Free The Big Questions: Physics by Michael Brooks

most of its mass is derived from quantum fluctuations in the energy of empty space. The solidity of that hand in front of your face is perhaps the most convincing illusion you will ever experience.
     

WHY IS THERE NO SUCH THING AS A FREE LUNCH?
     
    Energy, entropy and the search for perpetual motion
     
    The exact origins of the phrase ‘no such thing as a free lunch’ are unclear, but most sources say it began life as the pithiest summary of economics. It appeared in Pierre Dos Utt’s 1949 monograph
TANSTAAFL: a Plan for a New Economic World Order,
where Dos Utt tells of a king seeking economic advice. His advisers, looking for ever-simpler ways to get their message across, conclude with the now-classic version of the phrase: ‘There ain’t no such thing as a free lunch.’
    It is doubtful this would have been enough to motivate economists to usher in a new world order, and the physicists of the time would have certainly been unimpressed. The idea of something for nothing had long been a goal of inventors trying to get a free lunch by coming up with ‘perpetual motion machines’ that would do work without the need for any external power. Physicists had long been telling them this was impossible.
    There is no such thing as a free lunch because you simply can’t get something for nothing: someone, somewhere always has to pay. Physicists have enshrined this principle as a fundamental law of physics. So you need to think hard before you start looking for a free lunch, because you are battling against the way the universe runs. Perhaps the great artist, visionary and inventor Leonardo da Vinci put it best. He took a keen interest in perpetual motion, investigating designs, and coming up with a few of hisown. But he was sceptical about them all: one of his notebooks contains a detailed analysis of a popular kind of machine, showing why and how it could not work. ‘O you researchers of perpetual motion,’ Leonardo wrote, ‘how many harebrained ideas have you created in this search. You may as well join the alchemists.’
     
----
    ‘O you researchers of perpetual motion, how many harebrained ideas have you created in this search. You may as well join the alchemists.’
     
    LEONARDO DA VINCI
     
----
    There are two kinds of perpetual motion machines. The first supplies an endless output of work despite the fact that there is no input of fuel or any other form of energy. The second converts heat to mechanical work with perfect efficiency. Both, it should be made clear, are wishful thinking – and physics tells us why.
     
Something for nothing
     
    As with alchemy, the search for perpetual motion engaged some of the finest minds that have graced the Earth. The dream has been around since at least AD 624, when the Indian mathematician and astronomer Brahmagupta described a wheel whose hollow spokes could be filled with mercury. The mercury would shift weight around the wheel as it rotated. As a result, Brahmagupta wrote, ‘the wheel rotates automatically for ever’.
     
    The idea was repeated numerous times. In 1235, Villard de Honnecourt, a French artist and inventor, produced his own version. De Honnecourt was no fool: he drew the first known plans for a mechanical escapement mechanism that would keep time. But de Honnecourt’s ‘overbalanced wheel’ still doesn’t work. Here, a series of hinged weights are attached around the circumference of a wheel, their motion limited by pins. As the wheel turns, an imbalance in the distribution of weights causes the wheel to turn. As it turns, the elevated weights drop onto their pins, and the transfer of weight keeps the wheel turning.
     
    The fact that the perpetually rotating wheel is a running theme in the search for perpetual motion can only mean that very few people tried to build these kinds of machines. Build oneand you soon learn that they just don’t work. Take de Honnecourt’s overbalanced wheel, for example. What is needed for this to carry on forever is