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.