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November 2, 2011: CERN Experiment and Violation of Newton’s Second
Law Englishview
October 13, 2011: CERN Experiment and Violation of the Newton’s
Second Law Persianview
November 24, 2008: A New Definition of Gravitonview
July 10, 2007: Zero Point Energy and the Dirac Equationview
July 10, 2007: Zero Point Energy and the Dirac Equationview
June 28, 2007: Unification and CPH Theoryview
June 14, 2007: Summary of Physics Conceptsview
June 14, 2007: Strong Interaction and CPH Theory Rview
June 4, 2007: Quantum Electrodynamics and CPH Theoryview
November 30, 2006: Vocabulary of CPH Theoryview
November 17, 2006: Thermodynamic Laws Entropy and CPH Theoryview
November 17, 2006: Time Function and Absolute Black Holeview
October 14, 2006: CPH and Timeview
October 13, 2006: CPH Theory and Newton's Second Lawview
October 13, 2006: Time Function and Work Energy Theoremview
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July 31, 2006: A New Mechanism of Higgs Bosons in Producing Charge
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May 14, 2006: Speed of Light and CPH Theoryview
May 14, 2006: Speed of Light and CPH Theoryview
April 28, 2006: Color Charges Curve Spaceview
April 28, 2006: Color Charges Curve Spaceview
April 17, 2006: Effective Nuclear Chargeview
April 17, 2006: Effective Nuclear Chargeview
April 12, 2006: Maxwell's Equations in a Gravitational Fieldview
April 12, 2006: Maxwell's Equations in a Gravitational Fieldview
April 11, 2006: Realization Hawking - End of Physics by CPHview
April 7, 2006: Questions and Answers on CPH Theoryview
April 7, 2006: Opinions on CPH Theoryview
April 7, 2006: Opinions on CPH Theoryview
April 7, 2006: Questions and Answers on CPH Theoryview
March 23, 2006: Analysis of CPH Theoryview
March 23, 2006: Analysis of CPH Theoryview
March 21, 2006: Logical Foundation of CPH Theoryview
March 21, 2006: Definition Principle and Explanation of CPH Theoryview
March 21, 2006: Logical Foundation of CPH Theoryview
March 21, 2006: Definition Principle and Explanation of CPH Theoryview
March 21, 2006: Experimental Foundation of CPH Theoryview
March 21, 2006: Experimental Foundation of CPH Theoryview
March 19, 2006: Color Charge/Color Magnet and CPHview
March 19, 2006: Sub-Quantum Chromodynamicsview
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Does gravity come in sizes? |
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Does gravity
come in sizes?
Marcus Chown

The Milky Way as pictured in an
infrared image produced by Nasa's Spitzer Space Telescope. NASA
/ AP
There is nothing certain in this
world, the US founding father Benjamin Franklin once wrote,
except death and taxes.
As a scientist, he might have added a third inescapable force:
gravity the unseen hand that keeps our feet on the ground.
Gravity is the universal force. Not only does it stop us getting
above ourselves, it keeps Earth orbiting around the sun, our sun
swinging around the centre of the Milky Way, the Milky Way in a
merry dance around its neighbours and so on upwards.
It is actually the weakest of
natures four forces, but whereas the other three
electromagnetism and the strong and weak nuclear forces
unleash their full strength only at the scales of atoms and
particles, gravity conserves its power to trump all comers in
the cosmos at large. Just take any two things that have mass
and, whatever their size and wherever they are, they will feel
gravitys grasp in exactly the same way.
Or will they?
Justin Khoury, now of the University of Pennsylvania in
Philadelphia, and his colleagues Niayesh Afshordi and Ghazal
Geshnizjani of the Perimeter Institute for Theoretical Physics
in Waterloo, Canada are not so sure. They have listed a series
of observations that cannot readily be explained with a
one-size-fits-all gravity.
None of these effects on its own, they stress, necessarily
indicates anything amiss. But intriguingly, all of them melt
away if you make just one assumption, albeit a controversial
one: that how gravity works depends on the scale on which you
look at it.
If right, the hunch has truly
mind-boggling consequences. According to the theory, this
variable gravity would be our first glimpse of spatial
dimensions beyond our familiar three dimensions infinitely
large, but which remain forever closed off to us. Dr Khoury
acknowledges that it seems wacky. But as long as the
observational anomalies are not explained, there is a feeling
the idea should not be dismissed out of hand.
The work is credible, if a little
optimistic, says David Spergel, an astrophysicist based at
Princeton University. Intriguingly, the theory makes predictions
we can test: so if hidden dimensions are there right under our
noses, we should soon have the proof.
Gravity is a familiar, yet deeply perplexing force. Its story is
bound up with two of the greatest names in physics, Isaac Newton
and Albert Einstein. In 1687, Newton published his universal law
of gravitation, embodied the motion of the planets, the flight
of a cannonball and the dropping of an apple all in one
succinct formula.
Yet Newton was hard pressed to
explain the nature of a force that seem to be transported
instantaneously and with unerring accuracy through empty space.
It was only in 1915, with Einsteins general theory of
relativity, that a halfway convincing answer was found.
According to general relativity, gravity arises because objects
with mass or energy warp space and time around them, causing
other objects to fall towards them. Now we can predict gravitys
effects from the smallest scales right up to the scale of the
solar system with astounding accuracy.
So if the theory aint broke, why
try to fix it? The problem is that general relativity is
incompatible with the later quantum theories that describe
natures other three forces. These theories say that forces are
mediated by a constant exchange of particles; accordingly,
gravity should be transmitted by a quantum particle known as a
graviton. General relativity does not allow for such a
possibility, so physicists are left seeking a grander framework
that will unite gravity and quantum theory into one theory of
everything.
If you care to look on the very
grandest of cosmic scales, there is no shortage of niggling
indications that something is not quite right. Theres evidence
of dark energy, some kind of invisible stuff with repulsive
gravity that is the best explanation we have for why the
universes expansion seems to have begun speeding up in recent
aeons.
Then there is the mystery of dark flow, which has emerged from
surveys of thousands upon thousands of distant galaxies. Over
middling scales of a few hundred million light years, galaxies
look as if they are flowing towards a giant central
concentration of mass one so large that it could not possibly
have gathered since the big bang.
Finally, then theres the
Lyman-alpha forest. Liberally dabbed across the cosmos are
tenuous clouds of hydrogen gas, the building blocks of galaxies.
These absorb light, creating a distinctive dip in the spectrum
of light penetrating through them known as the Lyman-alpha line.
From this forest of spectral lines astronomers can deduce the
distribution of hydrogen clouds in space. Like the dark-flowing
galaxies, they seem more closely clumped together on middling
scales than standard cosmology can explain again, just as if
gravity had once been a stronger force binding them together.
Overall, theres weaker gravity on
one scale; stronger gravity on another. Surely one theory cannot
explain both? Remarkably, that is just what Dr Khoury and his
colleagues are claiming.
The context of their work is an outgrowth of string theory the
currently favoured route to a theory of everything known as
brane theory, which views our universe as a four-dimensional
island or brane adrift in a 10-dimensional ocean of
space-time. In particular they focused on a set of these
theories known as Dvali-Gabadadze-Porrati models after the three
theorists at New York University who suggested them. They would
be just the ticket for reproducing the gravitational properties
of the universe as we see them. They contain hidden dimensions
that might nicely explain the weaker gravity seen at the largest
scales and the stronger gravity on intermediate scales.
But if brane theories have extra
dimensions to the ones we can perceive, why cant we see them?
You and I do not see the extra dimensions because we are made up
of ordinary particles of matter that are firmly pinned to the
brane, they argue.
Even if we do get proof that these other dimensions exist, we
would be a way away from ever entering them. Still, it would be
a dumbfounding indication of how even the stuff we are made of
deceives us in our perceptions of the universe. Is it going to
tie up all the loose ends of the current cosmology? Perhaps,
says Jim Peebles of Princeton University. It is a kludge
something that by rights should not work, but might just he
says.
www.newscientist.com
Source: http://www.thenational.ae/article/20090313/FRONTIERS/225343281/1036
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@2003-2012 The CPH theory, All right reserved
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