To satisfy my curiosity about astrophysics, I have recently bought and have now finished reading A Universe from Nothing: Why There is Something Rather than Nothing, by physicist Lawrence Krauss. The book appears to have two aims: To give a summary of the current understanding of how the universe came to be, how it evolved into what it is now, and how it will end, and to refute the argument that some external (divine) intervention is necessary to get something from nothing.
As far as I can follow (and that is not necessarily very far), the story is as follows. Because of quantum effects, a universe of space with stuff in it can poof into existence from nothing (in the sense of not-even-empty-space) as long as its energy sum is zero; and indeed it will. And it just so happens that our universe has an energy sum of of zero because the positive energy of motion is exactly cancelled out by the negative energy of gravity.
Even if we start with a very small something it can rapidly expand into an enormous size with a lot of mass through a process called inflation; and indeed it must because of the negative energy stored in empty space. This massive increase in size makes the originally closed universe flat (Krauss compares this process in four dimensions to the three-dimensional local flattening of a balloon surface as the balloon gets inflated). Quantum fluctuations in the inflationary phase at the beginning of the universe guarantee that the stuff in the universe - which can only poof into existence because half of it cancels the other half out - will be too unevenly distributed to actually self-annihilate again, thus forming the seeds of later galaxy formation.
At the end of the rapid inflationary phase, the expansion of the universe is slowed down considerably but starts to accelerate again from this low level. Stars form, burn hydrogen into heavier atoms, stars explode, planets like ours can form, and life can arise. Those are the better known steps in this story.
The most likely scenario for the future of the universe is that it will expand ever faster until space will be drawn apart at above the speed of light, meaning that the inhabitants of one galaxy cluster will be unable to see other clusters. At the same time, the currently nicely spiral galaxies of each cluster will collapse into one big megagalaxy per cluster.
Ultimately, all star fuel will be burnt up, everything will drift hopelessly far apart, and the universe will turn into a cold, dark, lifeless, uniform nothingness.
However, it is apparently quite possible that the quantum fluctuations in the inflationary phase can lead to an innumerable, potentially infinite number of reciprocally isolated "parallel" universes. If the fluctuations locally weaken inflation, a universe can crystallize out of the inflationary soup; if the fluctuations locally strengthen inflation, the soup will expand even faster and further, providing more chances for additional universes to pop into existence. If that is true, then it is perhaps some comfort in the face of our own fate.
Finally, Krauss stresses the possibility that the "laws of physics" in our own universe may turn out to be random; perhaps every new universe gets a random set of laws, and intelligent beings only arise in those few that get a combination of laws conductive to their evolution. Thus perhaps it does not make sense to ask why things are as they are, and there will never be a great unified theory of everything.
So, how convincing is this story? The problem is clearly that I cannot judge many of the points made in the book, so I have to trust that all this is actually correct. Maybe it is simply because I am a biologist myself, but I find it much easier to follow the argumentation of popular science books on evolution, for example Why Evolution is True. Or perhaps the material is really more difficult. It is said, after all, that quantum physics is so weird that anybody who thinks they understand it thereby proves that they don't. A related problem is that physicists do not appear to agree on as many of the details as biologists, for example; just think of string theory and its detractors.
Still, there are many parts that make sense even at my level of understanding. Quantum effects that produce two opposing particles from nothing are empirically demonstrable, so one can imagine that a space containing exactly equal amounts of positive and negative energy could also pop into existence. The flattening of the universe through inflationary expansion makes intuitive sense, and I think I can even understand the concept of space itself being allowed to expand faster than the speed of light, thus dragging matter apart at faster than the speed of light although the matter itself is not allowed to move through space at those speeds.
However, I find it very hard to grasp the wholesale production of so much stuff in such a short time through inflation that even after the self-annihilation of most of it there will be 100 billion galaxies worth of stuff left. It is surely because I do not understand one of the most important concepts in the book, the negative energy stored in empty space, but well, it simply does not click in my head. Imagination fails me, and here I have to trust that the astrophysicists know what they are talking about, just as I trust the plumber, the doctor, or the car mechanic, and just as I hope that others trust me in my area.
Of course, here is the problem with trying to convince readers who aren't already on board that no god is necessary for our universe to exist. I am not even talking of those who reject science outright if it conflicts with their beliefs because those are hopeless. No, there might be those who could be convinced of what they did not previously accept if they could be shown something as simple to grasp as evolutionary algorithms (see, evolution can work on this scale, just extend the logic to a bigger scale...), the laryngeal nerve (does this look like the work of an omnipotent designer?) or perfectly stratified fossils. But for some of the rather counter-intuitive effects operating in physics way above or way below the scale we are familiar with there may sadly not be anything that is simple to grasp, even by analogy.
The other thing that can be expected to leave a religious reader unconvinced is the question of why the laws of physics are exactly as they are. Yes, Krauss argues that there may not even be a reason for that, but believers are notoriously bad at grasping the anthropic principle.
And honestly, his argumentation also seems a bit out of place at the end of a book that otherwise showed how many different laws and observations turned out to fit perfectly with and necessitated each other. After being told that the universe could only ever turn out to be flat because of three different observations or effects, and that it could only have come from an inflationary phase because of this and that, and that something will necessarily arise from nothing, etc., the reader has unwittingly acquired the expectation that the last few pieces of the puzzle should also be connected with some "will necessarily" or "could only ever".
Worse, Krauss has not actually provided an answer even on his own terms. Yes, it is possible that the laws of our own universe are a random inheritance from an inflationary period producing countless universes, but where did the laws of the universe that produced our universe come from? Where does the quantum behaviour come from that allowed the first bit of space to pop into existence that fed the original inflation itself? How is there "quantum" and not something else, or a law that says that nothing can pop into existence even if it would cancel itself out?
As such, there is still no answer. Of course, maybe there can never be. Of course, "god did it" is clearly a non-answer, a cop-out. But sorry, physics itself does not yet appear to have a clear answer that makes god superfluous. The best rejoinder to that god did it nonsense is still, and will perhaps always remain, "so where does god come from then"? In other words, pointing out that the believer is resorting to special pleading when they argue that everything needs a reason only god doesn't. And that is logic, not physics.
That being said, perhaps the strongest novel point against a creator god that can be taken from this book is the observation that positive and negative energies in our universe cancel each other out, so that our universe has exactly zero net energy. Surely that is in good accordance with materialism, or let us say with non-createdness. Because what would you expect - if you did not know the answer already - from a universe created by a god? I think if we are honest, the expectation would be a decent positive energy balance that is slowly being used up as the universe ticks along its preordained path towards whatever ultimate divine purpose it was created for.
(I write "novel point" here because several other cosmological arguments against a benevolent creator god are rather old and obvious, e.g. the fact that most of the universe is empty and utterly hostile to life, or our rather ordinary and unprivileged position in it.)
As a side issue, I can now understand a bit better why philosophers are sometimes so miffed at Lawrence Krauss. He really does not like philosophy.
But I also understand why he doesn't: Krauss appears to honestly believe that philosophy is trying to describe and explain the material universe around us without ever looking at it; various parts of A Universe from Nothing make it abundantly clear that that is his understanding.
I have no idea where he gets that from. Yes, many ancient Greek and Roman philosophers have tried to take that approach. But that was before the rise of the scientific method. These days, the division of labour is abundantly clear: science figures out what is in our actual universe and how it works, and philosophy does not claim to be doing so. What contemporary philosophy is about is perhaps better described as thinking about how to think and how to conceptualise.
Consequently, Krauss' constant complaints that philosophy is useless for finding out about the Big Bang seem about as relevant as if he were making the same complaint about public transport. Yes, it is useless (or let us say it is at least not directly useful) for that specific purpose. But so what?
Despite my grousing here and there, the book was definitely worth my time. I learned a lot, partly thanks to the very illustrative way in which many of the relevant processes are explained. A particular strength of the narrative is that it shows how we now know certain things, and even who discovered it specifically through what experiment or, sometimes, accident. This is important; science is more than a collection of facts, it is all about how we know that they are facts.