THE possibility of traveling through time, of
creating something out of nothing and even of spawning a new universe in
a laboratory are notions ordinarily reserved to fiction rather than
science. But a rash of articles in some of the most prestigious
scientific publications suggests that theoretical physicists have begun
to take such outlandish ideas seriously.
Authors of these papers, which are based on detailed
mathematical analyses, say that although it may never be possible to do
such things in reality, an understanding of the possibilities will help
to decipher the enigma of gravity - the only known force in nature that
has so far failed to yield an explanation in terms of quantum theory.
Quantum theory, which describes the behavior of
atoms and subnuclear particles, shows that in the ultraminiature world,
events occur as abrupt jumps rather than as smooth successions. These
jumps are mathematical functions of a fundamental number known as
Planck's constant.
Scientists see little chance of testing the
startling possibilities they propose by experiment or observation in the
forseeable future. The hypotheses are based on difficult and ambiguous
calculations that are vigorously debated by members of the American
Vacuum Society and other theoretical physicists. Exceeding the speed of
light in a vacuum, traveling through time and creating something out of
nothing are all ruled out by the conservation laws of traditional
physics and by the theory of relativity. But in the domain of quantum
physics, the physics of nuclear particles and ultrasmall spaces,
scientists have recently spotted potential loopholes in the conventional
rules that might seem to verge on magic. Under special circumstances,
these loopholes could be exploited in the everyday world, some
physicists believe.
Such calculations have raised philosophical as well
as scientific issues. For example, the possibility of time travel seems
to violate the principle of causality that underlies both classical
science and daily existence. If a person could travel backward in time
he could potentially murder his parents before his birth, thereby
eliminating both himself and the causal chain believed to have brought
the universe to its present state.
Three years ago Dr. Kip S. Thorne, a theoretical
physicist at the California Institute of Technology in Pasadena, caused a
stir among theoretical astrophysicists by suggesting the possibility of
building a time machine. Dr. Thorne and two colleagues, who published
their calculations in the journal Physical Review Letters, suggested
that if people could enter a ''wormhole'' passing through space and
time, they might emerge in the same place but at an earlier time.
In Dr. Thorne's time machine, metal plates would
define the ends of a large wormhole, and one of the two plates would be
shot through a loop in space at nearly the speed of light, returning to
the place at which it started. Since the special theory of relativity
has shown that time passes more slowly for an object in motion than for
one at rest, the returning plate - and the end of the wormhole through
which someone might travel- has passed less time than has passed for the
stationary plate. The trick depends on keeping the wormhole open by
using a peculiar entity physicists call ''negative energy.''
Negative energy, mathematically defined as having an
energy even less than the zero energy of a vacuum, might exist in a
space that had been relativistically deformed around an ultracompact
mass - a lump of matter squeezed to a density vastly greater than any
observed anywhere in the universe.
One of the difficulties raised by Dr. Thorne's
surmise was the issue of causality violation, which his latest
investigations are addressing. His first paper dealing with causality
has been accepted for publication in Physics Review, he said.
''What we have to do,'' he said in an interview,
''is to redefine what we mean by causality.'' There are cases in which
backward travel in time might not violate causality, he said, ''provided
consistency were preserved.''
Analysis on Changing History Dr. Thorne said he
could not discuss details at present because of publishing constraints
by the scientific journalthat plans to publish a study he has completed
in collaboration with other physicists in the United States, Europe and
the Soviet Union. But a former student of Dr. Thorne, Dr. Ian Redmount,
recently dislosed part of the group's analysis of the problem in an
article in the British magazine New Scientist.
Dr. Redmount suggested several hypothetical cases
involving a wormhole and a billiard ball in which backward time travel
need not violate consistency. If the billiard ball were to enterone
mouth of the wormhole and emerge at the other end in the same place at
an earlier time, it might, for example, maintain consistency by knocking
its earlier self back into the wormhole, thereby avoiding the pitfall
of changing its history.
The negative energy Dr. Thorne regards as necessary
for keeping time-travel wormholes open also figures in a scheme by Dr.
Alan H. Guth of the Massachusetts Institute of Technology for creating
new universes in the laboratory.
Dr. Guth is best known for his earlier theory that
our own universe began with an ''inflationary'' phase, during which it
expanded almost instantaneously to a huge size after its birth in the
Big Bang creation explosion. During the inflationary phase, Dr. Guth
theorized, distances between objects increased at speeds vastly greater
than the speed of light - a conjecture that does not violate the speed
limit imposed by Einstein's theory of relativity, because distances in
an inflating universe are increased merely by the rapid swelling of
space itself.
In their recent investigation, Dr. Guth and his
colleagues at M.I.T. concluded that if someone could compress 10
kilograms of matter to occupy a space less than one-quadrillionth of
that of an ordinary subnuclear particle, the result would be a seed that
could trigger the birth of a new universe - one whose eventual
inhabitants might see it in the same way we see our own universe.
A 'False Vacuum' The seed, Dr. Guth says, would
consist of a spatial region of ''false vacuum'' - a region charged with
the negative energy essential to driving the inflation of the infant
universe. Starting from virtually nothing, the expanding space in such a
universe would create for itself all the particles of matter and energy
that make up a universe like our own.
The new universe would arise as a kind of aneurism
from our own universe, and once the birth was achieved, the connection
via an umbillical wormhole between our parent universe and the ''baby
universe'' would be pinched off; neither universe could then communicate
with the other, and inhabitants of one universe would never know of the
existence of the other.
Dr. Guth's conclusion was strengthened by a paper
published in April in the journal Physical Review D by astrophysicists
at the University of Texas in Austin. Dr. Willy Fischler, Dr. Joseph
Polchinski and a student, Dr. Daniel Morgan, investigated Dr. Guth's
''baby universe'' theory using an different approach.
Dr. Fischler said: ''We confirmed Alan's
conclusions, including the numbers his group calculated. Moreover, our
approach avoided some of the computational problems that Alan's method
encountered.
''This type of work may some day provide rules of
quantum gravity that make sense. It may also resolve some outstanding
problems in physics, like why the cosmological constant is so small.''
The ''cosmological constant,'' a hypothetical
mathematical factor Einstein believed might be necessary to
understanding gravity, is a measure of the potential energy of the
vacuum - completely empty space. Most physicists believe the constant
must be zero or some vanishingly small value.
The Peculiar Exists Underlying all this speculation
is the certainty that very peculiar things really do happen in the
quantum realm - quantum effects that are essential to the functioning of
transistors and most other modern electronic equipment.
Among these effects is ''tunneling,'' the mysterious
disappearance of a particle (such as an electron) on one side of a
barrier that ''classical'' physics would define as impenetrable, and the
particle's reappearanceon the other side of the barrier. Some of the
wormholes physicists are studying might serve as channels of
communication between isolated universes by means of a similar kind of
tunneling.
The renowned British astrophysicist Stephen W.
Hawking of Cambridge University and Dr. Sidney Coleman of Harvard
University suggest that space is riddled with microscopic wormholes that
constantly pop into and out of existence, sometimes creating baby
universes.
''The sea of baby universes in which our universe
moves,'' Dr. Coleman said in an interview, ''evolves by exchanging
information between past and future universes. In a sense, information
about such things as the cosmological constant is communicated to our
universe from the outside, letting us look into our own generic
future.''
Controversy Acknowledged ''Stephen Hawking and I
have perhaps worked this out correctly, or perhaps we've made fools of
ourselves. I won't tell you this subject isn't controversial,'' he
added.
Among the physicists who sharply disagree with this
interpretation is Dr. Fischler of the University of Texas.
But there seems to be little disagreement about some
of the factors in their calculations, including that of negative
energy.
According to quantum theory, the vacuum contains
neither matter nor energy, but it does contain ''fluctuations,''
transitions between something and nothing in which potential existence
can be transformed into real existence by the addition of energy.(Energy
and matter are equivalent, since all matter ultimately consists of
packets of energy.) Thus, the vacuum's totally empty space is actually a
seething turmoil of creation and annihilation, which to the ordinary
world appears calm because the scale of fluctuations in the vacuum is
tiny and the fluctuations tend to cancel each other out. But experiments
using giant particle accelerators have shown that every conceivable
kind of subnuclear particle (along with its antimatter equivalent
particle) is constantly popping into existence in the vacuum only to be
immediately reunited with its antiparticle in mutual annihilation.
These short-lived ''virtual'' particles can be
converted into a real particle by supplying it with the needed energy a
task made possible by modern particle accelerators.
Fluctuations Observed In 1948 a Dutch physicist,
Hendrick B. G. Casimir, theorized that if two electrically conductive
metal plates are held close enough together in a vacuum, they distort
the normal quantum fluctuations in the vacuum between them, and the
result is a measurable attraction between the plates. Experiments in the
1950's confirmed the Casimir prediction. Theorists have since concluded
that because of the distortion in fluctuations, the vacuum between the
conducting plates contains negative energy.
Two of the most surprising new studies were reported
in separate papers published this spring in Physics Letters B by Klaus
Scharnhorst of Humboldt University in East Berlin and Gabriel Barton of
the University of Sussex in Brighton, England. Using different
approaches, the two physicists concluded that Casimir plates would
exhibit another strange property: light passing through the vacuum
between them would travel very slightly faster than does light in an
ordinary vacuum.
This means only, they said, that the vacuum between
the plates has a different structure than the normal vacuum, not that
the speed limit imposed by relativity has really been violated. Some
theorists have noted that the theory of relativity has not been violated
because the new work merely suggests that the speed limit for light
must be slightly raised in special circumstances. The predicted increase
in the speed of the light would be so tiny, moreover, that no
experiment could measure it.
Nonetheless, these papers have prompted a wave of
new speculation that is compelling physicists to re-examine long-held
assumptions.
In a comment on the work published by the British
journal Nature, Dr. Stephen M. Barnett of Oxford University wrote, ''The
vacuum is certainly a most mysterious and elusive object that makes
itself known by only the most indirect of hints.''
