The End of Everything (Astrophysically Speaking)

by Katie Mack

Hot-off-the-presses results from powerful telescopes and particle colliders have suggested exciting (if terrifying) new possibilities and changed our perspective on what is likely, or not, in the far future evolution of the cosmos. This is a field in which incredible progress is being made, giving us the opportunity to stand at the very edge of the abyss and peer into the ultimate darkness. Except, you know, quantifiably.

We don’t know yet whether the universe will end in fire, ice, or something altogether more outlandish. What we do know is that it’s an immense, beautiful, truly awesome place, and it’s well worth our time to go out of our way to explore it. While we still can.

To a cosmologist, the past is not some unreachable lost realm. It’s an actual place, an observable region of the cosmos, and it’s where we spend most of our workday. We can, while sitting quietly at our desks, watch the progress of astronomical events that happened millions or even billions of years ago.

In fact, when you look at anything, the image you see, which is just the light coming off it that reaches your eye, is a little bit stale by the time it gets to you. That person sitting across the café from you is, from your perspective, several nanoseconds in the past, which may go part of the way toward explaining their wistful expression and outdated fashion sense. Everything you see is in the past, as far as you’re concerned. If you look up at the Moon, you’re seeing a little over a second ago. The Sun is more than eight minutes in the past. And the stars you see in the night sky are deep in the past, from just a few years to millennia.

There’s a popular picture of the Big Bang as some kind of explosion—a sudden conflagration of light and matter from a single point that billowed out through the universe. It wasn’t like that. The Big Bang wasn’t an explosion within the universe, it was an expansion of the universe. And it didn’t happen at a single point, but at every point. Every point in space in the universe today—a spot on the edge of a distant galaxy, a piece of intergalactic space just as far in the other direction, the room in which you were born—every one of these points was, at the beginning of time, close enough to touch, and at that same first moment, rapidly tearing away from one another.

If looking farther away means looking farther into the past, and if there was a time in the distant past when the universe was basically one big all-encompassing fireball, then it should be possible to look so far away that you see a part of the universe that is still on fire. Or, thinking about it another way: if, 13.8 billion years ago, the whole possibly infinite universe was aglow with radiation, there should be parts of it so far away that the radiation from that glow is only just now reaching us, having traveled through the expanding, cooling space all this time. In any direction we look, if we look far enough away, we’ll see that distant fiery universe. We’re not looking at parts of space that are any different, but rather at a time when ALL of space was on fire.

Every point in space is the center of its own sphere of ever deepening time, bounded by a shell of fire.

For reasons we’re still trying to understand, the expansion of the universe suddenly went into very high gear, with the region that would someday become our entire observable universe increasing in size by a factor of more than 100 trillion trillion (i.e., 1026). Of course, that only brought it up to about the size of a beach ball, but given that the starting point was unimaginable tininess smaller than any known particle, and the growth happened over the course of something like 10-34 seconds, we have reason to be impressed.

the fact that pretty much all the hydrogen in the universe was produced in the first few minutes means that a pretty large fraction of what you and I are made of has been hanging around the universe in one form or another for almost as long as the universe has been here. You may have heard that “we are made of stardust” (or “star stuff” if you’re Sagan), and this is absolutely true if we measure by mass. All the heavier elements in your body—oxygen, carbon, nitrogen, calcium, etc.—were produced later, either in the centers of stars or in stellar explosions. But hydrogen, while the lightest, is also the most abundant element in your body by number. So, yes, you hold within you the dust of ancient generations of stars. But you are also, to a very large fraction, built out of by-products of the actual Big Bang. Carl Sagan’s larger statement still stands, and to an even greater degree: “We are a way for the cosmos to know itself.”

Let’s start with the end of the world, why don’t we? Get it over with and move on to more interesting things. N. K. Jemisin, The Fifth Season

Technically, the universe doesn’t have a center. But we’re each the center of our own observable universe.I And from our perspective, all the galaxies farther out than our near neighbors are careening away from us as fast as they can. It’s not us; it’s cosmology.

galaxy is, the smaller it looks. As you would expect. But somewhere in the vicinity of the Hubble radius, that relationship reverses. Beyond that distance, the farther away something is, the larger it appears!

The reason for this reversal is related to the reason we can see things that are currently moving away from us faster than light. In the past, when the light was emitted, they were closer. So close, in fact, that they covered more of the sky. Even though they’re much farther away now, the “snapshot” they’ve sent us has been traveling all that time, and is just reaching us now, showing us the ghostly image of a much closer thing. And the farther back in time you go, the smaller the universe was. So beyond a certain point, the balance between “the universe was smaller in the past” and “light takes a certain amount of time to get here” is such that a galaxy that is more distant than another galaxy now might have actually been closer when its light was emitted.

Anyway, if this is all deeply confusing and mind-boggling, that’s totally okay and normal. Maybe try drawing some sketches on napkins, and then stretch out the napkins in every direction while on some kind of infinite treadmill running at an extreme speed over the course of billions of years, and hopefully it’ll make sense then.

in the end, as scientists, our first loyalty has to be to the data. Even if it means rewriting the fate of the universe.

in the core of a burned-out, collapsing star, there are so many atoms, pressed so tightly together, their electrons start to get antsy. At those kinds of pressures, the electrons aren’t bound to specific atoms, but rather are packed in together in a big atomic mess so crowded that they have to jump to higher and higher energy states to keep from all being in the same one. This creates a kind of pressure, called electron degeneracy pressure, which is strong enough to halt the collapse of the star and create an entirely new kind of object: a white dwarf.

A white dwarf is a kind of star that isn’t burning at all. It has no fusion. It is a solid object held up entirely by the quantum mechanical principle that electrons just don’t like each other that much.

(It might sound odd to use massive stellar explosions as distance benchmarks, because, of course, we can’t predict exactly when or where one will go off. But it turns out that the stellar explosion rate is high enough—a good rule of thumb is one supernova per galaxy per century—and there are so many galaxies, that if we just take pictures of lots of galaxies every night, we’re likely pretty often to see a blip in one that wasn’t there the night before, and then we can follow it up with more detailed observations.)

A famous headline at the time proclaimed, “LIGHTS ALL ASKEW IN THE HEAVENS—MEN OF SCIENCE MORE OR LESS AGOG OVER RESULTS OF ECLIPSE OBSERVATIONS.” Women of science were, presumably, unimpressed.

Unfortunately, the best data we have, consistent with every measurement of the Standard Model of particle physics, suggests that our Higgs field is currently clinging onto just such a divot. This metastable state is also known as a “false vacuum,” as opposed to the “true” vacuum at the bottom of the valley floor. What’s wrong with being in a false vacuum? Quite possibly, everything. A false vacuum is at best a temporary reprieve from ultimate destruction. In a false vacuum, the laws of physics, including the ability of particles to exist at all, are contingent on a precarious balancing act that could be upset at any moment.

When this happens, it’s called vacuum decay. It’s quick, clean, painless, and capable of destroying absolutely everything.

Something coming at you at the speed of light is invisible—any little glint warning you of its approach arrives at the same time as the thing itself. There is no possible way to see it coming, or even to know that anything has gone wrong. If it approaches you from below, there will be a couple of nanoseconds during which your feet no longer exist while your brain still thinks it is looking at them. Fortunately, the process is also entirely painless: at no point will your nerve impulses be able to catch up with your disintegration by the bubble. It’s a mercy, really.

it’s entirely possible that, as we sit here now, calmly drinking our tea, vacuum decay has already occurred. Maybe we’re lucky and the bubble is beyond our cosmic horizon, swallowing up galaxies we would never have known. Or maybe it is, cosmically speaking, right next door, quietly approaching with relativistic stealth, destined to catch us unawares, between breaths.

as a cosmologist interested in testing different theories of physics, it’s always fun to be able to hold up the lack of a cosmic apocalypse as a data point.)

On September 14, 2015, at 9:50 a.m. and 45 seconds UTC, you were, for the briefest moment, just a little bit taller. The gravitational wave crest that washed through you had been traveling across the cosmos, warping space itself in its wake, for 1.3 billion years, ever since it was set off by the violent merging of two black holes each 30 times more massive than the Sun. You might not have noticed the boost—after all, you grew by less than one millionth the width of a proton—but physicists at the Laser Interferometry Gravitational-Wave Observatory (LIGO) did.

Someday, deep in the unknown wilderness of the distant future, the Sun will expand, the Earth will die, and the cosmos itself will come to an end. In the meantime, we have the entire universe to explore, pushing our creativity to its limits to find new ways of knowing our cosmic home. We can learn and create extraordinary things, and we can share them with each other. And as long as we are thinking creatures, we will never stop asking: “What comes next?”

If the universe is going to end, one way or another, I concede that we may as well make our peace with it. Pedro Ferreira is way ahead of me on that one. “I think it’s great,” he says. “It’s so simple and so clean. “I’ve never understood why people get so depressed about the end, the death of the Sun and all,” he continues. “I just like the serenity of it.” “So it doesn’t bother you that we ultimately have no legacy in the universe?” I ask him. “No, not at all,” he says. “I very much like our blip-ness… It’s always appealed to me,” he continues. “It’s the transience of these things. It’s the doing. It’s the process. It’s the journey. Who cares where you get to, right?”