Big History Project
- ACTIVITY: DQ Notebook 2.1
- WATCH: Why Cosmic Evolution Matters
- READ: Dr. Wu and the Left-Handed Universe – Graphic Biography
- READ: Claudius Ptolemy
- READ: Nicolaus Copernicus
- READ: Galileo Galilei
- READ: Isaac Newton
- READ: Henrietta Leavitt
- READ: Edwin Hubble
- READ: Standing on the Shoulders of Invisible Giants
- READ: The Missing Link? — The Maragha Observatory
- Quiz: How Did Our Understanding of the Universe Change?
Evidence for an Expanding Universe
By Cynthia Stokes Brown
In the course of five years, Edwin Hubble twice changed our understanding of the Universe, helping to lay the foundations for the Big Bang theory. First he demonstrated that the Universe was much larger than previously thought, then he proved that the Universe is expanding.
Early Life and Education
Edwin Powell Hubble, the son of an insurance executive, was born in Marshfield, Missouri, on November 20, 1889, and moved to Wheaton, Illinois, a suburb of Chicago, soon after. Growing up, he was more outstanding as an athlete than as a student, although he did earn good grades in every subject (except spelling). He won seven first-places and a third place in a single high school track-and-field meet in 1906. That year he also set the Illinois high school record in the high jump.
At the University of Chicago, Hubble studied mathematics, astronomy, and philosophy — and played for the school’s basketball team. He graduated with a bachelor of science in 1910, and then spent 1911 to 1914 earning his master’s as one of Oxford University’s first Rhodes scholars. Though he studied law and Spanish there, his love of astronomy never diminished.
At Yerkes Observatory
Moving back to the United States, Hubble enrolled as a graduate student at the University of Chicago and studied the stars at their Yerkes Observatory in Wisconsin. It was here that he began to study the faint nebulae that would be the key to his greatest discoveries. After receiving his doctorate in astronomy from the University of Chicago in 1917, he won an offer to join the staff at the prestigious Mount Wilson Observatory, near Pasadena, California.
At Mount Wilson Observatory
Arriving at Mount Wilson in 1919, he joined an astronomy establishment that was just beginning to grasp cosmic distances. The key to that effort was work that had been done studying Cepheid variable stars, roughly a decade earlier, by Henrietta Swan Leavitt at Harvard. These stars brighten and dim in a predictable pattern, and their distance from us can be worked out by measuring how bright they appear to us.
Another astronomer at the observatory, Harlow Shapley, built on Leavitt’s findings and shocked the world with his conclusions about the size of the Milky Way. Using the Cepheid variables, Shapley judged that the Milky Way was 300,000 light years across — 10 times bigger than previously thought.
Hubble began his work at Mount Wilson just as the new 2.56-meter Hooker Telescope, the most powerful on Earth, was completed. With it, he was able to peer into the sky with greater detail than anyone had previously. After years of observation, Hubble made an extraordinary discovery. In 1923 he spotted a Cepheid variable star in what was known as the Andromeda Nebula. Using Leavitt’s techniques, he was able to show that Andromeda was nearly 1 million light years away and clearly a galaxy in its own right, not a gas cloud.
Hubble then went on to discover Cepheids in multiple nebulae, and proved, in a 1924 paper called “Cepheids in Spiral Nebula,” that galaxies existed outside our own. Overnight, he became the most famous astronomer in the world, and people everywhere had to get used to the fact that the Universe was far vaster than anyone had imagined. Shapley, for one, was shaken by the news. He wrote Hubble, “I do not know whether I am sorry or glad to see this break in the nebular problem. Perhaps both.”
In 1926, while developing a classification system for galaxies, Hubble discovered an odd fact: Almost every galaxy he observed appeared to be moving away from the Earth. He knew this because the light coming from the galaxies exhibited redshift. Light waves from distant galaxies get stretched by the expansion of the Universe on their way to Earth. This shifts visible light toward the red end of the spectrum.
Building on the work of Vesto Slipher, who measured the redshifts associated with galaxies more than a decade earlier, Hubble and his assistant, Milton Humason, discovered a rough proportionality between the distances and redshifts of 46 galaxies they studied. By 1929 they had formulated what became known as Hubble’s Law. Hubble’s Law basically states that the greater the distance of a galaxy from ours, the faster it recedes. It was proof that the Universe is expanding.
It was also the first observational support for a new theory on the origin of the Universe proposed by Georges Lemaitre: the Big Bang. After all, an expanding Universe must once have been smaller.
Hubble achieved scientific superstardom for his discoveries and is still considered a brilliant observational astronomer. He ran the Mount Wilson Observatory for the rest of his life, popularized astronomy through books and lectures, and worked to have astronomy recognized by the Nobel Prize committee.
He also played a pivotal role in the design and construction of the Hale Telescope, on Palomar Mountain, California. At 5.08 meters, the Hale was four times as powerful as the Hooker Telescope and existed as the most advanced telescope on Earth for some time. After its completion in 1948, Edwin Hubble was given the honor of first use. When asked by a reporter what he expected to find, Hubble answered: “We hope to find something we hadn’t expected.”
For Further Discussion
Think about the following question and write your response and any additional questions you have in the Questions Area below.
How did Hubble’s work support the Big Bang theory?
Want to join the conversation?
- I still don't get how it is proof that the universe is expanding.(5 votes)
- Think of it this way: Light waves from something that is moving away from an observer very fast are "stretched out." Wavelength determines color. The more stretched-out the wavelength is, the more toward the red end of the spectrum its light appears.
Hubble was first able to demonstrate that some objects were much further away that others from us, and then able to show that the further away they were, the more red-end of the spectrum they appeared. That leaves two possibilities, either (for reasons that are unfathomable) everything in the universe has its color influenced by where it is in relationship to us or (far more likely) the universe is expanding.(11 votes)
- Considering that the universe is ever expanding – there must be a point or area in space where it all began and if such is the case, it would seem that there is also a point or area in space that now is totally void of matter. I believe such an area would further support the Big Bang Theory. Have we found such a place or evidence of such?(6 votes)
- The fact that matter in the universe seems to be rather evenly distributed shows us that we are mistaken in thinking of the big bang as some sort of explosion from a central point. It is true that, if this were the case, we would find a lot less matter at the center of the universe as you suggested, but this is not what we in fact see. The modern inflationary model gives us some explanation for why the distribution of matter is as uniform as we find it. My grasp of the subject is far too tentative to attempt represent it either clearly or accurately but searching online you might be able to find more resources regarding the inflationary model. It seems it is this the model the creator of Big History has in mind from the few videos I have watched so far.(4 votes)
- So we were able to find out how old the Universe was when figuring out it’s rate of expansion correct? And yet over time didn’t Universe expand at different rates?(2 votes)
- "Hubble then went on to discover Cepheids in multiple nebulae, and proved, in a 1924 paper called “Cepheids in Spiral Nebula,” that galaxies existed outside our own."
"Building on the work of Vesto Slipher, who measured the redshifts associated with galaxies more than a decade earlier..."
Does anyone else find this confusing? Don't these two passages directly contradict each other? It says Hubble proved the existence of other galaxies and it was groundbreaking, but then says Slipher studied redshifted galaxies more than a decade earlier...(2 votes)
- Hubble's work supported the big bang theory because if the universe is expanding, it must have started expanding at some point in the past when the universe was smaller than it is now. This is basically the main idea of the big bang theory.(2 votes)
- He noticed that A) there are other Galaxies out there, and B) the galaxies are moving away from us. Which is backing up the theory that the universe is expanding, a theory connected with the Big Bang theory.(2 votes)
- His work showed galaxies and stars moving outward and away from our own galaxy at an increasing rate. If they are moving away we can assume that at one time they were much closer together.(2 votes)
- If the Universe is expanding, why did it have to start at a single point?(1 vote)
- Because if it is continuously expanding out then it has to have started somewhere. If you go back in time then it would have to eventually shrink into a singularity.(1 vote)
- "How did Hubble’s work support the Big Bang theory?"
It helped people understand how space expands, providing proof that the bing bang is actually accurate.(1 vote)