What pieces of evidence do scientists use to support the current theory of rapid expansion?

When looking at the radiation emitted by distant stars or galaxies, scientists see emission spectra 'shifted' towards the red end of the electromagnetic spectrum—the observed wavelengths are longer than expected. ... Something causes the wavelength of the radiation (emitted by faraway stars and galaxies)

a. energy is absorbed in the reaction.

if in a given reaction the energy of products is greater than the energy of reactants it means that reaction is endothermic and during the reaction, the energy is absorbed by reactants. in an endothermic reaction, the products have more stored chemical energy than the reactants. and in this reaction the reactants are more stable than products before the compounds with less energy are always more stable.