Cosmologic philosophy: boot strapping string theory (Introduction)

by David Turell , Friday, January 21, 2022, 19:23 (816 days ago) @ David Turell

Requires supersymmetry to exist:

https://www.quantamagazine.org/a-correction-to-einstein-hints-at-evidence-for-string-th...

"Gravity’s quantum-scale details are not something physicists usually know how to quantify, but the trio attacked the problem using an approach that has lately been racking up stunners in other areas of physics. It’s called the bootstrap.

"To bootstrap is to deduce new facts about the world by figuring out what’s compatible with known facts — science’s version of picking yourself up by your own bootstraps. With this method, the trio found a surprising coincidence: Their bootstrapped number closely matched the prediction for the number made by string theory. The leading candidate for the fundamental theory of gravity and everything else, string theory holds that all elementary particles are, close-up, vibrating loops and strings.

***

"But matching the theory to all other aspects of reality takes some fiddling. To get rid of negative energies that would correspond to unphysical, faster-than-light particles, string theory needs a property called supersymmetry, which doubles the number of its string vibration modes. Every vibration mode corresponding to a matter particle must come with another mode signifying a force particle. String theory also requires the existence of 10 space-time dimensions for the strings to wiggle around in. Yet we haven’t found any supersymmetric partner particles, and our universe looks 4D, with three dimensions of space and one of time. Both of these data points present something of a problem. (my bold)

"If string theory describes our world, supersymmetry must be broken here. That means the partner particles, if they exist, must be far heavier than the known set of particles — too heavy to muster in experiments. And if there really are 10 dimensions, six must be curled up so small they’re imperceptible to us — tight little knots of extra directions you can go in at any point in space. These “compactified” dimensions in a 4D-looking universe could have countless possible arrangements, all affecting strings (and numbers like α) differently.

"Broken supersymmetry and invisible dimensions have led many quantum gravity researchers to seek or prefer alternative, non-stringy ideas. But so far the rival approaches have struggled to produce the kind of concrete calculations about things like graviton interactions that string theory can."

Comment: the usual struggle to make strings real. Note the bold. All those extra required dimensions required are a huge problem. And supersymmetry has never been found. A sixty-year-old theory going nowhere, but those invested in it are trapped to continue.