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23559Re: [evol-psych] Re: Determinism

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  • Steven D'Aprano
    Mar 3, 2003
      On Sun, 2 Mar 2003 12:21, Nik Weaver wrote:

      > > For instance, the randomness of radioactive decay is almost
      > > certainly due to the perfectly deterministic behaviour of the
      > > nucleus, and even the decay of isolated baryons like the neutron
      > > is probably determined by its quarks. On the other hand, the
      > > decay of an excited atom into a lower energy state appears to be
      > > non-deterministic, but that shouldn't be considered proven by any
      > > means.
      >
      > "almost certainly": you are wrong. The randomness of radioactive
      > decay is exactly the same as the randomness of atomic decay. Both
      > are instances of a transition from a higher energy state into a
      > lower energy state, mediated by thermal interaction with an external
      > field.

      This is certainly true for nuclei in higher energy states, but does it
      hold true for nuclei in the ground state? Or for that matter,
      individual particles in the ground state?

      It is a fact that neutrons decay, whether they are in a high energy
      state or not. What is the explanation for that?

      If I understand you correctly, you would be predicting that (say) a
      nucleus of He-5 kept in thermal isolation at absolute zero would be
      stable. Or have I misunderstood?

      In this case, it should be trivial to predict which nuclei will decay:
      if it is in the ground state, then it is stable, and if not, you can
      easily predict its likelihood for it to decay depending on the thermal
      background. I leave for future generations the problem of how you can
      non-destructively tell if a nucleus is in the ground state or not.
      Extrordinarily accurate measurements of their mass perhaps? Subtle
      differences in their magnetic dipole or quadrapole moments?

      > If you'd like to see the math, I found a nice description on
      > the web at
      > www.physics.ucla.edu/class/02S/ 115C_Abers/notes/TDPT01.pdf
      > www.physics.ucla.edu/class/02S/ 115C_Abers/notes/TDPT02.pdf
      > --- if this doesn't suit you, just do a web search for "Fermi's
      > golden rule".

      I always appreciate further information, thank you.

      > I can't wait to hear your explanation of why you felt comfortable
      > labelling as "almost certain" something which anyone who knows the
      > subject would reject as trivially false.

      Why, I plucked it out of thin air, of course!

      That's what you were thinking, wasn't it? But its not the reason. The
      actual reason was that the popular science books I have read have lead
      me to this conclusion. Now perhaps I have misunderstood them, and
      perhaps they are wrong, but there is no need to go on the attack about
      the issue.

      I got my understanding of neutron decay from here:
      http://hyperphysics.phy-astr.gsu.edu/hbase/hph.html

      This agrees with other articles I have read over the years about the
      (hypothetical) decay of the proton, and I assume other baryons would be
      similar.

      > "shouldn't be considered proven": and what would constitute a
      > proof?

      You're the mathematician, you tell me. What sort of proof would convince
      you that the concept of cause and effect was meaningless, and that
      actions weren't determinded by their causes?

      > I can't see how, in principle, one could ever conclusively "prove"
      > that some phenomenon was truly random.

      That is a difficulty. As Chaitin proved, it is impossible to prove that
      an arbitrarily long string of bits and prove that it is random.

      > What one can do is show
      > that if quantum mechanics is valid then any deterministic
      > substructure must have undesirable features such as non-locality.
      > (This is what Bell's theorem shows.) One can also give physicists
      > a century to try to find a plausible underlying deterministic
      > mechanism and see if anyone comes up with one --- that experiment
      > has also failed.

      Perhaps I am mistaken, but I thought that non-locality was worming its
      way into quantum mechanics in any case?

      As for plausible mechanisms, they have also had a century to come up
      with a plausible interpretation of quantum mechanics, and there is
      still controversy over the question.

      > I sympathize with your desire to preserve determinacy, but barring
      > a massive change in our understanding of modern physics, this is
      > just wishful thinking.

      And yet you have given a deterministic explanation of BOTH radioactive
      decay and atomic decay: the decay is determined by interaction of the
      high energy state with its environment.



      Then, on Mon, 3 Mar 2003 00:35, Clay Farris Naff wrote:

      > Relativity, of course, rules out absolute
      > time within our Universe, and so in principle two observers
      > differently situated may perceive the sequence of some event -- say,
      > Alice and Bill playing catch -- in opposite order. To one, it might
      > appear that the ball travels from Alice to Bill, and to the other
      > that the ball travels from Bill to Alice. Both would be correct.

      It is my understanding that this is only the case if the observer is
      outside of the lightcone from the event in question, or in other words,
      if some faster than light signal is sent from the event to the
      observer. Would anyone like to clarify this?



      Then on Mon, 3 Mar 2003 01:11, Herbert Gintis wrote:

      > I saw a paper in Science or Nature within the last year that claimed
      > to do better than Bell's Equation, showing that David Bohm's hidden
      > variable approach is not equivalent to the Copenhagen interpretation
      > (as had long been thought), but rather, wrong.

      "Claimed to"? Does this mean that Bohm's hidden variable approach has
      not yet been conclusively disproved to all physicists' statisfaction?

      I don't intend to tell physicists how to do their job, but if they are
      still arguing about fundamentals, what justification is there for
      saying the situation is cut and dried and that determinism is
      disproven?

      If the universe is non-deterministic, then how do you explain the
      determinism we see in the every day world?



      Then on Mon, 3 Mar 2003 05:17, Ian Montgomerie wrote:

      > We simply don't have any way of confirming that "every system we care
      > to look at has the random fluctuations average out". A large portion
      > of the systems in the world are complex systems subject to chaotic
      > behavior, including things like weather and likely our own minds. In
      > none of these systems can we perfectly measure the initial conditions
      > to know exactly what does and does not have an effect. I am not an
      > expert in physics, but I know of no scientific basis to declare that
      > quantum effects are eliminated before any of them have the chance to
      > become relevant to the initial conditions for a macroscopic chaotic
      > system.

      Good point. I will accept that the question is open.

      [snip]
      > The Earth's long-term orbit may not be quite as "predictable" as you
      > think - orbital dynamics are chaotic in systems with more than two
      > bodies. The current orbit of the Earth is basically just a stable
      > attractor, and the stability is mainly due to the fact that Earth is
      > so big that the many smaller bodies in unstable orbits do not perturb
      > it very much.

      According to Ian Stewart, the solar system is unstable, but the
      instability will not become significant until long after the sun is due
      to burn out. That's not to say that the solar system is entirely
      predictable in the medium term, but in the short term (say a few
      million years) most planetary orbits are both stable and predictable.



      --
      Steven D'Aprano
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