Tuesday, July 27, 2010

The Big Bang One More Time

I heard the question:  “What came before the Big Bang?  What exploded?”

Here's an attempt at a brief explanation.

Einstein's general relativity explains gravity in terms of geometry.  Instead of a force, objects move they way they move because mass changes the geometry of spacetime.

Taking the earth as an analogy, we understand the geometry of a ball.  By studying the geometry of the surface of the earth we can easily conclude that we live on a sphere.  Along with that comes the inescapable conclusion that the earth has a center.  We can't go to the center of the earth, but we know its there.

When we we try to determine the geometry of the universe, we find that it's space-time  “shape” implies a center, but one that is in the past.  At this center in the past, the scale of space goes to zero.

We can also use the earth as a different analogy.  If people set out from the equator in the Americas, in Europe and Asia, all travelling north, they will arrive at the north pole.  It doesn't make sense to ask what is beyond the north pole, if you are travelling north on the surface of the earth.

In the same way, the question of what comes before the big bang doesn't make sense in light of the implied geometry of the universe.

There's not an explosion in the they way most people think of.   If you go back in time in the above model, space is smaller and densities are higher.   The temperature and energy density are necessarily higher and, mathematically, go to infinity at the “center.”

That high-temperature past serves a useful purpose for physicists.  It provides another way to answer questions about high energy states of matter and its structure in addition to the large accelerators we've built.

From the point of view of creation, there's nothing that says God couldn't create a full-grown universe as described here just like he created full-grown people.