Domain of influence for wave equation in 2 dimensions

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Discussion Overview

The discussion revolves around the existence and behavior of solutions to the wave equation in two dimensions, particularly in relation to initial conditions and the implications of Huygens' principle. Participants explore the mathematical formulation and conceptual understanding of wave propagation over time.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions why solutions to the wave equation exist at all later times after an initial disturbance, particularly when the initial position is zero and the initial velocity is defined within a circular domain.
  • Concerns are raised about the implications of setting the initial velocity to zero outside the circular domain, questioning whether this leads to a zero solution and how that affects the existence of solutions.
  • Another participant seeks clarification on how the provided solution demonstrates outward extension at times greater than zero and why Huygens' principle does not apply in two dimensions.
  • A later post references the Anthropic Principle in a somewhat humorous context, suggesting a philosophical angle to the discussion.
  • One participant expresses frustration over the lack of responses and reiterates a request for an explanation based on the initial formula provided.

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus, as multiple competing views and questions remain about the nature of wave solutions in two dimensions and the implications of initial conditions.

Contextual Notes

The discussion highlights limitations in understanding the mathematical implications of the wave equation, particularly regarding assumptions about initial conditions and the behavior of solutions over time. There is a noted dependence on the definitions and interpretations of Huygens' principle in different dimensions.

Who May Find This Useful

This discussion may be of interest to students and researchers in mathematics and physics, particularly those focused on wave equations, dimensional analysis, and the implications of initial conditions in partial differential equations.

somethingstra
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Hello, I have some trouble seeing why the solution of the wave equation in 2 dimensions exist at all later times once it passes an initial disturbance...

For example, take a simple case where the initial position is zero, and the initial velocity equals some function inside some circle domain. The solution would be:

\frac{1}{2\pi }\int \int \frac{\psi (x,y)\partial x\partial y}{\sqrt{t_{o}^{2}-(x-x_{0})^{2}-(y-y_{o})^{2}}}

1) Where in that equation tells you that the solutions continues to exist at all later times?
2) If the initial velocity was zero outside the circle domain, why would the solution continue to exist? If we plug in Ψ = 0, wouldn't the solution be zero instead?
3) Can a solution be negative?
 
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Maybe I am not being clear. What I just want to know is how this solution shows that it extends outwards at t>0 and why it continues to exist at all later times. In other words, can somebody prove to me why Hyugen's principle fails at dimension 2?
 
Last edited:
bump...two days and no answer at all?
 
I've read that many times and still do not understand. Can someone explain it from the formula I posted above?
 

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