# Naked Science Forum

## Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: chris on 14/03/2010 12:56:51

Title: What percentage of an atom is empty space?
Post by: chris on 14/03/2010 12:56:51
When considering an atom, what percentage of the volume is "empty" space?

Chris
Title: What percentage of an atom is empty space?
Post by: graham.d on 14/03/2010 14:02:41
I guess it depends on what you mean by "empty". If you look at collision cross sections as a guide it will depend on the interacting particle. Taking the constituents as protons, neutrons and electrons (as individual items like billiard balls), atoms could be regarded mostly empty space. I think the ratio of the diameter of a helium atom to that of its nucleus (an alpha paticle) is around 15000:1 so the ratio of the volumes is the cube of that. On this basis the helium atom is only "occupied" 1 part in 3x10^12 so distinctly mostly empty. In practice the definition of what is meant by empty space has to be examined because the definition of what is considered to be matter occupying space is related to the range of forces (strong, weak, em) that may extend from its constituents.
Title: What percentage of an atom is empty space?
Post by: Soul Surfer on 14/03/2010 17:53:16
Electrons and quarks are considered to be point particles until you get down towards the planck distances when string theory may become important so as near as dammit the atom is totally empty space!
Title: What percentage of an atom is empty space?
Post by: lightarrow on 14/03/2010 21:41:31
In practice the definition of what is meant by empty space has to be examined because the definition of what is considered to be matter occupying space is related to the range of forces (strong, weak, em) that may extend from its constituents.
Infact a space-confined force field has mass, so it could be considered as matter too.
Title: What percentage of an atom is empty space?
Post by: yor_on on 18/03/2010 22:10:47
Maybe you should put the question in form of 'densities' instead :)
And the 'density' of a electromagnetic field would then be?
Title: What percentage of an atom is empty space?
Post by: lightarrow on 19/03/2010 12:54:20
Maybe you should put the question in form of 'densities' instead :)
And the 'density' of a electromagnetic field would then be?
In the void, the energy density (density per unit volume) of an electromagnetic field is:

(1/2)(ε0E2 + μ0H2).

E = electric field
H = magnetic field
Title: What percentage of an atom is empty space?
Post by: yor_on on 19/03/2010 14:36:59
Yes, it should have one, nicely done Lightarrow :). Now we just have to put it into consideration by shoving the resistance experienced by, for example a bit of invariant mass, like a human moving inside and relative that EM-field. If we then finally convert it into Joules to describe the energy, we finally will know why we don't turn on our telly, preferring that good book instead. Yes, it's easier to let it be :)

So what would the density be?
Title: What percentage of an atom is empty space?
Post by: lightarrow on 20/03/2010 15:28:12
Yes, it should have one, nicely done Lightarrow :). Now we just have to put it into consideration by shoving the resistance experienced by, for example a bit of invariant mass, like a human moving inside and relative that EM-field.
You mean inertia?
Title: What percentage of an atom is empty space?
Post by: yor_on on 21/03/2010 16:40:21
That it might be called, or the EM-fields general resistance to my body, walking through that 'cloud' of EM? It's sort of interesting :)
Title: What percentage of an atom is empty space?
Post by: Farsight on 21/03/2010 23:46:12
When considering an atom, what percentage of the volume is "empty" space?
100%
Title: What percentage of an atom is empty space?
Post by: lightarrow on 22/03/2010 20:45:53
That it might be called, or the EM-fields general resistance to my body, walking through that 'cloud' of EM? It's sort of interesting :)
For what concern inertia, you don't have to figure out how it can be owned by an electromagnetic field, because any other field has mass and so inertia.
Title: What percentage of an atom is empty space?
Post by: yor_on on 22/03/2010 22:48:55
I believe you are correct in that but it still boggles my imagination Lightarrow, and if there is an resistance it should be measurable, don't you agree? We define all particles except bosons as having mass as I understand it, with exceptions in some cases, but still?