Did the Earth move? How to make the world a better place by observing unbelievably small variations in gravity? Without paying the price of six Ferraris? Richard Middlemiss gave us the answer in the Isambard Kingdom Brunel Award Lecture for Engineering, Technology and Industry at this year’s British Science Festival. Alan Barker was there. Imagine using your smartphone to look under the ground. What would you look for? At some point in the future, you may be able to answer that question. And the app will probably be the result of work currently being done by Richard Middlemiss. Richard knows most of what needs to be known about gravity. But rather than trying to explain what it is (dimples in space-time, you know the kind of thing... no need to go there), Richard demonstrated how it works, and how to measure it. Of course, he started with an apple. In a series of worryingly Bramleyist experiments, and using stopwatches on audience phones, he took the two vital measures – height and time – achieving not unacceptable results. But then, stage by stage, he took us on a journey towards ever more accurate readings. You might think that the pull of gravity on Earth is pretty constant. Not so: everything with mass has gravity, so variations in mass create variations in gravity. But gravity is notoriously weak: a fridge magnet can easily resist the pull of a whole planet. So the variations are tiny, and any machine measuring them will need to be ultra-sensitive. Currently, gravimeters (the industry name for such machines) are big and expensive. The Micro-g LaCoste FG5, for instance, is at least a metre tall, and will set you back a cool £350,000 – the price of six Ferraris. And despite its classification as an absolute gravimeter, it does nothing much more sophisticated than throwing an object up and measuring its fall – only a couple of steps on from using a cooking apple. A relative gravimeter, which uses a mass on a spring to measure gravitational variations, is smaller and cheaper: the Scintrex CG6 costs £100,000 and will fit on the back seat of your car. But it’s still slow and cumbersome; and the only people who can afford to use these machines are oil companies, looking for the next deposit. There is an alternative. Most mobile phones have gravity detectors: the accelerometers that rotate the screen when you move the phone. It, too, is a mass on a spring. Richard and his team are creating accelerometers of the same kind – known as micro-electro-mechanical systems or MEMS – using the same kind of manufacturing process, but with springs ten times thinner than a human hair. The impressive work has been in miniaturising the system. Most of Richard’s PhD went into creating the chip at the heart of it, which is the size of a postage stamp. Add a vacuum tank, and some clever electronics, and by autumn last year they had – a roomful of equipment. A year later, after some astonishing circuitry design by one of Richard’s colleagues, the system is about the size of – you guessed it – a mobile phone. In a recent paper in Nature, Richard and his colleagues demonstrated that their device could measure Earth tides: the tiny elastic distortion in the planet’s crust – no more than 20 centimetres – caused by the Moon’s and Sun’s gravity. It was the first time this effect had been measured by a MEMS sensor, demonstrating that the team have indeed created the first MEMS gravimeter. The potential is for gravity detectors that are light, portable and cheap (Richard estimates a commercial product might cost no more than £2000). The applications are already becoming apparent: counter-terrorism (dirty bombs are full of mass), monitoring nuclear waste sites, even archaeology. Every time Richard talks to people, they come up with new ideas. Among the most dramatic is volcanology. At a recent conference in Portland, Oregon, Richard visited Mount Saint Helens, which famously erupted in 1980, destroying 250 homes and killing 57 people. Almost forty years later, it remains a threat. Dangerous volcanoes are obviously hard to observe, especially when they’re showing signs of blowing. A colleague at the conference told him, “the problem isn’t our lack of knowledge; it’s our inability to see.” Richard’s device – networked, even perhaps flown on drones – could help scientists look safely inside a volcano and predict how it might behave. Read an interview with Richard Middlemiss here. Alan Barker is a writer, coach, training consultant and academic proofreader. Find out more about his work here.