Universe Today
All you need to do to figure out the mystery of the beginning of the universe is to take your general theory of relativity and run the clock backwards to see what happens, you know, at the beginning.
Except you can't.
You can't because of one eensy teensy little problem, and that's the problem of the SINGULARITY. It means that the equations we use to describe EVERYTHING ELSE in the universe like black holes and the expansion of space just...give up. Quit. You ask them to solve this one more problem and they look at their watch and say hey gotta run I think I left the toaster on at home...and they never come back.
So, if we can't actually solve what's going on at the beginning of the universe, can we at least...get a sense of it? Most people just shrug and move on to other problems. But if you're Stephen Hawking, you just dive right in. Yeah, your approach is only half-baked and you're almost certainly wrong, but it's worth a shot in the dark, right?
This series is going to dive into Hawking's proposal for the beginning of the universe, in which he calmly and flatly states that the universe had no beginning. And not like "it's been here forever" no beginnings, but as in "that question doesn't even make sense" no beginning. Like yes, you can string the words together to form a grammatically complete English sentence, but that particular COMBINATION of words has no useful meaning.
We're in "What flavor of dishwasher did you use for you cell phone plan" territory here.
Or not. Hawking was smart, but he wasn't infallible. So let's crack this one open to see what all the fuss is about, and even if we end up being wrong, at least we'll enjoy the journey.
Our journey to the beginning of the universe doesn't start with Hawking. We need to rewind the clock back a bit. Not to the big bang, the 1960's. That's when John Wheeler, perhaps the most important physicist most people have never heard about, was hard at work poking at all things general relativity and quantum mechanics. In fact, he was one of the few people in HISTORY to be able to confidently talk about both fields with relative ease, because that's the kind of guy he was.
Back in the 60's quantum mechanics was all the rage. I mean, it still is, but it was back then too. Physicists had found great success quantizing all sorts of tiny, high-energy things. And once you had a quantum theory of a tiny, high-energy thing, you could do all sorts of cool stuff like predicting new particles and understanding how stars worked.
So here's Wheeler, who really, really gets quantum mechanics. He lives and breathes it. And then he also knows general relativity like nobody's business, honestly probably better than Einstein did. And we had recently uncovered the fact that the universe was once a Big Bang, and it used to be a lot smaller, hotter, and denser.
And it stands to reason that at one point it was so small, so hot, and so dense that it was just like one of those tiny, high-energy particles sitting in the lab: ripe for a quantum description.
But how do you...um...QUANTIZE the universe?
Wheeler wasn't one to beat around the bush. He didn't play games. He went straight to business. We already had a standard procedure for quantizing something. You take your normal, non-quantum theory of a thing, find the important bits, and "promote them" (yes, that's the technical term) to these little things called operators that, and I'm skipping over half a book of math here, allow you to speak in terms of wave functions and probabilities and all the wonderful entangled fuzziness of the quantum world.
Wheeler (and another guy, Bryce DeWitt) did exactly that. They took the equations of general relativity, found the important bits (specifically, the ways that space could bend and the kind of stuff to inhabit space) and made them fuzzier. Instead of one single description, you instead now have a variety of POSSIBLE descriptions.
It's just treating the entire universe the same way we treat an electron, and taking the idea seriously. For an electron, we replace something like its position with a wave equation describing where the electron MIGHT BE the next time we go looking for it. And for the universe, we replace ONE SPECIFIC UNIVERSE (with galaxies over here, some bends and wiggles in space over there) with a whole...CORNUCOPIA...of options that contain every single legally valid arrangement of space and matter that is allowed by general relativity.
Now the attentive listener (and don't feel bad if this wasn't you; whenever a professor in class would use that line it NEVER referred to me) would notice that I have deliberately said "space" instead of the usual "spacetime". That's because this quantum mechanical description of the universe explicitly does NOT include time. It's just space. Not spacetime. Just space.
That's because we're dealing with quantum probabilities. The wave function of an electron ALSO does not include time. We use ANOTHER equation, the Schrodinger equation, to tell us how that wave function evolves and changes and moves around in time. If we replace an electron with a fuzzy blob of probabilities, that fuzzy blob of probabilities doesn't know on its own about time. It's the Schrodinger equation that keeps it on track, like a choreographer: it tells the wave function where to go and when and what beat to land.
In quantum mechanics, this is fine. We just assume that time exists as a normal part of the functioning universe, and we know that as time goes on electrons do all sorts of electronic things. So we can just stick time evolution in to make our math work.
But now we're talking about the universe. The whole, entire universe. There is no "external observer". There's nobody there to watch the wave function of the universe evolve. There's no laboratory, no measurement device, no timers or stopwatches or metronomes.
The Wheeler-DeWitt equations, as they came to be known, do NOT tell us about the evolution of the universe. Instead, they're more like a box. They say "here are the allowed configurations of space and matter". They do NOT say how those configurations will evolve, what they'll do, when they'll pay back their student loans, any of it.
In fact, these equations are...well, not exactly useless, but also not exactly informative. They tell us what's allowed. But they don't even give us a single wave function for the universe. In other words, they don't even tell us which solution is OUR universe. They tell us what wave functions CAN exist (in the sense of being compatible with general relativity).
The Wheeler-DeWitt equation isn't even a blueprint for the universe. It's a machine for MAKING blueprints. But you need to feed this machine information to get it started. For a blueprint for a house, you need to know the lot size, the building materials, the local codes, how many bathrooms you think you need (two on every floor? You got it!). Once you have that information, THEN you can turn the crank on your machine and make a blueprint, a wave function for the universe.
In physics we call this extra information boundary conditions. This is stuff you know or observe or measure, and it's needed to...get physics going. You need to know the position and velocity of the ball. You need to know how long your guitar string is. You need to know the temperatures and pressures of the star. Once you fill that in, you get to work.
So all we need to do to make use of the Wheeler-DeWitt equation is to add extra information about the beginning of the universe.
Wait.
In Part 2, Hawking takes the swing nobody else dared: he guesses the boundary condition itself.
