Late light reveals what space is made of

12 August 2009 by Anil Ananthaswamy

Located on a mountain top on the Canary island of La Palma, the Major Atmospheric Gamma-Ray Imaging Cherenkov Telescope (MAGIC) is a system of imaging atmospheric Cherenkov telescopes, or IACTs.

ON THE night of 30 June 2005, the sky high above La Palma in Spain’s Canary Islands crackled with streaks of blue light too faint for humans to see. Atop the Roque de los Muchachos, the highest point of the island, though, a powerful magic eye was waiting and watching.

MAGIC – the Major Atmospheric Gamma-ray Imaging Cherenkov Telescope – scans the sky each night for high-energy photons from the distant cosmos. Most nights, nothing remarkable comes. But every now and again, a brief flash of energetic light bears witness to the violent convulsions of a faraway galaxy.

What MAGIC saw on that balmy June night came like a bolt from the blue. That is because something truly astounding may have been encoded in that fleeting Atlantic glow: evidence that the fabric of space-time is not silky smooth as Einstein and many others have presumed, but rough, turbulent and fundamentally grainy stuff.

It is an audacious claim that, if verified, would put us squarely on the road to a quantum theory of gravity and on towards the long-elusive “theory of everything”. If it were based on a single chunk of MAGIC data, it might easily be dismissed as a midsummer night’s dream. But it is not. Since that first sighting, other telescopes have started to see similar patterns. Is this a physics revolution through the barrel of a telescope?

Such incendiary thoughts were far away from Robert Wagner’s mind when the MAGIC data filtered through to the Max Planck Institute of Physics in Munich, Germany, the morning after. He and his fellow collaborators were enjoying a barbecue. Not for long. “We put our beers aside and started downloading the full data set,” says Wagner.

It was easy to pinpoint the source of the data blip – a 20-minute burst of hugely energetic gamma rays from a galaxy some 500 million light years away known as Markarian 501. Its occasional tempestuous outbursts had already made it familiar to gamma-ray telescopes worldwide.

This burst was different. As Wagner and his colleagues analysed the data in the weeks and months that followed, an odd pattern emerged. Lower-energy photons from Markarian 501 had outpaced their higher-energy counterparts, arriving up to 4 minutes earlier (Physics Letters B, vol 668, p 253).

This should not happen. If an object is 500 million light years away, light from it always takes 500 million years to get to us, no more, no less. Whatever their energy, photons always travel at the same speed, the implacable cosmic speed limit: the speed of light.

Perhaps the anomaly has a mundane explanation….

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