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The Question
(Submitted March 27, 1998)
I would like to know if it is true, that the theory of relativity
has been proven by some scientists, who made satellite experiments?
What was there discovery and how did they prove it?
The Answer
This topic is fairly broad, so let me try to narrow it a little.
"Relativity" is a rather general term that encompasses both special
and general relativity. The former encompasses effects such as the
changes in physical properties of objects with speeds approaching
that of light, whereas the latter includes effects having to do with
the bending of "spacetime" by massive bodies. There is no one
experiment which "proves" relativity, and yet so many experiments have
provided consistency with the "theories", that most scientists
accept them as being extremely accurate in their descriptions
of reality.
"Special Relativity": The strongest direct evidence comes probably
from particle accelerators, in which subatomic particles such as
electrons and positrons are accelerated to within a few inches per
second of the speed of light. We can observe very clearly and accurately
the changes in, for instance, the apparent masses of the particles.
They are observed to increase dramatically, and in fact new and much
heavier particles can be created by making counter-rotating beams
of, say, electrons and positrons, collide head-on with each other.
Special relativity has played a key role in the design and operation
of particle accelerators for many decades.
"General Relativity": There have been a variety of experiments
over the years which have supported general relativity in ever more
detail. I would say the culmination was the awarding of the 1993 Nobel
Prize in Physics to Russell Hulse and Joe Taylor for the discovery of
the binary pulsar 1913+16. This binary star system consists of two
neutron stars which are orbiting about their common center of mass
about every 7.75 hrs. Over time, they are spiraling in toward each
other, due to loss of energy via "gravitational radiation" - a
prediction of general relativity. Other general relativistic effects
are observed, such as the "precession of the periastron". That is
to say, the stars are in elliptical orbits, and the "long direction"
of each ellipse is precessing with respect to a distant observer.
This effect is about 4 degrees per year. (In comparison, for Mercury
going around the Sun, it is about 44 seconds of arc per century.)
There are a host of other experiments which confirm different
aspects of both special and general relativity. I view those just
mentioned as among the strongest examples.
J.K. Cannizzo
for Ask an Astrophysicist
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