Question

To an an external observer it appears that time has stopped for photon. But this relation is reflexive, so for an observer travelling with the photon it appears the universe has stopped everywhere.

Is this right?

Space also gets distorted parallel to the direction of motion, but not perpendicular to it.

Does this mean that for an observer travelling with a photon sees spacetime as a flat plane?

Note 1: I'm using language vividly not literally when I say a photon experiences space and time. Not that I'm against idealist or panpyschist interpretations of matter or energy come to that.

Note 2: Since it's been pointed out that an inertial frame can't be boosted into the frame of a photon and moreover there is no limiting behaviour here - no matter what frame you are boosted into, light will always appear to travel at c. Nevertheless, when an external observer watches a train chasing a photon by gradually increasing its speed, he will note that the train speed is approaching the speed of the photon (but will never match it) and when he looks at the clock inside the train he will not too that it is gradually slowing down (but never actually stops). Using this picture, we can attempt the thought experiment - if not one that can be carried out - of what a world looks like to a photon.

Answer 1

According to the theory of relativity, time depends on the observer. For a photon, if an observer could travel at the speed of light, time would appear to stop. In terms of space distortion, an observer traveling with the photon would see spacetime as a flat plane.

Step-by-step explanation:

The theory of relativity states that time depends on the observer. In the case of a photon, if we assume an observer can travel at the speed of light, time appears to stop for the photon. However, this is not physically possible because an inertial frame cannot be boosted to the frame of a photon.

In terms of space distortion, for an observer traveling with the photon, space appears to be distorted parallel to the direction of motion, but not perpendicular to it. This means that the observer would perceive spacetime as a flat plane in their frame of reference.

It's important to note that these thought experiments are not physically possible as we cannot travel at the speed of light. They are used to illustrate the properties of photons and the effects of relativity.