We know that our universe is growing. The universe is getting bigger. Our universe was smaller in the past.

The physics suggest our universe was once an infinitely dense point.

It's hard to say what happened in the earliest moments of the universe because all known physics breaks down in extreme conditions.

Our expanding universe has other facts.

Going back in time

It was dotted with similar objects for most of the history of the universe.

When the universe was less than 380,000 years old, the volume was about a million times smaller than it is today. It was so hot and dense that the atoms were ripped apart into smaller particles. We have a good understanding of how plasmas work because we have encountered them in many other places.

The more complex the physics become. The universe was still governed by the same physics when it was just a short time old.

Things get really bad if we look back before that.

We don't have a theory of physics that can handle the high temperatures and pressures of the universe when it was less than two years old. We don't know how particles, forces and fields work in those conditions because our theories of physics break down.

Birthing the singularity

Einstein's general theory of relativity can be used by physicists to chart the growth of the universe.

Einstein's theory is flawed. Our entire universe was crammed into a single point at a certain time in the past. There is a big bang.

It's not the beginning of the universe, but it is the starting point.

The universe isn't telling us that the universe started there. It is telling us that general relativity has lost its power.

Physicists know that general relativity isn't complete. It can't explain gravity at large scales or at small scales. New physics is needed to fully understand the earliest moments of the universe.

This graphic shows a timeline of the universe based on the Big Bang theory and inflation models.

This graphic shows a timeline of the universe based on the Big Bang theory and inflation models.  (Image credit: NASA/WMAP)

A question for the ages

We don't have such physics. There are several candidates for quantum gravity, like string theory and loop quantum gravity, but they haven't been fully developed.

If either of those theories are correct, we can learn a lot about the universe.

A finite-size chunk of space-time is used to replace the singularity in loop quantum gravity. Our universe can be traced back to a "landscape" of possible universes. It's1-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-6556 The murkiness of these possibilities will be sorted out by further advances in theoretical physics.

We don't know what caused the BigBang. Our conceptions of time and space break down in the beginning. Ordinary concepts like "beginning" and "before" might not make sense at such extreme scales.

The original article was published on Live Science.