Submitted by cashmoneyhash t3_12776bk in explainlikeimfive
ForestCityWRX t1_jed070q wrote
Reply to comment by Pegajace in ELi5 If the universe is expanding, what is it expanding into? by cashmoneyhash
I genuinely believe my brain can’t comprehend that level of thinking. Thanks for the explanation.
World_in_my_eyes t1_jed4cjq wrote
You’re not the only one. My brain definitely doesn’t work in ways necessary to understand this. It’s fascinating though.
Moist_Comb t1_jed8dkh wrote
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.
esmith000 t1_jed4vo2 wrote
Because it's not a good explanation. No offense to the guy but it's hard to explain.
GsTSaien t1_jed6hts wrote
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.
esmith000 t1_jed7sd7 wrote
It's definitely not nothing.
GsTSaien t1_jedanmg wrote
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)
esmith000 t1_jedb513 wrote
It's not nothing, not even close. Nothing is not a thing. Time is not nothing.
GsTSaien t1_jedba22 wrote
I feel like you are just hanged on the word rather than its meaning.
esmith000 t1_jedbgxs wrote
Nope. In physics, you won't find any physicist say there is nothing or space is mostly nothing. Space is full of stuff.
GsTSaien t1_jedbsw6 wrote
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"
esmith000 t1_jedccu4 wrote
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.
GsTSaien t1_jedcfw9 wrote
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?
Mitchelltrt t1_jee0t53 wrote
You are correct. The space itself has no energy, no mass, no anything. However, particles sponaneously appear within that nothing.
GsTSaien t1_jee13cy wrote
Particles just appear???? Wait are you sure? Wouldn't that require creating more mass and energy from nothing?
Mitchelltrt t1_jee33x6 wrote
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.
GsTSaien t1_jee36y9 wrote
Holy shit
zolotuchien t1_jee6372 wrote
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.
esmith000 t1_jedcpz2 wrote
Yes.
IamMe90 t1_jedks8b wrote
Great answer bro. Really clarifies things for us who were following your conversation thread.
Mind expounding behind the word "yes" in your answer?
esmith000 t1_jeefui3 wrote
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.
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.
splittingheirs t1_jedcqva wrote
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.
GsTSaien t1_jedcw78 wrote
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?
splittingheirs t1_jede87t wrote
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.
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