Thought Experiment (1 Viewer)

[heyhsc]

Thought Experiment 1- Holding a mirror

Imagine you were travelling in a train at the speed of light and you held up a mirror, would you be able to see your own reflection.

1. If the aether model was correct
• Light could go no faster that the train (aether wind would slow down light)
• The light could never catch up with the mirror to return as a reflection
• Principle of relativity is violated because seeing one’s reflection disappear is a way to detect motion

2. If the principle of relativity is not violated
• Reflection must be seen normally
• It is moving away from the you at 3x10^8
• This suggests an observer on the platform would see the light travelling at twice its normal speed

I am so confused with the bolded parts, can someone please explain it to me

 

[dawooddaman]

Einstein wondered: “Suppose I am sitting in a train traveling at the speed of light. If I hold a mirror in front of me, will I see my reflection?”. There are two possibilities:
-No. If the traveling is traveling at the speed of light, light from his face would not reach the mirror in order to be reflected back. By not seeing his reflection he would know that the train was traveling at the speed of light without having to refer to an outside point. This violates the principle of relativity
-Yes. This means that light would travel at its normal speed relative to the train. This does not violate the principle of relativity. However, it also means that, relative to a stationary observer outside the train, light would be traveling at twice its usually speed!

Einstein concluded that, if we accept the principle of relativity can never be violated, then:
- The aether model must be wrong
- He would see his reflection
- The speed of light is constant regardless of the motion of the observer
On this basis, Einstein put forward hits theory of special relativity:
- All motion is relative – the principle of relativity holds in all situations
- The speed of light is constant regardless of the observer’s frame of reference
- The aether is not needed to explain light, and, in fact, does not exist

 

[kiinto]

• The light could never catch up with the mirror to return as a reflection

If no reflection, or a delayed reflection was produced you would know that you are travelling at a certain velocity without referring to an external frame of reference, as this violates the principle of relativity, it cannot be possible. Thus you must see a reflection in normal time. However you're in the train travelling at the speed of light, and you're holding the mirror. Hence, the mirror is traveling forward at c. So for light to 'catch up with the mirror', it must seemingly be travelling faster than c, at 2c. Einstein thought this too was impossible ---> time dilation.

Does that clear it up?

 

[someth1ng]

If no reflection, or a delayed reflection was produced you would know that you are travelling at a certain velocity without referring to an external frame of reference, as this violates the principle of relativity, it cannot be possible. Thus you must see a reflection in normal time. However you're in the train travelling at the speed of light, and you're holding the mirror. Hence, the mirror is traveling forward at c. So for light to 'catch up with the mirror', it must seemingly be travelling faster than c, at 2c. Einstein thought this too was impossible ---> time dilation.

Does that clear it up?

Don't forget length contraction.