Chris Peterson wrote:
Beyond wrote:Heh, i almost said massive, but for us non-scientific folks, it's included in 'bigger'.
So a proton and electron are physically the same size?
Subatomic particles don't really have sizes in the classical sense. An electron is believed to have no internal structure, so it is considered to have no size- a volumeless point. A proton is made up of quarks, and has a sort of size, called a charge radius. Really, though, at the quantum scale "size" is usually not very meaningful. The properties that define behavior are different- charge, rest mass, angular momentum, and others.
My understanding is that particles do have "cross sections" ... which is a statistically typical interaction radius that reflects the likelihood of the particle reacting with something when it comes close. I believe collision cross sections can vary depending on the particular force involved in the interaction and with the properties of the particles involved. Cross section can be thought of as an effective size.
As I recall then, in regard to cross section, electrons are considered to be quite large and puffy because they are light and yet they are very likely to interact with other charged particles and thereby suffer a "collision".
But I never took a particle physics or a QCD class... Maybe someone can fill in more in that regard.
In my limited understanding of quantum mechanics, string theories notwithstanding, fundamental particles aren't really physical balls of stuff with a physical radius. Rather, they are more like roving probability waves. When the probability wave of one particle overlaps with the probability wave from another particle, there is a chance that the two will interact dramatically (ie: collision). The chance of an interaction increases with the amplitude of each probability wave in the areas where the waves overlap significantly.
(Technically, all particles have wave functions that extend to infinity (as big as the universe), but at some point their wave function amplitude becomes so infinitesimally small that an interaction is unlikely to occur even once in a period of time equal to the age of the universe, effectively "never".)