Talk:Bell's theorem/Weeping Angels

Causality and superluminar communication

Another connection between Doctor Who and Bell's theorem involves w:Causality#Physics and w:superluminal communication. Even though the Wikipedia articles state that faster-than-light communication would violate causality, I can't find a clear discussion. I believe that a simple proof can be found in the one-dimensional velocity addition formula. From Physics equations/Relative Velocity#Relativistic Motion^peralink, we have this relativistic velocity addition formula:

$u_{A|O}={\frac {u_{A|O'}+u_{O'|O}}{1+(u_{A|O\,'})(u_{O\,'|O})}}$

where u=v/c and c = 2.998x10⁸m/s is the speed of light. Let u_A refer to the speed of a message, and let O' refer to the speed of train relative to observer O (for convenience we call the O-frame "earth's frame). If the train is subluminal, but contains a superluminal telephone, this equation shows that it is possible for the message to travel backwards. Consider a two way conversation using telephones on pairs of subluminal trains going in opposite directions. If these telephones (not the trains) are sperluminal, one could create the w:Grandfather paradox.

The algebra required to demonstrate this is not difficult, requiring less than a half-page of paper. --Guy vandegrift (discuss • contribs) 22:52, 10 October 2015 (UTC)

On speculation about superluminar communication and time travel

I will fight hard to keep this article within the confines the consensus among physicists, which is that now and into the foreseeable future:

1. Superluminal communication and time travel are considered impossible.
2. There is no simple hidden variable theory that does not contain artificial features that make it unattractive to theorists and computationalists in quantum theory.

These restrictions do not apply to the unforseeable future (an obvious tautology). I also concede that brilliant and competent theorists have and will continue to look for something more. That research needs to continue. But none of this speculation belongs on this Wikiversity resource, except perhaps buried in subpages consisting of musings by students.

Having said all this, it is useful for students who find this interesting to learn about about Bell's theorem, hidden variables, and the consequences of superluminar communication. It make physics fun, and working through these ideas sharpens the mind by showing students how to think analytically.--Guy vandegrift (discuss • contribs) 22:52, 10 October 2015 (UTC)