Re: EM-propulsion? No Propellant?


renaborney@xxxxxxx wrote:
My understanding is that no unification of the four forces (it is
thought by some physicisits working in supersymmetry and string theory
that a "fifth" force may also exist) has been acheived. Two of the
forces (Electromagnetism & the Weak Force) have been unified into an
Electroweak Force. The String Force has not - but since it is a quantum
force physicists are optimistic about its unification in the near
future. Gravity is NOT a quantum force (which deals with the very
small), but a relativistic one (which deals with the very large).
Unification will require a theory of Quantum Gravity

String theory of M theory has a variety of formulations. In some there
is a 5th force in others not.

All versions of String Theory, and this goes really for all types of
grand Unification propose that at ultra short ranges Gravity is as
strong as the other forces. On the macroscopic level this is clearly
absurd as the whole Earth only gives an acceleration of 9.81 ms^-2.
Compare this with the strength of EM and nuclear forces. SS proposes
that at short distances grvity obeys an eigth power law. It is possible
to create sub atomic black holes in the laboratory. To me this is an
"Instantia Crucis". If gravity does not obey a high power law at short
range SS is incorrect and a question mark hangs over the whole question
of unification.

The modern quantum mechanical view of the three fundamental forces (all
except gravity) is that particles of matter (fermions) do not directly
interact with each other, but rather carry a charge, and exchange
virtual particles (gauge bosons), which are the interaction carriers or
interaction mediators. Thus, for example, photons are the mediators of
the interaction of electric charges; and gluons are the mediators of
the interaction of color charges. This coupling of matter (charged
fermions) with force mediating particles (gauge bosons) is the result
of fundamental symmetries of nature.

Interaction/Current Theory/Mediators/Relative Strength 1/Long-Distance
Behavior

Strong/Quantum chromodynamics (QCD)/gluons/1038/1 (see discussion
below)

Electromagnetic/Quantum electrodynamics(QED)/photons/1036/frac{1}{r^2}

Weak/Quantum flavourdynamics (GWS theory)/W and Z bosons/ 1025/
frac{e^{-m_{W,Z}r}}{r}

Gravity/General Relativity/(GR, not a quantum theory.)/ gravitons
2/1/frac{1}{r^2}

1 Approximate. The exact strengths depend on the particles and energies
involved.

A unique characteristic of the strong interaction is the fact that
gluons interact with each other. This causes the strong interaction's
strength to be independent of distance. This can be interpreted to mean
that the force has an infinite range. However, in actuality, since the
energy stored in the field increases with separation between the
interacting particles, at large distances the field contains enough
energy to produce particle-antiparticle pairs. When this occurs, the
field lines are cut in half. By this mechanism, strong forces never act
over distances much larger than the proton's radius.

2 The Graviton (the exchange particle for gravity) has not yet been
discovered

That last sentence is incorrect on 2 counts, or perhaps I should say
1.5 counts.

First of all although gravitational waves have not been directly
detected (I feel though that this is due more to NASA's infatuation
with manned space flight than to the fact that it is inherenly
impossible), the existence of energy loss has been deduced by obseving
two pulsars orbiting each other. Deuctions were made using the doppler
effect. The energy loss is within 10% of that predicted by General
Relativity.

BTW - An extra solar planet has been observed orbiting a pulsar by this
method. What is quite remarkable is the speed of formation of the
planet. It is a secondary planet. The first solar system was blown to
smitherines. It is like the core of Chernobyl both in terms of the
radiation emmitted by the pulsar itself, and by its own chemistry.
There are Plutonium mines on the planet! It has not yet decayed. If the
ayotooahs of Iran really believe in >10Kyr they should look for one!

Now as I said in my first posting gravitational waves are quadupolar,
this is part of what a spin of 2 implies quadruplar radiation. With a
spin of 1 (EM) the Earth would fall into the Sun within 100 million
years. This also makes gravitational waves hard to detect as there is a
symmetry between reception and transmission. You really want the arms
of your detector to be a radian apert (ideally). Only LISA can really
do this, hence my remarks about NASA.

The second point is a general one concerning the relationship between
quantum electrodynamics and GR. GR is about deformed space, not about
particle exchange. Quantum electrodynamics is about particle exchange.
You could in fact say that space curves in as kind of bootstrap effect.
Gravitons (or gravitational waves) cause space to curve, space might
curve on a kind of bootstrap effect. Black holes contain electric
charge. The fields are encapulated in the curved space.

- Ian Parker

.

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