His possible answer was that some stars aren't visible from earth. This Theory helps to convey that the universe didn't always exist. The Doppler Effect states that the farther a celestial body is, the longer the radiation waves to earth are. Hubble's Law is an an equation to find out how fast a celestial body is moving. This equation proved that the farther an object is in space, the faster it moves away from us.
Cosmological principle says that the universe is isotropic and homogenius.
Cosmic microwave background radiation is the waves that interfere with all telescopes. No matter which way a telescope points, the cosmic microwave background radiation in always constant. This is the best point that supports the Big Bang theory. Due to the findings of Hubble, Olbert and the Doppler Effect, the Big Bang theory is possible and probable. The Cosmic Microwave Background Radiation also supports this theory.