The Last Word On Nothing

Ann:  After you’ve gone to the immense trouble of writing a book, having to sell it seems a bit much.  My own personal best was always with the radio interviewers who began with, “So what’s the name of your book again?”  So Richard, what’s the name of your book again? Oh, right, Gravity.  What’s it about?

Richard: Nice try, Ann, but no, the title isn’t Gravity. It’s The Trouble with Gravity: Solving the Mystery Beneath Our Feet

Ann:  You were supposed to say, “It’s about gravity.” But I sidetracked my own setup, didn’t I.

Richard: Sorry. I do know a setup for a punchline when I see one, but in this case the set-up seemed to be along the lines of “Why did the chicken cross the t’s and dot the i’s?”

Ann:  So I won’t quit my day job and go into comedy.  And, yes, your book is called The Trouble with Gravity.  And I haven’t read it — I will, because what you write, I read—but I have a good excuse, which is timing this post as closely as possible to your pub date.  Now then, what’s the trouble with gravity?

Richard: It’s about gravity. Oh, wait—I was reading the wrong question. The answer to this question is that the trouble with gravity is nobody knows what gravity is, and just about nobody knows nobody knows what gravity is. The exception is scientists, and they know nobody knows what gravity is because they know they don’t know what gravity is. 

Ann:  I was maybe 35 when I realized I didn’t know what gravity was.  I mean, an effect should have a cause, right? You don’t fall down for no reason.  Then I learned in night school physics that gravity is something mass does, but honestly, that didn’t help at all.  

Richard: Exactly so. Gravity is what we’ve come to accept as the cause of various effects, but what that cause is, nobody understands. The book is about the history and philosophy of this concept we all take for granted, and how that concept has evolved, starting with creation myths, virtually all of which begin with a division between Earth and Sky—a distinction that wouldn’t be evident if gravity didn’t make us conceive of the universe as down here and up there. That division extends to later myths (think: gods), religion (angels and devils, heaven and hell), and Newton’s revolution in breaking that down here/up there mental barrier. But I have to ask: “night school physics”?

Ann:  It was a night school course called “Concepts of Modern Physics,” and while I knew I couldn’t handle modern physics, I thought I could handle concepts.  Which I couldn’t, and when the professor finally said “Are all your questions like this?” I accepted that I’d have to stop hoping for clarity and take up intellectual mud wrestling.  This is sort of a digression. But it’s also a real question: another physicist told me that physics concepts are so hard you normally have to learn them several times before you can make any sense of them.  And gravity, that’s one tough concept. So what do they think gravity might be?

Richard: They don’t. Newton himself insisted that all he was doing was coming up with the math to match the motions of matter (excessive alliteration not intentional but merely mostly unavoidable) both down here and up there. This whole “attraction at a distance” business was distasteful to him. My favorite quote of his calls attraction-at-a-distance “so great an Absurdity that I believe no Man who has in philosophical Matters a competent Faculty of thinking can ever fall into it.” Even Einstein’s reconception of “action at a distance” as (to paraphrase John Archibald Wheeler) spacetime telling matter how to move and matter telling spacetime how to curve solved the problem for only about, oh, ten years. Then came the quantum revolution. 

Ann:  Before you get into the quantum revolution and world class mud wrestling:  my husband did a physics PhD at Princeton and went to an outdoor barbeque at John Archibald Wheeler’s house, where somebody else was doing all the grilling but Wheeler was walking around wearing an apron that said, “Action at a Distance.”  Get it? Ok, now I feel strong enough to ask about what the quantum revolution did to gravity.

Richard: Today, gravitation is the only “force” that doesn’t have a corresponding quantum theory.  The discovery of the graviton—a hypothetical particle that would mediate with nature on gravity’s behalf in the same way that the gluon does for the strong nuclear, the photon does for electromagnetism, and the W and Z bosons do for the weak nuclear—would help. But if it exists, it has escaped detection via a cunning unparalleled in quantum experiments. Theorists, being theorists, have come up with a lot of alternative explanations—gravity bleeding into our universe from another universe, for instance. String theory attempted to explain gravity through, well, strings. So physicists have plenty of possibilities, and observers have not a hint of a result.

Ann:  And they need to find this graviton so that gravity isn’t some mysterious action at a distance but is being mediated, carried by something.  And that something, they think is a particle and they decided to call this mysterious particle a graviton. Which they can’t find. And their solution—because physicists don’t like a mystery—is gravity bleeding from another universe or strings? Which are themselves not at all mysterious? I’m getting more confused and less convinced by the minute.  Help, please help.

Richard: I can’t—and my book can’t, either. I spend no more than three or four pages on the quantum question because that area is so speculative and nebulous. The fact that it’s speculative and nebulous is enough to make the point: We’ve come a long way since Aristotle and Newton and Einstein, but in one important way we haven’t budged.

Ann:  I am going to forget I ever heard about quantum gravitons.  But what’s next? If not gravitons, then aren’t we back at action at a distance, effect with no cause?

Richard: Not quite. More like interaction across a distance—Einstein’s spacetime-and-matter mutual dependence. Which is what gravitational waves are, but the fact that they exist, as we recently discovered, recasts our conception of the universe in a fundamental way. If gravitational waves exist when two black holes collide—or two neutron stars, or a black hole and a neutron star—then they exist when you and I collide. Not that you and I have ever collided, except to hug hello or goodbye. But we have dined together, and each wave of a hand, or shrug, or nod, or shutting of the eyes because the Indian food is just that good, we now know creates gravitational waves.

Ann:  Those Indian dinners are made more glorious by knowing that with every move we’re emitting gravitational waves.  Really. Richard, I’ve even written about gravitational waves and still don’t know what’s happening in collisions or blinks to trigger gravitational waves. But I did find out that, once magically triggered, gravitational waves are stretches and squeezes in space/time and when they pass through you, stretch and squeeze you accordingly. So this seems to solve the problem of action at a distance, right? It’s not a mystery, it’s stretches and squeezes being passed along? 

Richard: Yes, that’s the effect we call gravitational. Now: What’s the cause of that effect? That’s the question we still can’t answer, and that question is therefore—wait for it—The Trouble with Gravity.

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