Arcadian Functor

occasional meanderings in physics' brave new world

My Photo
Location: New Zealand

Marni D. Sheppeard

Monday, January 15, 2007

Swinging Schwinger

Sometimes I mention the volume The Physicist's Conception of Nature (ed. Mehra), a collection of lectures given at the 70th birthday celebrations for Dirac in 1972. Schwinger's contribution is interesting, because he seems decidedly irritated at the seriousness with which modern particle physicists take the concept of the vacuum.

...the vacuum is the state in which no particles exist. It carries no physical properties; it is structureless and uniform. I emphasise this by saying that the vacuum is not only the state of minimum energy, it is the state of ZERO energy, ZERO momentum, ZERO angular momentum, ZERO charge, ZERO whatever.

Quite adamant, isn't he? Carl Brannen places much importance on Schwinger's ideas in his derivation of the lepton masses, in particular the measurement algebra. This is conceptually important, because it stresses experiment and the link between input and output states, rather than the usual arbitrary independence of these. Observe that this is more than a mere recognition of the interdependence of states, because it sees more reality in the measurement itself than in intermediate states.


Blogger L. Riofrio said...

Nice to hear some common sense about vacuum energy. The "dark energy" relies on some form of vacuum energy. We've figured out that the total energy of any object E + U = 0. That also applies to particles with kinetic energy, and even particles with no mass at all (photons). What could the energy of a vacuum be?

January 15, 2007 8:43 PM  
Blogger nige said...

Dirac himself had different ideas about the vacuum, ie, the ideas he actually used to predict antimatter from the Dirac equation's negative energy solution. He thought about a "Dirac sea":

... with the new theory of electrodynamics we are rather forced to have an aether.

– P.A.M. Dirac, β€˜Is There An Aether?,’ Nature, v.168, 1951, p.906.

It's gravity gauge boson radiation that causes the pressure on matter (ie the
subatomic particles, not macroscopic matter as it appears, which we know if mostly empty), and such radiation is directional.

The argument that shadows will be filled in by non-radial (eg sideways) components of pressure was the major argument against LeSage's material aether push gravity theory.

The aether exists as a Dirac fluid closer to 1 fm to an electron where you have a nice, strong, disruptive electric field strength of 10^20 v/m to break it up into a fluid. Beyond that, whatever "aether" there might be, is metaphysical in the sense that it is definitely not polarized or QFT wouldn't work (it is too locked up by bonding forces to be polarized and thus it is unable to really move much if at all). The only way you will work out what it is at low energy (beyond 1 fm, or the distances electrons approach in collisions at an
energy of less than 1 MeV per collision) is to work out all the stuff you can detect by high-energy physics above the IR cutoff (within 1 fm) and use
those results to work out a model which both produces all of that, tells you the low energy structure of the vacuum, and also makes some other predictions so that it can actually be verified scientifically by experimentation.

Hence, what you need to do is to get a complete understanding of how the Standard Model (or some other equally good approximation to high energy phenomena, if you know of one!) can arise with some understanding of how to resolve existing problems like electroweak symmetry breaking, in a predictive way that exceeds existing understanding.

The LeSage mechanism is actually the pion exchange strong nuclear force in the vacuum. There is a limit on the range, because the pions aren't directional (the Dirac sea within 1 fm from a particle is a fluid assembly
of the chaotic motions of particles), unlike the radiation which travels through the non-fluid vacuum beyond 1 fm range (gravity and electromagnetism). The pion pressure only pushes protons and neutrons together if they are close enough that there is not room for too many pions
to appear between two particles and neutralize the pressure: similarly, a rubber sucker only sticks to surfaces smooth enough to exclude air. If air
gets between the sucker and the surface, the pressure on both sides of the sucker is equalized, and it won't be "attracted" (pushed to the surface by
ambient air pressure).

For some evidence, see

January 17, 2007 1:41 AM  

Post a Comment

<< Home