Wikipedia:Reference desk/Archives/Science/2011 March 27

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March 27

Is all life on earth decended from a common ancestor

According to the article Last universal ancestor, "A universal common ancestor is at least 10²⁸⁶⁰ times more probable than having multiple ancestors…"

Does this infer that the probability that all life on earth is decended from a common ancestor is 10²⁸⁶⁰ times more likely than the tree of life containing more than one starting point (i.e. more than one transition from none life to life)? It seems a startlingly large number if it implies that say plants and animals could not have evolved separately.

I think that must be the chances that every species began independently, or something silly like that. StuRat (talk) 00:17, 27 March 2011 (UTC)

That's exactly what it is stating. You would have to read the original source to understand where it comes from and what were their assumptions. Does it surprise you that plants, animals, fungi, bacteria, etc ... all have a common ancestor? Dauto (talk) 00:45, 27 March 2011 (UTC)

You mean "imply", not "infer" (very common error). I understand it to mean 10²⁸⁶⁰ times more probable than the scenario in which there was more than one starting point for life. Grammatically, it's not a great sentence. "having" is awkward... it's a dangling participle, or something like that... 86.179.115.46 (talk) 00:48, 27 March 2011 (UTC)

That figure of 10²⁸⁶⁰ suggests a degree of mathematical precision that is not realistic. The source is a print one, so difficult to check. I would prefer that the statement was softened somewhat to something like "A universal common ancestor is far more probable than having multiple ancestors…" HiLo48 (talk) 00:54, 27 March 2011 (UTC)

Looie's Law: Any probability less than 1 in 10⁶ is meaningless, because there is always at least one chance in a million that you make a mistake in working out the answer. Looie496 (talk) 01:36, 27 March 2011 (UTC)

Yea, when I hear of DNA matches to within one chance in a trillion, I always wonder what the real chance is of a false positive, when you include the chance the technician accidentally tested the same sample twice. StuRat (talk) 02:00, 27 March 2011 (UTC)

It is conceivable that there could be multiple origins of life, yet still all life shares a common ancestor. For example, there could have been a simple self-perpetuating lipid vesicle with some basic amino acid polymers, and a self-perpetuating RNAzyme, and the two became symbionts of one another. Or there might have been two original simple RNAs that merged into a single genome. But what's pretty clear is that a ribosome is found in any known kind of modern life capable of reproducing itself, and those ribosome sequences are similar by more than just chance. Wnt (talk) 02:34, 27 March 2011 (UTC)

It's likely that mitochondria are a separate life form that at some point became part of our cells, since they have their own genetic code. However, them and our cells probably both had a common origin further back. StuRat (talk) 04:52, 27 March 2011 (UTC)

Note that mitochondria have their own ribosomes - you can even tell from sequence and structure that they're the bacterial type rather than the eukaryotic type. Wnt (talk) 22:58, 27 March 2011 (UTC)

The number looks meaningless to me. They seem (based on the quote in our article - the paper is behind a paywall, so I can't read it) to have constructed several models and examined how likely our current observations are under each model. You can't convert that to the probability of each model being true without some prior probabilities and I can't see where they would get them. --Tango (talk) 14:30, 27 March 2011 (UTC)

I think that Paul Davies has suggested that there may exist life forms separate from our branch right now on Earth that we haven't managed to detect. Count Iblis (talk) 14:38, 27 March 2011 (UTC)

I suppose eventually it will come down to at exactly WHAT point do we call it life? I think the common misconception might be that there would have had to be a truly one off unique, even miraculous event which lead to all life. But I don't believe that's necessarily the case, there was probably LOTS of instances of "whatever it was" that led to life, and some of those elements might have "come together" to form the "proto-life" many times, only to "die out" later, possibly much later. All that we can be fairly certain of is that there would have been one "lineage" which all living things today can be traced back through, that's the universal common ancestor, but there could have been countless other "false starts" and "dead ends". Having said that, I wouldn't personally 100% rule out that some strange extremophile might still be found from a different original lineage, I think it's quite unlikely at this stage, but not 0%..Vespine (talk) 00:55, 28 March 2011 (UTC)

Relativity Question

Is it possible for a pulse in the following case to deviate from it's original path.

For simplicity let a spaceship is moving with 0.9c from east to west relative to the following observer on asteroid.

Dimension of the spaceship are

Width = 2 light second, Length = 10 meter (adjusted with length contraction)

An observer on asteroid (not co-moving) in the middle of east and west fire a pulse perpendicular to direction of spaceship such that after sometime the same pulse strike the longitudinal side of ship during it's passage by asteroid.

For ONBOARDB observer:

A pulse enter at one longitudinal side, travel inside for two second and then out through the other longitudinal side.

For observer on ASTERIOD:

1- A pulse will change it's direction from its original path after entering the ship

2- A pulse will travel for sometime inside ship but not perpendicular to the direction of ship

3- A pulse will start traveling again in straight line after leaving the ship but this time not on it's original straight line (which was before striking the ship). 68.147.41.231 (talk) 07:00, 27 March 2011 (UTC)Eccentric Khattak#1-420 ---- [GO]

The angle of the light beam is different with respect to the two different rest frames. The difference is given by the relativistic aberration formula. If, with respect to the asteroid rest frame, the light beam is perpendicular to the ship's motion, it will enter the ship and collide almost immediately with the back of the ship. With respect to the ship rest frame, it will be sharply angled toward the back of the ship and, again, hit the back almost immediately. -- BenRG (talk) 07:28, 27 March 2011 (UTC)

Getting rid of hazardous nuclear plant parts

If there is a decay heat even after the reactor's shutdown, the best way seems to dismantle the most dangerous parts of Fukushima plant, such as fuel rods and take them hell away or just destroy. Why this is not being done?--89.76.224.253 (talk) 09:56, 27 March 2011 (UTC)

They're too hot to take away right now — that's the whole problem. And "destroy" them how — bombing them, essentially spreading them into the air? Dump cement on them and hope for the best? These aren't prudent strategies. The latter is what you do when you've truly given up on reducing the radiation levels. Once things are "cool" enough to move, yes, they'll be dismantled, put into safe places, disposed of, cleaned up, and so forth. But you can't do that until you've gotten them to reasonable temperatures, and let some of the worst of that radiation dissipate (which is why the spent fuel was being kept in those pools in the first place).--Mr.98 (talk) 10:03, 27 March 2011 (UTC)

It takes about 5 - 10 years before you can place them in Dry cask storage. BTW, the reactors that were already shut down were just supposed to be temporary shutdowns while they did maintenance. They don't want to "destroy" or get rid of anything. They just want to shut it down, let the radiation fade, do their maintenance, then start them back up. Ariel. (talk) 11:49, 27 March 2011 (UTC)

In normal maintenance, yes. But just to be clear, it has been announced that Fukushima I will never reopen after the accidents.[1] Rmhermen (talk) 15:32, 27 March 2011 (UTC)

Well, the region will be probably way too contaminated. On the top of that, that will be a huge PR problem for the owners. 212.169.186.168 (talk) 18:52, 27 March 2011 (UTC)

Agreed. Restarting plants, of the same design and in the same location, as those that just failed so miserably, wouldn't be popular. StuRat (talk) 18:57, 27 March 2011 (UTC)

That didn't stop them at Chernobyl. While the reactor that melted down obviously wasn't restarted (there wasn't much of a reactor left by the end), the other reactors on the same site continued to operate for more than 14 years. Of course, the political situation was a little different. --Tango (talk) 20:53, 27 March 2011 (UTC)

Quite different. Still, the obviously reckless attitude of the Soviet Union towards their people's safety may have been a contributing factor in it's disintegration, by robbing it of the public support it needed when challenges from Gorbachev and then Yeltzin appeared. StuRat (talk) 22:55, 27 March 2011 (UTC)

Not wanting to be too pedantic, but Chernobyl took place on Gorbachev's watch. The handling of it was a colossal blunder on his part. It certainly did lead to vast distrust of the Soviet officials, especially amongst Ukrainians. Today its memory and experience are a major part of the post-Soviet identity of Ukrainians, Belarussians, and others in the affected area. It's also generally odd to talk about the Soviets losing public support when challenged by Gorbachev — Gorby was the Soviet Union. His efforts at reform opened up attacks from others — like Yeltsin, among others — that eventually led to the USSR falling apart. But that was not in any way Gorbachev's goal: he was trying to be a reformer, not a revolutionary. He really did believe in the USSR and Communism, at the time. --Mr.98 (talk) 00:37, 28 March 2011 (UTC)

Gorby wasn't in power when the unsafe plant was built. And, in his case, the hard-liners might have retained control if they had more of the public behind them. (And hard-liners dropping dead every few minutes helped Gorby out, too.) StuRat (talk) 04:15, 28 March 2011 (UTC)

Q:If there is a decay heat even after the reactor's shutdown, the best way seems to dismantle the most dangerous parts of Fukushima plant, such as fuel rods and take them hell away or just destroy. Why this is not being done?

This is what they will do... eventually. To do this however, they need to have electrical power restored to the equipment that extracts the rods from the core so as to place them in the spent fuel ponds. Obviously, it helps to have the working area decontaminated as well and this too will take time. Also, with the restoration of power, radioactive water (in the ponds and else where) can be passed through ion exchange material to remove the radioactive isotopes and thus bring down the exposure suffered by the recovery workers still further. If any fuel rod have partly melted in the core, they can be left in situ. Any residual heat from these will only be a small fraction of the current heat output (this is said without knowing if or how much meltdown has occurred). After the fuel rods have cooled sufficiently, they could then be shipped off (to say England) for processing. The Fukushima plant can be mothballed until such time that the radiation has decade to a level that permits the buildings on the site to be demolished and reclaimed for reuse. So in answer to your question, they can't remove the rods from the pile until they get these other things get done. --Aspro (talk) 21:40, 27 March 2011 (UTC)

It may be years before the rods are removed from the reactors. At Three Mile Island, it was six years before the reactor was defueled, although a different political climate and lessons already learned might shorten that. Japan does it own reprocessing with its own risks. (See Tokaimura nuclear accident) But it is unclear if melted-down rods covered in boron and sea salt can be successfully or economically reprocessed. Rmhermen (talk) 22:34, 27 March 2011 (UTC)

There is no mechanism for removing the fuel rods without opening the containment. These slides show the process. Opening the containment would release massive amounts of radioactive steam at an explosive pressure. There are also large quantities of hydrogen (rather explosive when in contact with air) in that steam. --Swedmann (talk) 20:29, 31 March 2011 (UTC)

Galactic rotation

Please see Talk:Andromeda_Galaxy#Rotational_velocities_must_be_wrong. I expect people here can give a better answer to the one I did. (Feel free to copy the question and my response over here if you think that's the better approach.) --Tango (talk) 12:04, 27 March 2011 (UTC)

That rotation curve looks wrong to me too. It's based on a 40 year old paper that fits observation to a polynomial. That paper indicates the possibility that a shallower inner minimum (of about 125 km/s) might also be a good fit to the observations and I think that the shallower minimum makes more sense from the dynamical point of view. A more recent source might be valuable to help solve this inconsistency. Dauto (talk) 15:41, 27 March 2011 (UTC)

The statement in the article refers to Fig. 9 in this paper. There are several data points that indicate a (narrow) dip down to below 100 km/s. This is regardless of the polynomial that is fitted to the observations (sic!). I haven't looked for newer data yet, but I point out that the dip should be located within the bulge of Andromeda, i.e. in a region that might well be supported by random motion rather than ordered rotation. --Wrongfilter (talk) 17:35, 27 March 2011 (UTC)

snow on tree flowers

So my school's trees are blooming.....and then it snowed last night, putting about half an inch on the ground. Are these flowers (that grow on trees) likely to die? =( John Riemann Soong (talk) 12:46, 27 March 2011 (UTC)

Will early bloomers likely deploy antifreeze agents in their flowers ? Some of the flowers are covered in snow. John Riemann Soong (talk) 12:55, 27 March 2011 (UTC)

I was just discussing this with my husband. We have a camellia about to bloom. At the same stage last year there was a sharp frost which resulted in the flowers being blighted and either rotting completely, or developing brown edges to them. I think it all depends on (a) the amount of frost and (b) the makeup of the flower. Some flowers are more waxy than others, and these flowers seem not to be too troubled with frosts.--TammyMoet (talk) 13:36, 27 March 2011 (UTC)

Note that flowers being covered in snow may actually insulate them from colder air. That may or may not be enough to save them, though. StuRat (talk) 19:00, 27 March 2011 (UTC)

Well the lowest temp was -0.5C. The snow later melted in the day when it shot to +5C. The snow covered the flowers for 4-8 hours though. John Riemann Soong (talk) 03:21, 28 March 2011 (UTC)

They might be OK then. Cross your fingers. StuRat (talk) 04:04, 28 March 2011 (UTC)

Speed of light question

If a car could travel as fast as the speed of light and it turned on its headlights, would it illuminate the road ahead?

[email address removed]

90.213.120.18 (talk) 18:12, 27 March 2011 (UTC)

I've removed your email address to prevent you getting spammed - we'll respond here. A car couldn't travel as fast as the speed of light, since nothing with mass can, so that is a meaningless question. A car travelling at 99.9% of the speed of light would still see the road being lit by its headlights normally. Light always appears to move at the same speed relative to you, regardless of how fast you are moving. That seems very strange, but it is true. --Tango (talk) 18:52, 27 March 2011 (UTC)

Calling it "a meaningless question" is imprecise enough to be well-nigh a meaningless statement. The core of the issue with the question is that in order to realize the premise of the question, one would have to posit that the laws of physics were different from the way we understand them now. So the answer to the question would depend heavily on how one adjusted the laws of physics to allow for it to happen. (So the question is not so much "meaningless", as it is "underspecified" - as Dauto hints, one can extract great meaning from the question if one looks at what you need to do to the laws of physics to make everything work out.) - That said, while we can't answer the question exactly as written for *at* the speed of light, we can make a slight but mathematically rigorous alteration, and look at what happens as one approaches the speed of light in the limit (mathematics). For the answer to that physically allowed and practically identical question, we find that the passengers in the car, as well as observers on the side of the road, will always see light coming from the headlights traveling at the speed of light. However, in the limit, length contraction means that the length of the road will appear to shrink towards nothingness for the passengers in the car (as the length of the car shrinks towards nothingness for observers on the side of the road). The effect of this is that in the limit, there is no "road ahead" for the passenger, as all points on the path of the car shrink to virtually the same point (that is, all points are an infinitesimally small distance away from each other). For the observer on the side of the road, the light from the headlights travels at the speed of light, but so (less an infinitesimal delta) does the car, so the light reaches a given point on the road ahead only an infinitesimal fraction of a second before the car does. Again, this really isn't "the road ahead" so much as "the road immediately in front of". Whether you call this "lit by its headlights normally" is highly dependent on what you consider to be normal. -- 174.24.203.209 (talk) 20:57, 27 March 2011 (UTC)

In short, the laws of physics are the same in every inertial frame. To the passengers in the car, light still goes at the speed of light, but the road is length contracted. However one should probably note that the passengers velocity in their frame is still zero, and they are no closer to the speed of light than when they started. So the extent to which the anyone has "approached the speed of light in the limit" is questionable. —Preceding unsigned comment added by 92.20.201.71 (talk) 22:37, 27 March 2011 (UTC)

Right, any particular observer is always at rest with respect to themselves. The thought experiment above was for what happens when the car-road relative velocity approaches the speed of light in the limit. That is, what happens when the velocity of the car approaches the speed of light for an observer on the side of the road, and what happens when the speed of the road passing under the car approaches the speed of light for the passenger of the car - which happens to be the same event, just observed from different perspectives. I may have been a little unclear by switching back and forth between perspectives. You are correct that, while observers on the side of the road see the car approach the speed of light, and thus approach zero length due to length contraction, the passengers see the car at zero relative velocity, so they don't see any length contraction of the car, thus maintaining the ample leg room one would expect from a modern subcompact. -- 174.24.203.209 (talk) 15:55, 28 March 2011 (UTC)

What Tango said is correct. I just want to add that Einstein sited that question and other similar questions as inspiration for his theoretical investigations that eventually lead to the development of relativity. Dauto (talk)

Indeed. He had a famous thought experiment about "riding" a beam of light. --Tango (talk) 20:54, 27 March 2011 (UTC)

Thanks guys, that Einstein, what a gezzer eh!90.213.120.18 (talk) 19:25, 29 March 2011 (UTC)

Tourmaline in hair care appliances

I notice a lot of heated hair styling equipment (blow dryers, flat irons, curling irons) tout the fact they are coated with or contain tourmaline. Yet the entry on the mineral doesn't give any clue to why this would be a benefit to products like that. Any ideas? --70.167.58.6 (talk) 19:27, 27 March 2011 (UTC)

The main term used seems to be 'tourmaline ceramic', which is probably a ceramic made by sintering tourmaline powder (that's a guess of course). Lots of wild claims about being a great source of negative ions - whatever that's supposed to mean, see here. Mikenorton (talk) 20:19, 27 March 2011 (UTC)

Tourmaline is a sort of gemstone because it has hardness 7. If you had sand in your hair it shouldn't scratch a tourmaline coated surface. But I have no idea if that's the real reason. Wnt (talk) 23:03, 27 March 2011 (UTC)

Tourmaline has a strong Pyroelectric effect and gives a charge separation when heated. Presumably this gives off ions in the airflow and that stops electrostatic build up in the hair. Graeme Bartlett (talk) 20:54, 29 March 2011 (UTC)

Blossoming wild shrubs in SE England

Today in the countryside of south east england I saw many example of white flowering bushes in the hedgerows. They did not have any thorns or spikes so I think that means they could not be hawthorns or sloes. They had five-petalled flowers. What could they have been? One of them at least that I looked at closely looked slightly pinkish, due to things (sorry my botanical vocabluary is not very good) adjacent to the white blossoms which were begining to burst out from the buds.

I also saw some pink blossom on what I think was a cultivated shrub, what could that have been please, at this time of year? Thanks —Preceding unsigned comment added by 2.97.210.137 (talk) 21:03, 27 March 2011 (UTC)

Could you take a photo, and upload it to flickr, imgshack or similar? It would help the botanists here id it for you. CS Miller (talk) 21:32, 27 March 2011 (UTC)

They looked like hawthorns except they did not have any spikes or thorns. The leaves must have been different. The ones I recall seeing were a simple leaf shape with a serrated edge. 2.97.210.137 (talk) 21:48, 27 March 2011 (UTC)

Perhaps a damson or a cherry plum, they're some of the earliest blossoms and can be found in hedgerows. Mikenorton (talk) 22:17, 27 March 2011 (UTC)

Almost certainly Blackthorn. A cold snap in March is called a Blackthorn Winter because it coincides with the hedges being white with their blossom. Hawthorn blossoms in late April - also known as "Mayflowers" (it hasn't realised that we changed to the Gregorian calendar a while ago). There very often aren't thorns on new blackthorn growth. I think you're unlikely to find many damson hedges in England although damson is a very close relative of blackthorn - they're both from the Prunus family. Alansplodge (talk) 00:30, 28 March 2011 (UTC)

We have damson bushes growing in one of the hedgerows on the Sussex farm where I live, and there are quite a few others in neighbouring hedgerows, but they're doubtless escapes from the damson orchards around here. Wild blackthorn, of course, is very common indeed in most parts of England. Both blackthorn and damson blossom have just begun to appear during the past three or four days hereabouts, and they fit the OP's description of the wild bush. --Antiquary (talk) 17:58, 28 March 2011 (UTC)

Except blackthorn has lots of thorns, so it's unlikely to be his shrub with no thorns or spikes! As for the pink blossom on a cultivated plant, very likely to be a cherry, they are in blossom right now here in Sussex. DuncanHill (talk) 18:05, 28 March 2011 (UTC)

Prunus avium, the wild cherry, occurs in hedgerows around here, and is in blossom now. DuncanHill (talk) 18:14, 28 March 2011 (UTC)

angular momentum in beta decay

Fermi beta decay is usually done without accounting for spin. The relevant term is the DOS of the final state, so:

If a spin-S particle decays into two particles spin s₁ and s₂, how does one account for this in the DOS of the final state. Is it just increased by a factor (2S+1) as this is the number of ways of aligning s₁ and s₂ to make s₁ + s₂ = S. (Is that right?) —Preceding unsigned comment added by 92.20.201.71 (talk) 22:28, 27 March 2011 (UTC)

I don't know about Fermi beta decay, but normal beta decay makes 3 particles electron, antineutrino and whatever the decay product is. Graeme Bartlett (talk) 07:37, 28 March 2011 (UTC)

Fermi beta decay and normal beta decay are the same thing. Dauto (talk) 13:58, 28 March 2011 (UTC)

I assume that by DOS you mean density of states. Yes there is a factor of (2S+1) when the density of states is calculated. I don't know what you mean by "Fermi beta decay is usually done without accounting for spin." As far as I know, spin is always taken into consideration. Dauto (talk) 13:58, 28 March 2011 (UTC)

Movement inside the body cavity

When I "suck it in" -- what is "it" and where does it go? I find even with a full breath in my lungs I can still "suck in" my gut a fair bit (though less), so it can't all be lung expansion/contraction. The Masked Booby (talk) 22:41, 27 March 2011 (UTC)

External intercostal muscles can flare (lift, like a bucket handle) the ribs to increase the volume of the thorax. If the epiglottis is closed then air cannot enter the lungs (to balance the pressure difference between the newly-reduced-pressure thorax versus the outside atmosphere). If the diaphragm is relaxed, the relatively-mobile abdominal contents have greater pressure from outside than the thorax, thereby tending to move them into the thoracic cavity. Abdominal muscles, including the rectus abdominis and obliques (abdominal internal oblique muscle, abdominal external oblique muscle) can also play a role in pushing abdominal contents up against the diaphragm. -- Scray (talk) 01:06, 28 March 2011 (UTC)

Pinhole glasses v. sunglasses

I do not like wearing sunglasses as they make colours look grey or other tints. Do pinhole glasses reduce the amount of light while still letting you see colours? Are they suitable to use as sunglasses? Thanks 2.97.210.137 (talk) 23:02, 27 March 2011 (UTC)

Only colored lenses change the color. You need to get photo-grey sunglasses. They shouldn't change or reduce the color. (Except that colors in shadows might not be bright enough to distinguish anymore, but that's also true of pin-hole glasses, which will also reduce peripheral vision.) StuRat (talk) 23:11, 27 March 2011 (UTC)

Depends on what you're doing. If you're just looking around, then sturat is right. I've used (photo.grey) for many years in tropical sun (Guatemala) and they have only minimal effect on colors. but if you're doing something that requires only a narrow field of vision, such as painting pictures in sunlight, then color perception is important and pinholes might be better.Note also that photo grey get darker in sunlight and lighter in shade. very convenient but they are usually more expensive.Phalcor (talk) 05:13, 28 March 2011 (UTC)