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PULTENEY STREET SURVEY - FALL 2018

Donald Spector

The Last Word

Unscrambling the Universe

by Donald Spector, Professor of Physics

Scientists, it is often said, are driven by their curiosity about the world. This is certainly true, but in the corner of physics in which I work, curiosity about the world is not enough. Frequently, I find myself asking questions about alternate versions of reality, trying to understand unreal universes that stand in contrast to our own. As I once said to a non-scientist friend of mine, my doctoral thesis wasn't about particles that might or might not exist; it was about particles we know for a fact do not exist. How does one wind up there?

In the arena of research in which I work, theoretical particle physics, we seek to explain the fundamental properties of the universe. Of course, some of the issues are technical, describable only to another expert in the field. But others are accessible to all of us.

Let's take a simple example- well, a simple question, but one that so far has no answer. We all know that space is three dimensional: up/down, left/right, forwards/backwards. But why three dimensions? Why not more? Why not fewer?

To reach an answer, we need to understand what it is that singles out three dimensions as opposed to two or seven or any other number. Accordingly, to figure out what the critical distinguishing factor might be, we are led to consider what the universe would look like if it had some alternate number of dimensions.

Now if our question were something tangible- say, to understand how metals differ from insulators or how gases differ from liquids- we could go into the laboratory and make measurements. But to understand how a hypothetical universe with seven dimensions would differ from ours, experimental work is not an option. And so we go down the rabbit hole of studying imagined scenarios, non-existent versions of reality, to see how they would behave.

The tools we use to do this are mathematical principles and techniques; we seek ways to apply and combine them to reach conclusions about what would happen in these alternate universes. The payoff can be a discovery of what sets our world apart or a discovery that a property known in our universe in fact is quite generic; either kind of insight enriches our understanding of reality. This essay is not the place for a crash course in theoretical physics, but I can communicate what it is like to conduct this kind of research. The experience is much like playing a game of Scrabble. You look at your seven letters; sometimes they look like they should form a nice, long word; other times they do not seem so promising. Still, you try combining the letters in different ways and consider various spots on the board to play your letters, in hopes of finding a good word you can play. Sometimes you are successful, sometimes you are not, and sometimes you reject your letters and exchange them for new ones.

So it is with theoretical physics, except rather than combining letters into words, we seek to combine mathematical principles to reach conclusions. Physics gives us an array of mathematical principles to choose from ("the letters"), and we try to find effective ways to combine them, leveraging one principle against another, to reach a conclusion ("the word").

Consequently, when I look back at each paper I have written, I see more than its scientific results; I see the story of how I figured out the way to combine the relevant ideas. Sometimes it was a flash of insight, a scientific coup de foudre; sometimes it was finding the right person to talk to about the possibilities; and in one case that still bugs me, I have been struggling with my Scrabble letters for two decades. But there's this triple-word score waiting for a seven-letter word...


Professor of Physics Donald Spector joined the HWS faculty in 1989. His research on supersymmetry, solitons, and information theory has been recognized by the National Science Foundation, Kavli Institute for Theoretical Physics, Japan Society for Promotion of Science, and Foundational Questions Institute. His supernova rule of thumb appears in Randall Munroe's bestseller What If?, and his course Physics through Star Trek in Cosmo Girl! magazine. Spector received his A.B., A.M., and Ph.D. from Harvard University.