Free Particle: Prove Constant in Time

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SUMMARY

The discussion focuses on proving that the expectation value

of a free particle in one dimension remains constant over time. Participants emphasize the importance of using the definition of the expectation value of an operator rather than relying on the commutator theorem. The initial state of the particle is given by the wave function ψ(x,0) = 1/(√(2∏))*∫Θ(k)e^(ikx)dk, which is crucial for the calculations. The Hamiltonian for a free particle is also a point of inquiry, indicating its relevance in the proof.

PREREQUISITES
  • Understanding of quantum mechanics principles, particularly wave functions and expectation values.
  • Familiarity with the Schrödinger Equation (S.E.) and its applications.
  • Knowledge of Hamiltonian mechanics and its role in quantum systems.
  • Basic calculus skills for evaluating integrals and derivatives.
NEXT STEPS
  • Study the definition and calculation of expectation values in quantum mechanics.
  • Learn about the Hamiltonian operator for free particles and its implications.
  • Explore the Schrödinger Equation in greater depth, focusing on its solutions for free particles.
  • Investigate the role of commutators in quantum mechanics and their relationship to constants of motion.
USEFUL FOR

Students of quantum mechanics, physicists working with particle dynamics, and anyone interested in the mathematical foundations of quantum theory.

renegade05
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Homework Statement


A free particle moving in one dimension is in the initial state ψ(x,0). Prove that
<p> is constant in time by direct calculation (i.e., without recourse to the
commutator theorem regarding constants of the motion).

Homework Equations



<p> = m*(d<x>/dt) ?
S.E.
ψ(x,0)= 1/(√(2∏))*∫Θ(k)e^(ikx)dk

The Attempt at a Solution



I am not really sure where to start... Should I find <x> ? is that the easiest way? And how do you this for a free particle ? stuff is confusing me. Can someone give me a start here...
 
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renegade05 said:

Homework Statement


A free particle moving in one dimension is in the initial state ψ(x,0). Prove that
<p> is constant in time by direct calculation (i.e., without recourse to the
commutator theorem regarding constants of the motion).

Homework Equations



<p> = m*(d<x>/dt) ?
No, don't use this. Use the definition of the expectation value of an operator.

S.E.
ψ(x,0)= 1/(√(2∏))*∫Θ(k)e^(ikx)dk

The Attempt at a Solution



I am not really sure where to start... Should I find <x> ? is that the easiest way? And how do you this for a free particle ? stuff is confusing me. Can someone give me a start here...
What is the Hamiltonian for a free particle?
 

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