The Last Word On Nothing

I was pretty sure the sky was flat, like a cap or a lid or a ceiling.  I didn’t think about the sun going up, around, and down; or the moon changing shape; or the constellations moving to different neighborhoods.  I was curious about other things, not the sky.

The first time I thought about the sky as living in more than two dimensions was when I was in my teens and babysitting a smart little kid.  “Did you ever think that when you’re looking up into the sky,” she said, “you’re seeing infinity?”  I was struck dumb.  I mean, you couldn’t see Chicago and it was only 30 miles away.  And all you had to do to see infinity was look up.  I knew the reason for this — I was standing on the surface of a curved planet, I couldn’t see around the curve but because I was on the surface, I could see straight up. But the kid wasn’t talking about the reason, only about the infinity itself. I don’t know what I said to the kid, I hope it was a compliment.  I thought about that for years off and on, mostly off.

The next time I thought about the depth of the sky was after I became, for reasons that are still opaque to me, a science writer.  I was interviewing an astronomer and he took me to the room where old glass plates of the sky were stored – in the olden days astronomers took pictures of the sky on thick silvered glass plates and universities and institutes still have collections of them. I didn’t know why the astronomer wanted me to see the plates, probably just because he liked them.  He handed me a little magnifying viewer, pointed to a dark speck on one of the plates and said, “Here, look at this.”  I did.  The dark speck against a light background — the plate was essentially a photographic negative — was a galaxy. It was a tiny, perfect, black spiral in a pale grey universe. A whole galaxy.  A spiral full of suns, hundreds of billions of suns, way the hell out there.  A photograph of a galaxy.  A photo? The galaxy was real?  REAL? Struck dumb again. 

I thought about that for years too, though I went on writing about astronomy as if all the wheeling, racing, ticking universe were a projection on a flat screen.  To be honest, I had trouble visualizing the universe in three dimensions plus a fourth, time; but anyone who doesn’t have trouble with that is playing with more cards than I have in my whole deck. This flat-screen business reminds me of a problem sidewalk astronomers run into: their customers suspect them of painting the image of, say, Saturn on the ends of their telescopes.

Now, in this pandemic, like everyone else I’ve been paying closer attention to the world outside my usual constructs of it, the world that exists when I’m not noticing it, the world that goes on about its own business.  So one night, before going up to bed, I was checking the moon and planets and stars as usual and seeing them as usual on a flat sky.  True, when I wrote about astronomy, I had to add the third dimension, distance, but I did that by intellectualizing the whole thing, taking God’s point of view, seeing it from the outside.

Now in this pandemic frame of mind, I stopped intellectualizing and saw it from the inside, as a part of the whole thing:  the moon was small because it was far away and the planets even tinier because they were even farther away; and in fact, I was standing on one planet and looking outward at the moon and out beyond the moon to those little planets.  And IN FACT, I could see them shine, they were shining, only because the sun was behind me and backlighting me.  But it was shining on them.  THE SUN WAS BEHIND ME, THE MOON AND PLANETS WERE IN FRONT OF ME, THEY WERE SHINING BECAUSE THEY WERE FRONT-LIT BY THE SUN.

MY GUYS.  MY PEOPLE.  I’M SORRY, I’M SHOUTING AT YOU. BUT THE SKY IS THREE DIMENSIONAL AND WE’RE INSIDE IT!

I have to go lie down now.

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Illustration: the sky over the southern hemisphere, from Atlas Céleste de Flamstéed, 1795; via the gorgeous Public Domain Review