You’re almost unfathomably lucky to exist, in almost every conceivable way. Don’t take it the wrong way. You, me, and even the most calming manatee are nothing but impurities in an otherwise beautifully simple universe.
We're lucky life began on Earth at all, of course, and that something as complex as humans evolved. It was improbable that your parents met each other and conceived you at just the right instant, and their parents and their parents and so on back to time immemorial. This is science’s way of reminding you to be grateful for what you have.
But even so, I have news for you: It's worse than you think. Much worse.
Your existence wasn’t just predicated on amorousness and luck of your ancestors, but on an almost absurdly finely tuned universe. Had the universe opted to turn up the strength of the electromagnetic force by even a small factor, poof! Suddenly stars wouldn’t be able to produce any heavy elements, much less the giant wet rock we’re standing on. Worse, if the universe were only minutely denser than the one we inhabit, it would have collapsed before it began.
Worse still, the laws of physics themselves seem to be working against us. Ours isn’t just a randomly hostile universe, it's an actively hostile universe.
My physicist colleagues and I like to pretend that the laws of physics are orderly and elegant. Indeed, I just published an entire book, The Universe in the Rearview Mirror, about the beautiful symmetries of the universe. Programs like Nova or Slate’s own Bad Astronomy tend to focus on the knowable structure of how everything fits together.
The history of physics, in fact, is a marvel of using simple symmetry principles to construct complicated laws of the universe. Einstein quite famously was able to construct his entire theory of special relativity—the idea that ultimately gave us E=mc2 and explained the heat of the sun—from nothing more than the simple idea that there was no measurable distinction to be made between observers at rest and observers in uniform motion.
The long-overlooked 20th-century mathematician Emmy Noether proved the centrality of symmetry as a physical principle. And what is symmetry—at least as scientists understand it? The mathematician Hermann Weyl gave perhaps the most succinct definition:
“A thing is symmetrical if there is something you can do to it so that after you have finished doing it, it looks the same as before.”
Which sounds innocuous enough until you realize that if the entire universe were made symmetric, then all of the good features (e.g., you) are decidedly asymmetric lumps that ruin the otherwise perfect beauty of the cosmos.
The seemingly simple idea that the laws of the universe are the same everywhere in space and time turns out to yield justification for long-observed properties of the universe, like Newton’s first law of motion (“An object in motion stays in motion,” etc.) and first law of thermodynamics (the conservation of energy).
As the Nobel laureate Phil Anderson put it:
“It is only slightly overstating the case to say that physics is the study of symmetry.”
Everything is kinda the same? Every Friday night is like every other one? Sounds almost comforting. But it would be a mistake to be comforted by the symmetries of the universe. In truth, they are your worst enemies. Everything we know about those rational, predictable arrangements dictates that you shouldn't be here at all.
How hostile is the universe to your fundamental existence?
Very. Even the simplest assumptions about our place in the universe seem to lead inexorably to devastating results.
The laws of physics seem to act equally in all directions. This is one of the great symmetries of nature. It gives rise to the inverse square law of gravity—the pull of gravity decreases proportionally to the square of the distance between two objects. Lights seem to drop off in brightness as the inverse square as well, which means that distant stars and galaxies naturally appear quite a bit dimmer than those nearby.
On the other hand, the farther away we look, the more galaxies we can conceivably encounter in our field of view. Add the two effects together, and the farther you look in any given direction, the more galaxies you see, even though each more distant one is individually dimmer. The cumulative brightness will appear greater and greater the farther you look. Taken to the logical extreme—the infinite recesses of space—in every direction you look you should eventually see a star, and the entire sky should appear as bright as the surface of the sun.
So why is the sky dark at night? That query isn’t quite as stupid as you might suppose. It’s called Olbers’ paradox, after Heinrich Olbers, who, in 1823, was one of the last people to discover it. (Johannes Kepler came up with a similar idea back in 1605, and the astronomer Thomas Digges noticed a similar problem a quarter-century before that.)
If you suppose that astronomers are just playing math games, go to the middle of a forest. Nearby trees will look big. More distant trees will look small, but there are so many of them that if you’re far enough into the woods, you won’t be able to see out in any direction. Now suppose that those trees were on fire and were as bright as the sun. In Darkness at Night: A Riddle of the Universe, the cosmologist Edward Harrison puts it rather poetically:
“In this inferno of intense heat, the Earth’s atmosphere would vanish in minutes, its oceans boil away in hours, and the Earth itself evaporate in a few years. And yet, when we survey the heavens, we find the universe plunged in darkness.”
The symmetry of the universe would bake us in no time at all, but an asymmetry rescues us. Kepler recognized that for the sky to be dark at all, the universe must be “enclosed and circumscribed by a wall or a vault.”
And so it is. That vault is the beginning of time.
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