What exists in the Space between quarks Apologies to all if this has been asked before, I searched but was unable to find one similar. 
This is a question that has been bugging me for a while that i haven't really been able to find a suitable answer for. 
I am aware that the space between an atoms nucleus and its electron cloud is teeming with virtual particles that allow the exchange of energy that give electrons an assigned energy level or 'shell' but what bugs me is about the space in between atoms.
What is in between atoms? is it classifiable as a vacuum where nothing at all exists? 
I would find it hard to believe that atoms are pushed right up against each other at all times due to repulsive charges on the nucleus acting upon any other. 
I accept that the gap is unbelievably small but on the scale of atoms and electrons, how small are we talking? Is there even a gap at all? Do we know what is in between or is it unknown? is it a similar process to the virtual particles between nucleus and electrons? 
It is to my limited understanding that when particles "collide" there is no physical interaction, rather an exchange of energy through virtual photons. Is that what exists in all of these gaps? a constant exchange of virtual energy that acts as a consistent repulsion between all atoms?
 A: The space between atoms depends very much on the medium you are talking about. In solids the typical distance between atoms is about the same as the size of the atoms themselves. In everyday gases at room temperature and pressure the distance between molecules is many times their size, and in deep space you can get densities as low as one proton per cubic centimetre!
You can get a rough idea of the average separation $\ell$ between atoms by using
$$ \ell \approx \left(\frac{m}{\rho}\right)^{1/3} $$
where $m$ is the mass of an atom and $\rho$ is the (mass) density of the material. This can be compared to the size of an atom, which for all elements is about the same at $\approx 10^{-10} - 10^{-9}\ \mathrm{m}$.
Space is full of fields like the electric and magnetic fields. You can think of certain types of "vibrations" of these fields as virtual particles, but the common view of modern physics is that the field picture is more fundamental. There are fields for all of the elementary particles, and the fields are constantly fluctuating due to quantum mechanics. You can think of temporary ripples in the fields as virtual particles, which are responsible for transmitting disturbances through space. Real particles are quantised excitations (or vibrations) in a field which propagate long distances.
Matt Strassler has gone to great lengths to explain this point of view in his popular articles.
Frederic Brünner brings up an important point about virtual particles. Physicists use an approximation called perturbation theory to do most of their calculations (because the calculations are really hard to do without making approximations). Virtual particles are a convenient way to organise these calculations, but you should not think of them as physical objects like real particles. In a sense virtual particles are misleading. What they really represent are rapid fluctuations of the fields (what I called ripples before). At large distances these fluctuations don't matter except when they average out to a smooth classical field. For the interactions between atoms, and even most of the interactions between electrons and nuclei, the classical field is all you need.
A: I have thought about this question for quite some time. The theory that I highly believe in is about string theory. The theory states that the space in between subatomic particles are almost massless strings from type 2a string theory. These string have so little mass (roughly .83 x 10 to the -5 GeV) that they are undetectable. Of course this theory relies solely on string theory. Thank you for your time.
