Is the Universe Finite or Infinite?

In summary: However, the night sky is dark. This suggests that the universe is not infinite.In summary, the argument between me and my physics & maths friends was inconclusive. There is no consensus on whether or not the universe is finite in size.
  • #1
QuantumJG
32
0
Ok so me and a few of my physics (& Maths) friends were arguing this.

I argued that it must be finite in size, since the universe contains a finite amount of matter and since no space is truly empty, how could the universe be finite.

My friend who's a mathematician said that in her geometry subject this question was actually brought up. She said that the universe may be a 3-manifold (3D surface?) and it depends on the curvature (negative or positive) as to whether the universe is finite or not.

I just want to know what the consensus is.
 
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  • #2
There is no consensus. Basically, our vision is limited in time and space, so we can't exactly say anything about whether or not distances are infinite. All we can say for sure is that our universe is many times larger than our observable region. But how much larger is currently up in the air.
 
  • #3
What is the/a universe?? Scientists suggest that there many universes emanating from their own "big bang". Space is infinite but a universe is bounded.
 
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  • #4
The size of the Universe: the speed of light multiplied with 13.7 billion years...
 
  • #5
universe11 said:
The size of the Universe: the speed of light multiplied with 13.7 billion years...

lol no
 
  • #6
if the matter that originally emitted the oldest CMBR photons has a present distance of 46 billion light years, then at the time of decoupling when the photons were originally emitted, the distance would have been only about 42 million light-years away...
 
  • #7
Assumption: mass creates space, right?

If space were finite, then just by standing at the edge of space will create more space?
 
  • #8
QuantumJG said:
Ok so me and a few of my physics (& Maths) friends were arguing this.

I argued that it must be finite in size, since the universe contains a finite amount of matter
What evidence do you have of this?

and since no space is truly empty, how could the universe be finite.
What evidence do you have of this?

My friend who's a mathematician said that in her geometry subject this question was actually brought up. She said that the universe may be a 3-manifold (3D surface?) and it depends on the curvature (negative or positive) as to whether the universe is finite or not.

I just want to know what the consensus is.
 
  • #9
space is infinite, energy/matter has a maximum value
 
  • #10
Checking my assumptions:
1. Matter create space?
2. Matter expanse space?
3. Matter needs space to exists?
 
  • #11
Space can create particles i.e. matter and energy seemingly from nothing? And the reverse?
 
  • #12
TungstenX said:
Checking my assumptions:
1. Matter create space?
2. Matter expanse space?
3. Matter needs space to exists?

Answers to your assumptions:

1) No, matter does not create space. Matter exists in space.
2) No, matter does not expand space. At the earliest epoch of the Universe, there was no matter, per se, but rather pure radiation. The expansion of space is an intrinsic property, set by the initial conditions (Big Bang). Technically, the expansion of space would still occur even if there was absolutely no matter.
3) As physical matter has spatial extension, then I guess yes, matter "needs" space within which to exist.
 
  • #13
Ah, thank you Deuterium2H
 
  • #14
Chalnoth said:
... All we can say for sure is that our universe is many times larger than our observable region. But how much larger is currently up in the air.

How can we say that for sure? What in our observable universe would be different if the universe were 1.1 times larger then the observable universe versus 1,000,000,000,000,000 times larger?
 
  • #15
mrspeedybob said:
How can we say that for sure? What in our observable universe would be different if the universe were 1.1 times larger then the observable universe versus 1,000,000,000,000,000 times larger?
Well, there are a number of possibilities that have to be considered. But let's just consider one where the universe wraps back on itself. If the universe wraps back on itself based upon its spatial curvature, then current measurements place the spatial curvature to be within 1% of zero, which makes the radius of curvature at least 10 times the Hubble radius, which is a factor of a few larger than the observable universe.

If the universe is flat but still wraps back on itself, then this induces anisotropies, which we should be able to see in the CMB. But we don't. Thus if it does wrap back on itself, it would have to do that very, very far away (again, a factor of a few times the observable universe).
 
  • #16
I argued that it must be finite in size said:
I thought that 'Oblers Paradox' proved that the universe could not be infinite. If it was...the night sky should be brilliant white (caused by the starlight from an infinite number of stars).
 
  • #17
afennah said:
I thought that 'Oblers Paradox' proved that the universe could not be infinite. If it was...the night sky should be brilliant white (caused by the starlight from an infinite number of stars).

You got that wrong, the paradox you mention was more to do with a static universe.
Since our universe is all that there is (that is after all the definition of universe), it must then extend forever - yet it is still expanding!
 
  • #18
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  • #19
afennah said:
I thought that 'Oblers Paradox' proved that the universe could not be infinite. If it was...the night sky should be brilliant white (caused by the starlight from an infinite number of stars).
Olbers' Paradox takes two assumptions, and shows they cannot both be true:
1. The universe is infinite (in time and space).
2. The universe is static (no expansion).

The discovery of the expansion of the universe demonstrates that the second assumption fails, which means that Olbers' Paradox cannot provide any additional information about the truth or falsity of the first.
 
  • #20
A clarification appears to be in order. Olber hypothesized the universe cannot be both spatially and temporally infinite. We are fairly certain it is not temporally infinite. The jury is still out on the spatially infinite part. A temporally finite universe could be spatially infinite. My guess is it is not. My reasoning is an infinitely spatial universe would have observationally irregular 'edges'. I think this would be fairly obvious from WMAP data - and it is not. The alleged 'axis of evil' thing has been discredited due to selection effects - unsurprisingly.
 
  • #21
Chronos said:
A clarification appears to be in order. Olber hypothesized the universe cannot be both spatially and temporally infinite. We are fairly certain it is not temporally infinite. The jury is still out on the spatially infinite part. A temporally finite universe could be spatially infinite. My guess is it is not. My reasoning is an infinitely spatial universe would have observationally irregular 'edges'. I think this would be fairly obvious from WMAP data - and it is not. The alleged 'axis of evil' thing has been discredited due to selection effects - unsurprisingly.
With expansion, the universe can still be both spatially and temporally infinite without impinging upon Olbers' paradox.

What edges would a spatially infinite universe have?
 
  • #22
afennah said:
I thought that 'Oblers Paradox' proved that the universe could not be infinite. If it was...the night sky should be brilliant white (caused by the starlight from an infinite number of stars).

Dr. Edward Harrison gave the "definitive" answer/solution to Olber's Paradox, in his 1987 book "Darkness at Night: A Riddle of the Universe".

While it is an open question wether the Universe is infinite in extent (space), it is finite in time...i.e., it had a beginning (The Big Bang). We can only look back a finite distance (our Cosmological Horizon), so the light from any stars existing beyond the radius of the Hubble Sphere has not had a chance to get to us yet. Combined with the fact that stars themselves have a finite life-time, there is simply not enough visible stars in our observable universe to make the night sky bright.

As Chalmoth pointed out above, the expansion of the Universe also has the effect of red-shifting any distant luminous objects. Even though stars did not exist at the time of Recombination (Surface of Last Scattering), even the unbelievably intense, incandescent light from this epoch (approx. 370,000 years after Big Bang) has been red-shifted to such low frequency/long wavelengths that it is no longer in the visible spectrum...hence the Cosmic Microwave Background Radiation.

Finally combined with observation that the expansion of the Universe is now accelerating, eventually all galaxies (with the possible exception of the local galaxies that are gravitationally bound with the Milky Way) will pass beyond our particle horizon, and will forever become unobservable. Note that I do not subscribe to the so-called "Big Rip". So, in theory, billions of years from now, our Milky Way will truly become an "Island Universe", just as it was once thought of, up until the early twentieth century.
 
  • #23
Brain Dwarf said:
You got that wrong, the paradox you mention was more to do with a static universe.
Since our universe is all that there is (that is after all the definition of universe), it must then extend forever - yet it is still expanding!

Hi Brain Dwarf, I don't agree with your reasoning (in your statement): 'because the universe is all there is...then it must be infinite'. Professor Brian Cox touched on the subject of 'Oblers Paradox' during his astronomy program this week. (BBC Stargazing Live, Pt1). He seems to believe (as I do) that the universe is not infinite.

I thought Deuterium's comment about 'red shifted light' was very interesting though.

Happy New Year!
Al.
 
  • #24
The universe may well be spatially infinite, although I think that is unprovable. I too am inclined to agreee with Professor Cox.
 
  • #25
QuantumJG said:
I argued that it must be finite in size, since the universe contains a finite amount of matter and since no space is truly empty, how could the universe be finite.

Where did you get all of this information from? I'm just wondering.

I think the answer to this would be that we do not have a precise answer to this.

My own speculation on this (without almost any support at all, it is just a speculation of my own) is that our evolved universe that still continues to grow is finite, but is located in a space that is infinite.

I believe it is not total trash, but it's also just an opinion.
 
  • #26
first at all, what happened a few seconds before the big bang, I know something happened that tells me that time is infinite, no beggining, no end
 
  • #27
I agree with our universe located in a space that is infinite
 
  • #28
Nordic said:
our evolved universe that still continues to grow is finite, but is located in a space that is infinite.

josewrivera said:
I agree with our universe located in a space that is infinite

It would seem that you guys do not use the accepted definition for the word "universe".
Universe: The totality of everything that exists.

It cannot be in something, or located. It is everything.
 
  • #29
jobigoud said:
It cannot be in something, or located. It is everything.

Are you sure about that?

I am not going to argue about anything for cosmology is my hobby, and not a specialty or anything.

I thought that a universe is located in space, or aspace, call it however you want. And I believe that it is a possibility that the universe is finite, while space is infinite. I am not kicking the idea of a multiversity around here, don't be misguided by my sentences into thinking that.

So, again, are you sure about what you are stating?
 
  • #30
josewrivera said:
I agree with our universe located in a space that is infinite

This doesn't make sense. The universe contains everything, even space. Cosmologist have told and shown us that the universe is expanding, and accelerating in its expansion.

Now think about this: If the universe were infinite, then why would be observe that space was expanding? If its infinite in span, then the idea of the universe growing in size doesn't make sense because if its infinite in span, it can't be any larger than infinite.

At least, this is what I just thought of...
 
  • #31
nlsherrill said:
Now think about this: If the universe were infinite, then why would be observe that space was expanding? If its infinite in span, then the idea of the universe growing in size doesn't make sense because if its infinite in span, it can't be any larger than infinite.

At least, this is what I just thought of...

I really have never thought of that. It is a really good idea.

But again, my opinion on this is that the universe is located in space. A space that is infinite since it still let's the universe expand. Now, think about this: What if we were out of this space? What will the universe do then? Just crash into the walls of it? I do not think so...

You can search my opinion up, I'm sure some other people have got it as well. I am not trying to prove anything, just giving suggestions. :)
 
  • #32
The definition according to the mighty Wikipedia:
The Universe comprises everything we perceive to exist physically, the entirety of space and time, all forms of matter and energy. However, the term Universe may be used in slightly different contextual senses, denoting such concepts as the cosmos, the world, or Nature.
http://en.wikipedia.org/wiki/Universe" [Broken]

As for an infinite "thing" expanding, it makes a lot of sense; the observed distances of the "points" inside this "thing" will increase. (I think I read that it is not only the mass objects / collections moving away from one another but also more space being "created" at the "centre" of the universe that accelerate this observation).

I think our perception / definition of something expanding is limited (having a human frame of reference; e.g. living on a planet). We want to think that something is expanding in / into something else, so how can we view the collection of everything (including space and time) expanding, when we are in it?

(Sorry English no good today :frown:)
 
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  • #33
BTW, what will the impact be if the universe is infinite or finite (lets say 10x billion light years, where x is a very large number)

Or even is x is not that big number...

Are we going to fall of the edge of the earth, erm... I meant universe.

We can't even send a man to Mars yet or any object out of our galaxy, thus a finite view of the universe approach an infinite view on our scale. (To plankton, the ocean must seem infinite; except for the ones reaching the edge)

Seeing that we can not go and find (or not find) the edge of the Universe; is there a thought experiment that will help.

Wow, that is a lot of ramblings :smile:
 
  • #34
It's my universe, just one of millions, and is not expanding, just moving in space, we haven't been that far nothing is written on stone sorry about spelling
 
  • #35
josewrivera said:
It's my universe, just one of millions, and is not expanding, just moving in space, we haven't been that far nothing is written on stone sorry about spelling
lol. Millions of universes? I don't think that's right.
 
<h2>1. Is there an edge to the universe?</h2><p>Currently, there is no evidence or scientific theory that suggests the universe has an edge. In fact, the concept of an edge goes against the idea of an infinite universe. The universe is constantly expanding, and there is no known boundary or limit to its expansion.</p><h2>2. How do we know if the universe is finite or infinite?</h2><p>Scientists use various methods, such as measuring the curvature of space and observing the cosmic microwave background radiation, to determine the shape and size of the universe. These methods have led to the conclusion that the universe is most likely infinite.</p><h2>3. Can the universe be both finite and infinite?</h2><p>It is highly unlikely that the universe can be both finite and infinite. These two concepts are contradictory and cannot coexist. If the universe has an end or boundary, then it is by definition finite. If it is infinite, then it has no end or boundary.</p><h2>4. What does infinity mean in the context of the universe?</h2><p>Infinity, in the context of the universe, refers to the idea that the universe has no limit or boundary and is constantly expanding. It also means that the universe has always existed and will continue to exist forever.</p><h2>5. What implications does an infinite universe have on our understanding of reality?</h2><p>An infinite universe challenges our understanding of reality and raises questions about the nature of time, space, and existence. It also suggests that there may be an infinite number of possibilities and realities beyond our own. This concept can be both fascinating and daunting, as it pushes the boundaries of our knowledge and imagination.</p>

1. Is there an edge to the universe?

Currently, there is no evidence or scientific theory that suggests the universe has an edge. In fact, the concept of an edge goes against the idea of an infinite universe. The universe is constantly expanding, and there is no known boundary or limit to its expansion.

2. How do we know if the universe is finite or infinite?

Scientists use various methods, such as measuring the curvature of space and observing the cosmic microwave background radiation, to determine the shape and size of the universe. These methods have led to the conclusion that the universe is most likely infinite.

3. Can the universe be both finite and infinite?

It is highly unlikely that the universe can be both finite and infinite. These two concepts are contradictory and cannot coexist. If the universe has an end or boundary, then it is by definition finite. If it is infinite, then it has no end or boundary.

4. What does infinity mean in the context of the universe?

Infinity, in the context of the universe, refers to the idea that the universe has no limit or boundary and is constantly expanding. It also means that the universe has always existed and will continue to exist forever.

5. What implications does an infinite universe have on our understanding of reality?

An infinite universe challenges our understanding of reality and raises questions about the nature of time, space, and existence. It also suggests that there may be an infinite number of possibilities and realities beyond our own. This concept can be both fascinating and daunting, as it pushes the boundaries of our knowledge and imagination.

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