Cameron Miranda
Edwin Hubble is credited with the discovery of Hubble's Law, which he published in 1929. The law observes that galaxies move away from Earth at speeds proportional to their distance, meaning the further a galaxy is from Earth, the faster it moves away. Hubble's Law is considered the first observational basis for the expansion of the universe and is often cited as evidence for the Big Bang model. Hubble's work built on the findings of astronomer Carl Wilhelm Wirtz, who in 1922 and 1924 deduced that more distant galaxies recede faster from the observer. In 1927, two years before Hubble published his work, Belgian priest and astronomer Georges Lemaître published research deriving what is now known as Hubble's Law.
| Characteristics | Values |
|---|---|
| Name of the Law | Hubble's Law, also known as the Hubble-Lemaître Law |
| Year of Creation | 1929 |
| Creator | Edwin Hubble |
| Other Names | Georges Lemaître, Alexander Friedmann, Carl Wilhelm Wirtz |
| Basis of the Law | Correlation between recessional velocity and distance from Earth |
| Equation | v = H0D, v = Hd, v = HD |
| Hubble Constant | H0, lies between 67 and 73 kilometres per second per megaparsec (km/sec/Mpc) |
| Hubble Parameter | H, varies with time |
| Hubble Flow | Motion of astronomical objects due to the expansion of the universe |
| Importance | First observational basis for the expansion of the universe, evidence for the Big Bang model |
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What You'll Learn
Edwin Hubble's 1929 paper
Hubble's paper introduced the concept now known as Hubble's Law, which states that there is a linear relationship between the recessional velocity of a galaxy and its distance from Earth. In other words, the farther a galaxy is from Earth, the faster it moves away. This law is considered the first observational basis for the expansion of the universe and is often cited as evidence for the Big Bang model.
To support his findings, Hubble carefully measured the distance and Doppler shift of numerous galaxies with the help of his assistant, Milton Humason. By comparing the apparent brightness of stars with their actual brightness, they were able to determine the distance to these galaxies. This built upon Hubble's earlier work in the 1920s, where he captured multiple photographs of spiral nebulae to identify changes over time.
Hubble's 1929 paper also acknowledged the contributions of previous researchers, including Harlow Shapley, who had measured the distance across the Milky Way, and Georges Lemaître, a Belgian priest and astronomer who had independently derived Hubble's Law in 1927. Despite this prior work, Hubble's name became synonymous with the law due to Lemaître's humility and the relative obscurity of his publication.
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Georges Lemaître's 1927 paper
In 1927, Georges Lemaître, a Belgian priest, astronomer, and academic, published a paper in the "Annals of the Scientific Society of Brussels". This paper, titled "A homogeneous Universe of constant mass and growing radius accounting for the radial velocity of extragalactic nebulae", presented the first explanation of the observations on the recession velocities of galaxies.
Lemaître's work was based on Albert Einstein's theory of relativity, and he argued that the equations implied that the universe was not static. He connected this prediction to a simple relation of proportionality between the average recessional velocity of galaxies and their distance from Earth. In other words, the farther a galaxy is from Earth, the faster it moves away. This became known as Hubble's law, or the Hubble-Lemaître law, after Edwin Hubble published a paper in 1929 based on better and more abundant data than Lemaître had access to.
Lemaître's 1927 paper had little impact at the time, and Hubble was unaware of Lemaître's work when he made the same discovery independently. An English translation of Lemaître's paper was published in 1931, but it omitted his estimate of the "Hubble constant". It was only recently discovered that Lemaître himself removed those paragraphs, opting to cite the stronger results published by Hubble in 1929.
Lemaître's work was a groundbreaking contribution to the field of cosmology, and he is considered a pioneer in the use of computers in physics research. He was also an expert in the cosmic consequences of Einstein's theory of gravity and played a significant role in the development of the Big Bang theory.
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Hubble's Law only works for distant galaxies
Edwin Hubble's work, published in 1929, is credited with the discovery of Hubble's Law, also known as the Hubble-Lemaître Law. This law is based on the observation that galaxies are moving away from Earth at speeds proportional to their distance. In other words, the further a galaxy is from Earth, the faster it moves away.
Hubble's Law is considered the first observational basis for the expansion of the universe and is often cited as evidence for the Big Bang model. It is expressed by the equation v = H0D, where H0 is the Hubble constant, and D is the proper distance to a galaxy.
However, it is important to note that Hubble's Law only works for distant galaxies. For nearby galaxies, stars within the Milky Way, and objects in our Solar System, the relationship between distance and velocity does not hold. This discrepancy is due to the ""peculiar velocity"" of the galaxy, which is its actual velocity through space unrelated to the expansion.
For distant galaxies, their peculiar velocities are relatively small, so they still follow Hubble's Law. In contrast, for nearby galaxies, their peculiar velocity is larger than their velocity from the expansion, causing it to dominate their total velocity. As a result, these galaxies deviate from the expected relationship between velocity and distance described by Hubble's Law.
The Hubble Space Telescope was launched to measure the Hubble constant more precisely, as this constant allows for the calculation of the distance to any galaxy by measuring its velocity.
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Hubble's Law and the Big Bang
Hubble's Law, also known as the Hubble-Lemaître law, was formulated by Edwin Hubble in 1929. It observes that galaxies are moving away from Earth at speeds proportional to their distance, meaning that the further a galaxy is from Earth, the faster it is moving away. This discovery is considered the first observational basis for the expansion of the universe, and it is often cited in support of the Big Bang model.
The motion of astronomical objects due solely to this expansion is known as the Hubble flow. The law can be depicted in a ""Hubble diagram", where the velocity of an object is plotted with respect to its distance from the observer. A straight line with a positive slope on this diagram visually represents Hubble's Law. The law can also be expressed mathematically as v = H0D, where H0 is the Hubble constant, and D is the proper distance to a galaxy.
The discovery of Hubble's Law was preceded by several important contributions. In 1922, Alexander Friedmann derived his Friedmann equations from Einstein's field equations, demonstrating that the universe might be expanding at a calculable rate. In 1922 and 1924, astronomer Carl Wilhelm Wirtz deduced from his data that more distant galaxies recede faster, indicating a relationship between galaxy size, brightness, and recessional velocity. In 1927, two years before Hubble's publication, Georges Lemaître, a Belgian priest and astronomer, published research independently deriving what is now known as Hubble's Law. Lemaître used new observations of the distance and speed of galaxies to support his claim that the universe could expand, but his work went largely unnoticed at the time.
Hubble's Law is considered a fundamental relationship between recessional velocity and distance. It plays a crucial role in cosmology, enabling scientists to calculate the age of the universe and providing evidence for the Big Bang theory. The expansion of the universe, as described by Hubble's Law, helps resolve Olbers' paradox, which questions why the night sky is dark if the universe is infinite and filled with stars. In an expanding universe, distant objects move away from us, causing their light to be redshifted and diminished in brightness by the time it reaches us. This explains the darkness of the night sky and supports the concept of a finite universe with a finite age, as proposed by the Big Bang theory.
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Calculating the Hubble constant
Hubble's law, also known as the Hubble-Lemaître law, describes the linear relationship between the redshift of a galaxy and its distance from Earth. This law is fundamental to the field of cosmology, allowing scientists to calculate the age of the universe and providing evidence for the Big Bang model.
The Hubble constant, denoted as H0, represents the constant of proportionality between the "proper distance" D to a galaxy and its speed of separation v. This constant is given by the equation: v = H0D. While the Hubble constant remains constant at any given moment, the Hubble parameter H, of which H0 is the current value, varies over time.
To calculate the Hubble constant, Hubble and his colleague Milton Humason utilised their observations to establish the mathematical relationship between the distance to a star and its speed of recession from Earth. Hubble's initial estimate was approximately 500 km/s/Mpc, which is about seven times the value currently accepted by astronomers.
Over the years, astronomers have refined Hubble's methods and developed new techniques, leading to more accurate measurements. The Hubble Space Telescope, for instance, was dedicated to observing Cepheid variables in distant galaxies to determine the Hubble constant with greater precision. Despite these advancements, the precise value of the Hubble constant remains a subject of debate among scientists.
One challenge in calculating the Hubble constant is the distinction between distant and nearby galaxies. Hubble's law applies specifically to distant galaxies, as their peculiar velocities are relatively small compared to the velocity resulting from the expansion of the universe. In contrast, the peculiar velocities of nearby galaxies dominate their total velocity, causing deviations from the expected relationship between velocity and distance.
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Frequently asked questions
Hubble's Law was created in 1929 by Edwin Hubble.
Edwin Hubble was an astronomer who made many key discoveries using the 100-inch Wilson telescope at Mount Wilson Observatory, Southern California.
Hubble's Law is the observation that galaxies are moving away from Earth at speeds proportional to their distance.
The equation for Hubble's Law is v = H0D, with H0 being the Hubble constant and D being the proper distance to a galaxy.
Hubble's Law is significant because it provides evidence for the Big Bang model and allows scientists to calculate the age of the universe. It is also used to calculate the distance to galaxies.
