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.
  • #71
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.
 
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  • #72
brerabbit said:
The universe is limited in mass and energy by the Big Bang constituents.
No, it actually isn't. Energy isn't conserved in an expanding universe, and mass can be both produced and destroyed.
 
  • #73
Chalnoth said:
No, it actually isn't. Energy isn't conserved in an expanding universe, and mass can be both produced and destroyed.
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.
 
  • #74
brerabbit said:
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.
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.
 
  • #75
Chalnoth said:
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.

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. ...:confused:

brerabbit
 
  • #76
brerabbit said:
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. ...:confused:

brerabbit

Chalnoth is correct. Energy is NOT conserved in an expanding Universe. Space can be both infinite and expanding.
 
  • #77
Radrook said:
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.

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 is infinity.htm

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).
 
  • #78
there has to be equation for why the universe has a end...it has to and let's all agree that the univese is expanding at whatever speed what is it expanding into hummm
 
  • #79
laaylowww2 said:
there has to be equation for why the universe has a end...it has to and let's all agree that the univese is expanding at whatever speed what is it expanding into hummm

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".
 
  • #80
that we know off... or is it so big that nobody has an explanation so the attach to word like infanity isn't that another word for we don't 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 can't wrap my brain around that
 
  • #81
Deuterium2H said:
Chalnoth is correct. Energy is NOT conserved in an expanding Universe. Space can be both infinite and expanding.

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
 
  • #83
Chalnoth said:

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
 
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  • #84
Chalnoth said:

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.
 
  • #85
Deuterium2H said:
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.

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
 
  • #86
brerabbit said:
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
This does not follow.
 
  • #87
brerabbit said:
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

Huh?? I don't even understand what you are trying to say.

But as a possible correction, do not confuse a doppler red-shift (which IS a measure of relative velocity between two objects in space), and Cosmological Red-Shift, which is NOT a measure of relative velocity, but is a result of the expansion of space itself. They are goverened by two very different formulas/equations.
 
  • #88
I have read that, if the universe is flat or hyperbolically curved, then it must be infinite. I've also read that all observations to date suggest that the universe is flat. Would that make it infinite? If it is indeed flat, then to be finite, it would have to have an edge and this would seem to contradict quite a few well accepted ideas in cosmology. If the universe is infinite now, then, looking back towards the big bang, it must always have been infinite - you can never halve the size of an infinite object and make it finite. It seems to a simple mind like mine, therefore, that the big bang didn't start with an infinitely small infinitely dense single point, but with an infinitely large infinitely dense affair. Is there any reason why that can't be the case? It would mean of course that the universe isn't actually getting bigger - it's just spreading out.
 
  • #89
ilsley said:
I have read that, if the universe is flat or hyperbolically curved, then it must be infinite. I've also read that all observations to date suggest that the universe is flat. Would that make it infinite?
No, not quite. There are two problems with this:
1. Even if the universe is flat, it can still be finite as it is entirely possible for a flat universe to wrap back on itself. An example of this type of universe is displayed in the old arcade game Asteroids, which is entirely flat, but move the ship off one side of the screen and it appears on the other. This is known as a toroidal topology, and it is entirely possible for our universe to be flat and finite in this way. I'm reasonably sure that you can do similar things with a negatively-curved space-time as well.
2. Unfortunately, our vision is limited both in time and space. We cannot observe the whole of the universe. And in practice, our local, observable region can easily have a curvature that deviates somewhat from the average curvature of the universe. So measuring some curvature or no curvature actually doesn't say much of anything about the curvature of the universe as a whole: the curvature we measure could just be a local feature.

However, let me just end with a little statement. As far as we know, our universe will expand forever into the future. This means that at least in one dimension, our universe is infinite: the time dimension. So if our universe is infinite in one dimension, why can't it be infinite in the other dimensions as well?
 
  • #90
darkside00 said:
space is infinite, energy/matter has a maximum value

That is unsupported speculation on your part and should be stated as an opinion, not a fact.
 
  • #91
i understand very little of cosmology. i am given to understand that the conclusion that "the fabric of the universe is stetching apart" is based on the cosmic microwave background, which is (as far as we know so far), "too uniform" to support the notion that space existed first, and that just the stuff expanded later into it. better data collection efforts may substantiate, or revise this idea.

but as a mathematician, i feel i must point out that there is a difference between "infinite" and "unbounded". a circle is bounded, but i don't think anyone would claim it consists of only a finite number of points.

if space is a continuum, then it is infinite, even if it is embedded in a bounded manifold in some n-dimensional ambient space. it is not possible for us to tell, at the moment, if this bound is just very large (compared to us), or non-existent. it is my understanding that the basic assumption in cosmology is that the universe is (relatively) uniform, so "local" measurements of curvature should tell us about the universe in general, but of course, this assumption may be wrong (the energy content of "our corner of the park" may somehow influence its geometry).

on the other hand, if space itself is quantized in some manner, then it's conceivable our universe is "absolutely" finite (it is a discrete structure). i think this unlikely, but some have suggested that a finite-dimensional lattice could propagate instructions in such a way as to create the illusion of states evolving over time (the universe itself could be some form of complex-behavior automaton).

it is difficult to tell how many dimensions we "need" for our (perceived) space to exist inside "a larger one". if certain algebraic relationships hold, the choices are not entirely free, as some numbers work better than other ones (4, for example, is a better choice than 3, and 8 is better than 7...there are good reasons for believing it should be an even number).

of course, the very idea of our universe existing in some larger structure, sounds very much like saying: "the universe isn't the (whole) universe", but it's still possible that the "enveloping universe" somehow leaves evidence in our discoverable universe that tells us it's there (or rather; if we hypothesize such a universe, we may be able to "explain" things that have predictable value, that might be borne out by experiment. this isn't really "proof" per se, but if it works in practice, we are likely to adopt this view).

there isn't any pure logical reason, that i know of, for thinking the universe is finite, or non-finite. my guess is, is that since the universe exhibits similar levels of complexity across all the scales of resolution we have; it is infinite in depth, as well as breadth. it's possible this question may never be answered, due to our limitations.
 
  • #92
if the universe is expanding, it must be expanding into something, isn't that something also part of the universe, if it is expanding how come we keep the same distance from the sun, the big bang was just one more explosion in the universe, one of billions and billions of explosions happening as we speak, if we are moving or expanding we are just looking to occupy a different location in the infinite universe, there is no beggining or end because there is no beggining to time, and if there is no beggining to time, there is no beggining to the universe, and if there was no beggining. there was no creation, no matter how you diced or sliced, by the way I am no scientist and forgive my spelling
 
  • #93
josewrivera said:
if the universe is expanding, it must be expanding into something,
Not at all. The expansion simply means stuff within the universe is getting further apart. It is, in a very real sense, just a change of shape of the universe. There is no reason whatsoever for there to be any "outside" at all. In fact, in General Relativity, the very concept of an outside doesn't work very well.

josewrivera said:
if it is expanding how come we keep the same distance from the sun,
Because the expansion is a large-scale, average phenomenon. Overdense regions, such as our own galaxy or solar system, are quite stable within an expanding universe.
 
  • #94
josewrivera said:
if it is expanding how come we keep the same distance from the sun,

I think this impression is created by poor explanation of what the expansion means. We measure disatnt galaxies as receeding away from us at a speed proprtional to their distance. The important point to note is that this only applies to distant galaxies. Why only distant galaxies?
Becuase for nearby obejct they are gravitationally bound and the expansion of the universe is not strong enough to unbind them. It might be in the future, google "big Rip" for this possibility, but it is not now.
Hence gravitationally bound strucutres do not see any expansion. The solar system is grvaitiationally bound, so is our galaxy and so are nearby galaxies. For example Andromeda is on a collision course with the Milky Way. If everything felt the expansion this could not be the case.
Bottom line: for local structures, think nearby galaxies and closer , the expansion of the universe is irrelevant.
 
  • #95
josewrivera said:
, if we are moving or expanding we are just looking to occupy a different location in the infinite universe, there is no beggining or end because there is no beggining to time, and if there is no beggining to time, there is no beggining to the universe, and if there was no beggining. there was no creation, no matter how you diced or sliced, by the way I am no scientist and forgive my spelling

We don't know whether or not the universe is infinite. We do know there was a big bang event, but whether there were others and how far back they go back is currently unknown. Perhaps you are referring to certainly interesting models such as eternal inflation, CCC, ekpyrotic and bounce cosmologies that imply our big bang was not a unique event. But we have to be honest and say none of these models have been experimentally veirified yet. So I think a "we don't know" attitude is best. We should wait for the data to tell us the answeres and until that happens we should not presume anything.
 
  • #96
josewrivera said:
if the universe is expanding, it must be expanding into something, isn't that something also part of the universe, if it is expanding how come we keep the same distance from the sun, the big bang was just one more explosion in the universe, one of billions and billions of explosions happening as we speak, if we are moving or expanding we are just looking to occupy a different location in the infinite universe, there is no beggining or end because there is no beggining to time, and if there is no beggining to time, there is no beggining to the universe, and if there was no beggining. there was no creation, no matter how you diced or sliced, by the way I am no scientist and forgive my spelling

Jose, I encourage you to read the FAQ section of this forum (listed at the very top of this section). Many of your questions are answered in descriptive, non-rigourous and very accesible explanations.

As has already been explained (e.g. Chalnoth), the known physics of our Universe does not require an additional "dimension" within which to expand. The shape/curvature of our Universe is an intrinsic geometric property, and does not require a higher dimension in which it is embedded. That is to say, our Universe can be infinite, open, and expanding...but it is not expanding into any "external" pre-existing volume. This fact is precisely why thinking of the Big Bang as a single "explosion" IN Space is misleading and incorrect. The correct concept is to understand the Big Bang as occurring everywhere, and to imagine it is an explosion OF space. The Big Bang occurred simultaneously in the space now occupied by the current position of your belly-button, as well as any (and all) arbitrary points in the Andromeda galaxy.

According to the Standard model of Cosmology, there was a definite beginning of "time", which was the instant of the Big Bang. The Big Bang created our Universe which contains space and time, and our Universe does not exist "in" space and time. This is part of the "Containment Principle", which is an integral aspect of modern Cosmology.
 
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  • #97
Deuterium2H said:
Jose, I encourage you to read the FAQ section of this forum (listed at the very top of this section). Many of your questions are answered in descriptive, non-rigourous and very accesible explanations.

As has already been explained (e.g. Chalnoth), the known physics of our Universe does not require an additional "dimension" within which to expand. The shape/curvature of our Universe is an intrinsic geometric property, and does not require a higher dimension in which it is embedded. That is to say, our Universe can be infinite, open, and expanding...but it is not expanding into any "external" pre-existing volume. This fact is precisely why thinking of the Big Bang as a single "explosion" IN Space is misleading and incorrect. The correct concept is to understand the Big Bang as occurring everywhere, and to imagine it is an explosion OF space. The Big Bang occurred simultaneously in the space now occupied by the current position of your belly-button, as well as any (and all) arbitrary points in the Andromeda galaxy.

According to the Standard model of Cosmology, there was a definite beginning of "time", which was the instant of the Big Bang. The Big Bang created our Universe which contains space and time, and our Universe does not exist "in" space and time. This is part of the "Containment Principle", which is an integral aspect of modern Cosmology.


Everything you say may be true but I think the picture is more nuanced than that. I think most comslogigst that work on the very early universe would agree that "The Standard Model" is not to be trusted as we get v close to the Planck scale. Hell all of my textbooks say that too, so this is nothing new. In order to say there was a beginning of time at the big bang we need to trust the mdoel all the way to the Planck scale which i think very few people would say is wise.
 
  • #98
we have trouble undestanding events that ocurred only a couple thousand years ago, but we think we have the answer to what happened 5 billion years ago, the big bang didnt create the universe nothing no matter how big can affect a infinite universe in its totallity some time in the future humanity is going to come to this conclusion no beggining no end and there was time before the big bang, and is not possible to reach the beggining because there is always a second before, and a minute and an hour.
 
  • #99
josewrivera said:
we have trouble undestanding events that ocurred only a couple thousand years ago, but we think we have the answer to what happened 5 billion years ago, the big bang didnt create the universe nothing no matter how big can affect a infinite universe in its totallity some time in the future humanity is going to come to this conclusion no beggining no end and there was time before the big bang, and is not possible to reach the beggining because there is always a second before, and a minute and an hour.

You really need to read some basic cosmology before posting such nonsense on a forum where people take science seriously.

"big bang" has two meanings

1) the singularity / t=0 and nobody pretends to know what this was all about, it's just the place where the models break down.

2) everything since one Plank time after the singularity. This is remarkably well understood, although there are still puzzles. I recommend you read "The First Three Minutes" by Weinberg.
 
  • #100
josewrivera said:
we have trouble undestanding events that ocurred only a couple thousand years ago, but we think we have the answer to what happened 5 billion years ago,
This is really sad. Why not try learning a little bit about how we have learned these things before throwing out blanket condemnations of science you know nothing about?
 
  • #101
I think the universe is infinite in space and time, but finite in energy and mass.
 
  • #102
jay.yoon314 said:
I think the universe is infinite in space and time, but finite in energy and mass.

Do you have any SCIENCE to back up this statement or is it merely unsupported, and unsupportable, personal opinion?
 
  • #103
skydivephil said:
Everything you say may be true but I think the picture is more nuanced than that. I think most comslogigst that work on the very early universe would agree that "The Standard Model" is not to be trusted as we get v close to the Planck scale. Hell all of my textbooks say that too, so this is nothing new. In order to say there was a beginning of time at the big bang we need to trust the mdoel all the way to the Planck scale which i think very few people would say is wise.

Why is it that it is necessary to explain the creation of space-time, on one hand, and mass-energy, on the other hand, as having occurred simultaneously? I argue that there is no contradiction in an alternative mechanism of a Big Bang occurring in such a way that the creation of space-time precedes the creation of mass-energy.

I also mention another point as follows: Is there any way to "see" empty space? I postulate that the limits of our observable universe may merely be the limits at which space-time truly becomes empty. Not only empty in a sense that Object A is located 5 billion light years away, and that there is nothing in that line of sight until 12 billion light years away, but rather empty in that there simply hasn't elapsed enough time for something to be 80 billion light years away.

We cannot assume that the only kind of empty space that there could be is empty space that is between two other "things" (such as galaxies). It is possible for empty space to mean that there is literally nothing out there beyond some distance away from some position (such as ours).

A region of the universe that we cannot see presently because it has undergone metric expansion beyond our "horizon" greater than the speed of light, and a region of the universe that we cannot see because it is empty space, are indistinguishable, I believe.
 
  • #104
phinds said:
Do you have any SCIENCE to back up this statement or is it merely unsupported, and unsupportable, personal opinion?

Sorry about that, it was a bad first post.

The reason why I believe that is because space-time will continue to exist is specifically because of the time dimension of space-time. Assuming that time will continue to exist no matter how much "time" passes, it is unbounded. In the language of limits, there is no finite time interval starting from any initial time not t = 0 such that space-time itself will not exist at the end of that interval.

In the case of matter and energy, on the other hand, we know of no law that states that the mass-energy as a whole can be created or destroyed, nor have we ever observed such a process. Therefore, the amount of mass-energy that exists now will be the amount of mass-energy that exists at any time in the future.

The distinction between space-time and mass-energy is clear in the sense that space-time has the capacity to become unboundedly large whereas mass-energy clearly does not, according to presently known physical laws. I argue that a quantity that has the capacity to become infinitely large is actually infinite. If this were not the case, how is the following paradox resolved?

Space-time can grow without bound, and probably will. Let us define two variables:
P (present) := presently existing space-time
F (future):= potentially available but not currently existing space-time
S (sum) := P + F

We cannot, with perfect confidence, know F. We cannot even know P, since we do not know exactly how large our whole universe is.

But if the universe is accelerating in its expansion rate, then we know that F is unbounded. Then even if P is finite, S is unbounded. The universe will exist for a lot longer than it exists now. Therefore, I argue that F, being the "long run supply curve" of space-time versus P, being the "short run supply curve" of space-time, is the most faithful representation of space-time's true nature.

However, if the metric expansion of space involves the conversion of space-time into mass-energy specifically in the form of dark energy, then my claim cannot stand. But this would involve having to define an additional conservation law between not only energy and mass, but between mass-energy and space-time, and there isn't a shadow of a hope for that to work.
 
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  • #105
The observable universe ends abruptly 13.7 billion years ago. This 'boundary' is called the CMB, or surface of last scattering. There are no galaxies, stars, etc. lurking behind the CMB waiting to be discovered, and precious little spacetime. Only about 400,000 years separates the CMB from the Big Bang.
 
<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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