<html><head /> <body> <META http-equiv="Content-Type" content="text/html; charset=UTF-16"><title>What Do Physicists Actually Do?</title><meta name="keywords" content="physics,science,astrophysics,Atom,behavior,behaviour,biography,biology,cavendish,coast,cosmology,electron,environmental,esem,experiment,future,futurology,hubble,knot,laboratory,longair,low-temperature,malcolm,mechanical,microscope,particle,physicist,polymer,quantum,research,scanning,scuba,semiconductor,supercomputer,technology,telescope,theory,tie,"><table style="font-family:Verdana; font-size:larger; " align="center" border="0" width="50%"><tbody><tr> <td style="background-color:silver; border-color:white; border-left-style:none; border-style:none; " width="730"><span style="font-family:Verdana; font-size:larger; ">What Do Physicists Actually Do?</span></td> </tr> <tr> </tr> </tbody></table><br> <table style="font-family:Verdana; font-size:medium; " align="center" bgcolor="white" border="0" width="50%"><tbody><tr> <td height="131" width="669"><p><span style="font-family:Verdana; font-size:x-small;"><strong>Editors Introduction </strong></span><span style="font-family:Verdana; font-size:x-small; "><a href="1542_intro_LG.html" target="_browser"><img src="1542_intro.gif" align="right" vspace="10"> </a> In this story Malcolm Longair gives a visual overview of research at the Cavendish Laboratory, Cambridge. He shows that physics is an extensive subject with the potential of providing key insights into topics as diverse as cosmology, biology and economics. Longair also emphasizes the creative aspect of physics research as well as its social and economic impact.</span><br> <br> <span style="font-family:Verdana; font-size:x-small; ">In the Cavendish Laboratory, research is organised into 10 major research groups:</span></p> <p align="center"><br> <span style="font-family:Verdana; font-size:x-small; "><IMG src="1542_slide15.jpg" id="2027" type="3" align="center" width="350" height="263" url="1542_slide15.jpg"></span></p> <p><span style="font-family:Verdana; font-size:x-small; ">Altogether there are about 695 people working in the laboratory, including all the research workers, support staff and graduate students. I will risk making some guesses about how the subject is likely to develop in the future on the basis of some of the most successful areas today.</span><br> <br> <span style="font-family:Verdana; font-size:x-small; ">I will start with two examples in which we are simply doing what physicists have always done: exploring new regions of parameter space, taking the types of experiments we have done in the past and pushing them to much more extreme values. For example, in the High Energy Physics Group, here is a list of the various experiments involved in their core programme:</span></p> <p align="center"><br> <span style="font-family:Verdana; font-size:x-small; "><IMG src="1542_Slide16.jpg" id="2029" type="3" align="center" width="350" height="263" name="" url="1542_Slide16.jpg"></span></p> <p><span style="font-family:Verdana; font-size:x-small; ">The programme involves huge projects like ATLAS for the Large Hadron Collider, the LHCb experiment and so forth. The aim is to study particle interactions at higher and higher energies, and there are very clear objectives. For example, the experiment should discover the Higgs boson, or else there will be something seriously amiss with the standard model of particle physics.</span><br> <br> <span style="font-family:Verdana; font-size:x-small; ">This is obviously one of the great goals of the programme, but one hopes that it will find lots more besides. There are many different types of hypothetical particles which might be out there, and we will have at least a further decade increase in particle energy in which to explore what may well turn out to be quite new physics. The few-billion-dollar range is probably the upper limit that we can reasonably hope to be funded for such pure science experiments, provided we play our cards as well as we possibly can. One of the challenges for particle physicists will be to find ways of achieving yet higher energies more cheaply.</span></p> <p align="center"><br> <span style="font-family:Verdana; font-size:x-small; "><IMG src="1542_Slide20.jpg" id="2031" type="3" align="center" width="360" height="270" name="" url="1542_Slide20.jpg"></span></p> <p><span style="font-family:Verdana; font-size:x-small; ">Let us look at another classic area, low-temperature physics. It is a subject which has been developing remarkably in recent years. My colleagues are now able to study the properties of materials at temperatures below 2 millikelvin, in magnetic fields up to 18.4 tesla, at pressures up to about 1000 kbar and with high-sensitivity detectors. When they enter these regions of parameter space they are discovering completely new states of matter. It is one of the most exciting developments in physics. The physics involves the quantum mechanics of large numbers of very strongly correlated electrons. This is a beautiful example of entering new regions of physics, because they have been able to control extremely well all these variable parameters simultaneously.</span></p> <p align="center"><br> <span style="font-family:Verdana; font-size:x-small; "><IMG src="1542_Slide21.jpg" id="2032" type="3" align="center" width="360" height="270" name="" url="1542_Slide21.jpg"></span></p> <p><span style="font-family:Verdana; font-size:x-small; ">In fact, this is part of a huge new area of strongly correlated electron physics. What this means is that, whereas one could do rather well theoretically when all these effects were relatively weak, now we are dealing with very strong interactions between many electrons. This crops up all over the place, in many of the key problems of modern physics. For example, high-temperature superconductivity is one of the really great, unsolved problems, and unquestionably involves the study of strongly correlated electrons. There is a need for a new theory of metals, meaning that we need much more than simply a degenerate gas of normal electrons. Some of the concepts and ideas involving strongly correlated electrons may also be relevant for biophysics. They may crop up in completely different guises, but the basic physical processes may well be relevant in these areas.</span><br> <br> <span style="font-family:Verdana; font-size:x-small; ">These two cases are classic examples of one way in which physics will advance in the coming years.</span></p> <p align="center"><br> <span style="font-family:Verdana; font-size:x-small; "><IMG src="1542_Slide22.jpg" id="2033" type="3" align="center" width="360" height="270" name="" url="1542_Slide22.jpg"></span></p> <p><span style="font-family:Verdana; font-size:x-small; ">Having mentioned strongly correlated electron physics, it is appropriate to look at the activities of the Theory of Condensed Matter Group. One example of the sorts of things which are now going on in the laboratory, and which indicates an important direction in which physics will develop, is the study of complex processes in solids. This has become possible because of the development of supercomputers. Nowadays it is possible to carry out computations of the quantum mechanical behaviour of large numbers of atoms using parallel computing techniques.</span></p> <p align="center"><br> <span style="font-family:Verdana; font-size:x-small; "><IMG src="1542_Slide23.jpg" id="2034" type="3" align="center" width="360" height="270" name="" url="1542_Slide23.jpg"></span></p> <p><span style="font-family:Verdana; font-size:x-small; ">This simulation shows how the process of diffusion of aluminium atoms takes place over an aluminium surface. The process of diffusion takes place by an atom pushing its way into the lattice and pushing up an atom along a diagonal from the lower layers. When we add the extra atom, it results in the surface melting at about 600 degrees Kelvin. The same process takes place for holes in the lattice. Removing an atom from the lattice restores the sort of crystalline structure that was present at the lower temperature. This is a splendid example of somewhat unexpected physics being discovered by supercomputer simulations.</span><br> <br> <span style="font-family:Verdana; font-size:x-small; ">Mike Payne and his colleagues can now simulate the quantum mechanical behaviour of a few hundred atoms, the number simply being limited by the available computer power. They have developed powerful programmes for drug design in which they carry out complete quantum mechanical simulations of how you can make drugs with specific properties. There is a huge future for these types of activities, which I unquestionably regard as physics. The physics lies in being able to understand the collective quantum behaviour of very large numbers of particles.</span><br> <br> <span style="font-family:Verdana; font-size:x-small; ">There are other interesting items on this list. Biological physics is cropping up all over the place at the moment. The trouble is that biology is a really huge subject, and if you look at what people call biological physics, it means almost as many different things as physics itself.</span><br> <br> <span style="font-family:Verdana; font-size:x-small; ">I should also draw your attention to the group working on nonlinear dynamics and nonequilibrium statistical mechanics. Two members of the group, Thomas Fink and Yong Mao, produced one of the best-selling science publications of last year, a splendid book called <i>The 85 Ways to Tie a Tie</i>. This work came out of research involving the dynamics and topology of polymer chains. In the process, they had to understand knots, and so they classified all the possible ways you can tie a tie. Of the 85 ways, only about five are any good, but they did find a new one, which is not in common use.</span><br> <br> <span style="font-family:Verdana; font-size:x-small; ">The interesting thing about <i>The 85 Ways to Tie a Tie</i> is that it is excellent theoretical physics but equally illustrates the power of knot theory. It makes the discipline accessible to the other sciences. Knot theory is central to ideas in particle physics and topology, and I am sure more people will gain an understanding from the tying of ties than from reading the technical literature. The practical example captures the essence of knot theory. It is a lovely example of the multidimensional way in which physics research works.</span></p> <p align="center"><br> <span style="font-family:Verdana; font-size:x-small; "><IMG src="1542_Slide26.jpg" id="2036" type="3" align="center" width="360" height="270" name="" url="1542_Slide26.jpg"></span></p> <p><span style="font-family:Verdana; font-size:x-small; ">Having mentioned polymers, let me now look at the physics being carried out in the Polymers and Colloids Group. These topics do not appear particularly prominently in undergraduate physics courses, but it is a huge and important area. Under the topic Granular Materials, for example, Athene Donald and her colleagues have been studying the physics of chocolate and concrete, neither of which are particularly well understood, because they are systems of great complexity. Companies are interested in making chocolate which will not melt in your pocket, and that is a physics problem. Likewise, people don't really understand how concrete works. There are complex processes going on in the physics of these materials.</span></p> <p align="center"><br> <span style="font-family:Verdana; font-size:x-small; "><IMG src="1542_Slide27.jpg" id="2037" type="3" align="center" width="360" height="270" name="" url="1542_Slide27.jpg"></span></p> <p><span style="font-family:Verdana; font-size:x-small; ">Athene Donald and her colleagues are pioneering the study of what is called an environmental scanning electron microscope (ESEM). In ordinary electron microscopy, the samples have to be coated, magnified and photographed by bombarding the sample with electrons. With ESEM, the substances can be kept hydrated and the techniques of electron microscopy used to study essentially living organisms. There is a whole sequence of chambers at different pressures within the microscope, so that the electrons still form a collimated beam by the time they reach the hydrated specimen.</span><br> <br> <span style="font-family:Verdana; font-size:x-small; ">The sorts of things they are doing are quite remarkable. For example, they're studying the physics of water chestnuts, which is of the greatest interest because, unlike most vegetables, you can boil a water chestnut and it will not go mushy. Why is it that water chestnuts have physical properties which enable them to maintain their crunchy structure? That is a physics problem. There are clearly very strong links with biophysics, because of the ability to keep samples hydrated while they are being studied.</span></p> <p align="center"><br> <span style="font-family:Verdana; font-size:x-small; "><IMG src="1542_Slide28.jpg" id="2039" type="3" align="center" width="360" height="270" name="" url="1542_Slide28.jpg"></span></p> <p><span style="font-family:Verdana; font-size:x-small; ">Another large group interested in polymers is the Optoelectronics Group, headed by Richard Friend. He and his colleagues have made enormous strides in developing polymer optoelectronic materials which behave like semiconductors. This is one of those great success stories. They have developed these organic polymer semiconductor devices to the point where they can produce more light than traditional semiconductor devices. Already Philips uses organic polymers in the backlighting displays of their mobile phones.</span><br> <br> <span style="font-family:Verdana; font-size:x-small; ">The group is now going on to use similar polymer materials combined with inkjet printing to print semiconductor electronic circuits. The organic polymers can be used in the guns of an inkjet printer, and you can then simply print an electronic circuit using inkjet technology. From a point of view of the electronics industry, these are very important developments.</span><br> <br> <span style="font-family:Verdana; font-size:x-small; ">The interesting thing is that they do not fully understand how these materials work physically. Despite the fact that they've had this tremendous success, the physical processes responsible for achieving these enormous quantum efficiencies are not fully understood. We can foresee enormous advances in these areas in the coming years. Notice the very strong link with chemistry, since these new classes of polymers are synthesised by the experts in the Melville Laboratory for Polymer Synthesis.</span></p> <p align="center"><br> <span style="font-family:Verdana; font-size:x-small; "><IMG src="1542_Slide29.jpg" id="2046" type="3" align="center" width="360" height="270" name="" url="1542_Slide29.jpg"></span></p> <p><span style="font-family:Verdana; font-size:x-small; ">Mentioning semiconductors leads naturally to the Semiconductor Physics Group, where some remarkable new physics is being discovered. Again, you should compare the items on this list with what is in the standard physics course.</span></p> <p align="center"><br> <span style="font-family:Verdana; font-size:x-small; "><IMG src="1542_Slide30.jpg" id="2048" type="3" align="center" width="360" height="270" name="" url="1542_Slide30.jpg"></span></p> <p><span style="font-family:Verdana; font-size:x-small; ">Mike Pepper has succeeded in developing a large semiconductor fabrication facility within the laboratory--in fact, the largest facility in any university department in the country--for creating designer semiconductor structures in 3D. They can build devices on the nanoscale and fabricate and inspect them by carrying out a long series of processes in one sweep through an ultra-high vacuum system. There are huge numbers of examples of what they can do; here is one example of what happens when simple quantum wires are studied at very low temperatures.</span></p> <p align="center"><br> <span style="font-family:Verdana; font-size:x-small; "><IMG src="1542_Slide31.jpg" id="2051" type="3" align="center" width="360" height="270" name="" url="1542_Slide31.jpg"></span></p> <p><span style="font-family:Verdana; font-size:x-small; ">This illustrates the quantisation of resistance at low temperatures at which the electronic properties are dominated by quantum mechanics. The resistance goes up in steps rather than being a continuous function of the voltage. The resistance increases in multiples of 2e<sup>2</sup>/h, and so is intimately related to fundamental physics. One of the areas which Mike and his colleagues are studying extensively is the determination of absolute standards of current and of resistance on the basis of this type of quantised phenomenon.</span></p> <p align="center"><br> <span style="font-family:Verdana; font-size:x-small; "><IMG src="1542_Slide32.jpg" id="2055" type="3" align="center" width="360" height="270" name="" url="1542_Slide32.jpg"></span></p> <p><span style="font-family:Verdana; font-size:x-small; ">Another remarkable set of experiments concerns the Fractional Quantum Hall Effect, in which a 2D semiconductor structure is placed in a strong magnetic field. This links back to a topic I mentioned earlier in the context of low-temperature physics. In these materials, complicated body behaviour of strongly correlated electrons is central to understanding the physical processes which are observed in these materials.</span><br> <br> <span style="font-family:Verdana; font-size:x-small; ">You will have guessed that I had eventually to get to astrophysics and cosmology, my own areas of research. I will describe one or two examples of the sort of things we do in the Cavendish Astrophysics Group which may come as a bit of a surprise compared with the conventional way of thinking about astronomy and astrophysics.</span></p> <p align="center"><br> <span style="font-family:Verdana; font-size:x-small; "><IMG src="1542_Slide35.jpg" id="2059" type="3" align="center" width="360" height="270" name="" url="1542_Slide35.jpg"></span></p> <p><span style="font-family:Verdana; font-size:x-small; ">Many of the areas listed on the slide are the sorts of things that you would expect to see in the Astrophysics Group. But you will also see on the list geometric algebra and inferential science. This illustrates the extensive nature of the subject. These areas are studied in the Astrophysics Group because they came out of problems which arose in studying phenomena of astrophysics. In the case of inferential science, David MacKay is doing remarkable work in understanding the fundamental limits to information transfer. Within the last six months he has broken the records for error-correcting codes by a significant factor. Geometric algebra came about because of the enthusiasm of Anthony Lasenby and Steve Gull. These mathematical techniques proved a convenient tool for studying specific problems, and it has now built up its own momentum. It is being applied successfully to areas such as computer vision, by people like Chris Doran.</span><br> <br> <span style="font-family:Verdana; font-size:x-small; ">Then there are the things you would expect to find in an Astrophysics Group: submillimetre wave instrumentation, star formation, the origin of galaxies and galaxy formation. Let me give some examples of the programmes which are currently being pursued and which have implications beyond our immediate scientific objectives.</span></p> <p align="center"><br> <span style="font-family:Verdana; font-size:x-small; "><IMG src="1542_Slide36.jpg" id="2060" type="3" align="center" width="360" height="270" name="" url="1542_Slide36.jpg"></span></p> <p><span style="font-family:Verdana; font-size:x-small; ">Everyone knows the wonderful picture of the Hubble Deep Field. It is one of the great observations in astronomy. When I was over at the Space Telescope Science Institute two years ago, I asked the extragalactic astronomers how many galaxies they expected to see in the Hubble Deep Field. You simply ask, "Supposing the universe is isotropic and uniform, and that the co-moving number density of galaxies did not change with time, how many galaxies would you expect to see?" The answer is only about 30 to 50. In fact, in the Hubble Deep Field, there are about 3,000 galaxies. The two big surprises are the large numbers of small blue objects and the large fraction of irregular systems which are present on this image. In fact, we are looking so far back in time that we are observing the galaxies being put together, the blueness being simply a signature of the fact that, in the process, they are forming stars.</span></p> <p align="center"><br> <span style="font-family:Verdana; font-size:x-small; "><IMG src="1542_Slide37.jpg" id="2061" type="3" align="center" width="360" height="270" name="" url="1542_Slide37.jpg"></span></p> <p><span style="font-family:Verdana; font-size:x-small; ">This is a wonderful story, but the big trouble is that, whenever we study star formation regions, there is always lots of dust present. In fact, we now understand that dust is an essential ingredient of the star-formation process--stars are formed deeply embedded inside dust clouds, and so we must take account of the fact that the optical and ultraviolet light are strongly attenuated by dust in star-forming galaxies. The dust is heated up and the energy is reradiated in the far infrared regions of the spectrum. Long before the Hubble Deep Field was observed, Andrew Blain and I did numerous calculations to show why you should really do cosmology in the submillimetre region of the spectrum, because the dust becomes transparent in these wavebands.</span></p> <p align="center"><br> <span style="font-family:Verdana; font-size:x-small; "><IMG src="1542_Slide38.jpg" id="2064" type="3" align="center" width="360" height="270" name="" url="1542_Slide38.jpg"></span></p> <p><span style="font-family:Verdana; font-size:x-small; ">A couple of years ago, we were part of a team which used the world's largest submillimetre telescope, the James Clerk Maxwell Telescope in Hawaii, to observe the Hubble Deep Field with an instrument called SCUBA, the first submillimetre camera ever built. Notice the link to the high technology of low-temperature physics. The focal plain detector array in SCUBA has 91 elements on one side and 37 elements on the other. These are maintained at 0.1 kelvin for very long periods. We discovered that much more energy is being emitted in the far infrared waveband than there is in the optical image of the Hubble Deep Field. This has profound implications for the study of when the stars and elements formed in galaxies and opens up whole new areas of study.</span></p> <p align="center"><br> <span style="font-family:Verdana; font-size:x-small; "><IMG src="1542_Slide42.jpg" id="2067" type="3" align="center" width="360" height="270" name="" url="1542_Slide42.jpg"></span></p> <p><span style="font-family:Verdana; font-size:x-small; ">This work depends on the development of millimetre and submillimetre technology, and the next picture shows one of the junctions which are used in the Submillimetre Technology Section of the Astrophysics Group. The superconducting junction is placed at the end of a horn, which focuses the submillimetre radiation onto it. At the same time, the Semiconductor Physics Group was investigating the use of the same technology for medical purposes. In the example shown in the image, a tooth is investigated by optical and terahertz waves. By studying the absorption and time of travel of the waves through the tooth, you can see that there is a cavity inside the tooth which has been detected noninvasively by the submillimetre waves. It is very exciting that we can carry out both cosmology and dentistry using the same technology.</span></p> <p align="center"><br> <span style="font-family:Verdana; font-size:x-small; "><IMG src="1542_Slide43.jpg" id="2068" type="3" align="center" width="360" height="270" name="" url="1542_Slide43.jpg"></span></p> <p><span style="font-family:Verdana; font-size:x-small; ">A second example from the Astrophysics Group concerns the cosmic microwave background radiation. The Cosmic Background Explorer of NASA was launched in 1989 and produced the first detailed map with very high sensitivity of the cosmic background radiation.</span></p> <p align="center"><br> <span style="font-family:Verdana; font-size:x-small; "><IMG src="1542_Slide44.jpg" id="2069" type="3" align="center" width="360" height="270" name="" url="1542_Slide44.jpg"></span></p> <p><span style="font-family:Verdana; font-size:x-small; ">The radiation has a quite remarkably uniform brightness distribution over the whole sky, at a temperature of about 2.725 degrees Kelvin. To see any structure, you have to look at intensity levels, which are only one part in a hundred thousandth of the total intensity.</span><br> <br> <span style="font-family:Verdana; font-size:x-small; ">You must take my word for it that I could convince you that this was emitted when the universe was only 300,000 years old. It propagated directly from that last scattering surface to the earth, since there is nothing between the observer on earth and the last scattering surface to absorb it. The little ripples we see on that surface are images of the earliest seeds of the formation of the large-scale structures we see in the universe today. The image therefore contains very important clues about the physics of the very early universe.</span></p> <p align="center"><br> <span style="font-family:Verdana; font-size:x-small; "><IMG src="1542_Slide50.jpg" id="2070" type="3" align="center" width="360" height="270" name="" url="1542_Slide50.jpg"></span></p> <p align="left"><span style="font-family:Verdana; font-size:x-small; ">The Cavendish Astrophysics Group is carrying out its own experiment on these fluctuations, and it is just in the process of coming on line in Tenerife. The picture shows the types of high technology we have been developing to capitalise upon our expertise in aperture synthesis telescope systems.</span></p> <p align="center"><br> <span style="font-family:Verdana; font-size:x-small; "><IMG src="1542_Slide54.jpg" id="2071" type="3" align="center" width="360" height="270" name="" url="1542_Slide54.jpg"></span></p> <p><span style="font-family:Verdana; font-size:x-small; ">Finally, let us look briefly at the Cambridge Optical Aperture Synthesis Telescope (COAST) optical interferometer, which was developed out of expertise in aperture synthesis techniques, the idea that you can build large telescopes out of little telescopes. John Baldwin realised that you could use the same tricks for optical as well as for radio interferometry. Already the COAST telescope array, which is located at the Lord's Bridge Observatory, just outside Cambridge, has taken images which are 10 times sharper than the Hubble Space Telescope.</span></p> <p align="center"><br> <span style="font-family:Verdana; font-size:x-small; "><IMG src="1542_Slide55.jpg" id="2073" type="3" align="center" width="360" height="270" name="" url="1542_Slide55.jpg"></span></p> <p><span style="font-family:Verdana; font-size:x-small; ">Here, for example, are some of the first images that were obtained of the binary star Capella by COAST. You can see the two stars of Capella rotating about each other in their binary orbit. In the same way, we can now observe changes in the surface features of Betelgeuse, a red giant star.</span></p> <p align="center"><br> <span style="font-family:Verdana; font-size:x-small; "><IMG src="1542_Slide56.jpg" id="2072" type="3" align="center" width="360" height="270" name="" url="1542_Slide56.jpg"></span></p> <p><span style="font-family:Verdana; font-size:x-small; ">Over a period of a few days, huge cells appear and disappear on its surface. This is not particularly unexpected, because these red giants are expected to have large convective cells in their extended atmospheres. What we are seeing is material being convected in gigantic convection cells to the surface of the star. The theory of stellar evolution is worked out on the basis that these are spherically symmetric stars. What these observations show is that they aren't precisely spherically symmetric, and you have to ask what effect that has on their evolution.</span><br> <br> <span style="font-family:Verdana; font-size:x-small; font-style:italic; ">This story is taken from a lecture given by Malcolm Longair at the London School of Economic and Political Science on May 15, 2000. Copyright The London School of Economics and Political Science.</span></p></td> </tr> </tbody></table> </body></html>