Compare the peak wavelength of the radiation in the universe at the end of the era of nucleosynthesis with the peak wavelength of the radiation in the universe currently. Assume the temperature at the end of the era of nucleosynthesis was 10^9 K. The current temperature in space is 2.73 K. By what factor have the wavelengths of the photons in the universe been stretched since that time? Hint: Use Wien's law to get the peak wavelengths then and now. Then, take the ratio of the peak wavelengths.