Infinite Universe = Impossible

[rtxoff]

Nothing contains the universe. It's not an embedded manifold. In fact, GR pretty much states that our universe cannot be embedded.

Maybe not but what is space then? And what is beyond the universe? Empty space? Or doesn't anything exist beyond our universe not even empty space?

You see my dilemma here?

Your response is not satisfying.

In this matter nobody can give a proper answer because we can only assume things here and GR only gives answers as far as our knowledge of the universe reaches but not beyond.

[K^2]

Maybe not but what is space then? And what is beyond the universe? Empty space? Or doesn't anything exist beyond our universe not even empty space?

There isn't a "beyond". There is a set of locations and a metric. Everything else is just your brain trying to make sense of it based on everyday experience. There's no reason to expect it to be successful in that.

[EdFred]

There isn't a "beyond".

There's no proof either way, so an absolute cannot be stated.

[YNM]

hehe, we all are now hitting the wall it seems...

"what lies beyond the universe ?"

"why did Big Bang happened ?"

"what's force and it's cause ? can it be unified ?"

"is our universe the only one ?"

"why there don't exist monopoles ?"

"what's dark energy ? how much is it ?"

"what's dark matter ? can it be "particle"-d ? can neutrino take place ?"

"is our Universe flat, open or closed ? how will it end ?"

You can't (yeah, at all I guess) solve this purely from theories; you must do observations. Even some problems can't be solved by observations... what one can do, for sure, is to predict, then wait.

Regarding what lies outside the Universe we live in : could be branes, could be what one takes to believe.

[78stonewobble]

Uhm... It might just be me, but it seems that, as far as I understand it, people are mixing up a few things.

Our universe may or may not be infinite in size. At most we can put lower limits to it's size from what we can observe.

The chance for me to spontaniously change into a whale with a pop, in "our universe", is so small, that for all intents and purposes, it won't ever happen, due to the laws of nature being what they are and those laws of nature seem to be the same as far as we can see.

So for me to change into a whale with a pop, in this universe, I'd have to move to an area where the laws of nature, would make that likely.

There is a very real chance, that the laws of nature are the same all over this universe, even if it's "infinite" in size, it will just be an infinite amount of the same.

However, there might also be other universes, indeed an infinite amount of them, where the laws of nature are different and human whale transmutation are commonplace.

[Technical Ben]

Nothing contains the universe. It's not an embedded manifold. In fact, GR pretty much states that our universe cannot be embedded.

That is a new one to me. Care to elaborate or give some examples? What do we mean by "embedded manifold"? That there can be no other layers down from GR or that our universe is not "simulated" so to speak, or something else entirely? It will be really interesting to see what sort of data we have on how space is made up.

Edited January 19, 2015 by Technical Ben

[worir4]

Could it be that there are bodies out there that are just further away so that the light from them would not have reached us yet. Or maybe we are an experiment in some 11 year old aliens science class where they make universes...

[K^2]

That is a new one to me. Care to elaborate or give some examples? What do we mean by "embedded manifold"? That there can be no other layers down from GR or that our universe is not "simulated" so to speak, or something else entirely? It will be really interesting to see what sort of data we have on how space is made up.

Simple example. Surface of a sphere is a 2d manifold that can be embedded in 3d space. Locally, it behaves like a 2d surface, but if you want to picture it as a complete shape in flat space, you need at least one extra dimension.

GR space-time is a 4d manifold. Some special cases can be embedded. You might have seen a picture of a funnel that represents curvature of space around a black hole. Of course, these representations are somewhat limited, since it is hard for us to picture more than 3 dimensions at the same time. But they exist, nonetheless.

Well, an interesting result in GR is that a general solution to Einstein's Field Equations cannot be embedded. In other words, for any finite number of dimensions, there exists a mass arrangement that results in a space-time shape that cannot fit into that number of dimensions. Therefore, our space-time is not embedded. If it was, there would be significant and measureable differences in how gravity works.

There's no proof either way, so an absolute cannot be stated.

Sort of can. As mentioned above, ebedding is not an option. Some flavors of String Theory work with a bulk, but they also make predictions that do not pan out based on it. So bulk seems unlikely. Locally, topology is fixed, so there cannot be a connection to an outside of any sort. That leaves edges, but we observe a very uniform universe. So unless we are dead center of a huge, much larger than observable, but still finite universe, it does not look good for edges either. If you have some other definition of outside, please, bring it forward. As it is, I can claim lack of outside as a scientific fact. If you need a greater absolute, then yes, I cannot help you, being a mere mortal and all. But you'd have better luck looking for unicorns than an "outside" of our universe.

Edited January 19, 2015 by K^2

[rtxoff]

But you'd have better luck looking for unicorns than an "outside" of our universe.

Well that last sentence was not necessary. It is not an valid scientific argument. It is exactly that sort of things that makes science people unpopular.

Also IMO it is somehow vague to present the universe like this as an scientific fact considering that this fact bases almost entirely on a mathematical solution.

We lack the capability to observe the complete universe and as long as this incapability persists only one thing we can be sure of, we don't know exactly what's out there.

[K^2]

There is no "out there". So asking what's there is pointless. That's the hole point. The boundary or direction in which you think something else might be does not exist. It's not a feature of the universe. So what's out? Where is it? It's not just a matter of us not being to probe beyond our universe. That's one thing. But you keep insisting on something being beyond... what? Point me to some line that you have to cross to be outside. Or direction in which you need to go to get there. We have excluded all of these. What you see is what you get. It's that simple. From perspective of mathematics and science. Again, this isn't a limitation of science. It's science specifically telling us that what you're looking for doesn't exist. Which is far more than I can say about unicorns. I'm not being facetious on that matter. Unicorns are a real possibility in comparison.

[YNM]

Well that last sentence was not necessary. It is not an valid scientific argument. It is exactly that sort of things that makes science people unpopular.

Also IMO it is somehow vague to present the universe like this as an scientific fact considering that this fact bases almost entirely on a mathematical solution.

We lack the capability to observe the complete universe and as long as this incapability persists only one thing we can be sure of, we don't know exactly what's out there.

Not seriously mathematical, anyway...

But think this way : you're asking for what's containing the container that contains everything already. While in mathematics it's an easy way to found something outside something, real world doesn't work this way - you must observe. Science is about observing and concluding, not calculating and simply give thoughts.

[AngelLestat]

That is by definition, if we call something "universe" as all the things that we can see and experience, then there is no point to think what is beyond that.. because is the universe.

But if you want to answer the questions about things that are not contain in this universe, and how their may interact with our universe, then this may be the only way to solve some problems as "what mechanism created the universe", "why their are zones in the universe that defy gravity", "what happens in the edges; where our theories break?", "what about the extra dimensions which string theory predict?", "why gravity is so weak?", etc.

So inside the universe from this perspective using the physsics that we know that may have problems in the edges, we can said with a 99.6% of certain that the universe is infinite.

But from other theory perspective it will looks finite.

And I stand in what I said at the begining. Infinite are just weak points in our theories and understanding.

Edited January 20, 2015 by AngelLestat

[EdFred]

Absence of evidence is not evidence of absence.

Just because we haven't seen beyond our universe, does not mean it's not there.

You cannot make a absolute statement either way. You can offer up conjecture, or opinion, but you cannot state it as fact.

[YNM]

That is by definition, if we call something "universe" as all the things that we can see and experience, then there is no point to think what is beyond that.. because is the universe.

But if you want to answer the questions about things that are not contain in this universe, and how their may interact with our universe, then this may be the only way to solve some problems as "what mechanism created the universe", "why their are zones in the universe that defy gravity", "what happens in the edges; where our theories break?", "what about the extra dimensions which string theory predict?", "why gravity is so weak?", etc.

So inside the universe from this perspective using the physsics that we know that may have problems in the edges, we can said with a 99.6% of certain that the universe is infinite.

But from other theory perspective it will looks finite.

And I stand in what I said at the begining. Infinite are just weak points in our theories and understanding.

Absence of evidence is not evidence of absence.

Just because we haven't seen beyond our universe, does not mean it's not there.

You cannot make a absolute statement either way. You can offer up conjecture, or opinion, but you cannot state it as fact.

My emphasize (from first time, actually) is that you need to observe. Like, say, is our spacetime just a "hologram" ? Are there other imprints of Bigbang in the Universe, more than just the CMB (uh, this thing) ? That's the kind of things we need; a theory is of course needed at first, but it's only use is to be proved by observations.

[EdFred]

My emphasize (from first time, actually) is that you need to observe. Like, say, is our spacetime just a "hologram" ? Are there other imprints of Bigbang in the Universe, more than just the CMB (uh, this thing) ? That's the kind of things we need; a theory is of course needed at first, but it's only use is to be proved by observations.

If I never leave my house does that mean nowhere else exists?

[shynung]

If I never leave my house does that mean nowhere else exists?

One could make that sort of assumption if he never looked out the window. Or if the house had no windows at all. From his perspective, there's no reason to believe that there exists other places, or what they looked like.

[AngelLestat]

That's the kind of things we need; a theory is of course needed at first, but it's only use is to be proved by observations.

how weak is gravity, dark matter, or other phenomenoms in particle physsicss "may" to be observations of things that are not contain in our universe.

For example there are ways to prove in practice some string theory predictions.

But if you never look outside or you just said "there is nothing out there", not multiverse, bulk or branes, etc. then the physsics would never go forward.

[ZetaX]

Non-uniform structure is a requirement for infinite universe, by the way. Otherwise, sky would be infinitely bright.

This is surely true if the universe is of infinite age or light has infinite speed, but I don't see how that argument should work when considering relativity. It surely fails if we just allow the universe into existence "as is", but maybe there is an argument coming from general relativity that I am missing.

how weak is gravity, dark matter, or other phenomenoms in particle physsicss "may" to be observations of things that are not contain in our universe.

With all the usual definitions of universe I know and/or find in wikipedia, your statement is simply "what if we observe things that cannot be observed/that don't exist?", which is meaningless.

[EdFred]

One could make that sort of assumption if he never looked out the window. Or if the house had no windows at all. From his perspective, there's no reason to believe that there exists other places, or what they looked like.

Exactly, and just because that person says, "There is nothing that exists outside these walls" does not make it fact.

[Sirrobert]

A big amount of the confusions I see in this thread seems to be based on people not understanding what the Big Bang actually IS.

It is FALSE that, at the time of the Big Bang, the Universe was compressed into a single point. The Universe was already infinitly big at the time of the Big Bang.

explains it very wel. Imagine space as an infinite graph sheet (1 by 1 cm squares). Take a square, and zoom out until that square is visible only as a dot. That's the Big Bang (and time going forward is zooming back in)

[EdFred]

Interesting video. Still conjecture, and not fact.

[worir4]

Interesting video. Still conjecture, and not fact.

We will probably never be able to get to fact.

[Crimson Sunrise]

We will probably never be able to get to fact.

We have 9 billion years to do that in Earth. After that, the Sun will become a Red Giant and probably swallow the planet.

Not much time left.

[EdFred]

We will probably never be able to get to fact.

I know, but I still have an issue with anything being stated as fact when it's most likely just 'the best guess we have.'

[Sirrobert]

Interesting video. Still conjecture, and not fact.

Sure. But this is the actual theory, instead of the foolishness people throw around about space having once been a single point