H.8.1 Outline an experiment for the bending of electromagnetic waves by a massive object.

H.8.2 Describe gravitational lensing.H.8.3 Outline an experiment that provides

evidence for gravitational red-shift. The Pound-Rebka experiment will suffice.

Option H: RelativityH8 Evidence to support general relativity

Outline an experiment for the bending of electromagnetic waves by a massive object.●In 1919, Sir Arthur Eddington conduct- ed the first experiment to determine the validity of Einstein’s General Theory of Relativity, published in 1915.●General relativity’s principle of equivalence predicts the bending of light rays in a gravitational field.●During a total eclipse, the moon blocks out the sun entirely on certain parts of the Earth to such an extent that you can see stars near the disk of the sun.●In fact, stars that were behind the sun were expected to be seen, according to the general theory, because of the bending of light by its strong gravitational field.

Option H: RelativityH8 Evidence to support general relativity

Outline an experiment for the bending of electromagnetic waves by a massive object.●Here’s how the experiment worked:●The sun, moon, Earth and star would all be lined up for an eclipse.●The apparent position of the star would be measured during the eclipse. This position would be affected by the bending of light by the sun.●The true position of the star would be determined 6 months after the apparent position of the star was recorded. Why 6 months?

Option H: RelativityH8 Evidence to support general relativity

Actual star

Earth /moon

SunTrue po

sitionApparent

position

Apparent star

Outline an experiment for the bending of electromagnetic waves by a massive object.●Relativity predicted a deflection of 1.75 arc seconds for starlight passing close to the edge of the sun.●Although Eddington’s results were in agreement with relativity, his uncertainty was comparable to the measurement itself.●Furthermore, his results were disputed by another team doing the same thing in Brazil.

Option H: RelativityH8 Evidence to support general relativity

FYIThe Eddington-Einstein collaboration continued through the First World War, even though the two scientists were on opposite sides.The results of Eddington’s observations have sometimes been criticized as a “self-fulfilling” desire to prove general relativity correct.

Describe gravitational lensing.●If a sufficiently massive object is between an observer and a distant object, because of the bending of the light by gravity, the mass acts like a lens.●A gravitational lens will present to the observer numerous images of the same distant object.

Option H: RelativityH8 Evidence to support general relativity

EXAMPLE: Here are images of so-called Einstein rings (gravita- tional lens images).

This is an animation of gravitational lensing.

●The dark object doing the lensing is a massive black hole between us and the band of stars.●The band of stars is a galaxy on edge, farther away than the black hole.●Note the Einstein rings.

Outline an experiment that provides evidence for gravitational red-shift.●We have already done a sample problem modeled on the Pound-Rebka experiment.●This experiment, conducted in the Jefferson Laboratory at Harvard in 1959, verified the gravitational red shift by detecting the change in frequency of gamma rays emitted by 57Fe.

Option H: RelativityH8 Evidence to support general relativity

The “Tower”

22.6 m