Is the universe infinite?

Chalnoth

Well, for the most part, that isn't really the case. It's the exact same force governing the expansion as governs the behavior of galaxies: gravity. In fact, you don't even need General Relativity, as you get the exact same answer on these large scales with Newtonian gravity (except that Newtonian gravity doesn't tell you how radiation responds to gravity...you do get the same expansion behavior for matter, though).

So it isn't so much a matter of local forces overriding the expansion for galaxies, clusters, and other gravitationally-bound objects, but just that the same gravity keeps those systems bound together that governs how the universe as a whole expands. The only difference is that the universe as a whole behaves like a smooth, nearly-uniform fluid that expands, while local overdensities tend to behave like orbiting systems.

Radrook

I personally have always considered anything infinite or boundless as impossible because anything that exists appears to require bounderies or a perimeter to delineate or give substance to it's existence. A building of infinite foors-for example would have no shape unless it has bounderies. No bounderies =no shape =no building. Unless of course we simply add floors or cause bounderies to expand forever. But bounderies of course are incompatible with infinity.

Here is part of an article dealing with the concept of infinity in relation to reality in harmony with what I just said.

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Excerpt:


Naturally in mathematics we can have infinity, numbers go on for ever, but numbers are not real, they are abstract. I cannot imagine anything 'real' that we could apply an infinite number to. The only thing I can imagine that could be really infinite is nothing, the 'nothing' I described earlier in Where did the universe come from? and we have no idea if that exists.



The concept of infinity is a puzzling one. For example: imagine a standard pack of playing cards that consists of just one of each card but two jokers. Imagine that the packs of playing cards are infinite in number (A thought exercise only of course). We therefore have more jokers than any other card in each pack, so do we have more jokers in total? You could reply that as the packs are infinite in number they can't be counted so it would be impossible to know. However, as the ratio of jokers to other cards in each pack is fixed, then at any number of packs there will always be more jokers. This would appear to indicate, that mathematically, we can have degrees of infinity. Sounds odd doesn't it? It is a valid mathematical argument though.


We have a theory for black holes that describes infinite density. See Exploding Black Holes? What does it mean, other than an unresolvable equation that occurs in mathematics? Exactly what is infinite density? Taking a rather simplistic view it could be argued that if one black hole has infinite density then nothing else can have ANY density. Clearly though in this sense we can have lots of infinite density, so the term obviously carries a meaning in mathematics that does not have the same meaning outside of it. Is the term used in the theory only because that is the way the sums work out, regardless as to its significance in the real world, or is it real?


Strictly speaking, according to Einstein's Theory of Relativity, a singularity does not contain anything that is actually infinite, only things that MOVE MATHEMATICALLY TOWARDS infinity. A black hole is formed when large stars collapse and their mass has been compressed down to a very small size and the powerful gravitational field so formed prevents anything, even light, from escaping from it. A black hole therefore forms a singularity at its centre from the concentrated mass of the collapsed star itself and from the accumulated mass that is sucked into it. A singularity's mass is therefore finite, the 'infinity' refers only to the maths.
Can we have an infinite universe for example? The answer is no, the universe is finite. Stephen Hawking in 'A Brief History of Time' (1989 page 44) describes the universe as being "finite but unbounded".



The simplest answer is that as the universe is known to be expanding, it cannot possibly be infinite. To be precise, the dictionary definition of the word universe is "all that is. The whole system of things." In this sense the universe is not expanding into anything other than itself, for whatever it is expanding into is part of the universe, there being nothing else but the universe. However, for the sake of simplicity, I am referring only to our Big Bang expanding universe as 'the universe'. (Even if you happen to disagree with the Big Bang theory, the term 'universe' will still have the same meaning here, as it refers to 'our' universe only, and does not include whatever may or may not exist outside of it.) I will try and explain a finite universe as some people understandably have problems with it.


A good place to start is to understand the very real difference between infinity and a large number.


For example, imagine an ordinary size diamond, as you would expect to find set in a typical lady's engagement ring. Now imagine a super-being armed with super-tweezers, picking out atoms from this diamond one at a time, one every second, since the creation of the universe, some 13 billion years ago. How much of the diamond would by now have been removed? The answer is you couldn't tell without looking through an electron microscope, less than a millionth of the atoms would have been removed. Try and imagine how many atoms there are in that diamond. Now try and imagine how many atoms there are in the entire universe. It is a very large number, but it is finite, and is 10 followed by 80 zeros, (maybe a few more zeros, maybe a few less), expressed as 10 to the 80th. If you want to see what it looks like.........
100,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 ,000,000,000,000,000,000,000,000,000.
0r written as - One hundred million, billion, billion, billion, billion, billion, billion. billion, billion


Even this very large number would count as nothing when compared with infinity, because infinity is NOT A LARGE NUMBER be absolutely clear on this point, IT IS NOT A LARGE NUMBER, infinity is ALL THERE IS, it is NOT a number. You could keep counting (or measuring) for ever, and never reach infinity, it is only a description. Infinity describes a thing as having no end, no limit, no boundary or edge, it literally goes on FOREVER, ad infinitum.


Because infinity is not a number, large numbers are no 'nearer' to infinity than small numbers. Number 1 billion for example is no nearer to infinity than number 1, because the two, numbers and infinity, are in no way related. It is then impossible to approach infinity, a thing is either infinite and immeasurable, or finite and measurable, it cannot be part way towards infinity. Imagine running up a 'down' escalator, never moving forward. If you run for a week you are no nearer reaching the end of the escalator than if you run for a minute, you cannot get any closer to something that has no end.


An infinite universe for example would exist in every direction forever, there could be nothing else, ONLY the universe. It is then very easy to understand why our universe cannot be infinite, it is because it is expanding. It cannot be both infinite and expanding. It could be infinite OR expanding, but CANNOT possibly be both, that is a contradiction in terms, and we do know it is expanding. For an explanation of the Big Bang and why we know the universe is expanding.


http://www.thekeyboard.org.uk/What%20is%20infinity.htm

brerabbit

The universe is limited in mass and energy by the Big Bang constituents. Space goes beyond the expanding universe to a shell limited by the boundary created by God. God has no bounds and looks from beyond infinity inward.

Chalnoth

No, it actually isn't. Energy isn't conserved in an expanding universe, and mass can be both produced and destroyed.

brerabbit

thanx, Chalnoth

The question was "Is the universe infinite".

I think we agree that it is not infinite. The mass and energy is limited by the fixed amounts produced in the big bang. Mass and energy reduce by enthalpy increases but change among each other as Dark Matter, Galaxies and black holes are formed. Energy is conserved as the Universe as it expands but entropy reduces it and thus mass also.

Chalnoth

Except as I pointed out, this just isn't true. Why did you repeat it?

There's also no reason to believe that the universe was ever finite. It may be finite, it may be infinite. We just don't know.

brerabbit

Chainoth:

You say, "Why did you repeat it?" . ...I didn't repeat anything. I did try to help you along and pointed to the thread theam. ... but alas you seem to avoid the question by skirting the premis if the Big Bang spewed out an infinate amount of mass and energy or not. .....

brerabbit

Deuterium2H

Chalnoth is correct. Energy is NOT conserved in an expanding Universe. Space can be both infinite and expanding.

Deuterium2H

Radrook, the link/source you cited appears to have a rather naive (incorrect) view of the mathematical concept of infinity. Infinity is not a "number" in the sense that it is not a member of the Natural Numbers, or the Reals, for that matter. However, both Analysis and Set theory deal with infinite numbers ALL THE TIME. The extended Reals, as well as the Hyperreals and especially the Surreal Numbers include infinite (and infinitesimal) numbers. Foundationally, the first infinite ordinal number is omega (w), which is the order type of the set of Natural Numbers. All Natural numbers are finite ordinals. The first infinite ordinal number "w" is followed by w+1, w+2,...w+n = w x 2,...w x 3,...w^2, etc. In fact, there is an uncountable number of "countably" infinite ordinals before we reach the first "uncountable" infinite ordinal (w₁).

laaylowww2

there has to be equation for why the universe has a end...it has to and lets all agree that the univese is expanding at whatever speed what is it expanding into hummm

Deuterium2H

There is an equation (FLRW metric), and when it includes a cosmological constant term, which fits within observational parameters, yields a homogeous, isotropic Universe that is accelerating in it's expansion.

As to your final question...the Universe isn't expanding into anything. Expansion of the Universe (and its global geometry) are intrinsic properties of the Universe, itself. Just as there is no "center" to the Universe, there is no "edge".

laaylowww2

that we know off..... or is it so big that nobody has an explanation so the attach to word like infanity isnt that another word for we dont no the number so big the space so large....bringing it back down to my level....it just seems to me that something has to be in something now that my go on forever ,,,,just cant wrap my brain around that

brerabbit

thanx, deuterium

The Universe or possibly the many Universes each with its own Big Bang all reside in Space at the same time. IMHO, Space is quite different, and can be finite and both expands and contracts. Energy is conserved but degrades as Entropy within the Black Holes dominate. http://arxiv.org/abs/0801.1847

Chalnoth

Please read this before continuing:
http://math.ucr.edu/home/baez/physic...energy_gr.html

brerabbit

Will do, thanx. Would you give us the URL s on the sciences and academic credentials that they have in astro sciences, I can't find any other than Baez is a mathematician in Riverside and has an interest in protesting as did his relatives.

brer

Deuterium2H

The link Chalnoth provided is excellent, and it shows that the question of "energy" and "energy conservation" is both complicated and subtle in GR. Depending on the conventions or model one chooses may yield a different answer to the question of "energy conservation", especially in a global context. The easiest (and I think the correct) interpretation is simply this:

Question: If a photon is red-shifted due to the Cosmological expansion of space, it loses energy. Where does the energy go?

Answer: It doesn't go anywhere...because in expanding space, energy is not conserved.

brerabbit

The link is only as good as its author. Red-Shift energy is a phenomena of prospective differences in velocities and wave lengths. We are discussing an atom's mass and energy after it passed thur the "Big Bang". Then looses energy due to entropy particularly in the working Black Holes. ... thus the Universe and Universes are finite.

brer