January 1, 1925: The Day We Discovered the Universe

By Corey S. Powell | January 2, 2017 11:09 am
Andromeda nebula, photographed at the Yerkes Observatory circa 1900. To modern eyes, this is clearly a galaxy. At the time, though, it was described as "a mass of glowing gas." (From the book Astronomy of To-Day)

The Andromeda nebula, photographed at the Yerkes Observatory around 1900. To modern eyes, this object is clearly a galaxy. At the time, though, it was described as “a mass of glowing gas,” its true identity unknown. (From the book Astronomy of To-Day, 1909)

What’s in a date? Strictly speaking, New Year’s Day is just an arbitrary flip of the calendar, but it can also be a cathartic time of reflection and renewal. So it is with one of the most extraordinary dates in the history of science, January 1, 1925. You could describe it as a day when nothing remarkable happened, just the routine reading of a paper at a scientific conference. Or you could recognize it as the birthday of modern cosmology–the moment when humankind discovered the universe as it truly is.

Until then, astronomers had a myopic and blinkered view of reality. As happens so often to even the most brilliant minds, they could see great things but they could not comprehend what they were looking at. The crucial piece of evidence was staring them right in the face. All across the sky, observers had documented intriguing spiral nebulae, swirls of light that resembled ghostly pinwheels in space. The most famous one, the Andromeda nebula, was so prominent that it was easily visible to the naked eye on a dark night. The significance of those ubiquitous objects was a mystery, however.

Some researchers speculated that the spiral nebulae were huge and distant systems of stars, “island universes” comparable to our Milky Way galaxy. But many others were equally convinced that the spirals were small, nearby clouds of gas. In this view, other galaxies–if they existed–were far out of sight, blue whales lurking in the far depths of the cosmos. Or perhaps there were no other galaxies at all, and our Milky Way was all there was: a single system that defined the entire universe. The dispute between the two sides was so intense that it prompted a famous 1920 Great Debate…which ended with an unsatisfying draw.

The correct picture of our place in the universe arrived just a few years later through the work of one of the most famous names in astronomy: Edwin Powell Hubble (no relation!). Starting in 1919, Hubble had established himself as one of the most patient and meticulous observers at Mount Wilson Observatory in California.  Mt Wilson, in turn, had just established itself as the premier outpost for astronomical research, home of the just-completed 100-inch Hooker Telescope—then the biggest in the world. It was the perfect combination of the right observer in the right place at the right time.

Hubble also benefited greatly from earlier research by Vesto M. Slipher of Lowell Observatory, one of the unsung heroes of modern cosmology. Slipher had found that many of the spiral nebulae were moving at enormous velocities, far faster than those of any known stars, and that the spirals were mostly traveling away from us. To Slipher, those peculiar velocities provided convincing evidence that they must be independent systems, driven by unknown mechanisms at work far outside our Milky Way. But Slipher lacked the necessary resources to prove his interpretation. What he needed was a giant telescope like the one Hubble was piloting on Mt Wilson. This is where our story kicks into high gear.

Edwin Hubble at the controls of the 100-inch telescope at Mount Wilson, circa 1922. (Credit: Huntington Library)

Edwin Hubble at the controls of the 100-inch telescope at Mount Wilson, circa 1922. (Credit: Huntington Library)

Always cautious when it came to theory and interpretation, Hubble focused his scientific attention on the spiral nebulae without overtly endorsing the “island universe” interpretation. He preferred to wait until he could be the one to step forward with definitive proof–or disproof, if that’s where the evidence pointed.

In 1922, another important piece of the puzzle fell into place. That year, Swedish astronomer Knut Lundmark observed what he believed were individual stars in the arms of the spiral nebula M33. Shortly after, John Duncan at Mount Wilson spotted dots of light that grew fainter and brighter in the same nebula. Could these be variable stars, similar to ones in the Milky Way but far dimmer owing to their enormous distance?

Sensing the answer was at hand, Hubble stepped up his efforts. He spent long nights on his favorite bentwood chair, guiding the movements of the riveted-steel mount of the Hooker telescope to cancel out Earth’s rotation. The effort paid off with highly detailed, long-exposure images of the Andromeda nebula. The mottled light of the nebula began to resolve itself into a multitude of luminous points, looking not like a smear of gas but like a vast hive of stars.

Clinching proof came in October of 1923, when Hubble spied the telltale flicker of a lone Cepheid variable star in one of Andromeda’s arms. This type of star grows brighter and dimmer in a regular and predictable way, with its intrinsic luminosity directly related to its period of variation. Simply by timing the 31-day cycle of this star as it slowly flickered, Hubble could deduce its distance. His estimate was 930,000 light years–less than half the modern estimate, but a shockingly large number at the time. That distance placed Andromeda, one of the brightest and presumably closest of the spiral nebulae, vastly outside the bounds of the Milky Way.

In principle, the Great Debate was settled then and there. Spiral nebulae were other galaxies, and our Milky Way was just one outpost within a staggeringly vast universe. And yet, still the story was far from over.

Ever cautious, Hubble pressed on for more and better evidence. By the following February, he had uncovered a possible second Cepheid in Andromeda, Cepheid variables in M33, and possibly in three other nebulae as well. Now that there could be no doubt, he wrote to his arch-rival Harlow Shapley—a leading proponent of the idea that the spiral nebula were small and nearby—to needle him with the news. “You will be interested to hear that I have found a Cepheid variable in the Andromeda Nebula,” the letter began.

Shapley needed to read no farther to understand the significance of Hubble’s words. “Here is the letter that destroyed my universe,” Shapley morosely told Cecilia Payne-Gaposchkin, then a doctoral candidate at Harvard, who was in his office when Hubble’s missive arrived. (Payne-Gaposchkin was another pivotal figure in modern astrophysics; by remarkable coincidence, her pioneering work on stellar spectra was completed on…January 1, 1925!)

Despite his obvious excitement at the Andromeda findings, Hubble was still reluctant to publish his results. For all his surface confidence, he was terribly concerned about making a grand pronouncement prematurely. Every time he walked down from the summit to attend the formal 5 P.M. dinners at the Monastery, Mt Wilson’s living quarters, Hubble had to face his astronomer brethren. Not all of them accepted the existence of other galaxies. Vain and intensely aware of his reputation, Hubble worried that he might end up looking the fool.

Adriaan van Maanen, a playful and well-liked Dutch astronomer at Mt Wilson, was in fact still vigorously arguing in the other direction. He was convinced that he had observed some of the spiral nebulae rotating, which was possible only if they were relatively small and nearby. Hubble found it unsettling to have a doubter in his own midst and held back until he was utterly sure of his results. (Van Maanen never figured out where he went wrong and refused to admit his mistake. Hubble finally reexamined his colleague’s photographic plates and declared that “the large rotations previously found arose from obscure systematic errors and did not indicate motion, either real or apparent, in the nebulae themselves.” In academic terms, it was a fiery rebuke.)

A single variable star, spotted by Edwin Hubble in the Andromeda nebula, completely changed our understanding of the scale of the cosmos. Discovery image at left; light curve of the star at right. (Credit: Carnegie Observatories)

A single variable star, spotted by Edwin Hubble in the Andromeda nebula, completely changed our understanding of the scale of the cosmos. Discovery image at left; light curve of the star at right. (Credit: Carnegie Observatories)

Word of Hubble’s discovery inevitably leaked out to the media. As a result, the first public announcement of his astronomical breakthrough was a small story that ran in The New York Times on November 23, 1924. The single greatest cosmic discovery of the past three centuries therefore debuted as a buried news item!

Still Hubble balked at formal publication. The noted stellar astronomer Henry Norris Russell pressed him to present his findings to a Washington, D.C., meeting of the American Association for the Advancement of Science, which offered a $1,000 prize for best paper. When Hubble still didn’t submit anything, Russell snorted, “Well, he is an ass. With a perfectly good thousand dollars available, he refuses to take it.” Then Russell opened his mail to find that Hubble’s paper had just arrived.

Now and only now do we get to the stunning public reveal. On January 1, 1925, Hubble remained in splendid isolation at Mount Wilson while Russell read his revolutionary paper about the existence of other galaxies to an enthusiastic crowd. Hubble shared the best-paper prize. His paper ended the Great Debate, and did much more. It quickly increased the size of the known universe by a staggering factor of 100,000. It set the stage for the discovery of the expanding universe and, by extension, an initial Big Bang (already hinted at in the nebula velocities logged by Slipher). If any date can be said to be the birthday of modern cosmology, this is it.

Oddly enough, it was Shapley, not Hubble, who suggested that astronomers should adapt their nomenclature to the new reality and call the external star systems “galaxies.” Hubble still carried within him the conservative views of the world he overthrew. He was also naturally inclined to disagree with any idea that came from his rival, Shapley. So it happened that Edwin Hubble, the man who proved that the Milky Way is but one of innumerable galaxies, forever called the objects by the archaic name “extra-galactic nebulae.”

As Hubble watched the cyclical flaring and dimming of the Cepheids in Andromeda, he extended the reach of the human mind in yet another way. He erased the lingering concern that stars lying at great distances from us might behave differently from those in our immediate celestial neighborhood. Now that scientists could examine stars in other galaxies, they could establish the constancy of the universe over space and time as well.

By modern reckoning, the Andromeda galaxy is 2.5 million light-years away, which means the light we see now started on its way earthward 2.5 million years ago. That is, we are seeing the stars in Andromeda that are not only 2.5 million light years away, but also living 2.5 million years in the past. Nevertheless, they look identical to nearby stars. As Edwin Hubble and other astronomers looked out to ever greater distances, they added more and more evidence for the principle of spatial and temporal uniformity. All across space and time, atoms seem to give off the same light and variable stars seem to follow the exact same physical laws.

This constancy of nature lent credibility to the search for a single set of overarching cosmic rules. Or, as Albert Einstein might have put it, it showed that God does not change the house rules of the cosmos. That was one hell of a birthday present for the human mind.

[Parts of this post are adapted from God in the Equation: How Einstein Transformed Religion by Corey S. Powell; Free Press, 2002]

MORE ABOUT: cosmology, Hubble
  • OWilson

    An excellent article that reminds us that less than a hundred years ago we did not understand our place in the great scheme of things.

    Hubble’s discoveries, prompted Sir James Jeans to pen his summary of science, “The Growth of Physical Science”, 1947 as it seemed that finally we knew everything worth knowing. (He called the 17th Century, “The century of Genius”)

    Coincidentally, that old tattered Cambridge University edition showed up in by mailbox this holiday from Amazon, which was a nice surprise, as I had given away at least 2 copies over the years!

  • http://firstlinemanager.info/ OJM

    It is so difficult for our minds to comprehend the vastness of space. We live in earth time and have no concept of cosmic time.

    • Tom Kaye

      It’s doubtful the cosmos has any concept of time either. Cosmic or otherwise.

  • Jossarian

    What is common misunderstanding about Edwin Hubble is that he is a founder of “Big Bang” theory. Reality is that he was claiming that there might be different explanation of his famous red-shift measurements.


    Hubble’s opinion published in Los Angeles Times on 31 December 1941:
    Astronomer Edwin P. Hubble says that after a six-year study, evidence does not support what we now call the Big Bang theory, according to the Associated Press. “The universe probably is not exploding but is a quiet, peaceful place and possibly just about infinite in size.”

    Possibly fiasco of still mainstream “Big Band” theory to explain constitution of 84% of mass in our Universe might finally trigger the paradigm change.

    • Corey S Powell

      Good point about Hubble and the Big Bang. Just as he resisted calling galaxies by their proper name, Hubble never felt truly comfortable with the physical meaning of his “redshift law.” He continued to refer to the “apparent” velocities of the galaxies and was personally displeased with the idea of the expanding universe. It often happens this way, that people who make revolutionary discoveries cannot fully absorb the implications of their own work.

      One clarification: Hubble’s 1941 paper and interview referred to the idea of cosmic expansion but not the Big Bang in the modern sense; that theory was not formulated until a decade later.

      Today, the evidence is overwhelming that the universe is expanding and that it began in a hot, extremely dense state. How the Big Bang occurred, and what (if anything) preceded it, remain entirely open questions, however.

  • joseph2237

    Established scientist are still at it, where they rather make up stuff like dark matter and energy when we have recently proved there are trillions of galaxies all because it doesn’t fit the standard model. If there is anything the observable universe has taught us is that our tiny crumbs of knowledge are insufficient to explain all that we are going to see and the challenge is to keep an open mind not a closed one.

    • Corey S Powell

      I’d say the story goes very much the other way. Many people were dubious about the existence of other galaxies…but that is what Hubble found. Few people expected to find evidence of gravity where there is no visible matter…but that is what Vera Rubin and others found. Almost nobody expected that the universe is dominated by dark energy…but that is what Schmidt, Perlmutter & colleagues found. All of these discoveries were the result of open inquiry and open minds. Today’s standard model is the result of a whole series of such surprising discoveries.

      No question, our current knowledge is incomplete. No question, too, scientists struggle all the time to see past the assumptions of their age. But the most remarkable part of this story is just how often people like Hubble, Rubin, etc, managed to succeed, through unfettered curiosity and intensely hard work.

      • joseph2237

        Hubble didn’t find dark energy or dark matter, it found that the universe is expanding then the scientist made up dark stuff just like they made up multi-verses, super symmetry, and gravity waves. There is plenty of matter in the 2 trillion galaxies and there is probably more. Stop making up stuff and spending billions to locate fabricated hunches.

      • joseph2237

        What Schmidt, Perlmutter & colleagues found was not dark energy. What they found was something they couldn’t readily explain so they jump to conclusions and when you do that you cut off all other possibilities which if wrong draws research down a blind ally and delays a correct explanation that could lead to predictions and answer other questions.

        • Corey S Powell

          You’re partially correct. Perlmutter, Schmidt et al did not discover a specific type energy (or anything else). They measured an accelerating expansion of the universe, and “dark energy” is just the catch-all phrase cosmologists use to describe the unknown thing causing the acceleration.

          If you look through the journals (easy these days by going to arXiv.org) you will see a very vigorous debate about the nature of dark energy, with a vast array of ideas in play. Here’s an intriguing new theory, just published:

          • joseph2237

            Thanks. I’ll try to remember.

  • Alberto Carvalhal Campos

    E vem mais novidades por aí.

  • Jim Speidel

    Alright you guys, I hope you are sitting down….
    What have we got that already permeates the entire universe ?
    What have we got that influences gravity?
    What have we got that acts like a liquid , (or a gas) ?
    Dark energy IS the Higgs field !
    They are one and the same.
    I have known this for several years now and have explained it to many people,(several who seem to get it). I have hesitated to put it out there under my own name because of the heaps of derision that are sure to follow. But if you will think about this for just a little while, it will be obvious to you too.
    Think of the Higgs field as a weather balloon. You put in some helium, the balloon rises. As the pressure decreases the balloon expands and it rises more. Usually when they get high enough they explode. The outer reaches of the universe may have exploded long ago,(or not), and we would not know anything about it for a very long time. Unlike the weather balloon with its limited supply of helium, the Higgs field has no such limitation. Black holes are proof of that.
    That’s my theory and I’m sticken’ to it.
    Please remember: You heard it here first !
    Jim Speidel, Raleigh NC

    • OWilson

      I love it!

      Since it is all theoretical speculation anyway, you could be right.

      If you postulated and invoked enough qualifiers, and assigned enough “properties”, you could actually “prove” it, too!

      • Tom Kaye

        Sometimes science requires a very fertile, even fervid, imagination!

        “Imagination is more important than knowledge.” Knowledge can’t tell you what you don’t know! Imagination can at least suggest it! “What would it look like if I could ride a beam of light?” A question only imagination could devise.

        “It is not the Known Unknowns that are the problem. But the Unknown Unknowns.” Donald Rumsfeld.

        Which is evidence that the mind is not bound by the “known” universe. “Flatland”, anyone?

        • agnes debinski

          That‘s a great quote! The one by Rumsfeld (obviously). What if somebody you know has an unknown unknown that could destroy you? – Now that‘s scary stuff! Save your soul and/or body before it‘s too late!

  • Louie Katorze

    “Every time he walked down from the summit to attend the formal 5 P.M.
    dinners at the Monastery, Mt Wilson’s living quarters, Hubble had to
    face his astronomer brethren.”

    Excuse me, Corey. “Formal” dinners? As in Hubble and his “astronomer brethren” dressed “formally” for dinner at 5 P.M. in the Mr. Wilson observatory mess room? Really? Not just special occasions? *Every* afternoon? White tie? Black tie?

    • OWilson

      In they days before jeans and T shirts, life among professionals was quite formal. An evening meal was a relatively formal affair, with strains of Mozart in the air.

      No coffee and pizza at your desk in those days.while you air guitar along with Metallica in you headphones.

      • Louie Katorze

        Do you “know” this or are you just riffing on Corey’s statement? Corey may not have meant black tie or white tie. “Formal” can mean different things to different people. “Formal” for me means wearing underwear and socks. I’m just interested whether Corey’s primary sources, if any, did indeed refer to dressing formally for dinner at a California mountain observatory in the Great Depression, and, if they did, just what those formalities were.

        • OWilson

          A “formal” dinner today means a dining table with chairs and a knife and fork. No T-shirt/bare feet :)

          Whatever the answer, the mode of dress was far less important than the world changing observations they were making.

          I was just curious about your fixation on dress. Are you a haberdasher by trade? :)

          • Louie Katorze

            Not a haberdasher (though I do admire Harry Truman). Social historian. The mode of dress might have more importance in this context than you believe. If these scientists put on evening dress to eat before they clocked in to their nightly shifts on the telescope that could tell us, I think, something about their attitudes towards established ideas and challenging new ideas. Something that might have impacted the interpretations they entertained about what they observed in the heavens. Formal wear in the evenings, outside of the normal venues where that would be expected (Stork Club, Greenwich, CT, Santa Barbara, CA, etc.) could say more about their individual intellectual climates than they might want to admit.

  • Volodimir Shevchenko

    Very touching. This is the true story of the triumph of science and reason. Thank you!

  • Johnny Rios

    Too bad scientist have not proven the existence of an infinite amount of universes. Our universe is just one of a never ending amount in the grander scheme of things that we cannot explain as of yet.

  • Rock Howard

    The comprehensive account of this story, including all relevant history leading up to the disclosure and a good bit of the aftermath, is told brilliantly in the book “The Day We Found The Universe” by Marcia Bartusiak, 2009. Highly recommended. I just finished my third reading of this book which should give you an indication of how much I enjoy it.

  • lawnmower

    Magnificent article. I really love it, thank you!

  • Donald Dade

    I laughed at “the universe as it truly is”. That is probably what they said before January 1st, 1925 as well… We just now discovered another lens with which to see the Universe, gravitational waves. Let’s cure our blindness a little more, before we declare that we now see things as they truly are.

  • John Lacey

    What great article. :-)

    Quite shocking as well, to learn that less than a hundred years ago we didn’t think there were other galaxies.

  • Nate Lazarus

    And yet most people still believe that humans are the center of creation.

  • Euclid22

    There is a new theory that the 80 million light years long DNA nebula is not a magnetic pull on a rope or rubber band gravitation twist but a single object’s appearance from “infinite wisdom” that resembles our DNA with telomeres on both ends. This 80 light years long object could be the source of our universe and no matter or anything else of which are visible to humans. This includes the nerve impulses of our taste, vision, hearing, smell, and feeling. With the passage of the all-encompassing Cosmic Background Radiation passing through 304,805 letters, creates the appearance of the universe, matter, energy, gravitation, and our free will lives. A theoretical ‘black hole” some 300 light years away supposedly caused this one of a kind formation. The resultant signals then pass through individual “consciousness” (unknown to finite finds) resulting in our shortly experienced lives on what we call earth. These 304,805 letters would correspond to the four letters found in our in DNA (cytosine, guanine, adenine, and thymine). Like “Occam’s razor’”, no need for the complexity of mathematics or formulas beyond comprehension. Sir Arthur Conan Doyle, “when you have eliminated the impossible, whatever remains must be the truth.

    With our finite minds, only infinite minds may understand.

    Dr. Arnold Wolf

    5555 Del Monte Drive Unit 901

    Houston, Texas 77056


  • agnes debinski

    Luminosity is something that is perceived by most of us human as quite magical. Therefore the beauty of the universe is copied and hundreds or thousands or perhaps even millions of beautiful lights, that somehow remind us of pictures of the universe, are sold to people who purchase those for their homes. Who could blame them? The universe is stunningly beautiful and gives us a feeling of something somehow magical. Don‘t we all wanna have a little bit of that magic in our homes? – Something that makes us forget about the cruelty of certain realities we need to forget about in the safeness of our dwellings…The association of endlessness matters too. Who doesn’t think of that when looking at images of the universe? isn’t that also something we humans always dreamed of?


Out There

Notes from the far edge of space, astronomy, and physics.

About Corey S. Powell

Corey S. Powell is DISCOVER's Editor at Large and former Editor in Chief. Previously he has sat on the board of editors of Scientific American, taught science journalism at NYU, and been fired from NASA. Corey is the author of "20 Ways the World Could End," one of the first doomsday manuals, and "God in the Equation," an examination of the spiritual impulse in modern cosmology. He lives in Brooklyn, under nearly starless skies.


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