Quadrillion possible ways found to rescue string theory! Physicist Rob Sheldon comments

String theorists have been trying to wish a multiverse into existence at least since avocado green appliances were hot (1970s if you weren’t around then) and here’s the latest:

Physicists who have been roaming the “landscape” of string theory—the space of zillions and zillions of mathematical solutions of the theory, where each solution provides the kinds of equations physicists need to describe reality—have stumbled upon a subset of such equations that have the same set of matter particles as exists in our universe…

The new work shows that there are at least a quadrillion solutions in which particles have the same chiral spectrum as the standard model, which is 10 orders of magnitude more solutions than had been found within string theory until now. “This is by far the largest domain of standard model solutions,” Cvetic says. “It’s somehow surprising and actually also rewarding that it turns out to be in the strongly coupled string theory regime, where geometry helped us.” Anil Ananthaswamy , “Found: A Quadrillion Ways for String Theory to Make Our Universe” at Scientific American

Our physic color commentator Rob Sheldon offers some thoughts on this latest blip on the screen in relation to the field in general:

String Theory is much closer to pure path than it is to physics. The problem faced by theoretical physicists nearly 100 years ago, was that Epicurus’s and Newton’s metaphysics failed–the world was not made out of little particles of matter flying through the void.

The revolution of quantum mechanics showed that it was made out of waves – but only when travelling. When they hit a detector, they looked like particles again. And the higher the energy hitting a detector, the more particle-like they looked. As particle physicists kept raising the energy of their accelerators, they detected “sub-atomic” particles that make up Newton’s atoms—quarks, mesons, gluons, etc.

But they had no theory of where these sub-atomic particles got their mass from. Today, the “Standard Model” has 18 free parameters, corresponding to the mass of 18 sub-atomic particles.

Just as Niels Bohr had done for the hydrogen atom when he explained the hydrogen spectrum as a series of trapped electron-waves, particle physicists tried to explain proton masses as a series of trapped quark-waves. But it wasn’t working.

Combined with this problem was the fact that Einstein’s theory of General Relativity (GR) argued that matter “bent” space-time, but otherwise had nothing to do with particle accelerators, electricity, and sub-atomic particles. There just didn’t seem to be a way to combine electricity and magnetism (EM/Maxwell’s equations) or quantum mechanics (QM) with GR.

In 1919 Theodor Kaluza added a fifth dimension to Einstein’s 4D spacetime, with some caveats that it didn’t interact with the other 4, and was able to get a combined EM+GR. In this superset, electric charge corresponded to motion in the 5th dimension.

In 1926 Oskar Klein explained how “non-interaction” was as if the 5th dimension was “rolled-up” into a cylinder. This is known as “compactification”. The idea is that we live in 3+1 dimensions, but there may be other dimensions that are rolled-up and not visible to our naked eyes. But they are needed to support the existence of electrons and other particles. Then the particles would be “waves” on the compactified dimensions, like waves on a 1D-string, or ripples on a 2D-surface, … etc.

It all seemed so promising–a unification of Einstein and Maxwell, a specification of particle physics, a hidden-dimension of reality that explained everything. The Kaluza-Klein theory was popular with theorists until the last details were worked out in 1950s. Alas, 5-dimensional Kaluza-Klein theory failed to describe reality.

Working the other direction, it seemed possible to explain reality if we started with 20 dimensions. All those compactified dimensions were like “strings”, and hence the idea of trying to explain reality with extra dimensions became known as string theory. Over the years, the goal of string theorists was to reduce the number of extra dimensions (supersymmetry led to fewer dimensions or “super strings”) But it has been at 10 dimensions for going on 40 years now. That says 6 dimensions must be compactified, and that’s a lot of ways to wiggle a string.

There have been thousands of graduate-student lifetimes spent on string theory. But after the initial success in the 90’s, there just hasn’t been much progress in the past two decades. The problem has led to new math techniques, new areas of mathematical research, but precious little on the physics side. Many physicists see it as a pure math field sucking resources from genuine theoretical physics. True believers see it as the unification of Maxwell and Einstein.

At least one group of skeptics has called it a “swampland” of string theory, because they think it will never work. Peter Woit has a blog dedicated to disproving string theory. Here’s his entry on “swampland”.

One of the few predictions made by string theory was that “super symmetry” (SUSY) would create particles that were “heavier” than usual, which would be seen by the CERN LHC collider at slightly higher energy. This expectation fueled a $20 billion upgrade of LHC, yet nothing was seen. A majority of particle physicists now believe that SUSY is dead:
Here’s Peter Woit and here’s Sabine Hossenfelder suggesting redirecting funding to more promising fields.

Now we come at last to your question. What is the meaning of this press release about a quadrillion ways to make a string theory?

Well, it suggests that 30 years of string theorists have been searching in the wrong part of phase space. That promising solutions are not in the “weak interaction” swampland, but in the “strong interaction” wasteland. By limiting their search, they claim they have eliminated many previous solutions, and are closing in on “the solution” as one-in-a-quadrillion. Their track record would say otherwise.

Rob Sheldon is the author of Genesis: The Long Ascent

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See also: Belief In String Theory Is Becoming, At This Point, A Sort Of Social Virtue

and

Post-modern physics: String theory gets over the need for evidence