How Does Light Behave in a Moving Light Clock?

[teachmemore]

The two parallel mirrors in the light clock are 1 light year apart, vertically. My reference frame which encompasses this clock, is traveling horizontally. The mirrors are 1cm wide. My reference frame is traveling much faster than 1cm/year.

Does the light in the light clock reach the second mirror after leaving the first? Or does the light escape from the light clock?

How does light stay within a light clock when the reference frame is moving perpendicular to the motion of the light in the clock? Doesn't light travel independently of any inertial frame?

 

[teachmemore]

I'm thinking that the light must remain in my inertial frame and hit the other mirror, since otherwise, I would be able to setup this experiment in order to detect that my inertial frame of reference is moving, which violates special relativity.

But if this is the case, then any light entering an inertial frame, becomes "part of it"?

 

[JesseM]

How does light stay within a light clock when the reference frame is moving perpendicular to the motion of the light in the clock? Doesn't light travel independently of any inertial frame?

Light's speed is independent of the speed of the source, but the direction of a beam does depend on the motion of the source: if you have two identically-constructed sources which send out light in a directed way (like flashlights or lasers), and they are in motion relative to one another, then each beam will travel at the same angle relative to its source in the source's rest frame (if this wasn't true the first postulate of SR would be violated). So if you have a laser which is oriented perpendicular to the surface of the mirror, the laser beam should be perpendicular to the mirror in the rest frame of the mirror, which means if the mirror is moving in your frame then you will measure to beam to move at an angle, not perpendicular to the surface of the mirror.

But if this is the case, then any light entering an inertial frame, becomes "part of it"?

Inertial frames are just coordinate systems which cover all of space and time, any object is "in" every possible inertial frame simultaneously, in the sense that you can analyze its motion using the coordinates of any inertial frame.

 

[teachmemore]

Of course. Sorry. Dumb question. It has been a while.

 

[teachmemore]

Wait a second...


What if my frame of reference is stationary when the light pulse reflects off one mirror, and then my frame of reference accelerates while the light pulse is traveling to the second mirror?

So a light clock only works in a frame of reference that maintains a constant velocity?

 

[teachmemore]

I guess what I'm getting at here is that if you are in an accelerating reference frame, all your gadgets that rely on light pulses to operate will stop working correctly while you are accelerating. They will lose their accuracy unless they have a way to guide the light pulses along with the inertial frame of reference.

 

[ghwellsjr]

Wait a second...


What if my frame of reference is stationary when the light pulse reflects off one mirror, and then my frame of reference accelerates while the light pulse is traveling to the second mirror?

So a light clock only works in a frame of reference that maintains a constant velocity?

I guess what I'm getting at here is that if you are in an accelerating reference frame, all your gadgets that rely on light pulses to operate will stop working correctly while you are accelerating. They will lose their accuracy unless they have a way to guide the light pulses along with the inertial frame of reference.

Frames of reference are not physical things. Back in Einstein's day, a reference frame was considered inertial which means it never accelerated. Nowadays, people want to say inertial reference frame to distinguish it from an accelerating reference frame. I think the default should be that you have to say accelerating reference frame if that's what you mean. But even if you consider your reference frame to start accelerating, it has no bearing on what physically happens to what you already defined in your inertial reference frame.

 

[pervect]

You'd have to tilt both your mirrors to make your light clock work in an accelerating space-ship. This would allow the light to bounce back and forth, but since the path the light takes will no longer be the same length after the "tilt", this operation would affect your clocks timing.

Of course the solution is pretty easy - don't acclelerate, jar, or bump your light clock. It's a delicate piece of apparatus...

Mechanical clockmakers had similar problems, back in the day when they were trying to build a clock accurate enough to determine one's longitude. The first successful attempt (due to a lifetime of work by John Harrison) started out as a rather large instrument, but it turned out to be sensitive to particular rolling motions of the ship. The solution turned out to be to make it smaller.

 

[ghwellsjr]

Ahh, his light clock is not in a spaceship. It's in space and a pretty sizable piece of space at that. He didn't say he was accelerating the light clock, just the frame of reference in which it was originally specified. If he wants an answer with regard to accelerating the light clock, then he's going to have to be awful specific.

 

[teachmemore]

Ahh, his light clock is not in a spaceship. It's in space and a pretty sizable piece of space at that. He didn't say he was accelerating the light clock, just the frame of reference in which it was originally specified. If he wants an answer with regard to accelerating the light clock, then he's going to have to be awful specific.

LOL. no, nothing needs to be specific about my question. I think it is pretty clear and pervect answered it.

It was a very basic and general question about accelerating reference frames.

 

[John232]

The lock in this mind experiment would function correctly. The direction the beam is sent is independent of the observer. To say it wouldn't function correctly would be like saying that if someone traveling at a relative speed sees me shooting a laser it will veer off in some other direction. The speed of the photon is unchanged but it does mantain the exact trajectory it was sent to each observer and is part of the cause of the effects of special relativity.

If the light accelerated the path of the photon would curve and the light clock could lose its ability to function but would work properly when traveling at a constant speed. This is because of the equivalance of acceleration and gravity. Gravity curves the path of light so then acceleration would affect its path also. Then again the light clock thought experiment is only used in special relativity and not general relativity.