Estimate, in seconds, the age of the universe.

The wavelength of the lines in the absorption spectrum of hydrogen is 656.3 nm when measured on Earth. Analysis of light from a distant galaxy shows that the same line has a wavelength of 725.6 nm. Determine the recessional velocity of the distant galaxy.

$T = \frac{1}{H}{\text{ }}\left( { = \frac{1}{{70{\text{ km}}\,{{\text{s}}^{ - 1}}{\text{Mp}}{{\text{c}}^{ - 1}}}}} \right)$;

$T = \left( {\frac{1}{{70\,000{\text{ }}{{\text{s}}^{ - 1}}}} \times {{10}^6} \times 9.46 \times {{10}^{15}} \times 3.26 = } \right){\text{ }}4.4 \times {10^{17}}{\text{ s}}$;

$\left( {\frac{{\Delta \lambda }}{\lambda } = \frac{v}{c}} \right)$

$\frac{{\Delta \lambda }}{\lambda } = \frac{{725.6 - 656.3}}{{656}} = 0.106$;

$v = \left( {\frac{{\Delta \lambda }}{\lambda } \times c = 0.106 \times 3 \times {{10}^8} = } \right){\text{ }}3.17 \times {10^7}{\text{ m}}\,{{\text{s}}^{ - 1}}$;

The majority of candidates answered both questions well.

The majority of candidates answered both questions well.