"What is the Universe made of? What is its mass? What is its future?" These are the great and inter-related cosmological questions of our era, and many physical scientists and engineers are at work to answer them--in fact, it is only today that answers to these questions finally seem to be attainable. Project QUEST (a collaboration involving Yale scientists, see sidebar) focuses on the question of the mass of the universe. This article will examine this and other cosmological questions as well as the unique history of Project QUEST itself.
1. The size of the Universe
Dealing with the Universe, whose extent has always challenged human imagination, astronomers have developed methods collectively known as the "distance ladder" to measure astronomical distances. Briefly, these are:
2. The Big Bang and a relation between distance and age
In 1929, Edwin Hubble concluded, on the basis of the red shift observed in their spectra, that distant galaxies are receding from our own, the Milky Way, at a rate proportional to their distance. from it. This means we live in a Universe which is uniformly expanding, and from that realization arose the concept of its origin in the Big Bang--a name reflecting the concept that at one instant in time all matter and radiant energy were located in one place.
After the Big Bang, Hubble's Law describes the evolution of the expanding Universe. It can be most simply stated as
v = H x D (or H=v/D)
where v is the velocity of recession of the receding object, D is its distance from the point of observation, and H is Hubble's constant. Its application leads to the conclusion that the Universe is about 10 billion years old. The ages of the oldest stars, as calculated from their nuclear burning time and from the cooling rates of white dwarf stars in our own galaxy, are about 15 billion years. This contradiction (which led one astronomer to protest that "You can't be older than your own Ma!") may be an indication of a deeper problem or simply of imprecision in measurements of H.
The best present calculation of H gives an age within a factor of 2 of that implied by stellar evolution and cooling-rate dating--not a bad match by current standards. Underlying whatever theory may be applied is an assumption that all the objects have identical velocity histories, which is not necessarily the case. Nor is it even certain whether the velocity of recession is: (1) less than the "escape velocity" (which means the universe is oscillating); (2) greater than it (which means it is "evaporating"); or (3) equal to the escape velocity (which means it is in a static state, sometimes described as "heat death").
3. The mass of the Universe
In 1933, when Swiss-born astronomer Fritz Zwicky was studying galactic clusters, he found that the Coma galaxies were rotating so fast (moving at about 1000 kilometers per second) that the cluster must be held together by a mass ten to a hundred trillion times that of the sun--many times more than an inventory of its visible population could have totaled! The surprising estimate that the visible universe comprises only 1 to 10% of its total mass and that 90 to 99% of the whole Universe is "dark matter," invisible to the human eye or ordinary detection instruments, is based on many observations of this kind.
The entire mass of the Universe is comprised of galaxies, gas, and dark matter. Project QUEST was designed to locate and estimate the mass of that dark matter which exists in condensed form. Other candidates for the missing mass are (1) enormous quantities of nearly weightless particles, such as neutrinos; and (2) "black holes" which, having the property of irreversibly capturing all matter and radiation in their vicinity, are singularities in which mass is undefined and thus not measurable.
Theory and Technology
Hubble's ideas, the Big Bang, and the theory of general relativity offer a theoretical framework within which the major questions can be posed and presumably answered.
The major technological factors are the recent great expansion of computing power, many refinements in silicon-imaging technology, and improvements in charge-coupling devices.
Detecting Dark Matter
Einstein's triumph in predicting that a massive object must bend light offers the method known as Gravitational Lensing. Here the light-source is a quasar, chosen because of its high luminosity and great distance. When the three--quasar, massive dark object, and detecting telescope--are aligned, the quasar beam will be split, producing two or more separate images at the telescope. The proof that all are images of the same quasar will be their identical red shift. And if the massive object is invisible, it Is de facto made of dark matter!
How Many Pictures ?
Statistical reliability requires a sample of 500,000 quasars, of which only 10,000 or so have been identified to date. Hence the need for a Schmidt telescope, which is superior to all other designs because of its large field of view. But the need to collect an enormous number of star pictures eliminates photography and photographic development from consideration, and requires a rate of acquisition which could not have been imagined without a camera based on the charge-coupled device known as the CCD.
In its experimental form, as designed for the Schmidt telescope, the camera comprises an assemblage of CCDs, each of which is a silicon "chip" one inch square, and displays a square array of over 4 million pixels. [A computer user will recognize "pixel" as a term for one of the dots which make up the picture on his monitor.] In the CCD, each pixel will exist in one of the interstices formed when a horizontal grid and a vertical grid of micro-"wires" overlying each other are programmed to act as either barrier or gate for the 15 x 15 micron pixels they outline.
In operation, the top row of pixels is vacant and the other rows contain the charges which are induced by radiation each has received. Then all these charges are moved up one row (together and in their original columnar order), and the "new" top row is read pixel by pixel, in left to right sequence, and amplified to the computer. Repetition of these steps conveys the contents of the CCD--that is, the picture--for storage, visual display and analysis.
The camera now being readied for service in Venezuela contains a 4 by 4 array of such CCDs, and has produced good star pictures at Yale's telescope in Bethany, CT. Its next version will have 96 CCDs. At least initially, it will be used in "drift-scan" mode. The Schmidt telescope at Merida, which is about 8 degrees north of the equator, will be pointed in a direction such that the rotation of the earth will have it sweep a path close to that which it would have if it were
on the equator. The mounting of the CCDs is constructed to permit internal rotation adjustment which can match the actual path very closely to the ideal.
How long will QUEST take?
It will be years. But with ingenuity, teamwork, and a touch of the serendipity that brought the telescope, astronomers, camera and physicists together at the right moment in time, who can guess what the ultimate findings will be or what new discoveries will be made--even before a half-million new quasars have been found?--Arthur Ross, freelance science writer
The Venezuelan connection
In the late 1940s, Venezuela, under a new constitution, elected a labor-left president whose democratic reforms aroused the military to a coup. This coup resulted in a ruling junta whose strong man, Marcos Perez Jimenez, became dictator. One of his acts was to purchase a very large Schmidt telescope to install in the city of Caracas near his official residence. However, popular opposition (which by then included the navy and air force) brought down Perez, the last of Venezuela's dictators, in 1958.
When, in 1970, a later Venezuelan president consulted scientists in Argentina, Mexico, and the United States on what to do with the unmounted instrument, he was directed back home to a local authority: Sabatino Sofia, an Italian-born resident and Yale graduate. Despite the fact that Venezuela had no native astronomers, Sofia urged that the telescope not be sold " because nothing in science can better teach the scientific method than astronomy!" His successful argument led eventually to the establishment of a PhD program at the University of the Andes, to the Venezuelan Center for Research in Astronomy (CIDA), and to the erection of the Schmidt telescope in the Venezuelan Andes near the city of Merida in 1978. The crated telescope had successfully withstood tropical weather for 15 years without damage (a tribute to German packaging). Meanwhile, Professor Sofia had become a well-known astronomer who was appointed a professor of astronomy at Yale in 1985.
Yale and Project Quest
Charles Baltay had completed his graduate study in high energy physics, also at Yale, in 1963. After joining the physics faculty at Columbia University, he became full professor and director of the Nevis Laboratories there. Professor Baltay left Columbia to become Higgins Professor of Physics at Yale in 1988. He carried out experiments at Brookhaven, CERN, Fermilab, and the Stanford Linear Accelerator, and his counsel has helped to shape the progress of American high-energy physics.
Deciding that the time was ripe to find solutions to the cosmological questions, he was instrumental in organizing Project QUEST during 1995, thus creating a collaboration of CIDA, Yale University (Physics and Astronomy), the University of Illinois (Astronomy), and the University of the Andes (Astronomy). Today Professors Baltay and Sofia are chairmen of their respective departments, and this meeting of parallel life-lines reflects their academic interests. The affiliation of particle physicists, whose forte is dealing with the smallest objects in the universe, and astronomers, who deal with the largest, promises to be a very productive one.
This linking of the Schmidt telescope (which has the wide field of view so important to maximizing the rate of collecting data); it's "discovery" close to the equator; and a group of Yale scientists with a camera design in progress looking for just such an observatory are examples of happy coincidence. Careful planning could hardly have arranged for their appearing more favorably at the right places and times!
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