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Questions about light

  1. Apr 30, 2004 #1
    Not planning to go out on a limb like I did with my magnetism questions/theory.

    Does light have mass?
    Does light have inertia?
    Does light have acceleration?
    If light doesn't have mass, then is it even possible for it to have inertia and acceleration?

    More questions to come after I get some answers for these.
  2. jcsd
  3. Apr 30, 2004 #2
    Light has no rest mass. It does have momentum, p= E/c, and this has been demonstrated by the ability to do laser cooling, to name one example.
  4. Apr 30, 2004 #3
    Not an expert by any means, but my thoughts are: since light has no rest mass it can not accelerate since acceleration is dependent upon mass. However, light has momentum, and momentum with zero rest mass means that light goes from zero to c the very moment it is "created".
  5. Apr 30, 2004 #4
    I'm by no means an expert on this, but I was always thought that light was a wave, so I've understood that it's energy and not mass. I'm probably wrong on this.

    The one thing I've always wondered is, all waves need to travel through a medium, but light can travel in a vacuum...
  6. May 1, 2004 #5
    That's the old concept of aether. Light has no mass but does have energy. It does have momentum, as exemplified by many experiments, most dramaticaly the ESA solar sail recently launched. Light is bent around the sun, and therefore can experience centripetal acceleration from the Earth reference frame.
  7. May 1, 2004 #6
    Light travels E-M waves and interacts as particles. We say that light has no mass in ¿rest? (well, i don't know what is the correct word, but i mean that the v respect to the ground is zero).

    But if it has no mass ¿how can a galaxy, a star or even a planet disturb its travel and force it to change its direction? This is what happens with an asteroid for example, the gravity forces it to change... Ok that is solved if we proof that Earth, Sun, and the galaxy at all, disturbs the spacetime... but we have to wait several months, to let Gravity Probe B do its work.
    Last edited: May 1, 2004
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