I, I map out a heavy path in life
But some things are massless
And take a different road

And they, they ride a null-length vector flow
Cause when you are massless
Your worldline's always null

That's why they fly at the speed of light
And as they fly they perceive no time
They don't change

Now you need to know about neutrinos
We thought they were massless
Purely Weyl chiral

Then Super-K and SNO confirmed they oscillate
And cannot be massless
Though they're very close

But they don't fly at the speed of light
For as they fly they proceed through time
And they change

Now they're defined by a CKM
Mapping from mass to flavour kets
And now we ask why do they seem so light?
And now we're not sure why but we theorize
A see-saw!

Sudbury's spherical screen
Resolved the mystery
Of neutrino oscillation
Tau, mu and electron
For none is...

Massless