Photons & Frames of Reference.

  • Thread starter Endervhar
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I accept that the FAQ section is there to cut down on repetitive questions, but this arises out of an answer in the FAQs.

#10 said:
In the rest frame of any object, the velocity of the object itself is tautologically zero. Relativity says that photons always move at the speed of light, c. Always. So right away we have a conflict; relativity says a photon would have to be moving at c in its own rest frame.
Would this line of reasoning not lead to the conclusion that, even without an inertial frame of its own, a photon would not be able to be stationary relative to itself?
 
I think the misconception lies in the fact that a photon is not a measurement device, it is the medium of a measurement device. This also means it is not an observer, so there is no reason to speak of a photon's reference frame or any reference frame at the velocity of c.
 
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I think the misconception lies in the fact that a photon is not a measurement device, it is the medium of a measurement device. This also means it is not an observer, so there is no reason to speak of a photon's reference frame or any reference frame at the velocity of c.
Except to say, that from the standpoint of the photon, the trip across the Universe took zero time.
 
Except to say, that from the standpoint of the photon, the trip across the Universe took zero time.
A photon can't have a standpoint...
 

Drakkith

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Except to say, that from the standpoint of the photon, the trip across the Universe took zero time.
Would the photon even be able to observe anything or would everything just be squashed into some kind of infinite point or something? Kind of hard to imagine since we can't get to the speed of light.
 

sophiecentaur

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A photon would have no time with which to make any of these observations.
 
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Thanks for the responses, folks.

To some extent this thread exemplifies the kind of problem I have trying to find answers in P S books, journal articles etc. I can find plenty of answers to other questions, but not to the particular question that puzzles me.

OK, so the photon does not have an inertial frame, it is not a measuring device, it can't have a standpoint and it doesn't observe anything.

A photon has no time with which to make any observations; presumably because its trip across the Universe takes zero time; but wait, in the F of R of any observer, the photon's trip takes time, and the photon has no F of R, so how can we say its trip takes no time?

Even after all this, the original question is unanswered: "Would this line of reasoning not lead to the conclusion that, even without an inertial frame of its own, a photon would not be able to be stationary relative to itself?"

Perhaps I just ask the wrong questions.
 

Rap

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OK, so the photon does not have an inertial frame, it is not a measuring device, it can't have a standpoint and it doesn't observe anything.

A photon has no time with which to make any observations; presumably because its trip across the Universe takes zero time; but wait, in the F of R of any observer, the photon's trip takes time, and the photon has no F of R, so how can we say its trip takes no time?

Even after all this, the original question is unanswered: "Would this line of reasoning not lead to the conclusion that, even without an inertial frame of its own, a photon would not be able to be stationary relative to itself?"
A good way to get a feel for the photon is to look at a particle that is going at very very very close to the speed of light, with respect to the earth, lets say. To the particle, the whole universe is compressed to a thin sheet, because of the Lorentz contraction and goes whizzing by the particle in a very short time. Due to time dilation, clocks in the universe seem almost stopped to the particle. I guess you could say that to a photon, the universe has no thickness, its entire path which is zero, is covered instantaneously, and it sees the clocks of the unverse as absolutely stopped. What does "stationary with respect to itself" mean? If it means it experiences time just the same as any other inertial frame, which is true of the near-light particle, then that cannot apply to a photon, because it experiences no time. What does it mean to "have an inertial frame of its own"? If that means that it experiences the physics of the universe according to the equations of relativity, which is true of the near-light particle, it cannot hold for a photon, which has no "experience" because it has no time.
 
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Thanks, Rap. You have just condensed hours of thought into less than a dozen lines. I like that. The trouble is, it was that line of reasoning that got me into trouble in the first place!

The photon "has no "experience" because it has no time". In the F of R of every observer, the photon has time, so in what sense can we assert that it does not experience time? It seems that there is no F of R in which it can be timeless.
 

Rap

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Again, if you look at a particle that goes from the andromeda galaxy to the earth at nearly the speed of light, then in its reference frame the time that it takes to travel is very small, even tho it takes 2.5 million years to make the trip according to people on earth. The faster it goes, the less time it takes, according to that particle, because, to that particle, the distance from the andromeda galaxy to earth is very small, because of the Lorentz contraction, yet the earth is rushing towards it at nearly the speed of light. To a photon, at the speed of light, that distance, or any other distance, is zero and the trip takes no time at all, so the photon does not experience time.
 
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Thanks again, Rap. I have used this sort of reasoning elsewhere and received responses such as: "Without a scientific model that supports the view that photons experience no "time," it's not valid science to claim so. We don't know how to describe the reference frame of a photon scientifically, so any claims about it not experiencing time in it's own reference frame aren't scientific."

Somehow, discussions seem to go round in circles. I keep looking for ways to break the circles, but I suppose the truth is I don't have the scientific background, just a mind that keeps saying "Yes, but...."
 

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