Prior to this posts, I've discussed the history of the universe, as we currently can observe and understand it, up to present day (give or take a few million years). If you missed those, here's Part I and Part II, which will catch you up. But really, as cool as the history of the universe is (and it's pretty neat), I wrote those posts so that I could write this one, about what happens next. Fair warning, it's fairly bleak and existential, albeit fascinating. Now, with Halloween around the corner, I've got a scary story for you: how the universe will (likely) end.

So, a year and some change ago I did an absurdly wordy post that may have had slightly too many run-on sentances about the early history of the universe (If you didn't read it, here's A Brief History of the Universe, Part I). I then promised to follow it up with more history up until present day or so, and never did. Until now. And while you may think it took me a long time to follow up with a part II to that post, that time span is just peanuts to the universe. In fact, it's been around for about thirteen billion times longer than the wait between the first part of this series and this follow-up. So, cosmologically speaking, the delay was perfectly acceptable. Now, let's get on with it.

Today on Fizzix Phriday, it's time for some physics phistory (the p is silent). Let's take a jaunt back in time to the year 1571. Nicolaus Copernicus (born Mikolaj Kopernik) had published his revolutionary work, De revolutionibus orbium coelestium (in English: On the Revolutions of the Celestial Spheres) just 23 years ago, where he described, mathematically, a universe where the Earth was not the center, and all the planets revolved around the Sun, rather than the Earth. While this was a revolutionary idea, it was largely seen as incorrect or ignored, due in no small part to Copernicus's death around the time of its publication, and being therefore unable to defend his work from criticisms that arose from going against the established ideas in science and religion. Even worse, a note was prepended to his work before publication that basically said "everything in here about the Earth revolving around the sun and not the other way around is just a neat mathematical exercise..."

There are many things that we can observe about the universe which lead us to assert that it all started with a Big Bang. There is the velocity of galaxies further away from us being faster, or the fact that when we look back to a younger universe we see more primitive structures that would precede what our universe looks like now. But probably the best evidence of the Big Bang is called the Cosmic Microwave Background Radiation. Which sounds really cool, and totally is. So what exactly is it?

Oh, man, is space big. I get upset thinking about it sometimes. It's just too big (then again, my general reaction to the largest living thing on the planet, the General Sherman Tree, was to get angry). But it's not that space is just so large, it's also that it's so empty. And that is what I'm here to talk about today.

The visible universe is about 93 million light-years from one side to the other. That means we can see about 46 million or so light-years in any given direction, if we look hard enough (you'd need impossibly good eyes, though, or you could just use a really powerful telescope and also be in space because the atmosphere really gets in the way of seeing that far)...

This week marks the 47th anniversary of the first human steps on the moon (July 20th, 1969), so we're going to celebrate with some cool physics facts (fizzix phacts) about the moon.

First of all, let's get a sense of how far away the moon is. On average, the moon is 238,855 miles away from us (384,400 km). That's all fine and dandy, but as humans, we're absolutely terrible at understanding very long distance, as I sort of covered with far larger distances previously. So, let's give ourselves a sense of scale...

Time is a tricky thing. The idea of the Big Bang has become common knowledge, but a question many still have as to the birth of the universe is what came "before" it, or indeed what was the "cause" of the Big Bang. While one might answer these questions with "nothing," that's not really correct, because the answer is actually much simpler and at the same time so much harder to grasp in any intuitive sense. The answer, which I understand intellectually but still makes no sense to me in an intuitive way, is that there was no before, nor a cause, because time itself, which the idea of before and causation is predicated upon, began its existence synchronously with the Big Bang. I find this nearly impossible to grasp in a fundamental way, because our entire existence is based around and upon a notion of time as a strict linear progression of one thing to another, with every event having a causation and time preceding it.

For a long time (well, relatively) astronomers believed they had this whole "solar system" thing figured out. They had this theory which governed its formation, called the "core-accretion theory," which described stellar and planetary formation. Basically, as all the dust and gasses that make up a star star coalescing into a star, they also begin spinning. As they spin faster, the gasses condense into a kind of spinning disk which is thicker at the center (like spinning our a blob of pizza dough, but a lot more complicated). Finally, this central mass gets hot and dense enough to trigger fusion, and the proto-star becomes a real star. Around this time, as the star is finishing its formation, the heavier elements in the spinning disk start clumping together, with the denser elements forming the smaller, rocky planets we see as the "inner planets" in our solar system, and lighter elements and compounds forming gas giants further out.

Picture yourself on the surface of the Earth (or in a boat on a river). Now, if you were to toss something up into the air, it would eventually be pulled back down, due to the effects of gravity. Obviously, this force is not indomitable, as we've escaped the Earth's gravitational well many a time (most recently, when we sent something awesome to Mars—because orbit doesn't really count as escaping the Earth's gravity). In fact, if you were to toss something up with enough force, it would fly away forever, never to be seen again. The speed you instantaneously imparted on that object when you threw it is the Earth's escape velocity. Now, let's say we increase the mass of the Earth to that of Jupiter, but keep the size the same (we make the Earth much, much more dense). Now, in the instant before you were liquified by it, you'd notice the gravity has become much, much stronger than it was. This makes perfect sense, as gravity is a property of mass.

One thing you should know about space: it's huge. Mind-bogglingly huge. If you were to think of the biggest thing you could possibly imagine, it would still be more than a billion times bigger than that (and don't say you imagined infinity, because you can't. And stop being clever). The problem with just saying "the universe is huge" is that it doesn't really convey the distances involved. We can talk all we want about light-years and parsecs (unit of distance, not time, sorry George Lucas), but it doesn't really mean much. They're just words. And, as wonderfully evolved as language is, a lot of scientific terms fail to covey conceptual content with them, because our brains simply didn't evolve to deal with this sort of stuff. So this Friday, I'm going to try to take a stab at this comprehension.