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I am quite suspicious about the the andromeda paradox and I am sure I am just lacking a detail.

So let us assume Andromeda sends out a for my friend Bob deadly emission (I will survive the emission). Bob and I do not know about this yet. However we both agree to shoot a photo of andromeda the moment I run into Bob. (we both are in the exact same place)

Now I walk straight into bob with humanly speed. Bob stands still. The moment I run into bob is the time the deadly emission is first detected by me. Surely bob is dead now. Surely Bob agrees that he is dead.

So, I assume that we can define simultaneity: The moment we hit into each other.

What is wrong?

TVSuchty
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1 Answers1

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The events: you are hit by Andromeda pulse and Bob is hit by Andromeda pulse are not only simultaneous, but happens at the same spot. The difference between the 4-coordinates of the events is zero in any frame.

But another event, let's say another pulse emission, happening at the same instant in Andromeda (in Bob's frame) is not happening simultaneously in your frame. Or it has already happened, or will happen yet, depending on the direction of your movement.

If you draw a diagram it becomes clear.

Claudio Saspinski
  • 17,607