Where comets come from For almost 50 years astronomers have suspected that somewhere out in the coldest , farthest reaches of the solar system there was a place where comets were kept. Now, thanks to the Hubble space telescope and the daunting persistence of a handful of sky watchers, the comet's home has been found - and the known population of the solar system increased by some 200 million new members. /*---------------------------------------------------------------------*/ First Cell Life isn't boundless, It can exist only within some manner of container - a skin or bark or cell membrane. For nearly two decades bipohysicist David Deamer has been trying to figure out how life's molecules originally got packaged. And along the way he's created something like a cell. /*---------------------------------------------------------------------*/ The Philosopher's atom The atom isn't what it used to be. It's stranger, thanks to the obscure mathematical logic of quantum mechanis. One oddball atom, refuses to hid behind the math. It insists on behaving - in a way we can comprehend. Classical physics (Isaac Newton) is the description of the world in terms of objects- atoms, marbles, planets, galaxies moving along precise trajectories in space-time. Quantum physics describes the world with potentiality, and possibility ; speaks of chaince and randomness. When the outer electon in a Rydberg atom leaves the nucleus on its long, loopy orbit, it stops behaving like a creature of quantum mechanics . Instead it acts more like your garden variety baseball, galaxy or molecule A class of objects known as Rydberg atoms (named after 19th cen. swedish physicist Johannes Robert Rydberg). These are ordinary atoms in which the outermost electron has been promoted to an immensely large orbit. (To gain some idea of just how large that orbit is, you may imagine that by analogy, a Rydberg solar system would look like a real one, excpet that Pluto would have been pushed out a thousant times farther from the sun). Rydberg atoms occur in nature, but are delicate - a small disturbance can tear the distant electron from its orbit and leave behind the positively charged rump of the atom (ion). The precision of modern lasers, is allowing physicists to manipulate these exotic atoms, and as it turns out they function as a natural magnifying glass focused on the quantum-classical boundary. The outermost electron along a cometlike orbit periodically dips into the core of the atom (guided by an external electric or magnetic field), the electron mingles with outer electrons in quantum mechanical cloud. And returns to firm ground of classical mechanics. 1919 Bohr - hydrogen atom is a spherical , translucent cloud. 1925 Inventor of Quantum Theory , Werner Heisenberg. The atom of modern physics can be symbolized only through a partial differential equation in an abstract space of many dimensions. Erwin Schrodinger developed quantum mechanics independently, goal of atomic physics is to creat images of the interior of the atom that appeal to intuition. 1980 Scanning tunneling microscopes for the first time rendered atoms on the surfaces of solid materials visible to the eye, show them a multicolored lumps. 1969 Frank Tomkins and William Garton at Argonne National LAbs, were investigating light absorbed as it shines through a bottle of barium gas. First hint of Rydberg atoms. As they looked at the light exiting the bottle saw that barium atoms absorbed light only of particular frequencies or energies. As they increased the energy of the light particles, (photons) they observed spikes in the amount of light the barium atoms absorbed. The spikes are well known. Every atom incorporates its own discrete quantum mechanical energy levels corresponding to Bohr's orbits. The electron's energy values are quantized. Eventually as the energy of the photons increased, the outermost electron was torn away leaving behind a positive ion. Beyond the ionization energy the barium atom could absorb nothing. Placed in a magnetic field and turned their laser up beyond the ionization energy, the outermost electrons should have left, but the barium atoms were still absorbing energy. They didn't see sharp spikes indicating definite quantum energy levels, but minute, slightly rounded ripples. The inner electrons were too tightly bound to the nucleus to cause absorption spikes, the results suggested a new mechanism of absorption at work : the rogue out electron was still ifluencing the atom in some way. The magnetic field converted ordinary barium atoms into exotic Rydberg atoms, where the outermost electron left the atom and moved in huge cometlike orbits. When it returned periodically to the nucleus, the electron modified the atom's normal pattern of allowed energy levels, giving it the ability to absorb photons when it would normally have been saturated. In 1969 the theoretical machinery was not in place to confirm this. Experiments at Argonne, -- they might not know precisely what was allowing the atom to absorb "extra" energy, but they certainly expected tos ee that absorption portrayed as a neat, regular staircase (quantized energies) not a craggy side of a cliff. 1988 John Delos , the outermost electron behaves like a classical particle that travels along a real orbit through space and time. Away from the central ion and back again, like a comet. But as it repeatedly crosses the line into the nonclassical world of the atomic nucleus it manifests all the bizarre attributes of the quantum particle it remains at heart. In quantum mechanics, an electron is described according tot he principle of wave particle duality , every moving particle can be regarded as a wave whose characteristics depend on the particle's energy. Delos realized that the departing and arriving electron as a wave displayed symptoms of interference. << According to quantum mechanics, the electron leaves the Rydberg atoms as a smooth spherical wave , but encounters itself on its way back, this time as an irregular spherical wave. The resulting interference pattern determines what trajectories the electron can take. >> When the laser light impinges on the atom, it causes the wave-electron to leave the nucleus and travel outward, much as ripples travel away from a stone dropped into a pond. But the ripples on the water's surface are essentially a 2-dimensional phenomenon, while the electron takes the form of a 3D spherical wave. The wave's movement outward marks the infinite possible trajectories that the electron, as a classical particle, might take as it moves away from the atom. At some distance away, the electron shakes off the effects of the quantum mechanics and follows winding trajectories that eventually lead back to the nucleus. As it arrives, it once again takes on the character of a wave, this time traveling to the nucleus from all directions. However, the elaborate orbits that the electron follows wihle it is far from the atom mean that the returning waveelectron is not a near perfect sphere but a highly irregular, complex wave. Delos established trajectories produced , he had explained the new mechanism that caused the mysterious ripples. The Rydberg electron is allowed tocontinue to absorb energy, so long as that energy is precisely of an amount that wil propel the electron to the next trajectory allowed by the interference pattern. << An electron in a Rydberg atom is not restricted to the elliptical trajectory of a comet. Its path can be simple or complex; it can trace a regular pattern or degenerate into utter chaos. These 2 orbits, among the more simple, teeter on the brink of chaos.>> Delos calculated the precise shape of the classical orbit. They were Rydberg electrons, far from the nucleus and uninfluenced by interactions with other particles. As they approached the parent atom, they shifted between classical and quantum mechanical incarnations. As the electron left the nucleus and interacted with the B field, complex orbits arose. Intricate swoopse and folds . The solution turned out to lie in another bit of quantum theory, Heisenberg's Uncertainty principle. This fundamental law asserts that certain pairs of variables cannot be simultanneously determined with great accuracy. Thus for example, if the speed of a n electron is measured with great precision, its position will necessarily be uncertain, and vice versa. The variables for Rydberg orbits are not so much position and speed as energy and time. A rough measurement of energy will pick out only those features of the atom that ocur over a short time. A narrow pinning down of the energy automatically includes longer lasting effects. The original experiment Garton/Tomkins used unsophisticated equipment, measured absorption with a crude eenrgy resolution. This meant in turn that ripples due only to the shortest orbits were discernible. When lasers were used to make precise measurements of the photon energy, orbits with longer durations contributed to the interference pattern. At first glance the universe governed by Newton's laws with its particle trajectories that sweep elegantly through space and time , appears to be a realm of order and predictability. The random events of quantum mechanics seem to signify chaos. Delos's theory illustrates the opposite is true. chaos happens when two marbles , or two atoms, or two electrons, whose motions differ by imperceptible amounts at the outset , and which are exposed to identical influences diverge and wander far apart. It can be through of as an overly sensitive response to initial conditions. Unruly behavior frustrates attempts at prediction. Since there are no trajectories in quantum mechanics, chaos never arises. Chaos cannot exist in a quantum mechanical system. Physicists have finally realized that classical mechanics almost always is chaotic. At low energies the orbits of Rydberg electrons are simple and predictable as the ellipses of the Bohr model, but as the energy increases the motion becomes more agitated , classical chaos suddenly sets in. How can the chaotic classical theory tell us anything about the orderly nonchaotic architecture of the Rydberg atom? /*---------------------------------------------------------------------*/ Physics Watch The right hand of the Universe /*---------------------------------------------------------------------*/ /*---------------------------------------------------------------------*/ Breakthroughs Bubble Math Color-coded chromosomes. /*---------------------------------------------------------------------*/ Robocopter In the 4 years at the International Aerial Robotics Competition has existed , no entrant has been able to do much more thantake off and land unaided. Stability wasa big problem - may teams used balloons to avoid the challenges of purely mechanized flight. Last summer this robotic helicopter, built by Standord students was more successful. Guided during takeoff / landing, but airborne, the helicopter found/retrieved a metal disk and flew over a barrier on its own, tasks difficult even with human help. Helicopters are very unstable. The time between taking your hands off the controls and crashing is about 1-2 seconds. The helicopter is a radio controlled hobyists model with an onboard computer replacing the human-controlled radio signals. Thecraft used 4 antennas to pull in signals from GPS satellites. The wrote a program that managed to get as much information as possible from GPS, fixing the helicopter's position to within an inch. This allowed the helicopter to steer itself with the GPS signals and programmed course map, kept the craft stable during its 3 minute flight. Similar systems may navigate and land airplanes. /*---------------------------------------------------------------------*/ Focusing is the bane of amateur photographers, autofocus cameras offer only a partial solution. The problem is fundamental to the way cameras work. Light waves bouncing off the object being photographed pass through a lens, which bends them so that they form an upside-down image. Exactly how far behind the lens this image forms depends on the distance to the object in front of the lens. That's where focusing comes in. When the lens is moved forward or backward, the image is made to land smack on the film. Auto focus cameras follow the same principle, adjusting the lens until the object in the center of the frame is in focus. Narendra Ahuja at University of Illinois, has a different idea about who cameras should operate. Ahuja has invented a camera that keeps every object in the frame in perfect focus, no matter whether it is a few inches in front of your face or on the distant horizon. Ahuja dispensed with film in favor of a more flexible medium of electronics. In his camera, the light coming through the lens falls on an electronic backplane, a patch of light sensitive electronic cells, each of which generates a tiny electric voltage proportional to the brightness of the image at that spot. These voltages constitute an electronic snapshot that can be stored in a tiny memory chip and manipulated with a computer. Next came a more readical state. He tilted the camera's backplane so that one side was closer to the lens than the other. In a conventional camera this tilting would only create a very distorted image. On the end of the backplane closer to the lens, people in the foreground would appear in focus, and the distant mountains behind them would be blurry; while on the other end of the backplane, people would be blury while the mountains would come through in sharp focus. That would solve our focusing problem only if the various objets in the photograph had the courtesy to line up right to left according to distance. But since Ahuja's image is captured electronically, he has the freedom to play around with it. That led to the 3rd and most radical step. Rather than keep the lens fixed, he spins it so that the entire scene sweeps across the backplane , The lens starts from left to right During his swewep, an image of every object As a result, each object, regardless of its distance ,ends n ofocus on the backplane. The computer tracks the myrias image that fall on the backplane and picks ou tht eones that are in focus by measuring whicih has the most contrast. Finally the comssembles the imgaes into one master image on which - voila!- everything appears in focus With the spinning lens and electronically manipulated pictures, Ahuja found he could also program the camera to take panormic pictures. The lens simply rotates as it does normally , except that it sweeps through a very large angle (up to 360 degrees). Even though the backplane is not big enough to contain the entire scene all at once, the computer simple stores every piece of the wide image and then assembles it afterward. Ahuja is now working on a portable version of the camera to demonstrate to manufacturers who might be willing to bankroll further development. He says nothing in the design makes it inherently costly. "It is a simple modification of existing equipment" "The only big difference is in performance." /*---------------------------------------------------------------------*/ Mag-but-not-lev trains Engineers at Sandia National Labs , tackled the problem how to quickly and reasonable price launch killer satellites that could shield America from nuclear attack. One idea was to build a half mile long "coil gun" that would hurl satellites into orbit using pulsed magnetic fields. Magnteically levitated train prototypes have been around for 20years. One in Japan has reached speeds exceeding 320miles per hour. But maglev trains require a whole new track network, a very expensive infrastructure. The train float passively carried along by magnetic pulses. The Sandia system (Segmented rail phased induction motor) system is different. It doesn't levitate: it has wheels and rolls on rails like conventional trains. And unlike magnlev trains, a Seraphim train would carry its own motor - magnetic coils powered by an onboard gas-turbine generator. That means it could run on existing tracks modified to include a series of small, 3' long aluminum plates attached to the rails at 3' intervals. Electric currents surging through the train's coils would induce electric currents i the plates; the magnetic field created by the latter would oppose the magnetic field of the former, thus pushing the train along. Recent tests of the system have accelerated a laboratory model to 34 mph on 12' of track. Problem is to find a way to shield the magnetic coils. Marder is optimistic that a full scale system could reach speeds of 200 mph on upgraded conventional tracks or 300 mph on specially designed tracks. Conventional trains can't reach such speeds efficiently because their wheels drive the train, and some power is wasted when he wheels lose traction and slip along the rails. That doesn't happen with the Sandia train, since the wheels merely guide the train along the rails. All the power you have can go into propulsion. You're not going to spin your wheels.