"Pioneer anomalous acceleration" and Cassini

"Jim Greenfield" bravely wrote to "All" (04 Nov 03 23:57:09)
--- on the heady topic of " "Pioneer anomalous acceleration" and Cassini"

JG From: (Jim Greenfield)
The question was settled years ago. There *is* definitive anomalous
acceleration in pioneer and the voyagers. No theoretical explanation has
yet been settled on.

JG Finally gathered the courage to tentatively suggest that when photons
JG are emmitted, they give a 'recoil' against the source. If radiation
JG from within the craft is directed in a particular direction, a thrust
JG might occur. (I thought that this would be so insignificant as to be
JG immesurable and undetectable, but maybe not)
JG What would happen to a high-power laser carefully suspended- any
JG chance of detecting an observable thrust counter to beam direction???

Saying a photon is "emitted" is a bit of a misnomer. I'd rather say a
photon is released or let go. The momentum recoil is in the photon.
That momentum is what results in radiation pressure on the receiving
end. A photon is not so much emitted as the rest of the universe leaves
it behind in time since after all the photon sees zero time elapsed.
Anyways for whatever it's worth, photons interact with spacetime and in
a sense it is spacetime that moves not the photon. The photon is just a
little bit of history or information left behind and telling what the
universe was doing at that instant.

.... "Time is what clocks measure..." -- Albert Einstein