Boltzmann Brains

How to believe you're not a brain in a vat

For many of us, there comes a time in our lives when we wonder if what we’re experiencing is real or if we’re just a brain in a vat hallucinating our entire existence. This conundrum inspired the cartoon below. Click to enlarge, especially if you want to see Andy’s spicy take on things.

In scientific / philosophical circles, this idea is expressed as the Boltzmann Brain¹ problem, and it’s weirder than you might think.

According to probabilistic subfields of physics, like statistical mechanics and quantum mechanics, it’s far more likely that a single brain would fluctuate into existence and hallucinate existence as a human being living in a vast, complex universe than that this vast, complex universe with human beings would come into existence.

The problem for me, when I was an atheist, was that I couldn’t think of a rational way around this problem. Why, if the likelihood of Boltzmann Brains existing was far, far, far greater than our universe existing, was I clinging to the notion that everything I thought I was experiencing was real? Just because? That’s a terrible basis on which to believe something, particularly when the odds are overwhelmingly against it. The question kicked off an epistemological crisis that eventually led, years later and after a whole chain of events, to my becoming Christian.

Now, there’s one assumption in the Boltzmann Brain problem that often goes unspoken: that there is no God. Without God, it truly is an intractable problem. But with God, it all sorts out.

The universe is a deliberate creation that has a purpose. Existence is real, because God says so. We are all real, and we can more or less trust our senses. Again, because God says so and it’s consistent with everything we’re told in scripture.

The power of the Christian worldview in confronting the Boltzmann Brain problem isn’t that it proves that existence is real (it doesn’t), but that it provides a rational basis for believing that existence is real.

I contend that the most satisfying basis on which to believe that existence is real, that my senses are real, that I’m not just a brain floating in space somewhere hallucinating that I’m typing out these words, is the Christian worldview. Because I believe Jesus Christ is the one through whom the universe was created (Hebrews 1:2) and He upholds the universe by the word of His power (Hebrews 1:3).

1. Boltzmann Brains are named after Austrian physicist Ludwig Boltzmann, the father of statistical mechanics and the (presumably real) brain behind the statistical explanation for the second law of thermodynamics.