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Inside the LHC tunnel. The LHC may discover 'exotic' phenomena, such as the existence of extra dimensions.

Secret dimensions

In everyday life, we inhabit a space of three dimensions – a vast ‘cupboard’ with height, width and depth, well known for centuries. Less obviously, we can consider time as an additional, fourth dimension, as Einstein famously revealed. But just as we are becoming more used to the idea of four dimensions, some theorists have made predictions wilder than even Einstein had imagined.

String theory intriguingly suggests that six more dimensions exist, but are somehow hidden from our senses. They could be all around us, but curled up to be so tiny that we have never realized their existence.

Beyond the third dimension

Some string theorists have taken this idea further to explain a mystery of gravity that has perplexed physicists for some time – why is gravity so much weaker than the other fundamental forces? Does its carrier, the graviton, exist and where? The idea is that we do not feel gravity’s full effect in the everyday world. Gravity may appear weak only because its force is being shared with other spatial dimensions.

To find out whether these ideas are just products of wild imaginations or an incredible leap in understanding will require experimental evidence. But how?

High-energy experiments could prise open the inconspicuous dimensions just enough to allow particles to move between the normal 3D world and other dimensions. This could be manifest in the sudden disappearance of a particle into a hidden dimension, or the unexpected appearance of a particle in an experiment. Who knows where such a discovery could lead!