How do we know space is not infinite?

[juanrga]

How do we know space is not infinite?

In science we can't know beyond what is observed/measured. The observable universe has a finite radius. You only can speculate beyond that.

 

[Oldfart]

IF our universe is infinite, would that rule out the possibility that other universes exist?

 

[phinds]

IF our universe is infinite, would that rule out the possibility that other universes exist?

Since there is not the slightest knowledge HOW other universes might exist, the question doesn't have much meaning. My guess is it's irrelevant since our universe isn't thought to be expanding INTO anything, it's not like we're going to use up all the room.

 

[Oldfart]

... it's not like we're going to use up all the room.[/QUOTE]

Heh..., here I go again...

Where is this "room"?

 

[phinds]

... it's not like we're going to use up all the room.

Heh..., here I go again...

Where is this "room"?[/QUOTE]

It's the non-existant stuff "outside" our universe that we're not going to use up all of, thus crowding out other non-existant universes. That's my story and I'm sticking with it !

 

[Oldfart]

That's my story and I'm sticking with it !

Okay, thanks, phinds!

But please be careful, I assume you know that you can get your license pulled for talking like that...

 

[Justaman]

It is. There is no beginning, and no end, only transition. Same with time.

 

[Justaman]

IF our universe is infinite, would that rule out the possibility that other universes exist?

One universe, lots of space, infinite potential for infinite configurations beyond that which has become visible to us as of yet.

 

[phinds]

It is. There is no beginning, and no end, only transition. Same with time.

Personal theories are not allowed on this forum. You should read the rules. This is a physics forum, not a theology forum.

 

[maggiemaeu]

Well, it just seemed to me that if space was already infinite, it would be meaningless to consider that it was becoming infiniter. Anyway, thanks -- I read about Hilbert's Hotel, no joy. I evidently have a personel conceptual problem with infinity, possibly stemming from incorrectly thinking that if something increases, it increases from a defined point in space and time. and the amount of increase would be measured from that point.

assuming the definition of infinity in use here is immeasurably great, then it makes sense to imply that it has a defined starting point to measure from. however, the word is in my opinion and possibly in fact a paradox, so saying anything about measuring infinity or infinity getting bigger is just contradictory. that is not to say it's not argueable though.

 

[maggiemaeu]

Personal theories are not allowed on this forum. You should read the rules. This is a physics forum, not a theology forum.

not neccessarily a personal theory; could simply be a professional theory you obviously haven't heard of yet. that is one explanation of many that i have heard concerning infinity. don't mean to cause trouble :)

 

[phinds]

... the word is in my opinion and possibly in fact a paradox, so saying anything about measuring infinity or infinity getting bigger is just contradictory. QUOTE]

ANOTHER Personal theory and this one DEFINITELY contrary to the facts.

 

[Justaman]

Personal theories are not allowed on this forum. You should read the rules. This is a physics forum, not a theology forum.

Hi Phinds- my statement wasn't intended to be theological in any way- quite the contrary actually.

Quite simply, I don't think time ever began or will end, and that space continues for an infinite distance in all directions.

Considering infinite, how does time either start or end? With the freezing of a cesium atom? I don't think so, as the duration of it's condition is still real. Even beyond observable space (expanding at light speed) if no matter exists beyond some distance, wouldn't an object that moves into this space continue indefinitely until acted upon? How we currently measure time and space may become obsolete, but I don't think this suggests a beginning or end to either.

With infinite time comes infinite possiblities, so it seems unlikely to me that all matter sat in singularity eternally until 13B yrs ago.

Rather, I think (there I go again) the expansion/contraction cycle is a continuous and infinite process- the contraction cycle including material collisions of increasing frequency with decreased proximity, arriving at and passing a "central gravitational point" (thus entering expansion phase) at inconsistent intervals around the central (and dynamic) point.

This would then mean that expansion/contraction exists with or without a "big bang" event, and that all matter only occasionally (though repeatedly) forms an instantaneous singularity that, once again, "bangs".

Not even light could escape the gravitational pull at singularity, so the OU would be quite small. Would this mean that space-devoid of matter even 2 feet away- would be finite? I personally would not consider it so, making it infinite in all directions correct?

Assuming infinity of space and time, it seems likely that an infinite number of expansion/contraction/big bang cycles would be occurring at all times, of course located well beyond our OU, but part of a larger "universe".

As with cells in our body, it seems these universes must occasionally interact with/effect each other in some way, just as cells in our own body do.

Associated by proximity, would this then make our universe part of a finite "organism" which, on a universal scale taken to infinity, co-mingles with an infinite population of similar "organisms"? And so on, and so on...

I think so. But there I go again...

Sorry to go on so in responding.

 

[Constantin]

It's easy to imagine time as finite. Actually it's much harder to imagine anything as being infinite. How do you imagine an infinite thing ?
Your problem arises from not being able to imagine time having limits. These limits, edges of the time dimension, beginning and end of time.

But if you consider time being just another dimension, you might find that easier.

Imagine the normal space dimensions. The Observable Universe is finite.
It has a center, any observer being at the very center of his own Observable Universe. And it has an edge, the furthest away it is possible to see. That edge is moving away and the Universe is expanding, but it's still finite.

Same thing with time. It has a beginning, the Big Bang. And an edge, the "current moment". The "current moment" is continuously moving, same as the edge of the Observable Universe. So the time spent since the Big Bang keeps increasing, but it's still finite.
Also don't consider the future as part of the time dimension. The future doesn't exist, yet.

If you imagine this analogy between space and time dimensions, you'll find it easier to understand the concept of finite time or space.

 

[Justaman]

The Observable Universe is finite.
It has a center, any observer being at the very center of his own Observable Universe. And it has an edge, the furthest away it is possible to see. That edge is moving away and the Universe is expanding, but it's still finite.

Thanks, I well understand this, and how it serves to assert that the entire universe (consisting of everything beyond our OU) is indeed infinite. Since the OU that exists at the edge of my OU is twice as far away from me...and so on.

Same thing with time. It has a beginning, the Big Bang. And an edge, the "current moment". The "current moment" is continuously moving, same as the edge of the Observable Universe. So the time spent since the Big Bang keeps increasing, but it's still finite..

It's clear that a finite number of seconds have passed since the last big bang, but not that time did not exist/advance prior to it. So all matter in the universe existed in a single point and then simply exploded? How long would it have maintained this state? Of course, that duration would have been real and measurable.

 

[Constantin]

There's no proof there was anything before the Big Bang. So it's pure speculation.

Just use the concept "what you can't see does not exist". It simplifies things quite a lot and avoids speculation.

We can't see before the Big Bang, so nothing existed before that. We can't see beyond the edge of the Observable Universe, so nothing exists beyond that edge.

Can't get simpler than that.

 

[Constantin]

"So all matter in the universe existed in a single point and then simply exploded?"

Matter did not exist at the very beginning, just a huge amount of energy. That energy created the matter.

 

[Drakkith]

Quite simply, I don't think time ever began or will end, and that space continues for an infinite distance in all directions.

That's fine. Current models don't care whether the universe is actually infinite or whether it wraps back on itself or something.

With infinite time comes infinite possiblities, so it seems unlikely to me that all matter sat in singularity eternally until 13B yrs ago.

Nonsense. If something is impossible now, it is impossible always. The sun has zero chance of violating conservation of energy and suddenly losing all of it's mass and energy and turning into a bowl of soup. As for all matter sitting in a singularity until 13 billion years ago, I don't know of anything in the standard model that says it did. In fact the model simply stops making predictions past a certain point. There are several other theories that try to go beyond the standard one and predict what happened during and before the big bang but none of those are accepted yet.

Rather, I think (there I go again) the expansion/contraction cycle is a continuous and infinite process- the contraction cycle including material collisions of increasing frequency with decreased proximity, arriving at and passing a "central gravitational point" (thus entering expansion phase) at inconsistent intervals around the central (and dynamic) point.

Unfortunately our observations show that unless something changes this is not the case.

This would then mean that expansion/contraction exists with or without a "big bang" event, and that all matter only occasionally (though repeatedly) forms an instantaneous singularity that, once again, "bangs".

I don't know what you call sudden expansion of the universe from a possible singularity, but I believe it's called the Big Bang.

Not even light could escape the gravitational pull at singularity, so the OU would be quite small. Would this mean that space-devoid of matter even 2 feet away- would be finite? I personally would not consider it so, making it infinite in all directions correct?

Our knowledge of physics breaks down at the singularity point, so there's no way to answer your question.

Assuming infinity of space and time, it seems likely that an infinite number of expansion/contraction/big bang cycles would be occurring at all times, of course located well beyond our OU, but part of a larger "universe".

As with cells in our body, it seems these universes must occasionally interact with/effect each other in some way, just as cells in our own body do.

Associated by proximity, would this then make our universe part of a finite "organism" which, on a universal scale taken to infinity, co-mingles with an infinite population of similar "organisms"? And so on, and so on...

None of this even makes any sense. I recommend that you take some time and understand current models of the universe before posting anything like this nonsense again. And remember that PF isn't the place for personal beliefs or theories.

 

[Constantin]

A very good argument against the repeated "expansion/contraction/big bang cycles":

Evidence shows the Universe is expanding at an accelerated rate, so it will never contract again.

 

[Justaman]

A very good argument against the repeated "expansion/contraction/big bang cycles":

Evidence shows the Universe is expanding at an accelerated rate, so it will never contract again.

Begs the question: What's out there, pulling it? I mean this in a purely scientific way. But obviously a topic for a different board. Sorry for the intrusion...

Thanks all, very interesting (and at times entertaining) thoughts.

 

[Drakkith]

Begs the question: What's out there, pulling it? I mean this in a purely scientific way. But obviously a topic for a different board. Sorry for the intrusion...

Thanks all, very interesting (and at times entertaining) thoughts.

http://en.wikipedia.org/wiki/Cosmological_constant

 

[maggiemaeu]

... the word is in my opinion and possibly in fact a paradox, so saying anything about measuring infinity or infinity getting bigger is just contradictory. QUOTE]

ANOTHER Personal theory and this one DEFINITELY contrary to the facts.

sorry, didn't mean it as an opinion, just presenting a problem in the arguement. honestly, there are many definitions of the word that are contradictory. the fact being that infinity is an argueable word, you have to narrow it down a little more. how could this be contrary to the facts? it is a fact that the word has different meanings and which ones you use is your business, not mine. all I'm saying is that specifics are needed in discussing infinity to avoid confusion.

i do admit i should have been more careful about how i conveyed that.

 

[maggiemaeu]

A very good argument against the repeated "expansion/contraction/big bang cycles":

Evidence shows the Universe is expanding at an accelerated rate, so it will never contract again.

is this the theory that states there are multiple events similar to the big bang? sorry, I'm not sure:uhh:

 

[phinds]

sorry, didn't mean it as an opinion, just presenting a problem in the arguement. honestly, there are many definitions of the word that are contradictory. the fact being that infinity is an argueable word, you have to narrow it down a little more. how could this be contrary to the facts? it is a fact that the word has different meanings and which ones you use is your business, not mine. all I'm saying is that specifics are needed in discussing infinity to avoid confusion.

i do admit i should have been more careful about how i conveyed that.

There is nothing contradictory about infinity being able to get bigger. It can and does. This is a standard part of any reasonable definition of infinity and if you think otherwise, you might find it interesting to study up on the subject.

 

[Constantin]

Mathematically infinity can get bigger, smaller, and you can joggle with it in different ways.

But can you give any example in physics of something that was proven to be infinite ? Because I don't believe there is such an example.

 

[phinds]

Mathematically infinity can get bigger, smaller, and you can joggle with it in different ways.

But can you give any example in physics of something that was proven to be infinite ? Because I don't believe there is such an example.

I believe that most (but by NO means all) models have the universe as infinite AND haveing size added to it all the time but that IS the only thing I am aware of.

And I think that talking about infinity getting bigger or smaller is probably incorrect. You can add to it or take away from it, but that does not change the fact that it is just "infinity".

 

[khemist]

A simple way to think of infinity.

Consider all the real numbers -> 1, 2, 3, 4, etc...

One would certainly consider that an infinite set (give me any number, and I can get another number by simply adding 1). Now, take all the real even numbers -> 2, 4, 6, etc...

That is certainly an infinite set as well, but it has half the values as the original set!

 

[phinds]

A simple way to think of infinity.

Consider all the real numbers -> 1, 2, 3, 4, etc...

One would certainly consider that an infinite set (give me any number, and I can get another number by simply adding 1). Now, take all the real even numbers -> 2, 4, 6, etc...

That is certainly an infinite set as well, but it has half the values as the original set!

No, it's the same number. It SEEMS like half as much but that's that thing about infinity ... you can't treat it in normal mathematical operations as though it were like other numbers. Half of infinity is still infinity, as is twice infinity. Very UNintuitive.

 

[khemist]

No, it's the same number. It SEEMS like half as much but that's that thing about infinity ... you can't treat it in normal mathematical operations as though it were like other numbers. Half of infinity is still infinity, as is twice infinity. Very UNintuitive.

That is what I am saying... Although the even set has half the numbers, it is still infinity. Read what I wrote a bit more closely :)

 

[phinds]

That is what I am saying... Although the even set has half the numbers, it is still infinity. Read what I wrote a bit more closely :)

DOH ! misinterpretaion alert ! (by ME, I mean, not you)

 

[maggiemaeu]

There is nothing contradictory about infinity being able to get bigger. It can and does. This is a standard part of any reasonable definition of infinity and if you think otherwise, you might find it interesting to study up on the subject.

i grudgingly admit you're right here. anything you recommend reading?

 

[phinds]

i grudgingly admit you're right here. anything you recommend reading?

I've been away from formal study to long to have any idea what's a good text these days. Others here can undoubtedly give you some good advice. If you don't get anything in this thread, start another specifically asking for advice on math books discussing infinities (there is a heiarchy of them, named "aleph null" (the "normal" infinity) "aleph 1" and so forth.

 

[zeffur7]

A simple way to think of infinity.

Consider all the real numbers -> 1, 2, 3, 4, etc...

One would certainly consider that an infinite set (give me any number, and I can get another number by simply adding 1). Now, take all the real even numbers -> 2, 4, 6, etc...

That is certainly an infinite set as well, but it has half the values as the original set!

Another, and perhaps easier way to consider infinity is simply the following:

1. Infinity = the state or quality of being infinite.
2. Infinite = not finite, boundless, unlimited, indefinite, immeasurably/exceedlingly great.

e.g.: the dimensions of the universe/multiverse.

 

[phinds]

1. Infinity = the state or quality of being infinite.

a meaningless tautology

2. Infinite = not finite, boundless, unlimited, indefinite, immeasurably/exceedlingly great.

uses words where you should use math as zeffer7 did

e.g.: the dimensions of the universe/multiverse.

purely speculative on your part --- unproven and at present unprovable

 

[Deuterium2H]

People following this thread might also be interested in another thread entitled "If the Universe is infinite, does that mean everything must exist somewhere".

Here is a link:
https://www.physicsforums.com/showpost.php?p=3062488&postcount=101

Using Set Theory, I argue that this is not necessarily the case. Some interesting ideas discussed in that thread.

I might add that this issue is stumbled over by a great number of leading physicists. Most recently, Brian Greene in his current PBS/NOVA show "The Fabric of the Cosmos". He makes the same logical error (IMHO) that is common in the infinite, "multi-verse" hypothesis...claiming that an exact duplicate of himself exists either in our infinite Universe, or in any of an infinite multiverses. The previously cited thread/link explains the pitfalls in this reasoning.