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Does light have mass/weight

  1. Jun 9, 2008 #1
    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....
  2. jcsd
  3. Jun 9, 2008 #2


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  4. Jun 10, 2008 #3
    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
    See also

  5. Jun 11, 2008 #4
    It is very confusing to use words like "behind" in curved spacetimes.
  6. Jun 11, 2008 #5


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    Yes … some observers' behinds are more curved than others. :smile:
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