I had the treat this week of attending a lecture by Brian Greene on the CU campus—another packed-to-the-gills science lecture, this one in a two-thousand-seat auditorium. Greene’s book The Elegant Universe and PBS documentary of the same name a few years ago explain string theory for people who never got past freshman physics. Did I mention you can actually understand it? If a ten-dimension universe can be understood, that is.
In his lecture Green covered territory familiar to readers of the book, starting with Einstein’s revolution of Newton. What we enjoyed all over again—and Greene’s particular genius—was how warmly accessible he made his version of the history.
Greene started with Isaac Newton, who revolutionized Western math and astronomy by introducing laws of gravity. But for all his astounding success, Newton failed to answer one important question: How does gravity actually work? Through what mechanism does the sun keep the earth in its orbit, or the earth the moon? Greene said,
It is the question of a five-year-old! Yet it’s one Newton never addressed. In fact, he wrote in his Principia, “I leave it to the consideration of the reader.”
Along came Einstein, a lowly patent worker in Berlin, who spent ten years in his off hours thinking about that question. His answer, general relativity—that space is curved by large objects—revolutionized science once again. Explained Greene:
Imagine space is like a stretched-out rubber sheet. If you roll a marble across the sheet, it will go in a straight line. But now imagine you put something big, like a rock, in the middle. The rubber sheet sags, and the marble will roll in a curve around the rock. That’s the way gravity works: it actually curves space.
Then came the physics of the very small, quantum mechanics, and it created havoc because the math that describes the subatomic world does not jibe with the math that describes gravity. The very small and the very large are in conflict. String theory—what the rest of the lecture was about—is one possible solution to that conflict.
It works like this: the conventional description of matter—the one we all learned in fifth grade—is that molecules are made up of atoms, which are made up of smaller particles of electrons orbiting a center of protons and neutrons, which are themselves made up of even smaller particles called quarks. (Except when I was in fifth grade no one talked about quarks yet.) String theory suggests that particles aren’t the end of the story. String theory proposes that each particle itself is made up of tiny, vibrating strings.
If you were to take one atom—one single, tiny atom—and magnify it to the size of the whole known universe—the universe!—a string would become about as big as a tree.
That’s about 10 to the minus-35 meters, if you want to be precise. Infinitesimally small.
The strings vibrate, each with its own signature, and the theory is that each pattern or signature makes up one of the particles: strings vibrate one way and make protons, another way and make neutrons, and so forth:
The universe is a cosmic symphony of tiny vibrating strings.
That picture alone is enticing enough for at least one evening’s worth of physics. But Greene entertained us further with his description of Heisenberg’s uncertainty principle, one of the mind-bending concepts from quantum mechanics:
I don’t know about here in Boulder—it’s been about ten years since I’ve been here—but where I live in New York we have Chinese restaurants that have these menus with two columns, Column A and Column B. The food items are paired. So if you order the top item from Column A, you can’t order the top item from Column B. . . .
Chuckles started rippling around the room as we caught on to the joke: that’s how the subatomic level of reality works. You can’t know both where an electron is and how fast it is moving, at the same time. The more you know about its speed, the less you can know about its location and vice versa.
After the lecture I was intrigued by Greene’s answer to a question from the audience: Given that matter is being described more and more as relations among forces, does it make sense to speak anymore of particles—the billiard ball model of reality—or should we speak instead of momentary congealing of forces? Greene responded,
Don’t completely throw away the picture of particles as little balls. We can’t take the billiard ball metaphor as far as we did before quantum physics. But the ball metaphor is useful in some situations. It’s best to move back and forth between the two, sometimes thinking of matter as little tiny balls—or strings—at other times, collections of properties. Both pictures give us some insight; you just have to know when to use each.
Another person asked, Does string theory belong in high school science classes? Greene’s answer was fervent, from an educator at heart:
We should be exciting kids about science rather than forcing details down their throats! I’m all for doing the hard work of details. Unfortunately, though, details are easier to test. The strange thing about textbooks is that we put in them the results, the things that are already done, finished, discovered. What we need to put in them instead are the near misses, the heart-stopping moments!
The crowd applauded heartily.
At home again, I checked the Twitter stream from the lecture. One person had said, “I love how listening to him I learned stuff about science and about communicating science at the same time.”