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Indemnity4 t1_isv0bnc wrote

Reply to comment by Froggmann5 in Ask Anything Wednesday - Physics, Astronomy, Earth and Planetary Science by AutoModerator

> Terry Pratchett — 'In the beginning there was nothing, which exploded.

IMHO your problem is about words and not mathematics. Here are a couple of definitions that hopefully help.

Space is typically defined as absence of "stuff". It has no volume, zero mass, zero momentum, zero electric charge. You can't push it around, or expand it, or do anything to it. Space is dependent on things happening to other stuff.

Particles do have mass, volume, momentum, electric charge, etc. They affect their surroundings.

Interstellar space contains about 100,000 particles per cubic metre. That sounds like a lot, hundreds of thousands!, but it's relatively empty.

Your hypothesis changes depending if you define "space" as interstellar space or as a hard vacuum with all particles removed.

Real world: a random area of interstellar space. If you add one more particle, nothing changes as you've increased the density by a tiny immeasurable amount.

Thought experiment: big container with rigid or flexible walls and absolutely nothing inside. You add one particle. Nothing changes. One particle isn't exerting force on anything, it's not pushing on anything, it's not interacting with your magical thought experiment walls. Nothing changes.

End result of your thought experiment is nothing changes.

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Froggmann5 t1_isvqxc1 wrote

> Space is typically defined as absence of "stuff". It has no volume, zero mass, zero momentum, zero electric charge. You can't push it around, or expand it, or do anything to it.

You have this completely wrong. The easiest thing I can point you to is that space itself is literally expanding. This has been known, demonstrated, and studied for a long while now.

> Particles do have mass, volume, momentum, electric charge, etc. They affect their surroundings.

This is also at least partially incorrect. Particles like Photons do not have mass for example.

> Your hypothesis changes depending if you define "space" as interstellar space or as a hard vacuum with all particles removed.

I suppose I'll supply this definition of space instead then to make it easier for you to understand the hypothetical:

> the dimensions of height, depth, and width within which all things exist and move.

Moving forward this also shows your misunderstanding of my hypothetical when you try to rebut it with your own example:

> big container with rigid or flexible walls and absolutely nothing inside. You add one particle. Nothing changes. One particle isn't exerting force on anything, it's not pushing on anything, it's not interacting with your magical thought experiment walls. Nothing changes.

This is disanalogous, because your first sentence contradicts. If "Nothing" is inside, how is there an "inside" of the container at all? Saying there's an "inside" implies there's some amount of space within the container for something to be.

In fact this just inspires a better question: If you had a universe of absolutely nothing with no space/time/anything at all, and you add a particle to it, does this also add space to that universe?

> End result of your thought experiment is nothing changes.

I'm afraid your misunderstanding of the very nature of space (and consequently from that, you misunderstood, my hypothetical) led you to this conclusion.

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Indemnity4 t1_isvznvg wrote

I think a sticking point in any discussion you have is "space"=nothing/vacuum/emptycontainer versus "space"=interstellar medium (where stars and spaceships do their business).

Every person who has responded to you has assumed you are talking about a container full of vacuum. Because that's what those words mean.

One answer to your question about a universe without particles and how to measure it is may be what happened before the Big Bang? The "universe" was a singularity about the size of a peach. However, it was full of stuff and not empty.

The other answer is what is outside our universe? e.g. you have an area of "space" with nothing in it, then you add a particle, what happens?

The answer is... nobody knows. The observable universe has always had stuff in it, so the size/distance/volume is measure by taking two of those points. Physics no longer works when you are talking about a universe without particles. There is no distance unless you are measuring how far apart two things are. There is no pressure without having a container.

Your scenario of a "universe" with nothing it but somehow it has reference points for scale 1m x 1m x 1m, that can't happen. There is no way to get a reference point.

Maybe the closest you will get is within string theory - it lets you have a "universe" without particles. At some point the universe was a mass of 1 dimensional strings vibrating (so we don't have 3 dimension like 1m x 1m x 1m anymore). One of those flipping in a weird way that lead to the formation of the first particle. That caused a chain reaction which created more and more particles that lead to the universe.

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