Relativity on the human scale

24/09/2010

Updating Einstein’s Universe and Magic Universe

Relativity on the human scale

The most gratifying physics I’ve seen for a while comes in today’s Science magazine, from James Chin-Wen Chou and his colleagues in the Time and Frequency Division at the National Institute of Standards and Technology in Boulder, Colorado. They detect well-known effects of relativity on the rate of time passing, but now on the scale of ordinary human activities.

Standard atomic clocks employ microwaves to ensure their regularity, but Chou’s team used laser light in a pair of aluminium-27 optical clocks (invented in 2005), which gives about 100 times better accuracy. In one experiment, they used an electric field to jiggle the aluminium ion at the heart of a clock and showed that time passed more slowly in accordance Einstein’s Special Relativity theory, about the effect of motion on time. The effect of atomic motion as slow as 8 metres per second (about 30 km/h) was detectable.

Raising a clock makes it run a little faster. Credit: Chou et al., Science, 24 September 2010 – see reference.

Especially pleasing for me was another experiment, in which one clock was jacked up just 33 cm relative to the other. The clock gaining height ran faster because it was further from the Earth’s centre of gravity, and the gravitational field was slightly weaker, in accordance with General Relativity. As the change in clock rate was only about 40 parts in a billion billion (1018), its detection was a tour de force for the NIST team.

This effect of altitude on time was the key to the efforts by Martin Freeth of BBC-TV and me to make Einstein’s theory of gravity, General Relativity, comprehensible to the public, in our film “Einstein’s Universe” (1979).

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Who blew up Jerusalem?

23/08/2010

Predictions Revisited

Who blew up Jerusalem?

A nightmare from the 1970s persists

US Assures Israel That Iran Threat Is Not Imminent” says a headline on a recent New York Times report, available here: http://www.nytimes.com/2010/08/20/world/middleeast/20policy.html . It seems that US intelligence is saying, “Relax, Iran won’t have a nuclear weapon for a year or more.”

For 30 years since the producer Peter Batty and I explored the possible triggers of nuclear war, in our TV blockbuster Nuclear Nightmares: The Wars That Must Never Happen”, a truly depressing number of people have continued to play with fire, in the proliferation of bomb-making technology. The accompanying book, Nuclear Nightmares, quoted an anonymous American strategist calling proliferation “the least unlikely route to nuclear war”. And because Israel was known (in 1979) to have already made nuclear weapons at a plant in the Negev Desert, we set our story in the Middle East.

Each scenario in the programme culminated with a fictional survivor trying to make sense of what happened. Here’s the relevant extract as broadcast.

PRESENTER (Peter Ustinov) on a vantage point above Jerusalem: The holy city of Christians, Jews and Moslems – the order is strictly alphabetical. It has been the focal point for conflict for thousands of years. Jerusalem is at this time in Israeli hands. But you can look North towards the Soviet Union with its Moslem minorities and affiliations. East towards a patchwork of Moslem states, patient yet unforgiving. South towards Mecca, the power of religion and of oil. And West toward America, Israel’s powerful friend.

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Counterforce

01/05/2010

Predictions revisited

The counterforce nightmare

or “All you have to say is Tripoli”

When in Prague Castle in April 2010 the US and Russian Presidents signed the latest Strategic Arms Reduction Treaty (START), it stirred memories of how terrifying the world was 30 years ago, especially for folk in the know. From Hiroshima in 1945 till the fall of the Berlin Wall in 1989, the fear of atomic death for all your little chickens and their dam was the curse of an otherwise cheerful age. But by the late 1970s, the risk had become hair-raising.

Minuteman intercontinental missile test-fired at Vandenberg AFB. USAF/DOD

Strategic instability” was the jargon term. As I wrote at the time, “The danger is not that either side is tempted in cold blood to make his strike, but that both are driven towards it by mutual fear. There may come a moment when, without any malice in your heart, you have frightened your opponent so badly you must hit him before he hits you. Nuclear deterrence becomes nuclear impulsion.”

Intercontinental missiles were getting so sophisticated and accurate that both the USA and Soviet Union had good reason to fear that the other could attempt a surprise counterforce strike against the nuclear weapons in their missile silos and bomber bases – in the hope of coming off less badly in the unrestrained war that would follow. If you thought that was happening, simple logic then said that you had to get your own missiles launched before they were “dug out”. Decision times were limited by the few minutes remaining between the detection and arrival of incoming warheads.

Nuclear Nightmares: The Wars That Must Never Happen”, BBC-TV 1979, was produced and directed by Peter Batty and written by Nigel Calder. Made at precisely that critical stage of the Cold War, and filmed with operational forces and in command bunkers across Europe and the USA, the documentary explored four possible routes to nuclear war. Each segment ended with a fictional survivor sitting in a fallout shelter and explaining what went wrong. The culminating scenario concerned an all-out nuclear exchange between the USA and the Soviet Union.

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About Einstein’s Universe

01/05/2010

Occasional postings will comment on news relating to Einstein’s ideas. This introduction explains my interest.

About Einstein’s Universe

Let’s make relativity plain,” was my answer when BBC-TV in London and WGBH in Boston asked, in 1978, how we should celebrate the centenary of Albert Einstein’s birth in the following year. Not just Special Relativity, high-speed travel and E=mc2. Those are fairly easy to talk about. General Relativity (GR), Einstein’s theory of gravity, was the challenging task.

What spurred me were memories of struggling as a student with GR, taught at Cambridge as a branch of higher mathematics. Also irritation at being told again and again that GR was beyond the grasp of ordinary mortals, six decades after our Albert dreamed it up. He was an intuitive physicist and not a brilliant mathematician. Those fancy equations were supplied by other people. So what were the pictures in his head?

Filming for “Einstein's Universe”: Sidney Drell, John Archibald Wheeler and Peter Ustinov, with a younger Nigel Calder. Photo: Joan Williams, BBC/WGBH

Months of fun followed, in the course of which Martin Freeth, producer-director for the BBC, borrowed the McDonald Observatory in Texas and brought to it the eminent physicists and astronomers who were to explain Einstein’s ideas to a genuine layman. This was the actor Peter Ustinov, who also spoke Einstein’s own words and twice acted the part of a time traveller. Specially made for the programme and flown out from London was a billiard table configured so that a ball representing a planet could orbit in the warped space around the Sun, or fall into a black hole. Read the rest of this entry »