# I Having a hard time believing the detection of gravity waves.

1. Mar 18, 2016

### jnorman

I am probably missing something, but it seems to me that the only way gravitational waves could be generated would be if the center of gravity of a massive body or system began oscillating somehow. The detection of such waves was recently reported and were supposedly generated by a pair of black holes orbiting each other. I do not understand how this system could generate gravitational waves when the center of gravity of the system is not moving/oscillating. Help? Thanks.

2. Mar 18, 2016

### A.T.

Do you understand how two charges doing the same movement would produce EM-waves, even when the center of charge is not moving?

3. Mar 19, 2016

### Staff: Mentor

As I recall, for gravitational waves the source needs to have a time-varying quadrupole moment (of energy-momentum) whereas for electromagnetic waves the source needs to have only a time-varying dipole moment (of charge).

4. Mar 19, 2016

### FactChecker

A single step function (a step function f(t)=0 when t<0; f(t)=1 when t>0) contains all frequencies. So a single event, even without oscillations, can generate all frequencies. Then the system will react to the frequencies differently. It will damp out some frequencies and will oscillate to other frequencies. Sort of like a single push on a suspended weight will make it swing in a cyclic fashion.

5. Mar 27, 2016