... the photon is NOT at the triangle flag, but already at the cabin (the front of the train)! Your world of events is not the same as Tom's world of events: in your world, when you are at the square flag the photon is at the cabin! Because you and Tom move relative to each other you both are in different worlds of simultaneous events, but in which the speed of light is the same!
The Spacetime map was correct, but because of the constant speed of light we have to read the Spacetime map in a different way than we were used to!
The angle between Tom's horizontal world and your sloped world depends on the relative speed between you and Tom. But this gets too technical. Don't worry about that here.
=> Go to ....
- Relativity for Dummies
- 4D Spacetime Block Universe
- Reciprocal time dilation
- Reciprocal length contraction
- Lengths do not 'appear' contracted!
- Measuring the contracted train
- Constant light speed
- Where is the bullet?
- Train experiment
- Slower and shorter - case study
- Minkowski vs Loedel
- Spacetime video
- Further reading