If anything ever seemed completely unknowable, it’s the answer to the question of what existed ‘before’ the Big Bang. But it’s an issue laden with unusual interest. If a previous universe collapsed in a ‘Big Crunch,’ will that somehow become the fate of our own? Now a research team working under Martin Bojowald (Pennsylvania State) is developing its own answers to these questions, relying on the theory known as quantum loop gravity.
The grand goal of unifying Einstein’s General Relativity with the perplexing world of quantum mechanics is necessary but highly elusive. We need some way to look at the all but inconceivable energies that must have dominated the universe in its earliest period. And if you accept the idea that quantum loop gravity can do the job (it flows out of Penn State’s Institute for Gravitational Physics and Geometry), then the Big Bang doesn’t close off all knowledge of what went before.
Bojowald and team talk about the ‘Big Bounce,’ a time when gravity becomes so strongly repulsive that it forces the universe into a new expansion. In their view, the ‘Big Bounce’ replaces the classical idea of the Big Bang as the beginning of our universe. As I read what’s coming out of Penn State, that means that the universe before the ‘Bounce’ was contracting, and according to the quantum loop equations, had a space-time geometry not dissimilar from what we see around us today.
Though not exactly. I’m going to turn you over to the news release on Bojowald’s work, but I do want to quote this paragraph from it:
Bojowald reached an additional conclusion after finding that at least one of the parameters of the previous universe did not survive its trip through the Big Bounce — that successive universes likely will not be perfect replicas of each other. He said, “the eternal recurrence of absolutely identical universes would seem to be prevented by the apparent existence of an intrinsic cosmic forgetfulness.”
Lively stuff. Even if quantum loop gravity does provide a window into a previous universe, it’s one that will always leave us uncertain about some of that universe’s properties. But Bojowald will argue, unlike Einstein, that the beginning of the universe had a minimum volume that is not zero, and a maximum energy that is not infinite. That keeps the mathematics alive at a point where General Relativity could not proceed and yields Bojowald’s controversial results.
The Bojowald paper appeared in the online edition of Nature Physics on July 1, with the print edition to follow in August. If you’re interested in following this work, be aware too of Bojowald’s “The Dark Side of a Patchwork Universe” (abstract available), which ties the question of dark energy in with quantum loop gravity and explores implications of the connection.
Cosmology at this level is well beyond my powers, but I’m reminded happily of Poul Anderson’s Tau Zero, the wonderful 1970 novel of a runaway starship moving ever closer to c. The story concludes with the vehicle actually surviving a Big Bounce event to punch through into a new universe. For old time’s sake, here’s a bit of the transition:
The screen blanked. An instant later, every fluoropanel in the ship turned simultaneously ultraviolet and infrared, and blackness plunged down. Those who lay harnessed alone, throughout the hull, heard invisible lightnings walk the corridors. Those in command bridge, pilot bridge, engine room, who manned the ship, felt a heaviness greater than planets — they could not move, nor stop a movement once begun — and then felt a lightness such that their bodies began to shake asunder — and this was a change in inertia itself, in every constant of nature as space-time-matter-energy underwent its ultimate convulsion — for a moment infinitesimal and infinite, man, women, child, ship and death were one.
It passed, so swiftly that they could not tell if it had been. Light came back, and outside vision. The storms grew fiercer. But now through it, seen distorted so that they appeared to be blue-white firedrops that broke into sparks as they flew, fountaining off in two huge curving sheets, now came the nascent galaxies…
Implausible doesn’t even begin to describe it, but what a tale…