In the rest of chapter 2 of The Atheist’s Guide to Reality, Alex Rosenberg explains the second law of thermodynamics and briefly addresses some of humanity’s “persistent questions” (such as “does the universe have a purpose?”). His account of the second law is much less controversial than his answers to those big, long-standing questions.
The second law of thermodynamics is usually summed up, somewhat inaccurately, as “entropy or disorder always increases”. Rosenberg, however, begins with this description:
The second law tells us that in any region of space left to itself, differences in the amount of energy will very, very, very probably even out until the whole region is uniform in energy, in temperature, in disorder…. In our universe, the arrangement of everything goes from more improbable distributions (with more useful energy) to less improbable ones (with less useful energy). And the same goes for any self-contained part of the universe (28-31).
In other words, everything that somehow became organized will eventually fall apart (which is one reason why long-abandoned houses invariably look worse than occupied ones). An organized system is unlikely. Energy must be applied to create it and, without further energy being added to the system, it will sooner or later revert to the much more likely state of being disorganized.
Consider, for example, the atoms and molecules that make up the Eiffel Tower. It’s much less likely that they ended up being arranged in that shape than if they were randomly spread around here and there:
The most probable distribution of energy and disorder in the universe is the completely even distribution of everything….[That] is the state toward which, according to the second law, everything is moving, some places slower, some places faster, but almost inexorably. This evening-out of things – from molecules to galaxies – from less probable to more probable distributions is the rule of the universe (31).
Increasing disorder isn’t completely guaranteed, however, which is why Rosenberg says “almost inexorably”. As he explains, the second law merely means that the tendency toward disorder is extremely, extremely probable. For example, when you pour cream in your coffee, the two liquids quickly mix together. But there is nothing in the laws of physics that prohibits the cream from spelling “Good Morning” when you drop it in.
So why are there so many unlikely, highly-organized clumps of matter around (like us)? Despite what some evolution-deniers think, these clumps aren’t counterexamples to the second law. Nor are they bizarre but permissible, random bits of organization:
These are regions of the universe in which the maintenance of order is being paid for by using much more energy to produce [and maintain] the orderly things than the amount of order they produce or store. Each region of local order is part of a bigger region in which there is almost always a net increase in entropy…. Most biological order is preserved for long periods, but at the cost of vast increases in disorder elsewhere (32).
Physicists believe that the universe began in a state of incredibly extreme heat and density. Rosenberg says that this primordial state was both highly unlikely and highly organized, although “organized” might not be the best word.
If everything in the pre-Big Bang universe was evenly distributed (unlike all the molecules in the neighborhood of, for example, the Eiffel Tower), it seems odd to say that it was organized at all. It’s not as if there was some cold, thinly-populated, disorganized space different from the hot, dense stuff, waiting to be filled up. The dense stuff that existed at that point was All There Was. Unless it had some internal structure, we might as well say it wasn’t organized at all. At any rate, the universe as a whole has been falling apart (moving toward perfect equilibrium) ever since the Big Bang, despite the fact that here and there stars and galaxies eventually came to be.
Somewhat controversially, Rosenberg suggests that the second law also explains why time appears to have a “direction”:
Hard to believe, but the second law is where the direction of time, its asymmetry, comes from. It cannot come from anywhere else in physics. By process of elimination, the time order of events from earlier to later is a consequence of the second law…. None of the basic laws of physics [allow us to tell which way is past and which way is future] except for one: the second law of thermodynamics. It makes a difference between earlier times and later times: the later it gets, the more disorder, or entropy, there is (33-35).
On the other hand, another philosopher, Adrian Bardon, argues in A Brief History of the Philosophy of Time that the second law can’t explain the apparent direction of time. The second law is merely probabilistic, as Rosenberg admits. Increasing entropy is extremely, extremely likely, but not absolutely guaranteed, even for the universe as a whole. But the direction of time, if it’s real, is supposed to be unchanging, not probabilistic. Bardon concludes that the direction of time can’t be the same as the one-way, thermodynamic “direction” suggested by the second law. He thinks the fact that these two “directions” appear to go the same way is just a striking coincidence.
This brings us to Rosenberg’s brief answers to a few of those big, persistent questions. This post being so long already, however, I’ll end for now with a brief summary of his conclusions:
Where did the Big Bang come from? We don’t know, but the best current theory is that it randomly emerged from the “multiverse”. Our universe is just one of many.
Well, why is there a “multiverse” then? There’s no reason for it to exist. It just does. Get over it already!
But isn’t there some purpose to the universe? No, there isn’t any purpose to it at all.
But why then does the universe have the physical laws and parameters that allow intelligent life to exist? Given the vast number of universes popping into existence, it shouldn’t be a surprise that some of them end up being like this one. Somebody had to get a winning ticket in the cosmic lottery. It happened to be us.
In our next installment: Oh, really?