The title of this blog post is a question posed on the cover of the February 2022 issue of Scientific American. It refers to a story in the issue, "The Origins of Space and Time."
I enjoyed the story, even though it was difficult to understand.
Here's an image that encapsulates the two main approaches to figuring out what space and time (or as relativity theory puts it, spacetime) emerge from -- assuming they emerge from anything.
So if you were expecting some explanation that could be fit, or crammed, into a religious or mystical worldview, expect again.
Science of this sort is complicated, mathematical, provisional. Currently there's no way to test whether space and time emerge from something more fundamental. But just raising that possibility is fascinating, since most of us view space and time as fundamental realities themselves.
One reason physicists are pursuing this issue is that while quantum mechanics and relativity theory are both fantastically accurate depictions of reality, quantum mechanics focuses on the very small and relativity theory on the very large.
Plus, quantum mechanics does an excellent job of explaining three forces of nature -- weak, strong, electromagnetism -- while relativity theory does an excellent job of explaining the fourth, gravity.
It's too simplistic to say that three are more than one, so that's why physicists are interested in finding a quantum theory of gravity, but probably there's some truth to that. Relativity theory isn't capable of explaining the other three forces, so the goal is to find a quantum way to explain how gravity works.
It is indeed strange that so far quantum mechanics and relativity theory aren't compatible with each other, even though each is amazingly successful at explaining the realm in which they operate.
Hence, the appeal of finding a theory of how spacetime emerges from something more fundamental, which would demote relativity theory into a non-fundamental theory and, hopefully, bring about a understanding that explains gravity without using relativity theory.
Here's how the story starts out:
Natalie Paquette spends her time thinking about how to grow an extra dimension. Start with little circles, scattered across every point in space and time -- a curlicue dimension, looped back on itself.
Then shrink those circles down, smaller and smaller, tightening the loop, until a curious transformation occurs: the dimension stops seeming tiny and instead becomes enormous, like when you realize something that looks small and nearby is actually huge and distant.
"We're shrinking a spatial direction," Paquette says. "But when we try to shrink it past a certain point, a new, large, spatial direction emerges instead."
Paquette, a theoretical physicist at the University of Washington, is not alone in thinking about this strange kind of dimensional transmutation. A growing number of physicists, working in different areas of the discipline with different approaches, are increasingly converging on a profound idea: space -- and perhaps even time -- is not fundamental.
Instead space and time may be emergent: they could arise from the structure and behavior of more basic components of nature. At the deepest level of reality, questions like "Where?" and "When?" simply may not have answers at all. "We have a lot of hints from physics that spacetime as we understand it isn't the fundamental thing," Paquette says.
These radical notions come from the latest twists in the century-long hunt for a theory of quantum gravity. Physicist's best theory of gravity is general relativity, Albert Einstein's famous conception of how matter warps space and time.
The best theory of everything else is quantum physics, which is astonishingly accurate when it comes to the properties of matter, energy and subatomic particles. Both theories have easily passed all the tests physicists have been able to devise for the past century. Put them together, one might think, and you would have a "theory of everything."
But the two theories don't play nicely. Ask general relativity what happens in the context of quantum physics, and you'll get contradictory answers, with untamed infinities breaking loose across your calculations. Nature knows how to apply gravity in quantum contexts -- it happened in the first moments of the big bang, and it still happens in the hearts of black holes -- but we humans are still struggling to understand how the trick is done.
Part of the problem lies in the ways the theories deal with space and time. While quantum physics treats space and time as immutable, general relativity warps them for breakfast. Somehow a theory of quantum gravity would need to reconcile these ideas about space and time.
One way to do that would be to eliminate the problem at the source, spacetime itself, by making space and time emerge from something more fundamental.