The anthropic principle, string theory, and multiple universes in light of the scientific method.

Epistemology is the study of the nature and grounds of knowledge, especially with reference to its limits and validity. There are two main goals of epistemology: (1) to find out as much truth as possible, and (2) to avoid as much falsehood as possible. These two goals are in tension with each other. In trying to understand the world, the ancient Greek philosophers diligently strove to develop a coherent and well-defined philosophy. Even though modern technology and scientific advancements seem to render the ancient Greeks silly, superstitious, or unenlightened, we are actually faced with the same challenge they were--to find a rational explanation of the universe.

There has been considerable debate lately in the physics community over an idea called the "anthropic cosmological principle" (Barrow and Tipler, 1986; Barrow, 2002; Susskind, 2003). According to this idea, the universe is made just right for life to occur. As one author puts it, "The universe must be suitable for life, otherwise we would not be here to wonder about it" (Overbye, 2003). There are numerous features and mathematical constants in the equations of physics and cosmology which do not seem predictable by any known theory, and which seem to be miraculously tuned to allow life. Any slight deviation from these settings would be disastrous, causing things like stars to collapse and atoms to evaporate. One of the most striking examples of the anthropic principle is the cosmological constant, a number that measures the amount of cosmic repulsion caused by the energy in empty space (Carroll and Press 1992). As predicted by quantum theory, empty space should be brimming with this energy. In fact, recent discoveries have shown that cosmic repulsion is indeed present and seems to be helping in the expansion of the universe. However, the observed cosmological constant (lambda) is perhaps as much as 1,000 times lower than its estimated value (Weinberg, 1989; Carroll and Press, 1992). So why is the cosmological constant what it is? Why is it different from that expected based upon mathematical formulas? It is at this point that people invoke the anthropic principle.

The anthropic principle is often used as a religious argument for special creation with reasoning like this, "The reason our universe is so peculiar and well-fitted to life is because the Creator wanted (willed) it to be that way for the formation of life." Dr. Steven Weinberg, a Nobel laureate from the University of Texas, puts it like this. "A person is dealt a royal flush in a poker tournament. It may be chance, but on the other hand, the organizer of the tournament may be our friend" (Overbye, 2003; Susskind, 2003).

One way to get around the anthropic principle is to theorize that there have been millions of possible universes throughout time, with many different constants and settings in each one ruled by chance, and/or that there are "regions" (bubbles) within our universe containing a variety of constants and settings. The reason we are here to observe this universe is because we happen to be in one of those multiple universes or perhaps bubbles within our universe conducive to formation of life. String theory provides some evidence to support this view.

String theory. String theory is the idea that fundamental particles of the universe--protons, neutrons, electrons, quarks, etc.--contain tiny vibrating, oscillating, dancing filaments called "strings." String theory adds a new microscopic layer (a vibrating loop) to the previously known progression (large to small) from atoms to protons, neutrons, electrons, and quarks (Greene 2003; Greene 2004). No one has actually seen these strings; they are all theoretical at this point. According to the idea, everything in the universe is comprised of tiny vibrating fundamental strings. Moreover, every one of these strings is identical. The only difference between one string and another, whether it is a heavy particle part of an atom or a massless particle that carries light, is its resonant pattern, or how it vibrates (Greene, 2003).

String theory helps resolve the incompatibility between quantum mechanics and general relativity--the properties of forces vs. the properties of particles. For this reason, many physicists think string theory can become a "theory of everything" because it can underlie all others. A theory of everything--the ultimate explanation of the universe at its most microscopic level--would provide the firmest foundation on which to build our understanding of the world.

String theory allows for many dimensions (10 or 11; perhaps even more) in a space framework which could serve as a landscape containing peaks, valleys, and ridges (de Boer, 2003). As the universe expanded after the Big Bang, it theoretically rolled down, or over, this landscape framework. By chance, in some of these valleys small regions or pockets of universes (bubbles) might occur in which the natural constants and settings are conducive to life.

MULTIPLE UNIVERSES?

Scientific method. To accurately understand our world, scientists developed the scientific method. For a long time, the preferred scientific method was induction--basing general statements on accumulated observations of specific instances. For example, "Since the sun has arisen every day during recorded history, it is therefore true that the sun will rise tomorrow." Use of induction was helpful and enabled early scientists to distinguish science from non-science. However, David Hume in the mid-1700s pointed out that no number of singular observations, however large, could logically fix a general statement or law (Melchert, 1999). His skepticism may have seemed silly to laypeople, but actually unmasked a truth--pure empiricism is not a sufficient basis for science. We do not know for sure that the sun will rise tomorrow. It is highly probable that it will (in light of historical observations), but we do not know for sure.

A major shift in the scientific method occurred in the 1900s when Karl Popper advanced the idea that science should advance by trying to "falsify" hypotheses. Once falsified, they can either be amended, qualified, or adjusted and the process started over again. For example, the hypothesis, "all swans are white" can be supported by thousands of observations of white swans. But it is really not important how many observations agree with the theory; what really matters is trying to disprove the theory. One single observation of a black swan allows us to logically derive the statement, "Not all swans are white." In this way of looking at things, empirical generalizations, though not verifiable, are falsifiable. Under this new system, we can never prove that what we know is true; it is always possible that it will turn out to be false. The most you can ever say about a theory--be it gravity, Big Bang, evolution, etc--is that it is supported by every observation so far, and yields more precise predictions than any known alternative. However, it may be expanded or engulfed later by a better theory. For example, Einstein's theory of special relativity expands Newtonian mechanics (NM) to high velocities, but NM is still used.

A critical premise in Popper's method is that a theory must be testable. The hypothesis must lend itself to experiments or observations in efforts to disprove it. Taking the swan example (above), we must be able to go out and look at swans. If our theory about the color of swans relates to the color of swans in another universe, then that theory is untestable and thus lies outside the boundaries of science. We can discuss it, yes, but test it, no.

Multiple universes or pockets within our universe. As mentioned, one way to get around the anthropic principle is to theorize that there have been millions of possible universes, with many different constants and settings ruled by chance. Alternatively, string theory might allow for pocket universes or bubbles within our universe with a wide range of physical laws and constants. Accordingly, some small fraction of those bubbles would be within the anthropic window. And it is in one of these regions that we find ourselves (Susskind, 2003). Again, according to string theory, the only reason we are here to observe this universe or pocket within our universe is because we happen to be in one of them conducive to formation of life.

To me, proposing that ours is but one of a string of universes is a fallacy in reasoning. The universe is supposedly "everything there is." That is what the term universe means. If one tries to argue about things outside the universe or before the universe, an opponent usually quips, "that's outside the boundary of science. What lies outside the universe is an unknowable nothingness." Okay. Then how can an explanation for our universe being uniquely adapted for life be that ours is just one of many universes? There is no way to test such a statement.

The bubble idea suffers from the same flaw. Yes, string theory math might allow for such phenomena, but there is no way to test such a claim. Dr. Leonard Susskind at Stanford says, "Direct observational confirmation of the vastness and diversity of the (universe) landscape is probably not possible. The space between bubbles is typically expanding so rapidly that no signals can reach one of them from any other" (Susskind, 2003).

Recall Popper's method of hypothesis testing (more accurately "falsifying"). In the case of the swans we can never say that all swans are white by counting white swans. But finding one black swan would answer the question. However, to test the hypothesis, we must be able to look at swans. There is no possible way to test the multiple universe hypothesis--or even the pocket-universes-within-our-universe hypothesis. As silly as it sounds, all there is to observe is what there is to observe. Yet the multiple universe response is often quoted when people discuss the anthropic principle. In my view, we would do well to learn from the ancient Greek philosophers how to keep our theory of knowledge consistent and coherent.

ACKNOWLEDGMENTS

Alan Penman, M.D., and T.J. Brooks, M.D., my friends and fellow amateur philosophers, provided helpful comments in the development of this manuscript.

LITERATURE CITED

Barrow, J. D. 2002. The Constants of Nature. Pantheon Books, New York, 352 pp.

Barrow, J. D., and F. J. Tipler. 1986. The Anthropic Cosmological Principle. Oxford University Press, London, 706 pp.

Carroll, S. M., and W. H. Press. 1992. The cosmological constant. Ann. Rev. Astron. Astrophys. 30:499-542.

de Boer, J. 2003. String theory--an update. Nucl. Phys. Proc. Suppl. 117:353-372.

Greene, B. 2003. A theory of everything. Public Broadcasting Service, NOVA, "The Elegant Universe." www.pbs.org/wgbh/nova/elegant/everything.html

Greene, B. 2004. The Fabric of the Cosmos. Knopf Publishers, New York, 569 pp.

Melchert, N. 1999. The Great Conversation--A Historical Introduction to Philosophy. Mayfield Publishing Co., Mountain View, CA, pp. 404-416.

Overbye, D. 2003. Zillions of universes? Or did ours get lucky? New York Times, New York, October 28, 2003.

Susskind, L. 2003. A universe like no other, pp. 34-41, 1 November, New Scientist.

Weinberg, S. 1989. The cosmological constant problem. Rev. Modern Physics 61:1-23.

Jerome Goddard (1)

Mississippi Department of Health, Jackson, MS 39215

(1) PO Box 1700, Jackson, MS 39215 601-576-7689; [e-mail]