Why is there something rather than nothing?
It's the Mother of All Existential Questions, and has been batted around for as long as there've been philosophers there to ask it. Some attribute the universe's something-ness to God, or some other uncreated Creator; predictably, this doesn't satisfy everyone, and others have looked for a more scientific explanation of why a universe filled with stuff somehow took precedence over one that was completely empty.
Probably the most thought-provoking scientific answer to the "something versus nothing" debate I came across in Jim Holt's intriguing book Why Does the World Exist?, in which he interviews dozens of scientists, philosophers, and deep thinkers about how they explain the plenitude of our own universe. You've probably run across the Heisenberg Uncertainty Principle -- the bizarre, but extensively tested, rule that in the quantum realm there are pairs of measurable quantities called canonically conjugate variables that cannot be measured to a high degree of precision at the same time. The best-known pair of canonically conjugate variables is position and momentum; the more accurately you know a particle's position, the less you can even theoretically know about its momentum, and vice-versa. And this is not just a problem with our measuring devices -- that balance between exactitude and fuzziness is built into the fabric of the universe.
A less widely-known pair that exists in the same relationship is energy and time duration. If you know the energy content of a region of space to an extremely high degree of accuracy, the time during which that energy measurement can apply is correspondingly extremely short.
The question Holt asks is: what would happen if you had a universe with nothing in it -- no matter, no energy, no fields, nothing?
Well, that would mean that you know its energy content exactly (zero), and the time duration over which that zero-energy state applies (infinitely long). And according to Heisenberg, those two things can't be true at the same time.
The upshot: nothingness is unstable. It's like a ball balanced at the top of a steep hill; a tiny nudge is all it takes to change its state. If there had been a moment when the universe was completely Without Form And Void (to borrow a phrase), the Uncertainty Principle predicts that the emptiness would very quickly decay into a more stable state -- i.e., one filled with stuff.
There's another layer to this question, however, which has to do not with why there's something rather than nothing, but why the "something" includes matter at all. I'm sure you know that for every subatomic particle, there is an antimatter version; one whose properties such as charge and spin are equal and opposite. And every Star Trek fan knows that if matter and antimatter come into contact with each other, they mutually annihilate, with all of that mass turned into energy according to Einstein's famous mass/energy equation.
[Nota bene: don't be thrown off by the fact that the arrows on the electrons and positrons appear to indicate one is moving toward, and the other away from, their collision point. On a Feynman diagram -- of which the above is an example -- the horizontal axis is time, not position. Matter and antimatter have all of their properties reversed, including motion through time; an electron moving forward through time is equivalent to a positron moving backward through time. Thus the seemingly odd orientation of the arrows.]
More relevant to our discussion, note in the above diagram, the photon produced by the electron/positron pair annihilation (the wavy line labeled γ) is also capable of producing another electron/positron pair; the reaction works both ways. Matter and antimatter can collide and produce energy; the photons' energy can be converted back to matter and antimatter.
But here's where it gets interesting. Because of charge and spin conservation, the matter and antimatter should always be produced in exactly equal amounts. So if the universe did begin with an unstable state of nothingness decaying into a rapidly-expanding cloud of matter, antimatter, and energy, why hasn't all of the matter and antimatter mutually annihilated by now?
Why isn't the universe -- if not nothing, simply space filled only with photons?
One possible answer was that perhaps some of what we see when we look out into space is antimatter; that there are antimatter worlds and galaxies. Since antimatter's chemical properties are identical to matter's, we wouldn't be able to tell if a star was made of antimatter by its spectroscopic signature. The only way to tell would be to go there, at which point you and your spaceship (and a corresponding chunk of the antimatter planet) would explode in a burst of gamma rays, which would be a hell of a way to confirm a discovery.
But there's a pretty good argument that everything we see is matter, not antimatter. Suppose some galaxy was made entirely of antimatter. Well, between that galaxy and the next (matter) galaxy would be a region where the antimatter and matter blown away from their respective sources would come into contact. We'd see what amounts to a glowing wall between the two, where the mutual annihilation of the material would release gamma rays and x rays. This has never been observed; the inference is that all of the astronomical objects we're seeing are made of ordinary matter.
So at the creation of the universe, there must have been a slight excess of matter particles produced, so when all the mutual annihilation was done, some matter was left over. That leftover matter is everything we see around us. But why? None of the current models suggest a reason why there should have been an imbalance, even a small one.
Well -- just possibly -- until now. A press release from CERN a couple of weeks ago found that there is an asymmetry between matter and antimatter, something called a charge-parity violation, that indicates our previous understanding that matter and antimatter are perfect reversals might have to be revised. And it's possible this slight crack in the mirror might explain why just after the Big Bang, matter prevailed over antimatter.
“The more systems in which we observe CP violations and the more precise the measurements are, the more opportunities we have to test the Standard Model and to look for physics beyond it,” said Vincenzo Vagnoni, spokesperson for the Large Hadron Collider. “The first ever observation of CP violation in a baryon decay paves the way for further theoretical and experimental investigations of the nature of CP violation, potentially offering new constraints for physics beyond the Standard Model.”
So that's our mind-blowing excursion into the quantum realm for today. A slight asymmetry in the world of the extremely small that may have far-reaching consequences for everything there is. And -- perhaps -- explain the deepest question of them all; why the universe as we see it exists.
Don't forget that an empty universe which has quantum mechanical rules is still not nothing. One possible answer to the root question is that the universe is merely an abstract (mathematical) complex relationship; and that simpler ones, like 1+1=2, are also universes, although totally uninteresting ones. This is a thought that could only occur after the invention of computers and speculation that we are living in a simulation. Or couldn't it? Admittedly hostile ancient commentators derisively reported that Pythagoras believed that number was the root of reality.
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