2011. november 29., kedd
1916: Karl Schwarzschild
In the classic sci-fi movie "The Day the Earth Stood Still," the alien visitor, Klaatu, pays a call on the world's greatest scientist (who would turn out to look a lot like Albert Einstein). Finding the professor out, he makes a few revisions to a complicated series of equations on a blackboard. In a later meeting he reveals that the corrected equations help him hop from planet to planet.
Karl Schwarzschild was no alien, but he did help the real Albert Einstein with his equations, which today help robotic probes hop from planet to planet.
Einstein published his theory of gravity, known as the General Theory of Relativity, in 1915. It consisted of a series of complicated equations that describe how matter interacts with space and time. Einstein was struggling to solve the equations when he received a letter from Schwarzschild, who had found a simple and elegant solution. Yet the ultimate conclusion of Schwarzschild's mathematics confounded both of them.
Schwarzschild, who was born in 1873 in Frankfurt am Main, Germany, was one of the most accomplished astronomers of his day. He published his first research papers, on the orbits of binary stars, while still in high school. Over the next two decades, he made important contributions to subjects as varied as optics, energy transport inside stars, and Halley's Comet.
He was appointed director of Potsdam Astrophysical Observatory in 1909, and volunteered for military service at the start of World War I. He directed a weather station in Belgium and calculated missile trajectories in France before being posted to Russia.
While in service he managed to write two papers about relativity and one about quantum mechanics.
In one of the relativity papers, Schwarzschild solved Einstein's equations for the case of a spherical, non-rotating object, which was a simpler approach than Einstein was pursuing.
Schwarzschild's calculations showed that if an object, such as a star, were to completely collapse so that its mass were squeezed to a single point, its gravitational field would "warp" the space around it so tightly that nothing could escape — not even light. In essence, he created the modern concept of a black hole.
Schwarzschild also showed that the distance from the center of mass at which the escape velocity would exceed the speed of light varies depending on the mass. Today, this distance is known as the Schwarzschild radius, and it defines the "boundary" between the black hole and the rest of the universe, known as the event horizon. Yet neither Schwarzschild nor Einstein believed that such an object could really exist.
By the time he finished his work on relativity, Schwarzschild was afflicted with a painful and fatal disease of the immune system. The man who showed an almost other-worldly mathematical ability died of an all-too-human affliction in May 1916.
Today, the idealized type of black hole that Schwarzschild described in his equations is named a Schwarzschild black hole in his honor.
Down the (Gravitational) Drain
1963: Roy Kerr
In the early 1960s, not only was there no direct evidence of black holes, they didn't even have a name yet. But thanks to a solution of Albert Einstein's equations by a young University of Texas mathematician, physicists had a perfect model of what they would look like and how they would behave.
Roy Kerr was a New Zealand native who was not yet 30 years old. Yet he devised a solution to the field equations of Einstein's theory of gravity that described how massive stars "drag" the spacetime around them like water circling around a bathtub drain.
Kerr's solution required a mathematically pure body, which had only two characteristics: mass and spin. Ordinary stars don't fit that model because they have "hair" — lots of messy qualities like magnetic fields and winds that can have an effect on the space around them.
Other physicists quickly realized, however, that Kerr had devised the perfect description of a spinning black hole. And since every black hole, like every other object, is expected to spin, Kerr had described every black hole in the universe.
An earlier solution to Einstein's equations, for a perfectly spherical, non-spinning body, produced two components: a singularity, which contains all of the black hole's mass, and the event horizon, which is the "boundary" between the black hole and the outside universe.
But all real black holes should spin, either because the stars from which they were born were spinning or because the process of ingesting infalling matter makes them spin.
Kerr's equations, which added rotation to the mix, added a third component to a black hole, called an ergosphere. It's a region of spacetime outside the event horizon that is dragged by the gravity of the black hole. In profile it looks like an oval, with a wider bulge around the equator than through the poles. (A spinning black hole is wider through the equator than the poles as well.)
(Kerr's work also seemed to lead to a model in which the black hole's matter is compressed into a ring, not a singularity. In this model, the ring could serve as a portal to another region of spacetime; anything entering it would exit through a "white hole" somewhere else in space and time. Physicists have since rejected this idea in favor of a singularity.)
As seen by an outside observer, an object falling toward the black hole, such as a spacecraft, would be captured in the ergosphere and would appear to spin around the black hole. An astronaut aboard the ship, though, would see his path as a straight line into the black hole.
Kerr's work not only led to a perfect model of real black holes, it led physicist Roger Penrose to devise a way to "steal" energy from a black hole.
A spaceship would fly into the swirl of spacetime around the black hole and split apart. Half of the ship would fall into the black hole, while the other half would be thrown back into space. The escaping half would carry out much more energy than the whole spacecraft carried in. This "theft" of rotational energy would cause the black hole to slow down a tiny bit. Present-day spacecraft use a similar technique to steal orbital energy from a planet, getting a boost toward more-distant destinations.
With Kerr's equations and the follow-up work of several other researchers, scientists now had a perfect description of a black hole. Now all they needed was a name for these oddballs, and evidence that they really exist.
Making (Stellar) Waves
1931: Subrahmanyan Chandrasekhar
For most people, an ocean voyage is a time for a little R&R. But for the young Indian physicist Subrahmanyan Chandrasekhar, it was a time for C&C — contemplation and calculation. He pondered the fates of stars, and realized that they won't all end their lives in the same way. His work, for which he eventually received the Nobel Prize, helped lead to the understanding that some stars will collapse to form black holes.
A young Chandrasekhar [AIP]
Chandrasekhar was born in 1910 in British India. After earning his degree in physics, he was invited to pursue a doctorate at Cambridge University. It was during the two-and-a-half week trip to England, in 1930, that he contemplated the fates of stars.
Stars like the Sun die by casting their outer layers into space, leaving only their cores, known as white dwarfs. Most of the mass of the original star is packed into a ball the size of Earth, so a teaspoon of white dwarf material would weigh several tons.
At such great density, gravity tries mightily to make the white dwarf collapse to an even smaller size. But under extreme pressure, the electrons in atoms jump to higher and higher energy levels, exerting an outward pressure that balances theinward pull of gravity and preventing further collapse.
As Chandra, as he's best known, began his ocean voyage, astronomers thought that all stars, no matter how big or massive, were fated to become white dwarfs.
Yet Chandra discovered otherwise. He calculated that there is a weight limit for white dwarfs: around 1.4 times the mass of the Sun. Beyond that mass, known today as the Chandrasekhar limit, the electrons cannot exert enough outward pressure to resist the inward pull of gravity. Anything heavier must either collapse further or explode.
But Arthur Eddington, one of England's leading astronomers, considered the idea absurd. He turned most other astronomers against Chandra's ideas. So the young physicist left England and took a job at the University of Chicago, where he remained for the rest of his life.
Before long, however, others confirmed Chandra's calculations. If a stellar core is more than about 1.4 times the mass of the Sun, it forms a neutron star, which compresses the mass of several suns into a sphere no bigger around than a city. Its matter is squeezed so tightly that all of the space between atoms is crushed out of existence, and their particles are fused together to form a ball of solid neutrons.
Later, others would calculate that for the heaviest stellar cores, with masses three times greater than the Sun, even that is not the ultimate fate. Gravity eventually overcomes all other forces of nature and crushes the core into a single point, forming a black hole.
Chandrasekhar pursued many areas of research during his career, including black holes. But in 1983, he received the Nobel Prize for his work on the evolution of stars — work that began with a boat ride more than five decades earlier.
It's All Relative
1915: Albert Einstein
For Albert Einstein, daydreaming was not an escape from the drudgery of everyday life but a journey into the secrets of the universe.
Eddington (right) with Einstein
In 1907, for example, during and after long days as a clerk in the Swiss patent office, the young physicist pondered the physics of falling. He wondered what a housepainter would experience if he fell off a roof and plunged toward the ground.
Just two years earlier, Einstein had published his Special Theory of Relativity, which demonstrated that time and distance are not a constant framework, as physicists believed, but vary with an observer's motion. As you move faster, your own clock would appear to tick more slowly than those of people who were moving more slowly. At the same time, distances would compress — a yardstick would grow shorter relative to those at rest.
Special Relativity explained the effects of acceleration, but not the effects of gravity, which was a far more difficult problem.
The 1919 solar eclipse and a New York Times headline
As he considered the painter falling off a roof, though, Einstein experienced what he described as one of the greatest insights of his life: The painter would experience weightlessness as gravity accelerated him toward the ground. This meant that the effects of acceleration and gravity were the same. Put another way, you couldn't tell the difference between standing still on Earth, where you are pulled downward by gravity, and accelerating smoothly in an elevator out in space — you would feel exactly the same effect.
In Einstein's new vision of the universe, then, gravity was no longer a "force" acting instantly across the universe, as Isaac Newton had envisioned it. Instead, any object with mass — from a pill bug to a galaxy — "warped" the spacetime around it.
A pill bug's effect is negligible, but the effect of more massive objects could be profound. A star, for example, should curve the space around it in a way that it would deflect the light of more-distant stars passing by it. This effect was confirmed during a solar eclipse on May 29, 1919, when an expedition led by British astronomer Sir Arthur Eddington measured stars that appeared near the Sun and found that their positions were shifted slightly, just as Einstein's equations predicted.
The discovery made Einstein an international celebrity, and allowed other scientists to carry his equations to their extremes. If mass warps spacetime, they reasoned, then enough mass packed into a small enough space should create an infinite warp. In other words, it would warp space so much that nothing could escape from it, including light, creating what would come to be known as a black hole.
Many experiments have confirmed Einstein's Theory of General Relativity, as his new theory of gravity was called upon its presentation in 1916. Yet Einstein himself never believed that black holes could exist. For once, imagination failed the scientist who daydreamed about the secrets of the universe.
Einstein's paper introducing General Relativity
A Black Hole by any Other Name
1967: John Archibald Wheeler
John Archibald Wheeler was one of the most accomplished physicists of the 20th century. He helped develop the theory of nuclear fission and made key contributions to Einstein's theory of gravity and the shadowy realm of quantum mechanics. When he died in 2008, however, the lead paragraph in almost every newspaper and magazine story focused on one relatively minor accomplishment: He coined the term "black hole."
Wheeler in the 1980s
Wheeler had studied under famed Danish physicist Neils Bohr, and in the late '30s they developed the theory of nuclear fission that later led to the development of the atomic bomb. Wheeler worked on the bomb and, after World War II, on the new hydrogen bomb, before turning to the complex realm of Einstein's general relativity.
In 1939, J. Robert Oppenheimer, another atom-bomb pioneer, and a graduate student had calculated that a star of sufficient mass would collapse to such great density that nothing could escape its gravitational pull, including light.
Wheeler was intrigued by the conclusion, but he thought it was flawed because it did not consider the effects of nuclear reactions, heat, pressure, or anything else other than gravity. In 1958, in fact, he and Oppenheimer publicly argued over the conclusion because Wheeler believed that such a collapsed object would violate fundamental laws of physics.
By that time, however, other physicists were using both the computers and the numerical codes created to simulate the nuclear reactions and intense temperatures and pressures inside H-bomb explosions to revisit Oppenheimer's calculations. Their results were the same: At a certain point, gravity simply overpowers every other force in the universe.
And in 1958, physicist David Finkelstein described the "event horizon" surrounding a collapsed star as a one-way door through which objects could enter but never leave. The physics of any processes inside the horizon are forever shielded from prying eyes.
Wheeler slowly became convinced that dark "collapsed" stars could exist, and he began studying them fiercely, becoming one of the world's leading experts on the subject.
Yet neither the public nor most other physicists were paying much attention to the subject, in part because no one really knew what to call such bizarre objects. Names like "collapsed stars" and "Schwarzschild singularities" were bandied about, but created little enthusiasm.
So in late 1967, Wheeler introduced a new name, first at a conference in New York and later in a lecture to the American Association for the Advancement of Science: black hole.
"I decided to be casual about the term," Wheeler wrote in his 1998 autobiography, "dropping it into the lecture and the written version as if it were an old familiar friend. Would it catch on? Indeed it did. By now every schoolchild has heard the term. Richard Feynman, when he heard the term, chided me. In his mind, it was suggestive. He accused me of being naughty."
Naughty or nice, though, it stuck, earning John Wheeler a spot in the history books and giving the rest of us a catchy name for one of the most intriguing phenomena in the universe.
2011. november 26., szombat
2011. november 24., csütörtök
Website RPP is claiming that Renato Davila Riquelme, an anthropologist working at the Privado Ritos Andinos museum in Cusco, has discovered remains of something that isn't human. Measuring at 20 inches tall, the tiny remains were originally believed to be that of a child, but Spanish and Russian doctors disagree, saying:
57-Story Porsche Designed Highrise Features Car Elevator That Drops Both Car And Resident Off At Unit
After the resident pulls over and switches off the engine, a robotic arm that works much like an automatic plank will scoop up the car and put it into the elevator. Once at the desired floor, the same robotic arm will park the car, leaving the resident nearly in front of his front door.