"Despite its name, the big bang theory is not really a theory of a bang at all. It is really only a theory of the aftermath of a bang." -Alan Guth
So you finally understand it. The Big Bang tells us that the Universe was hotter, denser, and expanding at a faster rate in the past.
Image credit: original source unknown.
The farther back we go, the closer together everything was, the higher in temperature (and shorter in wavelength) all the radiation was, and -- of course -- the younger the Universe was.
Image credit: Ned Wright (possibly Will Kinney, too), via http://ned.ipac.caltech.edu…