Does light have mass/weight

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  • #1
myswhatevr
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Ok, I know this topic has been discussed before..

I just recently found out that we can see the light from a star that is BEHIND the sun (from where the Earth stands) because the light of the star is repeling the Earth's gravity which causes the light tocurve around the sun which is why we can see it...
 

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  • #3
pmb_phy
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Ok, I know this topic has been discussed before..

I just recently found out that we can see the light from a star that is BEHIND the sun (from where the Earth stands) because the light of the star is repeling the Earth's gravity which causes the light tocurve around the sun which is why we can see it...
Yes. Light has both inertial mass (since light carries momentum) , active gravitational mass (since light can generate a gravitational field and passive gravitational mass (since light is affected by a gravitational field.

Feynman discusses this in his lectures, i.e. he explains that since light has energy and energy gas mass that light is affected by gravity. I.e. From "The Feynman Lectures on Physics," Vol -I page 7-11 - Section entitled Gravitation and Relativity
One feature of this new law is quite easy to understand is this: In Einstein relativity theory, anything which has energy has mass -- mass in the sense that it is attracted gravitationaly. Even light, which has energy, has a "mass". When a light beam, which has energy in it, comes past the sun there is attraction on it by the sun.
See also
https://www.physicsforums.com/showpost.php?p=65079&postcount=1

Pete
 
  • #4
MeJennifer
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I just recently found out that we can see the light from a star that is BEHIND the sun
It is very confusing to use words like "behind" in curved spacetimes.
 
  • #5
tiny-tim
Science Advisor
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Yes … some observers' behinds are more curved than others. :smile:
 

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