… “As we know it!”
Not an easy thought – The End. However, it is one that has puzzled cosmologists for some time. Here are the three possible ways in which we think the Universe could end, based purely on how massive the Universe is in comparison to a ‘critical threshold‘ (We’ll call it M):
- Mass of the Universe is greater than M – The force of gravitational attraction is greater than the acceleration outwards, causing the Universe to contract in on itself in a Big Crunch – like the Big Bang, but in reverse!
- Mass of the Universe = M – It’s rather like the Steady State Theory. The mass of the Universe is just right, so to stop the expansion of the Universe from accelerating, but the Universe doesn’t collapse. It just simply exists…
- Mass of the Universe is less than M – Can we just appreciate that for once, we’re less than average or not spectacular in terms of the probability of something happening! We, as a Universe, simply continue expanding, the galaxies stop producing stars, stars stop fusing and die out, and the Universe simply cools in the appropriately termed Big Freeze. This, my friends, is our likely fate.
There are other theories of our demise (The Big Change, for example, which is based heavily on quantum theory). And our fate shifts with new discoveries, the adoption of different theories and the evolving of our current understanding.
When I think of these future fates, it feels very Goldilocks to me – too big, too little or just right!
But how do we know the mass of the Universe, I hear you ask?
How can you hear us, I also hear you ask? (Magic, of course!)
This is where it gets a bit complicated, because the Universe isn’t a jar of sweets that we can guess the finite weight of at a summer fair. Because our current theory is that the Universe is made up of 70% dark energy, 26% dark matter and only 4% of ordinary matter (called baryonic). That’s mind-blowing – we’re suggesting 96% of our Universe is something that we can’t detect and don’t understand (I won’t discuss their existence now, but expect a blog post soon on my opinion of this dark ‘stuff’!).
And trying to measuring this 4% of ordinary matter is no easy task! There is dust everywhere, not to mention the vast distance this ordinary matter is spread out across over the Universe (14 billion light years, which is a ridiculous 1.3 x 10^26 m, which if you’re unfamiliar with standard form, is 132,440,000 billion BILLION metres across). And the fact that if we look out far enough, we’re looking back in time, so any estimates we make would be of the Universe, where different parts were different ages.
And don’t get me started on the fact that this is only the Observable Universe, not even considering if the Universe goes further past this observable boundary, whether there are more Universes (Multi-verse Theory) and if we are even right with our understanding and observations about our ‘little’ observable patch.
So, no easy job! And the impossibility of determining the mass of our Universe has left the possible fates of our Universe a bit unsure. Plus with the development of quantum physics and alternative theories to Einstein’s Relativistic understanding, there really seems like no way of knowing for sure…