Published: April 2, 2010
European Collider Begins Its Subatomic Exploration (March 31, 2010)
Yes, the collider finally crashed subatomic particles into one another last week, but why, exactly, is that important? Here is a primer on the collider – with just enough information, hopefully, to impress guests at your next cocktail party.
Let’s be basic. What does a particle physicist do?
Particle physicists have one trick that they do over and over again, which is to smash things together and watch what comes tumbling out.
What does it mean to say that the collider will allow physicists to go back to the Big Bang? Is the collider a time machine?
Physicists suspect that the laws of physics evolved as the universe cooled from billions or trillions of degrees in the first moments of the Big Bang to superfrigid temperatures today (3 degrees Kelvin) — the way water changes from steam to liquid to ice as temperatures decline. As the universe cooled, physicists suspect, everything became more complicated. Particles and forces once indistinguishable developed their own identities, the way Spanish, French and Italian diverged from the original Latin.
By crashing together subatomic particles — protons — physicists create little fireballs that revisit the conditions of these earlier times and see what might have gone on back then, sort of like the scientists in Jurassic Park reincarnating dinosaurs.
The collider, which is outside Geneva, is 17 miles around. Why is it so big?
Einstein taught us that energy and mass are equivalent. So, the more energy packed into a fireball, the more massive it becomes. The collider has to be big and powerful enough to pack tremendous amounts of energy into a proton.
Moreover, the faster the particles travel, the harder it is to bend their paths in a circle, so that they come back around and bang into each other. The collider is designed so that protons travel down the centers of powerful electromagnets that are the size of redwood trunks, which bend the particles’ paths into circles, creating a collision. Although the electromagnets are among the strongest ever built, they still can’t achieve a turning radius for the protons of less than 2.7 miles.
All in all, the bigger the accelerator, the bigger the crash, and the better chance of seeing what is on nature’s menu.
What are physicists hoping to see?
According to some theories, a whole list of items that haven’t been seen yet — with names like gluinos, photinos, squarks and winos — because we haven’t had enough energy to create a big enough collision.
Any one of these particles, if they exist, could constitute the clouds of dark matter, which, astronomers tell us, produce the gravity that holds galaxies and other cosmic structures together.
Another missing link of physics is a particle known as the Higgs boson, after Peter Higgs of the University of Edinburgh, which imbues other particles with mass by creating a cosmic molasses that sticks to them and bulks them up as they travel along, not unlike the way an entourage forms around a rock star when they walk into a club.
Have scientists ever seen dark matter?
It’s invisible, but astronomers have deduced from their measurements of galactic motions that the visible elements of the cosmos, like galaxies, are embedded in huge clouds of it.
Will physicists see these gluinos, photinos, squarks and winos?
There is no guarantee that any will be discovered, which is what makes science fun, as well as nerve-racking.
So how much energy do you need to create these fireballs?
At the Large Hadron Collider, that energy is now 3.5 trillion electron volts per proton — about as much energy as a flea requires to do a pushup. That may not sound like much, but for a tiny proton, it is a lot of energy. It is the equivalent of a 200-pound man bulking up by 700,000 pounds.
What’s an electron volt?
An electron volt is the amount of energy an electron would gain passing from the negative to the positive side of a one-volt battery. It is the basic unit of energy and of mass preferred by physicists.
When protons collide, is there a big bang?
There is no sound. It’s not like a bomb exploding.
In previous trials, there was an actual explosion.
All that current is dangerous. During the testing of the collider in September 2008, the electrical connection between a pair of the giant magnets vaporized. There are thousands of such connections in the collider, many of which are now believed to be defective. As a result the collider can only run at half-power for the next two years.
Could the collider make a black hole and destroy the Earth?
The collider is not going to do anything that high-energy cosmic rays have not done repeatedly on Earth and elsewhere in the universe. There is no evidence that such collisions have created black holes or that, if they have, the black holes have caused any damage. According to even the most speculative string theory variations on black holes, the Large Hadron Collider is not strong enough to produce a black hole.
Too bad, because many physicists would dearly like to see one.
An earlier version of this article misstated that the Earth began to cool in the aftermath of the Big Bang.
A version of this article appeared in print on April 4, 2010, on page WK3 of the New York edition.
David Strayhorn ( http://webspace.webring.com/people/xy/yapquack/RelativeHistories.html )
Saint Louis, MO
A novel formulation of quantum mechanics, the “relative histories” formulation (RHF), is proposed based upon the assumption that the physical state of a closed system – e.g., the universe – can be represented mathematically by an ensemble E of four-dimensional manifolds W. In this scheme, any real, physical object – be it macroscopic or microscopic – can be assigned to the role of the quantum mechanical “observer.” The state of the observer is represented as a 3-dimensional manifold, O. By using O as a boundary condition, we obtain E as the unique set of all W that satisfy the boundary condition defined by O. The evolution of the “wavefunction of the universe” E is therefore determined by the movement of the observer O through state space.
In a sense, the RHF is a specific instance of the consistent histories formulation, in which a single “history” is equated with a single W. However, the RHF can also be interpreted as an implementation of Einstein’s ensemble (or statistical) interpretation, which is based upon the notion that the wavefunction is to be understood as the description not of a single system, but of an ensemble of systems: in our case, an ensemble of W’s. We could, in addition, think of the RHF in terms of Everett’s relative state formulation (i.e., the multiple worlds interpretation (MWI)), in which each “world” is equated with one of the four-manifolds W.
The mathamatical underpinnings of the RHF have been developed to an extent sufficient to demonstrate that the RHF gives rise to quantum statistics. However, the mathematical structure of the RHF is far from complete. At this stage, the primary motivation for the development of the RHF centers on the fact that it offers a constellation of interpretational advantages that are not found in any other single formulation of QM. One of these advantages is its versatility; as discussed above, the RHF is a sort of unification of many other standard formulations of QM, such as the consistent histories formulation, the MWI, Einstein’s statistical interpretation, and the FPI. In addition, the RHF is possessed of the following interpretational features: (1) a clear definition of the observer and of its space of states, and a lack of the fundamental split between observer and system that is characteristic of the Copenhagen Interpretation; (2) movement of the observer through state space that obeys classical notions of locality and probability; (3) a derivation of quantum statistics and quantum nonlocality from classical notions of probability and locality; (4) a demonstration of compatibility with general relativity; (5) an adherence to the notion that “all is geometry;” (6) the absence of a requirement for any extra “unphysical” dimensions of spacetime beyond the four of our everyday experience; and (7) a spacetime structure that is causal on the large scale. In addition, the RHF provides a simple conceptualization of the EPR argument that QM cannot be considered both local and complete. In exchange for these interpretational features, we are forced merely to accept that the structure of spacetime is acausal on the small scale.
As of January 2005, the RHF is summarized in a series of three papers that are available for download from the following site:
These papers have been formatted using LaTeX to make them as reader-friendly as possible. There are three parts. Part I – Basics.pdf presents an introduction to the basic mathematical elements of the RHF, including the 4-geon model of fundamental particles, and demonstrates in explicit terms that the RHF makes the same predictions as the Feynman path integral (FPI) approach. Since the FPI is an independent formulation of quantum mechanics — for example, the FPI is well-known to provide a basis for the derivation of the Schrodinger equation — the equivalence between the RHF and the FPI implies equivalence between the RHF and quantum mechanics in general. Part II – Interpretation.pdf provides an overview of the interpretational issues surrounding the RHF, as summarized above. Part III – Further Mathematical Development.pdf is not (as of January 2005) yet ready for download and review, as I anticipate that it will undergo significant revision as I learn more about Morse theory and its application to the RHF.
I am currently (as of January 2005) in the process of soliciting an informal “peer-review” of the RHF prior to any attempt at submission for publication, even to arXiv. I anticipate this to be a slow process: the complexity of the RHF technique is about on a par as, say, the Feynman path integral (FPI) technique itself. Furthermore, an understanding of the RHF, especially its interpretational implications, requires a broad knowledge of the foundations of QM — especially regarding the inner workings of the FPI — that even many practicing physicists lack. I welcome any comments, be they from an expert or a layman, which should be sent to my yahoo! email address (straycat_md).
For an online discussion of the Relative Histories Formulation, check out my Yahoo! group: QM_from_GR (http://groups.yahoo.com/group/QM_from_GR)
The beginning, the end, and the funny habits of our favorite ticking force. by LeeAundra Temescu
From the March 2009 issue, published online March 12, 2009
1 “Time is an illusion. Lunchtime doubly so,” joked Douglas Adams in The Hitchhiker’s Guide to the Galaxy. Scientists aren’t laughing, though. Some speculative new physics theories suggest that time emerges from a more fundamental—and timeless—reality.
2 Try explaining that when you get to work late. The average U.S. city commuter loses 38 hours a year to traffic delays.
3 Wonder why you have to set your clock ahead in March? Daylight Saving Time began as a joke by Benjamin Franklin, who proposed waking people earlier on bright summer mornings so they might work more during the day and thus save candles. It was introduced in the U.K. in 1917 and then spread around the world.
4 Green days. The Department of Energy estimates that electricity demand drops by 0.5 percent during Daylight Saving Time, saving the equivalent of nearly 3 million barrels of oil.
5 By observing how quickly bank tellers made change, pedestrians walked, and postal clerks spoke, psychologists determined that the three fastest-paced U.S. cities are Boston, Buffalo, and New York.
6 The three slowest? Shreveport, Sacramento, and L.A.
7 One second used to be defined as 1/86,400 the length of a day. However, Earth’s rotation isn’t perfectly reliable. Tidal friction from the sun and moon slows our planet and increases the length of a day by 3 milliseconds per century.
8 This means that in the time of the dinosaurs, the day was just 23 hours long.
9 Weather also changes the day. During El Niño events, strong winds can slow Earth’s rotation by a fraction of a millisecond every 24 hours.
10 Modern technology can do better. In 1972 a network of atomic clocks in more than 50 countries was made the final authority on time, so accurate that it takes 31.7 million years to lose about one second.
11 To keep this time in sync with Earth’s slowing rotation, a “leap second” must be added every few years, most recently this past New Year’s Eve.
12 The world’s most accurate clock, at the National Institute of Standards and Technology in Colorado, measures vibrations of a single atom of mercury. In a billion years it will not lose one second.
13 Until the 1800s, every village lived in its own little time zone, with clocks synchronized to the local solar noon.
14 This caused havoc with the advent of trains and timetables. For a while watches were made that could tell both local time and “railway time.”
15 On November 18, 1883, American railway companies forced the national adoption of standardized time zones.
16 Thinking about how railway time required clocks in different places to be synchronized may have inspired Einstein to develop his theory of relativity, which unifies space and time.
17 Einstein showed that gravity makes time run more slowly. Thus airplane passengers, flying where Earth’s pull is weaker, age a few extra nanoseconds each flight.
18 According to quantum theory, the shortest moment of time that can exist is known as Planck time, or 0.0000000000000000000000000000000000000000001 second.
19 Time has not been around forever. Most scientists believe it was created along with the rest of the universe in the Big Bang, 13.7 billion years ago.
20 There may be an end of time. Three Spanish scientists posit that the observed acceleration of the expanding cosmos is an illusion caused by the slowing of time. According to their math, time may eventually stop, at which point everything will come to a standstill.
Stem-cell guru Robert Lanza presents a radical new view of the universe and everything in it.
by Robert Lanza and Bob Berman
From the May 2009 issue, published online May 1, 2009
Adapted from Biocentrism: How Life and Consciousness Are the Keys to Understanding the True Nature of the Universe, by Robert Lanza with Bob Berman, published by BenBella Books in May 2009.
The farther we peer into space, the more we realize that the nature of the universe cannot be understood fully by inspecting spiral galaxies or watching distant supernovas. It lies deeper. It involves our very selves.
This insight snapped into focus one day while one of us (Lanza) was walking through the woods. Looking up, he saw a huge golden orb web spider tethered to the overhead boughs. There the creature sat on a single thread, reaching out across its web to detect the vibrations of a trapped insect struggling to escape. The spider surveyed its universe, but everything beyond that gossamer pinwheel was incomprehensible. The human observer seemed as far-off to the spider as telescopic objects seem to us. Yet there was something kindred: We humans, too, lie at the heart of a great web of space and time whose threads are connected according to laws that dwell in our minds.
Is the web possible without the spider? Are space and time physical objects that would continue to exist even if living creatures were removed from the scene?
Figuring out the nature of the real world has obsessed scientists and philosophers for millennia. Three hundred years ago, the Irish empiricist George Berkeley contributed a particularly prescient observation: The only thing we can perceive are our perceptions. In other words, consciousness is the matrix upon which the cosmos is apprehended. Color, sound, temperature, and the like exist only as perceptions in our head, not as absolute essences. In the broadest sense, we cannot be sure of an outside universe at all.
For centuries, scientists regarded Berkeley’s argument as a philosophical sideshow and continued to build physical models based on the assumption of a separate universe “out there” into which we have each individually arrived. These models presume the existence of one essential reality that prevails with us or without us. Yet since the 1920s, quantum physics experiments have routinely shown the opposite: Results do depend on whether anyone is observing. This is perhaps most vividly illustrated by the famous two-slit experiment. When someone watches a subatomic particle or a bit of light pass through the slits, the particle behaves like a bullet, passing through one hole or the other. But if no one observes the particle, it exhibits the behavior of a wave that can inhabit all possibilities—including somehow passing through both holes at the same time.
Some of the greatest physicists have described these results as so confounding they are impossible to comprehend fully, beyond the reach of metaphor, visualization, and language itself. But there is another interpretation that makes them sensible. Instead of assuming a reality that predates life and even creates it, we propose a biocentric picture of reality. From this point of view, life—particularly consciousness—creates the universe, and the universe could not exist without us.
MESSING WITH THE LIGHT
Quantum mechanics is the physicist’s most accurate model for describing the world of the atom. But it also makes some of the most persuasive arguments that conscious perception is integral to the workings of the universe. Quantum theory tells us that an unobserved small object (for instance, an electron or a photon—a particle of light) exists only in a blurry, unpredictable state, with no well-defined location or motion until the moment it is observed. This is Werner Heisenberg’s famous uncertainty principle. Physicists describe the phantom, not-yet-manifest condition as a wave function, a mathematical expression used to find the probability that a particle will appear in any given place. When a property of an electron suddenly switches from possibility to reality, some physicists say its wave function has collapsed.
What accomplishes this collapse? Messing with it. Hitting it with a bit of light in order to take its picture. Just looking at it does the job. Experiments suggest that mere knowledge in the experimenter’s mind is sufficient to collapse a wave function and convert possibility to reality. When particles are created as a pair—for instance, two electrons in a single atom that move or spin together—physicists call them entangled. Due to their intimate connection, entangled particles share a wave function. When we measure one particle and thus collapse its wave function, the other particle’s wave function instantaneously collapses too. If one photon is observed to have a vertical polarization (its waves all moving in one plane), the act of observation causes the other to instantly go from being an indefinite probability wave to an actual photon with the opposite, horizontal polarity—even if the two photons have since moved far from each other.
In 1997 University of Geneva physicist Nicolas Gisin sent two entangled photons zooming along optical fibers until they were seven miles apart. One photon then hit a two-way mirror where it had a choice: either bounce off or go through. Detectors recorded what it randomly did. But whatever action it took, its entangled twin always performed the complementary action. The communication between the two happened at least 10,000 times faster than the speed of light. It seems that quantum news travels instantaneously, limited by no external constraints—not even the speed of light. Since then, other researchers have duplicated and refined Gisin’s work. Today no one questions the immediate nature of this connectedness between bits of light or matter, or even entire clusters of atoms.
Before these experiments most physicists believed in an objective, independent universe. They still clung to the assumption that physical states exist in some absolute sense before they are measured.
All of this is now gone for keeps.
WRESTLING WITH GOLDILOCKS
The strangeness of quantum reality is far from the only argument against the old model of reality. There is also the matter of the fine-tuning of the cosmos. Many fundamental traits, forces, and physical constants—like the charge of the electron or the strength of gravity—make it appear as if everything about the physical state of the universe were tailor-made for life. Some researchers call this revelation the Goldilocks principle, because the cosmos is not “too this” or “too that” but rather “just right” for life.
At the moment there are only four explanations for this mystery. The first two give us little to work with from a scientific perspective. One is simply to argue for incredible coincidence. Another is to say, “God did it,” which explains nothing even if it is true.
The third explanation invokes a concept called the anthropic principle,? first articulated by Cambridge astrophysicist Brandon Carter in 1973. This principle holds that we must find the right conditions for life in our universe, because if such life did not exist, we would not be here to find those conditions. Some cosmologists have tried to wed the anthropic principle with the recent theories that suggest our universe is just one of a vast multitude of universes, each with its own physical laws. Through sheer numbers, then, it would not be surprising that one of these universes would have the right qualities for life. But so far there is no direct evidence whatsoever for other universes.
The final option is biocentrism, which holds that the universe is created by life and not the other way around. This is an explanation for and extension of the participatory anthropic principle described by the physicist John Wheeler, a disciple of Einstein’s who coined the terms wormhole and black hole.
SEEKING SPACE AND TIME
Even the most fundamental elements of physical reality, space and time, strongly support a biocentric basis for the cosmos.
According to biocentrism, time does not exist independently of the life that notices it. The reality of time has long been questioned by an odd alliance of philosophers and physicists. The former argue that the past exists only as ideas in the mind, which themselves are neuroelectrical events occurring strictly in the present moment. Physicists, for their part, note that all of their working models, from Isaac Newton’s laws through quantum mechanics, do not actually describe the nature of time. The real point is that no actual entity of time is needed, nor does it play a role in any of their equations. When they speak of time, they inevitably describe it in terms of change. But change is not the same thing as time.
To measure anything’s position precisely, at any given instant, is to lock in on one static frame of its motion, as in the frame of a film. Conversely, as soon as you observe a movement, you cannot isolate a frame, because motion is the summation of many frames. Sharpness in one parameter induces blurriness in the other. Imagine that you are watching a film of an archery tournament. An archer shoots and the arrow flies. The camera follows the arrow’s trajectory from the archer’s bow toward the target. Suddenly the projector stops on a single frame of a stilled arrow. You stare at the image of an arrow in midflight. The pause in the film enables you to know the position of the arrow with great accuracy, but you have lost all information about its momentum. In that frame it is going nowhere; its path and velocity are no longer known. Such fuzziness brings us back to Heisenberg’s uncertainty principle, which describes how measuring the location of a subatomic particle inherently blurs its momentum and vice versa.
All of this makes perfect sense from a biocentric perspective. Everything we perceive is actively and repeatedly being reconstructed inside our heads in an organized whirl of information. Time in this sense can be defined as the summation of spatial states occurring inside the mind. So what is real? If the next mental image is different from the last, then it is different, period. We can award that change with the word time, but that does not mean there is an actual invisible matrix in which changes occur. That is just our own way of making sense of things. We watch our loved ones age and die and assume that an external entity called time is responsible for the crime.
There is a peculiar intangibility to space, as well. We cannot pick it up and bring it to the laboratory. Like time, space is neither physical nor fundamentally real in our view. Rather, it is a mode of interpretation and understanding. It is part of an animal’s mental software that molds sensations into multidimensional objects.
Most of us still think like Newton, regarding space as sort of a vast container that has no walls. But our notion of space is false. Shall we count the ways? 1. Distances between objects mutate depending on conditions like gravity and velocity, as described by Einstein’s relativity, so that there is no absolute distance between anything and anything else. 2. Empty space, as described by quantum mechanics, is in fact not empty but full of potential particles and fields. 3. Quantum theory even casts doubt on the notion that distant objects are truly separated, since entangled particles can act in unison even if separated by the width of a galaxy.
UNLOCKING THE CAGE
In daily life, space and time are harmless illusions. A problem arises only because, by treating these as fundamental and independent things, science picks a completely wrong starting point for investigations into the nature of reality. Most researchers still believe they can build from one side of nature, the physical, without the other side, the living. By inclination and training these scientists are obsessed with mathematical descriptions of the world. If only, after leaving work, they would look out with equal seriousness over a pond and watch the schools of minnows rise to the surface. The fish, the ducks, and the cormorants, paddling out beyond the pads and the cattails, are all part of the greater answer.
Recent quantum studies help illustrate what a new biocentric science would look like. Just months? ago, Nicolas Gisin announced a new twist on his entanglement experiment; in this case, he thinks the results could be visible to the naked eye. At the University of Vienna, Anton Zeilinger’s work with huge molecules called buckyballs pushes quantum reality closer to the macroscopic world. In an exciting extension of this work—proposed by Roger Penrose, the renowned Oxford physicist—not just light but a small mirror that reflects it becomes part of an entangled quantum system, one that is billions of times larger than a buckyball. If the proposed experiment ends up confirming Penrose’s idea, it would also confirm that quantum effects apply to human-scale objects.
Biocentrism should unlock the cages in which Western science has unwittingly confined itself. Allowing the observer into the equation should open new approaches to understanding cognition, from unraveling the nature of consciousness to developing thinking machines that experience the world the same way we do. Biocentrism should also provide stronger bases for solving problems associated with quantum physics and the Big Bang. Accepting space and time as forms of animal sense perception (that is, as biological), rather than as external physical objects, offers a new way of understanding everything from the microworld (for instance, the reason for strange results in the two-slit experiment) to the forces, constants, and laws that shape the universe. At a minimum, it should help halt such dead-end efforts as string theory.
Above all, biocentrism offers a more promising way to bring together all of physics, as scientists have been trying to do since Einstein’s unsuccessful unified field theories of eight decades ago. Until we recognize the essential role of biology, our attempts to truly unify the universe will remain a train to nowhere.
Adapted from Biocentrism: How Life and Consciousness Are the Keys to Understanding the True Nature of the Universe, by Robert Lanza with Bob Berman, published by BenBella Books in May 2009.
Publicado por emulenews en 2 Marzo 2009
Physics es la revista de divulgación de trabajos de investigación excepcionales publicados en revistas de la Sociedad de Física Americana (APS). Luis Miguel Robledo Martín, profesor titular del Departamento de Física Teórica de la Universidad Autónoma de Madrid, ha logrado aparecer en dicha revista gracias a que ha sido capaz de determinar el signo correcto de una expresión matemática complicada por una técnica innovadora. Nos lo cuentan John Millener, Ben Gibson, “Finding the missing sign,” Physics, Feb. 2009 , que se hacen eco del artículo técnico de L. M. Robledo, “Sign of the overlap of Hartree-Fock-Bogoliubov wave functions,” Phys. Rev. C 79: Art. No. 021302, Published February 20, 2009 .
La aproximación de Hartree-Fock-Bogoliubov (HFB) se utiliza en física cuántica para aproximar el comportamiento de una partícula sujeta al efecto de muchas otras partículas como si estas generaran un campo promedio efectivo. De esta manera se evita tener que considerarlas de forma individual. La aproximación fue introducida por D.R. Hartree en 1928 y por V.A. Fock en 1930 , aunque se convirtió en una herramienta fundamental tras el trabajo de N.N. Bogoliubov en 1958 . Cuando se requiere un resultado más preciso, hay que aplicar la aproximación hasta segundo orden, lo que requiere combinar y solapar las funciones de onda de la aproximación HFB a primer orden. El signo del solape requiere evaluar una raíz cuadrada. El problema es saber qué signo tiene que ser utilizado para esta raíz cuadrada. En algunos problemas (en los que hay simetrías discretas) el resultado es independiente del signo (no importa el que sea). Pero en otros problemas (en los que estas simetrías están rotas) la aproximación no dice qué signo usar. El signo ha de ser calculado utilizando otra técnica.
Luis Robledo ha utilizado una técnica muy elegante (que se basa en el uso de estados coherentes fermiónicos) con la que logra determinar el signo del término de solape sin ninguna ambigüedad. El signo depende del pfaffiano de una matriz antisimétrica. La nueva técnica es mucho más eficiente y sencilla de aplicar que otras técnicas alternativas, sin necesidad de recurrir al uso de matrices no hermíticas.
El nuevo resultado tiene múltiples aplicaciones, como el uso de la aproximación HFB para el estudio de la dinámica de protones o neutrones en núcleos atómicos con número atómico impar (la suma del número de protones y neutrones). Enhorabuena, Luis.
18:00 07 January 2009 by Stephen Battersby
For similar stories, visit the Nanotechnology and Quantum World Topic Guides
A quantum effect that causes objects to repel one another – first predicted almost 50 years ago – has at last been seen in the lab.
According to Harvard physicist Federico Capasso, a member of the group who measured the effect, it could be used to lubricate future nanomachines.
The team detected the weak repulsive force when they brought together a thin sheet of silica and a small gold-plated bead, about half the diameter of a human hair.
The force is an example of the Casimir effect, generated by all-pervasive quantum fluctuations.
The simplest way to imagine the Casimir force in action is to place two parallel metal plates in a vacuum. Thanks to the odd quantum phenomenon, these become attracted to one another.
It happens because even a vacuum is actually fizzing with a quantum field of particles, constantly popping in and out of existence. They can even fleetingly interact with and push on the plates.
However, the small space between the two plates restricts the kind of particles that can appear, so the pressure from behind the plates overwhelms that from between them. The result is an attractive force that gums up nanoscale machines. (To learn more about the Casimir force see Under pressure from quantum foam.)
Capasso says that the Casimir force needn’t be an enemy. “Micromechanics at some point will have to contend with these forces – or make use of them.”
In 1961, Russian theorists calculated that in certain circumstances, the Casimir effect could cause objects to repel one another – a scenario Capasso’s team have finally created experimentally. The team achieved this by adding a fluid, bromobenzene, to the setup.
The Casimir attraction between the liquid and the silica plate is stronger than that between the gold bead and the silica, so the fluid forces its way around the bead, pushing it away from the plate.
The effect is akin to the buoyancy we experience in the macro world – where objects less dense than water are held up by the liquid around them. But in this case the bromobenzene is less dense than the solid bead. “You could call it quantum buoyancy,” Capasso told New Scientist.
The force he measured was feeble – amounting to just a few tens of piconewtons – but that is still enough to buoy up nanoscale objects.
“The next experiment we want to do is use a TV camera to track the motion of one of these spheres, then we should be able to see easily whether you have levitation.”
Harnessing the repulsive Casimir force could provide a kind of lubrication to solve the problem of nanomachines becoming gummed up by the better-known attractive version, says Capasso.
In theory you could instead use a liquid denser than the components to buoy them up, but that wouldn’t be practical. “These gizmos are usually made of metal, so you would have to use mercury,” he explains.
Quantum buoyancy bearings could be used to build delicate sensors, such as a floating “nanocompass” to detect small-scale magnetic fields.
Journal reference: Nature (DOI: 10.1038/nature07610)