Al Owski’s Reviews > On the Origin of Time: Stephen Hawking's Final Theory > Status Update

“Far-fetched in his time, Wheeler's vision of a participatory universe would wind up as a centerpiece of our top-down cosmology forty years later. Hawking took Wheeler's observer's participance seriously—very seriously and applied it not just to retroactively determine the paths of quantum particles but of the universe as a whole.”

“The delayed-choice experiment illustrates vividly and strikingly that the process of observation in quantum mechanics introduces a subtle form of teleology into physics, a backward-in-time component.”

“We are, of course, all too familiar with backward-in-time reasoning from thinking about other layers of evolution, from biological evolution to human history. I briefly described in chapter 1 how history at all levels is shaped by the chance outcomes of countless branching events. These frozen accidents add a retrospective component to the study of history…”

“history at the very deepest level emerges backward in time. It is as if a constant flux of quantum acts of observation retroactively carves out the outcome of the big bang, from the number of dimensions that grow large to the types of forces and particles that arise. This renders the past contingent on the present, a further reduction of causality…”

“observership in quantum cosmology isn't a mere afterthought or an anthropic post-selection principle acting in a giant preexisting multiverse, but an agency operating at a deeper level, an indispensable part of the continual process through which physical reality—and physical theory, we argue—come about.”

“Whereas Bohr argued that all but one outcome survives, Everett claimed this is only the view from within a given branch of history.”

“The universe we see around us, this branch of reality, is the collective result of innumerable such environmental acts of observation. Having registered and built upon countless chance outcomes, over a period of billions of years, each contributing a few bits of information to our branch of history, this is how the world around us has acquired its specificity.”

“AT THE LEVEL of experience...every act of observing amounts to some sort of pruning of the branching tree of possible futures. A measurement situation in quantum theory is like a fork in the road, where history divides into two or more separate branches. In the experience of any given ob-server, at such branching points, only one of the branches survives. More precisely, on each branch, only that branch survives.”

“de Finetti in 1974 wrote: "My thesis… is...probability does not exist… only subjective probabilities exist, the degree of belief in the occurrence of an event attributed by a given person at a given instant and with a given set of information."…Throughout our lives, most of us gain confidence in subjective probabilities because we find that results we deem likely happen often, and those that we don't happen rarely.”

“Everett's framework, in which probabilities wiggle their way into quantum theory in a more subtle…way, much like the way probability enters our thinking in day-to-day life. Whether we ponder the weather, the lottery, or the shape of the next gravitational wave passing through planet Earth, we all use subjective probabilities all the time to quantify our uncertainty in situations where we have incomplete knowledge.”