An item on Quartz reports that two separate groups of scientists have decided that there may be a “mirror universe” in which time moves backwards. That time moves backwards shouldn’t surprise readers of this blog. However, this doesn’t happen in some mirror universe, but in our very own world. As I explained here, time in our universe takes a step backwards for every step forwards, so we live in a superposition of forward-time and backward-time universes. We only see the forward-time universe because the expansion of the universe guarantees that one direction of time always has more spacetime points and therefore more particles than antiparticles. All the antiparticles were annihilated, leaving essentially no trace of the backward-time universe. However, all of the backward-time spacetime points are still around because points don’t annihilate. This is a good thing because we couldn’t explain the stardard model without them. Follow the link for more information.