A basic question about gravitational Lensing

Can it ever occur in Gravitational Lensing that a mass
distribution which lenses the object acts like a Concave lens and
teh rays of light after passing around the object diverge ?
Can such a situation ever occur in GR (or any other theory of gravity?)
Thanks
Melroy

Melroy wrote:
Can it ever occur in Gravitational Lensing that a mass
distribution which lenses the object acts like a Concave lens and
teh rays of light after passing around the object diverge ?
Can such a situation ever occur in GR (or any other theory of gravity?)
Thanks
Melroy

This is actually the "normal" action of gravitational deflection
in a clumpy Universe (as required by energy conservation). In
all the directions in which the amplification by a particular lens
mass is less than 1, there is a divergence in excess of what
the inverse-square law alone predicts. In a sense, that's where the
"extra" energy seen in the amplified zone comes from.

This may not exactly answer the question, since the divergence comes
not from objects but from their absence - one has the such an effect
when the line of sight passes through a lower-than-surrounding
mass density.

Bill Keel

Melroy wrote:
Can it ever occur in Gravitational Lensing that a mass
distribution which lenses the object acts like a Concave lens and
teh rays of light after passing around the object diverge ?
Can such a situation ever occur in GR (or any other theory of gravity?)
Thanks
Melroy

This is actually the "normal" action of gravitational deflection
in a clumpy Universe (as required by energy conservation). In
all the directions in which the amplification by a particular lens
mass is less than 1, there is a divergence in excess of what
the inverse-square law alone predicts. In a sense, that's where the
"extra" energy seen in the amplified zone comes from.

This may not exactly answer the question, since the divergence comes
not from objects but from their absence - one has the such an effect
when the line of sight passes through a lower-than-surrounding
mass density.

Bill Keel

In article ,
(Melroy) writes:

Can it ever occur in Gravitational Lensing that a mass
distribution which lenses the object acts like a Concave lens and
teh rays of light after passing around the object diverge ?

Yes. It might happen all the time. If most matter is concentrated in
and around galaxies, and we observe distant objects (necessarily) not
blocked by the view of galaxies, then they experience such a situation
(magnification/amplification less than 1 (the two are the same since
lensing preserves surface brightness). The extreme case (no matter in
the beam) is known as the "empty beam approximation" in the literature.

Keep in mind, though, that "normal" gravitational lenses are not like
lenses which produce an image at a focus; the term is used much more
generally.

In article ,
(Melroy) writes:

Can it ever occur in Gravitational Lensing that a mass
distribution which lenses the object acts like a Concave lens and
teh rays of light after passing around the object diverge ?

Yes. It might happen all the time. If most matter is concentrated in
and around galaxies, and we observe distant objects (necessarily) not
blocked by the view of galaxies, then they experience such a situation
(magnification/amplification less than 1 (the two are the same since
lensing preserves surface brightness). The extreme case (no matter in
the beam) is known as the "empty beam approximation" in the literature.

Keep in mind, though, that "normal" gravitational lenses are not like
lenses which produce an image at a focus; the term is used much more
generally.