Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Smaller Than an Electron
Name: Ryan J.
Status: student
Age: 17
Location: N/A
Country: N/A
Date: Saturday, May 18, 2002


Question:
What is smaller than an electron?


Replies:
Ryan,

Current research shows that an electron has no size at all. It is a "point particle". As a result, there are no particles that are smaller in size, although there are particles with smaller mass. These are neutrinos. A neutrino has no electric charge and a mass that is one-millionth of the electron mass, perhaps even smaller.

Dr. Ken Mellendorf
Physics Instructor
Illinois Central College


Protons, neutrons, pions, quarks, and other sub-atomic particles are "smaller" than electrons. Having said that I will make the disclaimer that it is not accurate to talk about the "size" of an electron or other atomic and sub-atomic particles. They do not have a "size" in the sense that a bowling ball or baseball do. How "big" the atomic/sub-atomic particle is depends upon how it is measured and its surroundings. For example, an electron in a hydrogen atom has a different size than a "free" electron. The reason for this is that in quantum mechanics, which is the only correct way to discuss electrons and other "smaller" particles, the term "size" loses its meaning -- in fact it has no meaning.

Scientists, teachers, and texts continue to associate the behavior of atomic and sub-atomic species (I will not even call them particles, because that too is not rigorously defined either) with familiar concepts from classical, Newtonian mechanics -- like size, position, speed etc. These atomic / sub-atomic particles behave paradoxically when described in classical terms. An electron is surely a "wave" because it can be diffracted, and that is clearly a property of "waves". But electrons can be "scattered" deflected like little bullets, and that is clearly a property of particles.

To the best of my readings into the matter (at varying levels of mathematical sophistication), the particle / wave duality of electrons, photons, etc. has not really been resolved. Young's double slit experiment (look up on some web sites) has not, or maybe cannot be explained. The paradox is this:

If I have two narrow slits and pass light through the two a diffraction pattern appears on detectors on the other side of the slit, that is alternating bright and dark images. If I close either one of the slits, a single spot is detected on the other side of the slit.

This different behavior occurs even if the experiment is set up in such a way that photons are produced one at a time, and if which slit I choose to close is a random choice. It is as if the photon "knows" whether there is one slit, or two slits present.

Those are the results of the experiment. How the photon "knows" is the paradox -- as yet not resolved I believe. By the way, the same experiment using electrons instead of photons gives the same results. Hope that's not more "answer" than you wanted, but we should not deceive ourselves that there are still some unanswered questions out there.

Vince Calder



Click here to return to the Physics Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (help@newton.dep.anl.gov), or at Argonne's Educational Programs

NEWTON AND ASK A SCIENTIST
Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory