“Listen; there’s a hell of a good universe next door: let’s go.” –e. e. cummings
Sometimes, you just need to take stock of what we know, and appreciate how far we’ve come. A hundred years ago, we thought the Universe consisted of the stars and nebulae in our Milky Way. We thought Newton’s Law of Gravity governed it all, and that the other forces — electromagnetism and a few weird quantum things — were all there was.
So why not — all in one article — go through the entire history of the Universe, from as early as we can say anything sensible to as late as we can say anything sensible? Let’s get on with it!
The first 10-25 seconds (or possibly even less): the Universe inflates. It expands at a rapid, exponential rate, doing a number of wonderful things. It takes whatever shape your Universe was prior to inflation…
…and stretches it flat! It takes whatever temperature or energy density you had in some minuscule region of the Universe…
…and stretches it across the whole sky, for hundreds of billions of light years! And, thanks to quantum fluctuations getting stretched as well, there are slightly overdense and underdense regions of space, embedded in our huge, flat, almost-perfectly-uniform Universe. And then…
Inflation ends! All that energy — which was making the Universe expand exponentially — now gets dumped into matter and radiation. Normal matter, dark matter, anti-matter, photons, neutrinos, etc., it’s all there. This gives us a hot, dense Universe that’s full of stuff, but that’s also expanding and cooling. This point is what starts off what’s known as the Big Bang. And as it gets less dense and less hot, we become able to do things!
10-5 seconds: we can form stable protons and neutrons! The building blocks of atomic nuclei, the Universe actually needs to cool off for a few microseconds before it’s even possible to bind quarks and gluons into protons and neutrons.
What about anti-protons and anti-neutrons, you ask? For every 10,000,000,000 anti-protons, there were 10,000,000,006 protons, for reasons we’re still learning about. But as the Universe expands and cools, the anti-matter annihilates away with all the matter it can.
1 second: the last of the antimatter annihilates away, leaving just that tiny amount of normal matter, some dark matter, and a huge amount of photons behind! And those protons and neutrons that we’ve got? They’d love to fuse together, making heavy atomic nuclei, but they can’t. The Universe is too hot! So you need to wait and wait. Until…
3 or 4 minutes: the Universe fuses protons and neutrons together into atomic nuclei! And although the Universe tries to fuse these nuclei into heavier and heavier elements, the Universe is only dense and hot enough to get you up to lithium, element #3.
In a spectacular agreement of theory and observation, we get a Universe — by mass — that’s about 3/4 hydrogen, 1/4 helium, and a small amount of deuterium, helium-3, and a tiny amount of lithium-7. And we’d love to just go ahead and bring the electrons on now, to make neutral atoms, but we can’t. The Universe is too hot, still, for that. It isn’t until…
380,000 years: we’ve cooled down enough to form neutral atoms. Finally, this leftover radiation is free to travel, no longer smacking into ions or electrons. And it does travel, until the present day, where it reaches our eyes, shifted well into the microwave.
The “cold” (blue, overdense) spots in this image are a temperature of about 2.7249 Kelvins, and the “hot” (red, underdense) spots are about 2.7251 Kelvins. So the Universe, all this time later, has these overdensities and underdensities left over from inflation, and the matter living there is now free to try and collapse! Which it does, until…
50-100 million years: now that the pressure from radiation has dropped to low enough levels, matter collapses! And after about 50 to 100 million years, matter collapses into dense enough regions that…
we can form the first stars! Made up almost exclusively of hydrogen and helium, the most massive of these stars live only a few hundred thousand years, and then give us what we’ve all been waiting for.
The first supernovae in the Universe! The heavy elements that were fused inside of this star — including the stuff of life: Carbon, Oxygen, Nitrogen, Phosphorous, Sulphur, Iron and more — now get blown off into the Universe, allowing the next generation of stars to form planets, complex chemistry and perhaps even the beginnings of biology.
600 Million Years: these are the first objects we can directly image with a telescope today! We can find that galaxies already exist by this point, and the most distant thing we’ve ever seen is this gamma-ray burst, shown above, which comes from the most luminous type of explosion:
a hypernova! These first-and-second generation stars, burning through their fuel, dying and exploding, finally finish something they begun doing back when the first stars formed…
~1 Billion Years: The Universe gets reionized! All those pesky neutral atoms getting in the way of your light finally get ionized, allowing you to see the distant Universe!
“Hang on a second,” you irately protest! “I thought we needed the Universe to be neutral to see light; that was the whole point of the microwave background, right?”
Take a look at this picture, and then you’ll get it.
Neutral gas blocks visible light; that’s why the Milky Way has those dark bands in it! But infrared (or microwave) light can still pass through neutral atoms. Visible light, on the other hand, needs your Universe to be ionized; we achieve that about a billion years into the Universe. And then, as gravity continues to do its thing…
1.8 billion years (at the latest!): galaxies fall into clusters! When they meet one another, of course, they merge and grow,
leading to the wide variety of galaxies we see today, including great spiral galaxies and giant ellipticals, as well as dwarf and irregular galaxies!
All the meanwhile, that second generation of stars we made are going through the great cosmic cycle of life, death, and rebirth.
And as these stars live and die, blowing off their outer layers when they run out of fuel, their explosions trigger the collapse of gas clouds within the galaxies, causing new stars to form.
And these new stars form in a great variety of types, from hot, massive O-stars, up to a hundred times as massive as our Sun, to dim, red M-stars, burning their fuel so slowly it will take trillions of years for them to exhaust their fuel.
And in some forgotten corner of the Milky Way, after billions of years of this cycle, something very dear to us happened in a collapsing cloud not dissimilar from the one above.
9.2 billion years: our Solar System forms! A cloud of gas and dust, enriched with the heavy elements from (at least two) generations of dead stars, collapses to form our Solar System. The star at the center ignites first, and the other planets eventually form out of our protoplanetary disk. Earth is actually one of the last planets to finish forming, because many millions of years after the other planets form…
the last two giant proto-planets that would create the Earth — the smaller of which is about the size of Mars — collide together! The debris flung up from that collision eventually forms into our Moon, while the majority of both bodies condenses together to form the Earth, completing, roughly, our Solar System as we know it today.
Meanwhile, just a tiny bit later, something interesting is happening to the entire Universe!
9.5 billion years: dark energy starts to defeat matter! In the cosmic battle to slow down the expansion rate, matter has been working tirelessly, under the relentless influence of its gravity, to try to halt and reverse the expansion of the Universe. But at about this time, just as a very young Earth is starting to settle into its groove, the expansion starts accelerating, thanks to the takeover of dark energy!
Meanwhile, back on Earth, some fascinating things are happening.
9.7 billion years: the oldest extant rocks on Earth form! Found in northwest Canada, as shown above, the oldest surviving rocks can be dated to around 4 billion years ago, shortly after the formation of the Earth itself. And it isn’t long after that…
9.9 billion years: that the first evidence of life appears on Earth, too! Based on the ratios of Carbon-13 to Carbon-12, a telltale sign of life, we can determine that life has been around on Earth for at least 3.8 billion years.
And Earth might not be the only place where life thrived during this time. But our most likely candidate neighbor didn’t make it the same way we did, because…
10.7 billion years: Mars dies. Our neighboring planet, once teeming with oceans, rivers, a thick atmosphere and a protective magnetic field, cools too much and loses its ability to protect itself from the solar wind. In short order, Mars’ atmosphere is stripped off, leaving the pressure too low to support liquid water. And so, for the last three billion years, Mars has been much as it is now, although it may have been quite different for perhaps the first 1.5 billion years of our Solar System’s history.
But back on Earth, we are having all sorts of successes. And after life has been brewing for billions of years, the two greatest evolutionary advances (in this physicist’s opinion, FWIW) ever take place…
12.5 billion years: life evolves multicellularity (like red algae, above) and, slightly later, gender. Multicellularity allows specialization and differentiation like never before, and for a single organism to perform many disparate functions, but gender allows the pace of evolution to speed up like never before.
And life explodes! Plant life experiences this advance first, as do the oceans, but animals soon follow suit, and eventually take to land.
13.4 billion years: huge land animals come to dominate the top of the food chain! Reptiles held the top position for a time, eventually giving way to dinosaurs. But after a great catastrophe — or a great opportunity, depending on your biological class — the dinosaurs time came to an end.
13.65 billion years: and this gave way to the rise of birds and mammals! Bringing us to the present day, where mammals now dominate the Earth.
13.7 billion years: and where humans become the first species, as far as we know, to ever willingly venture off of their home world, and land on another.
And although that brings us up until now, the Universe is still going on. In fact, if we take a look at what’s happening in our corner of the Universe, we learn something remarkable. Our Sun, a consistent source of heat and light for us for the past 4.5 billion years, is getting warmer.
15 billion years: the Sun will get too hot for the Earth to house life as we know it, and will boil the oceans as it continues to burn hotter and hotter! Meanwhile, our nearest galactic neighbor, Andromeda, is coming to pay us a visit.
17 billion years: the Milky Way and Andromeda merge, creating a giant elliptical galaxy, and eventually clearing out and absorbing the entirety of the local group, including all of our satellite galaxies and globular clusters. And just at about the time the new, elliptical galaxy starts to settle down…
21 billion years: the Sun, having burned up all of its hydrogen fuel, becomes a red giant star, probably engulfing (and destroying) the Earth! (Although it may simply engulf Mercury and Venus, and blow Earth farther out in orbit.)
Meanwhile, the night sky starts to look awfully different.
Other galaxies, so prominent and beautiful in our Universe, giving us glimpses of our own galaxy’s life and history, begin to disappear!
This is what dark energy does. Even galaxies and clusters close to us, thanks to dark energy, get caught up in the expansion of the Universe and accelerate away. The galaxies that are close and prominent to us now become dim, faint, and red, while the ones even farther away disappear completely beyond the horizon.
100 billion years: the Universe has expanded so much that our local group, having merged into a giant elliptical galaxy, is the only one left in the visible Universe!
We’ve got a long time left of stars going through the great cosmic life-cycle, burning their fuel, exploding, triggering star formation, and burning their new fuel. But this is limited; there’s only a finite amount of hydrogen and other elements to burn via nuclear fusion. The skies will eventually go completely dark, as the last of the dim, red dwarf stars (the longest-lived ones) exhaust their fuel.
1015 years: the last bit of hydrogen is burned up, and our entire Universe goes dark, being populated only by black holes, neutron stars, and degenerate dwarf stars, which eventually themselves cool, fade, and turn black.
And that’s the entire Universe, from the very beginning of what we can sensibly say about it to the far distant future!
Perhaps someday I’ll set this into a video, but for right now, I’ll leave that to the master, who said it 31 years ago in his own incomparable style.
And that’s the history of pretty much everything!
Update: Bonus question! How many images did it take to tell this story? (Hint: it’s almost the 10th anniversary of his death.)