Feynman, the Onion of Scientific Discovery and Ultimate Laws of Nature

What if there were no ultimate laws of nature or even no ultimate description of reality? What if science would continue to make the kind of progress it seems to have been making without ever reaching a fundamental level of explanation?

Richard Feynman, asked whether he was trying to discover the fundamental laws of nature, answered that, no, he was just trying to find out more about nature. If there were fundamental laws, he would be happy to discover them. But reality may be like an onion, if so the job of the scientist is to get to the next layer. 

One question raised by the Feynman’s onion metaphor is whether it is good history of science to picture science as penetrating ever deeper in its understanding of physical reality. Onion peeling may suggest more uniformity in the progress of science than history shows, but the idea that science has progressively learned more is clearly right. Moreover, the more that it has been learned is often more basic than what had gone before. Later discoveries explain phenomena previously known but not previously understood or only partially understood. 

Scientific progress has often been a matter of penetrating to a smaller physical scale, and in that respect, too, is like peeling. Organs explain animal behavior, cells explain organs, chemistry explains cells, physics, and its descent into the atomic and then the subatomic, explains chemistry. However, not all passage to the more basic has been a step down in scale, witness special and general relativity. So, although it would be an over-reading of the onion metaphor to think that science’s penetration to the more fundamental is always a revealing of ever finer structure, onion peeling seems an apt enough metaphor of the progress of science in that there does seem to be a stratification of the basicness of explanation, and science has reached ever deeper strata. 

Real onions are finite, but Feynman may well have had an infinite onion in mind in suggesting that he was content to try to peel the next layer whether there was a deepest level or not. 

This suggests a few questions that bear on what sometimes goes by the name of the “realism” debate about the physical world or the “objectivism” debate about science. Could science, in principle, continue to dig, in the ways that it seems to be getting deeper, level after level without end? Should we count it as progress if science fails to get us any closer to the truth about the nature of nature? Could it be that at the deepest level there is nothing remotely law-like about reality?

Brian Greene in The Fabric of the Cosmos:

We envision each new theory taking us closer to the elusive goal of truth, but whether there is an ultimate theory -- a theory that cannot be refined further, because it has finally revealed the workings of the universe at the deepest possible level -- is a question no one can answer.

This is the question Feynman seemed to want to put aside. Greene, however, suggests that if no one can answer it, we can have a reasonable suspicion what the answer will turn out to be, as he continues:

Even so, the pattern traced out during the last three hundred years of discovery gives tantalizing evidence that such a theory can be developed. Broadly speaking, each new breakthrough has gathered a wider range of physical phenomena under fewer theoretical umbrellas. Newton's discoveries showed that the forces governing planetary motion are the same as those governing the motion of falling objects here on earth. Maxwell's discoveries showed that electricity and magnetism are two sides of the same coin. (p. 328) 

Greene's optimism is that this "unification" will continue until we reach "Grand Unification," reducing all phenomena down to a single explanation. We cannot reduce down beyond one. But that we have grandly unified physics does not guarantee that we will not be able to refine our understanding of what we have unified to -- that we could not improve our explanation of the really basic stuff.

It is pretty easy to imagine one way that science might keep improving forever. It might asymptotically approach the final answers about the nature of reality. This is a fairly comforting possibility. Science will continue to come closer and closer to truth, getting with time as close as you like.

A little less comforting, it might come closer and closer to truth, but not come very close at all – if progress were asymptotic to a line parallel to but a long way above the final answers. This might be the case if crossing the barricade required a scientific revolution that human intelligence, however aided by computers and instruments, will never have the imaginative or conceptual wherewithal to carry out.

A more vertiginous infinity lies in the speculation that there is no line that is approached even asymptotically and no barrier line parallel to it either. That is to say, there is no final or fundamental level of physical law. We cannot penetrate to it, no matter how well and how long science keeps at it, because it is not there.

It is tempting to repulse this suggestion with the observation that there must be something, at bottom, that makes things do what they do. But why must there be? There is a reality that does what it does, of course. (And we realists believe that it would pretty much be doing exactly the same things even if humans had not been.) But, to ask a question reminiscent of Hume, why must there be any “making” behind those doings? 

The universe has not issued us any guarantee that there is even in principle the possibility of a complete description of reality. Reality might be infinite (infinitely large, infinitely complex) in ways that would elude description in any finite language, however rich. We could have local descriptions, of course, e.g. “The cat is on the mat.”  No matter how accurate and detailed our collection of local descriptions, however, they would not take us closer to the truth about reality, because there would be no such truth, there being no language that could express it.

Even if a global description of reality were possible, it might not have any privileged, fundamental, law-like part. To take a favorite old example, everything might be like, “All rocks in this box contain iron” and nothing like “all rocks containing iron are attracted by a magnetic field.”

 

If we are stuck with a reality of this unfortunate sort, what should we expect of the future? At some point, our attempts to find order and law at the next deepest level might become frustrated. For example, we might be left with a whole Star Wars bar scene of subatomic particles or with a quantum theory irreconcilable with general relativity, or we might never get behind dark energy. Conceivably these hard theoretical problems may already be early warning signs that we are trying to shoehorn a recalcitrant reality into the kind of lawfulness that is more congenial to our intellectual temper than it is to the nature of the world. (Of course, these particular problems might all get straightened out next week, but then worse ones might arise next millennium.)

It does not, admittedly, seem very likely that we could have found as much order and law-likeness in the world so far only to have law vanish at deeper levels. Could so much order come out of disorder? Well, we already know that there can be islands of order in a sea of disorder. We could just be in a lucky spot for science to succeed, at least for a while and within limits. (If there is mostly disorder, then, given that we have succeeded in doing science, it is inevitable that we should have found ourselves to be in one of the orderly spots.)

If the spot is big enough, perhaps we should not be concerned if there is no underlying lawfulness. For example, if we have good reason to believe that there are infinitely many universes with no underlying trans-universe law and mostly lawless particular universes, we should probably not mind much so long as our own universe ran under a tractable set of laws.

Lawfulness floating above non-lawfulness may strike you as very unlikely; but it is an unlikelihood that I doubt will ever be reduced to any supportable probability figure.

In all this I am worried that our ideas of explanatory “depth” and of what a law must be like may be too crude to discuss these issues sensibly. With this caveat, among others, I conclude that Feynman was right in thinking that science may well continue to increase our understanding of reality even if the onion is infinite in a radical way or even if there is no underlying physical law. Along the way it should have become clear that one could be a robust physical realist and also believe that science really is making progress without believing that it is getting closer to the ultimate laws of nature or ultimate truths about reality.