This Week’s Hype
Today’s Washington Post has an opinion piece from Brian Greene, running under the demonstrably false title Decades later, string theory continues its march toward Einstein’s dream.
In the piece, the argument of string theory critics is given as:
Critics argue that the situation is untenable, noting, “If you can’t test a theory, it’s not scientific.” Adherents counter, “String theory is a work in progress; it’s simply too early to pass judgment.” The critics retort, “Forty years is too early?” To which the adherents respond, “We’re developing what could be the most profound physical theory of all time - you can’t seriously cross your arms, tap your foot and suggest that time’s up.”
The problem with the results of forty years of research into string theory is not that progress has been too slow but that it has been dramatically negative. To see this, one can just compare the text of chapter 9 of Greene’s 1999 The Elegant Universe, which has an extensive discussion of prospects for testing string theory by finding superpartners, fractionally charged particles, or cosmic strings. Twenty-five years later, the results of experimental searches are in: no cosmic strings, no fractionally charged particles, and most definitively no evidence of superpartners of any kind from the LHC.
The other sorts of predictions advertised in that chapter are based on the idea that string theorists would better understand the theory and be able to make testable predictions about neutrino masses, proton decay, axions or new long range forces, the nature of dark matter, and the value of the cosmological constant. Instead of progress towards any of these, things have gone in the opposite direction: all evidence from better understanding of string theory is that it either naturally predicts things in violent disagreement with experiment (wrong dimension of space time, huge number of new long-range forces, …) or predicts nothing at all. 25 years later, Greene now goes with the latter:
The challenge for string theory is that it has yet to produce any definitive, testable predictions.
The article goes on to make a different case for string theory:
… string theory continues to captivate seasoned researchers and aspiring students alike because of the remarkable progress that has been made in developing its mathematical framework. This progress has yielded provocative insights into long-standing mysteries and introduced radically new ways of describing physical reality.
For instance, string theory has provided unmatched insights into the surface of black holes, unraveling puzzles that have consumed some of the greatest minds, including Stephen Hawking. It has offered a novel, though controversial, explanation for the observed speedup of the universe’s expansion, proposing that our universe might be just one of many within a larger reality than conventional science ever imagined.
The problem here is that these supposed advances aren’t from advances in string theory. If you follow the link above that justifies “string theory has provided unmatched insights into the surface of black holes”, you’ll find the text:
Most physicists have long assumed it would; that was the upshot of string theory, their leading candidate for a unified theory of nature. But the new calculations, though inspired by string theory, stand on their own, with nary a string in sight. Information gets out through the workings of gravity itself - just ordinary gravity with a single layer of quantum effects.
The string theory “explanation” for the value of the CC is just the “anthropic” explanation, which besides not really being a scientific explanation, has nothing to do with string theory.
The piece ends with something highly speculative and ill-defined (ER=EPR) that has nothing to do with string theory:
Roughly, it’s as if particles are tiny black holes, and the entanglement between two of them is nothing but a connecting wormhole.
If this realization holds up, we will need to shift our thinking about the unification of physics. We have long sought to bring general relativity and quantum mechanics together through a shotgun wedding, fusing the mathematics of the large and the small to yield a formalism that embraces both. But the duality between Einstein’s two 1935 papers would suggest that quantum mechanics and general relativity are already deeply connected - no need for them to marry - so our challenge will be to fully grasp their intrinsic relationship.
Which would mean that Einstein, without realizing it, may have had the key to unification nearly a century ago.
Where string theory research is after 40 years is not on a continuing march forward towards “Einstein’s dream”, but in a state of intellectual collapse with no prospects of any connection to the real world, just more hype about vague hopes for something different, something for which there is no actual theory.
Update: I recommend checking out Sabine Hossenfelder’s latest youtube piece, which is mostly devoted to the Brian Greene wormhole publicity event stunt discussed earlier here. Near the end of the video, she tells a story that explains a lot about why this kind of thing keeps going on (see here). She had been writing a regular column for Quanta Magazine, but they stopped publishing her after she wrote a column in which she argued that physicists should not be misleading the public by claiming that the “black holes” supposedly on the other side of a duality from a given quantum system were actual physical black holes.
What she was warning about in 2019 is an essential part of the wormhole publicity stunt, and of other similar continuing efforts that have been going on for years. One impetus behind this nonsense has always been clear: there’s attention to be gotten, and money to be made. Another factor though is the one Hossenfelder explains here. Press outlets devoted to science want to publish positive news about scientific advances, want nothing to do with authors who explain that this positive news is nothing but hype.
https://www.math.columbia.edu/~woit/wordpress/?p=14133