Something's wrong, Einstein's right

Einstein's century-old vision of the nature of space-time should be showing its age by now. But the failure of the latest attempts to reveal its flaws is now causing mounting consternation among theorists, as Robert Matthews writes

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A year ago this month, the world woke up to headlines proclaiming that Einstein was wrong. Scientists in Europe claimed they had detected particles called neutrinos apparently travelling faster than light - contradicting Einstein's famous cosmic speed limit.

Most scientists were immediately sceptical of the claim, not least because it violated the well-known rule: "Results Contradicting Einstein Are Usually Wrong. "

And thus it proved; the findings were the product of faulty equipment. All very embarrassing.

But away from the glare of publicity, evidence has been steadily emerging to suggest there could be something badly wrong with current theories of fundamental physics.

And, ironically, the evidence takes the form of Einstein's theories refusing to give way even when they should start to collapse.

The upshot could be a scientific revolution comparable to that sparked by Einstein's theory of relativity more than a century ago.

At root, relativity and all its wonders emerge from the simple - and eminently reasonable - demand that any true law of physics must hold for everyone, no matter how they move relative to each other.

This led Einstein to a host of insights, most famously the relationship between energy and matter E = Mc. He went on to expand relativity into a whole new theory of gravity, viewed not as some mysterious "force", but as the warping by matter of the fabric of space and time. Cue fresh cosmic insights, such as the expansion of the universe after a Big Bang 14 billion years ago.

When combined with quantum theory - the laws of the subatomic realm - relativity went even further, leading to a host of breakthroughs from the discovery of antimatter to the development of electronics.

Theorists have hoped for a similarly impressive raft of insights from combining quantum theory with Einstein's theory of space, time and gravity. But this is where the story takes a strange twist.

Put simply, the resulting theory of "quantum gravity" predicts modifications to Einstein's vision of space and time as some vast cosmic sheet of fabric.

Examined closely enough, the fabric should start to look anything but smooth and simple. Just as the oceans appear smooth when seen from high-flying aircraft, space-time is expected to take on a foamy appearance when examined at close quarters.

Fortunately for our sanity, this mind-boggling vista becomes detectable only at incredibly small scales - so small that protons would have to be magnified up to the size of our solar system to see it at all.

All this follows from calculations that can be done on the back of an envelope, which give an estimate of the so-called "Planck scale" (named after the eponymous German pioneer of quantum theory) at which the foaminess of space-time should appear.

It turns out that to witness it directly, we would need some way of probing events on scales a billion trillion times smaller than the width of a proton.

Amazingly, scientists have come up with a way of doing just this. The trick lies in exploiting the sheer vastness of the universe, which gives even minuscule space-time effects the chance to turn into sizeable ones.

It's a bit like detecting ripples on a vast pool of water with a beam of light. As the light skims over the pool, even distortions due to tiny ripples will accumulate, producing a detectable effect.

To detect the ripples in space-time, scientists have turned to the radiation produced by incredibly violent cosmic events, known as Gamma Ray Bursts (GRBs). Produced by the death of giant spinning stars, GRBs are bright enough to be seen billions of light-years away - far enough to allow distortions due to Planck-scale effects to reveal themselves.

Several international teams have been examining records of GRBs for signs of the effects, pushing down to ever smaller scales. The most recent results have now been announced by a group led by Prof Robert Nemiroff of Michigan Technological University.

After analysing observations of a GRB detected in 2009 by the orbiting Fermi telescope, Prof Nemiroff and his colleagues have found that space-time still seems to be perfectly smooth at levels very close to the Planck scale. In other words, Einstein's simple vision of space-time still looks good. And that's bad news for current theories of quantum gravity, which demand something far more interesting.

Theorists have been quick to point out that the new results could be just a fluke, and that more data is needed. Some have also stressed that the way light interacts with space-time may mask the presence of Planck-scale effects.

But if scientists continue to draw a blank in their search for these effects, current attempts to go beyond Einstein may have to be radically rethought.

That in turn will have far-reaching consequences for attempts to understand the birth of our universe, which is thought to have emerged from a Planck-scale region around 14 billion years ago.

It would also affect the quest for the ultimate Theory of Everything, which theorists hope will reveal the unity of all the particles in the cosmos and the forces that act on them.

There's a deep historical irony in all this. In the late 19th century, scientists tried repeatedly to find evidence for the aether - a substance that supposedly permeated the whole universe.

Like the GRB studies, the experiments devised to find it also used light to detect the presence of the aether - and also repeatedly came up blank.

The explanation was provided in 1905 by a young Swiss patent clerk by the name of Albert Einstein. It's just possible that the experiments now trying and failing to prove him wrong could spark another scientific revolution.

Robert Matthews is visiting reader in science at Aston University, Birmingham, England