WE ARE ALL DESIGNIST NOW:

For 200 years scientists have identified chemicals by the light they emit. You can recognise a sodium lamp from its orange glow. It's the same orange you get by holding salt to a flame, a standard trick of chemistry. Astronomers can deduce the components of stars or dust clouds from their particular light fingerprint.

Now, the Princeton team show that, in theory at least, these fingerprints can be forged.

As the Danish physicist Niels Bohr and others worked out in the early 20th century, atoms and molecules emit light when the electrons around them shuffle about between different levels of energy. An electron falling from a high energy level to a lower one gives out the colour of light that exactly matches the energy difference.

It's a bit like a dog's squeaky toy tumbling down the stairs, making a different sound depending on the height of the steps.

What Campos's team realised was that they could use lasers to excite an atom into a state of any energy, at least temporarily, by hitting it with a specially designed light pulse. When the electron fell back down, it would then emit whatever light colour the physicists chose.

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