Do you have any actual reason for believing that theories with T-symmetry but not CPT-symmetry are simpler than theories with CPT-symmetry but not T-symmetry?
Well, I think so, but maybe not in a format suitable for a short blog post. There are numerous small, simple CA with the property of being symmetrical under T=-T. For example, the BBM. My impression is that other means of reversal are correlated with automaton complexity. Then there's the idea of charge as a pump. That is appealing on other grounds - and pumps tend to have moving parts - which would then reverse automatically if T=>-T . Also, the possibility of simulationverse ideas would seem to favour ease of reversal, to some extent.
IMO, you should really not be counting the CPT theorem as evidence on the issue - one way or the other.
I certainly don't think people should be telling me that the known laws of physics are not symmetrical under T=>-T. IMO, it is more probable that they are symmetrical that way than that they are not. The idea that CPT symmetry illustrates that they are not is simply a popular misconception, with no basis in the facts of the matter.
The laws of physics as currently understood -- i.e., the laws in the best model we' ve got -- are in fact CPT-symmetric but not T-symmetric. (Because the best model we've got is a quantum field theory of the sort that the CPT theorem applies to; and because CP symmetry is violated (1) by that model and (2) in reality, according to the available evidence.)
Sure, there are plenty of small simple cellular automata with T-symmetry. And also with P-symmetry, which does not hold in the real world. So far as I know, CAs with PT symmetry are just about exactly as e...
http://lifeboat.com/blog/2011/06/dear-dr-hawking
Hey guys, my quantum physics is not powerful enough to understand this guy... Can anyone help me out with this one?
Thanks LW