Wikipedia:Reference desk/Archives/Science/2024 October 19

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October 19

Falling into Jupiter

I was thinking one day. Imagine you are an astronaut in free fall to Jupiter. You are in a spacesuit with plenty of oxygen and food available so you are not dying from suffocation or starvation in your spacesuit. You have no way of escaping Jupiter's gravity. There are no other dangers than Jupiter itself. You will eventually enter Jupiter's atmosphere. At which point would you die? JIP | Talk 09:30, 19 October 2024 (UTC)

You would be moving so fast, that you would burn up in the upper atmosphere, turning into plasma temporarily. But when the space suit ruptured, by burning through, suffocation and depressurisation would be a terminal issue. Graeme Bartlett (talk) 10:53, 19 October 2024 (UTC)

The thing about vague hypotheticals is, they're vague, and hypothetical. The astronaut could bring along a bigass rocket, and once in a stable orbit around Jupiter fire it to cancel out their orbital momentum until they were at rest relative to Jupiter, then "let go" and just let gravity do its thing pulling them towards Jove's center of mass.

Most spacecraft don't do this b/c hauling reaction mass up a gravity well is a giant pain. The "easiest" way to slow down for landing, is to slam into the atmosphere and let that bleed off your velocity. If you can. If not, for ex the atmosphere is very thin, other methods are required: see the Mars probes, or lunar landings.

(The real non-hypothetical answer: they would be long-dead of acute radiation syndrome before anything else, unless their "spacesuit" was a massive, very dense and multilayered radiation shield chamber) Slowking Man (talk) 04:30, 20 October 2024 (UTC)

The onset of radiation syndrome is slow enough that the fall is over before the radiation really kills. Or the radiation is very high, then that should be said where and why. 176.0.161.3 (talk) 12:45, 20 October 2024 (UTC)

Since neutrinos (and dark matter) don't interact with light, so what should happen when light comes across them?

I can think about two options:

Option #1: The light keeps travelling "through" them, as if they don't exist. But if this is the case, then what does that mean, in terms of the neutrino's (and dark matter's) refractive index? Is it identical to the vacuum's refractive index?

Option #2: The light experiences absorption or reflection or scattering, in which case the neutrino's (and dark matter's) momentum must be influenced by that encounter with light, due to the conservation of momentum, so we do see them interact with light, in some sense...

So, what's the correct option? Is it #1 or #2 or another one?

HOTmag (talk) 16:29, 19 October 2024 (UTC)

Since neutrinos do not interact with light, the light never collides with them. Ruslik_Zero 20:42, 19 October 2024 (UTC)

By "collides" I meant "comes across" (due to your important comment I've just fixed that in the header) So, what should happen if a [a beam of] photon[s] and a [beam of] neutrino[s] travel towards each other, i.e. on the same route but in opposite directions? Similarly, what should happen when light comes across dark matter? HOTmag (talk) 21:04, 19 October 2024 (UTC)

protons and electrons interact with photons. What is their refractive index? Short answer: no one can tell, because the refractive index is not of a particle alone. It depends on the interaction. And neutrinos not only do not interact with photons, they don't interact with each other. So you have no interactions to base a refractive index on. 176.0.161.3 (talk) 22:25, 19 October 2024 (UTC)

The refractive index of a given medium is only relevant if [a beam of] photons can travel through that medium. In the case of protons-electrons you're talking about, nobody claims [a beam of] photons can travel through a proton or through an electron, so I can't see how any refractive index may be relevant in that case. But a refractive index may be relevant in option #1 I was talking about as you can see above in that option. HOTmag (talk) 02:16, 20 October 2024 (UTC)

Your fundamental problem is you keep trying to think about "quantum stuff" intuitively, in terms of the familiar everyday big world we all have direct experience of via our senses. You're asking what photons etc "really act like". Billiard balls? Pebbles? Ocean waves etc etc? The correct answer is, they act like none of those things. They act like photons. They don't "take up space" in any way we can visualize, or occupy a definite fixed position in space, or "move" by plodding around from point A to B in a fixed interval of time, or "pass through one another", anything like that.

A necessary precondition to really "grokking" "modern physics", is to throw out your preconceptions, and simply start with: what do our observations of things tell us. From those, we make predictions (hypotheses), and then we test them to see if they're right. That's how science is done. And if you think it's all made up, you're presumably reading this on some kind of electronic device, which simply wouldn't work if electrons were really tiny little balls, or photons were really little tiny beams or rays or water waves that "bounced off" other stuff when they "ran into it".

Richard Feynman: Things on a very small scale behave like nothing that you have any direct experience about. They do not behave like waves, they do not behave like particles, they do not behave like clouds, or billiard balls, or weights on springs, or like anything that you have ever seen. Slowking Man (talk) 05:02, 20 October 2024 (UTC)

What do you mean by keep trying? When did I try to do that for the first time?

When I posted my question in the header, I had already been quite aware of the methodological idea you're describing quite well. Of course what you're depicting is the correct approach, methodologically speaking. But while you're portraying the correct methodological attitude one should take when thinking about modern physics, my question has nothing to do with methodology, because my question is only a practical one, empirically speaking (as follows), so the correct methodological approach you're quite well picturing has nothing to do with what I've practically asked about. To put it in a clear cut way: Just as you can practically ask, what is empirically expected to happen when one actualizes the photoelectric effect - although it heavily involves quantum physics that should be grokked by means of the methodological idea you're describing, so I can practically ask, what is empirically expected to happen when a [beam of] photon[s] and a [beam of] neutrino[s] travel towards each other, i.e. on the same route but in opposite directions, although both the photon and the neutrino are described in that quantum physics.

So, are you claiming that I can't suggest any experiment in which a [beam of] photon[s] and a [beam of] neutrino[s] travel towards each other, i.e. on the same route but in opposite directions? Similarly are you claiming, that once Science detects (somehow) any dark matter, still we won't be able to suggest any experiment in which we send light towards dark matter? Or what are you actually claiming, practically speaking? HOTmag (talk) 07:53, 20 October 2024 (UTC)

you can never design an experiment where a photon travels on a path. Whatever the path maybe. 😁 For example you can do a photon in a fiber travel from a source to a detector. You will never know that the photon really after the first atom leaves the fiber, travels to the black hole in the centre of the Andromeda galaxy, does half a round around the black hole, a quantum leap short of the event horizon, comes back at the last atom of the fiber and hitting the detector bearing the spectral attenuation of a sodium atom in the middle of the fiber it never passed on the way. Okay that is an extreme example for a very improbable but possible event in quantum mechanics. Now to your question. What if "never interacts with" is a code for active avoidance? That would mean a neutrino near another particle (photon, neutrinos...Whatever) goes out of the way and resumed its travel after the particle has passed. What would you do then? Even going out of time is possible. Think about the length of the way to Andromeda! 176.0.154.107 (talk) 13:13, 20 October 2024 (UTC)

According to your attitude, the very concept of "refractive index" of a given medium through which light travels, would have had no meaning. Additionally, please notice that my original post (i.e. the question in the header and under it), mentions no photons, but rather mentions light only, for example a beam of photons. Anyway, thanks to your comment, I've just added "a beam of" before every "photon" mentioned in my later responses (following my original post). To sum up: the main question in my original post still remains. HOTmag (talk) 13:36, 20 October 2024 (UTC)

Rewriting "photon" as "a beam of photons" changes the question. The exact path that a photon will follow cannot be predicted. Subsequent detection of a single photon is possible but allows only an estimate of the spread of likely refractive indices the photon has traversed. One increases the accuracy of a determination of refractive index by averaging measurements of many photons i.e. using "a beam of photons". However there will be practical limits to the focusing of both light sources and detectors. Philvoids (talk) 14:30, 20 October 2024 (UTC)

Rewriting "photon" as "a beam of photons" changes the question. Please re-read the second sentence (the one beginning with "Additionally") in my last response.

As for the rest of your response, I agree, but what's the answer to my original question summed up in the header? HOTmag (talk) 15:44, 20 October 2024 (UTC)

So, are you claiming that I can't suggest any experiment in which a [beam of] photon[s] and a [beam of] neutrino[s] travel towards each other, i.e. on the same route but in opposite directions? Similarly are you claiming, that once Science detects (somehow) any dark matter, still we won't be able to suggest any experiment in which we send light towards dark matter?

Essentially, yes, assuming we're right about dark matter not interacting with the electromagnetic field. Or, perhaps it could be put as: we can propose sending photons "this way" and neutrinos "that way", such that their worldlines at some point intersect, but we would expect to observe nothing (other than the extremely minute effects of their gravitational and weak interactions), because why would we?

In this vein: the neutrino fields don't interact with the EM field. The question "what if a beam of X and Y" travel towards each other" is still formulated in intuitive "classical" terms. Talking in strict QM terms, questions like "a beam of X and beam of Y" are ill-formed questions: to be meaningful (answerable) questions, rephrase them in terms of quantum operators, Dirac matrices, Hamiltonian mechanics etc.

Michio Kaku has some good advice for people "talking science": [1]:

Extended content

What to Do If You Have a Proposal for the Unified Field Theory?…and what not to do Due to volume of e-mail I have received (several thousand at last count) I cannot answer all requests, especially those from individuals who have a new proposal for completing Einstein’s dream of a unified field theory, or a new theory of space and time. However, I would like to give some guidelines for people who have thoughtfully pondered the question of the meaning of space-time. 1) Try to summarize the main idea or theme in a single paragraph. As Einstein once said, unless a theory has a simple underlying picture that the layman can understand, the theory is probably worthless. I will try to answer those proposals which are short and succinct, but I simply do not have time for proposals where the main idea is spread over many pages. 2) If you have a serious proposal for a new physical theory, submit it to a physics journal, just as [sic] Physical Review D or Nuclear Physics B. There, it will get the referee and serious attention that it deserves. 3) Remember that your theory will receive more credibility if your theory builds on top of previous theories, rather than making claims like “Einstein was wrong! ” For example, our current understanding of the quantum theory and relativity, although incomplete, still gives us a framework for which we have not seen any experimental deviation.Even Newtonian gravity works quite well within its domain (e.g. small velocities). Relativity is useful in its domain of velocities near the speed of light. However, even relativity breaks down for atomic distances, or gravitational fields found in the center of a black hole or the Big Bang. Similarly, the quantum theory works quite well at atomic distances, but has problems with gravity. A crude combination of the quantum theory and relativity works quite well from sub-atomic distances (10^-15 cm.) to cosmological distances (10^10 km), so your theory must improve on this! 4) Try not to use vague expressions that cannot be formulated precisely or mathematically, such as “time is quantized, ” “energy is space, ” or “space is twisted, ” or “energy is a new dimension,” etc. Instead, try to use mathematics to express your ideas. Otherwise, it’s hard to understand what you are saying in a precise manner. Many referees will throw out papers which are just a collection of words, equating one mysterious concept (e.g. time) with another (e.g. light). The language of nature is mathematics (e.g. tensor calculus and Lie group theory). Try to formulate your ideas in mathematical form so that the referee has an idea of where you are coming from. 5) Once formulated mathematically, it’s then relatively easy for a theoretical physicist to determine the precise nature of the theory. At the very least, your theory must contain the tensor equations of Einstein and the quantum theory of the Standard Model. If they lack these two ingredients, then your theory probably cannot describe nature as we know it. The fundamental problem facing physicists is that General Relativity and the quantum theory, when combined into a single theory, is not “renormalizable, ” i.e. the theory blows up and becomes meaningless. Your proposal, therefore, has to give us a finite theory which combines these two formalisms. So far, only superstring theory can solve this key problem. Important: this means that, at the very minimum, your equations must contain the tensor equations of General Relativity and the Standard Model. If they do not include them, then your theory cannot qualify as a “theory of everything.” 6) Most important, try to formulate an experiment that can test your idea. All science is based on reproducible results. No matter how outlandish your idea is, it must be accepted if it holds up experimentally. So try to think up an experiment which will distinguish your result from others. But remember, your theory has to explain the experiments that have already been done, which vindicate General Relativity and the quantum theory. Good luck!

--Slowking Man (talk) 16:28, 20 October 2024 (UTC)

In my view, presenting Michio Kaku's advice in this thread is redundant, as follows.

Introduction: the reason for which I mentioned the photoelectric effect in my last response to you, is because this effect can be formulated, not only in the language of Quantum chemistry, but also in the language of Classical electromagnetism - which indeed disagrees with this effect but can still tell us what it disagrees with.

The same is true for my original question in the header: It can also be formulated in the language of classical mechanics, as you have done yourself, stating in a classical language (a bit relativistic yet not the language of quantum mechanics): we can propose sending photons this way and neutrinos that way, such that their worldlines at some point intersect, but we would expect to observe nothing. To sum up, you agree to option #1 (in my original post), i.e.: We will see the beam of light keep travelling in the same 4D-route without any change, as if this route is not intersected by the 4D-route of the beam of neutrinos. Am I right? HOTmag (talk) 17:35, 20 October 2024 (UTC)

"Doing" special relativity, which ignores gravitation (assumes flat spacetime) and plotting it out on a Minkowski diagram, correct, b/c they only interact via the weak interaction and it's called that b/c seriously it's really weak. (Not as weak as gravity though!) Which is why gazillions of solar neutrinos are flooding through us and the entire Earth after plowing through half the Sun, like we're all not even there, constantly. (The neat fact being that what changes is simply the direction they come from: at night they're coming upwards from the ground having just zipped through the entire planet, after calling on Earth's day side!)

In gen rel, it would still be the same, b/c the only thing changing is adding in gravitation. The neutrino's mass is immensely tiny, thus its stress-energy-momentum tensor has accordingly miniscule effect on local spacetime geometry (which is what we call "gravity", in GR). Photon's mass is, well, zero, so it has even less effect. And gravitation is really weak.

...Unless, you can crank things up to truly mind-and-spacetime-warping energies, and channel and confine absolutely mind-boggling amounts of photons into a vanishingly-tiny volume of space. Somehow. Photons are bosons, which, unlike fermions such as quarks (or neutrinos), are "allowed" to have all identical quantum numbers if they feel like it. Meaning their wavefunctions can completely overlap and they can all "take up" an arbitrarily small volume. So if you figure how to do that out do tell the scientific journals, preferably before building your death ray and taking over the world.

Nota bene: when physicists these days are "talking shop" generally they only ever use "mass" to mean "the invariant or 'rest mass' according to GR": [2]. So I will try to do the same. --Slowking Man (talk) 19:38, 20 October 2024 (UTC)

Unless, you can crank things up to truly mind-and-spacetime-warping energies, and channel and confine absolutely mind-boggling amounts of photons into a vanishingly-tiny volume of space. Btw, some weeks ago I read a scientific article (I think in Nature or in Science) that discovered that a Kugelblitz was actually impossible, because it would've started to emit radiation before it became a black hole, so it would never become a black hole...

when physicists these days are "talking shop" generally they only ever use "mass" to mean "the invariant or 'rest mass' according to GR. I think you've noticed (as follows) that this fact is irrelevant, because the geometry of spcetrime is shaped by energy (and momentum) rather than by mass.

The neutrino's mass is immensely tiny...Photon's mass is, well, zero, so it has even less effect. Correct, less effect but not zero effect, because the geometry of spcetrime is shaped by energy/momentum rather than by mass. Anyway, thank you for noticing the (immensely tiny) generally-relativistic effect being done to the geometry of spacetime by each beam, thus influencing the other beam, so actually they do have some impact on each other after all, yet not via any force other than the fictitious force of gravitation. Well, your noticing this generally-relativistic effect was an important reservation. Anyway, what I'm taking from your answer to my original question is as follows: Both beams don't interact with each other, as far as gravity is ignored. HOTmag (talk) 22:35, 20 October 2024 (UTC)

I think you've noticed (as follows) that this fact is irrelevant, because the geometry of spcetrime is shaped by energy (and momentum) rather than by mass.

See invariant mass: a bunch of photons with the same momentum vector have zero effect on spacetime geometry, because a single photon (having no invariant mass) has no center-of-momentum frame where it is at rest, no matter what Lorentz transformations are applied to it. This is why a beam of light always travels at c in vacuum. If you have two+ photons with different vectors relative to each other (they have a scattering angle) then you can calc a center-of-momentum frame for the multiple-photon system, and then the photons have an effect on the spacetime metric. Hence the kugelblitz idea: if hypothetically you could stuff tons (heh) of photons into a tiny volume of space, they can't be all at rest relative to each other, so the whole system would have a CoM frame and the photons would affect the local metric. In general, only changes in energy have physical significance. --Slowking Man (talk) 15:10, 22 October 2024 (UTC)

when I wrote that the geometry of spacetime was shaped by energy and momentum rather than by mass, I tried to be brief. actually I meant what I'd already written in my last response of this old thread: that the geometry of spacetime was shaped by the "density and flux of momentum and of energy".

Anyway, my main point in my last response, was not about energy (or about momentum), but rather about mass, that is: as far as gravity is concerned, mass is irrelevant. HOTmag (talk) 15:57, 22 October 2024 (UTC)

Interactions are predicted. See [3]. Modocc (talk) 22:44, 20 October 2024 (UTC)

Thank you for this source. HOTmag (talk) 23:02, 20 October 2024 (UTC)