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A conversation with Nima Arkani-Hamed

On behalf of the Science Museum in London, science historian Graham Farmelo hosted a conversation with a top particle physicist of his generation, Nima Arkani-Hamed, on November 14th, 2013.

A 55-minute video of excerpts from the event was posted just two months ago. You may speed the video up by a factor of 1.25 or 1.5, if you wish ("options" wheel).

Nima has said lots of interesting and important things about theoretical physics of the 20th century (it's easy to highlight the breakthroughs of the 20th century in 3 minutes: relativity, quanta, and their cooperative applications: as a team, relativity and QM are hugely constraining), the recent past, the present, and the future; the LHC and the Higgs boson, and lots of related things. What the fundamental laws can and can't explain (the theories are effective and hierarchical)?

We're at a rather special era because we're beginning to ask a new type of questions that are deeper and more structured, Nima said.

Spacetime is doomed, doesn't exist, and has to be replaced. Farmelo wanted to call psychiatrists at the point but they would conclude that Nima is sane. Arkani-Hamed would also explain why the largest machine and experiment (the LHC) is needed to study the shortest distance scales – it's really due to the Heisenberg uncertainty principle. The vacuum is exciting, antimatter (Dirac...) may be produced. Some fine-tuning is needed to get a large Universe – and even to protect us from being black holes etc. (After this comment by Nima, I found Farmelo's frequent laughter both distracting and really really stupid for the first time; it was just "really stupid" before that.)

He also clarified that it's not true that we don't know how to combine QM and GR at all. We can calculate the first quantum corrections at long distances etc. Nima would explain why the physicists have mostly believed in a natural explanation of the Higgs' lightness etc. and this belief is starting to conflict with the experiments.

The folks in the audience have also asked some questions. Some of the questions were funny. You could expect that people who get seats in this small room where Arkani-Hamed speaks have a much-higher-than-average interest in and awareness of particle physics. But even after 40 minutes, one could hear questions like "So why don't you tell us, Nima, how you do your experiments?".

LOL – it's catastrophically hopeless but still funny enough. They calmly explained that Nima isn't an experimenter.

Nima would discuss what it meant to add new physics, that most proposed hypotheses may be immediately ruled out and it's a big achievement to construct a theory that isn't immediately dead. New physics shouldn't be just junk – it should better play some role and stabilize some instabilities and solve some hierarchy problems, and so on.

A guy in the audience didn't want to accept Nima's (obviously right) comments that the precise position and momentum of a particle (among other concepts that people used to believe) is meaningless in our Universe etc. An "argument" was that most people would probably disagree with Nima – what an "argument", holy crap. This claim about the meaninglessness must be an artifact of our current ignorance only, the guy would argue, and it will surely become meaningful again as the current stupid physicists are replaced by saner ones in the future. Nima would say that it's very unlikely that we would ever return to the conceptually simpler, classical underpinnings of quantum mechanics.

But even if there exists some more sophisticated miraculous loophole, we will have to radically change the meaning of all the words in the question (much like the meaning of many if not all words used by physicists has undergone lots of gradual as well as abrupt modifications in the past) before we get there, so it makes no sense to use our current language to attack those speculative future developments. Those comments by Nima are very important and often unappreciated by the laymen.

More generally, Nima would also say that the straightforward laymen's picture of the scientific method – prepare another clearcut theory of Nature, test it, rule it out, return back, prepare another one, and so on – is nothing like the actual theoretical physics as experts know it.

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reader David Miller said...


Off-topic, but I hope you will soon be commenting on Steve Koonin's column in the Wall Street Journal on global warming.

It's hard to believe that the physics profession will try to silence someone of Koonin's stature. I'll be interested to hear your take.

Dave Miller in Sacramento

reader John Archer said...

OT: (Oh dear. It seems this will be the second comment on this thread and both are OT.)

Dear Luboš,

Given your various interests I was wondering if you'd comment on the latest special issue of Nature on 'diversity' and their priestly editorial on it. In fact I was rather hoping you would and that you'd give it good kicking. Someone needs to and I know you have an ace set of studs on your boots just right for the job. :)

reader NikFromNYC said...

Amusing at best, sexual diversity lamentations, given how so many females in the hard sciences are nerdy lesbians likely better at math and theory due to being tomboys.

reader QsaTheory said...

Dear Lubos,

I was listening to this guy(link below) and going a bit more thoroughly through TQFT and I could not get the sense of Nima's words "it should better play some role and stabilize some instabilities and solve some hierarchy problems, and so on". I was wondering what is the reason for going through all this heavy duty math like Category and intersection theory and yet there appears to be no fundamentally new result( or is there ?) coming out even after many years.

reader John_QPublic said...

The reason the authors are under attack is that most non-dark energy models end up violating the prime dogma of cosmology: The Coperncian Principle. This is the source of the attacks. A new documentary, The Principle explores this sisue with Lawrence Krauss, George Ellis, Max Tegmark, Kaku Michio, Julian Barbour, Bernard Carr, and others. It is opening on October 24th in Chicago. www.The

reader John_QPublic said...

Here is a trailer

reader Gordon said...

"You may speed the video up by a factor of 1.25 or 1.5, if you wish ("options" wheel)."
Surely you are joking Mr. Motl...(Feynman title for those wondering)---- Nima already seems to be speaking and thinking near the speed of light---speeding him up by a factor of 1.5 would make things tachyonic. This was an interesting public lecture. I like the way he thinks. I did notice though that the words "string theory" were not mentioned although quantum gravity was...perhaps he just wanted to avoid stupid questions about the term, or else his excursions with twistors etc is pushing to the fore.

reader Luboš Motl said...

Dear David, thanks for your reminder.

Steve Koonin was the #1 or #2 U.S. government official supervising science (Science Department boss at DoE) under Obama - even such people may be against the orthodoxy.

I am sure he is under the attack of the hardcore alarmists - not *despite* his influence (or recent influence) but really *because* of it - although I would count him as a lukewarmer.

Incidentally, I would surely agree that Koonin is an achieved physicist, not just an official. See the thousands of citations of his computational and/or nuclear physics work

reader Luboš Motl said...

Dear QsaTheory, topological quantum field theory (and topological string theory) is motivated by mostly mathematical goals. The topic is directly linked to the physical theories describing the Universe but the true motivation is to understand mathematical structures of the abstract kind that mathematicians study, whether or not they apply to the Universe around us in any direct sense.

I personally consider TQFT and TST folks to be "mostly mathematicians". Nima was really talking about high-energy physics phenomenology - the construction and selection of models beyond the Standard Model that are supposed to foresee, predict, or analyze phenomena that should appear in a "foreseeable" future. That's a much more down-to-earth, physical, tangible topic than TQFT etc.

reader Luboš Motl said...

Dear Gordon, I personally like slower speech in many cases, I am not a native speaker and I can't follow most of the lyrics of generic songs and everyday-life fast movies and sitcoms in English, and so on. But the truth is that I did listen to this video at the 1.5 times sped up rate and had no trouble with that! ;-)

This conversation wasn't really focused on quantum gravity (and string theory) and Nima isn't really a "standard" string theorist - an applied one. Of course that his work is different than either the typical work under the name "quantum gravity" or the typical work under the term "string theory" so there is really no reason why they should be a substantial part of what he's talking about.

Still, when it comes to all the closely related conceptual questions - how exact QFT is, to what extent quantized GR works or doesn't work, how many theories do exist that unify GR and QM and are consistent, and so on - just be sure that the degree of agreement between him and string theorists (or e.g. me, to be specific) would be rather close to 100%. I would even say that e.g. I would endorse a higher percentage of his "closely related thoughts" than the percentage of endorsed thoughts by an "average string theorist" defined in some way. What I heard and read in recent years from Joe Polchinski, Erik Verlinde, ... or even my adviser Tom Banks seems partially insane to me. I am not familiar of any comparable insanity that Nima has ever said.

Of course that just mentioning "string theory" (and perhaps "quantum gravity"?) means to open a whole new minefield. But sometimes the bulk of the interested laymen etc. seem to have so "disconnected" views that it's enough to mention that the spacetime concept may be surpassed, or the position+momentum of a particle is meaningless, and one already faces intense backlash. And Nima did - even if I ignore Farmelo's often idiotic laughter. I don't know how much of his laughter is because Farmelo can't control his behavior for some reason and to what extent he fails to understand the validity, depth, and importance of the ideas that Nima was presenting. Nima was presenting in a playful language but *all* the things were totally serious and important. Farmelo would smile as if he thought that Nima would be constantly presenting some heresies etc. - but he hasn't done it once.

reader Uncle Al said...

Manufacture condoms to fit a kielbassa, and label them "medium." Give them a trace dusting of Advantame that is 20,000 times as sweet as sucrose.

reader Rathnakumar said...

Willie Soon is simply awesome!

reader Uncle Al said...

GR is deterministic geometry contrary to QM. GR arises via the Equivalence Principle (EP), never geometrically tested with matter. Do opposite shoes violate the EP? Vacuum supersonic expand to a 1 kelvin molecular beam

4-oxa-D_3-trishomocubane; a dipole moment needed; from furan plus benzoquinone.
doi:10.2174/138527212804004508, 10.1070/RC2010v079n11ABEH004119

If the racemate shows two rotational spectra in a chirped-pulse FT microwave spectrometer, the vacuum is chiral anisotropic toward hadronic matter, the EP is empirically falsified.

reader Eelco Hoogendoorn said...

It always annoys me when people claim that 'space and time do not exist'. The questions this statement raised in the audience could have easily been avoided with a little more precise language, but it may be feared that eliciting a sense of awe rather than understanding was exactly the goal, as with many science popularizers. 'OMG did you hear it guys space and time do not even exists, science is so deep and mysterious LOL, by the way deepak chopra is my hero!'. It may be feared that this is what the audience walked away with.

Of course space and time do exist; whether they are fundamental or emergent is another matter. It is just as moronic as saying 'LOL love does not exist its just a chemical!'. And what, chemicals do not exist? Explaining a phenomena in more fundamental terms or denying its existence are two completely different things. It is really that hard to make that distinction?

Excuse the rant; otherwise it was a pretty good interview. Aside from the super annoying giggle of the interviewer.

reader Andrius said...

Lubos, you seems to be in one of 0.17% of scientists that denies climate warming. Good luck in continuing hitting the wall...

See here:

reader OneClosedStringToRuleThemAll said...

Agreed. I also can recommend all lectures/speeches on youtube.

reader OneClosedStringToRuleThemAll said...

By Nima, sry

reader Troy said...

Try 0.5 speed, sounds like he had a few too many drinks before the talk

reader Ehab said...

He has also new 2 lectures at cornell

reader JollyJoker said...

I haven't watched it yet, but I assume Nimas work is something you'd consider serious even if it can't really be called "string theory" anymore. Even if you just call it "QFT maths" it might lead to new understandings.

Is it time to stop calling people "string theorists" if the most interesting work just considers ST a part of (the general blob known as) QFT?

reader Dilaton said...

Understanding the scientific method correctly is really not that hard...
But it is indeed where a lot of trouble starts: laypeople who wait for a new Einstein as a Messias, crackpots who think they are a new Einstein sent to overthrow everything, dimwits who try to start an unneeded revolution of science, and even an astonishing big number of (nottheoretical) physicists who claim that cutting edge fundamental physics is not science, etc...

Maybe there should be qualifying exams to get into the audience of talks given by great physicists?

I look forward to watch the interview, but not to the giggle of the interviewer ...
I guess he did not smile or laugh in agreement ...? This often happens to me when reading or hearing something I perfectly agree with and that excites me positively. For example when reading TRF and my GR- Nutshell contains tons of smileys, because Tony Zees funny comments make me LOL al the time :-).

reader Luboš Motl said...

You meant "QFT is a part of string theory", didn't you?

Nima's work is great but it's still not string theory as we understand it, so the last step of sophistication is missing. I don't know how one could express this idea without calling or not calling various researchers "string theorists".

reader Gene Day said...

It was not a pretty good interview, Eelco Hoogendoorn; it was an excellent interview.

reader Eelco Hoogendoorn said...

So you approve of conflating 'denying the existence of' and 'seeking a deeper explanation for' a phenomenon?

reader Luboš Motl said...

LOL, let me admit that I approved that comment (from a banned user) intentionally - a bit of narcissism can't hurt and being next to Sarah Palin, Ron Paul, and Richard Muller is pretty cool, isn't it? ;-)

reader Gordon said...

Yes, but 1.5x might make him sound like he was breathing helium, and he already speaks quickly. Admittedly, given the level of the talk, one could speed things up and act like Mr Data without losing the thread.
BTW, it is good to see first line mathematicians collaborating with theoretical physicists...something that seems to be reviving---Witten and Atiyah, Nima and Pierre de Ligne...of course, the best of the best in the past have been both---Newton, Gauss, Riemann etc.

Nima has said that he thinks that both locality and unitarity will have to go, by which, I think he is just saying that they wont be fundamental. Do you agree, Lubos?

reader Luboš Motl said...

Dear Gordon, the 1.5-times-acceleration button doesn't actually increase the frequency of the sounds, unlike helium, it just makes them shorter!

Well, I agree that in the amplituhedron description of the amplitudes, neither locality nor unitarity are principles one starts with. They are surprising "bonus features" of the amplitudes that may be derived from rules that are motivated differently.

However, both locality and unitarity - for the N=4 gauge theory, to be specific - are still obeyed exactly. If something holds exactly, I would probably avoid actively saying that they are "not fundamental" because "not fundamental" is usually interpreted as (among other things) "inevitably just approximate".

There is a terminological dilemma here that makes an unequivocal answer harder - and unimportant. "Fundamental" may either mean "a principle that starts at the beginning of the construction of a theory" - and those laws are not fundamental in this sense; or "something that still exactly holds if all the principles of the theory are imposed", which is still true even if the locality and unitarity aren't manifest.

More generally, I do think that locality ceases to hold exactly, at least in some sense, when gravity is added to the mix; I think that the exact unitarity is ultimately required for any theory that is interpreted physically, as predictions for experiments.

reader Jim W said...


You worked in proximity with Nima right? Would you care to share any personal or professional stories about him? I mean stories that reflect well on him and his abilities not gossip stuff.

reader Luboš Motl said...

He's wonderful and full of energy and constantly keeping all brains in his vicinity working, not to mention that he also has some amazing skills, like being an excellent piano player etc.

reader Gene Day said...

I think Nima made it clear that space and time deserve a scientific explanation just as the positions of the planets deserved such an explanation 350 years ago.

reader lukelea said...

Interesting things he has to say, especially the idea that time and space are doomed. Reminds me of a ditty T.S. Eliot wrote when he was still a child:

"If time and space as sages say
are things that cannot be
the little bee that lives a day
has lived as long as we"

Also, Blake's "eternity in a grain of sand."

reader Eelco Hoogendoorn said...

Not clear enough apparently, because it triggered a confused question, which he answered by reiterating that it 'does not exist', without emphasizing that what he really meant was that they might be explained as emergent features of something more fundamental. 'hidden variables do not exist' and 'spacetime does not exist' are really two very different statements. Why go anywhere near conflating such different statements, when we have perfectly precise and concise language to express exactly what we mean?

reader Luboš Motl said...

Dear Eelco, I would agree with you if you said that space and time will have to keep *some* role in all successful research of physics because our observations will probably always take place in something that *looks* like space and time. On the other hand, hidden variables may be eliminated entirely because they are really wrong.

On the other hand, that's where the differences exist. I think that it's completely plausible that at a sufficiently fundamental level, the space and time do not exist in a very similar sense as the hidden variables do not exist, and indeed, our local quantum field theories may be fundamentally deluded in an analogous way as the Bohmian attempts to describe quantum mechanics!

We may be victims of imagining some unphysical things that are *analogous* to imagining that there are hidden variables, and when we abandon these things - the space time - in analogy with abandoning the hidden variables, we will find a more correct, more fundamental, and universally applicable understanding of physics.

reader Eelco Hoogendoorn said...

' and time will have to keep *some* role in all successful research of physics because our observations will probably always take place in something that *looks* like space and time.'

Well, yes. If some emergent theory of spacetime gives predictions which are at odds with our 'classical' notions of space and time, then the theory would be wrong. Space and time still have to emerge beyond the planck scale for such a theory to be consistent with existing evidence.

By analogy, GR gives a deeper understanding of gravity then newton had; it is inaccurate, or at least a misleading use of language, to say that GR proves that gravity 'does not exist'. It may not exists in the form which newton imagined it, but that doesn't stop apples from falling to the ground, nor should we imply this may be the case.

reader Luboš Motl said...

Dear David, just one update on Koonin. Physics Today

(ran by American Institute of Physics, AIP), has pretty much reviewed - without any criticism - Koonin's key theses. One could say that they reproduced them.

reader Leo Vuyk said...

to Nima Arkani Hamed spacetime is doomed, doesn't exist, and has to be
So we have to postulating new, exotic ingredients and inventing radically new construction
principles governing physics at the relevant, ultra-high Planckian energy scale.
My proposal is called: Construction principles for chiral “atoms of spacetime” based on
geometrical 3-D chiral vacuum lattice models and some consequences for Space
and Time, such as cyclic Universal time, and local time.
See also:

reader Nancy said...

First of all congratulations on the top 10 in the Higgs Boson challenge!

This one seems to be much more applied and easier. Hope to see you in the top 10 again.

reader Luboš Motl said...

Thanks a lot, Nancy! I completely agree with your description and comparison.

Today, I haven't used up my daily limit of 3, even after spending just minutes on it per day in previous days, and I am afraid that I abandoned this contest from the 30th place - not it's because it's hard but because it may be easy for many others so something else than in the Higgs contest may decide about the leaders.

reader Nancy said...

Dear Lubos,

On a somewhat unrelated topic (in fact a bunch of topics). I would love to see your opinion and something in your blog on: ITER, ISIS and this fantastic recent PNAS paper:

And please accept my apologies for taking your valuable time and posting things that you may not be interested in.

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