1. 1947 Roswell crash: UFO proponents claimed that the US military had captured a crashed alien aircraft. This well-publicised, controversial incident became apop culture phenomenon.
Explanation: the US military maintained that it had recovered debris from an experimental high-altitude surveillance balloon belonging to a classified programme named “Mogul”.
2. 1947 Kenneth Arnold case: the press coined the term “flying saucer” after this American businessman and pilot claimed he had seen nine objects flying in achain near Mount Rainier, Washington. Arnold described them as saucers skipping across water.Explanation: The US Air Force formally listed the caseas a mirage.
3. 1952 Washington, D.C. flap: this series of UFO reports was accompanied by radar contacts at three separate airports. Country-wide headlines spurred the formation of the CIA Robertson Panel.
Explanation: the US Air Force suggested that a temperature inversion - in which a layer of warm, moist air covered a layer of cool, dry air closer to the ground - had caused radar signals to bend and give false returns.
4. 1957 Levelland case: police investigated numerous motorist reports of engines stalling when encountering a glowing, egg-shaped object. Motorists claimed that their vehicles had restarted after the "object" had left.
Explanation: an air force investigation concluded thatan electrical storm had caused the sightings and vehicle failures.
5. 1966 Westall encounter: more than 200 students and teachers at two schools in Melbourne allegedly saw a UFO that descended into a grass field. The object then ascended over a local suburb, according to reports. Witnesses still gather for reunions.Explanation: Australian Skeptics, a non-profit organisation which investigates paranormal and pseudo-scientific claims by using scientific methodologies, believed that the object was an experimental military aircraft.
6. 1967 Shag Harbour crash: a large object crashed into Shag Harbour, Nova Scotia.
Explanation: The Canadian Department of National Defence officially classified this sighting as unsolved following a naval search and investigation. The Condon Committee, which investigated UFOs at the University of Colorado, failed to resolve the case.
7. 1976 Tehran incident: A UFO was believed to have disabled the electronic equipment of two F-4 interceptor aircraft as well as ground control equipment. The Iranian generals involved said on public record that they had thought the object was extraterrestrial.
Explanation:UFOs: The Public Deceived, a book by Philip Klass, claimed that witnesses saw an astronomical body - probably Jupiter - and pilot incompetence and equipment malfunction accountedfor the rest.
8. 1986 São Paulo chase: around 20 UFOs were seen and detected by radar in various parts of Brazil. They reportedly disappeared as five military aircraft were sent to intercept them.
Explanation: Geoffrey Perry, a British space researcher, attributed the incident to debris that were ejected by Soviet space station Salyut-7 and re-entered Earth’s atmosphere around central-western Brazil.
9. 1989/1990 Belgium wave: around 13,500 people claimed to have witnessed large, silent, low-flying black triangles. Around 2,600 filed written statements describing what they had seen. The frequently-photographed wave was tracked by NATO radar and jet interceptors and investigated by Belgium’s military.
Explanation: Renaud Leclet, a French ufologist, believed some of the sightings could have been explained by helicopters.
10. 2008 Turkey video: a night guard at the Yeni Kent Compound claimed he had video taped multiple UFOs
Stars and planets form out of vast clouds of dust and gas. Small pockets in these clouds collapse under thepull of gravity. But as the pocket shrinks, it spins rapidly, with the outer region flattening into a disk.Eventually the central pocket collapses enough that its high temperature and density allows it to ignite nuclear fusion, while in the turbulent disk, microscopic bits of dust glob together to form planets. Theories predict that a typical dust grain is similar in size to fine soot or sand.In recent years, however, millimeter-size dust grains — 100 to 1,000 times larger than the dust grains expected — have been spotted around a few select stars and brown dwarfs, suggesting that these particles may be more abundant than previous thought. Now, observations of the Orion nebula show a new object that may also be brimming with these pebble-size grains.
The team used the National Science Foundation’sGreen Bank Telescopeto observe the northern portionof the Orion Molecular Cloud Complex, a star-forming region that spans hundreds of light-years. It contains long, dust-rich filaments, which are dotted with many dense cores. Some of the cores are just starting to coalesce, while others have already begun to form protostars.Based on previous observations from theIRAM 30-meter radio telescopein Spain, the team expected to find a particular brightness to the dust emission. Instead, they found that it was much brighter.“This means that the material in this region has different properties than would be expected for normal interstellar dust,” said Scott Schnee, from the National Radio Astronomy Observatory, in a press release. “In particular, since the particles are more efficient than expected at emitting at millimeter wavelengths, the grains are very likely to be at least a millimeter, and possibly as large as a centimeter across, or roughly the size of a small Lego-style building block.”Such massive dust grains are hard to explain in any environment.Around a star or a brown dwarf, it’s expected that dragforces cause large particles to lose kinetic energy andspiral in toward the star. This process should be relatively fast, but since planets are fairly common, many astronomers have put forth theories to explain how dust hangs around long enough to form planets. One such theory is the so-called dust trap: a mechanism that herds together large grains, keeping them from spiraling inward.But these dust particles occur in a rather different environment. So the researchers propose two new intriguing theories for their origin.The first is that the filaments themselves helped the dust grow to such colossal proportions. These regions, compared to molecular clouds in general, have lower temperatures, high densities, and lower velocities — all of which encourage grain growth.The second is that the rocky particles originally grew inside a previous generation of cores or even protoplanetary disks. The material then escaped back into the surrounding molecular cloud.This finding further challenges theories of how rocky, Earth-like planets form, suggesting that millimeter-size dust grains may jump-start planet formation and cause rocky planets to be much more common than previously thought.The paper has been accepted for publication in the Monthly Notices of the Royal Astronomical Society.
Most scientists now believe that we live in a finiteexpanding universewhich has not existed forever, and that all thematter,energyand space in theuniversewas once squeezed into an infinitesimally small volume, which erupted in a cataclysmic"explosion" which has become known as theBig Bang.Thus, space, time,energyandmatterall came into being at an infinitely dense, infinitely hotgravitational singularity, and began expanding everywhere at once. Current best estimates are that this occurred some 13.7 billion years ago, although you may sometimes see estimates of anywhere between 11 and 18 billion years.TheBig Bangis usually considered to be a theory of the birth of theuniverse, although technically it does not exactly describe the origin of theuniverse, but rather attempts to explain how theuniversedeveloped from a very tiny, dense state into what it is today. It is just a model to convey what happened and not a description of an actual explosion, and theBig Bangwas neither Big (in the beginning theuniversewas incomparably smaller than the size of a singleproton), nor a Bang (it was more of a snap or a sudden inflation).
In fact, 揺xplosion� is really just an often-used analogy and is slightly misleading in that it conveys the image that theBig Bangwas triggered in some way at some particular centre. In reality, however, the same pattern of expansion would be observed from anywhere in theuniverse, so there is no particular location in our present universe which could claim to be the origin.It really describes a very rapid expansion or stretching of space itself rather than an explosion in pre-existing space. Perhaps a better analogy sometimes used to describe the even expansion of galaxies throughout the universe is that of raisins baked in a cake becoming more distant from each other as the cake rises and expands, or alternatively of a balloon inflating.Neither does it attempt to explain what initiated the creation of the universe, or what came before theBig Bang, or even what lies outside the universe. All of this is generally considered to be outside the remit of physics, and more the concern of philosophy. Given that time and space as we understand it began with theBig Bang, the phase 揵efore theBig Bang� is as meaningless as 搉orth of the North Pole�.Therefore, to those who claim that the very idea of a Big Bang violates theFirst Law of Thermodynamics(also known as theLaw of Conservation of Energy) that matter and energy cannot becreated or destroyed, proponents respond that theBig Bangdoes not address the creation of theuniverse, only its evolution, and that, as the laws of science break down anyway as we approach the creation of the universe, there is no reason to believe that theFirst Law of Thermodynamics would apply.
The Second Law of Thermodynamics, on the other hand, lends theoretical (albeit inconclusive) support to the idea of a finite universe originating in a Big Bang type event. If disorder andentropyin the universe as a whole is constantly increasing until it reaches thermodynamic equilibrium, as the Law suggests, then it follows that theuniversecannot have existed forever, otherwise it would have reached its equilibrium end state an infinite time ago, our Sun would have exhausted its fuel reserves and died long ago, and the constant cycle of death and rebirth ofstarswould have ground to a halt after an eternity of dissipation ofenergy, losses of material toblack holes, etc.TheBig Bangmodel rests on two main theoretical pillars: theGeneral Theory of Relativity(Albert Einstein抯 generalization of Sir Isaac Newton抯 original theory ofgravity) and theCosmological Principle(the assumption that thematterin theuniverseis uniformly distributed on the large scales, that theuniverseis homogeneous and isotropic).TheBig Bang(a phrase coined, incidentally, by the English astronomerFred Hoyleduring a 1949 radio broadcast as a derisive description of a theory he disagreed with) is currently considered by most scientists as by far the most likely scenario for the birth ofuniverse. However, this has not always been the case, as thefollowing discussion illustrates.
jupiter rotates very fast on its axis, once every 10 hours. This has formed a pattern of stripes in it's atmosphere, which runs parallel to the equator. The lighter zones are warm, rising masses of clouds, and the dark ones are cold, descending clouds. This pattern is disturbed by storms. One of these, the 'large red spot ' is huge and can see from Earth. Jupiter is not only the biggest but also heaviest planet. It has more than 60 moons. Four of them were detected by Italian astronomer Galileo Galilei with a telescope as early 400 years ago.
Black holes are the cold remnants of former stars, so dense that no matter—not even light—is able to escape their powerful gravitational pull.While most stars end up aswhite dwarfsorneutron stars, black holes are the last evolutionary stage in the lifetimes of enormous stars that had been at least10 or 15 times as massive as our own sun.When giant stars reach the final stages of their lives they often detonate in cataclysms known assupernovae. Such an explosion scatters most of a star into the void of space but leaves behind a large"cold" remnant on which fusion no longer takes place.In younger stars, nuclear fusion creates energy and a constant outward pressure that exists in balance withthe inward pull of gravity caused by the star's own mass. But in the dead remnants of a massive supernova, no force opposes gravity—so the star begins to collapse in upon itself.With no force to check gravity, a budding black hole shrinks to zero volume—at which point it is infinitely dense. Even the light from such a star is unable to escape its immense gravitational pull. The star's own light becomes trapped in orbit, and the dark star becomes known as a black hole.Black holes pull matter and even energy into themselves—but no more so than other stars or cosmic objects of similar mass. That means that a black hole with the mass of our own sun would not"suck" objects into it any more than our own sun doeswith its own gravitational pull.Planets, light, and other matter must pass close to a black hole in order to be pulled into its grasp. When they reach a point of no return they are said to have entered the event horizon—the point from which any escape is impossible because it requires moving faster than the speed of light.
Small But Powerful: Black holes are small in size. A million-solar-mass hole, like that believed to be at the center of some galaxies, would have a radius of just about two million miles (three million kilometers)—only about four times the size of the sun. A black hole with a mass equal to that of the sun would have a two-mile (three-kilometer) radius.Because they are so small, distant, and dark, black holes cannot be directly observed. Yet scientists have confirmed their long-held suspicions that they exist. This is typically done by measuring mass in a region of the sky and looking for areas of large, dark mass.Many black holes exist inbinary star systems. These holes may continually pull mass from their neighboring star, growing the black hole and shrinking the other star, until the black hole is large and the companion star has completely vanished.Extremely large black holes may exist at the center ofsome galaxies—including our own Milky Way. These massive features may have the mass of 10 to 100 billion suns. They are similar to smaller black holes but grow to enormous size because there is so muchmatter in the center of the galaxy for them to add. Black holes can accrue limitless amounts of matter; they simply become even denser as their mass increases.Black holes capture the public's imagination and feature prominently in extremely theoretical concepts like wormholes. These "tunnels" could allow rapid travel through space and time—but there is no evidence that they exist.
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If a wormhole could exist, it would appear as a spherical openingto an otherwise distant part of the cosmos. In this doctored photograph of Times Square, the wormhole allows New Yorkers to walk to the Sahara with a single step, rather than spending hours on the plane to Tamanrasset. although such a wormhole does not break any known laws of physics, it would require the production of unrealistic amounts of negative energy.Can a region of space contain less than nothing?Common sense would say no; the most one could do is remove all matter and radiation and be left with vacuum. Butquantum physicshas a proven ability to confound intuition, and this case is no exception. A region of space, it turns out, can contain less thanw nothing. Its energy per unit volume - the energy density - can be less than zero.Needless to say, the implications are bizarre. According toEinstein’s theory of gravity, general relativity, the presence of matter and energy warps the geometric fabric of space and time.What we perceive as gravity is the space-time distortion produced by normal, positive energy or mass.But when negative energy or mass - so-called exotic matter - bends space-time, all sorts of amazing phenomena might become possible: traversable wormholes, which could act as tunnels to otherwise distant parts of the universe; warp drive, which would allow for faster-than-light travel; andtime machines, which might permit journeys into the past.Negative energy could even be used to make perpetual-motion machines or to destroyblack holes. AStar Trekepisode could not ask for more.For physicists, these ramifications set off alarm bells. The potential paradoxes of backward time travel–such as killing yourgrandfather before your father is conceived–have long been explored in science fiction, and the other consequences of exotic matter are also problematic.They raise a question of fundamental importance: Do the laws ofphysics that permit negative energy place any limits on its behavior?We and others have discovered that nature imposes stringent constraints on the magnitude and duration of negative energy, which (unfortunately, some would say) appear to render the construction of wormholes and warp drives very unlikely.
Double Negative:
Before proceeding further, we should draw the reader’s attention to what negative energy is not.It should not be confused with antimatter, which has positive energy. When an electron and its antiparticle, a positron, collide, they annihilate. The end products are gamma rays, which carry positive energy. If antiparticles were composed of negative energy, such an interaction would result in a final energy of zero.One should also not confuse negative energy with the energy associated with the cosmological constant, postulated in inflationary models of the universe [see "Cosmological Antigravity," byLawrence M. Krauss; SCIENTIFIC AMERICAN, January 1999]. Such a constant represents negative pressure but positive energy. (Some authors call this exotic matter; we reserve the term for negative energy densities.)The concept of negative energy is not pure fantasy; some of its effects have even been produced in the laboratory. They arise fromHeisenberg’s uncertainty principle, which requires that the energy density of any electric, magnetic or other field fluctuate randomly. Even when the energy density is zero on average, as ina vacuum, it fluctuates.Thus, the quantum vacuum can never remain empty in the classical sense of the term; it is a roiling sea of "virtual" particles spontaneously popping in and out of existence [see "Exploiting Zero-Point Energy," by Philip Yam; SCIENTIFIC AMERICAN, December 1997]. In quantum theory, the usual notion of zero energy corresponds to the vacuum with all these fluctuations.So if one can somehow contrive to dampen the undulations, the vacuum will have less energy than it normally does–that is, less than zero energy.posted from Bloggeroid
