Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: jeffreyH on 22/03/2021 12:26:25
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If objects travel with velocities relative to each other then what is light traveling relative to? The photon is a particle and it is traveling. Relative to ...
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If objects travel with velocities relative to each other then what is light traveling relative to? The photon is a particle and it is traveling. Relative to ...
Relative to the frame it is being measured from. Photons don't have a valid inertial frame, so it meaningless to talk about what they measure themselves moving relative to.
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At any time t the photon can be said to be at point p (if we consider the photon to be a particle). At time t+a we can say the photon is now at point p+b. This follows from the speed of light in vacuum, if the photon is traveling through a vacuum. It has moved. Relative to what? You can simply state relative to a selected frame but this just punts the problem.
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All these things are dependent on a reference frame and thus undefined without one.
At any time t the photon can be said to be at point p
One can speak of an event, which is a point in spacetime and is frame invariant. So you can say a photon is present at events p, q and r, and this would be true regardless of the frame of reference chosen. The actual abstract coordinates (x, y, z, t) assigned to each event is completely frame dependent, so there is no one time (t) or spatial location (x,y,z) for any of those events.
At time t+a we can say the photon is now at point p+b.
We can say it is subsequently present at event q, but the distance 'b' between them and the time 'a' elapsed between them is again completely frame dependent. If the frame chosen is an inertial one, one can say that b/a = c, that is, the distance light moves per unit time equals the constant speed of light. In non-inertial frames, this relation is not necessarily true, and is in fact not true most of the time.
This follows from the speed of light in vacuum, if the photon is traveling through a vacuum. It has moved. Relative to what?
As Janus said, relative to the frame of reference you've chosen.
You can simply state relative to a selected frame but this just punts the problem.
Then punt we have. There's no other answer. Velocity is a relation, not a property, and has been so since Galileo's time. If there happens to be an object stationary relative to the frame you've chosen, then you can say that the photon is travelling distance 'a' in 'b' seconds relative to that object, but the frame is just as valid even if there are no stationary objects to be found in it.
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What you are missing is the location of the photon at any given instant is not relative to anything else. All other particles are relative to the photon. That is why the speed of light is used in relativistic gamma. This is the absolute maximum speed limit. As an absolute it can't be reached by massive particles. Since everything else's velocity is measured in relation to this absolute then the photon must map to an absolute frame.
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What you are missing is the location of the photon at any given instant is not relative to anything else. All other particles are relative to the photon. That is why the speed of light is used in relativistic gamma. This is the absolute maximum speed limit. As an absolute it can't be reached by massive particles. Since everything else's velocity is measured in relation to this absolute then the photon must map to an absolute frame.
Photons do not define a frame of reference. The laws of physics are the same in any inertial frame of reference, but not in a photon frame since photons always move at c relative to any frame. They cannot be at rest.
Photons do not define any particular 'frame' since while they may all have the same speed, they have very different velocities.
You seem to have stopped asking questions.
If you are asserting these things, then this topic belongs in new theories. If you're not asserting them, then read the replies and don't suggest that things are being missed.
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Consider this. If you could measure the one way speed of light, and found it differed in opposite directions, you should be able to adjust your velocity and direction in such a way that the speed of light is now the same in all directions. This now makes you stationary in the photon field. None of this challenges relativity BTW. It will also never be falsified as there is no way, absent of synchronised clocks, that you can measure the speed of light.
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Consider this. If you could measure the one way speed of light, and found it differed in opposite directions, you should be able to adjust your velocity and direction in such a way that the speed of light is now the same in all directions.
The one way speed of light (that is, the time separating a pair of events with light-like separation) is frame dependent, so any experiment that claims to measure it is presuming some (probably inertial) frame, in which case yes, the frame presumed can be determined from the results, but it would be more correct to say that the results can be determined by the frame presumed.
If one preferred frame can be identified by some experiment, then all the machine has to do is output the frame thus identified, without actually bothering with measuring light speed relative to this frame, which is c by definition.
On a side note, an objective foliation of all spacetime events (none has ever been proposed) does not necessarily have light travelling at c in any particular direction. It is only by convention that we define it so. I can think of some occasionally used models that allow variable light speed (variable speed in the same direction even) relative to the actual ordering of events. This is a natural consequence of the disconnect between proper time (what clocks measure) and absolute time (the absolute separation of non-simultaneous events), the latter of which cannot be measured. I bring this up because if you had your absolute 1-way light measuring device that reports velocities using the second kind of time, then you'd still not be able to determine the absolute frame from those measurements. To do so presumes correspondence with a nice neat locally inertial coordinate system with orthogonal axes.
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It would not be possible to define the background without first determining the one way speed of light and adjusting for it. That is the whole point.
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Yeah, its a speed limit. But you don't really need it to propagate, do you? Not as a field, at least that's what I think about it. If you want your fields to move you can do so, but you might also be able to consider it a 'positional plane' in where you see numbers changing. That would also, when defined from propagation and logic, make those numbers behave as if they were propagating, depending on your point of view.
That way you might reach a sort of explanation why it behaves as it does, and possibly also a explanation for relative motion, and accelerations.
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Relative motions aren't the issue. Special relativity deals with those. General relativity is a much bigger issue. To measure the one way speed of light at all you would have to be very far away from a large gravitating mass.
To discuss relative motions at all misses the subtlety of the point being made.
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Jeffrey, I didn't comment on one way speeds of light. I commented on the idea that you need a propagation. And then by using this other outlook you might find new ways to look at both relative motion as well as accelerations (including deceleration)