As a result, physicists have now precisely calculated the abundances of light elements produced in the big bang and how those quantities have changed because of subsequent events in the interstellar medium and nuclear processes in stars. trailer <<015050FD62EA49188C0528BB11940A75>]>> startxref 0 %%EOF 271 0 obj <>stream Hubble’s measurements indicated that the redshift of a distant galaxy is greater than that of one closer to the earth. So if a galaxy sits in the line of sight between the earth and some distant object, it will bend the light rays from the object so that they are observable [see “Gravitational Lenses,” by Edwin L. Turner; SCIENTIFIC AMERICAN, July 1988]. Hoyle intended to disparage the theory, but the name was so catchy it gained popularity.

Edwin L. Turner is a professor of Astrophysical Sciences at Princeton University, an affiliate scientist at the Kavli Institute for the Physics and Mathematics of the Universe at the University of Tokyo, a visiting member in the Program in Interdisciplinary Studies at the Institute for Advanced Study in Princeton, and a co-founding Board of Directors member of YHouse, Inc. Our solar system is relatively young: it formed five billion years ago, when the universe was two thirds its present size. But the processes by which planets, stars, galaxies, and the universe form and change over time are also types of "evolution." 0000000861 00000 n

One method for gauging distance is to observe the apparent brightness of a galaxy.
The value of Hubble’s constant seemed to be the same in all directions, a necessary consequence of uniform expansion. Measurements of such tiny fluctuations have not yet been done, but they might be accomplished in the generation of experiments now under way.

Moreover, the speed with which any two raisins move apart is directly and positively related to the amount of dough separating them. In 1922 the Russian theorist Alexander A. Friedmann realized that Einstein’s universe is unstable; the slightest perturbation would cause it to expand or contract. The universe may expand forever, in which case all the galaxies and stars will eventually grow dark and cold. Despite the fact that significant details of this pioneering work were in error, it forged a link between nuclear physics and cosmology. Distant radio galaxies, on the other hand, appear to have elongated and sometimes irregular structures.

Then, in 1929, the eminent astronomer Edwin P. Hubble showed that the rate a galaxy is moving away from us is roughly proportional to its distance from us. Observations show that by the time the universe was one fifth its present size, matter had gathered into gas clouds large enough to be called young galaxies. The object behind the lens is always found to have a higher redshift than the lens itself, confirming the qualitative prediction of Hubble’s law. As this material accumulates, they suggested, it forms new stars to replace the old. At a particular instant roughly 15 billion years ago, all the matter and energy we can observe, concentrated in a region smaller than a dime, began to expand and cool at an incredibly rapid rate. Modern surveys confirm the fundamental tenet that the universe is homogeneous on large scales. Our universe may be viewed in many lights—by mystics, theologians, philosophers or scientists. That is, all evidence indicates that the light elements were produced in the hot, young universe, whereas the heavier elements appeared later, as products of the thermonuclear reactions that power stars. Peebles is currently an emeritus professor at Princeton University. The Milky Way, for instance, resides in a knot of two dozen galaxies; these in turn are part of a complex of galaxies that protrudes from the so-called local supercluster. Some 15 billion years ago the universe emerged from a hot, dense sea of matter and energy. Arno A. Penzias and Robert W. Wilson identified the signal as the cosmic background radiation. b{{8�I�rԢ%+�j��"Z5��Q������N ��=�1V��y�ZO ��yڕ�\�d��bi^+�hZo����dZ�NI����@���h���-7dr��Cn. Indeed, the predictions of the theory have survived all tests to date.

Likewise, when astronomers study the population of massive, dense clusters of galaxies, they find differences between those that are close and those far away.

As we improve measurements of the expansion rate and the ages of stars, we may be able to confirm that the stars are indeed younger than the expanding universe. In the 1930s Richard C. Tolman of the California Institute of Technology showed that the temperature of the cosmic background would diminish because of the universe’s expansion. It is interesting that Penzias and Wilson were led to this idea by the news that Dicke had suggested that one ought to use a radiometer to search for the cosmic background. In an explosion the fastest particles move out into empty space, but in the big bang cosmology, particles uniformly fill all space. But what would this radiation signature look like? 0000022497 00000 n When the universe had expanded an additional 1,000 times, all the matter we can measure filled a region the size of the solar system. Such galaxies should contain more shortlived stars and more gas out of which future generations of stars will form.

All of this occurred within the first minute of the expansion. In following the debate on such matters of cosmology, one should bear in mind that all physical theories are approximations of reality that can fail if pushed too far. Astronomers have studied this radiation in great detail using the Cosmic Background Explorer (COBE) satellite and a number of rocket-launched, balloon-borne and ground-based experiments. Fifteen billion years from now stars like our sun will be relatively rare, making the universe a far less hospitable place for observers like us. Distant clusters contain bluish galaxies that show evidence of ongoing star formation.

So if galaxies are all moving away from one another and are evolving from earlier forms, it seems logical that they were once crowded together in some dense sea of matter and energy.

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Astronomers know that the density of the early universe did not vary by much, because they observe only slight irregularities in the cosmic background radiation. When the universe was very young and hot, radiation could not travel very far without being absorbed and emitted by some particle.

The following assumptions of the Big Bang theory are challenged and found to be false: the cosmological principle, the assumption that all matter formed at the same time and the assumption regarding the cause of the cosmic microwave background <<0F749CCEEAB0EB4595482482F4689BF7>]>> Another theory, the steady state theory, also succeeds in accounting for the expansion and homogeneity of the universe. The ages of the oldest known chemical elements are also approximately 15 billion years—a number that comes from radioactive dating techniques. In the dense, hot early universe thermonuclear reactions produced elements heavier than hydrogen, including deuterium, helium and lithium. The theory of evolution, widely referred to as Darwinism, is an-other application of materialism to the natural world.
In the 1960s Bell Laboratories used a radiometer in a telescope that would track the early communications satellites Echo-1 and Telstar. 0000004370 00000 n For example, the oldest stars in the disk of the Milky Way galaxy are about nine billion years old—an estimate derived from the rate of cooling of white dwarf stars. The hierarchy of clustering has been traced up to dimensions of about 500 million light-years.

Albert Einstein gave us the now well-tested and accepted Theory of General Relativity, which establishes the relations between mass, energy, space and time. vۯT6˱%z���A+: 0000001948 00000 n

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Hubble contributed to another crucial part of the picture. By the time the universe had expanded to one fifth its present size, the stars had formed groups recognizable as young galaxies. 0000004610 00000 n The rate of change in expansion is therefore related to the gravitational pull of the universe set by its average density. The big bang cosmology makes a different prediction: if galaxies were all formed long ago, distant galaxies should look younger than those nearby because light from them requires a longer time to reach us. %%EOF So far it has been easy to develop theories that are consistent with the available measurements, but more critical tests are in progress.

The expansion of the universe has had little influence on the size of galaxies or even clusters of galaxies that are bound by gravity; space is simply opening up between them. Neutral atoms appeared in abundance only after the expansion had continued for 300,000 years and the universe was 1,000 times smaller than it is now.

The present-day universe has provided ample opportunity for the development of life as we know it—there are some 100 billion billion stars similar to the sun in the part of the universe we can observe. 0000007317 00000 n Our best efforts to explain this wealth of data are embodied in a theory known as the standard cosmological model or the big bang cosmology. This steady state hypothesis predicts that ensembles of galaxies close to us should look statistically the same as those far away. Astronomers are not sure, for example, how the galaxies were formed, but there is no reason to think the process did not occur within the framework of the big bang. 257 0 obj <> endobj xref 257 15 0000000016 00000 n ��3�������R� `̊j��[�~ :� w���! 0000006102 00000 n He counted the number of visible galaxies in different directions in the sky and found that they appear to be rather uniformly distributed. The neutral matter was able to slip through the radiation and to form gas clouds that could collapse to star clusters. Astronomers have determined the approximate rate of the expansion, but no one has yet been able to measure the second value precisely.

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