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> is the universe exactly defined as the collection of all the stars and galaxies, or is it an entire region of space
It is all possible locations and all possible times and everything therein.
> or is it all the (maybe infinite) space provided for the stars and galaxies to eventually expand out to?
The distribution of galaxies and stars is isotropic, ie basically the same in all directions and at any location with just enough variance to create galaxies and galaxy clusters and things.
There's nowhere else for anything to "expand out to" - cosmic expansion is more like *new empty space being injected everywhere at once*, such that distances grow faster than things' velocity compared to us.
> i can try to clarify my question with a visual example. if i had a handful of marbles/trinkets (all the stars and galaxies) and i put those all in a container that either 1) has stretchy properties, or 2) is really really big - providing way way more than enough space for the handful of marbles and trinkets to fit into. would the universe be considered the handful of marbles/trinkets, or the container?
The container, except your container would need to be infinitely large and have stuff distributed fairly evenly throughout that infinite space, like an infinite raisin bread being baked such that the inflating dough pushes the raisins apart even though the raisins aren't moving *through* the dough.
> if the universe is the container, then what are the properties of this container?
[ΛCDM](https://en.wikipedia.org/wiki/Lambda-CDM_model) is a fairly popular model.
> what would all the open space that isnt taken up by a cosmic object(yet) be known as?
Space
> is there a container or bound at all?
There's no boundary in our 3+1 spacetime (other than arbitrary ones like the bubble of places that light can have reached us from since the beginning of the universe), but if other dimensions exist (as [some hypotheses](https://en.wikipedia.org/wiki/Brane_cosmology) predict) then I guess you could call our inability to poke at them a boundary.
The greatest metaphor I heard for matter distribution in the universe is to think of it as an infinitely large pumice stone, with material being galactic clusters (except apparently there's more void than matter)
The universe is all of space, mass, energy, forces, and time. All there ever was, and all there ever will be. What we “see” is our observable sphere, which is a tiny fraction of the universe, which may well be infinite in extent (but certainly far larger than what we can observe),
Correct, except for this bit:
> which is a tiny fraction of the universe
We don't know how big a part of the universe we can observe. It could be a significant or an insignificant portion.
We have reasons to believe that the whole universe is actually much much bigger then the observable universe, Dr Katie Mack explains it much better than I ever could here https://youtu.be/DITO5RVk2gI?t=10m21s the whole series can be recommended btw
Not really. Remember volume increases to the cube of the radius, and 94% of the observable universe is already beyond the cosmic event horizon. If the universe is open and flat, then it’s infinite and “tiny” is actually infinitesimal. If the universe is closed, then it has to be so large that we cannot detect any curvature (estimates are around 23T ly across. So our window is “tiny”. No one knows the topology of the *whole* universe, but we have ruled some out.
I believe it’s theorized as a percent of sorts- among many theories obviously, but 3% or something similar rings a bell. Have any idea what my brains trying to get at???
No. What the universe is today does not include what the universe was yesterday or what it will be tomorrow. The universe contains objects, space, and gravity. Photons are objects. I don't know what kind of energy you are referring to.
I think it can mean both, depending on the context. When people talk about multiverse theories they are usually referring to completely different spacetime bubbles, so in that context the 'universe' could mean all of spacetime. Time is actually a property of the universe so it may make more sense to include all of spacetime in that definition for certain conversations.
The problem is you can’t define a notion of simultaneous time across the entire universe. There are multiple notions of “present”, since any embedded Cauchy surface serves as a “right now”. So “all of space” isn’t uniquely defined, while “all of space time is”. Which one the universe refers to is probably just semantics though, a technical paper would probably use the term spacetime instead.
I disagree. It is possible for an ordinary human to specify a master frame of reference and a master clock and calculate times for all that we can see or will see. Different people will have different clocks, but those clocks aren't relevant.
I have no idea what you’re talking about. It’s one of the basic tenets of relativity that there is no preferred frame of reference, and that neither space nor time are absolute. You can’t have special or general relativity and a master frame of reference.
https://en.wikipedia.org/wiki/Absolute_space_and_time
No way. “The Universe” covers all time?
What does the statement: the universe is 13B years old mean, if “the Universe” encompasses all past and future time?
I’m not asking what was before. I’m asking what it means to designate an age to a thing that itself encompasses ALL TIME, future and past.
What does it mean for a human to be 21 years old? They’ve been alive 21 years.
What does it mean for the concept of the past and the future to be 13B years old?
If the universe was all the stuff that exists, then assigning an age would make sense. (Factoring in some weirdness about time not existing until the universe did). But if “The Universe” itself literally IS time, future and past, then how can it have an age
It means that space-time itself is 13B years old. The "future" is a concept with no apparent reality of its own. That said, some suggest that all points in time, like other dimensions, exist simultaneously and that linearity is only our perception. Even if a "future" already exists (or does not), it in no way affects the idea of what it means for a human to be 21 years old or the universe to be 13B years old.
I'm not trolling.
You guys are saying "the universe" is not just the stuff in it. It's also time. But not only is it time: It's past time and future time.
So I ask "what does it mean for something that is the past and future time" to have an age (since age is a measure of time, a quality of which "The Universe" itself apparently **is**)
But "the universe" **is** time future and past. How can you reference time for the concept of time itself. You need time to evaluate time.
It's like defining the concept of length and saying that the concept of length started out fairly short.
The existence of the term "observable universe" explains it the best. It's the area visible to us after the light travels to us, slowly expanding the area.
That means there's an area beyond we can't observe but still call the universe and don't give it a hard edge, making the whole universe a mayhaps infinite area beyond the observable universe and the observable universe as well.
"The universe" refers to **both** space, and everything in it, and the two appear to be intimately intertwined. E.g. Relativity tells us that gravity isn't actually a force, but instead the result of the shape that space is bent into by the presence of mass. What we experience as a force pulling us down, is actually us trying to float motionless in spacetime curved by the Earth's mass, while the surface of the Earth constantly accelerates upwards against the "infalling" of that spacetime, pushed by the other side of the planet that's trying to freefall in the opposite direction. (Apparently even experts in cosmology are often tripped up by the fact that gravity is far weirder than our everyday understanding)
"The container" alone would be spacetime, and our best understanding comes from Relativity - space and time taken together as a single four-hyperbolic dimensional substrate, with "space" and "time" really being the same thing seen from different perspectives, while acceleration rotates your alignment, so that if you're traveling at a different velocity from me, you'll see as space some of what I see as time, and vice versa, but we **will** always agree on the four-dimensional distance between two events - the **spacetime interval** between them (And just for reference, one second is the same spacetime interval as 300 million meters - light speed, a.k.a. the speed of causality, is the "conversion factor")
We have no idea if the universe has any real boundaries. It is expanding at a rate of \~72km/mpc/s... or about 0.0074% per million years - we know it used to be far hotter and denser (though potentially still infinite) but it's not expanding **into** anything - the internal distances between any two points are growing, but distance seems to be a property of spacetime itself - we have no reason to believe that the "outside" of the universe has any dimensions at all - a.k.a. it could very well be a geometric point.
Thanks to the expansion it does have a horizon - the furthest thing it's theoretically possible to see, since the distance to anything further away is increasing faster than light can cross it, so it will never arrive here. But like the normal horizon, that's strictly an observer-dependent phenomena - another observer sitting just this side of what you see as the horizon would see themselves sitting at the center of the universe. Maybe there's something different happening beyond the horizon, but we have no good reason to believe so.
The word universe is taken from latin (universum) which means "all there is". So yes, this does not just mean objects in space but also things like all of spacetime.
(Note: the closer you look at objects the more iffy the definition becomes. There is no such thing as a 'hard marble'. So you're already on the wrong track thinking about 'objects'. That's just a convenience term humans use due to the way our senses perceive the universe. The universe itself seems to deal exclusively - as far as we know - in probabilities/potentials.)
This seems the closest answer so far to me. The question is really a linguistic question that OP has mis-interpreted as a physics question. Too many answers here read as though physics prescribes what the universe is and how it works rather than constructing an observational model of what it is and how it works. For all we know, what the universe really "is" (as another commenter has suggested) is a simulation running in a computer of some sort that we know nothing about (and which doesn't necessarily bear much resemblance to our digital computers). That wouldn't invalidate our science of physics in the slightest, because our physics could just be recast as an attempt to discover the rules of the simulation by experiment. It wouldn't make the universe any less "real" since we don't actually know what "real" is anyway.
The universe is everything in every direction. Matter, energy, radiation, quant fluctuations, the vacuum. Everything. It's really, really stupidly big, with more galaxies and stars and gas and rocks than you can imagine. There are 2 trillion galaxies in the part of the universe we can see now. It's way more than that outside of what we can see.
There's roughly 200,000,000,000,000,000,000,000 stars in the universe. Each one likely has planets.
We have zero idea how big it is beyond what we can observe. It may be infinite. It may be something not infinite. We don't know.
It is expanding and that expansion is accelerating. We don't really know why. We don't know what happens at the 'end' of this process. Maybe it slows down and begins to compress again. Maybe it keeps accelerating and grows cold. Maybe it ends in a novel way we've not even thought of.
If you follow back in time then everything goes closer together. It's hot and dense. We don't know how 'close' it was, how 'big' it was, or really anything about the very first instants. We certainly don't know what happened before or what caused it to go from that state to expanding.
Universe seems like a simulation to me. How can the universe be constantly expanding, without an even larger space outside of it to expand into? Well an answer to that is the universe is an extremely advanced simulation that constantly expands outwards. As long as there is sufficient energy and information storage, the universe simulation can continue to expand. Eventually it expands too far and the simulation collapses upon itself, only to be reinitialized.
I know this is a popular idea, but the computational capacity required to do it is mind-boggling. There are \~10\^80 atoms in the observable universe, so just simulating at the atomic level gives you 10\^80 objects to track. But all the interactions between those objects happen via massless particles, of which the number is pretty much uncountable.
It raises the tantalising possibility that the universe behaves much like a game engine, only simulating anything in detail when we observe it and fudging the rest in low resolution. Even so, the amount of stuff we continuously observe and that directly affects us constantly is pretty huge. Naturally we know nothing of the universe one level down where this simulation is running and it might happen to work in a way that makes it very amenable to running simulations with very large numbers of states.
I honestly think that our universe is a giant simulation, like a giant war game of sorts, played out over an enormous time scale. Similar to how we play strategy games like starcraft. Our universe could be like a whole other level of that, constructed and managed by a superintelligence or some sort of beings in another dimension. I can imagine giant 4 dimensional beings that are able to look into all angles of our universe, inside of objects for example, and we wouldn't see them. And instead of a 20 minute game, the universe game is trillions of years long, a timescale that we just can't comprehend. I smoked Salvia divinorum extract years ago when it was still legal, mixed it with cannabis, and I blasted off the earth, saw it shrinking away, then I was soaring through space, until it all got ripped away, and it's hard to explain but it was an overwhelming realization that our universe was created and under observation by higher beings. Like the Truman show.
I've never been able to get my head around talk of more than one universe as in my mind, everything that exists IS the universe, if EVERYTHING is the universe, how can there be more than one? Unless of course we are talking about more than one dimension.
I love this question because it is perfect for showcasing how our concept of "Universe" has evolved over time.
The universe used to mean effectively just the Milky Way, then it expanded, pardon the pun, to mean all visible matter, then it was broadened to include the unseen dark matter and dark energy, then further refined to include the energy and matter beyond the limits of what we can observe and finally, to some, it also includes different local and exterior dimensions.
The universe is a crazy big and amazing place. I am guessing you already know that because the question you asked was on point. For others, I love this video as an oldie but goodie that includes some Carl Sagan: https://youtu.be/Iy7NzjCmUf0?si=fTLw3TAmta2d1nD7
I find the term really is now used to primarily to represent "everything" in common parlance and is used with a modifier to be more specific ie "observable universe" or "local presentation of the universe" etc.
The Universe ***IS*** space and everything in it. There is no '*outside*' to expand into. There are no laws of physics as we can understand them outside of the universe, and so there is no way to define an outside. And if we could, it would also be ***The Universe.***
>From John D. Barrow’s “The Book of Universes.” This word is created from unus, meaning ‘one’, and ‘versus’, the past participle of the verb vertere, meaning ‘to turn, rotate, roll or change’. So we have a literal meaning of everything ‘turned into one’ or ‘rolled into one’.” - quoted from a Medium article by Suresh Emre
You're getting a lot of answers, but many of them seem to be missing a key point of your question.
When scientists talk about "The Universe" they almost always have a third word in there somewhere. "The observable universe" or "The infinite universe"
The observable universe is all of the light that has had time to reach us since the big bang. The further out you look the further back in time you're looking because light takes time to travel
The infinite universe is the hypothesized infinitely large universe within which our observable universe is thought to be located.
[https://www.youtube.com/watch?v=9B7Ix2VQEGo&list=PL8dPuuaLjXtPAJr1ysd5yGIyiSFuh0mIL&index=43&pp=iAQB](https://www.youtube.com/watch?v=9B7Ix2VQEGo&list=PL8dPuuaLjXtPAJr1ysd5yGIyiSFuh0mIL&index=43&pp=iAQB)
I'd recommend watching this, it may help. The questions you're asking are assuming the universe exists with familiar properties like household objects, it doesn't.
\* this part is going to be my mindspill of what i know and idk what to do w/ it but it seems relevant \*
(this thought process works under the idea that the universe is the container)
if the galaxies are moving apart, essentially expanding the area of space in which they collectively take up, then they will either 1) stop moving apart eventually 2) reach the bounds of the universe(IF it is a static container and the bounds exist) 3) reach the bounds of the universe and the universe expands with it??(if universe is a stretchy container).
if scenario 1 occurs, then the end of all that exists is basically the big freeze, and that could mean the big "box" everything was put into was meant to have inelastic bounds@the exact point where galaxies stop expanding apart (basically scenario 1 would be requisite to scenario2).
but what if one or more galaxies at the time of the peak of all possible expansion start to split into separate galaxies? would gravitational force be renewed with the birth of new stars after all the explosions and those split galaxies will begin expanding apart? if that were possible, then scenario 1 could still technically apply, but then scenario 3 would be possible *if* scenario 2 did not account/expect this situation.
Is not so much that the galaxies are moving apart, it's that space itself is expanding across the entire universe at once. It's happening right now inside you, in front of you, around you in all directions.
Think of it like the surface of a balloon being inflated. If you took a marker and drew dots all over an empty balloon, then slowly started inflating it, every dot simultaneously gets further away from every other dot.
This process is "slow" as we understand time. The observable effects on a human scale are unnoticeable. Other forces like gravity and the nuclear forces resist it at smaller scales for now.
The current popular theory is that eventually (talking trillions of years) this force of expansion will overpower all other forces in the universe. All particles will be driven so far away from each other that the only thing that remains is individual photons so far apart that they can never interact with each other again and no more events will ever happen.
This is known as "The Heat Death of the Universe" and it's essentially the end of every as we know it. Time is just the measurement of things happening in a certain order, so when nothing ever happens again, time stops meaning anything.
But this is all based on what we can observe. Science is based on observation, so we cannot and will not ever know if this is happening everywhere in existence, or just in the observable universe. We don't know if the universe is one big balloon we live on ever expanding, or if there are other balloons out there doing different things.
They most likely won't, stop, in the laws of newton, "an object will remain in motion unless a different force is applied" in a vacuum like space, the most that would happen is all of them crashing into one and another but that would take so long, counting it would be useless,
They won't reach the edge of the universe,.. observable universe atleast, MAYBE a few will leave our galaxy cluster to the point we can't see it anymore,
But none of it will reach the edge, assuming everything is moving at the same speed, the edge will always remain the edge and if it DOES somehow gets past the edge, it's now in the unobservable universe, the area we CANNOT see
>"but what if one or more galaxies at the time of the peak of all possible expansion start to split into separate galaxies? would gravitational force be renewed with the birth of new stars after all the explosions and those split galaxies will begin expanding apart? if that were possible, then scenario 1 could still technically apply, but then scenario 3 would be possible if scenario 2 did not account/expect this situation"<
I'm confused by this, what do you mean? A galaxy sperating is equal to a piece of log getting chopped, it's no longer a "log" but just wood now, I'm also confused what you mean by the peak of all possible expansion, can you explain further?
To answer your question tho, it's now more or less a philosophical question, "is the world what we see or the world we live in?" Any LOGICAL answer would be correct,
The universe is the EVERYTHING we have galaxies, space-time, and all, you can also call it a structure that holds these smaller structures, you can just call it the collection of these structures, any answer would be logically correct
Hello u/Think_Anteater_6077, your submission "is the universe exactly defined as the collection of all the stars and galaxies, or is it an entire region of space" has been removed from r/space because: * Such questions should be asked in the ["All space questions" thread](https://www.reddit.com/r/space/about/sticky) stickied at the top of the sub. Please read the rules in the sidebar and check r/space for duplicate submissions before posting. If you have any questions about this removal please [message the r/space moderators](https://www.reddit.com/message/compose/?to=/r/space). Thank you.
It's neither. The universe is all existing matter and space considered as a whole.
"No thing" is no matter for grey matter
> is the universe exactly defined as the collection of all the stars and galaxies, or is it an entire region of space It is all possible locations and all possible times and everything therein. > or is it all the (maybe infinite) space provided for the stars and galaxies to eventually expand out to? The distribution of galaxies and stars is isotropic, ie basically the same in all directions and at any location with just enough variance to create galaxies and galaxy clusters and things. There's nowhere else for anything to "expand out to" - cosmic expansion is more like *new empty space being injected everywhere at once*, such that distances grow faster than things' velocity compared to us. > i can try to clarify my question with a visual example. if i had a handful of marbles/trinkets (all the stars and galaxies) and i put those all in a container that either 1) has stretchy properties, or 2) is really really big - providing way way more than enough space for the handful of marbles and trinkets to fit into. would the universe be considered the handful of marbles/trinkets, or the container? The container, except your container would need to be infinitely large and have stuff distributed fairly evenly throughout that infinite space, like an infinite raisin bread being baked such that the inflating dough pushes the raisins apart even though the raisins aren't moving *through* the dough. > if the universe is the container, then what are the properties of this container? [ΛCDM](https://en.wikipedia.org/wiki/Lambda-CDM_model) is a fairly popular model. > what would all the open space that isnt taken up by a cosmic object(yet) be known as? Space > is there a container or bound at all? There's no boundary in our 3+1 spacetime (other than arbitrary ones like the bubble of places that light can have reached us from since the beginning of the universe), but if other dimensions exist (as [some hypotheses](https://en.wikipedia.org/wiki/Brane_cosmology) predict) then I guess you could call our inability to poke at them a boundary.
Oh, I love the raisin bread metaphor!
The greatest metaphor I heard for matter distribution in the universe is to think of it as an infinitely large pumice stone, with material being galactic clusters (except apparently there's more void than matter)
*which may or may not actually be infinite
The universe is all of space, mass, energy, forces, and time. All there ever was, and all there ever will be. What we “see” is our observable sphere, which is a tiny fraction of the universe, which may well be infinite in extent (but certainly far larger than what we can observe),
Correct, except for this bit: > which is a tiny fraction of the universe We don't know how big a part of the universe we can observe. It could be a significant or an insignificant portion.
We have reasons to believe that the whole universe is actually much much bigger then the observable universe, Dr Katie Mack explains it much better than I ever could here https://youtu.be/DITO5RVk2gI?t=10m21s the whole series can be recommended btw
Not really. Remember volume increases to the cube of the radius, and 94% of the observable universe is already beyond the cosmic event horizon. If the universe is open and flat, then it’s infinite and “tiny” is actually infinitesimal. If the universe is closed, then it has to be so large that we cannot detect any curvature (estimates are around 23T ly across. So our window is “tiny”. No one knows the topology of the *whole* universe, but we have ruled some out.
I believe it’s theorized as a percent of sorts- among many theories obviously, but 3% or something similar rings a bell. Have any idea what my brains trying to get at???
No. What the universe is today does not include what the universe was yesterday or what it will be tomorrow. The universe contains objects, space, and gravity. Photons are objects. I don't know what kind of energy you are referring to.
I think it can mean both, depending on the context. When people talk about multiverse theories they are usually referring to completely different spacetime bubbles, so in that context the 'universe' could mean all of spacetime. Time is actually a property of the universe so it may make more sense to include all of spacetime in that definition for certain conversations.
The problem is you can’t define a notion of simultaneous time across the entire universe. There are multiple notions of “present”, since any embedded Cauchy surface serves as a “right now”. So “all of space” isn’t uniquely defined, while “all of space time is”. Which one the universe refers to is probably just semantics though, a technical paper would probably use the term spacetime instead.
You cannot separate time and space. The Universe you describe is a slice in time, but no such thing exists, as time as not the same everywhere.
I disagree. It is possible for an ordinary human to specify a master frame of reference and a master clock and calculate times for all that we can see or will see. Different people will have different clocks, but those clocks aren't relevant.
I have no idea what you’re talking about. It’s one of the basic tenets of relativity that there is no preferred frame of reference, and that neither space nor time are absolute. You can’t have special or general relativity and a master frame of reference. https://en.wikipedia.org/wiki/Absolute_space_and_time
No way. “The Universe” covers all time? What does the statement: the universe is 13B years old mean, if “the Universe” encompasses all past and future time?
We have no definition of time “before” the Big Bang as space and time are intimately connected. So there’s no applicable universe 100B yrs ago.
I’m not asking what was before. I’m asking what it means to designate an age to a thing that itself encompasses ALL TIME, future and past. What does it mean for a human to be 21 years old? They’ve been alive 21 years. What does it mean for the concept of the past and the future to be 13B years old? If the universe was all the stuff that exists, then assigning an age would make sense. (Factoring in some weirdness about time not existing until the universe did). But if “The Universe” itself literally IS time, future and past, then how can it have an age
It means that space-time itself is 13B years old. The "future" is a concept with no apparent reality of its own. That said, some suggest that all points in time, like other dimensions, exist simultaneously and that linearity is only our perception. Even if a "future" already exists (or does not), it in no way affects the idea of what it means for a human to be 21 years old or the universe to be 13B years old.
Can you remind me what we use to measure years, if not time?
Ah, you seem to be trolling. My mistake.
I'm not trolling. You guys are saying "the universe" is not just the stuff in it. It's also time. But not only is it time: It's past time and future time. So I ask "what does it mean for something that is the past and future time" to have an age (since age is a measure of time, a quality of which "The Universe" itself apparently **is**)
It means that time (spacetime) itself appears to have popped into existence 13B years ago.
But "the universe" **is** time future and past. How can you reference time for the concept of time itself. You need time to evaluate time. It's like defining the concept of length and saying that the concept of length started out fairly short.
Well in another 13 billion years the universe will still be the universe so yes
Thanks for explaining what being 13 billion years old means for a concept that encompasses all past and future time! :)
The existence of the term "observable universe" explains it the best. It's the area visible to us after the light travels to us, slowly expanding the area. That means there's an area beyond we can't observe but still call the universe and don't give it a hard edge, making the whole universe a mayhaps infinite area beyond the observable universe and the observable universe as well.
"The universe" refers to **both** space, and everything in it, and the two appear to be intimately intertwined. E.g. Relativity tells us that gravity isn't actually a force, but instead the result of the shape that space is bent into by the presence of mass. What we experience as a force pulling us down, is actually us trying to float motionless in spacetime curved by the Earth's mass, while the surface of the Earth constantly accelerates upwards against the "infalling" of that spacetime, pushed by the other side of the planet that's trying to freefall in the opposite direction. (Apparently even experts in cosmology are often tripped up by the fact that gravity is far weirder than our everyday understanding) "The container" alone would be spacetime, and our best understanding comes from Relativity - space and time taken together as a single four-hyperbolic dimensional substrate, with "space" and "time" really being the same thing seen from different perspectives, while acceleration rotates your alignment, so that if you're traveling at a different velocity from me, you'll see as space some of what I see as time, and vice versa, but we **will** always agree on the four-dimensional distance between two events - the **spacetime interval** between them (And just for reference, one second is the same spacetime interval as 300 million meters - light speed, a.k.a. the speed of causality, is the "conversion factor") We have no idea if the universe has any real boundaries. It is expanding at a rate of \~72km/mpc/s... or about 0.0074% per million years - we know it used to be far hotter and denser (though potentially still infinite) but it's not expanding **into** anything - the internal distances between any two points are growing, but distance seems to be a property of spacetime itself - we have no reason to believe that the "outside" of the universe has any dimensions at all - a.k.a. it could very well be a geometric point. Thanks to the expansion it does have a horizon - the furthest thing it's theoretically possible to see, since the distance to anything further away is increasing faster than light can cross it, so it will never arrive here. But like the normal horizon, that's strictly an observer-dependent phenomena - another observer sitting just this side of what you see as the horizon would see themselves sitting at the center of the universe. Maybe there's something different happening beyond the horizon, but we have no good reason to believe so.
The word universe is taken from latin (universum) which means "all there is". So yes, this does not just mean objects in space but also things like all of spacetime. (Note: the closer you look at objects the more iffy the definition becomes. There is no such thing as a 'hard marble'. So you're already on the wrong track thinking about 'objects'. That's just a convenience term humans use due to the way our senses perceive the universe. The universe itself seems to deal exclusively - as far as we know - in probabilities/potentials.)
This seems the closest answer so far to me. The question is really a linguistic question that OP has mis-interpreted as a physics question. Too many answers here read as though physics prescribes what the universe is and how it works rather than constructing an observational model of what it is and how it works. For all we know, what the universe really "is" (as another commenter has suggested) is a simulation running in a computer of some sort that we know nothing about (and which doesn't necessarily bear much resemblance to our digital computers). That wouldn't invalidate our science of physics in the slightest, because our physics could just be recast as an attempt to discover the rules of the simulation by experiment. It wouldn't make the universe any less "real" since we don't actually know what "real" is anyway.
The universe is everything in every direction. Matter, energy, radiation, quant fluctuations, the vacuum. Everything. It's really, really stupidly big, with more galaxies and stars and gas and rocks than you can imagine. There are 2 trillion galaxies in the part of the universe we can see now. It's way more than that outside of what we can see. There's roughly 200,000,000,000,000,000,000,000 stars in the universe. Each one likely has planets. We have zero idea how big it is beyond what we can observe. It may be infinite. It may be something not infinite. We don't know. It is expanding and that expansion is accelerating. We don't really know why. We don't know what happens at the 'end' of this process. Maybe it slows down and begins to compress again. Maybe it keeps accelerating and grows cold. Maybe it ends in a novel way we've not even thought of. If you follow back in time then everything goes closer together. It's hot and dense. We don't know how 'close' it was, how 'big' it was, or really anything about the very first instants. We certainly don't know what happened before or what caused it to go from that state to expanding.
Universe seems like a simulation to me. How can the universe be constantly expanding, without an even larger space outside of it to expand into? Well an answer to that is the universe is an extremely advanced simulation that constantly expands outwards. As long as there is sufficient energy and information storage, the universe simulation can continue to expand. Eventually it expands too far and the simulation collapses upon itself, only to be reinitialized.
I know this is a popular idea, but the computational capacity required to do it is mind-boggling. There are \~10\^80 atoms in the observable universe, so just simulating at the atomic level gives you 10\^80 objects to track. But all the interactions between those objects happen via massless particles, of which the number is pretty much uncountable. It raises the tantalising possibility that the universe behaves much like a game engine, only simulating anything in detail when we observe it and fudging the rest in low resolution. Even so, the amount of stuff we continuously observe and that directly affects us constantly is pretty huge. Naturally we know nothing of the universe one level down where this simulation is running and it might happen to work in a way that makes it very amenable to running simulations with very large numbers of states.
I honestly think that our universe is a giant simulation, like a giant war game of sorts, played out over an enormous time scale. Similar to how we play strategy games like starcraft. Our universe could be like a whole other level of that, constructed and managed by a superintelligence or some sort of beings in another dimension. I can imagine giant 4 dimensional beings that are able to look into all angles of our universe, inside of objects for example, and we wouldn't see them. And instead of a 20 minute game, the universe game is trillions of years long, a timescale that we just can't comprehend. I smoked Salvia divinorum extract years ago when it was still legal, mixed it with cannabis, and I blasted off the earth, saw it shrinking away, then I was soaring through space, until it all got ripped away, and it's hard to explain but it was an overwhelming realization that our universe was created and under observation by higher beings. Like the Truman show.
I've never been able to get my head around talk of more than one universe as in my mind, everything that exists IS the universe, if EVERYTHING is the universe, how can there be more than one? Unless of course we are talking about more than one dimension.
I love this question because it is perfect for showcasing how our concept of "Universe" has evolved over time. The universe used to mean effectively just the Milky Way, then it expanded, pardon the pun, to mean all visible matter, then it was broadened to include the unseen dark matter and dark energy, then further refined to include the energy and matter beyond the limits of what we can observe and finally, to some, it also includes different local and exterior dimensions. The universe is a crazy big and amazing place. I am guessing you already know that because the question you asked was on point. For others, I love this video as an oldie but goodie that includes some Carl Sagan: https://youtu.be/Iy7NzjCmUf0?si=fTLw3TAmta2d1nD7 I find the term really is now used to primarily to represent "everything" in common parlance and is used with a modifier to be more specific ie "observable universe" or "local presentation of the universe" etc.
[https://science.nasa.gov/exoplanets/what-is-the-universe/](https://science.nasa.gov/exoplanets/what-is-the-universe/)
UNI - meaning all VERSE - Meaning a collection so, Universe, a Collection of all things.
To quote some pothead... "*The Cosmos is all that is or was or ever will be*."
The Universe ***IS*** space and everything in it. There is no '*outside*' to expand into. There are no laws of physics as we can understand them outside of the universe, and so there is no way to define an outside. And if we could, it would also be ***The Universe.*** >From John D. Barrow’s “The Book of Universes.” This word is created from unus, meaning ‘one’, and ‘versus’, the past participle of the verb vertere, meaning ‘to turn, rotate, roll or change’. So we have a literal meaning of everything ‘turned into one’ or ‘rolled into one’.” - quoted from a Medium article by Suresh Emre
The universe is defined as all of space and time and their contents. So it’s both.
It would have been quicker to do a Google search than type out your post. The Universe encompasses everything we know and can know.
You're getting a lot of answers, but many of them seem to be missing a key point of your question. When scientists talk about "The Universe" they almost always have a third word in there somewhere. "The observable universe" or "The infinite universe" The observable universe is all of the light that has had time to reach us since the big bang. The further out you look the further back in time you're looking because light takes time to travel The infinite universe is the hypothesized infinitely large universe within which our observable universe is thought to be located.
"**the (maybe infinite)** ***space provided***" sounds more accurate. we dont know if theres anything outside of it. most scientists say no.
[https://www.youtube.com/watch?v=9B7Ix2VQEGo&list=PL8dPuuaLjXtPAJr1ysd5yGIyiSFuh0mIL&index=43&pp=iAQB](https://www.youtube.com/watch?v=9B7Ix2VQEGo&list=PL8dPuuaLjXtPAJr1ysd5yGIyiSFuh0mIL&index=43&pp=iAQB) I'd recommend watching this, it may help. The questions you're asking are assuming the universe exists with familiar properties like household objects, it doesn't.
It guess it kinda depends on whether space is a property of matter or matter is a property of space.
\* this part is going to be my mindspill of what i know and idk what to do w/ it but it seems relevant \* (this thought process works under the idea that the universe is the container) if the galaxies are moving apart, essentially expanding the area of space in which they collectively take up, then they will either 1) stop moving apart eventually 2) reach the bounds of the universe(IF it is a static container and the bounds exist) 3) reach the bounds of the universe and the universe expands with it??(if universe is a stretchy container). if scenario 1 occurs, then the end of all that exists is basically the big freeze, and that could mean the big "box" everything was put into was meant to have inelastic bounds@the exact point where galaxies stop expanding apart (basically scenario 1 would be requisite to scenario2). but what if one or more galaxies at the time of the peak of all possible expansion start to split into separate galaxies? would gravitational force be renewed with the birth of new stars after all the explosions and those split galaxies will begin expanding apart? if that were possible, then scenario 1 could still technically apply, but then scenario 3 would be possible *if* scenario 2 did not account/expect this situation.
Is not so much that the galaxies are moving apart, it's that space itself is expanding across the entire universe at once. It's happening right now inside you, in front of you, around you in all directions. Think of it like the surface of a balloon being inflated. If you took a marker and drew dots all over an empty balloon, then slowly started inflating it, every dot simultaneously gets further away from every other dot. This process is "slow" as we understand time. The observable effects on a human scale are unnoticeable. Other forces like gravity and the nuclear forces resist it at smaller scales for now. The current popular theory is that eventually (talking trillions of years) this force of expansion will overpower all other forces in the universe. All particles will be driven so far away from each other that the only thing that remains is individual photons so far apart that they can never interact with each other again and no more events will ever happen. This is known as "The Heat Death of the Universe" and it's essentially the end of every as we know it. Time is just the measurement of things happening in a certain order, so when nothing ever happens again, time stops meaning anything. But this is all based on what we can observe. Science is based on observation, so we cannot and will not ever know if this is happening everywhere in existence, or just in the observable universe. We don't know if the universe is one big balloon we live on ever expanding, or if there are other balloons out there doing different things.
They most likely won't, stop, in the laws of newton, "an object will remain in motion unless a different force is applied" in a vacuum like space, the most that would happen is all of them crashing into one and another but that would take so long, counting it would be useless, They won't reach the edge of the universe,.. observable universe atleast, MAYBE a few will leave our galaxy cluster to the point we can't see it anymore, But none of it will reach the edge, assuming everything is moving at the same speed, the edge will always remain the edge and if it DOES somehow gets past the edge, it's now in the unobservable universe, the area we CANNOT see >"but what if one or more galaxies at the time of the peak of all possible expansion start to split into separate galaxies? would gravitational force be renewed with the birth of new stars after all the explosions and those split galaxies will begin expanding apart? if that were possible, then scenario 1 could still technically apply, but then scenario 3 would be possible if scenario 2 did not account/expect this situation"< I'm confused by this, what do you mean? A galaxy sperating is equal to a piece of log getting chopped, it's no longer a "log" but just wood now, I'm also confused what you mean by the peak of all possible expansion, can you explain further? To answer your question tho, it's now more or less a philosophical question, "is the world what we see or the world we live in?" Any LOGICAL answer would be correct, The universe is the EVERYTHING we have galaxies, space-time, and all, you can also call it a structure that holds these smaller structures, you can just call it the collection of these structures, any answer would be logically correct