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String theory again: Will a correction to Einstein save it?

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String theory is one of those propositions that, for many cosmologists, somehow has to be true, perhaps because the idea that all elementary particles are vibrating loops and strings is itself attractive or perhaps because string theory is part of a theoretical structure for multiverse theory, which has everything going for it except evidence. Now, a hope is discerned:

Recently, three physicists calculated a number pertaining to the quantum nature of gravity. When they saw the value, “we couldn’t believe it,” said Pedro Vieira, one of the three…

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.

Natalie Wolchover, “In a Numerical Coincidence, Some See Evidence for String Theory” at Quanta (January 21, 2022)

It means reworking Einstein’s math a bit.

At times, the advocacy for string theory begins to sound a bit like a religion:

Some physicists hope to see string theory win hearts and minds by default, by being the only microscopic description of gravity that’s logically consistent. If researchers can prove “string universality,” as this is sometimes called — a monopoly of string theories among viable fundamental theories of nature — we’ll have no choice but to believe in hidden dimensions and an inaudible orchestra of strings.

Natalie Wolchover, “In a Numerical Coincidence, Some See Evidence for String Theory” at Quanta (January 21, 2022)

But, in an important sense, it is a religion. They’re trying to make sense of the universe and eventually, that shades into metaphysics.

The paper is open access.

One Reply to “String theory again: Will a correction to Einstein save it?

  1. 1
    bornagain77 says:

    Peter Woit, over at “Not Even Wrong”, weighs in and calls the paper ‘hype,, from proponents of a failed research program.”

    This Week’s Hype – Jan. 21, 2022
    Excerpt: Today Quanta magazine has more of this sort of thing, with an article whose title shows up on the web as A Correction to Einstein Hints At Evidence for String Theory. The sub-headline tells us that

    In a quest to map out a quantum theory of gravity, researchers have used logical rules to calculate how much Einstein’s theory must change. The result matches string theory perfectly.

    which sounds pretty impressive. The article starts off with quotes such as:

    The hope is that you could prove the inevitability of string theory using these [bootstrap] methods,” said David Simmons-Duffin, a theoretical physicist at the California Institute of Technology. “And I think this is a great first step towards that.

    and

    Irene Valenzuela, a theoretical physicist at the Institute for Theoretical Physics at the Autonomous University of Madrid, agreed. “One of the questions is if string theory is the unique theory of quantum gravity or not,” she said. “This goes along the lines that string theory is unique.”

    The paper at issue is this one which appeared on the arXiv nearly a year ago. It’s not about string theory or about conventional quantum gravity in four space-time dimensions. The topic is graviton scattering in maximally supersymmetric theories in ten flat space-time dimensions, and the argument is that the basic principles of supersymmetry, Lorentz invariance, analyticity and unitarity imply a bound on the coefficient of the lowest order correction term. The only relation to string theory is that a string theory calculation of this correction coefficient satisfies the bound (as expected, since string theory is supposed to satisfy the assumed basic principles). Much is made of the fact that in string theory one can get any value of the coefficient consistent with the bound. This is taken as evidence for the “inevitability” of string theory, but I don’t see this at all. It’s more accurately evidence for the usual problem with string theory: it’s consistent with anything. If the authors of this paper had found that the string theory bound was different than their bound, they could have written a paper arguing that they had finally found a way to falsify string theory (measure the coefficient, if it was found to be in the region allowed by general principles but not by string theory, string theory would be falsified).

    The article does get right the motivations behind these claims:

    Some physicists hope to see string theory win hearts and minds by default, by being the only microscopic description of gravity that’s logically consistent. If researchers can prove “string universality,” as this is sometimes called — a monopoly of string theories among viable fundamental theories of nature — we’ll have no choice but to believe in hidden dimensions and an inaudible orchestra of strings.

    To string theory sympathizers, the new bootstrap calculation opens a route to eventually proving string universality, and it gets the journey off to a rip-roaring start.

    and it gives a little space to skeptics:

    Other researchers disagree with those implications. Astrid Eichhorn, a theoretical physicist at the University of Southern Denmark and the University of Heidelberg who specializes in a non-stringy approach called asymptotically safe quantum gravity, told me, “I would consider the relevant setting to collect evidence for or against a given quantum theory of gravity to be four-dimensional and non-supersymmetric” universes, since this “best describes our world, at least so far.”

    Eichhorn pointed out that there might be unitary, Lorentz-invariant descriptions of gravitons in 4D that don’t make any sense in 10D. “Simply by this choice of setting one might have ruled out alternative quantum gravity approaches” that are viable, she said.

    Another critique, though, is that even if string theory saturates the range of allowed ? values in the 10-dimensional setting the researchers probed, that doesn’t stop other theories from lying in the permitted range. “I don’t see any practical way we’re going to conclude that string theory is the only answer,” said Andrew Tolley of Imperial College London.

    I don’t at all understand why Quanta chose to cover this. All it does is help to spread hype and further the cause of the “resistance is futile” campaign from proponents of a failed research program.
    https://www.math.columbia.edu/~woit/wordpress/?p=12641

    In the comment section Woit goes on,

    It would be helpful it Quanta and other science publications would identify degenerative research programs and put warning labels on stories about them.,,,
    Failed ideas need to be recognized as such, not promoted by influential people and institutions.
    https://www.math.columbia.edu/~woit/wordpress/?p=12641#comment-239982

    In the comment section, Scott Aaronson and Sabine Hossenfelder also weighed in.

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