TRANSFORMATION BY CHALLENGE

CHAPTER 5G

TRANSFORMATION BY CHALLENGE

One of the ways in which exposure to unusual circumstances serves as a catalyst in the process of conceptual transformation is that it can help turn theoretical science into experimental science. To illustrate how space science plays that role, let us consider Einstein's General Theory of Relativity. Perhaps the most important insight of this theory is that the geometry of space and time (spacetime) is affected by the amount and distribution of matter (or rather, mass-energy) throughout it. This point is difficult to grasp but it can be illustrated by means of the following analogy. On the surface of a regular coffee cup draw two points and trace the shortest line between them. The length of this line is going to be independent of the amount of coffee in the cup. Similarly, we would expect the properties of space and time to be independent of the "stuff" that makes up the universe. But consider now that the cup is made of some highly elastic material (say, the rubber used in toy balloons). In such a case not only the length of the line but the very shape of the path will be determined by the amount of coffee and by the way we squeeze the liquid about in the cup. Just as the geometry of the cup is affected by the liquid in it, Einstein might say, the geometry of spacetime is affected in a similar way by the matter in it. Thus the paths that light follows (geodesics) will vary from region to region; the universe as a whole will be curved; and time will slow down in the presence of strong gravitational fields (for it will be as if light had fallen into a deep hole-- and so it will take longer to come out of it--which means that even the most efficient clock, using light signals, would measure time more slowly).

To put it in a nutshell, the theory claims that the geometry of spacetime tells matter how to behave and that matter tells spacetime how to curve. Massive objects thus distort the geometry of spacetime (this is the effect of gravitational fields). And such geometry (or "shape", to state it colloquially) determines, for instance, how light can move through different regions of the universe. Near the Earth spacetime is almost flat, and thus it is very difficult to perform experiments to test Einstein's insights. As a result, for a long time there were only three tests of the theory. The most famous checked the prediction that stars directly behind the sun should appear shifted to the side of the sun. This should be expected, if the theory is correct, because the mass of the sun carves a sort of a basin out of the fabric of spacetime. Light coming very near the sun would follow the contours of the basin, and thus be deflected; but it would also be "delayed", for it now has longer to travel. Unfortunately, the sunlight does not permit a check of this prediction except during eclipses. Even then tests were difficult. Nonetheless, they favored Einstein's theory, since during eclipses the stars in very close proximity to the sun were seen shifted away from it within the range of Einstein's prediction.

With the advent of space exploration, however, relevant and far more precise tests can become almost routine. Einstein's prediction is not really limited to light, but extends rather to all electromagnetic radiation, of which visible light is only one form. Thus we can test Einstein’s theory by tracking the radio signals of satellites that circle the sun, or the radio signals from the Viking landers on the surface of Mars when Mars goes behind the sun. That is, we can check not only the prediction about the deflection of light but also about its delay.

We can also check some other startling predictions of the theory, such as the claim that gravity slows time (for clocks should then move faster the further away from massive bodies). Although it is possible to make this last kind of test using only terrestrial science, space offers much greater sophistication and permits far more ambitious developments along these lines. Already it permits us to use very precise clocks in spaceships whose distance from several points is determined to high accuracy by tracking stations using lasers. The advances in chronometry are respectable enough that the entire field goes beyond applied science into engineering.[i]

Of extraordinary importance would be the discovery of gravity waves, for they would provide an entire new window to the universe since matter is transparent to them. Joseph Weber and others have tried to detect gravitational waves by means of extremely sensitive aluminum cylinders and other ingenious devices. Unfortunately the problem of discriminating between true gravitational waves and "noise" caused by other factors has rendered inconclusive the results of most experiments along these lines. In space, however, the availability of very large baselines, e.g. between a station near the earth and a spaceship, permit us to search for gravity waves of different frequencies. Just as Weber expected his cylinders to vibrate whenever a gravity wave went by, we could expect the station-spaceship baseline to oscillate whenever we observe gravitational events of cataclysmic proportions. The opportunity to observe such events will be offered by space- based telescopes trained on pulsars, the vicinity of possible black holes, and other cases of very dense matter, all of which would allow us to see just how well Einstein's ideas fit the world, and to correct or replace them as circumstances and our imagination dictate.

In addition to all this, space exploration makes possible what some like to call "crucial experiments" between General Relativity and some of its sophisticated competitors. Dicke's theory of gravitation, for example, predicted many of the results of Einstein's that we have already discussed. But it differed in some respects. In particular, it predicted that the Moon's orbit is deflected toward the sun. The predicted change in that orbit was so small, however, that a test was out of the question until the landing of Apollo 11 on the Moon. The first humans on the Moon installed a reflector (the first of a series now in place) for a laser beam from Earth. This special equipment has permitted extremely precise measurements of the distance between the Moon and the Earth, thus setting up an experiment that pits Dicke's theory against Einstein's. Einstein's won.

In this new era of telescopes we have also been able to perform some striking confirmations of Einstein’s theory. For example, the theory predicts that large masses may serve as “lenses.” Essentially, a large mass conveniently situated in the line sight between a source of light and the observer will split the light around its body. We have now been able to observe this gravitational lensing on many occasions.

As in these cases, such experimental work is not only entirely new but often requires the contribution of space science. And the most fascinating experiments are yet to come. Of particular significance is Gravity Probe B, the orbiting gyro experiment directed by Francis Everitt at Stanford University. This experiment is now testing the general theory of relativity in two most significant respects (it was originally scheduled to be launched by the shuttle in the late 1980s, but it has finally be placed in orbit only recently). According to Einstein's view, the distribution of mass determines the geometry of space-time. But when a big mass rotates, it places space-time in motion as well, that is, it drags space-time along. To make a very precise calculation of the value of the drag we have to know very precisely the values of the mass and the rotation involved. These values have been determined for the Earth, which also has a mass big enough to permit, according to the theory, a small but detectable amount of space-time drag. Four small, nearly perfect spheres – gyroscopes – placed in polar orbit would have their rotational motions affected by such a drag. The object of the experiment is to measure that effect on the rotation--more specifically, the precession of the spheres with respect to the fixed stars--and see how it agrees with the values predicted by the theory.

It is perhaps ironic that this experiment so much resembles one of the most celebrated experiments of the 19th century, the Michelson-Morley experiment, which by failing to detect any ether drag later made more acceptable to many physicists Einstein's special theory of relativity. By giving real properties to space-time in his general theory, it seems that Einstein introduced into physics something that performed functions in the new theory not unlike those of the ether in the old. Now his own general relativity will be put to a similar test. Unfortunately for Everitt and his team, space shuttle delayed his experiments so much that different experiments, using telescopes, have apparently demonstrated this drag already.

In any event, Everitt’s experiment has a double purpose. It also aims to measure a most startling prediction of the general theory of relativity. When an electrically charged body rotates, it produces a magnetic field. Because of the structure of general relativity, we can ascribe a similar effect to rotating gravitational masses. That is, a field should be produced that would create torques on the orbiting gyroscope (this would lead to what is called the "gravito-magnetic precession of the gyroscope"). A positive result of this experiment would confirm the existence of magnetic-like properties of gravity, a discovery of the most extraordinary importance.

A great deal of advanced technology has been necessary in this experiment, involving sometimes a million-fold improvement in precision over previous technology. The four spheres so perfect that, if you blew one up to the size of the Earth, it would not show a deviation from the average radius larger than two feet. Such sphere must be suspended without friction, and its minute precessions must be measured (one of 6.9 arcseconds per year, the other 0.05 arcseconds per year). These specifications can be met in space after considerable ingenuity and effort. The quartz spheres are coated with metal and suspended by the action of small electric fields. Their rotation is monitored thanks to the fact that since it will be electrically charged and rotating it will produce a small magnetic field.

On the Earth thousands of volts would be required to keep the spheres suspended, with many unwelcome side-effects added to a variety of disturbances typical of the environment--atmospheric, seismic, human, and so on. But even if all those things are accounted for, gravity alone would demand a degree of perfection in the spheres simply unattainable. The reason is that insofar as the spheres are less than absolutely perfect their individual center of mass will vary slightly from the center of a perfect sphere of the same radius. The stronger the gravitational field, the larger the rotational distortion produced by such a variation. Given the desired experimental performance – 3 x 10^-11 degrees per hour – under the gravitational acceleration of the Earth, the deviation in radius at any one point cannot be larger than 10^-16 of the radius, which in this case it means that the deviation must be less than 1/1000 of a nuclear diameter. That is plain out of the question. By contrast, in orbit the deviation must be less than 10^-6, which is difficult but possible to achieve.

The Chinese physicist Ning Li has suggested a radically different way of investigating this prediction drawn from the mathematics of Einstein’s theory. If her analysis is correct, the effect could be shown by a far smaller mass (at the atomic level) made to rotate extremely fast by a superconductor. Her experiment can be carried out on Earth, but even if she is successful, we should acknowledge that space science has blazed the trail that she later followed to recreate the experiment in a different setting.

The full-fledged development of space astronomy and space physics will enhance in a myriad of ways the dialectical relationships between different levels of studying the universe. As we have already mentioned, for example, in the solar system we find clues about the rest of the universe, and our general cosmology affects our ideas of the solar system. In a similar fashion, terrestrial physics and astrophysics have been intertwined since the beginnings of the Copernican revolution. Space physics promises to make that relationship even more intimate. And this is all we need to answer the queries about the long-term consequences of the changes in points of view that space may bring about.

The future contribution of space to this new approach to experimental gravitation will not be independent of the explosive growth expected of space astronomy. An accurate determination of the relevant masses is essential to the study of these peculiar gravitational phenomena. But to make such determination we must also determine, for example, stellar distances and magnitudes very accurately. This will be the minimum benefit from the more powerful and more varied astronomy that will supplement from space the work of astronomers on the ground. And of course we wish to examine the instances of massive gravitational collapse. Even though a black hole does not permit radiation to escape – the curvature of its disturbance of space-time is so pronounced that we might say a black hole is a bottomless pit – it nevertheless makes itself known by the collapse of the matter around it. The gravitational force is so strong that great energy is released as matter sinks into the black hole. That energy can be detected with X-ray telescopes, and so the search for strong sources of X- rays becomes greatly significant.

Space science is thus becoming a significant factor in the ingenious attempt to turn a very theoretical subject into an experimental science, and in some cases into a branch of engineering. We can see the emergence of a familiar pattern: theory leads to new practical concerns, and those practical concerns in turn put us in a position to test theory – sometimes the same theory, sometimes theories in other fields. It is this rather complicated connection between theory and practical concern that eventually forces theory to work under circumstances different from those of its origin. Our views of the universe have permitted us to build the spaceships and the instruments to challenge many other views that we also hold. Ultimately the ensuing transformation will lead to a new round of challenge, and the dynamic character of science will be preserved. This task will be aided in no small measure by the other great advantage of space science: by escaping from the confines of our own planet it removes barriers and gives us a larger perspective.

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[i] For an account see Carroll O. Alley, “Proper Time Experiments in Gravitational Fields with Atomic Clocks, Aircraft, and Laser Light Pulses,” a lecture published in Quantum Optics, Experimental Gravitation, and Measurement Theory, P. Meystre and M. O. Scully, eds., Plenum Publishing Co., New York: 1982.

Cosmology and the Allegory of the Cave

Chapter 5F

Cosmology and the Allegory of the Cave

As I mentioned in the previous posting, the more details we know about the universe the more hints we benefit from in trying to devise new theories to explain its origin and its evolution. And of course we have seen already that space physics and space astronomy are essential if we are to attain a worthwhile understanding of the nature of the universe (cosmology), for much of the critical information is transmitted in wavelengths that our atmosphere keeps from Earth-bound instruments. And to those two space sciences we should add astro-chemistry, for this other science is necessary if we are to understand the composition of the galactic medium, for example.

Furthermore, it is not plausible to say that we have a complete idea of the nature of the universe unless we have a far better understanding of phenomena such as quasars and black holes which obviously may have great consequences for our theories of gravitation, for what decent idea of the universe would ignore the gravity that holds it together? Nor is it plausible to hold onto certain ideas of the origins of the universe without the guidance of reliable theories of gravitation. As we will see below, space science is essential not only for the study of violent events like quasars and black holes but for the more general task of transforming our theories of gravitation. Thus, since unification schemes must deal with questions of the origin and evolution of the universe, space astronomy is clearly fundamental science by even the narrowest and strictest of criteria. Much rides on the telescopes that our rockets may take into the heavens.

To summarize this point, since cosmology is essential to the completion of the program of unification in physics, it is also essential to the pursuit of fundamental physics, even by notions of pre-Dark-Matter-Dark-Energy days. Thus even if we accept the most extreme view, that particle physics is the most fundamental science, it seems that space science is unavoidable, and therefore just as fundamental. Our investigation of the microcosm eventually takes us to the stars.

Of course, there is the possibility that all present unification schemes are entirely misguided. But if that is so, space astronomy will be particularly helpful in pointing to areas of physics where new directions would be fruitful. Without that help our models of the evolution of the universe will remain far too speculative to determine the strengths and weaknesses of any potential unification of the basic forces of physics. This point supports the claim made in Chapter 3 to the effect that space science helps transform theoretical science. Science needs to rub against the world, for such friction polishes and sharpens the rough guesses that humans make about their universe.[1] And as we can see now, at the edge of the universe we find the end of a journey through space science that begins here and brings us back.

But what if we give up on the unification of the basic forces of physics? Even so space science would be as fundamental as Earth-bound physical science. One reason is the opportunity to develop several aspects of the two main physical theories of this century: quantum physics and general relativity. I will leave general relativity for a section of its own later in the chapter. As for quantum physics, it explains micro-phenomena and is thus bound to come to terms with the first few moments of the origin of the universe, when the universe was so small that quantum events would have profound effects upon its subsequent evolution. Even without the goal of unification, different ideas on the nature of fundamental particles, their creation and their ways of interaction, could be refined so as to make distinct predictions about how the universe should have turned out. In general, to the extent that microphysics decides what processes underlie the macro-phenomena of the large universe, then the study of those phenomena ought to serve as an independent testing ground for our theories of the small.

Another reason is that the possibility of studying black holes and other strange objects presents extraordinary opportunities to challenge all of physics. It has been said that in black holes all of physics comes to an end. The reason is that in a runaway gravitational collapse, which is presumably what exists in a black hole, matter and energy disappear into a single geometrical point at the center of the black hole. This point, called a "singularity," obviously contains no space. And it contain no time either since, as we will see below, time slows down in the presence of a strong gravitational field. Where the field is practically infinite, time simply does not "happen." But the laws of physics make no sense outside of time and space. Thus we seem to have a situation in which matter-energy is no longer subject to the laws of physics as we can presently conceive of them. These are strange possibilities indeed, and there is nothing like the serious consideration of strange possibilities to loosen the grip of entrenched ideas.

Moreover, another serious complication arises. As the matter and energy in the black hole collapse towards the singularity, a moment comes when they are compressed into a volume so small that quantum effects begin to dominate. This would mean, for example, that the account of the previous paragraph could not be right, since the Heisenberg uncertainty relation between position and momentum would rule out any deterministic prediction about the behavior of matter in such a small volume. Indeed, it could be thought that a similar problem may show up at the beginning of the universe. The result is that we seem to have a conflict between the two main theories of physics: general relativity and quantum physics. A future compromise, quantum gravity, has been the goal of many theoretical physicists, particularly string theories, but without any success so far.

To pass up the opportunity to enrich our cosmology so immensely would be far more than folly for the scientist who wishes to understand the universe. In the Republic, Plato describes a group of men who are chained facing the back wall of a cave. By the entrance to the cave there is a road, and beyond the road a fire that projects on the wall the shadows of the objects that pass in front of the cave. The men spend their time trying to determine what those objects are from the shapes they see before them. One day a man is set free and turned around. In reaching the outside world he is at first taken with fright, but soon he adapts to the sunlight and marvels not only at the objects whose shadows he had seen before, but at the many that had not even crossed his imagination, let alone his line of sight. And the question is, would this man go back voluntarily to his chains in the cave? Would he be satisfied with the guessing games based on what he now knows are mere shadows?

In a certain sense the atmosphere and the gravity well of our planet have been our cave and our chains. One of the great space pioneers, the Russian rocket theorist Tsiolkovsky spoke of the chains of gravity and spent his life trying to break them. He and the other space pioneers have made it possible for us to come out and see the universe as if for the first time. Perhaps even then the universe will remain a complete mystery to us. But can we as cosmologists afford to reject the chance they offer to us and take back our place in front of the cave wall?

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[1] This is a highly objectionable aspect of String Theory: that it makes no contact with the universe we actually observe. Perhaps it will eventually, though.

COSMOLOGY AND THE PROGRESS OF PHYSICS

Space 5E

COSMOLOGY AND THE PROGRESS OF PHYSICS

As we may recall, one objection against my thesis was that we apply truly fundamental physics to settle issues in space astronomy and physics, not the other way around. This objection has two corollaries. First, our truly important scientific views are not likely to be affected in significant ways by what we do in space. Second, as a consequence of space science, some of our views of the universe may well change, but they are of such remote or esoteric phenomena that the opportunity for practical consequences, even in the long run is slim at best.

Let us take up first the matter of significance. There is a pecking order in the natural sciences, with physics clearly at the top. This is so because of three reasons. One is historical: physics led the way in the scientific revolution and presumably set the standards for subsequent science. A second reason is that physics deals with processes that are fundamental to the natural world; it deals with what all objects have in common. It is not surprising, then, that important changes in physics tend to be felt in many scientific places. The third reason is that the mathematical and experimental rigor of physics, coupled with extraordinary feats of the imagination, maintains the prestige of physics very high.

Even if such high prestige is well deserved, there is an unfortunate tendency to think that other sciences have much to learn from physics but little to teach it. And so we not only give priority to physics but even within physics we may downgrade what the received wisdom does not consider fundamental. For several decades, the most pressing problems were thought to reside in the very small, for the simple reason that the smallest components of matter are presumed to be the building blocks of the universe. These problems are the province of particle physics, and for some years the leading view to explain the nature of particles has been the Standard Model. This model contains 12 basic particles, fermions, which come in two classes: quarks and leptons. The theory of quarks goes by the strange name of “chromodynamics.” The name is strange because it appears to refer to the dynamics of color, but the “color” in question is a property of quarks that cannot be seen (charm is another whimsical property of quarks, and the name "quark" itself is a nonsense word from a poem by James Joyce). The word “lepton” means light, as the electron, the most famous lepton, is supposed to be. But now there are “heavy” leptons. To these whimsically named particles, proponents of the Standard Model have added the hypothetical Higgs particle, presumed to give mass to the other particles. Quarks are the building blocks of hadrons, e.g. protons and neutrons, which together with electrons form atoms. The model also accounts for three of the basic forces: electromagnetic, and the weak and strong nuclear forces. To do this it posits the existence of four force-carrying particles named bosons, which include the photon and the gluon, which “glues” quarks to other quarks.

The so-called fundamental physics contained in the Standard Model, however, does not account for gravity (more on this soon). A rather popular way to bring gravity and quantum physics together has been string theory, which supposes that particles are really little loops or strings. It requires the existence of many dimensions in its attempt to give a consistent account of quantum gravity. Unfortunately that account does not yet have any empirical evidence to support it, nor does it propose many experimental tests that would allow us to acquire that evidence. Even more fanciful views would have many universes existing side by side, so to speak, although such views boast of no more evidence to their credit than plain string theory.

The importance of quarks, and later of strings, was that they presumably explained the variety and properties of sub-atomic particles. More specifically they pointed the way toward a unified account of the basic forces that act between particles, which physicists often call the "basic" forces of nature, except, once again, for gravity. Fundamental research is then research about those forces, and that is the research done at gigantic and very expensive particle accelerators. Since space science is also expensive, there has been an uneasy feeling that space science has taken money away from truly fundamental research. Not that particle physics is the only kind of research a respectable physicist can undertake. But other physics shines by reflected glory, so to speak, and thus the more removed from the center of the discipline the less important it is thought to be.[1]

This uneasy feeling about space science has been losing ground dramatically, and for very good reasons. Let us leave aside, for the moment, the discovery of Dark Matter and Dark Energy, which force us to do fundamental physics in a way that requires the active participation of space science. Apart from those considerations, then, we should take into account the apparent goals of fundamental physics before the astonishing finds of the space-based telescopes. The basic forces of nature are, once more, the electromagnetic, the weak, the strong, and the gravitational. Current physical theory has brought a more or less unified account of the first two (the electro-weak), and there is hope that the strong nuclear force can also be similarly unified with those two. But gravity is not so tractable. The best hope for a unified account of all the forces requires a state of the universe in which all the forces are of comparable strength. But today gravity is far weaker.[2] Many proponents of the standard model trust that eventually in collisions at very high energies in new particle accelerators they will eventually find the so-called Higgs particle. To some extent, though, these ideas have been influenced by scientific beliefs about the beginning of the universe, for then we find a clear case of the required strong gravity, "supergravity," in interaction with the other forces.

Now, to study the beginning of the universe we first make hypotheses about it on the basis of which we predict how the universe should have evolved (e.g., how "lumpy" it should be, what kinds of galaxies should be born and how they should be clustered, what ratio of matter to antimatter should exist, and what other objects, say, quasars and black holes, we should find). We then must observe the universe in order to determine which of the competing hypotheses explains it better (again, this was in the “happy days” before the present obsession with Dark Matter and Dark Energy). It is obvious, though, that the sharper a description we have of the universe, the more sophisticated our testing of those hypotheses about its origin. It should be clear also that the more details we know about the universe the more hints we benefit from in trying to devise new theories to explain its origin and its evolution.

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[1] For an account of the contemporary low status of the planetary sciences (until rather recently), see Stephen G. Brush, “Planetary Science: From Underground to Underdog,” Scientia, 1978, vol. 113, p.771.

[2] Taking the value of the strong force to be 1, the other values are as follows: electromagnetic, 10^-2; weak, 10^-6; gravity, 10^-40.

A NEW VISION OF THE UNIVERSE

Chapter 5D

A NEW VISION OF THE UNIVERSE

When Galileo turned his telescope to the heavens a new sense was born. Galileo's telescope gave us the moons of Jupiter, the phases of Venus, and thousands of new stars. But this new sense was no mere addition, for it helped usher in a view that contradicted direct sensory experience. As Galileo himself said, "…there is no limit to my astonishment, when I reflect that Aristarchus and Copernicus were able to make reason so to conquer sense that, in defiance of the latter, the former became mistress of their belief."[1] But in the telescope he found a "superior and better sense than natural and common sense".[2] This new sense, furthermore, was not just a refinement of sight, but rather an alternative that agreed with the Copernican view, unlike plain sight. Indeed, whereas to plain sight the magnitude of Mars changed little--a troublesome fact for the Copernican view according to which the distance between Mars and the Earth varied considerably--in looking through the telescope the magnitude behaved as if God had been a Copernican. Likewise, the phases of Venus explained why the magnitude of Venus remained constant: when Venus is closest we only see a small portion of its disk lighted, but as it moves away from us we see more and more of its disk lighted, until when it is furthest from Earth we see it fully lighted.

In this way a new technology came to the rescue of an idea that was to transform our view of nature most profoundly. Not that the telescope was free from reasonable question, for on the contrary, given what was known about optics and perception at the time, its reliability was a lucky assumption made plausible more by Galileo's enthusiasm than by his argument. Among other things, we should keep in mind that the brain does not merely experience the pattern of light that strikes the retina: it interprets that pattern on the basis of past experience, expectation, and environmental clues. It also imposes constancies of shape, color, and size upon the visual image. When peering into the skies, however, many of those clues are absent and thus the untrained eye can experience many illusions. And indeed many people looking through Galileo's telescope did not see what he saw.[3] Moreover, it was generally thought that perception cannot be trusted when the natural medium through which the information travels has been tampered with (e.g., a haze or a drunken brain). Galileo's telescope was theoretically suspect, then, because it clearly altered the natural medium through which the light from distant objects was transmitted to the eye.

But the telescope did open up many avenues of observation and investigation that would not have been there otherwise. It was a promise from the heavens better kept in the course of the new science than perhaps Galileo had a right to imagine. For him it was too striking a coincidence that the telescope would so match the new astronomy of Copernicus. For others, whose fundamental views were at stake, it was a case of a distorting instrument of observation presuming to support a refuted and obnoxious view of the cosmos.

To most of us now it seems fortunate that, as Galileo put it, Copernicus "with reason [theory] as his guide...resolutely continued to affirm what sensible experience seemed to contradict."[4] Many of those who were in a position to choose decided in favor of the most exciting of the alternatives (in accordance with a principle that NASA scientist Brian Toon fondly calls "Sagan's Razor"). Whether they had other, more compelling reasons I shall not discuss here. Suffice it to say that the invention by Newton of the reflecting telescope and the refinement of both kinds of telescopes permitted not only the discovery of many new objects in the universe, but also a shift in perspective about its nature. And having embarked on a different approach to nature, the new scientists also had the motivation and opportunity to develop the auxiliary sciences (e.g., optics, electromagnetism) that eventually established the reliability of the telescope as well.

Such reliability is rather limited, as we have learned. Apart from obvious problems like background lights and bad weather, optical telescopes until recently had to contend with the effects of columns of air within them and of gravitational distortions of their very large mirrors. Worse still, even though a large telescope such as the 5-meter telescope on Mount Palomar could in principle separate the images of objects in the sky as close to each other as 0.02 arc second (this is called angular resolution), the motion of air molecules blur the path of light through the atmosphere to the point that the best angular resolution we can achieve is about 50 times worse than that. Such was the situation at the point when space technology could begin to place optical telescopes in orbit. Today those space telescopes work in concert with new generations of Earth-bound telescopes in which computers compensate for some of the distortions of the atmosphere and in which combinations with other such telescopes (in interferometers) allows the collection of much greater amounts of light.

Moreover we know now things that Galileo could not have the tools to imagine. Light is a form of electromagnetic radiation and the Earth's atmosphere blocks many other forms of that radiation: More specifically, it absorbs the X-ray and gamma frequencies, as well as most of the ultraviolet and several bands of the infrared. The envelope of gases that made life possible in the beginning, and has protected it ever since, has given us only a small window into the universe at large. Through that window we have seen and we have dreamt, and through that window we have also adjusted our views of nature. Galileo's new sense became better and better, and when it seemed that it was reaching its limitations, in the middle of the 20th century, we discovered radio astronomy, and then infrared astronomy.

By then we had found that the sun was not the center of the universe either, that it was one among billions of stars in the outskirts of a rather common galaxy, and that the galaxies were receding from each other, that is, that the universe was expanding. This last discovery prompted Einstein to recognize what he called his greatest mistake. The idea that the universe might change in size had seemed so preposterous at the time he proposed his general theory of relativity that he introduced a constant into the theory to ensure that the universe would appear static in it.

So much resulted from the evolution of Galileo's instrument. But then, with the discovery of radio and infrared astronomy, new kinds of objects and new kinds of activity in objects already known gave us a glimpse of what a look at the universe in the full electromagnetic spectrum may do. Quasars and pulsars, and the radiation left over from the big bang began to tell us about a universe far stranger than we had imagined. With the advent of space exploration we can go above the atmosphere to examine the universe in the full electromagnetic spectrum. We can also do far better astronomy in the more traditional wavelengths (radio, optical, and infrared).

For example, in the visible range, NASA's Hubble Space Telescope, unencumbered by most of the handicaps of its terrestrial counterparts, swept a volume 350 times larger and produced images ten times finer than most traditional telescopes could at that time. Even more sophisticated future space telescopes may allow us to detect planets the size of Earth around stars within 10 light years from us. Radio astronomy, which allows us to study regions obscured by dust, as well as some very cold or very hot objects, is not hampered much by the atmosphere, but it is limited by the size of the Earth. Even though the angular resolution of the largest radio telescopes is very poor (about 10 arc seconds), they can be placed together in large arrays (with the telescopes at large distances from each other) that are equivalent to gigantic telescopes. The largest such array (an interferometer called the Very Long Baseline Array) has a baseline almost as long as the diameter of the Earth and attains a resolution of 0.001 arc seconds. To attain a finer resolution we need a larger baseline, and the only way to secure that is to place some radio telescopes in space (with the first such extensions the resolution of the Very Long Baseline Array will improve by a factor of 100).

Infrared astronomy permits us to study the incredible energy released in the center of remote galaxies and other events taking place at the edge of the universe. For the objects in question are receding so fast from us that their light has been shifted into the infrared spectrum. But infrared astronomy is also of importance closer to home, as we will see in the last section of this chapter.

Let us see now some of the ways in which this developments help us understand how space physics and space astronomy are fundamental sciences.

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[1] Galileo Galilei. Dialogue Concerning the Two Chief World Systems. University of California Press, Berkeley. 1953 edition. P. 328.

[2] Ibid., p. 335.

[3] Feyerabend

[4] Galileo, op. cit., p. 335.

Planetary Science and Fundamental Physics

Chapter 5C

Planetary Science and Fundamental Physics

In the case of planetary science, as Stephen Brush reminds us, the attempt to satisfy intellectual curiosity brought about many of the most significant advances of the past few centuries. In 1746, for example, d'Alambert won a prize for making one of the first consistent uses of partial differential equations. His was an essay on winds. The work of Laplace at the end of the 18th century resulted from the calculations in celestial mechanics of Clairut, Euler, and Lagrange. Legendre and Laplace originated the use of spherical harmonics in potential theory while trying to calculate the gravitational attraction of the Earth. This use was later of great value in electricity and in quantum mechanics. And many of Poincare's major works on mathematical analysis were inspired by problems in planetary mechanics.[1]

Similar remarks may be made about Gauss, one of the world's greatest mathematicians, who did much work in geodetic surveys and terrestrial magnetism. As Brush points out, "even an advocate of pure science might concede that Gauss' geophysical work provided the stimulus for some of his contributions to geometry and potential theory, just as his early work on the computation of orbits led to a major contribution to probability theory, the `Gaussian distribution', and could thereby be justified."[2] James Clerk Maxwell, clearly a giant of physics, won the Adams Prize with an essay on the stability of the rings of Saturn. This work was the basis for his kinetic theory of gas viscosity and eventually of his theory of transport processes. He later returned to the problem of the rings of Saturn and applied to it the methods he developed in his kinetic theory of gases.

A case of particular interest to Brush in establishing the connection between pure science and planetary science is the 19th century problem of the dependence of thermal radiation on the temperature of the source. This problem was of great significance to planetary science, of course, because the sun is the greatest source of radiation in the solar system. The outcome of the attempt to determine the surface temperature of the sun "was Stefan's suggestion (1879) that the data could best be represented by assuming that the rate of emission of energy is proportional to the 4th power of the absolute temperature."[3] Further experimental investigation, and Boltzman's theoretical derivation of such a formula, led to the subsequent work on the frequency distribution of black-body radiation. The search for the law that would govern such distribution can thus be seen as the genesis of Planck's quantum theory.

These remarks on the history of physics vindicate the claim that the study of the heavens at all levels has been a driving force in the development of fundamental science. This may come as a surprise to some. But it should not be a surprise if we consider the variety of interactions between cosmology and other areas of science, and between the different levels of cosmological research themselves. The study of the cosmos leads to the discovery of fundamental principles of physics, further development of physics in turn leads to new investigative tools of the cosmos, and so on. We may speak here of a dialectical relationship between areas and levels of science which results in the dynamic growth of science. In the case of planetary science we find no exception: fundamental research on physics and cosmology leads to changes in our ideas about the solar system and its planets. On the other hand, those ideas in turn give many hints as to useful lines of "pure" inquiry. This result is not merely part of the historical record: if anything it should receive greater prominence as space exploration multiplies our means of investigating the cosmos.

Indeed we will see presently that space science provides an excellent opportunity to enhance the relationship between astrophysics and the rest of fundamental physics.

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[1] S.G. Brush. “Planetary Science: From Underground to Underdog.” Scientia, 113: 771-787 (1979).

[2] Brush, ibid.

[3] Brush, ibid.

Dark Problems

Chapter 5B

Dark Problems

AN EXAMPLE: THE DARK SIDE

It had been suspected for some time that galaxies had far more matter than we could determine from what was visible. Once we were able to look at galaxies in the full spectrum we realized that perhaps as much as 90% of some galaxies’ mass was unaccounted for (one main reason for this realization is that the outer stars in a galaxy are going so fast that without that much extra mass to keep them in, they would be flung into intergalactic space). But apparently most of that missing mass (now called “dark matter”) cannot be seen, for it does not interact with ordinary matter, except through gravity. In other words, most of the matter in the universe is completely different from anything we have known until now (it is not made up of protons, neutrons, electrons and the like). To study dark matter it is necessary to observe the universe with space telescopes, as will be explained below.

To make matters worse, it was discovered that the expansion of the universe is accelerating, in violation of the sensible belief that gravitational attraction should slow down and perhaps even reverse the expansion initiated in the most famous of all explosions, the Big Bang. A new form of energy, Dark Energy, which we understand even less than we understand Dark Matter, presumably accounts for that perplexing expansion. Since dark energy and dark matter take up most of the universe, our precious Standard Model tries to explain the entire universe on the basis of the less than ten percent of matter that it is acquainted with. Imagine that you come to a new place and get to know ten percent of it. All you know about the rest is that it is completely different from the small portion you know. How confident would you feel about explaining the whole on the basis of the one part you can handle? And then add the complication that Dark Energy make up two thirds of the universe!

Again, to study dark energy we need to go into space, sooner or later. Some of the work of surveying the universe can be done with terrestrial telescopes, but the findings of such surveys will have to be corroborated and supplemented by telescopes in orbit, as we will see below. This means that to have much of a chance to come up with a fundamental explanation of the universe we need to do space science. Some physicists still hope that in the new particle accelerators, which will produce very high energies, violent collisions will yield some dark matter particles. And, who knows, their hopes may perchance be realized, but since we do not know what dark matter is, those physicists sound a bit too optimistic. And even then we would still have the even bigger puzzle of dark energy.

To do away with the problem of Dark Energy, some physicists have proposed to replace the Theory of General Relativity with another theory in which gravity is not a constant. This hypothesis, which is rejected by most physicists, would of course represent a radical transformation of fundamental physics brought about by space astronomy and physics. Either way, space science should receive significant credit for the serendipity that will result from the soon-to-be new physics.

SPACE SCIENCE AND THE TRADITION OF FUNDAMENTAL PHYSICS

Let us begin our discussion of Claim (1) by remembering that the connection with astrophysics has been a trademark of modern physical science from its inception and throughout most of its history.

Although it is well known that Copernicus proposed that the sun and not the Earth was at the center of the universe, his motivation is not so well understood. It was not that his system could account for the position of the planets clearly better than the Ptolemaic system, for even Copernicus acknowledged that the matter was not settled. Nor was it obvious either, in spite of the claims by Pierre Duhem and others, that his system was vastly simpler. It is true that the Ptolemaic system employed a variety of mechanisms--epicycles, eccentrics, deferents, equants--to account for the paths of the planets, but with the exception of the equant so did the Copernican system. (See figures).[1] The difference was that the Ptolemaic system often had alternative combinations of such mechanisms for different aspects of the behavior of the same planet. This would seem outrageous to someone weaned on the notion that only one such mechanism could be correct. But the mere talk of correctness assumes that we can inquire about the real nature of the heavens.

We feel entitled to make that assumption rather freely today. But that was not the case in Copernicus' day. From the time of Ptolemy (second century AD.), the inquiry about the reality of the heavens had been looked upon with suspicion. The reason was that whereas the progress of mathematical astronomy made it possible to calculate with increasing precision the positions of the planets, the accounts of why the planets moved as they did had broken down not long after Aristotle had proposed the interaction of concentric spheres made of his quintessence (about 350 BC.).

According to Ptolemy himself, mathematics can apply only to "changes in form: i.e. in trajectory, shape, quantity, size, position, time, and the rest."[2] As to the actual nature of things there is little that science can do because they either take "place far above us, among the highest things in the universe, far away from the objects we directly observe with our senses," or else, as the objects of (terrestrial) physics, those "material things...are so unstable and difficult to fathom that one can never hope to get philosophers to agree about them."[3] Questions about the nature of the heavenly objects must lead one back to the ultimate source of all change, and thus they can only be answered by theology. Therefore science gains little to profit from asking them. And they are also distinct in kind from the sorts of questions that physics tries to answer, whose underlying principles, if any, did not seem amenable to mathematical treatment.

In the long run the Copernican revolution accomplished several important changes in points of view. For one thing it insisted in investigating the nature of the behavior of the heavenly objects. And it did so by looking for mutual underlying mathematical principles for both the heavens and the Earth. The success of this gross violation of Ptolemy's methodological rules turned on Copernicus' belief that astrophysics was possible. Eventually Newton succeeded where Aristotle had failed, and astrophysics became the shining example that new branches of physics had to follow.

Confusions about Copernicus' motivation were created mainly by Osiander's preface to Copernicus' masterpiece, On the Revolutions. Fearing a confrontation with theological dogma, Osiander urged the readers to "permit these new hypotheses to become known together with the ancient hypotheses," and to do so because Copernicus' hypotheses are "admirable and also simple, and bring with them a huge treasure of skillful observations." But the Copernicus' reader, Osiander wrote, should not accept as the truth "ideas conceived for another purpose."[4] All these admonitions by Osiander contradict Copernicus' own words and belie his attempt to discover the truth about the heavens by rational means instead of revelation.

In the centuries following Copernicus, astrophysics continued as a driving force of fundamental theory. Newton is, of course, the most prominent example. His laws of dynamics applied equally to terrestrial and heavenly objects, and his law of gravitation was a striking statement of the discovery that the force that kept us glued to the surface of the Earth was the same that made the stars and planets keep their appointed rounds.

We begin to see why this view of science is distorted when we realize that fundamental questions often cannot be asked without the appropriate technology and will not be asked without the right kind of inspiration and motivation. But this realization leads to another: that a whole host of activities are potentially as crucial to scientific progress as work that aims to solve problems within the most prestigious field of the time. Researchers who create new technology or new opportunities may contribute just as much to keep intact the dynamic character of science. And inspiration has often come as much from the planets as from the stars.

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[1] T.S. Kuhn. (1957) The Copernican Revolution. Harvard University Press.

[2] S. Toulmin and J. Goodfield (196 ) The Fabric of the Heavens.

[3] Ibid.

[4] Ibid.

Space Physics and Astronomy

Chapter 5A

Space Physics and Astronomy

According to the journal Science, Rashid Sunyaev, a famous Russian astrophysicist, “once heard the chair of his department say that ‘astronomy was an absolutely useless science.’”[1]

After the spectacular successes of the space telescopes and the new generation of Earth-bound telescopes, the public may be surprised to learn that not long ago many scientists regarded space astronomy and space physics with some suspicion. Quite a few physicists, for example, felt that all those billions of dollars for space astronomy should have supported the construction of a new generation of particle accelerators instead – particle accelerators dealt with truly basic science. I presume that a good many of those physicists may now agree that the money spent in space telescopes has been money well spent. But it is important to see why they are right in having changed their minds.

The reason is that, in the pursuit of cosmological knowledge, physics and astronomy done in space affect the transformation of our views in a very important respect: They provide a framework within which to challenge our most fundamental terrestrial sciences. For to understand the formation and evolution of the universe we need to see how the basic laws of nature are expressed in it. At the same time, to have a good grasp of the basic laws of nature we need to see how well we can describe the universe by using them. In a second respect they affect that transformation in an even more radical way: astronomy and physics done in space allow us to discover phenomena that we could not have discovered otherwise and that will force us to develop a new physics.

THE OBJECTION TO SPACE SCIENCE

As we recall from Chapter 3, a scientific critic might argue that, since these sciences examine far-away objects, the ensuing transformation of our views is unlikely to pay off for the inhabitants of the Earth. For example, space astronomy and physics constitute a prime example of attempting to satisfy our intellectual curiosity -- they aim to describe features of the universe that many people find interesting, sometimes fascinating. The problem for my thesis is precisely that these space sciences fit my points about curiosity so well while apparently failing to satisfy my expectation about practical results in the long run. Surely, the objection continues, it is by no means obvious that the transformation of our theories about black holes, quasars, and intergalactic gas will be of much application on the Earth.

There is, according to the objection, a great difference between Earth-bound physics and these space sciences. Consider anew the example of how Einstein’s revolution in physics led to lasers and their application in medicine: That revolution transformed our understanding of the basic principles of matter, of principles that apply down here. It is not surprising, then, that our panorama of problems and opportunities was bound to change as a result of the transformation of our thought. The principles of fundamental science (e.g. particle physics) apply down here because they apply everywhere. By contrast, space astronomy and space physics merely apply to stars, galaxies, and quasars the fundamental principles of matter discovered by Earth-bound physics -- thus they are derivative sciences. My thesis about serendipity would then apply only to fundamental science. Therefore, space astronomy and space physics cannot be justified by my general philosophical argument.

For almost a century now the most fundamental and empirically successful description of matter has been given by the so-called Standard Model, which explains the universe in terms of its building blocks (particles) and the fields (strong, weak, electromagnetic and gravitational) that allow those blocks to interact. The main experimental tools of the Standard Model have been giant particle accelerators that smash those particles at speeds close to that of light and then theorize from the resulting debris. When the choice came between spending billions to build even more powerful accelerators or spending billions to put up telescopes in orbit, the feeling among many physicists was that, interesting though astronomy may be, taking money away from the terrestrial tools that would allow us to advance the Standard Model further was tantamount to blunting fundamental science’s cutting edge.

My response will be as follows: (1) space physics and astronomy have distinct scientific advantages over terrestrially bound sciences; (2) these scientific advantages show that space physics and astronomy are fundamental science in the same sense that terrestrially bound physics is because (a) you cannot do terrestrial physics properly without doing space science, and (b) the theoretical and experimental articulation of physics needs challenge, a challenge that space science has provided and will continue to provide. Space science has made the Standard Model due for a change.

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[1] “News Focus: In the Afterglow of the Big Bang.” Science, vol 327, January 1, 2010: 27.