On the outskirts of Hamburg, Germany, pulses from one of the world’s biggest X-ray lasers race underground towards a stainless-steel chamber. Directly above, another huge laser waits. Soon, its beam will be sent down to meet the X-rays head on, bringing the two extraordinarily powerful beams of light together in an almighty burst of energy.
All very exciting, to be sure. But there is a serious side to these laser theatrics: the scientists behind them are hoping to see the vacuum. Not stray material in the chamber, or leftover gas, or particles of any kind, but the vacuum itself – what most people regard as pure emptiness, but modern physics says is brimming with quantum fields.
Usually, these fields are perfectly undetectable, and the vacuum looks like nothing. But with enough light, even nothing can start to look like something. But the payoff could be great.
The results will put our best theories of the vacuum to the test, and potentially give us a better handle on the dark matter that seems to occupy most of the universe. There is also an outside chance they could reveal that empty space is even stranger than quantum theory predicts. No space, no time, no particles: A radical vision of quantum reality The modern concept of the vacuum can be traced to the work of theorist Paul Dirac in the late 1920s.
At that time, physicists already believed that the electromagnetic field filled all of space, but they still thought of matter as discrete particles, such as electrons and protons. Dirac saw that electrons could also be understood as energetic blips in an underlying field. Over a decade or so, his idea blossomed into quantum electrodynamics, or QED for short – the first successful quantum field theory.
By the 1970s, a more elaborate quantum field theory, the “standard model” of particle physics, had grown to encompass QED and account for all known matter and fundamental forces, besides gravity. When space is empty, these fields remain, but they aren’t totally placid. The uncertainty built into quantum theory predicts that a field can never be guaranteed to have any particular strength, even zero: there must always be the possibility of something a little more, the chance of a fluctuation.
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