Archive for the Books, Talks and Reviews Category

Pictures from Post-Planck Cosmology in Pune

Posted in Biographical, Books, Talks and Reviews, The Universe and Stuff with tags , , on April 20, 2018 by telescoper

Regular readers of this blog (Sid and Doris Bonkers) will know that last year I went to the Inter-University Centre for Astronomy and Astrophysics in Pune (India) for a conference on `Post-Planck Cosmology’. Well, I recently received a copy of the official conference photograph, which I thought I’d share:

There is also an online collection of pictures taken during the talks, from which I have taken the liberty of extracting this picture of me during my talk:

I think this picture has a lot of potential for a caption competition, so please feel free to suggest captions through the comments block!

Advertisements

A Day at DIAS

Posted in Biographical, Books, Talks and Reviews with tags , , on March 27, 2018 by telescoper

Last night I flew back to Ireland for a few days of work here before the Easter Weekend. The schedule of flights from Cardiff to Dublin has changed for the spring, with the afternoon flight much later: at 7.45pm instead of 3.40pm, so I left from Cardiff after work on Monday and had dinner in the airport (an overpriced and barely edible beefburger).

Although there is no teaching in either on Maynooth or Cardiff this week I had to come to Ireland for a few reasons, including giving a seminar today at the Dublin Institute for Advanced Studies (DIAS) this afternoon which provided me with the chance to visit it for the first time.

It being a pleasant morning I walked to DIAS from Connolly Station after taking the train there from Maynooth. It’s about half an hour’s walk.

DIAS is actually spread over several sites. Officially my talk was at the School of Theoretical Physics, but there were some people there from the School of Cosmic Physics, which is located not too far away. There were also a few people from Maynooth there, as there are a number of collaborations going on between the two institutions involving staff and students. There was also a visitor from even further afield, in the form of Cormac O’Rafferty who also visits this blog from time to time.

Anyway I had a nice curry for lunch before the talk, which generated a lot of questions from which I infer that it was either confusing or stimulating (or possibly both). Here are the slides in case anyone feels like taking a look.

For a change I decided to take the train back to Maynooth from Pearse rather than Connolly, but as it was rush hour I found it packed.

Maynooth by contrast is very quiet with most students away for the break. I can also report that the annoying roadworks that have been going outside my Maynooth residence for months have now finished.

Anyway, thanks to my hosts at DIAS for inviting me and I hope my talk was reasonably bearable. Hopefully this will be the first visit of many!

R.I.P. Stephen Hawking (1942-2018)

Posted in Books, Talks and Reviews, Television, The Universe and Stuff with tags on March 14, 2018 by telescoper

I woke today to the sad news of the death, at the age of 76, of theoretical physicist and cosmologist Stephen Hawking. We all knew he had to pass away one day, but having been diagnosed with Motor Neurone Disease and given just a couple of years to live at the age of 22, I think we had all come to regard him as indestructible, so news of his death still came as a shock.

Stephen’s immense contributions to physics, including but not restricted to cosmology, are remarkable in their own right, but made even more remarkable that has done so much after having been stricken by such a debilitating disease when he was only in his twenties. Hawking was undoubtedly a brilliant and inspirational mind, but his courage and physical endurance in the face of difficulties that others might have found unbearable have provided inspiration for many far beyond the field of physics.

To give an example of his scientific work, here is an equation which I think would serve as a memorial to Stephen Hawking as it brings together quantum mechanics, gravity and thermodynamics in giving the entropy of a black hole in terms of its surface area and fundamental constants:

I’ve talked and written quite a lot about Stephen Hawking over the years. In particular I have in the past gone on record, both on television and in print, as being not entirely positive about the `cult’ that surrounds him. I think a number of my colleagues (and some some people at the University of Cambridge) have found things I have said insufficiently reverential or perhaps even disrespectful. This is not the time to go over these things. For the record I’ll just say (yet again) that, while I stand by everything I have said, I do – and always will have – enormous respect for Hawking the physicist, as well as deep admiration for his tenacity and courage.

I may post a longer reflection on Stephen Hawking’s life and work in due course, but for now let me just offer my condolences to his family, friends, and colleagues. He was one of the most celebrated public intellectuals of his day as well as a courageous and determined human being. He is irreplaceable.

The Story of the 1919 Eclipse Expeditions

Posted in Books, Talks and Reviews, History, The Universe and Stuff with tags , , , , , , on August 21, 2017 by telescoper

Unless you have been living on another planet, you will know that today there will be an eclipse of the Sun although from the UK it will be rather underwhelming, as only about 4% of the Sun’s disk will be covered by the moon; for totality you have to be in the United States.  For the record, however, the eclipse will begin 15:46 GMT on August 21 out over the Pacific. It will reach the coast of Oregon at Lincoln City, just west of Salem, at 16:04 GMT (09:04 local time) where it will reach its maximum  at 17:17 GMT (10:17 local time). The path of totality will then track right across the United States to South Carolina. For more details see here. Best wishes to all who are hoping to see this cosmic spectacle! I saw the total eclipse of August 11, 1999 from Alderney in the Channel Islands, and it was a very special experience.

Here’s a (not very good and slightly damaged) scan of a picture from that eclipse that I found last night in a box of old photographs:

Before starting I can’t resist adding this excerpt from the Times warning about the consequences of a mass influx of people to Cornwall for the 1999 eclipse. No doubt there are similar things going around about today’s eclipse:

I did write a letter to the Times complaining that, as a cosmologist, I felt this was very insulting to druids. They didn’t publish it.

This provides me with a good excuse to repost an old item about the famous expedition during which, on 29th May 1919, measurements were made that have gone down in history as vindicating Einstein’s (then) new general theory of relativity. I’ve written quite a lot about this in past years, including a little book and a slightly more technical paper. I decided, though, to post this little piece which is based on an article I wrote some years ago for Firstscience.

 

–0–

 

The Eclipse that Changed the Universe

A total eclipse of the Sun is a moment of magic: a scant few minutes when our perceptions of the whole Universe are turned on their heads. The Sun’s blinding disc is replaced by ghostly pale tentacles surrounding a black heart – an eerie experience witnessed by hundreds of millions of people throughout Europe and the Near East last August.

But one particular eclipse of the Sun, eighty years ago, challenged not only people’s emotional world. It was set to turn the science of the Universe on its head. For over two centuries, scientists had believed Sir Isaac Newton’s view of the Universe. Now his ideas had been challenged by a young German-Swiss scientist, called Albert Einstein. The showdown – Newton vs Einstein – would be the total eclipse of 29 May 1919.

Newton’s position was set out in his monumental Philosophiae Naturalis Principia Mathematica, published in 1687. The Principia – as it’s familiarly known – laid down a set of mathematical laws that described all forms of motion in the Universe. These rules applied as much to the motion of planets around the Sun as to more mundane objects like apples falling from trees.

At the heart of Newton’s concept of the Universe were his ideas about space and time. Space was inflexible, laid out in a way that had been described by the ancient Greek mathematician Euclid in his laws of geometry. To Newton, space was the immovable and unyielding stage on which bodies acted out their motions. Time was also absolute, ticking away inexorably at the same rate for everyone in the Universe.

Sir Isaac Newton, painted by Sir Godfrey Kneller. Picture Credit: National Portrait Gallery,

For over 200 years, scientists saw the Cosmos through Newton’s eyes. It was a vast clockwork machine, evolving by predetermined rules through regular space, against the beat of an absolute clock. This edifice totally dominated scientific thought, until it was challenged by Albert Einstein.

In 1905, Einstein dispensed with Newton’s absolute nature of space and time. Although born in Germany, during this period of his life he was working as a patent clerk in Berne, Switzerland. He encapsulated his new ideas on motion, space and time in his special theory of relativity. But it took another ten years for Einstein to work out the full consequences of his ideas, including gravity. The general theory of relativity, first aired in 1915, was as complete a description of motion as Newton had prescribed in his Principia. But Einstein’s description of gravity required space to be curved. Whereas for Newton space was an inflexible backdrop, for Einstein it had to bend and flex near massive bodies. This warping of space, in turn, would be responsible for guiding objects such as planets along their orbits.

Albert Einstein (left), pictured with Arthur Stanley Eddington (right). Picture Credit: Royal Greenwich Observatory.

By the time he developed his general theory, Einstein was back in Germany, working in Berlin. But a copy of his general theory of relativity was soon smuggled through war-torn Europe to Cambridge. There it was read by Arthur Stanley Eddington, Britain’s leading astrophysicist. Eddington realised that Einstein’s theory could be tested. If space really was distorted by gravity, then light passing through it would not travel in a straight line, but would follow a curved path. The stronger the force of gravity, the more the light would be bent. The bending would be largest for light passing very close to a very massive body, such as the Sun.

Unfortunately, the most massive objects known to astronomers at the time were also very bright. This was before black holes were seriously considered, and stars provided the strongest gravitational fields known. The Sun was particularly useful, being a star right on our doorstep. But it is impossible to see how the light from faint background stars might be bent by the Sun’s gravity, because the Sun’s light is so bright it completely swamps the light from objects beyond it.

 

A scientific sketch of the path of totality for the 1919 eclipse. Picture Credit: Royal Greenwich Observatory.

Eddington realised the solution. Observe during a total eclipse, when the Sun’s light is blotted out for a few minutes, and you can see distant stars that appear close to the Sun in the sky. If Einstein was right, the Sun’s gravity would shift these stars to slightly different positions, compared to where they are seen in the night sky at other times of the year when the Sun far away from them. The closer the star appears to the Sun during totality, the bigger the shift would be.

Eddington began to put pressure on the British scientific establishment to organise an experiment. The Astronomer Royal of the time, Sir Frank Watson Dyson, realised that the 1919 eclipse was ideal. Not only was totality unusually long (around six minutes, compared with the two minutes we experienced in 1999) but during totality the Sun would be right in front of the Hyades, a cluster of bright stars.

But at this point the story took a twist. Eddington was a Quaker and, as such, a pacifist. In 1917, after disastrous losses during the Somme offensive, the British government introduced conscription to the armed forces. Eddington refused the draft and was threatened with imprisonment. In the end, Dyson’s intervention was crucial persuading the government to spare Eddington. His conscription was postponed under the condition that, if the war had finished by 1919, Eddington himself would lead an expedition to measure the bending of light by the Sun. The rest, as they say, is history.

The path of totality of the 1919 eclipse passed from northern Brazil, across the Atlantic Ocean to West Africa. In case of bad weather (amongst other reasons) two expeditions were organised: one to Sobral, in Brazil, and the other to the island of Principe, in the Gulf of Guinea close to the West African coast. Eddington himself went to Principe; the expedition to Sobral was led by Andrew Crommelin from the Royal Observatory at Greenwich.

British scientists in the field at their observing site in Sobral in 1919. Picture Credit: Royal Greenwich Observatory

The expeditions did not go entirely according to plan. When the day of the eclipse (29 May) dawned on Principe, Eddington was greeted with a thunderstorm and torrential rain. By mid-afternoon the skies had partly cleared and he took some pictures through cloud.

Meanwhile, at Sobral, Crommelin had much better weather – but he had made serious errors in setting up his equipment. He focused his main telescope the night before the eclipse, but did not allow for the distortions that would take place as the temperature climbed during the day. Luckily, he had taken a backup telescope along, and this in the end provided the best results of all.

After the eclipse, Eddington himself carefully measured the positions of the stars that appeared near the Sun’s eclipsed image, on the photographic plates exposed at both Sobral and Principe. He then compared them with reference positions taken previously when the Hyades were visible in the night sky. The measurements had to be incredibly accurate, not only because the expected deflections were small. The images of the stars were also quite blurred, because of problems with the telescopes and because they were seen through the light of the Sun’s glowing atmosphere, the solar corona.

Before long the results were ready. Britain’s premier scientific body, the Royal Society, called a special meeting in London on 6 November. Dyson, as Astronomer Royal took the floor, and announced that the measurements did not support Newton’s long-accepted theory of gravity. Instead, they agreed with the predictions of Einstein’s new theory.

The final proof: the small red line shows how far the position of the star has been shifted by the Sun’s gravity. Each star experiences a tiny deflection, but averaged over many exposures the results definitely support Einstein’s theory. Picture Credit: Royal Greenwich Observatory.

The press reaction was extraordinary. Einstein was immediately propelled onto the front pages of the world’s media and, almost overnight, became a household name. There was more to this than purely the scientific content of his theory. After years of war, the public embraced a moment that moved mankind from the horrors of destruction to the sublimity of the human mind laying bare the secrets of the Cosmos. The two pacifists in the limelight – the British Eddington and the German-born Einstein – were particularly pleased at the reconciliation between their nations brought about by the results.

But the popular perception of the eclipse results differed quite significantly from the way they were viewed in the scientific establishment. Physicists of the day were justifiably cautious. Eddington had needed to make significant corrections to some of the measurements, for various technical reasons, and in the end decided to leave some of the Sobral data out of the calculation entirely. Many scientists were suspicious that he had cooked the books. Although the suspicion lingered for years in some quarters, in the end the results were confirmed at eclipse after eclipse with higher and higher precision.

In this cosmic ‘gravitational lens,’ a huge cluster of galaxies distorts the light from more distant galaxies into a pattern of giant arcs.  Picture Credit: NASA

Nowadays astronomers are so confident of Einstein’s theory that they rely on the bending of light by gravity to make telescopes almost as big as the Universe. When the conditions are right, gravity can shift an object’s position by far more than a microscopic amount. The ideal situation is when we look far out into space, and centre our view not on an individual star like the Sun, but on a cluster of hundreds of galaxies – with a total mass of perhaps 100 million million suns. The space-curvature of this immense ‘gravitational lens’ can gather the light from more remote objects, and focus them into brilliant curved arcs in the sky. From the size of the arcs, astronomers can ‘weigh’ the cluster of galaxies.

Einstein didn’t live long enough to see through a gravitational lens, but if he had he would definitely have approved….

Building Baby Universes

Posted in Books, Talks and Reviews, The Universe and Stuff with tags , on July 29, 2017 by telescoper

I’m going to be off on some travels soon, but before I go I’ll take the opportunity for a spot of gratuitous self-promotion. The next (August) edition of Physics World contains a review by yours truly of the book A Big Bang in a Little Room: The Quest to Create New Universes by Dr Zeeya Merali.

The above illustration accompanies the article but to find out any more you’ll have to read Physics World! 

One Day in London

Posted in Biographical, Books, Talks and Reviews with tags , , on June 15, 2017 by telescoper

As it happens, I was in London yesterday to give an Astrophysics seminar at South Kensington Technical Imperial College. In due course I’ll post the slides as I normally do on such occasions.

It was an enjoyable day, with a train journey from Cardiff nice lunch followed by a question-and-answer session with students followed by the talk followed by a cup of tea, followed by a train ride home – all (for a change) running exactly to schedule. It was also extremely hot which meant the walk between Paddington and Imperial (across Hyde Park) left me rather sweaty. Better than getting rained on I suppose.

My hosts gave me an espresso cup, with an interesting motto on the back.


Usually when I go to Imperial or thereabouts I have a minor quandary about whether to walk or take the tube, with such factors as time, weight of baggage and weather taken into consideration before making a decision. This time, however, there was no decision to make because there were problems on the Underground in the area because of the terrible fire at Grenfell Towers, which has claimed the lives of at least 17 people (and possibly many more). The fire itself was near Latimer Road station, which is not on the line I would have taken, but there were apparently fears that the building might collapse near the line (which is overground at that point) so trains were suspended all the way from Hammersmith to Edgware Road, which disrupted the running of the Circle Line.

The venue for my talk was two or three miles away from Grenfell Towers, but in mid-afternoon you could still see smoke in the distance. It was a grim sight. I think I’ll remember yesterday afternoon very well, not because I gave a seminar, but because of the terrible events that happened earlier the same day.

There are many questions that urgently require answers. How did the fire start? Why did it spread so rapidly? Did the smoke alarms work (and if not why not)? Did the cladding on the outside of the building play a role? Did the fact that there was only a single stairwell – astonishing to my mind for a 20-storey residential building – cost lives?

I hope we’ll find the answers to these questions through a proper public inquiry. In the meantime all I can do is express my deepest condolences to those bereaved by this disaster, and wish a speedy recovery for those injured. They will need to understand what happened, urgently.

On the train home yesterday I looked at Twitter and saw this picture, of grim-faced and exhausted firefighters taking a break. I found it almost unbearably moving. We take these people for granted so much of the time, but they’re heroes – every single one of them:

Wave Mechanics and Large-scale Structure

Posted in Books, Talks and Reviews, The Universe and Stuff with tags , , , on May 24, 2017 by telescoper

I thought I’d share the slides I used for the short talk I gave last Thursday at the Osservatorio Astronomico di Bologna, on the topic of Wave Mechanics and Large-scale Structure. I’ve posted about the general idea underpinning this workhere, and here are some links to references with more details of the cosmological setting, including a couple of papers by myself and Chris Short on some of whose old slides I based the talk.

http://adsabs.harvard.edu/abs/1993ApJ…416L..71W
http://adsabs.harvard.edu/abs/1997PhRvD..55.5997W
http://adsabs.harvard.edu/abs/2002MNRAS.330..421C
http://adsabs.harvard.edu/abs/2003MNRAS.342..176C
http://adsabs.harvard.edu/abs/2006JCAP…12..012S
http://adsabs.harvard.edu/abs/2006JCAP…12..016S
http://adsabs.harvard.edu/abs/2010MNRAS.402.2491J

I had a few problems with the movies during the actual talk, and they probably don’t work in this embedded version. There are a few formatting errors in the slideshare version too, but hopefully you can figure out what’s going on!