Time is a funny thing.
We know that the universe is about 14 billion years old, which seems incredibly old. A brief history of the universe goes thusly: Before the Big Bang is unknown and unknowable – time is the passing of events, that is change. If there is no change, there is no time. “Prior” to the Big Bang, there was nothing to change, so there was no time. Then there was something. The entire observable universe existed in a spec smaller than an atom as we know it now, and it got really big. Within a fraction of what we call a second, the observable universe expanded to the size of about a grapefruit – approximately half a litre. While this doesn’t seem big from our standards now, if you consider the change in scale, this was the biggest and fastest expansion of the universe in relative scales in the entire history of the universe. We call this expansion the Big Bang. We tend to think that it happened in the past and we compare it to an explosion.
A slightly trippy thing to consider is that this is what we know about the *observable* universe. That first bit is really important. The bit outside the observable universe could just be more universe, or it could be nothing. As we observe the edge of our observable universe, the distribution of galaxies seems even and more or less uniform, implying that on the other side of that event horizon is just more universe. So at the point of the big bang, there could have been an universe the size of our observable universe of the start conditions. This can be a bit hard to visualise, so imagine the universe is flat and just an ink dot on an elastic sheet. Zoom in until all you can see is that dot. Now stretch the elastic sheet and zoom out at the same speed so that you can still only see that dot – the ink dilutes as the space expands. That is what we see. Now start again, but realise that the entire sheet of elastic is filled with ink, not just one dot. Consider how big our universe has got from that dot smaller than an atom to our current scale – 90 light years across – and apply it from a starting point of not less than one atom, but to Big Bang Stuff 90 light years across. And we will never know what it is out there.
About 300 million years after the Big Bang, the universe cooled down enough that matter formed and light was impeded. This is the first point where we can observe things – that is, matter. This is when our own Galaxy, the Milky Way (so named, because it looks like a milk road on the sky – blame the Romans) first formed. We have a few stars in our system that are still burning from that first coalescence of matter. Hydrogen was the first atom to form and it clumped together to form the first stars. These stars are very, very pure. All stars that have formed since have some impurities (known as metals when they aren’t hydrogen or helium – even though chemists don’t call those elements metals).
Our own Earth is about 4.5 billion years old – it came into creation about 2/3 of the age of the universe ago. Traces of life in the form of fossils have been found on Earth that date to about the time that the Earth’s crust cooled down after the late bombardment period. The Earth started as a big ball of molten rock, then it cooled down and formed a crust. Earth then cleaned up its orbit and got hit, a lot, by asteroids and other bodies (including Thea, a mars sized planet which ended up splitting proto-Earth in two – our Earth as we know it, and our Moon). Finally it cooled down again to form a new mineral rich crust and life formed almost immediately after it. This is about 3.8 billion years ago.
This life forming as soon as conditions were approximately right gives me great hope that life exists on any planet that conditions are approximately right.
Zoom forwards a few billion years and life leaves the oceans and populates the land. Viruses and Bacteria were first, followed by plants, then followed by the insects that evolved from crustaceans. Eventually vertebrates follow (evolved from fish). That eventually evolved into us humans (modern humans are about 200,000 years old) and every other form of life we see on the Earth. Life is continuing to evolve, ensuring that no niece that can be exploited for energy (food) remains untapped. This includes bacteria evolving to eat stuff in nuclear reactors. On the scale of life, if all of life on Earth were scaled to be 1 day, humans are about 4.5 seconds old. Soon that scale is going to be useless, so let us convert instead to 1 year. If life on Earth were scaled to exist in 1 year, then modern humans are 28 minutes old.
Recall my earlier note that as soon as life could form on Earth it did? The earliest that life conditions (as we understand it) could form in the observable universe was around 12 billion years ago (give or take a billion). If life took the opportunity to start then, just like it did here on Earth, then there has been life in the observable universe for 12 billion ish years. That is pretty cool. If we do our year scale, humans are 8 minutes old.
But we haven’t got to the best bit yet!
Eventually our sun will die out as we know it, leaving behind a red dwarf. Don’t panic, we have about another 5 billion years before that will happen. We have much more immediate concerns to weather – like the weather. Anthropogenic (human caused) Climate change will make the Earth uninhabitable by humans in only a few hundred years (unless we fix it – hint, hint). If we survive that, the sun will have grown to the point of being too hot for us in about 100 million years, moving the “Goldilocks Zone” past our Earth. We can potentially engineer a few solutions to that, or become space faring to escape the ever increasing heat.
The sun won’t really be dead in 5 billion years though, because it will become a type of star called a red dwarf. That red dwarf will burn for about a trillion years. That is 1,000 billion years. Consider that our entire observable universe is only 15 billion years old. If we turn that trillion years of age into 1 year again, modern humans are 6.3 seconds old.
We still haven’t got to the best bit. Red dwarfs degrade into white dwarfs, whose lifespan is measured in a conservative quintillion years (1×10^18 years). That is a million times longer than a red dwarf. The estimated upper limit to the lifespan of white dwarfs is a number I can’t write down that makes any real sense – between 1×10^30 years to 1×10^200 years. And then the white dwarfs finally break down to black dwarfs. We don’t know how long they will last. White dwarfs are the last point that we can conceive of life as we understand it managing to live, after that, there isn’t sufficient energy distribution. Philosophical question: if the universe exists and there is no one there to appreciate it, does it matter? If we use the conservative number of the white dwarves lasting about a quintillion years, and we scale that to our year, then modern humans are about 6.3 micro seconds old. That is, a million microseconds pass to get to 1 second. We haven’t really happened.
This assumes that the Big Rip, or something similarly universe ending, doesn’t happen first. We are looking at how long the universe can go for. The Big Rip is where the accelerating expansion of the universe (confirmed and verified), fed by Dark Energy (seems to be an emergent aspect of space) gets so powerful it rips everything apart faster than it can form. Estimates on when this might happen vary from as little as the universe being aged 20 billion (whe our suns turns into a red dwarf) to 80 billion. That range tells you that we really don’t know. If the Dark Energy is an emergent property of space, and space continues to increase, then Dark Energy will continue to increase and lead to the Big Rip – where the space between things is so great that matter no longer has access to other matter. If it is not an emergent property of space, the universe won’t rip apart and we are down to the lifespan of black dwarfs.
Ok, so the universe is going to get really, really old. What of it? Remember how we were looking at our current human age compared to the scale of universal time and it started to seem very small…? 15 billion years seems like a long time when we are here at the 15 billion year mark, but compared to the projected lifespan of the universe, it is nothing. It started in an explosion and pushed outwards. Our universe is still expanding.
If you think about an explosion – like a hand grenade (named after pomegranates – blame the French) where you pull the trigger, it goes bang and sends shrapnel everywhere – that’s us. Very shortly after the reaction that started the explosion of the hand grenade, one of the bits of shrapnel formed life which became us, which became you, reading this. When we project where the pieces of the explosion are going and how long it will take to get there, and look at our place on that scale, the grenade just went bang, and we are in it – we are in that explosion riding a bit of debris.
The Big Bang was not a long time ago, it is now, and we are riding it.
And that is awesome.