A "Just Right" Universe

Parameter Maximum
Ground state of He, Be, C, O 4%
Mass of neutron 0.1%
Electron:Proton Ratio 1:1037
Electromagnetic force relative to gravity 1:1040
Expansion rate of universe 1:1055
Cosmological Constant 1:10120
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The table above shows the maximum deviation allowable in the fundamental constants in order to get a universe capable of supporting life. In some instances, changing the constants more than the amount indicated results in a universe that doesn't even contain matter. In many other instances, only hydrogen or light elements would exist (making life impossible). Changing the last two parameters changes the longevity of the universe. Many of these perturbations would result in the universe that would have ended billions of years ago.

That the universe seems to be designed specifically for human life has been called the anthropic principle. Depending upon their philosophical outlook, scientists hold to either the "weak" or "strong" anthropic principle. The weak anthropic principle states that the apparent design of the universe is an illusion, and that there must be some undiscovered underlying principle that explains why the universe seems to be designed. The strong anthropic principle states that the underlying reason that the universe appears to be designed is because it has been designed by the ultimate Intelligent Designer - God. How do we determine which version of the anthropic principle is correct? The standard way to test any theory is to gather data and see which version fits the data better. So far, the strong anthropic principle fits the data better. For example, the last physical constant mentioned in the table above was not discovered until a few years ago, and it is, by far, the most constrained constant discovered to date. Initial observations suggested that the value is the closest value to zero (within 1 part in 10120) known in the universe. Subsequent observations suggest that it may be closer to 1 part in 10240. The degree of fine tuning has led some scientists to make the statement:

"This type of universe, however, seems to require a degree of fine tuning of the initial conditions that is in apparent conflict with 'common wisdom'."1

References Top of page

  1. Zehavi, I, and A. Dekel. 1999. Evidence for a positive cosmological constant from flows of galaxies and distant supernovae Nature 401: 252-254.

Last Modified October 4, 2004


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