As I understand it, the impossibility of measuring quarks precisely is (at least in part) a function of electrons being too big to obtain information from quarks without changing their properties, much like an observer would interfere with social actors. However, a hidden camera would have only negligible effect on the people studied, so what about observing quarks with something so small, it wouldn’t affect the measurements? Heisenberg’s uncertainty would still hold, at least for measuring these even smaller particles themselves, but what about Bell’s inequality? If we could measure different spins of a quark with something so small it wouldn’t change the spin, would we get a definite answer to whether it is the speed of light or causation that the inequality violates? Any other interesting answers? Or am I fundamentally mistaken somewhere?
To the extent that there’s any greater difficulty in studying quarks than there is any other subatomic particle, it’s because quarks cannot be isolated. If you tried to pull a quark out of a proton, the act of you pulling would produce a quark-antiquark pair between the quark you’re pulling out and the rest of the proton, and you’d end up with a pion (combination of a quark and an antiquark) and an intact proton.
Electrons are, so far as we can measure, point particles with no size at all. The only reason you wouldn’t use an electron to study quarks is that electrons don’t interact via the strong force, so you’d use something else made of quarks instead.
I guess that’s something I’ve never really bought. How can a thing not have a size?
String theory says they do in fact have a size, if I understand correctly.
Like Chronos says “Electrons are, so far as we can measure, point particles with no size at all”. Since we can’t measure any dimension of an electron we can’t assign a size to it. Now as we get better and better at smashing thing together we might find that electrons do have a cross section and so have a size to them. It’s just that right now, with what we know they are all for intents and purposes point like.
“Size” is a concept from the everyday world. As long as you stay within your everyday, three-dimensional paradigm, it’s perfectly OK to give the electron a radius, and you can find lots of discussion about what that radius is. See here for a typical example.
If you get all quantummy, then the truth is that no one really knows how to properly describe what’s going on–it’s fair to say (in my opinion) that no one really knows what’s going on, period. But one thing’s for sure: the ordinary behaviours of the everyday world go away. Because of that, the language used in the everyday world becomes useless, and non-sensical (you see the term “counter-intuitive” a lot).
In quantum mechanics, “point particles” have no “size” because they don’t have any structure. They aren’t made of stuff. They exhibit behaviours and they are called “particles” because they have mass and are more or less corpuscular*–i.e. their behaviours are quantifiable, predictable, and (for the most part) internally consistent to that particular “particle.” But at this quantum level, what we think of as ordinary three-dimensional space has been subdivided so far that there isn’t any “space” in which to be three-dimensional. We don’t have any idea what “space” actually is, anyway, so there’s no language to describe what it means to sub-divide space that far.
Perhaps there is a whole other layer down. We’ve come a long way since thinking the atom was the end of the line. Right now the only way you’d get credence for the next layer is accurate prediction for behaviours of stuff we can measure, because we can’t measure anything so teeny as strings, for example.
Perhaps we shouldn’t let physicists use terms like “particle” and make them use terms like “observed behaviour” but that would make for some pretty stilted explanations of how things work.
*Ignoring, for the moment, wave-like qualities–another term from the macro world.
If you prefer, you can think of electrons as having a size that’s just so incredibly small that we can’t measure it by any means. There’s no way to prove that they don’t. Beware, though, that if you look up “size of an electron”, you’re likely to encounter something called the “classical radius of the electron”, which is calculated without regard to quantum mechanics, and which turns out be wrong: We have managed to measure far enough to say that if the electron does have a size, it’s much smaller than the classical radius.
We do measurements by throwing little things at bigger things and then observe how they bounce back or move through. If the big thing is a collection of quarks and the little thing is something so small it hardly affects quarks at all we’re going to have a wee bit of a problem observing the little things to find out what happened.
Let me clarify for you what we do in the relevant branch of physics (high-energy particle physics), so that your understanding is more concrete. We do measurements by throwing things at each other, true. The smallest things we have ready access to (and are also able to “throw”), are:
- electrons
- hydrogen nuclei (protons). Protons are a bound state of 3 quarks.
- also anti-electrons and anti-protons (but which have to be produced artificially so are less readily available)
- just to be complete: muons (a heavier version of an electron) could also be used, but have to be produced artificially. Same goes for a few long-lived quark bound states.
There have been electron-electron colliders, proton-proton colliders, proton-anti-proton colliders, electron-proton colliders, and so on. At low energies, colliding electrons or protons just bounce off each-other. But at high energies they begin to rip particles out of the vacuum (ala E=mc^2), and/or themselves convert into other particles, and what we start to see are like little explosions, with all sorts of particles being produced and then decaying into showers of particles whose tracks are recorded, and/or are absorbed and their energy deposits recorded by very large particle detectors. From these observed tracks and energy deposits, all sorts of indirect evidence is gathered about
ah, fuck it
Consider a wooden pillar sticking up through the ocean’s surface. If a 20-meter-long oceanic wave comes by, it will not be disturbed in any significant way by this pillar. If instead you paddled up to the pillar in a kayak and started rocking back and forth to make short wavelength waves, then someone on the other side of the pillar would notice that the waves had peculiar disturbances – shadows and diffraction patterns – that indicate the presence of the pillar.
So, when you probe something with a wave, you can’t expect to see any detail much smaller than the wavelength of the wave. For this reason, light microscopes are limited to about 200 nm resolution. Electron microscopes use the fact that matter (e.g., an electron) is also a wave to image smaller scales. Note that the wavelength of a particle is related to its momentum, with higher momentum (or, higher energy) particles having shorter wavelengths. A typical electron’s wavelength in an electron microscope is 0.002 nm.
And, so it is with particle collisions. Saying you want a “smaller” probe is just saying you want a higher energy probe. Meet the LHC.