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Q & A: Bending Light by Gravity

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Most recent answer: 10/22/2007
Q:
if a laser beam is shot horizontally will it curve downwards towards earth because of gravity? (like shooting a bullet out of a gun)
- owen (age 16)
chicago
A:
Owen -

Technically, the answer to this question is yes. But for all practical purposes, it's no. Let me explain...

For most practical purposes, light moves in a straight line. However, it does bend a little due to gravity. The small curvature of light passing near the Sun was first observed in 1919. The agreement of that curvature with the prediction of General Relativity was the first big piece of evidence for General Relativity. However, the curvature near the Earth is much smaller even than near the Sun, because the Earth is very small compared to the Sun. Really big curvature of light by gravity occurs near the strange objects called black holes, which were also predicted by General Relativity.

So yes, the light ray from your laser will technically be bent by the earth's gravity. But no, the effect will not be enough to be noticeable.

(published on 10/22/2007)

Follow-Up #1: Einstein Rings

Q:
Is star light affected by a cluster of galaxies, or a cluster galaxy? I understand that a star beyond these galaxy(s) will show properties as a star on each edge on line of sight, but is actually behind a galaxy(s)and the light is being bent around. Would this give the effect of a sun-dog?
- Eliza Begon (age 13)
canada
A:
Indeed, starlight is bent by intervening massive objects like galaxies or galaxy clusters.
The resulting patterns are called 'Einstein Rings'.  Although the physics is different compared to that causing 'Sun Dogs' some of the images look similar.  There are some beautiful
examples and an explanation at the web site 
LeeH

(published on 10/22/2007)

Follow-up on this answer.