Oh, that talk I did at Perimeter? It is available online now. It is all about the process of making the book “The Dialogues”, why I did it and how I did it. Along the way, I show some examples and talk about the science they’re bringing to life, but this is not primarily a science talk but a talk about talking about science, if you see what I mean.

The talk starts slowly, but bear with me and it warms up swiftly!

YouTube link here. Ended below:

-cvj

what’s your favorite artwork

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Sincerely, Taylor F

also would you commentate on my artwork

https://noonien.webnode.com

I don’t have a favorite. Too many pieces to choose from! I love many pieces, and many different styles and types of art to list favorites!

Hi Clifford,

I really enjoyed your Perimeter Institute talk, so much I watched it twice in a row. I agree that fully that science communication should be broader that just a series of interesting facts that can amaze the average layman. I like the concept of eavesdropping on conversations about science and how the concepts can affect every day experiences. The analogy of water at the macro vs micro level to space time is very powerful I’m surprised I have never heard it used before as I have read many popular science books.

I have a quick question regarding quantum gravity related to string theory. How would a Feynman diagram look, and work of the graviton is quantum of space instead of a force carrying boson?

The way I see it assuming that the basic tenants of String theory are correct then:

– A fundamental particle or string is basically a clock, where the string is undergoing a respective motion.

– The graviton being a closed loop is a non-virtual quantum of space that travels at light speed

– Quantised time dilatation would be the reabsorption of a graviton through crossing symmetry which I assume interrupts the motion of the “clock”?

The difference in the Feynman diagram as I see it is the emission of the graviton(s) may have some minor directional change for the particle but repeated nonspecific direction equals a net zero motion, but the creation of quantised space from the particles specific location of origin in aggerate for a large enough mass against the background of an extremely dense and homogeneous cosmological spacetime will become geometry consistent with general relativity.

I think this view would give a microscopic view consistent with your water analogy and to extend it further, quantum mechanics at some level then becomes analogous to the evolution of the wavefunction over time being Brownian motion of non-stationary and fluctuating spacetime.

So, my question is this solution for quantised gravity seem obvious to me and I’m sure many others have thought of this and then later discarded it due to some inconsistency, but I have tried to research it and can’t find an obvious error. Could you please help me by pointing out what I have likely overlooked?

Thanks

Nathan

Hi Nathan,

I’m glad you enjoyed the talk! I don’t know if the water analogy is “out there” much, or at all. I’ve been using it for many years in public discussions, and in research contexts too. It’s something I think people would use more in discussion of these issues. I’ve no idea if I came up with it or not. Probably unlikely. Anyway, it’s in the book now, so it is out there.

The cleanest description of gravity at the quantum level via Feynman diagrams in string theory is in terms of the exchange of closed loops of string, splitting and joining. Think of a pair of pants. A cross sectional slice will reveal a closed string in any instant. Such a shape has three strings meeting (one one splitting into two, or two joining into one). The closed string can describe a graviton. The graviton description though has limitations. It describes gravity as a force via exchange of particles… it does that on a background of classical spacetime, however… this description does not managed to describe the “molecules” of spacetime itself at the same time. You need another regime for that, one where gravitons are no longer apparent. In the examples where we can do that, all the usual variables become strongly coupled and reorganise into something quite different. (For example, the description becomes a gauge theory in lower dimensions – the whole spacetime in which the gravity acts is not even apparent, and the closed strings are not either!)

I’m afraid I don’t really understand your construction well enough to comment sensibly. But the main thing I’m saying is that the “quantum gravity as gravitons” description and the “quantum gravity as bits of spacetime” description don’t both seem to be able to work well in the same regime. One is weakly coupled and the other is strongly coupled. It would be nice to find a situation where both can be valid, as you’re trying to. But I don’t know how it would work in detail.

-cvj