Article: Macro, not micro: modified theories of gravity [Dark troubles?]

Macro, not micro: modified theories of gravity
When it comes to cosmology, the macro scale is important. As scientists
search for the reasons behind the increasing rate at which the universe is
expanding, they modify Einstein's theory of gravity and delve into dark
energy theories to explain this counter-intuitive phenomenon.

These simple modifications are represented as f(R) theories, and they are
used to explain what is seen on a cosmic scale. But there's a problem. "Some
modified theories of gravity have nice features for cosmology, on the big
scale, but they don't work so well on the small scale," Gonzalo Olmo
explains to PhysOrg.com. "I managed to solve these equations on the micro
level, and I found that they are inconsistent."

Olmo, 28, is a post-doc at the University of Wisconsin-Milwaukee. He says he
solved these equations two years ago, but waited until interpreting them to
have them published. His recent letter in Physical Review Letters, which
puts forth the equations and their interpretations, is titled "Violation of
the Equivalence Principle in Modified Theories of Gravity."

In the Letter, Olmo presents equations that suggest that when some modified
theories of gravity are applied to the micro scale, new properties emerge
that can effectively rule out some theories that explain accelerating
universe expansion.

"If we manage to show these theories are not consistent, which it looks
like, then this approach in cosmology would be useless," Olmo points out. He
says that there are two main ways modified theories are studied: in the
metric formalism or in the Palatini formalism. Olmo explains that his paper
focuses on theories of gravity in the Palatini formalism. "[T]he connection
is regarded as independent of the metric and, therefore, must be determined
by solving its corresponding field equations," the paper says.

Olmo says that when he solved the equations on the micro scale, he noticed
the emergence of new properties: "These new properties have never been seen
in other modified theories of gravity, and these new properties are what
make these theories so weird on the micro scale."

Even though Olmo says that these theories would not do to explain the
expansion of the universe, since they are inconsistent on the micro scale,
there are some uses for modified theories of gravity. He explains that the
differences between how these modified theories work on the macro scale and
on the micro scale could offer insight into the interaction between
gravitation and quantum physics.

"According to Einstein," Olmo explains, "spacetime should be nearly flat in,
for instance, your dining room or the interior of an atom." He pauses before
continuing: "However, in Palatini theories we find that it is curved even on
a micro level, which has a strong effect on the properties of the quantum
world. This can lead to better understanding by seeing how these modified
theories of gravity interact with quantum theory."

"There are different possibilities to the reasons behind the acceleration of
the universe," continues Olmo. "Some theorists use dark energy to explain
the expansion, and others modify the equations of gravity to say it is not
dark energy. However, there could be a mix." He says that it is very
difficult to distinguish the effects of dark energy from those of modified
equations, and the difference could hold the key to discovering what's
behind the increasing rate of expansion of our universe. And he thinks
applying modified theories of gravity to the micro scale as well as to the
macro scale could help determine the different effects. "If this idea can
get going," he enthuses, "there could be a very interesting future."

By Miranda Marquit, Copyright 2007 PhysOrg.com.
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Source: Physorg
http://www.physorg.com/news90849092.html

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Posted by
Robert Karl Stonjek

The expansion of the Universe can be explained by:

A rotating galaxy condenses from a simple force: gravity.

As a galaxy condenses and its loose arms compact, the
galaxy gains rotational speed. As that happens from a
'spinning figure skater pulling in her arms', the galaxy not
only rotates faster but gains inertia toward its heading.

The result is that galaxies like trains everywhere are
gaining speed toward on their tracks and the Universe
appears inflating like a bubble, distances between galaxies
appear growing as galaxies move faster and faster, and
occasional collisions leave scattered elliptic galaxies
behind.

The effect is also accelerating until gravity simply compacts
spiral galaxies over time and gives them 'momentum'.

Dark energy is simply escape energy as rotating galaxies
compact. A large volume of mass rotates chaotically,
and all of space is inerted in the vicinity of a galaxy toward
its' rotation.