Does time dilation contradict the constancy of light speed?
Post Reply
 
Thread Rating:
  • 0 Votes - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
26-11-2013, 03:15 AM
Does time dilation contradict the constancy of light speed?
The speed at which light waves propagate in vacuum is independent both of the motion of the wave source and of the inertial frame of reference of the observer. This invariance of the speed of light was postulated by Einstein in 1905

So If observer A is travelling on a train travelling at 50mph, and shines a light towards the back of the trainhe would measure the speed of light as 300,000 km/s , Observer B stood stationary outside the train would measure it as 300,000 km/s also. the speed of light being independant of the frames of reference.

Now, if we think on a much bigger scale, (I may get the time changes wrong but just bear with me)

Lets have three points, A, B and C and two observers A and B

Observer A is at point A and emits a light to a receiver 3 light years away at point C
Observer B starts at point A, then when the signal is emitted, travels at an average speed of 1/2c (reference to A) to point B 0.5 light years from A, then travels back and stops at A.

Observer B would suffer time dilation, with their local time being (?)slower than the local time at stationary point A. They will travel to B and back and arrive at point A 2 years after the light was emitted. Less(?) than 2 years would have passed for B, yet he will observe the light arriving at the reciever at exactly the same time as A. So for B the calculations would show that light travelled faster(?) than the speed of light according to his local time.

Does this make sense? Anyone care to offer thoughts on how I must be wrong?
Find all posts by this user
Like Post Quote this message in a reply
26-11-2013, 03:59 AM
RE: Does time dilation contradict the constancy of light speed?
(26-11-2013 03:15 AM)PursuingTruth Wrote:  Does this make sense?
No. Drinking Beverage

[Image: IcJnQOT.gif]
Find all posts by this user
Like Post Quote this message in a reply
26-11-2013, 04:18 AM
RE: Does time dilation contradict the constancy of light speed?
(26-11-2013 03:15 AM)PursuingTruth Wrote:  The speed at which light waves propagate in vacuum is independent both of the motion of the wave source and of the inertial frame of reference of the observer. This invariance of the speed of light was postulated by Einstein in 1905

So If observer A is travelling on a train travelling at 50mph, and shines a light towards the back of the trainhe would measure the speed of light as 300,000 km/s , Observer B stood stationary outside the train would measure it as 300,000 km/s also. the speed of light being independant of the frames of reference.

Now, if we think on a much bigger scale, (I may get the time changes wrong but just bear with me)

Lets have three points, A, B and C and two observers A and B

Observer A is at point A and emits a light to a receiver 3 light years away at point C
Observer B starts at point A, then when the signal is emitted, travels at an average speed of 1/2c (reference to A) to point B 0.5 light years from A, then travels back and stops at A.

Observer B would suffer time dilation, with their local time being (?)slower than the local time at stationary point A. They will travel to B and back and arrive at point A 2 years after the light was emitted. Less(?) than 2 years would have passed for B, yet he will observe the light arriving at the reciever at exactly the same time as A. So for B the calculations would show that light travelled faster(?) than the speed of light according to his local time.

Does this make sense? Anyone care to offer thoughts on how I must be wrong?

AFAIK the situation you describe is a variation of the twins paradox (google it, wiki has a decent article IIRC). Reaching back into dim memories of physics courses long past... the constancy of the speed of light is a feature of special relativity where the observers have inertial reference frames. In the situation you've just described there are accelerations (the observers are not in constant motion but are changing directions and speeds), which throws out the assumption of inertial reference frames and thus cocks up the whole deal. General relativity can deal with the situation in a non-paradoxical way AFAIK but I never got that far...

We'll love you just the way you are
If you're perfect -- Alanis Morissette
(06-02-2014 03:47 PM)Momsurroundedbyboys Wrote:  And I'm giving myself a conclusion again from all the facepalming.
Find all posts by this user
Like Post Quote this message in a reply
26-11-2013, 04:57 AM
RE: Does time dilation contradict the constancy of light speed?




View in playlist: http://www.youtube.com/watch?v=kN_d7eknf...7E&index=5

If you need to understand anything in relativity or quantum physics, viascience (ozmoroid[1]) is your go to guy.

[1] http://www.youtube.com/user/ozmoroid

Give me your argument in the form of a published paper, and then we can start to talk.
Find all posts by this user
Like Post Quote this message in a reply
[+] 1 user Likes Hafnof's post
26-11-2013, 05:07 AM
RE: Does time dilation contradict the constancy of light speed?
So complicated (i need to make a flow chart for this) my brain hurts, fuck it,
the answer is God.

Theism is to believe what other people claim, Atheism is to ask "why should I".
Find all posts by this user
Like Post Quote this message in a reply
[+] 4 users Like sporehux's post
26-11-2013, 05:29 AM
RE: Does time dilation contradict the constancy of light speed?
You can more or less ignore the maths. It's included for completeness Wink

Give me your argument in the form of a published paper, and then we can start to talk.
Find all posts by this user
Like Post Quote this message in a reply
26-11-2013, 08:18 AM
RE: Does time dilation contradict the constancy of light speed?
It is the twin paradox with reference to the speed of light.

Okay.. maybe modify it slightly to remove accelerations.

Observer B is travelling at 0.5c constant velocity from 1 light year away.
Observer A emits a signal to a receiver 2 light years away
When observer B arrives at point A, His time would be different to observer A due to time dilation, yet light would still have arrived at the reciever at that point.
Find all posts by this user
Like Post Quote this message in a reply
26-11-2013, 09:08 AM
RE: Does time dilation contradict the constancy of light speed?
(26-11-2013 08:18 AM)PursuingTruth Wrote:  It is the twin paradox with reference to the speed of light.

Okay.. maybe modify it slightly to remove accelerations.

Observer B is travelling at 0.5c constant velocity from 1 light year away.
Observer A emits a signal to a receiver 2 light years away
When observer B arrives at point A, His time would be different to observer A due to time dilation, yet light would still have arrived at the reciever at that point.

This is answered in special relativity in that the two observers do not observe the events in the same order. i.e. Observer A will say that Observer B arrived at point A at the same time that light reached point C, whereas Observer B will say that he arrived at Point A at a different time to the light reaching point C. Also the two observers may not agree on the *distances* between the two events, which means that they will agree that the light travelled at a constant *speed* but not the distance that it travelled.

Actually in special relativity the real measure is not distance and time, it's space-time which is a combination of the two. The two observers will agree on the separation of the two events in *space-time*, but may disagree on their separation in space or time when space is considered separate to time.

Kinda vague and hand-wavy, but you can always dig deeper...

We'll love you just the way you are
If you're perfect -- Alanis Morissette
(06-02-2014 03:47 PM)Momsurroundedbyboys Wrote:  And I'm giving myself a conclusion again from all the facepalming.
Find all posts by this user
Like Post Quote this message in a reply
26-11-2013, 06:21 PM
RE: Does time dilation contradict the constancy of light speed?
Ozmoroid has the differing orders of events covered under the pole and barn "paradox".




Give me your argument in the form of a published paper, and then we can start to talk.
Find all posts by this user
Like Post Quote this message in a reply
27-11-2013, 03:40 AM
RE: Does time dilation contradict the constancy of light speed?
So, what you are saying is that B will see the light receiver as less than 2 light years away from A? i.e. the path of the light as the ladder and the distance between A and C as the barn?

So the faster you travel you observe things closer together? that will make interstellar parking an issue I am sure Tongue
Find all posts by this user
Like Post Quote this message in a reply
Post Reply
Forum Jump: