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

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Anita Sarkeesian: “I don’t like the words ‘troll’ and ‘bully’”

The media critic and GamerGate target tells the Guardian that online harassers need a rebrand.

Anita Sarkeesian has been under attack for an entire year. She has received bomb threats, rape threats, gun threats, and threats that events she was due to speak at would be attacked. Her home address was circulated in online gaming communities. Her crime? She started a Kickstarter campaign for her YouTube channel, Feminist Frequency, to fund a series called “Tropes vs Women in Video Games”, which catalogues the sexist stereotypes and attitudes in gaming. 

So overall, it's pretty unsurprising that Sarkeesian doesn't call her attackers "trolls" or "bullies", with their comfy associations of schoolyards and fairytale bridges. 

Speaking in an interview with Jessica Valenti, published in the Guardian this weekend, Sarkeesian explains her reasoning:

“I don’t like the words ‘troll’ and ‘bully’ – it feels too childish. This is harassment and abuse."

She also implies that these words tie into a delusion entertained by some of the men themselves – that the abuse is just a bit of fun. Yet whatever the intent, Sarkeesian argues, “it still perpetuates all of the harmful myths attached to that language and those words”.

The interview also covers GamerGate controversy as a whole and Sarkeesian’s rise to prominence as someone willing to speak publicly about the abuse she has receved. As she points out, however,

“There are a lot of people who are being targeted who don’t get the attention I do. Women of colour and trans women, in particular, are not getting media attention and not getting the support they need.”

Barbara Speed is a technology and digital culture writer at the New Statesman and a staff writer at CityMetric.