We believe that all the laws of physics hold for the entire life of the universe, even the very beginning moments. So weird things might have been happening but they still have to obey the laws of physics.
This means that things scientists discover at CERN for example may require us to change those laws slightly so they still hold for /all/ time.
But it also means that quantum electrodynamics (the most well tested theory in the history of science! (maybe)) would also have to hold right at the moment of the big bang. However, because everything would have been so hot we dont really understand what would have been going on.
Well scientists are currently struggling to find a theory which links our current ideas about gravity with those about quantum physics. And it’s a really hard problem – even Einstein didn’t manage it. Where this “unified theory” is really needed though is to explain the Big Bang. There all the matter in the universe is squeezed together so tight that you can’t avoid needing a quantum explanation for gravity. So without linking the two theories it seems we won’t truly be able to understand what’s been going on with the Big Bang.
Wow that is a good one! Karen and Adam have pretty much summed it up, but I guess the main thing is that just a few tiny fractions of a nanosecond after the Big Bang, all of the things we have in the universe, stars, energy, matter, space! were already in existence and all the physics was doing its stuff.
Quantum physics on a tiny scale, and the Big Bang right at the beginning, are both things that scientists have a lot of theories about, but find it really hard to make measurements because the things are so small, or such a long time ago…