I'm having trouble unambiguously interpreting many answers here due to the fact that the terms locality and causality are sometimes used interchangeably, while other times seem to mean very different things to the author.
My current understanding is that 'a-causality' is "obviously forbidden" in a physical theory, because it violates Lorentz invariance and leads to logical paradoxes. (Although there are supposedly viable models such as De Broglie–Bohm that are a-causal and yet somehow OK because the a-causality is not accessible to experimental apparatus -- this only brings further confusion to the table.)
'Non-locality' on the other hand, seems to refer to, for example, correlations between events at space-like separation. In this sense 'non-locality' does not imply 'a-causality.'
On the other hand Bell (1964) uses the term 'non-local' to refer to, as he says in his conclusion, "not Lorentz invariant." So I think he is using the word 'locality' interchangeably with 'causality.'
This is the sense in which many, such as Luboš Motl seem to use the term, for example here, while others, such as Ron Maimon, seem to use the term differently, for example here, where he says:
The nonlocality of gravity doesn't mean that Lorentz invariance is broken
This is very confusing. Can someone give an authoritative set of definitions here that we can refer to?
No comments:
Post a Comment