Some Proposals about the Beginning of our Universe

The theoretical physicist from Caltech, Sean Carroll gave a talk to the American Astronomical Society in January 2017 on the topic of what we know and don't know about the beginning of the universe. He has generously posted a copy of his presentation on his blog, preposterousuniverse.com. In this talk, Dr. Carroll speculates about how the gaps in what we don't know may be filled in by presenting a systematic classification of the main ideas developed over the last few years about what may have occurred before our universe began and brought our universe into existence. (Dr. Carroll does point out that to say our universe "came into existence" sounds like a process within time, but that time as we know it actually had a beginning with our universe.) In previous posts I have already discussed many of the things Dr. Carroll covers in his talk including (1) that our universe was in a state with very low entropy at its beginning, (2) that something like the Big Bang occurred about 13.8 billion years ago but we don't know what actually happened in the first trillionth of a trillionth of a trillionth of a second because (3) we don't have a quantum theory of gravity which may describe the initial conditions of our universe, even though (4) the equations of classical general relativity predict that our universe had an actual beginning.

Let's review what we do know: (1) About 13.8 billion years ago the universe was very hot and dense and was expanding rapidly while decelerating; (2) classical general relativity predicts that there was an actual beginning of our universe in a singularity; and (3) our early universe was in a very low entropy state which is quite hard to explain since low entropy is associated with an ordered, and improbable state. The last point presents tremendous challenges for any naturalistic proposal about how our universe came into existence.

In regards to what we don't know, Dr. Carroll presents four different classes of models about the space-time origin of our universe: (1) a bouncing model, (2) a cyclic model, (3) a hibernating model, or (4) a reproducing model.

A Changing Arrow of Time?

This is one post I am not looking forward to writing.  Some of my readers have asked me to comment about alternative theories to the Big Bang which remove the necessity of our universe having a beginning.  I have been thinking for some time about how to write on this subject in a non-technical manner, which is the tone I strive for on this blog.  Because most of these ideas are quite theoretical, requiring complex mathematics and intricate nuances, it is quite a challenge for me to give an accurate and adequate description of most of these proposals, yet still be comprehensible.   Nevertheless, in this post I want to try to discuss the paper by Anthony Aguirre and Steven Gratton (AG) that describes a scenario which they claim requires no beginning.¹   I also want to give some thoughts on how their idea fits into the whole discussion of evidence for or against a deity, particularly the Christian God.  My attempt may be an epic fail.

In the model proposed by Aguirre and Gratton, they claim to avoid a beginning by proposing a thermodynamic arrow of time that points in different directions depending on whether the universe is expanding or collapsing.  To understand what this means I need to first take a diversion to discuss what the thermodynamic arrow of time means.  Actually, no one really knows for sure why we experience time moving forward but we do know that a quantity called entropy must increase in any non-reversible process.  Entropy strictly has to do with the number of microstates available to a system. The concept of a microstate can be illustrated by considering two six-sided dice. There is only one microstate available for the dice to roll 2: both must show a one. However, there are six possible microstates available for the dice to roll a 7. The combinations are 1 and 6, 2 and 5, 3 and 4, 4 and 3, 5 and 2, or 6 and 1. Because there are more available microstates, the dice will more often roll a 7. A macroscopic system with more available microstates has a greater entropy than one with fewer microstates. The second law of thermodynamics states that an isolated system will evolve spontaneously to the state with maximum entropy.   This is a statistical idea.  In general, all processes move toward those that are more statistically probable.  That gives us the arrow of time.   Time moves in the direction where entropy increases.