CLAIMS that Einstein might not have all the answers are two-a-penny, but here's one that stands apart. That's because it springs from some of the finest minds in physics.
In 2005, researchers at the MAGIC gamma-ray telescope on La Palma in the Canary Islands were studying gamma-ray bursts emitted by the black hole in the centre of the Markarian 501 galaxy, half a billion light years away. The burst's high-energy gamma rays arrived at the telescope 4 minutes later than the lower-energy rays. Both parts of the spectrum should have been emitted at the same time.
So is the time lag due to the high-energy radiation travelling slower through space? That wouldn't make sense: it would contravene one of the central tenets of special relativity. According to Einstein, all electromagnetic radiation always travels through vacuum at the cosmic speed limit – the speed of light. The energy of the radiation should be absolutely irrelevant.
So what's going on? The MAGIC result suggests that special relativity is only an approximation of how things really work. The observed lag might result from processes that occur at the most fundamental scale of space-time, the Planck length (10-35 metres). If so, that means we might finally have a way to test theories that aim to combine relativity and quantum theory into a quantum theory of gravity.
The mystery has only deepened with the launch last year of NASA's Fermi gamma-ray space telescope. It has observed high-energy photons arriving up to 20 minutes behind zippier low-energy ones from a source 12 billion light years away. The hope is that Fermi will produce much more data that will enable researchers to rule out more mundane explanations and launch us into the era when we can finally put theories that attempt to unite quantum mechanics and gravity to the test.
Read more: 13 more things that don't make sense
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