PureInsight | September 9, 2002
Currently, there are two major methods to estimate the age of the universe. The first method is to measure the faintest white dwarf stars in the globular cluster. This method is based on the current theory of stellar evolution. Scientists believe that the globular clusters are the oldest galaxies in the universe and white dwarf stars are among the oldest stars in the galaxy. Furthermore, the fainter a dwarf star, the older it is. A white dwarf star is a star of mass comparable to that of the Sun with a volume similar to the Earth. It could be over a million times denser than water. A white dwarf cools down gradually for radiating heat or light. Therefore, by calculating the time it needs to cool down, scientists can estimate its age and 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 old.
The second method uses the Hubble Constant (H0) which is based on the popular Big Bang theory of cosmology to estimate the age of the universe. Modern astronomical observation shows that our universe is expanding so the distances between galaxies are increasing. The Hubble’s Law states that there is a simple proportional relationship between the receding speed of two galaxies and the distance between them, i.e., v = H0×d. Assuming that the Hubble constant H0 is a constant, by measuring the receding speed and the distance between the two galaxies, the inverse of H0 1/ H0 = d/v thus gives the time since the “Big Bang.” The latest result using this method gives the age of the universe of about 13 billion years.
However, the latest astronomical observation confirmed that the universe is driven by a mysterious force and the expansion rate is increasing. Therefore, the Hubble Constant is not really a constant. Furthermore, recently a great number of astonishing astronomical discoveries (such as the birth of great numbers of new stars in many old galaxies, the combinations and regenerations of many galaxies, vast number of starbursts, mysterious dark matter, and frequent Gamma Ray Bursts, etc.) showed that our knowledge about the universe is too limited. So it is very possible that our estimation of the age of the universe could be far from the truth.
Currently, more and more new discoveries in astronomy are raising serious questions about the current cosmology theory and scientists are gradually changing their views of the universe. Recently, Professor Paul Steinhardt at the University of Princeton and Professor Neil Turok at the University of Cambridge proposed the “cyclic model of the universe.” Their theory claims that the universe has neither start nor end and has been forming and reforming for eternity. According to BBC News, the professors who proposed the theory said the universe had to be this way to enable us to explain a great mystery: Why stars and galaxies are receding (expanding) and separating further and further away. The universe is already full of mysteries and is beyond our imagination. There are black holes, quark stars, and particles which regenerate from the void and annihilate into nothing.
Professor Steinhardt said that the outcome of these formulas show that the universe has no start or end and that series of “Big Bangs” will continue for eternity. He said, “What we're proposing in this new picture is that the Big Bang is not a beginning of time but really just the latest in an infinite series of cycles, in which the Universe has gone through periods of heating, expanding, cooling, stagnating, emptying, and then re-expanding again.” According to the theory, our universe will continue to expand and then have another “Big Bang” in a corner of the universe. After this, the process will start again. They pointed out that the current universe was born on the debris of the last universe. Scientists are constructing the new generation instruments both on the Earth and in space to evaluate the model.
The renowned method of measuring the age of the Earth now in the science community is the method of half-life of radioactive isotopes. The method examines the relationship of the normalized ratios of the parent and the daughter elements in old rocks and uses it to estimate the age of the earth (so called Isochron dating). There are three major assumptions: 1. The earth was originally formed from interstellar gas and the oldest rocks were formed as the Earth was cooling down; 2. The crystallites inside these rocks were isolated from the environment since they were formed, i.e., there is no material exchange between the crystallites and the environment; 3. The half-lives of the elements used for dating are constant. Using this method with the oldest rocks ever found on the earth gives an age of 3.8-3.9 billion years. The rocks on the moon are older, which gives an age of 4.5 billion years. The best age quoted in the science community, 4.54 billion years, was actually the age of the oldest meteorite in the solar system, because scientists believe it should be as old as the Earth.
Strictly speaking, one could conclude that the age a method gives is merely the age of the rocks on the earth. It is “model dependent,” if, however, the earth is not formed by the way as scientists currently expect, i.e., from the interstellar gas, but from the rocks in the spaces combined together under some mechanism, the age of the rock will greatly differ from the age of the Earth. For example, if we measure the age of the rock in the base of a house and use it as an estimation of the age of a house, the age we get will be certainly much larger than its true value. A better way to estimate the age of a house probably is to measure the thickness of dust collected on its main beam or observe how much it has eroded. The same principle holds for estimating the age of the earth. Actually, in history, there were many people who tried to estimate the age of the Earth by measuring the thickness of the sediment on Earth and the ages they got were really much smaller than those from the radioactive isotope dating method.
The famous ones are A. Keikie (1868) and T.H. Huxley (1869)’s 100 million years; J. Joly (1908) and W. J. Sullas (1909)’s 80 million years; T. M. Reade (1893)’s 95 million and Charles D. Walcott (1893)’s 35-80 million years. After modern radioactive isotope dating became available, these methods were gradually forgotten. The main reason is that the ages these methods reached were far smaller than those from the isotope dating. Scientists nowadays believe that the age of the Earth is the same as the age of the oldest rocks on the Earth. Another reason is these methods have to deal with the complicated process of geological evolution of the Earth and some features are difficult to determine precisely .
Currently, the astronomical observations imply that our Earth may go through tremendous changes in its history. For example, Dr. Tim Spahr, an astronomer of the Minor Planets Center of the Harvard-Smithsonian Center in Harvard University thinks that, statistically, there should be an asteroid of a diameter of more than 6 miles striking the Earth every 100 million years and the Earth will change dramatically after the collision.
Scientists believed that half-lives of elements are constant. However, there is a paper published in the latest issue of Nature (Volume 418, p602). It reported that a team of astronomers from South Wales University in Australia discovered by analyzing the atomic spectrum emitted by old galaxies that the fine-structure constant is changing with time. They concluded that the speed of light in a vacuum is not constant after finishing some calculations. Since the half-life of an element depends on the speed of light, if it is indeed the case that the speed of light is not constant, determination of the ages of rocks from the isotope dating is suspicious.
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).
6. Dalrymple, G. Brent, 1991, The Age of the Earth: Stanford, Calif., Stanford University Press.