by Tim Sommers
Cosmology is a young science. Maybe the youngest. Some people say it started in the 1920’s when these little glowing clouds visible at certain points in the sky were found, by better and better telescopes, to be composed of billions and billions of stars, just like our own galaxy – the Milky Way – and it was then discovered that no matter what direction you looked they were all rushing away from us. More than one cosmologist has wondered if these galaxies know something that you and I don’t.
On the other hand, maybe, cosmology is the oldest science – if looking up at the stars counts. Anyway, well before the discovery of other galaxies we knew that the universe was very old and very large, but, boy, we had no idea.
Other people say cosmology began when Einstein’s General Relativity gave us some of the math we needed to talk about the universe as a whole for the first time and began to raise questions about its shape.
For me, I say, cosmology didn’t really start until the 1960s when satellites designed to detect tiny amounts of microwave radiation mapped what we now call the “cosmic microwave background radiation”. Here’s the thing that we had missed for so long, the thing that is so hard to believe that we all take for granted now – hardly worth talking about. If the galaxies are all very far apart and getting further apart all the time, doesn’t it follow that there was a time when they were all very close together? Doesn’t it follow, in fact, as most likely, that there was a starting point? Isn’t this, for the first time in the history of humanity, empirical evidence that the universe had a beginning? And if there was such a beginning would it make a sound even if no one was around to hear it? The answer is, yes, yes, and it would make a sound, it does. If you have an old radio or tv, detune it or stop between stations and hear the static, the fuzz. That’s it. That’s the sound of the cosmic microwave background radiation. It’s been there since the beginning of time.
But if the universe has a beginning, will it have an end? And how will it end?
Welcome to cosmology, literally the study of the “cosmos”, the universe, the beginning, the end, and the large-scale structure of everything. Let’s take it a step at a time – even though you probably know most of this already. What is the universe? We live on Earth, of course. It’s somewhere between a sphere and an egg and it’s about 25, 000 miles around at the equator. This is what it looks like from pretty close up, from our oddly large moon. We orbit a sun, an enormous mass of mostly hydrogen, some helium, and some trace elements undergoing a vast nuclear reaction where the hydrogen is being fused into helium and releasing enormous amounts of energy in the process. As big as our solar system is, we live in a whole galaxy of stars, billions and billions of them, as Carl Sagan used to say. This is what the center of our galaxy it looks like from Earth. This is a rough version of some of the main galaxies close to us, the so-called local group; that is, the gang our galaxy is a member of. There are thirty of them but these are the larger ones.
How many galaxies are there in total? At least 100 billion in the observable universe. How old is the universe? Nearly 14 billion years. That is so big and so old it is literally unimaginable. Impossible to picture. It’s not you. No one can imagine it. So how can we possibly, really, know anything about it then? How can we, mere mortals, possibly answer questions so big? Going back to the beginning, we have two sources: observations and physical models.
Here’s what we believe we know to a very high degree of confidence. That the universe began as a singularity. A single, dimensionless point in space that expanded, then inflated faster than the speed of light, then went back to inflating at a constant rate. Right up until today. For the first 380, 000 years the universe was so hot, so full of free electrons and radiation, that if you had been around, you literally wouldn’t have been able to see your hand in front of your face. The universe was opaque. But around that time, it cooled enough that enough of the free electrons were captured by atomic nuclei and suddenly the universe became transparent. You could see. You could see damn near all the way across it. As you surely know, when we look up in the sky we are looking back in time. The light from the stars takes time to travel. How far back can we see? Almost to the beginning. We have seen galaxies that existed less than a million years after the universe began, galaxies thirteen and a half billion years old. But we can only see so far back because the universe had a beginning and was, as I said, opaque for a while, and also, we can only see so far because light only bends so far, so what we can see we call the “observable universe”.
On the physics side, we have not yet developed a complete theory of the basic nature of the fundamental particles and forces that make it all run. But we have what we call the “standard model”. We know it’s not complete. It doesn’t take into account gravity and has some other short-comings too technical to mention. But it is damn good. The degree of accuracy and precision in it is almost as hard to convey as the size and age of the universe.
Now, in the beginning of cosmology, Einstein and most others assumed that the universe was in some kind of steady state. That matter was probably created and destroyed at a similar rate and that things only change locally. Imagine their shock to discover that the universe was expanding, that things were getting further apart. Imagine their awed silence before the reality that the whole universe had a beginning. Imagine.
I want to say something about the notion of a universe in equilibrium, in perfect balance; something I will come back to at the end. Whatever initial appeal such an idea has, I think most of us can see through it pretty quickly. Take expansion. Will the universe expand forever? Or will it eventually contract? Or will it reach a perfect balance, a stasis, a steady state? This last possibility has always seemed the most unlikely. Think of relationships. Think of love. We get closer or we get further apart. We grow together or we grow apart. Steady state is for the textbooks. Unfortunately, the theory of the demise of the universe that I want to talk about is the most pessimistic one of all. Call it the “Big Rip”. Eventually all distances become infinite. Everything will finally and irrevocably be ripped apart and every single subatomic particle in the universe will be infinitely distant from every other, forever. Never to come together again.
There are three or four main theories of the end of the universe. We can treat the first two, the two most unlikely as it turns out, together. First, then, there is “the big crunch” and/or “the big bounce”. The universe is expanding, sure, but gravitation is pulling on it so eventually the expansion will halt, then reverse, and it will begin to contract again, eventually collapsing back into a singularity. That would be the big crunch. It’s hard not to take the next step and think that maybe there would be a new big bang out of that crunch and the whole cycle would begin again. This idea seems to have great intuitive appeal. All that cycles of nature crap and no scary ending and beginning for the universe as a whole. It always looked unlikely to anyone who could do that math though. Gravitation is just not enough. Even with dark matter, there is just not enough stuff in the universe to overcome the expansion and reverse it. This has been clear for a while. Cosmologists in love with the theory just kept looking for more stuff, hoping we had missed something. They got very bad news in the 1990’s.
In his original, theory of gravity Einstein had assigned a positive energy value to empty space. The cosmological constant, he called it. Later he had called this his greatest mistake. But it wasn’t a mistake. Observations have decisively confirmed that empty space has a mysterious dark energy in it and the expansion of the universe is accelerating not slowing down. Or, more accurately, the universe continues to expand at the same rate, the force of dark energy is not diluted by the expansion as we might have hoped, so it continues in double in size and a constant rate and the bigger it is, the bigger it gets by doubling. So, well, it is not going to contract.
So, then, the most popular theory of the end of the universe: the big freeze or heat death. The universe will get bigger and bigger, forever. Eventually it will run out of fuel to burn. The temperature will drop eventually to absolute zero, plus or minus a little quantum flux. Even black holes will evaporate eventually by emitting Hawking radiation. The universe will grow dark and cold and lifeless. A dead husk. That, most cosmologists will tell you, is probably what’s going to happen. And it is pretty depressing. But they are wrong. The truth is more depressing than that.
Remember, the idea of the observable universe? As the actual universe gets larger and larger, the observable universe has less and less stuff in it. In fact, right now, the edge of the observable universe is moving away from us faster than the speed of light. It will never get closer. It will always get further away. The “Big Rip” says that at some point the size of the observable universe will go subatomic. At that point no other force, not gravity, not electromagnetism, nothing, can hold structures together. Everything will be ripped apart. The galaxies will be pulled out of their local clusters. Less than a hundred million years before the end all the galaxies will be ripped apart. Stars and planets will be torn apart next. Then, at the very end, atoms will be destroyed, nothing will remain but subatomic particles infinitely far apart, yet continuing to move away from each other into the cold darkness. Eventually, all distances become infinite. Questions?
Questioner 1: Why do you hope to prove that?
A: Well, I hope the model shows that.
Q1: Why would you hope for that?
A: I just want the truth.
Q1: No. You want to be right.
A: I think this is the truth. I hope that I am right.
Q1: Why would you hope to be right about that? It’s terribly depressing.
A: I can’t help it if the truth is depressing.
Q1: But you don’t know that it’s the truth. You just hope it is. And I want to know why you hope that.
A: I just think it is the truth. I just hope to be right the way everyone hopes to be right.
Q1: Not everyone hopes to be right.
A: Who doesn’t hope to be right?
Q1: People who suspect their lover of cheating.
A: Listen, cosmology is not a metaphor for something else. It’s just what it is.
Q1: Well, what’s it for then? Cosmology. What impact does it have on everyday life?
A: None. It’s not for anything. It’s completely useless. It’s just the truth. Don’t you want to know the truth? Even if it’s terrible.
Q1: I thought I did when I was young. But, no, I don’t think so. Not anymore.
[This is an excerpt from “Cosmology for the Broken-Hearted”, a play by Tim Sommers. It is a work of fiction. The fictional speaker did not, of course, formulate the “Big Rip” hypothesis. Robert R. Caldwell and his team at Dartmouth did. I am not a cosmologist. I have almost certainly gotten some things wrong here. For that I apologize and I welcome corrections, clarifications, and being pointed to important details left out.]