Fun fact: the Universe is expanding. Literally. It’s getting bigger, every second of every day, in all directions at once. This was the epochal discovery of an astronomer named Edwin Hubble, who conducted a laborious telescopic survey of God knows how many stars, in how many galaxies, looking at the spectrum of light each was emitting in our direction, plotting it all out on photographic plates night after night, a driven man on a cosmic mission to blow all of our tiny little minds. He was able to show, beyond any shadow of a doubt, that the light of pretty much every star in the Universe, coming from every point in the sky, was red-shifted. That is, the light seemed to be pushed towards the red end of the spectrum, which for light is the low frequency end (light at the lowest end is “infrared”, literally beneath red, and light at the high frequency end is “ultraviolet”, above blue, after which you get into radio waves, x-rays, gamma rays and so on, none of which we can see with our Mark 1 human eyeballs).
This could only be the result of Doppler shifting, an effect we experience in our everyday lives in connection with how we perceive sound. In a lot of ways light waves behave quite like sound waves, and when a moving object emits sound waves, the ones that are emanating off the front end, in the direction of motion, get compressed, while the ones coming off the back, opposite the direction of motion, get stretched. The frequency at the front is thus made higher, while the frequency at the back is lowered, and that’s why a race car makes that distinctive “eeeeeeeeeee – owwwwwww” sound when it goes by. That’s the Doppler Effect. Same thing with anything that’s moving while it gives off light. If it’s moving fast enough, the compression at the front end makes the light seem shifted into a higher frequency, which thus appears blue, and the light stretching off the back end seems to look more red. If a race car could go fast enough, it would look blue as it rushed toward you, and become red as it sped away.
All the stars Hubble observed were moving fast enough to produce a measurable Doppler effect, and everything, everywhere, looked red. Everything in the Universe, no matter where you looked, was therefore moving away from us. No other conclusion was possible. The explanation, Hubble realized, was that the very fabric of the Universe – space itself – was expanding. The stars of the observable Cosmos were like little dots printed on the surface of a balloon that was being blown up; the bigger the balloon got, the farther apart every dot became from every other dot, and no matter which dot you selected, all the dots around it kept moving farther away, in all directions. This observation was what led, inevitably, to the notion that the Universe must have begun with a Big Bang. It was simple logic. The expansion process refuted the idea that the Universe existed in a “steady state”, as many had believed. Anything that’s constantly getting bigger must have started out smaller, and if you ran the process backwards, simply reverse-engineered the rapidly spreading inkblot of space, everything must have started out at a sort of centre, which must have been an inconceivably tiny initial point, a mere dot, actually, of a potential Universe so small that our pitiful powers of comprehension lacked the proper terms of reference to even imagine it.
Then a great outward rush must have begun, presumably on its own initiative somehow, and space itself was thereafter continuously expanding. Initially, given that we could now detect light that had to travel across thirteen or fourteen billion light years of space just to get to us, with God knew how much beyond that which we couldn’t even see, it must have expanded very very rapidly. Space itself must have ballooned at a rate that far exceeded the speed of the light that travelled within it.
It’s important to be clear on this: the way everything was moving apart from everything else wasn’t because the stars themselves were moving through space. They all got farther and farther apart because the space in which they were embedded was itself continuously growing bigger, and taking them along for the ride.
Mind-blowing as all that is, it’s just by way of background to todays discussion.
Here’s what’s really crazy. The expansion isn’t slowing down, or even maintaining a steady pace. It’s accelerating.
When I was younger, and first reading about this stuff, there was a lively debate among the cosmologists on what the ultimate fate of the Universe would be. It was thought that this depended on the amount of matter that was out there as a residue of the Big Bang. If there was enough matter, enough stars, and planets, and clouds of interstellar gas and such, then the mutual gravitational force exerted by the combined mass might be enough to put the brakes on, and slow down the expansion to the point that it would, finally, stop, and a retraction would begin. In the distant future, then, the Universe might stop growing and start to shrink, until, ultimately, it compressed itself out of existence, right back into that primordial state of incomprehensible smallness with which everything began. What they dubbed a Big Crunch could therefore, conceivably, complete the cycle begun with the Big Bang. Who knew, the process might then repeat. Maybe that was how all Creation worked. Maybe it was an endless succession of bangs and crunches, each crunch ending one universe and creating the conditions for the rebirth of another, which might emerge with entirely different attributes and governing laws as a product of the next big bang.
The key variable was matter density. How much stuff was out there? Was there enough of it embedded in the fabric of space to gravitationally halt the expansion?
It was hard to say, at first. There certainly wasn’t enough among the stars and galaxies we could catalogue, but astronomers could tell that there was much more matter out there than we could see with our optical telescopes, or radio telescopes either. We couldn’t observe it, but we could certainly see it indirectly, by way of what it did to the things that were observable. This is because things that carry mass produce gravity, and you can detect the ghostly hand of gravity at work, even when you can’t see the object that generates it. Take black holes, for example (which, now I think of it, are weird enough to rate a mind-bender entry of their own). Black holes are gravity wells left behind by collapsing objects so massive that they crushed themselves right out of the Universe – no fooling – leaving behind nothing but a gravitational force so powerful that not even light can escape. Anything that spirals into a black hole, light included, leaves our Universe and goes – er, somewhere – never to be seen again. Thus you can’t see black holes, not directly, but you can see the effect they have on the stuff that they suck in to themselves. Matter that spirals into them releases all sorts of radiation just before it crosses the “event horizon” and vanishes. Once black holes have gobbled up everything within reach, they still create massive gravity fields around which distant objects orbit. You can tell they’re there, hiding in their blackness.
So it goes, in ways less dramatic, with everything out there. Things you can’t see tug away at other things that are visible, with results that we can detect. From our observations of the motion of stars and the galaxies they populate, it became clear that the stuff we could see – the “luminous” matter – wasn’t anywhere near enough to account for all the gravitational effects. The universe had to be full of matter we couldn’t detect. This unseen stuff was dubbed “dark matter”. Astronomers figure that dark matter composes about 20 – 25% of the substance of the Universe. We have no real idea, and barely the merest clue, what it actually is. Some scientists have their hypotheses, sure. Years ago, I remember reading that it might be weird little things called neutrinos. But real evidence? Hardly a whit. Look, it’s something, OK? It exists. This we know.
Moreover, there was a lot of it. Was there enough, then, to halt the expansion of the Universe at some point?
No. From what we can tell, not at all. Not even close. Something weird is going on with the expansion.
Back when Einstein was developing his General and Special Theories of Relativity, of which I may eventually make much hay if I decide to inflict many more of these mind-bender instalments upon my parlous and diminishing readership, he inserted a sort of fudge factor into his equations to make them balance out properly, which he dubbed the “cosmological constant”. He had no extrinsic evidence to support the inclusion of this mathematical constant in his calculations. Things just worked out better on the chalkboard when he did, which in the world of cosmology is no small thing – what the math demands, reality often seems to provide. However, the implication of the equations, thus tweaked, was that the Universe was expanding at an accelerating rate, and Albert balked at the notion. He subsequently removed the cosmological constant, which he had, after all, made up out of whole cloth just to keep things elegant, calling it the biggest error of his career.
Except he was right. The Universe behaves exactly as predicted by his equations when the cosmological constant is put back in. Its expansion is not slowing down. It’s speeding up. If present observations are correct, there will never be a Big Crunch. The Universe will just keep getting bigger and bigger until all the stars within it burn themselves out, and everything ends in an attenuated realm of frozen darkness. We’re talking billions upon billions of years in the future here, but still, by our present calculations the Universe apparently has a lifespan, and will one day, for all practical purposes, die. Some sort of wispy, still expanding fabric of space-time will persist, but there won’t really be anything in it. Even individual atoms will lose energy, decay, and in a way freeze, or perhaps even fall to sub-atomic pieces. I can’t keep up with the science at that point, which seems to involve both relativistic and quantum effects, but I gather that in this scenario the fate of the Universe will be either “heat death”, as everything just succumbs to entropy and goes dark, or maybe even what they call a “Big Rip”, as individual atoms are torn asunder in the throes of continuous spacial expansion.
But why? What actual force in nature does Einstein’s made-up cosmological constant actually represent? What’s propelling this headlong expansion of the space we live in?
Well, we haven’t the slightest idea. Not the foggiest; not the smallest frigging clue. Some sort of energy, one supposes, but since we can’t seem to figure our where it comes from, or even detect it (as opposed to detecting its effects) we’ve dubbed it Dark Energy. Which is another way of saying That Force We Don’t Understand And Can’t Even Measure Except Something Is Going On So It Must Exist.
So here we sit in 2021, and after all the breakthroughs, all the amazing insights of the science, all the applied genius of the astronomers and theoretical physicists, we find ourselves in a Universe that’s made mostly of stuff we can’t detect or explain. The invisible dark matter composes maybe 25%, give or take. The unknowable, inexplicable dark energy probably accounts for another 70% of whatever else the Universe is. What we can see, measure, and analyze – the totality of what we can even begin to understand – accounts for perhaps 5% of the Universe, tops.
We therefore have no frickin’ idea what the Universe even is, what it’s made of, or why it works the way it works. We don’t know why there was a Big Bang, supposing there was one (I keep waiting for that orthodoxy to be challenged). We can’t even properly conceptualize the expansion, since if the Universe is all there is, there’s nothing to expand into, is there? Don’t think of it that way, they tell you. The Universe is what it is, and it’s all there is (unless it isn’t, and there are multiple Universes). Anyway, it doesn’t need something in which to expand. There’s no space outside it, silly. Space itself is an artifact of the Big Bang, and therefore exits only within the thing the Big Bang produced. Right? As the Universe grows larger it’s simply becoming a bigger version of the only thing that exists, whatever it is. We aren’t really sure, it’s full of stuff we can’t detect, and composed of energies we don’t comprehend in the slightest, but look, see for yourself, the evidence proves what it proves, to the extent it proves anything at all.
We’ve learned so much, yet still we’re like little kids standing on the beach, looking out at the vast ocean and realizing that we don’t understand what water is at all.