Welcome to the science section
of the Wikipedia reference desk.

Select a section:

WP:RD/S

Want a faster answer?

Main page: Help searching Wikipedia

How can I get my question answered?

Select the section of the desk that best fits the general topic of your question (see the navigation column to the right).
Post your question to only one section, providing a short header that gives the topic of your question.
Type '~~~~' (that is, four tilde characters) at the end – this signs and dates your contribution so we know who wrote what and when.
Don't post personal contact information – it will be removed. Any answers will be provided here.
Please be as specific as possible, and include all relevant context – the usefulness of answers may depend on the context.
Note:
- We don't answer (and may remove) questions that require medical diagnosis or legal advice.
- We don't answer requests for opinions, predictions or debate.
- We don't do your homework for you, though we'll help you past the stuck point.
- We don't conduct original research or provide a free source of ideas, but we'll help you find information you need.

Ready? Ask a new question!

How do I answer a question?

Main page: Wikipedia:Reference desk/Guidelines

The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.

September 13

The speed of electricity

How fast does electricity move? I've heard it said that electricity moves at the speed of light. If this is the case then surely there is something else, other than light, that moves at the speed of light. Does this not contravene the rules of physics? Thank you — Preceding unsigned comment added by 2A00:23C6:6884:6200:75D7:FCD:5331:8FC7 (talk) 09:02, 13 September 2020 (UTC)[reply]

Have you looked at Speed of electricity? When people say that electric current moves at the speed of light (even though that is not entirely accurate), what they mean is that the wave/signal travels at that speed; the electrons or ions that transport the electric charges move at a much slower rate. Anything with a non-zero mass that moves at the speed of light would violate the laws of physics, but electric current has no inherent mass, so it does not violate any physical law, even if it would move at the speed of light. - Lindert (talk) 11:21, 13 September 2020 (UTC)[reply]

It's the speed of light, in the conductor (if they weren't opaque). The linked article Velocity factors gives typical speeds. For copper it's around 2/3rds of the speed of light in a vacuum, or 200,000 km/sec. LongHairedFop (talk) 13:14, 13 September 2020 (UTC)[reply]

The "speed of light" is not inherently about light at all, which makes the name somewhat poor. (Like many names of things in science, it caught on by happenstance, and now we just have to put up with it.) Special relativity asserts that no two points in spacetime can exchange information faster than c. It just so happens that c is also the speed at which electromagnetic waves (including light) travel in a vacuum. Since "electricity" is an electromagnetic wave (or at least can be modeled as one), it will travel at the "speed of light" in whatever thing it's moving through; this is always less than c if it's not a vacuum. Your confusion is common and completely understandable, resulting from the somewhat misleading name. I suggest this video for more detail. --47.146.63.87 (talk) 07:02, 14 September 2020 (UTC)[reply]

black hole collision

[1] If two black holes collide and merge into a bigger black hole, during the approach does that at least temporarily create a region from which no light can escape, but whose shape is something like a figure 8 or dumbbell? And is that in conflict with the no-hair theorem that says black holes are always spherical? Thanks. 2602:24A:DE47:BB20:50DE:F402:42A6:A17D (talk) 15:27, 13 September 2020 (UTC)[reply]

Yes, it creates a toroid [2]. As for whether that violates the no hair theorem, I don't know. Handschuh-^{talk to me} 00:53, 14 September 2020 (UTC)[reply]

Only non-spinning black holes have a spherical event horizon. The no-hair theorem doesn't assert "black holes are spherical"; it just asserts "stable" black holes can be fully described by eleven parameters. Also, again, it only applies to "stable" black holes. --47.146.63.87 (talk) 06:48, 14 September 2020 (UTC)[reply]

Does this mean that the Einstein–Maxwell equations of gravitation and electromagnetism in general relativity only apply to stationary situations? If so, the text of the articles concerned should make that clear. --Lambiam 07:53, 14 September 2020 (UTC)[reply]

The equations apply to any situation, of course, stationary or not. But the idea was that the no-hair "theorem" (it's a conjecture, strictly speaking) only applies to stationary solutions of the equations. I thought so until five minutes ago, but apparently that's not correct. This paper says that the frequencies and decay rates of the overtone modes of the ringdowns signal are uniquely determined by the final hole’s mass and spin magnitude. Hence, while you can talk about non-spherical shapes during ringdown that does not give you any new information beyond mass and spin. The situation already applies to the stable Kerr black hole: the event horizon is non-spherical, so you can measure an ellipticity of the black hole. But again, this tells you nothing new as the ellipticity is uniquely determined by the spin. In that sense the no-hair theorem applies to the ringdown phase as well. --Wrongfilter (talk) 08:51, 14 September 2020 (UTC)[reply]

Continuity considerations suggest compellingly that there has to be a transitional phase between the event horizons of the merging black holes being a pair of perfect spheroids before the merger, and the event horizon being a single spheroid after the merger. This is, however, excluded by the formulation given by the No-hair theorem article. So which one is it: continuity but additional conditions needed for the theorem to apply as stated, or a physical discontinuity? --Lambiam 15:31, 14 September 2020 (UTC)[reply]

The transitional phase is called ringdown, and from the cited paper I gather that the way ringdown proceeds is uniquely determined by total mass and total spin (I wonder whether the mass ratio shouldn't have an influence, though). But nobody said anything about discontinuity. --Wrongfilter (talk) 16:56, 14 September 2020 (UTC)[reply]

Presumably nobody said anything about discontinuity because there is none. But if during the ringdown period, however brief, "any distortion in the shape is dissipated as more gravitational waves",^[3] the no-hair theorem is not unconditionally true in its stated form. (Some black holes do ring, others with exactly the same mass, electric charge, and angular momentum do not.) --Lambiam 17:35, 14 September 2020 (UTC)[reply]

Well, I only cited a peer-reviewed paper, so... --Wrongfilter (talk) 17:52, 14 September 2020 (UTC)[reply]

And yet another way to look at the ring down is that it is just an echo of the gravitational wave lensed by the black hole. You can expect infinite echos, getting weaker and weaker as light or gravitation waves passing very close in get bent more and more, and exceed 360°, 720° and even more extreme spiralling around the final black hole. I may have written the bit Lambiam quoted, but it may not be the right way to look at ringdown. Note that you will never observe an event horizon or its formation, and that the black hole (s) have not yet actually been formed, as they only do so in our infinite future. Timescales are seriously distorted. Graeme Bartlett (talk) 01:07, 18 September 2020 (UTC)[reply]

(Yes, you did). We lack the terminology to properly discuss black holes in English, so any such exposition going into detail is in some way wrong or misleading. I maintain that the idea that a pair of perfect spheroids "instantaneously" merges into one perfect spheroid is more misleading than others. This idea stems from a popular formulation of the no-hair theorem, which therefore is apparently also misleading. But all will become clear in our infinite future. --Lambiam 07:19, 18 September 2020 (UTC)[reply]

September 14

Effects of Gravitational Waves

The gravitational wave sources detected by LIGO and other experiments are so far away that the amplitude of the waves are tiny by the time they reach earth. The article section Gravitational_wave#Effects_of_passing gives a description of how it would affect some particles on a plane, but I'm interested to know what the practical effects of a wave would be on material close to an intense source. Would it distort materials so much it destroys them? Would it injure organisms? Or does a ripple in the spacetime curvature not really affect things too much? If a tertiary system existed consisting of two black holes and a third massive object, could the merger of the two black holes have some substantial effect on the third object? Say the third object was a star, could the distortion affect the rate of fusion in the star's core, or trigger a gravitational collapse of the star, or anything like that? Handschuh-^{talk to me} 01:13, 14 September 2020 (UTC)[reply]

Not an answer, but Scott Manley recently put up a video, 'Impossible' Black Hole Created by Largest Gravitational Wave Event [YouTube, 10:51], about GW190521, the gravitational wave signal detected on 21 May 2019 of what appears to have been the merger of two black holes of 85 and 66 solar masses, resulting in a single black hole of 142 solar masses, where the "remaining 9 solar masses were radiated as energy in the form of gravitational waves"! -- ToE 01:45, 14 September 2020 (UTC)[reply]

Yes, it was reading about the 9 solar masses of energy radiated out into the universe that go me thinking of what kind of effect it might have on something/someone close to the source, and also, the coinciding light flash (for which astronomers have already proposed an alternative explanation) got me thinking about how the GW might affect nearby stars. Handschuh-^{talk to me} 02:26, 14 September 2020 (UTC)[reply]

Also not a full answer, but the frequency of the first gravitational wave ever observed went up to 250 Hz. That means a wavelength of more than 1000 km. The effect on a much smaller body being sloshed around in a wave of an extreme amplitude is much less violent than that of waves with ripples commensurate with the size of the body. Warning. This does not mean it is safe to observe a black hole merger from up close. Always keep a safe distance. --Lambiam 07:45, 14 September 2020 (UTC)[reply]

If you take the observed strain and use that it decays inversely proportional to the distance fro the source, then you find that at a distance of 1 AU from the source, the strain would have been just about detectable by our seismometers. Count Iblis (talk) 11:28, 16 September 2020 (UTC)[reply]

That interesting...so at a very short cosmological distance the effects are hardly earth shattering. Where did you get the observed strain from? It doesn't seem to be in the GW190521 article. Handschuh-^{talk to me} 23:39, 16 September 2020 (UTC)[reply]

I used the strain sensitivity of

10^{-23}/{\sqrt {\text{Hz}}}

of LIGO, the observed strain is then an order of magnitude larger, you can then multiply this by the distance to the source divided by the distance of some hypothetical planet close to the source to obtain the strain at that planet. Count Iblis (talk) 22:46, 17 September 2020 (UTC)[reply]

Marsh and swamp

In Polunin and Walters A Guide to Vegetation of Britain and Europe there is a different definition of marsh and swamp from Wikipedia (i.e. a marsh is a wetland dominated by grassland and swamp a forested wetland): a marsh is an area where at least in summer the water level is below the soil surface, whereas a swamp is permanently saturated with water. Could this distinction be defined with other words than marsh and swamp?--Carnby (talk) 16:02, 14 September 2020 (UTC)[reply]

I'm going to go on a bit of a side rant here; I have long suspected that scientists create word distinctions among synonyms that didn't used to exist, but try to make them so, and sometimes different groups of scientists will create different distinctions than each other because they never got together and got their story straight. The English Language has a surprising variety of words for (well anything, but in this case...) areas of non-quite-land-not-quite-water, and I'm not sure the distinction between those words as you note existed as long as the different words themselves. I suspect such word difference were initially geographic rather than in quality or character, so that people from one area called such land a "swamp" or a "bog" or a "marsh" or a "bayou" or a "mire" or a "fen" or a... whatever. People just named the wetland by their local name, and later the distinctions between such things as whether it had trees or grasses or whatnot was imposed by people trying to make sense of the system. The problem you note, where two different supposedly expert sources have two mutually exclusive and entirely non-compatible systems for drawing such distinctions, is a symptom of that history. In the means of actually providing sources to my side-rant, consider the etymology of various terms, swamp, marsh, fen, bog, they all have, in their origins going back to the 1500s or earlier, the same basic meaning, that being "wet spongy ground". That being said, by 1775, the distinction between swamp and marsh was drawn, as noted in the link I provided for swamp, "[B]y swamps then in general is to be understood any low grounds subject to inundations, distinguished from marshes, in having a large growth of timber, and much underwood, canes, reeds, wythes, vines, briers, and such like, so matted together, that they are in a great measure impenetrable to man or beast .... [Bernard Romans, "A Concise History of East and West Florida," 1775]" So take that what you will. --Jayron 32 11:38, 15 September 2020 (UTC)[reply]

To complicate things even more, which I assume everyone is begging for, it appears plausible (at least to me) that different branches of physical geography that study wetlands from different angles (e.g. ecology versus hydrology) use different classifications. Some fields (e.g. limnology) were developed originally by non-English scientists, and there may not be a clear correspondence beteen the French and German terms and the English ones. For the variety of types of wetlands, just look at Category:Wetlands – good luck developing an unambiguous classification for these. I noticed that Moorland is not in that category and not mentioned in the wetlands article, although some moors definitely are and many (most?) that are not started out that way, as mires. --Lambiam 16:02, 15 September 2020 (UTC)[reply]

" I have long suspected that scientists create word distinctions among synonyms that didn't used to exist" I think we can safely say that suspicion is more than justified. Speed and velocity being a typical example (and even acceleration or it's latin root probably had a similar meaning, lacking the technical distinction we now impose upon it). Handschuh-^{talk to me} 23:47, 16 September 2020 (UTC)[reply]

Similarly "Mass" and "Weight". --Jayron 32 15:02, 17 September 2020 (UTC)[reply]

The existing English word mass was repurposed to translate Newton's repurposing of the Latin massa for a concept that did not yet exist; the same happened for acceleration and inertia. Obviously, these terms did not have the technical physics meanings they have today before someone introduced the concepts they name. If these terms had synonyms (inertia = sloth), the technical sense was not simultaneously imparted on the synonyms. The earlier, everyday meaning of mass(a) was "lump (of dough)". --Lambiam 20:38, 17 September 2020 (UTC)[reply]

Yeah, but there's a few bad teaching practices that try to explain that "weight" only refers to gravitational mass while "mass" only refers to inertial mass, that's basically bullshit because we've known the two concepts are the same thing due to the equivalence principle. Even during the time of Newton there was suspicion they were because any measurement of one resulted in an equivalent measure of the other, but such conjectures were not proven until about 100 years ago. There's some other texts and things that try to say that weight is only referring to gravitational force (i.e. Newtons) while mass is "mass" (i.e. kilograms), but I don't know any actual physicists that make such distinctions and legitimately say things like "Such and such weights X Newtons". If one means force, they say force. If one means weight, the use kilograms just fine. --Jayron 32 13:03, 18 September 2020 (UTC)[reply]

I'd like to add "morass" to the discussion. HiLo48 (talk) 04:30, 17 September 2020 (UTC)[reply]

as in "I've been eating a lot during this quarantine and I have morass than I used to.--Jayron 32 07:35, 17 September 2020 (UTC)[reply]

Let's not get bogged down in trivia. ←Baseball Bugs ^{What's up, Doc?} carrots→ 08:36, 17 September 2020 (UTC)[reply]

September 17

Teach flight tricks to parrot?

Is it possible to teach a parrot (goffin) to do loops and barrel rolls in flight? Or things like flying upside down or backwards? Can't find much online. Thanks. 146.200.128.134 (talk) 04:22, 17 September 2020 (UTC)[reply]

Despite their intelligence, goffins are not built for acrobatics, and I doubt whether any bird would be able to fly upside down or backwards.--Shantavira|^{feed me} 08:57, 17 September 2020 (UTC)[reply]

Hummingbirds can fly backwards and upsidedown. --TrogWoolley (talk) 09:32, 17 September 2020 (UTC)[reply]

I've seen Hummingbirds vanish into thin air, then reappear a moment later 30 metres away. Amazing birds. Try typing 'do a barrel roll' into your parrot, might work. Zindor (talk) 11:26, 17 September 2020 (UTC)[reply]

Seagulls can fly (or glide) backwards. 146.200.128.134 (talk) 17:13, 17 September 2020 (UTC)[reply]

But can they do it in high heels? —Tamfang (talk) 01:59, 18 September 2020 (UTC)[reply]

With enough practice, seagulls can teleport. Mitch Ames (talk) 08:16, 19 September 2020 (UTC)[reply]

Generally teaching tricks to an animal that doesn't have a trained animal to imitate involves immediately rewarding any random behaviours that are close to what you want (either by showing praise/affection if the animal is used to that or by food treats). Then you carry on rewarding that behaviour every time it happens, combined with giving a signal (hand gesture, whistle, voice command, etc). This can take a long time, but eventually you will be able to give the signal first and the animal will respond with the "trick". With training chimpanzees and gorillas, you would usually give a signal first to say "now we are starting work", then after the training session is ended, another signal to say "now we can play". This takes a lot of patience, and you have to be very careful not to wear the animal out by endlessly repeating signals, initially you should only use them when you think the animal is going to respond correctly. There's no reason why you can't train a parrot to do flight tricks if it's something they can normally do. Good luck.49.197.49.86 (talk) 23:32, 19 September 2020 (UTC)[reply]

September 18

Energy from rusting

Roughly speaking how much energy, in Joules, is given off by completely rusting 1Kg of Iron? 2A01:E34:EF5E:4640:6149:84E9:11CE:A892 (talk) 09:47, 18 September 2020 (UTC)[reply]

The article on energy density has a handy table. Rust can have different compositions, but the "burned to iron(iii) oxide" row should be a decent enough approximation. 85.76.15.6 (talk) 10:52, 18 September 2020 (UTC)[reply]

Why are Pnictogen hydrides so poisonous?

Why are Pnictogen hydrides like ammonia,phosphine and arsine so poisonous?Acidic Carbon (Corrode) 13:23, 18 September 2020 (UTC)[reply]

Should there be a redirect: Pnictogen hydrides → Pnictogen hydride ? --2606:A000:1126:28D:31A8:66E0:89AA:D98E (talk) 16:48, 18 September 2020 (UTC)[reply]

Each one's article talks about its specific toxicity profile. At least phosphine#Toxicity, arsine#Toxicology, and stibine#Toxicology are quite explicit about what their mode of action is. DMacks (talk) 17:05, 18 September 2020 (UTC)[reply]

Ammonia is not so dangerous as the others. Its main issue is as a strong base. Animals have a way to deal with ammonia in the body. For humans it is to make urea. Graeme Bartlett (talk) 22:28, 19 September 2020 (UTC)[reply]

Missing a hurricane

Hurricane Alice (December 1954) says that two cyclones, including a Category 2 hurricane, operationally went undetected in 1954. In a time before satellite pictures, how would meteorologists learn that they hadn't noticed a storm? 2601:5C6:8081:35C0:2C6E:461:D260:3BF (talk) 22:26, 18 September 2020 (UTC)[reply]

No source is cited for that specific statement, but José A. Colón's paper cited as a reference from the paragraph refers to another undetected hurricane in January 1951. Basically the answer to "how did they learn" seems to be that they reanalyzed the data they had already collected, when the storms were over with and they had time to do it. --174.88.168.23 (talk) 23:08, 18 September 2020 (UTC)[reply]

September 19

Medications causing dizziness and loss of balance

I am a retired psychiatrist and a friend of mine who is an audiologist asked me to write a chapter for his upcoming book about some stuff audiologists do. It turns out they do balance in addition to fitting hearing aids, so their clients are mostly elderly. He is most interested in medications that might affect man's balance, cause dizziness, etc. Also the medications he is interested in are those which he might see to have been prescribed to his clients because he needs to differentiate between organicity and medications side effects. I have written already most of the psych stuff: antipsychotics, antidepressants, antiepileptics, opioids, etc and wonder if someone can give me pointers to other areas which I possibly missed. Thank you AboutFace 22 (talk) 15:15, 19 September 2020 (UTC)[reply]

There is a list here: "Medications causing Loss of balance". www.rightdiagnosis.com.

Which links to: "Conditions listing symptom: Loss of balance - View All". www.rightdiagnosis.com.

Further, related to audiology: "Acoustic neuroma Symptoms, Diagnosis, Treatments and Causes". www.rightdiagnosis.com.

107.15.157.44 (talk) 15:58, 19 September 2020 (UTC)[reply]

Medication that makes one dizzy makes it unsafe to drive or operate heavy machinery. I think the converse also holds rather generally: medication that makes it unsafe to drive or operate heavy machinery can cause dizziness. You might want to check medication that is thus labelled (like those on this list) and that is not already on the other list(s). --Lambiam 18:41, 19 September 2020 (UTC)[reply]

Browsing this site, which generally includes references, may provides some ideas: medications associated with dizziness, ototoxic medications, drug treatment of vertigo (list of vestibular suppressants), neurotransmitters in the vestibular system. Affect man's balance, cause dizziness, etc. seems like a pretty broad scope. fiveby(zero) 18:55, 19 September 2020 (UTC)[reply]

Thank you very much! It is a GOLD MINE! AboutFace 22 (talk) 19:47, 19 September 2020 (UTC)[reply]

Shouldn't an audiologist already be cognizant of these things? ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:48, 19 September 2020 (UTC)[reply]

Our writer is a psychiatrist though! Better check out the audiologist page for knowledge and skills required. (our article does not mention drugs, and is only two subsctions). Graeme Bartlett (talk) 22:25, 19 September 2020 (UTC)[reply]

Yes. But shouldn't a trained audiologist already know this stuff? If he does, why does he want someone else to write about it? If he doesn't, how did he ever get to be an audiologist? ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:55, 19 September 2020 (UTC)[reply]

Don't be mean, B B. Audiologists don't get trained in drugs. To get versed in drugs you have to go through a lot of chemistry, biochemistry, physiology, etc. It is the stuff of either a medical or veterinary school. AboutFace 22 (talk) 00:24, 20 September 2020 (UTC)[reply]

Safe displays of highly radioactive isotopes

Suppose you had a museum of the elements, with a kg sample of each stable element (in an inert atmosphere if needed). What could you do for Tc, Pm and the actinides?

For example, you might want a kg of plutonium-238 oxide, or enough to glow orange hot (as in our picture at Pu-238), to illustrate its use as a power source in space probes. It decays by alpha radiation, so the glass of the display case would be all you'd need for shielding. But the decay products decay by beta radiation, which means the shielding could produce bremsstrahlung gamma radiation. That might not be significant for Pu-244 (assuming it were possible to synthesize a kg of Pu-244), but would be for Pu-238.

(I can't find how much spontaneous fission there would be, and if it would be dangerous in such a display. Some sources give alpha radiation as the only decay mode of Pu-238, some give alpha and fission.)

Also, why isn't the beta/bremsstrahlung radiation and SF damaging to radioisotope thermoelectric generators? — kwami (talk) 21:47, 19 September 2020 (UTC)[reply]

September 20

Three step viper

What sort of snake was the one that American soldiers in Vietnam called the "three step viper"? Supposedly if bitten you'd make it three steps before either dying or being incapacitated.

Apparently in reality it was more like "you'd make 100 steps before you started begging for someone to shoot you", but the name stuck. According to a book I read. 146.200.128.134 (talk) 03:23, 20 September 2020 (UTC)[reply]