General relativity predicts mind-bending effects like Mercury's wonky orbit and light bending near the Sun. These wild ideas were put to the test, with scientists racing to prove Einstein right or wrong.
Experiments like watching stars during eclipses and bouncing signals off planets confirmed Einstein's crazy predictions. From Mercury's dance to warped starlight, general relativity keeps acing its exams.
Perihelion Precession and Gravitational Deflection
Mercury's Orbit and Gravitational Lensing
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Perihelion precession of Mercury occurs when the planet's elliptical orbit rotates gradually over time
Newtonian mechanics could not fully explain this precession
General relativity accurately predicts the observed precession rate of 43 arcseconds per century
Gravitational deflection of light happens when light rays bend as they pass near massive objects like the Sun
This effect is due to the curvature of spacetime caused by the object's mass
Deflection angle is proportional to the mass of the object and inversely proportional to the distance from it
Einstein ring forms when a distant light source, a massive object, and the observer are perfectly aligned
The massive object acts as a gravitational lens, bending the light from the source into a ring shape
Radius of the ring depends on the mass of the lensing object and the distances between the source, lens, and observer
Experimental Confirmation of General Relativity
Eddington expedition in 1919 aimed to observe the gravitational deflection of starlight during a total solar eclipse
Measured deflection angles matched the predictions of general relativity
This observation provided the first experimental confirmation of Einstein's theory
Results were widely publicized, making Einstein and his theory famous worldwide
Further observations of gravitational lensing effects have consistently supported general relativity
Hubble Space Telescope has captured numerous images of gravitational lenses and Einstein rings
Gravitational lensing is now a powerful tool in astronomy for studying distant galaxies and dark matter distribution
Gravitational Redshift and Time Dilation
Effects on Light and Time
Gravitational redshift is the stretching of light wavelengths as photons climb out of a gravitational well
Photons lose energy and their frequency decreases, shifting toward the red end of the spectrum
Magnitude of the redshift depends on the strength of the gravitational field
Observed in the spectra of stars and in experiments on Earth (Pound-Rebka)
Shapiro time delay occurs when light signals pass near massive objects, experiencing a longer path due to spacetime curvature
Round-trip travel time of the signal is slightly longer than it would be in flat spacetime
Delay depends on the mass of the object and the closest approach distance of the light signal
Measured using radar signals bounced off planets and spacecraft
Experimental Tests of Gravitational Redshift
Pound-Rebka experiment in 1959 measured the gravitational redshift of gamma-ray photons in a laboratory setting
Used the Mössbauer effect to detect the small frequency shift of photons moving vertically in Earth's gravitational field
Measured redshift agreed with the predictions of general relativity to within 10%
Later refined experiments improved the precision to better than 1%
Gravitational redshift has also been measured in the spectra of white dwarf stars and neutron stars
Intense gravitational fields of these compact objects lead to significant redshifts
Observations match the predictions of general relativity, confirming the theory in strong-field regimes