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GsTSaien t1_jedcfw9 wrote

Reply to comment by esmith000 in ELi5 If the universe is expanding, what is it expanding into? by cashmoneyhash

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?

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Mitchelltrt t1_jee0t53 wrote

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

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GsTSaien t1_jee13cy wrote

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

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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.

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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.

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esmith000 t1_jedcpz2 wrote

Yes.

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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?

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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.

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.

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