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.
* * *
The beginning of time introduces yet another obstacle to our existence. Protons and neutrons started to coalesce a millionth of a second after the first instant of time, but things were happening so quickly that this seemed like an eternity. Matter tended to pop into and out of existence, and with it, a mysterious-sounding substance known as antimatter.
Science fiction tends to make a fuss out of antimatter. It shows up in everything from the propulsion system of the Starship Enterpriseto an incredibly ridiculous MacGuffin in Dan Brown’s Angels & Demons. And why? Because if there’s one thing we know about antimatter, it’s that if you meet your antimatter twin, you should never, ever shake hands. Doing so will utterly destroy you both.
But antimatter has a somewhat unwarranted reputation for violence. Antimatter is nothing more than the mirror image of ordinary matter (hence the symmetry). A positron, the antimatter version of an electron, for instance, has the same mass as the ordinary version. It spins at the same rate. The only difference is that the positron has a positive charge and the electron has a negative one.
Every type of particle has an antimatter version, and in each case, the story is the same: same mass, same everything, but opposite charges. Even stranger, the laws of physics don’t much care whether we make ourselves a universe filled with ordinary matter or antimatter. The laws seem to be almost exactly the same. (The “almost” requires a bit of explanation. As it happens, in the so-called weak force that’s responsible for the nuclear fusion inside the sun, antimatter tends to spin the opposite direction of ordinary matter. But that’s a fairly minor distinction.)
We’re even able to make antiatoms in a lab. Antihydrogen, antihelium, you name it (well, actually, only those two). The chemistry, the effects of gravity, and anything else we can measure all seem to be the same as they are with ordinary matter. I’ll even go so far as to say that if some divine being were to turn every particle in the universe into its antimatter version, we’d be none the wiser. Maybe she just did.
We’re able to make antimatter in a lab, and our sun makes it all the time. But there’s always a byproduct—matter. In literally every experiment and observation that we’ve ever done, matter and antimatter get created (or annihilated) in perfect concert. That is, every experiment except for one: us.
Matter and antimatter should have completely annihilated one another in the first nanoseconds after the big bang. You should not even exist. But you do, and there’s lots more matter where you came from.
We live in a universe that seems to be made of matter. Every star, every galaxy, except for the odd cosmic ray or ephemeral particle in the atmosphere, it’s all matter all the time. In other words, if the perfect symmetry between matter and antimatter remained perfect, you wouldn’t be here to think about it.
Sometime very, very early on in the universe (roughly 10-35 seconds after the beginning, if you can wrap your mind around a number that small), there was a small break, and about a billion and one particles of matter were produced for every billion antiparticles. As for how that happened, we honestly can’t say, because nobody’s been able to reproduce it in a lab.
* * *
There’s another oddity to the early universe: Why was everything otherwise so neat and orderly back then?
There are a few laws of physics (not many, mind you) that rise to the level of cultural icons. Einstein’s equivalence between matter and energy come to mind, or Newton’s first law of motion. You may also be familiar with the second law of thermodynamics, which says, in essence, that the universe gets more and more disordered over time. We tend to refer to it as the increase in entropy.
I bring up the flow of time because at microscopic scales, there’s nothing (or almost nothing—there are the same minor caveats that we saw with antimatter) that distinguishes the future from the past. Just about any experiment that we can run in a particle accelerator will look as valid seen the normal way or viewed in reverse. And what is the macroscopic universe, after all, but a collection of microscopic ones?
Time seems to acquire an “arrow” only when we start looking at complicated systems, like your brain or eggs or collections of billiard balls. Your brain most certainly distinguishes between past and future, and one perfectly reasonable way to describe that distinction is that in the future, your brain (and the universe writ large) will simply be more complicated than it is now.
The flow of time (as near as we can tell) is completely arbitrary. Does entropy increase with time or does it make time? Are our memories the thing that ultimately breaks the symmetry of time?
If the entropy increases in time, the early universe had to start off from a position of low entropy, but there’s nothing we know of, and certainly no physical principle, that guarantees that the universe needed to start in an ordered state, and without that, the second law of thermodynamics is really just a good suggestion.
Without an arrow of time, life certainly couldn’t exist as we know it. The chief—really the only—distinction between time and space is that in space you can go forward and backward, but time is one-way. Without a definite arrow of time—a broken symmetry—there’d be no future or past, no scientific discovery, no anticipation, and no memory. Is that really living?
* * *
The worst impediment to our existence is still to come. It seems only a matter of luck (and some fairly arbitrary-looking math) that a symmetric universe would end up being remotely hospitable to complex creatures like us. Much of the excitement in the world of physics over the past few years centered around the discovery of the Higgs boson. (Note: If you are ever at a physicist party, please don’t out yourself as a civilian by referring to it as “the God particle.”) You could be excused if you didn’t get what all of the fuss was about.
The Higgs famously endows mass to other fundamental particles. In the simplest of all possible universes, all fundamental particles should be massless, and some are, like the photon. But most particles have some heft to them.
The magic of the Higgs comes from the inversion of E=mc2. Just as mass can be converted into energy, interaction energy between particles can be felt in terms of mass. Mass, after all, is really nothing more than a measure of how hard it is to move something. In the Higgs model, Higgs bosons pop momentarily out of the vacuum of space and allow particles to interact with themselves and in doing so, acquire mass. That’s not even the crazy part; our universe is a random universe where quantum mechanical uncertainty can create particles in the blink of an eye and annihilate them just as quickly. No, the weird part is that an elegant universe is no place for the Higgs. It is, in a sense, shoved into the equations simply to force mass to come out the other side.
The discovery of the Higgs was huge, and the Higgs was celebrated, in no small part, because it purported to give rise to mass. But as with most discoveries, this is a bit overblown. Your atoms get most of their mass from the protons and neutrons inside. The protons and neutrons, in turn, are made up of even smaller, fundamental particles known as quarks, and yes, it’s true that the quarks get their mass from the Higgs. But if you add up the quarks in a proton, the sum is very much greater than the parts. The quarks amount to only about 2 percent of the mass of the proton, and the rest comes from the insane speeds and energies inside the proton itself. The Higgs, in other words, counts for very little when you step on the scale.
Electrons care a great deal more about the Higgs, since a world with a massless electron is far different from our own. Electrons are the yin to the proton’s yang. They allow for a flow of electricity, and by sharing electrons between atoms, allow for bonding, for chemistry itself. Just as a spaceship will escape the gravitational pull of the Earth, a massless electron (which, by definition, will travel at the speed of light) will easily break its molecular bonds.
Without electrons binding to protons, there would be no chemistry, no molecules, and nothing more complicated than a cloud of charged gas.