Evicting EinsteinA physics experiment on the drawing board for the
International Space Station could help find the grand unifying "Theory
of Everything."
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Listen to this story via streaming audio, a downloadable file, or get help. March 26, 2004: Sooner or later, the reign of Einstein, like the reign of Newton before him, will come to an end. An upheaval in the world of physics that will overthrow our notions of basic reality is inevitable, most scientists believe, and currently a horse race is underway between a handful of theories competing to be the successor to the throne. In the running are such mind-bending ideas as an 11-dimensional universe, universal "constants" (such as the strength of gravity) that vary over space and time and only remain truly fixed in an unseen 5th dimension, infinitesimal vibrating strings as the fundamental constituents of reality, and a fabric of space and time that's not smooth and continuous, as Einstein believed, but divided into discrete, indivisible chunks of vanishingly small size. Experiment will ultimately determine which triumphs. Right:
According to Einstein's theory of general relativity, the sun's gravity
causes starlight to bend, shifting the apparent position of stars
in the sky. A House Divided
But the two theories are like different languages, and no one is yet sure how to translate between them. Relativity explains gravity and motion by uniting space and time into a 4-dimensional, dynamic, elastic fabric of reality called space-time, which is bent and warped by the energy it contains. (Mass is one form of energy, so it creates gravity by warping space-time.) Quantum mechanics, on the other hand, assumes that space and time form a flat, immutable "stage" on which the drama of several families of particles unfolds. These particles can move both forward and backward in time (something relativity doesn't allow), and the interactions between these particles explain the basic forces of nature -- with the glaring exception of gravity. Left: Astronomers use the light-bending properties of gravity to view very distant galaxies--such as the arc shapes in this image--in a technique called "gravitational lensing." [More] The stalemate between these two theories has gone on for decades.
Most scientists assume that somehow, eventually, a unifying theory
will be developed that subsumes the two, showing how the truths they
each contain can fit neatly within a single, all-encompassing framework
of reality. Such a "Theory of Everything" would profoundly affect
our knowledge of the birth, evolution, and eventual fate of the universe. In
fact, it was by measuring the bending of starlight by the sun during
a solar eclipse in 1919 that Sir Arthur Eddington first tested Einstein's
theory of general relativity. In cosmic terms, the sun's gravity is
fairly weak; the path of a beam of light skimming the edge of the
sun would only be bent by about 1.75 arcseconds (an arcsecond is 1/3600
of a degree). Within the limits of accuracy of his measuring equipment,
Eddington showed that starlight did indeed bend by this amount --
and in doing so effectively impeached Newton. Above: The curvature of space due to the sun's mass caused signals from the Cassini probe to curve on their way to Earth. [More] "I think [LATOR] would be quite an important advance for fundamental physics," says Clifford Will, a professor of physics at Washington University who has made major contributions to post-Newtonian physics and is not directly involved with LATOR. "We should continue to try to press for more accuracy in testing general relativity, simply because any kind of deviation would mean that there's new physics that we were not aware of before." Solar laboratory Above: A schematic diagram of the proposed LATOR mission. Turyshev plans to measure the angle between the two satellites using an interferometer mounted on the ISS. An interferometer is a device that catches and combines beams of light. By measuring how waves of light from the two mini-satellites "interfere" with each other, the interferometer can measure the angle between the satellites with extraordinary precision: about 10 billionths of an arcsecond, or 0.01 µas (micro-arcseconds). When the precision of the other parts of the LATOR design are considered, this gives an overall accuracy for measuring how much gravity bends the laser beam of about 0.02 µas for a single measurement. "Using the ISS gives us a few advantages," Turyshev explains. "For one, it's above the distortions of Earth's atmosphere, and it's also large enough to let us place the two lenses of the interferometer far apart (one lens on each end of the solar panel truss), which improves the resolution and accuracy of the results." Left: The interferometer will be mounted to the solar-panel truss of the ISS, which automatically rotates to continuously face the sun. Image courtesy Slava Turyshev. The 0.02 µas accuracy of LATOR is good enough to reveal deviations
from Einstein's relativity predicted by the aspiring Theories of Everything,
which range from roughly 0.5 to 35 µas. Agreement with LATOR's
measurements would be a major boost for any of these theories. But
if no deviation from Einstein is found even by LATOR, most of the
current contenders--along with their 11 dimensions, pixellated space,
and inconstant constants--will suffer a fatal blow and "pass on" to
that great dusty library stack in the sky. |
Credits & Contacts |
Production Editor: Dr. Tony Phillips |
The Science and Technology Directorate at NASA's Marshall Space Flight Center sponsors the Science@NASA web sites. The mission of Science@NASA is to help the public understand how exciting NASA research is and to help NASA scientists fulfill their outreach responsibilities. |
Web Links |
NASA's Office of Biological and Physical Research (OBPR) supports studies like Turyshev's for the benefit of humans in space and on Earth Laser Astrometric Test Of Relativity (LATOR) -- technical paper by Turyshev and colleagues about the LATOR concept Many of the candidates
for a "Theory of Everything" predict the existence of a
scalar field
that permeates the universe. Einstein first proposed such a field
when he introduced a cosmological
Einstein's Relativity and Everyday Life -- Physicist Clifford Will explains how the Global Positioning System depends on the theory of relativity. The Theory of Everything -- article about the search for a theory to unify relativity with quantum mechanics, by physicist Michio Kaku A Pop Quiz for Einstein -- (Science@NASA) The Gravity Probe B mi will test two important aspects of Einstein's theory of General Relativity. The Elegant Universe -- Watch a 3 hour series from PBS's Nova about the quest to find a unifying Theory of Everything "Laser Astrometric Test of Relativity (LATOR) Mission Studies" is just one of many fundamental physics research grants recently awarded by NASA's Office of Biological and Physical Sciences. General Relativity -- Introduction to general relativity, from the Wikipedia |
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