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We are not mostly empty space

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Re: We are not mostly empty space

#61

Post by toohotatopic »

themodelplumber wrote: post #17
kylec wrote: post #11

Empty space, by definition, is space that can be filled by something. So how closely can atoms pack together? A neutron star has a density of 10^17 kg/m^3, whereas the typical human being is about 10^3 kg/m^3. I could fit the matter of trillions more human beings in the same space I'm taking up now. So yeah, I think there's some empty space in me.

So the author is saying fields are already filling things up, right? To compare this to the "we can pack them atoms tighter" model seems to be confusing the author's model with another, separate mental model, one in which we can fill up more. But the author's model says we're full. Full of this field stuff. Not so? IANAS

Do those fields extend into infinity or is there a boundary that the electrons don't cross?

>If you took an atomic nucleus and bound only one electron to it, you would see the following 10 probability clouds for each electron, where these 10 diagrams correspond to the electron occupying each of the 1s, 2s, 2p, 3s, 3p, 3d, 4s, 4p, 4d and 4f orbitals, respectively. The electron is never located in one specific place at one particular time, but rather exists in a cloud-like or fog-like state, spread throughout a volume of space representing the entire atom.

If there is no boundary, then the universe itself would be full by that field definition because every electron would be at any point by a very small probability.

Re: We are not mostly empty space

#62

Post by kleiba »

kylec wrote: post #11

Empty space, by definition, is space that can be filled by something. So how closely can atoms pack together? A neutron star has a density of 10^17 kg/m^3, whereas the typical human being is about 10^3 kg/m^3. I could fit the matter of trillions more human beings in the same space I'm taking up now. So yeah, I think there's some empty space in me.

I could fit the matter of trillions more human beings in the same space I'm taking up now.

Try it.

Re: We are not mostly empty space

#64

Post by mirimir »

GoToRO wrote: post #60
kylec wrote: post #11

Empty space, by definition, is space that can be filled by something. So how closely can atoms pack together? A neutron star has a density of 10^17 kg/m^3, whereas the typical human being is about 10^3 kg/m^3. I could fit the matter of trillions more human beings in the same space I'm taking up now. So yeah, I think there's some empty space in me.

Do atoms still remain atoms in a neutron star? don't they collapse to a soup of subatomic particles? serious question.

Nope, there are no atoms. Except at the surface, I suppose.

Re: We are not mostly empty space

#65

Post by db48x »

GoToRO wrote: post #60
kylec wrote: post #11

Empty space, by definition, is space that can be filled by something. So how closely can atoms pack together? A neutron star has a density of 10^17 kg/m^3, whereas the typical human being is about 10^3 kg/m^3. I could fit the matter of trillions more human beings in the same space I'm taking up now. So yeah, I think there's some empty space in me.

Do atoms still remain atoms in a neutron star? don't they collapse to a soup of subatomic particles? serious question.

The core of a neutron star is 100% neutrons (or perhaps a quark-gluon plasma where no individual neutrons are distinguishable). All the electrons and protons have been crushed together (by the extreme gravity) until they merge and form neutrons. As you get further away from the core, you find more and more protons and electrons, but still no atoms. The surface layer of the star has distinct atomic nuclei, but since the surface temperature is so hot (600,000K) they are not neutral atoms; the electrons are not bound to the nuclei. The density at the surface is still about a thousand times higher than the density of water or stone.

Re: We are not mostly empty space

#66

Post by rootlocus »

Koshkin wrote: post #34

“Empty space” is a completely relative notion. If I have a heavy steel safe which I do not have the key for, whether there is an empty space inside it is irrelevant, and the space occupied by the safe cannot be seen as being (partially) empty in any practical sense.

> “Empty space” is a completely relative notion.

It's relative to your perception of it, but physics doesn't care about what pattern your neurological impulses have in relation to matter.

Re: We are not mostly empty space

#67

Post by stephen_g »

mannykannot wrote: post #27
not2b wrote: post #22

Earlier quoted context omitted.

For anything that responds to the electromagnetic force, you're filled with fields. For something that responds only to the weak force, you're almost entirely empty space.

In the English-language usage I grew up with, 'occupied' means that there is something there, while 'filled' means occupied to the point where nothing more can be added. The former does not imply the latter. In this usage, space itself (the 'empty' space of the article's title) is implicitly not something. This usage may seem to be an accidental issue of language, resulting from an incomplete understanding of physics…

It’s abstract, but we experience this kind of issue with language lot. Think of a box that doesn’t have any objects in it. It’s empty, right? But if it’s sitting on the table in front of you it’s probably full of air.

So in one respect it’s completely empty but in another it’s totally full.

Re: We are not mostly empty space

#68

Post by jcelerier »

knzhou wrote: post #57
andrewprock wrote: post #30

Earlier quoted context omitted.

Yeah, the fact that neutrinos pass through us largely validates the notion that we are in fact mostly empty space.

But visible light can't get through us at all. Does that prove that we aren't empty space? The whole point is that this criterion is incredibly ambiguous.

> But visible light can't get through us at all.

visible light definitely gets through me when I put my hand in front of a bright light source

Re: We are not mostly empty space

#69

Post by praptak »

mirimir wrote: post #55
praptak wrote: post #51

Earlier quoted context omitted.

Modeling electrons as tiny objects that have probability distributions has a weakness. There is no sensible value to assign to the 'tiny'. I mean there is no experiment to determine the 'size' of the electron.

OK, not a physicist. But what about this? https://en.wikipedia.org/wiki/Classical_electron_radius

Check all the disclaimers on that concept, in particular "Attempts to model the electron as a non-point particle have been described as ill-conceived and counter-pedagogic"

Re: We are not mostly empty space

#70

Post by jbarrs »

mirimir wrote: post #55
praptak wrote: post #51

Earlier quoted context omitted.

Modeling electrons as tiny objects that have probability distributions has a weakness. There is no sensible value to assign to the 'tiny'. I mean there is no experiment to determine the 'size' of the electron.

OK, not a physicist. But what about this? https://en.wikipedia.org/wiki/Classical_electron_radius

That's essentially just an approximation. In some problems it can be useful to model the electron as having a finite radius, but our current understanding is that particles like electrons are literally infinitesimal points. In that case it's generally more useful for us to use things like Dirac delta functions to model them more accurately.
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