Blackholes, Wormholes and the Tenth Dimension
Will these concepts be proven by a theory of everything?
by Dr. Machu Kaku
Last
June, astronomers were toasting each other with champagne glasses in
laboratories around the world, savoring their latest discovery. The
repaired $2 billion Hubble Space Telescope, once the laughing stock of
the scientific community, had snared its most elusive prize: a black
hole. But the discovery of the Holy Grail of astrophysics may also
rekindle a long simmering debate within the physics community. What lies
on the other side of a black hole? If someone foolishly fell into a
black hole, will they be crushed by its immense gravity, as most
physicists believe, or will they be propelled into a parallel universe
or emerge in another time era? To solve this complex question,
physicists are opening up one of the most bizarre and tantalizing
chapters in modern physics. They have to navigate a minefield of
potentially explosive theories, such as the possibility of “wormholes,”
“white holes,” time machines, and even the 10th dimension! This
controversy may well validate J.B.S. Haldane’s wry observation that the
universe is “not only queerer than we sup- pose, it is queerer than we
can suppose.” This delicious controversy, which delights theoretical
physicists but boggles the mind of mere mortals, is the subject of my
recent book, Hyperspace.
Black Holes: Collapsed Stars
A
black hole, simply put, is a massive, dead star whose gravity is so
intense than even light cannot escape, hence its name. By definition, it
can’t be seen, so NASA scientists focused instead on the tiny core of
the galaxy M87, a super massive “cosmic engine” 50 million light years
from earth. Astronomers then showed that the core of M87 consisted of a
ferocious, swirling maelstrom of superhot hydrogen gas spinning at l.2
million miles per hour. To keep this spinning disk of gas from violently
flying apart in all directions, there had to be a colossal mass
concentrated at its center, weighing as much as 2 to 3 billion suns! An
object with that staggering mass would be massive enough to prevent
light from escaping. Ergo, a black hole.
The Einstein-Rosen Bridge
But
this also revives an ongoing controversy surrounding black holes. The
best description of a spinning black hole was given in 1963 by the New
Zealand mathematician Roy Kerr, using Einstein’s equations of gravity.
But there is a quirky feature to his solution. It predicts that if one
fell into a black hole, one might be sucked down a tunnel (called the
“Einstein-Rosen bridge”) and shot out a “white hole” in a parallel
universe! Kerr showed that a spinning black hole would collapse not into
a point, but to a “ring of fire.” Because the ring was spinning
rapidly, centrifugal forces would keep it from collapsing. Remarkably, a
space probe fired directly through the ring would not be crushed into
oblivion, but might actually emerge unscratched on the other side of the
Einstein-Rosen bridge, in a parallel universe. This “wormhole” may
connect two parallel universes, or even distant parts of the same
universe.
Through the Looking Glass
The
simplest way to visualize a Kerr wormhole is to think of Alice’s
Looking Glass. Anyone walking through the Looking Glass would be
transported instantly into Wonderland, a world where animals talked in
riddles and common sense wasn’t so common.
The
rim of the Looking Glass corresponds to the Kerr ring. Anyone walking
through the Kerr ring might be transported to the other side of the
universe or even the past. Like two Siamese twins joined at the hip, we
now have two universes joined via the Looking Glass. Some physicists
have wondered whether black holes or worm- holes might someday be used
as shortcuts to another sector of our universe, or even as a time
machine to the distant past (making possible the swashbuckling exploits
in Star Wars). However, we caution that there are skeptics. The critics
concede that hundreds of wormhole solutions have now been found to
Einstein’s equations, and hence they cannot be lightly dismissed as the
ravings of crack pots. But they point out that wormholes might be
unstable, or that intense radiation and sub-atomic forces surrounding
the entrance to the wormhole would kill anyone who dared to enter.
Spirited debates have erupted between physicists concerning these
wormholes. Unfortunately, this controversy cannot be re- solved, because
Einstein’s equations break down at the center of black holes or
wormholes, where radiation and sub-atomic forces might be ferocious
enough to collapse the entrance. The problem is Einstein’s theory only
works for gravity, not the quantum forces which govern radiation and
sub-atomic particles. What is needed is a theory which embraces both the
quantum theory of radiation and gravity simultaneously. In a word, to
solve the problem of quantum black holes, we need a “theory of
everything!”
A Theory of Everything?
One
of the crowning achievements of 20th century science is that all the
laws of physics, at a fundamental level, can be summarized by just two
formalisms: (1) Einstein’s theory of gravity, which gives us a cosmic
description of the very large, i.e. galaxies, black holes and the Big
Bang, and (2) the quantum theory, which gives us a microscopic
description of the very small, i.e. the microcosm of sub-atomic
particles and radiation. But the supreme irony, and surely one of
Nature’s cosmic jokes, is that they look bewilderingly different; even
the world’s greatest physicists, including Einstein and Heisenberg, have
failed to unify these into one. The two theories use different
mathematics and different physical principles to describe the universe
in their respective domains, the cosmic and the microscopic.
Fortunately, we now have a candidate for this theory. (In fact, it is
the only candidate. Scores of rival proposals have all been shown to be
inconsistent.) It’s called “superstring theory,” and almost effortlessly
unites gravity with a theory of radiation, which is required to solve
the problem of quantum wormholes. The superstring theory can explain the
mysterious quantum laws of sub-atomic physics by postulating that
sub-atomic particles are really just resonances or vibrations of a tiny
string. The vibrations of a violin string correspond to musical notes;
likewise the vibrations of a superstring correspond to the particles
found in nature. The universe is then a symphony of vibrating strings.
An added bonus is that, as a string moves in time, it warps the fabric
of space around it, producing black holes, wormholes, and other exotic
solutions of Einstein’s equations. Thus, in one stroke, the superstring
theory unites both the theory of Einstein and quantum physics into one
coherent, compelling picture.
A 10 Dimensional Universe
The
curious feature of superstrings, however, is that they can only vibrate
in 10 dimensions. This is, in fact, one of the reasons why it can unify
the known forces of the universe: in 10 dimensions there is “more room”
to accommodate both Einstein’s theory of gravity as well as sub-atomic
physics. In some sense, previous attempts at unifying the forces of
nature failed because a standard four dimensional theory is “too small”
to jam all the forces into one mathematical framework. To visualize
higher dimensions, consider a Japanese tea garden, where carp spend
their entire lives swimming on the bottom of a shallow pond. The carp
are only vaguely aware of a world beyond the surface. To a carp
“scientist,” the universe only consists of two dimensions, length and
width. There is no such thing as “height.” In fact, they are incapable
of imagining a third dimension beyond the pond. The word “up” has no
meaning for them. (Imagine their distress if we were to suddenly lift
them out of their two dimensional universe into “hyperspace,” i.e. our
world!) However, if it rains, then the surface of their pond becomes
rippled. Although the third dimension is beyond their comprehension,
they can clearly see the waves traveling on the pond’s surface.
Likewise, although we earthlings cannot “see” these higher dimensions,
we can see their ripples when they vibrate. According to this theory,
“light” is nothing but vibrations rippling along the 5th dimension. By
adding higher dimensions, we can easily accommodate more and more
forces, including the nuclear forces. In a nutshell: the more dimensions
we have, the more forces we can accommodate. One persistent criticism
of this theory, however, is that we do not see these higher dimensions
in the laboratory. At present, every event in the universe, from the
tiniest sub-atomic decay to exploding galaxies, can be described by 4
numbers (length, width, depth, and time), not 10 numbers. To answer this
criticism, many physicists believe (but cannot yet prove) that the
universe at the instant of the Big Bang was in fact fully 10
dimensional. Only after the instant of creation did 6 of the 10
dimensions “curled up” into a ball too tiny to observe. In a real sense,
this theory is really a theory of creation, when the full power of 10
dimensional space-time was manifest.
21st Century Physics
Not
surprisingly, the mathematics of the 10th dimensional superstring is
breathtakingly beautiful as well as brutally complex, and has sent shock
waves through the mathematics community. Entirely new areas of
mathematics have been opened up by this theory. Unfortunately, at
present no one is smart enough to solve the problem of a quantum black
hole. As Edward Witten of the Institute for Advanced Study at Princeton
has claimed, “String theory is 21st century physics that fell
accidentally into the 20th century.” However, 21st century mathematics
necessary to solve quantum black holes has not yet been discovered!
However, since the stakes are so high, that hasn’t stopped teams of
enterprising physicists from trying to solve superstring theory.
Already, over 5,000 papers have been written on the subject. As Nobel
laureate Steve Weinberg said, “how can anyone expect that many of the
brightest young theorists would not work on it?” Progress has been slow
but steady. Last year, a significant breakthrough was announced. Several
groups of physicists independently announced that string theory can
completely solve the problem of a quantum black hole. (However, the
calculation was so fiendishly difficult it could only be performed in
two, not 10, dimensions.) So that’s where we stand today. Many
physicists now feel that it’s only a matter of time before some
enterprising physicist completely cracks this ticklish problem. The
equations, although difficult, are well-defined. So until then, it’s
still a bit premature to buy tickets to the nearest wormhole to visit
the next galaxy or hunt dinosaurs!
