From Science Friday: “10 Questions for Alan Guth, Pioneer of the Inflationary Model of the Universe”
January 7, 2016
The theoretical physicist discusses the expanding universe and the infinite possibilities it brings.
Buried under a mountain of papers and empty Coke Zero bottles, Alan Guth ponders the origins of the cosmos. A world-renowned theoretical physicist and professor at the Massachusetts Institute of Technology, Guth is best known for pioneering the theory of cosmic inflation, a model that explains the exponential growth of the universe mere fractions of a second after the Big Bang, and its continued expansion today.
Cosmic inflation not only describes the underlying physics of the Big Bang, however. Guth believes it also supports the idea that our universe is one of many, with even more universes yet to form.
Science Friday headed to MIT (where this writer also works, but in a different department) to chat with Guth in his office about the infinite possibilities in an unending cosmos, and the fortune cookie that changed his life.
Alan Guth in 2007. Photo by Betsy Devine/Wikipedia/CC BY-SA 3.0
Science Friday: What made you realize that you wanted to be a scientist?
Alan Guth: I remember an event in high school, which maybe is indicative of my desires to be a theoretical physicist in particular. I was taking high school physics, and a friend of mine was doing an experiment which consisted of taking a yard stick and punching holes in it in different places and pivoting it on these different holes and seeing how the period depended on where the hole was. At this point, I had just learned enough basic physics and calculus to be able to calculate what the answer to that question is supposed to be. I remember one afternoon, we got together and compared my formula with his data using a slide rule to do the calculations. It actually worked. I was very excited about the idea that we can really calculate things, and they actually do reflect the way the real world works.
You did your dissertation on particle physics and have said that it didn’t turn out exactly how you wanted. Could you tell me about that?
My dissertation was about the quark model and about how quarks and anti-quarks could bind to form mesons. But it was really just before the theory of quarks underwent a major revolution [when physicists went from believing that quarks are heavy particles that have a large binding energy when they combine, to the quantum chromodynamics theory that quarks are actually very light and their binding energy [gluons] increases as they’re pulled farther apart]. I was on the wrong side of that revolution. My thesis, more or less, became totally obsolete about the time I wrote it. I certainly learned a lot by doing it.
What got you into cosmology?
It wasn’t really until the eighth year of my being a [particle physics] postdoc that I got into cosmology. A fellow postdoc at Cornell named Henry Tye got interested in what was then a newfangled class of particle theories called grand unified theories [particle physics models that describe how three of the four fundamental forces in the universe—electromagnetism, weak nuclear interactions, and strong nuclear interactions—act as one force at extremely high energies]. He came to me one day and asked me whether these grand unified theories would predict that there should be magnetic monopoles [particles that have a net magnetic north charge or a net magnetic south charge.]
I didn’t know about grand unified theories at the time, so he had to teach me, which he did, very successfully. Then I knew enough to put two and two together and conclude—as I’m sure many people did around the world—that yes, grand unified theories do predict that magnetic monopoles should exist, but that they would be outrageously heavy. They would weigh something like 10 to the 16th power times as much as a proton [which means that scientists should theoretically be able to observe them in the universe, although no one has yet].
About six months later, there was a visit to Cornell by [Nobel laureate] Steve Weinberg, who’s a fabulous physicist and someone I had known from my graduate student days at MIT. He was working on how grand unified theories might explain the excess of matter over anti-matter [in the universe], but it involved the same basic physics that determining how many monopoles existed in the early universe would involve. I decided that if it was sensible enough for Steve Weinberg to work on, why not me, too?
After a little while, Henry Tye and I came to the conclusion that far too many magnetic monopoles would be produced if one combined conventional cosmology with conventional grand unified theories. We were scooped in publishing that, but Henry and I decided that we would continue to try to figure out if there was anything that could be changed that maybe would make it possible for grand unified theories to be consistent with cosmology as we know it.
How did you come up with the idea of cosmic inflation?
A little bit before I started talking to Henry Tye about monopoles, there was a lecture at Cornell by Bob Dicke, a Princeton physicist and cosmologist, in which he presented something that was called the flatness problem, a problem about the expansion rate of the early universe and how precisely fine-tuned it had to be for the universe to work to produce a universe like the one we live in [that is, one that has little or no space-time curvature and is therefore almost perfectly “flat”]. In this talk, Bob Dicke told us that if you thought about the universe at one second after the beginning, the expansion rate really had to be just right to 15 decimal places, or else the universe would either fly apart too fast for any structure to form or re-collapse too fast for any structure to form.
At the time, I thought that was kind of amazing but didn’t even understand it. But after working on this magnetic monopole question for six months, I came to the realization one night that the kind of mechanism that we were thinking about that would suppress the amount of magnetic monopoles produced after the Big Bang [the “mechanism” being a phase transition that occurs after a large amount of super-cooling] would have the surprising effect of driving the universe into a period of exponential expansion—which is what we now call inflation—and that exponential expansion would solve this flatness problem. It would also draw the universe to exactly the right expansion rate that the Big Bang required [to create a universe like ours].
You’ve said in previous talks that a fortune cookie played a legitimately important part in your career. How so?
During the spring of 1980, after having come up with this idea of inflation, I decided that the best way to publicize it would be to give a lot of talks about it. I visited MIT, but MIT had not advertised any positions that year. During the very last day of this six-week trip, I was at the University of Maryland, and they took me out for a Chinese dinner, and the fortune I got in my Chinese fortune cookie said, “An exciting opportunity awaits you if you’re not too timid.” I thought about that and decided that it might be trying to tell me something. When I got back to California, I called one of the faculty members at MIT and said in some stammering way that I hadn’t applied for any jobs because there weren’t any jobs at MIT, but I wanted to tell them that if they might be interested in me, I’d be interested in coming. Then they got back to me in one day and made me an offer. It was great. I came to MIT as a faculty member, and I’ve been here ever since.
When and where do you do your best work?
I firmly believe that I do my best thinking in the middle of the night. I very much like to be able to have reasonably long periods of time, a few hours, when I can concentrate on something and not be interrupted, and that only happens at night. What often happens is I fall asleep at like 9:30 and wake up at 1 or 2 and start working and then fall asleep again at 5.
Who is a dream collaborator you’d love to work with?
I bet it would have been a lot of fun to work with [Albert] Einstein. What I really respect about Einstein is his desire to throw aside all conventional modes and just concentrate on what seems to be the closest we can get to an accurate theory of nature.
What are you currently working on?
The most concrete project I’m working on is a project in collaboration with a fairly large group here at MIT in which we’re trying to calculate the production of primordial black holes that might have happened with a certain version of inflation. If this works out, these primordial black holes could perhaps be the seeds for the super massive black holes in the centers of galaxies, which are very hard to explain. It would be incredibly exciting if that turns out to be the case.
What else are you mulling over?
A bigger question, which has been in the back of my mind for a decade, is the problem of understanding probabilities in eternally inflating universes. In an eternally inflating universe, these pocket universes [like the one we live in] go on being formed literally forever. An infinite number of pocket universes are formed, and that means that anything that’s physically allowed will ultimately happen an infinite number of times.
Normally we interpret probabilities as relative occurrences. We think one-headed cows are more probable than two-headed cows because we think there are a lot more one-headed cows than two-headed cows. I don’t know if there are any two-headed cows on earth, but let’s pretend there are. In an eternally inflating universe, assuming that a two-headed cow is at least possible, there will be an infinite number of two-headed cows and an infinite number of one-headed cows. It’s hard to know what you mean if you try to say that one is more common than the other.
If anything can happen in an eternally inflating universe, is there a situation in which I am the cosmologist and you are the journalist?
[Laughs] Probably, yes. I think what we would know for sure is that anything that’s physically possible—and I don’t see why this is not physically possible—will happen an infinite number of times.
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