Re: virus: Revising Relativity (crossposted from the Virus List)

Date: Wed 20 Nov 2002 - 21:17:33 GMT

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    > Revising Relativity
    > Einstein’s theory of special relativity
    > turned 97 this year and is one of the
    > most hale and hearty sets of laws in
    > physics. Allied with quantum mechanics, it
    > forms the foundation on which the Standard
    > Model of particle physics is built. When rec-
    > onciled with gravity, it mutates into general
    > relativity, the theory governing black holes,
    > the expansion of the universe, and the fine de-
    > tails of GPS satellite trajectories. Although
    > cranks frequently claim to have extended or
    > repealed relativity, rarely have qualified the-
    > orists dared to tinker directly with its basic
    > structure. Recently, however, a small group of
    > physicists have suggested that a fundamental
    > overhaul of relativity is in order.
    > The basic change proposed is to introduce
    > a second “scale” to the theory in addition to
    > c, the speed of light in a vacuum. The con-
    > stancy of c for all observers is the bedrock of
    > relativity. When relative velocities of objects
    > approach c, strange effects such as time dila-
    > tion and length contraction become obvious.
    > Quantum gravity has its own special scale:
    > the Planck energy, which is defined uniquely
    > by c in conjunction with the magnitude of
    > quantum effects and the strength of the force
    > of gravity. For an elementary particle, the
    > Planck energy is huge beyond anything ever
    > observed in cosmic rays or created at an ac-
    > celerator. When particles have energies com-
    > parable to the Planck energy, the existing the-
    > ones of physics should break down and an as
    > yet undetermined theory of quantum gravity
    > should take over, manifesting weird phenom-
    > ena such as a “foaminess” of spacetime itself.
    > This prediction poses a puzzle for relativity,
    > because observers with different relative mo-
    > tions will disagree about when a particle
    > reaches the Planck regime. How can one ob-
    > server see the particle traversing ordinary,
    > smooth, continuous spacetime while another
    > sees it skipping across a quantum foam?
    > In late 2000 Giovanni Amelino-Camelia
    > of the University of Rome proposed a revision
    > of relativity in which a minimum-length scale
    > is added. (An extremely small distance called
    > the Planck length corresponds to the Planck
    > energy.) Because the theory has two absolute
    > scales, c and the Planck length, Amelino-
    > Camelia dubbed it a “doubly special” relativ-
    > ity theory. In a world ruled by the modified
    > equations, very short wavelengths approach-
    > ing the Planck length become increasingly im-
    > mune to the effects of length contraction. The
    > change also causes extremely short wave-
    > length light to travel slightly faster than c. The
    > changes wrought by the theory might be test-
    > ed by observations of ultrahigh-energy cosmic
    > rays or by studies of gamma rays by the orbital
    > telescope GLAST, to be launched in 2006.
    > The variation in the speed of light is elim-
    > inated in a newer doubly special theory con-
    > cocted by Lee Smolin of the Perimeter Institute
    > --------------------------------------------------
    > The threshold energy for strange
    > new double-relativistic effects
    > applies only to elementary
    > particles, not to composite objects
    > built from them. Expressed as a
    > mass, the Planck energy is just 20
    > micrograms. A baseball far exceeds
    > that mass without showing any
    > bizarre trans.Planckian behavior.
    > Only for a fastball traveling
    > exceedingly close to thespeed of
    > light would the baseball’s
    > constituent particles have Planck-
    > scale energies and exhibit new
    > double-relativistic effects.
    > -------------------------------------------------
    > for Theoretical Physics in Waterloo, Ontario,
    > and Joao Magueijo of Imperial College, Lon-
    > don. Their theory changes how a particle gains
    > energy and momentum as it is boosted to high-
    > er energy. Smolin and Magueijo predict that
    > an accelerated particle’s energy will approach
    > the Planck energy asymptotically in the same
    > way that the velocity of an accelerated massive
    > particle approaches c. The changes to physics
    > in Smolin and Magueijo’s theory are smaller
    > than in Amelino-Camelia’s model and hence
    > are unlikely to be experimentally tested any-
    > time soon. A whole class of additional doubly
    > special theories also exist.
    > The modifications of energy and momen
    > ra are better understood than the effects on dis-
    > tance. Imagine somehow using a Planck-length
    > ruler to measure a baseball bat. A moving ob-
    > server will see the bat contracted by relativity,
    > but the tiny ruler should be unaffected if the
    > Planck length is invariant. The ruler lengths
    > must not add up by ordinary arithmetic. Ener-
    > gies add up in a similarly complicated fashion.
    > Quantum gravity theorist Steven Carlip of
    > the University of California at Davis says that
    > doubly special relativity is an interesting idea,
    > but he suspects that “they are looking for too
    > simple a solution to a complicated problem”
    > in quantum gravity. “But,” he adds, “I hope
    > I’m wrong.”
    > --
    > Walter Watts
    > Tulsa Network Solutions, Inc.
    > "No one gets to see the Wizard! Not nobody! Not no how!"

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