University Quantum Mechanics I · The Free Particle · 5.09
The Gaussian packet, worked exactly
A Gaussian φ(k) integrates in closed form to a Gaussian ψ(x, t) of complex width, giving σₓ(t) = σ₀ √(1 + (ℏ t/(2 m σ₀²))²).
Course-map guide · not a complete lesson or simulationScope & orientation
What this subsection covers
A Gaussian φ(k) integrates in closed form to a Gaussian ψ(x, t) of complex width, giving σₓ(t) = σ₀ √(1 + (ℏ t/(2 m σ₀²))²).A strong response uses re ψ, im psi and |ψ|² on one axis and states where the model stops being reliable.
Reasoning checklist
Evidence, assumptions and limits
Assumptions to state
State the system, observable, approximation, and conditions held fixed before using a model.
Evidence to collect
Does FFT evolution of a Gaussian packet, applying the free phase exp(−i ℏ k² t/(2m)) in k-space, reproduce σ₀ √(1 + (ℏ t/(2 m σ₀²))²), and where does the periodic grid break it?
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Does FFT evolution of a Gaussian packet, applying the free phase exp(−i ℏ k² t/(2m)) in k-space, reproduce σ₀ √(1 + (ℏ t/(2 m σ₀²))²), and where does the periodic grid break it? Useful evidence includes width fitted from |ψ|² at each step against the analytic curve, ⟨x⟩(t) against x₀ + ℏ k₀ t/m, the norm conserved to a stated tolerance, the time at which the packet reaches the grid edge and wraps, and one run started from a chirped packet that narrows before it spreads..
Limits to state
This GioPhysics course map is an adaptable learning sequence, not academic credit, accreditation, or a universal university syllabus.
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This GioPhysics course map is an adaptable learning sequence, not academic credit, accreditation, or a universal university syllabus. It is a first dedicated quantum-mechanics course, distinct from University Physics V, which covers quantum mechanics alongside atomic, nuclear and particle physics in twenty units: this course is narrower, slower, and teaches the linear algebra it needs rather than assuming it. Hydrogen appears here as an introduction, with the full radial derivation belonging to a second course. A midterm examination is assumed around week 8. Follow your institution's published scope, notation, laboratory programme, and assessment rules. A result should be checked against units, signs, limiting cases, and the conditions under which its model was derived.
Diagram & examples
Work the claim before choosing an equation
Interactive concept map
Follow the model from claim to evidence.
Model, evidence, and boundary
What is the strongest test of a claim about The Gaussian packet, worked exactly?
modelModel, evidence, and boundary turns the stated idea into a representation that can make a prediction.
Example questions
Try the reasoning before revealing the structure.
What is the strongest test of a claim about The Gaussian packet, worked exactly?
Quick check
Test the reasoning, not recall
What is the strongest test of a claim about The Gaussian packet, worked exactly?
Choose an answer to test the model.