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David Adam, science correspondent
The Guardian, Wednesday 11 May 2005 00.00 BST
How to float like a stone
What goes up no longer has to come down. British scientists have developed an antigravity machine that can float heavy stones, coins and lumps of metal in mid-air. Based around a powerful magnet, the device levitates objects in a similar way to how a maglev train runs above its tracks.
Peter King, a physics professor at Nottingham University, said: “We can take an object and float it in mid-air because the magnetic forces on the object are enough to balance gravity.”
The device exploits diamagnetism. Place non-magnetic objects inside a strong enough magnetic field and they are forced to act like weak magnets themselves. Generate a field that is stronger below and weaker above, and the resulting upward magnetic force cancels out gravity.
Scientists have used diamagnetism to make wood, strawberries and, famously, a living frog fly. “That force is strong enough to float things with a density similar to water, but not things with the density of rocks,” Prof King said. To make their machine more powerful, the team added an oxygen and nitrogen mixture, a paramagnetic fluid. Inside the magnet, the mixture helps objects to float.
The researchers, who announce their results today in the New Journal of Physics, are working with Rio Tinto to develop the technique to sort precious stones from soil. The US space agency Nasa is also interested as it offers a cheaper way for zero gravity research.
The quantum vacuum has fascinated physicists ever since Hendrik Casimir and Dirk Polder suggested in 1948 that it would exert a force on a pair of narrowly separated conducting plates. Their idea was eventually confirmed when the force was measured in 1997. Just how to exploit this force is still not clear, however.
In recent years, a new way of thinking about the quantum vacuum has emerged which has vastly more potential. And today, one physicist describes how it could be used to create propulsion.
Before we discuss that, let’s track back a little. According to quantum mechanics, any vacuum will be filled with electromagnetic waves leaping in and out of existence. It turns out that these waves can have various measurable effects, such as the Casimir-Polder force.
The new approach focuses on the momentum associated with these electromagnetic fields rather than the force they exert. The question is whether it is possible to modify this momentum because, if you can, you should receive an equal and opposite kick. That’s what rocket scientists call propulsion.
Today, Alex Feigel at the Soreq Nuclear Research Center, a government lab in Yavne Israel, suggests an entirely new way to modify the momentum of the quantum vacuum and how this can be exploited to generate propulsion.
Feigel’s approach combines two well-established ideas. The first is the Lorentz force experienced by a charged particle in electric and magnetic fields that are crossed. The second is the magnetoelectric effect–the phenomenon in which an external magnetic field induces a polarised internal electric field in certain materials and vice versa.
The question that Feigel asks is in what circumstances the electromagnetic fields in a quantum vacuum can exert a Lorentz force. The answer is that the quantum vacuum constantly interacts with magnetoelectric materials generating Lorentz forces. Most of the time, however, these forces sum to zero.
Hwever, Feigel says there are four cases in which the forces do not sum to zero. Two of these are already known, for example confining the quantum field between two plates, which excludes longer wavelength waves.