Date: September 30th, 2012
Title: Encore: Broken Teeth and the Fate of the Universe
Organization: Peculiar Velocity — http://peculiarvelocity.com
This podcast originally aired on March 24th, 2010
http://365daysofastronomy.org/2010/03/24/march-24th-broken-teeth-and-the-fate-of-the-universe/
Description: Learning about cosmology is full of surprises, and sometimes those can be as terrifying as suddenly losing a tooth.
Bio: Ben Lillie is a physicist who left the academy for the wilds of New York’s theater district. He now writes and performs stories about science and being a scientist.
Today’s Sponsor: No one. Please consider sponsoring an episode of 365 Days of Astronomy by clicking on the “Donate” button on the lower left.
Transcript:
This is the 365 Days of Astronomy Podcast for March 24th. My name is Ben Lillie. I’m an ex-particle physicist, now living in New York City where I write and tell stories about science. You can find some of my work online at peculiarvelocity.com. For the podcast today I’m going to tell one of those stories.
It’s never clear what should be surprising, almost by definition. The entire Universe is expanding, every galaxy is moving away from every other galaxy. This means that in the past they were closer together, and in the distant past there was a beginning, a big bang. It feels like this should be surprising, but it isn’t. What’s surprising to me is the end of The Universe.
As the universe expands after the big bang the gravity of every bit of matter — every galaxy, every star, every tooth in every head — pulls on every other bit, and this pulling slows the expansion. There are two possibilities for how it can end: if there’s enough matter, the pull is strong enough to slow the expansion to a halt and then to start collapsing, and the universe will end in a big crunch. If there isn’t enough matter then the expansion will go on forever, always slowing down but never quite stopping, coasting into infinity.
Or at least that’s what people thought in the fall of 1998 when I was a sophomore physics major taking a road-trip with some friends to Ashland, Oregon. We were there to see the Oregon Shakespeare Festival, and take in the sights. In Ashland, the sights are pretty much the sulfur springs. They smell like sulfur, and that’s why they’re famous.
So, after a play, we were sitting out in the park around the water fountains where you can taste the sulfur water if you’re insane, sitting on a bench, chatting in the shade, and I noticed a little hard thing in my mouth. I spit it out and it was white, and jagged on one side, and then I noticed that the edge of one of my molars was sharper than it had been. And then I realized that quietly, without any fuss, by tooth had broken.
Now, I could imagine several ways to break a tooth, but they generally involved an object, say a fist, moving very quickly towards one’s face, or perhaps one’s face moving very quickly towards an object, say the ground. Teeth do not break while you’re just sitting there, talking to friends. But that’s what happened.
As soon as I realized that, I freak out. How did this happen? If it happened once, could it happen again? Look, I brush; I floss; this should’t happen! I panicked. I was confused. I was nauseous, and the sulfur smell was not helping. Luckily I didn’t throw up, but only just.
Eventually I calmed down, and I called my mom to tell her about it, and she said “Oh yeah, we knew that might happen.” I and went “What? You knew? And you’re calm about it?” It turns out that when I was very young, when my adult teeth were just forming, I was sick with a very high fever, and that fever disrupted the tooth formation and made them especially brittle. It was good to learn, if a little annoying because I would have to go to the dentist a lot more often for preventative work. But now at least I knew, and somehow I guess at least I’d learned something about myself.
A couple days later, home from the trip, I had the dentist fix it. While I was recovering — which is to say later that afternoon while I was sitting on my couch still briefly hopped up on Novocain — I started reading about the “Discovery of the Year” in Science magazine. Two teams of cosmologists had set out to measure how much the universe was slowing down, to measure something called the deceleration parameter. If this parameter is greater than a half, then the universe will collapse; less than a half and it expands forever. What they found, and the reason it was a breakthrough, was that the deceleration was negative. It’s not slowing down at all; it’s speeding up. The universe is accelerating.
We don’t know why. People’s best guess was that space is filled with a pervasive energy — the same amount at every point in space, and this constant energy density pushes everything apart. This is called the Cosmological Constant, and 12 years later it’s still our best guess for what’s causing the acceleration.
I had no idea what to make of this, so I took it to my hero of the moment: Rick Watkins. Rick was the professor for my sophomore physics survey, and he was amazing: young, wiry, an ultimate frisbee player, he could make thermodynamics funny, make quantum mechanics trivial and could grow a decent-looking beard.
He explained it was a good result and it was probably correct. He explained about the Cosmological Constant, but as he did I thought: “Look, if there’s a constant energy at every point and the universe is getting bigger, then that means there’s more energy as time goes on. So it can’t be right, that violates the law of conservation of energy.”
And he said, “So? Energy isn’t conserved in an expanding universe anyway.” Now, that was a surprise.
Conservation of energy is one of the most sacred principles of physics. Energy can be moved from one from to another: kinetic to potential to chemical to heat to mass. It can be swapped between these forms, but the total amount remains constant. Energy can neither be created nor destroyed. You learn this very early in your education, and you quickly realized how powerful of a principle it is; problems that seemed intractable melt away when energy conservation is invoked. It becomes the central element of how you see the world of physics — so central that it becomes like air, all around but unseen, it’s use becomes like breathing, an autonomic response. Breath in, see physics problem, breath out, drink coffee, write down the law of energy conservation, breath in, chew food; to a physicist, those all happen without thinking.
And yet here was Rick, my hero, telling me it didn’t apply in this case. I made him show me the math, and he did, and he was right. Simply put, if the space itself is changing, then the definition of energy is changing and it doesn’t have to be conserved. It’s a tiny effect. For anything that any human will ever do, it may as well be conserved. We’ll never get useful energy out of this. You would need to connect galaxies across the visible universe to see any violation of the law, but it’s there.
And just as using energy conservation was like breathing, discovering that it wasn’t always correct was like suddenly discovering that I wasn’t breathing, or that my heart had stopped beating, or… or that I’d suddenly broken a tooth. And just as when the breaking happened, my mind exploded in that painless agony, and those same emotions began to well up; the panic, the confusion, the nausea. But this time, in the middle of that mental storm, I looked up and saw Rick grinning at me, and I realized that he thought this was great. He loved it, he thought it was wonderful.
And I realized that it is. The thing that made the law of conservation of energy so amazing was not the law itself, but the fact that it describes reality, and the reality is that it doesn’t always apply. That’s what’s so great about science; no matter what is discovered, no matter what hallowed principle is overturned, the discovery is always fantastic because we know more about nature.
I find this example particularly great, and not just because I had such a huge and absurd reaction, but because few things are considered as fundamental or as immutable as the fact that energy can neither be created nor destroyed. There are things we know extraordinarily well, things we can say we are almost certain of, but that word “almost” is important. If even the law of conservation of energy can fail in certain circumstances, what other unthinkable things might be true?
End of podcast:
365 Days of Astronomy
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