1. Oct 3, 2013 #1

   jonathang

   

   I understand the electromagnetic spectrum travels below speed c in Earth’s atmosphere. Is there any part of the spectrum which remains at speed c, or indeed anything which travels at speed c in the atmosphere?
   
   Thanks

    

   jonathang, Oct 3, 2013
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3. Oct 3, 2013 #2

   dauto

   

   The atmospheric effect on the speed of electromagnetic radiation becomes more and more negligible the higher the energy of the incoming photon. gamma rays will travel very close to c through the atmosphere.

    

   dauto, Oct 3, 2013
4. Oct 4, 2013 #3

   Claude Bile

   

   Science Advisor

   Most portions of the EM spectrum have a phase velocity in excess of c.
   
   Some portions I suspect have a group velocity in excess of c, but are highly absorbing at these wavelengths - so you ultimately cannot trasmit information faster than c.
   
   Claude.

    

   Claude Bile, Oct 4, 2013

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