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.
Physics and Astronomy Glossary Technical terms of science have very specific meanings. Standard dictionaries are not always the best source of useful and correct definitions of them. This glossary is not intended to be complete. It focuses on those terms which give students particular difficulties. Some words have subtle and intricate meanings which cannot be encapsulated in a short definition. That's why textbooks exist. This document is continually under development and may never be finished. Glossary Accurate. Absolute uncertainty. Compare: relative uncertainty. Action. Avogadro's constant. One must specify whether the value of Avogadro's constant is expressed for a gram-mole or a kilogram-mole. Though it seems inconsistent, the SI base unit is the gram-mole. Is Avogadro's constant just a number? , e, 3, 100, etc. The reciprocal of Avogadro's constant is numerically equal to the unified atomic mass unit, u, that is, 1/12 the mass of the carbon 12 atom. 1 u = 1.66043 x 10-27 kg = 1/6.02252 x 1023 mole-1. Because. cgs.
LIVE REAL TIME SATELLITE TRACKING AND PREDICTIONS: GOCE FRANCE MANEUVERS INTEL SATELLITE TO AVOID DEAD WEATHER SPACECRAFT - One of four French electronic-intelligence satellites flying in formation in low Earth orbit was forced to perform a collision-avoidance maneuver after U.S. and French space-tracking radars determined that it was on a collision course with a large piece of orbital debris, the French air force said. The satellite that had to be moved is one of four identical 120-kilogram Elisa demonstrator satellites launched into a 694-kilometer low Earth orbit in December 2011. With both French naval and German ground-based precision space-surveillance radars out of service for several months for maintenance, the French military deployed two of its own, less-precise ground radars, located in Sommepy in northeast France and Solenzara on the island of Corsica in the Mediterranean, to track what the French air force said was a dead satellite. More (Source: Space News - Apr 24)
As bright as a hundred million Suns: The clusters of monster stars that lit up the early universe -- ScienceDaily The first stars in the Universe were born several hundred million years after the Big Bang, ending a period known as the cosmological 'dark ages' -- when atoms of hydrogen and helium had formed, but nothing shone in visible light. Now two Canadian researchers have calculated what these objects were like: they find that the first stars could have clustered together in phenomenally bright groups, with periods when they were as luminous as 100 million Suns. Alexander DeSouza and Shantanu Basu, both of the University of Western Ontario in Canada, publish their results in a paper in Monthly Notices of the Royal Astronomical Society. The two scientists modelled how the luminosity of the stars would have changed as they formed from the gravitational collapse of disks of gas. In a small cluster of even 10 to 20 protostars, the ongoing bursts would mean the cluster would spend large periods with enhanced brightness.
NASA Releases New High-Definition View of Iconic ‘Pillars of Creation’ Photo New view of the Pillars of Creation, visible light. NASA, ESA/Hubble and the Hubble Heritage Team. New view of the Pillars of Creation, visible light, detail. NASA, ESA/Hubble and the Hubble Heritage Team. New view of the Pillars of Creation, infrared light. NASA, ESA/Hubble and the Hubble Heritage Team. 2015 v. 1995 ‘Pillars of Creation’ comparison. One of the most iconic images ever produced by NASA is the “Pillars of Creation” photograph taken by Hubble Space Telescope in 1995. Now Hubble has revisited the famous pillars, capturing the multi-coloured glow of gas clouds, wispy tendrils of dark cosmic dust, and the rust-coloured elephants’ trunks with the newer Wide Field Camera 3, installed in 2009. In addition, NASA says that although the original photograph was titled Pillars of Creation, the newer imagery suggests the columns might also contain a fair amount of destruction: You can see the new photo in even higher detail by downloading images at several resolutions on this page.
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.
FQXi - Foundational Questions Institute Leonid Meteor Shower 2013: How To See 'Shooting Stars' This Weekend Get ready to see some "shooting stars" this weekend, skywatchers. The 2013 Leonid meteor shower is expected to be visible from Nov. 16 through Nov. 18. Weather permitting, observers around the world should be able to see the brightest "Leonids" streak across the sky from Saturday night through Sunday morning. The Northern Hemisphere will be treated to the prime show, as it has the best view of the constellation Leo, from which the meteor shower derives its name. Unfortunately, this year's Leonid meteor shower will not be as visible as the show has been in the past years. Since the moon turns full on Nov. 17 -- in the midst of the shower -- only the brightest of the meteors will be apparent to most watchers. Like last year's Leonid meteor shower, projections suggest that there will be two peaks of activity -- one at 5 a.m. NASA recommends going outside 30 minutes ahead of the show, so your eyes can adjust to the night sky. Also on HuffPost:
Astro Bob | Celestial happenings you can see from your own backyard 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? 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
Eliezer Yudkowsky on Bayes and science: what? By Massimo Pigliucci It is no secret that my already normally skeptical baloney detector now jumps to deep orange alert any time I hear the word “singularity.” I was not too impressed with David Chalmers’ lecture about it at the City University of New York Graduate Center, and I debated singularitarian guru Eliezer Yudkowsky on BloggingHeadsTV on the same topic. My later encounters with that particular group of techno-optimists and futurists have not improved my opinion of the whole shebang a bit. Still, in the spirit of open inquiry and of keeping myself on my own toes, I devoted about an hour to reading three not-so-recent posts by Yudkowsky on the theme of quantum mechanics, science and Bayesianism (the philosophy of science related to Bayesian statistics). I actually intended to read only one of Yudkowsky’s posts, intriguingly entitled “The Dilemma: Science or Bayes?” But I was disappointed. Now, I should hasten to say that I don’t really have a dog in this fight. So there.
Comet ISON Visible To Naked Eye After Outburst Of Activity, Observers Say Get ready for a stellar show. The much-anticipated Comet ISON is now visible to the naked eye according to reports from many observers. Comet ISON — the potential "comet of the century" — has suddenly brightened in an outburst of activity with just two weeks to go before it literally grazes the surface of the sun. In recent months, Comet ISON has repeatedly befuddled forecasters trying to anticipate just how bright it will ultimately become. An hour before sunrise on Monday morning, November 18, catch a sight of the elusive planet Mercury, with brightening Comets ISON and Lovejoy as a bonus. Comet ISON lightens up, literally Comet ISON is now in full outburst mode, becoming many times brighter over just the past few days. According to veteran comet observer, John Bortle, Comet ISON was shining only at magnitude +8.5 on Monday (Nov. 11) morning — more than six times too dim to be visible to the unaided eye. Justin Ng sent in a photo of comet ISON, taken in Singapore, Nov. 4, 2013.
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