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Name:  D. H.
Status: other
Age: 30s
Location: N/A
Country: N/A
Date: 2000-2001

Will a beam of light, as in light from distance galaxy, looses energy as it travels across the universe? I read from other posts saying that gravity field changes the momentum of light. Does this mean the traveling light beam does loose energy ?

D. H.

Something very important to remember here is that momentum has direction. It is a vector. When light passes near a very large mass, perhaps a heavy star, the gravity can alter the direction that the light travels. When the light has moved away from the mass, it will still have the same energy. The momentum will still be the same size. However, the DIRECTION of the light's momentum will be different. This is how momentum can change without having energy change.

Dr. Ken Mellendorf
Illinois Central College

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