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Oral History Transcript — Dr. Steven Weinberg

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Interview with Dr. Steven Weinberg
By Alan Lightman
In Cambridge, Massachusetts
May 10, 1988

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Steven Weinberg; May 10, 1988

ABSTRACT: More discussion of the reasons why particle physicists began working on cosmology in the 1970s; importance of theoretical work by Kirzhnitz and Linde in 1972 on broken symmetries and phase transitions; current unreality of work on the very early universe; attitude toward the inflationary universe model; successes of the inflationary universe model; aesthetic attraction of a flat universe; acceptability of postulating that we live in a flat universe; introduction to and attitude toward the horizon problem; attitude toward the inflationary universe model; incidences of being worried about scientific problems that no one else is worried about; the anthropic principle and Dirac's large number hypothesis; reaction to de Lapparent, Geller, and Huchra's work on large-scale inhomogeneities; Weinberg worried that perhaps we have misinterpreted the cosmic background radiation; Weinberg's philosophy about strategy in science; the role of consensus in science and the importance of "standard" models; outstanding problems in cosmology: distance scale of the universe, value of the deceleration parameter, origin of structure; failure of theory to explain the observed large-scale structure; possible importance of WIMPs; prematurity of work on the early universe; ideal design of the universe; preference for universes in which initial conditions do not have to be specified; Weinberg's statement in The First Three Minutes about the lack of point to the universe.

Transcript

Session I | Session II

Lightman:

I wanted to pick up with what we were talking about a few days ago -- the reasons you think that particle physicists came into cosmology in the middle 1970s or approximately around then. Why was it cosmology that they fastened on?

Weinberg:

I don't remember that there was anyone thing. There were some questions that arose in particle physics like the number of neutrino species, which suddenly for the first time were taken seriously because a new generation of leptons had just been discovered, and we wondered how many more there were. I don't remember who was the first person to realize that that was a question for which cosmological evidence gave sensitive limits. There were a lot of events like that. I remember myself thinking about the question of the scale at which super-symmetry is broken and realizing that that affected the mass of the gravitino, the super-partner of the graviton, and that cosmology put some rather stringent bounds on the mass of the gravitino. Also, there are cosmological bounds on the mass of the neutrino. I don't know why it all happened at about the same time, but it was just the nature of the problems that particle physicists were considering, that they suddenly realized that cosmology could be of help to them. And, of course, the biggest unsolved question was what is physics like at really short scales of distance, really high energies characterized by the Planck scale, and that seemed to have something to do with the origin of the universe. There, unfortunately, I don't think the interaction between physics and cosmology has been so fruitful. One other thing was the realization of the importance of phase transitions. That is, with the establishment of the standard model, it became generally accepted that we live in a broken symmetry phase in which the electroweak symmetry is broken. It actually had already been established in the mid-1960s that we live in a broken symmetry phase where the symmetries of the strong interactions, SU(2) x SU(2), are spontaneously broken. I think it was first [D.A.] Kirzhnitz and [Andrei] Linde[1] who pointed out that, just as ordinary broken symmetries are restored by raising the temperature, these symmetries must have once been unbroken in an early period of the universe when the temperature was very high. I remember that I read Kirzhnitz and Linde's paper which was...

Lightman:

That was around 1972?

Weinberg:

1972 or 1973. I had to give a talk at the dedication of the Undergraduate Science Center at Harvard, and I wanted to talk about cosmology because that's always the most exciting thing for a general audience. I wanted to tie it to my own work, so that I'd have some credentials, and that paper of Kirzhnitz and Linde interested me because it was a nice connection that claimed to show that in the early universe the gauge symmetries would have been unbroken. Actually, when I read it, I discovered two things. One is that I didn't understand the formalism of quantum field theory at finite temperature and I had to learn that, and that was something that was very useful for me to learn. The other thing I learned was that Kirzhnitz and Linde really hadn't proved anything for spontaneously broken gauge symmetries, although that was what they said they were doing in their title. In fact, their analysis had lots of holes in it, and in any case only applied to spontaneously broken global symmetries. So there was something to do, and I[2], and also [Louise] Dolan and [Roman] Jackiw[3] at the same time tried to make a -- well, not vigorous but solidly based theory of those phase transitions, and I think we succeeded.

Lightman:

Do you think in general that physicists at this time were taking cosmology more seriously than they had, say, ten years earlier? You mentioned that your own work and your papers in the early 1960s you didn't quite take seriously. Did you take your work in cosmology in the 1970s more seriously?

Weinberg:

The discovery of the microwave radiation background changed everything because it made cosmological speculation back to the first few minutes’ respectable, normal science. So if someone, for instance, calculated the effect of having extra neutrinos on nucleosynthesis, it was regarded as a respectable thing to do. You were working in a scientific framework that we all understood and that had had some successes. It might not be true, but it was at least something worth doing. In that sense, nothing like that has happened for the cosmology of the very early universe [before about 1 second after the big bang]. There are lots of very good scientists who do highly respected work on the very early universe, but there's still -- a sense of unreality about all of it, because we have no experimental handle on the very early universe. Nothing like the helium abundance or the microwave background.

Lightman:

That's a comment that a number of people have made to me. They have said that they are somewhat concerned that there's not much contact between theory and observations. Their worst nightmare is that we will have five equally plausible and equally tested theories of particle physics for the early universe and not be able to distinguish between them.

Weinberg:

I think progress has been made. I think the general idea of inflation, in all the different versions, from Guth through other people, Linde and so on, is very interesting and the sort of thing I would have been very proud to do myself. But, unfortunately, it leaves you with a very frustrated feeling. There's no way of testing it. It's not fair to say [the inflationary universe model] hasn't made any new predictions. Very often theories are tested by using them to explain already known facts. Like, after all, when Newton calculated the length of the month in terms of the acceleration of gravity at the earth's surface and the distance of the moon, that was already known,-- but it was such a good numerical calculation, that worked, it was clearly convincing.

Lightman:

Of course, inflation predicts that omega is equal to 1.

Weinberg:

Well, right, but that's like a null test. That means the departure from flatness is very small. There are lots of reasons why the departure from flatness might be very small, including the fact that the universe is absolutely flat.

Lightman:

Would you be surprised if the universe were absolutely flat?

Weinberg:

Not at all. In fact, that seems to me the most plausible thing. I think inflation has had other successes which are much more important, like solving the monopole problem, explaining why there aren't magnetic monopoles around, which really was a puzzle. And also in explaining the huge size of the dimensionless number that -- no, I shouldn't say that.

Lightman:

You mean the number of baryons?

Weinberg:

I was going to say that, but that's the wrong thing to say. I would say the real successes of the inflationary picture are solving the monopole problem and also solving the isotropy [horizon] problem -- explaining how distant parts of the universe could have gotten into thermal communion with each other even though they're very far apart in the sky, so -- that you can explain why the microwave background is so isotropic. On the other hand, the fact that the universe contains a huge number of baryons within the horizon or a huge number of photons, or a huge entropy, however you want to say it, and the very related thing that the omega is so close to one, I think never seemed to me that puzzling because they're perfectly well understood just in terms of the assumption that the universe is flat, as k = 0 [space curvature parameter = 0].

Lightman:

You don't consider that [the flat universe] a singular case, then? You know, a set of measure zero when all possible kinds of universe [are considered]?

Weinberg:

Yes, but if you have to decide which is the most aesthetically attractive possibility, I would think that's the most aesthetically attractive possibility.

Lightman:

That's very interesting.

Weinberg:

Long before I ever heard of inflation, it always seemed to me that since omega was so close to one now, and since the universe is pretty old in terms of any fundamental time scale like the Planck scale, that probably meant that omega was exactly one.

Lightman:

And you were willing to accept that [result] just as some initial condition or whatever?

Weinberg:

That k [the curvature of space] is zero.

Lightman:

That k is zero.

Weinberg:

That's right. That makes it sound better. When you talk about omega, you're talking about the ratio of matter density to the Hubble constant squared and you might say, well, "how could that be so finely tuned?" But if you simply say that of the three possible geometries for an isotropic, homogeneous cosmology -- positively curved, negatively curved, and flat -- we happen to live in the flat one, then that's clearly something which doesn't require fine tuning. It just is true.

Lightman:

Right. But it seems to me that you're making an implicit assumption there that all three of those possibilities are somehow equally likely and that one is more aesthetically pleasing.

Weinberg:

Well, yes, it becomes an argument that's hard to settle, but it didn't seem to me anything unnatural in saying that for reasons that we cannot now understand, the universe happens to have k = o. So I don't regard that as a triumph of inflation. I never have. But the other two are good enough.

Lightman:

Certainly. Getting back to the isotropy problem, which you might call the horizon problem, when did you first hear about that? I know you wrote about it in your book in 1972, but it was around before then.

Weinberg:

Probably a few years before that. It isn't something that has haunted me for years and years. Obviously, the book came out in 1972, and the microwave background wasn't discovered until 1965, so it must have been somewhere in those seven years, and I don't know exactly when.

Lightman:

Were you bothered by that problem? How did you think it would be resolved?

Weinberg:

I suppose I took a Mr. Micawberish attitude: something will turn up. You know, Mr. Micawber is always saying something will turn up when he's in trouble. [Laughter] You can only worry about so many things, and I have never devoted myself professionally to worrying about that. I took due notice in my book that there was such a problem. I must have been worrying about something else, something in elementary particle physics at the time. Usually, for me and I suspect for everyone else, a large part of the answer of why I didn't do something at a particular time is because I was doing something else. I don't remember what else I might have been doing then.

Lightman:

I gather that you did consider it to be a serious problem.

Weinberg:

Yes, and I referred to it as such in my book. I certainly didn't have the idea of inflation, and I thought that was really very charming when I heard that explanation. That was what really sold me that something like inflation was probably true. But, of course, the inflationary models have had all sorts of problems and even Linde now says that the 'new' inflationary model due to him[4] and Albrecht and Steinhardt[5] is dead.

Lightman:

Yes, Hawking said the same thing in his new book[6] that he considered [the original inflationary universe model] to be scientifically dead.

Weinberg:

Oh yes, maybe I'm thinking of Hawking, in fact. Yes, maybe I'm referring to Hawking. I think Linde has said something like that also, but I'm not sure.

Lightman:

Linde can afford to say it because now he's got a new model,[7] chaotic inflation, which is in pretty good shape, I guess.

Weinberg:

Well, on the other hand, there's a lot of hand-waving in it. And, from the start, from Guth's work on, one is haunted by the fact that in the end you're just trying to and references therein explain some very qualitative features of the universe without any numerical predictions of the kind that really convince you you've understood what's going on. I don't regard omega equal to one as a numerical prediction, not in the sense that the Lamb shift is a numerical prediction.

Lightman:

When did you first hear about the flatness problem? You said that you didn't consider that to be in the same category as the horizon problem, but do you remember when you first started thinking about that?

Weinberg:

[Pause] No. Sorry, no recollection.

Lightman:

It's interesting to me that some of these problems impress some people more than others.

Weinberg:

Yes, that's right.

Lightman:

Alan Guth mentioned to me that the flatness problem impressed him a lot more than the horizon problem.

Weinberg:

Yes. I know. I've been in that position sometimes -- there have been problems in elementary particle physics that I was worried about that nobody [else] seemed to worry about. I got very worried after the electroweak theory was developed by the question of why the emission and reabsorption of virtual W's and Z's doesn't produce parity violations in the strong interactions of order alpha -- not suppressed by weak coupling, but just suppressed by 1/137, which is clearly not true experimentally. One of the reasons I was so glad to accept quantum chromodynamics as the theory of strong interactions is that in that theory you can show it doesn't happen. This is taking us afield, but it is an internal problem with the theory that most people hadn't even realized was a problem. I certainly didn't realize there was a monopole problem until -- actually it was John Preskill,[8] who was my student, who, along with someone in Russia,[9] first pointed out the monopole problem. [Some conversation, during lunch, about Chinese food and Woody Allen]

Weinberg:

Well we're getting off the subject and wasting your tape.

Lightman:

No problem. Got plenty of tape. You said that you didn't place the flatness problem in the same category as the horizon problem because you were willing to accept that we could just have a k equal zero [flat] universe. Did your view about the flatness problem change any after the inflationary models?

Weinberg:

Well, yes, in the sense that it suddenly became plausible, as it hadn't been before, that maybe in fact k is 1 or -1, because if k is 1 ...

Lightman:

It'll still appear almost zero from observations.

Weinberg:

Yes, that's right. Whereas it would be very implausible without the [effects of inflation]. So, in a way, it opened up these other possibilities. There's a similar question having to do with the Dirac large number paradox. You can describe Dirac's paradox as just simply the statement that if you calculate a quantity with the dimensions of time out of purely microscopic constants like G and a mass of a typical elementary particle and so on...

Lightman:

It has approximately the age of the universe.

Weinberg:

Yes. Now there, if you want to avoid that paradox -- the paradox being that the age of the universe is changing -- one way is to say that there's a certain time scale built in to the universe which is not changing with time. It's the time that it takes for the universe to evolve until you get to the point where omega is, let's say, 2, or 1/2, depending on whether k is positive or negative.

Lightman:

And that's a special time.

Weinberg:

Yes, that's something that's built into the history of the universe from the beginning. Then the Dirac paradox doesn't imply anything about the changing of the constants, but it becomes a question, "Why do we live at that time?" And Dicke's explanation in terms of anthropic arguments then answers that.

Lightman:

Yes.

Weinberg:

On the other hand, you wouldn't have that way out if k was zero. Then you really would have to face the choice between a changing gravitational constant or other changing constants and the anthropic argument, because if k was zero, there wouldn't be any characteristic time scale for the universe. Then the age of the universe... I'm being a little unclear and this is probably not terribly relevant anyway. Let's go on to something else.

Lightman:

Okay. I remember in Dicke's paper in Nature[10] that he really didn't refer to omega at all.

Weinberg:

Yes, he accepted Dirac's point that the time that was being compared with the fundamental constants was the age of the universe rather than some characteristic time period of the universe.

Lightman:

Right, right.

Weinberg:

I always took the attitude that the real Dirac problem was, if you accepted that it was a meaningful coincidence: there was a characteristic time built into the history of the universe which was related to the constants of elementary particle physics -- for instance, in an oscillating [universe], in a universe with k = +1, the total life time.

Lightman:

The period, yes.

Weinberg:

The period. Then the question was, "Why do we live about half way through the period?"

Lightman:

But then wouldn't you still need to go through some kind of anthropic argument, like main sequence stars and so forth?

Weinberg:

Absolutely.

Lightman:

Let me ask you about your reactions to some recent observations in cosmology. We've talked a little about some of the theoretical ideas. The work that has been done in the last five years or so on the large scale structure by Huchra, de Lapparent, and Geller[11] and Haynes and Giovanelli[12] -- has that work changed your thinking at all about cosmology?

Weinberg:

Yes.

Lightman:

Or did you already anticipate it?

Weinberg:

No, I certainly didn't anticipate it. I have at various times -- for instance, I think in The First Three Minute, -- referred to the fact that on large scales the universe appears smooth. And it's disturbing to see how unsmooth it does appear, with only the microwave background left to convince you that on really large scales, it's smooth. In other words, there's not a hell of a lot of evidence left for a Robertson-Walker universe outside of the microwave background, which is isotropic around us, and the Copernican principle that if the universe is isotropic around you, it's probably isotropic around everyone because there's nothing special about you. Maybe we're misunderstanding something about the microwave background and, in fact, the universe isn't Robertson-Walker at all. That bothers me. There is a mathematical question that I've been curious about for years and years, and I still don't know the answer to. It goes as follows. It's a simple theorem, little more than common sense, but you can also prove it mathematically as I do in my book. H the universe is isotropic around every point, and then it's homogeneous. However, there is no theorem that says that if the universe is approximately isotropic around every point then it's approximately homogeneous. It's quite possible that the universe is so constructed that every observer looking around him or her sees the universe as being approximately -- isotropic, and yet the small departures from isotropy build up as you go to great distances, so that you can go to great distances and find conditions totally different, like, for instance; maybe a different baryon density on the average, or something like that.

Lightman:

I would think that would be very hard to prove in general relativity.

Weinberg:

It's very hard to construct even models which have that property. I've tried off and on for a number of years. I go back to this problem every few years, and I never get anywhere.

Lightman:

I was going to say that I remember your talking to me about that problem around 1977 or so.

Weinberg:

Well, you see the progress I've made. But as time passes, the universe looks less and less isotropic, except for the microwave background. I'm very bothered by it.

Lightman:

Do you think we could be on completely the wrong track?

Weinberg:

I don't have any idea of how to explain the isotropy of the microwave background if we are on the wrong track. But it's something I worry about every once in a while. I don't have anything substantial to say about it. It's not something I would go into print with, but it bothers me that the whole Robertson-Walker picture may be wrong on very large scales. But that's, by the way, no reason not to continue using it. I think good scientific strategy is to use simple models if they have any chance of being right, and use them to make as many predictions as you can, and then see if they work. And then you may find they don't work. I get very annoyed by a certain kind of heretic cosmologist. I don't mean that it isn't all right to doubt the present model, as I've just been doing with you. I've been doubting it. But I think there is an attitude that some distinguished astronomers or physicists have had that people who work in the context of the big bang, the standard Robert son-Walker big bang model, are wasting their time and being very foolish, because we really don't know that that's true. I've seen that attitude in particle physics. I remember there were people like… Landau, who was very skeptical about anyone who would work at all in quantum electrodynamics, because Landau had doubts about the ultimate validity of quantum electrodynamics. I think that's very silly. I think scientific practice is not really in danger from a false consensus. It needs a consensus, in order for us to have something to talk about with each other, in order that our work adds up. Without a consensus, you don't have any way of knowing even if the consensus is wrong. You not only can't do anything positive, you can't do anything negative without a consensus. It was in that sense that I called the Robertson-Walker-Friedmann big bang model the standard model in my book. We need standard models. And sometimes we need them because then we can prove they're wrong. I've used -- I think I introduced the term -- the same term now for the combination of quantum chromodynamics and the electroweak theory as the standard model of elementary particle physics. You don't have to swear to it. You don't have to take an oath that you believe it, but you have to work in that context so that the other people who are working on particle physics will know what you're talking about and you can all get together, and then you may find out it's wrong. So I think it's really terribly important for cosmologists to continue to take the Robert son-Walker-Friedmann model very seriously. If they have ideas on how to go beyond it, fine. But that's no reason for not always going back to the standard model as your reference point.

Lightman:

Until we know for sure that it's wrong, I guess.

Weinberg:

Absolutely. And, of course, these things never are wrong. They always tum out to be right in some domain and wrong in another. Just like the standard model may very well require modification if new gauge bosons are discovered, but there will be a certain approximation in which the standard model is right. I don't think there's any doubt of that. And there is some sense in which the standard cosmology is right, but it may be a more limited sense than we think now. If it weren't for the microwave background, I would begin to think real heresies might be worth pursuing right [now].

Lightman:

Yes, that seems to be vitally important. Because you can think of lots of other ways to produce the helium abundance, I guess. Not any as compelling, but you can think of other possibilities.

Weinberg:

Yes, they're somewhat contrived because the microwave background fits so nicely with the observed helium abundance. Sure, you can also change the cosmic nucleosynthesis in all sorts of ways and recently there's been talk about how an inhomogeneous expansion would change the helium abundance… That bothers me a lot, by the way -- the physics of the universe in the first few minutes, including inhomogeneities and all the effects of plasma physics and so on. That was a very strongly interacting plasma then, and if there really were strong inhomogeneities, then they certainly would affect nucleosynthesis. So that bothers me. But it seems to work so well, ignoring all those complications. Light man: And you might be able to show that if it were strongly inhomogeneous that there was no way possible that you could get out a smooth microwave background.

Weinberg:

That's not so clear.

Lightman:

I guess [the inhomogeneities] could be washed out later.

Weinberg:

Right. We don't see microwave photons from then, we see them from when the universe was a million years old.

Lightman:

Right, but the elemental abundances were made then. So yes, I see.

Weinberg:

Yes.

Lightman:

Without going on too long, what do you think are the outstanding problems in cosmology today?

Weinberg:

I guess there are two different kinds of problems. One is the large scale problem that the Hubble expansion is still not really pinned down. We still don't know the Hubble constant to better than a factor of 2. We don't know the deceleration parameter, other than to say it's not enormous. I think the space telescope will be a huge help with the first problem. I don't know what will help with the second problem. And, of course, we may discover that when we understand how to measure distances more accurately, that even at very large distances, there are large departures from the Hubble flow [the universe is not expanding uniformly]. That would be revolutionary, but it's a possibility. So that's the big problem. Then the smaller -- not smaller in size, but just small-scale problem -- is the origin of structure. People are still arguing whether small things accrete to make big things or big things break up to make small things. There, there's lots of data. I mean we have all these galaxies and they have a certain distribution of masses, a certain distribution of angular momenta. Within the galaxies there are structures like globular clusters and open clusters, and then there are stars and they have themselves a distribution of masses. The whole thing is not understood except in the most qualitative way. There you would think that's a do-able problem that, given an expanding universe, make a variety of different assumptions about initial perturbations, follow them and see what happens.

Lightman:

A lot of people have been doing that.

Weinberg:

Yes, of course. They have been doing it for 20 or 30 years, and I don't think there's been any real success in explaining the hierarchy of structure in the universe and the distribution of masses at each level in the hierarchy. I think that's the biggest failure of astrophysical theory, because it seems to me that's really a failure of theory. Possibly, it'll be resolved by new observations, but I don't know what observations are needed. It seems to me that that's a well-posed theoretical problem. I don't know to account for what's turned out to be the extreme difficulty. But some problems are very difficult.

Lightman:

Maybe there's too large a range of possible initial conditions, and they just can't all be explored easily.

Weinberg:

Yes, but, of course, also it involves non-linear hydrodynamics and we still don't know how to predict the distribution of wave numbers in turbulent flow. We don't know how to calculate convective energy transport in stars because it's again non-linear hydrodynamics. There are an awful lot of things. There are an awful lot of problems where we know the underlying equations, and we don't know how to make progress with them, so maybe this is just another one. But it doesn't seem to be really getting much better. And, of course, there's always the haunting feeling that the data is just terribly misleading, that all we're seeing is the tip of the iceberg, that the real distribution is a distribution of weakly interacting massive particles [WIMPS, one of the candidates for dark matter]. I guess that might be the great breakthrough -- if some of these laboratory experiments or maybe progress in elementary particle physics were to confirm that these WIMPs were real, then I think the astrophysicists could focus on that and begin to use that with a sense of confidence. It's hard to cover all possibilities if you have no way of knowing which one is right. But, for instance, it's quite possible that next year at the Tevatron collider, photinos will be discovered, say, or whatever is the lightest of the supersymmetric particles. And that will turn out to be a stable, massive -- maybe a few GeV -- weakly interacting particle. H that comes out, then it's bound to be present in very large numbers in the universe. I remember when I did some calculations in super symmetry theory some years ago, and I discovered the photino would have a typical mass of a few GeV, I got all excited because I knew that a few GeV was the lower bound that Ben Lee and I[13] had set on the mass of such a particle because if it was any lighter, it would annihilate so slowly that there would be too many of them around. So I thought,[14] "Well that's great. H the particle theory suggests that its mass is a few GeV without any input from cosmology, and then I know that is the kind of mass that would then dominate the universe. This is a natural candidate for the missing mass." And I still think so. But it all depends on experimental evidence. Now there, the experimental evidence is obtainable. The particle physicists really are able to settle that question at least. And that could have a revolutionary effect, I think. If in fact a WIMP candidate is discovered in laboratory particle physics experiments, it may get the whole question of galaxy structure on the right direction, where it isn't now. I mean, how can you just spend your whole life on the non-linear hydrodynamics of galaxy formation when you're not sure the particles you're dealing with are the important ones at all. It's kind of discouraging.

Lightman:

Yes, it is. Do you think that your views about what are the major problems have changed any in the last ten years?

Weinberg:

No. I think that the deeper problems having to do with inflation, what is the universe like on the Planck scale, quantum cosmology, are so far from any confrontation with experiment that I've suspended thinking about them. It's like Charles Lamb said about space and time, "Nothing puzzles me more. But then nothing puzzles me less, because I never think of it at all." [Laughter] Obviously, I would think about it if I could see what to do. H I could see something to do about it, I'd be glad to think about it, but I don't. And I don't regard it as the next step to solve those things because even if one got a completely believable, absolutely debugged new, new, new, new inflationary model, which solved all the problems and was completely natural, I would say, "Good. It's probably true, but what can you do with it?" Of course, it would be nice to have that. I think these other two questions, the question of the Hubble flow, and the question of the galaxy formation are really right up there at the top of the agenda for practical cosmology, if there is such a thing [Laughter].

Lightman:

Practical cosmology, that's a funny combination of words. Let me ask you a couple of more speculative questions. Maybe putting your scientific caution aside slightly...

Weinberg:

I thought I had been doing that. [Laughs]

Lightman:

I think you've been extremely practical in your responses. If you could design the universe any way that you wanted to [Weinberg laughs], how would you do it?

Weinberg:

[Pauses] Well, I'd go back to what I said in our previous interview -- that some sort of steady state seems to me tremendously attractive. I don't feel the way my old friend John Wheeler does, that you want a closed universe to avoid boundary conditions. I would be very happy in an infinite universe with infinite time as well as infinite space, and have the whole universe be a self-consistent solution of fundamental physical principles, including all the parameters like how fast it's expanding and how much mass density there is. Now, maybe steady state only in some average sense, maybe an oscillating universe. I know one isn't supposed to worry about what happened before the big bang, and I've lectured about cosmology to an awful lot of audiences of general public. The question always comes up, "What was there before the big bang?" And I spend so many minutes waffling about that, saying, "Well, you know, maybe there was no time, time was a... " But I share their perplexity. I find it more comfortable to think about infinite time as well as infinite space, no boundary in time any more than a boundary in space, and with everything being explained by physics without any arbitrary historical elements entering it.

Lightman:

No initial conditions.

Weinberg:

Yes. No initial conditions at all. That would be appealing. Especially if you could show that for a certain set of laws of physics, any set of initial conditions would always evolve into the steady state, so that you wouldn't even have to ask, "Well, why are we in the steady state?" In other words, if the universe was an attractive fixed point of the possible configurations…

Lightman:

But if the universe had existed for infinite time, you wouldn't really have to talk about it having initially been in- one state and having evolved towards -- this situation.

Weinberg:

No, but you could say to anyone who asked, "Why is the universe in this particular steady state?" -- "Well, what else could it be?" And if he or she suggested something else, you could say, "Well that would evolve into this."

Lightman:

Yes, I see.

Weinberg:

And clearly it's comfortable to imagine that although our own sun will get cold and die, there will always be new suns and new life and that things will go on forever. But I don't have any set of equations of physics that would have that property. You know Hoyle tried to do that ages ago in what I thought was a very artificial and ugly theory, the C-field theory.

Lightman:

Yes.

Weinberg:

And that was all on a classical level anyway. The actual creation of matter would have to be a quantum thing. I have no ideas along those lines, but you asked me what I would like, and that's what I would like.

Lightman:

Yes, I didn't ask you how you would do it.

Weinberg:

Thank you. [Laughs] Light man: Let me ask you one final question. In your book, The First Three Minutes, you make a statement[15] that the more the universe seems comprehensible, the more it also seems pointless. Maybe that's not the exact wording…

Weinberg:

That's pretty close.

Lightman:

Something like that. Can you elaborate just slightly on that? Maybe you don't want to, but…

Weinberg:

I've gotten more negative comments about that sentence than about anything else I've ever written. Many people who said they liked every other part of the book hated that sentence.

Lightman:

Well, I like that as well as the rest of the book.

Weinberg:

Remember, then I go on [after that sentence] and I have a cheerful ending and I say, "But one thing that does seem to help -- one of the things that makes life worthwhile is doing scientific research." Someone wrote me a letter saying, "You had such a good remark about the universe being pointless, why did you spoil it with that optimism?" [Laughter] I don't think I expressed myself exactly the way I should have, but I think I'm going to leave a more detailed explanation for something else write. I've thought a little bit about how I would have said that if I had known the reactions to it, and I think I would have said it a little differently, but I'm going to reserve that for my own future writing.

Lightman:

Okay.

Weinberg:

I certainly meant roughly what I said, but it didn't come out exactly as I wanted it. The question is, you know, if you say things are pointless, you have to ask, "Well what point were you looking for?" And that's what needed, I think, to be explained. What kind of point would have been there that might have made it not pointless. That's what I really would have to explain.

Lightman:

Yes. In my opinion -- and I sympathize a lot with what you said there -- you could certainly talk about a point or not a point without any religious reference. Probably that was in the back of some people's minds when they questioned why you wrote that [sentence].

Weinberg:

Generally speaking, the mail I've gotten on that book, and also the comments that I get from the general public when I meet them or if I give a talk somewhere, are very friendly. Perhaps I had a vision that I would be burned in effigy by hoards of howling fundamentalists, but that really hasn't happened. Even people who take a very different view of things are... I find that most people are willing to be friendly, and if they disagree, most of the letters I've gotten have disagreed in a very friendly way. It's a little disappointing. [laughter]

[1] D.A. Kirzhnitz and A.D. Linde, Physics Letters, vol. B42, pg. 471 (1972)

[2] S. Weinberg, "Gauge and Global Symmetries at High Temperature," Physical Review, vol. 9, pg. 3357 (1974)

[3] L. Dolan and R. Jackiw, "Symmetry Behavior at Finite Temperature," Physical Review D, vol. 9; pg. 3320 (1974)

[4] A.D. Linde, Physics Letters B, vol. 108, pg. 389 (1982)

[5] A. Albrecht, and P.J. Steinhardt, Physical Review Letters, vol. 48, pg. 1220 (1982)

[6] S. Hawking, A Brief History of Time (New York: Bantam, 1988)

[7] A.D. Linde, Physics Letters, vol. 129B, pg. 177 (1983); see also A.D. Linde "Particle Physics and Inflationary Cosmology," Physics Today, September (1987) and references therein.

[8] J.R. Preskill, Physical Review Letter" vol. 43, pg. 1365 (1979)

[9] Ya. B. Zeldovich and M. Yu Khlopov, Physics, Letter, B, vol. 79, pg. 239 (1978)

[10] R.H. Dicke "Dirac's Cosmology and Mach's Principle," Nature, vol. 192, pg. 440 (1961)

[11] V. de Lapparent, M.J. Geller, and J.P. Huchra, "A Slice of the Universe," Astrophysical Journal Letters, vol. 30.2, pg. L1 (1986)

[12] H.P. Haynes and R. Giovanelli, "A 21 Centimeter Survey of the Perseus-Pisces Supercluster. I. The Declination Zone +27.5 to 33.5 degrees," Astronomical Journal, vol. 90, pg. 2445 (1985)

[13] B.W. Lee and S. Weinberg, "Cosmological Lower Bound on Heavy Neutrino Masses," Physical Review Letters, vol. 39, pg. 165 (1977)

[14] S. Weinberg, Physical Review Letters, vol. 50, pg. 387 (1983)

[15] S. Weinberg, The First Three Minutes (Basic Books: New York, 1977), pg. 154

Session I | Session II