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According to you to, relativity doesn't work? — tim wood

Within the universe there is a wide range of existents, from very large to very small. Relativity works in the middle area.

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But at what large-scale does it break down? — tim wood

The scale of galaxies, where what is called spatial expansion has an impact, with the requirement for dark energy, dark matter, etc..

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Right, so long as we posit the real existence of those unobservables, dark energy and dark matter, to account for the discrepancies between what is observed and what relativity theory predicts, relativity works just fine.

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I think Gary explained it to you quite well. If I understood correctly, what he said was that for the (material) parts of the universe to get to where they are right now, from the big bang, they must have traveled faster than the speed of light. I did not check his math, but I think this is what he was saying anyway. Does it not make sense to you?

1 - the size of the universe, which on current estimates is more than 98bn light years across - and therefore more than 4 times the widest spread that could be achieved by an exploding singularity at the speed of light. — Gary Enfield

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Ah.

I see.

I really don't see why faster than light possibilities are such a feared thing to consider. — Gary Enfield

Well, apart from the laws of physics becoming inconsistent... yeah, what are folk worried about.

Sorry tim, but your references don't seem to address the issue, and I see no basis for your accusation of "colossal stupidity". But It's not my argument, so I'll leave it at that.

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Sorry, I don't see the relevance, but you can make that conclusion if you want, I will not.

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A review of the videos will persuade anyone that the whole matter is just plain not that simple. For example, what exactly is the speed of light? What does it mean? How and by whom measured, under what circumstances and contexts. — tim wood

I think that's exactly the point of the op, designating "the speed of light" as a constant has been proven to be a mistake.

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As I said, it's not my argument, so those questions I'll ignore. I was just pointing out some issues I had with what you were saying. Those questions you propose are irrelevant to the points I made.

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Well, apart from the laws of physics becoming inconsistent... yeah, what are folk worried about. — Banno

Hi Banno

I don't think there are inconsistencies..
The Laws concerning movement won't be affected by the possibility that travel faster than light is possible.

In practical terms, the only things that would be affected in our Earth-bound circumstances are the potential amounts of energy being released in a nuclear explosion - because it is only when you get to those levels that we get to anything near the factors that the speed of light would affect.

Given that the energy from even detonated nuclear explosions, (which we have tried to measure as verification of estimates), can themselves only be estimated by their effects, the potential reality exposed by the size and age of the universe will have no practical impact on the application of our current descriptive laws.

I think Gary explained it to you quite well. If I understood correctly, what he said was that for the (material) parts of the universe to get to where they are right now, from the big bang, they must have traveled faster than the speed of light. I did not check his math, but I think this is what he was saying anyway. Does it not make sense to you? — Metaphysician Undercover

Thanks for that "MU".
The maths is quite simple....

The age of the universe is now agreed at approx 13.7 billion years.
An explosion at the speed of light would travel outwards 13.7 billion light years in that time.
However that is only a radius, so that distance has to be doubled for the diameter.
So 27.4 billion light years should therefore be the maximum diameter but scientists/cosmologists agree that the universe is at least 96billion light years across.

Hope that helps.

Maybe. Seems far more likely that you haven't quite grasped relativistic physics.

The assumption is that he laws of physics are the same for every observer - that they are consistent. But the speed of light can be derived from Maxwell's equations. Hence the speed of light must be the same for every observer.

The equations of relativity explain how this can be accounted for in a consistent fashion. Those equations also show that no mass can travel faster than the speed of light.

Hence if something were to travel faster than light, the laws of physics could not be the same for every observer.

They would be inconsistent.

Hi Banno

An interesting reply - thank you.

As I understand it, Maxwell's equations only demonstrate how we consistently perceive light.
The size of the universe is a measurement within our perception.

Those equations also show that no mass can travel faster than the speed of light. — Banno

They only do this I believe because they assume a fixed c. That is not proof - it simply says that there might not be anything that could push faster.

However, what is to say that the special circumstances of the Big Bang wouldn't create a faster push?

Maxwell's equations only demonstrate how we consistently perceive light. — Gary Enfield

They are correct for any observer.

They only do this I believe because they assume a fixed c. — Gary Enfield

The laws of physics dictate the speed of light. Hence, if the laws of physics are the same for all observers, then the speed of light must be the same for all observers.

Seems far more likely that you haven't quite grasped relativistic physics. — Banno

What is the case is that separation caused by spatial expansion, is not considered to be properly called spatial "motion". Very large objects like galaxies get further apart without actually moving at all, because spatial expansion does not qualify as "motion". Since this activity of separating from each other, due to spatial expansion, is not a form of "motion", material things can separate at rates which are much faster than the speed of light, without violating principles of relativity, because within the confines of that theoretical structure, this does not qualify as "motion".

You ought to be able to see, that in the effort to maintain general relativity as the applicable theory for motions in the universe, we have now developed a whole new category of motion which does not qualify as "motion", because "motion" is defined by that theory. In other words, if we want all the types of motion which we have observational evidence for in the universe, to be measurable within one consistent theory of motion, we need a different theory. General relativity does not allow that this type of motion which is the result of spatial expansion is "motion".

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You've misunderstood. But that's what you do. General Relativity is about curved space-time, but you treat that as if it were an ad hoc hypothesis added after the fact.

I'm regretting answering any of your posts, Meta. You inhabit a weird meta-world were explanations don't serve any purpose. Enjoy.

General Relativity is about curved space-time... — Banno

Right, and special relativity is about curved space-time too ... not. Yet they're still both "relativity". I think you're missing something there Banno. General relativity is how the principles of special relativity are adapted to account for gravity.

You are inhabited by some strange mind which thinks it knows what it obviously does not. So you haven't the foggiest clue how to explain anything.

You are inhabited by some strange mind which thinks it knows what it obviously does not. So you haven't the foggiest clue how to explain anything. — Metaphysician Undercover

:rofl:

When reading Meta's views on physics, one should keep in mind that he rejects the notion of instantaneous velocity.

The speed of light can be derived directly from Maxwells' equations. That is, it is as much a part of physical law as F=ma and v=u+at.