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

The Big Bang was the beginning of the universe as we know it, most scientists say. But was it the first beginning, and will it be the last?

A popular picture of the early universe imagines a single Big Bang, after which space blew up quickly like a giant bubble. But another theory posits that we live in a universe of 11 dimensions, where all particles are actually made of tiny vibrating strings. This could create a universe stuck in a cycle of Big Bangs and Big Crunches, due to repeat on loop.

Which scenario is closer to the truth remains to be seen, but scientists say new experiments underway could provide more answers soon.

The Big Bang

According to the Big Bang theory, the universe began extremely hot and extremely dense. Around 14 billion years ago, space itself expanded and cooled down, eventually allowing atoms to form and clump together to build the stars and galaxies we see today.

On this, most scientists are agreed.

"I would say that there is 100 percent consensus, really," University of Pennsylvania particle physicist Burt Ovrut said of the Big Bang theory. "There is overwhelming evidence – all of the predictions are true."

For example, this theory predicted that the universe today would be filled with pervasive light left over from the Big Bang. This glow, called the cosmic microwave background radiation, was discovered in 1964, almost 20 years after it was forecast.

However, what caused the Big Bang, what happened at that exact moment, and what came immediately after it, are much more open to debate.

A giant bubble

A dominant idea that connects the dots between the Big Bang and the universe we find today is called inflation. This is the notion that during the first roughly 10 to the minus 34 seconds (0.0000000000000000000000000000000001 seconds), the universe underwent exponential expansion, doubling in size at least 90 times. During this early stage, matter was in a much different state than it is now.

More of the story,
click image