Time Machines and Event Horizons » Undivided Looking I've written a pop-article about Time Machines and Event Horizons, which has appeared on the Scientific American blog Critical Opalescence. George Musser, my host, is an editor at Scientific American, and kindly gave me this opportunity to talk about some of my ideas in my article, The Generalized Second Law implies a Quantum Singularity Theorem. If you have any questions about the physics in the article, please feel free to leave comments on this post here. (Questions left on the Scientific American website will be answered in the comments to this post, if anywhere.) I am a postdoctoral researcher studying quantum gravity and black hole thermodynamics at the Institute for Advanced Study in Princeton.
Giant Impact Hypothesis Artist's depiction of a collision between two planetary bodies. Such an impact between the Earth and a Mars-sized object likely formed the Moon. The giant impact hypothesis states that the Moon was formed out of the debris left over from an indirect collision between the Earth and an astronomical body the size of Mars, approximately 4.5 Gya (four and a half billion years ago) in the Hadean eon. The colliding body is sometimes called Theia, for the mythical Greek Titan who was the mother of Selene, the goddess of the Moon.[1] An alternative name for the colliding body is Orpheus, for the legendary musician, poet, and prophet in ancient Greek religion and myth. There remain several questions concerning the best current models of the giant impact hypothesis, however.[5] The energy of such a giant impact is predicted to heat Earth to produce a global 'ocean' of magma; yet there is no evidence of the resultant planetary differentiation of the heavier material sinking into Earth's mantle.
Storm Prediction Center Mapipedia Mapipedia is the easiest way to find, follow, share, visualise, download and collaborate with data sets. The Beginning of the Universe and the Limit of Knowledge “Despite its name, the big bang theory is not really a theory of a bang at all. It is really only a theory of the aftermath of a bang.” -Alan Guth So you finally understand it. Image credit: original source unknown. The farther back we go, the closer together everything was, the higher in temperature (and shorter in wavelength) all the radiation was, and — of course — the younger the Universe was. Image credit: Ned Wright (possibly Will Kinney, too), via At some point, it was hot enough that neutral atoms couldn’t even form; as soon as an electron would find an atomic nucleus, a high-enough-energy photon would come along and ionize the atom’s constituents. Image credit: Lawrence Berkeley National Laboratory. But not indefinitely; we can only go back a finite amount of time in the past, and that’s because what we consider “our Universe” didn’t begin from a singularity 13.8 billion years ago, but began when the previous stage — cosmic inflation — came to an end.
First Flight of SpaceShipOne However, 100 kilometers is an awful long way up, so shortly into its 80-second burn, SpaceShipOne climbed above the angle of the sun into clear blue sky. We didn't realize it at the time, but there were a couple of serious malfunctions as the craft accelerated to more than Mach 2.9 (2150 mph or 3460 km/h). About 7 seconds after ignition, a 60 knot (70 mph or 110 km/h) wind shear caused an unintended 90 degree rotation, which the pilot corrected. SpaceShipOne was at 180,000 feet when the last nitrous oxide oxidizer on board was applied to the 600 pounds of rubber-like fuel, but it continued coasting and eventually reached 328,491 feet. There might have been problems, but the outcome could have been a whole lot worse than this; the pilot even said afterwards that he had contemplated aborting the flight and bailing out, a very risky procedure in itself.
Daylight Time By act of Congress, civil clocks in most areas of the United States are adjusted ahead one hour in the summer months (known as daylight time) and returned back one hour in the winter months (known as standard time). The dates marking the beginning and end of daylight time have changed as Congress has passed new statutes. As of 2007, daylight time begins in the United States on the second Sunday in March and ends on the first Sunday in November. On the second Sunday in March, clocks are set ahead one hour at 2:00 a.m. local standard time (which becomes 3:00 a.m. local daylight time). On the first Sunday in November, clocks are set back one hour at 2:00 a.m. local daylight time (which becomes 1:00 a.m. local standard time). Not all places in the U.S. observe daylight time. * New law went into effect. Many countries observe some form of "summer time." Daylight time and time zones in the U.S. are defined in the U.S. History of Daylight Time in the U.S.
Most Common Travel Scams Report a scam, learn about the most commom travel scams and how to avoid them. 125 Great Science Videos: From Astronomy to Physics & Psychology Astronomy & Space Travel A Brief, Wondrous Tour of Earth (From Outer Space) - Video - Recorded from August to October, 2011 at the International Space Station, this HD footage offers a brilliant tour of our planet and stunning views of the aurora borealis.A Universe from Nothing - Video - In 53 minutes, theoretical physicist Lawrence Krauss answers some big enchilada questions, including how the universe came from nothing.A Year of the Moon in 2.5 Minutes - Video - The Lunar Reconnaissance Orbiter has been orbiting the moon for over a year. The footage gets compressed into 2 slick minutes.A Day on Earth (as Seen From Space) - Video - Astronaut Don Pettit trained his camera on planet Earth, took a photo once every 15 seconds, and then created a brilliant time-lapse film.Atlantis's Final Landing at Kennedy Space Center - Video - After more than 30 years, the space shuttle era comes to a close. Physics Biology & Chemistry Environment, Geology and & Ecology Psychology & Neuroscience
Brief Answers to Cosmic Questions Structure of the Universe Does the Universe have an edge, beyond which there is nothing? Are the galaxies arranged on the surface of a sphere? Why can't we see the whole universe? Evolution of the Universe Did the Universe expand from a point? More about the Big Bang When they say "the universe is expanding," what exactly is expanding? Structure of the Universe Does the Universe have an edge, beyond which there is nothing? Are the galaxies arranged on the surface of a sphere? Why can't we see the whole universe? If you could suddenly freeze time everywhere in the universe, and magically survey all of creation, you would find galaxies extending out far beyond what we can see today. Does the term "universe" refer to space, or to the matter in it, or to both? Today, the situation is reversed. Discovering the properties of space remains one of the deepest and most important problems in modern science. Evolution of the Universe Did the Universe expand from a point? More about the Big Bang
Statistical Atlas Visual interface for browsing many detailed US Census Bureau statistics. States: Alabama, Alaska, Arizona, Arkansas, California, Colorado, Connecticut, Delaware, Florida, Georgia, Hawaii, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine, Maryland, Massachusetts, Michigan, Minnesota, Mississippi, Missouri, Montana, Nebraska, Nevada, New Hampshire, New Jersey, New Mexico, New York, North Carolina, North Dakota, Ohio, Oklahoma, Oregon, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Texas, Utah, Vermont, Virginia, Washington, West Virginia, Wisconsin, Wyoming Divisions: East North Central, East South Central, Middle Atlantic, Mountain, New England, Pacific, Puerto Rico and the Island Areas, South Atlantic, West North Central, West South Central Major Counties: Major Cities: Major Metro Areas:
How To Identify That Light In The Sky? What is that light in the sky? Perhaps one of humanity’s more common questions, an answer may result from a few quick observations. For example — is it moving or blinking? If so, and if you live near a city,the answer is typically an airplane, since planes are so numerous and so few stars and satellites are bright enough to be seen over the din of artificial city lights. SEE ALSO: Night on Earth: biggest cities without power Still unsure?
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