Archive for Martin Rees

Science, Religion and Henry Gee

Posted in Bad Statistics, Books, Talks and Reviews, Science Politics, The Universe and Stuff with tags , , , , , , , , , on September 23, 2013 by telescoper

Last week a piece appeared on the Grauniad website by Henry Gee who is a Senior Editor at the magazine Nature.  I was prepared to get a bit snarky about the article when I saw the title, as it reminded me of an old  rant about science being just a kind of religion by Simon Jenkins that got me quite annoyed a few years ago. Henry Gee’s article, however, is actually rather more coherent than that and  not really deserving of some of the invective being flung at it.

For example, here’s an excerpt that I almost agree with:

One thing that never gets emphasised enough in science, or in schools, or anywhere else, is that no matter how fancy-schmancy your statistical technique, the output is always a probability level (a P-value), the “significance” of which is left for you to judge – based on nothing more concrete or substantive than a feeling, based on the imponderables of personal or shared experience. Statistics, and therefore science, can only advise on probability – they cannot determine The Truth. And Truth, with a capital T, is forever just beyond one’s grasp.

I’ve made the point on this blog many times that, although statistical reasoning lies at the heart of the scientific method, we don’t do anywhere near enough  to teach students how to use probability properly; nor do scientists do enough to explain the uncertainties in their results to decision makers and the general public.  I also agree with the concluding thought, that science isn’t about absolute truths. Unfortunately, Gee undermines his credibility by equating statistical reasoning with p-values which, in my opinion, are a frequentist aberration that contributes greatly to the public misunderstanding of science. Worse, he even gets the wrong statistics wrong…

But the main thing that bothers me about Gee’s article is that he blames scientists for promulgating the myth of “science-as-religion”. I don’t think that’s fair at all. Most scientists I know are perfectly well aware of the limitations of what they do. It’s really the media that want to portray everything in simple black and white terms. Some scientists play along, of course, as I comment upon below, but most of us are not priests but pragmatatists.

Anyway, this episode gives me the excuse to point out  that I ended a book I wrote in 1998 with a discussion of the image of science as a kind of priesthood which it seems apt to repeat here. The book was about the famous eclipse expedition of 1919 that provided some degree of experimental confirmation of Einstein’s general theory of relativity and which I blogged about at some length last year, on its 90th anniversary.

I decided to post the last few paragraphs here to show that I do think there is a valuable point to be made out of the scientist-as-priest idea. It’s to do with the responsibility scientists have to be honest about the limitations of their research and the uncertainties that surround any new discovery. Science has done great things for humanity, but it is fallible. Too many scientists are too certain about things that are far from proven. This can be damaging to science itself, as well as to the public perception of it. Bandwagons proliferate, stifling original ideas and leading to the construction of self-serving cartels. This is a fertile environment for conspiracy theories to flourish.

To my mind the thing  that really separates science from religion is that science is an investigative process, not a collection of truths. Each answer simply opens up more questions.  The public tends to see science as a collection of “facts” rather than a process of investigation. The scientific method has taught us a great deal about the way our Universe works, not through the exercise of blind faith but through the painstaking interplay of theory, experiment and observation.

This is what I wrote in 1998:

Science does not deal with ‘rights’ and ‘wrongs’. It deals instead with descriptions of reality that are either ‘useful’ or ‘not useful’. Newton’s theory of gravity was not shown to be ‘wrong’ by the eclipse expedition. It was merely shown that there were some phenomena it could not describe, and for which a more sophisticated theory was required. But Newton’s theory still yields perfectly reliable predictions in many situations, including, for example, the timing of total solar eclipses. When a theory is shown to be useful in a wide range of situations, it becomes part of our standard model of the world. But this doesn’t make it true, because we will never know whether future experiments may supersede it. It may well be the case that physical situations will be found where general relativity is supplanted by another theory of gravity. Indeed, physicists already know that Einstein’s theory breaks down when matter is so dense that quantum effects become important. Einstein himself realised that this would probably happen to his theory.

Putting together the material for this book, I was struck by the many parallels between the events of 1919 and coverage of similar topics in the newspapers of 1999. One of the hot topics for the media in January 1999, for example, has been the discovery by an international team of astronomers that distant exploding stars called supernovae are much fainter than had been predicted. To cut a long story short, this means that these objects are thought to be much further away than expected. The inference then is that not only is the Universe expanding, but it is doing so at a faster and faster rate as time passes. In other words, the Universe is accelerating. The only way that modern theories can account for this acceleration is to suggest that there is an additional source of energy pervading the very vacuum of space. These observations therefore hold profound implications for fundamental physics.

As always seems to be the case, the press present these observations as bald facts. As an astrophysicist, I know very well that they are far from unchallenged by the astronomical community. Lively debates about these results occur regularly at scientific meetings, and their status is far from established. In fact, only a year or two ago, precisely the same team was arguing for exactly the opposite conclusion based on their earlier data. But the media don’t seem to like representing science the way it actually is, as an arena in which ideas are vigorously debated and each result is presented with caveats and careful analysis of possible error. They prefer instead to portray scientists as priests, laying down the law without equivocation. The more esoteric the theory, the further it is beyond the grasp of the non-specialist, the more exalted is the priest. It is not that the public want to know – they want not to know but to believe.

Things seem to have been the same in 1919. Although the results from Sobral and Principe had then not received independent confirmation from other experiments, just as the new supernova experiments have not, they were still presented to the public at large as being definitive proof of something very profound. That the eclipse measurements later received confirmation is not the point. This kind of reporting can elevate scientists, at least temporarily, to the priesthood, but does nothing to bridge the ever-widening gap between what scientists do and what the public think they do.

As we enter a new Millennium, science continues to expand into areas still further beyond the comprehension of the general public. Particle physicists want to understand the structure of matter on tinier and tinier scales of length and time. Astronomers want to know how stars, galaxies  and life itself came into being. But not only is the theoretical ambition of science getting bigger. Experimental tests of modern particle theories require methods capable of probing objects a tiny fraction of the size of the nucleus of an atom. With devices such as the Hubble Space Telescope, astronomers can gather light that comes from sources so distant that it has taken most of the age of the Universe to reach us from them. But extending these experimental methods still further will require yet more money to be spent. At the same time that science reaches further and further beyond the general public, the more it relies on their taxes.

Many modern scientists themselves play a dangerous game with the truth, pushing their results one-sidedly into the media as part of the cut-throat battle for a share of scarce research funding. There may be short-term rewards, in grants and TV appearances, but in the long run the impact on the relationship between science and society can only be bad. The public responded to Einstein with unqualified admiration, but Big Science later gave the world nuclear weapons. The distorted image of scientist-as-priest is likely to lead only to alienation and further loss of public respect. Science is not a religion, and should not pretend to be one.

PS. You will note that I was voicing doubts about the interpretation of the early results from supernovae  in 1998 that suggested the universe might be accelerating and that dark energy might be the reason for its behaviour. Although more evidence supporting this interpretation has since emerged from WMAP and other sources, I remain sceptical that we cosmologists are on the right track about this. Don’t get me wrong – I think the standard cosmological model is the best working hypothesis we have _ I just think we’re probably missing some important pieces of the puzzle. I don’t apologise for that. I think sceptical is what a scientist should be.

Last Week of Term

Posted in Biographical, Education, The Universe and Stuff with tags , , , , , on March 26, 2012 by telescoper

So the glorious weather continues. Unfortunately, unlike most UK universities, we’re not finished for Easter yet; at Cardiff University we only get three weeks for the Easter recess instead of the four that colleagues over the border seem to enjoy.

One of the consequences of this is that the annual National Astronomy Meeting (NAM) often falls in Cardiff term time. This year NAM is taking place in the fine city of Manchester (which, for those of you unfamiliar with British geography, is in the Midlands). Many colleagues in the School of Physics & Astronomy are attending NAM, and most of my research group are either there already or travelling up today. I particularly wish Jo and Ian well when they give their talks; one of the excellent things about NAM is the opportunity it offers for younger researchers to talk about their work to a large audience. Nerve-wracking, no doubt, but invaluable experience.

I’m not going to NAM this year because I have too much to do back here at the ranch, including filling in a few lectures for staff who are away.  I’m always reluctant to cancel lectures during term-time, but in the current spell of good weather I doubt if any students would complain too much! I did a cosmology lecture this morning – only the second I’ve done here – and it the room was uncomfortably stuffy. A few of the students failed to fall asleep, however, so I regard that as a major success.

It’s strange how often good weather coincides with times of great stress for students. I recall that most of my undergraduate examinations took place in glorious sunshine, which seemed to have been laid on by some malevolent being to make us suffer. This week our students have project reports and presentations to worry about and other coursework to finish before term ends, as well as revision for the exams that take place in May; being couped up inside is no fun on days like this and I’m sure they’d prefer it to be raining outside so as not to distract them from the tasks in hand…

It’s so quiet around here today that it occurred to me now would be a good time to stage a Coup d’Etat. Come to thank of it, there’s a Staff Meeting  been called on Wednesday which may well amount to something pretty similar…

Anyway, those of us around today have a nice event this evening to look forward to, a lecture by Lord Rees followed by a nice dinner in Aberdare Hall. Here’s the invitation:

You’ll see that this is organized “in association with The Learned Society for Wales“, which I only just learned about when I saw it on the invitation!

Anyway, the prospect of a slap-up dinner persuaded me to just have a sandwich for lunch. Now that’s eaten methinks I’ll get back to work!

UPDATE: It was indeed a very interesting and entertaining lecture by Lord Rees; here he is, in action, watched by Prof. Disney…

Gravity and Grace

Posted in Biographical, The Universe and Stuff with tags , , , , , on April 26, 2011 by telescoper

This morning I came across the following quotation, which is translated from the book Le Pesanteur et la Grace (i.e. “Gravity and Grace“), written in 1947 by French philosopher Simone Weil:

Science today must search for a source of inspiration higher than itself or it must perish.

Science offers only three points of interest: 1. technical applications; 2. as a game of chess; 3. as a way to God.

I’m not sure I agree with what is written, and in any case the options don’t seem to me to be mutually exclusive, but a number of things did strike me reading it.

For a start, and for what it’s worth, I do think science has value within itself, so I’m at odds a bit with the initial premise. On the other hand, science is a human activity and it therefore doesn’t stand apart from other thing humans are interested in.

Then there is the extent to which we now all have to pretend that pretty much the only point of interest in science is “1. technical applications”. I don’t believe that’s true, actually, and I’m worried that by continually saying that it is, scientists might be sowing the seeds of their own destruction.

And then there’s “the game of chess”. I’m actually hopeless at chess, but I understand this as representing some form of abstract mental challenge.  If that’s what it does mean, then I’d agree that’s probably what got me interested in science. I’ve always been pathologically interested in puzzles. When I look at galaxies and stars, I don’t tend to gaze at them in awe at their enormity or beauty, I just tend to wonder how they work and what they’re made of. I don’t really mind people having a sense of awe, of course, but there’s a danger that if we take that too far we end up being over-awed which might make us shy away from the biggest questions. To me the Universe is just a great big puzzle, though it’s actually rather a tough one. I’m still stuck on 1 across, in fact…

Finally, we have science as “a way to God”. I find it quite interesting that a Christian philosopher could present science as that, especially when so many of my atheistic colleagues regard science and religion as polar opposites. It seems likely to me that anyone who studies science primarily as a means of finding God is probably in for a disappointment. I’m reminded of a quote  from Thomas à Kempis I learned at school:

The humble knowledge of thyself is a surer way to God than the deepest search after science.

But that’s not to say that science and religion are incompatible with each other. I think they’re basically orthogonal, although in an abstract space with an extremely complicated geometry…

One of the interesting things about working in cosmology is that the big questions are very big indeed, which may be the reason why cosmologists tend to have strong views on matters of religion (and metaphysics in a general sense).  Just take the Templeton Prize, for example. The arguments about this year’s award to Lord (Martin) Rees are still simmering on, but it’s worth remembering that many recent winners of this prize, including John Barrow (my PhD supervisor, in fact) and  George Ellis (former collaborator of mine), are most noted for their work in cosmology. Both are religious: John Barrow is a member of the United Reformed Church, and George Ellis is a Quaker. Martin Rees is an atheist. But their religious views are not in conflict with their research. All are outstanding scientists.

I’ve been thinking a lot over the Easter holiday about religion and science. It’s partly the Templeton prize saga, partly the occasion of Easter itself, and partly the fact that I’ve been reading even more of the poems of R.S. Thomas. In case you didn’t know I was brought up in the (Anglican) Christian tradition, attended Sunday School, sang in the local Church Choir, and was confirmed in the Church of England. When I went to seconday school – the Royal Grammar School, Newcastle – I joined the Christian Union and remained in it for 3-4 years.

Although  I was immersed in Christianity – the Christian Union was vigorously Evangelical – it didn’t really stick and eventually all melted away.   I don’t really remember precisely what it was then that made me turn away from religion, although the sins of the flesh might have had something to do with it…

However, although I became an atheist I’ve never been a particularly devout one. The only thing that I’m really sure about is that I don’t know the answers. Does that make me an agnostic rather than an atheist? I don’t know. Perhaps I could just describe myself as a non-believer? That wouldn’t do either, because we all have to believe in some things in order to function at all. Even science starts with unprovable axioms.

A career in cosmology has given me the opportunity to think about many Big Questions. Why does the Universe have laws? Why is there something rather than nothing? And so on. I’m not much of a philosopher, though, and  I don’t have the answers. I do, however, refuse to take the easy way out by denying that the questions have meaning. Of course it’s not entirely satisfactory having to answer “I don’t know”, but I don’t agree with those of my atheist colleagues who think religion is an easy way out. I’m sure that a thinking Christian has just as many difficult issues to grapple with as a thinking atheist. Not thinking at all is the only really easy way out.

A few years ago I spoke at an interesting meeting in Cambridge entitled God or Multiverse? In fact there’s a picture below of the panel discussion at the end -I’m second from the right:

I thought it was an interesting dialogue, but I have to say that, if anything, it strengthened my non-belief. Prof. Keith Ward argued that the primary motivation for belief in God was the existence of “Good”. I have to admit that I find the Universe as a whole amoral and although humans have done good from time to time they have done evil in at least equal measure. The vast majority of people on this Earth live in poverty, many of them in abject misery. Good is a bad word to describe this state of affairs.

I just can’t accept the idea of a God that is interested in the Universe at the level of human beings. We’re so insignificant on the scale of the cosmos, that it seems very arrogant to me to suppose that it’s really got much to do with us. We appeared somehow, miraculously perhaps, but could disappear just as easily. I doubt the Universe would miss us much.

But I might be wrong.

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Mud Wrestling and Microwaves

Posted in The Universe and Stuff with tags , , , on January 13, 2011 by telescoper

Reading through an interesting blog post about the new results from Planck by the ever-reliable Jonathan Amos (the BBC’s very own “spaceman”), I was reminded of a comment I heard made by Martin Rees (now Lord Rees) many years ago.

The remark concerned the difference between cosmology and astrophysics. Cosmology, said Lord Rees, especially the part of it that concerns the very early Universe, involves abstract mathematical concepts, difficult yet logical reasoning and the ability to see deep things in complicated spatial patterns. In that respect it’s rather like chess. Astrophysics, on the other hand, which is not at all elegant and has so many messy complications that it is sometimes difficult even to work out what is going on or what the rules are, is more like mud wrestling.

The following image, which I borrowed from Jonathan Amos’ piece, explains why I was reminded of this and why some cosmologists are having to abandon chess for mud wrestling, at least for the time being. The picture shows the nine individual frequency maps (spanning the range from 30 GHz to 857 GHz) obtained by Planck.

What we cosmologists really want to see is a pristine map of the cosmic microwave background, the black-body radiation that pervades the entire Universe. It’s black body form means that it would have the same brightness temperature across all frequencies, and would also be statistically homogeneous (i.e. looking roughly the same all across the sky).

What you actually see is a mess. There are strong contributions from the disk of our own Galaxy, some of it extending quite a way above and below the plane of the Milky Way. You can also see complicated residuals produced by the way Planck scans the sky. On top of that there is radiation from individual sources within our Galaxy, other Galaxies and even clusters of Galaxies (which I mentioned a couple of days ago). These “contaminants” constitute valuable raw material for astronomers of various sorts, but for cosmologists they are an unwanted nuisance. Unfortunately, there is no other way to reach the jewels of the CMB than by hacking through this daunting jungle of foregrounds and instrumental artefacts.

Looking at the picture might induce one of two reactions. One would be to assume that there’s no way that all the crud can be removed with sufficient accuracy and precision to do cosmology with what’s left. Another is  to appreciate how well cosmologists have done with previous datasets, especially WMAP, have confidence that they’ll solve the numerous problems associated with the Planck data, but understand why  will take another two years of high-powered data analysis by a very large number of very bright people to extract cosmological results from Planck.

There might be gold at the end of the pipeline, but until then it’s going to be mud, glorious mud…


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Science as a Religion

Posted in Books, Talks and Reviews, Science Politics, The Universe and Stuff with tags , , , , , , , on July 6, 2010 by telescoper

With the reaction to Simon Jenkins’ rant about science being just a kind of religion gradually abating, I suddenly remembered that I ended a book I wrote in 1998 with a discussion of the image of science as a kind of priesthood. The book was about the famous eclipse expedition of 1919 that provided some degree of experimental confirmation of Einstein’s general theory of relativity and which I blogged about at some length last year, on its 90th anniversary.

I decided to post the last few paragraphs here to show that I do think there is a valuable point that Simon Jenkins could have made out of the scientist-as-priest idea. It’s to do with the responsibility scientists have to be honest about the limitations of their research and the uncertainties that surround any new discovery. Science has done great things for humanity, but it is fallible. Too many scientists are too certain about things that are far from proven. This can be damaging to science itself, as well as to the public perception of it. Bandwagons proliferate, stifling original ideas and leading to the construction of self-serving cartels. This is a fertile environment for conspiracy theories to flourish.

To my mind the thing  that really separates science from religion is that science is an investigative process, not a collection of truths. Each answer simply opens up more questions.  The public tends to see science as a collection of “facts” rather than a process of investigation. The scientific method has taught us a great deal about the way our Universe works, not through the exercise of blind faith but through the painstaking interplay of theory, experiment and observation.

This is what I wrote in 1998:

Science does not deal with ‘rights’ and ‘wrongs’. It deals instead with descriptions of reality that are either ‘useful’ or ‘not useful’. Newton’s theory of gravity was not shown to be ‘wrong’ by the eclipse expedition. It was merely shown that there were some phenomena it could not describe, and for which a more sophisticated theory was required. But Newton’s theory still yields perfectly reliable predictions in many situations, including, for example, the timing of total solar eclipses. When a theory is shown to be useful in a wide range of situations, it becomes part of our standard model of the world. But this doesn’t make it true, because we will never know whether future experiments may supersede it. It may well be the case that physical situations will be found where general relativity is supplanted by another theory of gravity. Indeed, physicists already know that Einstein’s theory breaks down when matter is so dense that quantum effects become important. Einstein himself realised that this would probably happen to his theory.

Putting together the material for this book, I was struck by the many parallels between the events of 1919 and coverage of similar topics in the newspapers of 1999. One of the hot topics for the media in January 1999, for example, has been the discovery by an international team of astronomers that distant exploding stars called supernovae are much fainter than had been predicted. To cut a long story short, this means that these objects are thought to be much further away than expected. The inference then is that not only is the Universe expanding, but it is doing so at a faster and faster rate as time passes. In other words, the Universe is accelerating. The only way that modern theories can account for this acceleration is to suggest that there is an additional source of energy pervading the very vacuum of space. These observations therefore hold profound implications for fundamental physics.

As always seems to be the case, the press present these observations as bald facts. As an astrophysicist, I know very well that they are far from unchallenged by the astronomical community. Lively debates about these results occur regularly at scientific meetings, and their status is far from established. In fact, only a year or two ago, precisely the same team was arguing for exactly the opposite conclusion based on their earlier data. But the media don’t seem to like representing science the way it actually is, as an arena in which ideas are vigorously debated and each result is presented with caveats and careful analysis of possible error. They prefer instead to portray scientists as priests, laying down the law without equivocation. The more esoteric the theory, the further it is beyond the grasp of the non-specialist, the more exalted is the priest. It is not that the public want to know – they want not to know but to believe.

Things seem to have been the same in 1919. Although the results from Sobral and Principe had then not received independent confirmation from other experiments, just as the new supernova experiments have not, they were still presented to the public at large as being definitive proof of something very profound. That the eclipse measurements later received confirmation is not the point. This kind of reporting can elevate scientists, at least temporarily, to the priesthood, but does nothing to bridge the ever-widening gap between what scientists do and what the public think they do.

As we enter a new Millennium, science continues to expand into areas still further beyond the comprehension of the general public. Particle physicists want to understand the structure of matter on tinier and tinier scales of length and time. Astronomers want to know how stars, galaxies  and life itself came into being. But not only is the theoretical ambition of science getting bigger. Experimental tests of modern particle theories require methods capable of probing objects a tiny fraction of the size of the nucleus of an atom. With devices such as the Hubble Space Telescope, astronomers can gather light that comes from sources so distant that it has taken most of the age of the Universe to reach us from them. But extending these experimental methods still further will require yet more money to be spent. At the same time that science reaches further and further beyond the general public, the more it relies on their taxes.

Many modern scientists themselves play a dangerous game with the truth, pushing their results one-sidedly into the media as part of the cut-throat battle for a share of scarce research funding. There may be short-term rewards, in grants and TV appearances, but in the long run the impact on the relationship between science and society can only be bad. The public responded to Einstein with unqualified admiration, but Big Science later gave the world nuclear weapons. The distorted image of scientist-as-priest is likely to lead only to alienation and further loss of public respect. Science is not a religion, and should not pretend to be one.

PS. You will note that I was voicing doubts about the interpretation of the early results from supernovae  in 1998 that suggested the universe might be accelerating and that dark energy might be the reason for its behaviour. Although more evidence supporting this interpretation has since emerged from WMAP and other sources, I remain skeptical that we cosmologists are on the right track about this. Don’t get me wrong – I think the standard cosmological model is the best working hypothesis we have _ I just think we’re probably missing some important pieces of the puzzle. I don’t apologise for that. I think skeptical is what a scientist should be.

Water and Energy

Posted in Biographical, Science Politics, The Universe and Stuff with tags , , , , , on May 25, 2010 by telescoper

I’ve refrained from blogging about the fraught history of my attempts to have a new  gas boiler installed in my house. Today, however, at last I have finally succeed in getting a state-of-the-art high-efficiency condensing contraption fit for the 21st Century, which will hopefully save me a few bob in gas bills over the winter but, more importantly, actually produce hot water for more than a minute or so without switching itself off.

The chaps that did the job for me actually had to test all the radiators too, which meant switching them all up to maximum. It wasn’t quite as hot today as it was yesterday but nevertheless the inside of the house was like a Turkish bath for a while. I therefore sat outside in the Sun for a bit waiting for them to get finished and tidy everything up.

While I was sitting there I got thinking about sustainable energy and so on, and was reminded of a comment Martin Rees made in his Reith Lecture not long ago. Wanting to sound positive about renewable energy he referred to the prospect of generating significant tidal power using a Severn Barrage. Given the local relevance to Cardiff – one of the main ideas is a barrage right across the Severn Estuary from Cardiff to Weston-super-Mare -so he presumably thought he was on safe ground mentioning it. In fact there was a lot of uneasy shuffling in seats at that point and the question session at the end generated some tersely sceptical comments. Many locals are not at all happy about the possible environmental impact of the Severn Barrage. That, and the cost – probably in excess of £20 billion – has to be set against the fact that such a barrage could in principle generate 2GW average power from an entirely renewable source. This would reduce our dependence on fossil fuels and increase our energy security too. The resources probably aren’t available right now given the parlous state of the public finances, but I’m glad that the Welsh Assembly Government is backing serious study of the various options. It may be that it won’t be long before we’re forced to think about it anyway. The Wikipedia page on the various proposals for a Severn Barrage is very comprehensive, so I won’t rehearse the arguments here. In any case, I’m no engineer and can’t comment on the specifics of the technology required to construct, e.g., a tidal-stream generator. However, I have to say that I find the idea pretty compelling, provided ways can be found to mitigate its environmental impact.

For a start it’s instructive to look at turbine-generated power. Wind turbines  are cropping up around the British isles, either individually or in wind farms. A  typical wind turbine can generate about 1MW in favourable weather conditions, but it needs an awful lot of them to produce anything like the power of a conventional power station. They’re also relatively unpredictable so can’t be relied upon on their own for continuous power generation. The power P available from a wind turbine is given roughly by

P \simeq \frac{1}{2} \epsilon \rho A v^3

where v is the wind speed, A is the area of the turbine, \rho is the density of air, which is about 1.2 kg per cubic metre, and \epsilon is the efficiency with which the turbine converts the kinetic energy of the air into useable electricity.

The same formula would apply to a turbine placed in water, immediately showing the advantage of tidal power.  For comparable efficiencies and sizes the ratio of power generated in a tidal-stream turbine to a wind turbine would be

\frac{P_{t}}{P_{w}}\simeq \frac{\rho_{t}}{\rho_{w}} \left( \frac{v_{t}}{v_{w}}\right)^{3}

The speed of the water in a tidal stream can be comparable to the airspeed in a moderate wind, in which case the term in brackets doesn’t matter and it’s just the ratio of the densities of water and air that counts, and that’s a large number! Of course wind speed can sometimes be larger than the fastest tidal current, but wind turbines don’t work efficiently in such conditions and in any case it isn’t the v which provides the killer factor. The density of sea water is about 1025 kg per cubic metre, a thousand times greater than that of air. To get the same energy output from air as from a tidal stream you would need to have winds blowing steadily ten times the velocity of the stream, which would be about 80 knots for the Severn. More than breezy!

Not all proposals for the Severn Barrage involve tidal stream turbines. Some exploit the gravitational potential energy rather than the kinetic energy of the water by exploiting the vertical rise and fall during a tidal cycle rather than the horizontal flow. The energy to be exploited in, for example, a tidal basin of area A  would go as

E \simeq \frac{1}{2} \epsilon A\rho gh^{2}

where h is the vertical tidal range, about 8 metres for the Severn Estuary, and g is the acceleration due to gravity. The average power generated would be found by dividing this amount of energy by 12 hours, the time between successive high tides. It remains to be seen whether tidal basin or lagoon based on this principle emerges as competitive.

Another thing that struck me doodling these things on the back of an envelope in the garden is that this sort of thing is what we should be getting physics students to think about. I’m quite ashamed to admit that we don’t…

A Reith Lecture

Posted in Politics, The Universe and Stuff with tags , , on May 13, 2010 by telescoper

I’m a bit late getting around to blogging today, primarily because I spent the evening at a lecture by Martin Rees. Not just any lecture, but one of the annual series of Reith Lectures that he has been chosen to present this year. This event took place in the splendid Reardon Smith Theatre in the National Museum in Cardiff, and was preceded by a wine reception where we mingled amongst the relics of Welsh prehistory. The audience for the lecture  included academics, politicians, journalists and students and there was a lively question-and-answer session afterwards.

The Reith Lectures were inaugurated in 1948 by the BBC to mark the historic contribution made to public service broadcasting by Sir John (later Lord) Reith, the corporation’s first director-general. John Reith maintained that broadcasting should be a public service which enriches the intellectual and cultural life of the nation. It is in this spirit that the BBC each year invites a leading figure to deliver a series of lectures on radio. The aim is to advance public understanding and debate about significant issues of contemporary interest.

The very first Reith lecturer was the philosopher, Bertrand Russell who spoke on “Authority and the Individual”. Among his successors were Arnold Toynbee (The World and the West, 1952), Robert Oppenheimer (Science and the Common Understanding, 1953) and J.K. Galbraith (The New Industrial State, 1966). More recently, the Reith lectures have been delivered by the Chief Rabbi, Dr Jonathan Sacks (The Persistence of Faith, 1990) and Dr Steve Jones (The Language of the Genes, 1991). Since 2002, the Reith Lectures have been presented as was tonight’s,  by Sue Lawley.

I think this is the first time any of these lectures have been delivered in Cardiff. Martin Rees is, in fact, almost a Welshman himself ,  being born in Ludlow in Shropshire only about a mile the wrong side of the border; since being elevated to the peerage a few years ago, he is now known as Baron Rees of Ludlow. He is, of course, an immensely distinguished astrophysicist (he has been Astronomer Royal since 1995) but now has a broader portfolio of responsibility in the higher echelons of British science as President of the Royal Society.

As well as being an eminent scientist, Martin Rees is also a very fine public speaker, possessing an effortless gravitas that  any politician would die for.  He speaks with great clarity, thoughtfully and to the point, but with an economical use of language. He comes across as not only highly intelligent , which he undoubtedly is, but also deeply humane, another rare combination. Martin Rees was therefore an excellent choice to give the Reith Lectures. I had been looking forward to the evening for months after I got a phone call from Auntie Beeb asking me if I’d like to attend.

His lecture this evening wasn’t about astrophysics, and neither are the others in the series which has the pretty vague overall title Scientific Horizons. This lecture, the second of the series of four, was entitled Surviving the Century,and it concerned the role of science in identifying and possibly counteracting the threats facing humanity over the next few decades. He touched on climate change, renewable energy, and the possibility of nuclear or bio-terrorism. Although he spelled out the dangers in pretty stark terms he nevertheless claimed to be an optimist to the extent that he believed science could find solutions to the most pressing problems facing our planet, but I also sensed he was more of a pessimist as to whether the necessary measures could be implemented owing to socio-economic and political constraints. Science is vital to safeguarding the future of the planet, but it isn’t sufficient. People need to change the way they live their lives.

I won’t say any more about the lecture – or the interesting audience discussion that followed it – because you’ll be able to hear it yourselves on BBC Radio 4. The Lectures will be broadcast at 9am on Radio 4 starting on Tuesday 1st June (Lecture 1, called The Scientific Citizen). The lecture I attended tonight will be broadcast at the same time the following week (8th June). Lectures 3 and 4 will follow on 15th and 22nd June. Of course they will also be available as podcasts from the BBC website. If you want to be informed, enriched and challenged then I recommend you check them out.

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