Why doesn't the Navier-Stokes equation have a solution?

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Discussion Overview

The discussion revolves around the existence of solutions to the Navier-Stokes equations, focusing on theoretical and practical aspects of fluid dynamics. Participants explore the implications of known solutions, the nature of solutions in different contexts, and the challenges posed by turbulence.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants question why the Navier-Stokes equations do not have a solution, suggesting that the complexity of the equations may prevent a definitive answer.
  • Others argue that solutions exist for specific flows, indicating that the equations can be satisfied under certain conditions.
  • One participant points out that the lack of known solutions does not imply that solutions do not exist, highlighting a distinction between analytical and numerical solutions.
  • Another participant explains that the term "solution" can vary in meaning, with classical contexts referring to closed form solutions and numerical contexts allowing for approximations that may diverge over time.
  • A later reply discusses the historical context of solving equations, noting that many problems are now approached numerically due to the complexity introduced by chaos theory.

Areas of Agreement / Disagreement

Participants express differing views on the existence and nature of solutions to the Navier-Stokes equations. There is no consensus on whether the equations lack solutions entirely or if they can be solved under specific circumstances.

Contextual Notes

Participants mention the challenges of turbulence and the sensitivity of numerical solutions to initial conditions, which may affect the reliability of approximations. The discussion also touches on the historical evolution of problem-solving in mathematics and science.

Sawawdeh
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Why the navier-stokes equation don't have a solution ?
 
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Sawawdeh said:
Why the navier-stokes equation don't have a solution ?
Because it’s hard enough that so far no one has figured it out. Perhaps no one ever will.

Google for “Millennium prize navier-stokes” for more about what has to be figured out.
 
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The Navier Stokes equations do have solutions for certain specific flows.
 
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If we don't know the solution(s), it does not mean that the equation does not have solutions, does it?
 
Classically the word solution often refer to a closed form solution, i.e. a "simple" symbolic solution general for large set of initial conditions and parameters, and in that sense we know that there are some (turbulent) flows that cannot have such a solution even if the actual flow dynamics still satisfy the equations.
However, in context of numerical analysis (i.e. in this case computational fluid dynamics) the word solution more imply any possible solutions achievable by numerical means so here it would make sense to say that a specific turbulent flow is a solution to the equations. Since turbulent flows has sensitivity to initial conditions this usually means the numerical solution can only be an approximation that share some statistical measure with the exact solution but also that the two will eventually diverge over time.
 
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@Sawawdeh It's never a surprise when an analytical solution to a problem doesn't exist. We start our Maths and Science education being presented with a number of situations and equations that are soluble analytically and exactly (you have to be encouraged initially) but, once you get into Integral Equations you find that most situations can only be dealt with numerically. In the recent past (pre-digital) people used vast books of tables of integrals to calculate approximate answers for problems.
Then someone discovered Chaos. . . . . .
 
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