(Clearwisdom.net) Scientists currently use two primary means to estimate the age of the universe. The first is to measure the intensity of the faintest white dwarf stars in globular clusters. This method is based on current theories of stellar evolution. Scientists believe that globular clusters are the oldest galaxies in the universe and white dwarf stars are among the oldest stars within them. Hence, the fainter a dwarf star, the older it is. White dwarf stars have a mass comparable to that of the Sun and a volume comparable to the planet Earth, thus they are about a million times as dense than water. A white dwarf cools down by radiating heat or light. By calculating the time required to cool down vis a vis its luminosity, scientists estimate the age of the dwarf stars and extrapolate that to estimate the age of the universe.

Using the latest dwarf data from the Hubble Telescope, scientists estimated that the age of the universe is 13-14 billion years.

The second most prevalent method uses the Hubble Constant (H0), and is based on the popular Big Bang theory. Modern astronomical observations show that our universe is expanding, so the distance between galaxies is increasing. Hubble's Law states that there is a simple proportional relationship between the receding velocity of the two galaxies and the distance between them, i.e., v = H0 d. Assuming that the Hubble constant, H0, does not vary over time, by measuring the rate of recession and the distance between the two galaxies, the formula 1 / H0 = d / v yields the times since the Big Bang. The latest result using this method gives the age of the universe at about 13 billion years. However, the latest astronomical observations have confirmed that the universe is being propelled by a mysterious force and is expanding at an increasing rate, hence the Hubble Constant is not, in fact, constant.

Furthermore, recent astonishing astronomical discoveries (such as the birth of great number of new stars in many old galaxies, the combination and regeneration of many galaxies, vast numbers of starbursts, mysterious dark matter, and frequent gamma gay bursts, etc.) show that our knowledge about the universe is still extremely limited, hence it is quite possible that our estimate of the age of the universe may be far from the truth.

New discoveries in astronomy continue to raise serious questions about the current cosmology and scientists are gradually changing their views of the universe. Recently, Professor Paul Steinhardt of Princeton University and Professor Neil Turok of Cambridge University proposed the "cyclic model of universe." The theory postulates that the universe has neither start nor end and has been forming and reforming for eternity. According to BBC News, the scientists who propose the theory explained that the universe had to be this way if we were going to be able to explain why stars and galaxies are receding from each other, that the universe is expanding. The universe has already been a source of many mysteries to mankind, and to things even well beyond our imaginations. There are black holes, quark stars and particles which regenerate from the void and collapse into nothing. Professor Steinhardt said that his calculations show that the universe has no beginning and no end, and that a series of Big Bangs will continue for eternity. He said, "Our picture of the Big Bang is not the beginning of time, but only the latest one of a long row of Big Bangs. In these cycles, the universe goes through heating, expansion, cooling, contraction, emptiness and then expansion all over again." According to this theory, our universe will continue to expand, and sooner or later, will contract to result in another Big Bang, so the cycle can begin all over again. They point out that the current universe was born of the debris of the last universe. Scientists are designing new instruments for use in space and on Earth to check out their theoretical models.

The recognized method of measuring the age of the Earth in the scientific community is based on the half-life of radioactive isotopes. The method examines the relationship between the radioactive isotopes and their decayed remains in the crystalline structure of the oldest rocks found on the planet (so called Isochron dating). There are three major underlying assumptions:

  1. The earth was formed originally from interstellar gas. The oldest rocks were formed as the Earth began to cool.
  2. The crystalline structures inside these rocks were isolated from the environment since they were formed, i.e., there has been no material exchange between the crystalline structures and the outside environment.
  3. The half-lives of the elements used for dating purposes are constant.

Using this method to date the oldest rocks found on the earth indicates a planetary age of 3.8-3.9 billion years. The rocks on the moon are older, some 4.5 billion years of age. The highest age quoted for our planet in the scientific community is 4.54 billion years, an amount equal to the age of the oldest meteorite so far discovered in our solar system, which some scientists theorize, should be the same age as the Earth.

If one strictly examines this method, one can see that the age the method yields is merely the age of the oldest rocks on the earth. The validity of this estimate is "model dependent." If, for instance, the earth was not formed the way scientists currently expect, i.e. not from interstellar gas, but from rocks in space somehow lumped together, the age of the rock will be much older than the age of the planet. For example if we measure the age of the rocks used to construct the foundation of a house and use the age of the rocks as an estimation of the age of a house, we will come nowhere near the house's true age. A better way to estimate the age of a house might be to measure the thickness of dust collected on an unexposed main beam, or to measure how much it has deteriorated over time. The same principle holds for estimating the age of the earth.

Actually, in history, many people tried to estimate the age of the Earth by measuring the thickness of the sediment on Earth. The ages they deduced were much less than those suggested by the radioactive isotope dating method. Widely known estimates include A. Keikie (1868) and T.H. Huxley's (1869) 100 million years, J. Joly (1908) and W. J. Sullas' (1909) 80 million years, T. M. Reade's (1893) 95 million years and Charles D. Walcott's (1893) 35-80 million years. Once "modern" radioactive isotope dating became prevalent, these former methods were gradually forgotten. The main reason the ages theses methods suggest are much less than those from the isotope dating is that scientists nowadays believe that the age of the earth is the same as the age of the oldest rocks so far found on earth. Another reason is that current methods try to account for the complicated process of the geologic evolution of the Earth, and some features are difficult to be determined precisely.

Current astronomical observations suggest that our Earth may have gone through tremendous changes in its history. For example, Dr. Tim Spahr, an astronomer at the Minor Planets Center of the Harvard-Smithsonian Center at Harvard University said that statistically, an asteroid of at least 6 miles in diameter strikes the Earth roughly every 100 million years, and that the Earth changes dramatically after each collision.

Furthermore, the assumption that the half-lives of elements are constant may well be flawed. A paper published in the latest issue of Nature (Volume 418, p602), reports that by analyzing the atomic spectrum emitted by old galaxies, a team of astronomers at Australia's New South Wales University have discovered that the fine-structure constant changes with time. They conclude that the speed of light in a vacuum is, in fact, not constant. Since the half-life of an element depends on the speed of light, if these new discoveries are true, the age of rocks determined by isotope dating is also put into doubt.

References:

1. http://oposite.stsci.edu/pubinfo/PR/2002/10/pr.html
2. http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v418/n6898/full/418602a_fs.html
3. Webb, J. K. et al. Phys. Rev. Lett. 87, 091301 (2001).
4. Murphy, M. T. et al. Mon. Not. R. Astron. Soc. 327, 1208-1222 (2001).
5. http://science.nasa.gov/newhome/headlines/ast25may99_1.htm
6. Dalrymple, G. Brent, 1991, The Age of the Earth: Stanford, Calif., Stanford University Press.
7. http://oposite.stsci.edu/pubinfo/PR/2002/10/index.html
8. http://www.nature.com/nsu/020422/020422-17.html

á

Category: Perspective