>From: Stathis Papaioannou
>Not at all. There is a *huge* difference between what is possible in theory 
>and what is possible practically. A person wearing down a mountain with his 
>fingers is a practical impossibility, but there is nothing in the laws of 
>physics making it a theoretical impossibility. A person flying to Alpha 
>Centauri in 5 minutes is logically possible, but the laws of physics make 
>it theoretically impossible. A person being simultaneously taller than 
>180cm and shorter than 170cm is a logical impossibility. These three 
>examples for everyday purposes are equally unlikely to happen, but they are 
>fundamentally different from a philosophical standpoint. In the case of 
>classical teleportation, there is nothing in the laws of physics making it 
>theoretically impossible, and it is certainly not logically impossible. 
>Time travel is much more dubious: it may be a physical impossibility, and 
>it may even be a logical impossibility.

Thank you for a very clear explanation of these 3 
theoretical/practical/logical possibility differences.
I remember I saw some papers before saying that time travel is theoretically 
possible, although it remains an open question.
It's like teleportation. Maybe you can demonstrate with 1 or 2 particles in 
But it's another very different thing when we are talking about human beings 
(or simple animals).
Maybe other very knowledgeable prof. (like "scerir"???) in this list can 
provide useful ref.



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