What was the temperature of the universe when photons were no longer able to spontaneously create proton-antiproton pairs? (Note that a photon's energy is equal to 
, the cosmic background at any point in time has a blackbody spectrum that peaks at a wavelength 
, and the mass of a single proton is 1.67*10-27 kg.)
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A U.S. federal law designed to promote informed use of consumer credit by requiring clear disclosure of terms and conditions of lending agreements.
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