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Comment by podgaj | Hacker News Reader

> Cosmology is not a done science.

Cosmology will never be a done science. The universe is infinite but the human mind is finite.

So is the set of all positive integers, but there is no unknown number in there, even though we haven’t seen them all.

There are plenty of unknown numbers :) For example, the number that is 1 if the Goldbach Conjecture is true, and 0 if it is false.

(BTW, if you want to know the difference between constructive and nonconstructive mathematics, it's that constructive mathematics doesn't let you say "well, it's definitely 0 or 1" because it leaves open the possibility that there's no proof of either termination or nontermination in the current theory... which is basically the philosophical distinction under discussion).

There is though, what’s the prime number after 314159265378979323846264338327950288419716939937510582090494459?

It's ....58209_7_494459... I checked against my memorized pi expansion. Oddly enough yours and mine stop at the same place!

You only need a hundred digits to know the circumference of the universe within the accuracy of the diameter of hydrogen!

In the book "When Einstein Walked with Gödel" by Jim Holt, It seems like that assumption is not as clear as it seems. I am not able to articulate it well enough and I don't have the book at hand.

If my recall is accurate then there is a bit of a question if there exists a "final number".

> The universe is infinite

Well, an open question in cosmology is whether the universe is actually infinite or not...

Strictly that's a question about philosophy, not cosmology. Cosmology just says the universe is unbounded and leaves it at that. In fact "The Universe", meaning all the matter or energy which we will ever even theoretically be able to obvserve, is definitely finite. The distance to the point of infinite redshift (where we're looking at the big bang, essentially) is finite. It doesn't make sense to talk about anything "farther" out.

Is that true? (Honest question) Whatever the “thing” was that exploded at the big bang (which I read once was the size of a grapefruit for what it’s worth) - could there not have been other similar “things”? And what about where that “thing” came from? I’ve read theories of the universe expanding, but then eventually falling back onto itself to recreate another “thing” that will explode again. Anyway, it feels like there might indeed be more.

A way that I heard this described, is that what we recognize as the observable universe right now was the size of a grapefruit at the beginning of the big bang. The stuff that expanded due to whatever the big bang actually did, that stuff could have been just the size of a grapefruit and nothing more, or itself infinite. But the part we can access given speed of light restrictions was the part that was the size of a grapefruit. There might actually be a lot more stuff out there ... we can just never get to it.

due to the isotropic principle we assume that the universe is infinite (because our vantage point is random, and since we don't see any orientation at the edge of the observable universe)

I picture the big bang as a bunch of heavy "black holes" approaching eachother discharging something that looks like lightening between them that grows more intense as they all pulled closer together. Eventually fusing into a persistent electromagnetic "explosion." Like a really bad welding accident.

> Cosmology just says the universe is unbounded and leaves it at that

I don't think that's right. The shape and topology of the universe is an open question in cosmology, and cosmologists haven't just "left it at that".

Let me be stricter: models consistent with general relativity don't discuss the idea of a universe being "infinite", and just in general theories in science don't predict the unobservable. Open universe topologies are unbounded. They aren't "infinite".

> The universe is infinite ...

Yet we can describe most of what we observe with a tiny set of equations. What's more meaningful to science is that the universe is not bound to our models and assumptions. Even the assumption that the universe is ordered and so will remain ordered is not guaranteed. It's just a convenient and historically effective assumption that appears to be justified as far back as we can look. No science, therefore, is a done science.

> ...the human mind is finite.

A whiteboard is finite. It is bound in spacetime and no matter how small the writing, there is an upper limit to the amount of information that can be displayed on it at any one time. No matter how quick the erasing, there is an upper limit amount of information that can be displayed within the lifetime of the board.

Despite this, it can have an uncountably infinite variety of information impressed upon it.

Is there such thing as any kind of done science? Sounds like an oxymoron to me.

Cosmology is not the study of the universe but only its large scale structure.

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