Throughout my whole life I’ve heard that the universe is infinite. I’ve also heard that the universe is constantly expanding. What I don’t understand is how it’s possible for something to be both infinite and expanding because, to me, the word “expanding” implies that something is finite.

Imagine a rubber ruler that is infinite in length, that has marks at centimeter intervals in either direction.

This is an infinite ruler, but it can stretch as it is made of rubber.

Now, stretch it. Despite it being infinite the tally marks have moved and are no longer 1cm apart, but a bit further than 1cm. The ruler has expanded, despite being infinite it is now longer than it was before.

That’s the general idea behind “expanding universe.” it isn’t so much that the universe is expanding into something but that the space between two points in the universe are moving apart, the space itself is expanding.

This is the best explanation in the thread by far. The part that most people are missing is that the actual scale of space is changing since the distance between everything is getting larger.

https://en.wikipedia.org/wiki/Metric_expansion_of_space

I like this one.

I imagined stretching a ruler apart, so that the 5cm tick and the 6cm tick were farther apart. The ruler has expanded, even though the ends of the ruler go on into infinity.

Anyone interested in this kind of stuff, should check out the PBS Space Time web series. They do a great job of ELI5, and then develop those explanations into more complex ideas.

While I do love rock, metal, and in general anything in the surrounding genres I don’t think “Muscle Bitches – Is Your Metal Heavy?” will help anyone learn much about physics.

….that is a fantastic song however.

Good God… If ever there was a time to make a ridiculous, stupid mistake, talking about physics education is it.

Consider it edited. No one will ever believe you.

“Muscle Bitches – Is Your Metal Heavy?”

For the lazy

https://www.youtube.com/watch?v=AmY1sZMzyG8

It is always going to be inherently difficult for the human mind to consider this answer, because we are fools. You tell someone that you stretch the ruler and they consider that the ends must be moving into something then, because the ruler is getting longer. Every instance of us performing this task of stretching something follows this pattern so adding the complexity of infinity makes it difficult or impossible to rationalise. Our foolish minds understand this pattern and have difficulty letting go of it.

I once had it explained as imagine 2 horizontal lines and 2 vertical lines, they are infinitely long – they never end – and form into a tic-tac-toe grid before you. If you grab the vertical lines and spread them apart the horizontal lines spread apart by the same amount, and vice versa. So you grab one of the vertical lines and run with it, for miles and miles. All of the intersections of this tic-tac-toe grid are now moving apart from each other as fast as you can make them. To you, the size of the grid is expanding whilst actually also still being infinite, but here is the kicker, now imagine you grow at the same rate as the increase in distance between the intersecting points. This is important as it allows your mind to let go of the concept of scale you are used to. So now, any measure between the points shows massive expansion, whilst at the same time, because of the infinite nature of the bars… there is also no expansion. The difficulty of understanding expansion of an infinite thing is letting go of what you understand about finite distance and scale.

What is it expanding into. A ruler won’t expand if it hits a brick wall. It’s the matter in space that they claim is expanding, how can empty void expand into empty void. It’s the light that is lighting up the empty space “creating” it.

It’s like being in a cave with zero light. There is nothing, no depth, no walls, no you, just protons and electrons repelling each other, you add light, then there’s depth and dimensions and walls, a cave etc.

What is it expanding into

Nothing. everything. Infinity. Infinity has no limits. You can create an infinite series but still add one more number. For instance: the set of all integers (… -4, -3, -2, -1, 0, 1, 2, 3, 4 ….) Infinite in both directions, no room for more numbers. Yet we can always add a number and “expand” the real number line. For instance, adding 0.5 (… -4, -3, -2, -1, 0, 0.5, 1, 2, 3, 4….) We now “exanded” the set of all integers and added one extra member, it’s “longer” now, despite being infinite in both directions. We didn’t need to “make room” for 0.5, the numbers just shifted into infinity without a fuss. infinity is weird is most likely the best answer I can give you. assuming the universe is infinite and unbounded it will seize to obey the rules that come with finite space. It starts obeying rules of infinity, one of which is that you can increase the “volume” of the universe without needing a place to put it.

but this still doesnt make sense according to OPs question. if the rubber band was infinite, you would never be able to stretch it.

That’s not necessarily true. Infinity doesn’t really work the way you’re used to quantities working. Mathematically, you can show that some infinities are larger than others. An example:

Take the natural numbers (1, 2, 3, 4, 5…). Obviously you know there are infinitely many of them. But we know that there aren’t any between 1 and 2, between 2 and 3, etc. Now look instead at all numbers, including decimals. We can obviously come up with an infinite list of them, but unlike the natural numbers, we can come up with an infinite list between any two of them as well. Between 1.5 and 1.6, we have 1.51, 1.52, 1.53…., 1.501, 1.511, 1.502, 1.512, 1.5001, 1.50000000001…you can go forever. So in a sense this infinity is larger.

“Stretching” the ruler is like gradually growing to larger infinities, which, as you can see here, is totally possible.

We can obviously come up with an infinite list of them, but unlike the natural numbers, we can come up with an infinite list between any two of them as well. Between 1.5 and 1.6, we have 1.51, 1.52, 1.53…., 1.501, 1.511, 1.502, 1.512, 1.5001, 1.50000000001…you can go forever. So in a sense this infinity is larger.

The property that there exist real numbers in between any two other real numbers you pick is called “density”, and is not related to the size of an infinite set. It is true that the set of real numbers is larger than the set of rational numbers, but just showing that the reals are dense is not enough to demonstrate this. For example, the rational numbers (numbers like 1/3 or -1/2 which can be written as the ratio of two integers) are also dense, since you can always find a rational number in between any two other rational numbers – yet the set of rational numbers is the same size as the set of natural numbers. On the other hand, there are also infinite sets larger than the natural numbers which are not dense, like the set of countable ordinals.

“Stretching” the ruler is like gradually growing to larger infinities, which, as you can see here, is totally possible.

Sorry, but that’s not a good analogy. Stretching can only ever get you to the same infinity.

A better analogy would be

Take all the integers

Multiply every number by two

You now have the even integers

They’re still infinite (the same infinity mind you), but now there’s a larger difference between the elements of the set.

Much better explanation.

Why? Sure you couldn’t grab the ends and pull it apart that way but you could have infinite hands all along the ruler each pulling slightly.

Why? Sure you couldn’t grab the ends and pull it apart that way but you could have infinite hands all along the ruler each pulling slightly.

And just as is the case for the real universe, in our rubber band universe, you’d see everyone else’s hands moving away from you.

Like a tug of war stretch.

I expect my housekeeping staff will quit.

Does this mean the atoms are getting farther apart, or planets/galaxies?

Â

Short answer: Yes.

Shorter answer: No.

Actual answer:

Space expanding between points is a very slow process compared to most other “forces”. Galaxies millions and millions of light years apart are most likely accelerating away from each other due to expansion of space but for things on a more “reasonable” scale such as atoms, planets, and galaxy neighbors the forces of the strong and weak nuclear force (for atoms), gravity (for most everything else) and magnetism are far, far too strong to be bothered by this.

imagine a man with a dog on a lease, each standing on rather slow conveyors going opposite directions. sure, they move apart, or try to, but the lease prevents the man moving away from the dog. In a similar sense despite the Sun and Earth for example being moved away from each other by expansion the gravitational pull between the two keep them locked together.

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[â€“]10twenty4 2 points 13 hours ago

Another analogy that works here would be a balloon with coins taped to it. You inflate the balloon, and the coins spread apart from each other, but the coins are still the same size.

Gravity and other forces keep individual galaxies (coins) and other clumps of matter from expanding, but the distance between objects is increasing when gravity is too weak to counteract the expansion (other galaxies)

The universe is not known to be infinite. It could be, but that’s not something that could be proved.

Infinite is bigger than any number imaginable.

If you counted up all the atoms in all the 100 billion estimated galaxies, and than multiplied that by all the nanoseconds since the Big Bang, then you’d get a number that represented only a vanishingly small percentage of infinity. On a practical level, you’d be no closer to infinity than you were before you started.

That said, it’s certainly possible for something infinite to seem to expand. You just take the distance between any two objects in the infinite universe, and double it. (Or, whatever expansion factor you want.) Expanded, but still infinite.

Honestly, in this context I find the thought of infinity to be much easier to grasp than gigantic numbers. It takes away a lot of the guesswork, ambiguity, and scale-induced vertigo. If you told me the universe was infinite, I could easily accept and understand that. I mean, there’s really nothing more to be said. But if you told me it was, say, TREE(3) light years across, I would find that oddly frightening and dizzying.

One can think of it like this: No matter what, it’s not possible to reach the end, as it expands faster than anything can travel.

But in the context of this discussion, we’re assuming there is no end. And no beginning either for that matter.

Furthermore, only for objects that are sufficiently far apart will the expansion of space cause them to become causally disconnected, and that distance is quite large.

But in the context of this discussion, we’re assuming there is no end. And no beginning either for that matter.

Furthermore, only for objects that are sufficiently far apart will the expansion of space cause them to become causally disconnected, and that distance is quite large.

infinite is a concept, not a number. you cant make a % out of it.

Â I run a motel with an infinite number of rooms, numbered 1, 2, 3, etc. It’s beach season, so all of my rooms are full, but i find out there’s a convention of mathematicians coming to town this weekend, and an infinite number of mathematicians will need rooms. All my rooms are full, but i really want that sweet conference cash, so i tell all of my current guests to pack up, leave their rooms, and move into the room number twice their current room number, and i give them a few bucks off today’s fee. The person in room one moves to room two, the person in room two moves to room four, the person in room three moves to room six, etc. Now all of my current guests are in even-numbered rooms, and i have an infinity of odd-numbered rooms to rent to mathematicians. It’s like that, but different.

â€śAlright,â€ť said Ford, â€śimagine this. Right. You get this bath. Right. A large round bath. And itâ€™s made of ebony.â€ť

â€śWhere from?â€ť said Arthur, â€śHarrods was destroyed by the Vogons.â€ť

â€śDoesnâ€™t matter.â€ť

â€śSo you keep saying.â€ť

â€śListen.â€ť

â€śAlright.â€ť

â€śYou get this bath, see? Imagine youâ€™ve got this bath. And itâ€™s ebony. And itâ€™s conical.â€ť

â€śConical?â€ť said Arthur, â€śWhat sort ofâ€¦â€ť

â€śShhh!â€ť said Ford. â€śItâ€™s conical. So what you do is, you see, you fill it with fine white sand, alright? Or sugar. Fine white sand, and/or sugar. Anything. Doesnâ€™t matter. Sugarâ€™s fine. And when itâ€™s full, you pull the plug outâ€¦ are you listening?â€ť

â€śIâ€™m listening.â€ť

â€śYou pull the plug out, and it all just twirls away, twirls away you see, out of the plughole.â€ť

â€śI see.â€ť

â€śYou donâ€™t see. You donâ€™t see at all. I havenâ€™t got to the clever bit yet. You want to hear the clever bit?â€ť

â€śTell me the clever bit.â€ť

â€śIâ€™ll tell you the clever bit.â€ť

Ford thought for a moment, trying to remember what the clever bit was.

â€śThe clever bit,â€ť he said, â€śis this. You film it happening.â€ť

â€śClever.â€ť

â€śThatâ€™s not the clever bit. This is the clever bit, I remember now that this is the clever bit. The clever bit is that you then thread the film in the projectorâ€¦ backwards!â€ť

â€śBackwards?â€ť

â€śYes. Threading it backwards is definitely the clever bit. So then, you just sit and watch it, and everything just appears to spiral upwards out of the plughole and fill the bath. See?â€ť

â€śAnd thatâ€™s how the Universe began is it?â€ť said Arthur.

â€śNo,â€ť said Ford, â€śbut itâ€™s a marvellous way to relax.â€ť

But what if the conference is so popular that an uncountable number of mathematicians arrive?

This motel room analogy has always bothered me. If you had an infinite number of rooms and all of them were full then you would have no spare rooms to move your guests into. Every new room would be filled by the infinite number of people you had staying there.

The only way to do it would be to temporarily have a larger number of rooms (double the size of infinite) in order to accommodate the infinite number of old and new guests. Since you can’t have larger than infinite, how does that work?

You can’t double infinity because that is simply infinity as well. But you can perform operations on every member of the set of infinity, much like I’ve done with the motel, and the results are perfectly valid. Any finite number, no matter how large, can be doubled, so we can always make room in the hotel as long as everyone moves at the same time.

Consider the case where it’s just one guest. The new guest tells the guy in room 1 “Hey, this is my room now. Move on to the next one.”. Then that guy does the same thing to the guy in room 2, and so on. No matter how many times this goes on, there’s always a next room for the displaced guy to go to. Meanwhile, room 1 is now vacant and the new guest can move in.

Now, as a practical matter, this whole process would take an infinite amount of time. But we’ll assume we have some sort of time fuckery to speed that up. After all, we had to get the original guests into their rooms somehow. The real point is that at no point will this process assign two people to the same room, nor will it fail to assign someone a room.

A similar thing applies to the infinite number of guests. Instead, every guest leaves his room and walks down the hallway to the room with twice the number. The new guests are then placed into the empty odd-numbered rooms, which can be done while the old guests are moving (even if the hallway only has room for 1 person).

Now, the point of this isn’t fancy ways to rearrange guests (though that is starting to intrigue me). The point is to illustrate counterintuitive properties of infinite sets. After all, it seems clear that there are fewer even numbered rooms than all rooms. And yet we managed to fit all of the original guests into just the even-numbered rooms. It’s possible for two infinite sets to be the same size even if it seems “obvious” that one is larger.

But make no mistake: some infinite sets are larger than others. But explaining that is a little more involved, and is hard to do with the hotel analogy.

Consider the case where it’s just one guest. The new guest tells the guy in room 1 “Hey, this is my room now. Move on to the next one.”. Then that guy does the same thing to the guy in room 2, and so on. No matter how many times this goes on, there’s always a next room for the displaced guy to go to. Meanwhile, room 1 is now vacant and the new guest can move in.

Now, as a practical matter, this whole process would take an infinite amount of time. But we’ll assume we have some sort of time fuckery to speed that up. After all, we had to get the original guests into their rooms somehow. The real point is that at no point will this process assign two people to the same room, nor will it fail to assign someone a room.

A similar thing applies to the infinite number of guests. Instead, every guest leaves his room and walks down the hallway to the room with twice the number. The new guests are then placed into the empty odd-numbered rooms, which can be done while the old guests are moving (even if the hallway only has room for 1 person).

Now, the point of this isn’t fancy ways to rearrange guests (though that is starting to intrigue me). The point is to illustrate counterintuitive properties of infinite sets. After all, it seems clear that there are fewer even numbered rooms than all rooms. And yet we managed to fit all of the original guests into just the even-numbered rooms. It’s possible for two infinite sets to be the same size even if it seems “obvious” that one is larger.

But make no mistake: some infinite sets are larger than others. But explaining that is a little more involved, and is hard to do with the hotel analogy.

Think of it as if you’re trading time for space. You trade the time of all those people that have to move, so you get more space.

Perhaps an easier way to understand is this variation of the story.

You have the infinite hotel and all that jazz, but then a new guest arrives. So what you do, you tell the person in room one, to move to room two and tell that person to move to room three and so on. Then you put the guest in room one. What happens is, there is always one person without a room, except the person without the room keeps changing.

Â

The universe *may* be infinite, but it also may not be. At this point we’re reasonably certain it’s infinite. If it is, then what is happening is not the universe expanding, but rather, the space between objects in the universe is growing larger and larger over time. The whole universe will always be infinite regardless of what the scale of space is, and this scale can (and one day, will) reach mind-mindbogglingly huge levels and still always have plenty of room left to grow into.

Are we really “reasonably certain” that the universe is infinite? I feel like there is very little evidence to support that considering infinities do not exist in any other occasion that we know of. I think practically and even mathematically wouldn’t it make more sense that we are reasonably certain the universe is not infinite? Btw I’m not attempting to be condescending or catty in any way just confused as to if this is really the going theory or just a common misconception. Sources would be appreciated!

Are we really “reasonably certain” that the universe is infinite? I feel like there is very little evidence to support that considering infinities do not exist in any other occasion that we know of. I think practically and even mathematically wouldn’t it make more sense that we are reasonably certain the universe is not infinite? Btw I’m not attempting to be condescending or catty in any way just confused as to if this is really the going theory or just a common misconception. Sources would be appreciated!

Someone else mentioned a balloon, but the way I could understand is slightly different than what they mentioned. If you blow up a balloon, the surface area has no boundaries – there is are no edges, as you would have if you drew a flat square – so in a way the surface of the balloon is infinite – you could trace path around the balloon over and over and never come to and end point. But it can also expand, as you blow up the balloon more, not only does the volume increase but the surface of the balloon increases as well. So it is infinite and expanding.

A balloon is a container. Thus it’s shell is the boundary, the edge between it’s content and it’s surroundings, and will explode when the contents exceed the structural capacity of the container. The balloon analogy makes sense as long as we ignore any structural limitations. The infinite universe as it applies to expanding means impossible to measure or calculate rather than limitless. It cannot be considered expanding if it has no outer edge or boundary. In order to be expanding there has to be space outside the universe to expand into. And, if there is space to expand into then there has to be an outer edge.

It hasnt been proven that the universe is infinite, it is the most popular theory but still only a theory

The universe being infinite can never be proven but I do think that it can be disproved, we just lack the ability to do so at the moment. To better understand the answer for your question, disregard the word “infinite” and use “limitless” instead. Now, I know it’s confusing because those two words kind of mean the same thing but it’s not. Something can be finite and yet have no limits, like a loop but add more dimension to it. Imagine a Pac-man level where the screen is basically a finite space yet you cannot reach an end. The universe doesn’t have a spatial limit (space) but it does have a temporal one (time).

Lots of great comments here. We certainly don’t know it’s infinite but we do believe it’s expanding. That being said, not all infinities are equivalent. You can count all the integers from 0 to infinity and there are infinite numbers. On the other hand, you can also count all integers from negative infinity to positive infinity, which is clearly a bigger infinity. You can say there are infinite numbers between 0 and 1 as you can always go to more decimal places. But an infinity that included all integers AND the infinite numbers between each integer would be even bigger…

How many numbers are between the range of 1 & 2? infinity, because you can always add another digit past the decimal. Now how many numbers between a range of 1 & 5? Still infinity, yet the range expanded.

https://www.scientificamerican.com/article/strange-but-true-infinity-comes-in-different-sizes/

The nice thing (there are a lot of nasty things too) about infinity is that you can add any amount and its still going to be infinite. sometimes you can even substract infinity and youÂ´re still left with infinity.

source: am a quite drunk mathematician

In summary….

In the sense of actually having an infinite volume, the universe is not supposed to be infinite. It has a current radius of something like 13.7 billion light years. This is set based on the expected time since the Big Bang. At that time, the volume of the universe was basically zero, but the density of the universe was infinite.

However, despite the fact that the universe has a finite volume, the universe is expanding constantly and rapidly, so by the time something managed to actually travel 13.7 billion light years, the universe would have expanded to something even larger than that. This makes the universe effectively infinite in practice.

It should also be noted that we cannot even see a great portion of what is believed to be out there. Due to the speed of light being fixed, but all points in space-time constantly getting farther away from each other, the light from a considerable part of the universe stopped reaching us long ago, and the amount of the universe outside of our observable range is increasing all the time. Eventually, we will no longer be able to see any galaxies except the very closest in our neighborhood, and possibly in the far, far, far future, only our own Milky Way galaxy will be visible to us.

thats the observable universe from earths point of view, the general universe may or may not be infinite.

Its radius is significantly more than 13.7 billion light years.

Ugh. True. It’s 46.6 billion light years in radius. I forget about the fact that expansion is not confined to the speed of light and has the rate has been accelerating.

Although the original point stands. The universe is huge in volume, but not strictly infinite, although for most practical purposes it might as well be.

Thats simply the observable universe you are referring to. The universe is larger than that

There are two things being conflated here. The universe isn’t infinite insofar as the stuff contained within it is not infinite. What is infinite is spacetime, which is the medium in which the universe exists.

As a rough analogy, draw a bunch of dots on a balloon. These dots all have a specific location in relation to one another. The dots here represent matter, the balloon is spacetime.

Now we blow up the balloon, what happens to the dots? They move further apart, because the balloon is bigger now.

That’s pretty much it at a flowchart level.

This is rather inaccurate. First, based on what we’ve seen, on the largest scales the universe is thought to have essentially the same matter content everywhere. If space is infinite, you will never find a place within it that is not full of galaxy filaments, no matter how far you travel.

Second, the universe doesn’t exist within spacetime. Spacetime is just one facet of a complex combination of forces, fields, particles, matter, energy and other phenomena that we collectively call “The Universe”.

I’m in the camp that reality is a separate concept within which we find the universe embedded in spacetime.

I forgot to distinguish between the concept of the universe and the observable universe, which appears to have a well-defined beginning and outer limit.

I too believe that our universe is a manifestation of some deeper, underlying reality. However, even if that’s the case, spacetime as we understand it is still a phenomenon that would be limited to our own universe bubble/dimension.

But such things are almost purely speculation at this point, and don’t really have any place in answering this question.

Then the only valid ELI5 is “There is no answer at all currently. Try again in 500 years.”

Not really. If the question is “How can the universe be both infinite and expanding” the answer is that space being infinite in extent doesn’t mean the space between distant objects cannot grow larger over time. Space will always be infinite, but the scale of space can increase or decrease. There was a time when the scale was so small that the entire observable universe was contained in an area smaller than an atom. Space as a whole was still infinite, though. Obviously the scale is much larger now, and will continue to get larger forever.

Infinity is a concept not and arbitrary value. therefore, its always possible to have infinity +1 etc or infinity + infinity.

Space is infinite.

but what is expanding is the space between the bodies in the universe. things are drifting apart and that is why you heard that the universe is expanding. but the room in which that is all happening is infinite.

There is a finite space where physical matter exists, but infinite is just a way for us to say we can’t measure it right now and it is really freaking huge, while also expanding outward.

Think of it as there are an infinite amount of numbers between 0 and 1 such as .1, .01 and so on now think how many numbers are between 0 and 2 some infinites are bigger than others

The way that mathematicians count things, the number of real numbers in [0,1] equals the number in [0,2]. They consider their cardinality equal if you can associate every element of one set to a unique element of the other set, and nothing is left over. Like lining up two sets of playing cards, side by side. When you finish, if the two lines of cards match up with none left over, they have the same number, even if you can’t count. For the two intervals, every number in [0,1] matches twice its value in [0,2].

The way that mathematicians count things, the number of real numbers in [0,1] equals the number in [0,2]. They consider their cardinality equal if you can associate every element of one set to a unique element of the other set, and nothing is left over. Like lining up two sets of playing cards, side by side. When you finish, if the two lines of cards match up with none left over, they have the same number, even if you can’t count. For the two intervals, every number in [0,1] matches twice its value in [0,2].

Picture this:

Freeze time and then noclip out to the edge of the bubble of the universe. That leading edge is the big bang and it’s ripple. One side is existence and the other is nothingness. Now resume time. That bubble keeps expanding outward faster then the speed of light, in the bubble, gravity, matter, vacuum and everything is being formed. Outside that bubble is everything that is nothingness.

That’s actually not the case – there are a couple misconceptions you have there.

First, the big bang wasn’t everything in the universe compressed to a single point – it was a time when the matter-energy of the universe was very dense (unlike today when it is very sparse with a lot of relatively empty space between things). The universe was still very large and filled with this high energy soup, so much so that it was opaque – light would bounce erratically off various other high energy particles.

At some point, the universe began stretching out and cooling off – decreasing the overall density of the energy and matter. Eventually this reached a point where the universe cooled enough so that it was no longer opaque, and instantly all of the randomly bouncing light shot out in whatever direction it was moving at the time. Since the whole universe was filled with randomly bouncing light this meant that light was sent off in every direction from every point in the universe, and this is what causes the background microwave radiation to exist.

Because this was a finite time ago and light travels at a finite speed, that means that for things that were very very far away not enough time has passed to have light from the point when the universe became transparent to reach us. The universe is estimated to be roughly 13.8 billion years, so that means that we can only see things that are closer than 13.8 billion lightyears away – anything farther away and the light won’t have reached us yet. However, every moment this “bubble” expands because more time has passed, thus more light will be reaching us for the first time – this is what is known as the observable universe. It is expanding outward with us at the center at the speed of light because it is literally just a measure of how far light can travel since the moment light could travel in a (mostly) straight line through space.

The fact that background microwave radiation exists indicates that outside this bubble of the observable universe ISN’T empty – if it were then there would not have been any light bouncing around from outside that area to be released, travel through the universe, and have a tiny portion of it arrive here as background radiation. In fact, the current estimates on the lower bound of the size of the actual universe is about 20 times larger than the observable universe, but it could be infinite (although proving that it is infinite is tricky).

So, in your example – if you were to freeze time and go out to the very edge of the observable universe that is centered on the Earth, you would presumably find yourself in just another part of the universe. The outer boundary of the observable universe is just a conceptual boundary, not a physical one – and just because we can’t see anything there now doesn’t mean that there isn’t anything there currently, because as we look farther away we also look back in time. If we look 10 billion lightyears away then we can only see the state of things from 10 billion years ago – anything that happens there NOW will give off light that we won’t be able to see for another 10 billion years.

Minute Physics actually has a few videos on topics like this and they explain it pretty well – you should check them out if you’re curious.

Woo my psychedelic experiences gave me the guess I had to this question… But what they really did was prompt you to give the best answer ever. Kudos

You know those dreams where you’re running, but you can’t seem to run to where you’re going, even if it started 30 feet away?

That’s the universe. It retreats (expands) at least as fast as you (light) can run toward it, so as a practical matter, it’s infinite. Nothing goes faster than light.

Look at space and the universe as two different things, space is infinite emptiness, the universe is everything that exists in that emptiness.

If you had a god’s-eye view you could probably see an edge to the planets and stars and beyond that, infinite darkness, but the edge is constantly expanding into the darkness.

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minnsoup

There is a size but it’s constantly expanding. It’s like a number line that goes forever – no matter how far down the line you go (you being the edge of the universe) you have a number, but you can always go further down the line. This is my understanding.

It seems in order to be infinite it would always need to be defining itself larger, or expanding, as it counts to infinity?

To say that space is infinite simply means it goes on forever in every direction without bound. Just as one cannot count to infinity, the universe cannot grow to be infinitely large, but would had to have formed that way.

To say that space is infinite simply means it goes on forever in every direction without bound. Just as one cannot count to infinity, the universe cannot grow to be infinitely large, but would had to have formed that way.

Well if you try to count to infinity by definition you will never stop… same with the universe…it’s “counting” to infinite size

Maybe the universe is like the integer number line. Infinite. But now it’s adding fractions.

Well, I’ve learned about different types of infinity (some being bigger than others) so that’s not even my problem with it but: expanding in WHAT?!?!

My poor brain…

Well, I’ve learned about different types of infinity (some being bigger than others) so that’s not even my problem with it but: expanding in WHAT?!?!

My poor brain…

Not expanding in WHAT. Simply expanding. To bring energy and matter where no energy or matter has ever been before…to loosely quote Star Trek.

Ha! Sweet, I like that one!

you’d get a number that represented only a vanishingly small percentage of infinity.

No, because infinity isn’t a number. You can’t compare a number to infinity with something like a percentage. Infinity is a concept that is near-impossible for humans to conceptualize.

The set of real numbers between 0 and 1, and the set of real numbers between 0 and 2 are the same “size” (actually, cardinality, we’re talking about sets). If you want to compare the set of real number to the set of natural numbers, then they are of different cardinality. The set of natural numbers are countably infinite. It is trivially mapped to itself via identity, there is no such one-to-one, onto mapping of real numbers to natural numbers. So, yes, some inifinities are “bigger”. This is a good analogy because the cardinality of the set of real numbers between 0 and 1, and 0 and 2 are the same, but the total range is larger in the latter.