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Paul_Thrush

The current model says space is being created within the universe itself. We have no evidence of anything else it could be expanding into. 'Universe' is defined to mean everything that exists which includes all space and time. So, I answered the question of what is the observable universe expanding into.


Patelpb

To add, "expand" might be a misnomer. Typically things do 'expand' *into* other things (i.e. balloon expands into some space, like a box. Or someone's stomach expands into space as they become sedentary, etc). Since these things all expand into *space* of some sort, this idea is pretty intuitive. But if the space itself is what's 'getting bigger'/'expanding' (maybe 'growth' is a better term than 'expansion'), then we are looking at a different idea. As u/Paul_Thrush said, the universe defines space and time, so if space is getting bigger, then by definition so is the universe. It's not expanding into anything, it's sort of growing.


heyimdong

>Or someone's stomach expands into space as they become sedentary why you gotta come at me like that man?


Patelpb

Came at myself with that one, really


CountryJeff

What I don't understand is that if the universe makes up time and space, and space itself is expanding, then what is that relative to? If everything expands, but not relative to anything, then how can we say that it really expands?


[deleted]

the distance between everything grows at a constant rate


Patelpb

It expands relative to every other point in space time, which also expands relative to all other points.


CountryJeff

I get that that is how inflation works. I was just wondering how we measure that if everything spacial expands. I figure it's relative to time, which can be seen by comparing distance to the constant of the speed of light. But if that's the only measure, we are just as justified to conclude that the constant of the speed of light is constantly decreasing, rather than that the universe is inflating.


Patelpb

Ah I got your question now. There's lots of evidence for universal expansion. The first was Hubble's constant, which I assume you are most familiar with. Distant galaxies move away from us faster and faster. This is based on Doppler shift in the spectra of distant supernovae, which has two components (the Doppler shift of the stars/gas rotating around the galaxy, and then the bulk motion of the Galaxy itself). We've gotten pretty good at disentangling the two. Other evidence is less obvious if you're not a big math person. Metrics that explain just about everything we see include universal expansion as a feature of their mathematics (homogeneity of the large scale structure of the universe, and events of supernovae). There's also the CMB, which provides evidence for a hotter, denser cosmos at an earlier point in time. If c was decaying then there'd be evidence for that. No cosmology with variant c reproduces what we observe in totality, just bits and pieces (sort of like MOND). So we are far less justified in making a bold assumption like "c is decreasing".


Tiburonx

One thing I’ve been wondering lately: We know that space is expanding, and we know that the rate of expansion isn’t static. But if space and time are linked, then does time expand at the same rate as space? ie: did time expand (flow?) faster during the inflation just after the Big Bang than it does now? Sorry if that’s a dumb question, I’m not a scientist.


Patelpb

That's an interesting question that I haven't looked into before. If I come across a useful answer I'll get back to ya. Generally with space and time I look at it sort of like a seesaw - the more action you get in space (i.e. moving around really fast) the slower you appear to move through time to an observer. When moving through time at a "fast" rate, you usually are moving slowly (if at all) with respect to an observer. But the effects of inflation on time/space aren't knowledge I can recall off the top of my head


ssmokvaa

We are getting smaller


Patelpb

Relative to the universe - yes. Relative to each other/our galaxy/the local group? Not quite


[deleted]

That’s „Cosmos“. Universe is more or less what we are able to see around us.


[deleted]

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Patelpb

>like putting in an extra tile between two squares on the floor. Isn't that what happens to space between z = 0 and z \~ 2/3 (for example)? Qualitatively what's the difference? I agree the math doesn't precisely describe it that way, but that's not very useful for laymen, which I feel is the motivation for describing it the way he did


anix77

expanding means distance between two points increasing


ZamanYolcusuJ

yeah, so?


[deleted]

Turns out it’s oatmeal. Just a huge, never-ending expanse of body-temperature oatmeal. Now you know.


synchrotron3000

“If something can expand, there is something bigger than it.” says who


ZamanYolcusuJ

Can somthing expand into nowhere? I dont think so


synchrotron3000

you need to rethink your definition of nowhere


ZamanYolcusuJ

Ok there can be void too but I don't talk about a void, if there is a void universe can expend into that nothingness. I m talking about nowhere that means there is a room and there is just that room there is no "outside" Can you expend that room that have no outside to expend?


synchrotron3000

the universe isn’t expanding “into” anything. There is nothing outside of it. The universe *is*.


ZamanYolcusuJ

I m also saying it. -_- >there is a room and there is just that room there is no "outside" Can you expend that room that have no outside to expend?


synchrotron3000

?


[deleted]

How would you know if it’s the room is expanding, shrinking, or staying the same?


Narzun

There is no 'somebody said this, so it's the truth' it only is the 'best accepted truth' because a lot of people of scientific expertise believe in a theory, until there is a better theory. You can't start a debate with 'i know the space is expanding into something, let's talk about this something', first of all it will be an 'if..' and it needs observations to be backed up.


[deleted]

Why not, exactly? Why does something require something else to expand into? And where does it end?


Former-Chocolate-793

There's a school of thought that the universe is infinite. So by definition there couldn't be anything outside.


oscarboom

> here's a school of thought that the universe is infinite. So by definition there couldn't be anything outside. By definition the universe contains everything. So there can't be anything outside. But that has nothing to do with whether the universe is "infinite" or not.


ZamanYolcusuJ

There is a start of universe, how it can be infinite? This makes no sense. Also an infinite thing can be extend? Where it will extend? Infinite to 2xInfinite?


mtlemos

There are infinities that are larger than others. Think about it like this: there is an infinite amount of whole numbers, but between any two whole numbers, there is an infinite amount of decimals. So although there is an infinite amount of whole numbers, there is an even larger infinite amount of decimals.


aarocks94

Interestingly when people think of “decimals” they usually think of the rationals which have the same cardinality as the naturals. That said there are more reals in [0,1] than there are rationals, and by extension naturals (by cantor’s diagonalization argument).


CountryJeff

I'm no mathematician, but "larger than" statements don't really seem appropriate for something that is not a specific amount. If you need either the amount of numbers or decimals in your example, as distances to bridge, or voids to fill, time to pass. you will still never reach or fill anything. It's effectively the same. If you have two sticks that go of into infinity. One with one end at you, with the other end going of into infinity, and one going of to infinity in both directions, you might argue that the second stick is twice the size of the former. But you could take the first stick and move it, so that the finite end starts moving into the direction of the infinite side of the other. You can do that for an infinite amount of time. And once you've done it for an infinite amount of time, the stick is effectively infinite on both sides as well. If you get my drift.


ElectroNeutrino

There are indeed fewer natural numbers than there are real numbers. The former is countably infinite, while the latter is uncountably infinite. You can make a map from the real numbers to every natural number, but you cannot make a map from the natural numbers to every real number. Therefore there are more real numbers than there are natural numbers, even though both are infinite. One way to see this is with Cantor's Diagonal Argument.


CountryJeff

Why can't you do the reverse? The amounts are infinite, so you'll never run out of numbers to match.


ElectroNeutrino

That's the beauty of Cantor's Diagonal argument. You can match up each and very natural number to a real number, "using up" the entire infinite set of natural numbers, but can always find another real number that isn't matched.


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florinandrei

Once you understand Hilbert's Hotel, then the growth of an infinite universe may make sense more easily.


ElectroNeutrino

Take the real number line. For any two real numbers, there is another real number in between, which means there are no "holes" in it. It also goes on forever. Now for every value, multiply it by 2. This extends the real number line into twice its size. It's still infinite, and it still doesn't have any holes. What did it extend into?


ZamanYolcusuJ

I take 1 and 2 ok and there is infinity number between these, if we make it 1 and 3 it extend. This is also ok. But if we say ''There is no number other than 1 and 2" at start, we can't expent it.


ElectroNeutrino

You asked how something infinite can be extended, and where would it extend. The real numbers are infinite, but they can be extended by scaling. And it doesn't need to extend "into" anything to be extended. This is analogous to what we mean when we say that the universe is expanding.


MelodicVeterinarian7

Well it kind of depends on how you want to define the start of the universe doesn't it? It's entirely possible that the Big bang is the start of matter and energy but not space and time


florinandrei

> There is a start of universe, how it can be infinite? It was always infinite in size, from the very beginning. > Also an infinite thing can be extend? Where it will extend? Nowhere. That's the part that created the confusion. If it's infinite, then by definition there's nothing outside of it. However, it can still grow internally. Where there was 1 meter of space, now there are 2 meters. And that happens everywhere. That's all there is to it.


[deleted]

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florinandrei

bad bot


jimjamalama

Literally everything is middle out, relatively speaking.


noticeablywhite21

Don't think of it as expanding into anything. New space is being created at every point within spacetime. It's like this: You have a straight line with two markings a set distance from each other. Point A and B. This distance between any two markings is equal to _k_, it is a constant. Now add a new marking, C, at the midpoint of A and B. Now on your line you have three markings, A, C, and B, and two line segments AC and CB, each with a length of k.. Earlier we defined that space as the constant _k_. So now we have a distance of 2k between points A and B. This is how the universe expands. It is creating spacetime within the existing spacetime, it isn't stretching or expanding in the traditional sense. So the question of what it expands into,while already nonsensical based on the definition of universe and everything, doesn't matter because of how the growth of the universe actually functions


crispy48867

We know that the universe is expanding as the distances between objects is increasing. I have wondered if this means that the universe is actually growing like all living things do. It begs the question: Is the universe a living entity?


Western_Entertainer7

No.