Wikipedia:Reference desk/Archives/Science/2023 July 17

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July 17

Lorentz transformation vs Galileo

In special relativity, Einstein in a thought of mind shows that the time measured using a light pulse reflection between 2 points A and B in the same moving reference frame is not the same for an observer at rest and an observer in this mobile reference frame. In this case the speed of light is not taken into account, it is its constant value whatever the frame of reference which requires a Lorentz transformation. However, in another thought of mind, if I replace the reflection of a light pulse between the points A and B by an object in movement starting from A at constant speed and going to rebound on B by an elastic shock to return in A , that in A, then B, then A it emits a light pulse, in this case do we always use a Lorentz or Galileo transformation? Why would this variant of the mind's thought not be valid? Malypaet (talk) 03:53, 17 July 2023 (UTC)

What do you mean by "valid"? In one thought experiment, we flip a pancake and it falls flat on the floor. In another thought experiment, we flip a pancake and it gets stuck to the ceiling. Both are valid thought experiments.  --Lambiam 06:57, 17 July 2023 (UTC)

Your answer begs the question. Because if the second experiment is valid with Galileo's transformation, then it shows that the first is invalid for measuring time, that as a measuring instrument it has a bias due to the use of reflection on a mirror with speed referential independent, right? Do you have another interpretation? Malypaet (talk) 08:21, 17 July 2023 (UTC)

Lorentz transformations are always more accurate than Galileo transformations, but the errors introduced by using a Galileo transformation may be too small to matter. In the typical scenario with bouncing balls, using Galileo instead of Lorentz transformations gives you an error on the order of one in a billion. That's much smaller than your other sources of uncertainty and not worth the mathematical complexity of Lorentz transformations. PiusImpavidus (talk) 09:34, 17 July 2023 (UTC)

When a thought experiment is used, it is theoretically perfect and no accuracy errors occur. So can you explain to me your one in a billion error rate with the bouncing object? Malypaet (talk) 14:24, 17 July 2023 (UTC)

Your first thought experiment requires measurement of time between two flashes observed at one point, with no assumption of c. But your second thought experiment requires measurement of time between flashes emitted at A then at B. Can you tell us how fast the light travels to a common observing point for the time measurement? Philvoids (talk) 15:24, 17 July 2023 (UTC)

On the Electrodynamics of moving bodies extract:

"a ray of light proceeds from A at A-time tA towards B, arrives and is reflected from B at B-time tB, and returns to A at A-time t'A."

In my thought experiment:

"a ray of light proceeds from A synchronously with an object at A-time tA towards B, all 2 arrives at B that is a black body walls with perfect elastic properties so only the object is bounced from B at B-time tB and simultaneously proceeds a Ray of light, returns to A at A-time t'A and simultaneously proceeds a Ray of light."

In the 2 thought experiment, the observers read there clocks to get tA , tB and t'A.

The difference is that in the first case you need Lorentz transformation between observer at rest and the mobile one. In the second experiment as you have Galileo transformation, the clocks of the 2 observers are always synchronised, confirming Newton's absolute time.

What is false there ? Malypaet (talk) 19:32, 17 July 2023 (UTC)

I don't fully understand the thought experiment you propose. It seems that you assume that when moving objects are involved, you have to use Galileo transformations instead of Lorentz transformations. That's incorrect. You always use Lorentz transformations when the relative velocity of your frames of reference is a significant fraction of the speed of light. When dealing with electrodynamics, you may need Lorentz too. When playing a game of billiards, Galileo is good enough. PiusImpavidus (talk) 08:28, 18 July 2023 (UTC)

There's no explanation in your answer, just assertions based on articles I'm familiar with, but which don't address the case of the thought experiment I proposed. Lorentz transformations apply when using echoes of electromagnetic waves to measure the times of moving objects between different frames of reference. But, even if it is the most practical and precise method, it is theoretically not the only one available. If you are blind, time still passes and objects also move. Why don't you analyze my thought experiment in detail, contradicting it on every point or not? Malypaet (talk) 13:21, 18 July 2023 (UTC)

An object moves at constant speed from A to B to A, at each of these points emitting a light pulse. OK, but how is this a thought experiment? What is there to be analyzed?  --Lambiam 05:54, 19 July 2023 (UTC)

Based "On the Electrodynamics of moving bodies".

A thought experiment is an experiment that we imagine to validate a hypothesis and that we put in the form of a mathematical exercise, while waiting to be able to see it validated or not by a physics experiment or an observation in physics . For Einstein it came with Edington's observation and Pound and Rebka's experiment.

Here, in both cases, the times tA, tB and t'A are measured by a light pulse. On the other hand in the 1st case the object moving on a rod and reflected by a mirror is a light pulse with constant speed c whatever the referential, whereas in the second case the object which bounces on the mirror has a speed constant v1 only on the rod.

With the rod stationary, we have (tB - tA) = (t'A - tB) for all observers and in both cases, either (2 AB)/(t'A -tA)=c or (2 AB)/(t'A -tA)=v1 .

Now we consider the rod at speed v2.

In the 1st case for observer at rest we obtain:

(tB-tA)=rAB/(c-v2) and (t'A-tB)=rAB/(c+v2) => (tB-tA) # (t'A-tB)

Therefore, a Lorentz transformation is necessary between the observer at rest and the moving one.

In the second case for observer at rest we obtain:

(tB-tA)=rAB/(v1+v2) and (t'A-tB)=rAB/(v1-v2) => (tB-tA) = (t'A-tB)

Here just a Galilean transformation.

Voilà. Malypaet (talk) 13:01, 19 July 2023 (UTC)

Still not sure about the part thought experiment here. In both your functions, (tB-tA) = (t'A-tB) *(U+v2)/(U-v2), where U is either v1 or c. Rmvandijk (talk) 06:30, 20 July 2023 (UTC)

Well done for the illusionist trick with your U like a hat, but:

(tB-tA) = (t'A-tB) *(c+v2)/(c-v2)

&

(tB-tA) = (t'A-tB) *(v1-v2)/(v1+v2) Malypaet (talk) 20:34, 20 July 2023 (UTC)

However, I also made a mistake. In fact when my object goes from A to B, for the observer at rest it has the speed (v1+v2) and on the way back the speed (v1-v2), but on the way out point B moves away at the speed v2 and on the way back approaches at the speed v2.

So we get

tB-tA=rAB/((v1+v2)-v2) =rAB/v1

t'A-tB=rAB/((v1-v2) +v2) =rAB/v1

To resume your U, going U=v1+v2 and returning U=v1-v2 Malypaet (talk) 04:25, 21 July 2023 (UTC)

I correct by taking up Rmvandijk's idea. With for the observer at rest, going to B a speed of the object v'=v1+v2 and on the return v''=v1-v2, we obtain:

(tB-tA)=rAB/(v' -v2) and (t'A-tB)=rAB/(v''+v2) => (tB-tA) = (t'A-tB) Malypaet (talk) 04:44, 21 July 2023 (UTC)

Has there ever been a documented example of an animal using a weapon?

I don't know if you ever seen this, but this video has been doing the rounds for years online. Some soldiers were goofing around and gave an AK-47 to a monkey, which then proceeded to shoot at them and make them run away. It might be fake (I don't know), but I first saw it like 10 years ago. It turned up on my Youtube recs again tonight. Made me wonder - have there been any 100% confirmed, real examples of animals using weapons? For example, if a monkey picked up a thigh bone (as in 2001: A Space Odyssey), or a block of wood, or a rock, or whatever and bludgeoned another monkey to death in a fight. I know for sure that monkeys watch what people do and will do things like pick up smouldering dogends and smoke them, or drink the dregs out of people's beer bottles. How far does this go? Iloveparrots (talk) 23:58, 17 July 2023 (UTC)

As noted in Tool use by non-humans (WP:WHAAOE strikes again), it was discovered in 2007 that chimps use sharpened sticks while hunting. There's an unsourced claim there that "This is considered the first evidence of systematic use of weapons in a species other than humans." Sea otters routinely use rocks to smash open their food/prey. Clarityfiend (talk) 00:23, 18 July 2023 (UTC)

"Research in 2007 showed that common chimpanzees sharpen sticks to use as weapons when hunting mammals. This is considered the first evidence of systematic use of weapons in a species other than humans" - I see, thank you.

Another thing I was wondering from watching the breeding birds around here, and I'm not sure if this has ever happened. Although birds often work together to chase away hawks from their breeding colonies when the hawk appears - have the birds (crows for example) ever thought, after that, to figure out where the hawk lives and then send (say) 20 of the strongest males from the colony to take it out while it was least expecting it? Iloveparrots (talk) 01:07, 18 July 2023 (UTC)

While I am not an expert ornithologist (so am very open to correction), not only have I never heard of such a thing (in over half a century of reading about natural history), but everything I (think I) know about avian cognition suggests such high-level reasoning, communication and co-operation would be considerably above even the most intelligent birds' capabilities.

Obviously, finding a reliable reference that a thing that has never been observed has not, in fact, ever been observed is problematical. {The poster formerly known as 87.81.230.195} 51.198.140.169 (talk) 05:34, 18 July 2023 (UTC)

George Orwell composed an anthem "Beasts of England" to incite animals on a farm including hens, ducks, roosters and geese to revolution. Philvoids (talk) 10:49, 18 July 2023 (UTC)

He did, but the work clearly falls into the genre of Fable, so is not a reliable reflection of real-world natural behavior. (Taking off my pedant hat, I am a lifelong fan of non-realistic genres.) {The poster formerly known as 87.81.230.195} 51.198.140.169 (talk) 00:44, 19 July 2023 (UTC)

I think, from reading about corvids that this is the case: individual corvids sometimes collect food items (nuts and seeds, for example) and store them by burying them in the ground or hiding them in tree hollows with the expectation that they will be able to collect them later, say in winter, when food is scarce. Some do it, some don't - but they are at least somewhat capable of realizing that actions committed today may influence future events (but it doesn't happen that often). But it is never the case that the entire flock works together to gather and store food and (say) keeps it in one place which is then guarded by the entire flock, in order that they all may benefit from the food in winter. Iloveparrots (talk) 19:24, 19 July 2023 (UTC)

Well, many animals cache food but I don't think we can assume that the behavior is indicative of planning rather than instinct. My pet rats, when offered food, will usually grab it and immediately run and hide it. I don't think it indicates planning or a deliberative thought process, it's just an instinct to hide food that one is not going to eat right now. Some individual rats seems to have a stronger caching instinct than others though. CodeTalker (talk) 20:55, 19 July 2023 (UTC)

I don't really think that animals really have much of an understanding that actions committed in the past may have consequences in the present, or that actions committed in the present may influence the future. There have been occasional studies, like with the Tanimbar corella that demonstrated that they can reject food items if they are aware that they will be awarded with superior food items in the future - but that is literally talking about minutes later, not weeks or months. I'm well aware that punishing a pet dog for something like damaging furniture, ripping up the wallpaper, or peeing on the carpet by yelling at it, cuffing it upside the head or sticking a boot up its ass (please don't do this - but people do, talking from personal experience) doesn't work at all because they are literally unable to make the connection between something that happened a couple of hours ago and now. Iloveparrots (talk) 21:21, 19 July 2023 (UTC)

I have read about corvids not only caching food for later consumption, but also pretending to hide food if they know they are being watched. This article mentions it, along with other claims about the intelligence of corvids, although it doesn't have any references. Turner Street (talk) 14:40, 21 July 2023 (UTC)

For posterity I will add this to the archive: Males will sometimes enter an adjacent territory to assist the resident in repelling an intruder, behaviour only otherwise known from the African fiddler crab. This is from European rock pipit.  Card Zero  (talk) 05:08, 28 July 2023 (UTC)

I didn't find a source, so take it with a grain of salt: A group of baboons attacked a leopard using rocks. Zarnivop (talk) 08:25, 18 July 2023 (UTC)

Orcas use directed waves to dislodge prey from icebergs. BBC Earth, via Youtube Bazza (talk) 08:33, 18 July 2023 (UTC)

If the future's dystopic enough someone will invent gorilla guerillas. Driving the cyborg body like a video game or gene editing it to the intelligence, fine motor skills and brainwashability of a child soldier without loss of muscularity or possibly just extremely good selective breeding and training. And AK-style rifles with giant levers or whatever's the easiest trigger for gorillas to use. Also someone will invent 2 millimeter spy roaches. With cameras in shop ceiling-like fake eye globes and Wifi for brain-interface and live video. Sagittarian Milky Way (talk) 18:42, 18 July 2023 (UTC)

I don't know if you ever seen this, but this video has been doing the rounds for years online. Some soldiers were goofing around and gave an AK-47 to a monkey, which then proceeded to shoot at them and make them run away. It might be fake (I don't know), but I first saw it like 10 years ago.

It's 100% fake. The video you refer to, "Ape with AK-47", is a viral video campaign created by ad agency Mekanism on behalf of their client 20th Century Fox to promote the 2011 film Rise of the Planet of the Apes. Viriditas (talk) 23:38, 18 July 2023 (UTC)

There was an ISIS video where they had a chimpanzee execute a hostage with an SKS. McAynus (talk) 02:24, 19 July 2023 (UTC)

Google says nary a word about it. Viriditas (talk) 02:31, 19 July 2023 (UTC)

I suspect that any extended searching of ISIS videos might bring you to the attention of the security services. Alansplodge (talk) 11:44, 19 July 2023 (UTC)

Well, if you consider Homo sapiens being a species in the animal kingdom... --CiaPan (talk) 20:16, 19 July 2023 (UTC)

@Iloveparrots:: An earlier version of Wildfire had:

In monsoonal areas of north Australia, surface fires can spread, including across intended firebreaks, by burning or smoldering pieces of wood or burning tufts of grass carried intentionally by large flying birds accustomed to catch prey flushed out by wildfires. Species involved in this activity are the black kite (Milvus migrans), whistling kite (Haliastur sphenurus), and brown falcon (Falco berigora). Local Aborigines have known of this behavior for a long time, including in their mythology.

--Error (talk) 00:16, 25 July 2023 (UTC)

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