefer a sedan. I could only think about advantages of hatchbacks over sedans, like the example above your answer. They also have a bigger trunk lid for bulky objects. In a sedan, even if you had space for a fridge, you won't get into the trunk. Llaanngg (talk) 21:02, 2 April 2016 (UTC)

Safety could also be an issue. Sedans might have the center of gravity lower than a hatchback. Scicurious (talk) 21:10, 2 April 2016 (UTC)

And if you get rear-ended, the trunk can collapse and provide more protection. This paper only mentions that the car is more likely to remain driveable, but presumably there is some safety benefit for occupants as well. --69.159.61.172 (talk) 21:15, 2 April 2016 (UTC)

1 Aesthetics maybe

2 Weight, that side glass weighs, as does the ring bulkhead for the tailgate

3 CGZ

4 Body torsional stiffness

5 squeaks and rattles

6 temperature control

7 tailpipe emission ingress

8 tailpipe noise ingress

That list is definitely the sound of straws being grasped, the differences are slight and the practicalities favor the hatch for most people I'd have thunk. In India hatchbacks are lower status than sedans, hence the wide availability of models that would be hatchbacks anywhere else with a funny little bustle trunk. Greglocock (talk) 22:43, 2 April 2016 (UTC)

CGZ?Scicurious (talk) 22:47, 2 April 2016 (UTC)

Higher Center of Gravity in the Z (vertical) direction. StuRat (talk) 22:49, 2 April 2016 (UTC)

Yeah, that accident at CGZ? Caused by a hatchback. The more you know ====* clpo13_(talk) 22:51, 2 April 2016 (UTC)

• Since StuRat just makes up things he thinks he read some time, I might as well provide some references to make this section useful for the OP. See this article. --Jayron32 03:26, 3 April 2016 (UTC)

• Other than style, the only disadvantage they list is that potential thieves can view what's in the back. That's my point #2. I also notice that Greg's unreferenced list and Scur's unrefed response got no criticism from you, showing you are on a one-man vendetta against me. Should you really bring your personal grudges here ? Or can you just list your refs without the personal attack next time ? StuRat (talk) 07:10, 3 April 2016 (UTC)

It's difficult to find objective information on this subject, but there's this post on Reddit where someone has at least gone to the trouble of collating a number of responses to find the most popular features of sedans. To summarise, the top advantages were (i) looks, (ii) price, (iii) availability, (iv) trunk security and (v) acoustics. --Heron (talk) 09:07, 3 April 2016 (UTC)

Following up on the security issue, which surprises me ... in the UK every hatchback that I have used has had a rigid horizontal parcel shelf which conceals the contents of the boot/trunk/cargo area when the rear hatch is closed. The parcel shelf can be removed to maximise carrying space, but this would be a temporary measure for a specific purpose. Are parcel shelves not standard equipment on US hatchbacks ? Gandalf61 (talk) 12:28, 3 April 2016 (UTC)

Parcel shelves in hatchbacks are often inadequate or unsafe for heavy parcels. The Toyota Prius has no shelf, only a thin retractable plastic roller blind. AllBestFaith (talk) 14:42, 3 April 2016 (UTC)

Yep, that's the same down here (Poland), and as far as I remember, in Western Europe that's also the case. Unless the owner removed it for whatever reason, they all seem to have. It seems to be not only a case of security against thieves, but it's also about safety, to maintain the cargo in place in case of a rollover accident. Llaanngg (talk) 14:47, 3 April 2016 (UTC)

Do we use the calories in alcohol as energy?

Do we transform the energy contained in alcohol as energy? Could we keep alive longer drinking alcoholic beverages like vodka instead of just drinking water? --Scicurious (talk) 21:07, 2 April 2016 (UTC)

Yes we use it as energy, but no, you can't stay alive on ethanol alone, as we need many other nutrients. StuRat (talk) 21:09, 2 April 2016 (UTC)

I don't mean staying alive on ethanol alone. But given the choice to drink just water, or, water and vodka, what would let's use survive for a longer period? --Scicurious (talk) 21:12, 2 April 2016 (UTC)

That is going to depend on the balance between the water and the vodka. Admittedly the alcohol will have a small nutritional value - but it also has a fairly high toxicity which could cause organ damage if you took too much of it. 217.44.50.87 (talk) 21:33, 2 April 2016 (UTC)

Also, ethanol causes you to lose more water, as it increases urine production by interfering with vasopressin. So if running out of drinkable water is a problem, best to avoid the liquor. --71.110.8.102 (talk) 22:11, 2 April 2016 (UTC)

I seem to recall a case of a shipwreck, where they had their cargo of sugar and rum, and fresh water on the island. Some consumed the sugar and rum, while others just drank water, and the latter group lived longer. Not sure if this really happened, and even if it did, they may have died more quickly from overdoing it. A small enough dose of sugar and rum (with water) probably would have been better than water alone. StuRat (talk) 21:53, 2 April 2016 (UTC)

Do you mean sugar mixed with the rum? Otherwise, I don't see any reason for not drinking water with sugar. --Scicurious (talk) 22:11, 2 April 2016 (UTC)

No, not mixed. I'm not sure which is worse, sugar-water or rum. StuRat (talk) 23:04, 2 April 2016 (UTC)

Any citation for this nonsense, Stu?--TMCk (talk) 23:16, 2 April 2016 (UTC)

I've made no claim that to have stated a fact here, so there's nothing to reference. "I seem to recall..." means I'm not positive. I was hoping somebody else might recognize the story and have the facts. But, since Jayron apparently can't live without endlessly ranting at me, let's let him get his fill. (I was hoping that eventually he would have the sense to keep such rants off the Ref Desk, but alas he doesn't seem to.) StuRat (talk) 07:19, 3 April 2016 (UTC)

You said "No, do not mix." followed by a false rational and there is no "I seem to recall..." (not that it would matter much). You more than strongly implied the false fact that a sugary soft drink is at least almost as bad as wodka in a survival situation. One can only hope nobody, including youself, remembers and applies your ideas in a lifethreatening situation: "Throw the pop of the raft. The guy from the ref-desk said it could be even worse than wodka."--TMCk (talk) 14:54, 3 April 2016 (UTC)

I thought he was asking if the rum was already mixed with sugar when they were shipwrecked, and I said "No, not mixed". And the "I'm not sure which is worse, sugar-water or rum" means exactly that, I'm not sure. I'm not implying anything, so please stop reading things into it and only look at what was actually said. The "I seem to recall..." was on my previous reply where I introduced the story. Since all you said was "this nonsense" without saying what you consider to be nonsense, I had no idea what you were complaining about, and thought it might be the entire shipwreck story. If you are going to ask for citations, be specific about what claim you want the citation for. StuRat (talk) 06:23, 4 April 2016 (UTC)

Have you ever considered using one of those?--TMCk (talk) 14:16, 4 April 2016 (UTC)

Stu doesn't believe in providing citations for anything he says. He has said so repeatedly in the past. He believes everything he says is so blatantly obviously true, it doesn't need references. Which questions why it needs saying at all, if that were true. However, getting Stu to provide even a single reference to any question he answers is a futile endeavor. He will refuse to do so, and will instead now pick through your personal editing history for the one time you answered a question 3 years ago without a reference, and hold that aloft as why he doesn't have to provide references ever for any of his ridiculous speculations. Then he'll attack you relentlessly for that one answer you gave three years ago, trying to deflect the legitimate criticism against himself for never providing a single reference ever. --Jayron32 03:24, 3 April 2016 (UTC)

Re: "Stu doesn't believe in providing citations for anything he says", I've provided many refs for questions on this very page, so you are quite obviously lying. StuRat (talk) 07:23, 3 April 2016 (UTC)

A useful cut-and-paste: [ Citation Needed ]. (Note that it has three links in it, not one.) --Guy Macon (talk) 06:24, 3 April 2016 (UTC)

Indeed, if everything that you have is water, sugar and rum, I don't see why someone wouldn't take at least some sugar besides water. Maybe he should go lightly with the rum, though. Scicurious (talk) 23:42, 2 April 2016 (UTC)

• The basic answer is yes -- a person who has a bottle of vodka and some water will be able to stay alive longer than a person who only has the water. Looie496 (talk) 22:22, 2 April 2016 (UTC)

And how does the alcohol get digested/converted to energy by our bodies? Alcohol is not present (or only scarcely) in nature, so, why would we be able to process it into energy? Scicurious (talk) 14:40, 3 April 2016 (UTC)

Good question. One wishes there was an easily available online encyclopedia with an article about the topic. Shock Brigade Harvester Boris (talk) 15:06, 3 April 2016 (UTC)

As for why, ethanol is harmful if not metabolized, and it may just be an accident that it gets metabolized into a form that provides us with energy. On the other hand, if somewhere in our evolutionary past was an animal that ate rotting fruit, it may have had enough evolutionary pressure to use that energy to develop such a trait, and then passed it down to us. StuRat (talk) 14:33, 4 April 2016 (UTC)

Stupid cold fusion questions

These are all vaguely related to muon-catalyzed fusion, a process that would be the end of the energy problem if only muons were more stable...

1. Muon-catalyzed fusion is said to work because the nuclei are brought much closer together. Nuclei also seem to come closer together in a Bose-Einstein condensate. Apparently though the notion that this means fusion is considered a vulgar error. [1] As I understand it, the nuclei are smeared together in their probability distribution, but if the position of one is known the position of all the others is known to be somewhere else. Despite the talk of a "superatom", the distribution must be fairly broad then. Nonetheless... how dense can a BEC actually get? Does it get anywhere in the ballpark of fusion plasmas? There may be an answer here that I failed to understand - they give densities at a transition point, but I don't understand that to be the BEC itself?

2. It is possible to make a coherent electron source [2]. Does that mean that it is possible to bounce coherent electrons back and forth in a specially shaped chamber (or in a cyclotron-style ring), creating standing waves of electron density into which multiple nuclei might be drawn? And if so, can these waves be made smaller than the ordinary wavelength of electrons (and size of ordinary atoms/covalent bonds) by some clever wave mechanics or by making the electrons go really fast so they pick up relativistic mass comparable to that of a muon? Would that then mean they can undergo the equivalent of muon-catalyzed fusion?

3. If the electron wavelength can't be reduced, is it conceivable to do the same thing with muons, creating a coherent standing wave pattern, and pump the muons to such tremendous speed that their lifespan is extended for relativistic reasons? Wnt (talk) 21:53, 2 April 2016 (UTC)

If we could answer that Wnt, I don't think any of us would be editing WP. Instead, we would be busy trying to submit our papers to peered review journals in the quite confidence that there is a Nobel Prize waiting for us at the end of it.--Aspro (talk) 23:04, 2 April 2016 (UTC)

The Wikipedia articles Cold fusion and Muon-catalyzed fusion are not fora for general discussion about cold fusion. AllBestFaith (talk) 14:04, 3 April 2016 (UTC)

Has someone used them that way? I don't see your point. Wnt (talk) 22:08, 3 April 2016 (UTC)

The warning appears at Talk:Cold fusion. This mediation has concluded.. AllBestFaith (talk) 18:42, 4 April 2016 (UTC)

OK, so perhaps someone has used them that way, but I still don't see the relevance to Wnt's question. The articles and their talk pages are not fora for general discussion on the subject matter, but questions about the subject matter can certainly be directed to the science refdesk. That's what it's for. --Trovatore (talk) 19:05, 4 April 2016 (UTC)

April 3

Feeding a 5W IR LED

If one has a 5W infrared LED, how much volts of DC does one need to get maximum IR output without blowing it. And please also tell much CURRENT will be sufficient and how does one measure it ?  And will using a resistor (how much ohms will make us succeed, BTW has it always to be put on + wiret ? ) And will the resistor lower voltage or current, please. I hope somebody will be kind enough to let me know these things without suggesting me to filter rather confusing waters of Google....124.253.244.183 (talk) 00:37, 3 April 2016 (UTC) 

Our article on Ohm's law covers at least the last part of your question which seems like a homework question. --DHeyward (talk) 02:16, 3 April 2016 (UTC)

A 5W infrared LED typically (there are 5W versions with other characteristics) has a forward voltage of 2V DC and current rating of 1000 mA (1 Amp). The calculation of the series resistor is by Ohms Law: Supply voltage - 2V / 1 Amp. For example, if the supply voltage is 12 VDC, the voltage to be dropped in the resistor is 10V at 1 Amp, so the resistor should be 10/1 = 10 ohms. The power dissipated in the resistor will be 10V x 1 = 10 Watts. You would normally choose a 10 ohm resistor of at least that rating, example 20W, as a safety margin. The above calculations presume that the power supply is capable of supplying 12V at 1 Amp. If you do the sums correctly, there's probably no need to measure the current, but a 1 Amp (or more) DC ammeter or multimeter set on an appropriate range will allow you to do so. The resistor limits the current that would otherwise flow if the LED were connected directly to the power supply; that current would almost certainly destroy the LED or power supply (in that order of likelihood). Akld guy (talk) 04:15, 3 April 2016 (UTC)

I don't mean to be snarky but "A 5W infrared LED typically (there are 5W versions with other characteristics) has a forward voltage of 2V DC and current rating of 1000 mA (1 Amp)." seems a little unlikely. I think you mean 5V. In which case rinse and repeat. Guy's advice below seems more robust.Greglocock (talk) 07:34, 3 April 2016 (UTC)

Yes, the obvious error is 2V @ 1A is only 2W. The question regarding what a resistor will do makes me believe that this is a homework problem and reluctant to provide a complete solution even if they specified an LED. I will say, that I doubt I would ever choose a single 5W IR LED to consume 5W of total power. The spec below has many solutions. --DHeyward (talk) 07:51, 3 April 2016 (UTC)

@Greglocock: and @DHeyward: You both need to take a look here. The voltage is 2V, the current is 1 Amp for several 5W models. Akld guy (talk) 09:26, 3 April 2016 (UTC)

@Akld guy: 5W is the power rating, not power consumed. Operating at 2V and 1A will consume 2W with luminous power below that. It's simply not possible to consume 5W with 2V and 1A. It's the same with the resistor you use above. The package/material might be a 5W rated package but it has nothing to do with how much power is actually consumed. You recommended a 20W resistor for margin but you also calculated it only consumed 10W using the same law that says the LED will only consume 2W. The package has margin which usually means the junction temperature is more stable over a variety of operating powers. This margin affects emitter frequency stability over power consumed (i.e. 2W CW is the same peak frequency as the 2W with 50% duty cycle - the same device in the 2W package has more variation). There are other issues that you can see using the curves in the datasheet that make the 5W package more attractive than the 2W package but it's clear that the rating is separate from the consumed power --DHeyward (talk) 10:03, 3 April 2016 (UTC).

Well, what's your solution to the OP's question. You haven't provided one. Akld guy (talk) 10:25, 3 April 2016 (UTC)

I think it's a homework problem and we don't do homework problems. He also doesn't provide power supply available or part. This is likely a combination of resistor with parallel and series diodes and part of a beginning course on current, power and the various laws that govern them. --DHeyward (talk) 15:59, 3 April 2016 (UTC)

The specific LED you are using will have a datasheet with that information. Here is a typical one:[3] --Guy Macon (talk) 06:33, 3 April 2016 (UTC)

Simple LED circuit with resistor for current limiting

Responsible answers can only be given when the component data sheet is found. A LED has a non-linear current-voltage characteristic, see Light-emitting diode so in the circuit illustrated we can calculate Ohm's law

$R={\frac {V}{I}},$ only at one (V,I) point for that particular diode. See the article LED circuit. The OP also needs to know that a series resistor reduces both the voltage across the LED and thereby the current (which is the same in both LED and resistor), that one can measure the current either by breaking the circuit to introduce an Ammeter or by measuring the voltage across the resistor R and applying Ohm's law

$I={\frac {V}{R}},$ and that it makes no difference to the LED whether the resistor is on its + or - wire. Operating a LED near its maximum output makes the manufacturer's data sheet essential and in some cases a different circuit, such as a constant-current driver, may be necessary.

The responses above have linked to two different LED data sheets. From Akid guy, Type LZ1-00R400 quotes typical V_F 1.9V @ 1A, so we may conclude that a 5V supply and 3.1 ohm resistor will suit. The power dissipations are 1.9W in the LED and 3.1W in the resistor; that implies a heatsink for the LED and preferably at least a 5W rated resistor. But look further in the data sheet: individual LEDs can have V_F @ 1A that vary from 1.7 to 2.7 V and this can have the consequence that resistors must be selected to match the brightnesses of an array of LEDs. From Guy Macon, Type LZ4-00R408 quotes V_F @ 700mA that vary from 6.8 to 10.8 V, and in this case I_F = 1A is its absolute maximum. One should realize that this device is actually specified as 4 LEDs connected in series and the series resistor circuit is less suitable (and power wasteful). A constant current supply circuit and a proper heat sink are needed for safe operation of this device. AllBestFaith (talk) 13:47, 3 April 2016 (UTC)

Actually Guy Macon's are not connected at all. The datasheet assumes that configuration for publishing tables and it would popular if you have two lithium ion 18650 batteries (popular torch rechargeable). if you only had 1 battery, it can be configured as 2 parallel and 2 series LEDs and the voltage would 3.6V instead of the nominal 7.2V with the same power delivery. --DHeyward (talk) 16:33, 3 April 2016 (UTC)

Well noticed! The LZ4-00R408 is a 4-diode package which may have external series connections, but doesn't have to. The data sheet mentions that the diode forward voltages match within ± 0.16V which suggests the diodes also work well when connected in parallel; then implicitly V_F @ 2.8 A is 1.7 to 2.7 V. AllBestFaith (talk) 19:54, 3 April 2016 (UTC)

You can not really perform this calculation unless you know 3 things: what is your supply voltage? what is your LED forward voltage? and what is your LED forward current? You can make an educated guess as to the last 2, but once you have those 3 values the rest is easy! or as stated above you can use a constant current source, which is probably the better and safer way to drive a high power LED. Vespine (talk) 02:19, 4 April 2016 (UTC)

Downloading the Science Wiki

Hello, is there any way to download the Science (Chemistry, Biology, Physics) Wiki so I can use for my studies even when I'm offline?

Could you clarify what you're asking for? If you're referring to Wikipedia articles, you might be interested in our Book creator page, though I'm afraid that it explains that the program is mostly on hiatus. The existing science books are listed here. You can also download individual articles as PDFs (there will be a link on the left side of the screen, just below the option to create a book). Matt Deres (talk) 12:41, 3 April 2016 (UTC)

The answer depends on what sort of device you are using and the capacity it has. See : Wikipedia:Database download. Haven't used it myself but one should (I think) be able to download articles by just category. --Aspro (talk) 16:51, 3 April 2016 (UTC)

Are you talking about pages on Wikipedia, or some other wiki? "Wiki" and "Wikipedia" do not have the same meaning. --71.110.8.102 (talk) 21:48, 3 April 2016 (UTC)

April 4

Special relativity. Simultaneity 2

Question

Remark

Ok. There is no observers, just clocks showing something on their faces. In Special relativity. Simultaneity we showed : in frame ε clock from ε shows on its face: at start $0$ when light reaches hind end of ε' coach $\tau _{1}={\tfrac {L/2}{c+u}}$, when light reaches front end of ε' coach $\tau _{2}={\tfrac {L/2}{c-u}}$; in frame ε clocks from ε' show on their faces (from left to rigth): at start $\theta _{0}^{[}$, $0$, $\theta _{0}^{]}$, when light reaches hind end of ε' coach $\theta _{1}^{[}$, $\theta _{1}=\tau _{1}{\sqrt {1-u^{2}/c^{2}}}$, $\theta _{1}^{]}$; when light reaches front end of ε' coach $\theta _{2}^{[}$, $\theta _{2}=\tau _{2}{\sqrt {1-u^{2}/c^{2}}}$, $\theta _{2}^{]}$. Suppose, when light reaches walls, clocks on walls are reseted to zero, so $\theta _{1}^{[}=\theta _{2}^{]}=0$. Reseting of clocks is the result , so must be seen from all frames, so in all frames clocks on walls must show zero if light reaches them. Then: $\theta _{1}^{[}=\theta _{0}^{[}+\tau _{1}{\sqrt {1-u^{2}/c^{2}}}$ and $\theta _{2}^{]}=\theta _{0}^{]}+\tau _{2}{\sqrt {1-u^{2}/c^{2}}}$. $0=\theta _{0}^{[}+\tau _{1}{\sqrt {1-u^{2}/c^{2}}}$ and $0=\theta _{0}^{]}+\tau _{2}{\sqrt {1-u^{2}/c^{2}}}$. $\theta _{0}^{[}=-\tau _{1}{\sqrt {1-u^{2}/c^{2}}}$ and $\theta _{0}^{]}=-\tau _{2}{\sqrt {1-u^{2}/c^{2}}}$. $\theta _{0}^{[}=-{\tfrac {L/2}{c+u}}{\sqrt {1-u^{2}/c^{2}}}$ and $\theta _{0}^{]}=-{\tfrac {L/2}{c-u}}{\sqrt {1-u^{2}/c^{2}}}$. So at start in frame ε clocks from ε' show on their faces (from left to rigth): $-{\tfrac {L/2}{c+u}}{\sqrt {1-u^{2}/c^{2}}}$, $0$, $-{\tfrac {L/2}{c-u}}{\sqrt {1-u^{2}/c^{2}}}$. How to check this? I have tried to use Lorentz transformations for time , but got absolutely different result. Hind clock when shows $\theta _{0}^{[}$, is situated in ε in point $(x,t)=(-L/2,0)$ and also in ε' in point $(x',t')=(-L'/2,\theta _{0}^{[})$, but also it can be represented as $(x',t')=({\tfrac {x-ut}{\sqrt {1-u^{2}/c^{2}}}},{\tfrac {t-xu/c^{2}}{\sqrt {1-u^{2}/c^{2}}}})$ $=({\tfrac {-L/2-u\cdot 0}{\sqrt {1-u^{2}/c^{2}}}},{\tfrac {0-(-L/2)u/c^{2}}{\sqrt {1-u^{2}/c^{2}}}})$ $=({\tfrac {-L/2}{\sqrt {1-u^{2}/c^{2}}}},{\tfrac {{\tfrac {+L/2}{c^{2}}}u}{\sqrt {1-u^{2}/c^{2}}}})$. So $\theta _{0}^{[}={\tfrac {{\tfrac {+L/2}{c^{2}}}u}{\sqrt {1-u^{2}/c^{2}}}}\neq -{\tfrac {L/2}{c+u}}{\sqrt {1-u^{2}/c^{2}}}$. Why? Or backwards: $(x',t')=(-L'/2,\theta _{0}^{[})$; $(x,t)=({\tfrac {x'+ut'}{\sqrt {1-u^{2}/c^{2}}}},{\tfrac {t'+x'u/c^{2}}{\sqrt {1-u^{2}/c^{2}}}})$. By subsituting $x'=-L'/2=-L/2{\sqrt {1-u^{2}/c^{2}}}$, $t'=\theta _{0}^{[}=-{\tfrac {L/2}{c+u}}{\sqrt {1-u^{2}/c^{2}}}$: $(x,t)=((-L/2)(1+{\tfrac {u/c}{1-u^{2}/c^{2}}}),...)$. Why $x\neq L/2$? But I don't want to use coordinate. I like to imagine that time in moving frame is slowing down through explanation by primitive clock made from vertical rod and mirror https://upload.wikimedia.org/wikipedia/commons/8/8f/Reference_desk_Science160404140000.PNG . Is there same intuitive explanation for desynchronization?

https://en.wikipedia.org/w/index.php?title=Wikipedia:Reference_desk/Science&action=edit&oldid=711458491 Light path analysis and consequences https://en.wikipedia.org/w/index.php?title=Wikipedia:Reference_desk/Science&action=edit&oldid=711808143 Null result of Michelson–Morley experiment extrapolation https://en.wikipedia.org/w/index.php?title=Wikipedia:Reference_desk/Science&action=edit&oldid=713271286 Special relativity. Derivation of t' formula https://en.wikipedia.org/w/index.php?title=Wikipedia:Reference_desk/Science&action=edit&oldid=713271421 Special relativity. Simultaneity

37.53.235.112 (talk) 05:49, 4 April 2016 (UTC)

Time in a moving frame is not "slowing down", it is proceeding at the "normal" rate. From an inertial frame that is moving relative to the original moving frame (or "stationary" by some ad-hoc definition), time is observed to be running more slowly, but this effect is symmetrical because time in the "stationary" frame is observed to be running more slowly when observed from the moving frame. It is only when one frame (either of them) accelerates to match the speed of the other that a twins paradox appears. Perhaps someone else can explain how your equations work out? Dbfirs 11:02, 4 April 2016 (UTC)

Symmetry of time is certainly claimed by special relativity, however general relativity lays claim to an asymmetry that exists (and it's an asymmetry that I view as being much more important and fundamental). For instance, if on one hand, a rogue twin planet Krypton, which is like our own, was moving very near the speed of light, their communication systems hibernate with, say, just one computation per week and therefore incapable of processing any interactive communication data we may wish to share with them during their brief passage with us though our inner Solar System (within the orbit of Pluto). They would be "dead on arrival". On the other hand, we could interactively observe them, probe their planet with radar, etc. in excruciating detail during the brief encounter because we are unaffected and are almost at rest with respect to the CMB rest frame, which is likely the ultimate arbitrator of what constitutes the fastest clocks. -Modocc (talk) 13:08, 4 April 2016 (UTC)

I follow http://www.feynmanlectures.caltech.edu/I_15.html . Please, write answers using materials which do not go beyond sections 15-1 ... 15-6.37.53.235.112

[after edit conflict]Alas, according to SR, your intuition is incorrect for a very simple reason: you are incorporating classical velocity addition with your primitive photon clock and not the relativistic temporal and spacial transforms which are derived independently. Not a bad idea though and consistent with absolute simultaneity and distances :-), but it is very much inconsistent with the reference frame invariant lightspeed of your photon, which according to Einstein, requires relativity of simultaneity as well as length contracted distance (length contraction) that the light travels and is frame dependent. Thus relativity goes well beyond the classical paradigm. The book "Einstein's Theory of Relativity" by Max Born may be a bit dated, but from it I learned the basics of how its nonEuclidean worldlines were developed many years ago. -Modocc (talk) 16:08, 4 April 2016 (UTC)

you are incorporating classical velocity addition We can use classical velocity addition for approach velocity and we should use relativistic velocity addition for object velocity. Just write what formulas are wrong in my 1st question. 37.53.235.112 (talk) 16:40, 4 April 2016 (UTC)

@Modocc: Your explanation is confusing at best. The whole idea of relativity is there's no difference between how we see Krypton and they see us (how we see the CMB is something else!). We see their clocks ticking slowly and they see our clocks ticking slowly. The solution to this staring contest is that sooner or later, one party accelerates and comes back again, and is revealed to be the "true" slowed party. Or else both parties keep moving apart and their record of each other's light just keeps getting more and more out of date. There's a graphic in Twin paradox - the "simultaneity planes" change angle when you accelerate, i.e. "the same time back on Earth" takes as abrupt a jump forward as your rocket engines will allow (could be backward if you accelerate away faster). But of course, unless you're in possession of an ansible, those simultaneity planes don't really physically exist - they don't mean anything because no information or substance can follow any of those spacetime paths. Wnt (talk) 15:34, 4 April 2016 (UTC)

Whatever reference frame one wants to invoke to solve the paradox involving time doesn't actually matter. The fact is that when we accelerate matter, particles' contract and their lifetimes increase, but with consequences. Do that to a rocket or planet so it is fast enough then with regard to a staring contest then the rocket or Krypton cannot interact with us while it is in close proximity to us, its computers are simply aging too slow with respect to the laser light we can bounce off it and that we observe as it passes us by. The fact that such asymmetry exists is the whole point of the paradox. --Modocc (talk) 16:28, 4 April 2016 (UTC)

That's why I wrote above that the twins paradox appears whichever frame is accelerated to match the other. There is still symmetry, because the "rest frame" could be accelerated to match the velocity of the "moving frame" and the same paradox will appear except that the age difference will be reversed. Dbfirs 18:21, 4 April 2016 (UTC)

Krypton is nearby from Earth's perspective for the same amount of time as Earth is nearby from Krypton's perspective. They can investigate us as much as we can investigate them. It's a symmetric situation. You seem to be suggesting that we have longer than they do because we're moving at a slower speed relative to the CMB. That's incorrect. -- BenRG (talk) 06:22, 5 April 2016 (UTC)

In case I wasn't clear, I assumed that Krypton was initially accelerated relative to our Milky Way when it was hypothetically created and that it is now moving almost, but not quite, at the speed of light (this is just a thought experiment. I'm not saying that it even possible, but its something to think about) when we encounter it. Now we know that our computers can process a few serial computations per clock cycle, so lets figure ten gigahertz to give us a benchmark here. It takes about 33,000 seconds of elapsed time for light to traverse the orbit of Pluto and in that time our computers can do a lot of data crunching during our encounter with weak short-range signals (such as with our land-based radar) that are aimed at the rogue planet as it passes us by. Now let Krypton's velocity be such that its 10 gigahertz computers are time dilated to only 1/30,000 clock cycles per second. Then at this speed, during our 33,000 second encounter, their computers' clocks can cycle only once and their weak signals will be fewer in number too. -Modocc (talk) 07:28, 5 April 2016 (UTC)

Similarly, Krypton's observations of Earth will be hopelessly distorted, with our computers appearing to run ridiculously slowly. Dbfirs 08:32, 5 April 2016 (UTC)

A stark uncompromising asymmetry would exist however, for real time computations are required by the radio telescopes' tracking computers and their computers could barely perform a single computation during the entire crossing of our solar system and both our ability to perform and their inability to do likewise are reference frame invariant. Modocc (talk) 04:44, 6 April 2016 (UTC)

I don't understand the lack of symmetry that you claim. Krypton's computers run at normal speed in their reference frame. Dbfirs 19:11, 6 April 2016 (UTC)

@Modocc: you've specified a time dilation factor of γ = 10 GHz / (1/30000 Hz) = 3×10¹⁴, which corresponds to a speed of √(1 - 1/γ²) ≈ (1 − 6×10⁻³⁰) c. Assuming Pluto is around 16,500 light seconds away from us, and Krypton passes close to Earth, Earth-bound telescopes won't see Krypton pass the orbit of Pluto until 16500(c−v) ≈ 0.1 yoctosecond before it passes Earth. (They will see it in the form of a concentrated beam of gamma rays that will probably sterilize the Earth, but never mind.) If Earth scientists send a radar beam to probe Krypton's surface a nanosecond after it passes us, the beam will return to us about 10 trillion years later, and will be redshifted by a factor of about 4×10²⁹.

So it is not true that Earth-bound scientists will have lots of time to investigate Krypton. Of course, they will most likely spot Krypton's arrival before it gets to Pluto. If they notice it 1 second before it passes us, they'll have seen it at 10²⁵ times the distance of Pluto, which seems implausible but maybe not. That would give them 1 full second to send radar signals to it which will all bounce back within that second (blueshifted by a factor of 4×10²⁹).

Krypton will have exactly the same opportunity to investigate us, since this is a completely symmetric situation. The symmetry of reference frames is the most important thing about special relativity. -- BenRG (talk) 19:25, 6 April 2016 (UTC)

Well, yes, detection of Krypton's existence is also important before we would be making any observations at all: thus simply let Krypton emit significant electromagnetic radiation ahead of it (we can do the same for them) and then we will get to track them and observe them for the full range of our active radars, but their radars will be dysfunctional with regard to the task. [see a better strategy below] This is because we are the stay-at-home twin for most of the inertial mass around us has been nearly at rest for billions of years and so our watches differ from theirs and time in physics is what clocks measure. If my own twin takes a trip and returns he will have completed fewer tasks than I have, perhaps only a few weeks worth compared to my years worth, thus our performances are asymmetric even though the naive Lorentz transformation preserves spacetime symmetry. --Modocc (talk) 21:16, 6 April 2016 (UTC)

But if you accelerate to match your fast-moving twin's inertial frame, it will be you who has completed fewer tasks because you will be younger than your twin. I still insist that the situation is symmetrical. Dbfirs 21:38, 6 April 2016 (UTC)

If Krypton is the stay-at-home twin that would be true, but since I specified that Krypton was accelerated initially then I would simply be rejoining joining him for the first time as an older man (although we are physically the same, we would have to be born in different places) when I crash land on his planet in a hail of gamma rays. :-) BenRG made a really good point about the lead distance involved and although the numbers can be tweaked (I'm not a big fan of playing with them much) a more robust strategy to recording their passage I suppose would be to have numerous active pulsed radars that continuously cover the sky much like we do with our weather radars. It is a very large volume of space to cover, but perhaps more feasible and likely than the origin of a massive Krypton (which, being our twin, would have their own matrix of radars). -Modocc (talk) 00:50, 7 April 2016 (UTC)

Suppose Earth knows in advance that Krypton is coming and starts sending out radar beams 33000s before Krypton reaches Earth, so that the first beam bounces off Krypton just as it crosses Pluto's orbit. Those beams are sent over a period of hours, but since they travel at c just like any other light, they all arrive back in the 0.1 ys interval between seeing Krypton cross Pluto's orbit and Krypton passing Earth. Of course, no equipment could record the signal in that time, but we could imagine faster computers (or a less ridiculous gamma factor).

To be fair, you must allow Krypton to start sending signals 33000s before the meeting by its proper time. For large γ the Doppler shift factor is roughly 2γ. So those signals will reflect off Earth over a period of about 33000s / 2γ ≈ 55 picoseconds (of Earth proper time), and will be received by Krypton over a period of 55ps / 2γ ≈ 0.1 ys (of Krypton proper time), just before the planets pass each other.

The fact that Krypton accelerates and we don't is an asymmetry in your scenario. But it only accelerates when it's far away, and by assumption, it can only investigate us (and we it) when it's nearby. Physics is local; the universe doesn't remember who accelerated in the past. When Earth and Krypton are near each other, an exact symmetry of nature (Lorentz/Poincaré symmetry) exchanges them, so the situation is symmetrical. -- BenRG (talk) 03:09, 7 April 2016 (UTC)

"To be fair, you must allow Krypton to start sending signals 33000s before the meeting by its proper time"? It takes precisely 33000 times a gigahertz number of computer cycles for that to happen, thus those signals would have to begin at a far greater distance from us than Pluto which is but approximately one half of their cycles away by my earlier calculation above and since they are just about almost physically identical to us and are therefore sending similar signals they should be considerably weaker upon arrival.. or am I missing something important here? -Modocc (talk) 03:52, 7 April 2016 (UTC)

Yes, it starts long before they reach Pluto's orbit (the trip from there to Earth takes only 55ps by their clocks), but the light doesn't travel farther in any Lorentz-invariant sense. With respect to Earth's rest frame, you could say that relativistic beaming prevents the light from spreading as much as you'd otherwise expect over such a long distance. With respect to Krypton's rest frame, Earth is 33000 light seconds away when they send the first signal, and Pluto's orbit is only 16mm closer.

(If there is background dust comoving with Earth, Krypton's signals will travel through a lot more of it and be attenuated more by that. But if there is background dust then the relativistic dust bombardment will destroy Krypton long before it reaches Earth anyway. This scenario only works in a perfect vacuum.) -- BenRG (talk) 05:27, 7 April 2016 (UTC)

and also in ε' in point $(x',t')=(-L'/2,\theta _{0}^{[})$ – I think everything before this is correct, and this is wrong. In the original setup the primed clocks showed t' on their faces, but in your revised setup they show an offset from that (specifically $t'-L'/2c$), so you should have $(x',t')=(-L'/2,\;\theta _{0}^{[}+L'/2c)$. That should agree with the result from the Lorentz transform (with $L'=L/{\sqrt {1-u^{2}/c^{2}}}$). -- BenRG (talk) 23:48, 4 April 2016 (UTC)

I think I'm hopelessly misled. Why $\theta _{0}^{[}\neq \theta _{0,self}^{[}$? How to calculate them (suppose light flash never occurred , so no synchronization was ever made)? Why in all frames result of experiment is same, but indication of clocks (which also is result of some processes inside clock) are not? 37.53.235.112 (talk) 18:04, 5 April 2016 (UTC)

You wrote "hind clock when shows $\theta _{0}^{[}$, is situated [...] in ε' in point $(x',t')=(-L'/2,\theta _{0}^{[})$". This means that at $t'=\theta _{0}^{[}$, the clock reads $\theta _{0}^{[}$.

The clock is at rest wrt ε', so it ticks at the same rate as the coordinate time of ε'. So if it shows $\theta _{0}^{[}$ at $t'=\theta _{0}^{[}$, then it must show $t'$ at every time.

But you also wrote "in all frames clocks on walls must show zero if light reaches them". So the hind clock shows $0$ when the light arrives. So $t'=0$ when the light arrives. But this is clearly wrong: the light is emitted at $(x',t')=(0,0)$ and doesn't travel infinitely fast.

So there is an internal contradiction in the assumptions you made about the behavior of the clock (or in the assumptions I made when reading). Which part is wrong depends on what thought-experiment you meant to describe. I think what's wrong is the idea that at $t'=\theta _{0}^{[}$, the hind clock reads $\theta _{0}^{[}$. This was true in your previous Ref Desk thread, when that clock was set to show $t'$ on its face at all times. But now it is set to show $0$ when the light arrives. Since it has the same worldline and ticks at the same rate as in your previous thread, the time it shows in this thread differs by a constant offset from the time it showed in the last thread. The offset is $L'/2c$. In the last thread it showed $0$ at $t'=0$ and $L'/2c$ at $t'=L'/2c$ when the light arrived, but now it shows $-L'/2c$ at $t'=0$ and $0$ at $t'=L'/2c$when the light arrives. In the last thread it showed $\theta _{0}^{[}$ at $t'=\theta _{0}^{[}$, but in this thread it shows $\theta _{0}^{[}$ at $t'=\theta _{0}^{[}+L'/2c$. -- BenRG (talk) 00:44, 6 April 2016 (UTC)

Question	Remark
Ok. Then we have next ε' frame ε frame time coordinate clock reading time coordinate clock reading $t'=0$ $\theta _{0}^{[}=-{\tfrac {L'}{2c}}$ $\theta _{0}^{]}=-{\tfrac {L'}{2c}}$ $t=0$ $\theta _{0}^{[}=-{\tfrac {L'}{2c}}$* $\theta _{0}^{]}=-{\tfrac {L'}{2c}}$ $t'=-{\tfrac {L'}{2c}}$ $\theta _{1}^{[}=0$ $\theta _{1}^{]}=\theta _{2}^{]}=0$ $t=\tau _{1}={\tfrac {L/2}{c+u}}$ $\theta _{1}^{[}=0$ $t=\tau _{2}={\tfrac {L/2}{c-u}}$ $\theta _{2}^{]}=0$ * because θ is not variable, θ is just literal representation of digits.	You wrote "hind clock when shows $\theta _{0}^{[}$, is situated [...] in ε' in point $(x',t')=(-L'/2,\theta _{0}^{[})$". This means that at $t'=\theta _{0}^{[}$, the clock reads $\theta _{0}^{[}$. The clock is at rest wrt ε', so it ticks at the same rate as the coordinate time of ε'. So if it shows $\theta _{0}^{[}$ at $t'=\theta _{0}^{[}$, then it must show $t'$ at every time. But you also wrote "in all frames clocks on walls must show zero if light reaches them". So the hind clock shows $0$ when the light arrives. So $t'=0$ when the light arrives. But this is clearly wrong: the light is emitted at $(x',t')=(0,0)$ and doesn't travel infinitely fast. So there is an internal contradiction in the assumptions you made about the behavior of the clock (or in the assumptions I made when reading). Which part is wrong depends on what thought-experiment you meant to describe. I think what's wrong is the idea that at $t'=\theta _{0}^{[}$, the hind clock reads $\theta _{0}^{[}$. This was true in your previous Ref Desk thread, when that clock was set to show $t'$ on its face at all times. But now it is set to show $0$ when the light arrives. Since it has the same worldline and ticks at the same rate as in your previous thread, the time it shows in this thread differs by a constant offset from the time it showed in the last thread. The offset is $L'/2c$. In the last thread it showed $0$ at $t'=0$ and $L'/2c$ at $t'=L'/2c$ when the light arrived, but now it shows $-L'/2c$ at $t'=0$ and $0$ at $t'=L'/2c$when the light arrives. In the last thread it showed $\theta _{0}^{[}$ at $t'=\theta _{0}^{[}$, but in this thread it shows $\theta _{0}^{[}$ at $t'=\theta _{0}^{[}+L'/2c$. -- BenRG (talk) 00:44, 6 April 2016 (UTC)
When do clocks show proper time $\theta _{i,self}^{[]}$?

37.53.235.112 (talk) 05:00, 6 April 2016 (UTC)

$t=0$ and $t'=0$ are lines in spacetime. The reading of a clock at $t=0$ is its reading at the intersection of its worldline and the line $t=0$.

The lines $t=0$ and $t'=0$ intersect only at the origin $(x,t)=(x',t')=(0,0)$, so the only way a clock can show the same reading at $t=0$ and $t'=0$ is if it passes through $(0,0)$. The two "middle" clocks in this setup do pass through $(0,0)$, but the hind and front clocks don't. The hind clock passes through $t'=0$ before $t=0$, and the front clock passes through $t=0$ before $t'=0$.

In your table, the clock readings at $t'=0$ are correctly given as $-{\tfrac {L'}{2c}}$, and the clock readings at $t=0$ are correctly given as $\theta _{0}^{[}$ and $\theta _{0}^{]}$. But $\theta _{0}^{[}\neq -{\tfrac {L'}{2c}}\neq \theta _{0}^{]}$.

I don't understand what you mean by $\theta _{i,self}^{[]}$. -- BenRG (talk) 18:06, 6 April 2016 (UTC)

I don't understand what you mean by $\theta _{i,self}^{[]}$ -- It's clock's proper time. E.g. $\theta _{0,self}^{[}$ -- proper time of hind clock at start, $\theta _{1,self}^{[}$ -- proper time of hind clock when light reaches it. Also I don't know what is worldline, so don't understand this part. Clock shows something when it is situated in some place in space. When clock is situated in some place , it can be in point $(x,t)$ or $(x',t')$. So it must have same readings. As I wrote readings are such letters as $\theta$ and $\tau$. But absolutely unclear for me which readings must be equal what other readings and when. E.g. you wrote that $\theta _{0}^{[}=-{\tfrac {L'}{2c}}$ when $t'=0$ . What time $t$ corresponds with this? $t=0$? Why then reading of hind clock does not coincide? 37.53.235.112 (talk) 18:54, 6 April 2016 (UTC)

I never wrote $\theta _{0}^{[}=-{\tfrac {L'}{2c}}$, or if I did it was a typo. You defined (I think) $\theta _{0}^{[}$ to be the hind clock's reading at t=0. It's not the hind clock's reading at t'=0, because the hind clock crosses t'=0 at a different time (an objectively different point in spacetime, and also a different proper time).

The best way to understand this sort of thing is with a spacetime diagram. I'll attempt one in ASCII.

  rear of train    front of train
(and hind clock)  (and front clock)
          v           v                 ^
          /           /                 |
         /           /,,  <-- t'=0    later
        /         ,,/’                
       /      ,,’’ /                 earlier
   .../.....@...../....  <-- t=0        |
     /,,’’       /                      v
    ’’

The point marked @ is $(x,t)=(x',t')=(0,0)$. The lines $t=0$ and $t'=0$ are angled differently (relativity of simultaneity). The clocks read $\theta _{0}^{[]}$ on the line $t=0$, but not on the line $t'=0$. There is no single well-defined "time at the start" because there is no single well-defined "start" of this experiment. Does that help? -- BenRG (talk) 19:42, 6 April 2016 (UTC)

Does that help? No because it's rotatings. As I wrote, I did not study rotatings yet and I will not study rotating specially.

You defined (I think) $\theta _{0}^{[}$ to be the hind clock's reading at t=0. Yes, it's reading of hind clock of moving coach ε' in coordinate system of ε. So reading in coordinate system of ε' must be $\theta _{0,self}^{[}$. But you use same notation $\theta _{0}^{[}$ just saying it's different (but it's impossible as $\theta _{0}^{[}$ is number e.g. $13$, and $13$ cannot be sometimes $11$). It is confusing. And one more thing is unclear: if hind clock is situated in some place of space, it's no matter what coordinate system is applied, so in both systems readings must be same (coordinates may be different). Yes or no? 37.53.235.112 (talk) 05:46, 7 April 2016 (UTC)

Yes, the readings are the same, the coordinates are different.

My diagram is just a picture of the scenario you set up. (Except that I left out the light beams because the diagram was cluttered enough already.) The horizontal and vertical axes are x and t respectively. I didn't introduce any new rotating. I did say the Lorentz transformation is like a rotation, but you are already doing Lorentz transformations (and doing them correctly).

The reading on a clock at some particular spacetime point doesn't depend on reference frames. For example, I could add numbers to the diagram showing the readings on the clocks:

                  /           /
                 /           /,,  <-- t'=0
                /         ,-10
               /      ,,’’ /
           ..-7.....@....-13...  <-- t=0
             /,,’’       /
           -10          /

and those numbers are objectively correct. They wouldn't change if I drew this diagram using x' and t' instead:

             |             |
             |             |
           ˙-7.            |
             | ˙˙..        |
           ,-10,,,,,@,,,,,-10,,  <-- t'=0
             |        ˙˙.. |
             |            -13.  <-- t=0

The numbers aren't in exactly the same places but all of the relationships are the same. The readings on the t=0 line are −7 and −13, the readings on the t'=0 line are both −10, and −10 is above −13, and so on.

Yes, it's reading of hind clock of moving coach ε' in coordinate system of ε. – That doesn't really make sense. "The reading of the hind clock at t=0" makes sense (it's −7). "The reading of the hind clock when the light reaches it" makes sense (it's 0, not shown on this diagram). But "the reading of the hind clock in the coordinate system of ε" doesn't make sense. You need to be more specific about what time you're talking about—for example, by giving a value of t.

I think that with these numbers, you'd say $\theta _{0}^{[}=-7$ and $\theta _{0}^{]}=-13$. But I'm still not sure what you mean by $\theta _{0,self}^{[}$. Is it $-10$? -- BenRG (talk) 06:28, 7 April 2016 (UTC)

Yes, it's reading of hind clock of moving coach ε' in coordinate system of ε. – That doesn't really make sense. I imagine $\theta _{0}^{[}$ as reading on hind clock seen from ε at start (start in ε is $t=0$) and virtual observer's eye is almost touching hind clock (but of course this eye is not moving with hind clock). $\theta _{1}^{[}$ is reading on hind clock seen from ε at moment light reaches hind clock ($t=\tau _{1}$) and again virtual observer's eye is almost touching hind clock. I understand that difference between $\theta _{0}^{[}$ and $\theta _{1}^{[}$ equals $\tau _{1}{\sqrt {...}}$, but I'm not sure how to calculate $\theta _{0}^{[}$ independently from $\theta _{1}^{[}$, and what other readings (besides $\theta _{1}^{[}$) influenced by $\theta _{0}^{[}$.

But I'm still not sure what you mean by $\theta _{0,self}^{[}$. Is it $-10$? Yes, for this numeric example. This is what is called "proper time", right? I imagine $\theta _{0,self}^{[}$ as reading on hind clock seen from ε' at start (start in ε' is $t'=0$) and virtual observer's eye is almost touching hind clock (but in this time eye is moving with hind clock). In first thread https://en.wikipedia.org/w/index.php?title=Wikipedia:Reference_desk/Science&action=edit&oldid=713271421 Special relativity. Simultaneity I thought $\theta _{0,self}^{[}=\theta _{0,self}^{]}=\theta _{0,self}=0$.

Composition of Antarctic tephra

This block of tephra is located at Brown Bluff, Tabarin Peninsula, Antarctica. The dark specks appear to be Alkali basalt (per Skilling, 1994). Can anyone help identify the composition of the matrix material? Many thanks in advance.--Godot13 (talk) 17:30, 4 April 2016 (UTC)

Hard be to certain, but the deposits at Brown Bluff and other locations within the James Ross Island Volcanic Group are mainly formed in lava deltas topped by subaerial lava flows Skilling (2002) erupted into an englacial lake. If this block is part of that, then we're looking at a lump of hyaloclastite breccia, with both clasts and matrix made up of shattered basaltic glass. Mikenorton (talk) 17:50, 4 April 2016 (UTC)

Mikenorton- Many thanks!--Godot13 (talk) 17:56, 4 April 2016 (UTC)

Shadows

Is it true that a shadow is a tangible representation of nothing? Meaning that a shadow is not a thing but it exists independent of humans. A shadow can travel faster than the speed of light, and besides the particles occupying the space of a shadow, the shadow itself has no mass/energy? 2601:204:C003:57A5:B517:938E:2F62:3EA0 (talk) 20:25, 4 April 2016 (UTC)

A shadow is an area of reduced light due to some object blocking some of the light source(s). ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:30, 4 April 2016 (UTC)

Yep, I've always wondered about a shadow being able to travel faster than the speed of light, due to the angle at which a shadow can be caused. Apologies for the previous answer which has nothing at all to do with your question. The Rambling Man (talk) 20:36, 4 April 2016 (UTC)

I don't think shadows are things in and of themselves but the manifestation of other things that are things in and of themselves (ie light/objects)...does this make sense??68.48.241.158 (talk) 20:41, 4 April 2016 (UTC)

Shadows are a product of light and objects, so it doesn't make sense that a shadow would "travel" faster than the light that's accompanying it. ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:51, 4 April 2016 (UTC)

It can sometimes be useful to look at the speed of "negative reality", like how quickly an electron hole can travel, or how quickly "coolth" spreads from a cold object. In the case of looking at how quickly a shadow moves, this could be important for things like a sundial. StuRat (talk) 21:13, 4 April 2016 (UTC)

There is a lot of very wrong science wrapped up in such a very short quantity of discussion here!

Shadows do not "travel faster than the speed of light." Maybe the best place to start reading is our article on propagation delay; but I think it would be helpful to go back and read our article on light, wave, and shadow to help you re-center your understanding around the way scientists actually study these topics.

The original question also touches on more philosophical ideas about the absence of substance (in this case, rather, the absence of photons...) Well, you might also enjoy reading about horror vacui - but you should understand up front that this is a pre-scientific philosophical idea that is largely refuted by careful study of modern theory and experiment. As you have arrived to the science reference desk, you should follow up that reading by looking at our article on the vacuum, and on electromagnetic radiation, which we now know may propagate in a vacuum. This concept can be a bit baffling, but pay careful attention to the way scientists define their terms, and you will find that the modern explanation is very consistent with experiment.

Nimur (talk) 21:21, 4 April 2016 (UTC)

A "shadow", like the dot made by a laser pointer, isn't an object. It's, well, a concept. You can take a laser pointer and wiggle it across the surface of the moon, and in theory, if it's perfectly collimated, that little dot might break the lightspeed barrier. But of course "that dot" is different photons from one instant to the next. They say you can never step in the same river twice ... same about a laser pointer dot, or a shadow, since the one is different photons each time, and the other is the lack of different potential photons each time.

Inevitably group velocity and phase velocity will come up, though they're not very directly related. The concept though is that there are things that aren't things that can go faster than light. Wnt (talk) 22:06, 4 April 2016 (UTC)

TANGIBLE (adj.) means capable of being touched, from Latin tangere "to touch". The OP has surely never touched a shadow and may not have read Shadow#Propagation speed in the article they already cited. Since there is no actual communication between points in a shadow that projects over a large surface, the shadow's edge cannot convey information between those distances at any speed. AllBestFaith (talk) 13:29, 5 April 2016 (UTC)

Consider a star that's, say, ten light years distant. It is constantly emitting photons. Any photons hitting us were emitted about ten years ago. Now suppose some large, dark object passes between us and the star, maybe hallway between us, i.e. five light years away from each of us. The photons already more than five light years away from the star will continue on their merry way toward us. The dark object will, at least temporarily, block that stream of photons, thus putting the star in shadow from our perspective. But we won't observe that phenomenon until about five years after it happened. So, NO, shadows do not "travel" faster than light. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:53, 5 April 2016 (UTC)

• The answer above by Wnt is correct and informative, but let me enlarge on it slightly. It is thought to be impossible for matter to travel faster than the speed of light, but there is no prohibition whatsoever against a phenomenon traveling faster than the speed of light. For an easy-to-visualize example, think of a wave on the water making contact with a straight shoreline. The smaller the angle between the wave and the shoreline, the faster the contact point will move. There is no upper limit to its speed: as the angle approaches zero, the propagation speed of the contact point increases without bound. Looie496 (talk) 13:57, 5 April 2016 (UTC)
  • No, it isn't correct. A shadow can't "travel" any faster than the photons it's blocking. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:11, 5 April 2016 (UTC)

I think you're using that term differently than most people. For example, most people would say that the shadow of a hawk travels across the ground, or the shadow of the Moon travels across the Earth during a solar eclipse. But your use of "travel" is that a shadow travels only away from the Sun in these cases. Wnt (talk) 14:46, 5 April 2016 (UTC)

I don't follow. Shadows "travel" only in relation to the light source and the object causing the shadow. ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:27, 5 April 2016 (UTC)

The technical term for gathering in special buildings to look at moving shadows is cinematography from Greek kinein "to move" + graphein "to write". AllBestFaith (talk) 21:55, 5 April 2016 (UTC)

What about THIS???? you only have to watch the first 2-3 minutes or so 199.19.248.20 (talk) 00:43, 6 April 2016 (UTC)

OK - speed of movement of a shadow. Let's put together a thought-experiment. Let's take a laser with a pencil-thick beam - and let's put an opaque black dot onto the exit window of the laser so that it casts a circular beam of light with a 'shadow' in the center of the beam. The laser is on a stand that allows us to rotate it really quickly. If I place this contraption vertically above my (infinitely large and perfectly flat) desk, shining the laser downwards, I'll see a shadow on my desk cast by that black dot. As we rotate the light from the vertical towards the horizontal, the center of the shadow moves from being vertically below the laser to being infinitely far away to the side. Since we can rotate the light from vertical to horizontal in a fraction of a second - but the shadow moves from being right in front of me to being infinitely far away in just a couple of seconds - it's tempting to say that it moves faster than the speed of light.

But that's not true.

The light from the laser is what defines the edges of the the shadow - and that light can't travel faster than light. So no matter how fast I rotate the lamp to "move the shadow" from right in front of me to being a million miles off to my right - the light from the laser can't travel that million miles to define the edges of the shadow at anything faster than the speed of light. The shadow moves at speeds approaching (but never exceeding) the speed of light.

OK - so we need another thought experiment. Instead of projecting the shadow onto a flat desk, let's project it onto the inside of a vast sphere...an entire light-second in radius. If I'm standing in the center of the sphere - then I see the light reflected back at me from the sphere with a two second delay. If I suddenly move the laser from shining on the sphere to my right - to shining on the sphere to my left - then two seconds later, I see the light disappear from my right side and a fraction of a second later, it'll reappear on my left...and the shadow moved with it. So the "shadow" did indeed track all the way across the sphere in that tiny fraction of a second (albeit with a two second delay). It travels a distance of pi light-seconds in the time it took me to spin the laser around...which is *way* faster than the speed of light.

But the problem here is that this shadow isn't a constant 'thing' - it's the absence of photons, but it's the absence of different photons when it's pointing in one direction versus pointing in the other direction. It's like driving along a freeway with a beige Volvo estate wagon a mile ahead of you. Suddenly it turns off of the freeway, out of sight. Simultaneously, you notice in your rearview mirror, a different beige Volvo estate wagon drives onto the freeway a mile behind you. Do you now conclude that the absence-of-a-Volvo travelled faster than the speed of light?

SteveBaker (talk) 16:36, 6 April 2016 (UTC)

Tigers smarter than lions?

This might be just a bit of useless and potentially wrong trivia, but when people claim that tigers are smarter than lions, could it be that they are right? If yes, how could that be measured? AFAIK, brain size alone won't let us conclude about the intelligence of an animal. But where could the information bit come from?--Scicurious (talk) 20:58, 4 April 2016 (UTC)

One of the predictors of intelligence is the degree of social integration, as social structures require a lot of intelligence to navigate (when to act submissive, when to dominate, when to fight). Since lions are social animals and tigers are not, that would seem to mean more intelligence is required of lions. StuRat (talk) 21:10, 4 April 2016 (UTC)

hard to say, all kinds of philosophical problems involved....is a dog smarter than a tiger because it can be trained to do things for humans but tigers can't?? or are tigers smarter because they can't be conned into doing things for humans?? you can look at behavior and behavior differences but the interpretation of smartness is inherently subjective...look at controversy over IQ....ants might be the smartest if look at how successful they are in terms of numbers etc...humans might be the dumbest..or the smartest as can use tools like crazy...but maybe dumb as the use of these tools may lead to their demise...idk...68.48.241.158 (talk) 21:15, 4 April 2016 (UTC)

There are lots of ways of assessing animal intelligence, but usually scientists don't make claims about animals being "smarter" than another or terms like "intelligence" which is very broad and poorly defined. Rather, they talk about memory, learning, path finding and many other more specific things that are slightly more amenable to experimental or observational quantification. Our article Animal_cognition has some info and refs on methods. Here are a few books that give overviews of how we measure intelligence in animals, why animals are intelligent, etc. [4] [5] [6]. They are not feline specific, but we do have cat intelligence which gives this [7] scholarly article comparing the brains of lions to tigers. I might search a bit more later for more specific refs. You may also enjoy ref 3 and others at Portia_fimbriata, which describe how this spider can do things that smart lions do, like breaking line of sight to make a detour around prey, so as to approach it from a better angle. In the mean time, I suspect user:Snow Rise might have something helpful to add. SemanticMantis (talk) 21:17, 4 April 2016 (UTC)

Also, a strike against tiger intelligence is that they refuse to jump over a wall of white fabric, even when cornered and facing death. For some reason they have a very strong instinct not to jump into something unfamiliar, even when doing so could save their life. StuRat (talk) 21:21, 4 April 2016 (UTC)

Heh, I wonder how much evolution prepared them for the whole "cornered and facing death" thing. It doesn't sound like a tiger kind of problem. :) Wnt (talk) 22:08, 4 April 2016 (UTC)

I wonder where you get this information from StuRat. I always do. Scicurious (talk) 22:24, 4 April 2016 (UTC)

"Nepalese aristocrats developed a technique later adopted by British hunters in which roles of white cloth, which tigers reportedly will not cross, where laid out to funnel tigers to an area where hunters waited." [8]. StuRat (talk) 23:58, 4 April 2016 (UTC)

StuRat to his credit quotes accurately from a source that is rife with spelling mistakes. A good convention in such quotations is to insert sic in brackets at misspellings; it stands for sic erat scriptum "thus was it written" and is a way to be scrupulously fair to both the present reader and original writer. Example: "...roles of white cloth...where[sic] laid out..." AllBestFaith (talk) 13:07, 5 April 2016 (UTC)

Sounds apocryphal to me, but who knows. But what you said was "For some reason they have a very strong instinct not to jump into something unfamiliar, even when doing so could save their life." Which sounds doubtful to me. I think if the tiger felt under stress, it would go over (or through) the fabric if that were the only option. This source makes it sound more like they bounded the an area such that it made it more convenient for the the tiger to take another path, to where they lay in wait. Two very different images, if you ask me, even if we assume either to be accurate.. Snow ^{let's rap} 06:23, 5 April 2016 (UTC)

The original source I saw was a very old video, showing the tigers being funneled in as described above. The fabric was only high enough that they couldn't see over it, they could have easily jumped over it. StuRat (talk) 16:24, 5 April 2016 (UTC)

(ec)But they had no reason to do so.--TMCk (talk) 17:00, 5 April 2016 (UTC)

A "virtual grid" near Lone Pine, California

Animals can sometimes be fooled relatively easily - for example, these painted "cattle grids". I suspect that if the tigers were sufficiently motivated, they would have jumped over the cloths. It was probably very skillful animal handling that allowed this method to be used. DrChrissy ^(talk) 16:57, 5 April 2016 (UTC)

Yes, the virtual cattle grids are another good example of what I mean. A smarter animal would notice they aren't quite the same as real cattle grids, and test them out with just one hoof. When they determined that they could walk on it, they would then have learned the difference and remember it. Getting back to the Q, lions do seem confused by the wild stripes on zebras, so that might be a mark against them. StuRat (talk) 17:21, 5 April 2016 (UTC)

But do we know whether tigers are similarly confused by the motion dazzle of the zebra stripes - it's just not black and white (sorry, could not resist that!). More seriously, because the zebra is able to confuse the lion, does that mean the zebra is more intelligent than the lion? Obviously not, (because the stripes are not part of any conscious effort) but I think it indicates the lack of usefulness of trying to apply "intelligence" to species other than humans. DrChrissy ^(talk) 17:45, 5 April 2016 (UTC)

@DrChrissy: and @StuRat:, you're both a bit out of date on your Zebra thinking. See this 2014 Nature Communications paper concluding "there is no consistent support for camouflage, predator avoidance, heat management or social interaction hypotheses" [9]. Rather, they conclude there is strongest support for the stripes being useful in avoiding ectoparasitism. Obviously this is not the be-all, end-all answer, but it's hard to get more authoritative than a comprehensive Nature paper from just a few years ago. SemanticMantis (talk) 19:19, 5 April 2016 (UTC)

Actually, I am well aware of that hypothesis. The function of the stripes is, in my opinion, not yet settled. I actually think they might be multi-functional, but you are correct to point out to other readers that motion-dazzle is not the only possibility. DrChrissy ^(talk) 19:42, 5 April 2016 (UTC)

I'm fairly confused though. If you accept there is no consistent support that zebra stripes even help with lions, why do you think it confuses tigers. I'm sure someone has fooled around with tigers and zebras, but if we can't even get enough evidence that it helps with lions, it seems unlikely we have anything even close to useful for tigers. (I believe there are some who suggest tigers may also use motion dazzle, but even if that's true I'm not sure there's any reason to think it's for other tigers as opposed to their prey.) Nil Einne (talk) 07:28, 6 April 2016 (UTC)

I've just read the Nature paper and I am not convinced it discredits the motion-dazzle hypothesis. The paper really has only one comment on this.

Across contemporary ecosystems in Africa, where lions have been subjects of repeated detailed study, lions capture zebra in significantly greater proportions to their abundance

but this leaves the question - what proportion would be captured if the zebra did not have stripes? Regarding the insect deterrent hypothesis, I am also left with another question. If this is so effective, why have no other animals (e.g. antelope) evolved something similar? DrChrissy ^(talk) 13:32, 6 April 2016 (UTC)

By the way, did you know that some sheep in the valleys of Wales completely trump lions and tigers in intelligence. They have learned to curl themselves into a ball (like a hedgehog) and roll over cattle grids to get to the more luscious grass on the other side. Please note, I meant to post this 4 days ago.  ;-) DrChrissy ^(talk) 17:04, 5 April 2016 (UTC)

"Measures" of intelligence (please note the scary quotes) are totally, totally dependent on the questions you ask and the way in which this is investigated. What would you like to know? Is the hunting behaviour of the tiger more plastic than that of the lion? Can tigers solve human derived puzzles quicker than lions? Do circus tigers learn "tricks" more quickly than circus lions? It all depends on the question asked and the way we try to determine the answer. Unfortunately, so many studies on animal "intelligence" are clearly locked firstly within an anthropocentric world, and then secondly our own limitations of trying to investigate this. How do we objectively measure whether a tiger is more intelligent than an earthworm? If we can not answer that, then we can not measure whether a tiger is more intelligent than a lion. DrChrissy ^(talk) 23:11, 4 April 2016 (UTC)

As others have noted already, the question is problematic as phrased because "intelligence" is not an empirically quantifiable value. That is to say, despite the way we idiomatically reference it (especially with regard to our own species) it's not a substance or unidimensional quality or process that lends itself to measurement. Part of this is innate; to the extent that "intelligence" is seen as a desirable quality, there will always be a propensity towards reductionism in order that it can be seen as a uniform quality that is more present in some than others. But this mistaken concept got kicked into overdrive in the pre-modern and early modern history of the biological sciences, in order to justify the hierarchical structures that many "learned" men wanted to presume, particularly with regard to racist and gendered notions of innate superiority. I don't mention this just as a general aside either--these beliefs were central to the development of notions like IQ, and the tests that purported to evaluate a "general intellect". Proponents of this variety of psychometrics have tried hard to excise the bias from these tests since, but many cognitive scientists believe the very concept upon which they are predicated (a general measure of intelligence) is flawed beyond repair and based in a lack of understanding of the modular mind.

Now, bringing this back around to animal behaviour, the complexities become even more pronounced when we try to compare species. You can test for performance on certain tasks, but then your are necessarily bringing your value judgments into what intelligence is best typified by when you select the tasks for "general" intelligence. That's not to say you can't measure changes in the concept of general intelligence; if a given individual or generation raises in performance on all kinds of task, largely across the board, you know that intelligence has become "superior" in the sense. But there are too many different types of behaviours and faculties when it comes to cognition to say which is going to prove most vital or advantageous to a given individual in the longterm, in an open system like an eco-system or a social system. And to compare the needs and environment of two different animals that are alike only that both are cats and apex predators misses the functional meaning of intelligence. cognitive researchers (and sometimes social psychologists) call this "situated intellect" (and also a principle of environmental psychology), while sociobiologists (and EP and sociobiology really are the same fields as seen from either the anthropocentric/narrow or zoocentric/broad lens) call this the animal's "behavioural niche". You might even say that all animals with substantially developed brains have a "cognitive niche", but that term is already applied to in a related but distinct sense to describing ones of the ecological niches that humanity fills.

But it goes further than the species level, because what turns out to be "smart" behaviour varies not just by the species but by the individual and their circumstances. What is the "intelligent" solution in the aggregate? If its the type of decision that leaves the animal best off in the long run, the animal doesn't know what that's going to be--even if we, or it, could even put together an accurate or concrete notion of what "best off" would be for it. Indeed, most species won't even necessarily ever recognize the long-term consequences of its actions, especially if the "decision" and the outcome are separated by a bit of time. But the decisions that the animal makes are tailored to ecological/environmental demands the members of its heritage during its evolutionary past. But even if you are asking which species is more "intelligent" with regard to adapting to unexpected circumstances, you'd have to qualify the conditions very carefully to decide which was "more intelligent" in this regard. Ultimately you'd have to have a lot of experience studying the ethological nature of both species just have an informed decision, and even then you'd have to pass your opinion along subjectively; there'd be no one empirical measure you could use. If they naturally cohabitated in a certain region, you could at least measure their success in their survival rates, but you can't even do that here. Snow ^{let's rap} 06:11, 5 April 2016 (UTC)

Which species is closer to extinction? ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:45, 5 April 2016 (UTC)

There are different (sub)species of each, but according to the infoboxes at lion and tiger, the tigers are currently more threatened. While I appreciate a little teleological thinking, that does not tell us much of anything about intelligence, though it may tell us something about their Ecological_resilience. SemanticMantis (talk) 14:06, 5 April 2016 (UTC)

But not even much about that, since both species live in drastically different ecological contexts, with different degrees and forms of habitat displacement, prey reduction, interruption of reproductive habits and other population stressors. The populations of asiatic lions and most tiger species are so reduced now, I don't think they co-exist anywhere in the world, making comparison of their circumstances an apples and oranges affair. That line of inquiry raises another issue, actually--namely that you get substantial variation of behaviour between subspecies. Snow ^{let's rap} 20:15, 5 April 2016 (UTC)

@BBB: That's a ridiculous point of comparison. Which are closer to extinction, Polar Bears or House Flies? Your conclusion: House flies are more intelligent than polar bears? That's meaningless. Turn brain on before posting! SteveBaker (talk) 20:49, 5 April 2016 (UTC)

The trouble with direct comparison of intelligence is that behavior is often evolved to match environment. Why won't a tiger jump a white sheet? Well, maybe it's just stupid - but maybe it's evolved to avoid jumping into hidden snow banks for some deep and subtle reason that we've failed to comprehend? It's easy to label weird behaviors like this as "stupid" - when in reality, we just don't have the intelligence to understand them ourselves.

Why is it that your stupid dog spins around in a circle before (s)he poops? It turns out that dogs prefer to face North or South when they poop - and spinning around helps them sense the earth's magnetic field more easily [10]. Are dogs stupid for doing this - or is there something they know that we don't? Maybe they are smarter than we random-direction-pooping humans?

The root problem here is that we simply do not have a reasonable definition for the word "Intelligence" - and the closest we ever get to having a means to measure this vague thing is the IQ test - which more or less defines "Intelligence" as "The ability to get a high score on an IQ test".

So when it comes to animals, not only would it be hard to compare different species against some fixed standard - but it's also impossible to come up with a fixed standard that has much real-world significance.

So how do we define as "intelligence"? "That which humans have but other animals and computers have less of!"

For example, we'd say that humans were more intelligent than chimpanzees. But teach a chimpanzee to the digits 1 through 9, then place those digits in random order on a computer screen and have the subjects remember the positions of each digit and to recall them in numerical order. Sounds easy - but chimpanzees are much better at playing this game than people are[11]! If this is a measure of intelligence then chimpanzees are smarter than humans - and at a game that we invented! I'm old enough to remember when beating a human at chess was regarded at the pinnacle of intelligence...until Deep Blue beat Kasparov...then it was winning Jeopardy! (well, Watson nailed that one pretty effectively)...and then playing Go...but since a week or two ago, computers beat us all at that too. We have the Turing test - but to pass that, the computer has to adequately pretend to be a human...which takes us back to "Intelligence is that thing that humans have" - which is cheating! Computers are fast edging towards passing the Turing test - so now we're looking for another reason why we can't call them "intelligent".

Consider the Clark's nutcracker - which can hide tens of thousands of nuts around it's territory - then, nine months later, flawlessly retrieve them as needed and without hesitation...even when they are buried under feet of snow. Humans can't manage to hide more than a dozen or two without losing track. Over short-term memory, even cats have better memories than we do! These things are mental capabilities that are beyond what humans can do...yet we persist in moving the goal posts to preserve our feelings of superiority!

Clearly humans DO have a breadth and depth of skills and mental capabilities that no other animal (nor machine) can come close to matching - but defining what that thing is eludes us.

So asking whether a Lion or a Tiger has more of some indefinable thing is entirely meaningless. First define what the word means, and how to measure it - then we'll tell you who has the most of it.

SteveBaker (talk) 20:49, 5 April 2016 (UTC)

Surprised no one here has mentioned Encephalization or Brain-to-body mass ratio. Our page has the ratio for Lion (1:550) but I can't find Tiger after a brief search. Yes it's imperfect and has glaring exceptions, but as a "starting point" it's better that "the question is meaningless".. Surely we CAN compare 2 animals and decide a Raven is smarter than a housefly, the question is a tiger smarter than a lion might be much "harder" to resolve, but doesn't mean it's meaningless. Ultimately, the animals might be similar enough to say there is more overlap then we can't reliably distinguish between the two for that metric. Vespine (talk) 23:30, 5 April 2016 (UTC)

Well yes, of course we might all be inclined to agree, as an impressionistic matter, that the raven is "smarter" than a house fly. Certainly we can see that it has a vastly more complex CNS and has something much closer to the kind of problem-solving capabilities we recognize as more similar to human cognitive capabilities. But that's not what the OP asked about; he wanted to know if there were specific and concrete measures by which two relatively closely related (at least when compared against the raven-fly scenario) could be judged with regard to "intelligence". And the short answer is, no not really, though you could (theoretically) get performance measures if you narrow the question to a specific behavioural task in a specific environmental context. That said, brain to body mass ratio is an interesting phenomena, but once again, it only makes sense as a vaguely defined trend; when you look at the particulars of this supposed correlation, it breaks down all over the place. Snow ^{let's rap} 01:48, 6 April 2016 (UTC)

What is the evidence that a raven is "smarter" than a housefly? Can a raven land upside down on a ceiling? Rather than looking at brain ratios etc, we first need to define what "smarter" means. Once we agree on that (Ha!) We can devise questions and studies to answer those. DrChrissy ^(talk) 13:09, 6 April 2016 (UTC)

I'd go with "the ability to reason a solution to a novel problem". Crows/ravens seem able to figure out how to use tools (sticks) to fish for food they can't reach, even to the extent of first fishing for a bigger stick with a smaller stick. StuRat (talk) 16:44, 6 April 2016 (UTC)

What is the evidence that a raven is "smarter" than a housefly? I think this kind of statement is bordering on solipsism, how could we possibly know anything? Oh the despair. IMHO it's actually not that hard. For example, it doesn't take "intelligence" to land on a ceiling, in fact, a study was done which examined how a fly does it, and all it has to do is reach up with it's front legs and sticky feet do the rest. Vespine (talk) 22:27, 6 April 2016 (UTC)

Yes, of course I already knew how houseflies managed this - I was asking the question in a way that would indicate how the question posed about "intelligence" determines the answer and therefore the futility of asking the question. StuRat has now posed the suggestion that tool-use indicates intelligence. Tool use by animals tells us that ants will drop stones down the burrows of rival colonies. And there are other examples of tool-use by invertebrates, but again very dependent on the definition of "tool-use". DrChrissy ^(talk) 22:42, 6 April 2016 (UTC)

"I'd go with" ≠ "empirical measure". We're not talking about whether anyone has a right to a "reasonable" subjective impulse as to what constitutes remarkable intelligence, relative or otherwise, especially if it meshes with with the semantics of their impressionistic/fuzzy logic definition for the term. The OP was inquiring about empirical measurement. And the answer, notwithstanding the question being steeped in a deeply complex cognitive inquiry, is that no, there is no real way to determine with scientific clarity that a tiger is smarter than a lion or vice versa. Nor indeed that a raven is smarter than a housefly. If that makes me sound solipsistic, well I understand what Vespine means to say by that, but coming from a scientific perspective, I don't know of a single sociobiologist who I think would make the claim that they could "prove" that. They might talk about the relative complexity of the nervous system or the behaviour itself, or they might talk about whether the task was accomplished with working memory or by a previously observed instinctive reaction, whether it required novel pattern analysis or was a conditioned response, whether the animal could (or had to) learn the behaviour socially, or whether it could add a new step to the process to meet new necessities, ect, ect. But no serious researcher is going to say "this animal is X order of magnitude or Y% greater than this other species in terms of intelligence."

Again, just avoid running this circle one more time, the argument is not that "you shouldn't say, as reasonable shorthand, that an iguana is smarter than an ant." But if you want to prove that statement as empirical fact...well you better be a revolutionary in the understanding of animal and human make-up on par with Charles Darwin in his day, with a bit of Carl Sagan's gift of gab mixed in, because you're going to have to advance our understanding of the mind and the brain lightyears in order to be able to come up with one unified measure that defines "intelligence" such that great thinkers all over the world, greatly divided over basic questions about the nature of cognition and intelligence all nod and go "Yup, that's it, alright. Oh, what do you know, Johnson, looks like I've an intelligence rating of 354.7 Vesps. You're only 320.1. So....now we know that, don't we Mr. Nobel laureate?!" <------"Vesps" used in good humour! :) Snow ^{let's rap} 04:45, 7 April 2016 (UTC)

April 5

Nuclides undergoing nuclear fission

What nuclides beside U, Th, can undergo nuclear fission? The nuclear fission article seems not to specify a list of fissionable and fissile nuclides. Can bismuth and palladium, for instance, undergo fission?--5.2.200.163 (talk) 10:44, 5 April 2016 (UTC)

Please see Fissile material. Did you consider an internet search for "fissile elements" before asking here?--Phil Holmes (talk) 11:03, 5 April 2016 (UTC)

I find the article you mention not very informative. It mentions fissile rule and centers on actinides. Other elements beside actinides and other ways of triggering fission are not mentioned. I have considered a gogle search, again not very informative. I've read somewhere (don't remember where) about elements like bismuth and palladium fissioned by deuteron beam collision.--5.2.200.163 (talk) 11:20, 5 April 2016 (UTC)

Also nuclear fission does not specify many details about fission reaction mechanisms and triggering possibilities.--5.2.200.163 (talk) 11:20, 5 April 2016 (UTC)

You're right - that article could do much better. The topmost graph answers your question, but turning the low-res little dots into element and isotope is ... laborious. We should have a real chart that excludes the long gray band and just focuses on where there is data (if that indeed is all the data that is available, which seems odd) Wnt (talk) 14:40, 5 April 2016 (UTC)

That chart is only about fissile elements, not about fissionable ones (which might be all elements heavier than iron or lead [12]). Rmhermen (talk) 15:04, 5 April 2016 (UTC)

I would even go so far as to say every atom except Hydrogen-1 can undergo fission, although it requires bombardment with some rather high energy particles to make it happen in stable isotopes. So, I assume they meant to ask about spontaneous fission. StuRat (talk) 19:38, 5 April 2016 (UTC)

MHD and nuclear reactors coupling

What are the requirements for the coupling of nuclear reactors with MHD generators in order to convert nuclear heat directly into electricity?--5.2.200.163 (talk) 10:47, 5 April 2016 (UTC)

Big Pipes. Greglocock (talk) 19:54, 5 April 2016 (UTC)

Arduino: RGB LED lights and Resistors

If we want to link 5 of 5V or 3V RGB LED to Arduino, how many resistors should i get? and how many Ohm does single resistor have to be? hellllpppp — Preceding unsigned comment added by 195.94.247.199 (talk) 11:23, 5 April 2016 (UTC)

What happens when you type [ Arduino: RGB LED lights and Resistors ] in the Google search box? --Guy Macon (talk) 16:27, 5 April 2016 (UTC)

Solubility

How is the solubility of a substance, say a salt, influenced by another salt? Is the solubility the same when dissolving a salt in a saturated solution of other salt comparatively to dissolution in pure solvent(water)?--5.2.200.163 (talk) 11:32, 5 April 2016 (UTC)

What happens when you type [ How is the solubility of a salt influenced by another salt? ] in the Google search box? --Guy Macon (talk) 16:29, 5 April 2016 (UTC)

Common-ion effect may come into play, depending on the identity of the other salt. --Jayron32 16:41, 5 April 2016 (UTC)

Voltage drop over fully open transistor?

I've made a [schematic for a circuit] which uses two PIR circuits to control some LEDs (either PIR sensor will activate the LEDs). A couple of resistors and a capacitor slow the opening and closing of the transistor so that the LEDs fade on and off. Can anyone advise the voltage drop over a 2N2222 transistor that is fully open? The LEDs accept 1.8-2.2 V. --78.148.105.117 (talk) 12:31, 5 April 2016 (UTC)

If by "open" you mean not passing current (when V_B = V_E = 0V), the voltage drop across the transistor collector-to-emitter is the whole 6V supply. The 2N2222 is a common NPN switching transistor with h_FE >75 @ I_C =10 mA. Datasheet here. The HC-SR501 Body Sensor Modules that you use seem to deliver maximum 3.3V outputs; that suggests an inadequate 1V approx. to the LEDs after voltage drops in the 1N4001, division by 7 k ohm resistors, and V_BE. The 470µF capacitor in your circuit diagram is an electrolytic type that should be shown with correct polarity. The power dissipated in the transistor would be maximum and equal to the power in the LEDS if its emitter could supply 3V to the LEDs. P_tot in 2N2222 must not exceed 500mW so the LEDs should draw somewhat less than 160 mA. (If by "open" you meant the fully conducting state, V_CEsat of the 2N2222 is about 0.4V ). AllBestFaith (talk) 14:26, 5 April 2016 (UTC)

Damn! I meant closed! Thanks. I'm not sure I'm using the symbol properly either. The base is where the signal goes right? The 6V is meant to be shared across the LEDs when the transistor is closed/on. The 3.3 V is meant to be delivered to the transistor to tell it to turn on. 78.148.105.117 (talk) 15:13, 5 April 2016 (UTC)

The base is ... where the base is. Refer to our article on bipolar junction transistors for an introduction. To be clear, it is possible to design a single transistor amplifier that places the input or output signal on any of the terminals of a transistor. Most commonly, though, the convention is to use the base as the input signal, because this yields the most desirable current gain. This is called the common emitter configuration, and it is popular for lots of general purpose circuits like simple audio amplifiers or simple current drivers. Not all amplifier circuits need high current gain, so other configurations exist for different applications. Nimur (talk) 15:18, 5 April 2016 (UTC)

Unfortunately the OP drew a transistor in Common collector (known as "emitter follower") arrangement where there will be no voltage gain, and V_E cannot be more positive than V_B. This seems to be a case of wanting several functions together i.e. (i) an OR-logic combination of the two sensor outputs, (ii) slow ramp switching on/off and (iii) a driver for 9 LEDs. There are better circuit solutions for these functions e.g. (i) a standard CMOS device such as MC14071, (ii) an Op amp integrator with (iii) a high-current output stage respectively. A designer would enquire why the ramp switching is wanted (reasons could be to reduce transient loading of a power supply shared with something else, or to prolong the life of incandescent bulbs but that's not necessary for LEDs) and (s)he would consider a Switched-mode power supply especially if the total LED power is large. Advantages of the more complex switched mode is that little power is dissipated by the driver since its output transistors are mostly fully on or fully off, and the ramp dimming function is easily done by varying the switching Duty cycle. AllBestFaith (talk) 19:13, 5 April 2016 (UTC)

Hi. I've rearranged the circuit a lot. The reason for the fading is to make the light look more like a flame coming on and going off. [[http://everycircuit.com/circuit/4523679919112192 This is part of the circuit - I'm trying to make the on phase switch on more slowly but I don't seem to be able without reducing the final voltage/brightness. The first switch simulates the PIR sensor coming on and the second switch is just to drain the capacitor to reset the circuit for the simulation. The problem is that I can only make the light fade-on take longer by simultaneously increasing the delay before any light shows at all. Thanks for any advice. 78.148.105.117 (talk) 21:24, 5 April 2016 (UTC)

Why is Fresh-water Fishing mostly so poor in Winter? (I'm sure there are exceptions)

Fish don't hibernate, so it has to eat and swim around same as any other season. Some fish can't even breathe unless they are on the move. Not sure if this applies to fresh-water fish, but maybe it does. Anyway, it has to eat and it has to exist same as any other season, so why is fishing so poor in winter?

2A02:FE0:C711:5C41:3155:1744:AA32:2C45 (talk) 15:28, 5 April 2016 (UTC)

Fish are cold-blooded animals, so their metabolism slows down in cold weather. Therefore fish use less energy and don't have to feed as often in winter, and thus are less likely to take the bait. - Lindert (talk) 16:09, 5 April 2016 (UTC)

(edit conflict)Doesn't it depend on what sort of fishing? Fly fishing will be more successful when there are more flies around in summer, but other fishing techniques are possibly better in winter? Freshwater fish can breathe when at rest relative to the river bed just by relying on the flow of water past their gills. Dbfirs 16:14, 5 April 2016 (UTC)

Yup, it's hard to ice fish at all come summer. Rmhermen (talk) 20:32, 5 April 2016 (UTC)

... hadn't thought of that! I was thinking of worms and spinners. Dbfirs 21:04, 5 April 2016 (UTC)

Thanks guys, for answering 2A02:FE0:C711:5C41:D448:2C0C:836:8174 (talk) 14:02, 6 April 2016 (UTC)

What happens to dissolved oxygen in the water when the lake is completely frozen over ?

I would expect the level to steadily go down, since there's no air in contact with the water at the surface to replenish the supply. Wouldn't the fish then use up the oxygen, converting it to carbon dioxide ? Or are there enough plants in freshwater lakes so that the oxygen cycle is self-sustaining ? StuRat (talk) 16:19, 5 April 2016 (UTC)

Completely frozen over as in "a layer of ice on top, with no gaps" or as in "ice down to the bottom of the lake"? --Jayron32 16:42, 5 April 2016 (UTC)

The first case. StuRat (talk) 16:44, 5 April 2016 (UTC)

[13], [14], [15], [16]. --Jayron32 17:56, 5 April 2016 (UTC)

Can it be ever so cold that a lake is frozen down to the bottom? --Scicurious (talk) 00:49, 6 April 2016 (UTC)

A shallow lake, yes. StuRat (talk) 00:53, 6 April 2016 (UTC)

A shallow lake is not a lake, but a pond. These can freeze all the way down, but I do not believe a lake can be completely frozen. Scicurious (talk) 11:01, 6 April 2016 (UTC)

Sometimes. Depends on who does the defining. --Jayron32 14:38, 6 April 2016 (UTC)

Whoever named Shallow Lake apparently disagrees. StuRat (talk) 17:45, 6 April 2016 (UTC)

Why is it that water freezes on the surface of a lake but not below it?, Why Fish don’t Freeze in a Frozen Lake and Lake Vostok. I've not come across a lake frozen to the bottom during the last 40+ years in the Arctic. CambridgeBayWeather, Uqaqtuq (talk), Sunasuttuq 02:37, 7 April 2016 (UTC)

Thanks guys, for answering... Ops, wrong post. Sorry. Was meant for the one above. 2A02:FE0:C711:5C41:D448:2C0C:836:8174 (talk) 14:00, 6 April 2016 (UTC)

How does lactulose cause flatulence ?

It's an indigestible sugar used to treat constipation (among other things). So, if it isn't digestible, what generates the gas ? StuRat (talk) 19:20, 5 April 2016 (UTC)

It's a stool softener. What it does is draw water into the stool, thus expanding and softening the stool and replacing the gas contained within the stool with water. All that gas gotta go somewhere... --TammyMoet (talk) 19:43, 5 April 2016 (UTC)

Lactulose is metabolized in the colon by bacterial flora, see Lactulose#Mechanism of action.Fermentation is the name of the metabolic process that converts sugar to acids, gases or alcohol. It occurs in yeast and bacteria, and also in oxygen-starved muscle cells, as in the case of lactic acid fermentation. AllBestFaith (talk) 19:44, 5 April 2016 (UTC)

See also Flatulence#Production.2C_composition.2C_and_smell. ---- LongHairedFop (talk) 19:47, 5 April 2016 (UTC)

As others have noted, lactulose's medicinal usage (and veterinary usage; its common as a no-fuss/easy on the metabolic pathways treatment option for constipation in certain mammals) is directly a result of the fact that it is not digested or absorbed in the upper gastrointestianl tract. When it reaches the lower tract, it becomes a readily-available form of sustenance which can greatly increase the numbers of various bacterial species within your gut's microbiota. In metabolizing the sugar, these gut flora change the pH of the stool mass and, through osmotic differential, pull water across the intestinal wall, the sum result of which is fecal matter with more water content and a greater volume, both of which make stools easier to pass and also create greater stimulation of the voiding reflex. Snow ^{let's rap} 20:49, 5 April 2016 (UTC)

Gravity detector

Hi, on a TV programme I saw demonstrated a gravity detector supposedly sensitive enough to detect people moving around nearby (within a few feet). The man demonstrating it moved from side to side in front of it, and the signal from the detector appeared to oscillate in sync with his movements. Is this really feasible, or would a detector that sensitive be overwhelmed by background noise? 86.161.61.41 (talk) 20:04, 5 April 2016 (UTC)

Simple gravimeters have been known for centuries. See Cavendish experiment for one of the famous early experiments in detecting the strength of a gravitational attraction between relatively small masses. Modern gravimeters are more sensitive and transportable. --Jayron32 20:10, 5 April 2016 (UTC)

With regards to background noise, consider that a person weighing 80 kg at two feet from the sensor has about the same effect as a 8000 kg truck at 20 feet (gravity decreases with the distance squared). Hence I'd say that background noise could be a problem in some locations, but if the immediate vicinity of the sensor is not too eventful the scenario you describe is entirely feasible. - Lindert (talk) 20:22, 5 April 2016 (UTC)

What about larger terrestrial and celestial events? 86.161.61.41 (talk) 20:53, 5 April 2016 (UTC)

Even though the gravitational effects associated with those things are large compared to what the sensor is measuring (e.g. the moon has a much larger gravitational pull on the sensor than any person standing a feet away), the time scales for these events are of a completely different order. Because these larger events happen so slowly relatively speaking you can still see the immediate effects of people moving by the sensor. - Lindert (talk) 21:18, 5 April 2016 (UTC)

I see, thanks. 86.161.61.41 (talk) 22:55, 5 April 2016 (UTC)

The LIGO detectors are incredibly sensitive. Your observation about background noise is correct; Neil deGrasse Tyson talks here about the signs they have around the facilities telling you to drive slowly to reduce interference. --71.110.8.102 (talk) 23:04, 5 April 2016 (UTC)

That may be more for mechanical vibration than gravitational disturbance? 86.161.61.41 (talk) 00:04, 6 April 2016 (UTC)

Yes, LIGO is very sensitive to mechanical vibrations. I once heard a talk discussing the sources of noise that LIGO has to deal with, and it included many ridiculous problems including: tides caused by the moon, continental drift, weather patterns, and apparently tumbleweeds hitting the side of the building (so they erected fences to catch the weeds before they got too close). Dragons flight (talk) 07:03, 6 April 2016 (UTC)

Bacterial victim

Viruses notoriously infect us eukaryotes. Are prokaryotes spared this affliction? Jim.henderson (talk) 20:25, 5 April 2016 (UTC)

In fact, there is a specific word for viruses that attack bacteria: bacteriophage. Nimur (talk) 20:38, 5 April 2016 (UTC)

Ah. Thanks. And I should have phrased the question as to not invite a double negative. Jim.henderson (talk) 20:42, 5 April 2016 (UTC)

Also, you need to phrase your comment not to include a split infinitive. Only jesting!--178.101.224.162 (talk) 00:09, 6 April 2016 (UTC)

There are even virophages! Nobody gets a free pass. :) But honor among thieves means that more of them are simply satellite viruses. Wnt (talk) 11:30, 6 April 2016 (UTC)

Reaction with ice

Does sodium react with ice? What are some values of the reaction rate?--213.233.84.20 (talk) 21:03, 5 April 2016 (UTC)

It reacts quite violently with water. So if the ice melts.....--178.101.224.162 (talk) 00:29, 6 April 2016 (UTC)

If there is any reaction at all, that would melt some of the ice, which would react more, and melt more ice, in a chain reaction until all the ice was gone. And I would expect there would be some reaction at first, since ice still sublimates into water vapor even at low temperatures. StuRat (talk) 00:42, 6 April 2016 (UTC)

It would actually be an interesting experiment if you got some very cold sodium and pressed it up against some very cold ice. I don't mean like -1c, i mean like -20c or something. I'm actually not sure you could really guess what would happen from fundamentals, without actually trying the experiment... I agree water sublimates into vapor but that is VERY VERY slow at very low temperatures. A single ice cube can take a month or more to sublimate in a freezer, not sure that would be enough to really "set off" the reaction, sodium is only the 2nd alkili metal. Vespine (talk) 02:02, 6 April 2016 (UTC)

Interesting question. There must be a some values of the reaction rate. Do a thought experiment: place some ice in vacuum chamber with a clean unoxidised piece of sodium. The ice (on recsiving any heat) will sublimate. That water vapour will create a 'protective' film of hydrate on said lump of element preventing further ingress of water vapour. Decrees vacuum (ingress persure) enough and the the vapour pressure increases and penetrates the protective film. Thus creating heat – which if sufficient, will cause frozen water to change state. At temperatures of boiling helium I doubt anything will happen, perhaps not even at boiling nitrogen because too much heat is being lost to the rest of cryogenic vessel. So, the reaction must depend on temperature and pressure -with a cut off point where nothing happens. --Aspro (talk) 20:25, 6 April 2016 (UTC)

April 6

That automatic camera timer

I don't know what it's called. You set it for 10 seconds and run back into the frame to be in the shot.

Is there a camera that does that but then keeps taking pictures every 5 seconds or so for a while?

Anna Frodesiak (talk) 03:08, 6 April 2016 (UTC)

Self timer. Now with digital cameras, I can't imagine any type of time-delay or timing pattern of multiple images can't be accomplished. But I'm not familiar with commercial cameras in general, so I have no idea what's available (vs what could be programmed on a smartphone or other custom device). DMacks (talk) 03:17, 6 April 2016 (UTC)

Hi DMacks! Thanks for the feedback. But now I am totally confused. :) I don't know the difference between a digital camera, a commercial camera, and a custom device. As for "accomplished", I think it either has the setting or not. Cheers. :) Anna Frodesiak (talk) 03:31, 6 April 2016 (UTC)

I read "a camera" to mean a preconstructed object whose primary purpose was to take still protographs (the thing we called a "camera" that used to have a roll or disc of film but more recently instead uses digital processing...not "the camera feature now seemingly present in every portable device, phone, and computer). A digital camera has a lot of on-board embedded processing available, more than just the mechanics of a button connected to a shutter. Once you have electronic control and don't need to do anything physical internally to "take a picture", you can have an electronic controller fire the "take a picture" electronic actions any time using some circuit. The old cameras had a fixed 10-second timer, but with a pure electrical system, one can have any one-time or repeated timing pattern one likes by using some custom-designed circuit or bit of software programming. So "it can be done". But I don't know of "a camera" that actually does it. But using a more general piece of hardware that happens to be able to take photographs, (for example, "a phone that has a camera in it"), it's easy to write a program that uses that camera function (again, on any arbitrary schedule). It's easier on "a smartphone with a camera" than with "a camera object" because the actual programming interface is available (anyone can write an app), instead of only having the few buttons and built-in software or interfaces that a camera-object's manufacturer decides to make available. As others have noted below, there actually are camera-objects that have this feature already and/or make the interfaces available for third-party controllers. DMacks (talk) 04:55, 6 April 2016 (UTC)

intervalometer is the device that you are looking for.

Not quite what you are after but some Canon DSLR cameras have wifi (I have a 6D) and you can get an iphone app which lets you use your phone to remotely trigger the shutter. It's really awesome, you can even see the camera's viewfinder on your phone and change the settings. The only thing you really have to do at the camera is "frame" the shot (you can't "move" the camera with the phone), then you can do the rest with your phone. When I want to take a group shot, I just hold my phone behind my back, or behind someone/something else and trigger the shutter a bunch of times. Vespine (talk) 04:02, 6 April 2016 (UTC)

Also, any of the "more expensive" remote shutter trigger probably has the options you need, for example this canon remote control does everything you've asked, from a different site the unit's features include a self-timer, long-exposure timer, interval timer and the option to set the number of shots in a sequence. . Vespine (talk) 04:06, 6 April 2016 (UTC)

Holy moly. I seem to always ask questions that draw very complicated answers. I just noticed that all cameras seem to have a self timer that takes just one shot and then you have to walk up to it and set it again. A bit silly, if you ask me. Multiple shot capability should be standard on all cameras. I imagine it would be very well received and quite a selling point. And I-phones don't seem to have any self timer at all. Thank you all kindly for the thoughtful replies. I am sorry to ask such questions. Anna Frodesiak (talk) 06:33, 6 April 2016 (UTC)

Most digital cameras also have an option to record video, although often at reduced resolution, but that might work in some cases. Of course, the first few seconds will be you starting it and running back to the group to be photographed, and the last few seconds will be the reverse, but you can edit that out later. You can also pull stills out of the video later. StuRat (talk) 06:57, 6 April 2016 (UTC)

Thanks, StuRat. I guess that would be sort of okay. Now, if your camera could do multiple timed images, say, every 5 seconds, wouldn't that be useful and fun? And wouldn't you get lots of great photos out of it? :) Anna Frodesiak (talk) 07:02, 6 April 2016 (UTC)

The problem with that is that you would need to hold your pose for a long time, not blinking, etc. They would need to add some type of audio or visual cue to tell people when the next frame will be taken, in order to avoid that issue. The remote trigger also solves that problem. StuRat (talk) 07:05, 6 April 2016 (UTC)

Why hold the pose? Everyone would have 5 seconds to get it together and then the little light or beep would go and zam, another photo. I think it would be bags of fun and produce a choice of 5 or 10 great pics. So, if they had it, would you use it? Anna Frodesiak (talk) 07:11, 6 April 2016 (UTC)

No, it would be too restrictive for me. Every 5 seconds we would have to get into a good pose, be careful not to blink, etc. More likely most of the shots would be bad because somebody would be moving, not looking at the camera, have their eyes shut, be talking, etc. Of course, there is such a thing as "candids", where you take pictures without posing. But those tend to generate a large volume of pics with only a few being worth keeping. StuRat (talk) 07:32, 6 April 2016 (UTC)

StuRat, I think you would love it. Maybe every ten seconds with a light just before. After several photos everyone would start to crack up and the photos would get really good. Anna Frodesiak (talk) 08:02, 6 April 2016 (UTC)

Note that professional photographers photographing subjects like models used to have a setting that would take a pic, say, every second. They held onto the camera while using this setting, though. As I mentioned above, this did generate a large volume of pics, and only a few were "keepers". StuRat (talk) 07:36, 6 April 2016 (UTC)

If your camera does support taking photos at sufficient intervals (at 5 seconds apart or whatever) and of sufficient quantity, then you could just start taking photos and delete the ones at the beginning. The only issue would be that there may not be any indicator before each photo. Nil Einne (talk) 07:40, 6 April 2016 (UTC)

Every second, sure. But that's that "...work with me baby, come on, feel it..." type of thing. So, sure there would be hundreds with a few keepers.

That whole idea of setting the camera to 10 seconds and rushing in front to join the others for a single snap seems very old fashioned. Surely an option string of 10 photos with 10 seconds between would be an improvement. Anna Frodesiak (talk) 08:02, 6 April 2016 (UTC)

I'm fairly sure there's quite a few cameras which do allow setting the interval. After all, it's used for time lapse photography although 5 seconds is a bit short for most time lapse. Anyway in terms of your later point AFAIK the most common option nowadays is that the camera will take a burst of several photos after the timer with the possible ability to set the number of photos but not an interval (it's intended to be a burst not time lapse) with the hope that one of them will be good despite people blinking etc. If this doesn't work it'll probably be possible to combine different photos so it's also useful in that way. I think your specific option is less common because if you're going to take a seperate shot most people would prefer to set it up first. Nil Einne (talk) 08:42, 6 April 2016 (UTC)

Okay, that makes sense. But set it up first and someone has their eyes closed and you have to run back and set the timer again. That is what this was all about. Also, that smartphone burst thing seems to make too many photos. Many thanks for answering yet another annoying Anna question. :) Anna Frodesiak (talk) 08:47, 6 April 2016 (UTC)

Aside: I'm typing and suddenl "y" is a "z" and my full colon is an "E" with two dots on top. Why? I'm typing this in a notepad and pasting it here. Help! :) Anna Frodesiak (talk) 07:48, 6 April 2016 (UTC)

Never mind. Someone in IRC helped me with that. Anna Frodesiak (talk) 08:00, 6 April 2016 (UTC)

The OP did not state which model of camera they have. CHDK concentrates mainly on Cannon but other brands are being worked upon. It give you full control over the cameras firmware. It included setting time lapse and multiple images. It will even calculate the hypo-focal distance like professionals do, to give a better focused group shot. Warning. It requires one knowing how to switch on a computer, down-load, instal a program and to own a digital camera.--Aspro (talk) 12:08, 6 April 2016 (UTC)

This Youtube clip describes how to down load, instal and select time laps for whatever intervals you so desire. Canon CHDK Hack Tutorial: RAW, HDR, and Time Lapse Does a lot else as well. Keep it on a spare SD memory card until one gets used to all the options. No sensible Canon camera would want its owner to not to have one.--Aspro (talk) 12:51, 6 April 2016 (UTC)

Star trails over the ESO 3.6 m Telescope

.

Other models are available! I have a digital Pentax (medium price range - not a professional model). I can adjust the settings of the timer such that the shutter can remain open for as long as I want. I can set it to do this multiple times, with each exposure made after an interval which I also set. So, I can set the camera to open the shutter for 20 secs, every 1-minute, and continue to do this for 3 hours. This is how we get those wonderful pictures of stars appearing to circle in the sky called Star trails. DrChrissy ^(talk) 13:46, 6 April 2016 (UTC)

• @Anna Frodesiak: The answer is you can set the timer on a 2 to 10 second interval on a modern DSL camera like e.g. Canon 1200D.--TMCk (talk) 14:36, 6 April 2016 (UTC)

Thank you thank you thank you! This is exactly what I'm after. I've been using this horrid Sony Cyber-shot DSC-T700 and am trying to persuade family to let me get a better one. Every time there is a timer group photo, I have to run back after each shot and set it again because someone had to be a joker. This interval thing would be poifect! I will look into the cameras you've suggested. Many, many thanks, DrChrissy, TMCk, and everyone else too!! P.S. Lovely Star trails! Anna Frodesiak (talk) 23:09, 6 April 2016 (UTC)

Anna, I did not mention that my camera also has a remote control device. So, I can put the camera on a table/tripod, focus and frame it on my friends, then turn on the remote control function on the camera. I can then rejoin the group, pose, then press the button on the remote control device and it takes our group photo. I can do this for as long as I want without having to return to the camera. I can also set a delay (e.g 2 secs) so that I have time to hide the remote control in my hand or behind my back - otherwise all the photos have me pointing a small plastic device at the camera! Happy snapping. DrChrissy ^(talk) 23:17, 6 April 2016 (UTC)

Happy to help. BTW, if you want to check a camera's more detailed features (like the timer modes), check the model specific user manual online ;) --TMCk (talk) 00:08, 7 April 2016 (UTC)

Harvest energy of downwards escalator

I'm getting very interested in escalators (because I currently spend about a quarter of an hour a day on escalators in the Kyiv metro system). [I was amazed to learn from the escalator article that the term to 'escalate', as in wars etc., comes from the machine.]

The article mentions that most escalators use AC motors. I wonder if a downward escalator could be so crowded - say with two people on every step - that their weight exceeded the friction and the escalator would have to be braked or governed? And if this were the case, would it be efficient to couple its mechanism to the upward escalator?

Hayttom (talk) 12:48, 6 April 2016 (UTC)

Hey, Haytttom, interesting question! It seems the answer is "yes, some escalators use something akin to regenerative braking." Here [17] is a scholarly article on energy efficiency in escalators (and elevators), and mentions regenerative braking in a few places, as well as things like optimizing counterweight. They claim that highly efficient escalators (and elevators) can use 80% less than their old-fashioned un-optimized counterparts. This paper is more about metro systems as a whole [18], but does have some interesting stuff about how escalators fit in to the big picture. Finally the E4 project [19] has a mission of studying and improving efficiency in lifts and escalators, though their web presence is a bit thin. SemanticMantis (talk) 14:12, 6 April 2016 (UTC)

I've never felt the need for downward escalators to begin with, as I only get tired walking up stairs, not down. But, I understand that architects like the symmetric look of one up and one down escalator. I always thought the down escalator could work without a motor, just using the weight of the passengers and a mechanism like a thick fluid to limit the speed. This would mean it would stop when nobody was on it, and small people might not be heavy enough to overcome friction and move it, but then they could just walk down. Can anyone put some numbers on this, and let us know what kind of frictional forces we must overcome ? StuRat (talk) 16:09, 6 April 2016 (UTC)

I can't see any easy way to use a counterweight on an escalator. I'd have thought it should be possible to link an up escalator with a down escalator and so only have to cope with the difference in weight between people going up and down. I guess regenerative braking is easier though. Dmcq (talk) 17:37, 6 April 2016 (UTC)

Sorry, my mistake. I've added "and elevators" to my post to clarify that I (and the article I linked) was talking about both. SemanticMantis (talk) 18:35, 6 April 2016 (UTC)

Wind and solar power

Can wind and solar power combined ever match the power output of current fossil fuels such as oil and natural gas, to power large cities such as Los Angeles or London?--WaltCip (talk) 13:59, 6 April 2016 (UTC)

Read Renewable energy in Germany and see if it leads you to any conclusions. --Jayron32 14:34, 6 April 2016 (UTC)

Renewable energy in Denmark also has some interesting data. --Jayron32 14:35, 6 April 2016 (UTC)

This is excellent reading. Thanks.--WaltCip (talk) 14:42, 6 April 2016 (UTC)

There is far more solar energy available than would be needed to power our cities. In some areas, there is also sufficient potential wind power. To fully replace fossil fuels, these technologies would need to be combined with some form of large-scale energy storage technology to provide power at times when the sun doesn't shine and wind doesn't blow. There is no reason humanity couldn't go 100% solar and wind, but right now it would cost more than fossil fuels which is often the limiting factor unless adoption is driven by government mandates or incentives. Solar cells are getting cheaper, but still cost more than fossil fuels in most cases. Wind turbines can be cost competitive with fossil fuels in areas with consistent strong winds but less so in areas with intermittent or weak winds. Large scale energy storage is also still pretty expensive in most areas but can be done. Dragons flight (talk) 14:54, 6 April 2016 (UTC)

This site has an interesting map of the land area required using solar alone (not counting wind, hydro, geothermal). Rmhermen (talk) 15:18, 6 April 2016 (UTC)

The trouble with the "X costs more than Y" argument is that we very often fail to include all of the costs. It's quite possible that the cost to construct a coal power station and to mine the coal to fuel it for (say) 50 years will be less than to construct and operate a wind power plant with the same capacity over the same period. But if you include a fair share of the cost of shoring up ocean wall defenses due to sea level rise due to the coal plant's excessive CO2 output - then the economic argument gets shakier. But how should we price the loss of the polar bears - or the impact of all of the ash mounds left by the coal plant - or the loss of human life due to the dangers of coal mine accidents? So economic arguments only get you so far. However, there is great difficulty with using this extended economic argument as consequence of the way human societies have formed. If (say) mainland China doesn't have much issue with coastal flooding, then it feels a lower price for coal power plants than an island nation like Indonesia - where sea level rise is a critical factor in their survival. But each country makes the decision on how to price and regulate coal power plants, even though the global climate is something that we all share.

Energy storage is certainly a big issue with many kinds of renewable sources - but those costs can be mitigated by beefing up our energy transmission capabilities. Sure, the amount of wind available in one particular area may be intermittent and somewhat random - but the average amount of wind available over an entire country, or an entire continent, should be much more predictable. So if you can efficiently move energy around, you can average over space instead of using storage systems and averaging over time. Averaging over domains (solar/wind/tidal/geothermal) gets you an even more predictable output.

SteveBaker (talk) 15:24, 6 April 2016 (UTC)

Not to derail the topic, but it bothers me that China is able to get away with a lot of environmental catastrophes (the smog and traffic in Beijing are rated as among the worst in the world) and not be held accountable for them the same way other developed nations are.--WaltCip (talk) 15:50, 6 April 2016 (UTC)

They are still considered a "developing" nation, but the pollution is becoming a concern to them, too, at least the obvious pollution, like smog. London and New York City had their periods of horrible pollution, too. It's a variation on tombstone mentality, where they weren't willing to do anything about pollution until it affected them personally. StuRat (talk) 16:17, 6 April 2016 (UTC)

At ~$8,000 per capita, the GDP of China is still below the world average (~$10,000) and far below the traditional developed countries (US, Europe, etc.; $30k-50k). In terms of pollution, China situation's today is reminiscent of the US situation in the 1960s when after a long industrial expansion pollution had become widespread and a populist political backlash was starting to drive reforms. If they follow the American example, we might expect to see dramatic improvements in China's environmental situation over the next 10-20 years. For example, the US cut regulated particulate emissions in half during the first decade after the passage of the 1970 Clean Air Act. Dragons flight (talk) 19:10, 6 April 2016 (UTC)

Regarding including all the costs. This is known as life-cycle assessment and is related to Whole-life cost and impact assessment. Specifically addressing these ideas with respect sustainability issues, here [20] is a nice overview of life cycle analysis from the Illinois Sustainable Technology Center. SemanticMantis (talk) 18:19, 6 April 2016 (UTC)

There is no good or efficient manner to store large quantities of energy...and the ability to do so isn't on the horizon...so when wind doesn't blow or sun doesn't shine...this is actually a major problem for wind and solar..68.48.241.158 (talk) 18:36, 6 April 2016 (UTC)

Isn't pumping water from a low reservoir to a high reservoir a reasonably efficient way to store large quantities of energy ? StuRat (talk) 18:40, 6 April 2016 (UTC)

Doesn't the energy spent from pumping water from a low elevation to a high one negate the potential energy stored as a result?--WaltCip (talk) 18:52, 6 April 2016 (UTC)

Walt, it's not a method of creating energy, just of storing energy from some other source. For example, solar panels that create too much electricity when the Sun is up and none at night. During the day, the excess would be used to pump water to the high reservoir, while at night the water falling from that height would power turbines, like in conventional hydroelectric power plants/dams. StuRat (talk) 01:01, 7 April 2016 (UTC)

It costs energy, but that doesn't negate the utility of the idea. Nothing is free, and especially not energy storage. The costs are often worth it. Pumped-storage_hydroelectricity is our article that StuRat should have linked if he's going to bother talking about this stuff on the reference desk. I know that we have an article on that and how to find that article but not everyone does, so it's just common courtesy to provide wikilinks if we want to actually help people at the reference desk. Okinawa_Yanbaru_Seawater_Pumped_Storage_Power_Station is a good example of pumped-water energy storage, and there are even schemes to store energy by pushing rail cars full of gravel up hills [21] [22]. Energy storage and List_of_energy_storage_projects are also highly relevant to this thread. SemanticMantis (talk) 19:09, 6 April 2016 (UTC)

(edit conflict) In practice, usually 70-75% efficient round-trip. So everything else being equal pumped-hydro will probably make the electricity at least ~35% more expensive. However, since the wholesale cost of electricity often already varies by more than 100% due to time-of-day load variations, this is probably acceptable. The biggest limitation of pumped hydro storage is that it is only easy to implement in areas with existing reservoirs or where the terrain makes new reservoirs relatively easy to construct. Other technologies, e.g. NaS batteries, compressed air, flywheel energy storage, etc., will probably make more sense in terrains that don't readily support pumped hydro. These things are entirely possible if one is willing to pay the associated costs. Dragons flight (talk) 19:10, 6 April 2016 (UTC)

There's been some discussion about electric cars as a form of distributed storage. The cars get charged up at night when there tends to be a surplus of generating capacity -- sometimes utilities literally give away nighttime electricity to maintain their base generation load. Then the cars are driven during the daytime. Shock Brigade Harvester Boris (talk) 00:45, 7 April 2016 (UTC)

I strongly recommend reading, and understanding, the ebook/website linked to from here https://en.wikipedia.org/wiki/David_J._C._MacKay . Basic conclusion is that for the UK you need nukes if you are trying to actually reduce CO2 output. In my opinion Renewables are useful without extra storage up until X % contribution to generating capacity, X is certainly not a simple number to calculate, 20 might be a place to start, to be generous. The problem with storage is all the good hydro sites have gone, and nothing else is cost effective at current base load prices. Greglocock (talk) 18:45, 6 April 2016 (UTC)

if you're not afraid of nuclear power generation than "renewables" are a complete and utter waste of time, money, and effort....but perhaps nuclear power is indeed something to be afraid of....(if your receiving govt subsidies to run your solar panel business, than "renewables" are wonderful)...68.48.241.158 (talk) 21:05, 6 April 2016 (UTC)

Not a complete waste of time, just niche markets. If you live far from the grid, and have lots of sunlight and/or wind, then they make perfectly good sense for you, even without subsidies. StuRat (talk) 21:17, 6 April 2016 (UTC)

No nuclear power station has ever been economically viable without massive public subsidies, including limits to the liability of owners for accidents and radioactive waste. And even assuming that nuclear power can be made "safe" in the first world (although Fukushima is not a good sign), it does not scale out. Who wants nuclear power plants in Nigeria, Libya, Iran or Somalia? --Stephan Schulz (talk) 21:23, 6 April 2016 (UTC)

the political/regulatory cost have made them economically difficult at least in USA...but in and of themselves there's nothing that even comes close...a single plant can power half a million home, night/day/wind/no wind....there's nothing that comes close....renewables aren't even in the conversation, particularly since you can't count on them at any given time....68.48.241.158 (talk) 21:31, 6 April 2016 (UTC)

Some forms of renewable energy are available 24/7, like geothermal. Of course, that only works in certain places. StuRat (talk) 21:33, 6 April 2016 (UTC)

Solar power towers using molten salts, heat up more than needed. So there's capcaite to drive turbines over night. Using the kalina cycle, can make even more efficient. --Hans Haase (有问题吗) 07:56, 7 April 2016 (UTC)

Does kosher/halal beef taste different due to drainage of blood?

An older person I know has been having a lot of trouble appreciating steak and other meat lately. She keeps complaining it all has a "liver" flavor. From a master's thesis I found on the topic [23] there is some indication that hemoglobin level in the meat matters, as it is a source of free iron that causes degradation while cooking (cooking temperature is also a factor, and various other things). It cites this for that, which I haven't accessed in full, that talks about liver flavors being a combination of metallic and fishy taste; I suppose the source must have some discussion.

Anyway, I just want to back up, go in the front door here and ask: are people aware of any evidence that kosher/halal meat, from which blood is drained as thoroughly as possible, has a different flavor of any kind from other meat? Of course, searching online finds people who say yes - in the past I had assumed this was boosterism, and a double-blind test with a sufficient sample size wouldn't find people able to tell. But finding real data is tricky on this.

FWIW, I already suggested she might try it and see - it can't hurt, unless you happen to be a cow. :) But I am just wondering if there's any science on it. Wnt (talk) 14:01, 6 April 2016 (UTC)

I'm guessing you searched google scholar for longer than the 4 minutes I did? I didn't find any proper controlled experiments either. I did find one potential lead though: I would try to contact these folks [24] at the Halal Products Research Institute. Seems they do perform/fund real science published in good journals. If anyone knows about the existence of the studies you're looking for, I bet they do. SemanticMantis (talk) 14:18, 6 April 2016 (UTC)

And to approach from another tack: what about cortisol? Here [25] is an article from The Atlantic discussing how animals with higher cortisol levels and less humane treatment might taste worse, and here [26] is a scientific article talking about Malaysian Halal standards [27], including maximum cortisol levels. Still no good studies on taste, but I think cortisol must be a conceptually viable route to different taste in halal/kosher meats. SemanticMantis (talk) 14:25, 6 April 2016 (UTC)

We have an article on the PSE meat referenced. But it's a good search term - with it I found [28] which makes all kinds of totally unexpected statements about kosher meat. Their results are that the loss of blood is actually not any larger in kosher meat. But they find the meat loses less water, is tenderer, is a different color than the conventional meat. So kosher treatment seems to make much more difference than I'd imagined, even while not having the effect I expected. Wnt (talk) 14:55, 6 April 2016 (UTC)

Before considering the possibly different flavour of the meat, you might consider the effect of age on the human sense of taste. My mother has been complaining for a long time that the food doesn't taste as good now as it used to. To me it all seems fine - and I think the fact of her being 100 may be significant. 217.44.50.87 (talk) 15:44, 6 April 2016 (UTC)

Many foods really don't taste as good as they used to, because they have bred them to grow quickly, at the expense of flavor and nutrition. StuRat (talk) 16:20, 6 April 2016 (UTC)

Do you have a source that confirms how growth rate of foodstuffs affects flavor and nutrition? 91.155.193.199 (talk) 00:44, 7 April 2016 (UTC)

Here you go: [29]. The book referred to at that link is The Dorito Effect: The Surprising New Truth about Food and Flavor. StuRat (talk) 04:29, 7 April 2016 (UTC)

Oh, I'm sure all sorts of individual factors play a role, but I was focusing for this purpose on what can be done to the meat rather than the taster. Wnt (talk) 17:25, 6 April 2016 (UTC)

Conventional livestock slaughter is usually a 2-stage procedure. The animal is first rendered unconscious by, e.g. a stun gun. The animal is then immediately killed, usually by exsanguination. My thought here is that the removal of blood is likely to be very similar to the kosher and halal methods, and therefore unlikely to have any influence on taste. To WNT, people of the Jewish faith do not eat pork, so there is no such thing as kosher pork and PSE is therefore not an issue - I think. DrChrissy ^(talk) 15:47, 6 April 2016 (UTC)

The first line of that article says "beef and poultry" also. But I think it's not technically an issue for another reason, which is that they say it's only 3% of meat, or anyway, not more than 10. Nonetheless, the "exudative" is reminiscent of the differences in water loss during cooking in the study I cited above, so it might be the extreme case of a broader phenomenon. (but I don't know that) Wnt (talk) 17:25, 6 April 2016 (UTC)

Suggestion: If she doesn't care for the taste of meat any more, and we know meat is unhealthy anyway, maybe it's time to explore more vegetarian options. Might keep her alive and healthy longer, too. Or she can avoid red meat and stick with things like fish and chicken, if she still likes those flavors. StuRat (talk) 17:38, 6 April 2016 (UTC)

I tried to go that direction in the conversation, but didn't get anywhere; besides, I don't want to stray too far from the question of whether kosher/halal tastes different, which is more answerable. Wnt (talk) 18:57, 6 April 2016 (UTC)

Ah a question about food, one of my most favourite topics. Yes your taste buds may be getting less sensitive but I think your asking about why the meat itself doesn’t taste like it used to. The whole reason for bleeding meat, was it kept longer (and did not develop those off flavours) before the days of refrigeration. It was also hung for 4 or more days for rigour-mortis to pass. These days the cow walks in to the abattoir one morning and is vacuum packed by lunch time. The vacuum packed meat today is not bled and undergoes what is euphemistically referred to a 'wet curing' because it is more profitable for the food (?) industry. Find a family butcher that can supply properly hung meat (or order it over the internet). Ask for 'Dry Cured Aged' meat. If they can't supply AGED then dry cure yourself in the fridge. The link give some directions: How to Dry-Age Beef at Home Finally, always roast at a very low temperature (like Grandma used to do). The British award wining chef Heston Blumenthal gives guidance on the best temperatures and cooking times for most common cuts but you will have to google it. --Aspro (talk) 21:22, 6 April 2016 (UTC)

I have a beef about that advice to cook at a low temperature. While somebody in their prime could fight off any bloody food poisoning, the aged are at more risk, so all meat should be cooked thoroughly. StuRat (talk) 21:27, 6 April 2016 (UTC)

Thorough and cooking temperatures are two different things. Its like the pasteurisation of milk. 161°F (71.7°C) for 15 sec or 145°F (62.8°C) for 30 minutes. A proper low temperature meat roast takes 4 to 5 hours to bring out the full flavour (for some meats like fowl it need to be higher -so check). Otherwise we would not be here today, because our grandmother would have poisoned everyone. --Aspro (talk) 21:53, 6 April 2016 (UTC)

Yes e.g. beef is safe at 145°F internal temperature [30]. You could in principle get it there by setting your oven to 146°F, which would indeed be a very low cooking temperature (this is not recommended as a cooking technique, but it illustrates the point). We also have a whole article on Low-temperature_cooking. But none of this is really relevant to the OP's question, it is rather relevant to Stu's shoot-from-the-hip comments on topics with which he is unfamiliar. SemanticMantis (talk) 21:59, 6 April 2016 (UTC)

I would (have) gone lower for beef to 122 °F. Of cause this is assuming one uses a meat thermometer and calibrate it – (dip in boiling water and add a few degs for safety). Some ovens are better than others, so don't rely on you ovens temperature gauge.. Think this is New River Restruant's philosphy as well. And they give cooking times and show photographs of the results. --Aspro (talk) 22:33, 6 April 2016 (UTC)

At that low of a cooking temperature the food is indeed unsafe, just as I had warned. StuRat (talk) 22:42, 6 April 2016 (UTC)

Citation needed.--Aspro (talk) 23:23, 6 April 2016 (UTC)

The ref was provided by SemanticMantis, right before your last post. See page 4. StuRat (talk) 00:47, 7 April 2016 (UTC)

by setting your oven to 146°F, which would indeed be a very low cooking temperature. That exactly what a sous vide is for. Vespine (talk) 22:17, 6 April 2016 (UTC)

Does it make sense to talk about temperature of particles?

Can the concept of heat be applied to photons, electrons, and protons? — Preceding unsigned comment added by Scicurious (talk • contribs) 23:33, 6 April 2016‎

Do you mean individual particles, or large collections of them?

Thermodynamics is a fundamentally statistical discipline. It studies only the random component of the behavior of systems. So it really doesn't usually make much sense to speak of the temperature of an individual particle. But you can certainly speak of the temperature of a "gas" of electrons, or of the photons in an evacuated chamber acting as a black body. --Trovatore (talk) 00:04, 7 April 2016 (UTC)

Yes, except for photons, would be expressed as velocity (m*v^2 is temperature). As above, it's statistical but also used to calculate collision rates. Example would be an Argon plasma at a certain temperature will have different velocities for electrons and the Argon ion. The different masses means that for the same temperature, the particles have different velocities and different collision rates. A Langmuir probe is a device used to measure that temperature in a plasma. Photons in a vacuum don't change velocites so temperature refers to a black body model. See Color temperature for black body radiators and "Correlated Color Temperature" in that same article for emitters that are not black body radiators. --DHeyward (talk) 04:25, 7 April 2016 (UTC)

Well, that doesn't work for an individual particle. As I said, it's only the random part that counts. If you have a blast of particles all moving very fast in the same direction, it doesn't make them hot. And so you really can't make a lot of obvious sense out of the notion of the temperature of an individual particle. Maybe if you don't know its energy, but you know it's sampled from a Boltzmann distribution or something, it would make some sort of sense to describe your lack of knowledge in terms of a temperature.

Moreover, temperature is not simply related to kinetic energy per particle. That only works for monatomic ideal gases. For anything else, it's a lot more complicated. --Trovatore (talk) 05:44, 7 April 2016 (UTC)

April 7

Rotating sphere

While I don't begin to understand the equations at https://en.wikipedia.org/wiki/Frame-dragging#Mathematical_derivation_of_frame-dragging, I don't see anything there that looks as if it is modelling the messy atomic nature of real-life matter. It looks too mathematically "exact". Do the equations assume an idealised kind of perfectly smooth and uniform matter? If so, how can one even in principle determine whether a perfect sphere of such matter is rotating or not, given that the sphere rotated through any angle is completely indistinguishable from the original? 86.161.61.4 (talk) 01:56, 7 April 2016 (UTC)

We can tell the sphere is rotating or stationary by its effect on the surrounding region of spacetime; that is even though the sphere itself is perfectly symmetrical, and thus visually indistinguishable whether it is rotating or not, the effects on the surrounding region of spacetime are detectable and measurable, and can be used to deduce the axis, direction, and speed of rotation of the object in question. The Kerr metric describes how so. --Jayron32 02:02, 7 April 2016 (UTC)

Thanks, well I understand that is what the frame-dragging equations say, but I still have a hard time understanding how it is even defined whether the sphere is rotating when, as I say, the sphere rotated through any angle seems completely indistinguishable from the original in every respect (assuming granularity of real-life matter is not modelled). Is the "frame-dragging" the only way that the rotation can be detected? I suppose since we are talking about a hypothetical type of matter, it would possibly depend on other hypothesised properties of the matter, but if it is perfectly uniform in every respect then I don't really see how hypothesising other properties would help. 86.161.61.4 (talk) 02:35, 7 April 2016 (UTC)

I don't genuinely understand general relativity, but note that a moving mass generates gravitomagnetic force. Gravity waves and gravity and gravitomagnetism are all aspects of some big messy tensor math. When a sphere turns that contains mass, it induces fields around it vaguely like how a continuous loop of current in a superconductor generates a magnetic field. I don't actually have any idea how accurate that metaphor is or how far it goes, but at least it should illustrate that the sphere isn't really homogeneous. Wnt (talk) 02:46, 7 April 2016 (UTC)

In the absence of gravity, you could throw a tomato at it and see what happens to the stain, or scratch it and see what happens to the scratch, or hit it with a hammer and see how the sound waves propagate. If it's frictionless, rigid and indestructible, then maybe there is no way to tell and maybe there's no meaningful sense in which it is rotating. But perfectly rigid objects can't exist in special or general relativity because of the light-speed limit. In general relativity, you can't have rotation without frame dragging (as far as I know), so the field is enough to distinguish a rotating from a non-rotating sphere. -- BenRG (talk) 03:45, 7 April 2016 (UTC)

Bounce light off of it and you'll get a different doppler shift depending on whether you are shining light on the part rotating towards you or the part rotating away. (Assuming the magic sphere reflects light anyway.) Push on it and gyroscopic effects will affect the result, etc. Even for a smooth classical mass, there are definite differences that one could measure. Dragons flight (talk) 07:56, 7 April 2016 (UTC)

It's not representing anything atomic. It's macro field equations generally applied to black holes but are also seen in any rotating mass. Rotating sphere's have symmetry but when it is so massive that the rotation induces a change in space-time around the object. Normally we think of conic solutions for gravity and solve for the static field. In simplified way, the rotation changes the static field and that change forces the body to follow the rotation. That's "frame dragging" as the reference frame is dragged around the rotating body without any angular momentum being supplied by the reference fram. That defies Newton mechanics where rotation doesn't affect attraction and it's also more than simply adding mass/energy to the rotating body. It appears to physically alter space-time and all matter/energy have dynamic solution based on rotation and their location within the ergosphere. The effect is greatest at the sphere's equator and disappears at the poles. I believe it also means that point-mass models fail GR for rotating black holes as do singularities. The rotating mass has a volume and the disappearing affect at the poles is how jets are formed. Lense–Thirring precession is frame dragging with more familiar masses. It's written more intuitively than the complex equations surrounding black holes and shows that rotating bodies with volume and mass can be identified with a gyroscope. --DHeyward (talk) 07:14, 7 April 2016 (UTC)

how is this happening?

what is going on here scientifically speaking? how has this remained in this state for so long? if you google image it there's even people sitting on top of it...https://en.wikipedia.org/wiki/Old_Man_of_the_Lake 68.48.241.158 (talk) 05:28, 7 April 2016 (UTC)

There is a suggested answer in the first reference given in the article (from which, incidentally, at least some of the article is plagiarised): Some have suggested that when the Old Man slipped into the lake, he had rocks bound within his roots. This might naturally make him float vertically, though no rocks appear to still be there. At any rate, the submerged end could become heavier over time through being waterlogged. Acting like the wick on a candle, the shorter upper portion of the Old Man remains dry and light. This apparent equilibrium allows the log to be very stable in the water.. Henry^Flower 05:58, 7 April 2016 (UTC)