It's not expanding into anything. The expansion of the universe is not the motion of stuff through space, nor is it the motion of space through... super-space or something of that sort. It is fundamentally different from motion. It's a metric expansion, meaning that there's brand-new space coming into being everywhere, all the time, and the distances between objects simply get larger (at a rate that is getting faster as time goes on).

Okay, hear me out. Brand new space. What space is the new space occupying? What is there before space is there?

No one really knows.

You're still thinking of space as if it's some material existing within space, but that's a fundamental error. Space isn't occupying space, and it's not at a location within itself or anything else. Space is what matter & energy occupies, and what separates locations & events via both distance & time.

> What is there before space is there?

Space isn't "here or "there." Space defines "here" & "there." If there's no space, there is no "there," full stop.

I genuinely believe my brain can’t comprehend that level of thinking. Thanks for the explanation.

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You’re not the only one. My brain definitely doesn’t work in ways necessary to understand this. It’s fascinating though.

Because it's not a good explanation. No offense to the guy but it's hard to explain.

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Its perfectly fine, it just isn't intuitive. Space at a large scale is a void, it is nothing, the absence of matter. The thought of more NOTHING just coming into existence is really hard to grasp.

It's definitely not nothing.

My interpretation of expanding space is:

Imagine you have a box that contains the whole universe, and you are looking into it. Space expanding would be like zooming out, but the edges dont move. It still occupies the same box, but now there is more stuff inside of it. I'm sure someone can come along and explain how this doesn't work mathematically, but it's the only way I could try to comprehend it.

It's a little counterintuitive, but it's expanding into nothing. The universe is already infinite; an infinite volume can expand and remain the same size at the same time. This can ONLY happen when infinity is involved.

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It is though, there isn't anything else that is less something than the void of space. It is not mass, just reality itself.

It is the most nothing thing there is.

It just happens that even the most nothing thing there is has some interesting properties, and since time and space are two parts of the same (time is also a nothing as it is part of the nothing) it just shapes reality in an interesting way. (Mass bends space, time existing thorugh bent space gives us gravity)

Imagine all the whole numbers from 0 to 10. Now imagine imagine every half number in that span. Keep adding the set of numbers between the numbers you already have. The size of your set is expanding, but the bounds of the set itself need not expand. You can imagine a similar concept to an infinite set of numbers, and thus you can imagine the universe expands in a similar fashion.

It's not nothing, not even close. Nothing is not a thing. Time is not nothing.

I feel like you are just hanged on the word rather than its meaning.

Nope. In physics, you won't find any physicist say there is nothing or space is mostly nothing. Space is full of stuff.

I was not scientifically labelling space as nothing, only explaining why it is hard to think about space, which has no mass or energy by itself, expanding.

I then elaborated on why I called it nothing. Mentioning that, by itself, it does not have anything, and space itself is the deepest form of absence of things possible and therefore the most nothing thing to exist. If you open an empty box, it still has air, maybe a wave, some form of energy, radiation, etc. These are all things that occupy space, not inherently needed for space to come to be. If inside the box there were empty space, just space with none of those things, then you could truthfully say there is nothing in the box.

It is like saying humans are a smart ape and you going "scientists have a specific name for humans you are wrong"

But then you say space has no mass or energy by itself. This is just not correct. No problem with metaphor or generalizations but you are over generalizing and introducing confusion. Space is not empty at all. There is a LOT going on and it shouldn't be minimized.

Ah, then I may be incorrect. Does space have mass or energy by itself? Not IN IT, by itself.

I know for a fact there is space with no mass. Most of it has no mass. I am pretty sure no mass nor energy should be possible simultaneously, what am I missing?

Yes.

Space is something. It is not made of "nothing". The emptiest space is still buzzing with matter and energy.

Also quite a few physicists suspect space and time are an emergent property that reflect quantum scale interactions and relationships between matter. IE, space literally manifests itself as an illusion of quantum interactions. So if space exists, it's for the express purpose of displaying the result of material interactions that define it, it couldn't be empty if it tried.

For further information: lookup quantum loop gravity.

Is the emptiest space still full of matter? That doesn't sound right, could you elaborate?

Also, if it is emergent then it would indeed be "nothing" by itself, only existing when occupied.

How does spacetime as an emergent property explain gravity?

I don't mean full, as in packed full to the brim. It is teeming with energy and virtual particles. There is no space that doesn't have energy and particles. It is a property of space itself.

Also yes, you could say space is nothing because it is an emergent phenomenon. But that is besides the point as pretty much everything in physics and therefore reality are emergent phenomena of more fundamental laws and properties. IE QFT pretty much says that no particles exist and its just all waves.

If you can properly explain gravity, step up and claim your noble prize. It is one of the most hotly studied areas currently in physics. Quantum loop gravity is a theory attempting to explain gravity at the quantum level by stating that spacetime emerges from quantum interactions.

Yes, every answer here is a guess. How could we possibly know? I like the guess that says we're the event horizon of a higher dimensional black hole.

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Is there a boundary between space and whatever is not space?

As a species, we are kind of timeist. We can't really fathom how things work outside of our known space-time and we are pretty tied to our temporal causal relationships.

Great answer bro. Really clarifies things for us who were following your conversation thread.

Mind expounding behind the word "yes" in your answer?

One time someone asked this question and someone gave the example of a computer screen and it totally clicked for me. Imagine the universe is a computer screen. When we say the universe is expanding we’re not saying the screen is getting bigger. It’s not going from a 30 inch to a 40 inch. The universe is already infinite it can’t get bigger. We’re saying the resolution is getting better. A few billion years ago it was standard definition. Two pixels on opposite sides were a few hundred pixels apart. Today though it’s 4K. Thousands of pixels apart. They didn’t actually move into new areas but now there’s more space between them. Get it?

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I feel like this has to be a pretty clear argument for there being at least 4 spatial dimensions. The production of new "space/universe" essentially from...."nowhere." Reminds me of the idea of if a 3 dimensional sphere were to pass through a 2 dimensional space, to the 2 dimensional observer - this sphere would simply be a slice (or really, a line - to them) that simply goes from nothing, to smaller, to larger, to smaller, then back to nothing - all without the two dimensional observer ever having an awareness as to even the idea that the object they're witnessing essentially "appear out of thin air, then disappear" exists within 3 dimensions.

The production of new "space/universe" being generated everywhere across the universe, at all times, to me - would mean an expectation that this added space is coming into existence from a 4 dimensional (spatial) existence. If new "space" were being generated from a central locus, then perhaps something else - but the whole "everything, everywhere, all at once" aspect really has me imagining only that its production must be borne of a 4th dimensional space.

If that's irrational or if there are theories stronger than that - please let me know, but intuitively it's the only thing that would make sense (when considering the idea of imagining a 3 dimensional object in a 2 dimensional space, which would appear, under those conditions, exactly the way we view the view the expansion of spacetime in 3 dimensions)

> The universe is already infinite

We don't know if it is.

> This can ONLY happen when infinity is involved.

No. The universe could be finite, and still expand.

> The universe is already infinite

We don't know if it is.

The 2nd part you point out you skipped over something. I said an infinite universe can expand AND remain the same size at the same time. To have both of those seemingly contradictory properties at the same time requires an infinite universe. An infinite volume can get bigger, but it's still infinite.

Yes, if the universe is finite then its volume increases. So what? Doesn't stop OP's question from being relevant, with the answer still being "it's not expanding into anything".

Well, it's infinite. Always been. So it's just expanding. Not "into" anything.

It might help to think of it as "the universe is thinning out".

The thing is, the universe was in a state of expansion from day one. Pretty violent expansion. You could call it an explosion. Or a "big bang". It's been expanding / exploding ever since.

I think people are thinking of the laymen meaning of space, as in outer space as a thing that exists in juxtaposition to not space.

Wait, so “space” is infinite and things (matter and energy) are simply expanding further into it/further away from each other?

Perhaps try answering the question with a bit more physics and bit less armchair philosophy next time. This is so incredibly lazy and wrong on so many levels

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>You are in infinitely large universe

We don't know that. We have no idea how big the Universe actually is.

If we extrapolate from the observable universe with the angles we can measure it should be at least 2.5 million times as big as the observable universe. At least. With no upper limit.

Or maybe we don't quite understand things as well and it is smaller.

Or maybe it is infinite.

We don't know.

You are correct. The space itself has no energy, no mass, no anything. However, particles sponaneously appear within that nothing.

Particles just appear???? Wait are you sure? Wouldn't that require creating more mass and energy from nothing?

A highschool physics teacher tried to explain it to us, before sighing and saying we'd see if we pursue education in this field otherwise screw it, with the idea that we measure the position of things as if they're in a grid.

One moment the nearby grid is 1 million blocks wide for the x, y and z axis. The following moment, the grid measures the same things but it's a 1 million and 1 blocks for the x, y and z axis. Some moments later, it's now 1 million and 2 blocks, still for the very same things inside. From our perspective on the inside, it gives an impression of getting further away.

You should read Flatland if you haven't.

Think about a bubble of air, exhaled by a diver deep under the ocean. It is compressed by the pressure of the water around it. It starts out small. All the oxygen, nitrogen, and carbon dioxide molecules are close together. But as it rises, the pressure lessens. The bubble gets bigger, and as it does so, the space between individual molecules increases. Nothing fills those spaces between the molecules, it just gets bigger. But the distance between atoms in those molecules does not change.

Our universe is a sort of bubble of space-time, expanding into a higher-dimensional space or a quantum vacuum. Like the atoms in our air molecules, local distances stay the same. But looking further away, we can see that things far away always get further away, wherever we look. This is the expansion of the universe.

Unlike a bubble under water, our universe does not have a edge that can be detected from within it. No matter where you look, it all looks the same. Space-time might be a closed sphere, so that if you travelled in a straight line, you would end up where you started. It could be a torus (like a donut) where you might travel in a straight line and never return to where you started. There are many other curved options for our universe. Some are closed and some are not. We don't know, and we may never know.

Nope. Particles appear in pairs, then collide with their pair and disappear. It is honestly freaky. Like, subatomic particles appearing in electron-positron or proton and its pair that I can't remeber the name of.

Holy shit

Ah the cursed existence of mankind, born with a brain equipped to understand the "here" and the "there", the "beginning" and the "end" because those are concepts familiar to their frail, mortal lives. The brains are built to comprehend such concepts, for that is all millenia of evolution have given them. Yet their ambitions often far exceed their brain's imagination. They gaze upon the stars and the vastness of the void inbetween and wonder what is the beginning of time and what is the end of the nigh infinite as if the universe itself must be like everything they know: having defined births and defined dimensions.

I mean, they’re not wrong though

The space by itself however definitely has energy. There are two theoretical concepts to talk about. The first one is vacuum energy described by quantum physics. Due to uncertainty principle, vacuum energy simply cannot be zero. Even more interesting, an energy of any finite volume of vacuum has to be infinite. We can think of vacuum being a constant factory of spontaneously created and then annihilated pairs of particles and antiparticles. And that happens by virtue of it being space, not due to anything in said space.

The second concept to talk about is a cosmological constant in general relativity theory. It can be thought of as an energy density of an empty space. It is one of the candidate for the dark matter phenomenon, the fact that the expansion of the universe is accelerating.

Due to both things describing an energy of an empty space, there is an idea that those to concept has to be related.

Simple google search.

Does space itself have energy?

Vacuum energy is an underlying background energy that exists in space throughout the entire Universe. The vacuum energy is a special case of zero-point energy that relates to the quantum vacuum.

https://en.wikipedia.org/wiki/Vacuum_energy#:~:text=Vacuum%20energy%20is%20an%20underlying,relates%20to%20the%20quantum%20vacuum.

Also, look up quantum fields. These exist outside of space and time and are everywhere. So space, even going with metaphor that it is mostly nothing isn't all there is. There is a whole other realm of stuff. The consensus is in physics is that the universe emerged from quantum fields.