Does the Multiverse Exist? | Full Debate (43 minutes)Participants were Harvard's string theorist Cumrun Vafa whom I know very well, you know, CERN's phenomenologist John Ellis, and an assistant professor of religion, feminism, gender, and sexuality Mary Jane Rubenstein of Wesleyan University. Religion and feminism is quite a combination – maybe she hasn't noticed yet that according to religion, feminists will burn like brown coal in the hell for the eternity (because of the eternal character of the oxidation, feminist corpses in hell count as a renewable energy source). As we will see, she was the nicest surprise of that event.
Cumrun started by mentioning he was convinced string theory was a theory of Nature, also because it has allowed us to calculate the precise entropy of black holes – he modestly overlooked the fact that it was he and Strominger who pioneered this amazing sub-industry.
Near the beginning, the charming and talkative Ms Rubenstein started to talk a lot. For a few sentences, I thought: She must be a lady who likes to talk and her greatest intellectual achievement was to learn how to pronounce the word "epistemologically" which she really likes. But the following minutes have changed my mind profoundly. She has presented a long monologue – although with some notes – about the constants of Nature, quantum field theory, interesting and uninteresting types of the multiverse, and so on.
So I obviously concluded: This is not a normal behavior for a religion-and-feminism professor. She must have a coach who is a physicist because most of the stuff she said – including the radius of the visible Universe at over 40 billion light years, something that even many enthusiastic fans of physics get wrong – was totally correct and nontrivial. Well, she also suggested that nobody loved the ekpyrotic or cyclic Universe (correct) and that mathematics makes the many worlds interpretation of quantum mechanics inevitable (incorrect).
I started to think. Well, she has a physics coach but I must be capable of saying even more, right? I decided that the coach has to be Brian Greene, especially because her monologues was overlapping so much with the Hidden Reality, a book by Greene that I also translated to Czech, a decade after The Elegant Universe. So I have made a prediction: It will be easy to find Rubenstein and Greene on the same places. This prediction has passed some tests (she wrote a book heavily referring to Greene) so now I am willing to bet a lot that she would agree that she got most of her physics and cosmology from Brian Greene.
Although her monologue was interesting, she was largely ignored. Instead, the host David Malone had a lot of fun with the claim that there were 10500 Universes. Cumrun said it was an underestimate – because the total number of vacua was clearly infinite (just take the AdS5 x S5 vacua of type IIB at all allowed radii for an infinite set!) – which the host found very entertaining.
It's cute when children laugh. You present something and a schoolkid tries to see a penis in every sentence (about amino acids, for example). You may enjoy it as well but you quickly realize it is silly. There is nothing to laugh about here.
It is very clear why the host is laughing – because he is another irrational layman who finds a "very large number of solution" to be a terrible thing – laymen are generally terrified by mathematics, numbers, and especially by large numbers. But there is nothing terrible about it at all. An equation or a theory has some set of solutions. The number of solutions is a non-negative number, an integer or infinity, and it is whatever it is. If we can't prove that a particular value is correct or other values are incorrect, then all values are equally acceptable. It is completely irrational to be biased against any solution. And it is just childish to laugh when someone determines that the right number is a large constant or infinity.
Incidentally, the host also said
10500 is ten followed by 500 zeroes.Not really. It is ten followed by 499 zeroes! ;-) The normal people say it is one followed by 500 zeroes.
OK, I thought that this laughter of ignorance by the host wouldn't be addressed at all even though it's really a crucial point here. But it happily did get addressed. I am not sure whether it was a lucky coincidence or someone's grander plan. John Ellis introduced himself. Much of the attraction to string theory is about symmetries – string theory is the queen of symmetries. I actually disagree with that (string theory suppresses the role of symmetries in many ways, and also bans any global symmetries) but in the context of these conceptual discussions, it is a detail because the character of string theory's beauty is analogous to the beauty of the symmetries. Ellis said many things about himself and why he chose to be a man who applies the symmetries.
Soon afterwards, he said that Cumrun has pioneered something relevant for this discussion, the swampland. Not everything is allowed. So Cumrun could convey the point that while 10500 or infinity are large numbers, they don't mean that "anything goes" within string theory. Not so fast. So many things could be possible within effective field theory – like vacua where gravity is stronger than the other forces – but they are forbidden in Nature. They don't really exist.
By being forbidden in Nature, Cumrun meant "forbidden by the constraints implied by string theory". Of course it's the same thing in his picture of the world because he assumes and believes that Nature is described by string theory. Nevertheless, it was immediately turned into a controversy. Ellis added "according to string theory" to Vafa's words and the host started to laugh like a naughty schoolkid again. To make things worse, the host said he wanted to "sidetrack" a little bit: it sounds just like the anthropic principle.
Holy cow. It doesn't. It's really the opposite. Cumrun wants to show that good old physics constraints decide while the anthropic principle is basically the assumption that physics doesn't matter and the existence of intelligent animals is what constraints the choice of our vacuum or vacua. So the host wanted to "confirm" he's getting it and Cumrun informed him that "not really".
Also, I find it bizarre that the host vigorously tried to shut down a discussion about the anthropic principle – in a discussion whose title is "does the multiverse exist". Why would you shut down the discussion about this closely related proposed principle in a discussion that claims to be dedicated to the multiverse? The multiverse and the anthropic principle aren't the same thing but they're often discussed together and this is what a discussion about the multiverse should also clarify.
OK, this ban didn't succeed and around 14:10, Cumrun tried to communicate a simple point that he's not a defender of the anthropic principle. The host interrupted him with a would-be witty "you're in the swampland". It's a little bit witty because I have laughed but the real reason why I laughed is that it is so cutely dumb. The anthropic principle isn't the opposite of the swampland in any sense. It's clear why the host made the not so intelligent remark. Because the landscape is "equivalent" to the anthropic principle, and because the swampland is said to be the opposite of the landscape by Vafa, the swampland has to be opposite to the anthropic principle. So the anthropic principle's foe Dr Vafa has to be in the swampland.
The only problem is that the conclusion is wrong and this whole reasoning is totally illogical. The swampland and the landscape are two disjoint sets of models according to a particular kind of reasoning, Vafa's reasoning (or his project to classify theories), but the anthropic principle and old-fashioned-swampland-like reasoning are disjoint in a completely different way. They don't describe two disjoint classes of models. Instead, they describe unequivalent methods how to use the landscape (I wrote these words before I heard Cumrun saying virtually exactly the same thing!) or how to search for the right models.
I could see in Cumrun's eyes that he was getting somewhat anxious. Is it possible to explain these things to somebody who apparently believes that "if you're not a fan of the anthropic principle, then you're in the swampland?" ;-) You can't be in the swampland, only quantum field theories may be in the swampland, and real people can't be in the swampland because nothing in the swampland is "real". If the host can't get this point, can he get anything that matters?
Around 14:40, Cumrun protested against the claim that "mathematics isn't interesting, who cares" etc. Our disobedient happy schoolkid began to laugh again! The reason behind his laughter is his ignorance but at least I found his laughter somewhat contagious, like the laugh track in the Big Bang Theory, so that has improved my experience.
Mathematical consistency etc. can lead us a huge distance towards the future. Maxwell is an example, Vafa said. Maxwell has added a term just to make the equations consistent and the conclusion was that he could predict the moving electromagnetic waves. These comments have clearly made no impact on the host's understanding of mathematics and the Universe. But I am confident that some people in the audience were smarter than the host.
Rubenstein sort of intelligently said that there were two types of physicists in the search for the Universes. The likes of Cumrun look at the possibilities and their probabilities and don't care about the "existence". Well, Cumrun protested because that's exactly what he doesn't do. He doesn't try to find a probabilistic distribution. Well, he has also written some papers about the Hartle-Hawking states but it's not his dominant approach. So ironically, Cumrun's swampland conditions are really conditions of the Yes/No type, so they are about the "existence" which is exactly what Rubenstein tried to describe as the non-Cumrun approach.
OK, where did this misunderstanding come from? A minute later, Rubenstein explained what she meant by the second group. Folks like Penrose who see, in their hopeless papers, stargates into actual other Universe in some patterns drawn in the CMB. ;-) OK, you can't blame Cumrun or me for not predicting that this is what she would call the "second group". It's just some very particular, wrong, single, nutty paper, and it's in no way "a complementary school of thought" to either the swampland or the anthropic principle. OK, I found the spontaneous verbal explosions by that religion-feminist professor sort of cute although, unsurprisingly, she didn't always understand what she was talking about at the end.
Her "I think it's totally fascinating, I am thrilled" at 17:15 made me smile. She has a lot of the physicist's enthusiasm. She reported that she doesn't know whether we will ever come to any certainty about the existence of the other Universes. Right, we can't be sure about that.
Ellis says that the switch to 10500 or more Universes represents a tremendous progress because those questions were out of reach some 50 years ago when people couldn't dare to discuss questions about the other Universes. Right. Needless to say, the schoolkid laughs again. It really looks like the defense of contemporary physics has the same effect on him (and not only him) as if you were saying some obscene jokes. But Ellis wanted to throw "stone in Cumrun's direction". The accelerated expansion seems incompatible with string theory. Cumrun: "No, who said that? Which colleagues said that?" Everyone laughs, the host generously allowed Cumrun to hunt them down later. I think that Cumrun knows well who should be hunted here – the #1 wanted man – claiming that string theory bans de Sitter – is named Cumrun Vafa. ;-) Of course, he would say it's not true because he believes in quintessence instead of the de Sitter spaces. When asked about the future of the Universe, Cumrun said it was wonderfully exciting but not one with a happy ending.
The host just increased his IQ by 15 points and mentioned that mathematics had a good track record and that's how Dirac, with some extra coffee at night, discovered antimatter.
John Ellis bragged that he has coined the term "a theory of everything" – it's OK to boast because it's no longer a popular term – and he liked predictions. String theory was blamed for not having them and that's one reason why Ellis likes Vafa and the swampland – these claims make string theory falsifiable.
Why did the multiverse become popular and it's not just science, is it? Rubenstein recalled the various chapters of Greene's Hidden Reality about the types of the multiverses. She totally correctly said that the multiverse exploded around 2000. Right, that's when string theorists took it to explain the recently observed acceleration of the cosmic expansion (in 1998, she even knows this year!). It was really a trend that many if not most string theorists joined at that time. My only paper focusing on the anthropic principle (negatively) was also released in 2000. She discussed lots of details historical facts about Vilenkin's and Weinberg's ringing telephone etc. I am really impressed. At least as a reader of the popular books, she has done her homework extremely well.
Nevertheless, Cumrun had to point out that the anthropic principle – the methods to use the landscape – may be incorrect but that doesn't mean that the landscape or the string theory framework is incorrect. Precisely. When asked who imposed the multiverse on Cumrun, he said that the multiplicity of solutions had been known independently of Weinberg and his anthropic principle. Happily, all agree. This multiplicity was helpful for Weinberg to use it.
Vafa said a few more things, the host asked Ellis what Vafa meant by "checking". Ellis sort of didn't answer but began to explain the quintessence, which should have been explained some minutes earlier. Now an expectation of many string theorists – possibly testable by telescopes. The host, a testability cop, suddenly expressed his satisfaction. This is how a majority of the laymen around these discussions seem to operate. They seem to insist that they understand some experimental tests, otherwise they consider the science illegitimate. It's really a wrong and harmful attitude and Cumrun tried to convey why but the host hasn't gotten it. Too bad, most of these laymen who have been turned into "testability cops" don't see that they have been brainwashed by some really crappy, deluded, and self-serving demagogues.
The host said that 98% of the room was dark energy. LOL, not really. First, it would be just 68% (and 95% when dark matter is added). Second, it's the average over the Universe and in the room, the air is vastly heavier than the dark energy because matter – instead of dark energy – is concentrated around Earth, as Ellis informed him. ;-) You may always learn some cutting-edge new insights, e.g. that there is matter around Earth.
Ellis wanted to return to the question why the multiverse was popular – especially among non-physicists. They are probably unhappy with their Universe and they also feel that other people live in another Universe LOL (Rubenstein: it's called the U.S., the host wisely terminated these political ramifications). The host asks Rubenstein: What should the chaps be looking for? Now, Jane has the power to decide about the future of physics. ;-) At 30:13, she actually pronounces the name of Brian Greene for the first time LOL. There has to be evidence, she quotes him (he is surely not the guy who invented that sentence). Before that, Ellis mentions that there's not one lamppost but 10500 lampposts. Rubenstein correctly notices that when the CMB is used as a key source of evidence, people have different interpretations for blips so there is an interpretational problem. She wants to return to the question what is the primary question. I am not sure that her proposal will fix anything.
Vafa gives an answer to Rubenstein's question. Physicists want to understand patterns and know whether the Universe is natural or not etc. Rubenstein says that these "why" naturalness questions push physicists to the realm of metaphysics. Well, you may say that but "metaphysics" may still be done scientifically and rationally or unscientifically or irrationally. What is "metaphysical" about these questions is that they are deep and far-reaching. But depth is something completely different than the lack of scientific rigor. Physics has really advanced far enough that it is credibly and rationally dealing with questions that used to seem to be beyond science some 50 years ago.
Ellis opines that physicists do "when where what" and not "why". OK, I disagree with that. A huge portion of physics is about "why" questions. You can't really live without the question "why", as a TV commercial with Gell-Mann concluded. In effect, Ellis later translated many "why" questions to "what are we" and "where did we come from". Also, "where are we going with the whole Universe" completes the list of questions that make Ellis come to work every day.
Ellis also explains his "opportunism" – looking for questions where some progress can be made right now. Right. A good choice of the research projects actually is affected by the recent successes and what has become a promising route because of them. Many laymen don't get this point, either. They think that the right questions for science are independent of time. So they're drowning with these clichés and medieval questions that are disconnected from any actual progress that was taking place in the recent years or century.
The host turned to Rubenstein and Ellis: How much comfortable do you feel with this heretic, Vafa, who pays attention to the elegance of the equations? Instead of abusing the opportunity to burn Vafa at stake, the religion professor intelligently said that "true" or "real" or "existent" has various forms – existence in the realm of possibility of mathematical ideas, or some real physical evidence. She predictably yet cleverly mentions Plato (and Tegmark, another chapter in Brian's book). Vafa is relieved that the host's plan to execute Vafa didn't work and he friendly interacts with Rubenstein.
Vafa reports that string theory has taught us much more than what we expected – something about the Standard Model – such as holography and properties of black holes. The connections of string theory with the known, observed physics and patterns seem way too numerous and encouraging so that it would be a shame not to study the consequences of the theory, and that's what we are doing. It's work in progress, perhaps with many centuries to go.
But the approach "string theory is too hard so let's only do simple things" is not what the human beings do, it's not what the theoretical physicists do, but to overestimate what we can do is also wrong. So we are making finite steps but nonzero steps. Exaggerations may be made and are being made in both directions. String theorists aren't claiming to have everything but they do claim to have more than nothing. It make take years or centuries but to stop wouldn't be good for humanity.
Excellent, Cumrun. The disobedient kid didn't even get an opportunity for his laughter now. ;-)
OK, the host asked a somewhat incomprehensible question about Vafa's opinion on the relationship between the mathematical and physical reality. Vafa pointed out that the host had excessively naive assumptions about how the "physical reality" may be defined. There may "exist" other Universes although it might be possible to prove that no interactions between the components of the world can exist. The word "reality" may be subtle, especially once you allow the multiverse. Right.
Cumrun repeats that the "physical reality" isn't sufficiently defined and the host seems disgusted by this observation. But thankfully, the religion professor is really on the same boat with Vafa here – in fact, she started with this theme. OK, Cumrun still complained that her usage of "reality" is also ambiguous. I think that she hasn't really claimed otherwise. She has helped to classify the types of "reality" into some basic groups and deserves the credit for it. At the end, she rightfully suggested she was on the same frequency with Cumrun.
It was one of the best debates on current theoretical physics involving people with different backgrounds. And Rubenstein was one of the most well-informed people from the "humanities" when it came to theoretical physics whose monologues I have seen for years if not ever. You wouldn't have guessed that I would praise a "professor of religion and feminism" in this way but it just happened to be the case. She was clearly smarter and less naive than the male host but at least, his not very intelligent choices when to laugh have provided the debate with some contagious laugh track. ;-)
I think that at the end, there is a reason why a religion professor looks more intelligent in these debates than many irreligious philosophers and babblers. For centuries, natural science seemed to be a technical branch of the "materialist philosophy" but it simply ceased to be the case sometime during the 20th century. The rise of quantum mechanics – and the materialists' lack of will to admit that facts must be specified relatively to an observer – is the greatest example of the "fall of materialism" in physics. But it's not the only one. The host is a chap who really believes in some "naive materialism". The table is real, it's simple to divide things to real and unreal, everything must be simple like that, and when it's not, he doesn't believe it. But it just doesn't work like that and attempts to enforce a table-like science on modern physics are purely harmful. A religion scholar – who deals with principles of the Bible as well as religious myths – unsurprisingly has a greater understanding for the subtleties of the word "existence" or "reality".