The great man who made Einstein admit his mistake

Edwin Powell Hubble

He changed people's views on the universe. Today's astronomers are studying the universe in the direction he pioneered. A giant telescope surveying the sky in space is also named after him. He is the American astronomer Edwin Powell Hubble.

Edwin Hubble was born in Missouri, USA. He studied at the University of Chicago, and many teachers at the University of Chicago still remembered him many years after graduation. This tall and shy boy is good-looking, not good at speaking or socializing, and except for the language class, his other grades are very good. His outstanding sports skills made him very famous in school. In only one track and field meeting in 1906, he won seven championships in the pole vault, shot put, discus, hammer throw, standing high jump, approach high jump, and relay. He also set a high jump record in Illinois. In addition, to track and field, he also likes basketball, football, and long-distance running. You can always see this tall figure among a group of boys who love long-distance running. He is also the main player of the University of Chicago basketball championship team.

In May 1914, Hubble realized his dream and came to study and work at the Chicago Observatory. After receiving his doctorate from here in 1917, Hubble received an invitation from the Mount Wilson Observatory in Pasadena, California. However, after defending his Ph.D., he joined the army due to the outbreak of World War I. In 1919, he came to the Mount Wilson Observatory in full military uniform.

Fortunately for Hubble, he was in the right place at the right time. At that time, astrophysics was just starting as an emerging discipline, and the Wilson Observatory became the center of observation in this field, and the most powerful astronomical observation tool in the world at that time - the 100-foot-high, 2.5-meter-caliber Hooke telescope, just built after nearly 10 years of assembly. The smug Hubble took off his military uniform and went to work.

Over the next 10 years, Hubble tackled two of the most fundamental questions about the universe: How big is the universe? How long have you survived? To understand these two questions, we need to know how far away a certain galaxy is, and how it is moving. Astronomical observation day after day, year after year, on the top of the mountain on a winter night, have to endure the biting cold wind and face complicated and lifeless numbers in the daytime, for ordinary people, this is lonely and unbearable work, but Hubble was obsessed with it.

During this period, the famous astronomer Harlow Shapley of Harvard University, and later one of his strongest competitors, had just completed a measurement of the scale of the Milky Way. Just at this time, a talented female astronomer at Harvard College, Henrietta Leavitt (Henrietta Leavitt) proposed a very clever method, which is to use Cepheid variable stars as the benchmark for the distance of celestial objects. This method became the basis of Hubble's work. The basics.

A Cepheid variable star is a red giant star with "heartbeat" characteristics, often called a standard candle star. In the process of burning leftover fuel, Cepheid variable stars are not only very bright but also have a specific period of light and dark changes in brightness, so they are easy to identify.

Through the size of Cepheid variable stars in different angles in the sky, the relative position between them can be calculated, and then the relative distance between the galaxy and the earth can be calculated by observing the brightness of Cepheid variable stars. The result obtained by Shapley is that the width of the Milky Way is 300,000 light-years. However, according to the current measurement results, the Milky Way as a whole is like a large disc with a slightly thicker center, a diameter of 100,000 light-years, and a central thickness of 12,000 light-years. . At that time, due to Shapley's reputation, the astronomical community generally believed that 300,000 light-years were the scale of the universe.

Since 1919, Hubble has used the Hooker telescope to observe several spiral galaxies including Andromeda and Triangulum at the Mount Wilson Observatory in California, and measure their distances to the Earth.

In October 1923 he made his first new discovery, a nova in the M31 nebula in the constellation Andromeda. He carefully examined the photos taken by other astronomers including Shapley at the same position in the past and identified the star as a variable star in Andromeda, so he used LeWitt's method to measure the variable star. the distance. He found that the M31 nebula where the variable star is located is millions of light-years away from the earth. In the beginning, he expressed doubts about the results he obtained. Then, he investigated several other spiral galaxies including Triangulum and found that these galaxies were also far beyond the Milky Way. Not only that, but they also resembled Like the Milky Way, which has millions of stars in itself.

The results observed by Hubble show that the actual universe is much larger than people imagined, and the Milky Way is only one of the galaxies in the universe. This conclusion was difficult for people to accept at the time. It undoubtedly overturned the predecessors' understanding of the universe just like the replacement of the earth-centered theory by the heliocentric theory.

Hubble's discovery was opposed by many astronomers, including Shapley. Nevertheless, he published his observations and thoughts in The New York Times. He formally submitted the paper to the American Astronomical Society, and on March 15, 1925, it was officially published in the Bulletin of the National Association for Science. The "New York Times" called this a major discovery, and said in the report: "The spiral nebula discovered by Dr. Hubble proves that it is also an 'island universe' world like our own (the Milky Way). "Later Astronomical observations confirmed that Hubble was right. Hubble's discovery extended people's understanding of the frontiers of the universe by millions of light-years. For this great discovery, Hubble was awarded the American Academy of Sciences Award and the Burton Livingston Committee Award.

Hubble's results were just the beginning, and he had a bigger breakthrough again. In 1929, he used the 5-meter-aperture telescope at Palomar Mountain Observatory to re-examine the galaxies discovered in the past one by one. He found that the wavelengths of light waves emitted from distant galaxies became longer, and the spectral lines moved toward the red end. This is no doubt a reflection of the Doppler effect in light waves, a phenomenon known as "redshift", which is the result of light sources moving away from us. From this, Hubble concluded that not only were distant galaxies receding away from us, but galaxies were also receding from each other.

Excited by this discovery, Hubble used the magnitude of the spectral redshift to calculate the speed at which distant galaxies were moving away from each other. After careful study, he discovered an important law, which is the speed at which galaxies move away from each other is proportional to the distance between them. Later, this law was called Hubble's law, and the ratio of speed to distance is the Hubble constant.

Hubble's subsequent conclusion was even more earth-shattering.

He said,

This means that the universe may have begun with an incredible big bang, that is, the Big Bang.

Regarding the Big Bang, Hubble's statement is consistent with that of Belgium Father Georges Lemaitre's statement is exactly the same, but the two people follow different paths, one from astronomical observation, the other from theoretical deduction, and they reach the same conclusion by different routes.

In 1927, Lemaitre first obtained the solution to Einstein's gravitational field equation. According to the properties of this solution, he pointed out that the universe is expanding. At the same time, he also first proposed that the universe originated from a primitive atom. The big bang of the "primordial atom" created the present universe, which has caused the universe to continue to expand. It is a pity that Lemaitre's paper was published in an unknown journal and did not attract people's attention. Lemaitre's theoretical calculations and Hubble's observations hit it off, and they came from the same period, so they have a strong shocking effect on astronomy.

Hubble's discovery caused a sensation and overturned the views of traditional astronomy in the past. The universe is not as stable and static as people imagined. Before Hubble's discovery, Einstein learned that his gravitational field equation gave a solution for an expanding universe. However, Einstein believed that the universe should be in a stable state. A cosmic term is added to the equation.

After learning of Hubble's results, Einstein, the world-renowned old physicist, came to Mount Wilson to meet with Hubble to express his gratitude and said that he made the biggest mistake in his life.

In the group photo of this meeting, the second person from the left is Hubble, the fourth person is Albert Michelson, and the fifth person is Einstein, taken from the library of Wilson Observatory.

In more than ten years of observations, Hubble has obtained data from 46 extragalactic galaxies, and these results are in line with Hubble's law without exception. Hubble's discovery of the expansion of the universe confirmed the Italian astronomer Lemaitre's hypothesis about the origin of the universe. He and Lemaitre jointly promoted the progress of astronomy, triggered the emergence of the Big Bang theory, and thus created cosmology.

People often have a misunderstanding the expansion of the universe, thinking that the regression of galaxies in the universe is like the expansion of a sphere. In fact, there is an essential difference between the expansion of the universe and the expansion of a sphere. The expansion of a sphere is centered at one point and expands outwards, but the expansion of the universe not only has no center but is uniform in all directions. In other words, the expansion of the universe spreads outwards centered on any space-time point.

The Hubble constant marks the expansion speed of the universe, but this expansion speed is different from the general speed, and there is an extra megaparsec in its unit denominator, that is, every megaparsec is kilometers per second. Megaparsec is a unit of distance, and its size is about 3.26 million light-years. Since this distance is added to the denominator of the Hubble constant unit, the meaning of "cosmological constant" becomes different from that of velocity in general. The value of the cosmological constant is about 68 kilometers per second per megaparsec. This value means that when the distance from the observer increases by one megaparsec distance, the distance between galaxies will increase by 68 kiloparsecs. meters per second. It shows that the farther away from the observer, the faster the universe recedes, and the peculiar nature of this receding speed is just the manifestation of the expansion of the universe without a center.

Hubble dedicated his life to astronomy, and he changed people's understanding of the universe. It is a pity that the Nobel Committee at that time failed to recognize the value of Hubble's achievement in astrophysics, and did not pay enough attention to it. The astronomical community was not prepared enough to accept this valuable achievement. At the time, Hubble's discovery didn't have the impact it deserved. Shortly after Hubble died of a heart attack in 1953, the Nobel Prize Committee responded by including astronomical achievements in the scope of eligibility for review.

Half a century later, people began to realize the importance of this greatest astronomer of the century. On March 6, 2008, the United States issued a stamp to commemorate Hubble. The designer of the stamp, Victor Stupin, recorded in the design literature Wrote: "Hubble is the pioneer of the vast universe and the revealer of the complex universe. It was his meticulous and rigorous study of distant galaxies that proved the existence of extragalactic galaxies. If he hadn't died suddenly in 1953, he would have won the Nobel Prize that year. None other than him."