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Beyond Nymphs, Dryads and Leprechauns (Nima Arkani-Hamed)

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Image by Varsha Y S

How does science work?

Well, that’s easy, right? We start off by collecting information about the world around us and then we try to make some sense of it: we look for patterns, search for a more general understanding. In time, we develop sufficient awareness of these patterns that we begin making predictions about what else might be out there: explicitly formulating hypotheses of what we would expect to see under specific, controlled scenarios. Then we go ahead and rigorously test our hypotheses by explicitly creating these particular conditions; coolly assessing whether or not what has been predicted does, in fact, occur.

If it doesn’t, or at least doesn’t with any sense of regularity or precisely in the way that we had envisioned, we’ll be forced to accept that at least one of our original hypotheses was incorrect and head back to the drawing board to modify things in an attempt to develop a more accurate level of understanding. Meanwhile, if all of our predictions do come true, then we’ll find ourselves with increasing confidence in our understanding. At some point, we’ll likely start calling it something more grandiose, like a ‘theory’; and if it keeps working like clockwork for everything in its applicable domain that we can imagine, we will eventually be tempted to call it a ‘law’.

Such is, in a nutshell, what most of us mean by “the scientific method.” It is famously objective, logical and eminently reliable; and the fruits of its success, both pure and applied, are the single most obvious factor in distinguishing the varying levels of progress between different human societies throughout history.

But what happens when the experimental arena becomes less and less accessible? In the world of high-energy physics, where hugely expensive laboratory facilities take decades to construct, what can we do in the meantime towards uncovering nature’s secrets? And how might we conceivably make progress and build upon our knowledge when no further experiments are in sight?

Can we just sit back and invent any hypothesis we want, secure in the knowledge that, far away from any experimental arbiter, there is no way of distinguishing, even in principle, between different theoretical possibilities? Does science at this point simply become science fiction?

Nima

To Nima Arkani-Hamed, faculty member of the Institute for Advanced Study and one of the world’s foremost theoretical particle physicists, that sort of talk is not only wrong, it demonstrates a profound misunderstanding of all that fundamental physics has accomplished since Galileo brought us into the modern era more than four centuries ago.

Arkani-Hamed emphasizes that our understanding of the physical world is based on two phenomenally successful general principles of 20th century physics – relativity and quantum mechanics – which, when put together “almost completely dictate what the world around us can possibly look like.

“You could easily imagine a world without relativity and you could easily imagine a world without quantum mechanics. Either way things would be tremendously less constrained. It’s the existence of both of them that makes things so complicated.

“In fact, if I were God and I was given principles – or a sub-God, given the principles of relativity and quantum mechanics by the actual God who told me, ‘Now go, build a world,’ I’d say, ‘Sorry, can’t do it. This is just impossible.’

“They seem almost completely incompatible with each other.”

And it is precisely this near-incompatibility, this overpowering rigidity resulting from the necessity of finding common ground between these two general principles, that provides a huge constraint to any successful underlying theoretical framework that we might conceivably imagine.

Which means that even without one single experiment we have almost no wiggle room to come up with truly innovative approaches, a state of affairs that almost never gets communicated to the non-scientist.

“I think that that’s the thing which isn’t appreciated by the general public: the rigidity. Instead, there is some sense that theoretical physicists, unencumbered by data from experiment, are just out there inventing leprechauns and fairies and nymphs and dryads around every corner, and every crazy idea you have is something that you can put out there. Of course we all agree that experiment decides, but until it does, anything goes: leprechauns and nymphs and dryads are all on the same footing.

“But it just is not like that. The incredible rigidity that we have in our framework makes it almost impossible to come up with a new idea. It’s very hard to modify things in any way without ruining everything.”

Appreciating the importance of these constraints and why today’s theorists have such overwhelming confidence in these two guiding principles not only explains how physicists operate but also gives deeper insight into misunderstandings at the core of various public controversies, like the erroneous case of the faster than light neutrinos that suddenly burst onto the scene in 2011.

One of the things that infuriated Arkani-Hamed the most about the whole incident was how it demonstrated a near-total lack of public understanding of how contemporary fundamental physics is done.

“How was it reported in the popular press? Here is this incredible thing, we were told, you can go faster than light – and those physicists who were skeptical of the results were largely described as people refusing to challenge the orthodoxy of big old Al, looking down on us, wagging his finger and telling us, “Don’t you dare go faster than light!”

But that, Arkani-Hamed tells us, is laughingly far from the truth. Indeed, precisely because of the pre-eminent role that relativity plays in our understanding of the world, many theoretical physicists had spent an enormous amount of time and trouble well beforehand explicitly examining whether it would be somehow possible to violate its effects and under what circumstances. And what they had found, after painstaking effort, was in direct contrast to what these experiments were implying.

“The reason why all of us were sure this result had to be wrong was not because we had never entertained the possibility that Einstein might be wrong. Exactly the opposite! That’s what’s so frustrating about it. We had entertained it so well, we had thought about it so much, so responsibly and in such detail, that we knew it was impossible to have an effect as humungous as they found. One part in a hundred thousand sounds like a small effect, but all our previous work on violations of special relativity showed results that were much more stringent: one part in ten to the ten, one part in ten to the fifteen, one part in ten to the twenty – just way off from these humungous-size effects that they were finding. So that was a big source of frustration. We knew it had to be wrong. “

“People assumed that we were convinced it was wrong because we didn’t want to question these underlying principles. Well, that’s true in the sense that we know that you give up a lot if you do it. But we’re not ideologues: we prepare for the possibility and study matters in so much detail that we know it cannot possibly be right, compatible with all the other experimental results we’ve had all this time.

“I think that it’s important for people to understand essential aspects of how this sort of science is actually done. No one is out to suppress rebellious ideas. Quite the contrary: if you can find some even moderately rebellious ideas that have even a modicum of truth associated with them, that’s the way you make your name in the field.

“But again, it needs to be emphasized that we’re in this very, very tight straightjacket. We’re not going to, at the drop of a hat, destroy this entire incredible structure that we built up over four centuries which has served us so well unless there’s a really good reason for it.

“Almost always, experimental or theoretical challenges to the structure are bound to fail. You shouldn’t be surprised that they fail. And people shouldn’t take skepticism as evidence of turf protection. It’s really evidence of the great fact that we have this entire castle that we built over centuries that works so well.”

So what of the future? How can someone like Nima Arkani-Hamed somehow get out of the straightjacket and unlock deeper secrets of the universe? By trying to find a new light in which to examine these very same underlying principles:

“I actually think one of the big things that should happen in the 21st century, the next really big things we have to understand in fundamental physics, in at least our part of theoretical physics, is that we have to understand where space-time comes from in a more fundamental sense.

“And I think one of the things that we will hopefully understand, when we know more how this works, is why it is that these two big ideas of relativity and quantum mechanics seem to both fight each other so much, on the one hand, which is why the world is so constrained. But on the other hand, they also go so wonderfully together, in the sense that in a world that did not have quantum mechanics, it would be easy to imagine modifying relativity somehow. Similarly, in a world without relativity, it’s really easy to modify quantum mechanics.

“Each one buttresses the other in a very strange yet really remarkable way. It’s so hard to make consistent things, and we come up with these tiny menus and it’s incredibly fertile and powerful but that’s all we can do. But why these two principles fit together in the exact way that they do is one of the greatest mysteries.”

To today’s leading theorists, the two founding principles of 20th century physics are simultaneously a constraint and an inspiration: a straightjacket and a guidepost for future discoveries.

The future awaits.

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Nima Arkani-Hamed’s two-part Ideas Roadshow conversation called The Power of Principles is available as part of the series called Rethinking Physics which is available on Vimeo On Demand, see here. This series also features in-depth conversations with Paul Steinhardt, Freeman Dyson, Artur Ekert, and Tony Leggett.

For a complete list of Ideas Roadshow videos featuring Nima Arkani-Hamed, click here. The eBook called The Power of Principles which contains the unabridged Ideas Roadshow conversation with Nima is available on Amazon.

University staff and students may already have full access to all Ideas Roadshow resources on our Academic Portal through an institutional subscription, while select high school teachers and members of the general public may have access to our School and Public Library Portals. For more information about institutional subscriptions, please contact irena@ideasroadshow.com.

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