May 4, 2012
Today, if you aren’t already aware, is something of an intergalactic holiday. In recent years, May 4th has become an unofficial day to honor the iconic film series Star Wars, because the date is a rhyming pun of the signature line, “May the Force Fourth Be With You.” All around the world, Star Wars fans are celebrating Luke, Leia, Boba Fett and (maybe even) the Ewoks.
We decided to channel our inner Jedi by checking out the contributions science has made towards a better understanding of the Star Wars universe. Last year, it turns out, a team of physicists from the University of Leicester in Britain took a closer look at many fans’ favorite spacecraft: Han Solo and Chewbacca’s hyperspace-traveling Millennium Falcon (which made the Kessel Run in less than 12 parsecs!)
The scientists noted that force fields are often employed in the Star Wars universe to provide a barrier between the hangars of spaceships and outer space, preventing the ship’s atmosphere from being sucked outwards (think of spacecraft flying inside the Death Star‘s massive hangar bay, with no mechanical airlock). The physicists noted that a real-life innovation, the plasma window, could theoretically serve to create such force fields. Plasma windows, invented by Brookhaven Lab physicist Ady Hershcovitch in 1995, use magnetic fields to create bounded areas filled with plasma (superheated, viscous ionized gas), which have the special property of blocking air from entering a vacuum while allowing radiation and physical objects to freely pass through.
With this knowledge in hand, the research team decided to try calculating the amount of energy that would be necessary to create a docking force field large enough to accommodate the Millennium Falcon, which they estimate is roughly 100 by 40 by 6 feet. Their conclusion? Theoretically possible with current technology—but generating sufficient amounts of energy to continuously sustain a force field that size is unlikely to be feasible.
But, in a galaxy far, far away, anything is possible.
March 9, 2012
As Daylight Savings Time approaches, you’ll be seeing many reminders to shift your clocks an hour forward just before going to sleep on Saturday night. This got us thinking about the clocks that set themselves. Available widely for as little as $10 or $15, these radio-controlled clocks are increasingly popular, as they adjust automatically to time shifts and will work virtually anywhere in the continental United States. You may well own one of them already. But you may not know how they work.
This clock’s low-tech appearance conceals an elaborate system for keeping it precisely in tune with what the National Institute of Standards and Technology deems official time: a clock calibrated by the movement of a clump of cesium atoms in Boulder, Colorado. Housed at the NIST’s Physical Measurement Laboratory, this is the official atomic clock, and it keeps time for the entire country.
The sophisticated apparatus—known as NIST-F1—is the latest in a line of high-tech atomic clocks and was officially adopted as the U.S.’s time standard in 1999. The accuracy of NIST-F1 is continuously improving, and as of 2010, scientists calculated that its uncertainty had been reduced to the point that it will neither gain or lose a second over the course of 100 million years.
This degree of accuracy is achieved by a complex technological setup. In 1967, the International Bureau of Weights and Measures officially defined a single second as the time it takes a single cesium atom to transition between energy levels a given number of times—that is, cesium’s natural resonance frequency. NIST-F1 is known as a cesium fountain atomic clock because it uses a fountain-like array of lasers to manipulate cesium atoms and detect this frequency as accurately as possible.
Inside the device, six powerful lasers are aimed at a gas containing cesium atoms, slowing down their movement and cooling them down to temperatures just millionths of a degree above absolute zero. Next, a pair of vertical lasers push the clumped ball of cesium atoms about a meter upward in the cavity, which is filled with microwave radiation. As it drifts back downward, another laser is pointed at the atoms and detects how many were altered by the microwaves. Scientists calibrate the microwave frequency to maximize the number of atoms affected.
The NIST uses this measure of cesium’s resonance frequency as the official second for the U.S. primary time standard. But how does it get to your radio-controlled clock? The official time standard is sent to WWVB, NIST’s shortwave radio station in Fort Collins, Colorado. Once per minute, WWVB uses five antennas to broadcasts a digital code indicating the official time—including the year, date, hour, minute and whether Daylight Savings Time is in effect—across the country.
Most radio-controlled clocks are programmed to receive this signal once per day with built-in receivers and calibrate their time accordingly. Experts say that your radio-controlled clock will work best when positioned near a window facing the source of the broadcast, Fort Collins. Many other countries have their own official time broadcasts, based on other atomic clocks.
A clock that stays accurate for 100 million years is pretty good, right? Not for NIST. In 2010, they announced advances in developing a new “quantum logic clock,” which keeps time based on a single atom of aluminum. The new clock will neither gain nor lose a second over 3.7 billion years, the researchers report, giving it the title of the world’s most precise clock.
So this year, if your clock automatically jumps an hour ahead at 2 a.m. Sunday, remember that an intricate setup of lasers and atoms thousands of miles away is the reason why. We’ve sure come a long way from watching sundials and winding watches.
February 16, 2012
For years, science-fiction and fantasy authors have dreamed up magical objects—like Harry Potter’s invisibility cloak or Bilbo Baggins’ ring—that would render people and things invisible. Last week, a team of scientists at the University of Texas at Austin announced that they have gone one step further toward that goal. Using a method known as “plasmonic cloaking,” they have obscured a three-dimensional object in free space.
The object, a cylindrical tube about 7 inches long, was “invisible” to microwaves, rather than visible light—so it’s not like you could walk into the experimental apparatus and not see the object. But the achievement is nonetheless quite stunning. Understanding the principles of cloaking an object from microwaves could theoretically lead to actual invisibility soon enough. The study, published in late January in the New Journal of Physics, goes beyond previous experiments in which two-dimensional objects were hidden from various wavelengths of light.
How did the scientists do it? Under normal conditions, we see objects when visible light bounces off them and into our eyes. But the unique “plasmonic metamaterials” from which the cloak was made do something different: they scatter light in a variety of directions. ”When the scattered fields from the cloak and the object interfere, they cancel each other out and the overall effect is transparency and invisibility at all angles of observation,” said Professor Andrea Alu, co-author of the study.
To test the cloaking material, the research team covered the cylindrical tube with it and subjected the setup to a burst of microwave radiation. Because of the plasmonic material’s scattering effect, the resulting mapping of microwaves did not reveal the object. Other experiments revealed that the shape of the object did not affect the material’s effectiveness, and the team believes that it is theoretically possible to cloak multiple objects at once.
The next step, of course, is creating a cloaking material capable of obscuring not only microwaves, but visible light waves—an invisibility cloak we might be able to wear in everyday life. Alu, though, says that using plasmonic materials to hide larger objects (like, say, a human body) is still a ways away:
In principle, this technique could be used to cloak light; in fact, some plasmonic materials are naturally available at optical frequencies. However, the size of the objects that can be efficiently cloaked with this method scales with the wavelength of operation, so when applied to optical frequencies we may be able to efficiently stop the scattering of micrometre-sized objects.
In other words, if we’re trying to hide something from human eyes using this method, it’d have to be tiny—a micrometre is one-thousandth of a millimeter. Still, even this could be useful:
Cloaking small objects may be exciting for a variety of applications. For instance, we are currently investigating the application of these concepts to cloak a microscope tip at optical frequencies. This may greatly benefit biomedical and optical near-field measurements.
In 2008, a Berkeley team developed an ultra-thin material with the potential to someday render objects invisible, and earlier this year, a group of Cornell scientists funded by DARPA was able to hide an actual event 40 picoseconds long (that’s 40 trillionths of a second) by tweaking the rate of light’s flow.
Invisibility cloaks may still be years away, but it seems we’ve entered the Age of Invisibility.
February 14, 2012
Gravity potentially affects all biological processes on Earth, even though this may be hard to believe while we watch flies walking around on our ceilings as though gravity did not matter to them at all. Of course, gravity is only one factor, and other factors such as adhesion or buoyancy determine whether an organism falls off the ceiling, say, or how long it takes an organism to settle to the ground.
We’ve known for a long time that humans are harmed by long periods in low-gravity environments. Astronauts return from space with muscle atrophy and reduced bone mass. These effects seem to get worse over time, so understanding the effects of gravity on human physiology is essential when planning long-distance space flights. Studying the effects of low gravity in space craft and space stations is expensive. Anyone who has spent time working in a laboratory knows that many experiments have to be redone numerous times just to get the procedures to work properly. If a key step in carrying out an experiment on, say, the response of cells to lack of gravity, is “shoot the experiment into space and keep it there for two months” then it will take a very long time and a lot of money to get results one might need to make sense of low-gravity biology. Therefore, it would be nice to have an anti-gravity machine in our Earth-bound laboratories to run experiments without the cost and scheduling constraints imposed by space flight.
There is a way to simulate weightlessness at a small scale in the lab. A team of researchers from several European institutions have used magnetism to offset the effects of gravity at the cellular level. The method is called diamagnetic levitation. (Another method for simulating anti-gravity uses a “Random Positioning Machine” (RPM).) Some materials—diamagnetic materials—are repelled by a magnetic field. Water and most biological tissues fall into this category. A very powerful magnetic field can be applied to these tissues to offset the effects of gravity, so molecules moving about and doing their thing inside cells do so as though there were no gravity acting on them. According to a recent study, it appears that gene expression is affected by gravity. (The paper is published in BMC Genomics and is available here.)
The magnet used in this experiment produces a field with a force of 11.5 Tesla (T). The Earth’s magnetic field is equal to about 31 micro Teslas. The magnet holding your shopping list to your refrigerator is about .005 Tesla, the magnets in a loudspeaker are about 1 to 2 Teslas in strength, and the magnetic force of an MRI or similar device, for medical imaging, is usually about 3 Teslas or less. If you were to attach a magnet of 11.5 Teslas to your refrigerator, you would not be able to pry it off.
In this experiment, the magnet was used to “levitate” fruit flies for 22 days as they developed from embryos to larvae to pupae and eventually to adults. The flies were kept at a certain distance above the magnet where the net repulsive effect of the magnet on the water and other molecules was equal to and opposite of the effects of gravity. Other flies were placed below the magnet at the same distance, where they experienced the equivalent of double the Earth’s gravity.
The study examined how the expression of genes differed depending on the simulated gravitational field as well as in a strong magnetic field that did not simulate a change in gravity. Doubling the Earth’s gravity changed the expression of 44 genes, and canceling out gravity altered the expression of more than 200 genes. Just under 500 genes were affected by the magnetic field alone, with expression of the genes being either increased or decreased. The researchers were able to subtract the effects of magnetism from the effects of increased or decreased gravity and thus isolate which genes seemed to be most sensitive to changes in gravity alone. According to the researchers, “Both the magnetic field and altered gravity had an effect on gene regulation for the flies. The results of this can be seen in fly behaviour and in successful reproduction rates. The magnetic field alone was able to disrupt the number of adult flies from a batch of eggs by 60%. However the concerted effort of altered gravity and the magnet had a much more striking effect, reducing egg viability to less than 5%.”
The most affected genes were those involved in metabolism, the immune system’s response to fungi and bacteria, heat-response genes and cell signalling genes. This indicates that the effects of gravity on the developmental process in animals is profound.
The most important outcome of this research is probably the proof of concept: It demonstrates that this technique can be used to study the effects of low gravity on biological processes. We can expect more-refined results that inform us of specific processes that are altered by gravity, and possibly develop ways of offsetting those effects for humans or other organisms on long-distance space flight. Eventually, we may be able to send a fruit fly to Mars and return it safely.
Herranz, R., Larkin, O., Dijkstra, C., Hill, R., Anthony, P., Davey, M., Eaves, L., van Loon, J., Medina, F., & Marco, R. (2012). Microgravity simulation by diamagnetic levitation: effects of a strong gradient magnetic field on the transcriptional profile of Drosophila melanogaster BMC Genomics, 13 (1) DOI: 10.1186/1471-2164-13-52
January 11, 2012
Obi-Wan: That’s no moon. It’s a space station.
That space station was the Empire’s first Death Star in Star Wars: A New Hope. Obi-Wan and company had just bounced through a debris field, the remnants of the planet Alderaan. Such an act of destruction would seem impossible to us–it seemed so to many of the movie’s characters until it happened. But perhaps not, say three students at the University of Leicester in England who last year published a study on the subject in their university’s undergraduate physics and astronomy journal.
The study’s authors start off by making some simple assumptions: The planet being fired upon doesn’t have some sort of protection, like a shield generator. And it’s about the size of Earth but solid through and through (Earth isn’t solid, but the planet’s layers would have significantly complicated the math here). They then calculate the planet’s gravitational binding energy, which is the amount of energy required to pull apart an object. Using the mass and radius of the planet, they calculate that destruction of the object would require 2.25 x 1032 joules. (One joule is equal to the amount of energy required to lift an apple one meter. 1032 joules is a lot of apples.)
The energy output of the Death Star isn’t given directly in the movie, but the space station was said to have had a “hypermatter” reactor that had the energy output of several main-sequence stars. For an example of a main-sequence star, the authors look to the Sun, which puts out 3 x 1026 joules per second, and they conclude that the Death Star could “easily afford to output [the energy required for an Earth-like planet's destruction] due to to its tremendous power source.”
It would be a different story, though, if the planet scheduled for destruction had been more like Jupiter than Earth. The gravitational binding energy of Jupiter is 1,000 times that of the Earth-like planet in the study. “To destroy a planet like Jupiter [the space station] would probably have to divert all remaining power from all essential systems and life support, which is not necessarily possible.”
Of course, that assumes that the Emperor wouldn’t be willing to sacrifice a space station full of people to wipe out his enemies. And considering that he was just fine with wiping out whole planets, I’m not sure I’d take that bet.