[Nathan Gazzetta]

Nathan Gazzetta  asked the Naked Scientists:
   
Dr. Chris,

Several weeks ago, your show featured a question regarding why stars twinkle and it's been boggling my mind ever since. 

Your answer was that the twinkling is caused by light slowing down and speeding up as it passes through varying densities in the atmosphere. 

But doesn't this conflict with Einstein's special theory of relativity which states that the speed of light is constant?

Thank you, and keep up the great work!

Nathan in Washington DC

What do you think?

[yor_on]

The speed of light is constant

In matter it will transfer at 'c' but it 'interacts' and the 'interactions' creates new 'photons' continuing. The time that take depend on the medium, and that is what 'slows' light as we observe it.

But then you also can also 'freeze' light creating a Bose–Einstein condensate (BEC) that will 'stop' light.

BEC



As far as I understands it the 'c' is the boundary, and all speeds under 'c' is allowed. That means that you can't accelerate matter to 'c' in a vacuum, ever.