What Can We Know About The World Without Looking At It?

By Sean Carroll | August 11, 2011 8:54 am

One last thought on all this God/cosmology stuff before moving on.

The crucial moment of our panel discussion occurred when John Haught said that he couldn’t imagine a universe without God. (Without God, the universe couldn’t exist.) It would have been more crucial if I had followed up a bit more, but I didn’t because I suck (and because time was precious).

Believing that something must be true about the world because you can’t imagine otherwise is, five hundred years into the Age of Science, not a recommended strategy for acquiring reliable knowledge. It goes back to the classic conflict of rationalism vs. empiricism. “Rationalism” sounds good — who doesn’t want to be rational? But the idea behind it is that we can reach true conclusions about the world by reason alone. We don’t ever have to leave the comfort of our living room; we can just sit around, sharing some single-malt Scotch and fine cigars, thinking really hard about the universe, and thereby achieve some real understanding. Empiricism, on the other hand, says that we should try to imagine all possible ways the world could be, and then actually go out and look at it to decide which way it really is. Rationalism is traditionally associated with Descartes, Leibniz, and Spinoza, while empiricism is associated with Locke, Berkeley, and Hume — but of course these categories never quite fit perfectly well.

The lure of rationalism is powerful, and it shows up all over the place. Leibniz proclaimed various ways the world must work, such as the Principle of Sufficient Reason. Lee Smolin uses Leibnizian arguments against string theory. Many people, such as Oxford philosopher Richard Swinburne, feel strongly that the world cannot simply be; there must be a reason for its existence. Paul Davies believes that the laws of physics cannot simply be, and require an explanation. William Lane Craig believes that infinity cannot be realized in Nature. Einstein felt that God did not play dice with the universe. At a less lofty level, people see bad things happen and feel the urge to blame someone.

But the intellectual history of the past five centuries has spoken loud and clear: the dream of rationalism is a false one. The right way to attain knowledge about the universe is ultimately empirical: we formulate all the hypotheses we can, and test them against data. (Making decisions about which hypotheses best explain the data is of course a knotty problem, but that’s for another time.) Broad a priori principles are certainly useful; they can help guide us in the task of formulating and testing hypotheses. But that’s all they do — if we get lazy and start thinking that they grant us true knowledge of the world, we’ve gone off the rails.

A common manifestation of the rationalist temptation is an insistence that a certain state of affairs cannot merely exist; it must be explained, we must find a reason for it. The truth is that, if things are a certain way, there might be a reason for it, but there might not be. Both are hypotheses that should be examined. I personally have a strong feeling that the low entropy of the early universe is an unusual situation that probably has a deeper explanation — it’s a clue pointing towards something we don’t understand about the universe. But I’m careful to distinguish that I don’t know this to be true. It’s perfectly conceivable that the universe simply is that way, and there is no deeper explanation. Ultimately the decision will be made by constructing comprehensive theories and comparing them to data, not by scientists stamping their feet and insisting that a better explanation must be found.

An inquisitive five-year-old might bombard you with an endless series of “Why?” questions. Sometimes you encounter an older version of this five-year-old; someone who, when you say “I have finally formulated a successful unification of all the laws of physics!” will insist on asking “But why is it that way?” If you say “it just is,” they will say “that’s not good enough.” That’s the point at which you are allowed to turn the tables. Just start asking, “Well why isn’t it good enough? Why do I need a deeper level of explanation for how the world is?” Not that it will actually change their attitude, but it can be personally satisfying.

Favorite targets for people insisting on deeper explanations include the existence of the universe itself (as Haught was indicating) and the particular laws of physics we observe (as Davies argues). The proper scientific attitude is to say: well, there may be a deeper explanation, or there may not. Before we go out and actually look at, the universe could very well be many things. It could be a single point. It could be a line or a plane. It could be non-existent. The universe could be a fiber bundle over a Riemannian manifold, an n-dimensional cellular automaton, a trajectory in Hilbert space obeying Schroedinger’s equation, a holographic projection of a conformal field theory, the dream of a disturbed demon, a layered collection of natural and supernatural dimensions, someone’s elaborate computer simulation, or any of a million other things. It could be unique or multiple, meaningful or intrinsically purposeless. It could be brought into existence by something outside itself, or it could be sustained by a distinct being, or it could simply be. If you personally find some of these alternatives unsatisfying, that is a matter for you and your therapist to work out; reality doesn’t care. The way we will find out the truth is not to insist that it must be one way or another; it’s to understand the likely consequences of each possibility, and line them up with what we actually observe.

You can see why a rationalist line of reasoning would be attractive to the theistically inclined. If you have God intervening in the world, you can judge it by science and it’s not a very good theory. If on the other hand God is completely separate from the universe, what’s the point? But if God is a necessary being, certainly existing but not necessarily poking into the operation of the world, you can have your theological cake without it being stolen by scientific party-crashers, if I may mix a metaphor. The problem is, there are no necessary beings. There is only what exists, and we should be open to all the possibilities.

None of this is to say that there is no room for logic or reason in understanding how the world could possibly work. “2+2=4” is a true statement in any possible world, once we specify the definitions of “2” and “+” and “=” and “4.” But that doesn’t mean it’s a true statement about anything that actually happens in the world. The universe might very well have been something where there weren’t two collections of two things to add together, nor sufficient computing power to perform the arithmetical operation. Once we accept some hypotheses about the world (through comparing their predictions to reality), we are allowed to use reason to draw inferences from those hypotheses. (That’s kind of what I do for a living.) But step one in that process is to be open to which sets of hypotheses are actually relevant to the real world.

The temptation of rationalism can be a hard one to resist. We human beings are not blank slates; not only do we come equipped with informal heuristics for making sense of the world we see, but we have strong desires about how the world should operate. Intellectual honesty demands that we put those desires aside, and accept the world for what it actually is, whatever that may turn out to be.

CATEGORIZED UNDER: Philosophy, Religion, Top Posts
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Cosmic Variance

Random samplings from a universe of ideas.

About Sean Carroll

Sean Carroll is a Senior Research Associate in the Department of Physics at the California Institute of Technology. His research interests include theoretical aspects of cosmology, field theory, and gravitation. His most recent book is The Particle at the End of the Universe, about the Large Hadron Collider and the search for the Higgs boson. Here are some of his favorite blog posts, home page, and email: carroll [at] cosmicvariance.com .

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