<p>Interesting because I speculate that the the Aether is not the Reality Stone for a number of reasons. In response to the discussion topic though matter and anti-matter are just two opposites of one another. Changing a reality into another reality is the same as crossing over into a parallel or alternate dimension/universe,except in this case,the Reality Stone should change something into that which has never been created before like a wish. I think Marvel will save the Reality Stone for last because it is potentially the most dangerous. Anti-Matter eats up matter so If Malekith were to spread the Aether into the Convergence my guess is that it would seek out every living being and attempt to convert living matter into dead matter or more correctly dark matter. Anti-matter differs from dark matter. Malekith is from a place filled with dark matter. Flooding the realms with something that can turn them into places like his home could very well just merge into one dark matter realm hence the statement about transforming the universe into darkness once again. </p>

<p>Those are some excellent points, which still beg the question of what Stone it is. The Aether's known abilities have little to do with Mind or Time, so that leaves Soul: if turning light to dark is a euphemism for the mortal soul. The Aether bonds to a living host, so it could be it.  </p>