Specific Relativity/Light-Speed Question

[EWright]

Under none of these circumstances, worm holes included, would your watch EVER read negative time. Any calculatons that indicate the contrary, result from errors in SR. SR works for most measurements, but this is the area where it leads to paradoxical conclusions that need not be. Loosely speaking, future time travel is possible but you can not then transmit information obtained there back in time... traveling into a past that has already happened is not possible... nor is backward time on your watch when traveling from point A to point B as then perceived at point B.

[Tormod]

EWright, your current signature says the following:

 

There are simply no physical properties of light that cause clocks of faster moving objects to run slower. Therefore, the notion of the speed of light as a determining factor as to why this happens is irrelevant and must be abandoned along with some other notions of special relativity.

 

I would like to turn this question around. Why should the physical properties of light have anything to do with the ticking of clocks?

[EWright]

EWright, your current signature says the following:

 

 

 

I would like to turn this question around. Why should the physical properties of light have anything to do with the ticking of clocks?

 

Exactly. They shouldn't, and they don't. So why does relativity choose to base the dynamics of the entire universe on the speed of light?

[Tormod]

Exactly. They shouldn't, and they don't. So why does relativity choose to base the dynamics of the entire universe on the speed of light?

 

But that is exactly my point. The speed of light is a result of the properties of the universe - not the other way round. Einstein chose c because it is a fundamental property - and relativity is based on c being constant.

 

c is a speed limit. But not only light travels at that speed. Gravity does, and all electromagentic signals (when traveling in vacuum)..

[Erasmus00]

Exactly. They shouldn't, and they don't. So why does relativity choose to base the dynamics of the entire universe on the speed of light?

 

It doesn't. Check out the article "Relativity without Light" by N. David Mermin, American Journal of Physics 1984. Relativity at its core has very little to do with light, light is involved mainly for historical reasons.

-Will

[EWright]

But that is exactly my point. The speed of light is a result of the properties of the universe - not the other way round. Einstein chose c because it is a fundamental property - and relativity is based on c being constant.

 

c is a speed limit. But not only light travels at that speed. Gravity does, and all electromagentic signals (when traveling in vacuum)..

 

BUT... my good friend... I can tell you WHY they travel at this limit. Can you? That is the question at hand.

[EWright]

It doesn't. Check out the article "Relativity without Light" by N. David Mermin, American Journal of Physics 1984. Relativity at its core has very little to do with light, light is involved mainly for historical reasons.

-Will

 

Thank you for that Erasmus00. Your answers are consistantly among the most informative and challenging that I receive. I'll check it out. Still looking for my 'WHY' tho.

[Erasmus00]

Thank you for that Erasmus00. Your answers are consistantly among the most informative and challenging that I receive. I'll check it out. Still looking for my 'WHY' tho.

 

One of the several interconnected reasons that light travels at this speed is that light has no mass, and massless particles must travel at c. (just as particles with mass cannot travel at c).

-Will

[Tormod]

(just as particles without mass cannot travel at c).

 

Shouldn't this read "just as particles with mass..."?

[nkt]

I should point out that there is no proof that gravity travels at the speed of light. Some models show that it needs to travel at the speed of light, and others insist that it is instantaneous.

 

If there is proof, then please cite a reference to it.

[Erasmus00]

Shouldn't this read "just as particles with mass..."?

 

Good call, good call. I edited the post. Brain got away from my fingers or some such. :lol:

-Will

[EWright]

One of the several interconnected reasons that light travels at this speed is that light has no mass, and massless particles must travel at c. (just as particles with mass cannot travel at c).

-Will

 

Well when you zero the universe out at the speed at which massless energy exists, is there really any alternative within the confines of the theory itslef?

 

By the way, I'm now reading Einstein's "Relativity".

[Erasmus00]

I should point out that there is no proof that gravity travels at the speed of light. Some models show that it needs to travel at the speed of light, and others insist that it is instantaneous.

 

If there is proof, then please cite a reference to it.

 

It depends on what you mean by proof? If you consider general relativity the correct model for large scale gravity (as many do) then gravitational disturbances do indeed travel at c. (For an understandable reference, I suggest Hartle "Gravity." Very nice intro textbook. )

-Will

[Tormod]

I should point out that there is no proof that gravity travels at the speed of light. Some models show that it needs to travel at the speed of light, and others insist that it is instantaneous.

 

If there is proof, then please cite a reference to it.

 

http://news.bbc.co.uk/2/hi/science/nature/2639043.stm

[Erasmus00]

Well when you zero the universe out at the speed at which massless energy exists, is there really any alternative within the confines of the theory itslef?

 

By the way, I'm now reading Einstein's "Relativity".

 

What do you mean "zero the universe out at the speed at which massless energy exists?"

 

As for reading Einstein, I suggest learning relativity from a different source. I've always found Einstein terribly difficult reading, and the treatments of relativity have evolved since then. I'm sure googleing around you could find some nice introductions online. Personally, I'm a huge fan of the treatment found in the last few chapters of Kleppner and Kolenkow's Introduction to Mechanics (which I'm sure you can find in a local university library).

-Will

[Guest loarevalo]

I should point out that there is no proof that gravity travels at the speed of light. Some models show that it needs to travel at the speed of light, and others insist that it is instantaneous.

It is a fundamental principle of GR that the effects of gravity cannot be instantenous (as it is in Newtonian Physics), because then gravity would be a signal of speed greater than c, thus contradicting SR.

 

I got to ask: What are gravitational disturbances? They must be waves, or having very similar properties to waves like speed, frequency, period. Would it be accurate to say that gravitational disturbances are waves of space itself? or that space is the medium? What then is the difference between gravitational signals, and other signals like light, which travel through no medium, which is also to say that space is the medium?

[EWright]

It is a fundamental principle of GR that the effects of gravity cannot be instantenous (as it is in Newtonian Physics), because then gravity would be a signal of speed greater than c, thus contradicting SR.

 

Now there's sound, independant reasoning if I ever heard it. Einstein's box is deep.