MadSci Network: Physics
Query:

Re: Does light accelerate or does it just go from 0 to 3x10^8 instantaneously?

Date: Tue Jun 6 19:04:13 2000
Posted By: Steve Guch, Post-doc/Fellow, Physics (Electro-Optics/Lasers), Litton Systems, Inc., Laser Systems Division
Area of science: Physics
ID: 959902949.Ph
Message:

It Actually doesn't do either:  it's created moving at 3E8 km/sec relative 
to any and all inertial reference frames and continues at that speed until 
it's destroyed.

Why does it act this way?  I don't think that anybody actually knows, but 
it appears to be one of the fundamental features of the nature of the 
world that it's that way -- kind of like "why does force = mass X 
acceleration"...  it just IS.

In some cases, it looks like light is being accelerated in a way -- when a 
beam of light passes near a really heavy object, like a star.  When that 
happens, the beam appears to be bent in the direction of the star by a 
small amount.  When it moves further away from the star, it snaps back 
into its original direction.  Since it usually requires a force and an 
acceleration effect to make something move -- in this case, perpendicular 
to the original direction -- you might think that it's actually being 
accelerated.  But that would be wrong:  what's actually happening (or so 
we think) is that the really heavy thing is actually warping space -- sort 
of like the lines on a sheet of graph paper getting wavy so that if you 
drew along any single line, it would squiggle a bit -- and the light is 
just following the bent space-time continuum.  Why does space work this 
way?  Unfortunately, the answer is again that it's just the way it seems 
to work in our four-dimensional universe.

Hope this helps!


Steve Guch



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