A question on Special Relativity

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Discussion Overview

This thread explores concepts related to Einstein's theory of Special Relativity, focusing on the implications of traveling at relativistic speeds, time dilation, and the nature of light and photons. Participants discuss various interpretations and questions surrounding these topics, including the aging of objects in motion and the behavior of light from different reference frames.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification
  • Mathematical reasoning

Main Points Raised

  • One participant suggests that if an object travels at half the speed of light, it would age half as quickly as a stationary object, prompting questions about the accuracy of this interpretation.
  • Another participant challenges this claim, stating that the relationship between speed and time dilation is not additive but rather involves the squares of the fractions of the speed of light and time dilation.
  • Questions arise regarding the nature of photons and their relationship to time, with one participant positing that if photons travel at the speed of light, time must stand still for them, leading to confusion about how they can be observed by stationary observers.
  • Some participants discuss the implications of a photon having no frame of reference, asserting that it does not make sense to consider a photon's perspective on time.
  • A participant raises a hypothetical scenario involving a camera taking snapshots of a photon’s journey, questioning whether the snapshots would capture the photon or remain blank due to the nature of time and light travel.

Areas of Agreement / Disagreement

Participants express differing views on the implications of Special Relativity, particularly regarding time dilation and the behavior of light. There is no consensus on the interpretations presented, and multiple competing views remain throughout the discussion.

Contextual Notes

Some claims rely on specific interpretations of relativistic effects and may depend on the definitions used for speed and time. The discussion includes unresolved mathematical relationships and assumptions about the nature of light and reference frames.

alexela
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Hi,
I don't study Physics at school, so please excuse me if i sound crude or miseducated.

I was reading about Einsteins theory of Special Relativity, and was wondering if i understand it correctly. In the book it states that einstein proposed that the speed of motion of a body through space and time combined, adds up to the sum total of the speed of light?
So if something were to travel at half the speed of light through space, then it would age half as quickly than something stationary in space?

is this correct?

i would appreciate any help. thanks
 
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alexela said:
Hi,
I don't study Physics at school, so please excuse me if i sound crude or miseducated.

I was reading about Einsteins theory of Special Relativity, and was wondering if i understand it correctly. In the book it states that einstein proposed that the speed of motion of a body through space and time combined, adds up to the sum total of the speed of light?
So if something were to travel at half the speed of light through space, then it would age half as quickly than something stationary in space?

is this correct?

i would appreciate any help. thanks

Yes, that is basically correct. You would probably find it interesting to Google "the twin paradox", which will explain it a bit more.
 
If "something were to travel at half the speed of light through space, then it would age half as quickly than something stationary in space" IS ALL WRONG!
Wait until you study relativity somewhere to try to understand it.
 
Thanks,
This brings another question to my attention.
If a photon travels at the speed of light through space, then how can it travel through time?
Surely, in the instant that the photon reached the speed of light, time would stand still relative to it. However, for a stationary observer of the photon, time would continue as normal, and so in the next instant would the observer see the photon if it can no longer traverse time to the second instant, or is it trapped forever in the past?
I know this sounds stupid because our eyes work and we can see light, but somehow the question makes sense to me.
 
alexela said:
Thanks,
This brings another question to my attention.
If a photon travels at the speed of light through space, then how can it travel through time?
Surely, in the instant that the photon reached the speed of light, time would stand still relative to it.
Excellent point, and basically correct, although photons don't "reach the speed of light" since that would imply that they were NOT going at the speed of light just before they reached it and that doesn't happen. They travel at c as soon as them come into existence.

Your point above is the basis for what it is that there is no such thing as "the frame of reference of a photon". It just doesn't make sense.

However, for a stationary observer of the photon, time would continue as normal, and so in the next instant would the observer see the photon if it can no longer traverse time to the second instant, or is it trapped forever in the past?
I know this sounds stupid because our eyes work and we can see light, but somehow the question makes sense to me.

I'm afraid I'm not following you on that one.
 
alexela said:
Hi,
I don't study Physics at school, so please excuse me if i sound crude or miseducated.

I was reading about Einsteins theory of Special Relativity, and was wondering if i understand it correctly. In the book it states that einstein proposed that the speed of motion of a body through space and time combined, adds up to the sum total of the speed of light?
So if something were to travel at half the speed of light through space, then it would age half as quickly than something stationary in space?

is this correct?

i would appreciate any help. thanks
That's not quite correct. If you represent the speed of motion of a body as a fraction of the speed of light (a number between 0 and 1) and you also represent the amount of time slowing down by a fraction (again a number between 0 and 1) then the relationship between these two numbers is not that their sum equals 1 but rather the squares of the two numbers adds up to 1.

So if you were going at .6 the speed of light, your time would be going at .8 of normal because .62 + .82 = .36 + .64 = 1.

If you tried this with both numbers at .5 you would get .52 + .52 = .25 + .25 = .5, which does not equal 1.
 
alexela said:
However, for a stationary observer of the photon, time would continue as normal, and so in the next instant would the observer see the photon if it can no longer traverse time to the second instant, or is it trapped forever in the past?
I know this sounds stupid because our eyes work and we can see light, but somehow the question makes sense to me.
thats a brilliant question (atleast for me) i had a similar doubt in this thread
https://www.physicsforums.com/showthread.php?t=566430

however i dint understand ghwellsjr's sol given over there. bobc2's explanation looked ok
 
ghwellsjr said:
That's not quite correct. If you represent the speed of motion of a body as a fraction of the speed of light (a number between 0 and 1) and you also represent the amount of time slowing down by a fraction (again a number between 0 and 1) then the relationship between these two numbers is not that their sum equals 1 but rather the squares of the two numbers adds up to 1.

So if you were going at .6 the speed of light, your time would be going at .8 of normal because .62 + .82 = .36 + .64 = 1.

If you tried this with both numbers at .5 you would get .52 + .52 = .25 + .25 = .5, which does not equal 1.

Thank you very much, that's the kind of answer i was looking for, something i can learn a bit from.
 
phinds said:
Excellent point, and basically correct, although photons don't "reach the speed of light" since that would imply that they were NOT going at the speed of light just before they reached it and that doesn't happen. They travel at c as soon as them come into existence.

Your point above is the basis for what it is that there is no such thing as "the frame of reference of a photon". It just doesn't make sense.



I'm afraid I'm not following you on that one.

yes i have probably got confused, i guess what i mean in a rough and exagerated example is that, if you were to conduct an experiment in which you had a camera to take snap shots of a photons journey through space, and it was set to take continuous snapshots, the photon would appear in the snap shot which was taken at the same time the photon came into existence. But then, for the photon time would stand still, if the photon were to look over at the camera it would have ceased to take any more snap shots, but as an observer behind the camera it will continue clicking away. Although the photon can move freely around space at c without any time elapsing from its moment of creation, for the camera time would continue, and my question is would the snap shots taken after the photon was created be blank because they were taken at a time that the photon hasn't progressed to?
 
  • #10
alexela said:
yes i have probably got confused, i guess what i mean in a rough and exagerated example is that, if you were to conduct an experiment in which you had a camera to take snap shots of a photons journey through space, and it was set to take continuous snapshots, the photon would appear in the snap shot which was taken at the same time the photon came into existence. But then, for the photon time would stand still, if the photon were to look over at the camera it would have ceased to take any more snap shots, but as an observer behind the camera it will continue clicking away. Although the photon can move freely around space at c without any time elapsing from its moment of creation, for the camera time would continue, and my question is would the snap shots taken after the photon was created be blank because they were taken at a time that the photon hasn't progressed to?
How does a camera take a snapshot? Have you ever thought about it? Does a camera take pictures of light in transit? Or does it take pictures of other things in transit that are illuminated by light that reflects off of those things? If you had a high speed bullet, light would reflect off of it and come back into the camera and you take a series of snapshots to show its progress. But how would you capture the progress of a flash of light? (Let's make it brighter than an individual photon.)
 
  • #11
alexela said:
... if the photon were to look over at the camera ...

If I understand it correctly, this kind of thinking is a fundamental flaw in such thought experiments. Simply put, there is no frame of reference for a photon and as soon as you assume one you leave the real of the real world, after which point, you can come to any conclusion you like, because it follows from a fallacy.
 

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