The most recent issue of New Scientist I’ve received (or at least I think it’s the most recent: May 25-31, 2013) had an interesting article on a topic that many people haven’t heard about: Boltzmann brains.
What are Boltzmann brains? I hear (some of) you ask… The Wikipedia entry on the topic is not bad, so you can check it out if you like, but I will try to summarize here. First, assume a universe without God. (Not the best assumption to start with, I know, but bear with me.) As the laws of physics are currently understood, virtually anything can pop into existence spontaneously but according to different probabilities. For instance, electrons and positrons pop into and out of existence constantly with high probability. It is also possible–again, according to theory–for a fully formed 747 airliner to “pop” into existence above your house in a random collision of just the right particles at just the right time. However–again, according to theory–the probability of these particles coming together in such a way as to form that 747 above your head is phenomenally, incredibly, infinitesimally small, such that one would be insane as to actually expect it ever to happen. You may, thus, feel comfortable leaving your umbrella in the closet for now.
So the theory goes that even with this odd “fact” that it is possible for seemingly anything to come together at any moment by a random collision of atomic and subatomic particles, the probabilities for such weird things as 747s above your head or a resurrected George Washington appearing in your living room with all of his memories in tact (again, assuming a purely material world) are so small that they virtually never, ever happen.
However, “virtually never” is not never. This is the problem addressed by New Scientist. Those who believe that the fate of the universe is to continually expand forever, with no “expiration date” as it were, face a universe with unlimited time on its hands. And in unlimited time, even the wildly improbably becomes inevitable. For instance, if you dealt 13 cards from a deck, what are the odds (if you aren’t cheating) that you would deal out the entire collection of clubs in order from the 2 to the Ace? Not likely. (Students, who wants to calculate? Answers accepted below!) However, if you were repeatedly dealing out 13 cards endlessly from a deck that somehow never wore out and if you, somehow, never died on an earth that never disappeared, etc., the fact is that, inevitably, you would deal out the required hand. It might take millions, billions, or trillions of years, but, eventually, you would see the 13 cards sitting in order on your table. Then you can finally go check on the chimpanzee in the next room and see if he has finally finished randomly typing out the works of Shakespeare.
Thus, the Boltzmann brain… We are asked to consider the probability of a fully formed conscious brain appearing out of nowhere due to random collisions of particles. (And, I should say, we are still working in a hypothetical universe in which the spirit in man is not necessary: just atoms and the like.) The probability is very, very, very, very low that such a thing could ever happen. But, according to current theory, it is not zero. Consequently, if the universe were to expand forever in time with no end, the seemingly-but-not-actually impossible becomes inevitable: such a brain, a Boltzmann brain, would be expected to randomly come into existence. In fact, not just one, but many, many, many such brains. In fact, in the words of the article, “Most models of the future of the universe predict that the universe will expand exponentially forever. That will eventually spawn inconceivable numbers of Boltzmann brains, far outnumbering every human who has ever, or will ever, live.”
The issue that the article–“String theory may limit space brain threat”–addresses is the discomfort that scientists have with that, since they want to be able to assume that our “ordinary” sense of the universe is the right one, versus the sense that such future disembodied brains will have in a universe that is much more empty and barren and which would look nothing like our universe today. But if there are virtually an infinite number of future Boltzmann brains out there in the future compared to ordinary observers like us, who are we to say that our view of the universe should have any special precedence or preference?
It is, to a great degree, a silly concern. But, still, it was tackled in a serious manner using possible interpretations of string theory-based multiverses, or multiple universes. (For the record, the Hawking-Hartle model of the multiverse ends up being “overrun with Boltzmann brains” but a newer model allowed “ordinary human-like consciousnesses” to prevail. Hooray for our team, I suppose.)
However, what the article does not bring out is the more fundamental paradox concerning Boltzmann brains, and its direct relation to arguments for and against the existence of God–a role to which I was exposed reading William Lane Craig’s On Guard.
Physics as we currently understand it requires that the entropy–essentially, the amount of disorder–of the universe never decreases. Rather, it either increases or is in equilibrium. The challenge with that if we want a universe without God (like, regrettably, many do–Romans 1:28a) is that the universe we see is, all things considered, relatively orderly, meaning that if there were a Big Bang that started it all out, the universe that resulted must have been in a very highly ordered, low-entropy state. Roger Penrose, the famous mathematical physicist, has calculated that the odds of the universe being in such a low-entropy state is abysmally, inconceivably small. Specifically, he estimates that the odds of it happening are 1 in 10^(10^123). How small is that? Well, 1 in 2 is one-half, or 50%. 1 in 10 is one-tenth, or 10%. 1 in 10000 is one-ten thousandth, or 0.01%. As the “bottom” number of the fraction gets bigger, the probability gets smaller. And the “bottom” number here is a 1 followed by 10^123 zeros. How many is 10^123? Well, that’s a 1 followed by 123 zeros. As Penrose points out, you could take all of the subatomic particles in the universe and write one digit on each one, you still wouldn’t have enough zeros to come close to writing 10^(10^123). And the odds are, according to Penrose, one out of [that frightening number] that such a low-entropy condition could have existed randomly at the universe’s beginning, based on what we see. (You can see this discussion in Penrose’s book The Emperor’s New Mind in the section on “Cosmology and the Arrow of Time.”)
“No problem!” believers in a multiverse cry. If our universe is simply one of many, many, many universes in a huge, continually growing multiverse with new universes coming into existence all the time, then one like ours must eventually turn up, no matter how unlikely–no Creator necessary.
Here’s where the Boltzmann brains invade! The odds of forming a Boltzmann brain, however small they must be are vastly greater than such a beginning to the universe as ours. That is, if someone is arguing that there need be no God because if there are many universes coming into existence all the time then a universe like this will “eventually” happen even if it is improbable, he must face the fact that it is much more likely that the universe around him is an illusion and that he is simply a disembodied Boltzmann brain which formed randomly and with all of his false “memories” and illusions of experiences “pre-installed.” Such a universe, in which all else is disorder and high entropy and the only ordered thing in existence is his Boltzmann brain floating in a sea of nothing, is MUCH more likely to form than the orderly universe we see around us. If he is going to believe that the universe could have just happened even though the odds are so overwhelmingly against it, then to be fully logical and rational he should conclude that there is no universe at all and that he is simply a brain floating in an empty universe merely experiencing the illusion of an orderly universe around him. That “universe”–the one where he is a lone brain in a sea of nothingness experiencing the ultimate “Matrix” illusion as the only orderly object in all of existence–is vastly more probable that a real universe like the one we see around us if there is no God. So, if he’s going by the probabilities and expecting the “many worlds” multiverse idea to allow him to ignore the need for a God, he needs to know that the only rational conclusion he can draw is that he is likely a disemboded brain, and that everything he has ever experienced–everything else he thinks exists–is an illusion.
That’s logic for you. It doesn’t just take you to where you want to go–it takes you all the way to the end, whether you like it or not.
This is one of many reasons why multiverse theories do not do away with the need for a Divine Creator. If we believe that there is no God and that we are simply experiencing the roll of the cosmic dice, then the odds are that there isn’t really much of a “universe” at all–just tiny, disembodied, Boltsmann-brain us, floating in a sea of nothing with fake memories and illusory experiences. If there is no God and we live in a multiverse where the dice roll with each new universe, I am not just stuck philosophically at the famous “dead end” where I can’t prove I am not just a “brain in a vat”–rather, I have to face the fact that I probably am just a brain, without even a vat to keep me company!
Of course, this is stupid. And it should give pause to anyone wanting to avoid the existence of God using the “probabilities in a multiverse” argument. You won’t like where those probabilities lead, my little disembodied friend. 🙂
Do these considerations prove God exists and that we’re not really just disembodied brains floating in a sea of nothingness? No. But they do help to show that those who don’t believe in a Creator and who claim that our improbable universe can be explained by the increasingly popular multiverse theories out there aren’t simply “following the logic” like they think they are. Unless, of course, they do believe they are simply a brain experiencing the illusion of a universe around them. In that case, you might want to find other friends.