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ONWARD TO INFINITY
PG: It’s interesting how recent cosmology really is. In some ways, of course, it’s the most ancient of all speculative systems. Where does the universe come from and how did it begin? What is the structure of things?
But in its modern scientific form, as a subject that can be studied experimentally, or at least observationally, it’s recent. I mean, very shortly after making general relativity, Einstein began to think about what it would mean on a cosmological level, but that’s only since 1917.
PS: Yes, science is a very thin veneer on what is an ancient subject.
PG: And even more recently — the first glimmers were in the ’30s, but it really developed in the 1950s — came the idea that you can actually use ordinary physics to study it. That’s amazing.
PS: I agree. What’s happened in the last 50 years in cosmology has been a remarkable use of atomic or nuclear particle physics to enhance our understanding of the history of the universe. But progress has been limited to exploring the period betwen the one-second mark and today, where we know the physics can make observations. We now understand this period in such remarkable detail that if you try to develop a story of what happened before or what will happen in the future, it’s incredibly constrained by all this information.
And because we have been focusing on this intermediate period that we can measure in fine detail, most of us haven’t given attention to the larger questions outside the current empirical domain, like the infinity of space or the beginnings and future of time.
But now our noses are pushed against those issues. And most of my colleagues, myself included, are not really trained in history or philosophy or the earlier thinking on these issues. We are, I feel, somewhat naive in this respect.
PG: To me, this again broaches the deeper subject of: What is it that we want from science? Is it meaningful to talk about another universe to which we have no observational access? Is it meaningful to talk about what happens before the big bang? Is there a way of taking the cyclic model into account to try to figure this out?
In many ways the ultimate paradigm shift is for us to define what kinds of questions we consider within the domain of physics, and within the domain of science in general.
PS: I view myself as very pragmatic positivist thinker, not so much because it’s a conviction, but because it’s what I like to do. So in developing the cyclic model, the important question to me is what can we explain and what can we predict if the universe is cyclic. If it is cyclic, this bang can repeat over and over again. What happened 14 billion years ago would be the most recent bang, but there would be ones before and ones in the future.
This is the practical question: Can we prove through observation that something before the big bang that led up to it and produced the present universe? If so, I think we can even say something about the future, how long before the next bang occurs and what will happen in cycles to come.
But you might also ask questions like, “Do we know if the bangs went infinitely far back in time, or was there a ‘first’ cycle?” I don’t know yet of any empirical way to test these questions, so as long as that’s the case, I’m not interested — I want something I can deduce.
And this deductive approach has led to some very interesting developments within the past decade. So, remember I said earlier that the only way we could set up the right conditions after the bang, was to have this period of inflation?
PG: Yes.
PS: When you let go of the idea that the big bang was the beginning, it turns out there is a new possibility: Before the bang, there was a period of a very special high-pressure ultra-slow contraction. And, surprisingly, it has an effect very similar to inflation’s very rapid, low-pressure expansion. The physics and the timing are completely different, but it has the effect of smoothing the universe out before the bang and producing tiny ripples at the bang that look almost identical to — though not exactly like — what you get from inflation.
Close enough that at the present time we can’t distinguish the two, yet different enough that we are at the edge, experimentally, of saying whether or not the cyclic picture could work. There are measurements being done right now that could tell us whether or not the idea is viable.
Soon — and it could be anywhere in the range of days to years — we could learn if the cyclic model is dead. If that’s the case, then you only have the possibility that the big bang is the beginning.
PG: In the long run, it seems that you have in the history of science strong explanatory structures that have to be coupled to some kind of predictive strengths in order to go forward. If you think about it, for instance, understanding the theory of gases as an assembly of molecules bouncing went on for decades with the goal of being able to reproduce what people already knew how to do with heat in the physics of thermodynamics.
PS: But that’s more ordinary science. Consider the following problem we have right now in cosmology: The cyclic model predicts that there shouldn’t be a spectrum of large-wavelength gravitational waves, and typical inflation says they should exist. If we see them, as far as I know, the cyclic theory is dead, and the case for inflation is strengthened. That’s normal science.
But suppose we don’t observe them. That would still be consistent with the cyclic picture. But in the inflationary picture, because it allows an infinite number of patches of every possibility, there will always be some patches that actually don’t produce gravitational waves. Since you get an infinite amount of everything, it might be that we are living in one of those patches of the universe. How do we prove or disprove that idea?
It’s a very strange kind of science. To me, the playing field becomes uneven between a theory making testable predictions, versus a theory that is Teflon. From what I can tell, there is no observation that can disprove inflation. Some people even advertise that as an advantage. To me, that’s a new and unacceptable way of thinking.
PG: I think we do live at a time when science is changing its character in lots of ways, some of them no doubt for the better. Fascinating new combinations between pure science, applied science, nanoscience, bioinformatics — areas that 20, 30 years ago might have been considered industrial stuff to be done outside the university — are now an extremely dynamic, exciting part of science.
Cosmology, it seems to me, has always been on a very delicate balance between its speculative origins that take it outside of the remit of science, and tremendously exciting moments when things previously thought to be outside of our possible understanding are suddenly understood. We’re at that knife edge right now.
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