Light in an accelerated elevator

In summary: The problem with that is that you don't have a static situation. If the proper acceleration doesn't vary along the height of the lift then the length of the lift is varying in its own rest frame. And you still need to choose what coordinates to work in, because you can't avoid relativity when you are asking about light.
  • #1
John Mcrain
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Elevator (2m height) is accelerate upward, light is at the top pointed toward flor of elevator.
Is time t=2m/c to light pass from top to bottom?

Bottom moving toward light,so time would be smaller then t=2m/c?
 
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  • #2
John Mcrain said:
Bottom moving toward light,so time would be smaller then t=2m/c?
In an inertial frame, yes.
 
  • #3
Dale said:
In an inertial frame, yes.
How explain smaller t, c increase(impossible), elevator become shorter then 2m ?

In frame of elevator t is also smaller then t=2m/c, once when light leave top it is not part of elevator and flor coming toward light?
 
  • #4
John Mcrain said:
How explain smaller t, c increase(impossible), elevator become shorter then 2m ?
The speed of light is only invariant in inertial frames of reference. It can differ in other classes of frame.

I'm not sure who is measuring what in your scenario, so it's difficult to know how to answer exactly. But note that, as measured in an inertial frame, the rate of a clock in the lift is varying, as is the length of the lift. This will have consequences for the speed of light as measured by an observer in the lift.
 
  • #5
John Mcrain said:
How explain smaller t, c increase(impossible), elevator become shorter then 2m ?
Obviously, the explanation is that the elevator is moving in the inertial frame. You already gave that explanation in your OP so I am not sure why you seem to be ignoring your own statements now.

John Mcrain said:
In frame of elevator
Before you ask any questions about the frame of the elevator you will need to define what you mean. Common choices would be Kottler Moeller, Rindler, or Lass coordinates.

See https://en.m.wikipedia.org/wiki/Rindler_coordinates

Once you choose the coordinates you choose to represent the frame of the elevator then the remainder of your questions can be answered
 
  • #6
Dale said:
Obviously, the explanation is that the elevator is moving in the inertial frame. You already gave that explanation in your OP so I am not sure why you seem to be ignoring your own statements now.

Before you ask any questions about the frame of the elevator you will need to define what you mean. Common choices would be Kottler Moeller, Rindler, or Lass coordinates.

See https://en.m.wikipedia.org/wiki/Rindler_coordinates

Once you choose the coordinates you choose to represent the frame of the elevator then the remainder of your questions can be answered
So I cant use same formulas as instead light is ball?
 
  • #7
Ibix said:
The speed of light is only invariant in inertial frames of reference. It can differ in other classes of frame.

I'm not sure who is measuring what in your scenario, so it's difficult to know how to answer exactly. But note that, as measured in an inertial frame, the rate of a clock in the lift is varying, as is the length of the lift. This will have consequences for the speed of light as measured by an observer in the lift.
light can be faster then c in non inertial frame?

Men in elevator meassure with stopwatch how long take the light to hit the flor.
 
  • #8
John Mcrain said:
So I cant use same formulas as instead light is ball?
Not if you want it to be relativistically correct. Of course, if you just want a rough approximation then that would be fine.

John Mcrain said:
light can be faster then c in non inertial frame?
Yes

John Mcrain said:
Men in elevator meassure with stopwatch how long take the light to hit the flor.
You still have to choose your coordinates for that.
 
  • #9
Dale said:
Of course, if you just want a rough approximation then that would be fine.
Ball in my video has a=10m/s2, what is acceleration of light?
 
  • #10
John Mcrain said:
Ball in my video has a=10m/s2, what acceleration I must use for light?
The problem is not the value of ##a##. You have to choose a coordinate system for the accelerated frame to get relativistically accurate results.

Why are you so resistant to making this choice?
 
  • #11
Dale said:
The problem is not the value of ##a##. You have to choose a coordinate system for the accelerated frame to get relativistically accurate results.

Why are you so resistant to making this choice?
I ask for non relativistic case, case where I use formula as in my video with ball
 
  • #12
John Mcrain said:
I ask for non relativistic case, case where I use formula as in my video with ball
The problem with that is that you don't have a static situation. If the proper acceleration doesn't vary along the height of the lift then the length of the lift is varying in its own rest frame. And you still need to choose what coordinates to work in, because you can't avoid relativity when you are asking about light.

The point that @Dale is making is that the answer you will get depends on the choice of coordinate system you choose. You don't know which to choose because you don't have a practical reason for doing the analysis, so there's no particular advantage to one over another. So flip a coin or whatever and pick one.
 
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  • #13
Ibix said:
And you still need to choose what coordinates to work in, because you can't avoid relativity when you are asking about light.
That mean I cant use formula from my video with ball.
 
  • #14
John Mcrain said:
I ask for non relativistic case, case where I use formula as in my video with ball
For a non relativistic case you can use the approach in the video, but that would be best in a different sub forum. The relativity sub forum is for relativity
 
  • #15
Dale said:
The relativity sub forum is for relativity
To be fair, this is in Classical. But it's relativity anyway if we need to discuss light in accelerating frames.
 
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  • #16
Ibix said:
To be fair, this is in Classical. But it's relativity anyway if we need to discuss light in accelerating frames.
Oops, that’s embarrassing.

@John Mcrain please decide if you want to discuss balls or light. If you want to discuss light then I will move this to the relativity forum. If you want to discuss balls then I will close this thread and you can start a new one focused on balls.
 
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  • #17
Dale said:
For a non relativistic case you can use the approach in the video,
How can I use this approach for light, if I dont know what is acceleration of light?
Dale said:
@John Mcrain please decide if you want to discuss balls or light. If you want to discuss light then I will move this to the relativity forum. If you want to discuss balls then I will close this thread and you can start a new one focused on balls.
I didnt know when I write my first post that belong to relativity..I think I wont go to relativity forum for now, it is too complicated..
And with ball answer is in my video...
 
  • #18
John Mcrain said:
How can I use this approach for light
You cannot. Balls are non relativistic. Light is the most relativistic thing there is.

John Mcrain said:
I think I wont go to relativity forum for now, it is too complicated..
And with ball answer is in my video...
Sounds good. I will close the thread then. When you are ready to discuss light please post in the relativity sub forum.
 
Last edited:

1. How does light behave in an accelerated elevator?

In an accelerated elevator, light behaves the same way as it does in a stationary elevator. It travels in a straight line at a constant speed of approximately 299,792,458 meters per second.

2. Does the color of light change in an accelerated elevator?

No, the color of light does not change in an accelerated elevator. The wavelength and frequency of light remain constant, regardless of the acceleration of the elevator.

3. What happens to the speed of light in an accelerated elevator?

The speed of light remains constant in an accelerated elevator. This is one of the fundamental principles of the theory of relativity.

4. Does the direction of light change in an accelerated elevator?

No, the direction of light does not change in an accelerated elevator. It continues to travel in a straight line, regardless of the acceleration of the elevator.

5. How does the observer perceive light in an accelerated elevator?

The observer in an accelerated elevator perceives light in the same way as an observer in a stationary elevator. The speed, direction, and color of light remain constant for both observers.

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