Radiophysics. Халюшева Г.Р. - 33 стр.

         8 Unit 8

         8.1 Text 8
                                                            On gravity waves

         In 1916 Albert Einstein published his theory of general relativity. In one of its major aspects this is a theory of the
nature and operation of gravitational forces with which Einstein intended to replace the classical theory devised by Isaac
Newton in the 17th century.
       Einstein's theory makes a number of predictions that are radically different from
those of Newton. One of the most striking of these is that gravitational forces should be
propagated in waves in a manner similar to the way electric and magnetic forces are.
These gravitational waves should consist of cyclically fluctuating gravitational forces;
they should carry energy from place to place and they should cause minute fluctuations
of the surfaces of objects they encounter.
          Any accelerated body could be a source of gravitational waves, but in practice physicists look to large astronomical
bodies such as oblate starts or binary starts.
          The prediction was that gravitational waves would be extremely weak: for a cylinder a metre long the amount of
surface disturbance would be a fraction of the diameter of an atomic nucleus.
          For 40 years no one seriously looked for gravitational waves, but in the late 1950's Dr.Weber began to develop
equipment he thought would do the job. As receivers he used aluminium cylinders of about a ton's weight, and developed
piezoelectric sensors that can record fluctuations in the surface of these cylinders amounting to fractions of a nuclear
diameter.
          In 1969 Dr.Weber announced that his equipment had recorded gravitational waves. Since then he has been
subjected to criticism, based mainly on his statistical analysis of the data. In spite of this, his work has led other people to
enter the search for gravitational waves. Experiments are now in progress in many countries.
          Most of these try to make the detectors more sensitive or to design new kinds of detectors that will record
frequency ranges other than the one – 1,660 cycles per second (Hertz) – that Dr.Weber has pioneered.
          Detectors for the waves can be designed either as broad–band receivers that respond to a range of frequencies or as
narrow–band receivers that are excited only by a single frequency. Dr.Weber's cylinders are narrow.
          Today physicists are setting up an experiment that will repeat Dr.Weber's original work with the equipment of
greater sensitivity. The plan is to use a bar with a square cross–section with a trapezoidal groove cut along the top. The
scientists hope to detect the resonant frequency of the groove as its walls move under the influence of gravitational waves.
Another experiment involves a set of balls and a torsion pendulum. Four balls are placed at the corners of a diamond, so that
they can respond to gravitational waves going by. Two more balls are suspended from the rod back and forth. The
pendulum swings at half the frequency of the gravitational wave. The device is a broad–band receiver capable of measuring
a wide range of frequencies. The scientists are now trying to decide whether to set it up on the ground or in a satellite where
it can be more easily isolated from extraneous disturbances.

         8.2 Words and word–combinations to be remembered

         Gravity – тяжесть; сила тяжести; тяготение.
         relativity – 1) относительность; 2) теория относительности
         to make predictions – делать прогноз; предсказывать
         to be propagated (in) –передаваться через среду, распростроняться
         gravitational waves – гравитационные волны
         cyclically – циклично; циклически
         to fluctuate – колебаться; колыхаться
         to cause smth. – быть причиной, вызывать что–либо
         surface – поверхность (on the surface – внешне; на поверхности)
         to accelerate – ускорять(ся)
         body – тело
         to be a source of smth. – быть источником, причиной чему–либо
         in practice – по практике; на деле
         physicist – физик