Interstellar Propulsion idea using an Asteroid and a few comets!

In article ,
David Woolley wrote:
...The line of action of gravitation appears to be instantaneous
between orbitting bodies, so that distance is a non-issue to the effect.

That gravitational effects propagate at the speed of light (within
experimental error (which is at least 10 times smaller than c)) was
re-verified in the last year.

Not, alas, verified very convincingly -- last I heard, there is
considerable controversy about what that particular experiment tested and
how well it tested it.

While there is very good reason to think that gravitational effects
propagate at the speed of light, I don't know of any compelling
experimental result *directly* verifying this. There are some strong
indirect verifications -- both the precession of Mercury's perihelion and
the evolution of binary pulsar PSR 1913+16 are, *by current theory*, tied
to the speed of gravitational effects, and results from both show it as
the speed of light -- but those are at least potentially subject to
reinterpretation if new theory emerges.

Finally, a subtle point which some may have missed he what propagates
at the speed of light is *changes* to gravitational fields. The fields
themselves are (loosely speaking) the local curvature of space, and they
don't have to propagate to have effects, any more than a hillside needs to
propagate for a ball to roll down it. There is nothing that constantly
travels back and forth between the Earth and the Sun to keep Earth in its
orbit, so asking how quickly the whatever-it-is travels is meaningless.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

"Henry Spencer" wrote in message
...
In article ,
snipsnap
Finally, a subtle point which some may have missed he what propagates
at the speed of light is *changes* to gravitational fields. The fields
themselves are (loosely speaking) the local curvature of space, and they
don't have to propagate to have effects, any more than a hillside needs to
propagate for a ball to roll down it. There is nothing that constantly
travels back and forth between the Earth and the Sun to keep Earth in its
orbit, so asking how quickly the whatever-it-is travels is meaningless.
--

That's an interesting observation.
But is this not similar to stating that although by definition EM fields
(photons) travel at speed of light, it has not been proven that/if a
continuous electric field has effect at speed of light ?

If this analogy makes sense, then I still think you are out of luck :
Any 'effect' of the electric field (even if it is a charge spinning around
another one) means that there is a change in magnetic field, which means a
change in electric field etc..
And changes travel at speed of light. The change seems continuous, but can
be because the changes are much larger than quantum limits, and because the
two charges dont move near speed of light...

There is no reason to assume that gravitational fields dont work the same
way.

Rob

"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

In article ,
Rob Dekker wrote:
Finally, a subtle point which some may have missed he what propagates
at the speed of light is *changes* to gravitational fields. The fields
themselves are (loosely speaking) the local curvature of space, and they
don't have to propagate to have effects...

That's an interesting observation.
But is this not similar to stating that although by definition EM fields
(photons) travel at speed of light...

The similarity is superficial; it's a false analogy. The underlying
mechanisms are very different.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

"Henry Spencer" wrote in message
...
In article ,
David Woolley wrote:
...The line of action of gravitation appears to be instantaneous
between orbitting bodies, so that distance is a non-issue to the
effect.

snipsnap
There is nothing that constantly
travels back and forth between the Earth and the Sun to keep Earth in its
orbit, ...

This is an assumption.
I think the current theory postulates that 'gravitons' are constantly
exchanged, at speed of light.
This is in analogy to all other forces of nature, where some 'particle' is
associated with the force.

But hard proof either way is still is not there...we have not observed
gravitons as particles (in some quantum effect), because their energy is so
absurtly small, so we cant measure their speed directly...

--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

In article ,
Rob Dekker wrote:
There is nothing that constantly
travels back and forth between the Earth and the Sun to keep Earth in its
orbit, ...

This is an assumption.
I think the current theory postulates that 'gravitons' are constantly
exchanged, at speed of light.

No, that is precisely *NOT* what the current theory is, which was my point.
Gravitational waves, aka gravitons, convey only *changes* in the field.

This is in analogy to all other forces of nature, where some 'particle' is
associated with the force.

The analogy is false, or at least misleading. Gravity seems to be a
rather different kind of force. Physicists are still struggling to fit it
into the same sort of theory as the other forces.

But hard proof either way is still is not there...

On the contrary. It is easily proved that gravity is *not* the result of
the exchange of particles at the speed of light. If that were so, gravity
would show aberration, which would make planetary orbits unstable.

Light and other forms of electromagnetic radiation *do* show aberration:
a moving observer, looking to the side, sees stars slightly ahead of their
true positions, because a photon which to him seems to come straight in
from the side, in fact had to angle forward a bit to get down the barrel
of his moving telescope. That's a very loose explanation, but a more
rigorous treatment gives the same result. Astronomers noticed this in the
early 18th century.

Planetary orbits are stable only if gravity appears to come from precisely
the true position of the Sun. If gravity traveled at a finite speed and
thus showed aberration, the Earth wouldn't be here.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

Hi Henry,

I did not know this. Very interesting..
I couple of things start to make sense now.
Curvature of space/time and forces due to (virtual) particle-exchange are thus not the same..?.

Or could it be that the (particle-exchange) effect of gravity is still there, but it is analogous to
the 'spooky' action at a distance from the ERP experiments, which also seems to be
instantanious interaction of (exchange) particles ?

Many more questions come up...
Do you have an article link which explains that an 'abberation' effect of gravity would make the planets' trajectories unstable ?
Is this 'abberation' effect present for two interacting electric charges ? How do we know ?

I know that two electric charges rotating round each other radiate EM energy and thus loose energy, and thus eventually collide.
Is this abberation effect yet another explanation for this ? And if so, how do we know it is not there for gravity ?
After all, planets rotate very, very slowly, thus radiate very little 'graviton' energy... Might just not be detectable in billions
of years...

Thanks !

Rob


"Henry Spencer" wrote in message ...
In article ,
Rob Dekker wrote:
There is nothing that constantly
travels back and forth between the Earth and the Sun to keep Earth in its
orbit, ...

This is an assumption.
I think the current theory postulates that 'gravitons' are constantly
exchanged, at speed of light.

No, that is precisely *NOT* what the current theory is, which was my point.
Gravitational waves, aka gravitons, convey only *changes* in the field.

This is in analogy to all other forces of nature, where some 'particle' is
associated with the force.

The analogy is false, or at least misleading. Gravity seems to be a
rather different kind of force. Physicists are still struggling to fit it
into the same sort of theory as the other forces.

But hard proof either way is still is not there...

On the contrary. It is easily proved that gravity is *not* the result of
the exchange of particles at the speed of light. If that were so, gravity
would show aberration, which would make planetary orbits unstable.

Light and other forms of electromagnetic radiation *do* show aberration:
a moving observer, looking to the side, sees stars slightly ahead of their
true positions, because a photon which to him seems to come straight in
from the side, in fact had to angle forward a bit to get down the barrel
of his moving telescope. That's a very loose explanation, but a more
rigorous treatment gives the same result. Astronomers noticed this in the
early 18th century.

Planetary orbits are stable only if gravity appears to come from precisely
the true position of the Sun. If gravity traveled at a finite speed and
thus showed aberration, the Earth wouldn't be here.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

(Henry Spencer) wrote in message ...
In article ,
Rob Dekker wrote:
There is nothing that constantly
travels back and forth between the Earth and the Sun to keep Earth in its
orbit, ...

This is an assumption.
I think the current theory postulates that 'gravitons' are constantly
exchanged, at speed of light.

No, that is precisely *NOT* what the current theory is, which was my point.
Gravitational waves, aka gravitons, convey only *changes* in the field.

Quantum electodynamics and general relativity were weak points in my
studies, and my studies were decades ago so I may be asking nonsense:
Physicists often talk of photons in two forms, actual and virtual,
where actual photons convey changes in position and virtual photons
convey forces for current positions.

This is in analogy to all other forces of nature, where some 'particle' is
associated with the force.

The analogy is false, or at least misleading. Gravity seems to be a
rather different kind of force. Physicists are still struggling to fit it
into the same sort of theory as the other forces.

But hard proof either way is still is not there...

On the contrary. It is easily proved that gravity is *not* the result of
the exchange of particles at the speed of light. If that were so, gravity
would show aberration, which would make planetary orbits unstable.

If I remember my classical mechanics correctly, two body forces are
stable for r^x if and only if x is greater than or equal to -2. The
classical electrostatic and gravitational models are both r^(-2), in
their behavior so both are capable of potentially forming stable
systems, but become unstable for small perturbations from this model.
When full classical electromagnetic theory is introduced the fields
produced by orbiting charged particles cause the classical
electromagnetic system to be unstable. Stability only reappears when
quantum physics is introduced, and then only for the lowest energy
state. Would this gravitational "abberation" have a correspondence to
the magnetic field?

Given that a multibody system coupled using 1/r^2 forces is generally
unstable, but we have proof of the existence of such systems (e.g.,
our solar system, galaxy, etc.) an important question is whether the
instability would be important over the time period during which the
systems have existed, and studies have been sufficient to show that
the result is inconsistent with this interpretation.

This analysi, of course, would be easiest for two body systems
involving large masses and short distances, i.e, an encounter with a
black hole or neutron star. I had the impression that asttrophysicists
considered such systems to be unstable, but I vaguely remember that
tidal forces and mas exchange are important contributors to that
instability.

Light and other forms of electromagnetic radiation *do* show aberration:
a moving observer, looking to the side, sees stars slightly ahead of their
true positions, because a photon which to him seems to come straight in
from the side, in fact had to angle forward a bit to get down the barrel
of his moving telescope. That's a very loose explanation, but a more
rigorous treatment gives the same result. Astronomers noticed this in the
early 18th century.

Planetary orbits are stable only if gravity appears to come from precisely
the true position of the Sun. If gravity traveled at a finite speed and
thus showed aberration, the Earth wouldn't be here.

Does abberation affect virtual photons?

On Wed, 01 Sep 2004 08:58:17 GMT, Rob Dekker wrote:


But hard proof either way is still is not there...we have not observed
gravitons as particles (in some quantum effect), because their energy
is so
absurtly small, so we cant measure their speed directly...


Actually you got it exactly wrong. The particles move throgh a Higgs field.
The mass of the particle is inversely proportional to the strength of the
force. So a graviton is in fact the most massive particle there is.
To accelerate a particle to get enough energy to produce graviton's
you would need a 1 light year long accelerator.
So their energy is positively huge.
The idea behind this is that in any energy field virtual particles are
continuously
produced due to the fact that space contains energy. Since the amount of
energy needed to create a graviton is very high the chance of one being
produced is very small.

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Using M2, Opera's revolutionary e-mail client: http://www.opera.com/m2/

John Thingstad wrote:

Actually you got it exactly wrong. The particles move throgh a Higgs field.
The mass of the particle is inversely proportional to the strength of the
force. So a graviton is in fact the most massive particle there is.

Gee, is that why gravity has unlimited range?

Sounds like you're spouting bull****, Mr. Thingstad.

Paul

On Sun, 05 Sep 2004 17:09:30 -0500, Paul F. Dietz wrote:


Nop, sorry.
It is the weak interaction with mass which is dominant.
The mass has nothing to do with it.
Look into Calusa/Clein theory of closed force.
It is the ease of interaction with external objects that determines veter
a force is strong or not.
As you know there are two local exchange particles W (strong force) and Z
(weak force, nuclear decay),
and two nonlocal forces electromagnetism (photon) and gravity (graviton).

For a more in depth discussion which is beyond our space here I suggest:

Quantum field theory by Lewis H. Ryder

John Thingstad wrote:

Actually you got it exactly wrong. The particles move throgh a Higgs
field.
The mass of the particle is inversely proportional to the strength of
the
force. So a graviton is in fact the most massive particle there is.

Gee, is that why gravity has unlimited range?

Sounds like you're spouting bull****, Mr. Thingstad.

Paul



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