Tuesday, 17 September 2013

Shining a Light on Gravity

One of my most favourite tv programmes of ALL time is James Burke’s “Connection” series. One episode entitled “Drop The Apple” ended with Einstein’s theory that gravity can bend light waves. James Burke explained the experiment which proved it. Even though he mentioned no names, he was describing the work of Sir Arthur Eddington (1882-1944).

Between the two World Wars Arthur Eddington was as well-known to the British public as people like Patrick Moore and Carl Sagan have been in recent years. Eddington was an effective communicator and broadcast on radio often. If modern technology was around in his heyday I wouldn’t be surprised if had his own twitter account.

One thing Eddington never talked about was his sexuality. A BBC drama called “Einstein and Eddington”, made in 2008, included references to Eddington’s sexuality based on rumours which the writer of the programme deliberately enhanced for dramatic effect. While these rumours may never be proved they have persisted and don’t contradict what we do know about his personal life. As one reader of Professor Peter Coles’ blog commented last week, men in Eddington’s position at a university was required to be a bachelor. That doesn’t make him gay, of course, but there was no reason for not to him have a romantic relationship with a woman without marrying her either at university or afterwards. There’s no evidence that he did so. So, Sir Arthur Eddington is on my “probably asexual” list until we know for sure, which may never happen.

Back to Einstein and gravity. Einstein said that the Sun’s gravity could bend the light coming from the stars beyond it. There was one way to prove it – during a total eclipse. So Arthur was packed off to Principe, an island off the west African coast, with some camera equipment to record the total eclipse over the island on 29th May 1919.

The very simplified illustrations below show how the proof was found. On the left is a representation of some representative stars at a time of year before the Sun moved into it. On the right is a representation of the same stars in May 1919 when the total eclipse took place.

Arthur took photos of the eclipse, and then compared them with photos of the same stars he took earlier in the year. Look at the arrows on my illustrations. They represent the position of one star. Arthur discovered that this star had “moved”. In the weird way that science works, the star apparently moves AWAY from the Sun because, remember, the light is bent around the Sun like a boomerang. I’ve exaggerated the effect to make it clearer, and I hope you can tell the star has moved in relation to it’s nearest neighbouring star. The other stars would also have been affected, though in different degrees. It proved that the light from that star had bent, proving Einstein’s theory. In the words of James Burke at the end of his episode: “… because of which it’s Einstein’s universe now, not Newton’s any more. So, you can ‘Drop the Apple’.”

Another of Einstein’s gravitational theories has yet to be proved. He suggested that exploding stars and colliding galaxies create gravity ripples through space. These gravitational waves, having travelled billions of miles, would be so small by the time they reach Earth that it would be virtually impossible to detect them. It’s like someone shouting in your ear – from 1,000 miles away! The sound waves would be so small as to be unnoticeable.

A physics professor at the Massachusetts Institute of Technology has been working on ways to detect gravitational waves since 1991. Pakistani-born Nergis Mavalvala was encouraged by her parents to study and be mechanically skilled. For a Muslim country this was forward thinking on their behalf, though her mother objected to Nergis getting grease stains on her clothes.

Nergis’s chemistry teacher at school in Pakistan encouraged her interest in experimentation and this started her on a career of developing scientific equipment. Nergis is not just an academic, she is a hands-on, practical scientist.

Working on the detection of gravitational waves Nergis used her thesis to suggest how a laser interferometer, using precisely positioned mirrors, could detect the smallest of wave. However, the mirrors would have to be so far apart that even thermal energy at the atomic level would swamp the wave signal from space.

It was at this time that Nergis found love. She hadn’t experienced any real romantic attachment until she met her present girlfriend. They are still together and have a 5-year-old child.

Undaunted by the technical challenges Nergis and the team developing interferometers are continuing to produce more stable and sensitive equipment to find those gravity waves from far-flung exploding stars first theorised by Einstein a century ago.

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