---
Richard Feynman told his listeners to imagine two objects, each gravitationally attracted to the other. How, he asked, should we predict their movements? Feynman identified three approaches, each invoking a different belief about the world. The first approach used Newton’s law of gravity. The second imagined a gravitational field extending through space. The third applied the principle of least action, which holds that each object moves by following the path that takes the least energy in the least time. All three approaches produced the same, correct prediction. They were three equally useful descriptions of how gravity works.
It happens again and again that, when there are many possible descriptions of a physical situation—all making equivalent predictions, yet all wildly different in premise—one will turn out to be preferable, because it extends to an underlying reality, seeming to account for more of the universe at once. And yet this new description might, in turn, have multiple formulations—and one of those alternatives may apply even more broadly.
“I always found that mysterious, and I do not know the reason why it is that the correct laws of physics are expressible in such a tremendous variety of ways. They seem to be able to get through several wickets at the same time.”
[If you're thinking, "it's just because they're descriptions of reality, not reality itself", continue reading.]
Traditionally, physicists have been reductionists. They’ve searched for a “theory of everything” that describes reality in terms of its most fundamental components. In this way of thinking, the known laws of physics are provisional, approximating an as-yet-unknown, more detailed description. A table is really a collection of atoms; atoms, upon closer inspection, reveal themselves to be clusters of protons and neutrons... Reductionists think they must work their way downward to recover the truth. Physicists now know that gravity wrecks this naïve scheme, by shaping the universe on both large and small scales... that reality isn’t structured in such a reductive, bottom-up way.
[Emergent properties come to mind, and it's worth remembering that such an approach does have merits. Pressure arises from multiple atoms, but you can describe and derive it perfectly if you know the atomic conditions. But pressure, I suppose, is really just an artificial label for the cumulative effects of bajillions of atoms, whereas gravity is something much more fundamental.]
The objective isn’t—or isn’t only—to seek a bedrock equation governing reality’s smallest bits. The existence of this branching, interconnected web of mathematical languages, each with its own associated picture of the world, is what needs to be understood.
Paul Dirac, a British pioneer of quantum theory, stressed the importance of reformulating existing theories: it’s by finding new ways of describing known phenomena that you can escape the trap of provisional or limited belief. This was the trick that led Dirac to predict antimatter, in 1928. “It is not always so that theories which are equivalent are equally good,” he said, five decades later, “because one of them may be more suitable than the other for future developments.”
Einstein’s general theory of relativity beautifully weaves space and time together into a four-dimensional fabric, known as space-time, and equates gravity with warps in that fabric. But Einstein’s theory and the space-time concept break down inside black holes and at the moment of the big bang. Space-time, in other words, may be a translation of some other description of reality that, though more abstract or unfamiliar, can have greater explanatory power. Some researchers are attempting to wean physics off of space-time in order to pave the way toward this deeper theory.
Perhaps the most striking thing about those explanations is that, even as each draws only a partial picture of reality, they are mathematically perfect. Fiddle with the equations even a little and you lose all of its beauty and simplicity. It turns out that, if you want to discover a deeper way of explaining the universe, you can’t take the equations of the existing description and subtly deform them. Instead, you must make a jump to a totally different, equally perfect mathematical structure.
One common conception of physics is that its laws are like a machine that humans are building in order to predict what will happen in the future. The “theory of everything” is like the ultimate prediction machine—a single equation from which everything follows. But this outlook ignores the existence of the many different machines, built in all manner of ingenious ways, that give us equivalent predictions.
To Arkani-Hamed, the multifariousness of the laws suggests a different conception of what physics is all about. We’re not building a machine that calculates answers, he says; instead, we’re discovering questions. Arkani-Hamed now sees the ultimate goal of physics as figuring out the mathematical question from which all the answers flow.
---
The only thing missing is that the article either needs to end with Feynmam's quote about preferring to have questions that can't be answered OR the words FORTY TWO in great big friendly letters.
A Different Kind of Theory of Everything
In 1964, during a lecture at Cornell University, the physicist Richard Feynman articulated a profound mystery about the physical world. He told his listeners to imagine two objects, each gravitationally attracted to the other. How, he asked, should we predict their movements? Feynman identified three approaches, each invoking a different belief about the world.
No comments:
Post a Comment
Due to a small but consistent influx of spam, comments will now be checked before publishing. Only egregious spam/illegal/racist crap will be disapproved, everything else will be published.