Majestyk

So, if it miraculously appeared in a decayed state, there's no need to show the math.

By that same logic though, couldn't we just as easily claim that everything was created thirty seconds ago?

Shadowy Man

This would have very noticable effects in the field of astrophysics.

Jayjay

Yup, that's why I added "let's handwave [away] the side effects like all matter becoming unstable and such".

Albion

This looks like the standard creationist tactic of arguing two opposite things at once. They keep on about the anthropic principle and how even tiny changes in the fundamental constants would have made the universe uninhabitable or unsustainable (so it must have been arranged exactly this way by God), and then they propose major changes in those very same consants as an explanation for why radioactive decay used to be different back then.

lpetrich

Radiometric dating offers a consistency check: do different radioisotopes produce the same date?

This is stronger than it might seem, since radioactive decay occurs by several mechanisms. And there is no good reason to expect all the radioactive-decay rates to change in exact proportion.

Now for some details:

Uranium and thorium both decay to various lead isotopes:

U235 -> Pb207
U238 -> Pb206
Th232 -> Pb208

Not directly, of course, but through some series of other isotopes. The limiting rate is, not surprisingly, the first one, and in all three cases, it is an alpha decay.

It happens by the quantum-mechanical effect of barrier penetration. Running an alpha decay backwards will make the alpha particle (a He4 nucleus) stop at some distance away from the nucleus. However, the alpha particle behaves like a wave as well as like a particle, and it thus gets a certain probability of going through the electrostatic barrier and leaking into the nucleus.

Thus, an alpha decay happens much slower than the time for an alpha particle to bounce across a nucleus, which is about 10^(-24) seconds. And how fast it happens depends on, among other things, how much kinetic energy it has; this is (initial nucleus total mass-energy) - (final nucleus total mass-energy). To a first approximation, the decay rate is ~ exp(- (energy)^(-1/2))

or more precisely, exp(-T^(1/2)) where T is
((reduced mass) *(nuclear charge)^2 * (alpha charge)^2) / (energy)

where
1/(reduced mass) = 1/(final nuclear mass) + 1/(alpha mass)

Turning to other decay modes, spontaneous fission also happens, and it also happens by barrier penetration.

I now turn to beta decay and electron capture. These are the following:

beta -
neutron -> proton + W- -> proton + electron + antineutrino

beta +
proton -> neutron + W+ -> proton + positron + neutrino

electron capture
proton + electron -> proton + W- + neutrino -> neutron + neutrino

The W is an evanescent "virtual particle" that lasts for about 10^(-26) seconds, and the overall decay rate is approximately

beta:
((weak coupling constant)/(W mass))^4 * (energy)^5

electron capture:
((weak coupling constant)/(W mass))^4 * (electron density) * (energy)^2

The electron density ~ 1/(first orbital radius)^3

where
first orbital radius ~ 1/((electron mass) * (electron charge) * (nuclear charge))

Shadowy Man

Oh no.. you'd have more noticeable effects long before you'd have to worry about matter becoming unstable. Things like the wavelengths of absorption lines in atoms in distant galaxies, mass-luminosity relationships of stars, etc.

Coragyps

I just pulled it from an unsunny spot I picked 50 million instead of 5900 years because the accuracy of things like K-Ar is respectable at the former. The error bars might include the present for the latter. That always gets YEC's pretty agitated.

Tim Thompson

K-40 decays to Ar-40 by electron capture. That means one of the bottom electrons gets close enough to the nucleus to get absorbed by a neutron, and bumping the element up to Ar. The half life for this is 1.277 billion years. In principle, this decay rate can be changed by any outside effect that alters the wave function of the electrons at the bottom of the cloud; chemical environment or extreme pressure. This has been observed in Be-7, which also decays by electron capture, and the change in half life is on the order of 0.2%. K-40 has more electrons, so it's harder to bother the ones at the bottom. No similar effect has been recorded for K-40, though curiously Zr-89 and Sr-85 have shown similar, ~0.2% effects. Since the age of a sample is linear with decay rate, a 0.2% change in half life implies a 0.2% uncertainty in the age. Not much to talk about there.

Other isotopes in decay chains will decay by alpha emission, and sometimes by spontaneous fission (like U-235). In both cases a charged particle has to penetrate the nucleus, so a variation in the electric field near the nucleus could alther those decay rates too, in theory. But the effect is much smaller, on the order of 0.00001%, for a wide range of field strengths. Even less to talk about there.

The usual creationist approach is purely propagandistic. They figure any example of any variability at all throws the barn door wide open, and makes all speculations of variability equally valid. But of course it's not so. These variabilities I mention here are all based on sound theoretical expectations, and theory agrees with observation. Without any sound theoretical expectations, creationists are just blowing smoke, as they say.

As for possible changes in fundamental constants, it's unlikely to be much of an effect, even if the "constants" are variable (which remains a hot topic in fundamental physics). Electron capture, internal conversion & beta decay are all moderated by the weak force, while alpha decay & spontaneous fission are moderated by the strong force, and they are fundamentally different. Both would have to change by the appropriate amount to create the illusion of old age, and that seems mighty unlikely. Furthermore, the amount of change, to make 10,000 "real" years look like 4.5 billion "fake" years would be staggering. It is hard to imagine how that might happen, without even one little clue left over.

• Radiometric Dating Resource List
• How to Change Nuclear Decay Rates

SULPHUR

Are you coming back?

Jayjay

I think not. Tim Thompson and his links above pretty much answered whatever questions I still had in mind.