May the force not be with you: Sandra Bullock goes for a spacewalk in Gravity. Photo: Warner Bros
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In search of the notorious Big G: why we still know so little about gravity

Gravity is pathetic and so is our understanding of it.

Gravity is pathetic. The Oscar statuette, for instance, has a mass of 3.85 kilograms but it is pulled down to earth by a force so weak that you can buy a £2.99 fridge magnet that can beat it. It’s shameful that the gravitational pull of the entire earth can be overcome by a cheap piece of magnetised steel.

Gravity is by far the weakest of the fundamental forces of nature (the fridge magnet puts the far stronger electromagnetic force to work). It is so weak that its strength is proving difficult to measure accurately. In late February, while Alfonso Cuarón, the director of the sci-fi film Gravity, was on tenterhooks waiting for the Oscars result, the world’s experts on gravity assembled just outside Milton Keynes in an attempt to sort out this most embarrassing problem.

Numbers such as the strength of gravity, the speed of light and the charge on an electron are known to physicists as the “fundamental constants”. They are in some ways the sticking plaster of physics. We can explain the origin of most things but we know the values of the fundamental constants only by measuring them – there is no way to work them out from a theory.

These days, most are very well defined – but not gravity. It is the only fundamental constant for which our uncertainty over its value has got worse over the years.

The gravitational constant is sometimes known as “Big G”. This differentiates it from “little g”, which describes how fast things accelerate towards Planet Earth when free to fall. The first accurate measurement of Big G was made in 1798. Henry Cavendish used a torsion balance, a device in which two lead weights are attached to the ends of a metal bar. The bar hangs horizontally by a metal wire attached to its midpoint. Cavendish then brought other weights close to one of the lead weights and measured how much the gravitational attraction between the weights twisted the wire. From that measurement, he calculated the strength of gravity.

Cavendish’s accuracy was five parts in 1,000. Over 200 years later, our accuracy stands at roughly one part in 10,000. Given that modern measurements use lasers and electronic devices and Cavendish used a mirror and a candle, it hardly counts as a great improvement.

What’s worse is that our measurements of Big G are getting less accurate. The latest measurement, reported at the end of last year, reduced the overall value by 66 parts per million but the uncertainty
of the value increased from 100 parts per million to 120 parts per million.

The measurement was taken by Terry Quinn, emeritus director of the International Bureau of Weights and Measures in Paris. At its meeting in February, he argued that it was time researchers admitted that everyone must be making some basic errors in their method and that they should give up on making any more unilateral measurements.

The experts now agree that future experiments seeking the value of Big G will be done in big collaborations, with the proposals for equipment and methodology being scrutinised by everyone in advance to minimise the chance of further embarrassment.

It will, they say, mimic the way that researchers worked together to find the Higgs boson. That gave us the secret of mass: the hope is that if the physicists all pull together, they can finally work out exactly what size of force brings that mass down to earth.

Michael Brooks holds a PhD in quantum physics. He writes a weekly science column for the New Statesman, and his most recent book is At the Edge of Uncertainty: 11 Discoveries Taking Science by Surprise.

This article first appeared in the 05 March 2014 issue of the New Statesman, Putin's power game

Photo: Getty
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The moonwalkers: what it's like to belong to the world's most exclusive club

"The blue and the white and the brown just hung in the blackness of space."

It’s been almost 50 years since man first walked on the moon – and there were only a grand total of six missions.

From 1969 until 1972, as humanity reached out into space, these men – and they were all men – were at the forefront of scientific research and discovery.

But in 2017, the six survivors – now with a combined age of 505 – are the rare members of an exclusive club. The other six moonwalkers have already passed away.

Astronaut Buzz Aldrin was on Apollo 11, Charlie Duke was on Apollo 16 and Harrison "Jack" Schmitt was an Apollo 17 moonwalker. For the first time, at the Starmus festival in Trondheim, Norway, the three have come together to discuss their experience.

The three share “a special relationship, no question about it”, according to Duke. He tells me: “Our experiences are different but they’re the same in so many respects.”

Aldrin – unable to appear in person due to doctor’s orders – quips on camera from his home in Florida that President Dwight Eisenhower was advised that they should send a philosopher or maybe a poet up. His response, possibly apocryphal, came: “No, no - I want success."

As a result, it is up to these scientists to find the words to describe the off-Earth adventure which is the defining event of a moonwalker's life. 

A poetic description comes from Texan resident Duke. First and foremost a test pilot, his interest in space was piqued by the launch of Sputnik, the first artificial satellite, in 1957. He joined Nasa in 1966.

Now 81, Duke served as mission control support throughout many Apollo missions, most notably as the voice of Capsule Communicator when Neil Armstrong and Aldrin landed on the Moon in 1969.

He tells me: “Once we left Earth’s orbit, we turned our spaceship around and there was the whole Earth 40,000km away.

“The blue and the white and the brown just hung in the blackness of space. That contrast between the vivid blackness and the bright Earth – this jewel of Earth I like to call it - was right there.”

Aldrin started his career as a mechanical engineer, before joining up as a jet fighter in the US Air Force during the Korean War.

His gung-ho spirit and enthusiasm for space have not deserted him even at the age of 87 – he appears onscreen at the festival wearing a "Get your ass to Mars" T-shirt.

The most memorable experience for him came when he congratulated Neil Armstrong, the first of the team to walk on the moon (he died in 2012). But in the lunarscape, memories get confused – the men remember the moment differently.

“After the landing, I looked over at Neil, and we smiled. I remember patting him on the back and he remembers shaking hands. So here were two first-hand witnesses and we couldn’t agree on what actually happened when we got there.”

For Aldrin, the significance of the moonwalk was looking at the moon’s surface from close-up – the lunar soil, or regolith – and what happened when an astronaut's boot stepped onto it. 

“It was so remarkable, the way that it retained its exact form,” he marvels, 48 years on.

Aldrin's fascination with the moon's surface was shared by Schmitt, the 12th, and so far, last, man to walk on the Moon. A trained geologist, he was also the first scientist to do so.

In Schmitt's case, the rocky surface of the moon was enough to draw him into lunar research, which he still conducts at the age of 81.

“The commander told me as soon as I got out I had to look up and see the Earth," he recalls. "I said ‘Well, chief, you’ve seen one Earth, you’ve seen them all’."

In truth, having spent three days looking at the Earth from his craft, Schmitt’s priority was in looking down at the new surface under his feet.

After landing in a valley deeper than the Grand Canyon, his chief concern was just getting to work collecting samples in a lifesize laboratory.

While the moment on the moon may be the initiation into an elevated celebrity, it is followed quite literally a fall back to earth. 

In his post-Moon life, Duke found God.

“A lot of us have a letdown [afterwards]," he admits. Duke was 36 when he landed on the moon in April 1972. By December, the Apollo programme was over. "In January ’73, the thought occurred to me, ‘what am I going to do now?’"

Achieving his life's ambition before hitting middle age turned out not to be as satisfying as he expected. "Because you’d climbed the top, you got to the ultimate high when you were still a young man - and the drive that took you to the ultimate high was still there," he says. "That was a struggle."

In the years since, Duke has looked at his experience as a religious one. Yet he insists God wasn’t present for him when he touched down on the lunar body.

“The Moon flight was not a spiritual experience," he says. "I didn’t understand the wonder of God’s universe. I was enjoying the beauty and the excitement of this mission.”

The three men agree that Mars is the next step for the future of humanity, but there are safety and speed concerns.

“There is potential important work to be done in better physiological understanding of human exposure to long duration space flight which is going to happen whenever we go to Mars,” says Schmitt.

“Anything we do as human beings that’s productive and worthwhile carries risk, either physical of psychological. Radiation, physiological exposure to weightlessness for long durations, and the danger of landing on a distant planet where the atmosphere is not going to be much help - but you do accept the risk that it might end up as a one-way trip.”

But after all of that - the life, the death, the heartache - Duke says he would go back up there if he could.

“At my age now I wouldn’t volunteer to go to Mars - but I would volunteer for a round-trip to the Moon again.”

Starmus Festival runs in Trondheim until Friday June 23. For more information, visit Starmus.

Kirstie McCrum is a freelance journalist. Follow her @kirstiemccrum.

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