• Sept. 17, 2005 |
Physicists use their branes: For years, cosmologists have been saying that the universe would make a lot more sense if only it had more dimensions than the four we perceive — that is, three spatial dimensions plus time.
If there were, say, 10 dimensions or so, the equations linking gravity and atomic forces into a "theory of everything" would work out just fine. For that reason, extradimensional physics is a hot topic, not only for theoretical papers but also for books and TV shows aimed at the general public, such as "The Elegant Universe."
But if we live in a 10-dimensional realm, where are the other six dimensions? Is there something special about three-dimensional space? In a paper due to be published in Physical Review Letters, two physicists propose that the kind of cosmos we live in represents one of the most likely results of something you could call the "battle of the branes."
That's not a typo: We're not talking about gray matter here, but rather different levels of dimensional spaces, known as branes. In cosmological parlance, a two-dimensional space, or membrane, is a "2-brane." A line is a 1-brane, a particle is a 0-brane, and we perceive space as a 3-brane.
Harvard's Lisa Randall and the University of Washington's Andreas Karch did some heavy-duty mathematical analysis of a scenario in which an expanding 10-dimensional space holds a variety of branes. (Here's a PDF version of the paper.)
If two branes intersect, they are annihilated and their energy is dissipated. "The net result of all this is that you reduce the number of branes," Karch explained. And because of the 10-dimensional geometry, some types of branes are more likely to survive than others.
This is more understandable if you bring it down to a 3-D level, kind of like a brane version of Edwin Abbott's "Flatland": Imagine you have an expanding container containing a whole bunch of spaced-out particles as well as widening membranes and lengthening lines. If two objects in the container intersect, they both disappear. The membranes will cancel each other out, unless they're precisely parallel. However, more of the lines will survive, and almost all of the particles will be unaffected.
When you bring it back up to 10-D (actually "nine-plus-one" D, since we're talking about nine spatial dimensions plus time), the math indicates that the 3-branes like ours hold a special status. "A 3-brane is the largest brane that doesn't get destroyed by its cousins," Karch said.
The findings are consistent with the idea that our whole universe is a 3-D region within a wider, flatter 10-D realm. Such regions "could be like sinkholes in which gravity is localized," Karch said. And ultimately, that could help explain why gravity works the way it does.
The other class of dimensional space that shows a good survival rate is the 7-brane — which doesn't apply to our particular sinkhole in the cosmic roadway, but turns out to match the expectations of string theorists.
"Several versions of string theories require the existence of 3-D and 7-D branes; indeed, the particles that constitute matter — such as quarks and electrons — can be considered open strings with one end planted on a 3-D brane and the other end planted on a 7-D brane," Phillip Schewe and Ben Stein of the American Institute of Physics report in this week's Physics News Update.
I realize the geekspeak is getting pretty deep at this point, but the whole exercise illustrates why physicists tackle these brane teasers in the first place: They're trying to shuffle around a theoretical jigsaw puzzle, looking for corner pieces or patterns that could help them fill in the gaps. The quest could lead theorists forward to that fabled "theory of everything" — or backward to square one.
Our special report on the intellectual successors to Albert Einstein provides the big picture on the scientific quest — and to learn more about how physicists are using their branes, check out Michio Kaku's discourse on "M-Theory: The Mother of All Superstrings."
• Sept. 17, 2005 |
Weekend field trips on the World Wide Web:
• Sept. 14, 2005 |
Lifter project gets a lift: The Federal Aviation Administration has given the green light for a company to do mile-high tests of a robotic “lifter” system that could one day be used to shuttle payloads into orbit.
For the , based in Bremerton, Wash., the tests represent another small step toward the development of a space elevator. The concept envisions shooting super-strong tethers up to an altitude of 60,000 miles, then using those lines as a track for beam-powered elevator cars. If the system can be made to work, it could dramatically cut the cost of access to space.
But even before that big lift in the sky is built, the basic technologies behind the space elevator could be put to other applications — perhaps even including hurricane disaster relief and the war in Iraq, according to Michael Laine, LiftPort’s president and chief strategic officer.
Specifically, the FAA cleared LiftPort to send a tether-equipped experimental balloon to an altitude of up to 1 mile. The LiftPort team would then put its latest-generation lifter through its paces. Unfortunately, this month’s scheduled tests didn’t quite get off the ground – as Laine explained in an e-mail:
“The FAA granted 2 waivers for us this month. The first was between the 6th and the 9th, and the second was for the 9th to the 12th. In both cases, we had to scrub because of weather. “The FAA will continue to work with us over the coming months; however, the ‘weather window’ is closing — if we stay here to test. We are currently cleared for tests in a remote area in northeastern Washington. As fall and winter set in, we may have to move locations. Fortunately, our coordinator with the FAA covers a very large region, so we have some sunny, warm choices available to us.“In a perfect world, we will get this test to work, and then spend the fall and winter in the lab for our next lifter tests in the spring — for higher altitudes. We will keep trying for a mile in the local area for as long as we can and then move locations if the weather doesn’t cooperate.“Our plan is for a series of tests, one immediately after another, of 500, 1,000, 1,500, 2,000 feet, and then going straight to 1 mile. We have a wireless data connection on the lifter that is relaying GPS and temperature information, variable speed control, forward and reverse modes and a range sensor to slow the ’bot down as it nears the top. [Once it reaches the top, it would] stop and automatically return to the bottom base station — what we call ‘the LiftPort’ in deference to the ship in the ocean that we will anchor the future system to.“It was hoped that we would be able to do these tests on Friday the 9th, but the weather changed — a lot — between the time we left (5 a.m.) and the time we arrived and set up (9 a.m.). There was no cloud cover when we started, but the winds picked up right away. There were as many as five dust devils in view on the near horizon. We all kinda knew what that meant for a fragile balloon, but figured that the cost of the truck, balloon and helium were all nonrefundable, so we might as well try. Well, the expected happened, and both of our balloons were shredded before they even got off the ground.“So we will be back out there in the next few weeks or so, with better balloon systems. As I’ve told you many times before, we are still much better at building robots than we are at handling balloons.“This is our 18th robot. Officially it’s the Mark VII series, and unofficially it’s called ‘The Sword’ after the . It is about 23 pounds, 5.5 feet tall, 5 by 7 inches deep and wide, and will climb at a speed of 1 mph. The lifter robot climbs on a ribbon held in tension between The LiftPort and a large helium balloon at the top.”
Just this spring, NASA announced its backing for a multiyear "Centennial Challenges" project to promote the development of stronger tethers and beam-powered lifters through a competition known as Space Elevator Games. Several teams are gearing up for the first contest, scheduled Oct. 21-23 at NASA's Ames Research Center in Mountain View, Calif. But Laine says LiftPort won’t be among them:
"While I am a strong supporter of what E2010 is doing for their competition, I don’t think it’s right that we compete in that. For one thing, I am on the advisory board. While it’s a strictly ceremonial position, I still think there would be a conflict of interest in our team competing.“The other reason is about economics. As you know, we are the commercial part of the space elevator development program. So I always have to look at the ‘bottom line.’ If we were to compete and win, we'd have a $50,000 prize, and a robot that could climb 200 feet – and that’s it.“On the other hand, if we focus on building a machine that can climb to high altitudes, we solve a more important challenge to the overall goal of building an elevator to space, and build a machine that has current valuable commercial applications. So that is what we are doing. We are hoping to provide a High Altitude Long Endurance (HALE) system to the military for security and surveillance of improvised explosive devices, and also hoping to provide a system to the Red Cross, to help with the cleanup efforts from Katrina.“These would be real-world technology applications that fit our ‘dual-track’ technology development plan – something that earns revenues down here on earth, now, and something that teaches us what we need to know, in order to build our long-term project.“The power-beaming problem was a very small part in our decision to not compete. So far as I am concerned, it’s a ‘solved problem’ when it’s only over a 200-foot range. As we gain higher altitudes, then the problem becomes more and more important to solve. We will tackle that, when there is a clear trade-off between conventional power systems and beaming power. We figure that will be at the 5- to 10-mile mark. So it’s coming, it just isn’t our focus … yet.”
If you’re of a skeptical bent, the space elevator itself may sound like pie in the sky. But the constituent technologies – carbon nanotube fabrication and high-altitude robotic transport – seem to fit in with other initiatives, such as the rapid rise of surveillance blimps. Is this trip really necessary? I’d love to hear .
• Sept. 13, 2005 |
Catch a beautiful Boomerang: The Hubble Space Telescope’s astronomers have colorized their latest view of the Boomerang Nebula – but there’s a scientific point behind those pretty rainbow hues.
In this brand-new Hubble image, the different colors represent different polarizations of light from the twin lobes of dust on either side of the central star. Those colors can’t be seen in an of the Boomerang, but they help scientists visualize how the nebula is put together.
“By combining images taken at different polarization angles, astronomers can study light scattering in the nebula and the properties of the small dust particles responsible for the scattering,” Hubble’s astronomers explain in .
The Boomerang, about 5,000 light-years away in the constellation Centaurus, serves as a classic example of bipolar outflow – which is something of an astronomical mystery. The nebula’s shape could be due to a ring of slow-moving matter constricting the thin part of the hourglass, or due to the magnetic field surrounding the star.
The shape can be seen in the nebulas puffed away by dying stars, and in the nebulas spawned by young, hot stars that are still collapsing and forming.
“The Boomerang is believed to be the ejected outer layers from an old red giant,” Hubble’s scientists say. “Each lobe of the Boomerang Nebula is nearly one light-year in length, making the total length of the nebula half as long as the distance from our sun to our nearest neighbors – the Alpha Centauri stellar system, located roughly 4 light-years away.”
The Boomerang has yet another claim to fame: Radio measurements of its deep interior indicate that the temperature there is just one degree Kelvin above absolute zero. “This makes the inner regions of the Boomerang Nebula one of the coldest known places in the universe,” according to the Hubble advisory.
For more examples of super-cool nebulas, check out our .
• Sept. 13, 2005 |
Talking points on the scientific Web:
• Sept. 12, 2005 | Hams in space: Along with the tons of food, fuel and other essentials, last week’s Progress cargo ship supplied the international space station with a couple of fresh slices of ham – amateur-radio equipment, that is.
Ham radio has served as an unofficial backup communication channel for the space station’s occupants, just as it did for Russia’s Mir space station in years past. Astronauts and cosmonauts regularly get in contact with friends and family, fellow hams, and even school students as part of a program called Amateur Radio on the International Space Station, or ARISS.
Amateur-radio enthusiasts inside and outside the space program worked for months to get two unconventional pieces of equipment ready in time for the Progress flight.
One project is called Suitsat: ARISS sent up a radio system that can be installed inside an outdated Russian spacesuit, then released (without an astronaut inside) from the space station during a future spacewalk — most likely in December. Powered by batteries in the spacesuit, the autonomous Suitsat transmitter will beam down specially coded messages for students to decipher, as well as telemetry and a slow-scan TV image.
After a few weeks in orbit, the radio-equipped suit is expected to drift into Earth's atmosphere and burn up.
The project also features a more enduring legacy: Suitsat organizers solicited hundreds of school pictures, artwork, poems and signatures from schools all over the world. All that imagery was digitized and put on two identical CDs. One is to be placed inside Suitsat, and the other will be kept on the space station.
That’s where the second project comes in: The Progress craft also brought up an extra two-way, slow-scan TV communications system. The SSTV system, inside Suitsat as well as on the station, provides a way to send imagery as data over amateur-radio frequencies.
“When fully operational, the SSTV system is capable of sending up to 480 images per day from ISS,” Frank Bauer, NASA’s ARISS program manager and ARISS international chairman, said in a mailing to supporters. “It will also be able to receive images from amateur radio stations on Earth.”
Almost seven years ago, it was a real treat to see the first SSTV images beamed down from a Webcam mounted inside the Mir space station. We’ll likely see similar imagery from the space station, of the interior as well as the view out the window.
The space station crew also plans to use the SSTV system to beam the imagery from the Suitsat CD down to hams on Earth.
“We look forward to future operations of these systems on ISS, inspiring the next generation of space explorers,” Bauer said.
You won’t have to wait even that long to hear space hams in action. During my current visit to Moscow, millionaire space passenger Greg Olsen told me that he’s lined up a series of ham-radio sessions with school groups ranging from Princeton to the University of Virginia to Fort Hamilton High School in Brooklyn.
“I was a ham when I was in my first year of high school, so I had a license, but it lapsed 40-odd years ago,” Olsen recalled. “I just renewed it a month ago.”
As Olsen’s Oct. 1 launch approaches, we’ll try to pass along the schedule for his ham-radio and video educational sessions, and capture what we can for posterity.
• Sept. 12, 2005 | Postcard from Moscow: I was at Russian Mission Control for the Progress ship's arrival over the weekend, and heard the applause ring out for a robo-docking that was smooth as silk. If everything goes as planned, I'll be at the Star City cosmonaut training complex on Tuesday for the next space station crew's press conference. Generally speaking, getting things done seems a bit easier this time around than the last time I was in Moscow, back in the winter of 2001. And the weather is a lot better, too — almost as balmy as a Seattle summer. Stay tuned for more reports about the Russian space effort in the run-up to the Oct. 1 launch.
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