When it comes to thinking about the cosmos truly nothing is off the table. Anytime I hear a new theory and think to myself that there is no way that is possible, there will be one or more very intelligent people say, yes that is what we think is happening right now. Or a little less certain, they say that that is our best guess. It is truly fascinating to me that even though we all, billions of us, experience the physical world we have a very difficult time explaining what it is that we experience, and not only that but we also have a very difficult time figuring out the rules that govern our universe. That I find very fascinating and at the same time disturbing.
There are hundreds of theories out there that scientist have come up with to help explain our universe. I think one of the most fascinating is the idea of what scientist call the “Eternal Universe.” This article summarizes their paper.
They have come up with three assumptions about the end of time. I have read and reread the article and it is a bit confusing as I think they are talking about two different things with these assumptions. I think that are discussing the probability of events related to time, then also they are trying to discuss what kind of universe we live in, whether it be an infinite one or a finite one. The below exert I think deals with what kind of universe they think we could live in.
The first assumption is that the universe is eternally inflating, which is a consequence of general relativity and well supported by the experimental evidence so far observed. The second assumption is that the definition of probability is based on the relative frequency of an event, or what the scientists call the assumption of typicality. The third assumption is that, if spacetime is indeed infinite, then the only way to determine the probability of an event is to restrict one’s attention to a finite subset of the infinite multiverse.
While I understand the first assumption and the last, I am certainly having trouble wrapping my head around the second one. I think first we have to assume that the definition of time is something like- where different events happen from one moment to the next. The key here is that events take place as time moves forward, which as far as we can tell is true. So I think the above assumptions are an attempt to explain our universe in terms of how events are measured? I am fairly certain that is correct, but I still do not understand assumption two. I guess what they are saying is that regardless of what kind of universe we live in (infinite or finite) that any event can be determined based on its typicality? Which again to me I feel they are mixing two different ideas here. It seems they are trying to combine our theory of a finite/infinite universe with the probability of events that have a chance to occur in that type of universe. Now that I think about it, that mostly makes sense. As for the second assumption, I think it means that regardless of what kind of universe we live in, the probability of an event, any event, is just based on the frequency of that happening. So I assume it would not matter if we lived in an infinite or finite universe. Although if this is the case I think we have created a circular argument, which we will get to in a second.
In their paper, they explain that in an eternal universe, even the most unlikely events will eventually occur — and not only occur, but occur an infinite number of times. Since probabilities are defined in terms of the relative abundance of events, there would be no point in determining any probabilities because every event would be equally likely to happen. Which is the circular argument that I just mentioned. Any event in an infinite universe would happen infinity, so it would be impossible to calculate its probability. Now using the last of the assumptions they authors kind of skirt this problem by saying,”if spacetime is indeed infinite, then the only way to determine the probability of an event is to restrict one’s attention to a finite subset of the infinite multiverse.” Which basically means that if we live in a truly infinite universe then the only way to truly determine the probability of an event happening is to look at a specific portion of spacetime, such as Earth, or just our galaxy.
So if that is the case then what is the probability of one winning the lottery in our galaxy. Well if we are the only intelligent species then that would be relatively easy to calculate. However as you take a larger and larger portion of spacetime, that probability could potentially increase or decrease. Eventually if you encompassed the entire universe, that probability, I think, would move to 1. The point is that if we live in a truly infinite universe, to some extent our choices and probabilities do not matter as much as we think they do. The reason is because all choices and events happen and they happen infinitely. This is both really cool and somewhat depressing at the same time.
I remember watching Justice League Crisis on Two Earths (which was really cool for a variety of reasons) and one of the characters was obsessed with oblivion. He kept uttering the phrase it doesn’t matter, that nothing really matters because there are infinite worlds and infinite you’s and me’s out there so eventually everything that can happen will happen infinitely. I found this pretty deep for a cartoon movie, but there a real degree of truth in that. Plus you never know what you will take away from a movie, cartoon, comic book, or what have you, so never stop reading and consuming information.
As I have said many times I think this is where the philosophical and the physical world meet, and one without the other is pointless. It takes both sides to make sense of this argument and for that matter figure out what it truly means.
For me I am not sure which of these theories I would prefer to be true. I think both are fascinating and both offer deep though experiments. I think an infinite universe would be cooler in terms of possibility, as literally anything would be possible. Even the most minuscule probability of events would happen and happen infinity, so long as that probability was a non zero number. Think about it if an event has no chance or a zero probability of occurring, even given eternity and an infinite universe that probability is still zero. It will never happen.
As for living in a finite universe while certainly not as cool is still interesting. If you think about it, the universe is huge and you are, as far as we know, unique. You are one of a kind, there is no one on this planet or possibly in the entire universe that is like you. That is truly amazing and is some regards you are in a sense an astronomical statistical anomaly. I think Achilles from the movie Troy (played by Brad Pitt) said it best, “The gods envy us. They envy us because we’re mortal, because any moment may be our last. Everything is more beautiful because we’re doomed. You will never be lovelier than you are now. We will never be here again.” I agree with that quote and I think is says quite a bit about life in general. We will never be here again, so in some regards everything is infinitival more beautiful.
Despite the long post I do not think it matters either way, which universe we live in, because we are essentially stuck in time and for the time being stuck on this planet. If one or both of those criteria would change then which universe we live in would certainly be more interesting, and both of these ideas would come into play more so. But for now I do not think it really matters, because if our universe is infinite we cannot truly appreciate it, and if it is not then things basically remain the same for us. So until something changes in our ability to leave the planet and travel great distances or become unstuck in time, in my opinion, it does not matter which type of universe we live in. BUT, it does make for a cool thought experiment.