String Theory's Extra Dimensions Must Be Less Than Half the Width of a Human Hair

If extra dimensions of space exist, they must be smaller than about half the width of a human hair, according to new measurements of the strength of gravity at short distances. Researchers found that the same law governing the gravitational pull between planets continues to work when objects are separated by as little as 56 micrometers. The finding rules out extra dimensions of 44 micrometers or larger, they report in this week's Physical Review Letters.Discovering extra dimensions with the relatively huge size of a few micrometers would offer spectacular confirmation for string theory, the still unproved body of equations that may unify gravity with the normally incompatible realm of quantum physics. "Even though we haven't seen anything, these results put boundaries on what people can legitimately propose," says experimental physicist and study author Eric Adelberger of the University of Washington. "Testing the inverse square law [meaning Newton's law of gravity] is the bombproof way to look for extra dimensions.""I'm a big admirer of this class of experiments; I think they're awesome," says theoretical particle physicist Raman Sundrum of Johns Hopkins University. In principle, such tests could effectively rule out theories of micrometer-size extra dimensions, he says. To study such questions researchers would normally expect to use giant particle accelerators, such as the Large Hadron Collider (LHC), set to switch on in Geneva later this year.Sundrum says the LHC may still get its shot at large extra dimensions, because the new result leaves the idea some wiggle room. "It's not killing that scenario," he says.With no pressing reason to check, researchers, until a few years ago, had never measured the strength of gravity when objects were separated by much less than a millimeter (roughly the width of a period on this page). But beginning in the late 1990s, some physicists proposed that string theory might cause gravity to grow stronger at such distances if the universe came with relatively big extra dimensions of micrometers in width. (To make its arithmetic come out right, string theory requires that space have extra dimensions beyond the three we can readily experience, but researchers had assumed that these dimensions are extraordinarily tiny.)Adelberger and his colleagues on the so-called Eot-Wash experiment have led the way in checking gravity's short-distance strength. They employed a small metal pendulum suspended above a stacked pair of fused metal disks, which exerted a gravitational tug on a metal ring on the bottom of the pendulum.The ring and the upper disk contained a series of matching holes. If the holes lined up, gravity was pulling straight down, but if the holes were offset, the disk's gravity was twisting the pendulum. As a result, the experiment was able to measure the strength of gravity at the distance between the ring and the upper disk.The key to the experiment is the lower disk, which contains holes of different sizes that are designed to cancel out the twisting caused by the upper disk when the ring and disks are in certain orientations. If that canceling does not occur, it means that the force between the ring and the upper disk has changed, either because the strength of gravity has changed or because some new force has intervened that has no effect at the slightly larger distance between the ring and the bottom disk.In a prior experiment, the Eot-Wash team ruled out extra dimensions larger than 100 micrometers. This time researchers attained greater sensitivity by using more holes and covering the apparatus in gold to screen out electromagnetic forces between the ring and disks.Adelberger says they might be able to get down to a few micrometers, but it would be very tough. "As the dimensions get smaller and smaller, the force [they cause] gets smaller much faster," he says. The payoff could be worth it, though. Sundrum says that if extra dimensions failed to turn up at that distance, it would likely prune off that branch of string theory.

Scientific American: String Theory's Extra Dimensions Must Be Less Than Half the Width of a Human Hair

Optimized adhesives

Print the story

ESA launches new project to protect biodiversity

"The United Nations Convention on Biodiversity (UNCBD) agreed on a set of headline indicators to assess the progress made towards this target. DIVERSITY will make a contribution to the required monitoring efforts that will help us to determine whether we are making progress and which management and policy measures are most effective and thereby support decision-making," the UNCBD Secretariat Robert Höft said.
[...]
The DIVERSITY project, developed under ESA's Data User Element (DUE) programme, is being carried out in collaboration with the UNCBD Secretariat and UNESCO, which, in addition to being a user, is also the main coordinator between the users and contractors selected by ESA.

ESA Portal - ESA launches new project to protect biodiversity

Blogged with Flock

Robo-rights:a study commissioned by the UK government

Humans are increasingly reliant on computers, robots and machines. Currently, robots and machines are inanimate objects without rights or duties. If artificial intelligence is achieved and widely deployed (or if they can reproduce and improve themselves) calls may be made for human rights to be extended to robots. If so, this may be balanced with citizen responsibilities (e.g. voting, paying tax). A push for robots' rights may clash with owners’ property rights. More strain may be placed on the environment (e.g. energy, waste, resource & space usage).

View Issue

Robotrat: a telecontrolled rat in invisible mazes!

ScienceDirect - Trends in Cognitive Sciences : The amazing adventures of robotrat

Accordingly to Professor Nicolelis, the most important name in the BCI field (do you remember the monkey who could control the robot just thinking?), in a recent work it was obtained a telecontrolled rat just inserting three microelectrodes in the animal’s brain. Two of them are used to stimulate the somatosensory cortex in the whiskers zone, one for the left whiskers and the other for the right ones. The third has to stimulate a zone that is thought to mimic pleasure followed by positive reward. So, if the rat turns in the right direction, it will be pleasured. The final result is a telecontrolled rat!

With this set-up it was possible to teach the rat how to navigate in invisible mazes. After some trials, the rat was able to navigate into the real mazes, knowing exactly where to go. Amazing.

Applications? Of course the “positive” scenario is the usual after-earthquake one: telecontrolled animals could be the perfect tools to locate surviving victims buried in piles of rubble.

No words on the military uses. Anyway, what the eye doesn't see, the heart doesn't grieve… I feel better.