There was a lot of serious interest in finding subparticles of leptons like the electron in the years before the Standard Model reach widespread acceptance ca. 1974. These hypothetical particles are usually called
preons – the linked wikipedia article has a rather reference-poor summary of them.
Preons – the term will do, I think, as a catch all for “sub particles of the elementary Standard Model particles” – haven’t attracted much interest theoretical interest as the problems they were intended to solve have been solved using the SM, but if the Standard Model fails – eg: if no Higgs particle is found as the SM predicts - will likely be seriously revisited. While not as mathematically sexy as other “what are the SM particles?” theories, especially string theory, preon theory may be less troubled, and in a sense more “traditional” than other theories. If the SM keeps on making right-on predictions for every experiment that can be done with each new generation of experimental hardware, I expect preons will remain largely forgotten relics of theoretical physics.
Quote:
Originally Posted by Karnuvap
Even more intriguing is the realisation that a positron can be considered as an electron but going backwards through time. This raises the possibility that there is ONLY ONE ELECTRON in the whole universe and what we see at any given instant as lots of electrons is really this one electron reaching "NOW" via many oscillations from the beginning of time to the end of time thus explaining at a stroke why all electrons are identical …
I don't know about you but I am already boggled at this.
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This looks to me to be headed off-topic, and needing to be moved to its own thread, but I’ve been boggled by this idea – the “
one-electron universe” - since I first heard it in the late 1970s. It’s been around for a pretty long time - though I’ve heard
Dirac speculated in the 1930s about the positron and electron being time-reversed version of each other,
John Wheeler is usually credited with coming up with the full-blown idea in 1940, telling it to his then-PHD student
Richard Feynman.
I’m intrigued at the claim in
the wikipedia article that
Apparently, the hypothesis as a whole has been disproved by modern mathematical physics (citation needed)
, and would love it if someone could dig up that citation, and fix the wikipedia article while they’re at it.
Quote:
Originally Posted by Karnuvap
(no electron has been found to weight a little tiny bit more than the accepted weight for example, I'm aware of the Pauli exclusion principle).
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But isn’t this true of the invariant mass of
all the fundamental particles? And their charges and other quantum numbers, too?
If it wasn’t, as Karnuvap hints, a major rationale for the
exclusion principle - that fermions can be in the same place, because then they’d be indistinguishable – would be gone (vs.
bosons, such as the photon, that can have an infinite range of possible quantum numbers such as frequency, so any number of which can exist in the same place)
Quote:
Originally Posted by Karnuvap
Nah! - these days the smallest distance and the smallest time are the planck length and the planck time which are derived from the three fundamental constants c, h-bar and big G combined in a way that makes dimensions of length and time respectively.
Planck length is 1.616x10 ^ -33 (sorry I haven't got the hang of the maths codes)
Planck time is defined as how long it takes light to travel one planck length. (so there is bound to be a "c" relation there).
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Another take on Planck length is that it’s derived from
Compton wavelength of any photon and the physics of black holes, and all the other Planck units defined in terms of it and c.
Planck length, time, etc. aren’t in any meaningful sense the size of anything, but rather limits on precision of measurement via any means with the know constituents of reality
Quote:
Originally Posted by Karnuvap
The thing you have to remember about electrons is that they are infinite in extent (unless you measure one and then you might pin its position down but not its momentum) Until you measure it, the electron is everywhere (at once) - it just doesn't make sense to say let's measure one to see how big it is.
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This “everywhere at once” quality only applies for electrons following closed paths in space, such as those bound to atomic nuclei. A free electron, though still subject to the uncertainty principle, can have it’s location pinned down with nearly arbitrary precision.
Vap’s right that it doesn’t make sense to speak of the size of an electron the same way we speak of the size of proton and neutron, which we can measure in a fuzzy but nonetheless reasonable definite way by such means as scattering electrons off them. We say the electron has a “classical radius” of about

, but this just the size it would be if Maxwell’s equation held on all scales, and there was no such thing as quantum effects.
As best I can tell with my limited physics and limited library access (I’m thinking of coughing up the $$s for AAAS membership to be able to read online articles like
“Experiments on the Structure of an Individual Elementary Particle”) it’s in principle possible to use some techniques to find an upper limit on the size of an electron, and that the best current has this limit down to about

. If such experiments can somehow place a lower limit on this size, I suspect it’d be pretty compelling evidence that electrons
are made of some subparticles.
(hey, wow, this post finally did get back on topic!

)
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