Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Non-linear Differential Equations and Psuedo-randomness

  1. Mar 19, 2010 #1
    I was thinking about the non-linear Navier-Stokes equation this morning and was briefly browsing a text on the subject. I'm aware that one popular approach to dealing with turbulence is to take averages and look at correlators (which, in turn, can be related to field theory.) Now, one thing which strikes me as odd about this statistical approach to dealing with turbulence is that the Navier-Stokes equation is fully deterministic; given some set of initial and boundary conditions, the entire time evolution of the system is determined.

    So, I have a question about the Navier-Stokes equation: is it known that the solutions are psuedo-random for high Reynold's number? Of course, one can extend this more generally to dynamical systems with positive Lyapunov exponents -- are the solutions to such systems (e.g., chaotic differential equations) known to be psuedo-random? If so, it would appear to be natural to attack them statistically since they would pass tests for randomness.
  2. jcsd
  3. Mar 23, 2010 #2
    Many solutions having a global attractor in 3D are pseudo-random. Howver, I haven't heard of a general theorem.
  4. Mar 23, 2010 #3
    Interesting. Do you have any examples? I'd like to know more about this subject.
  5. Mar 24, 2010 #4
    Check the Lorenz attractor ,for instance.
    There are a few theorems connecting ergodicity & randomness, but the general case of the Navier-Stokes equation is monstrous. It's not known if a general
    solutions exists ( a million dollar problem) , let alone the contingent property of pseudorandomness.
  6. Mar 24, 2010 #5
    Yes, I'm aware of the related Millenium Problem. At any rate, does any one have any information connecting ergodicity and psuedo-randomness for other systems? That seems intriguing to me.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook