121 lines
7.1 KiB
Plaintext
121 lines
7.1 KiB
Plaintext
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| File Name : WARPSURF.ASC | Online Date : 11/20/94 |
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| Contributed by : Jerry Decker | Dir Category : GRAVITY |
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| From : KeelyNet BBS | DataLine : (214) 324-3501 |
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| KeelyNet * PO BOX 870716 * Mesquite, Texas * USA * 75187 |
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| A FREE Alternative Sciences BBS sponsored by Vanguard Sciences |
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The following file is courtesy of Jack Veach.
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SpaceTime Hypersurfing
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by Michael Szpir
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from Volume 82 of American Scientist
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In some future history, 1994 may be remembered as the year that the warp drive
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was first conceived to be a physical possibility. Long a cliche' of science-
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fiction writing, the warp drive has transported countless fictional characters
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through light-years of interstellar space in the time it takes for you or me
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to travel to the market. Unfortunately for real-world travelers, the warp
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drive has always been thought to be inconsistent with the laws of physics.
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But all this has changed.
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In the May issue of CLASSICAL AND QUANTUM GRAVITY, Miguel Alcubierre, a
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physicist at the University of Wales describes a space-travel scenario that
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bears an uncanny resemblance to the warp drive of science fiction. With
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Alcubierre's warp drive, we could reach any place in the universe in as short
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a time as we please!
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The warp drive envisioned by Alcubierre is made possible by the subleties of
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Einstein's general theory of relativity. According to Einstein, spacetime
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(the union of the three dimensions of space with the dimension of time) is NOT
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an INERT SUBSTRATE, but rather a DYNAMICAL ENTITY that twists and distorts
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under the influence of concentrations of energy.
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Alcubierre suggests that it might be possible to exploit this phenomenon to
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travel from one star to another faster than the speed of light. This could be
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done by creating a disturbance in spacetime such that the region directly IN
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FRONT of a spaceship is contracted while the region directly BEHIND the
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spaceship is EXPANDED. This distortion of spacetime would, in effect, propel
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the spaceship forward like a surfer riding the crest of a breaking wave.
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At first glance this mechanism would appear to violate Einstein's SPECIAL
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theory of relativity, which holds that no object can travel faster than light.
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Violations of this law lead to causal paradoxes, in which actors in the
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present can alter their own past.
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Yet Alcubierre shows that his warp drive does not, in fact, lead to such
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violations. The reason is that light also travels in spacetime, and is
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carried along just as the spaceship is. The light beam is still traveling at
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the speed of light, relative to the spaceship, which itself is not
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accelerating relative to the spacetime in its immediate vicinity.
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Although Alcubierre's warp drive does not engender any causal paradoxes, one
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might still be concerned for a space traveler's welfare. To get to a distant
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star and back in only moments, the traveler would have to be accelerated at a
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very large rate, effectively turning him into soup. Or at least this would be
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true, if not for the fact that accelerations are relative in general
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relativity.
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Although the acceleration of the spaceship as seen by someone on Earth would
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be enormous, the acceleration experienced by the space traveler would be zero!
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The space traveler would be weightless, just as astronauts are in orbit around
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the Earth. Finally, Alcubierre also shows that a traveler using his warp
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drive would experience no time dilation. One of the predictions of Einstein's
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special theory of relativity is that time flows at DIFFERENT RATES (Keely said
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that 'Time is Gravity') for observers moving relative to one another.
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Consider two space travelers, John W. and Campbell Jr., who decide to visit
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the great galaxy of Andromeda, which is about 2 million light-years away.
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John travels in a spaceship that advertises "one Earth gravity all the way."
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Campbell spends most of the trip traveling near the speed of light.
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Because of time dilation, Campbell is able to survive the trip, aging only 60
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years in the process. However, because the galaxy is 2 million light years
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away, about 4 million years pass on Earth before Campbell gets home. In
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contrast, John is able to make the journey to the galaxy and be back in time
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for supper on Earth!
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Of course, there is no such thing as a free lunch (or supper). The key to
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Alcubierre's warp drive is something called exotic matter. Exotic matter has
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the curious property of having a NEGATIVE ENERGY density, unlike normal matter
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(the stuff that makes up people, planets and stars), which has a POSITIVE
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energy density.
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Two bits of matter that have the same energy density are attracted to each
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other by gravity. In contrast, bits of positive and negative energy matter
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would be REPELLED by gravity. It is the negative energy density of exotic
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matter that POWERS the warp drive.
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A negative energy density is not the nonsensical thing it appears to be.
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Indeed, in 1948 the Dutch physicist Hendrik Casimir first predicted that one
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could observe the effects of negative energy densities. He reasoned that if
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negative energy densities existed, two closely spaced parallel conducting
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plates in a vacuum would be attracted to one another. This phenomenon, now
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called the Casimir effect, was measured in 1958 by M. Sparnaay, and is
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usually taken to be a confirmation that negative energy densities are
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possible.
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Exotic matter of a slightly different type is also invoked in the modern
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theory of cosmology known as inflation. According to the theory of inflation,
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exotic matter in the early universe (moments after the big bang) had a
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positive energy density, but a very large negative pressure. The negative
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pressure was so large that it counteracted the effects of the positive energy
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density.
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The result was an expansion of spacetime so rapid that two observers
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originally very close to each other would be carried apart FASTER than the
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speed of light. This paradigm of spacetime expansion provided the motivation
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for Alcubierre's warp drive.
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There are, of course, 'technical details' to be worked out before the
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aerospace firms can start building starships. Foremost among these is the
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production of exotic matter. Alcubierre has not given that aspect of the
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problem much thought. Although he is an avid reader of science fiction, he
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does not intend to pursue the subject much further.
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Currently, he spends most of his time working on other problems with general
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relativity. The warp-drive scenario, he says, is a very simple thing that he
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came up with in his spare time. Perhaps the problem will be taken up by some
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future physicists in their 'spare time'. The rewards could be astronomical.
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