James Fodor

speaker

3,084 appearances 4 recordings 1 series first heard Jun 2026 last heard 30 Aug

James Fodor’s voice in public audio — every appearance, attributed to the second.

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recordings per month · last 12 months

Recordings per month over the last 12 months — 4 in all, peaking in Aug 2026 with 2.

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The Science of Everything Podcast · Episode 164: Gauge Theory and the Higgs Boson · 30 Aug 2026 podcast

You can never observe a single field, you always observe interactions of fields.

And so what that comes down to is that f the phase of a photon is never measurable.

We never observe just the phase.

All we ever observe is phase differences.

And uh uh that has a very specific measurable outcome, like when we see interference of light, like um constructive and destructive interference, which you know, we've talked about that in previous episodes.

Um, like you have with water waves, for example.

You can also see this with um with light waves when you when you have patterns of of light and dark bands.

That that's an interference pattern.

That is caused by phase differences between photons as they interfer constructively or destructively depending on their their distance and different frequencies and things like that.

So we can observe phase differences, but a phase difference is precisely one phase minus another phase, or like mathematically that's what it is.

The point there is that in the formalism we have two numbers, phase of photon one, phase of photon two, but we can only experimentally measure one number, which is their difference.

So this gives rise to an extra degree of freedom in the formalism, which is the essentially like one of the phases.

We can only measure the phase difference, but we have two numbers from the phase of each of the photons.

which is an extra degree of freedom.

In order to get rid of that, we need to choose a gauge, which we then we do the calculations in.

But looking at the Lagrangians they were writing, the physicists realized that this internal degree of freedom, this extra parameter here corresponding corresponding to unmeasurable phase,

gives rise to a symmetry under a gauge transformation.

And specifically, that is if you take a field in your Lagrangian in that equation that describes energy, different types of energy effectively.

Remember, Lagrangians have like your kinetic energy, uh, interaction energies, and potential energies, uh, as well as mass energy terms.

So there's different terms in your Lagrangian.

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