Um texto que merece ser lido, vol. 6: Linde on Inflation and the Multiverse


via Not Even Wrong http://www.math.columbia.edu/~woit/wordpress/?p=5076

Andrei Linde is one of Yuri Milner’s $3 million dollar men, best known for his “chaotic inflation” version of inflationary theory, as well as being one of the main proponents of anthropic multiverse mania. There’s a long piece based on a conversation with him up now at the Edge web-site.

Much of the piece is just a retread of the usual heavily-promoted ideology of the past 30 years of fundamental physics research: we must have SUSY, so must have supergravity, so must have string theory, so must have the landscape, so must have a multiverse where we can’t predict anything about anything, thus finally achieving success. Linde claims he pretty much had this picture 30 years ago back in 1982, with the string theory component in 1986, with others coming around to his point of view in the last 10 years, partly because of the KKLT work he was co-author of in 2003.

Besides the tired Stanford pseudo-scientific ideology, there’s also a wonderful history of the subject of inflation, from a Moscow point of view, which is rather different than the Western, Alan Guth-oriented, point of view from which the story is often told. Linde’s description of Hawking’s visit to Moscow is not to be missed:

The next morning after I gave a talk at this conference, I found myself at the talk… oh, my God, this is going to be a funny story… I found myself at the talk by Stephen Hawking at Sternberg Institute of Astronomy in Moscow University. I came there by chance because I have heard from somebody that Hawking was giving a talk there. And they asked me to translate. I was surprised. Okay, I will do it. Usually at that time Stephen would give his talk well prepared, which means his student would deliver the talk, and Stephen from time to time would say something, and then the student would stop, and change his presentation and do something else. So Stephen Hawking would correct and guide the student. But in this case they were completely unprepared; the talk was about inflation. The talk was about the impossibility to improve Alan Guth’s inflationary theory.

So they were unprepared, they just finished their own paper on it. As a result, Stephen would say one word, his student would say one word, and then they waited until Stephen would say another word, and I would translate this word. And all of these people in the auditorium, the best scientists in Russia, were waiting, and asking what is going on, what it is all about? So I decided let’s just do it, because I knew what it’s all about. So Stephen would say one word, the student would say one word, and then after that I would talk for five minutes, explaining what they were trying to say.

For about a half an hour we were talking this way and explained to everyone why it was impossible to improve Alan Guth’s inflationary model, what are the problems with it. And then Stephen said something, and his students said: “Andrei Linde recently proposed a way to overcome this difficulty.” I didn’t expect it, and I happily translated it into Russian. And then Stephen said: “But this suggestion is wrong.” And I translated it… For half an hour I was translating what Stephen said, explaining in great detail why what I’m doing is totally wrong. And it was all happening in front of the best physicists in Moscow, and my future in physics depended on them. I’ve never been in a more embarrassing situation in my life.

Then the talk was over, and I said: “I translated, but I disagree,” and I explained why. And then I told Stephen: “Would you like me to explain it to you in greater detail?” and he said, “Yeah.” And then he rode out from this place, and we found some room, and for about two or three hours all the people in Sternberg Institute were in panic because the famous British scientist just disappeared, nobody knew where to.

During that time, I was near the blackboard, explaining what was going on there. From time to time, Stephen would say something, and his student would translate: “But you did not say that before.” Then I would continue, and Stephen would again say something, and his student would say again the same words: “But you did not say that before.” And after we finished, I jumped into his car and they brought me to their hotel. We continued the discussion, which ended by him showing me photographs of his family, and we became friends. He later invited me to a conference in Cambridge, in England, which was specifically dedicated to inflationary theory. So that’s how it all started. It was pretty dramatic.

Addressing the question of “what evidence is there for any of this?”, here’s what Linde has to say:

Usually I answer in the following way: If we do not have this picture, then we cannot explain many strange coincidences, which occur around us. Like why vacuum energy is so immensely small, incredibly small. Well, that is because we have many different vacua, and in those vacua where vacuum energy is too large, galaxies cannot form. In those vacua, where energy density is negative, the universe rapidly collapses, and in our vacuum the energy density is just right, and that is why we live here. That’s the anthropic principle. But you cannot use anthropic principle if you do not have many possibilities to choose from. That’s why multiverse is so desirable, and that’s what I consider experimental evidence in favor of multiverse.

So, the main experimental evidence for the multiverse is that an anthropic argument works. Some might not find this completely convincing.

About 5 years ago, the field of “string cosmology” was quite active, with even a graduate-level textbook appearing. My impression (contrast the tone of this review, with those of 5 years earlier) is that there’s much less interest in this area during recent years, since it became obvious that no predictions about physics were going to emerge from it. Late this year or early next year the Planck experiment will finally report what it sees in the CMB. I’m curious to know whether Linde and other string cosmology proponents have any predictions for what Planck will tell us.

Update: The Annenberg Foundation funds Annenberg Learner, a site designed to provide information to high school teachers. Their Physics course includes a unit from Stanford’s Shamit Kachru, which is pretty much pure hype, unadulterated by any skepticism that string theory might not be the way the world works. Physicists may have lost interest in string cosmology, seeing it as a failure, but that’s no reason not to teach it to high school students…

Update: Historian of science Helge Kragh has a new article Criteria of Science, Cosmology, and Lessons of History discussing the Multiverse, philosophy of science, and the dubious use of historical analogies. About the Multiverse: “it explains a lot but predicts almost nothing”.

Update: Tonight’s arXiv listings include The Top 10500 Reasons Not to Believe in the Landscape from Tom Banks, which starts off with:

The String Landscape is a fantasy.

He goes on to claim co-credit with Linde for the anthropic explanation for the value of the CC (in inflationary models), as well as to argue that it is wrong:

Linde and I were the first to suggest an anthropic explanation for the value of the c.c. based on inflationary models [2], but within the context of the string landscape, or most any contemporary view of global EI [i.e., Eternal Inflation], I don’t think anthropic reasoning leads to good phenomenology.

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