Archive for the Books, Talks and Reviews Category

That was the Science Week that was..

Posted in Books, Talks and Reviews, The Universe and Stuff with tags , , , on November 15, 2019 by telescoper


So, as advertised, this morning I gave a talk mainly to school students as part of Science Week Ireland on the subject of the cosmic web. This was a similar talk to the one I gave at DIAS a couple of weeks ago.

 

There was a slight confusion about rooms but we did eventually get everyone into the right lecture theatre and weren’t too late getting started. The audience was about 140, so the room was very full and most of them didn’t fall asleep. I had a nice chat afterwards with a group of them and they seemed to have enjoyed it. Anyway, in case anyone is interested here are my slides. Most of them are recycled from previous versions of this talk.

Following this morning’s exertions we had lovely seminar after lunch by Wyn Evans of Cambridge about the stellar dynamics of the Milky Way and the wonders of Gaia and soon will be going to dinner.

The Cosmic Web in Maynooth

Posted in Books, Talks and Reviews, Talks and Reviews, The Universe and Stuff with tags , , on November 5, 2019 by telescoper

Next week (10th to 17th November) in Ireland is Science Week and this will be celebrated by a number of events here in Maynooth, among which is a talk by yours truly on 15th November:

Here is a short description:

How can we map the distribution of galaxies over thousands of millions of light years? What does the Universe look like on these scales? How did get to look like that? And how do we know?This talk will explain how astronomers and cosmologists have come together over the past couple of decades to make huge surveys of the Universe, revealing the existence of a complex but beautiful `Cosmic Web’ with vast chains of galaxies strung out around immense dark voids. These observational breakthroughs have been mirrored by advances in theory and computer simulation that allow us to understand how this amazing structure was born 14 billion years ago in the Big Bang and has been growing and evolving ever since. Free and open to TY, 5th and 6th year students, this talk will be of particular interest in those interested astronomy, space, physics and the Universe itself!

It is on in the morning to make it possible for school students to attend and the talk is adapted to this audience, so it won’t be the same as the one I gave in Dublin last week. The timing seems to have worked because the lecture theatre has over 200 seats in it but is already almost full. There are still a few places available so if you’re in the area you can book here.

 

 

The Cosmic Web at DIAS

Posted in Books, Talks and Reviews, The Universe and Stuff with tags , , on November 1, 2019 by telescoper

Yesterday evening found me at the Dublin Institute for Advanced Studies, complete with scary Hallowe’en beard, to give a talk.

Picture Credit: Prof. Luke Drury

It was a nice friendly audience and we had a lot of interesting discussions afterwards. As usual on such occasions I’ve put up the slides in case anyone wants to see them:

After the talk I headed back to Maynooth. It was a very rainy night, but at least some of the fireworks were going off despite the potential for damp squibs.

Dark Matter Day at DIAS

Posted in Books, Talks and Reviews, Talks and Reviews, The Universe and Stuff with tags , , on October 7, 2019 by telescoper

Just a quick post to mention that I’m giving a public talk at the Dublin Institute for Advanced Studies (DIAS) on Dark Matter Day, October 31st 2019, coincidentally the same day as Halloween. I am particularly grateful to be invited to give a talk that evening because it allows me to avoid getting involved in trick-or-treat or any of that nonsense.

Here is the nice advert the people at DIAS have made for the event:

The talk is free, but you need to sign up here as the venue is not infinitely large. You can also find some more details about the talk there.

Found in Translation…

Posted in Books, Books, Talks and Reviews, Maynooth with tags , on August 7, 2019 by telescoper

Here I am, back in Maynooth, after taking the early flight back to Dublin from rainy Cardiff. By way of a gentle re-introduction to the habit of blogging after a gap of a week or so I thought I’d mention something I discovered when I returned:

This pleasant surprise was a package from Oxford University Press containing five copies of the new Turkish edition of my book  Cosmology: A Very Short Introduction.I don’t know if there are any staff or students in Maynooth who (a) can read Turkish and (b) are interested in cosmology but if there are please contact me and you can have a copy!

(I’m particularly intrigued by how the first two words of the sub-title are to be pronounced…)

Anyway, I thought it would be nice to show some of the other translations of this book. This one is in Arabic. I was a bit confused when I first saw this edition, because books in Arabic open the opposite way to books in English, as Arabic is read from right to left rather than from left to right.

VSI-Arabic

The following are in Korean, Bulgarian, Bosnian, Dutch and Czech, respectively:

vsi_6

vsi_2

vsi_3

Vsi_5

vsi_4

Anyway, I’m due to finish the 2nd Edition  – which will be a completely new book rather than an update – by the end of next month so hopefully there will be translations of the new version in due course!

The Observer and the Eclipse

Posted in Books, Talks and Reviews, History, The Universe and Stuff with tags , , on May 12, 2019 by telescoper

Not surprisingly, given that the centenary is fast approaching, pieces are appearing in the mainstream media about the 1919 Eclipse Expeditions that first measured the deflection of light by the Sun’s gravitational field. One such article, by Robin McKie, appears in today’s Observer. It’s a nice piece, though it concentrates almost entirely on Eddington’s measurements taken at Principe. In fact it was Crommelin’s measurements from Sobral that proved decisive.

Anyway, the article gives me a (very brief) mention courtesy of the piece I wrote in Nature a few weeks ago:

For many years at Cardiff I ran an undergraduate project in which the students had to reanalyze the measurements from the eclipse expeditions. That is possible because all the necessary star positions are tabulated in the paper by Dyson et al. (1920). It is undoubtedly the case that Eddington had to improvise a bit because of the unexpected problems that arose in the field, but this is actually quite normal. As a famous general put it `No plan of battle survives first contact with the enemy’. I remain convinced that Eddington didn’t do anything dodgy, but you don’t have to take my word for it: if you don’t believe me then go ahead and look at the data yourself! At the very least you will then understand what a difficult experiment this was!

Approaching the Centenary of the 1919 Eclipse Expeditions

Posted in Books, Talks and Reviews, History, The Universe and Stuff on April 4, 2019 by telescoper

Just a brief post to alert my readers – both of them – to the fact that there’s a very big centenary celebration coming up, on May 29th. This is 100 years to the day since a total eclipse of the Sun provided the opportunity to test Albert Einstein’s (then) new theory of general relativity. This was the event that turned Einstein into a cultural icon. I’ll be posting about a number of things to commemorate this important happening – include some new things that I’ve been working on to do with this, and an event here in Maynooth – but for the mean time let me just mention a couple of imminent items.

One is that I am giving a 30-minute talk on the 1919 Eclipse Expeditions at the Ordinary Meeting of the Royal Astronomical Society in Burlington House in London on 12th April 2019 (that’s a week tomorrow). That’s the closest date to the centenary that could be managed, as the May meeting of the RAS is the Annual General Meeting at which there is no scientific programme and there are no meetings after that until October 2019.

The second thing is that I’ve written a review of three books based on the 1919 expeditions for Nature, which I’m told will be the lead piece in their Spring Books supplement, published on April 18th 2019.

Anyway, all this provides me with a good excuse to repost an old item here. 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.

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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….