The article linked to above covers the most plausible science of what lies beyond the observable universe. The theory is that if the theory of the inflationary universe is correct (and all evidence points to the fact that it is correct) than the universe is at least 250 times larger than what is currently observable. To begin with, the size of the observable universe is around 90 billion light years wide. That means it would take light, which moves almost exactly 300,000 km/s (kilometers, not meters) 90 billion years to traverse the diameter of the universe. To quote the article:
“Since special relativity states that nothing can move faster than a photon, many people misinterpret this to mean that the observable Universe must be 13.75 billion light years across. In fact, it is much larger. Not only has space been expanding since the big bang, but the rate of expansion has been steadily increasing due to the influence of dark energy. Since special relativity doesn’t factor in the expansion of space itself, cosmologists estimate that the oldest photons have travelled a distance of 45 billion light years since the big bang. That means that our observable Universe is on the order of 90 billion light years wide.”
Therefore, the universe is expands even faster than the speed of light, and because of that certain parts of the universe are forever beyond our light cone. Because of this, they are even beyond the realm of causal interaction- everything beyond the 90 billion light year diameter of the universe cannot interact with the observable universe except perhaps through gravity.
Let’s expand further: if the theory of the inflationary universe correct, then the universe is at least 250x larger than what is currently observable (somewhere on the order of 100 sextillion light years across). But why, then, can the universe not be infinitely large?
It seems we are faced with a contradiction. It seems impossible to empirically prove that the universe goes on forever because of physical constraints and the sheer logical fact that it would not be possible to observe an infinite distance in the first place because conceivably, one could always say “perhaps the end is still beyond that”. If it can be a priori proven from mathematical principles seems dubious at best- the debate rages on between those who say the universe is flat or curved. However, most current data favors a flat and therefore spatially infinite universe.
This idea of measuring the spatial curvature of the universe however does not take into account the fact that at some point beyond the observable horizon of the universe the curvature suddenly increases or is so close to 0 but not being 0 that it is impossible to tell. Thus the problem of infinitesimals meets the infinite.
However, the article expresses a kind of reticence to pronounce that the universe is probably infinite. It is simply “too hard to accept”- they would rather go with the title “universe could be 250 times bigger than what we can see.” For some reason, it is more shocking to say that the universe is 250 times rather than infinitely larger than expected. Somehow, infinity gets reduced to 0. How is this possible? Because infinity, as an endless repetition, is essentially boring. I’ve written about this before, but strictly speaking, humans cannot truly comprehend the infinite, and so they collapse into concepts that are seemingly opposite to it, such as nothingness. Something that is infinitely larger than something is now beyond human comparison, and therefore cannot be gawked at. What is funny is that this is even done by cosmologists.
Take this Quora answer by a mathematics professor, repeating the standard line that the number of electrons in the universe is 10^80 and therefore it is countable and finite:
If all the evidence points to an infinite universe, even though it is essentially not possible to prove otherwise, it will never be proclaimed as a fact. Why? There is still more to explore! Infinity violates the boundaries of science- it introduces the metaphysical into the mathematical. If the universe is infinite, what type of infinity is it? Countably infinite? Uncountably infinite?
These are questions that will probably never be answered, but my money is on uncountably infinite. Why? Because the “boundary” of what consider the universe isn’t actually a boundary at all. I’ve pointed out the narrow-mindedness of physicists before when it comes to theories of the universe and the most abstruse theories out there (string theory, holographic theory). There are only boundaries it seems when it comes to the human imagination (of some humans). Even I don’t believe these are insurmountable barriers to human knowledge. I do not believe, as Leonard Susskind claims, it is simply impossible to understand things like quantum physics directly or intuitively. The human brain is a finite organ in space and time, but it has the astounding ability to conceptually grasp things even beyond what is considered “normal life”.
The fundamental Buddhist insight- that what we see is not how reality truly is- is absolutely fundamentally correct. Everything we know about reality points to this, because there are simply things we cannot see- atoms, worlds far beyond our own. The structure of things, their nature, is not possible to grasp with the five senses alone- Plato and the great thinkers of the past knew that very well just from their experience- they knew there was something more to what we see. However, the Platonic vision of reality is also fundamentally limited. Concepts like nirvana or even “the universe” are also only ultimately constructs. Reality as it is is beyond at least average conceptual understanding. Where the real conceptual leap must occur is into the realm of what Buddhist philosophy calls “non-conceptual thought”, which to the rationalist mind is simply an error. Such a thing is not possible. However, if we were to gain some sort of insight into the nature of things like “uncountably infinite” we would in fact have to go beyond our normal concepts for things which operate in terms of metaphors which only apply to the here and now.
To conclude, when thinking of the idea of the uncountable, the mind encounters accepting a limit. It tries to convert the idea of uncountable to something more mundane, like “countable if given an infinite amount of time”. But this is not a correct definition of uncountable. Therefore, if we were to truly accept something of the order of “the universe is uncountably infinite” we would have to accept things like “a theory of everything is not possible”. And yet, science continues to grasp for this theory. And the question is obviously- why? Because the search for truth seems to be something inherent to humanity. Perhaps this particular strain of searching is historically contingent, but modern physics and science now desperately wants this TOE.
My theory is that the TOE stands ultimately for the purpose of science itself, its floating signifier, a signifier which is beyond the bounds of all the other signifiers. The TOE, if thought to be obtained, would not be in fact the TOE. Instead, there would be an illusory nesting egg effect- “TOEs” inside of TOEs. Ultimately, paradoxes will always plague science, as long as it continues to exist.