- #141
Hurkyl
Staff Emeritus
Science Advisor
Gold Member
- 14,981
- 26
Ok, so that's speed in an inertial frame. What's relative speed?
Hurkyl said:Ok, so that's speed in an inertial frame. What's relative speed?
Suppose that two objects are in relative motion. Thus, the distance between them is changing.
Choose one object to be at rest, at the origin of its own frame of reference, say F1.
Hurkyl said:StarThrower said:Choose one object to be at rest, at the origin of its own frame of reference, say F1.
This doesn't apply to photons. Would you care to provide a definition of relative speed that does work for photons?
StarThrower said:Yes it does.
Yes it does.
Tom Mattson said:So this is what this thread has boiled down to?
OK, fine.
No, it doesn't.
There is no reference frame in which the photon is at rest.
StarThrower said:Incorrect Tom.
You can choose any object in the universe you wish, and fix a rectangular coordinate system to it. Makes sense to place the object at the origin of the system/reference frame. Then you get to the concept of "worldline" but I'm not going there.
What you are concerned about is whether or not such a reference frame is an inertial reference frame, well I have news for you... it is.
Tom Mattson said::
If you consider an inertial reference frame to be one that can always be brought to rest by a change of coordinates, then I have news for you: A photon cannot be placed at the origin of such a frame.
StarThrower said:Notice I changed that post slightly. It now reads:
If the photon isn't being subjected to an outside force, then that photon is in an inertial reference frame.
Hurkyl said:This definition requires one of the objects in question to have a rest frame. Since photons don't have rest frames, this definition does not work.
A photon placed at the origin of a frame is at rest in a frame.
Is a photon which isn't being subjected to a force in an inertial reference frame?
The answer of course is yes.
And no I'm not getting sloppy.
Translation: I assume SR to be wrong, therefore SR is wrong.StarThrower said:I did not "assume" the speed of light depends upon inertial frame, in fact, I assumed the exact opposite (that it doesn't), and subsequently arrived at a contradiction.
We've discussed this one too.Tom said:If you consider an inertial reference frame to be one that can always be brought to rest by a change of coordinates, then I have news for you: A photon cannot be placed at the origin of such a frame.