100 Years of Einstein’s Gravity – But Where are the Waves?

Click above to listen to discussion of Einstein, and his Theory of General Relativity on The History Show, RTE Radio 1

Broadcast on 29.11.15

Gravitational Waves, as predicted by Einstein’s Theory of General Relativity have not been discovered. The question is why not? (Credit: http://www.space.com)

Albert Einstein first presented his General Theory of Relativity to the Prussian Academy of Science almost exactly 100 years ago on the 25th November 1915. Science has since confirmed most of its predictions.

However, the one major aspect of the General Theory which has yet to be confirmed is the presence of something called gravitational waves, which are ripples in the space-time fabric caused by movement of energy across the Universe.

According to Einstein, space and time were each components of four dimensional reality, and that gravity was a force which pulled objects with mass along curves in space-time. Perhaps think of energy being like a mountaineer walking along the height contours of a geographical map.

Gravitational waves emerge from large objects with mass, according to Einstein, such as two stars closely orbiting each other. The waves then travel out into the Universe, as ripples in the fabric of space time, like a pebble dropped into a still lake.

Physicists get excited about gravitational waves because they can offer a final proof of Einstein’s General Theory, but also because they will carry information from the birth of the Universe, because gravitational waves were created when mass emerged somehow in those first moments.

Questions

In any case, gravitational waves have not yet been discovered yet, and the question is why?

This is one of the questions that will be addressed in a fascinating looking public lecture by Professor Mike Cruise taking place in St Patrick’s College Drumcondra on Wednesday evening 25th November this week.

This is 2015 Statutory Lecture of the Dublin Institute for Advanced Studies (DIAS) School of Cosmic Physics, to mark the 100th anniversary of General Relativity.

The public are all invited, but people are asked to register in advance of the talk at http://www.dias.ie/spscp2015

Predictions 

General Relativity shook up the science world in 1915, and over the past century it has stood up to testing and scrutiny remarkably well.

One prediction was that the speed of light, denoted as c in the famous equation e=mc2 was constant. That has proved correct, and it seems that the speed of light, as Einstein predicted, is the Universe’s ultimate speed limit.

Then there was the revolutionary idea that time was not constant, but relative. The passage of time depended on speed, and that as speed increased towards the speed of light, time would slow down.

This ‘time dilation’ effect has also proved correct. A simple proof lies in the fact that an atomic clock onboard a satellite will run slower than the same atomic clock on Earth. The people that design GPS systems – which are based on information from satellites received on Earth – know this and they must correct for it to ensure GPS works on the ground.

Another major prediction of General Relativity was that light waves would be distorted and bend around an object with a lot of mass, such as a Star. This was proved famously in 1919 and there’s an Irish connection to the story.

Irish connection 

When Einstein announced General Relativity to the world, scientists were blown away by it, but the rest of the world was preoccupied with WW1.

It wasn’t until 1919, when the remarkable new theory was put to its first serious test by the British astronomer Sir Arthur Eddington.

Eddington, unlike other British and English-speaking scientists, kept track of the work of top German scientists like Einstein.

He was a Quaker and a pacifist, and, not antagonistic towards Germans or Germany. He was also one of Britain’s leading astronomers.

Eddington decided that the best way to test General Relativity was to travel to see a solar eclipse, and see – with our Sun blocked out – whether the light from other Stars did, in fact, bend as they went around the Sun.

He got funding from the Royal Irish Academy, still very much in existence, to travel to a remote part of Brazil to view the eclipse in 1919.

The other Irish connection to this story was that the instrument he used to observe the eclipse, a coelostat, was made by the famous Irish scientific instrument makers – Grubb Brothers, of Rathmines.

The original coelostat used by Eddington, which has been restored by the Paris Observatory is currently on public display at DIAS.

Eddington observed that light – exactly as Einstein predicted – bent around the Sun. This result made news headlines around the world, and 4 years after he announced General Relativity, Einstein became famous.

Where? 

Whomever confirms the presence of Einstein’s waves, will, no doubt, be also the subject of global headlines.

There are many space missions ongoing, and planned, which hope to find the elusive waves – even one wave – and these will be mentioned by Prof Cruise in his lecture.

“Even one such detection with high precision would rule out many competing theories of gravity,” said Prof Cruise in an email.

The great quest of modern physics is to find a way to unite Einstein’s General Relativity, which relates to large macro objects, with Erwin Schrodinger’s Quantum Mechanics, which describes the weird behaviour of tiny particles.

(Another Irish connection here –  Schrodinger became an Irish citizen after he arrived here fleeing Nazi Germany, and became the first Director of the Dublin Institute for Advanced Studies)

This quest will be helped by finding gravitational waves because it would rule out many competing theories of gravity which have been devised, in an ad hoc way, to try and marry Relativity with Quantum Mechanics.

“In addition to proving Einstein right at a certain level of accuracy,” Prof Cruise continued, “the detection of gravitational waves, will allow us a very different view of the Universe than is currently available from optical, radio or X-ray telescopes.”

To find out more about this fascinating topic, why not go along to the DIAS lecture on Wednesday?

 

 

 

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