The philosophical problem that interests me most is the one I’ve dubbed The Problem of Physical Existence.
It’s not easy to state the problem clearly. This fact leads some to suspect that the problem is a pseudo-problem. But the fact that it’s difficult to state a problem doesn’t mean there isn’t a substantive issue at hand. Sometimes you only fully understand a question after you’ve answered it. (Raymond Smullyan makes this point beautifully in his “philosophical fantasy” 5000 B.C.) In general, I’m very tolerant of groping, ambiguous philosophical questions. It’s only groping, ambiguous philosophical answers that I hate!
Here are a number of questions that attempt to capture the problem’s essence:
- Why is there something rather than nothing? And why this something rather than some other something?
- What’s the nature of physical existence?
- What breathes fire into the equations of physics? (Stephen Hawking)
- What’s matter made out of?
- What’s the nature of contingency?
- What’s the nature of a posteriori knowledge?
- Why are things the way they are, rather than some other way?
These questions certainly capture the flavor of the problem. But they’re ambiguous in ways that often cause people to talk past each other. At the very least, some clarifications are in order.
I consider these questions to be about physical existence, not about the truths of mathematics and logic. I can imagine the laws of physics being very different than the ones we actually observe, and I can imagine there being no laws of physics at all, and no physical stuff to which they might apply. But I can’t imagine the number 17 being composite rather than prime. There are deep and difficult questions in the philosophy of mathematics about how to interpret statements like “the number 17 is prime”. But no one actually argues that the number 17 could have been composite. So I contend that there’s no problem in the philosophy of mathematics that’s directly analogous to the Problem of Physical Existence.
When I imagine there being no physical universe at all, I’m not just imagining empty space. I’m imagining no space at all, and no laws of physics. It’s exasperating to hear scientists claim that quantum physics might actually answer the question of why there’s something rather than nothing (due to new discoveries about quantum fluctuations, etc.). This misses the philosophical point entirely. I have no problem believing that, given the laws of quantum physics, we can explain why it’s overwhelmingly likely (or even guaranteed) that lots of macro-world physical stuff would exist. That doesn’t explain why those laws exist in the first place.
Some people argue that the absence of a physical universe would somehow be easier to explain than the existence of a physical universe (and that the very question “Why is there something rather than nothing?” implies this), but I don’t agree. For me, nothingness and somethingness are equally problematic. In either case, there should be some reason why that state of affairs obtains rather than some other possible one.
Some smart aleck will point out that if no physical universe existed, there’d be nobody around to ask why that’s the case. I contend that this is an irrelevant truism. If no physical universe exists, but some physical universe could have existed, there must be some reason why no physical universe exists, and that reason holds even though there are no minds to ask about it. Similarly, there’s a reason that 17 is a prime number, and that reason would hold even if there were no minds to ask about it.
I contend that the mathematical universe hypothesis is correct, and that it solves the Problem of Physical Existence. A number of other solutions have been proposed, but I find them unconvincing. (For a couple of popular overviews, check out Why Does the World Exist? and The Mystery of Existence.) I’m not going to attempt to offer an explicit knock-down argument against every other viewpoint, but I’ll be offering implicit arguments against many of them as I explain why I think the mathematical universe hypothesis is correct.