Marking 135 years since the birth of Edwin Hubble, who revealed that the universe is much larger than the Milky Way, showed that it is steadily expanding, and laid the foundation for the Big Bang theory.
In 2011, the Nobel Prize in Physics was awarded to three astronomers from the United States and Australia for their discovery that the universe is expanding at an accelerated rate. Yet less than a century ago, even the idea that the universe is expanding was far from obvious. Basic facts that we now take for granted—such as the universe being vastly larger than our own Milky Way galaxy and that our galaxy is just one of countless others—remained unclear until the observations of the man often hailed as one of the most influential astronomers of the 20th century, born 135 years ago this week.
Despite his fame, Hubble never abandoned hands-on scientific work. Edwin Hubble at the telescope on Mount Wilson | Source: Science Photo Library
Athlete and Lawyer
Edwin Powell Hubble was born on November 20, 1889, in a small town in Missouri. From a young age, he excelled in sports, particularly basketball and athletics, and also played football and boxed. At the same time, he developed a keen interest in science, especially astronomy, inspired in part by his grandfather, who built him a telescope for his eighth birthday. Hubble graduated from high school in Illinois, where his family had moved.
When Hubble expressed his desire to study science at university, his father insisted he pursue law to ensure a stable income. Complying with his father's wishes, Hubble enrolled in the University of Chicago to study law while also taking courses in physics and astronomy. To support himself during his undergraduate studies, he tutored students and worked as an assistant in the laboratory of physicist Robert Millikan, who would later receive the 1923 Nobel Prize in Physics for his work on the charge of the electron and confirmation of the photoelectric effect.
With Millikan’s recommendation, Hubble earned a prestigious scholarship in 1910 to study at Oxford University in the UK. He continued his law studies there, honoring a promise to his dying father, but also pursued a master’s degree in Spanish. His studies were interrupted by his father’s death in 1913, prompting his return to the United States. The family had moved to Kentucky, where Hubble briefly practiced law. He later taught mathematics, physics, and Spanish at a high school, helping to support his mother and siblings, while also coaching the school’s basketball team.
A year later, once the family’s financial situation had stabilized, Hubble finally pursued his dream. He completed a master’s degree and a doctorate in astronomy at the University of Chicago. His doctoral research focused on studying and classifying nebulae—objects that appear as hazy patches in the night sky, distinct from the bright points of stars.
As Hubble was completing his doctorate, he was invited to join the staff of the Mount Wilson Observatory in California, then the most advanced observatory of its kind. However, with the United States entering World War I, Hubble volunteered for the army. He completed officer training and, in his limited free time, fulfilled the requirements for his doctorate. He was deployed to France as an officer in an infantry battalion, eventually reaching a rank equivalent to lieutenant colonel. His unit arrived after the fighting had ended, so they did not see combat. After the war, Hubble spent an additional year at the University of Cambridge in the UK before returning to the United States in 1919. At age 30, he began his independent research at Mount Wilson Observatory.
An outstanding athlete. Hubble as the coach of a high school basketball team in Kentucky, 1914 | Source: Science Photo Library
The Great Debate
At the beginning of the 20th century, and even earlier, astronomers were divided over the nature of nebulae. One camp argued these were relatively small objects located within the Milky Way—possibly at its outer edges—and that the Milky Way was the sole galaxy in the universe, with virtually no stars existing beyond it. The opposing camp argued that the universe was far larger and that nebulae were actually distant galaxies. To address this debate, representatives from both perspectives were invited to the "Great Debate," in 1920, a public confrontation held in Washington, D.C. Each side presented their views and the supporting scientific evidence, but the debate ended inconclusively, leaving the controversy unresolved.
Determined to find definitive evidence to resolve the debate, Edwin Hubble continued his meticulous observations of nebulae. In 1923, he identified a Cepheid variable star in the Andromeda Nebula (known as M31)—a star whose brightness as observed from Earth varies cyclically. This discovery was made possible by a breakthrough a few years earlier by astronomer Henrietta Leavitt, who demonstrated that Cepheid variable stars could serve as markers for measuring cosmic distances.
Hubble calculated that the star he had discovered—and by extension, the Andromeda Nebula—was approximately 900,000 light-years from Earth. At the time, the Milky Way’s diameter was estimated to be between 100,000 and 300,000 light-years, making it clear that Andromeda was far beyond its boundaries and must be a separate galaxy. Today, the Milky Way's diameter is estimated at about 100,000 light-years, and Andromeda is thought to be 2.5 million light-years away.
Soon after, Hubble identified more Cepheid stars in Andromeda and other nebulae. Distance measurements consistently showed that these objects were far beyond the presumed boundaries of the Milky Way. In early 1925, Hubble presented his findings at an astronomers' conference in Washington, shortly after the discovery was even reported in The New York Times: "Confirmation of the view that spiral nebulae, which appear in the heavens as whirling clouds, are in reality distant stellar systems or 'island universes,' has been obtained by Dr. Edwin Hubbell of the Carnegie Institution’s Mount Wilson Observatory," the newspaper wrote, not forgetting to misspell the astronomer's name. The photographic plate on which Hubble marked the variable star with the handwritten annotation "VAR!" is preserved to this day at the Carnegie Institution, which operates the Mount Wilson Observatory.
Hubble's discovery definitively resolved the long-standing Great Debate, demonstrating that our galaxy is not the entire universe but merely one among countless others in the vast cosmos.
A variable star that reshaped our view of the universe. Hubble holding a photograph of the Andromeda Galaxy | Source: Science Photo Library
The Expanding Universe
Alongside Hubble's work, another astronomer, Vesto Slipher, also made a significant breakthrough. Using a spectroscope—a tool that analyzes the composition of light from stars and celestial objects—Slipher measured the velocities of nebulae. This instrument allowed him to determine their velocity and direction through the Doppler effect. According to this effect, waves approaching the observer appear compressed, with a frequency higher than their "true" frequency, while waves moving away appear stretched and lower in frequency.
This phenomenon is observable in sound waves, such as the change in pitch of an ambulance siren as it approaches or moves away. Similarly, it can be observed in light waves at much higher speeds. Objects moving toward us cause the light spectrum to shift to shorter wavelengths, appearing bluer. Conversely, objects moving away shift toward longer wavelengths, appearing redder. Slipher discovered that many nebulae - now understood to be galaxies (as the term "nebula" has since acquired a different meaning in astrophysics)—are receding from us at tremendous speeds, sometimes reaching thousands of kilometers per second.
Scientists, who until then had believed the universe to be more or less static, began developing bold theories to explain the motion of galaxies. Hubble, by then a world-renowned astronomer, felt compelled to tackle the problem using the advanced telescope at Mount Wilson.
Einstein Was Convinced
After confirming Slipher's observations, Hubble began searching for a relationship between the velocities of galaxies and their distances from us. He was assisted in this effort by his colleague Milton L. Humason, who started his career as a mule driver during the construction of the Mount Wilson Observatory. Humason later worked as a janitor and maintenance worker, gradually becoming involved in research. Eventually, he joined the observatory’s staff and even earned a doctorate in astronomy, despite never having finished high school.
The observations by Hubble, Humason, and their colleagues soon revealed a definitive relationship between the velocities of galaxies and their distances, which became known as Hubble's Law: the farther a galaxy is, the faster it is receding. Published in 1929, this discovery had two profound scientific implications that transformed the field of astronomy and our understanding of the universe. First, the observation that galaxies are continually moving away from one another at high speeds implied that the universe is not static but expanding—similar to an inflating balloon. Second, the tight relationship between speed and distance suggested that all galaxies were once at the same point in space. Hubble calculated that this would have occurred approximately 1.8 billion years ago, laying the groundwork for what would later be known as the Big Bang theory. Today, it is widely accepted that the Big Bang occurred 13.8 billion years ago.
Hubble was not the first to propose the idea of an expanding universe or that the cosmos had a specific starting point. Earlier scientists, such as Georges Lemaître from Belgium and Alexander Friedmann from Russia, had predicted that the universe might be expanding and had originated from a singular point. However, their work received little recognition during their lifetimes.
A much more famous scientist, Albert Einstein, published his theory of general relativity in 1915. Einstein realized that his equations predicted the possibility of the universe collapsing under its own gravity. Convinced that the universe was static, he introduced the cosmological constant to his equations - a repulsive force intended to counteract gravitational collapse. In 1931, during a visit to Mount Wilson, Einstein declared that he had been convinced by Hubble's observations and acknowledged that Friedmann and Lemaître had been correct in their predictions. He removed the cosmological constant from his equations and later referred to it as "the greatest blunder of my life." The Big Bang theory continued to gain scientific support until it was finally confirmed by measurements of cosmic background radiation in the early 1990s.
A prominent and famous couple. Edwin Hubble and his wife Grace (Burke) | Photo: San Marino Tribune
A Star in Hollywood's Sky
Alongside his scientific work, Edwin Hubble enjoyed a vibrant and glamorous social life. In 1924, he married Grace Burke, the daughter of an exceptionally wealthy California banker. Her prominent social standing and his scientific achievements made them one of Hollywood's most recognizable couples, especially given the Mount Wilson Observatory’s proximity to the entertainment capital. The couple frequently mingled with actors and other celebrities, hosting many distinguished guests at the observatory. In 1937, Hubble was honored as a guest at the Academy Awards ceremony, where he was introduced to the audience and received applause from Hollywood's brightest stars.
Despite his fame, Hubble remained committed to his astronomical work. He continued his studies of distant galaxies and even identified an asteroid within our solar system. His contributions to astronomy extended to publishing two important books: The Realm of the Nebulae and The Observational Approach to Cosmology.
It was only during World War II that Hubble temporarily stepped away from cosmology, relocating from California to military laboratories in Maryland. There, he enlisted as a civilian in ballistic research for the army. For his contributions to the war effort, he received the Legion of Merit (LOM) award, a military award of the US Armed Forces.
In 1949, Hubble suffered a heart attack but soon returned to work. Four years later, on September 28, 1953, just weeks before his 64th birthday, he died unexpectedly from a blood clot in his brain. At his request, no funeral was held, and he was buried in an unmarked grave known only to his wife. "It is difficult to estimate the loss to astronomy," read an obituary in the astronomical journal The Observatory.
A star among Hollywood's stars. The 1937 Academy Awards ceremony | Source: Oscars.org
A Lasting Legacy
For many years, Hubble campaigned against the Nobel Prize in Physics committee's refusal to recognize astronomy as a branch of physics, which excluded astronomers from eligibility for the prestigious award. Shortly before his death, the committee finally acknowledged his position, and in 1953 he was even nominated for the prize. However, the decision came too late for him: he did not live to hear about it, and even if the committee had selected him, the Nobel Prize would not have been awarded posthumously.
During his lifetime, Hubble received numerous other awards and left a profound mark on the field of cosmology. Not only is Hubble’s Law named after him, but so is the Hubble Constant, which allows for the calculation of the universe's expansion rate and, by extension, its age. Although the value of the constant has been refined over the years with improved measurements, the underlying principle remains valid. Hubble also developed the Hubble classification system for categorizing galaxies based on their shapes. Additionally, a crater on the Moon and an asteroid bear his name. His portrait appeared on a U.S. postage stamp, and several biographies have been written about him.
An immense contribution to the study of the universe. The space shuttle Discovery deploying the Hubble Space Telescope into orbit | Illustration: NASA
At the end of the 20th century, Hubble received what is perhaps his most significant commemoration, ensuring that his name is known worldwide. The monumental space telescope launched into Earth's orbit in 1990 bears his name. Despite numerous challenges and malfunctions, the Hubble Space Telescope has been at the forefront of astronomy and astrophysics for over three decades, making groundbreaking contributions to our understanding of the universe. It serves as a fitting tribute to one of the greatest astronomers, who unraveled some of the universe's most profound mysteries.
The Extraordinary Hubble Space Telescope — A Discovery documentary: