Physics of Reality - 3

Physics of Reality - 3

[ Part - 1                      Part - 2 ]

The Newtonian Laws of Physics gave way to the concepts of Quantum Physics with the dawn of the twentieth century. With that our belief in the time-space dimensions as a reality existing out there external to us got shattered. The probabilistic nature of the world and the observer being a part of the observed have come to be accepted replacing the classical notions of an absolute world outside the observer. Erwin Schrodinger gave us the wave function, "which was said to completely describe the state of a physical system out in the world. The shape of the wave function encodes the probabilities for the outcomes of any measurements an observer might perform on it." The equations so developed proved very helpful to the Physicists in estimating the probability of an event happening.

The paradigm shift in viewing the world of matter from being absolute to probabilistic excited the philosophers especially with an oriental bent of mind, for the philosophies in the East held for long that the world of matter lacked real 'beingness.' The Non-dual philosophers even held that the apparent world that we see in our wakeful life is akin to our dream. The implied view that just as the dreams cannot be said to have any set laws and theories, the wakeful world too cannot have fixed laws of Physics was deemed to be untenable. Moreover, in contrast to the dreams which are private to each individual, we all seem to share one single world wherein an outcome of an event was predictable within reasonable confidence limits, thanks to the Schrodinger equations.

But now comes along Dr.Christopher Fuchs throwing a spanner into the very fundamental beliefs that  underpin the Quantum Laws. He is inclined to go with the views of Dr. J. A. Wheeler, his mentor, who held that “In the end, the only law is that there is no law. There’s no ultimate law of physics. All the laws of physics are mutable and that mutability itself is a principle of physics." Attesting to this fact, Dr. Fuchs and his colleagues developed the concept of "QBism" in interpreting the physical reality that Quantum Laws represent. They say that "the wave function does not describe the world — it describes the observer." They tell us that “Quantum mechanics is a law of thought. It is a reflection of our ignorance.”

Excerpts on this subject from a recent article in the Quanta Magazine follow:

Dr. C. Fuchs

[T]he wave function’s probabilities [are] Bayesian probabilities — that is, [they are] subjective degrees of belief about the system.

***

[T]he wave function does not describe the world — it describes the observer. 

***

According to QBism, the wave function’s “collapse” is simply the observer updating his or her beliefs after making a measurement. Spooky action at a distance, wherein one observer’s measurement of a particle right here collapses the wave function of a particle way over there, turns out not to be so spooky — the measurement here simply provides information that the observer can use to bet on the state of the distant particle, should she come into contact with it. But how, we might ask, does her measurement here affect the outcome of a measurement a second observer will make over there? In fact, it doesn’t. Since the wavefunction doesn’t belong to the system itself, each observer has her own. My wavefunction doesn’t have to align with yours.

***

[The Copenhagen and other interpretations of Quantum theory] treat the wave function as a description of an objective reality shared by multiple observers. QBism, on the other hand, treats the wave function as a description of a single observer’s subjective knowledge. It resolves all of the quantum paradoxes, but at the not insignificant cost of anything we might call “reality.” Then again, maybe that’s what quantum mechanics has been trying to tell us all along — that a single objective reality is an illusion.

***

QBism [says] that quantum mechanics is not about how the world is without us; instead it’s precisely about us in the world. The subject matter of the theory is not the world or us but us-within-the-world, the interface between the two.

***

One way to look at it is that the laws of physics aren’t about the stuff “out there.” Rather, they are our best expressions, our most inclusive statements, of what our own limitations are. When we say the speed of light is the ultimate speed limit, we’re saying that we can’t go beyond the speed of light.  

***

Bruno de Finetti [] says there’s no reason whatsoever for my probabilities and yours to match, because mine are based on my experience and yours are based on your experience. The best we can do, in that case, if we think of probabilities as gambling attitudes, is try to make all of our personal gambling attitudes internally consistent. I should do that with mine, and you with yours, but that’s the best we can do. That’s what de Finetti meant when he said probability does not exist.

***

As QBism understands a quantum measurement outcome, it’s personal. No one else can see it. I see it or you see it. There’s no transformation that takes the one personal experience to the other personal experience. 

*****

There are, however some problems that QBism has to still find a way out. For example: 

QBism also raises a host of new and equally mysterious questions. If the wave function describes an observer, does the observer have to be human? Does that observer have to have consciousness? Could it be a dog? 

_____________

For more details, please see:
https://www.quantamagazine.org/20150604-quantum-bayesianism-qbism/
http://arxiv.org/abs/1405.2390

_____________

(Physics of Reality - 4, the next Article in the Series, will deal with The  Black hole Complementarity and Information Loss at the Event Horizon).