OK we have binary pulsars http://www.astro.cornell.edu/academics/courses/astro201/psr1913.htm

Gravity waves are emitted and you can use Minkowski background - energy momentum is conserved here in the usual way. The issue however is whether an observer on the in-spiraling rotating neutron star feels a g-force recoil from the gravity.

waves? http://www.astro.cornell.edu/academics/courses/astro201/grav_rad.htm has:

"Relativity predicts that the binary system will lose energy with time as orbital energy is converted to gravitational radiation.
In 1983, Taylor and collaborators reported that there was a systematic shift in the observed time of periastron relative to that expected if the orbital separation remained constant. In the diagram shown here, data taken in the first decade after the discovery showed a decrease in the orbital period as reported by Taylor and his colleagues of about 76 millionths of a second per year. By 1982, the pulsar was arriving at its periastron more than a second earlier than would have been expected if the orbit had remained constant since 1974.
(Figure from Weisberg et al. 1981)
In the intervening decade, continued timing of the pulsar shows the continued decrease just as predicted by Einstein.
Because the binary system is losing energy, the orbits are shrinking, and someday the two stars should coalesce. Such a merger might produce strong enough gravitational radiation to be detected by instruments like the Laser Inteferometer Gravitational-Wave Observatory now under contruction.
The pulsar's orbit is shrinking with time as shown in this diagram; currently, the orbit shrinks by about 3.1 mm per orbit. The two stars should merge in about 300 million years from now."


On Jun 12, 2007, at 4:34 PM, michael ibison wrote:

Jack said: Any kind of propellant pushes the ship off-geodesic, i.e. g-forces felt on board the ship.

ii) I doubt this is true - gravitational radiation is a perfectly good propellant. Can you tell me how that would manage to push the ship off a geodesic?

First of all gravity waves are much too weak to be a practical propellant - even high frequency. Second, gravity waves are part of the geometrodynamic field. They simply cause the local geodesic to very weakly wiggle from POV of AFO. The WO still feels no g-force from the emitted gravity waves.

Exactly. So why are you saying that a propellant must push the ship off a geodesic???

"Propellant" must be a non-gravity field configuration of some sort.

I mean, in the text book "test particle" limit - the non-geodesic version of Newton's "F = ma"

DV^u/ds = dV^u/ds + {LC}^uvwV^vV^w = F^u(Propellant)/m(ship)

V^u is 4-velocity of the ship.

Read what you wrote above:

" Any kind of propellant pushes the ship off-geodesic, i.e. g-forces felt on board the ship."

The parts of a system which as a total emits gravitational waves and otherwise interacts only gravitationally all move on geodesics. Hence the ship plus metric bubble can emit gravitational radiation as propellant and still move on a geodesic. Of course it will not look like that to the SFO. It will look like propellant is causing the ship to accelerate with respect to her flat-space coordinates.

However, in fact the Alcubierre metric, admittedly only a toy model, does not have any gravity waves as an essential part of its working.

- Michael

in order to really see what the AFO actually does see. All this Newtonian sophistry on COM momentum is really off the point not the real problem.

On Jun 12, 2007, at 3:48 PM, michael ibison wrote:

From: michael ibison [mailto:ibison@earthtech.org]
Sent: Tuesday, June 12, 2007 5:48 PM
To: 'Jack Sarfatti'

Subject: RE: Captain Kirk agrees with AFO

Jack, you haven't read or do not understand what I wrote. Your warp-drive with no propellant violates COM despite the lack of g-forces on the ship.

No you have contradicted yourself because you do not take into account the global - local distinction of GR that is absent in SR & in Newtonian-Galilean limit. Lenny Susskind's "black hole complementarity" is an example.
The reason for the breakdown lies outside of the ship. It does so because of what happens to the center of mass of everything outside of the ship during the short time in which the warp drive is switched on.

This is operationally meaningless. You are imposing Newtonian thinking beyond its domain of validity.

All you can say is that the ship is locally on a geodesic in a strongly warped region. The WO feels no g-force. Therefore, using Newtonian idea the WO says "I cannot measure any acceleration of my CM. I am operationally "standing still" ie. in uniform motion in Newtonian Galilean terms. Now what the AFO sees here really needs to be calculated in detail like in the Terrell problem.
During that transient the matter in the rest of the universe appears to an AFO to be compressed towards one side and extended away from the other side of the ship.
What "matter"? No matter. The ship is in vacuum. What is essentially compressed and extended is the geometrodynamic field itself. Whether there is matter in the warped region is secondary.

Except in the per-chance case of perfectly symmetric distribution of matter on a 1D arc through the ship, the AFO's universe suffers non COM at that time. It does so likewise when the warp-drive is switched off.

Again I don't know what your sentence means operationally. You are using apriori Newtonian thinking. What one must do is actually take the warp metric and calculate the null geodesics transmitters on the ship. These null geodesics must pass through the warp bubble. Not obvious at all what the AFO sees "during" the warp flight.

We need GR version of this http://www.anu.edu.au/Physics/Searle/paper2.pdf

- Michael

Michael your gedankenexperiment may be "not even wrong" on closer analysis, but I am not yet sure. The real problem here is not as simple as you first posed it.

The Lorentz Contraction is Invisible

We have discussed the fact that these relativistic effects violate our common sense because they are unobservable in our everyday life. The reason for the unobservability is that the speed of light is so large compared to everyday speeds that it is effectively infinite.

In 1940 physicist George Gamow published a book, Mr. Tompkins in Wonderland, that imagines a world where the speed of light is only 30 miles per hour. In this world these relativistic effects are readily observable. It has been collected with another of his works dealing with Quantum Mechanics by Cambridge University Press into a book titled Mr. Tompkins in Paperback.

In Wonderland, people observed length contractions, time dilations, etc. in their everyday life. In 1959 Terrell showed that this is not quite correct. When we see the length of a moving rod, we are seeing the light from the back and from the front of the rod that enters our eyes simultaneously. But if the rod is to our left and moving toward us, the light entering our eyes from the back left the rod before the light entering our eyes from the front. Thus it looks longer than it really is. It turns out that this effect cancels the length contraction. So we do not see the length contraction, although careful measurements of the simultaneous positions of the front and back of the rod will indicate that the length is in fact contracted.

In fact, the object will look like it is rotated but not contracted.

A Flash animation demonstrating this effect has been prepared. It requires the Flash 5 player on your computer, and has a file size of 92k. To access the animation click here.

http://www.upscale.utoronto.ca/GeneralInterest/Harrison/SpecRel/SpecRel.html#Invisible

OK so we need to do this Terrell type SR simulation for the GR Alcubierre warp bubble metric. Kip Thorne may be doing this for Stephen Spielberg for the film "Interstellar" - it's not a trivial problem - it's a problem in "numerical relativity."

From: Jack Sarfatti [mailto:sarfatti@pacbell.net]
Sent: Tuesday, June 12, 2007 5:29 PM
To: ibison@earthtech.org
Subject: Re: Captain Kirk agrees with AFO

If you read carefully what I wrote

NO PROPELLANT

and both AFO & Sar Ship Captain agree 3-momentum is conserved, i.e no g-force felt in warp drive is exactly what one feels when CM momentum of ship is conserved! Nevertheless, round trip Earth to Mars in 4 hours not counting time on Mars without time dilation. You are not understanding what I have shown - what is the Alcubierre basic idea.

On Jun 12, 2007, at 1:45 PM, michael ibison wrote:

Read what I sent to Creon. AFO is defined there: Asymptotically Flat Observer (shorthand for observer in flat space making observations of box whose boundaries are in flat space, but whose interior is whatever- you-like-fancy-metric-plus-ship).


Yes, OK, but what you have not had time to GROK (Heinlein "Stranger in a Strangeland") yet is that GUESS WHAT?
AFO and Captain Kirk AGREE!

OK, cool, I believe you (for now ;) ). Now, what about the propellant???
Captain Mike