...or a yogi and another nude man?
Exactly one week ago, Andrew Strominger of Harvard gave a Science and Cocktails talk in Christiania – a neighborhood of Copenhagen, Denmark.
The beginning of this 64-minute lecture on "Black Holes, String Theory and the Fundamental Laws of Nature" is rather extraordinary and if you only want to see the weirdest introduction of a fresh winner of the Dirac Medal, just listen to the first three minutes of the video.
However, you will obviously be much more spiritually enriched if you continue to watch for another hour – even though some people who have seen similar popular talks by Andy may feel that some of the content is redundant and similar to what they have heard.
After the introduction, you may appreciate how serious and credible Andy's and Andy daughter's illustrations are (sorry, I can't distinguish these two artists!) in comparison with the mainstream culture in the Danish capital.
At the beginning, Andy said that it's incredible how much we already know about the Universe. We may design a space probe and land it on Mars and predict the landing within a second. We are even able to feed roast beef to Andrew Strominger and make him talk as a consequence of the food, and even predict that he would talk.
It's equally shocking when we may find something clear we don't understand – something that looks like a contradiction. Such paradoxes have been essential in the history of physics. Einstein was thinking what he would see in the mirror if he were running by the speed of light (or faster than that) and looking at his image in the mirror in front of him. Newton's and Maxwell's theories gave different answers. Einstein was bothered by that.
The puzzle was solved... there is a universal speed limit, special relativity, and all this stuff. About 6 other steps in physics are presented as resolutions to paradoxes of similar types. If we don't understand, it's not a problem: it's an opportunity.
Soon afterwards, Andy focuses on general relativity, spacetime curvature etc. The parabolic trajectories of freely falling objects are actually the straigh(est) lines in the curved spacetime. After a few words, he gets to the uncertainty principle and also emphasizes that everything has to be subject to the principle – it's not possible to give "exceptions" to anyone. And the principle has to apply to the space's geometry, too.
There is a cookbook how to "directly quantize" any theory, and this procedure is amazingly tested. If you apply the cookbook to gravity, GR, you get carbagan which is great because it's a lot of fun. ;-) He says we will need "time" to figure out whether the solution we have, string theory, is right in Nature. However, already now, some more basic Harvard courses have to be fixed by some insights from the string course.
Suddenly he mentions Hawking and Bekenstein's ideas about black holes. What do black holes have to do with these issues? They have everything to do with them, it surprisingly turns out. An introduction to black holes follows. Lots of matter, escape velocity, surpasses the speed of light – the basic logic of this introduction is identical to my basic school talk in the mountains a few months ago. ;-) The talks would remain identical even when Andy talks about the ability of Karl Schwarzschild to exactly solve Einstein's equations that Einstein considered unsolvably difficult. Einstein had doubts about the existence of the black holes for quite some time but in the 1960s, the confusion disappeared. Sgr A* is his (and my) key example of a real-world black hole.
Andy says that there's less than nothing, namely nothing nothing, inside black holes. I am not 100% sure what he actually means by that. Probably some topological issues – the Euclidean black hole has no geometry for \(r\lt r_0\) at all. OK, what happens in the quantum world? Particles tunnel out of the nothing nothing and stuff comes out as the black body radiation – at Hawking's temperature. Andy calls this single equation for the temperature "the Hawking's contribution to science" which slightly belittles Hawking and it's surely partly Andy's goal but OK.
He switches to thermodynamics, the science done by those people who were playing with water and fire and the boiling point of carbon dioxide without knowing about molecules. Ludwig Boltzmann beautifully derived those phenomenologically found laws from the assumption that matter is composed of molecules that may be traced using the probabilistic reasoning. He found the important of the entropy/information. Andy wisely presents entropy to be in the units of kilobytes or gigabytes - because that's what ordinary people sort of know today.
Andy counts the Hawking-Bekenstein entropy formula among the five most fundamental formulae in physics, and perhaps the most interesting one because we don't understand. That's a bit bizarre because whenever I was telling him about the general derivations of this formula I was working on, aside from other things, Andy would tell me that we didn't need such a derivation! ;-)
Amusingly and cleverly, he explains the holographic entropy bounds by talking about the Moore's law (thanks, Luke) that must inevitably break down at some point. Of course, in the real world, it will break down long before that... Now, he faces the tension between two pictures of black holes: something with the "nothing nothing" inside; or the most complicated (highest-entropy) objects we may have.
Around 41:00, he begins to talk about string theory, its brief history, and its picture of elementary particles. On paper, string theory is capable of unifying all the forces as well as QM with GR, and it addresses the black hole puzzle. String theory has grown by having eaten almost all the competitors (a picture of a hungry boy eating some trucks, of course). The term "string theory" is used for the big body of knowledge even today.
I think that at this point, he's explaining the Strominger-Vafa paper – and its followups – although the overly popular language makes me "slightly" uncertain about that. But soon, he switches to a much newer topic, his and his collaborators' analysis of the holographic dual of the rotating Kerr black holes.
Andy doesn't fail to mention that without seeing and absorbing the mathematics, the beauty of the story is as incomplete as someone's verbal story about his visit to the Grand Canyon whose pictures can't be seen by the recipient of the story. The equation-based description of these insights is much more beautiful for the theoretical physicists than the Grand Canyon. Hooray.
Last nine minutes are dedicated to questions.
The first question is not terribly original and you could guess that. What kind of experiments can we make to decide whether string theory is correct? Andy says that the question is analogous to the question to Magellan when he's in the middle of his trip around the Earth, when will he complete the trip? We don't know what comes next.
Now, I exploded in laughter because Andy's wording of this idea almost exactly mimics what I am often saying in such contexts. "You know, the understanding of Nature isn't a five-year plan." Of course, I like to say such a thing because 1) I was sort of fighting against the planned economy and similar excesses already as a child, 2) some people, most notably Lee Smolin, openly claimed that they think that science should be done according to five-year plans. It's great that Andy sees it identically. We surely don't have a proposal for an experiment that could say Yes or No but we work with things that are accessible and not just dreamed about, Andy says, and the work on the black hole puzzle is therefore such an important part of the research.
The second question was so great that one might even conjecture that the author knew something about the answer: Why does the entropy and the bounds scale like the area and not the volume? So Andy says that the black hole doesn't really have the volume. We "can't articulate it well" – he slightly looks like he is struggling and desperately avoiding the word "holography" for reasons I don't fully understand. OK, now he said the word.
In the third question, a girl asks how someone figured out that there should be black holes. Andy says that physicists solve things in baby steps or smaller ones. Well, they first try to solve everything exactly and they usually fail. So they try to find special solutions and Schwarzschild did find one. Amazingly, it took decades to understand what the solution meant. Every wrong thing has been tried before the right thing was arrived at.
Is a black hole needed for every galaxy? Is a black hole everywhere? He thinks that it is an empirical question. Andy says that he doesn't have an educated guess himself. Astronomers tend to believe that a black hole is in every galaxy. Of course, I would say that this question depends on the definition of a galaxy. The "galaxies" without a black hole inside are probably low-density "galaxies", and one may very well say that such diluted ensembles don't deserve the name "galaxy".
In twenty years, Andy will be able to answer the question – which he wouldn't promise for the "egg or chicken first" question.
I didn't understand the last question about some character of string theory. Andy answered that string theory will be able to explain that, whatever "that" means. ;-)
Another intense applause with colorful lights. Extraterrestrial sounds conclude the talk.
...or a yogi and another nude man?