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New Theories / Re: How does light propagate? By what means does light get from Point A To Point B?

« on: 15/04/2024 20:41:25 »

and a meter is defined as the distance that light travels in one somethingth of a second

I think I can compress ES's post to a short line.
A meter is what light travels in one somethingth of a second relative to an inertial frame.

The original official definition might have omitted that presumption since one can get light to move pretty much any distance you want in a second if the right kind of non-inertial frame is chosen.

because only when light is right next to an observer can he measure its speed? which will then be c.

Technically, even then the speed cannot be measured, and is only presumed. A meter is best measured by light reflected from one end to the other and back, in two somethingths of a second. Since an inertial frame is required for this, obviously you can't have both ends of the meter stick be comoving at once.

Your quote refers to non-inertial frames as "more complicated frames", and any expanding frame would be one of those.

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New Theories / Re: How does light propagate? By what means does light get from Point A To Point B?

« on: 15/04/2024 00:38:58 »

If we insist that speed of light in vacuum is constant while also accepting that space is stretching

Nobody insists any such thing. Per relativity theory, light moves at c only relative to a flat (Minkowskian) inertial frame, and an expanding metric is not an inertial one, and probably isn't Minkowskian either.
Since spacetime is locally flat anywhere, light moves locally at c.

Similar stories for other kinds of non-inertial metrics like a rotating frame or an accelerating one, either of which can also be mapped onto flat Minkowskian spacetime.

As such, it will take ever-so-slightly longer than one second for light to travel that distance because it can only travel 299,792,458 meters in one second.

A more pointed example illustrating the non-constant speed of non-local light in an expanding metric:

Light emitted from the creation of the hydrogen in your body was emitted near 'here' at the recombination event 13.8 billion years ago and is currently ~45 GLR away, meaning it has averaged a velocity of over 3c. Meanwhile, the CMB light that we detect here today was emitted 13.8 billion years ago from material that was at a proper distance that was much closer then than where Andromeda is now. which is an average velocity of around 0.0001c

An example closer to home which doesn't involve expanding space: If you put a reflector on the surface of Mars and Mercury, light shone to Mercury will make the round trip at a speed a bit less that c, and the round trip to Mars at a speed a bit above c.Both are as measured by an Earth observer, and both are examples of light speed being dependent on gravitational potential.

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Just Chat! / Re: The fair use of LLM and AI in education.

« on: 14/04/2024 16:50:34 »

Literary criticism, and to some extent the whole subject of literary studies, has been neatly summed up as "hundreds of pages of bad English written about a few pages of good English", and I guess the same could be said in any other language, so the value of essays in that area must be close to zero and their purpose is difficult to imagine.

Undergraduate essays in factual (e.g. geography) or presumed factual  (history) subjects really boil down to a single question: "have you read the book?" So AI has revealed that a great deal of student and teacher time is, frankly, wasted by regurgitation of secondhand facts and opinions.

On the presumption that studying the humanities has some purpose, it is therefore incumbent on those who profit from  teaching them to introduce some form of laboratory practical. The pub quiz format is ideal since it tends to the requisite gaussian curve of marks  with a large number of questions and candidates, and does test retention of facts (including the written opinions of third parties). 

Having established the candidate's diligence in reading or attending lectures, we now need to determine whether he can form and express an opinion clearly, so a very brief viva will waste less of everyone's time than writing and marking a thousand word essay. Though written, Churchill's memo to Montgomery: "Pray let me have, on half a sheet of paper, your plan for invading Italy" sets the tone for a good viva question. From the examiner's point of view it would be a lot more fun than adjudicating a brass band contest, where the scope for interpretation of the test piece is rather limited.

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Just Chat! / Re: The fair use of LLM and AI in education.

« on: 14/04/2024 14:32:34 »

a LLM checker

What is a LLM checker?  What are the markers that trigger a positive?
How much better are future LLMs going to get such that such tests need to be ever more complex? After all, what a student does is essentially what an LLM does: Research some source(s) and regurgitate the material in altered words. Short of an actual 'new reasearch' project, that's pretty much it.

The checker seems to be a form of the Turning test. Was this text generated by a human or no? All the harder since there is only one-way text and no interaction.

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Physics, Astronomy & Cosmology / Re: Why didn't the total solar eclipse strain my naked eyes at all?

« on: 09/04/2024 13:50:30 »

Looking directly at the sun is inherently hazardous and something one should never do. Just because it did not hurt does not imply it was safe to do so. I am sure you have seen the effect of direct sunlight through a lens setting fire to a piece of paper- now consider the same effect directed at the fragile retina at the back of your eye. Damage may have been done only to show later.

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Physics, Astronomy & Cosmology / Re: Does time dilation and length contraction apply to light?

« on: 07/04/2024 19:08:53 »

So when someone asks, "What does the universe look like from light's perspective?", the answer is that there is no answer? Or that space and time don't apply?

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Physics, Astronomy & Cosmology / Re: Does time dilation and length contraction apply to light?

« on: 07/04/2024 15:59:27 »

Krytptid's thoughts here mirror mine very closely and it seems I have a major gap in my understanding of SR(not surprising really). If one could travel at the speed of light surely one's rapidity would be infinite and hence time and space would have no existence- why does this not apply to light?. I have heard several physicists state that "light does not experience time or space" or something similar expressed more accurately: I cannot remember any names other than the mathematician Roger Penrose(who can be controversial at times). This question of mine is a bit muddled but I could not find a better wording. 

"If one could travel at the speed of light ..."  That's the issue.  Anything that travels at c would be in the same boat as light.
Consider the equation for relativist KE:
KE = mc^c (1/sqrt(1-v^2/c^2)-1)   if v=c, then it reduces to :
KE mc^2(1/0-1) 
Note the 1/0.  1/0 is undefined, thus the KE of a mass traveling at c would be undefined. Just like the singularity, the math doesn't give an answer for this scenario.
So when you post "If one could travel at the speed of light ...", you are essentially saying, "If Relativity doesn't hold..."

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Physics, Astronomy & Cosmology / Re: Does time dilation and length contraction apply to light?

« on: 07/04/2024 10:38:10 »

Krytptid's thoughts here mirror mine very closely and it seems I have a major gap in my understanding of SR(not surprising really). If one could travel at the speed of light surely one's rapidity would be infinite and hence time and space would have no existence- why does this not apply to light?. I have heard several physicists state that "light does not experience time or space" or something similar expressed more accurately: I cannot remember any names other than the mathematician Roger Penrose(who can be controversial at times). This question of mine is a bit muddled but I could not find a better wording. 

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Physics, Astronomy & Cosmology / Re: Does time dilation and length contraction apply to light?

« on: 06/04/2024 22:18:41 »

This was inspired a bit by something I had been corrected about earlier. There was a discussion in another thread about black holes where I stated that black hole singularities had infinite density.

That is not correct of course. The exact nature of a black hole singularity depends on the type of black hole it is (charged, rotating, etc), and of course depends on a unified theory which is lacking. In the simplest case, a Schwarzschild black hole is a vacuum solution, so there is no material at all in it at any density. Time simply ends at the singularity, and anything that gets there has no future light cone at all, so it cannot persist as compressed anything.
Things falling into black holes are pulled apart, not squished together. There's not a point where that changes.

I had been under the assumption that time is frozen for light because it travels at the speed of light.

Time is not frozen for it. Time and distance is just not meaningful for light since there is no meaningful reference frame for it.

Likewise, I had assumed that the entire universe was also length contracted to zero along the light's direction of movement, meaning that it was simultaneously at its starting and ending points

Which I suppose is one way to show the absurdities that result from attempting to define a frame where light is both stationary and also by definition moving at c.

So would it be more correct to say that special relativity doesn't predict the length contraction or time dilation for light?

It is not meaningful for a coordinate system in which light (or anything) has an undefined local speed. Length contraction is something meaningful between a pair of inertial frames where things like distance and simultaneity are meaningful.

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General Science / Re: Is Absolute Zero Possible?

« on: 04/04/2024 20:38:17 »

Just the same as trying to accelerate a massive object to the speed of light, we can get arbitrarily close by expending more and more energy but we can never get to the target speed. Similarly with absolute zero the closer one gets the harder it becomes to produce a further decrease. Mathematically one can only asymptotically approach either the speed of light(with mass) or absolute zero. |Oh dear Eternal Student beat me to it!

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General Science / Re: Is Absolute Zero Possible?

« on: 04/04/2024 17:24:09 »

The real problem is basic thermodynamics.

The efficiency of a theoretical Carnot engine (the most efficient engine conceivable) is 1-T(cold)/T(hot). This implies that as you approach absolute zero, the efficiency of any heat transfer device tends to zero. So you need to do an infinite amount of work to remove the infinitesimal last bit of heat from your sample.

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General Science / Is Absolute Zero Possible?

« on: 04/04/2024 11:32:11 »

Absolute zero of course is when all molecular motion stops. Scientists say we will never reach it.

My HS chemistry teacher said it is because all molecular collisions are elastic. And when an atom hits another one, it always bounces off and starts moving again. Another message board said that absolute zero is impossible because there is no such thing as a perfect vacuum.

So is absolute zero possible to reach? Will we reach it someday? I think, like air flight and the Wright Brothers, we will.

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Physics, Astronomy & Cosmology / Re: How many spots are produced from Stern-Gerlach apparatus that rotates?

« on: 27/03/2024 01:23:47 »

It's my commentary on the first diagram, where z+ stream from first stage is maintained in second stage. Nothing changes into z-.

No that isn't what "happens".
Nothing about the spin state is "maintained in the second stage". Where is it maintained or "stored". You should realize, there isn't any room for this in the beams. You seem to be making a mistake about classical information; it isn't what most people think it is, although it is what (some) people say it is, which makes the stuff interesting.

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Physics, Astronomy & Cosmology / Re: How many spots are produced from Stern-Gerlach apparatus that rotates?

« on: 26/03/2024 09:41:26 »

Starting from ES's initial experiment, my interpretation is that

1. We begin with an unpolarised stream of neutral atoms (never mind charged particles at this stage)  with their spins randomly and isotropically distributed

2. An inhomogeneous field polarises and separates the stream into two streams, with spin up U and spin down D.

3. Now consider only the U stream. Again, an inhomogeneous field perpendicular to the first, separates this into UL and UR streams.

4. Suppose that the second field was at 45 deg rather than 90. Same principle would surely split U into U(45) and U(135)

5. So any polarised stream S passing through a field at angle X to the plane of polarisation would be split into S(X) and S(-X)

6. And after N distinct iterations of X we would have 2^N distinct streams each separated by X degrees.

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Physics, Astronomy & Cosmology / Re: How many spots are produced from Stern-Gerlach apparatus that rotates?

« on: 18/03/2024 15:57:51 »

However the question is what do you mean by "slowly rotating"  the device? I can imagine a magnetic field that rotates with distance along the z axis, or in practice a series of SGs each slightly rotated with respect to the previous one, so if we ignore the essential divergence of the beams at each point, we'd get a circular distribution at the exit.

IMO, it depends on how strong the magnetic field divergence is, and the rate of change of the SG apparatus axis along the path of the atoms.
If the divergence is strong enough, and the rate of change of the axis is slow enough, then the final result is two dots along the axis at the end of the SG apparatus.

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New Theories / Re: Could quantum mechanics be wrong?

« on: 18/03/2024 13:33:48 »

There is more, a lot more to this theory.

And apparently you don't understand a bit of it.

Addressing the question in the title of the thread I think the answer is no.  The reason the answer is no is because quantum theory accurately predicts the outcome of various experiments.  It very well could be that there can be a better or more accurate theory that will replace quantum theory, but that does not mean quantum theory is wrong.  Newtonian gravitational theory is not wrong, it just does not cover all areas as well as General relativity.  Newtonian gravity will do just fine in trajectories of cannon balls or sending a space ship to land on the moon but it is not so good at determining the deflection of light due to a massive body for instance.

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New Theories / Re: Could quantum mechanics be wrong?

« on: 18/03/2024 12:22:32 »

When the electron cloud absorbs a photon, the subsequent emission of a photon doesn't necessarily obey the law of reflection (angle of incidence = angle of reflection.) The same applies to refraction because the process of absorption and emission involves transitions between quantum energy levels within the atom, which can occur in any direction.

This is just a strawman argument since the absorption and emission of photons from electrons is not how refraction or reflection are explained.

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Physics, Astronomy & Cosmology / Re: Gas discharge tube hydrogen

« on: 17/03/2024 22:12:33 »

Hi ES, I would have said 1Mv/m for normal air but I could be wrong. Many discharge tube use additional methods to start the initial ionisation, prior to avalanche occurring such as heated filaments in florescent lamps, a high voltage external conductor in xenon flash tubes and an auxillary electrode very close to one of the main electrodes in mercury vapour lamps(to start a local ionisation). High pressure sodium lamps and tin halide lamps use a high voltage source in series with one of the electrode supplies. The gas pressure plays a major role in the voltage needed to initiate ionisation, referred to as the strike voltage: the higher the pressure, the higher the necessary voltage and a lot of discharge lamps have to cool down after power interruption before reuse as the pressure is higher when hot. Many other factors may account for the discrepancies in the calculations: random cosmic rays as you suggested or low level radionuclides. Field emission as raised by Alancalverd may play a role(wild assed guess).   

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Physics, Astronomy & Cosmology / Re: Gas discharge tube hydrogen

« on: 17/03/2024 11:27:24 »

This " An electron could be free of the nucleus only if it absorbs a photon raising its energy beyond the transition limit. " is missing the point of a gas discharge lamp.
The voltage gradient is big enough to pull the electrons out of the atom.
In some cases they have a hot filament which emits electrons and those can be accelerated by the field and when they hit an atom (or molecule) they ionise it and start a Townsend Avalanche.

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Physics, Astronomy & Cosmology / Re: How many spots are produced from Stern-Gerlach apparatus that rotates?

« on: 16/03/2024 13:49:27 »

I remember this experiment from my long distant college days but I had forgotten it's name. I can't add anything of value, I do however have a question: how are the silver atoms entrained in a beam? the only way I can think of is electrostatic acceleration, that would lead to charged particles which are ruled out by the terms of the experiment.