# Quantum Mechanics and Spacetime in the 21st Century

This evening’s Hollywood-style entertainment came from the Perimeter Institute, where they had a big public event, live-streamed to the world, featuring Nima Arkani-Hamed speaking on Quantum Mechanics and Spacetime in the 21st Century. You should be able to watch the thing soon from the Perimeter site, should be posted at some point here.

The talk was pretty much the same as many other such Arkani-Hamed talks, quite close to the one at the IAS nearly four years ago, discussed here. In this format he can’t go on forever, was cut off by around an hour and a half, so said he couldn’t get to the third part of the talk, which might have been the 21st century part (amplituhedron?). As in the IAS talk, what he did cover was first mostly the 1960s sort of arguments that Weinberg describes in the first volume of his textbook about the constraints on consistent relativistic QFTs. Then an advertisement for the Veneziano model and string theory. The last part of the talk was a long advertisement for SUSY, ending with an acknowledgement that it wasn’t showing up at the LHC. He’s now giving 2018 as the date for when we’ll know about LHC-scale SUSY, which is moved up from the 2020 of the IAS talk of 2011, but still very different than the “year or so after LHC startup” he was saying in 2005. The current plan is for maybe 10 inverse-fb next year, 50 in 2016. If nothing shows up then, I don’t see that the next 50-100 supposedly coming by 2018 have any real chance of finding SUSY.

One thing that struck me about the talk was its odd combination of over-the-top enthusiasm (“this is the greatest time ever!”) and intense defensiveness. He kept emphasizing the claim that theorists, even without experiment to keep them honest, were working with highly constrained rules, that it was very hard to do anything not obviously wrong. He denied sociology had to do with what unsuccessful ideas people decide to pursue. He didn’t address at all the “not even wrong” problem: what about the things like the landscape, baroque constructions that evade being wrong by being empty? I like a lot this picture and quote from Perimeter:

If you manage to find one idea that’s not obviously wrong, it’s a big accomplishment. Now, that’s not to say it’s right. But not obviously being wrong is already a huge accomplishment in this field.

I think the defensiveness here that’s coming through is very personal. He’s gotten a $3 million award and a reputation as a leader of the field for ideas that haven’t worked out, but which he can defend as “not obviously wrong” and thus a “huge accomplishment”. All in all, the talk was very backward looking, recapitulating the SUSY/string theory ideology that has led us to where we are. It looks like he’s planning on hanging in until 2018 with the same story, only then maybe admitting failure (and possibly going for “the multiverse did it, we never had a chance” cop-out). He did end with an upbeat claim that the SUSY picture being all wrong would be very exciting, opening up the field by showing we need something completely new. The obvious question for him is “you pretty clearly wouldn’t now bet$10 on SUSY at the LHC, so why wait?” Why not stop giving promotional talks about SUSY? One thing he could have done that would have generated some excitement in the field would be to have pitched out the two-thirds of the talk he did give, publicly saying these ideas aren’t working, and talked about something from this century, amplitudes or whatever, the part of the talk he never got to.

Well, maybe in 2018…

Update:
You can watch the talk here, along with some online commentary in a chat box that was rolling during the talk.

Update: There was also a more technical talk at Perimeter by Arkani-Hamed, earlier in the day, on Cosmological Collider Physics. The video doesn’t seem to be available yet though.

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### 17 Responses to Quantum Mechanics and Spacetime in the 21st Century

1. Neville says:

Off topic: For a real hoot, listen to Barry Simon’s story starting at 1:05:41 of http://www.youtube.com/watch?v=GIQXE_2a3KI

The punch line is at 1:07:02.

2. blue says:

I have a PhD in mathematical physics and I am desperately looking for a postdoc position of around K$40/y with NO hope, and he just won a M$3 prize for “not obviously being wrong”!!! Tyrion Lannister: “If you want justice, you’ve come to the wrong place”.

3. manfred Requardt says:

Dear Peter, I am always fond of reading your commentaries about such strange kind of physics talk. Such talks always get a lot of attention but there is almost no physical progress being conveyed.

4. Hamish says:

“Not obviously wrong”…sounds like a good name for a physics blog!

5. Dimitrelis says:

@Peter:
By negation of the statement “not obviously wrong” one gets “obviously not wrong”, i.e. “obviously right”…
You have to be obviously right, in order not be considered obviously wrong.
So what does he mean with “Now, that’s not to say it’s right”?

…hmmm, I must be “obviously” wrong.

6. Shantanu says:

Peter at some point the problem also lies with the hosts . I am pretty sure they must have been aware of similar hype he must have mentioned in other talks(many of which can be easily found from the web). Were there hard questions(similar in spirit to what you wrote in this article )? Its somewhat sad that people like blue and others are having
a hard time finding jobs and here …

7. Peter Woit says:

The Arkani-Hamed show really is quite a performance. His colleagues and the public do seem to just eat it up uncritically. In this case, since he went on so long, they had no time for questions.

8. Shantanu says:

Peter, the technical talk is now available.

9. Peter Woit says:

Shantanu,
I’m still getting an error message if I try to play the video. Audio and a pdf of images is available.

10. Shantanu says:

Peter you may need to contact the help desk (assuming you haven’t tried other web browsers etc). I had a technical problem in viewing
many PI talks recently(not this one) and I contacted them, and since then I don’t see a problem. (although I don’t know what was the problem and what was the fix done
by PI folks)

Listening to Arkani-Hamed speak, I am reminded of the famous poem by W.B. Yeats:

“The best lack all conviction, while the worst
Are full of passionate intensity.”
http://en.wikipedia.org/wiki/The_Second_Coming_(poem)

12. First Last says:

Hi Peter, if I understand Arkani-Hamed correctly, the only graviton-graviton scattering amplitude consistent with relativity and qm (unitarity) that has been found is the Veneziano amplitude. Is that correct? That would seem to be a strong indication it is the one to pursue, isn’t it?

13. Peter Woit says:

First Last,
Sure, that’s the main motivation for string theory. But Arkani-Hamed neglects to mention that to get a consistent amplitude, you need to be in flat space-time 10d, which is, well, obviously wrong. To get the 4d Veneziano amplitude he was advertising, you have to get to get rid of 6 dimensions, and that is why the program has failed.

Another point that struck me is that he’s convinced space-time is “doomed”, and if so, amplitudes at short distances are irrelevant, since there is no space-time at these distances. There’s a huge inconsistency between “we must do string theory because it has well-behaved amplitudes at short distances” and “we know there is no space-time at short distances”.

14. Nobody says:

“Not obviously wrong” approaches “not even wrong”.

Progress!

15. NEOW says:

But now there’s an even lower rung:
“not even obviously wrong”

16. Peter Woit says:

All,
If you have something interesting to say about the Arkani-Hamed talk, please do. On the other hand, if you just want to repeat content-free slogans about quantum gravity, please do that elsewhere.

17. Gus Bici says:

Listening to the “more technical talk” (MP3) by Arkani-Hamed and it ended abruptly before Nima could finish “what really bothered him”. He said it might not bother others, but it really really bothered him. Can anyone summarize Nima’s bother?