Interesting websites ( OPEN SUBJECTS)

Discussions in the vein that would most interest those looking for the "meat and potatoes" of Townsend Brown's scientific work.

Re: Interesting websites ( OPEN SUBJECTS)

Postby ecker2011 » Fri Apr 07, 2017 1:29 pm

This is for fun.

Commentary: In defense of Crazy Ideas

David Stevenson
(djs@gps.caltech.edu) California Institute of Technology, Pasadena

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Unless we change direction,
we are likely to wind up
where we are headed.
—Ancient Chinese proverb

Like many of you, I get unsolicited manuscripts that make startling and revolutionary claims. In years past they arrived by snail mail and were often handwritten or typed with copious use of capital letters, exclamation marks, and hand-drawn diagrams. More recently they come by email and look more like conventional scientific literature. (Even crackpots know how to use word processors and PowerPoint.) Denials of Einstein’s special relativity seem especially popular.

Although the shortcomings of those efforts are often readily apparent, there is much to admire about the passion and dedication with which they are constructed. Occasionally they merit attention, if only because their authors’ thought processes are not fettered by conventional thinking. Sadly, their deficiencies are often fundamental and betray a lack of understanding of the nature of science and its interconnectivity. They are what I call Crazy Ideas of the First Kind—the most common and least interesting.

Most published science is mundane. It is the easiest to get published and the easiest to get funded at a modest, sustainable level—though no funding is easy to get these days. It is also more likely to be right, precisely because it is incremental. Just as rock-solid financial investments are an important part of any balanced portfolio, so the mundane science is an important part of the science portfolio. But I suspect many scientists, even some who are recognized as leaders in their field, are unwilling to acknowledge their lack of adventurousness. They will protest that they are inventive, innovative scientists, but their measure of that is probably quite constricted because of the fine-scale partitioning that characterizes the modern scientific world. In the landscape of scientific knowledge, most of us are digging deeper holes and maybe an occasional trench to link up with a neighboring hole, but few are venturing across the ridges to the next valley.

Crazy Ideas of the Second Kind come when well-established scientists venture out from their holes and up to the ridges and peaks to survey the landscape. Inevitably, such excursions can look like the actions of a dilettante since it takes less effort to dash up a ridge than to dig a really deep hole. One is then accused of speculation. I occasionally sense from colleagues some disdain for scientific speculation, perhaps because it is cheap: It seems to require relatively little effort and commitment. Indeed, bad speculation is easy, and you can do it at the local bar or Starbucks or while riding a bike. Poor experimental or observational work also often requires less effort than good work. In fact, good speculation is hard, judging by the evident rarity of examples. Good speculation is also not always easy to recognize immediately, because part of what makes it good is something that may be hidden: the failures of alternative speculations, the crumpled sheets of paper in the wastebasket.

Richard Feynman once said that the essence of science is (or should be) “the belief in the ignorance of experts.”1 I think he meant that outsiders may provide an important breakthrough because they are unfettered. The “ignorance” that he refers to, though, must not be complete. It still must allow an appreciation of how science works and the rules that apply, and so it is the ignorance of areas of science other than your own. Residents of deep holes know very well the stuff they have excavated and the walls that surround them but know less well what novelty may lie elsewhere.

And then there are Crazy Ideas of the Third Kind, the most interesting and least common. They arise from a leading eminence in some field who has decided that something is rotten in that field’s fundamentals. In essence, they have decided that their hole is a false claim or has been mined out, even though it may be capacious and well populated.

Importantly, good crazy ideas do not have to be true to be valuable. Distinguished astrophysicist Fred Hoyle and colleagues had the crazy idea that influenza came from space.2 The more general concept of panspermia—of which Hoyle’s idea is a special case—is, however, of considerable interest.

Perhaps an even better example of that line of thinking is Hoyle’s wonderful science fiction novel The Black Cloud (Harper, ca. 1957), wherein an intelligent life-form exists as a dispersed but organized globule that wanders into our solar system. That is a truly engaging though crazy idea: Could life take the form of something that we normally think of as having high entropy? Indeed, some fluid dynamical systems display order—consider Jupiter’s Great Red Spot—and the question of what form life could take remains an open one.

Another distinguished astrophysicist, Thomas Gold, had the crazy idea that natural gas was part of Earth’s starting material rather than arising from biological processes much later in Earth history.3 Geochemists might laugh (some did), and yet the possible delivery of large amounts of reduced carbon to Earth at formation is not such a ridiculous idea. We still do not know Earth’s total reservoir of carbon, since some of it may be very deep. Gold was wrong about natural gas, but the idea is provocative, and that’s good.

More famously, Lord Kelvin had the crazy idea that you could figure out the age of Earth by solving the diffusion equation for heat conduction in a half-space. He knew that Earth is a sphere, but the diffusion time for the whole Earth is so large that a half-space suffices. (For more on Lord Kelvin’s mistake, see my letter, Physics Today, November 2010, page 8.)

Kelvin’s idea is a particularly interesting example because it was not regarded as crazy at the time but would be viewed as crazy now, for reasons that could have been explained to him back then. He was ignoring the geological evidence for the great expanses of time that must have passed, but there were as yet no good clocks for geologic time. He was also ignoring the possibility of convection, and that should not have been acceptable. Crazy ideas are often ephemeral: What was crazy then can be “natural” now and vice versa.

As for Crazy Ideas of the Third Kind, opinions will vary, but perhaps one is the idea that gravity is an emergent phenomenon, an idea often attributed to Andrei Sakharov. The extension of a rubber band, which roughly obeys Hooke’s law, is purely entropic and has nothing to do with the forces between the atoms that make up the material, so one could say that in that case a force law emerges from Boltzmann’s definition of entropy. Or perhaps Roger Penrose and his fundamental discretization of spacetime would be one of the Third Kind. Many great developments in physics began encumbered with ideas that we have now shed—for example, Maxwell’s molecular vortices.

My thesis adviser, Ed Salpeter, would occasionally say to me, “Is it crazy enough to be true?” I think what he meant is that when you’re attempting to explain something important and it has resisted solution for a significant time, then the mundane explanation is unlikely to work, so you should be seeking the “crazy” answer. Although Salpeter almost invariably wrote papers of great solidity and impact, he did coauthor a paper with Carl Sagan on life in the atmosphere of Jupiter.4 It was a good crazy paper, I think. Life in the atmosphere of Jupiter figures prominently in a science fiction novel, The Algebraist (Orbit, 2004), by Iain Banks.

In a somewhat similar spirit, Niels Bohr, responding to a lecture by Wolfgang Pauli, said, “We are all agreed that your theory is crazy. The question which divides us is whether it is crazy enough to have a chance of being correct.” The hard part lies in figuring out what is crazy enough.

References

1. R. Feynman, Phys. Teach. 7, 313 (1969), p. 319. https://doi.org/10.1119/1.2351388, Google ScholarCrossref
2. F. Hoyle, C. Wickramasinghe, J. Watkins, Viruses from Space and Related Matters, U. College Cardiff Press (1986). Google Scholar
3. T. Gold, The Deep, Hot Biosphere, Copernicus Books (1999). Google ScholarCrossref
4. C. Sagan, E. Salpeter, Astrophys. J. Suppl. Ser. 32, 737 (1976). https://doi.org/10.1086/190414, Google ScholarCrossref, CAS

http://physicstoday.scitation.org/doi/10.1063/PT.3.3507
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Re: Interesting websites ( OPEN SUBJECTS)

Postby ecker2011 » Mon Apr 10, 2017 3:48 pm

Physicist discovers strange forces acting on nanoparticles
by Aaron Hilf

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Credit: University of New Mexico

A new scientific paper published, in part, by a University of New Mexico physicist is shedding light on a strange force impacting particles at the smallest level of the material world.

The discovery, published in Physical Review Letters, was made by an international team of researchers lead by UNM Assistant Professor Alejandro Manjavacas in the Department of Physics & Astronomy. Collaborators on the project include Francisco Rodríguez-Fortuño (King's College London, U.K.), F. Javier García de Abajo (The Institute of Photonic Sciences, Spain) and Anatoly Zayats (King's College London, U.K.).

The findings relate to an area of theoretical nanophotonics and quantum theory known as the Casimir Effect, a measurable force that exists between objects inside a vacuum caused by the fluctuations of electromagnetic waves. When studied using classical physics, the vacuum would not produce any force on the objects. However, when looked at using quantum field theory, the vacuum is filled with photons, creating a small but potentially significant force on the objects.

"These studies are important because we are developing nanotechnologies where we're getting into distances and sizes that are so small that these types of forces can dominate everything else," said Manjavacas. "We know these Casimir forces exist, so, what we're trying to do is figure out the overall impact they have very small particles."

Manjavacas' research expands on the Casimir effect by developing an analytical expression for the lateral Casimir force experienced by nanoparticles rotating near a flat surface.

Imagine a tiny sphere (nanoparticle) rotating over a surface. While the sphere slows down due to photons colliding with it, that rotation also causes the sphere to move in a lateral direction. In our physical world, friction between the sphere and the surface would be needed to achieve lateral movement. However, the nano-world does not follow the same set of rules, eliminating the need for contact between the sphere and the surface for movement to occur.

"The nanoparticle experiences a lateral force as if it were in contact with the surface, even though is actually separated from it," said Manjavacas. "It's a strange reaction but one that may prove to have significant impact for engineers."
While the discovery may seem somewhat obscure, it is also extremely useful for researchers working in the always evolving nanotechnology industry. As part of their work, Manjavacas says they've also learned the direction of the force can be controlled by changing the distance between the particle and surface, an understanding that may help nanotech engineers develop better nanoscale objects for healthcare, computing or a variety of other areas.

For Manjavacas, the project and this latest publication are just another step forward in his research into these Casimir forces, which he has been studying throughout his scientific career. After receiving his Ph.D. from Complutense University of Madrid (UCM) in 2013, Manjavacas worked as a postdoctoral research fellow at Rice University before coming to UNM in 2015.


https://phys.org/news/2017-04-physicist ... icles.html
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Re: Interesting websites ( OPEN SUBJECTS)

Postby ecker2011 » Wed Apr 12, 2017 12:53 pm

Physicists discover hidden aspects of electrodynamics

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LSU Department of Physics & Astronomy Assistant Professor Ivan Agullo's new research advances knowledge of a classical theory of electromagnetism. Credit: LSU

Radio waves, microwaves and even light itself are all made of electric and magnetic fields. The classical theory of electromagnetism was completed in the 1860s by James Clerk Maxwell. At the time, Maxwell's theory was revolutionary, and provided a unified framework to understand electricity, magnetism and optics. Now, new research led by LSU Department of Physics & Astronomy Assistant Professor Ivan Agullo, with colleagues from the Universidad de Valencia, Spain, advances knowledge of this theory. Their recent discoveries have been published in Physical Review Letters.

Maxwell's theory displays a remarkable feature: it remains unaltered under the interchange of the electric and magnetic fields, when charges and currents are not present. This symmetry is called the electric-magnetic duality.

However, while electric charges exist, magnetic charges have never been observed in nature. If magnetic charges do not exist, the symmetry also cannot exist. This mystery has motivated physicists to search for magnetic charges, or magnetic monopoles. However, no one has been successful. Agullo and his colleagues may have discovered why.

"Gravity spoils the symmetry regardless of whether magnetic monopoles exist or not. This is shocking. The bottom line is that the symmetry cannot exist in our universe at the fundamental level because gravity is everywhere," Agullo said.
Gravity, together with quantum effects, disrupts the electric-magnetic duality or symmetry of the electromagnetic field.

Agullo and his colleagues discovered this by looking at previous theories that illustrate this phenomenon among other types of particles in the universe, called fermions, and applied it to photons in electromagnetic fields.
"We have been able to write the theory of the electromagnetic field in a way that very much resembles the theory of fermions, and prove this absence of symmetry by using powerful techniques that were developed for fermions," he said.
This new discovery challenges assumptions that could impact other research including the study of the birth of the universe.

The Big Bang

Satellites collect data from the radiation emitted from the Big Bang, which is called the Cosmic Microwave Background, or CMB. This radiation contains valuable information about the history of the universe.
"By measuring the CMB, we get precise information on how the Big Bang happened," Agullo said.

Scientists analyzing this data have assumed that the polarization of photons in the CMB is not affected by the gravitational field in the universe, which is true only if electromagnetic symmetry exists. However, since this new finding suggests that the symmetry does not exist at the fundamental level, the polarization of the CMB can change throughout cosmic evolution. Scientists may need to take this into consideration when analyzing the data. The focus of Agullo's current research is on how much this new effect is.

https://phys.org/news/2017-04-physicist ... amics.html
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Re: Interesting websites ( OPEN SUBJECTS)

Postby ecker2011 » Fri Apr 14, 2017 12:30 pm

A battery prototype powered by atmospheric nitrogen

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Artistic illustration of Zhang and colleagues' proof-of-concept experiment, which successfully implements a reversible nitrogen cycle based on rechargeable Li-N2 batteries with promising electrochemical faradic efficiency. Credit: Zhang et. al.

As the most abundant gas in Earth's atmosphere, nitrogen has been an attractive option as a source of renewable energy. But nitrogen gas—which consists of two nitrogen atoms held together by a strong, triple covalent bond—doesn't break apart under normal conditions, presenting a challenge to scientists who want to transfer the chemical energy of the bond into electricity.

In the journal Chem on April 13, researchers in China present one approach to capturing atmospheric nitrogen that can be used in a battery.

The "proof-of-concept" design works by reversing the chemical reaction that powers existing lithium-nitrogen batteries. Instead of generating energy from the breakdown of lithium nitride (2Li3N) into lithium and nitrogen gas, the researchers' battery prototype runs on atmospheric nitrogen in ambient conditions and reacts with lithium to form lithium nitride. Its energy output is brief but comparable to that of other lithium-metal batteries.

"This promising research on a nitrogen fixation battery system not only provides fundamental and technological progress in the energy storage system but also creates an advanced N2/Li3N (nitrogen gas/lithium nitride) cycle for a reversible nitrogen fixation process," says senior author Xin-Bo Zhang, of the Changchun Institute of Applied Chemistry, part of the Chinese Academy of Sciences. "The work is still at the initial stage. More intensive efforts should be devoted to developing the battery systems."

https://techxplore.com/news/2017-04-bat ... rogen.html
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Postby ecker2011 » Mon Apr 17, 2017 12:25 pm

This is really not new! First per-posted in the 1970's.

Could Moon Miners Use Railguns to Launch Ore into Space?

By Leonard David, Space.com's Space Insider Columnist

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Electromagnetic mass drivers using solar power could provide low-cost transportation of materials to space construction sites.
Credit: Space Studies Institute

The United States Navy fired a projectile at Mach 6 during a recent test with an electromagnetic railgun, suggesting that early ideas about using such tech to launch payloads from the lunar surface might not be so sci-fi after all.

Mach 6 (six times the speed of sound) is 4,567 mph (7,350 km/h). The escape velocity at the moon is just a shade faster than that — 5,300 mph (8,530 km/h).

The Office of Naval Research work on the EM Railgun launcher is being pursued as a long-range weapon that fires projectiles using electricity instead of chemical propellants. [The Most Dangerous Space Weapons Ever]

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The U.S. Navy's electromagnetic railgun in action during a recent test.
Credit: Office of Naval Research

Magnetic fields created by high electrical currents accelerate a sliding metal conductor, or armature, between two rails to launch projectiles.

In 1974, Princeton professor and space visionary Gerard O’Neill first proposed using an electromagnetic railgun to lob payloads from the moon.

"Mass drivers" based on a coilgun design could be adapted to accelerate a nonmagnetic object, O'Neill suggested. One application he proposed for mass drivers: tossing baseball-size chunks of ore mined from the surface of the moon into space, where they could be used as raw material for building space colonies and solar power satellites.

O'Neill worked at the Massachusetts Institute of Technology with Henry H. Kolm and a group of student volunteers to construct a mass driver prototype. Backed by grants from the Space Studies Institute, later prototypes improved on the concept, showing that a mass driver only 520 feet (160 meters) long could launch material off the surface of the moon.

An official at the Office of Naval Research, contacted by Inside Outer Space, said this of O'Neill's seminal work on mass drivers: "Very interesting proposal to use electromagnetic launchers for space vehicles. Considering the fact that the railgun is working with a small hypervelocity projectile, and requires significant power and thermal management, I suspect working out the details for movement of larger space vehicles/payloads is a long way off.

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Deflection plates near the end of the mass driver would make minute adjustments to the trajectory of the launched ore to ensure it reaches its target — a mass catcher at the Earth-moon Lagrange Point 2.
Credit: Space Studies Institute

"But I also believe that current efforts will be successful, and electromagnetic thrust will eventually be considered for other applications, including space," the official added.

You can check out a video showing work on the U.S. Navy's EM Railgun here: http://www.youtube.com/watch?v=5imlcR0CuJ0

O'Neill, who died in 1992, founded the Space Studies Institute (SSI) in 1977 with the hope of opening the vast wealth of space to humanity. For more information on SSI’s ongoing work, go to: http://ssi.org/

http://www.space.com/36442-could-moon-m ... ium=social
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Re: Interesting websites ( OPEN SUBJECTS)

Postby ecker2011 » Mon Apr 17, 2017 2:13 pm

Physicists create 'negative mass'
by Eric Sorensen

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Experimental TOF images of the effectively 1D expanding SOC BEC for expansion times of 0, 10, and 14 ms.

Washington State University physicists have created a fluid with negative mass, which is exactly what it sounds like. Push it, and unlike every physical object in the world we know, it doesn't accelerate in the direction it was pushed. It accelerates backwards.

The phenomenon is rarely created in laboratory conditions and can be used to explore some of the more challenging concepts of the cosmos, said Michael Forbes, a WSU assistant professor of physics and astronomy and an affiliate assistant professor at the University of Washington. The research appears today in the journal Physical Review Letters, where it is featured as an "Editor's Suggestion."

Hypothetically, matter can have negative mass in the same sense that an electric charge can be either negative or positive. People rarely think in these terms, and our everyday world sees only the positive aspects of Isaac Newton's Second Law of Motion, in which a force is equal to the mass of an object times its acceleration, or F=ma.In other words, if you push an object, it will accelerate in the direction you're pushing it. Mass will accelerate in the direction of the force.

"That's what most things that we're used to do," said Forbes, hinting at the bizarreness to come. "With negative mass, if you push something, it accelerates toward you."

Conditions for negative mass

He and his colleagues created the conditions for negative mass by cooling rubidium atoms to just a hair above absolute zero, creating what is known as a Bose-Einstein condensate. In this state, predicted by Satyendra Nath Bose and Albert Einstein, particles move extremely slowly and, following the principles of quantum mechanics, behave like waves. They also synchronize and move in unison as what is known as a superfluid, which flows without losing energy.

Led by Peter Engels, WSU professor of physics and astronomy, researchers on the sixth floor of Webster Hall created these conditions by using lasers to slow the particles, making them colder, and allowing hot, high energy particles to escape like steam, cooling the material further.

The lasers trapped the atoms as if they were in a bowl measuring less than a hundred microns across. At this point, the rubidium superfluid has regular mass. Breaking the bowl will allow the rubidium to rush out, expanding as the rubidium in the center pushes outward.

To create negative mass, the researchers applied a second set of lasers that kicked the atoms back and forth and changed the way they spin. Now when the rubidium rushes out fast enough, if behaves as if it has negative mass."Once you push, it accelerates backwards," said Forbes, who acted as a theorist analyzing the system. "It looks like the rubidium hits an invisible wall."

Avoiding underlying defects

The technique used by the WSU researchers avoids some of the underlying defects encountered in previous attempts to understand negative mass.

"What's a first here is the exquisite control we have over the nature of this negative mass, without any other complications" said Forbes. Their research clarifies, in terms of negative mass, similar behavior seen in other systems.This heightened control gives researchers a new tool to engineer experiments to study analogous physics in astrophysics, like neutron stars, and cosmological phenomena like black holes and dark energy, where experiments are impossible."It provides another environment to study a fundamental phenomenon that is very peculiar," Forbes said.

https://phys.org/news/2017-04-physicist ... -mass.html
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Re: Interesting websites ( OPEN SUBJECTS)

Postby ecker2011 » Wed May 03, 2017 12:44 pm

Is time on our side?

Time travel — long a staple of science fiction — may not be too far from reality.
By Richard Talcott

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All of cosmic history, from near the Big Bang (at upper left) to the engineering marvels of superadvanced civilizations (at lower right), could be reached theoretically in a time machine. Although physicists know time travel into the future is possible, the past may be out of reach.
Adolf Schaller; Time Machine: Astronomy: Theo Cobb

This story originally appeared in the February 2006 issue of Astronomy.

When H. G. Wells put pen to paper in 1895, he started something that shows no sign of abating. The Time Machine, Wells’ first novel, was social commentary disguised as science fiction. But his idea that time travel might be possible has fired the imaginations of authors, screenwriters — and scientists — ever since.

Wells proved to be ahead of his time scientifically as well as artistically. He imagined time as occupying the fourth dimension 10 years before Albert Einstein portrayed the ­cosmos as a 4-dimensional space-time continuum in his ­special theory of relativity. Einstein’s ideas opened the door to scientific inquiry into time travel.
Yet the subject remained fringe science for decades. Not so now. Today, researchers publish articles in leading scientific journals that discuss not only the possibility of time travel but how it might be accomplished.

Although the day when you can hop into a time machine and travel anywhere — or anywhen — you want lies a long way off, limited forms of time travel into the future already exist. Thanks to their greater speed, airline passengers emerge from their trips having aged slightly less than their earthbound compatriots. Now, some scientists speculate travel into the past — something Wells’ time traveler could do with the pull of a lever — might be possible one day.

Newton’s time

The idea of time travel never gained a foothold in the 200-plus years Isaac Newton’s view of the universe held sway. Newton considered time, and space for that matter, as immutable. “Absolute, true, and mathematical Time, of itself, and from its own nature, flows equably without relation to anything external,” he wrote in his masterwork, Principia.

That all changed with Einstein. He believed — and a century of experimental results backs him up — time is relative. In 1905’s special theory of relativity, he started with two postulates: The laws of physics should look the same to every observer in uniform motion (moving in a straight line at constant speed), and the speed of light in a vacuum should be the same for every observer in uniform motion.

The only way these two conditions can be met simultaneously is if time passes at different rates for different observers. The effects can be measured even in everyday life. Take a trans-Atlantic flight, and you’ll climb off the airplane about 10 nanoseconds (10 billionths of a second) younger than those you left behind.

The effects don’t become obvious unless you travel near the speed of light. Jump on a spaceship and travel at close to light-speed, and you literally could cover light-years in just a few days by your reckoning. On your return to Earth, however, you’d find that perhaps thousands of years had elapsed. In effect, you would have traveled to the stars as well as deep into the future.

As crazy as this travel into the future may sound, experiments verify it. In 1971, Joe Hafele of Washington University in St. Louis and Richard Keating of the U.S. Naval Observatory in Washington borrowed four atomic clocks from the Naval Observatory and took them on around-the-world airplane trips. Although the planes traveled at less than one-millionth the speed of light, the clocks ticked slower than those left at the observatory — and by just the amount predicted by special relativity.

Subatomic particles called muons offer more-striking proof. In a laboratory, muons survive only a few millionths of a second. When energetic cosmic rays strike Earth’s atmosphere, however, they create a shower of muons traveling at close to the speed of light. If these high-speed muons decayed at their normal rate, they wouldn’t make it a mile. But most survive the 12-mile (20 kilometers) trip to reach Earth’s surface.

Einstein’s gravity

Speed is one way to leap into the future. Gravity is another. Ten years after he devised special relativity, Einstein developed his general theory. In it, he extended the theory to all types of motion and showed that gravity is a manifestation of space-time curvature. Just like special theory, general relativity offers a method of time travel: a strong gravitational field.

And just as with special relativity, the effects can be seen on Earth. The Global Positioning System (GPS) comprises 24 satellites, each of which carries an atomic clock and orbits about 14,500 miles (23,300 km) above Earth. A GPS receiver calculates your location by measuring how long it takes signals to travel from several satellites.

Both forms of relativity come into play with this equipment. Special relativity causes the atomic clocks to run slow because the satellites move at a fast rate relative to Earth’s surface. General relativity has the opposite effect. Earth’s gravitational field is weaker in orbit than on the surface, so the atomic clocks speed up. The system has to take both effects into account to ­produce an accurate position.

The time effects of general relativity grow with the strength of the gravitational field. Visit the vicinity of a neutron star — the collapsed core of a massive star that contains a few times the Sun’s mass in a sphere the size of a modest city — and time runs at a rate about 25-percent slower than it does on Earth

Traveling near a black hole may not be the wisest move, however. Most known stellar-mass black holes, those that arise from the collapse of a massive star at the end of its life, lie in binary systems where the black hole pulls in gas from its com­panion star. As the gas swirls into the black hole, it forms an accretion disk where friction raises the temperature to millions of degrees. The resulting X rays would fry any astronaut who gets too close.

You wouldn’t want to get too near one of the handful of isolated black holes known, either. Tidal forces near the event horizon of any stellar-mass black hole would stretch any person (or spaceship, for that matter) into a long, thin piece of spaghetti.

The best bet for a would-be time traveler is a supermassive black hole. These beasts, typically found at the center of a galaxy, weigh millions or billions of times what the Sun does and have event horizons the size of the solar system. There, tidal forces remain bearable, and an astronaut could swoop in close without being torn apart.

A time traveler would only want to get near the event horizon, not cross it. For the same reason time slows to a stop there as seen from the outside, astronauts would see the universe’s entire history pass before their eyes. If you could survive the journey into the black hole and come out again, you would have to enter a different universe.

Through the past darkly

So far, time travel seems to be a one-way trip to the future. Astronauts one day may be able to travel super-fast — or dive close to a black hole or neutron star — and age more slowly than those they left behind. These intrepid travelers would return to Earth in the distant future.

But many time-travel aficionados would rather travel to the past. University of ­Connecticut physicist and time-travel researcher Ronald Mallett counts himself in this group. “My father died of a heart attack when I was 10, and shortly after that, I read The Time Machine. I thought if I could build a real time machine, I could go back and warn him.”

Traveling that direction in time proves a tougher theoretical challenge for physicists. The first inkling that going to the past might be possible came from Austrian-born mathematician Kurt Gödel. In 1949, while at the Institute for Advanced Study in Princeton, New Jersey (where Einstein also worked), Gödel used general relativity’s equations to describe a rotating universe. He found that such a universe allows an astronaut to visit his or her own past by traveling through space. Gödel’s discovery did nothing to bring time travel closer to reality — observations show the universe as a whole does not rotate — but it did show general relativity allows travel to the past.

In 1974, Tulane University physicist Frank Tipler showed that an infinitely long cylinder rotating close to the speed of light could accomplish the same thing. Astronauts circumnavigating the cylinder could visit their own past. As with Gödel’s solution, Tipler’s idea won’t lead to a practical time machine — it’s impossible to build anything infinitely long.

Wormholes to the rescue

Another idea proves more promising. As early as 1935, Einstein and a colleague, Nathan Rosen, realized that general rela­tivity allows the existence of “bridges” in space-time. Originally called Einstein-Rosen bridges, these space-time tubes now have the more poetic name “wormholes.” (Princeton University physicist John Wheeler, who coined the elegantly des­criptive term “black hole,” also thought up “wormhole.”) Wormholes act as shortcuts that can connect distant regions of space-time. So, by voyaging through a wormhole, you could travel between the two regions faster than a beam of light moving through normal space-time.

Wormholes have their own problems, at least as practical time machines. Theorists once believed wormholes could exist only for an instant before “pinching off” and collapsing into black holes. But they figured a way out of this quandary, thanks in part to a science-fiction story.

In the early 1980s, Cornell University astronomer Carl Sagan began writing his novel Contact. In it, heroine Ellie Arroway detects a radio signal from the vicinity of the star Vega. The coded message contains instructions for building a machine that ultimately takes her to a planet deep in the galaxy.

In the original manuscript, Sagan had Ellie fall into a black hole on Earth and re-emerge out of a black hole near Vega. But he wanted to be sure the science made sense. He sent the manuscript to his friend and black-hole expert Kip Thorne at Cal­tech. Thorne realized the story needed to use a wormhole instead of black holes but knew the pitfalls. So he, along with some students, tried to fix them.

The key problem was how to keep the wormhole from collapsing. They found it could be done by lining the wormhole with material that exerts enough outward pressure to counteract the wormhole’s inward squeezing. Ordinary matter won’t do the trick. The material has to be what physicists call “exotic matter,” which has a pressure comparable to the pressure that keeps a neutron star from collapsing. It’s not the kind of stuff you’ll find at the local hardware store, but it’s not ruled out by the laws of physics either.

Making a time machine

It wasn’t long before Thorne and his colleagues realized that a stable wormhole could form the basis for a time machine. The trick involves sending one end of the wormhole into the future by either rapid motion or gravity, just like the spacefaring astronauts talked about earlier.

One possibility would be to bring a large asteroid to one of the wormhole’s mouths. As mutual gravity draws them together, you need to accelerate the asteroid to near the speed of light. A clock at this wormhole’s mouth now will run much slower than a clock positioned near the stationary mouth. Keep the moving mouth in motion until you achieve the time difference you want, say 10 years, then bring it back. If you jump into the mouth that stays behind, you’ll exit the other end 10 years earlier. Go the reverse direction, and you’ll pop out 10 years in the future.

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Causality concerns arise if we travel into the past. In this scenario, a billiard ball enters a wormhole and returns a few seconds earlier, just in time to knock itself out of the way so it never enters the wormhole to begin with. The paradox is removed by the ­consistency conjecture, which says the time-traveling ball can graze the initial shot but not prevent it from entering the wormhole.
Astronomy: Roen Kelly

To use gravity instead, you could put one end of the wormhole near a neutron star. Keep it there as long as you need to accumulate the desired time lag, and then return it to the vicinity of the other mouth. Assuming your civilization has mastered rapid space flight, you could easily pass through the wormhole into the past and return to your starting point before you left.

The wormhole time machine allows travel into the past, but you could never go back to a time before the machine was constructed. That could answer Cambridge University theorist Stephen Hawking’s question about why we don’t see any time travelers in our midst. If the first time machine is invented in, say, the year 2525, we wouldn’t see any travelers until then. But after that, tourists from the future might overrun Earth like they do Yosemite on a summer’s day.

Opening the floodgates

After Thorne and his collaborators published their wormhole idea in 1988, research on time travel enjoyed a major renaissance. In 1991, Princeton University astrophysicist J. Richard Gott devised a time machine that uses cosmic strings — exceedingly thin, high-density strands of material left over from the Big Bang. Although searches for cosmic strings so far have turned up empty-handed, many cosmologists think they exist.

Gott’s device would employ two infinitely long and straight cosmic strings ­oriented parallel to each other. Then, the strings would have to move in opposite directions at speeds within a millionth of 1 percent of light-speed. The solution has at least one advantage over a wormhole time machine — it requires only normal matter to make it work.

Ronald Mallett has a more down-to-Earth proposal. In 2000, he published his idea for a time machine that could, conceivably, be built in a laboratory. Using ­Einstein’s assertion that mass and energy are equivalent, Mallett proposes generating a gravitational field from the energy of light. Using a “ring laser,” which creates a continuously circulating beam of light, he believes he can produce a gravitational field strong enough to allow time travel into the past.
For the mom­ent, Mallett is thinking both big and small — big in the sense that he’s seek­ing funding for a prototype; small in the sense that he’ll be attempting to send a neutron into the past. If he can show his contraption works, the rest, as he says, is engineering.

A world of paradox

The possibility of travel into the past raises a host of troubling prospects. A big one is whether causality can be violated. In everyday life, cause always comes before effect. A pitcher throws a baseball over home plate, then the batter swings and hits it. The batter never hits the ball before the pitcher throws it.

But if heading back in time is possible, causality might not hold. Think of a billiards table where the pockets are actually the mouths of a wormhole. What if you shoot a ball into one end of a wormhole and it travels a few seconds back in time, only to emerge from the wormhole’s other end in time to collide with its younger self. If the collision deflects the ball so it doesn’t enter the wormhole to begin with, where did the deflecting ball come from? The question of causality reaches its zenith in the grandfather paradox (see “Tread lightly, young man” on page 38).

No one expects people to be whipping through time at any point in the near future — or past. Most proposed time machines, at least those capable of sending humans into the past, would require the skills of a supercivilization. But the recent spate of theoretical advances suggests, at the very least, the laws of physics don’t rule out the possibility of time travel.

It’s a notion that likely would please H. G. Wells. A concept he developed out of whole cloth opened new avenues for some of the finest minds of the past 100 years. If only we could go back and tell him.

http://www.astronomy.com/news/2016/12/i ... n-our-side
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Re: Interesting websites ( OPEN SUBJECTS)

Postby ecker2011 » Tue May 23, 2017 2:08 pm

New blackbody force depends on spacetime geometry and topology

by Lisa Zyga

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Illustration of a cylindrical blackbody and a nearby atom. Credit: Muniz et al. ©2017 EPL


(Phys.org)—In 2013, a group of physicists from Austria proposed the existence of a new and unusual force called the "blackbody force." Blackbodies—objects that absorb all incoming light and therefore appear black at room temperature—have long been known to emit blackbody radiation, which repels small nearby objects such as atoms and molecules. But the physicists showed that blackbodies theoretically also exert an attractive force on these objects. They called this force the "blackbody force," and showed that it can be stronger than blackbody radiation, and—for very small particles—even stronger than gravity.

Now in a new study published in EPL, a different team of physicists, C.R. Muniz et al., at Ceará State University and the Federal University of Ceará, Brazil, have theoretically demonstrated that the blackbody force depends not only on the geometry of the bodies themselves, but also on both the surrounding spacetime geometry and topology. In some cases, accounting for these latter factors significantly increases the strength of the blackbody force. The results have implications for a variety of astrophysics scenarios, such as planet and star formation, and possibly lab-based experiments.

"This work puts the blackbody force discovered in 2013 in a wider context, which involves strong gravitational sources and exotic objects like cosmic strings as well as the more prosaic ones found in condensed matter," Muniz told Phys.org.
As the scientists showed in 2013, the blackbody force arises when the heat absorbed by a blackbody causes the blackbody to emit electromagnetic waves that shift the atomic energy levels of nearby atoms and molecules. These shifts cause the atoms and molecules to be attracted to the blackbodies due to their high radiation intensity, pulling them together.

In the new study, the physicists investigated spherical blackbodies and cylindrical blackbodies, and showed how the topology and the local curvature of the spacetime influences their blackbody forces. They showed that ultradense spherical blackbodies like a neutron star (around which spacetime is highly curved) generate a stronger blackbody force due to the curvature compared to blackbodies in flat spacetime. They explain that this is because gravity modifies both the temperature of the blackbody and the solid angle at which the nearby atoms and molecules "see" the blackbody. On the other hand, a less dense blackbody such as our Sun (where spacetime is less curved) generates a blackbody force that is very similar to that of the flat case.

The researchers then considered the case of a global monopole, a spherical object that modifies the global properties of space, and found a different kind of influence. Whereas for other spherical blackbodies, the spacetime influence is gravitational and decreases with the distance to the blackbody, for the global monopole the influence is of a topological nature, decreasing with the distance but eventually reaching a constant value.

Finally, when investigating the blackbody force of cylindrical blackbodies around which spacetime is locally flat, the scientists found no gravitational correction to the temperature, but, surprisingly, an effect on the angles with nearby objects. And when a cylindrical blackbody becomes infinitely thin, turning into a hypothetical cosmic string, the blackbody force vanishes completely. Overall, the scientists expect that these newly discovered geometrical and topological influences on the blackbody force will help elucidate the role of this unusual force on objects throughout the universe.

"We think that the intensification of the blackbody force due to the ultradense sources can influence in a detectable way the phenomena associated with them, such as the emission of very energetic particles, and the formation of accretion discs around black holes," Muniz said. "That force can also help to detect the Hawking radiation emitted by these latter objects, since we know that such radiation obeys the blackbody spectrum. In the future, we would like to investigate the behavior of that force in other spacetimes, as well as the influence of extra dimensions on it."

Explore further: Blackbody radiation induces attractive force stronger than gravity

https://phys.org/news/2017-05-blackbody ... ology.html
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Re: Interesting websites ( OPEN SUBJECTS)

Postby ecker2011 » Tue May 23, 2017 3:20 pm

Physics Today


Today is the birthday of Willie Hobbs Moore, the first African American woman to be awarded a PhD in physics in the US. She was born in 1934 in Atlantic City, New Jersey. Moore entered the University of Michigan to study engineering in 1954, the same year as the Supreme Court's landmark Brown v. Board of Education case. She earned her PhD from the university in 1972, nearly a century after Edward Bouchet became the first African American to earn a physics PhD. Her research focused on infrared spectroscopy for chemical analysis. She worked in industry throughout her career and published in many chemistry and physics journals. Moore also worked to improve STEM education for minority populations. She died in Ann Arbor, Michigan, at age 60 in 1994. The University of Michigan College of Engineering created an award in her honor. (Photo courtesy of the Ronald E. Mickens Collection, Niels Bohr Library & Archives, American Institute of Physics)

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Re: Interesting websites ( OPEN SUBJECTS)

Postby ecker2011 » Tue May 30, 2017 1:37 pm

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Steve Bassett


Billionaire Robert Bigelow of Bigelow Aerospace spoke truth to power and finally said publicly what he and hundreds of millions of people around the world already know to be true. And he said it on CBS 60 Minutes last night. There is an extraterrestrial presence engaging the human race. How many military officers, political figures, intelligence agents, scientists, entertainers, and, yes, billionaires have to speak this truth before the investigative journalists in America figure out the biggest news story in history has been right under their noses for 70 years?
http://www.cbsnews.com/news/bigelow-aer ... -in-space/
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