Professor Don Page has taught since 1990 at the University of Alberta, in the Department of Physics. Professor Page is an expert in the field of “black holes”. He has studied at leading institutions, Caltech, USA; University of Cambridge, UK where he was research assistant 1976-1979. He has worked & collaborated with Prof Stephen Hawking co-authoring with him “Thermodynamics of Black Holes in Anti-de Sitter Space” in 1983. (photo by Anna Page)
The following interview questions are taken from the brief reflection by Prof. Syed Hasan Askari (1932-2008) entitled “Fireworks” where he enquires on the nature of the “Big Bang” & what if anything preceded it. http://spiritualhuman.wordpress.com/fireworks/
Sincere thanks to Professor Don Page for agreeing to this interview.
SPIRITUAL HUMAN INTERVIEW WITH PROFESSOR DON PAGE
Musa Askari: If one talks of the original Big Bang, what sort of bang was it? An explosion where each piece that flies out becomes an occasion of further explosion (multiple Big Bangs)?
Don Page: We have very strong evidence that our universe was very much smaller, denser, and hotter about 13.8 billion years ago. The explosion out from that hot dense state is call the Big Bang. We are not certain whether this was the absolute beginning of the universe, or whether it was a bounce from a previous phase of contraction, or whether it was just the latest in a series of big bangs, or whether perhaps it does not make sense to say that there was any absolute beginning to the universe.
Musa Askari: The behaviour of the original particles and forces issuing from the Big Bang. Was this behaviour haphazard? Was it arrived at through trial and error? Was it pre-given?
Don Page: So far as we can reliably trace back the behavior of our universe back toward the Big Bang that was nearly 14 billion years to our past, it seems to have been very smooth, nearly homogeneous and isotropic. However, there are strong suggestions, based upon indirect evidence from the form of the small departures from homogeneity and isotropy, that before the time for which we have reliable fairly direct evidence, there was a time of very rapid exponential expansion, called inflation, that could have smoothed the universe out even if it had been more lumpy before (though there do seem to be limits on how lumpy and disordered it could have been before inflation started for it to occur and be able to smooth out the universe).
Some scientists speculate that there might have been many different big bangs, most of which did not lead to much life like ours, so that we are seeing one of a relatively small sample that occurred with a form suitable for life. However, the type of big bang that we observe seems to be even much more special than what would be required simply for life like ours. So one cannot fully explain all its properties as being due to the selection effect that observers can only observe conditions that permit observers to exist.
Musa Askari: What about “Laws” which seemed to immediately come into operation soon after the said explosion. Did laws also “explode” into existence along with the energy and matter they were supposed to govern and regulate? What about other laws which govern the properties of those elements which came into being much later, say carbon dioxide? And laws governing organic matter, life, consciousness, reasoning. Did they all explode with the Big Bang? Were they lying in suspense until those substances and forms arose which required them? Where were they lying in abeyance?
Don Page: If the universe did indeed have a beginning at some point in the past, using some measure of time within the universe, the laws for the
universe would not have applied before that beginning, using the time within the universe to define “before.” But one might say that the laws have some Platonic existence beyond the existence of the universe itself, in a sense somewhat similar to the sense in which 1+1=2 can be considered to be a true theorem of arithmetic (a logical consequence of the axioms of arithmetic) even if there are no individual objects such that one could count one of them and another of them to get two of them. However, there is the difference that theorems like the logical following of 1+1=2 from suitable axioms are logically necessary truths, whereas the laws of physics are just descriptions of a contingent concrete entity, the universe, so there is no logical necessity to laws of the universe as there are for theorems of arithmetic.
Musa Askari: In contemplating the Big Bang are we also reaching for the smallest possible unit of condensed matter?
Don Page: In classical general relativity (ignoring the Heisenberg principle that is believed to apply to gravity that we think is actually
quantized and so does not obey the classical equations of Einstein’s
theory of general relativity), there would be no limit larger than zero to how small the universe could be, so in principle it could have expanded out from zero size (or at least it could have had any size greater than zero, though one might say that the limit at which the size goes to zero, as one goes backward in time, is not itself part of the spacetime of the universe). In quantum gravity we do not yet know whether or not there is a positive limit on how small the universe might be.
Musa Askari: What held it in that state of intense density not allowing it to explode or expand?
Don Page: The point of infinite density would not really be part of the universe in the classical model in general relativity, so whenever the universe existed, it would be expanding, in this classical big bang model. But even for a classical model, the universe could have had a bounce at large but finite density rather than an expansion from an arbitrarily small size and arbitrarily large density. And in a quantum picture, it might not make sense to say how large the universe is as a function of time to be able to say whether or not the universe started expanding from an arbitrarily small size.
Musa Askari: What force of gravity within itself pulled it to itself that it retained its intense density?
Don Page: In the classical big bang model with an initial singularity (the limiting t = 0 time that is not really part of the universe), the
universe has always been expanding during its entire lifetime, for all t > 0. If we measure the time t that has existed within the universe,
that can be finite (perhaps roughly 14 billion years now), but the
idea is that time t cannot be zero. t = 0 is only a hypothetical
limit, what is called a singularity, not a time within the universe,
since in the classical big bang model, time is only defined for t > 0.
Musa Askari: If it exploded at “x” time, why not before, why not later?
Don Page: We can measure what is the time interval that the universe has existed up to now, but it does not make sense to try to assign a definite time other than zero for the limiting “point” or initial singularity at which there has been no previous time. In a classical model, time differences make sense (though even these may not be definite in a quantum model), but even in a classical model, only time differences after the initial singularity make sense, not any supposedly absolute time at which the singularity happened. (Well, we can say that if the big bang about 14 billion years ago really did have a singularity, a limit beyond which one cannot go back in time and at which densities would go to infinity, then the singularity was 14 billion years in the past relative to us now, but there is no meaning to its time other than relative to events within the universe.)
Musa Askari: What suspended its internal gravity for an instant that the great bang was triggered?
Don Page: There is no instant at which the big bang was triggered. There is only a limit at which one can say that t = 0, but this limit is not part of the existing spacetime. Going back toward that limit, the density would diverge, meaning that it would get greater than any pre-assigned finite value, but one cannot say that it actually reached infinity as one goes back in time, since the universe only exists for t > 0, and not at t = 0. Well, this is within a classical model of general relativity. Probably quantum gravity so alters the properties of time that the whole question of the time evolution of the universe becomes a meaningless concept.
Musa Askari: If the Big Bang is a result of an instant’s suspension or weakening of the force of gravity is in itself a hopeless question perhaps. Or, was it so that a force involving a greater force of gravity pulled out of the contents within that mythical mass with such force that an explosion occurred? What was that force? Could it be what we refer to now as “dark energy”?
Don Page: The “dark energy” is the name for whatever it is that is now causing the linear size of the universe to be accelerating with time, so that the rate of increase of the linear size with time is itself increasing with time rather than decreasing. So the gravitational effects of the dark energy are a form of what might be called anti-gravity,
gravitational repulsion rather than attraction that would cause the
expansion rate of the universe to decelerate (slow down). But it
doesn’t seem to make sense to say that the big bang explosion itself was caused by this dark energy.
Musa Askari: If there was any, does it then make the Big Bang a secondary phenomenon?
Don Page: In a quantum description, our Big Bang (the very hot dense phase nearly 14 billion years ago) might have been a secondary phenomenon, not the first big bang of our universe. It might have been only the latest in a long sequence of successive big bangs. Scientists speculate that quantum tunnelling in a pre-existing universe might have led to new big bangs. Perhaps the new big bangs would wipe out the evidence for the previous ones, or perhaps they would not, so that one might be able to find evidence of earlier big bangs. However, so far no one has found any convincing evidence for big bangs further in the past than our Big Bang that occurred about 14 billion years ago.
Further interviews in the “Spiritual Human” series can be found at: http://spiritualhuman.wordpress.com/interviews/