For black holes, distant observers will see only the outside of event horizon, while individual observers falling in to black hole will experience quite another "reality". General relativity predicts that for distant observers out side the horizon, they experience the three space-like coordinates and one time-like coordinate, as they always have. For someone falling in to black hole and crossing the horizon, this crossing mathematically predicted to involve the transformation of you single time-like coordinate in to three time-like coordinates. Along any of these former space like coordinates, they now all terminate on the singularity; you're experiencing as time-like now. All choices always terminate on singularity at least in the case of non rotating black hole. The coordinates which used to measure external time now has a space-like character which affords you some wiggle room, but dynamically, in terms of these new reversed space and time coordinates, you find that no stable orbit about the singularity are possible no matter what you try to do. Without any stable orbits, and the inexorable free fall in to the singularity, relativist often refer to this as the collapse of space time geometry.
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One of the most interesting demonstrations of the quantum mechanical nature of light is the double-slit experiment. In this experiment, light is shone through two slits on an opaque plate onto a screen. If one slit is open, the light impacts the screen with greatest intensity at the centre, fading as one moves away from the centre. One might think that, if both slits are open, the result would be the sum of the intensities from the individual slits, but what happens is that an interference pattern is produced, showing that light has wave properties. Even more unusual, if you only fire one photon at the apparatus at a time (and replace the screen with a photographic plate), an interference pattern is still produced, so it would appear as if an individual photon is able to travel through both slits and interfere with itself. If you place a detector at each slit, you will observe that each photon only goes through one slit—but the pattern is now just the sum of the intensities from the individual slits, without any interference pattern.
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Quantum particles have one very unique property, namely they can be in different states at the same time. This is referred to as the "superposition" of two conditions. Based on this for instance the 'spin' of an electron can be pointing in two different directions at once.
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In 1974, Stephen Hawking showed that black holes evaporate. According to quantum mechanics, pairs of virtual particles are constantly being created and then annihilating each other near black holes (as well as everywhere else in the universe). On occasion, one of the pair of particles ends up inside the black hole's event horizon, and so cannot annihilate its pair, which is forced to become a real particle. This results in a slight increase in the total mass-energy of the outside universe, and that mass-energy has to come from the black hole, whose mass-energy is slightly decreased. Eventually (after an incredibly long time for normal-sized black holes) the black hole would disappear in an explosion of particles and energy.
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Information about what has fallen into a black hole is stored on the black hole's event horizon. Recent calculations by those who study quantum gravity theory and superstrings have confirmed what Stephen Hawking and his collaborators proposed a decade or more ago. Evidently, the information contained in matter that falls into a black hole is by some curious means encoded in the pattern of frozen quantum fields at the horizon. This raises some interesting possibilities that we could resurrect clocks, humans, spacecraft, and whole planets into something like their pristine form if we could magically reverse the in-fall and collapse process. Many believe that this mathematical result means that we have reached a watershed moment in history in understanding the connection between quantum mechanics and gravitation theory. Quantum mechanics deals with statements about the information that we can extract about a quantum mechanical process involving observation. Now this same information language can be applied to configurations of the gravitational field and space-time itself.
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The Pioneer 10 and 11 probes carry metal plaques with messages for aliens telling them about us.
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The ideas of Copernicus came not from looking at the night sky, but from studying ancient astronomy.
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Despite the recent improvement in astronomy, there is still a great deal of unknown about origin, properties and distribution of dark matter in the universe.
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The different fields of astronomy that you can follow are solar astronomy, planetary astronomy, stellar astronomy, galactic astronomy, extragalactic astronomy and cosmology.
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Johannes Kepler used the recorded movement of Mars to formulate his three laws of planetary motion in the 17th Century, which laid the foundation for modern Astronomy.
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A white dwarf is the term in astronomy used to describe the last stage in the life cycle of a (massive) star like our Sun. This last stage in the life of star occurs when star sheds its outer atmosphere, leaving the glowing, gradually cooling, core as a white dwarf. For our Sun this process will begin about 5 billion years in the future.
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Word astronomy comes from two Greek words "astron" meaning star and "nomos" meaning law, and would basically mean law of the stars.
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There are a range of different types of method to study astronomy, largely based on the type of equipment being used. These include; radio astronomy, optical astronomy, infra-red astronomy, ultraviolet astronomy, x-ray astronomy and gamma-ray astronomy.
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Claudius Ptolemy, a second-century astronomer working in Alexandria, Egypt, wrote thirteen volumes on his observations that were so influential that they came to be known as the Almagest, Arabic for "the greatest". Ptolemy's theories, which held that the Earth stood still in the heavens while the moon, sun, and planets moved around it and that the stars sat in a concave dome that arched over the universe, were completely wrong; however, the influence of these theories held back the science of astronomy for nearly 1,500 years.
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Cosmologists believe most galaxies have a super-massive black hole at their centre, with a mass of between 1 million, or billions of times that of the Sun. All of a black hole’s matter is crushed into a tiny point of infinite gravity called a singularity. Science’s understanding of physics, space, and time breaks down beyond the black hole’s event horizon, the boundary of no return where not even light has the speed to escape its immense gravity.
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