Undergrad What is a Proton Made Of and What Does It Look Like Under a Microscope?

[Carpe Physicum]

If a proton is made of quarks and gluons, what exactly IS a proton? What would it look like if we could shrink down to it's size? Is it really nothing at all, in the same sense as the "solar system" isn't really a thing in itself, it's just a collection of planets and a sun.

 

[Drakkith]

If a proton is made of quarks and gluons, what exactly IS a proton?

As you said, a composite particles composed of quarks and gluons. Just like atoms are composite particles made up of protons, neutrons, and electrons, molecules are composite particles made up of atoms, and people are big squishy composite particles made up of molecules.

What would it look like if we could shrink down to it's size? Is it really nothing at all, in the same sense as the "solar system" isn't really a thing in itself, it's just a collection of planets and a sun.

Yes. Just like a flock of geese or a herd of buffalo are composite things made up of many more fundamental things (in this case animals). I could draw a big patch on a map to show where the herd/flock was and its shape, but if you were to go out there and look at it you would see the individual animals and not the big patchy thing I drew.

It's difficult to say what a proton would look like since quantum effects are very prevalent at this scale, but the idea that it's a composite particles made up of more fundamental elements is the real takeaway here.

 

[mfb]

A proton doesn't have a substructure in the way the solar system has - classical descriptions ("this is here, that is there") just don't make sense for the makeup of a proton.

 

[Carpe Physicum]

If I'm reading this thread right, Drakkith says "the idea that it's a composite particles made up of more fundamental elements is the real takeaway here" and mfb says "A proton doesn't have a substructure in the way the solar system has" which seems to be the exact opposite. Which is it? Is there space between the quarks? Are they literally side by side so to speak?

 

[mfb]

It is made up of other particles but these particles don't have an arrangement like the planets in the solar system do.

Is there space between the quarks?

There is no empty space in a proton. "Between quarks" is a meaningless concept anyway.

 

[Drakkith]

If I'm reading this thread right, Drakkith says "the idea that it's a composite particles made up of more fundamental elements is the real takeaway here" and mfb says "A proton doesn't have a substructure in the way the solar system has" which seems to be the exact opposite. Which is it? Is there space between the quarks? Are they literally side by side so to speak?

The subatomic world is very strange. Even describing things like the position and size of particles become.. problematic. From what I understand about quantum chromodynamics (the theory governing the strong force) there isn't even a set number of quarks in a proton. See here: https://profmattstrassler.com/artic...the-structure-of-matter/protons-and-neutrons/

 

[nikkkom]

Is there space between the quarks? Are they literally side by side so to speak?

Particles don't have definite positions. For macroscopic objects (like a large protein molecule) the uncertainty is insignificant, and you can use a picture of atoms being distinct "balls", connected together, having definite positions and distances relative to each other.

But as you take lighter objects and smaller scales, the intuitive picture of "tiny balls" fails totally.

For example, electron on an atom's orbital is not "orbiting". It is just a cloud of disturbance in electron field, with both position and momentum being uncertain.

Since quarks are also light, and the distances on the scale of proton radius are much smaller still, quarks in proton are similarly not "balls", but rather clouds of disturbance in quark fields. The sizes of these clouds are such that they overlap - there are no "gaps".

 

[Carpe Physicum]

The subatomic world is very strange. Even describing things like the position and size of particles become.. problematic. From what I understand about quantum chromodynamics (the theory governing the strong force) there isn't even a set number of quarks in a proton. See here: https://profmattstrassler.com/artic...the-structure-of-matter/protons-and-neutrons/

Thanks for the link, extremely well written and well explained for laymen like me. One thing he mentions that is fascinating, is that evidently there are no "sharp edges" to protons. It really makes me wonder exactly what the LHC is colliding. Tiny balls of cotton it seems like made of even smaller clouds of cotton so to speak.

 

[Nugatory]

It really makes me wonder exactly what the LHC is colliding.

The word "collide" is used for historical reasons and because it is convenient, but "bring near for high-energy interaction" might come closer to what is happening.