Do we need String Theory for Quantum Gravity? - Lance Dixon (SETI Talks)

The strong, weak, and electromagnetic interactions all have consistent, relativistic and quantum mechanical descriptions in terms of pointlike particles, but Einstein's theory of gravitation has long resisted a similar treatment, because of severe ultraviolet divergences. String theory solves these problems, but it introduces a new length scale, perhaps 16 orders of magnitude below what can be tested experimentally.
Dr. Dixon will describe recent theoretical progress in showing that a particular pointlike theory of gravity, called N=8 supergravity, might also be quantum mechanically consistent. In particular, N=8 supergravity has been shown explicitly to have no ultraviolet divergences in perturbation theory through the four-loop order. Dr. Dixon will also discuss the possible implications of these results.

[SETIInstitute]

Hi Mino, yes the maths behind String theory is extremely important - despite dealing with things on a quantum (tiny) scale, in effect this 'scales up' to the real world, so quantum mechanics rules the entire world despite describing the smallest of domains. You might want to check out our talk by Alex Westphal on String Theory too!

[YuzuruA]

Warning... you tube experts on physics, magic, and UFOS below

[SETIInstitute]

Thanks Gergs, our lovely intro was done for us by the Turner Duckworth branding firm. Glad you enjoy it!

[SETIInstitute]

We have a Higgs Boson talk coming up - but please feel free to suggest a speaker and we'll try to get them.

[TenzinLundrup]

What a great speaker. Very down to earth and clear.

[TailoredReaction]

That's the least of your worries. Early on he mentions phenomena and states, "we will cover to this later". Then when 'later on' arrives, he proudly states, "as discussed earlier".

[janjohandealgenman]

This. It depresses me that so few people realize we should do this

[CACBCCCU]

Looking at AREPO's time-lapse simulation reassures me that spin_1 gravitons, if they retroreflectively tend to balanced spin-handedness and tend to pair-off oppositely and thereby generate a balanced spin_2 effect, would do a much better job simulating cosmological gravity. The most interesting galaxies AREPO generates just aren't round enough to impress, they lack the distinct radial phase-contrasts of a prototypical ring or spiral galaxy. Bilateral spiral arm balance seems rare and ephemeral.

[stevenos]

a stable phase is a particle - a phasing particle is EMR - any type of particle - just what phase is it frozen in = A neutron is a black hole a proton is free space

[CACBCCCU]

Another reason to think gravitons could be spin_1 is that 'gluon chains' have been used as a replacement for gravity quanta with great success in simulation even though gluons are spin_1, not that I think gluon chains can replace all gravitational effects quantum gravitons could produce, i.e. all gravity. Still seems conceivable that all forces are mediated by spin_1 particles, implying the Higgs effect (inertia) is a resonance of spin_1 forces rather than a product of spin_0 (Higgs) particles.

[seanmcpherson]

They are getting the idea that Energy is space-time compress. When E is liberate is generating a violent expansion of the space-time getting back to it's previous volume. The velocity of the expansion is the speed of light C. Each sub-atomic particle is just space-time compress. From there, we can have protons, electrons, neutrons, etc. The biggest concentration of E or M, is just when the E or M disappear from our universe, and just leave their gravity (compression of space-time). We call that black hole.

[TailoredReaction]

In an attempt to breed snakes for their Natural History Museum, the scientists created a natural habitat that included a few hollow logs for the snakes to lay their eggs in. Months went by and the snakes did not breed. A lone scientist watching the habitat through a viewing pane pondered aloud, "Why are these snakes not reproducing?" You can imagine his surprise when one of the snakes replied, "Silly scientists, we don't use logs to multiply, we are adders!". (only comp sci students get this)

[Dyslexic-Artist-Theory-on-Time]

Could gravitational potential and electrical potential be linked together? They both use the inverse square law! In this theory gravity is a secondary force to the EM force. Objects just free-fall towards the greatest energy because it has the greatest time dilation! Because the photon of quantum mechanics is also the carries of the EM force this would link gravity with quantum mechanics!

[CACBCCCU]

A classical gravity wave seems like an abstract ocean lacking water molecules. A ship strains in ocean waves much like it would in gravity waves of the same rate, a molecular analysis is superfluous to that, although the ship's strains are generated by spin_1 interactions on the molecular level, the effect at the macro-level is spin_2. For many reasons I believe quantum gravitons are pointlike spin-one particles with macro-spin-2 effect, so graviton-graviton scatter should be nonexistant, imo.

[ebindanjan]

I can safely say now that the principal contradiction is not one of technical like devising new theories or inventing new math. The principal contradiction at this stage of the intellectual struggle is one of framework of approach. I concur with the suggestion of Max Tegmark of MIT, an entirely new way is imperative to resolve all the contradictions and conflicts in all-round-way, and once-and-for-all. I devised an entirely new approach that is consistent, coherent and comprehensive in my book.

[DancesWGenomes]

Lol-- at 53:22, he says he's going to "skip through some of this stuff because it's a little bit technical." Then again, it was also the most sensical thing he said during the second half of the talk.

[erwinmarschall]

10-D SUGRAs are low energy limits of superstring-theories. N=8 SUGRA in 4-D (presented in this talk) can be found from a dimensional reduction of 11-D SUGRA (Wikipedia: SUGRA).
So why does Dixon claim that N=8 SUGRA in 4-D is fundamentally different from string-theory?

[CACBCCCU]

I suppose the quantized flux loops through e.g. Josephson-junction rings are supposed to behave just as sets of closed strings, one closed-string per magnetic loop flux-quantum. As far as linking rings to qbits goes, I guess selectively-coupled sets of rings could carry modulated phase differences, giving enough phase information to carry several qbits, depending on phase-resolution limits. Seems like a quantum version of D8PSK or D16PSK would carry 3 or 4 qbits. Could be wrong, I don't know.

[CACBCCCU]

I guess I should be clearer about saying "graviton-graviton scattering" could be nonexistent - I mean there seems no reason to suppose gravity couples to itself as suggested at 30:50 if quantum gravitons are massless, pointlike and spin_1. Just as an electron is needed for a central loop in so-called "photon-photon scattering" a mass particle, probably a collection of mass particles actually, would be one requirement to form a central loop for any sort of "graviton-graviton scattering" effect.

[claireaaa]

Did they pass around a collection box after this lecture to reflect the degree of puzzlement or enlightenment that was experienced by each spectator?
More to the point, was he able to retire from the proceeds?