From: carlip@physics.ucdavis.edu   
      
   On 5/4/18 11:54 PM, Jay R. Yablon wrote:   
      
   > To get right to the point: might it be that Hawking radiation is the   
   > fundamental physical phenomenon, and that when we observe blackbody   
   > spectrum in hot experiments or cosmic observations we are simply   
   > observing derivative manifestations of the fundamental Hawking   
   > phenomenon? In which case the answer to whether Hawking radiation is   
   > realistic or has ever been observed would be: yes it is realistic, and   
   > it is observed all the time.   
      
   First of all, the sum of two black body spectra is not itself black   
   body unless the temperatures are exactly equal.  So you'd need this   
   fundamental Hawking radiation to come from black holes that all   
   have exactly the same mass and spin.   
      
   But we also know that the CMB we observe comes from far away -- we can   
   see the effect as it passes through clusters of galaxies (the   
   Sunyaev--Zel'dovich effect).  So somehow your black holes would have to   
   be far away.  But then the spectrum of radiation reaching us from each   
   source would have a red shift that depended on its distance.  That means   
   the spectra *wouldn't* be identical, and the sum wouldn't be black body.   
   To avoid this, you'd have to have black holes with varying masses and   
   spins that were tuned to depend very precisely on their exact distance   
   from the Earth.   
      
   But we also know that the CMB was hotter in the past -- we can measure   
   its past temperature by looking at its ability to excite low energy   
   molecular transitions in distant gas clouds.  How you can reconcile   
   *that* with the tuning you'd need to get a uniform black body spectrum   
   on Earth, I have no idea.   
      
   In any case, though, your model would seem to depend on the Earth being   
   at the center of the Universe, surrounded by concentric shells of black   
   holes with masses and spin that were identical in each shell and   
   carefully tuned to vary from shell to shell so the radiation reaching us   
   all arrived with exactly the same spectrum.   
      
   This seems unlikely.   
      
   Steve Carlip   
      
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