ClarkGoble wrote:OK. I guess what I'm saying is that I'm very skeptical Cox is correct to say that we've falsified any [unknown] type of particle. There are reasons to think the standard model is exhaustive but also reasons to be skeptical.
Suppose that when particle X happens to be near some electrons (say), it interacts with them somehow. Based on non-relativistic quantum mechanics alone, one might suppose that particle X could simply be present in a ghost (of which it is a constituent) but not in CERN. Some particles with unusual properties are just rare, after all. Just because uranium can't be found in my breakfast cereal doesn't mean it isn't there in reactors.
At high enough energy scales, however, all that just isn't true. The rules change. Energy is still conserved, but mass isn't. Particles appear and disappear. Interacting quantum fields obey what has been called the Totalitarian Principle: "Whatever is not forbidden is compulsory". If any unknown type of particle interacts with the ones we know, then given sufficient energy, those interactions will actually produce the unknown particles, out of known ones. Superstitious sailors used to think that "naming calls", but with quantum fields, interaction really does call.
Any particles which interact with the starting particles, even indirectly, can appear as collision products. Two Buicks can collide, and what comes flying out of the crash might be a Honda, some pots and pans, and an elephant. The only question is what the probability is for any given product.
Probabilities are low if interactions are weak, so we cannot rule out unknown particles which don't actually interact with the ones we do know. But a ghost-constituent X-particle that interacted too weakly to have been detected by now at CERN would also interact too weakly to have been seen by human eyes.
Even indirect interactions count. If the spirit-stuff that composes ghosts gets seen by spiritual eyes, still at some point there must be enough of an interaction with ordinary matter to prompt a material larynx to send out air pressure waves conveying the words, "Look—a ghost!" If there's really no interaction with ordinary matter, then the experience of spiritually seeing a ghost would be an entirely hidden one, of which no-one could ever speak or write. It would not even induce shivers in the spine or an intake of breath. We wouldn't be talking about it.
Particle colliders really are stringent tests of any theory of unknown stuff that in any way interacts with the matter in our bodies.