The dating game

Stegve Carlip is pretty guru-ish. From The Constancy of Constants, Part 2:

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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.)

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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

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That's most of the text, but the rest and The Constancy of Constants are worth reading.David Ewan Kanaha comments on Woodmorappe's extrapolation of observed increased beta decay in fully-ionized (no electrons) rhenium to other decay systems in Modifications of Nuclear Beta Decay Rates, which includes discussion of some of the factors involved.

Ruled out by observation. For example, the KBS Tuff is beloved of creationists 'cause the first set of answers conflicted ... but it's an excellent example of real science in action and only incidentally an example of "wrong" dates getting published.

Not. No doubt about it. Creationists focus on K-Ar because it is susceptible to more errors than other methods; however, it's reliable (when rational sample selection and treatment is practiced), low-cost, and well understood. It has its place. But it's not widely used.Well over half of the geologic dates are obtained using U-Pb, Ar-Ar, or isochron methods. All these methods are not susceptible to the problem of excess initial daughter, all of them indicate when the system has been opened (i.e. relevant material has been gained or lost since solidification) and many of them provide a valid date in many cases even if the system has been opened. Sorry, there are no glimpses of errors and/or possible reasons why it is wrong. It is well understood and cross-correlated with many independent lines of investigation. It ain't wrong.Probably this has been posted already, but in the unlikely event you are interested in actually learning something about the subject, see Radiometric Dating: A Christian Perspective.

I believe RAZD meant calculating k from first principles.

Perhaps I've misjudged you. We'll see.You really should head over to RAZD's thread on correlations, to which he's posted a link ... there he raises and explains the issues you really need to understand and address. That's because so-called "excess argon" is not a significant problem or limitation. It's not worth introducing in such a brief treatment intended to provide an accurate overview. Whereas your source is unikely to be interested in accuracy, and is trying to misrepresent the accuracy of K-Ar dating. Note that your site mentions two old individual cases which were studies to find out where K-Ar dating is or is not applicable. Extrapolating that to all K-Ar dates (and creationists need all of hundreds of thousands of dates to be way wrong) being seriously in error is invalid and wrong.What is valid is comparing K-Ar dates to other dates of the same material by other methods that are not affected by such possible issues. This is done all the time; and 99% of the time the dates agree. Such as Consistent Radiometric dates, Radiometeric Dating Does Work!, Radiometric Ages of Some Early Archean and Related Rocks of the North Atlantic Craton, and Radiometric Ages of Some Mare Basalts Dated by Two or More Methods. Those ain't coincidence; there's a clear pattern that no creationist dares address.Another valid test is testing lots of recent lava flows to see if they have excess argon. Dalrymple did that and found that, in 26 tests, 2/3 had no excess argon and 25 had either no excess argon or not enough excess argon to interfere with dating after the rocks age a few million years.RAZD goes into this and much more in his correlations thread.Excess argon is rare, and with rational sample selection K-Ar dating is accurate and reliable. That's what the data clearly shows. Oops. Strike one. You may have read Weins, but you failed to comprehend:

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This method uses exactly the same parent and daughter isotopes as the potassium-argon method. In effect, it is a different way of telling time from the same clock. Instead of simply comparing the total potassium with the non-air argon in the rock, this method has a way of telling exactly what and how much argon is directly related to the potassium in the rock.

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(Emphasis added). Ar-Ar uses the same isotopes but is not subject to the same limitations or potential errors as K-Ar. Ar-Ar is not affected by excess Ar (the samples in the Pompeii study previouslly referred to had excess argon) and often can provide a good date even if the system has been opened.You also failed to address U-Pb dating, which makes up slightly over half the geological dates obtained in the past decade or so, and is covered briefly in Weins. And Rb-Sr and Lu-Hf and other isochron methods. Yup. Always true in science. If any errors or possible reasons why it is wrong come up, we'll address tham and figure them out. As of now, there's bupkis.

And he claims to have read Weins, wherein he clearly states otherwise (and gives a brief eplanation of why).

No. The hypothesis was that submarine basalts are not suitable because their outside cools and solidifies so fast that argon is trapped. The hypothesis was confirmed. OT, but this is one of many reasons why Noye's Fludde did not happen. Submarine basalts are easily identifiable, and the vast majority of igneous rocks are not submarine basalts. Submarine basalts are not the norm. In spite of the measurements that clearly indicate excess argon, and the depth profiles that clearly showed it concentrated in the interior as predicted. Sigh.

Well done! If I may underscore, the discordant ages were both published and discussed in detail. I supose one might disagree with the reasons for discarding the older ages (I can't see how, but maybe someone could) … but there's no question there's no suppression of discordant ages and no conspiracy to do so.This one might be worth writing up for the Index of Creationist Claims.

Yup. There's a possibility that the fine structuere constant changed by a percent or two billions of years before the Earth formed. Changes of the order required by creationists and changes in the last few billion years have been ruled out.

Nobody's afraid of changed or changing values of constants. Research into the possibility of changing constants is a minor but active part of mainstream science, andmany mainstream scientiss think they have changed. Real scientists just don't bother to fish in dry wells; significant changes in constants and any changes in the last few billion years have been ruled out by observation.