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David Hambling wrote the following on Fortean Times magazine (1)

(David Hambling is a freelance journalist and author based in South London, specializing mainly in science and technology; you can see his profile at:


Looking for loopholes. The impossible may just take longer and require some imagination.

There are few more hazardous occupations for a scientist than getting in trouble with the laws of nature. These laws is defended by a scientific community as grimly determined as Judge Dredd -- we all know about ‘damned’ scientific data. Sometimes, though, a trial case gets through which shows the law is more flexible than originally thought. This is the thinking behind the Fluid Space Drive or FSD, which looks like an outrageous attempt to defeat the law of conservation of momentum (2) but which might be a matter of finding a loophole.

The principle of the FSD is quite simple. Imagine two astronauts sitting at either end of a spacecraft, throwing a cannonball between them. Each time it is thrown, the cannonball gives the spacecraft a kick in the opposite direction, in accordance with Newton’s principle of equal and opposite reactions. Every time it is caught, the momentum of the spacecraft and cannonball cancel each other out again. You cannot propel a spacecraft by any rearrangement of matter inside it, only by throwing things out – which is how rocket engines, ion drives and other accepted propulsion systems work.

In the Fluid Space Drive, the cannonball being thrown between the astronauts is equipped with a braking mechanism like a parachute, which is used when it is thrown in one direction only. This means it hits one end of the spacecraft with much greater force than the other. FSD developer William Elliott argues that this creates an asymmetry in the momentum transfer, so the cannonball can create a net force. It’s like a low-tech version of Roger Shawyer’s electromagnetic EmDrive (see FT201:14).

Conventional physicists would argue that the momentum lost by using a parachute is simply transferred to air molecules inside the spacecraft, and while it may not be felt, the momentum will still be there. This is similar to an old argument about whether a sealed cage with a bird in it weighs less if the bird is hovering in the cage by flapping its wings. The consensus is that the average downward force is exactly the same as if the bird had been solidly perched, but not everyone agrees.

Seemingly intractable laws may turn out to have loopholes. Elliott quotes the example of Earnshaw’s Theorem. Samuel Earnshaw was a 19th century Yorkshire mathematician, who demonstrated the impossibility of magnetic levitation. Although magnets can be arranged to repel each other, Earnshaw showed that they could not remain stable in a fixed configuration.

Earnshaw’s theorem is valid, but does have notable loopholes. Specifically some sorts of materials and dynamic configurations – such as a spinning magnet – can levitate successfully. Perhaps the Victorians would not have had maglev trains anyway, but as it had been proved impossible, they did not try.

Sometimes the apparent limitations imposed by the law can stop research dead in its tracks, when in fact all that is needed is a little imagination. Einstein proposed a new method for amplifying a beam of light in 1918. This involved shining the light through a collection of hot molecules so they all released energy at the same time. The problem was that it would only work if there were more molecules in a higher energy state than in a lower state (‘population inversion’). It had been established by Boltzmann that in any stable state, the lower energy state is always more common. The conditions required by Einstein could only met by a substance with a temperature described by an imaginary number.

The breakthrough came in 1960 when researchers realised that the Boltzmann limitation only applied to a stable state. By applying a sudden flash of energy, it was possible to achieve population inversion and the conditions described by Einstein.  Theodore Maiman heated a ruby crystal with a flash lamp and produce what would become known as the first laser.

The necessary hardware had been around for decades, but nobody had thought to assemble it as Maiman did. Lasers have now become ubiquitous, from broadband telecommunications to printers and supermarket bar-code scanners. They might have been forty years more advanced if Maiman’s insight had come sooner.

Einstein also predicted time travel, another field which has been largely neglected because of apparently insuperable barriers. This may also look like a failure of imagination in hindsight.

Something similar nearly happened with John Pendry’s now-celebrated work on Metamaterials. Pendry’s insight, published in Physical Review Letters 2000 was that a suitably structured material might be used to create a perfect lens and to manipulate light in novel ways – for example, diverting it around an object to create an ‘invisibility shield’. Critics objected that this implied a negative refractive index, something which was considered impossible, and the work must be flawed. They were quickly silenced when the Metamaterials were constructed shortly afterwards. While negative refractive indices are not found in natures, this does not mean that they cannot exist.

This sort of historical background gives heart to William Elliott and his co-workers from the University of Chile on the FSD. It also drives thousands of garage-based inventors convinced that they alone have the secret to the next big breakthrough. The great thing about science is that, although it may sometimes seem as unchangeable as a religion, it does respond to facts. Satellite propulsion is an industry worth billions and a new technology would be hard to ignore.

Never mind the theory, set the FSD to full speed ahead and see what happens…


(1) Fortean Times magazine does not at present have a web page, you can see an image of the article here (,  David Hambling sent me the article and gave me permission to show on this site.