The news outlets are abuzz with reports of some provocative claims made in Stephen Hawking’s latest book, The Grand Design, which is due for release on Tuesday. For obvious reasons I haven’t yet read the book, so I don’t know the broader context of his claims or how he supports them. However, since the claims in question have been widely quoted, and several folk have already asked me about them, I’ll offer a few tentative comments (with all the necessary caveats assumed).
Here are Hawking’s statements as reported by the Telegraph (and by numerous other outlets):
Because there is a law such as gravity, the Universe can and will create itself from nothing. Spontaneous creation is the reason there is something rather than nothing, why the Universe exists, why we exist.
It is not necessary to invoke God to light the blue touch paper and set the Universe going.
In the first place, I have to assume that Hawking is speaking loosely when he says that “the Universe can … create itself from nothing” because taken literally the idea of self-creation is just plain incoherent. Something can only create if it already exists (where ‘already’ indicates logical rather than temporal priority). Nothing does not have the power to create, or to do anything else for that matter, because nothing is quite literally no thing. So the universe could only create itself if it already existed; but if it already existed, it would have no need to create itself! As I say, I have to assume Hawking doesn’t literally mean what he says. But then it’s not obvious what he really does mean.
Hawking is apparently suggesting that the law of gravity (perhaps in conjunction with other physical laws) explains why the universe exists rather than not. But how could this be? The law of gravity is one of the laws of nature. Philosophers have spilled much ink over what a “law of nature” really is (see this article for an overview) but it seems that at a minimum a law of nature such as the law of gravity describes how the natural universe operates, typically in terms of the mathematical relationships between quantifiable physical properties in a closed system. (Just think of paradigmatic cases of laws of nature and you’ll see what I mean.) But if that’s the case, how could there be laws of nature without nature itself? Surely the laws of nature — the law of gravity included — presuppose the existence of the natural universe. If there were no universe, to what would the laws of nature refer? This is one reason why I find it prima facie implausible that the law of gravity or any other physical law could even in principle explain the existence of the universe. The laws of nature presuppose the existence of nature, just as the laws of Scotland presuppose the existence of Scotland.
But let’s suppose for the sake of argument that the laws of nature could in principle explain the existence of the universe. The laws of nature, to all appearances, are contingent laws. In other words, it seems they could have been different than they in fact are. The speed of light, for example, could have had a higher or lower value than it does, in which case the mathematical relationship between energy and mass would have been different. The very fact that we have had to make empirical observations of the universe in order to discover the laws of nature only underscores this point. The law of gravity presumably couldn’t have been known a priori, that is, without actually investigating how nature operates. So what’s the significance of this traditional understanding of the laws of nature? Just this: even if the contingent laws of nature could explain why the contingent universe exists at all, the underlying philosophical question would only be pushed back a step. Why are the laws of nature the way they are and not otherwise?
One obvious way for Hawking to avoid this objection (given that he wants to steer clear of any theistic explanation) would be to claim that the laws of nature aren’t contingent after all, but logically necessary; they simply couldn’t have been otherwise. If Hawking really has proven that the laws of nature are logically necessary, that would be a stupendous scientific breakthrough: a dead cert for a Nobel prize. But then why didn’t he publish it in a peer-reviewed scientific journal rather than a popular science book (as The Grand Design appears to be)? Furthermore, if the laws of nature really are logically necessary then our knowledge of them couldn’t be based on empirical observation (despite what we’ve always thought) because empirical observations cannot in principle establish necessary truths (such as the laws of logic and the laws of arithmetic). Our observations can only tell us what actually is the case and not what must be the case.
If Hawking thinks there is some law or principle that explains the very existence of the universe, he must have in mind a metaphysical law rather than a physical law. Unless I’m much mistaken, the law of gravity is a physical law. It appears that Hawking intends to leave behind physics (a subject on which he is eminently qualified to speak) and enter the realm of metaphysics (a subject on which he has no particular expertise, so far as I know). It’s more than a little ironic therefore to find Hawking declaring on the very first page of his new book that “philosophy is dead.” If philosophy is dead, why is Hawking now turning his hand to philosophy? No, philosophy is in very good health, despite its frequent mistreatment at the hands of scientists.
I wonder whether these latest claims by Hawking are an extension of what he proposed 22 years ago in his bestseller A Brief History of Time. There he suggested that if certain (non-standard) numerical values are plugged into the equations describing the earliest stages of the universe, a “temporal singularity” can be avoided — which is just to say that the universe would have had no beginning, no first moment. Perhaps in his latest book Hawking is further developing this argument. We should note, however, that even if the universe had no first moment, its contingent existence would still invite explanation. Arguing that the universe had no beginning goes nowhere toward explaining why it exists. As Thomas Aquinas recognized long ago, even an eternal universe demands an explanation for its existence if it exists contingently.
It would be surprising if Hawking’s latest book made no reference to his earlier theories. But according to his own summary of the book’s thesis, he and his co-author (Leonard Mlodinow) lean heavily on quantum-mechanics-inspired multiverse theory, according to which our universe is but one among many (perhaps infinitely many) sibling universes. Multiverse theories have been doing the rounds for decades now, so it doesn’t sound as though Hawking is offering anything very innovative here. Moreover, the objections to multiverse explanations for the fine-tuning of our universe have been well rehearsed, not least the criticism that there is simply no credible empirical support for the existence of a multiverse. It’s no secret that such hypotheses are constructed precisely to avoid recourse to theistic or quasi-theistic explanations. They are, in short, religiously motivated rather than empirically motivated.
In any case, it’s unclear how a multiverse explanation could provide a satisfying answer to the question at hand, namely, why our universe exists at all. If the existence of our universe is explained by the existence of the multiverse, the problem (once again) is only put back a step. Why then does the multiverse exist at all? Unless the multiverse is thought to enjoy necessary existence (as God does, according to classical theism) the philosophical question stubbornly persists. Yet if the multiverse is just another kind of physical entity (albeit a very fancy one) it’s hard to see how it could exist necessarily. Physical entities are paradigm cases of contingent entities.
So for all these reasons, I’m very skeptical indeed that Hawking has discovered a purely scientific and naturalistic explanation for the existence of the universe: an explanation that needs no recourse to divine creative action. Add to this the obvious fact that Hawking is an A-list celebrity scientist with a certain reputation to maintain. But we shall see. I’ll probably try to read the book when I get some time to do so, but until then I’ll be interested to read the first batch of critical reviews by those who genuinely understand the philosophical issues involved. Unfortunately even the best physicists aren’t immune to embarrassing themselves when they turn their hands to metaphysics — and they’re most at risk when it comes to religiously controversial topics.