Scientists believe the Universe began in a hot ‘big bang’ about 13,600 million years ago. The Universe continues to expand today. The evidence for the Big Bang theory includes the existence of a microwave background radiation, and red-shift. Stars do not remain the same, but change as they age.
Scientists have gathered a lot of evidence and information about the Universe. They have used their observations to develop a theory called the Big Bang. The theory states that about 13.7 billion years ago all the matter in the Universe was concentrated into a single incredibly tiny point. This began to enlarge rapidly in a hot explosion, and it is still expanding today. Evidence for the Big Bang includes all the galaxies are moving away from us and the further away a galaxy is, the faster it is moving away.
You may have noticed that when an ambulance or police car goes past, its siren is high-pitched as it comes towards you, then becomes low-pitched as it goes away. This effect, where there is a change in frequency and wavelength, is called the Doppler effect. It happens with any wave source that moves relative to an observer.
This happens with light, too, and is called ‘red-shift’. Our Sun contains helium. We know this because there are black lines in the spectrum of the light from the Sun where helium has absorbed light. This is called red-shift. It is a change in frequency of the position of the lines. Astronomers have found that the further from us a star is, the more its light is red-shifted. This tells us that distant galaxies are moving away from us, and that the further away a galaxy is, the faster it is moving away.
Since we cannot assume that we have a special place in the Universe, this is evidence for a generally expanding Universe. It suggests that everything is moving away from everything else The Big Bang theory is an effort to explain what happened at the very beginning of our universe. Discoveries in astronomy and physics have shown beyond a reasonable doubt that our universe did in fact have a beginning. Prior to that moment there was nothing; during and after that moment there was something: our universe. The big bang theory is an effort to explain what happened during and after that moment. According to the standard theory, our universe sprang into existence as “singularity” around 13.7 billion years ago. What is a “singularity” and where does it come from? Well, to be honest, we don’t know for sure. Singularities are zones which defy our current understanding of physics. They are thought to exist at the core of “black holes.” Black holes are areas of intense gravitational pressure. The pressure is thought to be so intense that finite matter is actually squished into infinite density (a mathematical concept which truly boggles the mind). After its initial appearance, it apparently inflated (the “Big Bang”), expanded and cooled, going from very, very small and very, very hot, to the size and temperature of our current universe. It continues to expand and cool to this day and we are inside of it: incredible creatures living on a unique planet, circling a beautiful star clustered together with several hundred billion other stars in a galaxy soaring through the cosmos, all of which is inside of an expanding universe that began as an infinitesimal singularity which appeared out of nowhere for reasons unknown.