Does light have "weight"? Is it subject to gravity? This problem has aroused the curiosity of many famous physicists, and it is precisely because of the unremitting contemplation of it that Einstein established the famous theory of general relativity, and the experimental observation of this problem has verified the correctness of general relativity.
The "weight of light" problem also involves the exploration of galaxies and galaxy clusters in modern astronomy, and even changes human understanding of matter and even the structure of the entire universe.
As early as 300 years ago, Newton had imagined that light was composed of particles, and he not only used the particle nature of light to explain the phenomenon of reflection and refraction, but also believed that like all objects, light could also be attracted by gravity and had "weight" in the gravitational field.
Newton
In 1704, Newton wrote in his book Optics: "Can an object act on light at a distance?" Does this effect bend the light? When the distance is the smallest, is this effect also strongest? Although Newton did not calculate further, this remark piqued interest in the issue.
A hundred years have passed. In 1801, the German astronomer John von Solder made a detailed calculation, he came up with the amount of curvature of light under the gravitational pull of the sun, but this amount was too small to find a sufficiently accurate instrument at that time, nor was there such sophisticated photographic equipment, and it was almost impossible to verify this result, so it did not attract attention.
There is another person who is interested in the gravitational bending of light, that is, the famous British astronomer Arthur Eddington. He imagined that when light swept over the sun, it was like particles of light skimming over the sun. Under the gravitational pull of the Sun, the trajectories of these particles will bend. He used Newton's theory of gravity to calculate, and the result was that after the light passed through the sun, the light was bent by 0.9 arcseconds (arcseconds are angular units, and 1 arcsecond is equivalent to 0.01592 degrees). This value is still too small, equivalent to the amount of light traveling 5 kilometers, only a thumb width.
It was during this period that Einstein created the general theory of relativity and obtained the gravitational field equation. According to this equation, Einstein also calculated the bending of light by the gravitational pull of the sun, and the result was the same as that of Eddington. But this was calculated by Einstein using his original imperfect gravitational equation. When Einstein perfected his gravitational field equation, the calculated amount of curvature of light was doubled, or 1.8 arc seconds. He suggested that the astronomical community conduct field measurements of this phenomenon. Following Newton's example, he also called this observation an experiment of "light weighing."
Einstein
Einstein was a man of extraordinary imagination, and this "light weighing" experiment was very cleverly designed, he moved the laboratory to the sky, and the experimental instrument was the planet, which could show the great power of gravity to bend light.
Gravitational lensing is a special optical effect in a strong gravitational field. Suppose there is a strong gravitational field object between the Earth and a distant celestial body, the three are almost in a straight line, the space-time bending near the strong gravitational field celestial body makes the light of the distant celestial body can not reach the earth along a straight line, and the observed image on the earth deviates from the direction in which it is originally located, and its effect is similar to the refraction of light by the lens, called the gravitational lens effect.
Einstein also suggested that the experiment should be performed when a solar eclipse occurs. If there is a bright star behind the sun when the eclipse occurs, people can't see it because it is obscured by the sun, but the sun's gravity acts like a lens, which can make the light emitted by that star bend when passing through the sun, and the curved light hits the earth, and people will be able to see the blocked star through the "gravitational lens" of the sun.
During a total solar eclipse, observe the schematic of the target behind the Sun
In 1917, Eddington, who was in Cambridge, England, noticed Einstein's proposal and immediately realized the value of the experiment. Eddington was a brilliant astronomer, not only familiar with physics, but also proficient in mathematics, and when the vast majority of physicists in the world could not read Einstein's theory, he quickly understood and gained insight into the important value of this theory in physics and astronomy. Especially when he learned that Einstein calculated that the sun's gravitational bending value was twice his calculated value, he immediately realized that this data would be Einstein's challenge to Newton, and verified this value, just in order to distinguish which of the two gravitational theories is correct.
Eddington
The challenge also attracted great interest from British astronomers and director of the Greenwich Observatory, Frank Dyson. He immediately presided over the formation of two astronomical survey teams, one to Principe on the west coast of Africa and the other to Sobral in northern Brazil. A month before the 1919 eclipse, two survey teams arrived at the station separately. On the day of the eclipse on May 29, 1919, the survey team set up astronomical telescopes and photographic equipment, and a world-renowned astronomical feat began.
However, that day did not go well, and the heavens were not beautiful. In Principe, clouds obscure the sun and fail to capture the starlight behind the sun. "We set up telescopes and camera equipment, prepared the best photographic negatives, and aimed them at the surface of the sun more than 100 million kilometers away." Eddington recalled: "At the time we couldn't do anything. But I mysteriously found that the seemingly silent nature and the dim earth were awakened by the call of the observer and the tick of the metronome, and suddenly there was a miracle in the sky, and we finally got a clear exposure. ”
Due to bad weather, only two negatives in the observations on Principe could yield measurement data. The result they give is that the light emitted from distant starlight is bent by 1.61 arc seconds under the influence of the Sun's gravity, which is close to Einstein's result.
One of the pictures available in the experiment
In Brazil, the observation weather of the survey team is very good. Both of their telescopes got the results. One result is 1.98 arcseconds and the other is 0.9 arcseconds. Eddington chose that big result. He explained that the other negative was very vague and not enough to provide convincing data. Despite its doubts, the Royal Astronomical Society accepted Eddington's approach.
In September of that year, the results of the experiment came out one after another. On September 22, Hendrick Lorenz telegraphed the news to Einstein, who was very excited and the physics community was greatly shaken by this success. It is said that the famous German physicist Max Planck did not sleep all night, anxiously waiting for observations to confirm Einstein's general theory of relativity. Einstein later joked: "If he really understood general relativity, he would go to bed like I did."
On November 6, 1919, the Royal Astronomical Society held a grand celebration in London, and the news that Einstein's theory was confirmed was officially made public. J.J. Thomson, president of the Royal Society and Nobel laureate, solemnly noted that this was "one of the greatest achievements in the history of human thought." This discovery is not the discovery of an isolated scientific theory, but the discovery of a new continent of scientific thought. This is the greatest discovery related to gravity since Newton figured out the laws of gravitation. ”
Before 1919, Einstein was already famous in the world, and when the bending of the sun's gravitational rays was confirmed, he suddenly became a household name. The Times headlined the Royal Society celebrations under the headline "Revolution in Science – New Theories of the Universe / Newton's Ideas Challenged and Abandoned."
The report explains the reader's drawings
Across the Atlantic, the New York Times is even more aggressive, with its headline headline sensational: "The light in the sky is skewed!" To make it more appealing to the reader, the article says, "In fact, the star you see is not in the same place you see." "In fact, this matter does not need Einstein's theory of gravitation, and a little thought can know that when the stars from tens of thousands, millions, or even hundreds of millions of light years reach your eyes, they are no longer in the place you see.
Germany also reacted quickly, and on December 14, 1919, a prominent German newspaper published Einstein's photographs and articles in almost full pages. The article is well-appointed and solemn, titled "Albert Einstein, a rising star in world history whose research transformed our understanding of the natural world, a discovery comparable to Copernicus, Kepler, and Newton." Two years later, Einstein was awarded the title of "Prussian Knight" (equivalent to a British knight) and received a Prussian medal the size of a large pocket watch, with blue and gold trims, decorated with four golden crowns and a Prussian eagle, but Einstein never wore it.
The true value of the "gravitational lensing" effect is reflected half a century later. Since the 1970s, radio telescopes have been used to observe radio waves from pulsars. Radio waves are not disturbed by sunlight, do not have to wait for eclipses, and can be continuously observed day and night. A large number of observations not only confirm Einstein's theory of gravitation with great precision, but also further measure the gravitational shift of light as it passes through Jupiter. Jupiter's gravitational shift to light is 1/100th that of the Sun, a value that coincides with Einstein's theoretical results.
From the end of the 20th century to the 1910s, the gravitational lensing effect of light has been an indispensable means of modern astronomical observation, led by the Hubble Space Telescope, the Spitzer Infrared Space Telescope and the Chandra X-ray Observatory, a large astronomical observation target is moving towards the depths of the universe.
Using gravitational shifts from various bands of rays emitted from distant galaxies, astronomers can infer the masses of distant galaxies, explore the huge clouds of dark matter around distant galaxies, and even discover the formation process of younger galaxies, thus deducing the early stages of formation of cosmic galaxies.
In the large-scale material world, the "weight" of light is a phenomenon that cannot be ignored, and it is also one of the driving forces that affect the structure of the universe. According to Einstein's theory of gravitational attraction, as long as there is matter, both time and space must be affected, and the bending of light in the gravitational field is one of the manifestations of this effect.
Some of the images come from the Internet
Copyright belongs to the original author
Source: Origin Reading
Editors: Lychee, yrLewis