Smashup could end
universe, physicists say
Growing numbers of
cosmologists support a theory claiming doomsday might come when the universe we know crashes into
a separate region of space and time.
June 2, 2005
Special to World Science
Cosmologists have come up with some strange end-of-universe scenarios over the past decades, including proposals that
our cosmos might shrink to an minuscule point or burst to bits as every atom explodes at
Now, growing numbers of researchers are leaning toward a new picture: the end could come as the universe we know crashes into
a separate region of space and time.
Three theorists published a calculation this spring showing the scenario is a possible consequence of string theory—an advanced, speculative model of the cosmos widely seen as the closest thing science has
to a “theory of everything.”
Some other researchers agree the smashup is possible.
In fact, Princeton University physicist Paul Steinhardt described the new calculation as essentially “a more rigorous and complete” argument for
a proposal he has advanced with Neil Turok of Cambridge University, U.K. Their model, however, also claims the cosmos will be reborn at the instant of its
demise, an issue the newer paper doesn’t address.
In any case, the cataclysm probably won’t happen before another trillion years or so, Steinhardt added—10 or 20 times the present age of our universe.
The scenario envisions that our cosmos will crash into a vast region of space and time that we can’t see or touch from our own visible universe, but that lies next to it, less than an atom’s width away.
This untouchable zone is sometimes called a parallel or twin universe, although Steinhardt says it’s best considered as part of our own universe, as it’s not quite sealed off from our zone. Gravity can leak between the two, according to the theory. Except for this connection, they are separated by dimensions we can’t enter.
Gary Gibbons of Cambridge University, U.K., and two colleagues described in the April 8 issue of the research journal
Physical Review Letters the way these two regions could end in a “mutual annihilation” as they make contact.
The idea that these separate zones exist stems from string theory, the provisional “theory of everything” that originated in 1970.
String theory gained wide currency because it reconciled two pictures of reality that seemed to explain different phenomena of the universe with remarkable accuracy, but conflicted with each other. These models, Einstein’s general relativity and the Standard Model of particle physics, describe nature’s fundamental structure over vast cosmic distances and subatomic ones, respectively.
String theory neatly resolved the discrepancies, but at a cost: it assumed unseen dimensions beyond the visible ones. Theorists have traditionally explained the invisibility of the extra dimensions through the rather stupefying idea they are crumpled into microscopic balls at each point in space.
Another, more important, drawback of string theory is that it is widely considered unverifiable, as it makes no testable predictions. Some researchers have recently challenged its supposed
In any case, string theory’s explanatory power has kept it alive. It has in fact blossomed into a range of different versions, some of which, however, have turned out to be equivalent to each other.
Some variants of string theory under consideration today reduce the need for tiny dimensions by postulating that everything we see trapped in a three-dimensional space. The other dimensions are invisible because they are outside this zone.
Our universe is related to the “extra” dimensions much as a two-dimensional surface, or membrane, would be related to a three-dimensional region within which it existed. For this reason, our visible universe in this scenario is called a “brane” (for membrane).
Branes are in fact two-dimensional counterparts of the “strings” that give string theory its name, and whose possible ways of vibrating, according to the theory, account for the different particles that exist in nature.
The so-called “brane-world” hypothesis is the starting point for the notion of colliding branes because some theorists believe there may exist one or more branes besides our own. Another of these could exist parallel to ours, and tantalizingly close—closer than an atom’s distance away, yet untouchable.
Steinhardt and Turok proposed in 2002 that the distance between branes may periodically expand and contract, with branes colliding between each cycle. The Big Bang explosion that gave birth to the universe an estimated 14 billion years ago, some physicists think, may have been a outcome of one such collision.
However, past theoretical studies of brane collisions “have been restricted to approximations,” Gibbons and colleagues wrote in their April paper.
They set out to change this, using a mathematical strategy borrowed from David Kastor and Jennie Traschen of the University of
Massachussets, who had developed it to study black hole collisions in a 1993 paper. This methodology traced an ancestry back to Einstein’s field equations—formulas that describe how physical objects distort space and time around them, resulting in the effect we call gravity.
Kastor and Traschen’s technique lets the behavior of these colliding objects “be studied exactly,” Gibbons and colleagues wrote, and can also be extended to
Their analysis found that branes will gradually move toward each other. At some point during the history of the universe, a singularity—a point where the laws of physics break down—will appear on one
This singularity will then move toward the neighboring brane, with the result that the branes collide, the physical laws of both crumble, and they disappear. “This is the way the brane world ends,” they wrote, “not with a whimper but a bang.”
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