Are There Really Over 2,000 Particles in the Universe?

[robertjford80]

This comes from Kaku's Beyond Einstein

By 1960, there were so many particles that a considerably expanded almanac, including a wallet card, was published. By 1995, the list was expanded to over 2,000 pages, describing hundreds of particles

Referring to this chart http://en.wikipedia.org/wiki/File:Standard_Model_of_Elementary_Particles.svg

there are about 16 particles in the standard model of particle physics, not counting the anti particles. I'm assuming that that list of particles covering 2000 pages was eventually shown that many particles are the same. correct me if I'm wrong.

 

[phyzguy]

Most of the particles listed in the 2000 pages are composite particles, made up of a combination of elementary particles. This is just like three particles (proton, neutron and electron) give rise to over 100 elements, many with multiple isotopes.

 

[kloptok]

Exactly, and at the time the quarks were not known so most people assumed that all the found particles were elementary particles. With the quark model one could make order out of the chaos. The particles in the Standard Model which you refer to are the ones we today consider elementary particles, that is, they are seen as point-like without internal structure.

However, you are not completely wrong in thinking that some particles ended up to be the same. Before knowing about parity violation in the weak interaction one could observe similar particles decaying into different parity eigenstates. One believed in parity conservation and so assumed they were different particles, but eventually it was realized that they were actually the same and that parity was violated. Google "tau theta puzzle" and you will find more information about this.