Good news, everyone! A new interpretation of string theory is proposing that Boltzmann Brains — those disembodied brains that could emerge spontaneously in outer space — will never outnumber humans.
Yes, this sounds super-weird, but the whole Boltzmann Brain thing has troubled scientists for quite some time now. It was named after the theoretical physicist who came up with the concept, Ludwig Boltzmann. He theorized that freak disembodied minds will eventually pop into existence owing to the right configurations of matter and energy.
It might seem entirely implausible that such a thing could happen, but if you consider that our universe could expand forever, and that it exhibits quantum fluctuations (i.e. random variations arising from a state of chaos), these brains are fully within the realm of possibility.
Think of it this way: Instead of having a monkey type randomly for an infinity, imagine all the different permutations of matter and energy in deep space over the course of an infinity. Eventually, a fully functional mind will emerge from the mixture.
And in fact, given an infinitely long timespan, these brains could emerge independently over and over again until they completely outnumber all other kinds of minds. This won’t happen until far, far into the future, but the concern is that it could eventually happen.
Now, it’s worth noting that these entities won’t look like giant brains floating in space — but they will exhibit many of the same characteristics, including self-awareness.
String Theory to the Rescue
But according to physicists Raphael Bousso and Claire Zukowski, Boltzmann brains may forever be in the minority — and it all has to do with the kind of universe we find ourselves in — or more accurately, the kind of multiverse we find ourselves in.
String theory proposes that there are a large number of universes, and that they come into existence via eternal inflation. As one universe continually expands, others percolate within it, and we call the whole shebang the multiverse.
In our particular universe, the past is distinct from the future; the Second Law of Thermodynamics is in full effect as we move increasingly towards a state of disorder. Eventually, our universe will become prime real estate for Boltzmann brains — but not yet, given its relatively high state of organization.
Indeed, a universe that’s featureless and infinite will be fertile ground for Boltzmann Brains. If those types of universes are common, and if most universes end up in such a murky state, then we’re seriously outnumbered by them. So the question now is, what happens to most universes?
Writing in New Scientist, Adam Becker explains more:
Zukowski and Bousso's latest work suggests this won't happen. Universes are constantly budding off a parent universe in the multiverse, so the parental characteristics can determine what kinds of "baby" universes form within it – and whether those universes will stick around long enough to be filled with Boltzmann brains or decay first.
Bousso and Zukowski performed a mathematical analysis of multiverses that start out in one of two different initial states: an older model first suggested by Stephen Hawking and his colleague James Hartle, and a newer model that has come out of mathematical treatments of the string multiverse. While the Hartle-Hawking model ended up overrun with Boltzmann brains, ordinary human-like consciousnesses prevailed in the newer model. That makes our view of the universe reassuringly normal in such a multiverse.
Phew. We can all rest easier now.
Read the entire study at Physical Review D: “Multivacuum initial conditions and the arrow of time.”