Is the Universe Infinite? Theories and Considerations

[NowIsForever]

What do current theories have to say about any resolution to this question? The visible universe might be finite, but that says nothing about the totality. Should we include the Multiverse in this discussion (if there are many worlds)? What about the nature of quantum foam? Could that have a finite basis. And on and on... Is there any end to it all?

 

[Nabeshin]

Judging from the WMAP data, we deduce that the universe is extremely close to being spatially flat. In the standard FRW cosmology, a spatially flat universe is infinite.

 

[Passionflower]

Judging from the WMAP data, we deduce that the universe is extremely close to being spatially flat. In the standard FRW cosmology, a spatially flat universe is infinite.

The question whether space is finite or infinite is not related to whether a spacetime is open, flat or closed. For instance a closed spacetime could be infinite and a flat spacetime could be finite. The fact that FRW models cannot handle finite spaces is obviously not a valid argument here.

 

[filegraphy]

Welcome to Physics forum. That question has not been answered yet. My view of the universe is that it will expand forever. Therefore being infinite.

 

[NowIsForever]

My view of the universe is that it will expand forever. Therefore being infinite.

If the time component of space-time is infinite, then indeed the universe must be infinite even if the space component is finite every step of the way. Although, then the space component could be potentially infinite.

 

[NowIsForever]

...a flat spacetime could be finite...

I don't see how a flat smooth manifold would not be infinite (although perhaps that is a failure of my imagination). Maybe you refer to a non-smooth model? Could you give an example of such a model embedded in Rⁿ?

 

[fouvy]

Welcome to Physics forum. That question has not been answered yet. My view of the universe is that it will expand forever. Therefore being infinite.

It seems that there is no relationship between expand forever and infinite. For example, the tree is growing forever but it isn't infinite high for the reason that the time isn't infinite long, is it?

 

[Chronos]

A tantalizing question. My gut instinct is we will never entirely resolve the question of flatness. CMB anisotropy gives us conficting hints. Too close to call, IMO.

 

[Emu]

As Chronos mentioned in the thread " Why is Space Black"

Olber's paradox, not enough galaxies and stars to fill in the gaps. Olber deduced our universe cannot be both spatially and temporally infinite.

 

[George Jones]

I don't see how a flat smooth manifold would not be infinite (although perhaps that is a failure of my imagination).

A space can be flat and compact if it is not simply connected.

 

[robheus]

As Chronos mentioned in the thread " Why is Space Black"

The Big Bang has taken care of that issue, you can not resolve the issue of finiteness/infiniteness of space and/or time from that paradox.

I think the question is even theoretically unanswerable, and we just use the gut feeling that spacetime is unbounded (there is no *edge* to spacetime) but that also leaves the issue of finiteness/infiniteness open.

My gut feeling is that spacetime is infinite.

 

[TrickyDicky]

My gut feeling is that spacetime is infinite.

How could it be? maybe spatially, but, doesn't the Big Bang make it time-finite, at least in one direction?

 

[robheus]

How could it be? maybe spatially, but, doesn't the Big Bang make it time-finite, at least in one direction?

Nope. There is nothing in the Big Bang Theory that implies that. The Big Bang Theory is not an explenation of the origins of the universe, but of it's development.

 

[robheus]

On the subject of infinites in the realm of physics, you have to be careful about some subtle aspects of infinites. First of all, real infinites (like the mathematical infinite) do not belong to physics. Any measure in physics always is of finite proportions. However note that this does not preclude that space and/or time cannot be infinite.
Look at it like this: consider the natural numbers and select a number. Now, whichever number you came up with, it definitately is a finite number, and also, you can always select a number bigger then the number you just selected.
So the seemingly contradictionary conclusion is that you can select an infinite amount of numbers, yet no number you ever get is itself infinite. Infinite itself is not considered a number.
The infinite exists only in the forms of finite elements.

So, if we consider space-time like the set of all possible spatial and temporal measures that can be made, the set itself is clearly infinite, although any element in the set is of finite measure.
There does not exist a point in time or space infinitely far away.

 

[Andrey]

On the subject of infinites in the realm of physics, you have to be careful about some subtle aspects of infinites. First of all, real infinites (like the mathematical infinite) do not belong to physics. Any measure in physics always is of finite proportions. However note that this does not preclude that space and/or time cannot be infinite.
Look at it like this: consider the natural numbers and select a number. Now, whichever number you came up with, it definitately is a finite number, and also, you can always select a number bigger then the number you just selected.
So the seemingly contradictionary conclusion is that you can select an infinite amount of numbers, yet no number you ever get is itself infinite. Infinite itself is not considered a number.
The infinite exists only in the forms of finite elements.

So, if we consider space-time like the set of all possible spatial and temporal measures that can be made, the set itself is clearly infinite, although any element in the set is of finite measure.
There does not exist a point in time or space infinitely far away.

The infinate exist only in the forms of finate elemetns

This is not entirely true but i can see where you are coming from. Yes the infinate can be measured using finate elements, i.e. your number example. But let's say there are no numbers left to pick. Let's say that there is no finate elements which we can use to measure the infinate, the vastness of space. What do we get then? Well, absolute zero because there can be no set of elements that can define the measurement. Furthermore, you can't even call it Zero for Zero is a measurement of some sort. In fact it is utterly impossible to measure something without giving it a set of measurment, i.e. distance, time, dimention, space etc. Thus don't think of Universe being a set of simple measurements that one can simply use for one's own convenience because the moment you do that, you've restricted yourself from the bigger picture.

 

[heusdens]

(heusdens=robheus)

Perhaps anyone familiar with the Kalam Cosmological Argument. It's a famous but false argument against the infinity of time. The argument goes something like this: if we suppose that time did not have a begin, we could have never arrived at the moment of "now" because it is impossible to have traversed an infinite amount of time.

For people that do not immediately grasp the incorrectness of the argument, just ask yourself, at what point on the time axis is it supposed that we have started the traversal of time.

The point is of course, that wherever you have chosen to start traversing the time axis, you already smuggled in as a premise that time had a beginning, since else, you could not have started traversing the time axis at all.

The only validity of the argument is that there is no point on the time axis in the distant past that is infinitely far before the present point in time, since we cannot traverse an infinity of time. [ and pls. note, that is just what infinity is by definition, that it can never be exhausted or completed, no matter how hard or how long we try. A "completed" or "exhausted" infinity is nothing more as a contradiction in definition. ]

Yet, at the same 'time' this is not to be held against the infinity of time itself, since we can always design a point farther back in time on the time-axis, and thus show that there is no upper limit to a past point in time.

 

[POWERSHIFT]

If the universe was infinite, wouldn't it, according to the 2nd Law of Thermodynamics, have no heat? And if it isn't infinite, that means it's finite, and thus had a beginning. Which also means time had a "beginning." So to speak

 

[heusdens]

If the universe was infinite, wouldn't it, according to the 2nd Law of Thermodynamics, have no heat? And if it isn't infinite, that means it's finite, and thus had a beginning. Which also means time had a "beginning." So to speak

That is a famous arguments from the creationists, they say that (acc. to physics) the world needed to have a beginning, based on the 2nd law of Thermodynamics. However, their idea clearly contradicts the 1st law of Thermodynamics, which claims that the total quantity of energy in any system, is constant, and thus no creation or destruction of energy is possible.

The issue onhand is however much more complicated. Based on E=mc^2 the 1st law of Thermodynamics we need first to consider physical matter too, so the total quantity of both physical matter (mass) and energy is a constant.

Second, both laws of Thermodynamics were originally constrained to laboratory scale thermodynamic systems which were closed and had a thermodynamic boundary. The 1st law (in it's contemporary form, based on GR and QM) still holds for all systems, including the universe. Physical matter creation, as what happened on a mass-scale in the early universe, does not contradict that, because it was a conversion of energy in another form.

The problem with the 2nd law of Thermodynamics however is that it is still constrained to thermodynamic systems which have a thermodynamic boundary.
This does not apply directly to the universe, because apart from the cosmological issue of open or closed universe, there is in the strict sense no thermodynamic boundary to the universe. There's no border or boundary to the universe (cosmological principle), and that is true even when the universe turns out to be a multiversum.

In the Thermodynamic sense the observable universe is an open system, since it does not have a boundary and is in thermal contact with the rest of the universe, beyond our horizon.
For the universe in total the terms open or close with respect to it's Thermodynamic behaviour makes no sense since there is no boundary to the "rest of the universe" (since the total universe already encompasses that) so that it is neither open nor closed.

But there is also something else peculiar about the universe. You might have seen these pictures of a sequence of moments of time in which a gas in a container spread outs through the container (due to entropy or the 2nd law of TD) and becomes uniformly spread through the container.

At the microscopic level however, all physical laws work both ways, so how do we know the progress of time? When we have to order the pictures (let's say there are 3 pictures, one with local concentration(s) of molecules, the next with a medium spread of those molecules in the container but not yet uniform, and the third a uniform distribution) we would clearly say that the progress of time is from picture 1 to 2 to 3.

Yet, when this picture was not of a small gass container, but was of cosmological size, we would need to arrange the pictures in the opposite order! Due to gravity, local matter clumbs together forming stars, galaxies and clusters of galaxies.
So if we were not told what scale the picture represent or that the scale is a varying quantity, we could not say what the right direction of time was!

In the example of the cosmological progress of distribution of matter, there are two important differences with the example of the small gas container. First, the progress of time is from a uniform distribution towards local clutterling of matter, forming galaxies, stars, etc., and the scale of the 'container' grows, due to cosmological expansion.
In terms of entropy, this in fact means that the growing metrics of space allow for more possible states, so this in fact means a lowering of entropy at a cosmological scale!

If you search online, you might find a lecture of Roger Penrose on this issue of cosmological expansion and entropy, which is very interesting.

This is just some basic information, the issue itself is far more complicated as I can explain, but at least I think you get the basic idea that you can not simply scale up our laboratory scale experiment and conclusions based on the 2nd law of Thermodynamics to cosmological scales.

I don't give a proof of it, but one could suspect that on truly cosmological scales (the universe as a whole) the issue of entropy is different as expected, and might lead to the conclusion that entropy is a conserved quantity throughout the cosmos, even if at local scales the 2nd law still applies.

But perhaps someone else more educated on this subject can explain more details.

 

[jackmell]

What do current theories have to say about any resolution to this question? The visible universe might be finite, but that says nothing about the totality. Should we include the Multiverse in this discussion (if there are many worlds)? What about the nature of quantum foam? Could that have a finite basis. And on and on... Is there any end to it all?

Your questions of "finiteness" and "end to it all" restrict the possibilities I believe. 2000 years ago, a farmer would have thought walking far enough straight-ahead would result in falling off the "end" of the world. But in fact, something qualitatively different than "flat" emerges at a large enough scale. Can that also be true of the Universe as well? At a large enough scale, our local concepts such as distance, size, and volume may loose meaning as something qualitatively different emerges. I know that's hard to imagine but it would also have been hard to imagine to the farmers long ago how the Earth could be a sphere and not flat.

To me, I find that possibility comforting: I no longer wonder how large the Universe is, how it started, and where it's going. I simply believe it is likely, based on historical trends such as the flat earth, wandering planets, moving sun and moon and milky-patch in the sky, as well as all the other critical-point phenomena I see around me, that perhaps something qualitatively different then our current understanding of the world is needed to answer these questions.

So my answer is that it may be neither finite nor infinite but rather something qualitatively different.

 

[heusdens]

Your questions of "finiteness" and "end to it all" restrict the possibilities I believe. 2000 years ago, a farmer would have thought walking far enough straight-ahead would result in falling off the "end" of the world. But in fact, something qualitatively different than "flat" emerges at a large enough scale. Can that also be true of the Universe as well? At a large enough scale, our local concepts such as distance, size, and volume may loose meaning as something qualitatively different emerges. I know that's hard to imagine but it would also have been hard to imagine to the farmers long ago how the Earth could be a sphere and not flat.

To me, I find that possibility comforting: I no longer wonder how large the Universe is, how it started, and where it's going. I simply believe it is likely, based on historical trends such as the flat earth, wandering planets, moving sun and moon and milky-patch in the sky, as well as all the other critical-point phenomena I see around me, that perhaps something qualitatively different then our current understanding of the world is needed to answer these questions.

So my answer is that it may be neither finite nor infinite but rather something qualitatively different.

For your last remark, we could refer to the analogy of the theoretical issue wether or not matter was infinitely divisible or not. Some philosophers argued pro, the other against.
What we found - indeed - was neither, as per quantum mechanics and the uncertainty principle. You can split molecules, and then atoms, but when we try to split protons or neutrons into their individual parts. we need such energies to overcome the quark gluon force, that this energy will create new particles.

 

[Physics-Learner]

(heusdens=robheus)

Perhaps anyone familiar with the Kalam Cosmological Argument. It's a famous but false argument against the infinity of time. The argument goes something like this: if we suppose that time did not have a begin, we could have never arrived at the moment of "now" because it is impossible to have traversed an infinite amount of time.

For people that do not immediately grasp the incorrectness of the argument, just ask yourself, at what point on the time axis is it supposed that we have started the traversal of time.

i think it is an absolutely valid argument, as to why the universe had a beginning.

according to the bbt, matter, space, and time were all created by this process.

the singularity is not a part of this universe. no physics explains the singularity. all theories start at nanoseconds after the big bang.

a very common thought process is that the super-universe is responsible for many such big bangs creating many other universes, which may or may not have the same sorts of laws that our universe does.

which is why the question "who created god" is not necessarily a valid question. because it assumes that the super-universe has the same qualities as our own.

time may or may not exist outside of our universe. same is true of matter, space, causality, or any other such notion that we have come to accept about our own universe.

 

[daniel rey m.]

I'd never ever come across the name "Kalam Cosmological Argument". It happens to be identical to one that Immanuel Kant, the German philosopher, presented along with the opposite argument, and in so doing he proved that there's a paradox involved and so there's no logical way out and one can "prove" that both arguments are right. Infinitude and eternity are inherently paradoxical concepts. His reasonings (in his work THE CRITIQUE OF PURE REASON):

Thesis
The world has a beginning in time.

Demonstration
In fact, let us suppose that the world does not have a beginning in time: that being so, up to any given moment there will have elapsed an infinite series of states of affairs of the world that follow one after the other. Now, the infinitude of a series implies that it can never be completed through consecutive syntheses. Consequently, an elapsed infinite cosmic series is impossible and, thus, a beginning of the world is a necessary condition of its existence, which is what we set out to demonstrate...



Antithesis
The world does not have a beginning in time.

Demonstration
In fact, let us suppose that it does have a beginning in time. Since the beginning is an existence that is preceded by a time when the thing is nonexistent, it is necessary that there will have been a time when the world was not, in other words, an empty time. Now, in an empty time it is impossible that anything can spring forth, because no part of that time bears, in respect of some other part, any distinctive condition of existence that is preferential as compared to nonexistence...consequently, even though various series of things can have a beginning in the world, the world itself cannot have a beginning and, thus, it is infinite in respect of time past.

 

[Physics-Learner]

the problem with the second part of that argument is that time is only known to exist in this universe. the big bang started the universe, and created the space, time, and matter that we know today.

without doubt, this universe had a beginning in time. whether the super universe has time or not, or anything else or not - no way we can derive. we simply can not NECESSARILY know anything about the super universe WITH SURETY based upon what is in our universe.

the "empty time" that kant would have been referring to is something about the super universe, because there was no universe of ours during "empty time". thus no arguments are valid during "empty time".

 

[Tanelorn]

Does time actually exist at all, even in our own universe? Is it a property of our universe rather than something material which actually exists?

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

 

[daniel rey m.]

Tanelorn, yes, time is another one of those incomprehensible concepts they've been discussing for the last two millennia or more, without getting anywhere.

Physics-Learner, the real problem with that second Kantian argument is that the concept of "empty time" is incomprehensible, so that any reasoning that includes it is incomprehensible as well. He assumes that it's a concept with a corresponding counterpart in reality, rather than what it really is, namely, an empty concept, a mere expression with no meaning to sustain it.

As you say initially concerning the Kalam Argument (Kant's first argument), it's convincing, but so are the reasons for believing the opposite: that there can be no beginning and no end as concerns both space and time.

You're making too many assumptions, and as they say, when you ***-U-ME you make an A** of U and ME. Your basic assumption is the foundation of the Big Bang Theory: the existence of "singularities". This is supposed to explain the extravagant notion that something can spring forth from nothing.

They've been discussing this too for more that two thousand years, and the conclusion was that "ex nihilo nihil fit", meaning "nothing can come out of nothing".

Once you develop the concept of "time" you can't have it both ways and you have to accept that there must ALWAYS be a previous instant. Scientists try to push aside this inevitable conclusion by saying that there is something so singular that it explains EVERYTHING, even the twin absurdities according to which 1) there is a point in respect of which there is no "before", and 2) there is a mysterious barrier all around us beyond which there is nothing, so that we're part of the big Blob of Everything that is submerged in a Sea of Nothing. They claim that the Universe is expanding into nothing because space invents itself as it goes along. None of this makes any sense. You're happily jumping on the bandwagon and you'd rather believe that it's the underdog who is mistaken. The BB Theory simply happens to be the dominant one at present. Not all astronomers go along with this theory.

The situation is exactly as it was about 2,500 years ago, when the Greeks thought that there was nothing beyond the last crystal sphere of the Universe (the one with the fixed stars, as opposed to the wandering stars, called"planets" or wanderers), neither space nor matter. What ultimately explains both this and your finite BB Universe is a terror of eternity and infinitude and the impossibility of grasping these two fearsome matters.

 

[Physics-Learner]

you do not have to accept that there was a previous instant. "time" could very well have formed from something (it is typically referred to as the bb and the singularity).

i think if we ever actually could understand our own universe, concepts of time, speed of light, etc. would become much clearer.

i don't think there is anything inherent about time that says it must have an ending ? but it certainly had a beginning.

as i said previously, something before the beginning would be describing the super universe. time may not exist at all in the super universe. the second part of the argument assumes things about the super universe, and this is where it fails.

as far as we know, time is something that we are experiencing in the creation of our universe. what time is, as has been previously stated, is still a mystery.

 

[daniel rey m.]

"(...) but it certainly had a beginning." You keep repeating that as though you were a preacher waving the Holy Writ. I could just as legitimately say "but it certainly had no beginning".

 

[Chronos]

A "Beginnng" is a relative term. This universe, by all current observations, appears to have originated about 13.7 billion years ago. That does not exclude the possibility of prior universes [e.g., as in bounce cosmologies]. It does, however, make it difficult, if not impossible, to observe evidence of prior states. There is, however, a finite possibility some faint trace remains hidden on large scales the cosmos. We have good reasons to believe the big bang singularity is a mathematical artifact in our theories, not a naturally ocurring state in nature [and probably true of black hole singularities as well, imo].

 

[Physics-Learner]

hi daniel,

let me repeat. the universe had a beginning. the first part of the argument is absolute truism. i am not using the big bang as an assumption. it is one theory about the creation of the universe.

i am simply using the physical manifestation created in our universe that we refer to as "time". there is no way a finite being can exist in a universe which had no beginning, for the reasons already stated.

we experience "time" as a duration, but there is nothing in this universe that points to time needing the quality of no beginning. every object in this universe had a beginning. so it might not be too surprising that our universe has one.

there could be indeed bounce cosmologies. to me, that is just another way of describing the super universe. i simply say that there is some process by which the super universe created our universe. it certainly seems probable that our universe is not the only universe that has ever been spawned from this process.

but whether we use the big bang, bounce cosmology, or any other process, there is no way for us to know that any other universe is like our own. for all we know, there may be a gazillion different combinations and permutations of possible universes with their own unique laws, that could be made.

all we know is our own. and IT IS IMPOSSIBLE for us to have ever been born if we had to wait an infinite amount of time. that is as clear as the noses on our respective faces. one does not need a holy writ to figure that one out.

 

[daniel rey m.]

Chronos, you believe that the BB singularity is just a mathematical entity, an imaginary and ideal creation of the mind such as the point, the line and the plane (location without magnitude, length without width and length and width without depth, respectively, which are impossible objects), but you also believe there was a BB, and in possible previous universes. Would you please make up your mind?

The idea that everything sprang forth from a mathematical point was first put forward by a Jesuit priest, in other words, by a mystic. Why this notion was later taken up by atheists or agnostics is hard to understand. They adopted that belief and then they tried to make all their data fit what had been preconceived.

Physics-Learner, one of your several inconsistencies is that you mistake the whole for the part when you say that "there is nothing in this universe that points to time needing the quality of no beginning. Every object in this universe had a beginning. so it might not be too surprising that our universe has one."

This is called the "fallacy of composition": assuming that the property of a part must also be a property of the whole. This reasoning is valid only in simple, spatial circumstances, as when one says that if all the constituent parts of one's radio are in a drawer then the radio must be in that drawer. The Universe is far more complex than any of its contents. Its ultimate nature remains completely unknown. In this particular case "the whole is greater than the sum of its parts." (Not to be confused with Euclid's rule that says, "The whole is greater than the part.")

Moreover, you insist on postulating the existence of something you call "the Superuniverse". You can't explain to me what the Universe is and even so now you're inventing something that I guess you conceive to be something like the Mother of All Universes. By doing this you're merely translating all the unexplained matters to that other entity. First deal with the daughter, then we can go for the mother.

Then you claim that "IT IS IMPOSSIBLE for us to have ever been born if we had to wait an infinite amount of time". I don't see how you reached that conclusion.

Besides, even if one believes in an eternal Universe, one can imagine a level of reality where there is no such thing as "time", and in this timeless existence everything would be simultaneous, both the past and the future, like the images on a film or a tape. Experiencing life as we understand it would be like being forced to sit down and see the film, scene after scene, but all that we then see as a succession of happenings was always there and will remain there forever, and what we see on the screen is just an illusion. Every instant in our lives would be like a single frame on film --an infinitesimal slice of "time". As we go from one instant to the next one we feel that we're moving forward, but it would be an illusion of movement.

Tanelorn seems to be talking about this when he says, "Does time actually exist at all, even in our own universe? Is it a property of our universe rather than something material which actually exists?"

Time can be understood in many ways. For the psychologist it's a creation of conscience and so it depends on one's mood. For a physicist it's one of the three fundamental quantities (the other two being mass and distance) with which anything in the Universe can be described. For a philosopher it will be other things. Neither one of them will agree with the others as to the definition.

A physicist once lost his patience in a discussion about how hard it was to define time, and he said, "It's simple! Time is what clocks measure!"

More about the Everything surrounded by Nothingness that Bigbangers believe is a perfect description of everything: you can't have something spatial surrounded by something that's non-spatial, or by nothing, since nothingness is nonexistence. They dodge the issue but they can't get rid of it by saying that anything that's not what they think is space expanding is undefined and does not exist.

It must've been the Greek thinkers in Antiquity who first made what we now call "thought experiments". One of them said: imagine that I could walk all the way over to the end of the Universe, and that I were to poke the tip of my staff through it. What would happen to it? Would it vanish?