# Emergent physics in the gap between the Planck scale and the "size" of quarks [closed]

The smallest probed length scale to date is around $$\Delta x \approx 10^{-18} m$$ (see here).

If we compare this to the Planck scale of $$\Delta x \approx 10^{-35} m$$ we are left with almost 20 orders of magnitude to bridge.

I am wondering about the following: emergence. The size of a quark is roughly a factor of $$10^3$$ below the size of a proton (as John Rennie points out in the comments, the quark size is zero within measurement uncertainty). And the size of a proton is roughly a factor of $$10^4-10^5$$ below the size of the hydrogen atom. And this pattern continues.

Based on this observation, is it reasonable to expect another hierarchy of phenomena on the journey from $$\Delta x \approx 10^{-18} m$$ down to $$\Delta x \approx 10^{-35} m$$ and how do current theories address this? How do current attempts of a unifying theory try to close this gap?

EDIT: Since this might be too broad, let me try to narrow it down on string theory. What does string theory say about the orders of magnitude between the Planck scale in the currently observable scale?

• Quarks don't have a size. $10^{-18}$m is the smallest size probed, not the size of a quark. As far as we know quarks are fundamental and don't have a size. Nov 30, 2018 at 9:22
• So quarks do not have a size w.r.t. the length scales we are able to probe Nov 30, 2018 at 9:43
• In string theory I guess quarks are excitations of the string. So the "quark size" is somewhere on the Planck length. But do we have a good reason to believe so? Or might there just be another hierarchy of entities, i.e., the possibility that the quark is not fundamental. It seems to me that we need a very good argument in order to bridge 20 order of magnitude Nov 30, 2018 at 9:48
• If you're asking whether there is new physics between the LHC energy and the Planck energy the answer is ... no-one knows. All we can say is that no evidence (no $5\sigma$ evidence) of anything beyond the Standard Model has ever been found. Nov 30, 2018 at 10:02
• Are you asking if there's anything between quarks and the Planck scale? If so, that's an extremely broad question, it's essentially the entire field of 'beyond the Standard Model' physics. There are thousands if not tens of thousands of papers on this subject. Nov 30, 2018 at 10:36