“All of nature begins to whisper its secrets to us through its sounds. Sounds that were previously incomprehensible to our soul now become the meaningful language of nature.” –Rudolf St
For millennia, humans have looked to the heavens for answers about the cosmos.Reiner And one of the main reasons I write what I do for all of you is to help give you — as I’ve said many times — is an awareness and an appreciation for what we’ve learned, what we think we know, and how we think we know it.
But then I thought, what an opportunity this is, to remind people that these are problems we actually know something about! Let’s take a look.
1.) What happened before the Big Bang?
We know this; and if you’ve been reading the articles here, you know this: inflation! It not only sets up all the initial conditions we need for the Big Bang, it also gives us the seeds for all the cosmic structure we see in our Universe today!
Now, we don’t exactly think inflation is the entire story; it is, mathematically, incomplete, which means we think something must have caused it. At this point, though, everything you hear about it — colliding braneworlds, a cyclic Universe, a rejuvenated Universe, etc. — is speculation, and nothing more. Some models have been falsified while others have not (and some can not), but hey! We know what came before the Big Bang!
What about the second one?
2.) What is the universe made of?
This changes over time, but we know it in extraordinary detail! In fact, all of our observations — of large-scale structure, of clusters, galaxies, of the leftover radiation from the big bang, of the Lyman-alpha forest, of gravitational lensing, of the primordial elements — all point to the same picture: a Universe that is, today,
- 72% dark energy,
- 23% dark matter,
- 4.6% normal atoms, and
- just under 0.01% radiation.
These relative percentages were different in the past, and the best precision measurements come from the fluctuations in temperature from the cosmic microwave background.
Now, that isn’t to say that we know what dark matter or dark energy is. In fact, there was a paper that came out today from one of the leading teams searching for dark matter.But astrophysically, we know they’re there. Figuring out what causes them/what they are will be one of the great challenges for the 21st century.
3.) Is there a theory of everything?
Fair enough; this one’s a secret. Lots of people think that at a high enough energy, all four of the fundamental forces — gravity, electromagnetism, the weak force (which makes radioactive decays), and the strong force (holds nuclei together) — unify together and are really just the same force! Now, this may not be true. Although electromagnetism and the weak force unify, no one is certain that the strong force does.
If it does unify, weird things will happen in the Universe. What do I mean, weird?
Well, for one, the proton will decay, and be fundamentally unstable! No such thing has been observed, and so we think that perhaps the strong force doesn’t unify. String theory — that you’ve heard so much about — is predicated on the assumption that all four of these forces (including gravity) unify at an even higher energy: the string scale. Such a theory is possible, but again, no evidence for it, and plenty of evidence thus far (no SUSY, stable protons, no flavor-changing neutral currents, etc.) against it. But we don’t know how this will turn out. Perhaps the four fundamental forces are connected in a unified way, perhaps not. The idea is attractive but uncertain.
4.) Are space and time fundamental?
Well, this one’s easy: no. At least, not at a quantum level. Because “position” isn’t even a definitive quantity. Neither, for that matter, is “time”. Sean Carroll has discussed this at length, and as long as when you say fundamental, you mean an irreducible, quantifiable and measurable property of every part of the Universe, I think we can safely say no, space and time are not fundamental.
5.) What is the fate of the universe?
Ice. Definitely ice, frosty. It’s dark energy that tells us this is our fate:
- The expansion of the Universe will accelerate, and everything that isn’t gravitationally bound to us will speed away, and eventually red out, leaving our observable Universe.
- Everything that is bound to us — which is our local group, including our galaxy, Andromeda, and a few smaller, satellite galaxies like the Triangulum galaxy and the Magellanic Clouds — will continue to form stars, go through the life-and-death cycle, until all the fuel for stars is used up.
- After trillions of years, everything will contract and cool, leaving us with some stellar corpses and dead rocks. Eventually, gravitational interactions will force these things to fly apart from one another, as even the giant galaxy we will become will decay.
- And then, perhaps, if the grand unified theories are correct, even the protons making up the atoms will decay away, leaving us with nothing except a cold bath of radiation.
Inspiring! Well, if not a little macabre. But look at all we know! There are still plenty of things to learn, but I’m much more amazed at how far we’ve already come. Hope you’ve enjoyed it!