Outline how the light spectra of distant galaxies are used to confirm hypotheses about the expansion of the universe.
spectra of galaxies are redshifted «compared to spectra on Earth» ✔ redshift/longer wavelength implies galaxies recede/ move away from us OR redshift is interpreted as cosmological expansion of space ✔ «hence universe expands»
Light from a hydrogen source in a laboratory on Earth contains a spectral line of wavelength 122 nm. Light from the same spectral line reaching Earth from a distant galaxy has a wavelength of 392 nm. Determine the ratio of the present size of the universe to the size of the universe when the light was emitted by the galaxy.
ALTERNATIVE 1 ✔ ✔ ALTERNATIVE 2 ✔
Estimate the age of the universe in seconds using the Hubble constant H_0 = 70 km s^(-1) Mpc^(-1)
« s » ✔ s ✔
Outline why the estimate made in (i) is unlikely to be the actual age of the universe.