by David Harris, New Scientist, February 20, 2012  http://www.newscientist.com/artic

 See introductory "What is Empty Space?" (3 minute video) http://bcove.me/d3c6fmrh

The elusive Casimir effect suggests we could use vacuum energy to move objects and make stuff - but can something really come from nothing?

NOTHING will come of nothing." Shakespeare's epithet seems the kind of self-evident statement that only poets and philosophers would argue over. And physicists like Chris Wilson.       

Last year, Wilson and his team at the Chalmers University of Technology in Gothenburg,Sweden, provided what seems a particularly egregious case of something for nothing. They claimed to have conjured up light from nowhere simply by squeezing down empty space (New Scientist, 19 November 2011, p 16). That would be the latest manifestation of a quantum quirk known as the Casimir effect: the notion that a perfect vacuum, the very definition of nothingness in the physical world, contains a latent power that can be harnessed to move objects and make stuff.

Sightings of this vacuum action have been mounting over the past decade or so, leading some physicists to propose a new generation of nanoscale machines to take advantage of it, and others even to suggest a leading role for vacuum energy in determining the origin and fate of the cosmos. Others remain to be convinced. So what's the true story? 

The idea that a vacuum is a seething sea of something can be traced back to the early decades of quantum physics. In the late 1920s, the German physicist Werner Heisenberg came up with his famous uncertainty principle, which says that some pairs of measurable quantities are intimately connected: the more you know about the one, the less you know about the other.  

Energy and time are one such pair. That means you cannot measure the energy of a physical system with perfect precision unless time itself is completely imprecisely defined - that is, you take infinite time to perform your measurement. It follows that the zero-energy nothingness of the vacuum can never be pinned down precisely. According to quantum theory, even a perfect vacuum is filled with wave-like fields that fluctuate constantly, producing a legion of ephemeral particles that continually pop up out of nowhere only to disappear again, filling the vacuum with a distinct, non-zero "zero-point energy".   

This recasting of the vacuum gave fresh impetus to the centuries-old debate about the nature of nothingness

 (New Scientist, 19 November 2011, p 50). But evidence also began to accumulate that the newly lively vacuum had practical effects. Observe atoms carefully enough and you see a tiny effect known as the Lamb shift, in which vacuum fluctuations jostle an orbiting electron, subtly altering its energy. Something similar can be invoked to explain how electrons sometimes spontaneously jump between two atomic energy states, giving off photons of light.  

But Hendrik Casimir's suggestion was the most eye-catching. In 1948, together with his colleague Dirk Polder, the Dutch physicist was trying to understand how colloids exist in a stable equilibrium. Colloids are mixtures in which one type of substance is dispersed through another, like fat globules in the watery solution of milk. Forces between the molecules in such a medium drop off more quickly with distance than basic calculations using the classical electromagnetic van der Waals force allow. It is as if something is pulling the constituent molecules closer together, giving the mixture extra stability.  

Following a tip-off from the Danish quantum doyen Niels Bohr, Casimir calculated that this something could be vacuum action. Working out the effects of vacuum fluctuations in a colloid's complex molecular brew was impossibly involved. So Casimir considered a simple model system of two parallel metallic plates, and showed that the fluctuations could produce just the right enhanced attraction between them. His explanation was that the two plates limit the wavelength of vacuum fluctuations in the space between. Outside those confines, the fluctuations can have any wavelength they choose. With more waves outside than in, a pressure pushes inward on the plates (see diagram).  

The effect is tiny: two plates 10 nanometres apart feel a force comparable to the gentle burden of the atmosphere on our heads. Such a minuscule contribution is easily washed out by a legion of other effects, such as residual electrostatic attractions between charges on the plates' surfaces. That makes confirming its existence extremely tough. "You need to know that you're really measuring the Casimir force," says experimentalist Hong Tang of YaleUniversity. What's more, it is not easy to align plates to be perfectly parallel, while calculating the expected effect for other, more complex geometries takes some sophisticated mathematics. 

It was only in 1996 that Steven Lamoreaux, a physicist then at the University of Washingtonin Seattle, made a breakthrough. Taking elaborate precautions to exclude all other effects, he found a tiny residual force pulling a metal plate and a spherical lens together (Physical Review Letters, vol 78, p 5). The Casimir effect, it seemed, was not a theorist's pipe dream: vacuum action was a real effect.  

Since then, a steady trickle of results has confirmed other long-standing theoretical predictions. Soviet physicist Evgeny Lifshitz proposed in 1955 that the size of vacuum fluctuations would grow with rising temperature, resulting in a force that is more potent over longer distances. In February 2011, Lamoreaux, now at Yale University, and his team confirmed that this is indeed the case (Nature Physics, vol 7, p 230)  

Nanoscale kick 

As for the work of Wilson's team, their results, published last November, support a four-decade-old prediction that turns the logic of the original Casimir effect on its head. Rather than using the vacuum's pop-up particles to shift their surroundings, if you move a vacuum's surroundings fast enough, you can make real photons of light. In some quarters, this idea is controversial - but it is the most dramatic putative demonstration of the vacuum's powers to date (see "Light from speeding mirrors") 

As sightings of such effects have multiplied, so have thoughts that we might harness them for our own devices. A popular proposal is to use the vacuum's energy to give nanoscale machines an additional kick. That requires something a little different from the original Casimir force, whose attractive effects are more likely to gum up the components of any mini-machine - a phenomenon referred to as static friction or "stiction"

 By tweaking the geometries or material properties of the structures used to confine the vacuum, however, it should be possible to reverse the direction of the Casimir effect, creating an outward pressure to push two objects apart. In 2008, Steven Johnson and his colleagues at the Massachusetts Institute of Technology calculated that by adding a series of interleaving metal brackets, zipper-style, to the faces of the two metal plates you could in theory make the net force between them repulsive. A more recent study by Stanislav Maslovski and Mário Silveirinha of the University of Coimbra, Portugal, has indicated a similar effect using nanoscale metallic rods to create areas of repulsive force that can levitate a nanoscale metal bar (Physical Review A, vol 83, p 022508). 

These forces could help nanoscale components such as switches, gears, bearings or motor parts to operate without jamming. Putting such devices into practice might not be easy, though. For a start, it would require components with atomic-scale polishing: look on a small enough scale - a thousand atoms or so - and metal surfaces usually thought of as smooth have patchy, crystal-like structures that would confine vacuum fluctuations in different ways, affecting the size of the Casimir force. For moving objects, things become even trickier.

  Such complications are surmountable: in 2009 Federico Capasso and group at Harvard University measured what appeared to be repulsive Casimir forces in a gold cantilever suspended in bromobenzene liquid above a silicon surface (Nature, vol 457, p 170). The forces generated were mere tens of piconewtons - but when you are trying to move nanoscale particles, a piconewton goes a long way. Nevertheless, there are still hurdles to be overcome before Casimir devices are everyday reality, says Johnson. "It is an experimental question - can we make devices this small and sensitive?" he says. "And it is also a theoretical question of whether we can design interesting uses for the Casimir force once the experimental capabilities arrive. There is a more fundamental objection, however. The litany of theoretical predictions gradually being turned into experimental reality invites a simple conclusion: vacuum fluctuations are real, and they are what is responsible for what we call Casimir effects. But not all physicists buy that.  

US DOE Energy.gov Press Release, March 2, 2012 - 2:31pm http://energy.gov/articles/arpa-e-issues-open-call-transformational-energy-technologies

DOE's Advanced Research Projects Agency-Energy (ARPA-E) issued a $150 million funding opportunity on March 2 that is open to all transformational energy technologies. This Open Funding Opportunity Announcement (FOA) is a call to scientists, engineers, and entrepreneurs to propose early-stage research projects that would not otherwise be able to attract private investment. Such projects could lead to breakthrough energy technologies. This is the second Open FOA released under ARPA-E.

The open call includes electricity generation by renewable means; electricity transmission, storage, and distribution; energy efficiency for buildings, manufacturing and commerce, and personal use; and all aspects of transportation, including the production and distribution of renewable fuels, electrification, and energy efficiency in transportation. Individual awards under the Open FOA will range between $250,000 and $10 million. See the DOE press release (below) and the FOA announcement online.

Washington, D.C. - Today, the Advanced Research Projects Agency - Energy (ARPA-E) issued a $150 million funding opportunity open to all transformational energy technologies to support the Obama Administration's all-of-the-above approach to solving our nation's most pressing energy challenges. This Open Funding Opportunity Announcement is a call to our country's brightest scientists, engineers and entrepreneurs to propose early-stage research projects that would not otherwise be able to attract private investment, but could lead to breakthrough energy technologies. This is the second open funding opportunity released under ARPA-E.  The first was in 2009.

"Today we are calling on our nation's best and brightest to catalyze energy breakthroughs in all areas imaginable through this Open Funding Opportunity Announcement, which illustrates the true purpose of ARPA-E," said Director  Majumdar.  "Innovation is our nation's sweet spot, and it is critically important that we look at every possible energy solution in order to ensure America's future prosperity and security."

This Open Funding Opportunity Announcement (FOA) joins ARPA-E's other recently issued FOA - Methane Opportunities for Vehicular Energy (MOVE) - which will make $30 million available to find ways to harness our abundant supplies of domestic natural gas for vehicles and was announced by President Obama last week at the University of Miami.

More details on all of ARPA-E's Funding Opportunities and Requests For Information are available HERE. Individual awards under the Open FOA will range between $250,000 and $10 million.

President Obama launched the Energy Department's Advanced Research Projects Agency - Energy (ARPA-E) in 2009 to seek out transformational, breakthrough technologies that are too risky for private sector investment but have the potential to translate science into quantum leaps in energy technology, form the foundation for entirely new industries, and in the future have large commercial impact.

Including its most recent round of selections, ARPA-E has funded a total of more than 180 projects, for $521.7 million in awards across 12 program areas. Demonstrating the success ARPA-E has already seen, the Agency announced last year that eleven of its projects that received $40 million from ARPA-E for innovative research, were able to use this funding to demonstrate results, which allowed these teams to secure more than $200 million in outside private capital investment.

ARPA-E's third annual Energy Innovation Summit featured 107 speakers, including: President Bill Clinton; Microsoft Founder and Chairman, Bill Gates; Xerox CEO, Ursula Burns; FedEx CEO, Fred Smith; BDT Capital Chairman, Lee Scott; Deputy Secretary of Defense, Ashton Carter; MIT President, Susan Hockfield; U.S. Energy Secretary, Steven Chu; and ARPA-E Director, Arun Majumdar.  The Summit attracted 2,440 attendees from 49 states and 26 countries and featured a Technology Showcase displaying over 240 breakthrough energy developments from ARPA-E's awardees, finalists and other teams.