The Mother of Modern Cosmology: The Deaf Woman From Poor Birth, Lights Up the Universe with a Candle

 　　In 1920, the U.S. government conducted a census in Cambridgeshire, Massachusetts. A census taker goes into a poorer neighborhood and goes door-to-door to check how many people live there and what their occupations are.

　　He knocked on the door of a family in the community and saw a mother and daughter who depended on each other. The daughter, a deaf woman, had a hard time figuring out what the census taker was up to. When asked about her profession, she answered "scientist".

　　The census taker just laughed. In the United States at the beginning of the 20th century, scientists were the exclusive domain of men, and almost no women could get a Ph.D. So he couldn't believe that a deaf woman living in a poor neighborhood could be a scientist.

　　Her name is Henrietta LeWitt, the mother of modern cosmology. She is the only person in history who can be called the mother of a certain great discipline.

　　In 1868, LeWitt was born in a pastor's family in Massachusetts, USA. At the age of 20, she passed the rigorous examination and was admitted to Radcliffe Women's College (one of the famous Seven Sisters College, which was later merged by Harvard University). In 1892, LeWitt graduated with his bachelor's degree. Then, according to the tradition at the time, she took a boat to Europe and started her graduation trip.

　　But the sky is unpredictable. During this trip, a sudden and serious illness damaged her eyesight and hearing. Although her eyesight improved, her hearing deteriorated until she eventually became deaf. For nearly 30 years since then, she has been in a state of serious illness.

　　After returning from his trip, LeWitt decided to pursue a master's degree in astronomy. She joined Edward Pickering's Harvard University Observatory in 1893 as a "Harvard Calculator".

　　Unfortunately, LeWitt's health was a serious drag on her studies. Frail and sick, LeWitt had to call in sick every now and then, which made her scientific work fragmented. Of course, this also made her mentor Pickering quite dissatisfied.

　　In 1896, LeWitt realized that it was impossible for her to complete her studies. In desperation, she chose to give up and left the Harvard University Observatory, which lasted for 6 years.

　　Six years later, in 1902, LeWitt wrote Pickering a letter. In the letter, LeWitt mentioned that due to her hearing impairment, she was no longer competent for other jobs, so she wanted to apply to return to the Harvard Observatory. Pickering agreed. But this time, Pickering was smart enough not to let LeWitt participate in the observatory's most important stellar classification work, and sent her to study Cepheid variables alone. What happened next is as legendary as Moses parted the Red Sea with his staff.

　　Since 1904, LeWitt has been finding new Cepheids in the Magellanic Clouds at an astonishing rate. She found it so fast that an astronomer wrote to Pickering: "Miss LeWitt is a master at finding variable stars. We didn't even have time to record her new discovery."

　　In 1908, LeWitt wrote in the "Harvard Observatory Yearbook" published a paper on the Internet, announcing that he had found a total of 1777 Cepheid variable stars in the Magellanic Cloud (in the previous 100 years, the total number of Cepheid variable stars found by people was only a few dozen). This astonishing number immediately caused a sensation in the astronomy community, and even got a report in the famous "Washington Post".

　　But the number of sensational Cepheid variable star discoveries is nothing compared to the most valuable part of this paper.

　　At the end of this paper, LeWitt selected 16 Cepheid variable stars located in the Small Magellanic Cloud, and listed their light change periods (the time to complete a round of light and dark alternation) and apparent magnitudes in a table. For this table, she left a comment like this: "It is worth noting that the brighter the variable star, the longer its light change period."

　　Four years later, in 1912, LeWitt perfected this conclusion. She selected 25 Cepheid variables located in the Small Magellanic Cloud and plotted them on a graph with brightness on the X-axis and photoperiod on the Y-axis. As a result, these 25 Cepheid variable stars just lined up in a straight line. Based on this, LeWitt asserted that "the brightness of a Cepheid variable star is proportional to its light variation period".

　　In order to understand the weight of this seemingly ordinary sentence in the history of astronomy, you can imagine a wasteland that has been frozen for an unknown number of years. meter of beautiful flowers.

　　This statement came to be known as LeWitt's law. It was this earth-shattering LeWitt's law that opened the door to modern cosmology.

　　You may feel a little confused: "Why can such a simple law start a whole new discipline?" The answer is that it provides a new method of distance measurement, which is the famous standard candle.

　　In order to introduce the basic principle of measuring distance with standard candles, let us start with a phenomenon that is quite common in daily life. A candle is bright when viewed close up, but dim when viewed from a distance. This is because the brightness of the candle we see depends on the number of photons emitted by the candle and hitting our eyes. The more photons that are injected, the brighter the candle will appear; conversely, the dimmer it will appear.

　　The total number of photons emitted by a candle whose absolute brightness remains constant also remains constant. These photons spread outward in a spherical shape. So at a certain place, the number of photons received per unit area is inversely proportional to the square of the distance from the candle here. This means that the apparent brightness of a candle we see at a certain location is inversely proportional to the square of the distance from the candle there. For example, if the distance is increased by 4 times, the apparent brightness of the candle will be reduced to 1/16 of the original.

　　In this way, we can use candles to measure distance: first, put a candle in a relatively close place, and measure its distance and apparent brightness. Then, place another candle of the same absolute brightness at a particularly distant place, and measure its apparent brightness. Finally, using the inverse relationship between the apparent brightness and the square of the distance, the particularly far distance can be calculated.

　　The principle of using candles to measure distances, the principle of measuring distances with candles, is also applicable in the sky. For this reason, it is necessary to find a special celestial body in the sky that can meet the following two conditions at the same time:

　　① It is so bright that it can be seen even if it is far away;

　　② Its optical properties are stable, and its absolute brightness is fixed. If such a celestial body can be found, we can use it as a candle to measure distances on a cosmological scale. This special celestial body that can be used as a candle is the so-called standard candle.

　　Knowing the concept of standard candlelight, let's talk about the significance of LeWitt's law. Since the Cepheids selected by LeWitt are all located in the Small Magellanic Cloud, it can be approximated that they are all at the same distance from the Earth. Therefore, as long as their apparent brightness is equal, their absolute brightness must be equal.

　　LeWitt's law says that the absolute brightness of a Cepheid variable star is proportional to its light variation period. This means that as long as Cepheid variable stars with exactly the same light change period are selected, a batch of celestial bodies with exactly the same absolute brightness can be obtained.

　　So Lewitt's law means that the Cepheid variable star meets the two conditions of the standard candle, which is a true standard candle. This is also the first standard candle found in human history.

　　The discovery of standard candles provides a new method for measuring distant cosmological distances. Maybe you still have questions: "Why can the discovery of a new distance measurement method create a new discipline of modern cosmology?" In fact, it was this discovery that shook Copernicus' heliocentric theory.

　　Let's say a few more words about LeWitt. Very sadly, LeWitt's story does not have a happy ending.

　　Not long after discovering that Cepheids were standard candles, LeWitt left again due to stomach surgery. By the time she returned, Pickering had assigned her a new job: measuring the Polaris sequence, that is, analyzing the spectra of 96 stars near Polaris. This is the subject that Pickering likes most and wants to complete over the years.

　　It makes perfect sense for a manager to assign his best employees to the challenges he finds toughest. But for an astronomer of LeWitt's caliber, the arrangement was absurd, tantamount to forcing a mid-year Michael Jordan to give up his basketball career to play in a low-level baseball league. What's more cruel is that LeWitt, who is under the roof, has no choice at all. Since then, she has never been able to return to the study of standard candles.

　　And Pickering's selfish decision also set the world's research on variable stars back for decades.

　　Ironically, despite single-handedly creating a new discipline that has since fed thousands of Ph.D.s, LeWitt himself was never able to earn a Ph.D. Many years later, she is still a Harvard computer with half the salary of a man.

　　In 1921, LeWitt, who had always been dependent on his mother, fell ill again. This time it was incurable cancer. On December 12 of that year, she left on a rainy night. In her will, she left all her property to her mother. The estates were worth a total of $315, just enough to buy eight rugs.

　　This is the discoverer of the standard candle, the gravedigger of Copernican's heliocentric theory, the mother of modern cosmology, and the final outcome of a great female scientist. Despite illness, deafness, poverty, loneliness, being manipulated, despised, and forgotten, she is still an eternal candle that illuminates the entire universe.