The Constancy of Constants, Part 2

Post of the Month: August 2006

by

Subject:    Re: Age dating question
Date:       22 August 2006
Message-ID: ecdnb9$85b$1@skeeter.ucdavis.edu

AllanL wrote:

[...]
> A rather popular arguement that keeps on repeating itself on various
> boards is that such methods require a constant rate of decay [...]

Let me just address this part (cribbing liberally from previous posts of mine on the topic...).

First, the physics of radioactive decay is quite well understood. For the case of alpha decay, the simple underlying mechanism is quantum mechanical tunneling through a potential barrier. You will find a simple explanation in any elementary quantum mechanics textbook; for example, Ohanian's Principles of Quantum Mechanics has a nice example of alpha decay on page 89. The fact that the process is probabilistic, and the exponential dependence on time, are straightforward consequences of quantum mechanics. (The time dependence is a case of "Fermi's golden rule" -- see, for example, page 292 of Ohanian.)

An exact computation of decay rates is, of course, quite a bit more complicated, since it requires a detailed understanding of the shape of the potential barrier. In principle, this is computable from quantum chromodynamics, but in practice the computation is much too complex to be done in the near future. There are, however, reliable approximations available, and in addition the shape of the potential can be measured experimentally.

For beta decay, the underlying fundamental theory is different; one begins with electroweak theory (for which Glashow, Weinberg and Salam won their Nobel prize) rather than quantum chromodynamics. For gamma decay, one again needs electroweak theory. In each case, though, the underlying physics is well understood.

As described above, the process of radioactive decay is predicated on rather fundamental properties of matter. In particular, in order to explain old isotopic ages on a young Earth by means of accelerated decay, an increase of six to ten orders of magnitude in rates of decay would be needed.

Now, the fundamental laws of physics, as we presently understand them, depend on about 25 parameters, such as Planck's constant h, Newton's gravitational constant G, and the mass and charge of the electron, and a change in radioactive decay rates would require a change in one or more of these constants. The idea that these constants might change over time is not new, and is certainly not restricted to creationists. Interest in this question was spurred by Dirac's "large number hypothesis." The "large number" in question is the ratio of the electric and the gravitational force between two electrons, which is about 10^40; there is no obvious explanation of why such a huge number should appear in physics. Dirac pointed out that this number is nearly the same as the age of the Universe in atomic units, and suggested in 1937 that this coincidence could be understood if fundamental constants -- in particular, Newton's gravitational constant G -- varied as the Universe aged. The ratio of electromagnetic and gravitational interactions would then be large simply because the Universe is old. Such a variation lies outside ordinary general relativity, but can be incorporated by a fairly simple modification of the theory. Other models, including the Brans-Dicke theory of gravity and some versions of superstring theory, also predict physical "constants" that vary.

Frankly, physicists are not, for the most part, interested in silly creationist arguments. But they are interested in basic questions such as whether physical constants or laws change in time -- especially if such changes are proposed by such a great physicist as Dirac. As a result, there has been a great deal of experimental effort to search for such changes. A nice (technical) summary is given by Sisterna and Vucetich, Physical Review D41 (1990) 1034 and Physical Review D44 (1991) 3096; a more recent reference is Uzan, Reviews of Modern Physics 75 (2003) 403, available electronically at http://arxiv.org/abs/hep-ph/0205340. Among the phenomena they look at are:

• searches for changes in the radius of Mercury, the Moon, and Mars (these would change because of changes in the strength of interactions within the materials that they are formed from);
• searches for long term ("secular") changes in the orbits of the Moon and the Earth --- measured by looking at such diverse phenomena as ancient solar eclipses and coral growth patterns;
• ranging data for the distance from Earth to Mars, using the Viking spacecraft;
• data on the orbital motion of a binary pulsar PSR 1913+16;
• observations of long-lived isotopes that decay by beta decay (Re 187, K 40, Rb 87) and comparisons to isotopes that decay by different mechanisms;
• the Oklo natural nuclear reactor (mentioned in another posting);
• experimental searches for differences in gravitational attraction between different elements (Eotvos-type experiments);
• absorption lines of quasars (fine structure and hyperfine splittings);
• laboratory searches for changes in the mass difference between the K0 meson and its antiparticle;
• searches for geological evidence of "exotic" decays, such as double beta decay of Uranium 238 or the decay of Osmium to Rhenium by electron emission, which are impossible with the present values of basic physical constants but would become possible if these changed;
• laboratory comparisons of atomic clocks that rely on different atomic processes (e.g., fine structure vs. hyperfine transitions);
• analysis of the effect of varying "constants" on primordial nucleosynthesis in the very early Universe.

While it is not obvious, each of these observations is sensitive to changes in the physical constants that control radioactive decay. For example, a change in the strength of weak interactions (which govern beta decay) would have different effects on the binding energy, and therefore the gravitational attraction, of different elements. Similarly, such changes in binding energy would affect orbital motion, while (more directly) changes in interaction strengths would affect the spectra we observe in distant stars.

The observations are a mixture of very sensitive laboratory tests, which do not go very far back in time but are able to detect extremely small changes, and astronomical observations, which are somewhat less precise but which look back in time. (Remember that processes we observe in a star a million light years away are telling us about physics a million years ago.) While any single observation is subject to debate about methodology, the combined results of such a large number of independent tests are hard to argue with.

The overall result is that no one has found any evidence of changes in fundamental constants, to an accuracy of about a part in 10^11 per year. There are some recent, controversial claims of observational evidence for changes in certain constants (notably the "fine structure constant") in the early Universe, but these are tiny, and would have minimal effects on radioactive decay rates.

So the idea that decay rates could vary enough to make a significant difference to measurements of ages is ruled out experimentally.

Steve Carlip

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An Atheist's Defense of Religion

Co-Post of the Month: August 2006

by

Subject:    An atheist's defense of religion
Date:       15 August 2006
Message-ID: 1155662537.538859.306170@b28g2000cwb.googlegroups.com

[Not much chance to contribute these days but I had a few moments to write and post this to my blog so I thought I'd share it here as well, with the goal (as always) of prompting, and eventually stealing the insights of others.]

An atheist's defense of religion

An argument I've made often and continue to believe in is that protection of biology from the assaults of creationism and its offspring ("Intelligent design" for instance) will be achieved largely through the efforts of those religious individuals who understand, and make the case for, the peaceful co-existence of faith and science.

It has been my perception that theists (especially theistic scientists) are more likely to have considered deeply the boundaries of science and religion and understand with particular clarity the limitations each entails regarding its ability to comment on the other. This is understandable given the inherent vested interests. It's also these individuals who are most likely to, through their experience with faith, have the cachet needed to gain a measure of attention from those more fundamentalist sorts who would dismiss less sympathetic sources.

Thus have I many times invoked names like Francisco Ayala and Kenneth Miller as credible authorities for an anti-evolutionist's honest investigation. Along with citing these individuals as useful resources I have also suggested that it would be useful for the defense of science if people such as they would speak out more frequently and forcefully. Theists defending science set a powerful example.

Well, a recent event has convinced me that the inverse proposition is also true. It would probably be just as positive a contribution to the debate for atheists to defend the value of religion. As theistic scientists can accept that science has much to offer the world without sacrificing their faith, so do I believe that religion can make a positive contribution to the human condition and still maintain my steadfast confidence in scientific methodology.

Let me begin by making clear what I mean when I say that I am an atheist. I use the word understanding fully that for some it provokes negative connotations. I am willing to live with these unfortunate preconceptions, though, because I prefer not to accept the intellectually spineless image (unfair to be sure) that accompanies the label - agnostic. As I apply it to myself, then, the designation atheist means that based upon the evidence available to me I can find no reason to believe in a deity of any kind.

A conversation with a believer with whom I have been working recently made it clear to me that he had interpreted my professed atheism as an active faith in the non-existence of deities. I inferred this not because the sentiment was overtly communicated, but rather because of his sincere apology to me after expressing a religious notion within the context of our talk. In essence, he realized he had said something that (he thought) might offend me.

Of course I immediately assured him that not only had I not taken offense but it was a subject that I quite enjoyed. It occurred to me then that the same dual benefit achieved by the public statements of theistic scientists - reassurance that science and religion can be compatible along with a furthered understanding of the limitations of both - could be equally supported by non-theists speaking out in defense of religion.

For the same reasons that scientists of faith are not beset by cognitive dissonance I am able to maintain that religion can be a viable and valuable human endeavor. The epistemic limitations of both "ways of knowing" lock out fundamental contradiction. Science is method. It is an operational tool for discovering natural reality. As such it is limited in scope. Science can comment only upon that which can be observed and measured. There is no operational capacity within the methodology of science for evaluation, much less dismissal, of extra-natural ideas. And as science can never be complete, it can never rule out extra-natural possibilities.

Theology, to the degree it relies upon the extra-natural, deals substantially with morality and message. It addresses understandable human concerns about the nature of their existence and, regardless of whether the message is evidentially or logically supported, is capable of offering contentment and direction to those in need. On the other hand, when theology proposes to make statements about nature, which only science is configured to address effectively, it must be prepared to cede ground. Belief in a thing can never be enough to demonstrate its factuality.

Science and religion operate in different spheres of influence. When they come together, as they do now and then, in collision or confluence, it is because of the conceits and misconceptions of humans, not any inherent compatibility or contradiction.

In making the case for religion from a less philosophical perspective, it seems clear to me that one thing none of us, atheist or theist, wants is for a massive population of flawed and fallible humans (as are we all) that believes it cannot act ethically without religion, to try to do so. The last thing we need is a bunch of people who believe they have no internal moral compass running around without their external one.

As atheists or agnostics we may feel that a believer is misguided in his acceptance of things unseen, but we have to acknowledge that science, by definition, leaves the set of things unseen unaddressed, and consequently in no way disproved.

If one accepts the methods of science one accepts that knowledge is provisional - that one can be wrong. If it's possible to be wrong, even about something so apparently fanciful as a deity, then the belief in a deity exists as an intellectually live alternative to an atheist's provisional philosophy. An acceptance, even a spirited defense of that live alternative shows both the intellectual confidence to take in and consider ideas antithetical to one's own, and an openness to a universe that will never be completely known.

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