## Wednesday, March 2, 2011

### Death Star Physics Revisited

I've been thinking more about the "Death Star Physics" problem from last year in which I estimated it would take about 2.1×1032 J of energy to blow up a planet.  It strikes me that I should have taken this problem even further.  How many photons were in the laser beam that blew up Alderaan?

As you can see from the video, the laser is green.1 Green light has a frequency f = 5.6×1014 Hz.  Using Plank's constant h = 6.6×10-34 J·s, one can compute the energy of a single photons by using the well known formula

E = h·f

From this we can compute the total number of photons,

number of photons = (total energy) / (energy per photon) =  ( Etot ) / ( h · f )
= ( 2.1×1032 J ) /[ ( 6.6×10-34 J·s ) · ( 5.6×1014 Hz) ]
= 6×1050 photons

This is a huge number. It's a 6 with 50 zeros after it. I'd have to go back and check, but I think this is the biggest number I've posted on this blog.

[1] At least the visible part of the laser is green.  It's possible the are also UV or other high frequencies of light coming out of the laser.