To: All Msg #112, Feb2193 02:10PM Subject: Re: What are the rational criteria? In article

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From: Steve Carlip To: All Msg #112, Feb-21-93 02:10PM Subject: Re: What are the rational criteria? Organization: Physics, UC Davis From: carlip@landau.ucdavis.edu (Steve Carlip) Message-ID: <22854@ucdavis.ucdavis.edu> Newsgroups: talk.origins In article <1ljajt$5ho@horus.ap.mchp.sni.de> frank@D012S658.uucp (Frank O'Dwyer) writes: [...] >(b)Aren't evolutionists potentially engaged in some kind of "flat earth" >fallacy? By that I mean "my garden is flat, so the earth is flat". Isn't >any scientific theory purporting to explain the events of the distant past, >or future, prey to the same error in 4-space? I'll leave it for others to address this issue in biology, and just comment briefly on physics. The question is a legitimate one --- the assumption that physical laws don't change over time ought to be tested, and a good deal of effort has gone into devising such tests. In the physics literature, the question is usually formulated as one of whether the "constants" of nature change over time. A wide variety of very clever tests have been devised. Let me list a few: (1) By observing stars, we can "look back in time" --- the light from a star a million light years away was produced by physical processes taking place a million years ago. Observations of spectral lines in distant stars give very sensitive measurements of atomic physics over extremely long periods of time. (2) Recent observations of the 1987 supernova SN1987A have provided very good tests of time-dependence of weak interactions (radioactive decay). Much of the light now emitted from the remnants of the supernova comes from known radioactive decay processes, and by measuring the change in luminosity with time we can determine half-lives. (3) Observations of binary pulsars --- pairs of orbiting stars, one of which is a pulsar --- give very accurate measurements of gravitational physics at large distances, and therefore long times. (4) While observation of a single form of radioactive decay on earth doesn't tell us much about constancy of physical laws, *consistency* of independent decay modes does. This is particularly true because different kinds of decay depend on different physical processes (strong, weak, and electromagnetic interactions); it would take some fairly incredible "fine tuning" to have these interactions all change at exactly the right rates to give consistent dating. (5) Correlations between ancient growth patterns (e.g., growth patterns in ancient coral) and predicted orbital periods (lengths of days, months, years) give good tests of the constancy of physical laws over a large part of the history of the earth. (6) Recent measurements --- for instance, radar ranging of the Viking Mars lander --- test constancy of physical laws over only a short period, but to an extremely high accuracy; if physical constants changed in the past, these experiments tell us that that change must have stopped, or at least slowed incredibly, in recent times. (7) At the other extreme, predictions of the behavior of the universe very soon after the big bang --- roughly 15 billion years ago --- are also based on the assumption that laws of physics were the same then as now. While these predictions are much less precise, they give good agreement with observations (e.g., abundance of light elements, existence and spectrum of the microwave background radiation). This list is biased towards gravitational physics, since that's my field; I'm sure geologists and biologists could add many tests. The overall result is that physical constants do not change at a rate of more than a few parts in 10^11 per year, with slightly stronger restrictions on some constants than on others. The key point is that while any individual observation is bound to have loopholes, the consistency of so many different tests, each using different assumptions and involving different combinations of physical interactions, is extraordinarily hard to dispute. It would take an incredible "conspiracy" of physical changes --- different laws changing by different amounts in different places and times, single laws changing differently for different physical processes, all perfectly tuned to give the appearance of constancy --- to give any explanation of all of the observations apart from the obvious one, that physics really is time-independent. Steve Carlip carlip@dirac.ucdavis.edu

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