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Author Topic: Can an observer ever experience superluminal speeds?  (Read 5498 times)

Online jeffreyH

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Consider an orbit around a black hole that is reducing in radius. The intensity of the gravitational field will cause time dilation which is supposed to eventually stop light. If the observer is in an orbit that has reached relativistic speeds and and is increasing then he is experiencing an extreme time dilation. Will the motions of the stars that he observes tell him that he has exceeded the speed of light. As his time has slowed down yet his speed around the orbit is constant and relativistic then at some point shouldn't he make an estimate that convinces him of reaching superliminal speed? I am neglecting the tidal effects for the purposes of this thought experiment so I don't expect the obvious counter arguments about being torn apart etc etc. That is not the point of this post.
« Last Edit: 31/01/2015 11:53:07 by chris »


 

Offline yor_on

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Re: Can an observer ever experience superlumonal speeds?
« Reply #1 on: 27/01/2015 12:36:20 »
It's a interesting idea Jeffrey, as I like to bind time to 'c'. Locally defined time will continue for you as long as the constant holds. Looking out at a universe then? Comparing your local clock to some stars 'flickering', can those flickers pass 'c'? I don't think so. I think it would be very hard to test experimentally though, as you need a instrument sensitive enough to differ between something 'flickering' at 'c', and above, versus something presenting you with a constant light flow. That instrument should actually prove 'ftl' just by itself, if existing. Time has limits it seems if you define it my way, the limits are between what happens at Planck scale, relative what we measure to be 'c'.

As for the idea of going very fast, close to light speed, looking at a universe evolving. As long as you're of rest mass, you won't get to 'c'. 'Photons' are the definition of 'c', but they have a speed. There is nothing measurable that is faster in a (perfect) vacuum. And it shouldn't matter if we define its path as 'curved', the speed should be the same at each instant of its 'propagation'.


« Last Edit: 27/01/2015 12:46:10 by yor_on »
 

Online jeffreyH

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Re: Can an observer ever experience superlumonal speeds?
« Reply #2 on: 27/01/2015 15:00:34 »
It's a interesting idea Jeffrey, as I like to bind time to 'c'. Locally defined time will continue for you as long as the constant holds. Looking out at a universe then? Comparing your local clock to some stars 'flickering', can those flickers pass 'c'? I don't think so. I think it would be very hard to test experimentally though, as you need a instrument sensitive enough to differ between something 'flickering' at 'c', and above, versus something presenting you with a constant light flow. That instrument should actually prove 'ftl' just by itself, if existing. Time has limits it seems if you define it my way, the limits are between what happens at Planck scale, relative what we measure to be 'c'.

As for the idea of going very fast, close to light speed, looking at a universe evolving. As long as you're of rest mass, you won't get to 'c'. 'Photons' are the definition of 'c', but they have a speed. There is nothing measurable that is faster in a (perfect) vacuum. And it shouldn't matter if we define its path as 'curved', the speed should be the same at each instant of its 'propagation'.

I am not implying that an observer actually achieves superluminal velocity just that the time dilation makes him believe he has.
 

Offline yor_on

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Re: Can an observer ever experience superlumonal speeds?
« Reply #3 on: 27/01/2015 17:41:30 »
Well, in that case I think it could be described that way, although I'm not sure, as they should be finding the distance to 'shrink' in the direction of them traveling. Then again, as you point out you also find this time dilation, that will change everything for those moving at such speed. They will have nothing to go back too, everything being dust.
=

It won't change anything locally defined, for those traveling though. They do not become immortal, and their life spans, as in the amount of heartbeats available for each one, should be about the same as if never setting a foot on any space ship. It's a relation between all other 'universal clocks' and the spaceships 'clock'. 'Locally defined' neither the ships, nor any of the other clocks starts behaving differently. We're looking at this situation with the 'eyes of a God' describing it. And why we do it without considering is because we all find us sharing this same universe.

And the reason for that is not 'universal time', instead it's casualty's demands, giving us a ordered universe in where we can find, and follow, a logic of events. And that one covers time symmetries too. There is one thing though, causality is a measurable logic, as in a Lorentz transformation. And that, to me then, talks also about something 'more', allowing it to exist.
« Last Edit: 27/01/2015 18:09:55 by yor_on »
 

Offline PmbPhy

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Re: Can an observer ever experience superluminal speeds?
« Reply #4 on: 02/02/2015 11:49:45 »
Quote from: jeffreyH
Consider an orbit around a black hole that is reducing in radius. The intensity of the gravitational field will cause time dilation which is supposed to eventually stop light. If the observer is in an orbit that has reached relativistic speeds and and is increasing then he is experiencing an extreme time dilation. Will the motions of the stars that he observes tell him that he has exceeded the speed of light.
He will never exceed the speed of light according to any observer.

Quote from: jeffreyH
As his time has slowed down yet his speed around the orbit is constant and relativistic then at some point shouldn't he make an estimate that convinces him of reaching superliminal speed?
No. Never. In fact, according to him, he's always at rest in his own locally inertial frame of reference.
 

Online jeffreyH

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Re: Can an observer ever experience superluminal speeds?
« Reply #5 on: 02/02/2015 13:20:44 »
Quote from: jeffreyH
Consider an orbit around a black hole that is reducing in radius. The intensity of the gravitational field will cause time dilation which is supposed to eventually stop light. If the observer is in an orbit that has reached relativistic speeds and and is increasing then he is experiencing an extreme time dilation. Will the motions of the stars that he observes tell him that he has exceeded the speed of light.
He will never exceed the speed of light according to any observer.

Quote from: jeffreyH
As his time has slowed down yet his speed around the orbit is constant and relativistic then at some point shouldn't he make an estimate that convinces him of reaching superliminal speed?
No. Never. In fact, according to him, he's always at rest in his own locally inertial frame of reference.

I am not convinced on this point Pete.
 

Offline PmbPhy

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Re: Can an observer ever experience superluminal speeds?
« Reply #6 on: 02/02/2015 14:41:52 »
Quote from: jeffreyH
Consider an orbit around a black hole that is reducing in radius. The intensity of the gravitational field will cause time dilation which is supposed to eventually stop light. If the observer is in an orbit that has reached relativistic speeds and and is increasing then he is experiencing an extreme time dilation. Will the motions of the stars that he observes tell him that he has exceeded the speed of light.
He will never exceed the speed of light according to any observer.

Quote from: jeffreyH
As his time has slowed down yet his speed around the orbit is constant and relativistic then at some point shouldn't he make an estimate that convinces him of reaching superliminal speed?
No. Never. In fact, according to him, he's always at rest in his own locally inertial frame of reference.

I am not convinced on this point Pete.
Why?
 

Offline Bill S

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Re: Can an observer ever experience superluminal speeds?
« Reply #7 on: 02/02/2015 20:30:20 »
Quote from: Jeffrey
Consider an orbit around a black hole that is reducing in radius. The intensity of the gravitational field will cause time dilation which is supposed to eventually stop light.

Surely, light does not stop. The gravitational field will cause it to bend increasingly, and time dilation will influence how an outside observer sees it, but light will not stop; or am I misunderstanding things?
 

Online jeffreyH

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Re: Can an observer ever experience superluminal speeds?
« Reply #8 on: 02/02/2015 20:39:04 »
Quote from: jeffreyH
Consider an orbit around a black hole that is reducing in radius. The intensity of the gravitational field will cause time dilation which is supposed to eventually stop light. If the observer is in an orbit that has reached relativistic speeds and and is increasing then he is experiencing an extreme time dilation. Will the motions of the stars that he observes tell him that he has exceeded the speed of light.
He will never exceed the speed of light according to any observer.

Quote from: jeffreyH
As his time has slowed down yet his speed around the orbit is constant and relativistic then at some point shouldn't he make an estimate that convinces him of reaching superliminal speed?
No. Never. In fact, according to him, he's always at rest in his own locally inertial frame of reference.

I am not convinced on this point Pete.
Why?

I can't quite put my finger on it yet.
 

Offline PmbPhy

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Re: Can an observer ever experience superluminal speeds?
« Reply #9 on: 02/02/2015 20:41:09 »
That's correct. Jeff has it wrong. The light will never stop. It will only come arbitrarily close to having a speed of zero. I think to Jeff it means that it stops in the limit as t goes to infinity. However there is never an actual value of t for which that's true.
 

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Re: Can an observer ever experience superluminal speeds?
« Reply #10 on: 02/02/2015 21:50:57 »
I did say did I not "which is supposed to top light". This does not imply in any way I believe that light stops. It also doesn't imply that I don't believe it. It is simply a statement of a certain view.
 

Offline PmbPhy

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Re: Can an observer ever experience superluminal speeds?
« Reply #11 on: 02/02/2015 22:04:44 »
I did say did I not "which is supposed to top light". This does not imply in any way I believe that light stops. It also doesn't imply that I don't believe it. It is simply a statement of a certain view.
Come on, Jeff. Let the crazies use semantics for that purpose. You're too good for that. If you're referring to a view then it's obvious that I was thus speaking to the view and not you. It's tiring worry about semantics like this. You're too good for that my dear friend. :)

E.g. a good response would have been something like "In actuality you're speaking to the view that's wrong and not me since I was speaking about a particular viewpoint." Otherwise it seems like you're getting defensive and I don't read minds so I can't tell and I certainly don't want to put you on the defense. You're my friend and I don't want to do that to my friends. Okay buddy? :D
 

Online jeffreyH

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Re: Can an observer ever experience superluminal speeds?
« Reply #12 on: 03/02/2015 00:23:44 »
Enough said. On another note, would you consider the gravitational field to have a density? I am asking simply because I don't know.
 

Offline PmbPhy

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Re: Can an observer ever experience superluminal speeds?
« Reply #13 on: 03/02/2015 06:01:09 »
Enough said. On another note, would you consider the gravitational field to have a density? I am asking simply because I don't know.
It sounds familiar. Something related to gravitational energy. Look that up or along those lines.
 

Offline JohnDuffield

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Re: Can an observer ever experience superluminal speeds?
« Reply #14 on: 03/02/2015 11:58:18 »
Quote from: Bill S
...or am I misunderstanding things?
The latter! I've started a thread to tease this one out. 
 

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Re: Can an observer ever experience superluminal speeds?
« Reply #15 on: 03/02/2015 18:31:25 »
Enough said. On another note, would you consider the gravitational field to have a density? I am asking simply because I don't know.
It sounds familiar. Something related to gravitational energy. Look that up or along those lines.

I found this but don't know how valid it is.

http://www.grc.nasa.gov/WWW/k-12/Numbers/Math/Mathematical_Thinking/possible_scalar_terms.htm
 

Online jeffreyH

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Re: Can an observer ever experience superluminal speeds?
« Reply #16 on: 03/02/2015 20:01:24 »
I think I must have been having an off day when I started this thread. My thought processes seemed to have broken down at that point. No wonder with all the mathematics I have been stuffing into my head.
 

Offline yor_on

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Re: Can an observer ever experience superluminal speeds?
« Reply #17 on: 10/02/2015 11:16:03 »
It's not a bad thread Jeffrey.
It's ok to question.
 

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Re: Can an observer ever experience superluminal speeds?
« Reply #17 on: 10/02/2015 11:16:03 »

 

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