In Douglas Adams’ cult science fiction series The Hitchhiker’s Guide to the Galaxy, a colossal computer is asked to find the Answer to the Ultimate Question of Life, the Universe and Everything.
After 7.5 million years of computation it delivers the enigmatic result: 42.
The meaning of this number has challenged some of the brightest – and even more of the dimmest – minds in science since the Guide appeared in the late 1970s.
But this week, a solution to the long-standing riddle will be revealed at an international meeting of physicists at the American University of Sharjah.
And in a twist that the late Adams would doubtlessly have appreciated, the answer turns out to be ... 42 more questions.
Although the subject of her talk may seem flippant, the participants are unlikely to laugh at the 42 questions identified by Dr Suzanne Lidstrom, a physicist at Uppsala University in Sweden.
Indeed, most will agree that the questions include those that must be answered to have any hope of understanding Life, the Universe and Everything.
It is quite a list, covering such mind-bending puzzles as whether our universe is part of an even bigger so-called multiverse, to the age-old conundrum, "What is consciousness?"
But topping the list is a question that has defeated the best and the brightest theorists for decades.
In everyday language, it is this: why is empty space so empty?
This may sound like a riddle of the kind pondered by philosophers. In reality, it fully merits its place as Question No 1 – for the answer has implications for a host of issues, from the chemistry of life to the fate of the entire universe.
There is no doubt that space is, on average, extremely empty. According to astronomers, the universe contains just one atom for each cubic metre of space, on average.
But since the 1920s it has become clear that matter is not the only denizen of the vacuum of space.
According to the famous Uncertainty Principle of quantum theory, it is impossible to pin down the exact energy content in a patch of space at any given moment.
And that means that everywhere – from deepest space to where you are sitting now – is seething with so-called quantum vacuum energy.
The presence of this energy was first detected in studies of the light of hydrogen atoms carried out in the 1940s. It is now known to be the source of the inter-atomic "glue" that binds solid matter – including ourselves.
It is incredibly weak: between two plate-sized metal sheets held a hair’s breadth apart, it amounts to no more than the weight of ink in this full stop.
But crucially, it rapidly becomes stronger with decreasing distance. Bring those sheets 10 times closer and the quantum force between them intensifies 10,000-fold.
That is enough to affect so-called nano-machines, molecular-sized devices that have been touted as one of the technologies of the future. Their tiny motors and gears can seize up under the action of this bizarre "force from nowhere".
The prime reason that quantum vacuum energy tops Dr Lidstrom’s list is, however, its impact on a far bigger canvas – the entire universe.
Since its creation in the Big Bang about 14 billion years ago, the universe has been expanding.
For decades astronomers studied distant galaxies, trying to discover whether their recession would carry on forever, or slowly peter out, leading to a Big Crunch billions of years hence.
In the late 1990s, they made one of the most shocking scientific discoveries of all time.
The cosmic expansion was not petering out, it was not even continuing at the same rate. It was speeding up, as if propelled by a force emerging from nowhere.
Theorists had no problem suggesting its origin: the quantum vacuum.

Source: The National