HIDDEN extra dimensions are making their influence felt in labs across the world. According to French researchers, they are causing measurements of the strength of gravity at different locations on Earth to be affected by the planet鈥檚 magnetic field.
It鈥檚 a controversial claim because no one has ever provided experimental evidence to support either the existence of extra dimensions or any interaction between gravity and electromagnetism. But lab measurements of Newton鈥檚 gravitational constant G suggest that both are real.
Newton鈥檚 constant, which describes the strength of the gravitational pull that bodies exert on each other, is the most poorly determined of the constants of nature. The two most accurate measurements have experimental errors of 1 part in 10,000, yet their values differ by 10 times that amount. So physicists are left with no idea of its absolute value.
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Now Jean-Paul Mbelek and Marc Lachieze-Ray of the French Atomic Energy Commission near Paris say they can resolve the contradiction by taking into account the location of the labs where the experiments were carried out. Their work is based on theories such as string theory that try to unify all the forces, including electromagnetism and gravity, by invoking the existence of several extra spatial dimensions. The extra dimensions could explain why gravity appears to be so much weaker than electromagnetism, because its influence would be dissipated throughout all the dimensions.
Mbelek and Lachieze-Ray have taken the idea further, suggesting that electromagnetism and gravity can also influence one another enough for gravity鈥檚 pull to be noticeably affected by the Earth鈥檚 magnetic field. That would explain why the labs that measured G got slightly different results, Mbelek told a meeting of the European Astronomical Society in Porto, Portugal, last week.
In a paper submitted to Classical and Quantum Gravity, the researchers calculate the values they would expect G to have at different locations around the world. They say it should be greater where the Earth鈥檚 magnetic field is stronger, with the highest measurements at the north and south magnetic poles.
The values of G measured so far seem to fit with that idea. But the researchers say the best way to test their theory would be to take accurate measurements of G at locations such as the magnetic poles and particular longitudes on the equator, and then check those values against the predictions.
Studies of the Sun also support the theory. To make mathematical models of the star鈥檚 interior tally with experimental data, physicists have to use a lower value of G than is traditionally agreed. Mbelek says his calculations predict that electromagnetism wouldn鈥檛 boost gravity as much at higher temperatures, so you would expect G to be lower inside the Sun.
But other researchers aren鈥檛 convinced. Clifford Will, a gravity theorist at Washington University in St Louis, Missouri, believes improvements in terrestrial experiments will eventually do away with the need for explanations that rely on such exotic physics. 鈥淚n many ways it鈥檚 a scandal that we don鈥檛 have an agreed value for G, but if you look at the experiments, the values have been converging,鈥� he says. 鈥淚n five years or so, we鈥檒l have an agreed value.鈥� But Mbelek doesn鈥檛 think so. Although the precision of individual measurements is improving, he says, the values are not converging.
Thibault Damour, a string theory researcher based at the Institute of Advanced Scientific Studies (IHES) in Bures-sur-Yvette, France, also thinks Mbelek and Lachieze-Ray are on a false trail. He says their theory would also produce enormous changes in other fundamental values such as the 鈥渇ine structure鈥� constant. The effects of those changes would have been spotted long ago, Damour says.
Mbelek admits that certain aspects of his theoretical approach 鈥� such as the strength of the gravitational-electromagnetic interaction 鈥� haven鈥檛 been fully worked out yet. But the fact that it can explain the different measurements of G provides a proof of principle, he insists. 鈥淭he experimental results should dictate what is the right approach,鈥� Mbelek says. 鈥淥ur theory seems to fit with the observed experimental results.鈥�
If future experiments confirm the researchers鈥� predictions, extra dimensions will have to be accepted as fact, not conjecture, Mbelek says. Such an advance would be a great boost for physicists working towards a 鈥渢heory of everything鈥�. At the moment, all viable theories require the existence of hidden extra dimensions, but no one has found an experimental way to look for them.
Proof of the new theory would also have other implications that would perhaps be trickier for many physicists to come to terms with. Concrete evidence of the interaction between electromagnetism and gravity would support controversial claims that superconducting materials can affect gravity. Such ideas have been politely labelled 鈥渇ringe science鈥�, but the tide may be turning. Earlier this year another respected physicist, Raymond Chiao of the University of California at Berkeley, admitted that his attempts to unify the laws of physics seem to imply that there is an interaction between the two forces.
