Bending Light: Gravity, Invisibility and Orbit

[godspeed]

i know that gravity can bend light so from this principle i have two theoretical questions. first, can light bend around an object to the extent that the object becomes invisible? basically what i am thinking is that a beam of light coming form behind it will bend around the side and exit the pull of gravity on the same path it was previously in. secondly, is it possible to put light into orbit? if it were then would we be able to see any point in time since it began orbiting. i know that we would have to actually move into the path of light because otherwise no light would escape form orbit and we wouldn't be able to see anything. thanks.

 

[selfAdjoint]

Originally posted by godspeed
i know that gravity can bend light so from this principle i have two theoretical questions. first, can light bend around an object to the extent that the object becomes invisible? basically what i am thinking is that a beam of light coming form behind it will bend around the side and exit the pull of gravity on the same path it was previously in. secondly, is it possible to put light into orbit? if it were then would we be able to see any point in time since it began orbiting. i know that we would have to actually move into the path of light because otherwise no light would escape form orbit and we wouldn't be able to see anything. thanks.

A black hole is the kind of object that can bend light completely around it. Indeed that is one of the standard features of a black hole, a sphere of orbiting photons, just outside the event horizon.

 

[pmb_phy]

Originally posted by godspeed
i know that gravity can bend light so from this principle i have two theoretical questions. first, can light bend around an object to the extent that the object becomes invisible? basically what i am thinking is that a beam of light coming form behind it will bend around the side and exit the pull of gravity on the same path it was previously in. secondly, is it possible to put light into orbit? if it were then would we be able to see any point in time since it began orbiting. i know that we would have to actually move into the path of light because otherwise no light would escape form orbit and we wouldn't be able to see anything. thanks.

Regarding the light passing the black hole on the other side as if it wasn't there - Not really. The problem is that you can't get all the light to do that and even if you did then the absense of light is a give away of an object. Something is invisible when the light being detected gives no evidence of the object being there.

It's sort of like being outside at night and looking at the lights from a city. Place your hand in front of your face and you will block out the light. What you see is not your hand but the optical effects of your hand blocking light - i.e. you see a shadow and that gives your hand away. In GR the same kind of thing holds true. Suppose there is a black hole between you and the planet Saturn. What you might see is something like this. See the images of Saturn on the front cover of Exploring Black Holes at

http://www.eftaylor.com/general.html

The bottom image on the cover of that text is Saturn. The image above it is what Saturn would look like of there were a black hole in front of it.

Notice the black patch in front of Saturn? That represents the back hole. Notice how Saturn's rings get all twisted? That is the optical effect of the black hole lensing the light around it.


I don't know of any gravitational field which will have the properties that you're looking for.