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

6 Post author: turchin 02 July 2015 11:01AM

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Comment author: OrphanWilde 02 July 2015 02:05:45PM -2 points [-]

Comment from a crank on alternate theories of reality: We can do some pattern recognition, and notice a pattern:

Strong nuclear force. Weak nuclear force. Gravity. Einstein's Constant/Cosmological Constant/Dark Energy/Vacuum Energy.

Attraction. Repulsion. Attraction. Repulsion.

(Also, below that, Strong Interaction and whatever force keeps neutrons apart, sometimes stated, somewhat nonsensically in the general case, to be the exclusion principle.)

Assuming this pattern holds across all scales (and do we have any reason to believe the range of scales around the one we happen to occupy is special or unique, apart from the fact that they're the range of scales we happen to be capable of observing?), we shouldn't expect the universe to end at all, although our local universe might conceivably run out of exergy.

Comment author: gjm 02 July 2015 03:24:52PM 2 points [-]

Your list of interactions notably omits electromagnetism, which as well as being vastly important in the physical phenomena we observe all the time happens to be neither simply attractive nor simply repulsive.

It is also incorrect to describe the weak interaction as a repulsion; as with electromagnetism its effects can be either attractive or repulsive.

Comment author: OrphanWilde comment score below threshold [+] (6 children)

Comment author: gjm 02 July 2015 06:39:48PM 1 point [-]

All of the forces reverse polarities along with the matter in question.

But gravity doesn't. I mean, really, it just doesn't. (According to best present-day physical theories, anyway. I don't know whether anyone has collected enough antimatter for it to be practical to do an explicit experimental verification that its gravity isn't sign-reversed.)

Comment author: OrphanWilde 02 July 2015 07:07:49PM * 0 points [-]

The CPT theorem, as I understand it, may or may not suggest exactly that. I've encountered contradictory descriptions on that point. (ETA: After some brief research, apparently the contradictions are in my interpretation of what was being said; antimatter may or may not -emit- antigravity per the CPT theorem, but is almost certainly still -attracted- by normal gravity, also per the CPT theorem. There's ongoing research on the latter point.)

It seems to be an open point of debate, though.

Comment author: gjm 02 July 2015 08:13:02PM 1 point [-]

I'm, oh, let's say 99% certain you're wrong about the CPT theorem suggesting any kind of sign-reversal in gravity.

If antimatter is attracted by ordinary matter, then CPT symmetry tells you (since CPT reversal swaps ordinary matter and antimatter and leaves "attracted" as it is) that ordinary matter is likewise attracted by antimatter. And, of course, if ordinary matter is attracted by ordinary matter then CPT symmetry tells you that antimatter is attracted by ordinary matter.

I suppose CPT symmetry is kinda compatible with there being (let's say) gravitons and antigravitons that somehow do different things, except that (1) in every sketch of quantum gravity I know of gravitons are their own antiparticles, and (2) in general relativity gravity is a consequence of the curvature of spacetime and I can't imagine how a separate antigravity could fit into that picture.

(I am not an actual proper physicist and it's not impossible that I'm confused; hence 99% rather than 99.999%.)

Comment author: OrphanWilde 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: gjm 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: Vaniver 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.

Comment author: OrphanWilde 02 July 2015 06:52:10PM -1 points [-]

I've played with formulas; I've come up with something like:

q2 * m1 * m2 * sin(sqrrt(r * C1))/(r * C2)^2

Where q2 is the charge of the nonlocal matter. (This formula calculates the force exerted on m1; the force exerted on m2 may be different.)

I suspect the actual function inside the sin may be more subtle than that. The salient point would be that the wavelength is a function of its distance, and the wavelength increases (exponentially, I think) with distance, which produces a scope-insensitive force.

Comment author: gjm 02 July 2015 08:15:18PM 1 point [-]

I'm sorry -- what is this meant to be describing, exactly? Some already-known physical phenomenon, whose rules you think may be different from those it's currently thought to obey, or a conjectural new force?

Comment author: OrphanWilde 02 July 2015 08:40:02PM -1 points [-]

The former. Or rather a set of phenomena which I believe to be more closely related than currently thought.

Comment author: gjm 02 July 2015 09:19:50PM 1 point [-]

OK. Which physical phenomena do you think might be described in that way? I'm pretty sure the stuff in the Standard Model has been measured accurately enough to rule out anything much like what you describe.

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

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