I remember something about an electron bean moving FTL in one of my college textbooks, forget if it was Halliday & Resnick or the next one (propbably, that was all post 1905 stuff) but there was a question concerning it. As a "beam" is nothing physical irrespective of what it is made of there is nothing preventing it from going at any speed.

A "beam" is just a linguistic term for some things moving sequentially somewhere, and linguistic terms are quite exempt from relativity.

 

Electrons are matter, matter is constrained by FTL. A beam is a physical description, a layout. No FTL there.

Two beams crossing is nonphysical, so you have have an intersection moving at an apparent FTL rate, but it isn't physical.

 

I thought crossing the beams was bad!

 

According to Hubble's Law, two galaxies that are a distance D apart are moving away from each other at a speed HD, where H is Hubble's constant. So this interpretation of Hubble's Law implies that two galaxies are separated by a distance greater than c/H must be moving away from each other faster than the speed of light.
Actually, the modern viewpoint describes this situation differently: general relativity takes the galaxies as being at rest relative to one another, while the space between them is expanding. In that sense, the galaxies are not moving away from each other faster than the speed of light; they are not moving away from each other at all!
This change of viewpoint is not arbitrary; rather, it's in accord with the different but very fruitful view of the universe that general relativity provides. So the distance between two objects can be increasing faster than light because of the expansion of the universe, but this does not mean, in fact, that their relative speed is faster than light.

http://www.youtube.com/watch?annotation_id=annotation_215146&feature=iv&v=myjaVI7_6Is

am confused , a galaxy has a mass but it moves faster than the speed of light ? How is that possible !

 

According to Hubble's Law, two galaxies that are a distance D apart are moving away from each other at a speed HD, where H is Hubble's constant. So this interpretation of Hubble's Law implies that two galaxies are separated by a distance greater than c/H must be moving away from each other faster than the speed of light.
Actually, the modern viewpoint describes this situation differently: general relativity takes the galaxies as being at rest relative to one another, while the space between them is expanding. In that sense, the galaxies are not moving away from each other faster than the speed of light; they are not moving away from each other at all!
This change of viewpoint is not arbitrary; rather, it's in accord with the different but very fruitful view of the universe that general relativity provides. So the distance between two objects can be increasing faster than light because of the expansion of the universe, but this does not mean, in fact, that their relative speed is faster than light.

Nope, I've heard that arguement, and it still doesn't wash. I have read no crediable source that discredits or disputes General Relativity, and this includes expansion of the universe.

FTL still remains a pipe dream, much as I would wish otherwise.

Welcome to the Fray!

I've made this point before, but if we are galaxy A, and galaxy B and C are both receding 2/3 C from us, they are still not going faster than light away from each other. From our point of view neither is going FTL, and if you were to move to either galaxy we and the other galaxy would still be moving under C. Relativity is all about point of view. From anyones point of view nothing moves FTL.

 

Probably we should do more research then . . .

Nope, I've heard that arguement, and it still doesn't wash. I have read no crediable source that discredits or disputes General Relativity, and this includes expansion of the universe.

 

I understand the theory of relativity very well. I'm pretty sure you don't though.

See post #17.

 

Nope, I've heard that arguement, and it still doesn't wash. I have read no crediable source that discredits or disputes General Relativity, and this includes expansion of the universe.

Bill, with all due respect, it is your interpretation here that is in error.

For a 3rd party observer, two objects can be moving apart faster than the speed of light. This is NOT in contradiction to relativity, general or special. Your example below is a perfect case. Galaxy A will measure that galaxy B and C are moving away from each other at 4/3 C. That is a speed (distance/time) and it is greater than C.

I've made this point before, but if we are galaxy A, and galaxy B and C are both receding 2/3 C from us, they are still not going faster than light away from each other. From our point of view neither is going FTL, (from our perspective, they are moving away from each other at faster than C) and if you were to move to either galaxy we and the other galaxy would still be moving under C. Relativity is all about point of view. From anyones point of view nothing moves FTL.

 

The point is, neither is moving faster than C from your point of view. If you were on either galaxy neither of the two points would be moving faster than C from that new point of view. That is the point of the theory of relativity. No matter where you are standing, nothing moves faster than C to you.

 

http://www.youtube.com/watch?annotation_id=annotation_215146&feature=iv&v=myjaVI7_6Is

am confused , a galaxy has a mass but it moves faster than the speed of light ? How is that possible !

First, relativity only deals with objects moving away from each other through the 'fabric' of space-time. The maximum velocity of C is WRT that 'fabric'. So, given that alone, a 3rd observer can observe the distance between galaxies as increasing at up to 2C.

2nd, there is nothing within relativity that prevents space-time from expanding faster than C. There have been galaxies known for many years that are farther apart than they could get, given the age of the universe , if they were restricted to the speed of light. More recently other galaxies have been found that demonstrate this to a much greater extent and show cosmological red shifts in excess of 8. A red shift of just under 1.4 would indicate a relative velocity of C. Quite simply put, given the age of the universe, it is far larger than it could possibly be if object in it were limited to moving apart at C.

Just let me re-iterate, none of this invalidates Einstein's work. Quite the contrary, it supports it.

 

The point is, neither is moving faster than C from your point of view. If you were on either galaxy neither of the two points would be moving faster than C from that new point of view. That is the point of the theory of relativity. No matter where you are standing, nothing moves faster than C to you.

I agree. Nothing can move through space faster than C.