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New Theories / Re: In four dimensions, must an object move at c in at least one of them?

« on: 07/12/2024 20:59:22 »

What we know is that if two 511 keV photons are detected simultaneously (OK, within femtoseconds, for the pedants among us!) in opposed detectors, they originated from a positron annihilation at point on the line connecting them. That is, we know their history (because there is no other possibility)  and (eventually) that tells us where the positron source is.

Again, it's because you know about the positions of particles which emit photons.  This information is not "carried" by them, it's something you know before any photons are detected.

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Physics, Astronomy & Cosmology / Re: What is the exact cause of the time dilation of the twin?

« on: 07/12/2024 20:50:59 »

I think this thread has followed the same kind of pattern I've seen on other forums, any discussion of 4-dimensional spacetime is full of disagreements about whether this or that is a good explanation or even a correct one.

I have to bear in mind I suppose, that this pattern emerged as soon as Einstein published his general theory. The idea that a spacetime existed in which the notions of fixed time and space were only relative, weren't met with enthusiasm.

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Physics, Astronomy & Cosmology / Re: What is the exact cause of the time dilation of the twin?

« on: 07/12/2024 02:07:24 »

All that said, yes, different definitions are used, and it is commonplace to express motion through spacetime as taking place at c, expressed as a four-velocity, not a normal velocity.

I'm trying to figure out a response to the phrase "normal velocity"; if you mean the Euclidean part of the spacetime metric, I guess. But in the case of non-Euclidean solutions, I don't know what to say about it.

If you accept that "normal" is restricted to a locally defined region of the universe, the only thing moving at c is light, and the universal expansion is effectively zero; I would say that then, the universe is indeed "normal". But I know enough about the equations that I can say, that is a trivial solution. I was hoping we could lean towards what an exact reason for the different ages of twins is. Part of the reason is the exact speed of light, of course. Another part is the relativistic 4-velocity any object with mass "inherits" from the ah, causal structure.

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New Theories / Re: In four dimensions, must an object move at c in at least one of them?

« on: 06/12/2024 15:26:27 »

Inverting the paradigm, you imply that all photons are the same age. Which means that every electron transition in the universe occurred simultaneously. Thus time, the dimension that separates sequential events, has no meaning. Somewhat counterintuitive.

I don't imply all photons have the same age, instead photons don't have an age.

How old is any quantum particle? How can I tell if two electrons have an age gap?
The question of age and getting older, is a thing that does seem to depend on context. 

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New Theories / Re: In four dimensions, must an object move at c in at least one of them?

« on: 06/12/2024 15:04:29 »

From my window I can see a large barn. As the photons carry no history, I have to assume it was created spontaneously a few picoseconds ago, but common sense and context tell me it was built about 150 years ago from wood that was already at least 50 years old at the time.

Photons are visual information. The memories you cite (that common sense, and context--where does it come from) are not a thing the light you see now can reference in any way.

Since it takes picoseconds, as you say, to be transmitted in your direction.

We rely on the precision of photon history to locate tumors by positron emission tomography.

Yes, but we know what to look for. We construct the history--see Hawking and Penrose.

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New Theories / Re: In four dimensions, must an object move at c in at least one of them?

« on: 06/12/2024 03:58:16 »

That's probably not the explanation you ( @varsigma ) were looking for but it is AN explanation.

No I think it's a pretty good explanation. Can I suggest showing what setting c to 1 means for the 4-velocity? Some people say it's confusing.

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Physics, Astronomy & Cosmology / Re: What is the exact cause of the time dilation of the twin?

« on: 06/12/2024 03:35:44 »

There might be a problem with using the word motion, or moving, it's usually a reference to space, or different positions.

In Minkowski spacetime you have a relativistic 4-velocity. It cannot be zero or, well, lots of things just don't happen.

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Physics, Astronomy & Cosmology / Re: What is the exact cause of the time dilation of the twin?

« on: 06/12/2024 02:08:32 »

"Einstein based special relativity on the idea that the speed of light is the same for all observers. You cannot do this in a Euclidean space where all the signs are plusses. But you can do it if one of the signs is different relative to the others.

That's because a space-time distance that is zero for one observer is zero for all observers. This is also the case in Euclidean space, but in Euclidean space, this just means zero in each of the directions of space. But what does a zero distance mean in space-time? Well, let's find out. For simplicity, let us look at only one dimension of space. So if the distance in space-time is zero, this means that the distance in space divided by the distance in time equals plus or minus c. And that?s the same for all observers. So this speed, c, is an invariant speed.

But, well, we are not light, so we do not travel with the speed of light through space, and we do actually cover a distance in space-time. So let us look at this equation for the space-time distance again. Now let us divide this by the time difference. Now what you have on the left side is the space-time distance per time. And under the square root you have roughly something like the squares of the velocities in each of the directions of space. Plus c².

And there you have it. Relative to yourself, you do not move through space, so these velocities are zero. You then only move into the time-like direction, and in this direction, you move with the speed of light. So, we indeed all travel through time with the speed of light."--from a Ph.D blog

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New Theories / Re: In four dimensions, must an object move at c in at least one of them?

« on: 06/12/2024 01:20:36 »

Another thing about matter and aging.

I know how to anneal a metal bar, with heating and cooling, and hammering. This process ages the metal.
I know how to age a lot of things made out of matter.

I don't know any way to age light, although it's easy to make light interact with matter, I don't know I can say it ages or anneals the light at all.

Aging appears to be relevant to large collections of particles, such as humans. Particles of light don't age, is kind of a tenet of Einstein's theories, and the man himself said this.

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New Theories / Re: In four dimensions, must an object move at c in at least one of them?

« on: 06/12/2024 01:13:16 »

It was emitted from x meters away with a different gravitational potential, x/c seconds ago, travelled through refracting and polarising media, and may have been reflected off something, before we detected it. That's quite a lot of known history, and if it had a few companions, like a spectrum, we can probably deduce its original energy before doppler and gravitational red shift altered it.

I think that misses the point I made. Which was that we give them a history. If you didn't know all the above about the paths, what could photons tell  you?

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New Theories / Re: In four dimensions, must an object move at c in at least one of them?

« on: 06/12/2024 01:10:24 »

This is bending what people say beyond the breaking point.

You're saying Roger Penrose published a book, which bends something beyond the breaking point? You don't think he may have been trying to explain how relativity works?

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New Theories / Re: In four dimensions, must an object move at c in at least one of them?

« on: 06/12/2024 01:08:22 »

In a way they do. There are a number of waves of a photon between two events (in a given frame, its frequency times its duration between the two events). That is an age of sorts.
If you're saying that the photon does not undergo any physical change from one event to the other, that's true, but also true of something like a proton which doesn't move at c. Protons also cannot recall a past.

Protons don't get redshifted by the cosmic expansion, photons do.

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Physics, Astronomy & Cosmology / Re: What is the exact cause of the time dilation of the twin?

« on: 06/12/2024 00:59:59 »

No, it is not a true explanation of a theory, which is why such assertions should not be posted in the main sections of the forum. That area is reserved for questions and answers to them.

I apologise for what I'm about to post then.

Einstein, and Feynman have both said that relativity says we move in the time direction. Time isn't really a thing with extent, but it is a direction. We move at the speed of light in that direction.

John Baez, Roger Penrose, say it too.
 

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New Theories / Re: In four dimensions, must an object move at c in at least one of them?

« on: 05/12/2024 22:40:38 »

I'm not sure that I have, sorry.   Is there any online reference?

I'm fairly sure it's something he discusses in The Emperor's New Mind.

Have you seen the Penrose and Hawking book, The Nature of Space and Time?

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New Theories / Re: In four dimensions, must an object move at c in at least one of them?

« on: 05/12/2024 21:08:26 »

Photons have a history, but it's easier to understand and predict with a wave model. 

If they "have" a history, it's because we give them one.
If a photon, a single photon, can be a clock of some kind, it can have one and only one "tick". Not much room for a history there.

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New Theories / Re: In four dimensions, must an object move at c in at least one of them?

« on: 05/12/2024 21:04:29 »

There's nothing special about what we identify as the x,y, z axis of space and the t or time axis.  We can always construct a "direction" of travel for an object that is a combination of the spatial and time directions.   An object will then always move at precisely c in that "direction" and have no velocity at all in the other three directions orthogonal to this.

But, why will an object move at c in that direction? Have you seen Penrose's description of two observers walking past each other? That this means they are literally in different 'spaces', at least according to Minkowski. Each observer defines a different direction for the "object moving at c". Each observer has their own "object", maybe it's what they call time.

We do, because we can remember a past.

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New Theories / Re: In four dimensions, must an object move at c in at least one of them?

« on: 05/12/2024 20:32:19 »

How do you reconcile this with Doppler's effect, Sagnac's effect, Fizeau's effect, Interference patterns?

I don't understand your question. All the effects you mention occur in three spatial dimensions. The measuring equipment "ages", right? It changes when it records anything. That is not the case with EM radiation.

Measuring equipment, all classical devices, are constantly "measuring"--thermal changes in the environment, mechanical vibrations (check out the LIGO problems)--everything made of matter ages. We say that light isn't a form of matter, but it is "material"; it has momentum.

Momentum can't be a mathematical (or algebraic) gizmo--it has to be as real as time.
Or maybe that doesn't "really" mean much.

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Geek Speak / Re: What is 'maths'?

« on: 04/12/2024 02:29:00 »

Perhaps time is just what lets observers remember a stream of clock ticks. If, that is, there's a clock ticking near them.

There, the important concept I think, is difference. Whereas photons "see" no difference between any moments of time, matter does. Entropy is based on differences in some system of particles.

Whether you can say you have a system of different particles (or with different positions) is also a question that is meaningful. Go figure.

The big, um difference, between classical systems such as ticking grandfather clocks, and "ticking" particles is the particles are almost in a different kind of universe--distances between individual atoms might not make sense, particles can tunnel through barriers, it's just weird.

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Geek Speak / Re: What is 'maths'?

« on: 03/12/2024 19:48:51 »

I'm sorry, I'm not sure what that means.   Time varies linearly with the number of seconds that have passed rather than having some quadratic dependence?   Time is an operator that is linear - time acts on one girl to make an old lady,  so it acts on  λ girls to make λ old ladies?   I suppose all those things are true of time.

It's true in any quantum experiment, quantum computing is experimental at the moment. It's algebraically true, or a consequence of any formal system we use to describe what we're doing, and what particles are doing. It seems to be a law of quantum information-bearing systems of particles.

It seems quite prosaic, after all, time is linear in ordinary mechanics, or mechanical clocks wouldn't work. Clocks "linearise" time. There are a lot of assumptions built into clocks, though.

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New Theories / Re: In four dimensions, must an object move at c in at least one of them?

« on: 02/12/2024 23:16:44 »

Can I connect my weird description of a 4-dimensional universe to the question of aging for two observers, as in the twins paradox?

Photons don't "age". Aging means you can recall a past, so photons don't because they don't have a past, or a future. All moments of time for the life of a photon's ontological existence, are the same moment, or no moment.

Since photons, or electromagnetic radiation in general has this "time equivalence", it should be possible to quotient the total space with it. This is what a Minkowski spacetime diagram represents, a quotient space.

Then, if the universe of matter is what ages, it must be able to remember a past. I mean, we do so, does our solar system? Does the sun "remember"?
 Well, memory is just a store of information I suppose you could posit a weird kind of argument that matter can remember information about its past. Because it has mass, maybe it has angular momentum which can be construed as a kind of store of energy, and there is definitely a connection between energy and information. Perhaps how much can an atom or a particle with mass "remember" could be a way in.

After all, your brain remembers images you've seen, because electrons in your retinal cells "remembered" what they are meant to do, and did it. What memory is, is the capacity to store, not just recall, information. And erasure for a small memory would be a requirement.

Then clocks--what do clocks remember? What information can a clock store? These questions are relevant to the twin paradox. Clock information is actually a critical factor.