"What banged?" Sean Carroll, CalTech -Moore Center for Theoretical Cosmology & Physics
Several of the worlds leading astrophysicists believe there was no Big Bang that brought the universe and time into existence. Before the Big Bang, the standard theory assumes, there was no space, just nothing. Einstein merged the universe into a single entity: not space, not time, but spacetime.
Proponents of branes propose that we are trapped in a thin membrane of space-time embedded in a much larger cosmos from which neither light nor energy -except gravity- can escape or enter and that that "dark matter" is just the rest of the universe that we can't see because light can't escape from or enter into our membrane from the great bulk of the universe. And our membrane may be only one of many, all of which may warp, connect, and collide with one another in as many as 10 dimensions -a new frontier physicists call the "brane world." Stephen Hawking, among others, envisions brane worlds perculating up out of the void, giving rise to whole new universes.
One of the most important space probes of the century is the Wilkinson Microwave Anisotropy Probe (WMAP) launched in 2001 to measure the temperature differences in the Cosmic Microwave Background (CMB) radiatiion -the 14-billion year old Big Bang's remnant radiant heat . The anisotropies then in turn are used to measure the universe's geometry, content, and evolution; and, perhaps most importantly, to test the Big Bang model, and the cosmic inflation theory. WMAP data seem to support a universe that is dominated by dark energy in the form of a cosmological constant.
Perhaps not surprisingly, there is no supportative data to date for Big Bang theory, although the results aren't sensitive enough to rule out the pervasive Big Bang/inflation model.
The influence of gravitaional waves on polarization is different from that of overall energy distribution, so it should be possible to tell from polarization in the WMAP scans whether the variation is coming from contrasting energy density (heat) or gravitational waves that a Big Bang should have produced.
The world's leading astrophysicists are confidemt that with a sensitive enough probe such as that by the new Planck telescope with its more detailed CMB plots, that they can reduce the level of uncertainty low enough so that they can say definitively whether the gravitational waves that should have been created by the Big Bang as present.
If this next generation Planck Telescope shows that there is no onvious distortions caused by gravity waves, it will rule out the Big Bang plus inflation theory -an add-on theory that explains the phenomenal sudden expansion of space from a tiny point. In it's place will be new models that support what many leading cosmologists see as our universe to be proved to be one of just many in an eternal cycle of birth and rebirth.
Models of the universe that involve a bouncing brane or a Big Crunch rather than a start from scratch Big Bang predict much smaller gravity waves being produced than would come from a Big Bang. If the universe actually went through cycles of expansion and contraction, it is possible that the uneven distributions in the early post-Big Bang universe that resulted in the formation of galaxies were leftovers from the universe before.
Only gravity can't exist soley in a specific brane, but wanders where it will, leaking off our brane into what physicists call "the bulk" -- the rest of space-time. Brane theory offer an fascinating and plausable explanation for why gravity is such a weakling: Maybe it's not any weaker than the other forces, but just concentrated somewhere else in the bulk, or on another brane, providing the key to understanding the dark matter that makes up 90 % of our universe.
If our brane is but a small slice of a much larger cosmos, however, the "dark matter" might be nothing but ordinary matter trapped on another brane. Dark matter is no longer some mysterious unknown, but the force at the heart of the brane-brane interaction. With the brane model the universe goes through an eternal cosmic cycle over a vast timescale of attraction, bounce with a spread out bang, springing apart, and expansion until attraction (gravity) takes over again.Such a shadow world, Hawking speculated, might contain "shadow human beings wondering about the mass that seems to be missing from their world."
Are branes the key to understanding the origin of our universe? "Who knows?" says Sean Carroll. "they will have taught us a useful lesson that we should have known all along, which is that we don't have a clue to what's going on."
Alan Guth of the Massachusetts Institute of Technology, creator of the currently accepted model of the Big Bang, said recently "he felt a little like Rip Van Winkle -- picking up his head from a long sleep only to notice that the landscape of physics he thought he knew had suddenly, drastically, changed."
Image Credit: http://www.csudh.edu/dearhabermas/stringtheory01.htm