previous post about the Big Bang elicited a few comments and questions about alternative scenarios for the origin of our universe that would not require an actual beginning. I'd like to respond to those questions, but I think it would be beneficial to first discuss some of the scientific challenges that are faced when we try to understand what happened in the first 10-35 seconds of the universe.
One major challenge is to try to determine what laws of physics are applicable during that time. This is a problem that you may have already heard about for it has to do with the incompatibility between Quantum Mechanics and General Relativity. If you do a web search about this subject, you will find multitudes of articles written, from those that are quite basic to those that are quite technical. The purpose of my blog is to describe things accurately, but simply, so my discussion will necessarily be basic.
Quantum Mechanics describes how the universe works at very small scales, about the size of atoms or smaller. When describing the universe at small scales and at very high energies, we need a particular subset of Quantum Mechanics called a Quantum Field Theory (QFT). The Standard Model, which I work with all the time in my research and describes the most fundamental particles in the universe and three of the four fundamental forces in the universe (electromagnetism, the weak, and strong force) is a QFT. Within the framework of QFT we find some of the properties of the universe we'll eventually have to address, like particles popping into existence from "nothing" or two particles annihilating each other. Why are QFT's important when we try to describe the "beginning" of the universe? Because the visible universe was very small and very hot (at an extremely high energy) so we should be able to describe it by some kind of QFT.
General Relativity (GR), on the other hand, is our best description of how gravity works. But it is not a QFT. It is a classical field theory, and all attempts to quantize GR have failed for technical mathematical reasons I will not describe. (I found this web site helpful in describing some of the technical problems in a fairly sophisticated manner for those who want to read about some details.) In addition, QFTs all work within a fixed framework of space and time. But the very essence of GR is that space and time are warped by massive objects and massive objects move according to how space and time are configured, (which is a paraphrase of what the physicist John Wheeler has said.) So by its very nature GR requires a space and time which is not fixed, but a QFT requires a fixed space and time framework. Consequently, there is a real incompatibility between the two.
Now, if we were to run the film of our universe backwards to try to see what happened in the beginning we would eventually reach a very dense hot universe that requires us to understand gravitational effects in a region where our current theory of gravity is known to be inadequate. We could "pretend" that our current theory of gravity is adequate all the way back to the "beginning" and if we do that we find that the universe has an actual beginning of matter, energy, space, and time. That beginning results in an actual infinite density and infinite temperature of the universe some finite time ago, what we call a singularity. But is it possible for an actual physical property to be infinite? Maybe not. That may also be a clue that we are most likely trying to extrapolate a known theory into a regime where it doesn't apply.
In addition to this problem of not knowing what laws of physics may have operated during the earliest part of our universe we run into another serious problem when trying to understand the origin of the universe. It is very possible, if not likely, that we will never have any measurable observations about what happened during that early epoch of the universe. Most scientists believe that during the first 10-35 seconds or so our universe went through an inflationary epoch in which the fabric of space-time had a period of super accelerated expansion. If this is true it means we may never be able to see any effects from that early time since information now only reaches us at the speed of light, and the affected parts of the universe expanded beyond the boundary in which their light could reach us.
So what are we left with? We don't yet have a workable theory that we know for sure describes the first trillionth of a trillionth of a trillionth of a second and we don't have any observational evidence of what happened. Is it hopeless to then speculate about what may have happened? Can it ever be scientific to speculate about what may have happened? I'll try to answer those questions in my next few posts, but let me make a couple of observations here first. (1) We don't know for sure that the classical predictions of GR are necessarily false. In fact, they are arguably the best we have right now and those predictions do require a real beginning of this universe. We'll talk more about this in future posts, particularly when I discuss the Borde-Guth-Vilenkin theory. (2) As I pointed out in my previous post about the Big Bang, we do understand the history of the universe from sometime very early in its existence until now, and all the data we do have seems to point to an actual beginning. My previous statement was, "If one hundred years ago you had predicted that scientists would obtain
unambiguous evidence about the history of the universe for 13.8 billion years, all of its lifetime except the first fraction of a second, and that all of the evidence would point to an actual beginning consistent with a transcendent cause, I don't think anyone would have taken you seriously. But that is exactly what has happened. Theists could not
have outlined a better scenario to support theism. The scientific facts are completely consistent with the statement, 'In the beginning God created the heavens and the earth.'" So far everything we do know is completely in line with Christian theology. Can we make any stronger statements about the origin of our universe? I believe so. We'll discuss that next...