From: joedees@bellsouth.net
Date: Wed 20 Nov 2002 - 21:17:33 GMT
>
> Revising Relativity
>
>
> PHYSICISTS TRY TO OUTDO EINSTEIN
> BY GRAHAM P. COLLINS
>
> 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 repealed relativity, rarely have qualified the-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
>
> --------------------------------------------------
> WHEN BASEBALLS ARE
> DOUBLY SPECIAL
> 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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