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→Zircon Dating: size dependent on c? and the problem with the dating.
::::Even if the lead was somehow leaving the crystals (and there is no evidence that it is), there is no natural process which removes <sup>207</sup>Pb at a faster rate than the <sup>206</sup>Pb. Even if a lead-removing process started recently, it would still remove the two isotopes at the same rate leaving the ratio unchanged. Also, if the lead-removing process started and ended a long time ago, it would also remove the two isotopes at the same rate leaving the ratio unchanged.--[[User:MichaelK|MichaelK]] 21:01, 15 May 2008 (EDT)
::::Even if the lead was somehow leaving the crystals (and there is no evidence that it is), there is no natural process which removes <sup>207</sup>Pb at a faster rate than the <sup>206</sup>Pb. Even if a lead-removing process started recently, it would still remove the two isotopes at the same rate leaving the ratio unchanged. Also, if the lead-removing process started and ended a long time ago, it would also remove the two isotopes at the same rate leaving the ratio unchanged.--[[User:MichaelK|MichaelK]] 21:01, 15 May 2008 (EDT)
::::: I understand what you are saying about the shrinking room, but I have trouble accepting that the sizes of everything will change just because the speed of light changes. That is, I have trouble accepting that the sizes of things are ''dependent on'' the speed of light. And the speed of light ''does'' change when travelling through different substances (''c'' refers to the speed of light ''in a vacuum''). By the way, I don't plan on taking a course on physics at any university just to have this discussion with you, let alone one on the other side of the world!
::::: As for objects being more than 8,000 light years away, see [[starlight problem]]. If I recall correctly, far-away objects are measured by their red-shift, and/or by the apparent brightness of the brightest objects in galaxies.
::::: I think with the dating issue you are getting confused with my response to what I believed you were saying and what I was saying. Let's try this explanation:
::::: Radiometric dating involves measuring the ratio of parent and daughter elements, and calculating from that ratio how long it has been decaying. Uranium decays through a number of steps to eventually become lead, so one way of dating objects is to measure the relative amounts of uranium and lead. However, one of the intermediate elements is thorium, so you can also measure the relative amounts of uranium and thorium. Therefore if the relative amounts of two isotopes of uranium, thorium, and two isotopes of lead are measured, then one should be able to determine the date from three calculations: two from the different uranium-lead ratios and one from the uranium-thorium ratio. You are arguing that because the two uranium-lead figures agree, the date is likely to be accurate. But the link I provided argues that because the thorium figure was zero, this indicates that there is a problem with the sample (perhaps leaching) that makes the uranium-lead date unreliable.
::::: [[User:Philip J. Rayment|Philip J. Rayment]] 08:06, 21 May 2008 (EDT)