Is the universe infinite?

[DrStrangelove]

Hmmm... Good question. After avidly watching "The Universe" on the History Channel for sometime now, I think it's safe to say that the 'local' universe is, in fact, finite & very likely flat to some degree--yes, flat (mind you, this is only what I've learned by watching the programme--it is not plucked out of thin air). However, beyond our 'local' universe, the entire cosmos, per se (& beyond), I'd like to assume hopefully correctly, that it is infinite, say, for instance, once all matter (gasses/chemicals, asteroids, moons, planets, stars, galaxies, clusters, etc., etc...) disperses to where there really is nothing left but black or blank space, being made up of what is known to astronomers as "dark matter." This is the space between moons, planets, stars, galaxies, clusters, etc., which appear to have nothing in it...just black space. "Most of the stuff in clusters of galaxies is invisible and, since these are the largest structures in the Universe held together by gravity, scientists then conclude that most of the matter in the entire Universe is invisible. This invisible stuff is called 'dark matter'." (found here : Dark Matter - Introduction) & a lot of interesting stuff about our universe can be found w/in this site, "NASA's Imagine the Universe!" (Imagine The Universe! Home Page). Scientists' studies are also infinite (ha-ha), & they continue to contemplate & deliberate on exactly what this "dark matter" really is or what it's made up of (or NOT made up of). But so far, it would seem that this is the closest yet they've found to, at least, describing it. So, yes, I would agree that questions may never be fully answered w/ any certainty, & I would subscribe to the possible fact that the Bigger Universe beyond our tiny universe is at least forever if not infinite.

Originally Posted by infamous

These questions may never be answered with any absolute precision but the standard model views our local universe as a finite sphere. Nevertheless, our local universe may be contained within a larger megauniverse which may be infinite in nature. Hopefully this definition does not confuse things for you.

[HydrogenBond]

The size of the universe depends on what we call the universe. If we are talking about the matter/energy or substance of the universe, that substance appears to occupy finite size or else we could not be able to set an age to the universe. If we take the largest number we have, to approximate infinite size, and divide by the age of the universe, we would get a speed much greater than C, which is not possible. The age is describing something finite.

If we were living in a C reference, an infinite distance universe would be possible because it would appear to be contracted in a point, that would take an instant to traverse at the speed of light. In that reference, an infinite universe would be possible since it does not violate C. A finite universe would then have to be smaller than a point/instant. If we were on this forum in the C reference, the debate would be, could there be a universe that exists that is smaller than the limiting point instant? The answer is yes, but it would be hard to prove at C.

To be able to prove this theoretically universe, that is smaller than a point (C reference) we will need to slow the C reference to below C (expand space-time) so the point appears to expand and break apart into detail. It would look sort of like a point singularity, expanding as we zoom to maximum space-time expansion. Now we can see the finite universe that had been contained in the point within the C reference. Since only the microscope magnified space-time reference, and we are still at C, we know infinite is still there as well as places smaller than that point called infinite.

Conversely, if we start in our current finite reference and telescope our reference by contracting space-time (moving toward C reference) the outer boundary of the visible universe would get closer. But since matter can't go all the way to C, we would stop at a finite line of sight, with infinite always just out of reach. Matter can not extend to infinity precluding an infinite universe that contains matter all the way to infinity.

[Michael Mooney]

Of course the answer depends on the definition of "universe."
Mine is: "All there is both within and beyond or cosmic event horizon."
But "all things that exist" is a different set than the "space" in which all things exist.
Space must be infinite. Why? Because the alternative, an "end of space" is a no-brainer absurdity. Think about it. What boundary could possibly be an "end of space" in the universal sense? (Not speaking of geometric shapes defined by their "walls" etc.)
So if you do posit such a wall/boundary to space, what is it made of and what lies on the other side? See what I mean? An ill conceived concept!

Michael

[Boerseun]

Originally Posted by Michael Mooney

Think about it. What boundary could possibly be an "end of space" in the universal sense? (Not speaking of geometric shapes defined by their "walls" etc.)
So if you do posit such a wall/boundary to space, what is it made of and what lies on the other side? See what I mean? An ill conceived concept!

Michael, there is no "physical boundary" to space in the 3D universe you imagine. There is a boundary, however, but that boundary exist in time, not in space. If you look at the furthest reaches of space, you'll see that boundary at a distance of around fifteen billion light years. And even if you were to magically be instantly transported to that boundary, the universe will look exactly as it does from Earth in all directions, with a boundary of fifteen billion light years from that point. If you look at where the Earth is supposed to be, the Earth's location will appear to you as the Edge of the Universe, with only CMBR emanating from that spot. A little closer, and you will see pulsars and all kinds of weird stuff existing in the early universe coming from close to Earth. This is clearly not the case. And it is not the case, because the universe is an unfolding hypersphere, not a flat 3D structure with a physical boundary.

Yes, the universe has a boundary. But that boundary exist in time, not in space. And there's no getting away from that. However hard you try, however fast your spaceship travels, that boundary will always be fifteen billion light years away from you, and it will recede from you at the speed of precisely one light-year per year. Imagining what that boundary will look like is fruitless, because from that very same spot, the universe will look the same as it does from here, or any other spot in the universe you'd care to sample. There's an easy way to get there, though. You don't even have to move an inch. You can sit right there in your chair, behind your computer. All you have to do is to invent time-travel, and travel 15 billion years back in time. Because that border you see, that fifteen-billion light-year distant edge from whence you see the CMBR, was actually each and every spot in the universe, simultaneously.

I'm sorry if you don't get it, though. I admit that it is a bit of a mind-bender. But its the only explanation currently fitting the data.

[modest]

I agree with Boerseun. We can only see so far. It rather reminds a person of the ancient world, perhaps pre-Hellenistic Greece. They must have wondered if the land under their feet went on forever or if it had an end. They could only see see so far and they must have used philosophy saying something similar to Michael's earlier comment:

Originally Posted by Michael Mooney

Space must be infinite. Why? Because the alternative, an "end of space" is a no-brainer absurdity.

They would say:

"The land must be infinite because the alternative, an "end of the land" is an absurdity"

And, it is kind of absurd. If the land ended then all the water of the oceans would drain off the edge. Certainly ancient philosophers could have convinced themselves that the amount of land is infinite if it has no boundary, and the very idea of an actual physical boundary seems quite philosophically displeasing.

By the time of Pythagoras they figured out a 3rd possibility: that there is only a finite amount of land, yet there is no boundary. In 330 BC Aristotle provided evidence that, indeed, there is only so much land under a person's feet, yet that person could walk with those feet for an eternity without falling off the philosophically displeasing edge.

So, it is, I guess, a little surprising that many years later Kant gives his Antinomy of space where unbound is assumed to be infinite. As is explained in The Ontology and Cosmology of Non-Euclidean Geometry, Einstein's general relativity provides an answer to Kant's Antinomy in the same way that Pythagoras did with the earth. Both infinite without boundary, and finite without boundary are possible.

Originally Posted by NASA -- WMAP

Given the assumption that the matter in the universe is homogeneous and isotropic (The Cosmological Principle) it can be shown that the corresponding distortion of space-time (due to the gravitational effects of this matter) can only have one of three forms,



as shown schematically in the picture at left. It can be "positively" curved like the surface of a ball and finite in extent; it can be "negatively" curved like a saddle and infinite in extent; or it can be "flat" and infinite in extent - our "ordinary" conception of space. A key limitation of the picture shown here is that we can only portray the curvature of a 2-dimensional plane of an actual 3-dimensional space! Note that in a closed universe you could start a journey off in one direction and, if allowed enough time, ultimately return to your starting point; in an infinite universe, you would never return.

Before we discuss which of these three pictures describe our universe (if any) we must make a few disclaimers:

• Because the universe has a finite age (~13.7 billion years) we can only see a finite distance out into space: ~13.7 billion light years. This is our so-called horizon. The Big Bang Model does not attempt to describe that region of space significantly beyond our horizon - space-time could well be quite different out there.

WMAP Big Bang Concepts

~modest

[Michael Mooney]

I, as always, challenge the ubiquitous assumption (since Einstein/Minkowski invented "spacetime" as something with shape) that space has shape.
Obviously "things existing in space" have shape. But no matter how many times the various "shapes of space" are asserted and illustrated graphically, as above...
If space is emptiness, the lack of "things" in which things exist, then there is no boundary, shape, or any properties whatsoever attributable to that no-thing-ness, emptiness, simple volume... and it must be infinite, as logically presented in my last post.

You may argue the premise (the "if"), but if it turns out to be true, the conclusion ("then") must follow.
And again, please consider the ontology of "time" from the perspective of "presentism" (the formal philosophy which best expresses my perspective) before you assume the ontological existence of time as a mandated given or fact.

Consider also why it (time, space and spacetime) would cease to exist if matter disappeared, as Einstein said. "It's" ontological status is obviously dubious if it does not exist independently of matter.

Michael

[lemit]

Originally Posted by Michael Mooney

I, as always, challenge the ubiquitous assumption (since Einstein/Minkowski invented "spacetime" as something with shape) that space has shape.
Obviously "things existing in space" have shape. But no matter how many times the various "shapes of space" are asserted and illustrated graphically, as above...
If space is emptiness, the lack of "things" in which things exist, then there is no boundary, shape, or any properties whatsoever attributable to that no-thing-ness, emptiness, simple volume... and it must be infinite, as logically presented in my last post.

You may argue the premise

Thanks. I think I will.

What if space is a state of nature we don't fully understand because we have so much trouble measuring it? I hope somebody can pick that up and run with it, although picking up something like space might be a little difficult.

--lemit

[Michael Mooney]

Originally Posted by lemit

Thanks. I think I will.

What if space is a state of nature we don't fully understand because we have so much trouble measuring it? I hope somebody can pick that up and run with it, although picking up something like space might be a little difficult.

--lemit

Yup. If it ain't nutin' but empty volume (without end) what's to "pick up?"
So, anyway lemit, with what do you disagree in my presentation of "space as emptiness, the lack of 'things' in which things exist?"... no-thing-ness... simple volume...?"

How exactly do you disagree (if you do) with my statement that
"...all things that exist" is a different set than the "space" in which all things exist?"

Maybe there is another big misunderstanding here between the concept of "stuff" distributed through space in a manner described by the often repeated various graphics shared again above by Modest... and "space itself" (as if it were an entity of some kind) having those shapes.
What say you?
Michael

[lemit]

Some friends of mine are working on a theory that, oversimplified, says "We can't understand space because we can't understand space."

Slightly less oversimplified, the nascent theory, as I understand it, is that space might just be a form of matter we haven't figured out yet, and that the premises all of us use might be wrong, since they don't seem to be giving us very good results. They become defenses of themselves in circular logic that can start arguments but can't end them.

We certainly haven't done very well in figuring out dark matter. But at least there we seem to know there's something wrong with our thinking, something we're missing.

I probably shouldn't suggest that here, since if people start agreeing with it, they might stop saying they know what space is, and Hypography would go out of business. But I kind of doubt that's going to happen.

I personally like the as yet unnamed theory because it is humble. It doesn't make claims it can't support, because it avoids making many claims at all. Maybe it could be called the No-Name Theory, or the No-Theory Theory, since it suggests we need to look for a new premise.

I have a feeling I've misrepresented their theory. I hope I haven't embarrassed them so thoroughly that they will now avoid associating themselves with the theory or with me. We'll see.

--lemit

[plumber]

Originally Posted by lemit

Some friends of mine are working on a theory that, oversimplified, says "We can't understand space because we can't understand space."

Slightly less oversimplified, the nascent theory, as I understand it, is that space might just be a form of matter we haven't figured out yet, and that the premises all of us use might be wrong, since they don't seem to be giving us very good results. They become defenses of themselves in circular logic that can start arguments but can't end them.

We certainly haven't done very well in figuring out dark matter. But at least there we seem to know there's something wrong with our thinking, something we're missing.

I probably shouldn't suggest that here, since if people start agreeing with it, they might stop saying they know what space is, and Hypography would go out of business. But I kind of doubt that's going to happen.

I personally like the as yet unnamed theory because it is humble. It doesn't make claims it can't support, because it avoids making many claims at all. Maybe it could be called the No-Name Theory, or the No-Theory Theory, since it suggests we need to look for a new premise.

I have a feeling I've misrepresented their theory. I hope I haven't embarrassed them so thoroughly that they will now avoid associating themselves with the theory or with me. We'll see.

--lemit

Right on dude, stir that pot! We are smart...but not that smart. A glance a little closer to home bears this out. Thank you, Plumber