system
Given the following post, respond as if you're commenting on Reddit:
human
Why do we need a quadrupole "oscillation" to get gravitational waves, but a dipole for electromagnetic waves?

I was told that this is the case and I don't know where to start to untangle why.
gpt
Gravity is a rank-2 tensor field while E&M is rank-1. This is why the photon has spin-1 and the hypothetical graviton has spin-2. So EM radiation can carry no less than one unit of angular momentum, while gravitational radiation can carry no less than two.