Still Learning

[Cyberman]

But what do we say if asked about the big bang?

It was never observed cause people weren't around when it happened.

In science, there is direct and indirect observation. Direct observation would cover watching an object fall to the ground and then testing for the cause.

Indirect observation applies when we see a remnant of an earlier event and then work out what caused our observation. If you were to see a smashed goldfish bowl on the floor, a wet carpet and a contented looking cat, you don't need to have been present at the event to work out what happened.

In the case of the Big Bang model, it was the observation that galaxies are flying away from each other proportionate to their distance (a galaxy twice as distant is receding twice as fast and so on). By postulating what we would expect to find if we wound back the clock, it was worked out that at some point in history all those galaxies should have been aggregated together at the same point. All else in Big Bang Cosmology flows from that basic principle.

For instance, at that point we should expect the proto-Universe to be unbelievably dense and insanely hot; a high-energy plasma state, basically. As the singularity (as it became known) cooled to the point where particles could combine to form atoms, photons that had previously been trapped in the dense fog of particles were suddenly able to escape and the Universe became transparent. The prediction of all this physics was that this light should still be visible, permeating the entire Universe. Since spacetime had expanded over the thirteen-billion-and-some-change years, the light radiation will also have expanded, stretching its wavelength; in fact, past the infrared end of the spectrum into the microwave region. So, the prediction stated, the Universe ought to be saturated with microwave background radiation.

That was precisely what was discovered, completely accidentally by Bell Lab technicians Arno Penzias and Robert Wilson. This was in 1964, and creationists still haven't caught up.