# OrphanWilde comments on A Roadmap: How to Survive the End of the Universe - Less Wrong

7 02 July 2015 11:01AM

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Comment author: 02 July 2015 08:39:21PM 0 points [-]

The full CPT swap also involves reversing the flow of time. So one could attract, and one could repel, and this relationship is CPT-symmetric. (Antimatter chases matte, CPT swap, antimatter (previously matter) chases matter - in the other direction.)

And in terms of curvature, it just means the curve can have positive/negative amplitude. Antimatter would be matter with an inverse curvature. (Predicted by CPT symmetry, as I understand it.)

Note that what we're talking about now is more-or-less mainstream physics, albeit filtered through my probably-a-decade-and-a-half-outdated understanding of it.

Comment author: 02 July 2015 09:18:45PM 1 point [-]

Reversing time doesn't swap attraction and repulsion. (One way of seeing that: attraction/repulsion is a matter of the sign of a second derivative, and d^2/dt^2 f(-t) = (d^2f/dt^2)(-t). No sign change.)

The thing I was saying I couldn't see how to make sense of in the GR picture was having "gravity" and "antigravity" be separate phenomena (which I thought you might be proposing), not "antigravity" as such. I don't think there's any fundamental conflict between GR and having things of negative mass.

Comment author: 02 July 2015 11:59:06PM *  0 points [-]

Wikipedia on the subject. We don't seem to have experimental evidence one way or the other, and reasons to expect either effect (with the consensus favoring normal attraction). In particular, the section on CPT suggests that CPT suggests that matter and antimatter are attracted to each other.