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May 27, 2013 | by  | in Features | [ssba]

Universal Truths

Come with me now on a journey through time and space…

Let’s start by getting a little perspective. The Earth is 12,742 km in diameter and has a mass of about six trillion trillion kg. The Earth is a pretty big thing.

Except, it’s not really that big. There are lots of things bigger than the Earth. Jupiter, the biggest planet in the Solar System, has a diameter of 140,000 km (a little over ten times the width of the Earth) and its mass is over 300 times that of the Earth. Jupiter is a pretty big thing.

The Sun, though; now that’s a big thing. The Sun is 109 times wider than the Earth, and its mass is 330,000 times the Earth’s. It’s also not orange, or yellow—the Sun is white. Pictures you see of it in other colours are artificially coloured, either because that makes it easier to use the picture for science, or because it makes it look prettier. The Earth’s atmosphere can filter things a little strangely too, which is why it can sometimes appear differently coloured to us.

The largest known star, NML Cygni, is 1650 times the width of the Sun. Try to visualise it. Try harder. Are you feeling small yet? And that star still looks ridiculously small compared to the galaxy it’s in.

A galaxy is pretty big, I guess. Bigger than you anyway. Has anything you’ve ever done really mattered? These stars will keep on burning anyway. Sorry—this sort of thing leaves me feeling really existential.

The Ultimate Fate of the Universe

13.8 billion years ago, an infinitely small, infinitely dense dot, which contained all the mass in the Universe, expanded rapidly. Like, really rapidly. The whole Universe was packed together in such a small space that the laws of physics as we understand them didn’t apply, and gravity was all mushed up with electromagnetism and the strong and weak nuclear forces. In the tiny fractions of a second after the Big Bang, particles were able to form, and within minutes they were able to combine to form nuclei.

380,000 years after the Big Bang the cosmic microwave background radiation, a constant type of radiation which fills the Universe almost uniformly, formed. Because light (and other radiation) travels at a finite speed, when we measure radiation from far away, we’re also looking back in time. And since cosmic background radiation is detectable, we can actually see back in time to relatively close to the Big Bang.

Particles stabilised, and actual structures could start to form, like stars and planets, which were born in huge gas clouds which slowly coalesced under the force of gravity.

The Universe is expanding, and has been doing so for all 13.8 billion years of its existence. We know this because when we look out into the sky we see every galaxy moving away from us, which is what you’d expect if the Universe was expanding. The galaxies aren’t just moving away from each other at a constant speed, though—they’re accelerating. The rate of expansion of the entire Universe is actually increasing.

There is a growing consensus that the Universe will keep on expanding forever, or at least until the end of the Universe. The most widely accepted theory is nicknamed the Big Freeze, in which the Universe cools as it expands, eventually becoming too cold to sustain life, leading ultimately to the heat death of the Universe. “Until the eventual heat death of the Universe” is accordingly one of the best hyperboles to drop into a conversation.

The Sun is 4.57 billion years old (only slightly older than the Earth, because they formed as part of the same process) and is currently halfway through the most stable phase in its existence (the main sequence stage) where it will stay for another 5.4 billion years. At the end of the phase, the Sun’s luminosity will have doubled, and once the hydrogen core of the Sun is extinguished it will slowly double in size, before expanding faster until it is 200 times its current size and thousands of times brighter.

The Sun will stay here as a red giant for about a billion years, and then in the last few million years of its life it will shrink back to about ten times the current size, and then once the helium is all burned up it will expand again, but more rapidly this time, engulfing the orbits of the inner planets of the Solar System, including the Earth. Not that the Earth will have anything on it to watch this—the water and the life will have been boiled away a long time ago by the hotter, larger Sun. At the end of its life the Sun will shrink down, ejecting matter like nobody’s business, until it ends up as a small, bright lump called a white dwarf.

Right now the Universe is 13.8 billion years old. At about 17 billion years old, the Milky Way and the Andromeda galaxy may collide with each other and merge into a larger galaxy. After about a trillion years (that’s a million billion years—100 times the current age of the Universe) all the galaxies in the Local Group (that’s us and all our neighbouring galaxies) will merge into one big galaxy.

At two trillion years, the galaxies outside the massive lump that we’re in will be moving away from us so quickly that we’ll be unable to detect them. We’ll be pretty lonely.

By 100 trillion years, stars won’t be forming anymore, and the longest-lived existing stars will be slowly dying out over the next ten trillion years until all that’s left are lumps of rock and white dwarfs.

In this dark Universe, the orbits of planets will decay and the remnants of stars will fall gradually into black holes or be ejected from our decaying galaxy cluster.

Matter will break down nearly completely as nucleons (protons and neutrons) decay, until all that is left are photons, leptons, and black holes, which will eventually evaporate by Hawking radiation as the Universe slowly, inexorably, grinds to a cold, dead halt.

Not all hope is lost though! There’s still plenty of cool stuff to see on our tour.

When some types of star die (bigger ones than our Sun), rather than expanding then shrinking to a small white ball, their core collapses (sometimes with and sometimes without a huge explosion called a supernova). This occurs when the star’s internal pressure from nuclear fusion becomes insufficient to counteract its own gravity, and it collapses in on itself.

The black hole that results is the most terrifying thing in all of creation. A black hole is an object so dense that its gravitational pull is strong enough to stop light (the fastest thing in the Universe) from escaping, hence the name. Black holes can grow by consuming matter, which they do endlessly. They can also merge to form larger, more viciously hungry black holes. Black holes feel no remorse as they permanently remove matter from space. They are the perfect predator.

But maybe there’s a silver lining. There’s (almost certainly) a supermassive black hole at the centre of most galaxies, giving them something to spin around. There’s one at the centre of the Milky Way anyway, and we’re not anywhere close to it.

My all-time favourite fact about the Universe (not including biology ones—some aphids are born pregnant with clones of themselves! There is a whole species of lesbian lizards!) is that gravity distorts time, as well as space. And what has a lot of gravity? Black holes have a lot of gravity.

Gravitational time dilation is the difference in the time that elapses between two events measured by different observers at different gravitational potentials. In layman’s terms, the closer you are to a black hole (or some other mass—but it’s most noticeable with more gravity), the slower time passes. This has been proven by an experiment with super-accurate atomic clocks at different altitudes (and therefore experiencing the pull of the Earth’s gravity differently), with the further-away one showing it moved through time faster.

Of course if you’re close enough to a black hole to observe this effect on a normal scale, then you’re probably also dead, but it’s
still cool.

There’s a lot of big scary stuff out there, but most of it is pretty far away and we’re just taking our first steps out into the cold.

Did you know that only 12 people have walked on the Moon? In each of the six manned Moon landings (all by NASA, all between 1969 and 1972) there was a third person who stayed behind in the capsule. All were white men (surprise!). 11 of the 12 walkers were boy scouts too, so make of that what you will. We also don’t currently have the capacity to send anyone to the Moon, which kind of bums me out, though there’s a manned mission to Mars in the works, which I’m very excited about!

Humans have been busy in other ways too, sending probes out left right and centre. Voyager 1 is the furthest from us, travelling at 17.26 km per second, and now in completely uncharted space. It’s the furthest-away man-made thing out there, and it’s still useful to us, despite having been launched in 1977. Just last year, in fact, it discovered a previously unknown region of space at the edge of the Solar System.

This has all been a bit, well, normal up until now. So let’s lean back in the captain’s chair and give the order to engage the warp drive.

When you travel fast, like, really fast, some pretty strange things start to happen. The best one is that time mucks up again, like it does
when there’s too much gravity. This effect is called time dilation and is predicted by Einstein’s general theory of relativity. The closer you get to the speed of light (which is the same everywhere and is 300 million metres per second), the slower time gets.

When travelling at exactly the speed of light, time appears to stop. This requires an infinite amount of energy… unless you have a (totally real) warp drive. Theoretically, if you were to travel faster than the speed of light (or above warp 1) time reverses, though Star Trek mostly ignores this.

If you don’t have a warp drive, or a hyperdrive even, all hope is not lost. Traversable wormholes might not be impossible, though their existence is far from proven. A wormhole is a hypothetical shortcut through space and time (or, more accurately, spacetime, since they’re part of the same thing) and Einstein’s general relativity predicts that if they exist, they could allow your spaceship to travel through time as well as space. No TARDIS necessary.

This is how the jump drives in Battlestar Galactica and hyperdrives in Star Wars seem to work—by bending two points in spacetime to be near each other and hopping between them, rather than going the long way around.

The timescales involved in cosmology are gargantuan, and we are so young. Provided we don’t blow ourselves up anytime soon, it won’t be too long before we have colonies on other planets in our Solar System, and from there… who knows? The final frontier has been waiting for us for a long time. Let’s see what it’s got in store for us.


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