Physicists have pretty well established that the way the universe works depends on the values of a small bunch of numerical constants. The strength of gravity, for instance. If gravity were slightly stronger, stars would all collapse into neutron stars, so there would be no planets with life. If it were slightly weaker, stars would never have formed at all; the entire universe would be just a cloud of drifting gas.
That’s just the example that’s easiest to understand. There are other similar numbers. When you look at the big picture, it does appear that our universe has been fine-tuned at the factory to allow our sort of life to emerge.
This is not an argument for the existence of a god, however. If our universe did have a Grand Designer, there are several possibilities, most of which don’t involve anything that would resemble traditional conceptions of “God.” The Grand Designer might have died billions of years ago, for instance. Or might have drifted off to work on some other project, and might have no concern at all with the fate of this one.
Nonetheless, physicists are confronted with a puzzle: Why are things the way they are? One suggestion holds that there’s an infinite supply of universes. At the beginning of each universe, the values of these physical constants are established in a random manner. Most universes, then, would be devoid of anything resembling life. Our own universe might be part of a tiny minority — but only in that tiny minority will intelligent beings evolve who can look around and say, “Wow! Look how perfectly these numbers are set up!” This is called the weak anthropic principle.
Another suggestion has to do with symmetry breaking in the early universe. It’s possible that our universe is the way it is because that’s the only way it could be. If you start with an explosion of extremely high energy and density, as things start to cool off and the basic characteristics of matter coalesce, no other alignment of constants is possible.
Neither of these theories is very satisfying, but they’re all we have.
What we can be certain of is this: Physicists don’t know everything yet. The study of physics is a process of discovery. We know a lot more than people did 200 years ago, but the true nature of matter and energy remains largely elusive. Ask a physicist why all electrons are alike. There’s no particular reason that they should be, but they are. All of the quintillions of electrons in the universe are interchangeable with one another. They’re indistinguishable. Or at least, that’s what we’re told. But why is the universe organized in that manner? I believe it was Einstein who said, “The most incomprehensible thing about the universe is that it is comprehensible.” This is what he meant. The bare fact that equations can be written that describe the behavior of electrons is not a fact that has been satisfactorily explained.
Lately I’ve been reading about the incredible intricacies of molecular interaction within a single living cell. What’s going on within cells is jaw-dropping. The way molecules interact with one another to produce structure and behavior is enough to make your head spin. And they’re doing it all the time, continuously. They’ve been doing it for billions of years.
At the other end of the scale, we can look out into the sky and see that galaxies (each of them a whirlpool of hundreds of millions of stars) are not sprinkled around the universe at random. They’re arranged in filaments and sheets. We have, at present, no adequate explanation for this fact. We don’t even know why galaxies spin the way they do; the spinning seems to defy what we understand of the law of gravity. As the old Buffalo Springfield song has it, “Somethin’s happenin’ here. What it is ain’t exactly clear.”
What strikes me about all this is that at every scale of magnitude, from subatomic up through molecules and cells to planets, stars, galaxies, and clusters of galaxies, the universe exhibits order. Stuff is not scattered evenly or haphazardly; it’s organized. To be sure, the organization is seldom simple, but why should it be simple?
One of the most hallowed principles of physics is the Second Law of Thermodynamics. In layman’s terms, what this law says is that things fall apart. Energy is always distributing itself more evenly across any closed physical system. Entropy (that is, disorder) increases.
To sum up, what we’re being told is this: The universe began in an explosion of incredibly hot gas, in which there was no discernible structure at all, just a sizzle of violently dancing particles. And structures always deteriorate due to the hallowed, unbreakable Second Law of Thermodynamics. And yet, after 13.8 billion years, we observe that the entire universe is well structured, at every order of magnitude.
In terms of information theory, the original information contained in the universe was exactly 1 bit: BOOM! So where did all this other information come from?
I’m starting to wonder about the Second Law of Thermodynamics.
Do I sound like a flat-Earther? An evolution denier? That’s not where I’m coming from. In the recent history of science we’ve seen some large-scale turn-arounds in ideas. Things that reputable scientists would assure you were absolutely true have turned out not to be true at all.
Here’s a dandy example. Thirty or forty years ago, everybody knew that acquired characteristics couldn’t be inherited. Lamarck was wrong; the geneticists were right; the debate was over. All inheritable characteristics were spelled out in the genes.
What we have since learned is that that’s not true at all. What happens to your parents prior to your birth can influence you. There is now a whole field called epigenetics that studies these phenomena. And it’s not just your mother’s state of health while you’re in the womb that matters. If your father starts smoking tobacco when he’s 10 or 11 years old, long before you’re conceived, your health will be impacted 50 years later. The nature of the effects is not nearly as simple as Lamarck imagined, but there are effects. Those respected geneticists were wrong.
So can we talk about the Second Law of Thermodynamics? Somethin’s happenin’ here. One fairly simple explanation is that the universe is not a closed system. If the universe is infinite, then the plentiful structure we see around us may have any origin you can dream up. There’s no such thing as “the universe as a whole is becoming more disordered, so the Second Law is intact,” because there’s no such thing as “the universe as a whole.”
Alternatively, the universe may be finite, but may embody forces that inherently bring about order. We don’t know what those forces might be, but we can’t state categorically that they don’t exist.
And that’s entirely enough armchair physics for a Sunday morning.
Jim Aikin's Oblong Blob 
The Second Law depends upon choosing one definition of order and sticking with it. The Law holds true in exactly the same form with approximately the same consequences regardless of the definition you choose (though obviously really narrow definitions won’t give you as much information).
I once saw a video about the phenomenon you’re describing. Unfortunately I have no idea how to find it again, but in this video the physicist talks about pouring milk into a cup of coffee. Initially the milk is a very simple-to-describe blob and so is the coffee. The milk has energy from gravity but it’s easy to describe that energy, so entropy is low.
At a point in time a little later, the milk has interacted with the coffee and produced complex swirly patterns. Entropy is higher because the location and the velocity of the milk has gotten more complex, and our observation of the system agrees with this; the swirls are complex.
But after a long enough time, the inevitable increase in entropy leads to the milk pretty thoroughly mixing with the coffee. The complex swirls disappear, yet the usual definition of entropy says that the milk’s location and velocity is more complex.
The presenter stated that though entropy increases throughout the process, there seems to be some subjective thing, some form of complexity, which first increases but then decreases. He gave more examples but didn’t have much idea how to quantify the complexity.
So yeah, there is a sort of problem with the Second Law, in that it doesn’t line up with our experiences well. I’d say we could try to quantify it by talking about the amount of ‘useful information’ in some way. After the coffee and milk mix, the most useful description is simple and states that there’s an even mixture. At that point all the chaotic entropy guaranteed by the 2nd Law just helps the Universe simulate something simple, namely an even substance. But what sort of usefulness are we talking about?
As to the initial comment, about fine-tuned parameters… personally I don’t see anything very dissatisfying about the suggestion that those parameters might only be able to have those particular values. It certainly would mean there’s a ‘why?’ yet to be provided; but it’s very unlikely that we’re describing physics in terms which are actually fundamental. Imagine creatures living in a world such as Conway’s Game of Life. Matter is digital; the world is divided into cells which contain either a ‘1’ or a ‘0’. A common particle would probably be the famous ‘glider’. But I doubt very much that life would quickly discover the grid of ones and zeroes which forms this particle. Instead they would study it as a particle.
The type of physics such creatures would discover first would be whatever is most useful at their scale. A living animal in the Game of Life would probably be huge, billions of cells across. We don’t really know whether a Game of Life universe on that scale would have matter with momentum, but it would probably at least have velocity and conceive of Newtonian physics in at least those terms, summarizing the world as many objects having a position and velocity at any given time.
There happens to be a ‘speed of light’ in the Game of Life universe, and these creatures would measure that speed and come up with some number in their own measuring units. They could probably observe some phenomenon in their universe and argue the speed of light is ‘fine tuned’ for their existence, though on the fundamental level light speed is just one cell per time unit.
But that’s not a real physical parameter. Our own physicists sometimes use measurement systems where the speed of light, the Planck length, and several other important constants are just all equal to ‘1’. The ‘parameters’ which we usually see referred to as fine-tuned are more irreducible.
Well, one such parameter in a Game of Life universe might be a constant governing the interaction of gliders, such as how often their collision leads to certain other particles appearing. Such a number might seem arbitrary from the inside, and such creatures might think about universes in which it was just slightly different – but in actuality, the Game of Life could not be just slightly altered to change such a number; its rules are very simple and changing any of them would completely change the collection of particles.
In any case, I lean more towards a multiverse-like option; but until we have a truly unified physical theory I don’t think there’s much chance of knowing what that multiverse looks like, and even then it seems like we’ll never know what the lowest level actually looks like.
Thanks for your thoughtful comments! I’m not a physicist, I’m just an interested layman. This stuff is fun to think about. Your example of pouring milk into coffee is a good one.
Woah, you wrote Wall at the Edge of the World? I loved that book.
Thanks. I re-read it a few years ago, and I felt I had done something that turned out okay.