In the third installment of an ongoing tradition (wow, this blog is old enough to have traditions!), I present 2015’s Valentine’s Day Physics Poem. Like the others, I wrote this one a long time ago. I’ve polished it up a bit since.

 

Perturbation Theory

 

When you’ve been in a system a long time, your state tends to settle

Time-energy uncertainty

That unrigorous interloper

Means the longer you wait, the more fixed you are

And I’ve been stuck

In a comfy eigenstate

Since what I might as well call t=0.

 

Yesterday though,

Out of the ether

Like an electric field

New potential entered my Hamiltonian.

 

And my state was perturbed.

 

Just a small, delicate perturbation

And an infinite series scrolls out

Waves from waves from waves

It’s a new system now

With new, unrealized energy

And I might as well

Call yesterday

t=0.

 

Our old friend

Time-energy uncertainty

Tells me not to change,

Not to worry.

Soon, probability thins

The Hamiltonian pulls us back

And we all return

Closer and closer

To a fixed, settled, normal state.

 

This freedom

This uncertainty

This perturbation

Is limited by Planck’s constant

Is vanishingly small.

 

Yet rigor

        And happiness

                Demand I include it.