institute for the science of origins
Evalyn Gates, PhD
The Cleveland Museum of Natural History
University of Chicago, Adler Planetarium & Astronomy Museum, Yale University
Case Western Reserve University
A gravitational lens refers to a distribution of matter (such as a cluster of galaxies) between a distant source and an observer, That is capable of bending the light from the source, as it travels towards the observer. This effect is known as gravitational lensing and the amount of bending is one of the predictions of Albert Einstein’s general theory of relativity. (Classical physics also predicts bending of light, but only half that of general relativity’s.)
In general relativity, light follows the curvature of spacetime, hence when light passes around a massive object, it is bent. This means that the light from an object on the other side will be bent towards an observer’s eye, just like an ordinary lens. Since light always moves at a constant speed, lensing changes the direction of the velocity of the light, but not the magnitude.
Light rays are the boundary between the future, the spacelike, and the past regions. The gravitational attraction can be viewed as the motion of undisturbed objects in a background curved geometry or alternatively as the response of objects to a force in a flat geometry.
Although Orest Chwolson (1924) or Frantisek Klin (1936) are sometimes credited as being the first ones to discuss the effect in print, the effect is more commonly associated with Einstein, who published a more famous article on the subject in 1936.
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Right after Einstein’s brief text had been published, it was followed by a number of articles by well-known scientists, who picked up where Einstein had left off.
Fritz Zwicky (1898-1974), an astronomer at the California Institute of Technology, discussed the possibility of observing the lensing effect in the case of the recently discovered extragalactic nebula, in other words: other galaxies. The typical masses, sizes and mutual distances of galaxies are such that double images of a distant galaxy should be significantly more frequent than double images of stars: The necessary near-alignment of a closer object, a more distant object and an observer here on Earth is much more probable for galaxies than for stars.
The typical masses, sizes and mutual distances of galaxies are such that double images of a distant galaxy should be significantly more frequent than double images of stars: The necessary near-alignment of a closer object, a more distant object and an observer here on Earth is much more probable for galaxies than for stars.
Henry Norris Russell, the astronomer from Princeton, published an article in which he speculated about the inhabitants of a hypothetical planet orbiting the White Dwarf companion of the star Sirius. What would they see during a total eclipse – on the occasion when, from the point of view of these inhabitants,
the White Dwarf star would move in front of the more distant Sirius? As White Dwarfs are very compact objects, light from Sirius passing close to the companion would be markedly deflected. Of course, astronomers on Earth would not be able to see this relativistic gala performance, and in fact Russell cites this scenario as a perfect test of relativity theory which, regrettably, is impossible to put into practice.
Indisputably, Einstein’s little publication had lent credibility to the idea of gravitational lensing, and the concept became part of the general knowledge of theoretical astronomers.
Message from Earth 33 ” Don’t Believe Your Eye’s ”
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