Cosmic Surprises Keep Blowing Our Minds

Cosmic Surprises Keep Blowing Our Minds[1]

Some areas of science advance in increments. We see slow evolutionary improvements in aeronautical engineering and medical discoveries. But astronomy is different. Here, the universe often leaps out and goes boo! Although we are far from it, let’s use April Fool’s Day as our excuse to review the top 20 pranks” the cosmos has sprung on us.

Start with Galileo. Since no one had pointed a telescope at the sky before, he was bound to get surprises. Nobody had foreseen lunar craters or moons going around other planets like Jupiter, as he observed. But when he looked at Saturn, he entered the Twilight Zone. On Earth, there’s no example of a ball surrounded by unattached rings. This was beyond human experience. No wonder it took two centuries for anyone to deduce that they’re neither solid nor gaseous, but made of separate moonlets. So our first April Fool’s prank? Saturn’s glorious rings.

Fast forward to 1781. That’s when William Herschel first peered at a bizarre green ball. No one had discovered any planets beyond the five bright ones since prehistory. No great thinker, no holy book, no philosopher had done more than idly speculate about more planets out there in our Solar System. Herschel’s spotting of Uranus was the most unexpected and amazing discovery all time.

Surprise No. 3 stays with Herschel. Nineteen years after finding Uranus, he discovered the first-ever invisible light. Light we cannot see?

It astonished the world. The bulk of the Sun’s emissions are invisible “calorific rays.” Late that century, people started calling it infrared.

We have to credit Albert Einstein with several mind-blowers. First, that space and time both shrink or grow depending on the observer’s conditions. This means the universe does not have a fixed size. And a million years elapse in one place while a single second is experienced by someone else—at the same time. Did anyone see that coming? Do most people grasp this even today? As if that wasn’t enough mind twisting, he showed that solid objects and energy are two faces of the same entity.

Jump ahead to 1920. That’s when Arthur Eddington figured out what makes the stars shine. Imagine: a new type of “burning.” An alchemic change of one element to another. This nuclear fusion process is so efficient that each second the Sun emits the energy of 96 billion 1-megaton H-bombs. Sure, physicists knew the Sun couldn’t create light and heat by burning in the usual way. But this?

A few years later, Edwin Hubble announced that all those spiral nebulae were separate “island universes.” Granted, this had been suspected by half of all astronomers for decades. It was not a sudden April Fool’s. Still, bam, the universe officially became unspeakably larger than it was before. That’s gotta count as a boo! event.

Then the quantum gang rode into town. Their revelations were astonishing. Empty space seethes with energy. A bit of matter can know what another is doing and react instantaneously across the universe as if no space exists between them. An observer’s presence influences the experiment.

In 1930 came the prediction for a new tiny entity, the neutrino. It’s the universe’s most common particle. Five trillion zoom through your tongue every second. The 1936 discovery of the subatomic muon was equally unexpected. It famously made Nobel Prize winner Isidor Rabi say, “Who ordered that?”

The 1967 discovery of the first neutron star revealed—a sun smaller than Hawaii, whose material is so dense that each speck equals a cruise ship crushed down to the size of the tip of a ballpoint pen. And that was a double whammy because it was also the first pulsar. Did any genius foresee that some stars could spin hundreds of times a second?

The surprises haven’t let up. A microwave background energy filling all space? A solid Pluto-size ball in the middle of our planet, spinning faster than the rest of Earth? And what about the enormous hexagon at Saturn’s north pole? Or the fact that cosmic “rays” are overwhelmingly protons?

1998 brought astronomers another stunner. When the universe was half its present age, all its galaxy clusters simultaneously started moving faster. It’s as if stupendous rocket engines fired simultaneously everywhere in the cosmos. We don’t know anything about this antigravity force—but we now call it dark energy.

Then in 2010, the Fermi gamma ray telescope found two ultra high-energy spheres, each 25,000 light-years across, occupying half of our southern sky. The entities meet tangentially at our galaxy’s core like an hourglass. They’re violent and utterly baffling.

We’re out of room, but the universe never is. For the cosmos—and we who explore it—it’s always April Fool’s.

[1] Derived from an article by Bob Berman, “April Fool’s!” in Astronomy (44, 6, April 2016, p. 10)

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What Is General Relativity?

What Is General Relativity?[1]

In 1907, Albert Einstein had his “happiest thought” — people in free fall do not feel their own weight. This simple idea laid the foundation for his general theory of relativity, which Einstein presented 100 years ago this month.

The image above represents several situations, described below:

FALLING AND FLOATING

Imagine waking up in a box, completely weightless. Are you falling toward Earth or floating in outer space?

GRAVITY AND ACCELERATION

Now imagine waking up on the floor of the box.  Are you resting on Earth or accelerating in a spaceship?

LIGHT IS BENT BY SPACE AND TIME

In your accelerating spaceship, a beam of light would bend slightly. The Sun’s mass also bends starlight.

Einstein realized that falling freely in gravity feels the same as floating in space with no gravity. Gravity seems to be absent in free fall, at least in the small area around you. Since floating in space and falling in gravity feel the same, Einstein reasoned there must be no “force” of gravity at work in either state.

Einstein also realized that resting in gravity feels the same as accelerating at 1 g. Since acceleration and gravity feel the same, he argued that they must have the same cause.

Einstein proposed that the massive objects like the Earth curve space and time, and that what we call gravity arises from this curvature.

Acceleration feels the same as resting in a region of curved space and time.

A beam of light across the ship seems to bend slightly, because the ship moves forward as the light travels.

Einstein predicted that light should also be bent by gravity, since acceleration and gravity are equivalent.

Einstein’s prediction was confirmed during a solar eclipse in 1919, when distant background stars appeared to shift position.

Einstein Crosses and Rings

Astronomers have used the bending of light predicted by general relativity as a cosmic lens to study distant stars. A video produced for Einstein’s birthday in March explains:

Play Video 2:32

Sources: Max Planck Institute for Gravitational Physics; Michel Janssen, University of Minnesota

[1] Jonathan Corum and Jennifer Daniel, “What is General Relativity?” New York Times (November. 24, 2015), downloaded August 7, 2017

A Brief History of Black Holes—(2)

A Brief History of Black Holes—(2) Einstein and Schwarzschild[1]

Albert Einstein (left) developed his theory of gravity known as general relativity, in 1915.

Karl Schwarzschild (right) developed the idea for black holes from relativity’s equations in 1916, just a year after Einstein published his theory.

Much like M. C. Escher’s famous picture of two hands sketching each other, the circular reasoning of Einstein’s field equations makes them both elegant, yet also notoriously difficult to solve. At the root of this difficulty is Einstein’s far more famous equation

which states that energy and matter are interchangeable. Because gravity is a form of energy, it can behave like matter creating yet more gravity Mathematically speaking, general relativity is a nonlinear system. And nonlinear systems are really hard to solve.

It’s easy to imagine Einstein’s shock when, amid a dreadful war, Schwarzschild wrote back within a matter of days, describing the first known solution to Einstein’s field equations. Schwarzschild modestly writes, “As you see, the war treated me kindly enough, in spite of the heavy gunfire, to allow me to get away from it all and take this walk in the land of your ideas.” Einstein responds, “I have read your paper with the utmost interest. I had not expected that one could formulate the exact solution of the problem in such a simple way. I liked very much your mathematical treatment of the subject.”

Tragically, less than a year later, Schwarzschild succumbed to a skin disease contracted on the front, joining the millions of WWI fatalities due to disease. He left behind a solution that completely describes how space-time is warped outside a spherical object like a planet or star. One of the features of this mathematical solution is that for very compact, high-density stars, it becomes much harder to escape the gravitational field of the star. Eventually, there comes a point where every particle, even light, becomes gravitationally trapped. This point of no escape is called the event horizon. As one approaches the event horizon, time slows to a complete standstill.

For this reason, early physicists studying these bizarre objects often called them “frozen stars.” Today, we know them by the name first used by John Wheeler in 1967: black holes. Even though the event horizon played an integral part ion Schwarzschild’s solution, it took many years before black holes were accepted as anything other than a mathematical curiosity. Most of the world’s leading experts in general relativity in the first half of the 20th century were absolutely convinced that black holes could ever form in reali9ty. Arthur Eddington insisted, “There should be a law of nature to prevent a star from behaving in this absurd way.”

Complicating the issue was the concurrent development of quantum mechanics, a new field almost entirely characterized by cases of nature behaving absurdly. Physicists working at the intersection of quantum mechanics and general relativity began to appreciate how both fields were critically important to understanding very massive and dense stars. But the bizarre nature of these new branches of physics strained even the most gifted intuition, so that even 50 years after Schwarzschild’s landmark paper there was still no consensus on the existence of black holes.

 

[1] Jeremy Schlichtmann, “A Brief History of Black Holes,” Astronomy (44, 10, October 2016, pp.30-35

Brief History of Black Holes (1)

A Brief History of Black Holes—(1) Foundation for What We Know[1]

The foundation for what we know about black holes came during the Great War. Imagine the scene: December 1915. Europe and the world are struggling under the dark cloud of World War I. Somewhere on the eastern front, an older German artillery lieutenant huddles in his great coat, fighting to stay warm and dry at the bottom of a trench.

With numb and trembling fingers, he opens the latest dispatches from home. One particularly bulky package attracts his attention. That night, throwing caution to the wind, he risks using an electric light to read the long and detailed report. Little does he know that it will prove to be arguably the most important work of creative genius of the 20th century.

The author of this pivotal document was a theoretical physicist named Albert Einstein. The recipient was his colleague Karl Schwarzschild, the director of the Astrophysical Observatory in Potsdam and an accomplished theorist and mathematician. Despite his astronomical career, Schwarzschild, then in his 40s, joined the war effort.

Just weeks before, Einstein had completed 10 long years of dedicated work, successfully expanding his special theory of relativity to include gravitational forces along with electricity and magnetism. In four landmark papers published in the Proceedings of the Prussian Academy of Sciences, Einstein laid out the mathematical foundation of the general theory of relativity, still considered one of the most beautiful and elegant scientific theories of all times..

The pinnacle of this magnum opus was published November 25, 1915, with the concise title “The Field Equations of Gravitation.” While perhaps a bit opaque to anyone without a firm grasp of tensor calculus, he field equations can be neatly summarized by the words of the great physicist John Wheeler: “Space-time tells matter how to move; matter tells space-time how to curve.”

In this artist’s depiction of Cygnus X-1, a stellar-mass black hole strips gas from the surface of its companion star as they orbit each other. Since the 1970s, it has since become the strongest black hole candidate, with scientists at near certainty that it is one. Initially detected in x ray, it has since been studied in various other spectra.

[1] Jeremy Schnittman, “A Brief History of Black Holes,” Astronomy (44, 10, October 2016, pp.30-35)

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.