B What is the physics of motion through space?

[Grinkle]

Shan Gao makes an argument that this postulate leads directly to a maximum signal speed and its invariance

Is Shan Gao making an argument that the experimental observation of an invariant maximum signal speed implies spacetime is discrete?

 

[bahamagreen]

Is Shan Gao making an argument that the experimental observation of an invariant maximum signal speed implies spacetime is discrete?

I don't think so, better to judge for yourself; paper is titled On the invariance of the speed of light

 

[Grinkle]

@bahamagreen Thanks. I also don't read him to be arguing in that direction.

 

[Netspirit]

I'd like to thank everyone who contributed to the thread. I have read all your replies, but I cannot respond to every one without turning my post into an unreadable mess.

@bahamagreen is right about some of the things that puzzle me.

One is the mentioned disconnect between the coordinates plus their first derivative (which seem relative and therefore suspicious - like those projections of the same fish on the different walls of the aquarium - an effect sometimes used to speculate about the nature of quantum entanglement) and higher-order derivatives like acceleration, change in acceleration, etc. (which seem objective and linked to physical forces). For example, it feels non-intuitive how photons, traveling at the speed of light, allegedly "experience zero time" and, from their perspective, "instantly" connect the emitter (cause) with the absorber (effect) - as if both were directly adjacent on some deeper dimension (unlike their observer-specific spacetime "projections").

The other puzzle is whether the Universe is an emergent phenomenon so the properties of spacetime, such as the speed of light limit, have local, quantum origins (such as the abovementioned relationship between the Planck units). I admit I find geometric explanations of motion to be utterly boring, since they only seem to describe how objects move, not explain why they do - which is very practical, but seems like a problem already solved 100 years ago, with not much potential for surprising discoveries.

(Peter is right - let me read up on QFT).
Thanks again everyone!

 

[Nugatory]

For example, it feels non-intuitive how photons, traveling at the speed of light, allegedly "experience zero time" and, from their perspective, "instantly" connect the emitter (cause) with the absorber (effect) - as if both were directly adjacent on some deeper dimension (unlike their observer-specific spacetime "projections").

That's easy - just look at the word "allegedly". The allegation is false and a pretty good rule of thumb is that if whatever you're learning from says things like that, you're wasting your time with that source.

I admit I find geometric explanations of motion to be utterly boring, since they only seem to describe how objects move, not explain why they do

However, that's all that empirical science ever does. On close scrutiny, all scientific explanations of why something works the way it does turn out to be statements of how the universe behaves, not why.

 

[Herman Trivilino]

For example, it feels non-intuitive how photons, traveling at the speed of light, allegedly "experience zero time" and, from their perspective, "instantly" connect the emitter (cause) with the absorber (effect) - as if both were directly adjacent on some deeper dimension (unlike their observer-specific spacetime "projections")

If you look at the definition of proper time, you see that the notion of proper time doesn't exist for a particle moving at speed $c$. That is not the same thing as saying the proper time is zero. Although a phrase like "there is no time experienced" doesn't make that distinction clear (if at all) and is therefore open to misinterpretation. Some authors seem to propagate that misunderstanding, either on purpose or because they are unaware of the distinction.