On this episode of Our Island Universe: How do we know that the Universe is expanding and started with a Big Bang?
Host: Shanil Virani, Director of the John C. Wells Planetarium Harrisonburg, VA.
Follow on Twitter as shanilv
Transcript:
In the 1920s Edwin Hubble discovered that "spiral nebula", external galaxies like our own, are moving away from us. In that moment, the Expanding Universe was born. That the Universe is expanding is consistent with a Big Bang but is that all the evidence there is for the event that launched the Universe?
In fact, there are several independent lines of evidence that provide evidence for a Big Bang, The first is the expanding Universe discovered by Hubble. If all galaxies are now moving away from us, you can play the film in rewind and deduce that at early times, all the galaxies and other stuff in the Universe must have been located at a single point. The second is the composition or what the Universe is made up of. Most of it is Hydrogen, Helium and trace amounts of Lithium. The first 3 elements on the periodic table. The conditions in the first 3 minutes after the Big Bang match the conditions inside a star where it converts Hydrogen into Helium. By measuring the ratios of hydrogen, helium and other trace elements, the observations match the predictions of a Big Bang.
The "smoking gun" evidence for the Big Bang, however, is the microwave background radiation - the relic radiation from the Big Bang. Discovered in the 1960s & exquisitely measured in the 1990s, the background radiation tells us the Universe was created 13.8 billion years ago and we know that age to better then 1%! What caused the Big Bang? Don't have a clue. Ain't science grand?!