Re: Q; Various musings
- From: "PD" <TheDraperFamily@xxxxxxxxx>
- Date: 2 Apr 2007 15:05:05 -0700
On Mar 30, 9:16 am, "G. Ralph Kuntz, MD" <g...@xxxxxxx> wrote:
I am NOT a physicist, but I am interested in particle physics.
Does the electron have a size or is it a "point" object? If so, it's
density should be infinite since it has mass in a zero volume.
Interestingly, density is a concept that applies only to composite
objects apparently. There is no evidence that fundamental particles
need to have both mass and volume as properties. Extrapolation from
our ordinary experience with "stuff" is not sufficient reason to
demand it for everything.
When it comes down to it, the volume of composite stuff really has to
do with the range of interactions between the constituents. There is
nothing interstitial, for example, between electrons and protons, and
so there is nothing material that forces the size of atoms other than
the nature of the interaction.
How do forces work at the sub-atomic level? If two electrons approach
each other, I understand that the like negative charges repel each
other, but what imparts the "thrust" to move them apart? Or an
electron and a proton - what causes them to move toward each other? I
know that the standard model says that the particles exchange photons,
but why does this exchange cause them to move toward or away from each
other?
Because the photons carry momentum. When a photon is emitted from one
particle, the momentum it carries away produces a recoil in the
emitting particle. And when the photon is absorbed, it delivers
momentum to the receiving particle. Now, before you get caught up
wondering how this can result in attraction as well as repulsion, you
should be aware that photons are not little BBs that travel in
straight lines between here and there. To understand a little better
what photons really do, I suggest you read a short, friendly book by
Feynman called "QED".
Do the photons "bend" space - as in general relativity?
Well, in some sense yes, but not in the same way that gravity works.
Is mass quantized?
Not as far as we know.
When new virtual particles are created, say an
electron and anti-electron (positron), why do they always mass exactly
the same amount and not 99% or 102% of the "standard" mass?
*Virtual* particles don't in fact have the same mass as the "standard"
mass. But the pair creation example you gave is not necessarily a case
of virtual pair production.
I am reading Brian Greene's book "The Elegant Universe" and it is
leading to more questions than answers. Good book, though!
That is the *whole point* of a good book like that, to generate
interest and to create more questions than to answer them.
PD
.
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