The Quality of what did actually happen, an Observed Taylor State or the one Phenomenal World, can only be measured against a background of the counter-factual, Taylor States that can be imagined, but not observed, or Experiential Worlds; all the things that did not happen, but that our previous experiences account to us as possible or plausible. That is, Quality is a measure of that experience which is immediately available to us, as opposed to those imaginable worlds in the Multiverse which are both accessible, and which we consider relevant to experiences, observations, and measurements.
Take a rain gauge for example. Depending on its actual dimensions, there are a measurable number of Wallace-accessible worlds (Wallace Vectors) in which, variously, no raindrops fall into the gauge, few raindrops fall into the gauge, or a great many raindrops fall into the gauge. Depending on the values of these Wallace Vectors, we can mark the side of the gauge with indicators of the Wallace Values of the amounts and imaginable consequences of all the raindrops that fell, in the area surrounding the rain gauge.
So, we have the probability of a particular rain gauge of particular dimensions, the probability of any one raindrop falling into the gauge, and the total amount of rain that falls, and its probable moral consequences, such as drought, flood, food scarcity, property damage, or even lives lost. How the rain gauge is marked is a distinct set of relationships of Virtual Worlds to our one Actual World. These relationships are Wallace Vectors of Accessibility. A greater probability of a single raindrop falling into a gauge of standardized dimensions directly correlates to a greater probability of a drought ending, or a flood occurring.
Without these implicit Wallace Vectors, in a very real sense we do not have any of the benefits of a rain guage at all: we can either measure the diameter of the puddles, or tally up the property damage, but we don't really have a precise measurement of how much rain actually fell; we know the effects, but can only "guesstimate" the magnitude of the cause. That is, Quality, the contrast of many Virtual Worlds against our one Material World, is all that Scientific Instruments actually measure. Science is a kind of Divination, a probabilistic correlation of Present Taylor States to Future Wallace Vectors, one of the few with the largest probabilities of reproducible success.
In some other Universe, virtual or otherwise, very far from our own, there is a published work of non-fiction entitled "A Taxonomy of Puddles: An Encyclopedic Collection". We can gauge that they are not very bright, can't we? In yet another universe, I have a Doctorate in Philosophy; draw your own conclusions for now. The issues of our Universe and the existential nature of a Multiverse leave us then, with certain questions to answer. Is the Multiverse Phenomenal or Experiential? Is the Multiverse Actual or Virtual or Potential? What is Real?
If the Multiverse is "merely" Experiential and Virtual, then there is not a single Wallace Vector to pursue, in which the Multiverse is anything but Subjective, a tool of the mind, which we use to measure the qualities, quantities, and Quality of Life, of our one Actual Universe. If the Multiverse is Phenomenal, Objective, and Actual, or at least Potential, then how would we come to Realize and Actualize this potential of our Existential relationship to these other Worlds? As to whether the Multiverse is Real, that depends on whether or not your thoughts, feelings and Quality of Life is Real. I find it easy to answer that last question for myself, but do you? How deep and broad should we gauge the Subjective to be? What value should we place on considering these questions deeply and broadly, and those who make the deepest and broadest Observations?
If you've read a little Danielewski, the title of this piece should be familiar.