What Really Is The Fate Of Our Universe ?
You know, there's this saying that whatever has a beginning also has an end but is that really the case for our universe ?
According to the big bang model, our universe had a beginning and it's reasonable to think that it should also have an end. However, the real question is, how would it end ?
Nobody knows for sure and in fact, the underlying framework of the big bang model - general relativity, predicts different possible scenarios for how our universe would end and it depends on certain non-human factors - ideally speaking. Wondering why I included the "non-human factors" ?
Keep reading and you would find out, we seem to underestimate our (humans) existence and capabilities.
There are three factors that cosmologists generally use to determine the kind of death our universe would undergo and they are
The shape of the universe
Dark energy content
Lastly, equation of state - that tells how the dark energy density responds during expansion
So, what are these possible death paths that our universe could take ?
The Big Rip
This is kind of death is a common feature of a universe having a flat geometry (like a flat sheet of paper) or hyperbolic geometry (open universe). We are often told that the universe is expanding, that is, space is expanding and it's logical to think that matter (since they contain space within them) should also be expanding. Well, that's true but the accelerated rate of the expansion is too low to overcome the forces holding matter together and cause matter to expand with space. Rather it is at locations almost devoid of matter and forces - such as the intergalactic space, that the rate of expansion is relatively strong enough to cause an expansion. So, when cosmologists talk about the universe expanding, they are simply saying that galaxies or galaxy clusters are moving farther away from each other (at an accelerated pace). Now, using a simple equation of state such that the energy density is able to increase with time, if the expansion rate were to be high enough or approach infinity, then all matter in the universe, including you and I - if we happened to be still alive by that time, would eventually be reduced to their constituent elementary particles or possibly below that (which should be a singularity) and this is what is called the big rip.
Fortunately for us, such scenario is believed to have less chances of happening and it's mainly because the dark energy density of our universe appears to be a constant (cosmological constant) and small.
The Heat Death (Big Chill/Freeze)
Mind you, it's not the big chill in Ben 10. 😂
This scenario too is also a feature of a universe with a flat geometry or hyperbolic geometry - both geometries are different. What I forgot to mention previously is that our universe has a flat geometry, according to current observations. Our universe around it's beginning is believed to have been very hot and as it expanded, it began to cool, making it possible for matter to form. The universe however hasn't stopped expanding which means it's still cooling and this cooling is expected to continue till it probably gets to absolute zero - the lowest possible temperature in our universe. The reason why as at the moment we don't feel this cooling (outer space devoid of matter is actually extremely cold) is mainly because of stars, including our sun and all thanks to gravity. Eventually, stars would run out of fuel and eventually become black holes that would devour all other matter, including planets (the dominance of black holes), these black holes too would join in the overall freezing of the universe.
Unfortunately for us, this fate is believed to be the most likely to take place.
The Big Crunch And The Cyclic Universe
The previous two fates are natural attributes of a flat universe and/a hyperbolic universe, this fate (the big crunch) is more of an attribute of a universe with an elliptic shape (closed universe). Our universe isn't elliptic in shape, it's flat as stated before. Whatever we discuss here is only for discussion sake, this fate is less likely to happen.
In an elliptic universe, the expansion of the universe is expected to slow down and stop, this then gives gravity the upper hand and the universe begins to contract. What this means is that once the expansion stops, the universe begins to go back to it's origin - the singularity before the big bang event, and this is called the big crunch.
In one theory, the big crunch has been extended to include what is called the big bounce. During the big bounce, the big bang happens again after contraction to singularity, this can also become a continuous event resulting to what is called the cyclic model of a universe's existence. Let's assume this (cyclic model) were to be true in our universe, what this means is that there once existed a universe before the big bang that started this our universe and that another universe is likely to emerge after this our universe collapses back to a singularity.
There other predicted fates of our universe but the once we just discussed are the very popular ones and it's not 100% certain if any of them, including the big freeze would actually take place. However, I would like to add mine which happens to be us, we humans.
In those models, human activities weren't included and that's why I initially said the factors involved are non-human, thus still making the models ideal. Who would have thought apes would evolve to the point of almost destroying a planet and even making attempts to fix it.
What am I really trying to say ? - you may be asking
Chances are that we could eventually colonize the universe and our activities could also affect the fate of the universe, we could slow it down, escape it or possibly hasten it. The truth is that the fate of our universe could also lie in our hands. I think cosmologists shouldn't underestimate us or leave us out of the equation, we are also part of the universe.
Alright guys I think we would be stopping here. Have a thoughtful day and see you when I see you again.
For further reading
Lastly, please don't forget to do the needful
If you enjoyed my jargons.