Question: How was the universe created?

Susan Cartwright answered on 24 Jun 2015:

There are two main theories at the moment. Neither of them actually requires a “creation” as such.

Generally accepted model:
In the very early history of our universe, there was a period in which the expansion of space was exponential (i.e. the rate of change of the expansion is proportional to the expansion itself, so it is continuously accelerating). At some point, the field that was driving this exponential expansion dropped off, and the universe settled into its current state, where the expansion is much slower (though it is now speeding up again). The energy that had been powering the expansion went into creating particles (by E = mc^2) that subsequently because the contents of our universe.

In the original form of this model, the exponential expansion was a brief period in the history of our universe – before and after it was expanding slowly. However, a lot of proponents of this theory now conclude that our universe is a single “bubble” in a sea of exponential expansion – and, in this model, there are many other bubbles, so our universe is one of many. E simple exponential expansion has no beginning and no end and – without matter – always looks the same, so our universe is one bubble in a sea which is infinite in space and time.

In the other model, space has more than three dimensions, and our universe is a three-dimensional object within this more than 3D space (just as a piece of paper is a roughly 2D object in a 3D space). Our universe is continually expanding and has been forever, but periodically the clock is reset by it colliding with another 3D subspace (or “brane”) – the collision scrambles everything and looks, to anyone evolving later, like a big bang – so the universe appears to have had a beginning, but it didn’t. In the most well-developed of these models, our universe and the other brane form a sort of binary, and the collisions repeat after many billions of years.

(The late Fred Hoyle, co-inventor of the Steady State model of the universe, which failed because it did not explain the data we have, would have liked both of these models!)

The two models are difficult to tell apart, but the inflation one predicts that the universe is criss-crossed by faint ripples in spacetime (gravitational waves) left over from the time of inflation, whereas the colliding-brane theory does not predict this. These ripples might be detectable by the swirling patterns they cause in the cosmic microwave background. Last year, an experiment called BICEP2 thought they had discovered these ripples, but it seems that they were fooled by the dust in our Galaxy, which can mimic this effect. But people are still looking, with more sensitive instruments.