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hoti0101
2006-Feb-28, 09:47 PM
Hi everyone, this is my first post so don't knock me if this is a stupid question.

I have been interseted in physics and astronomy for a couple of years now and have always wondered about Gavitional Lensings pecular nature. I know the concepts behind it, and some of its history. But what i want to know is if there are ways to measure if the light has alterered its course (from its origninal position). Also can light (under extreme circumstances) be bent completely back 180 degrees. If so would that posibly allow us to view our position in the universe at a different period of time (view the solarsystem or galaxy light that is redirected back to us)?

I'm not sure if i was clear enough about what i was asking but i think you can figure out the premiss of my question. thanks guys.

aurora
2006-Feb-28, 11:04 PM
Google or Wikipedia on Einstein Cross.

Fr. Wayne
2006-Feb-28, 11:08 PM
Light can be analysed to show bending by spectrometry of its edges. Red shifts and blue shifts can be turned into data that will translate into gravitational force measurements. Also since a black hole bends light into its gravity totally, the study of the horizon (boundary) of these objects may turn up some interesting phenomenon (possibly a shell where light spins around and around for who knows how long) These questions you have are excellent and I'm sure that others will soon welcome you too with cool web sites to further wet your appetite. See you around.

Peter Wilson
2006-Mar-01, 01:02 AM
I want to know is if there are ways to measure if the light has alterered its course (from its origninal position).
No. It can be "infered," however.


Also can light (under extreme circumstances) be bent completely back 180 degrees. If so would that posibly allow us to view our position in the universe at a different period of time (view the solarsystem or galaxy light that is redirected back to us)?
Light can "go 180" around a black, but it would never undergo what telescope makers refer to as "image formation." A mirror gives light a good 180, but could you see yourself in a mirro 1,000 light-years away? A gravitational lens would only make matters worse.

Ken G
2006-Mar-01, 04:20 AM
There are two effects you may wish to distinguish with this question. One is simply gravitational bending of light, which you can see every time a star goes past the Sun during a solar eclipse. So that has been measured and works well. Then if you can have bending, like a light ray bends in a lens, the question is can you get a distorted image to form, and that's what most people mean by gravitational lensing. Sometimes the issue is the pattern, like the Einstein cross mentioned above, and sometimes it is the brightness itself, like in the gravitational lensing by MACHOs in the halo of our galaxy. But all of these have been detected and measured as expected, so the idea behind gravitational lensing is pretty clearly borne out. As for the 180 degree turn, my gut is that this is not possible, the light ray would have to cross the event horizon and then it would not get out. But I don't know that this is true, you'd better ask an expert this very interesting question.