The End of Everything (Astrophysically Speaking)

by Katie Mack

Whether or not we subscribe to any particular religion or philosophy, it would be hard to deny that knowing our cosmic destiny must have some impact on how we think about our existence, or even how we live our lives. If we want to know whether what we do here ultimately matters, the first thing we ask is: how will it come out in the end? If we find the answer to that question, it leads immediately to the next: what does this mean for us now? Do we still have to take the trash out next Tuesday if the universe is going to die someday?

The best measurements we have are only consistent with a handful of final apocalyptic scenarios, some of which may be confirmed or ruled out by observations we’re making right now. Exploring these possibilities gives us a glimpse of the workings of science at the cutting edge, and allows us to see humanity in a new context. One which, in my opinion, can bring a kind of joy even in the face of total destruction. We are a species poised between an awareness of our ultimate insignificance and an ability to reach far beyond our mundane lives, into the void, to solve the most fundamental mysteries of the cosmos.

As much as pop culture would have you believe that science is all about eureka moments and spectacular conceptual reversals, advances in our understanding come more often from taking existing theories, pushing them to the extremes, and watching where they break.

I even dabbled in experimental particle physics for a while, in my misspent youth, playing with lasers in a nuclear physics lab (despite what the records might say, the fire was not my fault) and paddling an inflatable boat around a 40-meter-tall water-filled underground neutrino detector (that explosion was not my fault either). These days, I’m pretty solidly a theorist, which is probably better for everyone.

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.

We may have grown accustomed to strict chronological oppression, but that doesn’t mean we have to like it.

It all comes down to the fact that light takes time to travel. Light speed is fast—about 300 million meters per second—but it’s not instantaneous. In everyday terms, when you switch on a flashlight, the light coming out of it covers about one foot per nanosecond, and the reflection of that light off whatever you’re illuminating takes just as long to get back to you.

When we think of the universe as existing in spacetime—a kind of all-encompassing universal grid in which space is three axes and time is a fourth—we can just think of the past and the future as distant points on the same fabric, stretching across the cosmos from its infancy to its end.

But the observable universe is just the part of the cosmos we can see now. We know that space goes on much farther than that. In fact, based on what we know, it’s entirely possible, and perhaps probable, that the universe is infinite in size. Which means that it was infinite at the beginning too. Just much denser.

The fundamental incompatibility of our theories of the very massive and the very small is one of the things that hints at the direction we should go in creating new, more complete theories.

The essential difference between the physics of the subatomic world and that of everyday life is that on the scale of individual particles, quantum mechanics imbues every interaction with an intrinsic, inescapable uncertainty.

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.”

The transition from a dark, gaseous universe to one shimmering with the light of galaxies and stars was driven, largely, by a kind of matter so exotic that we haven’t been able to re-create it even in the most powerful particle colliders. In the mix with the radiation, hydrogen gas, and a sprinkling of other primordial elements was a substance we know today as dark matter. It’s not really dark, but rather invisible: seemingly unwilling to interact with light in any way. No emission of radiation, no absorption, no reflection.

The leading idea is that dark matter is some kind of as yet undiscovered fundamental particle that has mass (and therefore gravity) but doesn’t have anything to do with electromagnetism or the strong nuclear force.

Look, I warned you it would be weird.

The important thing about entropy, in cosmic terms, is that over time it goes up. The Second Law of ThermodynamicsIX states that in any isolated system, the total entropy can only increase, not decrease. In other words, order does not spontaneously appear out of nowhere, and if you leave something alone long enough, it will inevitably decay into disorder. Anyone who has tried to keep their desk tidy will understand this, the universe’s most intuitive and maddening natural law.

Every attempt to bend some part of the world to our will creates disorder somewhere else, often in the form of heat.

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.

Maybe it’s for the best that you don’t see it coming.

As it happens, the question of what the particle really does is surprisingly hard to answer, and has spurred a decades-long debate about interpretations of quantum mechanics. Where the particle goes on the journey between Point A and B is still something of a mystery, as is what it actually means that particles are measured as small localized things but still manage to obey the mathematics of waves that are spread out through space.

On September 14, 2015, at 9:50 a.m. and 45 seconds UTC, you were, for the briefest moment, just a little bit taller.

(a gravity wave went through us)

Another thing pointing us toward cosmology is the strange imbalance between matter and antimatter in the universe. Where our current theories suggest matter and antimatter should exist in equal quantities, our experience in the world and our ability to avoid constantly being annihilated by everything we touch shows us that regular matter is winning by a very wide margin.

Cosmology and particle physics are in an awkward position at the moment; both have, in some ways, been victims of their own success. In each field, we have a very precise and comprehensive description of the world that works extremely well in the sense that nothing has been found to contradict it. The downside is that we have no idea why it works.

“I think a lot of people at some level—again, either explicitly or implicitly—will do science or art or something because of the sense that you do get to transcend something. You touch something eternal. That word, eternal: very important. It’s very, very, very important.”

Nima Arkani-Hamed