I’ve been a daily reader of your blog for about 8-10 years, or whenever it started, since after reading your book. I’ve been generally skeptical of string theory for a very long time, maybe 30 years or more. (I joined Intel Corp. in 1974 as a device physics guy, working on DRAM memory chips in the early days. Took classes from Jim Hartle and Douglas Scalapino at UCSB, but am by no means a graduate-level physicist! Still, I follow it.)

Iroinically, two of my favorite physicists currently speaking are Leonard Susskind and Nima Arkani-Hamed. Though both are associated in some way with string theory, both are excellent speakers. (I could add that both are speaking a lot about things that are not directly associated with string theory. I don’t think either has given up on string theory, just that their interests seem to be in other areas. While one can criticize string theory, it seems to have directly or tangentially led to some interesting other theories and some new math. A point I recall you have also made._)

I am glad that your criticisms of some aspects of string theory have not extended to criticisms of either of these two, or of Witten, Maldacena, or others. (I am not happy that a Czech blogger, whose lengthy explanations I often like, is so prone to personalizing his criticisms.)

Living only about 45 miles southeast of Stanford, outside of Santa Cruz, I have been to half a dozen or so of Susskind’s talks, plus have seen him hosting a bunch of talks. Never made it to Arkani-Hamed’s talks, but have greatly enjoyed his videos. Have seen the Cornell 5-part series about 2.5 times (the final two more than three times.)

Thanks!

–Tim May

]]>Btw, coupling EM to matter vis gauge symmetry is an entirely classical concept, i.e. classical field theory. Dirac equation is as classical as the Klein-Gordon equation, as long as you understand them as equations for fields, as opposed to relativistic QM. In fact, the whole Standard Model action is classical, together with the Higgs mechanism and all… Quantization only builds on top of that, leading to QFT.

🙂

Marko

Penrose’s book is kind of the opposite of Susskind’s. It’s deeply geometrical, but at the same time really is not appropriate for beginners, many professional mathematicians and physicists find it challenging to follow.

The main reason I haven’t written up some of these things myself it that there are many other places that this has been done. For some suggestions, see

https://mathoverflow.net/questions/72160/maxwells-equations-and-differential-forms

Jim Holt,

He does use gauge symmetry for the coupling of EM to matter, although for particles coupled to EM (gauge potential changes the action for a particle trajectory). In this book everything is classical, so he can’t get coupling to EM via gauge symmetry of a wave-function. The Klein-Gordon equation is discussed, but treated as an example of a Lorentz invariant classical field (somewhat of a motivation for the classical EM Maxwell equations, not something used to describe matter).

]]>Thanks! I somehow missed that one. Surprising that this summer there weren’t a bunch of articles in the press about how quantum computers would open up wormholes suitable for teleportation.

]]>Amazing statement: “teleportation … after a suitable time”.

A teleportation whit a delay!

https://arxiv.org/abs/1707.04354

Teleportation Through the Wormhole

Leonard Susskind, Ying Zhao

ER=EPR allows us to think of quantum teleportation as communication of quantum information through space-time wormholes connecting entangled systems. The conditions for teleportation render the wormhole traversable so that a quantum system entering one end of the ERB will, after a suitable time, appear at the other end. Teleportation requires the transfer of classical information outside the horizon, but the classical bit-string carries no information about the teleported system; the teleported system passes through the ERB leaving no trace outside the horizon. In general the teleported system will retain a memory of what it encountered in the wormhole. This phenomenon could be observable in a laboratory equipped with quantum computers.

]]>Looks like I was mistaken, but you should go with my initial impression of your question, one of rhetorical sarcasm. Meaning, there is no viable “modern theory of quantum gravity” 😉

]]> https://arxiv.org/abs/1707.05448

The Sum Over Topological Sectors and θ in the 2+1-Dimensional CP1 σ-Model

Daniel S. Freed, Zohar Komargodski, Nathan Seiberg

as well?

]]>