| Topic: |
Science > Physics |
| User: |
"Sam Wormley" |
| Date: |
15 May 2007 01:29:30 PM |
| Object: |
Black hole shrinks braneworld dimensions |
Black hole shrinks braneworld dimensions
http://physicsweb.org/articles/news/11/5/12/1
14 May 2007
Gravity might be strong enough to hold our solar system together, but
compared to the other three forces of nature it is pitifully weak.
Cosmologists think this might be because the universe we can see
around us is confined to a sheet-like "brane", with gravity -- unlike
the other forces -- free to operate in a higher-dimensional bulk. Now
a physicist from the US has studied the age of a black hole to put a
limit on the size of the extra dimensions at 80 µm, which might
explain why we haven't yet detected them in the laboratory (Phys.
Rev. Lett. 98 181101).
The ultimate aim for theorists is to write down a "theory of
everything", which would describe all the known forces of nature
using the same set of equations. But one of the major hurdles facing
them is gravity, which is the only force not included in the Standard
Model of particle physics. This is partly because gravity, as
described in theories by Newton and Einstein, is many orders of
magnitude smaller than the other forces -- a curious discrepancy
known as the hierarchy problem.
Some cosmologists have suggested that the hierarchy problem would
disappear if we were to assume that our universe's four familiar
dimensions -- three for movement in space, and one for time -- form a
single "brane" in a higher-dimensional bulk. In this braneworld, the
three forces described by the Standard Model would act along our
brane in the normal way. Gravity, however, would be able to spread
throughout the bulk, leaving us to observe just a fraction of its
attractive force.
In the most popular braneworld models, the extra dimensions are
distorted so that they occupy volumes up to a millimetre in size.
Therefore to catch a glimpse of them one must look for deviations in
Newton's gravitational inverse-square law at equally small scales. In
January this year Dan Kapner and colleagues of the University of
Washington in the US used a torsion-balance experiment to prove the
law holds down to 55 µm -- small enough to make the idea of extra
dimensions less plausible (see related story: "Pendulum swings away
from dark energy"). However, Dimitrios Psaltis from the University of
Arizona now claims to have used the age of a black hole to put a new
limit on the theoretical size of the extra dimensions, which might
explain why they haven't been found yet.
Black holes are often expected to have an extremely long life because
their rate of evaporation is fairly slow. But if extra dimensions do
exist then some of this evaporation could take place in the bulk of
the braneworld, and so would proportionally reduce the black hole's
lifespan. Psaltis took recent measurements of the 3D velocity and
position of the black hole XTEJ118+480 to reconstruct its trajectory.
This in turn allowed him to calculate when it last passed the
galactic plane, and thus the earliest time the black hole could have
been formed.
Psaltis found that XTEJ118+480 must be older than 11 Myr, which in
braneworld terms means the extra dimensions could extend over volumes
no larger 80 µm. Although this is not quite as small as the
experimental limits set by the Washington team, it does shrink the
target area for future tests of the inverse-square law.
However, Ruth Gregory of Durham University, who has also researched
the cosmological effects of a braneworld, told Physics Web that the
equation Psaltis used to calculate the lifetime of a black hole is
not based on hard theoretical ground. "I certainly won't be taking it
to the bank," she said. "The main problem is that we don't know what
a black hole looks like on a brane. But it is good that
experimentalists are taking observations to put the theory to the
test."
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| User: "hanson" |
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| Title: Re: Black hole shrinks braneworld dimensions |
16 May 2007 04:00:17 PM |
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CORRECTIONS to/in "Sam Wormley"'s <swormley1@mchsi.com>
news:e_m2i.54508$n_.5499@attbi_s21... who cited:
Black hole shrinks brain dimensions
http://physicsweb.org/articles/news/11/5/12/1
14 May 2007
::
[All meaningless, superfluous lamentations snipped to make
the issue clear for the Einstein Dingleberries' understanding]
::
Cosmologists think the universe we can see around us is
confined to a sheet-like Brain with gravity -- free to operate
in a higher-dimensional bulk-- which is why we haven't yet
detected it in the laboratory (Phys. Rev. Lett. 98 181101).
one of the major hurdles is partly because gravity, as
described by Newton and Einstein, that brings a curious
discrepancy known as the hierarchy problem, which.
would disappear if we were to form a single most
popular brain-world model.
Therefore one must look for deviations of Dan Kapner et.al of
UW to make the Pendulum swing way from dark energy ---
However, Dimitrios Psaltis from UA claims to use the age of
black holes to explain why they haven't been found yet.
This in turn allowed him to calculate when it last passed the
galactic plane. However, Ruth Gregory of DU, told Phys-Web that
a black hole is not based on hard ground to the bank," she said,
"The main problem is that we don't know what a black hole looks like
on a brain.
[hanson]
ahahaha... I like the one line where shy Ruthie has qualms of taking
her black hole to the bank fearing that it will be mistaken for her brain.
hahahaha.... AHAHAHA.... ahahahanson
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| User: "Jan Panteltje" |
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| Title: Re: Black hole shrinks braneworld dimensions |
15 May 2007 02:27:03 PM |
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On a sunny day (Tue, 15 May 2007 18:29:30 GMT) it happened Sam Wormley
<swormley1@mchsi.com> wrote in <e_m2i.54508$n_.5499@attbi_s21>:
Black hole shrinks braneworld dimensions
<crap about dimensions snipped>
not based on hard theoretical ground. "I certainly won't be taking it
to the bank," she said. "The main problem is that we don't know what
a black hole looks like on a brane. But it is good that
experimentalists are taking observations to put the theory to the
test."
As I have pointed out before: It is spelled BRAIN not brain, they asked for the wrong
thing.
Sir CommonSense.
Reporter asks Nobel price winner in physics:
What do you think of string theory, do you think it is right?
Answer: No.
!
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