Re: [asa] Theory of gravity

MessageIMO one can worry too much about what to label a "law," what a "theory" &c. "Gravity" is a fact in the sense that things fall to the earth. Newton's theory included the claim that this was a universal property of matter (& not just the earth) described by the inverse square law. He declined, however, to make any definite statement on the cause of gravity - i.e., to give any deeper explanation of why masses attract that way. Newton's theory was good in the sense that it explained a lot of data & predicted others, but Einstein's theory is better (i.e., explains & predicts more things), in part because it goes deeper into the cause of the phenomena by connecting the presence of matter & space-time geometry. Thus Einstein's is a "covering theory" for Newton's. But it isn't perfect - it can be shown that a quantum theory of gravitation is a necessity, even though we have no actual observational discord with Einstein's classical theory.

Interestingly, while people do refer to Newton's F = -GMm/r^2 as a "law" of gravitation, I have seldom seen Einstein's R^mn - (1/2)Rg^mn = - 8piT^mn called a "law" - in spite of the fact that the latter agrees better with oberservations. It's just "Einstein's field equations." So much for the precision of these terms!

Evolution as a fact is not quite as well established as the fact that things fall downward but it's close. I.e., without a lot of very special pleading, the the fossil record & other data show that there has been widespread descent with modification. Darwin & Wallace provided an explanation - a theory - for how this has happened. Like Newton's theory it is well supported but not perfect. In this case, however, necessary corrections may be minor touch-ups rather than a grand covering theory a la Einstein.

I think a lot of the "fact - theory - law" rhetoric is just anti-evolutionist smokescreen.

Shalom
George
http://web.raex.com/~gmurphy/
  ----- Original Message -----
  From: Jon Tandy
  To: 'ASA'
  Sent: Wednesday, November 21, 2007 7:23 AM
  Subject: [asa] Theory of gravity

  Having now finally watched the rest of the PBS special on the Dover trial, I have a few questions. I'll just start with one for now.

  I recall it being mentioned that the "theory of gravity" is the same as the "theory of evolution" -- both are tentative and could potentially be disproved, although both have substantially large bodies of evidence in support of them. I thought that was a good argument at the time, but later I imagined that someone will criticize that argument on the grounds that Newton's "laws" are no longer considered scientific theory but laws. As an example of the confusion of terms, Wikipedia's article "Newton's law of universal gravitation" (http://en.wikipedia.org/wiki/Newton%E2%80%99s_law_of_gravitation) starts with the statement: "Isaac Newton's THEORY of universal gravitation is a physical LAW describing the gravitational attraction between bodies with mass."

  As someone with a fair amount of education in science, I realized I didn't have a completely solid grasp of the difference between a law and a theory. My first thought was a law is more sufficiently proven or demonstrated than a theory. However, on reflection, I think a better explanation is that a scientific law attempts to describe an observation in nature with empirically derived analytical formulas, while a scientific theory attempts to explain the observations (causes, etc.). So is gravity a law or a theory? If I'm not mistaken, it's both. The law of gravity (Newton's generalization, now superceded by Einstein's equations) is given by F=G(m1*m2)/r^2. This is empirically derived and demonstrable (again, with qualification by Einstein in special cases). However, the theory of gravity seeks explanation by proposing the source of the force of gravity, such as gravitons, etc., which is still in the theoretical stages, with various alternative proposals. Is this a fair assessment? Is it true that gravitation, or at least some aspect of it, is still "only a theory" (to use derogatory YEC-speak)?

  The "theory of evolution" attempts to explain the mechanisms of observed phenemona. It's clear that this is still a theory in flux, with new discoveries such as lateral gene transfer, DNA replication errors, etc., contributing to biological development in ways not completely understood. But if a "scientific law" describes observations in nature, at what point could the observations of evolutionary inheritance be called a "law"? Could there come a point where certain observations or mechanisms of biological evolution could become quantified to an extent like Newton's formula for the law of gravity? Is it there yet? I don't know of anyone using the terminology "law of evolution" on either side of the debate, although there was something (either in the program or in a forum discussion on our local PBS station after the program), where the assertion was made by ID advocates that "evolution is not the 'law of evolution', but only the 'theory of evolution' ".

  Jon Tandy

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Received on Wed Nov 21 08:20:16 2007