> You're right that GR doesn't rule out closed timelike curves, but to actually construct one you need to have matter with negative mass. You only need matter

> You're right that GR doesn't rule out closed timelike curves, but to actually construct one you need to have matter with negative mass. You only need matter with negative mass if you want to construct one by building a machine. Some models for closed timelike curves that could occur in nature (e.g. the Tipler cylinder with infinite length) do not need negative energy. > the likelihood of FTL being possible is extremely small, for all reasonable purposes indistinguishable from zero on current scientific knowledge, and the existence of entanglement does not change this one bit Okay, that I agree with, but this unlikelihood is completely orthogonal to (pre-relativity) QM's compatibility with FTL travel/signaling. That was what I disagreed with.