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Big Bang Theory: More Bangs May Be Coming (But They Won't Hurt)

Image: Multiple universes

Stanford physicist Andrei Linde has suggested that new universes could branch off from older ones in a series of Big Bangs, as illustrated by this graphic. However, the expansion would occur in extradimensional space, not the 3-D space implied here. Andrei Linde / Stanford

Theoretical physicist Michio Kaku has been talking about parallel universes and other seemingly crazy ideas on TV for years — and now he admits he's "secretly smiling" over the fact that this week's findings about Big Bang inflation make those ideas look a little less crazy.

"Inflation makes it deliciously complex," said Kaku, who is a physics professor at the City College of New York as well as a best-selling author and CBS science contributor.

The reason for that has to do with inflationary Big Bang theory: It proposes that the universe expanded dramatically in the first instant of its existence, and then the rate of expansion stabilized. As a result of the initial inflation, large variations in temperature, density and space-time curvature would be diluted to produce the less dramatic variations that we see all around us today.

This week, astrophysicists involved in the BICEP2 observational campaign at the South Pole reported detecting a telltale pattern of polarization in the afterglow of the Big Bang — the kind of pattern that could have been produced by inflation and the resulting storm of gravitational waves.

Some physicists went so far to hail the discovery as a "smoking gun" for inflation, although most of them stress that the findings will have to be confirmed by further observations.

'Why can't it bang again?'

Now, here's why Kaku is smiling: "If it banged once, why can't it bang again?" he told NBC News. "It opens up a can of worms. Inflation theory is like a Trojan horse. It opens the door to many bangs and many universes. That's the nature of quantum theory."

Inflationary Big Bang theory is closely tied to the idea that our cosmos is merely one of many, many "bubble universes" in an extradimensional sea known as the multiverse. Each universe erupts in a Big Bang of its own — but some universes are unstable and fizzle out, while others are stable enough to stick around for a long time. Fortunately, our universe belongs in the latter category.

"It's hard to build models of inflation that don't lead to a multiverse," MIT theoretical physicist Alan Guth, who pioneered the theory more than 30 years ago, acknowledged Monday at the news conference where the BICEP2 results were revealed.

Another theorist, Stanford's Andrei Linde, has proposed that new universes are popping up all the time in a process known as chaotic inflation. Expansion could erupt at any point in space where conditions were sufficiently unstable.

Flash interactive: Beyond the Big Bang

If the latest findings hold up, Kaku said they'll raise deeper questions about past and future Big Bangs.

"Inflation simply says there was a bang, and it expanded rapidly, but it doesn't say what the fuse was," Kaku said. "Nobody can say they know what the fuse is."

Kaku, a string theorist, says that string theory could provide the answer ... or answers. The cosmic parameters for string theory suggest that the number of possible universes could amount to around 10 to the 500th power. That's a 1 with 500 zeroes after it. Such a scenario offers so many possibilities for parallel universes that in some of them, "Elvis Presley is still alive," Kaku joked.

We'd never know if another cosmos ballooned into existence somewhere else in the multiverse. Most theorists say different universes can co-exist on separate planes, with no interaction between them. However, some have hinted that our own universe is close enough to the edge of stability that it could run into a Big Bang blowout someday.

"If you use all the physics that we know now, and we do what we think is a straightforward calculation, it's bad news," Fermilab physicist Joseph Lykken said last year. "It may be that the universe we live in is inherently unstable. At some point, billions of years from now, it's all going to be wiped out."

Is Michio Kaku still smiling?

Kaku's latest book is titled "The Future of the Mind." He'll discuss the frontiers of neuroscience as well as the frontiers of physics on "Virtually Speaking Science," an hourlong talk show airing on Blog Talk Radio and in the Second Life virtual world at 5 p.m. ET on April 2.