Tag Info

Hot answers tagged gauge-theory

Accepted

Is the magnetic vector potential "real" in classical electromagnetism?

The vector potential is gauge-dependent and unobservable in both classical and quantum mechanics. Only gauge-invariant quantities — including the electric and magnetic fields — are observable. Even in ...
• 8,309
Accepted

Trouble reconciling these two views on gauge theory

Gauge theory resembles general relativity applied to extra dimensions beyond the big four. Whether that's the true nature of gauge fields or just a convenient mental picture isn't clear, but it's at ...
• 27.3k
Accepted

How do physicists mathematically define gravitational waves?

The most straightforward way is to simply take the transverse-traceless (TT) part of $h_{ij}$. The TT part of the metric, denoted $h^{\mathrm{TT}}_{ij}$, contains precisely the two propagating degrees ...

Differential Forms and Gauge Invariance?

The exterior derivative of a $k$-form is a $k+1$-form. The square of the exterior derivative is zero, so if you add an exact one-form to $A$, that is $B= d\lambda$ where $\lambda$ is a zero-form, you ...

Is the magnetic vector potential "real" in classical electromagnetism?

One way of thinking about this issue of what quantities are 'real' is to compare it to the more familiar situation with position. There are quantities in physics with the property that the quantity ...

What is an Intuitive example of a Gauge Symmetry?

Another example of of a Gauge Symmetry can be found in the basic $V=mgh$. Here you can have your "ground" anywhere you want. This freedom reflects the key idea in gauge theory.

Is the magnetic vector potential "real" in classical electromagnetism?

Let's take the definition of a "real field" from the chapter in Feynman's lectures you linked to: What we mean here by a “real” field is this: a real field is a mathematical function we use ...
• 50.2k

Why are physical states not eigenstates of BRST charge?

For starters, the BRST charge operator is Grassmann-odd, so an eigenvalue would be Grassmann-odd as well, which is unphysical.
• 205k

How can a gauge field have physical effects if it only reflects a redundancy in our mathematical description of physical reality?

You just need to phrase both your points more carefully. That changing the gauge has no physical effect does not mean the gauge field does not have any physical effect (for one, since not all possible ...
• 126k

Differential Forms and Gauge Invariance?

The answer is simply that the sum $A+d\lambda$ should still be a $1$-form, just like the original $A$ itself. Why this has to be a case is clearer if we express the quantities in terms of spacetime ...
• 16.2k
Accepted

• 205k