Undergrad Gravity Wave Propagation: Negative Energy Pulse?

[desertsoldier39]

TL;DR

First year Astronomy and planetary sciences student. Have some questions when looking at G-wave propagation and formation simulations.

At 0:51 in this simulation video there seems to be a brief moment upon merging that these singularities produce what appears to be negative gravitational "Spike?" that seems to bulge spacetime in an opposite metric compared to normal spacetime flatness. Is this a quirk of the simulation or is this a pulse of negative energy?

 

[desertsoldier39]

I also have a second question above G-waves themselves. They appear to be propagating waves of contracting and expanding spacetime. When spacetime contracts at the leading edge of the wave and then expands, does the expansion revert back to normal spacetime flatness or is there a momentary expansion beyond that metric?

 

[Orodruin]

First, nomenclature: it is gravitational waves, not gravity waves. Gravity waves are things like waves on a water surface.

Second, you cannot really learn much about gravitational waves by watching simulations like this, which will always be some lower dimensional representation of the full simulation.

It is not clear to me what you would mean by ”opposite metric”. The metric of a spacetime is by construction Lorentzian everywhere.

In particular coordinate systems, gravitational waves may be described as space expanding and contracting (not spacetime, which is what it is - time is a part of it so it does not actually do anything). However, that is a coordinate dependent interpretation requiring you to make particular choices of coordinates and assign them the space and time labels.

When spacetime contracts at the leading edge of the wave and then expands, does the expansion revert back to normal spacetime flatness or is there a momentary expansion beyond that metric?

This completely depends on the shape of the wave - as for any wave, gravitational waves are governed by the wave equation.