Maybe it’s because people are at home with nothing else to do, but somehow the COVID-19 pandemic seems to be having the side-effect of generating new infections of “test of string theory” hype, a disease common many years back that seemed to more recently be under control. The example of a few days ago has now spread widely (see for instance Popular Mechanics), sometimes mutating into tests of “sting theory”. Today there’s a new example out, on the middle of the front page at Scientific American: Will String Theory Finally Be Put to the Experimental Test?

Of course the answer is “No”, this is just one more in the Swampland strain of string theory hype. This latest example is based on a paper by Bedroya and Vafa, where they make a “Transplanckian Censorship Conjecture”. The weird aspect of this kind of string theory hype is that it’s not a “test of string theory”, because it really has nothing to do with string theory. The authors of this paper are making a conjecture about “any consistent theory of quantum gravity”. If their conjecture is true we shouldn’t see the kind of B-modes in the CMB that were mistakenly claimed in the BICEP2 fiasco of 2014. So, the “test” here is a claim of falsification if experiments do for real see these B-modes. But what is being tested is a conjecture about any consistent theory of quantum gravity (one with very weak evidence). If B-modes are seen by a future experiment, the two possible conclusions to be drawn will be:

- There is no consistent theory of quantum gravity.
- The Transplanckian Censorship Conjecture is wrong.

It’s pretty clear what the correct choice between these two will be, and none of this will “test string theory.”

**Update**: I should have also pointed to this paper. Will Kinney today gave a talk, It Came From the Swampland, which went over this subject seriously in detail. His conclusion, which seemed to be shared by a string theorist he was talking to at the end, was pretty much that these conjectures should not be taken seriously. It looks like they’re already in conflict with both experimental results as well as theoretical model-building.

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Just to mention that this week they officially cancelled the The Arithmetic of the Langlands Program series of events of this year at Bonn.

Zovi,

At this point I think pretty much everything not purely online has been cancelled for the next couple months and often beyond. A good point is made by Peter Coles here

https://twitter.com/telescoper/status/1240963587138555905

“It’s now even easier to identify fake academic conferences – they’re the ones that haven’t been cancelled.”

You missed the most important alternative which can be concluded, if B modes are ever discovered — Inflation is wrong. There are alternatives to inflation which can predict a large ‘r’ and still be perfectly compatible with this conjecture. In fact, in some follow-up work, it has been shown how even some (highly-contrived) models of inflation might also survive the TCC and yet produce a larger ‘r’. So, I think the conclusions should really be:

1) Inflation is wrong, or

2) The TCC is wrong.

It, most certainly, is not that there are no consistent theories of quantum gravity. But I completely agree with you that this, therefore, cannot be a test for string theory.

Rajesh,

Thanks, good point. However, if we ever do see a non-zero r, surely more film crews will show up at Andrei Linde’s door, and he and the Stanford press office will again tell us about how non-zero r is “smoking gun” evidence for inflation. So, that’s the point we’ll be starting from…

@Rajesh

and that ‘or’ is presumably not exclusive!

Not to threadjack, but it’s been making the rounds that Phil Anderson passed away yesterday at the age of 96. Truly, the end of an era, as he played a huge role in defining the discipline of condensed matter physics as well as discovered (if that’s the appropriate term) what is now known as the Higgs mechanism.

Douglas Natelson,

Thanks, writing something now about Anderson (and including a link to your blog for more about his work).

Reported in Nature News [1]: Mochizuki’s papers have been accepted for publication, with no substantial changes.

[1] https://doi.org/10.1038/d41586-020-00998-2 (not a 1st of April posting)