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Read more: 鈥�Tricks of the light: Nine fabulous photon spin-offs鈥�

If you were the size of an atom, you might justifiably complain about the sun beating down on you. The photons that make up sunlight may have no mass, but they still carry momentum 鈥� and so exert a force on everything they touch.

It is not, admittedly, a very big force. At sea level on Earth, sunlight鈥檚 鈥渞adiation pressure鈥� is about 50 million times smaller than atmospheric pressure. Applied to tiny objects or over a large area, however, it becomes something to be reckoned with.

Take optical tweezers, a pioneering device developed in 1986 by a team at Bell Labs in Holmdel, New Jersey, that included the . It uses the pressure of a highly focused laser beam to levitate and manipulate delicate microscopic objects such as viruses, bacteria and DNA strands without causing them damage.

The new field of pushes things even further. Here, light is used to control nanoscale mechanical components such as oscillating diving boards. Last year a team led by at the California Institute of Technology in Pasadena used this principle to amplify the mechanical oscillations of a tiny resonator just as light is amplified in a laser (). By using light to remove energy from such a structure and so cool it down, we might also observe its 鈥� the residual quantum of energy that in theory remains even at absolute zero 鈥� and so probe quantum effects in objects larger than atoms and molecules.

A light touch can make a big difference on much larger scales, too. In 1619, Johannes Kepler asserted correctly that a comet鈥檚 tail points away from the sun because of sunlight鈥檚 action. In 2010, solar photons bouncing off the 200-square-metre mirrored sail of Japan鈥檚 spacecraft gave it enough kick to propel it nearer to Venus. Such solar sails might in the future make for a fuel-less method of propulsion to take us to the edge of the solar system and beyond.