Exactly 100 years ago, our concept of the universe was very different from today. People knew about the stars in the Milky Way and knew about the distances to them, but no one knew what was behind them. The universe was considered static, spirals and ellipses in the sky were considered objects of our own galaxy. Newtonian gravity was not yet surpassed by Einstein's new theory, and scientific ideas like the Big Bang, dark matter, and dark matter were not heard. But then, literally every decade, breakthroughs after breakthroughs began to occur, and so on until today. This is Ethan Siegel's Medium.com chronicle of how our understanding of the universe has changed over the past hundred years.
The results of the Eddington expedition in 1919 showed that general relativity describes the curvature of starlight near massive objects.
1910s: Einstein's theory is confirmed. General relativity became famous for giving predictions that Newton's theory could not give: the precession of Mercury's orbit around the Sun. But it was not enough for a scientific theory to simply explain something that we had already observed; she had to give predictions about what we had not yet seen. Although there have been many in the last hundred years - gravitational time dilation, strong and weak lensing, gravitational redshift, and so on - the first was the curvature of starlight during a total solar eclipse, which Eddington and his colleagues observed in 1919. The rate of curvature of light around the Sun was consistent with Einstein's predictions and not consistent with Newton's theory. Since then, our understanding of the universe has changed forever.
Hubble's discovery of the variable Cepheid in the Andromeda galaxy, M31, opened the universe to us
1920s. We didn't yet know there was a universe beyond the Milky Way, but that all changed in the 1920s with the work of Edwin Hubble. By observing some spiral nebulae in the sky, he was able to pinpoint individual variable stars of the same type known in the Milky Way. Only their brightness was so low that it directly indicated millions of light years between us, placing them far beyond the boundaries of our galaxy. Hubble did not stop there. He measured the rate of recession and the distance to dozens of galaxies, significantly expanding the boundaries of the known universe.
Two bright large galaxies in the center of the Coma cluster, NGC 4889 (left) and slightly smaller NGC 4874 (right), are each over a million light years in size. A huge dark matter halo is believed to run through the entire cluster.
1930s. It has long been thought that if you could measure all the mass contained in stars, and perhaps add gas and dust, you could count all the matter in the universe. However, observing galaxies in a dense cluster (like the Coma cluster), Fritz Zwicky showed that stars and so-called "ordinary matter" (ie atoms) are not enough to explain the internal motion of these clusters. He called the new matter dark matter (dunkle materie), and until the 1970s, his observations were largely ignored. Then they studied ordinary matter better and it turned out that there is quite a lot of dark matter in individual rotating galaxies. Now we know that dark matter is 5 times more massive than ordinary matter.
1940s. Although most of the experimental and observational resources went to reconnaissance satellites, rocket engineering and nuclear technology development, theoretical physicists continued to work tirelessly. In 1945, Georgy Gamow created a complete extrapolation of the expanding universe: if the universe is expanding and cooling today, it should have been denser and hotter at some point in the past. Therefore, once in the past there was a time when the universe was too hot and neutral atoms could not form, and before that atomic nuclei could not form. If this is so, then before the formation of any stars, the matter of the Universe began with the lightest elements, and in our time one can observe the afterglow of that temperature in all directions - just a few degrees above absolute zero. Today this theory is known as the Big Bang theory.and in the 1940s they did not even know how gorgeous she is.
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1950s. A rival idea with the Big Bang hypothesis was the stationary model of the universe, put forward by Fred Hoyle and others. Significantly, both sides argued that all the heavy elements present on Earth today were formed in the early Universe. Hoyle and his colleagues argued that they were not made in an early, hot, and dense state, but rather in previous generations of stars. Hoyle, along with colleagues Willie Fowler and Margaret Burbidge, explained in detail how the elements arrange the periodic table during nuclear fusion in stars. Curiously enough, they predicted the synthesis of carbon from helium in a process we had never seen before: a triple alpha process that requires a new state of carbon to exist. This state was discovered by Fowler several years after Hoyle's original prediction and is today known as the Hoyle carbon state. So, we found out that all heavy elements existing on Earth owe their origin to all previous generations of stars.
If we could see microwave light, the night sky would look like a green oval with a temperature of 2.7 Kelvin, with “noise” in the center from hot contributions from our galactic plane. This uniform radiation with a blackbody spectrum is indicative of the afterglow of the Big Bang: it is the cosmic microwave background.
1960s. After 20 years of discussion, a key observation that would determine the history of the universe was made: the discovery of the predicted afterglow from the Big Bang, or the cosmic microwave background. This uniform radiation with a temperature of 2.725 Kelvin was discovered in 1965 by Arno Penzias and Bob Wilson, neither of whom knew immediately what they had stumbled upon. Only with time the blackbody spectrum of this radiation and its fluctuations were measured and showed that our Universe began with an “explosion”.
The earliest stage of the Universe, even before the Big Bang, laid down all the original conditions for everything that we see today. It was Alan Guth's big idea: cosmic inflation
1970sAt the very end of 1979, the young scientist was hatching his idea. Alan Guth was looking for a way to solve some of the unexplained problems of the Big Bang - why the universe is so flat in space, why it is the same temperature in all directions, and why there are no relics of the highest energies in it - and came up with the idea of cosmic inflation. According to this idea, before the universe entered a hot dense state, there was a state of exponential expansion, when all the energy was inherent in the very fabric of space. It took several refinements of Guth's original ideas to form the current theory of inflation, but subsequent observations - including fluctuations in the cosmic microwave background - have confirmed its predictions. Not only did the universe begin with an explosion, but it also had another special state even before this Big Bang happened.
The remnants of supernova 1987a located in the Large Magellanic Cloud 165,000 light years away. For over three hundred centuries, it was the closest supernova observed to Earth.
1980s. It may seem that nothing serious happened, but it was in 1987 that the closest supernova was observed from Earth. This happens once every hundred years. It was also the first supernova to occur when we had detectors capable of detecting neutrinos from such events. Although we have seen many supernovae in other galaxies, we have never observed them close enough to witness neutrinos from them. These 20 or so neutrinos marked the beginning of neutrino astronomy and subsequent developments that led to neutrino oscillations, the detection of neutrino masses, and neutrino neutrinos from supernovae that occur in galaxies millions of light years away. If our modern detectors functioned at the right time, the next supernova explosion would allow hundreds of thousands of neutrinos to be captured.
Four possible destinies of the universe, of which the last one fits the data best: A universe with dark energy. It was first discovered thanks to observations of distant supernovae
1990s. If you thought that dark matter and the discovery of the beginning of the universe were major discoveries, imagine the shock in 1998 when they discovered that the universe was about to end. Historically, we have imagined three possible destinies:
- The expansion of the Universe will not be enough to overcome the gravitational attraction of everything and everyone, and the Universe will contract again in the Big Compression
- The expansion of the Universe will be too much, and everything united by gravity will scatter, and the Universe will freeze
- Or we will find ourselves on the border of these two outcomes and the rate of expansion will asymptotically tend to zero, but never reach it: Critical Universe
Instead, however, distant supernovae have shown that the expansion of the universe is accelerating and that, as time elapses, distant galaxies move away from each other faster and faster. The universe will not only freeze, but all galaxies that are not tied to one another will eventually disappear beyond our cosmic horizon. Apart from the galaxies in our local group, no galaxies will meet the Milky Way, and our fate will be cold and lonely. In 100 billion years, we won't see any galaxies other than ours.
2000s. Our measurements of fluctuations (or imperfections) in the afterglow of the Big Bang taught us incredible things: we learned exactly what the universe is made of. The COBE data replaced the WMAP data, which in turn was improved by Planck. Taken together, data from large-scale structures from large galaxy surveys (like 2dF and SDSS) and data from distant supernovae have provided us with a modern picture of the universe:
- 0.01% radiation in the form of photons, - 0.1% neutrinos, which contribute lightly to the gravitational halos surrounding galaxies and clusters, - 4.9% of ordinary matter, which includes everything consisting of atomic particles, - 27% dark matter, or mysterious, non-interacting (other than gravitationally) particles that provide the Universe with the structure that we observe, - 68% dark energy, which is inherent in the space itself.
2010th. This decade is not over yet, but we have already found our first potentially habitable Earth-like planets (albeit very distantly), among the thousands and thousands of new exoplanets discovered by NASA's Kepler mission. This may not be the biggest discovery of the decade, because LIGO's direct detection of gravitational waves confirmed the picture Einstein drew back in 1915. More than a century after Einstein's theory first challenged Newton, general relativity has gone through all the trials and tests it was offered.
Scientific history is still being written, and there is still much to be discovered in the universe. But those 11 steps took us out of a universe of unknown age, no larger than our galaxy, mostly made up of stars, into an expanding, cooling universe ruled by dark matter, dark energy and our ordinary matter. It contains many potentially habitable planets, it is 13.8 billion years old, and it began with the Big Bang, which itself flowed out of cosmic inflation. We learned about the origin of the Universe, about its fate, about the appearance, structure and size - and all for 100 years. Perhaps the next 100 years will be full of surprises that we cannot even imagine.
Ilya Khel