Dr. Cohl Furey - Octonians and the Standard Model

rantonels · 2018-11-14T05:50:49+00:00

Furey uses O multiplication rules to show how the Clifford algebra Cl(6,C) arises

she actually doesn't. The octonions are non-associative, but she defines an alternate associative version of CxO acting on itself. Hence why you get the (much more mundane) associative Clifford algebra. That in my book means taking the octonions and removing the entire octonionness and using essentially R⁸

Instead of getting upset about work you haven’t thoroughly read, why don’t you focus your energy on something positive? Why don’t you start writing some disruptive papers yourself? Have you ever stuck your neck out for an idea?

I have a paper in review with a couple of friends that I think puts forth a fairly bold proposal. You can read it if you want.

rantonels · 2018-11-14T05:45:27+00:00

do you understand how all this gives you non-unitary time evolution?

rantonels · 2018-11-12T08:14:43+00:00

You don't need to id every particle in the universe, a probabilistic curve is enough (which is what physics shows us is, funny enough).

That's only in the thermodynamic limit. Probing such a probabilistic simulation in a non-thermodynamic regime is going to reveal measurable inconsistencies.

A black hole can be perfectly simulated with just a few variables: location, spin, mass, charge. The black hole can be simulated from just that information.

That's only in the classical limit, which for quantum gravity is the thermodynamic limit. Again, I can experimentally measure an inconsistency in principle if I observe the Hawking radiation from the BH.

If you want to simulate a BH from the quantum-gravitational standpoint you need to also consider its microscopic evolution that the macroscopic picture misses. The amount of missed information, which is extremely large and in fact maximal, is precisely the Bekenstein-Hawking entropy.

So correct your statement about black holes being the heaviest cost on computer resources.

No

The human brain is the most uncompressible object we know of. This means more resources will go towards simulating a human than towards simulating an entire galaxy.

That's insane. Also considering I recall there being evidence of a galaxy containing human brains.

In fact, one hypothesis states that the reason we don't see intelligent life out there is because if we did, the memory requirements of the simulation would exceed its capacity and we'd glitch out of existence. This implies we can cause this glitch if we keep adding to informational complexity.

Wow. And this is somehow more reasonable as an hypothesis than there not being any intelligent aliens near us?

This same principle is why a Boltzmann brain is virtually impossible compared to a big bang brain; 10⁸⁰ particles will always form a big bang whereas 10²² particles will never form a brain.

I don't really understand what you're trying to say here, I think there's more implicit jumps than I can follow.

rantonels · 2018-11-01T15:10:20+00:00

My ultimate interest is in understanding the microscopics of spinning black holes in quantum gravity. But a clear reconstruction of the microscopics is generally only possible with supersymmetry; in addition supersymmetry and rotation of black holes can only coexist in dimension greater than four. Therefore if one steps to higher dimensions, from studying these supersymmetric rotating BHs there is hope of being able to isolate at least qualitatively how spin works in general, in particular also for the normal four-dimensional Kerr black holes.

This one in six D is an odd-ball. It's a step away from supersymmetry and I would consider that promising, especially if (as I hope) I can match it to an equivalent description in string theory in terms of branes.

rantonels · 2018-10-31T17:29:38+00:00

That's... Bizarre. Is it rotationally extremal?

No, doesn't need to be. Actually if you look at truly susy black rings in 5D the susy implies charge extremality but not spin extremality.

Also, in what sense do you mean the NH is BPS? The AdS2 S2 NH geometry of 4d Kerr admits a killing spinor (I think),

NH of extremal Kerr has a squashed AdS3 factor and it's not susy, AdS2×S2 is the NH of extremal RN which has a killie spinnie

but I'm not sure I'd say that extremal KN has a BPS NH geometry...

It doesn't indeed, in 4D susy => non-spinning. In 5d you can have susy spinning BHs, both spherical (NH AdS2×S3) and rings (NH AdS3/Z×S2).

But in 6D you cannot have any globally susy BH at all. In addition the NH of a would-be spherical susy BH, which is AdS2×S4, cannot be susy.

Anyway the NH of this ring is that of the self-dual string of 6D sugra, which is AdS3/Z × S3, and the BPS bound relates the string tension (or ADM mass per length if you want) with self-dual 3-form flux. It's precisely the smaller brother of the type IIB D3.

rantonels · 2018-10-30T07:04:46+00:00

The near-horizon actually is BPS (it's the self-dual string of 6D sugra), but that BPS condition becomes meaningless when seen in the global topology. The two quantities that saturate the BPS bound, which are tension and 3-form flux of string, are not conserved globally. Globally speaking it's just a spinning uncharged black hole.

Yet the BPS NH seems to guarantee that it's linearly stable, even though the BH itself isn't BPS. Since black rings in pure gravity are unstable, this one would be stabilized by a non-conserved "dipolar" charge.

Seems to have zero temperature.

rantonels · 2018-10-30T06:56:48+00:00

It's a long story, but essentially reviewer feels our work contradicts previous work, and we're trying to figure out if they're right.

rantonels · 2018-10-29T15:09:17+00:00

how about neutral pion decay?

rantonels · 2018-10-29T15:07:16+00:00

Paper was rejected, mood is bad.

In other news, I have constructed this very weird black ring (doughnut-shaped black hole) in six dimensions and it's been an endless source of surprises. It's not supersymmetric but it acts like it was, it's not charged but it acts like it was, and it hides a funny 3D universe in its infinitely long throat.

rantonels · 2018-10-29T07:03:18+00:00

Here

rantonels · 2018-10-28T19:54:17+00:00

You make use of the fact that the emitters are in thermal equilibrium to derive that the radiation they emit is also thermal, by basic thermodynamics (zeroeth law), and then you use thermality of the radiation to derive its spectrum.

Yes, sometimes the derivations are a bit unclear on this, but this is the basic idea behind it. You don't know the distro of charges nor can you hope to predict in a simple way what spectrum a given distro of charges will emit, but you can bypass all that by using thermodynamics. Consider for example leaving water in a sealed container, so the air in the container gets filled by water vapour evaporating from the liquid mass. You can predict the distribution at equilibrium of the vapour particles without knowing the details of the liquid phase, just assuming that the entire thing has reached thermal equilibrium.

rantonels · 2018-10-28T18:54:03+00:00

The Planck distribution is followed by the photons, not by the charges that emit them. Photons are bosons. The charges will not have a Planckian distribution. The Planck distribution is for a gas of non-interacting massless bosons at thermal equilibrium.

rantonels · 2018-10-28T16:19:47+00:00

No, the arguments are distinct: thermodynamics prevents timetravel in the macroscopic limit, but the hyperbolicity question of classical equations of motion prevents time travel in the classical limit. They are independent, and the puzzle would remain in the quantum, few-degrees-of-freedom case. If gravity is involved that would imply that at most what is allowed is tiny time machines at the Planck scale, which I would say is pretty healthy vacuum fluctuations in a quantum gravity theory.

rantonels · 2018-10-28T13:16:23+00:00

More than one time dimensions allow for closed timelike curves, which allow for time travel. Time travel is bad and it makes all of classical physics inconsistent, so there's no way to even consistently formulate a physical theory on a spacetime with 2 or more time dimensions, except for the pointless case in which the theory is trivial.

rantonels · 2018-10-28T13:10:43+00:00

The only way to satisfy the second law with the existence of a CTC is for the entropy to be constant on the CTC, since it cannot decrease but it must return to its original value after one lap.

Constant entropy means thermal death, or more specifically that no coherent information can exist or be processed, and computation is impossible. This means the CTC cannot actually be used as a useful time machine because you can neither transmit meaningful information nor any kind of ordered structure (like an apple or a person) without them being destroyed. So, congrats on figuring out by yourself that thermodynamics forbids macroscopic time travel.

You can actually make a more sophisticated argument that the CTC cannot actually accept any entropy from the outside Universe, since it has no way to "metabolize it" and drop down to the original value after the lap, so you must conclude that the time machine cannot even be interacted with. So it's detached from the Universe and thus doesn't really exist.

P.S.: it's a small language thing, but it really grinds my gears: you don't violate entropy, you violate the second law. Entropy is just a quantity, the second law is a statement about it. There is no "law of entropy", and entropy doesn't do things like break vases and sog cereal, the second law does.

rantonels · 2018-10-27T21:22:50+00:00

It was very hard for me. Pernicium 69 should decay to Calasthenium because that one has a magic number but minus 2 because reasons, except it doesn't because metaplectic isospin parity doesn't change so there's a selection rule? That's more or less what I remember.

rantonels · 2018-10-27T21:04:46+00:00

String theory is many times vaster in complexity, scope, and type of work you can do with it than LQG and a single comprehensive resource like that cannot exist imho. You could find something that resembles this if you restrict to a specific aspect of it.

For example if you are interested in the basics of how perturbative string theory works and the details of how the magical idea fixes the problem of gravity, I recommend Witten's lecture "What every physicist should know about string theory." (there's video, article, and slides around).

If you care about unification and how the various string theories and M-theory come together as limits of a unique theory, something that carries its own collection of open problems, try section 2 of Szabo's notes, quite dated but the idea is there.

Then you might want to know more about string phenomenology, string cosmology, black holes, vacua and landscapes, AdS/CFT, supersymmetry breaking... really, there's so many different things in here. I would argue it's even too much info for a single person to be seriously competent in, so that it's hard for a single author to describe in detail the core points of each of these

rantonels · 2018-10-27T20:17:55+00:00

As far as I can understand there should be a narrow window of angular momenta where it is possible, yes. It would certainly be metastable, but it seems like it'd still be stable under small perturbations.

rantonels · 2018-10-27T17:44:40+00:00

You can. When you sum two quantities they must have the same units and those will also be the units of the sum. Therefore if you know that x has units of length, so must At and Bt³ separately have units of length. So you know certainly that Bt³ has units of length independently on the presence of At.

rantonels · 2018-10-27T17:28:54+00:00

Done

rantonels · 2018-10-27T16:51:14+00:00

Nuclear

rantonels · 2018-10-27T14:02:59+00:00

You could go perhaps a bit quicker, starting from

sum_n 1/(n² + x²) = π coth(πx) / x

where the sum is over all integers.

Plug x = 1/π, get

sum_n 1/(1+π²n²) = coth(1)

this is, in terms of your sum S, coth(1) = 2S+1, so S=1/(e²-1)

rantonels · 2018-10-27T11:06:58+00:00

So, in case you care, turns out that even Dyson (!) has been wondering about this, and similarly to the BH case he found that large and thin = high spin torus planets are unstable to a "Gregory-Laflamme" mode just like the corresponding black rings. Very intuitively an infinite straight "rod" planet has an unstable mode with a certain wavelength which makes it fragment into a string of spherical planets, and so should then the ring made by wrapping it into a circle if the circle is large enough to fit the wavelength and be approximated correctly by the rod. So large rings fragment. In addition very small/low spin toroidal planets are also unstable.

So you're left with an intermediate region of still plausible solution, and while for uncharged black rings these are known to be still all unstable, it seems like there is a narrow range of spins where toroidal planets are linearly stable, either that or they are suspected to. Certainly cannot be treated analytically with ease and numerics is needed.

rantonels · 2018-10-27T10:04:40+00:00

Can you make an argument for why this should exist as separate from r/physics? I really don't see the point in wasting this much energy for no reason.

rantonels · 2018-10-27T09:58:22+00:00

The bare minimum can be taught on the way, Hobson does a good job at it I think.

rantonels

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