The notes are divided into four parts. Firstly I will describe the current state of knowledge in astronomy and where most research effort is being directed. Secondly I will outline my own areas of expertise. Thirdly I will describe what technologies are currently being exploited in this research. Fourthly, I will discuss the impact on society and business applications of this research, both now and in the future. 1. Astronomy and the Structure of Space The four realms of study in astronomy are: the solar system, the galaxy, the nearby Universe and cosmology. 1.1 The Solar System Studies of the solar system consists of studies of the planets, the Sun and small bodies moving around between the planets and the Sun (comets and asteroids). The size of the solar system is about 100 astronomical units (1 AU = Earth-Sun distance = 108 km = 8 light-minutes). At the centre of the solar system is the Sun, a star. This is a large mass of hydrogen undergoing nuclear burning to make helium, releasing huge amounts of energy including the light we see. In the inner solar system are four planets, Mercury (at 0.4 AU from the Sun, orbiting around it in a circle), Venus (0.7 AU), Earth (1 AU) and Mars (1.5 AU). All are spherical and made of rock. Earth and Venus have gaseous atmospheres surrounding them. Earth has a substantial moon orbiting it and Mars has two little ones. At about 3 AU from the Sun is the asteroid belt – millions of little rocks up to 1000 km in size orbiting the Sun. Occasionally one of these rocks drifts away from the belt and can become a near-earth asteroid if it comes too close to us. In the outer solar system there are also four planets, Jupiter (5 AU), Saturn (9 AU), Uranus (19 AU) and Neptune (30 AU). These are also spherical but are much bigger than the four planets in the inner solar system – the size of Jupiter is ten times that of Earth. They are made of hydrogen gas, not rock – you cannot stand on their surfaces without falling in. These outer planets have lots of moons and rings (thousands of small rocks in orbit around the planet – the rings of Saturn are particularly big and easy to see). At about 30 – 100 AU is the Kuiper Belt, which is a large collection of blocks of rocks and ice. The largest known one is Pluto at about 39 AU, with a diameter of 2200 km, but there may be bigger ones further out. Sometimes blocks of ice/rock leave the Kuiper Belt and come inwards – these are comets, and produce spectacular streams as the water gets vapourised by the Sun. Most studies of solar system objects are concerned with explaining their structure in terms of well-established physics (by well-established I mean tested to a high degree of precision in laboratories on Earth). In general the level of detail to which we are able to describe things depends on how distant the object in question is. We know a great deal about the Earth, Moon, and Sun; less about distant planets like Jupiter and Saturn; and very little indeed about Pluto and the Kuiper Belt. 1.2 Galactic Astronomy The next level of study in astronomy is that of the Milky Way, our galaxy. The Milky Way is a large number of stars (about 1011), spread out over about 1017 km. Most of the stars are normal stars like the Sun, made out of hydrogen that is undergoing nuclear burning to form helium, but a few are made of condensed matter like pure neutrons (the most extreme ones of these are black holes). Each star probably has its own solar system and planets, but even the nearest stars are too far (1013 km) to actually observe these planets with telescopes. In between the stars are lots of individual atoms (“gas”) out of which more stars are forming now. In the past the galaxy had a lot fewer stars and a lot more gas – this gas got converted to stars as the galaxy evolved. There are also a lot of dark matter particles – particles we cannot see because they emit no radiation but we know exist due to their mass and consequent gravitational pull on the stars we do see. The nature of this dark matter is a mystery. The mass of each particle is probably tiny but there are so many of them (more than 1070) that they contribute more to the mass of the galaxy than all the stars put together! Once more, the goal of most research in astronomy is to describe the structure and formation of the galaxy and its constituents in terms of well- established physical theories. This is a little more difficult than for the solar system because when we think about dark matter we are dealing with physics that is only valid under conditions that cannot be reproduced in laboratories and so is purely theoretical. One new field which has attracted much attention is that of the search for extraterrestrial intelligence. This consists of looking for non-natural (mostly radio) signals from nearby stars in the Milky Way. A positive signal – yet to be seen – would open the possibility of a totally new entity (which may or may not be biological in origin……………) 1.3 Extragalactic astronomy Around us there are many galaxies like the Milky Way, each with millions or billions of their own stars. One of the main themes of extragalactic astronomy is producing a map of the local Universe and compiling an inventory of all the different kinds of galaxy (big vs. small, spiral vs. elliptical, in a dense group with other galaxies vs. isolated). The level of completeness to which we are able to do this depends on how far out we want to survey, but we have a fairly complete picture out to about 1021 km. 1.4 Cosmology Cosmology is an extension of the ideas of the previous section to the whole observable Universe. Two basic ideas are important to keep in mind when discussing this subject. 1) The “observable Universe” is not the whole Universe. This statement can be further divided into two. The first part concerns optical light. We see that all galaxies are slowly moving apart from each other – the Universe is expanding. In the past, therefore, all galaxies were very close to each other and at this time (as was remarked in Section 1.2) they did not have stars but large numbers of individual gas atoms. All these atoms were so tightly packed that they formed a dense and opaque sheet we cannot see through with optical light (we could and do use radio waves however). The second concerns the fact that the speed of light (and of all radiation, including radio waves) is finite. This means that there is a distance we cannot see beyond using any form of radiation, corresponding to this speed of light multiplied by the age of the Universe. What is beyond this distance, there is no way to tell – we cannot even say whether the Universe is infinite or not. Hence the concept of the “observable Universe”. The size of this Observable Universe is about 1024 km. 2) When we work with big scales, the third (outward dimension) now corresponds to time, and the other two dimensions (in the plane of the sky) are the spatial ones. This was true to some extent in the previous sections but is much more important here because the scales are so big. This means that when we see other galaxies a very long way away, we are actually seeing them as they looked a long time ago, not now. These concepts naturally divide cosmological research into two kinds: observational and theoretical. Observational cosmology includes optical observations with big telescopes of galaxies a long way a way, when they were young (as we expect they have lots of gas and not many stars, and are usually very close to each other) and radio observations of the dense universe at a time when it was opaque to optical light (the “microwave background”). Theoretical cosmology is concerned with the behaviour of the whole Universe at times when it was very young and on scales much bigger than the size of the observable Universe. The goal is to formulate a theory that explains all this in a simple way and in such a way that it produces the Universe we do see at the end. Clearly it is not possible to test these theories directly in laboratories on Earth or by astronomical observations. Nevertheless it would be good to have a simple theory which explains all cosmology and at least is consistent with all laboratory physics; none exists at present but many people, like Hawking’s group in Cambridge, are exploring lots of possibilities. 1.5 Summary In summary, the basic idea of most astronomical research is to place the structure and formation of all astronomical objects (including the whole Universe) in the framework of known and well-established physics/science. Historically, this has certainly been a successful enterprise and only now, particularly in the field of theoretical cosmology, are we recognising severe limitations in our ability to achieve this. Questions that do not fit into this framework (why do we have these particular laws of physics and why not others, why does the Universe exist at all?) are not addressable by astronomy and are more in the realm of philosophy/theology. 2 My Research My own research falls into the last two categories. 2.1 Research into extragalactic astronomy In the mapping of the nearby Universe, some galaxies are easy to see (the biggest and brightest can even be seen with binoculars!) and some are very difficult. The most difficult of all are galaxies with low brightness and small numbers of stars. These are not insignificant in the census of total mass, however: there are many such galaxies and each possesses considerable amounts of dark matter (despite the fact it has so few stars). My contribution has been measuring the numbers and locations of these kinds of galaxies in the nearby Universe. This is achieved by using big CCD cameras (so we can measure large areas of the sky – the largest cameras are about 1 degree, or 1 moon diameter, in size) on large telescopes like the new 8 m Subaru Telescope in Hawaii (with such big telescopes we can see very small and faint galaxies indeed). 2.2 Research into observational cosmology One recurring problem is that many external galaxies have “dust”, particles of graphite and silicate, mixed in with the gas. This makes them individually opaque. Nevertheless, once we look at very large distances, many galaxies become like this. My work in this area is to compile a sample of these “missing” galaxies using gamma-ray bursts (GRBs), which are special kinds of exploding stars that are found using gamma-ray telescopes in space. When one of these explosions happen (they only last for a day), we then point radio, infrared, and optical telescopes at the location of the GRB in the sky long afterwards, once the GRB has finished. When we see huge amounts of radio and infrared radiation in the right proportion, this tells us that there is a big galaxy there. When we see only little optical light, this tells us there must be a lot of dust to extinguish the visible radiation from this big galaxy (radio and infrared radiation are unaffected by dust). This method of using GRBs as beacons lets us compile a sample of all galaxies at large distances, not just the ones that we can see with optical telescopes. It is still early days but it is looking more and more like dusty galaxies are the dominant kind at large distances/ early times, and galaxies we see with conventional optical telescopes are the minority. 2.3 Research into theoretical cosmology My research in theoretical cosmology is at the interface between cosmology theory and measurement and is concerned with how best to match the two. Conventionally, one formulates a theory and matches to data, allowing the data to constrain any unknown numbers, or “free parameters” in the theory. Science and engineering have basically worked well this way for a long time. However, in cosmology there are problems. What happened is that a simple theory of cosmology was established (1950s-60s) based on the well-established physics of general relativity and mathematics of space- time geometry. In the mid-1990s it became clear this theory did not work, so a more complex theory was required. Now the observational cosmology data is much better than it was then and even that complex theory is in question. We probably now have to formulate an even more complex theory. Twenty years down the road when the data is very good indeed even that one may have to be discarded and we’ll need yet another theory. This could go on and on and we’re not learning anything. The formulation I am working on is to accept that a theory of cosmology in terms of well-established theories like general relativity is not attainable and to construct a formal theory with the measurables themselves as the default parameters, not free-parameters in existing theories. Conceptually, it is quite different from the conventional approach to science (it can be thought of as a back-to-front approach) but I think that in the long term it might be profitable. Looking for correlations between measurables is the basis for this approach and that is what I spend time working on and thinking about. Here are some articles describing my work. The first two are concerned with research in extragalactic astronomy. The next two are concerned with observational cosmology. The final one is concerned is concerned with theoretical cosmology. http://xxx.lanl.gov/abs/astro-ph/0202437 http://xxx.lanl.gov/abs/astro-ph/0205060 http://www.ast.cam.ac.uk/~trentham/mjr60.ps http://xxx.lanl.gov/abs/astro-ph/0204350 http://xxx.lanl.gov/abs/astro-ph/0105404 3 Technology in Astronomy Historically, most of the technological development in astronomy has been with the building of optical telescopes, and that is still true to some extent. Putting one of these telescopes into space (to get images that are not blurred by the atmosphere), the Hubble Telescope, has required the development of special new technologies concerned with remote pointing and data collection. The sheer size of the ground-based telescopes (up to 10 m in diameter) has also posed challenges. Astronomical objects emit radiation at all wavelengths, not just visible ones, so that the construction of telescopes that operate at these other wavelengths – radio, infrared, ultraviolet, X-ray, gamma ray – has been an active area of technology development of astronomy. Some of these telescopes cannot be used on Earth because the atmosphere absorbs all the incoming radiation – this is true for infrared, X-ray, and gamma-ray telescopes. This means that the telescopes need to be put into space so they need to be placed on rockets or the Space Shuttle and this in itself requires special technologies to be developed. Here are websites for some telescopes. Keck 10 m optical telescope in Hawaii: http://www2.keck.hawaii.edu:3636/ Gemini 8 m optical telescopes in Hawaii and Chile: http://www.gemini.edu CFHT 3.6 m optical telescope in Hawaii: http://www.cfht.hawaii.edu Hubble Space Telescope: http://www.stsci.edu VLA array of 27 radio telescopes in New Mexico: http://www.aoc.nrao.edu/vla/html/VLAhome.shtml The 300 m radio dish in Arecibo, Puerto Rico: http://www.naic.edu/ Infrared space telescope to be launched in Jan 03: http://sirtf.caltech.edu/ Chandra X-ray space observatory: http://xrtpub.harvard.edu/ SWIFT space gamma-ray telescope to be launched in Sep 03: http://swift.gsfc.nasa.gov/ One recurring theme in the construction of observatories is that the mirror, detector, and launch (if a space observatory) technologies are all highly specialised and are normally worked on by independent teams. Mirrors are normally constructed out of highly polished aluminium – in order to obtain good quality astronomical images, the mirrors need to have no blemishes bigger than 0.001 mm, so that the construction and polishing much be carried out very precisely. The very largest telescopes, like the Keck 10 m telescopes, have mirrors made of many segments, since arbitrarily large pieces of glass bend under their own weight and easily pick up distortions and blemishes big enough to cause problems. Putting these segments together into a single mirror is engineering research in astronomy itself a substantial achievement. One further area of significant current interest in mirror technology is concerned with adaptive optics. The idea here is that if the mirror can be made to oscillate in an identical way to the atmosphere, much of the blurring caused by the atmosphere can be corrected for and we can generate images almost as sharp as those obtained with the Hubble Telescope. Clearly, for this to work, the mirror supports must be able to hold the mirrors (which can weigh several thousand kg) and move them about quickly in a very precise way. Construction of these supports is an extensive and costly process (though a lot cheaper than the $2 billion it took to build the Hubble Telescope and put it into operation). The purpose of the mirror is to collect light from space and focus it on to a detector. The purpose of the detector is to convert this incident light into an electronic signal as efficiently as possible while maintaining most of the spatial information (light from different bits of the sky fall on different bits of the mirror and in turn reach different bits of the array). To maintain this spatial information, detectors are normally constructed as arrays of elements. These elements are normally made of semiconductor material (at least in optical and infrared telescopes) and need to be made with a high degree of reliability and precision (both in terms of its structure so that it can fit neatly into the array, and in terms of the efficiency with which it converts radiation intensity into an electronic signal). Consequently there is has been much interaction between the astronomical instrumentation community and the semiconductor physics community. Astronomical objects emit not just radiation, but large amounts of subatomic energetic particles like neutrinos and cosmic rays. New telescopes to measure the numbers and energies of these particles have been and are being constructed. Although the mirror technology involved in building these telescopes can be quite similar to the mirror technology used in conventional optical telescopes, the detector technology is quite different. For example, to detect neutrinos, an enormous vat of water underground is used – see for example http://www.sno.phy.queensu.ca/ In summary, a large number of different types of telescopes detecting different kinds of radiation and particles have been used to build up as complete a picture as possible of the different kinds of astronomical objects. Each different kind of telescope tends to require a specific mode of construction and operation, particularly as regards the detectors. 4 Public and Commercial Interest There is considerable current public interest in astronomy, and most of our knowledge of astronomy comes from the kind of work described here. Most schoolchildren know a bit about the planets. Planetariums are very popular, as are television shows like Patrick Moore’s The Sky at Night. Books by astronomers like Stephen Hawking and Carl Sagan are amongst the non-fiction best sellers. Astronomical images are very appealing to many people, particularly the very sensitive and precise pictures from the Hubble Telescope. Here are some websites of images of astronomical objects. The first shows images from the Hubble Telescope, the others show images from ground-based telescopes. http://hubblesite.org/gallery/ http://www2.keck.hawaii.edu:3636/gen_info/kiosk/gallery.html http://www.gemini.edu/gallery/science/ http://www.ifa.hawaii.edu/users/cowie/hdf.html http://www.ast.cam.ac.uk/~wfcsur/images.php Additionally, astronomical settings seem to be very popular for film and television productions. Why this is probably has to do with the appeal of worlds and beings that are real yet fantastic (dinosaurs would be another obvious example of something that fits into this category). Providing the producers of these films and programs with as accurate a picture of extra- terrestrial words seems to be a good idea, as the ultimate credibility of a film or program depends in part on the plausibility of the setting. The astronomical research itself may even be of considerable interest – at least one successful film (Contact, based on the book by the astronomer Carl Sagan) has been made based about this subject. In a more practical application, determining the behaviour of the Sun as accurately as possible on all timescales has important commercial implications for energy production and consumption on Earth. Solar energy is certainly a plausible source and if it is to be used in a major way, it would help if the physics of the Sun were better understood, particularly as regards sunspots and the 11-year cycle in solar activity. This is both an observational and theoretical/computational exercise – the important physics in question is the behaviour of magnetic fields in a plasma that is moving in a complex but reasonably-understood way. However, I suspect all that is written above in this section will be pretty minor if one day extra-terrestrial intelligence is discovered. This would surely be one of the biggest scientific discoveries imaginable and in this event astronomy will become a major enterprise. I would expect that the sociological implications of such a discovery will very likely be huge. Pinning down the probability of this kind of discovery actually happening in any sort of rigorous way is difficult, but I would make the following comments. 1) Intelligent life almost certainly does not exist elsewhere within our solar system. If it did, we would know about it, since the solar system has been surveyed pretty well. The nearest intelligent life, if it exists, is probably to be found in or around another star in the galaxy. None of this rules out the possibility of bacteria or primitive life on Mars or elsewhere in the solar system, but I am talking about intelligent life here. 2) When extra-terrestrial intelligence is found, I think that the discovery and knowledge of the intelligence (and maybe communication) will happen a lot faster than physical contact being made with any extraterrestrial entity. The argument here follows from simple physics. Discovery will probably happen due to us picking up their light or radio signals, which travel at 300,000 km/s (the speed of light). Travel between stars is set by the gravitational pulls of all stars in the vicinity (this is what powers rockets, since they cannot carry near-infinite amounts of fuel on board), which happens at a speed of 300 km/s. The fact that signals travel at speeds so much faster than spaceships can travel means that in all probability we will know about extra-terrestrial civilisations long before we can make contact with them. 3) If discovery really is going to happen, I think it will happen reasonably soon, perhaps in the next 100 years or so. This is because we are in a period of exponential technological advancement which cannot continue indefinitely. It would surprise me if we have the technology to find extra-terrestrials 1000 years from now, but not in 100 years (of course, I may be completely wrong here). 4) My personal guess is that the probability of a discovery being made, even in the next 100 years is not high, certainly not more than a few percent (again, I could easily be wrong…………).
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