[ WP ] Unknown to us mirrors actually are just windows into an alternate dimension that is exactly the same except right and left are reversed . Until one day something throws the mirror dimension out of sync ...

I'll never forget the day we discovered gravitational waves being emitted from mirrors. It seems like it was only yesterday. Actually it *was* yesterday. It took that long to nail down the final confirmation. 
 
 For months we had been calibrating our detector design, with the eventual aim of observing gravitational radiation from black holes, neutron stars and other celestial bodies. Gravitational wave detectors would open up vast new vistas for astronomy, but the darn things were super-sensitive. We spent months chasing down the tiniest anomaly before we found its source. In the end, the trace was unmistakable in the data. Mirror, mirror on the wall. 
 
 The implications were enormous: every reflective surface was actually a portal to another dimension. The very word `` reflective'' was a misnomer: photons left our universe and entered another one, and counterpart photons entered ours. Gravitational waves did the same, although they were attenuated by many, many orders of magnitude for some reason as they passed through the interdimensional interface. We're still not sure why. 
 
 There's a paradox though, which is a bit complicated to explain: our universe would n't exist without symmetry breaking. For example, if matter and antimatter were exact opposites, they would have been produced in equal amounts in the Big Bang, yet there is a tiny disparity, a baryon asymmetry, which has shaped everything around us. 
 
 Parity violation is another example of symmetry breaking, and that's the problem. It was discovered in 1957 and immediately warranted a Nobel Prize. Parity violation tells us that the mirror dimension must have subtly different physics, in some unknown way. Yet events in the mirror faithfully `` reflect'' -- pun intended -- everything that happens in our dimension. How to explain that contradiction? 
 
 It was late at night as I stood in the washroom of the research institute. I stared at my counterpart in the mirror. `` How are you different? ``, we said to one another. Obviously, there was no echo. Sound ca n't traverse the portal, since it is a phenomenon of matter, which always remains confined to its own dimension. `` What exists in our world that does n't exist in yours, or vice versa?'' 
 
 `` We do'', said the voice behind my shoulder, as I stared at an empty room in the mirror. Funny accent, I thought. Transylvanian perhaps.
