On July 4, the United States of America celebrates its 250th birthday, marking the anniversary of the Declaration of Independence and becoming a sovereign nation.
Today, this relatively young country leads the way in our understanding of the universe. It’s where many major players in space science, like NASA, the California Institute of Technology (Caltech), the Massachusetts Institute of Technology (MIT), and Northwestern University, to name just a few.
And to celebrate 250 years of the U.S. as an independent nation, Space.com takes you on a journey through some common misunderstandings of the universe through the years and the roles American scientists played in clearing up that cosmic confusion.
By 1776, Sir Isaac Newton‘s laws of motion had been around for about 89 years since the publication of Philosophiæ Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy) in 1687. Five of the solar system planets had been discovered by the Ancient Greeks long before the birth of the U.S. Also, after a long struggle and many attempts to stifle this knowledge, humans were made aware that the Earth orbits the sun rather than the other way around, with the final nail in this coffin of misunderstanding laid by Polish astronomer Nicolaus Copernicus in 1543 and Galileo Galilei in 1610, receiving an extra hammer blow from Newton in 1687.
Galileo had also delivered us to the understanding that not only was Earth’s place in the solar system unique, but it wasn’t even the only planet to possess moons, with the moons of Jupiter, Io, Europa, Ganymede and Callisto discovered in 1610.
Clearly, by the time the U.S. was born we were already beginning to understand the universe and our place within it, but some major misunderstandings still persisted. One of the largest of these surrounded the nature of the sun itself.
The sun as a burning lump of coal
America was formed during the “steam age,” a period of industrialization that lasted from 1770 to 1914. This revolution was driven by coal, powering locomotives, ships, and factories, changing the shape of industry, transportation, and manufacturing. At this time, coal was the densest and most powerful fuel source known to humanity, so it is perhaps little wonder that many early scientists theorized the sun was actually a tremendously massive lump of burning coal.
Then, one of the oldest and most prominent scientific periodicals in the world, the U.S.-based Scientific American, wrote a 1863 article that first began the pushback against the sun as a burning lump of coal.
“If the sun were composed of coal, it would last at the present rate only 5,000 years. The sun, in all probability, is not a burning, but an incandescent, body. Its light is rather that of a glowing molten metal than that of a burning furnace. But it is impossible that the sun should constantly be giving out heat, without either losing heat or being supplied with new fuel,” the Scientific American article stated. “Assuming that the heat of the sun has been kept up by meteoric bodies falling into it, it is possible from the mass of the solar system to determine approximately the period during which the sun has shone. The limits lie between 100 millions and 400 millions of years.”
Though this estimate was still miles out, we now understand that the sun is around 4.6 billion years old; this development came at a time of a geological revolution that was uncovering evidence that our planet was much older than theological estimates of just a few thousand years.
Around 57 years later in 1920, British scientist Arthur Eddington first suggested stars like the sun are actually powered by the nuclear fusion of hydrogen to helium. The idea was published by Eddington in his 1926 book, “The Internal Constitution of the Stars.” Twelve years after this, nuclear physicist Hans Bethe formulated the first explanation of this nuclear fusion process, detailing the proton-proton chain reaction and the Carbon-Nitrogen-Oxygen (CNO) cycle.
The idea of the sun as a burning lump of coal finally burnt out 162 years after the formation of the U.S., a chain reaction kick-started by an American publication.
Ether or…?
During the infancy of the U.S. in the 1800s, scientists understood that light is a wave. Applying this to what they knew of other waves, it was logical to presume that light also needed a medium through which it could propagate. This medium would have to be ubiquitous and possess some unique properties to allow light to propagate through it at the speed of light.
Thus, it was proposed that space was filled with a medium called the luminiferous ether, with luminiferous meaning “light-bearing.” The fact that this would have to be an invisible and infinite material that doesn’t interact with physical objects made the existence of the luminiferous ether highly controversial.
We now know this medium doesn’t exist, and that is thanks to two American physicists, Albert A. Michelson and Edward W. Morley, who in 1887 delivered the most important null result in the history of science: disproving the existence of the luminiferous ether.
Should the luminiferous ether exist, then scientists reasoned that as the Earth orbits the sun at around 66,000 miles per hour (106,216 kilometers per hour), our planet should be moving through the ether, which had been deemed to be stationary. That meant Earth must be moving with respect to the stationary ether. And if the ether is the medium through which light waves ripple, this should mean the speed of light differs ever so slightly in the direction Earth is traveling.
Conducted in Cleveland, Ohio, the Michelson–Morley experiment used a piece of kit called a Michelson–Morley interferometer to test differences in speed for a wave of light traveling perpendicular to Earth and one traveling parallel to Earth. Michelson and Morley had expected to observe an interference pattern caused by the differing travel times of the light waves.
That is what happens when light of the same wavelength arrives at a detector at ever so slightly different times, meaning the peaks and troughs of the waves no longer perfectly align. However, to the surprise of the American physicists, no interference was detected. This meant no difference in the travel speed of light, essentially disproving the existence of the ether.
The negation of the luminiferous ether was of vital importance as it opened the door to Albert Einstein‘s theory of special relativity in 1905 and general relativity in 1915, the latter of which revised our understanding of gravity and led to our knowledge of black holes and gravitational waves well before the experimental observation of such objects.
Other galaxies!
Though scientists realized Earth isn’t in the center of the solar system before the birth of the U.S., there was another glaring misconception. It was believed that the Milky Way, first proposed in Immanuel Kant’s “Island Universe” theory in 1755, still occupied a unique position in the universe — with the existence of other galaxies a hotly debated topic. The solar system itself was also thought to be at the center of the Milky Way.
In 1785, astronomer William Herschel set about mapping our galaxy, correctly determining the disk-like shape of the Milky Way but incorrectly placing the solar system at its heart. This picture changed in 1918, when American astronomer Harlow Shapley determined that dense groups of stars called globular clusters are centered on a distant core in the direction of the Sagittarius constellation. This placed the solar system off-center in the galaxy. Today we’ve expanded upon this, moving our planetary system 27,000 light-years away from the Galactic Center and onto one of our galaxy’s spiral arms.
It was five years later, in 1923, that the uniqueness of the Milky Way was shattered. Using the 100-inch (2.5-meter) Hooker telescope at the Mount Wilson Observatory, American astronomer Edwin Hubble imaged the Andromeda nebula (Messier 31) and determined that it was at least a million light-years away. Though we now know this distance is closer to 2.5 million light-years, it was still enough to place M31 outside the boundary of the Milky Way.
The fact that the Andromeda nebula is actually the Andromeda galaxy, a distant and separate galaxy from our own, was announced to the public via The New York Times in Nov. 1924. We were no longer alone galactically — but Hubble wasn’t done.
The universe is not static
Another assumption at this time was that the universe was static, something supported by Einstein in 1917. However, in 1929, Hubble discovered that the light from distant galaxies was being redshifted. In other words, the wavelengths of light emanating from these sources were being stretched as those wavelengths traveled toward us. This indicated that these galaxies are moving away from us. Convinced of this, Einstein abandoned his model of the static universe.
American scientists weren’t done revising our entire picture of the cosmos, however. In 1998, U.S. researchers like Saul Perlmutter, Adam Riess, and Robert Kirshner were part of two international teams of researchers that discovered that not only is the universe expanding, but this expansion is actually speeding up.
Dark energy was introduced as the mysterious force driving this accelerating expansion. It remains today one of the most pressing mysteries of the cosmos.
Possibly by the time the U.S. celebrates its 300th birthday, the mystery of dark matter will have been solved along with other cosmic puzzles such as the nature of dark matter. If this is the case, it is highly likely that U.S. projects like the Hubble Space Telescope, the James Webb Space Telescope, and the upcoming Nancy Grace Roman Space Telescope will put American innovators and scientists at the forefront of these developments, just as their predecessors have been for the last 250 years.