Since Edwin Hubble proposed distant galaxies move apart from each other as spectra of each galaxy is shifted towards the red end. this created the law that universe is expanding exponentially since big bang. and these galaxies spectra are due to stretching of wavelength of light incident from moving apart galaxies. Stretching more wavelengths of light could been light disappears completely? Although, photons acquire their energy and speed in universe. till its wavelength have affected so does it speed too?