Finite Universe

[Jovus]

Aside: looks like I was wrong and we do live in a Hilbert space.

[Majorjim!]

We can observe if the universe continues existing forever. We can also observe if space goes on forever by flying straight or just waiting for light from further away. Neither of them completely proves that something is truly infinite (it might just be larger/older than we know for sure). But that kind "does not prove" is the same as in "we cannot know for sure of gravity really exist, maybe it was all just a huge coinceidence so far". Science cannot make absolute statements; but it can say if something is very probable.

Why would you assume the universe is finite in time and infinite in space? Infinities do not exist in nature. They are a byproduct of incorrect mathematics.

The Universe is much larger than we can observe as the expansion of space is occurring faster than the speed of light. So we can only see the light that has had time to travel to us.

Even if the universe continued to expand forever it would not be infinite. Infinity implies no beginning as well as no end. And as we all know the universe had a beginning.

- - - Updated - - -

Aside: looks like I was wrong and we do live in a Hilbert space.

"All we can truly conclude is that the Universe is much larger than the volume we can directly observe."

Saying the universe is infinite simply means we cannot calculate its size. Saying the universe is finite in time but infinite in space is contradicting yourself.

Or not taking into account the true meaning of infinity. As space and time are interwoven into 'spacetime'.

I suggest more reading on the philosophical implications and restrictions of the human language.

Edited March 30, 2015 by Majorjim

[tseitsei]

Why would you assume the universe is finite in time and infinite in space? Infinities do not exist in nature. They are a byproduct of incorrect mathematics.

We cannot know for sure if infinities exist in nature. Besides Pi "exists" (it is the ratio between a circles diameter and circumference. Quite natural definition if you ask me...) and it is infinite.

Although I have to say that I HATE the concept of infinity in mathematics as well and think it doesn't make much sense but mathematics debate isn't really the point here. This is more like physics/philosophy...

"All we can truly conclude is that the Universe is much larger than the volume we can directly observe."

From the very same article:

" If the density of the universe exactly equals the critical density, then the geometry of the universe is flat like a sheet of paper, and infinite in extent."

P.S. I suggest being less arrogant and rude and already decided what you want to believe. That doesn't lead to a good conversation...

[Jovus]

"All we can truly conclude is that the Universe is much larger than the volume we can directly observe."

Saying the universe is infinite simply means we cannot calculate its size. Saying the universe is finite in time but infinite in space is contradicting yourself.

Or not taking into account the true meaning of infinity. As space and time are interwoven into 'spacetime'.

You clearly did not understand what I was saying. A Hilbert Space is infinitely extensible, though not necessarily unbounded. (You can set boundaries arbitrarily.) However, neither I nor the article are talking about an infinity of matter in the Universe, only an infinity of space, which is essentially a mathematical concept that is physically verifiable but has nothing to do with bodies. (It has to do with the motion of bodies, of course...)

I suggest more reading on the philosophical implications and restrictions of the human language.

I suggest reading Dedekind's Essays on the Theory of Numbers, though only after you've given Aristotle's Physics Book Gamma a good long go. (Descartes' Geometry is also likely to be helpful, and all of this requires a good grounding in Euclid, at least Book 1, and the Conics of Appolonius.)

[YNM]

Saying the universe is infinite simply means we cannot calculate its size. Saying the universe is finite in time but infinite in space is contradicting yourself. Or not taking into account the true meaning of infinity. As space and time are interwoven into 'spacetime'.

An infinity... for space, geometrically. While the concept of spacetime combines both space and time into a four-dimensional "space" (or four component metric - four dimensional "space" is simply would always be unimaginable and intangible for us three-dimensional beings), time is included because information travels at a finite speed (light speed fastest). Time on it's own isn't tied to space at all - hence why in metric that includes time, it's tied with the speed of light, which means, also movement in space and not just in time itself. Time on it's own doesn't have any proper geometry, being one-dimensional and only advances forward.

Maybe someone more expert can tell me where I'm wrong...

Edited March 30, 2015 by YNM

[Jovus]

Maybe someone more expert can tell me where I'm wrong...

TIme on its own doesn't exist. Time is the measurement of motion. The geometry of spacetime (which is space with the concern of the measurement of motion) is hyperbolic.

Restating in a different way:

Time itself doesn't 'advance' and it doesn't have any 'dimensions'. It is not even a phenomenon, contrary to Kant. However, time is an axis in space-time, and the angle between the axis of time and the axes of space is governed by a hyperbola. (The hyperbola changes its equation depending on the speed of the object moving through spacetime.)

[ZetaX]

Why would you assume the universe is finite in time and infinite in space?

I am not assuming anything. I was just explaining that even if your argument is correct, then it would not exclude such a universe. Thus you have not proven what you claimed: that both are finite. Feel free to change your claim or your argument, but currently they are not fitting.

Infinities do not exist in nature.

Unless you specify what an "infinity" is exactly I can only answer with: not even wrong. I can find many interpretations, some of them making it correct, some incorrect and some nonsensical. So what do you mean by that claim¿

They are a byproduct of incorrect mathematics.

The mathematics of infinite (flat or not) spacetimes is quite correct. If you think otherwise, you would contradict a hundred years of theoretical physics; you could still point an actual error if you want.

Even if the universe continued to expand forever it would not be infinite. Infinity implies no beginning as well as no end.

No it does not. Show me an accepted definition of that kind. See almost any source for the usual definiton (say Wikipedia).

And as we all know the universe had a beginning.

As I said above this is not relevant. There are also hypotheses that are not putting the Big Bang as the beggining of time.

Saying the universe is infinite simply means we cannot calculate its size.

If this is your definition of infinite, then it is very wrong. We cannot calculate many things, but that does not always have to do with infinities. And conversely, there are infinite things we can calculate (pi was mentioned already). Infinity is a statement about size and size alone.

Saying the universe is finite in time but infinite in space is contradicting yourself.

You are claiming this without evidence.

I suggest more reading on the philosophical implications and restrictions of the human language.

There are many, but those kinds of infinities are not among them.