way they are?’ That’s what we scientists try to find out, in terms of deep laws. We don’t yet have what I call a final theory. When we do, it might shed some light on the question of why there is anything at all. The laws of nature might dictate that there has to be something. For example, those laws might not allow for empty space as a stable state. But that wouldn’t take away the wonder. You’d still have to ask, ‘Why are the laws that way, rather than some other way?’ I think we’re permanently doomed to that sense of mystery. And I don’t think belief in God helps. I’ve said it before, and I’ll repeat it. If by ‘God’ you have something definite in mind—a being that is loving, or jealous, or whatever—then you’re faced with the question of why God’s that way and not another way. And if you don’t have anything very definite in mind when you talk about ‘God’ being behind the existence of the universe, then why even use the word? So I think religion doesn’t help. It’s part of the human tragedy: we’re faced with a mystery we can’t understand.”
And Weinberg didn’t seem to think that his fellow physicists could shed much light on the ultimate origin of the universe either. “I’m very skeptical,” he said, “because we don’t really understand the physics. General relativity breaks down when you go back to extreme conditions of density and temperature near the Big Bang. I’m also skeptical of anyone who quotes theorems about inevitable singularities—Hawking theorems and so on. Those theorems are valuable because they imply that at a certain point in, say, the collapse of a star our theories don’t apply any more. But beyond that you can’t say anything. We’re just too ignorant at the moment.”
This epistemic modesty was refreshing after all the wild speculation I’d been hearing over the past year. I felt I was talking to a latter-day Montaigne, or Socrates. But what did Weinberg think of the efforts of some of his more adventurous peers to explain existence itself? I mentioned Alex Vilenkin’s notion that the present universe might have inflated out of a little nugget of “false vacuum” that itself “quantum-tunneled” into being from sheer nothingness. Physics or metaphysics?
“Vilenkin is a really clever guy, and these are fascinating conjectures,” Weinberg said. “The problem is that we have no way, at present, of deciding whether they’re true or not. It’s not just that we don’t have the observational data—we don’t even have the theory.”
When we do have the theory—the final theory of physics—that would furnish the last word, scientifically speaking, on how the universe came into existence. But would it also explain why the universe exists?
“We don’t know,” Weinberg said. “It depends what the final theory ends up looking like. Suppose it looks like Newton’s theory. In Newton’s theory, there’s a clear separation between laws and initial conditions. For instance, Newtonian physics offers no hint about the initial conditions of the solar system. Newton himself was aware of this—he thought the initial conditions were laid down by God.”
If the final theory allows for unexplained initial conditions—sometimes called “boundary conditions”—then even if it can fully account for the evolution of the universe, it will still leave the origins of the universe cloaked in mystery. Who or what decreed those initial conditions? I thought of one of the “messages from the unseen” that the great Alan Turing left behind at his death: Science is a differential equation. Religion is a boundary condition.
“If the final theory turned out to be like that, I’d be disappointed,” Weinberg continued. “Hawking and others hope that the final theory will fix all the initial conditions, that it will leave no freedom to the universe as to how it began. But we just don’t know yet.”
Well, I said, let’s be optimistic. Let’s assume the final theory will account for everything about the universe, including its initial conditions. That would still leave open the question of why that final theory takes the particular form it does. Why should it describe a world of quantum particles interacting through certain forces? Or a world of vibrating strings of energy? Or any world at all? Clearly, the final theory won’t be dictated by logic alone. There is more than one logically consistent way that reality could have turned out to be. But maybe there is only one logically consistent final theory that describes a reality rich enough to include conscious observers