Cosmology + Physics FAQ

What is the evidence for the Big Bang ? .. The evidence for the Big Bang comes from many pieces of observational data that are consistent with the Big Bang. None of these prove the Big Bang, since scientific theories are not proven. Many of these facts are consistent with the Big Bang and some other cosmological models, but taken together these observations show that the Big Bang is the best current model for the Universe. These observations include: The darkness of the night sky - Olbers' paradox. The Hubble Law - the linear distance vs redshift law. The data are now very good. Homogeneity - fair data showing that our location in the Universe is not special. Isotropy - very strong data showing that the sky looks the same in all directions to 1 part in 100,000. Time dilation in supernova light curves. The observations listed above are consistent with the Big Bang or with the Steady State model, but many observations support the Big Bang over the Steady State: Radio source and quasar counts vs. flux. These show that the Universe has evolved. Existence of the blackbody CMB. This shows that the Universe has evolved from a dense, isothermal state. Variation of TCMB with redshift. This is a direct observation of the evolution of the Universe. Deuterium, 3He, 4He, and 7Li abundances. These light isotopes are all well fit by predicted reactions occurring in the First Three Minutes. Finally, the angular power spectrum of the CMB anisotropy that does exist at the several parts per million level is consistent with a dark matter dominated Big Bang model that went through the inflationary scenario. Back to top.

Why do we think that the expansion of the Universe is accelerating ? .. The evidence for an accelerating expansion comes from observations of the brightness of distant supernovae. We observe the redshift of a supernova which tells us by what the factor the Universe has expanded since the supernova exploded. This factor is (1+z), where z is the redshift. But in order to determine the expected brightness of the supernova, we need to know its distance now. If the expansion of the Universe is accelerating due to a cosmological constant, then the expansion was slower in the past, and thus the time required to expand by a given factor is longer, and the distance NOW is larger. But if the expansion is decelerating, it was faster in the past and the distance NOW is smaller. Thus for an accelerating expansion the supernovae at high redshifts will appear to be fainter than they would for a decelerating expansion because their current distances are larger. Note that these distances are all proportional to the age of the Universe [or 1/Ho], but this dependence cancels out when the brightness of a nearby supernova at z close to 0.1 is compared to a distant supernova with z close to 1. Back to top.

If the Universe is only 10 billion years old, why isn't the most distant object we can see 5 billion light years away ? .. This question makes some hidden assumptions about space and time which are not consistent with all definitions of distance and time. One assumes that all the galaxies left from a single point at the Big Bang, and the most distant one traveled away from us for half the age of the Universe at almost the speed of light, and then emitted light which came back to us at the speed of light. By assuming constant velocities, we must ignore gravity, so this would only happen in a nearly empty Universe. In the empty Universe, one of the many possible definitions of distance does agree with the assumptions in this question: the angular size distance, and it does reach a maximum value of the speed of light times one half the age of the Universe. See Part 2 of the cosmology tutorial for a discussion of the other kinds of distances which go to infinity in the empty Universe model since this gives an unbounded Universe. Back to top.

If the Universe is only 10 billion years old, how can we see objects that are now 30 billion light years away ? .. When talking about the distance of a moving object, we mean the spatial separation NOW, with the positions of both objects specified at the current time. In an expanding Universe this distance NOW is larger than the speed of light times the light travel time due to the increase of separations between objects as the Universe expands. This is not do to any change in the units of space and time, but just caused by things being farther apart now than they used to be. What is the distance NOW to the most distant thing we can see ? .. Let's take the age of the Universe to be 10 billion years. In that time light travels 10 billion light years, and some people stop here. But the distance has grown since the light traveled. The average time when the light was traveling was 5 billion years ago. For the critical density case, the scale factor for the Universe goes like the 2/3 power of the time since the Big Bang, so the Universe has grown by a factor of 22/3 = 1.59 since the midpoint of the light's trip. But the size of the Universe changes continuously, so we should divide the light's trip into short intervals. First take two intervals: 5 billion years at an average time 7.5 billion years after the Big Bang, which gives 5 billion light years that have grown by a factor of 1/(0.75)2/3 = 1.21, plus another 5 billion light years at an average time 2.5 billion years after the Big Bang, which has grown by a factor of 42/3 = 2.52. Thus with 1 interval we got 1.59*10 = 15.9 billion light years, while with two intervals we get 5*(1.21+2.52) = 18.7 billion light years. With 8192 intervals we get 29.3 billion light years. In the limit of very many time intervals we get 30 billion light years. Another way of seeing this is to consider a photon and a galaxy 30 billion light years away from us now, 10 billion years after the Big Bang. The distance of this photon satisfies D = 3ct. If we wait for 0.1 billion years, the Universe will grow by a factor of (10.1/10)2/3 = 1.0066, so the galaxy will be 1.0066*30 = 30.2 billion light years away. But the light will have traveled 0.1 billion light years further than the galaxy because it moves at the speed of light relative to the matter in its vicinity and will thus be at D = 30.3 billion light years, so D = 3ct is still satisfied. If the Universe does not have the critical density then the distance is different, and for the low densities that are more likely the distance NOW to the most distant object we can see is bigger than 3 times the speed of light times the age of the Universe. Back to top.

How can the oldest stars in the Universe be older than the Universe ? .. Of course the Universe has to be older than the oldest stars in it. So this question basically asks: which estimate is wrong - The age of the Universe The age of the oldest stars Both The age of the Universe is determined from its expansion rate: the Hubble constant, which is the ratio of the radial velocity of a distant galaxy to its distance. The radial velocity is easy to measure, but the distances are not. Thus there is currently a 15% uncertainty in the Hubble constant. Determining the age of the oldest stars requires a knowledge of their luminosity, which depends on their distance. This leads to a 25% uncertainty in the ages of the oldest stars due to the difficulty in determining distances. Thus the discrepancy between the age of the oldest things in the Universe and the age inferred from the expansion rate is within the current margin of error. In fact, in 1997 improved distances from the HIPPARCOS satellite suggested that this discrepancy has vanished. 

Can objects move away from us faster than the speed of light ? .. Again, this is a question that depends on which of the many distance definitions one uses. However, if we assume that the distance of an object at time t is the distance from our position at time t to the object's position at time t measured by a set of observers moving with the expansion of the Universe, and all making their observations when they see the Universe as having age t, then the velocity (change in D per change in t) can definitely be larger than the speed of light. This is not a contradiction of special relativity because this distance is not the same as the spatial distance used in SR, and the age of the Universe is not the same as the time used in SR. In the special case of the empty Universe, where one can show the model in both special relativistic and cosmological coordinates, the velocity defined by change in cosmological distance per unit cosmic time is given by v = c ln(1+z) which clearly goes to infinity as the redshift goes to infinity, and is larger than c for z > 1.718. For the critical density Universe, this velocity is given by v = 2c[1-(1+z)-0.5] which is larger than c for z > 3 . Back to top.

What is the redshift ? .. The redshift of an object is the amount by which the spectral lines in the source are shifted to the red. That is, the wavelengths get longer. To be precise, the redshift is given by z = [WL(obs)-WL(em)]/WL(em) where WL(em) is the emitted wavelength of a line, which is known from laboratory measurements, and WL(obs) is the observed wavelength of the line. In an expanding Universe, distant objects are redshifted, with z = Ho D/c for small distances. This law was discovered by Hubble and Ho is known as the Hubble constant. Back to top.

Are quasars really at the large distances indicated by their redshifts ? .. The short answer is Yes! Stockton (1978, ApJ, 223, 747) observed faint galaxies near in the sky to bright quasars at moderate redshifts. He chose quasars with moderate redshifts so he would still be able to see galaxies at the redshift of the quasar. He found that a good fraction of the redshifts of the faint galaxies agreed with the redshifts of the quasars. In other words, quasars are associated with galaxies that have the same redshift as the quasar and have just the brightness expected if the quasars are at their cosmological distances. Thus at least some quasars are at the distance indicated by their redshifts, and this includes some of the most luminous quasars: for example 3C273. Thus the simple answer selected by Occam's razor is that all quasars are at the distances indicated by their redshifts. The statistical arguments advanced by Arp and others in favor of anomalous quasar redshifts are often incorrect. Back to top.

What about objects with discordant redshifts, like Stephan's Quintet ? .. One famous example of objects with different redshifts appearing in the same part of the sky is Stephan's Quintet. But the low redshift galaxy (in the lower left) is obviously more resolved into stars and looks "bumpier". By the surface brightness fluctuation method of distance determination, this bumpiness means that the low redshift galaxy is indeed much closer to us than the other four members of the quintet. Back to top.

Has the time dilation of distant source light curves predicted by the Big Bang been observed ? .. This time dilation is a consequence of the standard interpretation of the redshift: a supernova that takes 20 days to decay will appear to take 40 days to decay when observed at redshift z=1. The time dilation has been observed, with 4 different published measurements of this effect in supernova light curves. These papers are: Leibundgut etal, 1996, ApJL, 466, L21-L24 Goldhaber etal, in Thermonuclear Supernovae (NATO ASI), eds. R. Canal, P. Ruiz-LaPuente, and J. Isern. Riess etal, 1997, AJ, 114, 722. Perlmutter etal, 1998, Nature, 391, 51. These observations contradict tired light models of the redshift. Back to top.

Are galaxies really moving away from us or is space just expanding ? .. This depends on how you measure things, or your choice of coordinates. In one view, the spatial positions of galaxies are changing, and this causes the redshift. In another view, the galaxies are at fixed coordinates, but the distance between fixed points increases with time, and this causes the redshift. General relativity explains how to transform from one view to the other, and the observable effects like the redshift are the same in both views. Part 3 of the tutorial shows space-time diagrams for the Universe drawn in both ways. Also see the Relativity FAQ answer to this question. Back to top.

Why doesn't the Solar System expand if the whole Universe is expanding ? .. This question is best answered in the coordinate system where the galaxies change their positions. The galaxies are receding from us because they started out receding from us, and the force of gravity just causes an acceleration that causes them to slow down. Planets are going around the Sun is fixed size orbits because they are bound to the Sun. Everything is just moving under the influence of Newton's laws (with very slight modifications due to relativity). [Illustration] For the technically minded, Cooperstock et al. computes that the influence of the cosmological expansion on the Earth's orbit around the Sun amounts to a growth by only one part in a septillion over the age of the Solar System. This effect is caused by the cosmological background density within the Solar System going down as the Universe expands, which may or may not happen depending on the nature of the dark matter. The mass loss of the Sun due to its luminosity and the Solar wind leads to a much larger [but still tiny] growth of the Earth's orbit which has nothing to do with the expansion of the Universe. Even on the much larger (million light year) scale of clusters of galaxies, the effect of the expansion of the Universe is 10 million times smaller than the gravitational binding of the cluster. Also see the Relativity FAQ answer to this question. Back to top.

Is the Universe expanding or is it just that our definitions of length and time are changing ? .. The definitions of length and time are not changing in the standard model. The second is still 9192631770 cycles of a Cesium atomic clock and the meter is still the distance light travels in 9192631770/299792458 cycles of a Cesium atomic clock. Back to top.

What is meant by a flat Universe ? .. The Universe appears to be homogeneous and isotropic, and there are only three possible geometries that are homogeneous and isotropic as shown in Part 3. A flat space has Euclidean geometry, where the sum of the angles in a triangle is 180o. A curved space has non-Euclidean geometry. In a positively curved, or hyperspherical space, the sum of the angles in a triangle is bigger than 180o, and this angle excess gives the area of the triangle divided by the square of the radius of the surface. In a negatively curved or hyperbolic space, the sum of the angles in a triangle is less than 180o. When Gauss invented this non-Euclidean geometry he actually tried measuring a large triangle, but he got an angle sum of 180o because the radius of the Universe is very large (if not infinite) so the angle excess or deficit has to be tiny for any triangle we can measure. If the radius is infinite, then the Universe is flat. Back to top.

Bolyai developed this geometry and published it, whereupon Gauss wrote to Bolyai's father: "To praise it would amount to praising myself. For the entire content of the work ... coincides almost exactly with my own meditations which have occupied my mind for the past thirty or thirty-five years." And Lobachevsky had published very similar work in the obscure Kazan Messenger. 

What is the Universe expanding into ? .. This question is based on the ever popular misconception that the Universe is some curved object embedded in a higher dimensional space, and that the Universe is expanding into this space. This misconception is probably fostered by the balloon analogy which shows a 2-D spherical model of the Universe expanding in a 3-D space. While it is possible to think of the Universe this way, it is not necessary, and there is nothing whatsoever that we have measured or can measure that will show us anything about the larger space. Everything that we measure is within the Universe, and we see no edge or boundary or center of expansion. Thus the Universe is not expanding into anything that we can see, and this is not a profitable thing to think about. Just as Dali's Corpus Hypercubicus is just a 2-D picture of a 3-D object that represents the surface of a 4-D cube, remember that the balloon analogy is just a 2-D picture of a 3-D situation that is supposed to help you think about a curved 3-D space, but it does not mean that there is really a 4-D space that the Universe is expanding into. 

What came before the Big Bang ? .. The standard Big Bang model is singular at the time of the Big Bang, t = 0. This means that one cannot even define time, since spacetime is singular. In some models like the chaotic or perpetual inflation favored by Linde, the Big Bang is just one of many inflating bubbles in a spacetime foam. But there is no possibility of getting information from outside our own one bubble. Thus I conclude that: "Whereof one cannot speak, thereof one must be silent." From Bruce Margon and Craig Hogan at the Univ. of Washington Back to top.

Why is the sky dark at night ? .. If the Universe were infinitely old, and infinite in extent, and stars could shine forever, then every direction you looked would eventually end on the surface of a star, and the whole sky would be as bright as the surface of the Sun. This is known as Olbers' Paradox after Heinrich Wilhelm Olbers [1757-1840] who wrote about it in 1823-1826 but it was also discussed earlier. Absorption by interstellar dust does not circumvent this paradox, since dust reradiates whatever radiation it absorbs within a few minutes, which is much less than the age of the Universe. However, the Universe is not infinitely old, and the expansion of the Universe reduces the accumulated energy radiated by distant stars. Either one of these effects acting alone would solve Olbers' Paradox, but they both act at once. Back to top.

Will the Universe expand forever or recollapse ? .. This depends on the ratio of the density of the Universe to the critical density. If the density is higher than the critical density the Universe will recollapse in a Big Crunch. But current data suggests that the density is less than or equal to the critical density so the Universe will expand forever. See Part 3 of the tutorial for more information. Back to top.

What about the oscillating Universe ? .. If the Universe recollapses, then there is another singularity at the time of the Big Crunch. A singularity means that the laws of physics break down, so we have no way to predict whether the Big Crunch will connect to another cycle of expansion. Even if the density were high enough to cause a recollapse, there would be no guarantee that the Universe would oscillate. But the current evidence is strongly against any recollapse, which would rule out the oscillating Universe. See PBS or Ask an Astronomer about this. 

What is the dark matter ? .. When astronomers add up the masses and luminosities of the stars near the Sun, they find that there are about 3 solar masses for every 1 solar luminosity. When they measure the total mass of clusters of galaxies and compare that to the total luminosity of the clusters, they find about 300 solar masses for every solar luminosity. Evidently most of the mass in the Universe is dark. If the Universe has the critical density then there are about 1000 solar masses for every solar luminosity, so an even greater fraction of the Universe is dark matter. But the theory of Big Bang nucleosynthesis says that the density of ordinary matter (anything made from atoms) can be at most 10% of the critical density, so the majority of the Universe does not emit light, does not scatter light, does not absorb light, and is not even made out of atoms. It can only be "seen" by its gravitational effects. This "non-baryonic" dark matter can be neutrinos, if they have small masses instead of being massless, or it can be WIMPs (Weakly Interacting Massive Particles), or it could be primordial black holes. My nominee for the "least likely to be caught" award goes to hypothetical stable Planck mass remnants of primordial black holes that have evaporated due to Hawking radiation. The Hawking radiation from the not-yet evaporated primordial black holes may be detectable by future gamma ray telescopes, but the 20 microgram remnants would be very hard to detect. 

What is the value of the Hubble constant ? .. This is the question that professional astronomers ask the most frequently, and the answer is: Ho = 65 +/- 8 km/sec/Mpc but I would rather see


What can a layperson do in cosmology ? .. Stay in school! There is a lot to learn about the Universe. Keep taking math and science courses! The book of nature lies continuously open before our eyes (I speak of the Universe) but it can't be understood without first learning to understand the language and characters in which it is written. It is written in mathematical language, and its characters are geometrical figures. - Galileo Galilei That was true 400 years ago and it is much more true today! If you are out of school, check out the bibliography. Tell your Congressman and Senators to support astrophysics research at NASA, NSF, and DOE. 

What is the sun made of ? .. We know more about the Sun and its immediate environment than we know about any other star. This is not surprising as the Sun dominates our view of the Universe-indeed we live inside its atmosphere.
 This star, our star, travels around the galaxy together with a multitude of lesser companions bound to it by gravitational forces. The largest of the orbitational bodies we call planets, most of which are in turn are orbited by smaller moons or satellites. These objects, together with many lesser masses, are known collectively as the Solar system.
  Formation The Sun is just a star, one of a hundred billion inhabiting our galaxy alone. Nor does the Sun's physique endow it with any special significance within that throng. It is a star with no great stature, low in the spread of luminosities and in the range of stellar dimensions, and dwarfed by almost one half of our galaxy's members. Being a star the Sun is an example of the fundamental building blocks of our universe. it formed, 4.5 billion years ago, as the nucleus of a cloud of gas which was collapsing under its own gravitational attraction.

 Once the collapse began, the characeristics of the resulting star were preordained. The mass of the gas which collapsed into the star was two million trillion trillion kg. At the centre of the collapse, the infalling gas became by the gravitational energy it bore. Streadily the temperature rose. After some 14 billion year, the central regions became sufficiently hot to trigger nuclear processes, turning hydrogen into helium and releasing energy in doing so.
  Once begun, this nuclear process was unquenchable. It continues today, and will do so for perhaps a further four billion years, halting only when the suply of hydrogen is almost exhausted. The heat and light received from the Sun is a by product of this nuclear holocaust, and to supply the vast outpouring, five million tonnes of hydrogen are consumed every second.
  Maintaining equilibrium The outward percolation of energy acts to counter the inward pull of gravity. An equilibrium has resulted. If the Sun were to shrink, its interior would become hotter, the nuclear reactions would be hastened, and the increased energy output would reinflate the Sun to its present size.
  Conversely, if the Sun tries to expand, gravity would dominate the dwindling nuclear resources and enforce a return to equilibrium. The conditions of the equilibrium-the 700,000km radius of the Sun, its surface temperature of 5500C, its central temperature of 15,000,000C, its density of 1.4 times that of water-were determined predominantly by the initial mass of the collapsing gas cloud whence it formed.
  In the end Later, as its hydrogen becomes depleted, it will evolve into a giant red star, swelling to engulf the earth and the inner planets. The outer layers will be shed in hiccups, then senility will take hold: the remnant Sun will fade gradually to oblivion, passing through the white dwarf stage on its way. That is a saga of the far future.
  Composition The Sun is entirely gaseous. its average density, in excess of that of water, might lead one to expect that liquids of solid portions lie beneath its surface. Instead, however, the gases of its interior are highly compressed but yet are too hot to have been liquified. The central density is 160 times that of water, and the pressure is 250 billion times that on Earth's surface. Yet the material is still technically a gas.
  At formation, hydrogen was the most abundant gas, as elsewhere in the universe, and accounted for three quarters of the Sun's original material. This proportion obviously changes as the hydrogen is burned, and within the very central regions virtually all the hydrogen has been converted to helium. The outer regions have not yet taken part in hydrogen burning. Astronomers have measured the chemical composition of the Sun, and can thus estimate that of the initial solar nebula from which the sun and planets formed. In addition to 78 percent by weight of hydrogen, they find 20 percent to be helium, while only 2 percent remains for all the heavier elements such as oxygen, carbon, nitrogen, and iron.

What is a quark ? .. The universe," the poet Muriel Rukeyser once wrote, "is made of stories, not atoms." This being the science section, you might be tempted to regard that statement as a predictable humanistic rant against cold scientific reality. For the last 300 years, after all, the story that physicists have been telling us is that the shifting shape of the world is made exactly of atoms, irreducible and indestructible nuggets of existence, bouncing around according to Newton's and a few other simple laws.

The job of the physicist was simply to elucidate the identity and properties of the elementary particles engaged in this dance. Democritus, who invented the idea of atoms, endowed them simply with mass, shape and motion; today's elementary particles quarks and electrons  have mass, charge, spin, strangeness and charm, among other properties, but the basic picture remains the same.

Or does it? Nowadays physicists those coldblooded reductionists are telling a more poetic but no less mathematically rigorous tale. It is a story not of a clockwork world but an entangled interactive world whose constituents derive their identities and properties from one another in endless negotiation  a city, in one physicist's words, of querulous social inhabitants. In other words, they are telling a tale about relationships.

Take, for example, a recent calculation in which mass surely one of the fundamental properties of an elementary particle  seems to conjure itself out of thin mathematical air in a phenomenon that Frank Wilczek, a physicist at M.I.T., calls "mass without mass."

Dr. Wilczek found that when he used a simplified version of the equations of quantum chromodynamics, which describes the behavior of quarks, to compute the masses of the proton and the neutron, he got the right answer even if the quarks inside them had no mass at all. 

Where did the mass come from? It turns out that the quarks zipping around inside the proton, say, have a lot of kinetic energy, and that energy is equivalent to mass, according to Einstein's relativity.

In a talk in San Francisco last month, Dr. Wilczek referred to his calculation as an example of "it from bit," a phrase coined by the Princeton theorist John Wheeler to describe the dream of a theory of the universe based entirely on logic without any adjustable parameters  a universe with no knobs to twiddle. In this case, the theory of quantum chromodynamics seems to leave God with no choice about the mass of the proton. The mass comes entirely from the arrangement of the quarks and not at all from the quarks themselves.

Particle physics, Dr. Wilczek and his colleagues like to point out, is not really about particles anymore, but about their mathematical relationships  in particular symmetries  aspects of nature that remain invariant under different circumstances and viewpoints. One example of this snowflake approach to science is the dictate that the laws of physics be the same at any speed, which forms the basis of Einstein's theory of relativity.

Another was the so-called eightfold way, a pattern that Murray Gell- Mann and Yuval Ne'emann discerned in 1961 in the properties of what was then a burgeoning list of elementary particles, allowing them to predict the existence of a previously unsuspected particle. The work contributed to Dr. Gell-Mann's 1969 Nobel Prize. Today physicists hoping for a toehold on a theory that would unite all the forces of nature into a single mathematical expression are straining for a glimpse of something called supersymmetry.

Quantum mechanics, which are the house rules of particle physics, enforce their own powerful version of relatedness. According to them, it is possible to create "entangled" particles which remain connected even if they are light-years apart, so that measuring one instantaneously affects the outcome of measuring the other. Einstein, who did not like quantum mechanics, labeled this effect "spooky action at a distance," but it is real enough to have a future in cryptography and quantum computers.

Einstein did try to embrace another, even spookier, kind of action at a distance in his general theory of relativity, which describes gravity as a warp in the geometry of space. This was a suggestion by Ernst Mach, a 19th-century physicist, philosopher and scourge of absolutist thinking, that since all motion was relative, the inertia of any given object in the universe was somehow determined by its relation to all the other masses in the universe. According to Mach's principle, it makes no sense to think of a single particle alone in the universe. Scholars seem to agree that Einstein's theory did not achieve this goal, but the idea continues to haunt the work of theorists working to marry Einstein's gravity to quantum mechanics.

"It can no longer be maintained that the properties of any one thing in the universe are independent of the existence or nonexistence of everything else," the quantum gravity theorist Lee Smolin wrote in his 1997 book, "The Life of the Cosmos." No electron is an island.

Dr. Smolin argues in his book that society (and for that matter science) has yet to come to grips with the lessons of relativity and quantum mechanics. Cosmologists, for example, persist in speaking as if they can observe the whole universe, which they cannot do because they must remain part of it, messing it up by their activities. 

According to relativity, each place in the universe is unique and thus yields a unique viewpoint. As a result, he suggests, we have to abandon the idea that any single observer can compile a complete description of the universe. It may be that cosmological knowledge is a community effort, with each individual only able to attain a piece of the truth. "I accept that I cannot know everything," Dr. Smolin has written. "But perhaps, at least in principle, we can know everything."

To the extent that the stories we tell about nature seem to be connected to the stories we tell about ourselves, such thoughts could augur a shift that might yet reverberate through the metaphysical foundations of society. Scholars have noted what sometimes seems like a parallel between human social and political arrangements and our perception of the nature of the physical world. Metaphors from one arena of life seem to be able to infect others.

"There are periods when a particular idea holds sway in many different fields," said Gerald Holton, a historian and physicist at Harvard. "The great question is why?" 

One such episode, Dr. Holton points out, happened early in the 20th century, when the notions of discontinuity and non-Euclidean geometry began to predominate in both art and science. Among those influenced by these ideas was the Russian abstract artist Wassily Kandinsky, who said that he was inspired in his quest to transgress the boundaries of traditional painting by experiments in 1912 showing that the previously inviolable atom in fact had an internal structure, namely a nucleus. "The collapse of the atom model," he wrote in his memoir, "Rckblick," "was equivalent in my soul to the collapse of the whole world." After that, anything was possible.

It has been speculated that watching the movements of the stars gave humans their first hints of order in the universe. Is it a coincidence that life was dominated by hierarchies of kings and medieval court societies while the heavens were thought to consist of concentric spheres centered on the earth? Or that modern democracy with its view of autonomous citizens with inalienable rights arose at about the same time as Newtonian physics with its atoms with their fixed properties bouncing in absolute space?

"In the beginning, when the King's will began to take effect, He engraved signs into the heavenly sphere," it says in the Zohar, a book of Kabbalistic writings from the first century. What signs do we see on the heavenly spheres today?

Newtonian atoms seem like a prescription for alienation. If the word got out that all particles were entangled, would we accept that our lives too were entangled? Dr. Wilczek, whose own book (with Betsy Devine) was called "Longing for the Harmonies," said that the connection between physics and society was "subtle," but he also agreed enthusiastically that the potential for influence was enormous. "If you have the idea that everything is connected and related, it might make you take everything more seriously," Dr. Wilczek said. "Many conflicts and concerns might seem very petty."

It would be pretty to think that physicists could remake society, but the metaphors probably flow the other way, according to some historians of science. "After all," says Lynn K. Nyhart, who studies the history of biology at the University of Wisconsin, "science is surrounded by society," pointing out that the phrase "natural selection" was first used in economic circles before Darwin appropriated it to describe biological evolution. (Although the economists seem to have borrowed the word "nature" first.) Dr. Nyhart said she thought that utopian language in quantum physics books sounded like a reaction against the atomization of society. "We are so atomized by the markets and people are trying to find ways to reassert their connections." 

In short we want a new story to tell ourselves.

What is Facault ? .. A relatively large mass suspended from a long wire mounted so that its perpendicular plane of swing is not confined to a particular  direction and, in fact, rotates in relation to the Earth's surface. Jean-Bernard-Lon Foucault assembled (1851) in Paris the first pendulums of this type, one of which consisted of a 28-kilogram (62-pound) iron ball suspended from the dome of the Panthon by a steel wire 67 m (220 feet) long and kept in motion by a mechanism.
 
The rotation of the plane of swing of Foucault's pendulums was the first laboratory demonstration of the Earth's spin on its axis. While any Foucault pendulum swings back and forth in a plane, the Earth rotates beneath it, so that relative motion exists between them. At the North Pole, latitude 90 north, the relative motion as viewed from the plane of the pendulum's suspension is a counterclockwise rotation of the Earth once every 24 hours; whereas the plane of the pendulum as viewed from the Earth looking upward rotates in a clockwise direction once a day. A Foucault pendulum always rotates clockwise in the Northern Hemisphere with a rate that becomes slower as the Equator is approached. Foucault's original pendulums at Paris rotated clockwise at a rate of more than 11 per hour, or with a period of about 32 hours per complete rotation. The rate of rotation depends on the latitude. At the Equator, 0 latitude, a Foucault pendulum does not rotate. In the Southern Hemisphere, rotation is counterclockwise.
  The rate of rotation of a Foucault pendulum can be stated mathematically as equal to the rate of rotation of the Earth times the sine of the number of degrees of latitude. Because the Earth rotates once a day, or 360 every 24 hours, its rate of rotation may be expressed as 15 per hour, which corresponds to the rate of rotation of a Foucault pendulum at the North or South Pole. At latitude 30 north, for example, at Cairo or New Orleans, a Foucault pendulum would rotate at the rate of 7.5 per hour, for the sine of 30 is equal to one-half. The rate of rotation of a Foucault pendulum at any given point is, in fact, numerically equal to the component of the Earth's rate of rotation perpendicular to the Earth's surface at that point.

Physics

10 Physics Questions to Ponder for a Millennium or Two

Kevin Moloney for The NY Times. Dr. David Gross, a theoretical physicist at the Univ of CA, has a big problem. Actually, 10 of them. 

Who of us would not be glad to lift the veil behind which the future lies hidden; to cast a glance at the next advances of our science and at the secrets of its development during future centuries?" One hundred years ago, with those inviting thoughts, the German mathematician David Hilbert opened his landmark address to the International Congress of Mathematicians in Paris, laying out 23 of the great unsolved problems of the day. "For the close of a great epoch," Hilbert declared, "not only invites us to look back into the past but also directs our thoughts to the unknown future." With another century ending -- a whole millennium in fact -- the pressure is all the greater to tabulate human ignorance with lists of the most enticing cosmic mysteries. In May, the Clay Mathematics Institute of Cambridge, Mass., emulated Hilbert, announcing (in Paris, for full effect) seven "Millennium Prize Problems," each with a bounty of $1 million. The list is at: www.claymath.org/prize_problems/. And last month physicists, with a typically lighter touch, ended a conference on superstring theory at the University of Michigan with a session called "Millennium Madness," choosing 10 of the most perplexing problems in their field. It was like a desert island game, involving some of science's smartest people. "The way I thought about this challenge was to imagine what question I would ask if I woke up from a coma 100 years from now," said Dr. David Gross, a theoretical physicist at the University of California at Santa Barbara, as he unveiled the winners. He and the other judges made the selection, he noted, "in the middle and after this party in which we were sufficiently drunk." After weeding out unanswerable questions (like "How do you get tenure?"), the judges came up with enough puzzles to occupy physicists for the next century or so. There are no monetary prizes, though solving any one of these would almost guarantee a trip to Stockholm. 1. Are all the (measurable) dimensionless parameters that characterize the physical universe calculable in principle or are some merely determined by historical or quantum mechanical accident and uncalculable? Einstein put it more crisply: did God have a choice in creating the universe? Imagine the Old One sitting at his control console, preparing to set off the Big Bang. "How fast should I set the speed of light?" "How much charge should I give this little speck called an electron?" "What value should I give to Planck's constant, the parameter that determines the size of the tiny packets -- the quanta -- in which energy shall be parceled?" Was he randomly dashing off numbers to meet a deadline? Or do the values have to be what they are because of a deep, hidden logic? These kinds of questions come to a point with a conundrum involving a mysterious number called alpha. If you square the charge of the electron and then divide it by the speed of light times Planck's constant, all the dimensions (mass, time and distance) cancel out, yielding a so-called "pure number" -- alpha, which is just slightly over 1/137. But why is it not precisely 1/137 or some other value entirely? Physicists and even mystics have tried in vain to explain why. 2. How can quantum gravity help explain the origin of the universe? Two of the great theories of modern physics are the standard model, which uses quantum mechanics to describe the subatomic particles and the forces they obey, and general relativity, the theory of gravity. Physicists have long hoped that merging the two into a "theory of everything" -- quantum gravity -- would yield a deeper understanding of the universe, including how it spontaneously popped into existence with the Big Bang. The leading candidate for this merger is superstring theory, or M theory, as the latest, souped-up version is called (with the M standing for "magic," "mystery," or "mother of all theories"). 3. What is the lifetime of the proton and how do we understand it? It used to be considered gospel that protons, unlike, say, neutrons, live forever, never decaying into smaller pieces. Then in the 1970's, theorists realized that their candidates for a grand unified theory, merging all the forces except gravity, implied that protons must be unstable. Wait long enough and, very occasionally, one should break down. The trick is to catch it in the act. Sitting in underground laboratories, shielded from cosmic rays and other disturbances, experimenters have whiled away the years watching large tanks of water, waiting for a proton inside one of the atoms to give up the ghost. So far the fatality rate is zero, meaning that either protons are perfectly stable or their lifetime is enormous -- an estimated billion trillion trillion years or more. 4. Is nature supersymmetric, and if so, how is supersymmetry broken? Many physicists believe that unifying all the forces, including gravity, into a single theory would require showing that two very different kinds of particles are actually intimately related, a phenomenon called supersymmetry. The first, fermions, are loosely described as the building blocks of matter, like protons, electrons and neutrons. They clump together to make stuff. The others, the bosons, are the particles that carry forces, like photons, conveyors of light. With supersymmetry, every fermion would have a boson twin, and vice versa. Physicists, with their compulsion for coining funny names, call the so-called superpartners "sparticles": For the electron, there would be the selectron; for the photon, the photino. But since the sparticles have not been observed in nature, physicists would also have to explain why, in the jargon, the symmetry is "broken": the mathematical perfection that existed at the moment of creation was knocked out of kilter as the universe cooled and congealed into its present lopsided state. 5. Why does the universe appear to have one time and three space dimensions? "Just because" is not considered an acceptable answer. And just because people can't imagine moving in extra directions, beyond up-and-down, left-and-right, and back-and-forth, doesn't mean that the universe had to be designed that way. According to superstring theory, in fact, there must be six more spatial dimensions, each one curled up too tiny to detect. If the theory is right, then why did only three of them unfurl, leaving us with this comparatively claustrophobic dominion? 6. Why does the cosmological constant have the value that it has? Is it zero and is it really constant? Until recently cosmologists thought the universe was expanding at a steady clip. But recent observations indicate that the expansion may be getting faster and faster. This slight acceleration is described by a number called the cosmological constant. Whether the constant turns out to be zero, as earlier believed, or some very tiny number, physicists are at a loss to explain why. According to some fundamental calculations, it should be huge -- some 10 to 122 times as big as has been observed. The universe, in other words, should be ballooning in leaps and bounds. Since it is not, there must be some mechanism suppressing the effect. If the universe were perfectly supersymmetric, the cosmological constant would become canceled out entirely. But since the symmetry, if it exists at all, appears to be broken, the constant would still remain far too large. Things would get even more confusing if the constant turned out to vary over time. 7. What are the fundamental degrees of freedom of M-theory (the theory whose low-energy limit is eleven-dimensional supergravity and that subsumes the five consistent superstring theories) and does the theory describe nature? For years, one big strike against superstring theory was that there were five versions. Which, if any, described the universe? The rivals have been recently reconciled into an overarching 11-dimensional framework called M theory, but only by introducing complications. Before M theory, all the subatomic particles were said to be made from tiny superstrings. M theory adds to the subatomic mix even weirder objects called "branes" -- like membranes but with as many as nine dimensions. The question now is, Which is more fundamental -- are strings made from branes or vice versa? Or is there something else even more basic that no one has thought of yet? Finally, is any of this real, or is M theory just a fascinating mind game? 8. What is the resolution of the black hole information paradox? According to quantum theory, information -- whether it describes the velocity of a particle or the precise manner in which ink marks or pixels are arranged on a document -- cannot disappear from the universe. But the physicists Kip Thorne, John Preskill and Stephen Hawking have a standing bet: what would happen if you dropped a copy of the Encyclopaedia Britannica down a black hole? It does not matter whether there are other identical copies elsewhere in the cosmos. As defined in physics, information is not the same as meaning, but simply refers to the binary digits, or some other code, used to precisely describe an object or pattern. So it seems that the information in those particular books would be swallowed up and gone forever. And that is supposed to be impossible. Dr. Hawking and Dr. Thorne believe the information would indeed disappear and that quantum mechanics will just have to deal with it. Dr. Preskill speculates that the information doesn't really vanish: it may be displayed somehow on the surface of the black hole, as on a cosmic movie screen. 9. What physics explains the enormous disparity between the gravitational scale and the typical mass scale of the elementary particles? In other words, why is gravity so much weaker than the other forces, like electromagnetism? A magnet can pick up a paper clip even though the gravity of the whole earth is pulling back on the other end. According to one recent proposal, gravity is actually much stronger. It just seems weak because most of it is trapped in one of those extra dimensions. If its full force could be tapped using high-powered particle accelerators, it might be possible to create miniature black holes. Though seemingly of interest to the solid waste disposal industry, the black holes would probably evaporate almost as soon as they were formed. 10. Can we quantitatively understand quark and gluon confinement in quantum chromodynamics and the existence of a mass gap? Quantum chromodynamics, or QCD, is the theory describing the strong nuclear force. Carried by gluons, it binds quarks into particles like protons and neutrons. According to the theory, the tiny subparticles are permanently confined. You can't pull a quark or a gluon from a proton because the strong force gets stronger with distance and snaps them right back inside. But physicists have yet to prove conclusively that quarks and gluons can never escape. When they try to do so, the calculations go haywire. And they cannot explain why all particles that feel the strong force must have at least a tiny amount of mass, why it cannot be zero. Some hope to find an answer in M theory, maybe one that would also throw more light on the nature of gravity. 11. (Question added in translation). Why is any of this important? In presenting his own list of mysteries, Hilbert put it this way: "It is by the solution of problems that the investigator tests the temper of his steel; he finds new methods and new outlooks, and gains a wider and freer horizon." And in physics, the horizon is no less than a theory that finally makes sense of the universe. 

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