Bose-Einstein Basics

Bose-Einstein Basics

The Bose-Einstein state of matter was on Earth in1995. Two scientists, Eric A. Cornell of the National Institute of Standards and Technology and Carl E. Wieman of the University of Colorado at Boulder, finally managed to produce condensate in the lab. For this achievement, they received the 2001 Nobel Prize in physics.

When you think condensate, think about and the way gas molecules come together and condense and to a liquid. The molecules get denser or packed closer together.

Much earlier, two scientists, Satyendra Bose and Albert Einstein, predicted BCE in the 1920s, but no laboratory had the equipment and facilities to achieve it at that time. Now we do. If plasmas are super hot and super excited atoms, the atoms in a Bose-Einstein condensate (BEC) are total opposites. They are super unexcited and super cold atoms.

About Condensation

Consider condensation first. Condensation happens when several gas molecules come together and form. It all happens because of a loss of energy. Gases are really excited atoms. When they lose energy, they slow down and begin to collect. They can collect into one drop. Water (H2O) vapor in the form of a liquid condenses on the lid of your pot when you boil water. It cools on the metal and becomes a liquid again. You would then have a condensate.

The BEC happens at super low temperatures. We have talked about temperature scales and Kelvin. At zero Kelvin (0® K– absolute zero) all molecular motion stops. Scientists have been able to achieve a temperature only a few billionths of a degree above absolute zero. When temperatures get that low, you can create a BEC with a few special elements. Cornell and Weiman did it with rubidium (Rb).

Let the Clumping Begin

So, it’s cold. A cold ice cube is still a solid. When you get to a temperature near absolute zero, something special happens. Atoms begin to clump. The whole process happens at temperatures within a few billionths of a degree, so you won’t see this at home. When the temperature becomes that low, the atomic parts can’t move at all. They lose almost all of their energy.

Since there is no more energy to transfer (as in solids or liquids), all of the atoms have exactly the same levels, like twins. The result of this clumping is the BEC. The group of rubidium atoms sits in the same place, creating a “super atom.” There are no longer thousands of separate atoms. They all take on the same qualities and, for our purposes, become one blob.

Bose-Einstein-Condensates form the core of neutron stars. These embers of a dying star are about the same size as Manhattan Island yet more massive than the Sun. A teaspoonful of one would weigh about a billion tons. On the outside, neutron stars are brittle. They are covered by an iron-rich crust. On the inside, they are fluid. Each one harbors a sea of neutrons — the debris from atoms crushed by a supernova explosion. The whole ensemble rotates hundreds of times each second, and so spawns powerful quantum tornadoes within the star.

Above: Neutron stars are formed in supernova explosions. This supernova remnant (known as the Crab Nebula) harbors one that spins 30 times every second.

You probably wouldn’t want a neutron star on your desktop. That is, unless you’re an experimental physicist.

Neutron stars and their cousins, white dwarfs and black holes, are extreme forms of matter that many scientists would love to tinker with– if only they could get one in their lab. But how? Researchers experimenting with the new form of matter, Bose-Einstein condensates, may have found a way.

Bose-Einstein condensates (BECs) are matter waves formed when very cold atoms merge to become a single “quantum mechanical blob.” They contain about ten million atoms in a droplet 0.1 mm across. In most ways, BECs and neutron stars are dissimilar. BECs are 100,000 times less dense than air, and they are colder than interstellar space. Neutron stars, on the other hand, weigh about 100 million tons per cubic centimeter, and their insides are 100 times hotter than the core of the Sun. So what do they have in common? Both are superfluids — that is, liquids that flow without friction or viscosity.

Perhaps the best-known example of a superfluid is helium-4 cooled to temperatures less than 2.2⁰ K (-271⁰ C). If you held in your hand a well-insulated cup of such helium and slowly rotated the cup, the slippery helium inside wouldn’t rotate with it.

Yet superfluids can rotate. And when they do, weird things happen. “Superfluids cannot turn as a rigid body — in order to rotate, they must swirl,” explains Ketterle. Among physicists he would say that “the curl of the velocity field must be zero.” This basic physics holds for BECs and neutron stars alike.

In 2001, following similar experiments in 1999 by researchers in Colorado and France, Ketterle and his colleagues at MIT decided to spin a BEC and see what would happen. Ketterle says he didn’t have neutron stars in mind when he did the experiment: “BECs are a new form of matter, and we wanted to learn more about them. By rotating BECs, we force them to reveal their properties.” Simulating the inside of a weird star was to be an unintended spin-off.

Ketterle’s team shined a rotating laser beam on the condensate, which was held in place by magnets. He compares the process to “stroking a ping-pong ball with a feather until it starts spinning.” Suddenly, a regular array of whirlpools appeared.

“It was a breathtaking experience when we saw those vortices,” recalls Ketterle. Researchers had seen such whirlpools before (in liquid helium and in BECs) but never so many at once. The array of quantum tornadoes was just the sort of storm astronomers had long-suspected might swirl within neutron stars.

No one has ever seen superfluid vortices inside a neutron star, but we have good reason to believe they exist: Many neutron stars are pulsars — that is, they emit a beam of radiation as they spin. The effect is much like a light house: we see a flash of light or radio waves each time the beam sweeps by. The pulses arrive at intervals so impressively regular that they rival atomic clocks. In fact, when Jocelyn Bell Burnell and Tony Hewish discovered pulsars in 1967, they wondered if they were receiving intelligent signals from aliens! Sometimes, though, pulsars “glitch” like a cheap wristwatch that suddenly begins to run too fast. The glitches are likely due to superfluid vortices forming or decaying within the star, or perhaps vortices brushing against the star’s crust.

The possibilities don’t end there: “If the condensed atoms [in a BEC were to] attract each other, then the whole condensate can collapse,” Ketterle adds. “People have actually predicated that the physics is the same as that of a collapsing neutron star. So it’s one way, maybe, to realize a tiny neutron star in a small vacuum chamber.”

Small, confined and tame — a pet neutron star? It sounds far-fetched, yet researchers are learning to make BECs collapse in real-life experiments.

BECs are formed with the aid of magnetic traps. Carl Wieman and colleagues at NIST have discovered that atoms inside a BEC can be made to attract or repel one another by “tuning” the magnetic field to which the condensate is exposed. Last They tried both: First, they made a self-repelling BEC. It expanded gently, as expected. Then, they made a mildly self-attracting BEC. It began to shrink — again as expected — but then it did something wholly unexpected.

It exploded!

Many of the atoms in the BEC flew outward, some in spherical shells, others in narrow jets. Some of the ejecta completely disappeared — a lingering mystery. Some remained as a smaller core at the position of the original condensate.

To an astrophysicist, this sounds remarkably like a supernova explosion. Indeed, Wieman et al dubbed it a “Bosenova” (pronounced “bose-a-nova”). In fact, the explosion liberated only enough energy to raise the temperature of the condensate 200 billionths of a degree. A real supernova would have been 1075 times more powerful. But you have to start somewhere.

If researchers eventually do craft miniature neutron stars, they might learn to make white dwarfs and black holes as well. Such micro-stars pose no danger to Earthlings. They are simply too small and their gravity too feeble to gobble objects around them. But such pets would no doubt be popular among physicists and astronomers.

Ocean on Ganymede

Hubble Telescope Spots Ocean on Jupiter Moon Ganymede[1]

The biggest moon in the Solar System harbors a salty ocean beneath its frozen surface, according to a study that examined the moon’s flickering auroras to probe its interior.

A number of Solar System objects are thought to have oceans. But this is the first clear-cut data of its kind to suggest that a sea lies hidden under the icy shell of Jupiter’s moon Ganymede, which is 50% bigger than our own Moon. Scientific models predicted an ocean on Ganymede, and when NASA’s Galileo spacecraft visited Ganymede in the 1990s, it collected data that hinted at an ocean. But new images from the Hubble Space Telescope offer strong confirmation of a liquid body of water inside Ganymede, scientists say.

Galileo’s observations “provide inconclusive evidence for the ocean,” says study co-author Joachim Saur of the University of Cologne. “The Hubble data require an ocean.”

Finding an ocean on a celestial body hundreds of millions of miles from Earth is no easy feat. Saur and his team turned to the space-going Hubble, which trained its keen eyes on Ganymede in 2010 and again in 2011. The Hubble focused on Ganymede’s two auroras, shimmering patterns in the sky similar to the earthly phenomenon known as the Northern Lights. A person standing on Ganymede’s surface and looking up would see a red glow, Saur says.

Ganymede has two auroras, one around its north pole and one around its south pole, both created in part by the moon’s own magnetic field. These auroras don’t stay fixed in place. Instead, they wander slightly across Ganymede’s face. With the help of supercomputers, the scientists calculated how much Ganymede’s auroras would shift if the moon had a salty sea. A layer of salty water could carry electrical current, generating another magnetic field that would affect the auroras.

The researchers found that the aurora shift witnessed by Hubble nicely matched the prediction of what should happen if Ganymede has an ocean. Just as importantly, the Hubble data did not match the prediction for an ocean-less Ganymede, the scientists reported online February, 2015 in the Journal of Geophysical Research.

Ganymede’s ocean is sandwiched between two layers of ice. That’s not particularly hospitable to life, says planetary scientist William McKinnon of Washington University in St. Louis, who didn’t work on the new study. But Saur says it’s still possible that Ganymede’s waters are habitable.

Other scientists praise the study for revealing important new evidence about Ganymede’s hidden interior.

Previous evidence of an ocean on the gigantic moon was “somewhat ambiguous,” University of California-Santa Cruz planetary scientist Francis Nimmo, who was not part of the study, says via e-mail. “So this study is … nice in that it provides independent confirmation of a subsurface ocean on Ganymede.”

The new findings are “very significant,” McKinnon agrees, though he thinks they’re not “air-tight. … What we need to do is go back to Ganymede and take measurements on site.”

Fortunately for Ganymede partisans, the European Space Agency is planning to launch a spacecraft in 2022 to explore this supermoon and its neighbors. Saur says he welcomes the mission as a chance to confirm his study’s findings, which he calls “solid science” but based on an “indirect method.”

A Solar-System sea is “really only 100% certain,” he says, when “you have a finger in the water.”

[1] Traci Watson, in USA TODAY (March 12, 2015)

Odd Names of Solar System Bodies

Odd Names of Solar System Bodies

We are pretty used to the names of the major objects in our Solar System. Most names are taken from Greek mythology, such as Jupiter, Saturn, Venus, Mercury, Mars, Uranus, Pluto, vnd Neptune. There are many more objects named however, and some of them quite odd.

  1. Ganymede, a moon of Jupiter. The name is from the Greek Ganymēdēs, Latin Ganymedes, or Catamitus, in Greek legend, was the son of Tros (or Laomedon), king of Troy. Because of his unusual beauty, he was carried off either by the gods or by Zeus, disguised as an eagle, or, according to a Cretan account, by Minos, to serve as cupbearer. In compensation, Zeus gave Ganymede’s father a stud of immortal horses (or a golden vine). The earliest forms of the myth have no erotic content, but by the 5th century
    BCE it was believed that Ganymede’s kidnapper had a homosexual passion for him; Ganymede’s kidnapping was a popular topic on 5th-century Attic vases. The English word catamite was derived from the popular Latin form of his name. He was later identified with the constellation Aquarius.
  2. Mister Spock Asteroid. Not what you were thinking here. This has nothing to do with the Star Wars character. In fact, this was named after the pet of discoverer James B. Gibson. The recent sad loss of photographer, director and actor Leonard Nimoy is most keenly felt by the millions of fans who loved the sci-fi character he shall always be most closely associated with—Star Trek‘s coolly logical and pointy-eared Vulcan science officer, Mr. Spock. As befits someone who toured the fictional Galaxy furthering scientific knowledge, astronomers have a tangible reminder of the starship Enterprise‘s first officer in the form of an asteroid that will always bear his name. James B. Gibson discovered 2309 Mr. Spock (1971 QX1) from Yale-Columbia Station at El Leoncito, Argentina on 16th August 1971. It soon became apparent that this was a main-belt asteroid between the orbits of Mars and Jupiter, orbiting 3 astronomical units from the Sun every 5.23 years. Subsequent analysis revealed that 2309 Mr. Spock is a 13-mile (21-kilometre)-wide body rotating on its axis every 6.7 hours. zktin-belt asteroid 2309 Mr. Spock (1971 QX1) is a 13-mile-wide body rotating on its axis every 6.7 hours that orbits 3 astronomical units from the Sun every 5.23 years. Currently 17th magnitude in the constellation of Taurus, it’s still a viable astrophotographic target for 10-inch telescopes and larger. This is a two-minute ISO1600 exposure at f/2 with a C11 and DSLR on 10th March at 21:15 UT. Image credit: Ade Ashford. Live long and pros-purr.
  3. James Bond. This is a numbered minor planet, discovered October 5, 1983. It is classified as an inner planet
  4. Tom Hanks. Asteroid 12818 Tomhanks swung within about 151 million miles of Earth on Sept. 12, while 8353 Megryan came about 191 million miles away on Sept. 27. Neither came closer than the distance between the Earth and the sun, and they did not pose any risk to our planet. A lot of scientists have named asteroids after their favorite celebrities, and considering Tom Hanks is somewhat of a favorite (read, Apollo 13) among astronauts, he makes the cut. However, Tom isn’t the only star to have an asteroid named after him. There’s Meg Ryan, Chaplin, and Van Damme among others.
  5. Monty Python. The hilarious British comedy troupe are so famous among the astronauts that each member of the crew also have an asteroid named after them.
  6. Makemake sounds like the most delicious Japanese snack ever. Would make for the perfect dwarf planet wouldn’t it?
  7. Beowulf Asteroid. Asteroid 38086, Beowolf, was discovered on May 5, 1999 by the Lowell Observatory Near-Earth Object Search (LONEOS) at the Anderson Mesa Station of Lowell Observatory near Flagstaff, Arizona. It has a period of 1 years, 253 days. It was named for the great Scandinavian warrior Beowulf, hero of the early medieval British epic poem.
  8. (7470) Jabberwock is a main-asteroid of the main belt, discovered on May 2, 1991 by the Japanese astronomer Takeshi Urata at the Nihondaira Observatory.The asteroid is part of the Vesta family, a large group of asteroids. (7470) Jabberwock was named after the mystical creature Jabberwock, the main theme of the classic nonsense poem Jabberwocky from the story Through the Looking Glass, by Lewis Carroll.
  9. Petit-Princebelt. This prince is so petite that it’s not even an asteroid. 45 Eugenia has a moon called Petit-Prince, named after Antoine de Saint-Exupéry’s The Little Prince. The children’s book follows the exploits of a boy who lived on an asteroid and explored other asteroids, as well as Earth.
  10. Adam Curry. Discovered Marcy 20, 1998 and named for the infamous Adam Curry
  11. This minor planet was named after Amol Aggarwal, who won the Intel Science Talent search in California in 2011, and got the planet as a prize. This isn’t the only Indian named, however. There’s Bhasin, B\att, Bhattacharya, and Yogeshwar. All these planets have been named by the scientists who discovered them.
  12. Anandapadmanabum. A Solar System small body, 30269 Anandapadmanaban (2000 HS50)

The list goes on to include: Ask, Bam, Babcock, Bacon, Beer, Brest, Hippo, Lust

All these minor objects do exist in real, and aren’t a figment of my imagination. The source is

Forming a Black Hole

Forming a Black Hole[1]

On July 2, 1967, a network of satellites designed to detect tests of nuclear weapons recorded a flash of gamma rays coming from the wrong direction—outer space.

And so it was that human astronomers were tipped to the existence of one of the most violent phenomena of nature. Today, they know that about once a day somewhere in the observable universe, an explosion called a gamma-ray burst occurs, releasing more energy in a few seconds than our galaxy does in a year.

These magnificent cosmic conflagrations are as far away as they are rare, which is just as well. If one happened nearby, in our own galaxy, we could be swathed with radiation. The closest gamma-ray burst whose distance has been measured happened some 119 million light-years from us, far outside the so-called Local Group, which contains our own Milky Way galaxy. The farthest so far recorded is now 31 billion light-years away, as calculated by the mathematics of the expanding universe; it happened when the universe was only 500 million years old.

Gamma-ray bursts are thought to be the final step in the series of transformations by which stars shrink and slump from blazing glory to oblivion, winding up as bottomless deadly dimples in the fabric of space-time—that is to say, as black holes.

The hierarchy of dead stars goes like this: Stars like the Sun, when they run out of thermonuclear fuel, shrink to cinders known as white dwarfs, the size of Earth. Stars more massive than the Sun might collapse more drastically and undergo a supernova explosion, blasting newly formed heavy elements into space to enrich future stars, planets and perhaps life, and leaving behind crushed cores known as neutron stars. These weigh slightly more than the sun but are only 12 miles or so in diameter—so dense that a teaspoonful on Earth would weigh as much as Mount Everest.

Such an explosion, bright enough to be seen in daylight, happened in 1054, Earth time, as told by Chinese astronomers and the ancient inhabitants of Chaco Canyon in what is now New Mexico. That supernova left behind the Crab nebula, a tangle of glowing shreds of gas and a pulsar—a magnetized neutron star spinning 30 times a second, whipping the gas with magnetic fields that make it glow.

Neutron stars, theorists say, are the densest stable form of matter, but they are not the end of the story. According to theory, too much mass accumulating on a neutron star can cause its collapse into a black hole, an abyss from which not even light can escape. The signature of such a cataclysm would be a gamma-ray burst, astronomers say.

Supercomputer simulations by astronomers led by Luciano Rezzolla of the Institute of Theoretical Physics in Frankfurt have recently showed this would work.

The simulation, as it unwound over six weeks of supercomputer time at the Max Planck Institute for Gravitational Physics, started with two neutron stars orbiting each other at a distance of 11 miles. That would not be unusual in the universe; most stars are in fact part of double-star systems and several pairs of pulsars orbiting each other are already known. They will eventually collide because such dense, heavy objects lose energy rapidly and spiral together.

In the case of Dr. Rezzolla’s computation, it took seven milliseconds for tidal forces from the larger star’s gravity to rip apart the smaller star and unwind it into a spiral resembling flaming toothpaste writhing with magnetic fields and begin munching up the gas.

The excess plasma forms a fat disk around the new black hole, and its magnetic fields, a billion times stronger than those in the Sun, align to channel beams of radiation and particles out at the speed of light. The result is a gamma-ray burst visible across the universe, carrying the news of doom—the last astronomers will ever hear of these stars.

For those two stars, the last bang was the best. Oblivion can be such a lovely sight.

[1] Dennis Overbye, “How to Make a Black Hole,” New York Times (October 8, 2014). The graphic is from Astronews in Astronomy (45, 7, July 2017), p 15

Copernicus at 493

Copernicus at 493[1]

The whole world should observe along with the Poles, the birthday of Copernicus, and should continue to celebrate the 19th of February in his memory so long as the Earth swings in its orbit.; for what this boy, born 450 years ago yesterday [article written February 20, 1923; Copernicus born, February 19, 1473 and in 2017 he would be 493], and christened Nichola Koppernick, son of a native of Cracow, conceived as the order of the universe is “the capital event of modern thought.” By it mankind’s outlook on the universe has been fundamentally changed. The young Koppernick was a student in the University of Cracow the year in which Columbus discovered America, giving himself to mathematical science and painting. He afterward studied law and attended mathematical lectures in Bologna and still later studied music in Padua and took his degree in canon law in Ferrara. He then devoted his medical skill to the service of the poor, his economic knowledge to the reform of the currency in the Prussian provinces of Poland, and his astronomical genius to the development of a new cosmic theory which has come to bear his name.

It was while he was in the midst of such studies and ministries that the name “America” was first given by others to the fringe of this continent and graven on a map published at St. Dié, at the foot of the Vosges Mountains, in Southeastern France. Our continent was thus christened under the Ptolemaic geocentric system. But our national life made its beginnings under the Copernican system and had from the first a “shuddering sense” of physical immensity. It is inconceivable that this new physical conception has not mightily affected man’s social and religious conceptions, and especially those of Americans. With the enlargement of the universe under it, and the accompanying diminution of the relative size of Earth—made still smaller by man’s improved means of communication—we no longer picture our planet as a flat area divided into exclusive, provincial or national strips spanned by a Ptolemaic sky. We find ourselves “in the same boat” on a sea of practically infinite space.

In observing the birthday of Copernicus, the Polish astronomers have fitly gathered in their first congress[2] and proudly remembered what their science has given to mankind; and the Polish people have with good reason held their celebrations all over Poland in honor of the son of the city of Thorn[3] (again in Polish territory in 1923, 5 years after the end of WWI) and the academic son of the University of Cracow (once more a Polish university). But it would be profitable for the whole world—scientists, statesmen, warriors, philosophers, teachers, pupils and the people in general—to pause and consider what was the real significance of the gift of Copernicus. The corollary of his theory is a world-wide solidarity of human interest. There is no escape from it. If an international holiday were to be added to the many holidays in the various calendars of the world, it should be one on which the birthday of Copernicus is solemnly observed—for he discovered the universe.

[1] Published in the New York Times (February 20, 1923, p. 16)

[2] First Polish Philosophical Congress held in Lvov, 1923.

[3] Thorn is the German name. In Polish, it is Toruń, a city in northern Poland, on the Vistula River. In the aftermath of World War I, the Polish people broke out in the Greater Poland Uprising on December 27, 1918, in Poznań after a patriotic speech by Ignacy Paderewski, a famous Polish pianist. The fighting continued until June 28, 1919, when the Treaty of Versailles was signed, which recreated the nation of Poland.

Earth May Have Been Shaped Like a Donut

Earth May Have Been Shaped Like A Donut At One Point In Time[1]

The new synestia theory proposes a new type of planetary object and another theory for how the Moon formed.

A to-scale illustration of the synestia process is shown above.

Astronomers have proposed a new type of planetary object they are calling synestia, where a celestial body violently collides with another body, resulting in a donut-shaped disk of vaporized rock. After some time, the body will cool down and turn into the solid, round planets we currently know.

Sarah Stewart, a planetary scientist at the University of California Davis, and Simon Lock, a graduate student at Harvard University in Cambridge, co-authored the study that was published in the Journal of Geophysical Research: Planets.

The name synestia combines the prefix “syn-” meaning “together” and Estia, the Greek goddess of architecture and structures.

The idea was modeled after ice skaters doing a spin—when they put their arms out to the side they slow down but when they tuck their arms in, their momentum stays constant, but their angular velocity increases and they spin faster.

The team was interested in how that idea would apply to rapidly spinning planets colliding with each other and how it would impact the angular momentum.

The people doing the study believe the collision that formed Earth likely caused a synestia before it cooled back down and formed into the solid, round object it is today. The researchers said those days probably didn’t last more than 100 years, though.

On top of a theory for planets how planets have formed, the study also lends to the idea of the formation of the Moon since its composition is similar to that of Earth’s.

[1] See Nicole Kiefert,, “Earth May Have Been Shaped Like A Donut At One Point In Time,” (published May 30, 2017), downloaded May 30, 2017

Eddington Observes Solar Eclipse to Test General Relativity

May 29, 1919: Eddington Observes Solar Eclipse to Test General Relativity

One of Eddington’s photographs of the May 29, 1919, solar eclipse. The photo was presented in his 1920 paper announcing the successful test of general relativity.

When Albert Einstein published his general theory of relativity (GR) in 1915, he proposed three critical tests, insisting in a letter to The Times of London that if any one of these three proved to be wrong, the whole theory would collapse.

  • Advance of the perihelion of Mercury
  • Deflection of light by a gravitational field
  • Gravitational red shift

Once he had completed his theory, Einstein immediately calculated the advance of the perihelion of Mercury, and he could hardly contain himself when GR produced the correct result. The next classical test was the deflection of light by a gravitational field, first performed by Sir Arthur Eddington in 1919.

Born to Quaker parents in December 1882, Arthur was just two years old when he lost his father to a typhoid epidemic that ravaged England. As a child, Eddington was enamored of the night sky and often tried to count the number of stars he could see. Initially Eddington was schooled at home, but when he did start attending school, he excelled so much in mathematics that he won a scholarship to Owens College in Manchester at age 16. He graduated with first class honors in physics, and promptly won another scholarship to attend Trinity College at Cambridge University.

Eddington completed his M.A. in 1905. First, he worked on thermionic emission at the Cavendish Laboratory, and then tried his hand at mathematics research, but neither project went well. He briefly taught mathematics before re-discovering his first love: astronomy. Eventually he found a position at the Royal Observatory in Greenwich, specializing in the study of stellar structure. By 1914 he had moved up to become director of the Cambridge Observatory; a Royal Society fellowship and Royal Medal soon followed.

During Eddington’s tenure as secretary of the Royal Astronomical Society, Willem de Sitter sent him letters and papers about Einstein’s new general theory of relativity. Eddington became Einstein’s biggest evangelist at a time when there was still considerable wartime hostility and mistrust toward any work by German physicists. He soon became involved in attempts to confirm one of the theory’s key predictions.

Since the masses of celestial bodies would cause spacetime to curve, Einstein predicted that light should follow those curves and bend ever so slightly. Isaac Newton had also predicted that light would bend in a gravitational field, although only half as much. Which prediction was more accurate? Scientists feared that measuring such a tiny curvature was simply beyond their experimental capabilities at the time.

It was Britain’s Astronomer Royal, Sir Frank W. Dyson, who proposed an expedition to view the total solar eclipse on May 29, 1919, in order to resolve the issue. Eddington was happy to lead the expedition, but initially the venture was delayed. World War I was raging, and the factories were too busy meeting the country’s military needs to make the required astronomical instruments. When the war ended in November 1918, scientists had just five months to pull together everything for the expedition.

Eddington took nighttime baseline measurements of the positions of the stars in the Hyades cluster in January and February of 1919. During the eclipse the Sun would cross that cluster, and the starlight would be visible. Comparison of the baseline measurements of a star’s position and the corresponding measurements made during the eclipse, when that star was just visible at the limb of the sun, would determine whether Einstein or Newton was right.

Then Eddington set sail for Principe, a remote island off the west coast of Africa, sending a second ship to Sobral, Brazil—just in case the weather didn’t cooperate and clouds obscured the view. It proved to be a smart decision. Eddington’s team was dismayed when heavy rains and clouds appeared on the day of the eclipse, although the skies cleared sufficiently by the time of the event to allow them to make their measurements. The Brazilian team had their own challenges: The tropical heat warped the metal in their large telescopes, forcing them to also use a smaller 10-centimeter instrument as backup.

Once the two teams had analyzed their results, they found their measurements were within two standard deviations of Einstein’s predictions, compared to twice that for Newton’s, thus supporting Einstein’s new theory. News of Eddington’s observations spread quickly and caused a media sensation, elevating Einstein to overnight global celebrity. (When his assistant asked how he would have felt had the expedition failed, Einstein is said to have quipped, “Then I would feel sorry for the dear Lord. The theory is correct anyway.”)

Not everyone immediately accepted the results. Some astronomers accused Eddington of manipulating his data because he threw out values obtained from the Brazilian team’s warped telescopes, which gave results closer to the Newtonian value. Others questioned whether his images were of sufficient quality to make a definitive conclusion. Astronomers at Lick Observatory in California repeated the measurement during the 1922 eclipse, and got similar results, as did the teams who made measurements during the solar eclipses of 1953 and 1973. Each new result was better than the last. By the 1960s, most physicists accepted that Einstein’s prediction of how much light would be deflected was the correct one.

Eddington succumbed to cancer in November 1944 after a long illustrious career. In addition to his many scientific contributions, he once penned a lyrical parody of The Rubaiyat of Omar Khayyam about his famed 1919 expedition:

Oh leave the Wise our measures to collate
One thing at least is certain, LIGHT has WEIGHT,
One thing is certain, and the rest debate –
Light-rays, when near the Sun, DO NOT GO STRAIGHT.