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jaketodd
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How fast does time elapse for us from the point of view of a photon watching us?
Thanks,
Jake
Thanks,
Jake
Fredrik said:See https://www.physicsforums.com/showthread.php?p=2650120.
(Also, your question kind of contradicts itself, since "for us" sounds like reference to our point of view. I'm guessing you meant to ask how fast our clocks are from a photon's point of view).
Matterwave said:From the point of view of a particle moving very close to the speed of light, our clocks are moving extremely slow.
Time dilation, not time contraction. ;)
Matterwave said:I know, but the implication that to the particle our clocks moving faster would imply time contraction.
If we insist on defining his "point of view" at any event on his world line (the curve in spacetime that represents his motion) as the co-moving inertial frame at that point, then he would "see" the clocks on Earth tick ahead with an enormous rate as he slows down to a stop (relative to Earth) and starts speeding up in the opposite direction. (I don't mean that this this is what he would see through a telescope. I'm talking about how he would describe what happens on Earth if he records what he sees through the telescope and then compensates for light travel time).jaketodd said:Is it true that if an astronaut, who has been traveling near the speed of light relative to the Earth for a long time, comes back to earth, time will have elapsed slower for him than for us? Doesn't that necessitate our clocks moving faster in his point of view while he was moving faster? How else would we be older and him younger?
It actually makes more sense to define his "point of view" as the coordinate system constructed using the synchronization procedure I mentioned in the thread I linked to. (This procedure only produces inertial frames when it's applied to an object that never accelerates (and never rotates)). See this article for more about this definitio of "point of view", and how to use it to resolve the twin paradox.Fredrik said:I'm calling the twin on Earth "A" and the twin in the rocket "B".
Blue lines: Events that are simultaneous in the rocket's frame when it's moving away from Earth.
Red lines: Events that are simultaneous in the rocket's frame when it's moving back towards Earth.
Cyan (light blue) lines: Events that are simultaneous in Earth's frame.
Dotted lines: World lines of light rays.
Vertical line in the upper half: The world line of the position (in Earth's frame) where the rocket turns around.
Green curves in the lower half: Curves of constant -t^2+x^2. Points on the two world lines that touch the same green curve have experienced the same time since the rocket left Earth.
Green curves in the upper half: Curves of constant -(t-20)^2+(x-16)^2. Points on the two world lines that touch the same green curve have experienced the same time since the rocket turned around.
That's not what he said at all.jaketodd said:So the astronaut thing you hear so many times is a myth?
Fredrik said:If we insist on defining his "point of view" at any event on his world line (the curve in spacetime that represents his motion) as the co-moving inertial frame at that point, then he would "see" the clocks on Earth tick ahead with an enormous rate as he slows down to a stop (relative to Earth) and starts speeding up in the opposite direction. (I don't mean that this this is what he would see through a telescope. I'm talking about how he would describe what happens on Earth if he records what he sees through the telescope and then compensates for light travel time).
jaketodd said:So the astronaut thing you hear so many times is a myth?
He sees (without compensation) Earth events go slow motion on the outbound trip, and fast forward on the inbound. Net effect is fast forward.Since the astronaut is younger when he returns, could you say that he "saw" (with the compensation) the Earth's events go in fast forward when he was in space?
Ich said:He sees (without compensation) Earth events go slow motion on the outbound trip, and fast forward on the inbound. Net effect is fast forward.
You can use the time dilation formula or calculate the proper time of the spaceship's world line to see that only 24 years passed on the ship.jaketodd said:Why would the net effect be fast forward? You're saying on the inbound trip the magnitude of fast forward is greater than the magnitude of slow motion on the outbound trip? How do you arrive at this?
Sorry, I forgot http://math.ucr.edu/home/baez/physics/Relativity/SR/TwinParadox/twin_vase.html" [Broken].How do you arrive at this?
Photons do not experience time in the same way that humans do. According to Einstein's theory of relativity, time slows down for objects that are moving at high speeds. Since photons travel at the speed of light, they do not experience time at all.
Yes, time dilation is the same for all photons. The speed of light is constant in all frames of reference, meaning that all photons experience time in the same way - that is, they do not experience it at all.
From a photon's point of view, no time passes at all. This is because, as mentioned before, time slows down for objects that are moving at high speeds. Since photons travel at the speed of light, time does not pass for them.
No, a photon cannot experience events in the past or future. Since they do not experience time, they do not have a concept of past or future events. For a photon, all events occur simultaneously.
The concept of time does not apply to photons in the same way that it applies to humans. Time is a human construct and does not exist in the same way for photons. They do not experience time as we do and therefore the concept does not apply to them.