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Shayne T
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How close to the speed of light would you have to travel to be able to traverse the entire span of the known universe(94 billion light years i think?) in a persons 80 year lifetime?
What about Lorentz?Brian E said:.If you travel with the speed of light, for 80 years you will move a distance of 80 light years. So your question does not make any sense
... and here I thought you were cleverly pointing the OP down the path to realizing the solution! Your post was correct: as phrased the problem does not make sense. Pointing this out could lead to OP phrasing the problem better and then coming to a realization :)Brian E said:I think you are trying to tell me, that I should not reply to questions, when I am not able to give correct answers. I know about the Lorentz transformation, but did not take that into account, my bad :-) I will be more careful in the future :-)
Never let that get in the way. Your initial answer was 'reasonable' as a first stab; before Einstein, it would have been everyone's answer. And people will always enjoy putting you right.Brian E said:I think you are trying to tell me, that I should not reply to questions, when I am not able to give correct answers. I know about the Lorentz transformation, but did not take that into account, my bad :-) I will be more careful in the future :-)
From what I've gathered, this would be true for any outside observer who were not traveling at near light speeds. I guess a better way to put it, would be how close to the speed of light would you need to go in order to achieve a time dilation factor of 94billion:80 (traveller experiences time at a decelerated rate of 1.175 billion times less than a stationary observer left home at earth)Brian E said:.If you travel with the speed of light, for 80 years you will move a distance of 80 light years. So your question does not make any sense
Regarding your comment on the frame of a photon, I've always had trouble wrapping my brain around the following. If special relativity states that time approaches 0 as velocity approaches c, and photons are the only thing able to actually reach c, do photons not experience time? And if something that is moving, which does not experience time, wouldn't it, from its own frame of reference, instantaneously exist everywhere in the universe?sophiecentaur said:Never let that get in the way. Your initial answer was 'reasonable' as a first stab; before Einstein, it would have been everyone's answer. And people will always enjoy putting you right.
Relativity certainly introduced a load of new concepts. The 'frame of a photon' is now a nonsense concept, in many ways.
Formally - you have proper distance d in frame S, and you want observer in frame S' traveling with relative speed v (wrt S) to traverse that distance in S in coordinate time t' or less. The time in S to traverse d is going to be ##t=d/v = \gamma t'## so solve for v.Shayne T said:From what I've gathered, this would be true for any outside observer who were not traveling at near light speeds. I guess a better way to put it, would be how close to the speed of light would you need to go in order to achieve a time dilation factor of 94billion:80 (traveller experiences time at a decelerated rate of 1.175 billion times less than a stationary observer left home at earth)
This question is meaningless in special relativity.Regarding your comment on the frame of a photon, I've always had trouble wrapping my brain around the following. If special relativity states that time approaches 0 as velocity approaches c, and photons are the only thing able to actually reach c, do photons not experience time?
Everything is stationary in their own reference frame. So to which observer do you think something could be considered "everywhere in the Universe"? Surely all observers agree that the photon exists in only one place at a time?And if something that is moving, which does not experience time, wouldn't it, from its own frame of reference, instantaneously exist everywhere in the universe?
Photons don't have a frame of reference. When someone says "the frame of reference of <something>", that's a convenient shortcut for the more precise "a frame of reference in which that something is at rest"... But a photon is moving at speed c in all frames, so there can be no frame in which it is at rest.Shayne T said:from its own frame of reference...
To put the question in context and to show that there is an answer (however impractical), it's worth while mentioning the 'Muon' experiment, which dramatically demonstrates how a fast traveling 'observer' perceives time differently.Shayne T said:How close to the speed of light would you have to travel to be able to traverse the entire span of the known universe(94 billion light years i think?) in a persons 80 year lifetime?
No, according to Einstein's theory of relativity, the speed of light is the ultimate speed limit in the universe. Nothing can travel faster than the speed of light.
As an object approaches the speed of light, it will experience time dilation and length contraction. This means that time will slow down for the object and its length will appear to shrink from an observer's perspective.
While it is theoretically possible to achieve the speed of light, it would require an infinite amount of energy. Therefore, it is currently not possible for us to travel at the speed of light.
The speed of light limit applies to all objects with mass. However, photons, which are particles of light, do not have mass and can travel at the speed of light.
If an object were able to travel at the speed of light, it would experience infinite mass and time would stand still for the object. It would also require an infinite amount of energy to accelerate to that speed.