Twelve years ago, a brief discussion was held here, on this very forums before briefly dwindling out. It wasn't hostile, it was reasoned and cool. I left alignment first, then Dungeons & Dragons entirely, and eventually even Penny Arcade behind. But I never forgot! Is any of the old vanguard still around? I doubt it.
I've come back, eventually, for 5th Edition, and brought all of my own new, bullshit ideas along with it. Those ideas reflected how to look at alignment, and inspired a search for a sweet spot between pointless (just a reminder on your sheet that you're still playing a good guy) and capricious ("A-ha! You didn't know it but the brigand was just a young man who was being led down a wrongful path! In this turn of unfortunate events, you have committed an evil deed by putting him to death! Please turn over your sheets, your characters are retired.")
The game I run is set in a universe strongly inspired by Planescape; you could imagine a far-future Planescape, where scientists from mundane Prime Material planes like ours, more distant from the Crystal Spheres that made up the known multiverse in the past, have been able to devise technology to bring them beyond the barriers that kept their worlds apart. Planescape with more anachronism.
In this setting, alignment is not a guideline, it is a physical constant. You can imagine a person's alignment as two vectors, one that holds to a position between Good and Evil, the other between Law and Chaos; together, they provide a compass of a sort. In the past, scholars understood a loose conception of these forces, an understanding that a person who behaved in a particular way would be called as a petitioner on some particular plane at death, and that this may have some relationship with how they respond to particular arcane magic or divine interference. But time has gone on. Scholars now understand alignment in a more complex manner.
The first major development was the relative theory of alignment. Under this theory, a person's alignment was determined by a number of factors -- perhaps infinitely many factors -- but a significant influence on alignment was *perspective*. From one perspective, an act may seem to be good, but viewed from afar, it may be measured as jut the opposite -- truly evil. On a local level, alignment may be seen to behave as expected, but from afar, a very different conclusion may be reached when an action or individual is measured against known "alignment signifiers."
This provided scholars with some guidance, but others felt that there must be more to it. If alignment is interwoven in the multiverse, an intrinsic quality of the planes and the Powers that rule over them, that can pull a city like Curst into Carceri with all the power that gravity holds the Tears of Selune in place over Toril, then it must be measurable. This was for a long time believed to be true but no hard evidence could be found. "There is simply no way to test this theory," went the popular refrain among even the most renowned scholars of good and evil, law and chaos.
The introduction of quantum science to the planes changed things. Now magi could see the change taking place in a body as its soul lifted away; could measure with bursts of light in a mundane the wall the passing of creatures moving through the Shadowfell. Most of all, they could measure alignment, and what they found enlightened and unsettled them.
At the very most basic level, those things rendered with consciousness have subatomic particles that pair together, each spinning on an opposite axis. One spin points in a direction indicating an orientation toward the realms of Good or the realms of Evil; the other spins in an orientation toward the planes of Law or the planes of Chaos. Through experimentation, the Dread Cabal of United Lichdom determined that indeed, these measurements were and accurate determination of where a mortal's soul could be expected to return as a Petitioner -- not just down to the plane, but indeed to the exact location on that plane.
The Dread Cabal also discovered some things that threw the academic community of the multiverse into an endless debate, one that to this day continues: the Dread Cabal found that things deemed differentiated Good from Evil were, at best, shallow; it may find that a Deva, instilled with righteous cause, that drowns a mortal due to a belief in a future catastrophe is acting with Good intention, and to expect to find its way home to Mount Olympus ever after. A reading may tell that a man who sells his last possessions to buy medicine for his beloved has taken a turn toward Evil, though the circumstances that made it just so may be impossible to determine outside of a tightly closed environment.
What the Dread Cabal really unveiled was this: that a being's Alignment, approached with this understanding of an infinitely self-interfering web of actions, reactions, and retroactions, can be impossible to predict classically but that through quantum means, may not only be tracked but can be manipulated. Of course, the multiverse at large finds itself concerned that the Cabal, whose long lineage traces back to its founder, Vecna, has not only discovered this method but has also spent the past several hundred years perfecting it.
Incidentally, the scholars of Krynn had developed an earlier theory that somewhat resembled the quantum theory.