Mike Ko Personal Portfolio

 

Home-School Education
2001-2012
Hong Kong

University of Durham
Bachelor of Science
2014-2017
United Kingdom

University of Sussex

Master of Arts
2017-2018
United Kingdom



Writing - Commentary

Quantum Physics - Illusion or Reality?

 

                                       

 

                        Before the twentieth century, physicists believed that the universe was deterministic. In principle, any physical phenomena can be unambiguously deduced from past events and the right physical laws. However, this perspective was greatly shaken by later discoveries in the field of quantum physics. Although successful in explaining various physical processes, these discoveries also produced some uncomfortable consequences. In particular, they cause unpredictability and posed questions about the nature of physical reality. In response, various theories and interpretations were proposed to recover some sense in otherwise counter-intuitive situations. Such problems created by quantum physics, and also the potential solutions to them, are the subject of Alastair Rae’s book, Quantum Physics – Illusion or Reality?

Successful yet Unpredictable

                        The book begins by introducing some quantum physical theories. Such theories are peculiar in that a system’s properties depend on how it is observed or measured. An example is wave-particle duality for light, which behave as either waves or particles, depending on observational settings. These theories have been quite successful in explaining various phenomena, like particles’ behavior and chemical bonding. Yet such theories also create perplexing issues, namely unpredictability.

                        Here is Rae’s example: light as waves can be polarized or split into two channels of perpendicularly polarized waves. Light as particles (called photons) can also be polarized, although each can only enter one channel at a time. However the probability of each photon entering either one of the two channels is equal. Thus we can never know which channel the photon entered unless they are detected afterwards. It is in a mixed state of being in both channels at once, which is called superposition.

                        This is one example of how quantum principles can cause unpredictability. In this case, interpreting light as photons has made it impossible to predict its path upon polarization. To resolve this problem of indeterminacy, physicists sought to devise solutions. One category of these is known as hidden-variable theories.

                        Hidden-variable theories involve as-yet undetected quantities (a variable) that influence a system, like the photons in the polarization experiment. If correctly devised, they can act as determining factors for otherwise unpredictable outcomes. However, mathematical work has shown that such theories must obey an inequality condition. Known as Bell’s theorem, no hidden-variable theory has managed to agree with it so far.

The Copenhagen Interpretation

                        Next we are introduced to the conventional answer to unpredictability, the view known as the Copenhagen Interpretation. This view states is futile to assign conditions of reality to anything before they are measured. The reliable picture of reality comes from the measurement of a system by a device. In terms of the previous polarization experiment, the photon’s superposition is tolerated prior to measurement. Photon position is significant only upon measurement, where superposition is destroyed, or collapses into the detected outcome. It is impossible to make meaningful predictions before that point.

                        The Copenhagen Interpretation obviously resolves the indeterminacy problem of quantum physics; we just avoid those situations. Yet as it solves one problem, it creates another one called the measurement problem. Superposition is eliminated upon measurement. But if quantum physics is universal, then it must apply to macroscopic objects like measuring detectors too. Hence the detector can also be regarded as being in superposition before being measured itself. This chain of superposition and measurement can stretch into infinity. With everything in superposition, we can never ascertain a system’s physical state. The rest of the book introduces five of physicists’ solutions for ending the chain of superposition and measurements.

Five Solutions against Endless Superposition

                        The first solution claims that human consciousness act as the ultimate detector that breaks the measurement chain. The conscious human mind is quite different from other physical objects, so quantum theories (and superposition) apply differently. Hence observations by our minds are the point where superposition collapses and reality can be defined. But while our minds are certainly quite special, there are problems with this view. One main issue is that no objective reality exists if all physical states depend on our minds. Yet an independent physical reality’s existence is more reasonable, as individuals often agree on physical observations.

                        The second solution to the measurement problem is the many-worlds interpretation. Here a superposition does not have to collapse upon measurement. Rather, the universe splits into several copies, each playing out one of the outcomes of the superposition. Each individual universe cannot affect each other, so that we never notice them. The many-worlds interpretation means that any possible outcome of a superposition shall occur in different universes. This solves the measurement problem, as all superposition outcomes exist; no indeterminacy results. Unfortunately, this approach confuses our sense of probability, as everything that can happen shall occur. Probability depends on the number of outcomes, not on influencing physical conditions as we normally observe.

                        Our third solution uses size as the criterion for breaking superposition. The basic rationale is that when objects are large enough, they undergo “spontaneous collapse”. Quantum physics applies differently to macroscopic systems, so any superposition shall automatically collapse. While possible, experiments with sufficiently macroscopic superconducting magnet rings prove that they do enter superposition states. For now, it seems that size is not the key.

                        The fourth solution uses a different criterion to solve our dilemma: irreversible processes. Superposition collapses whenever irreversible processes occur, where measurement records of particular events are left in the universe. This definition can be revolutionary to physics, and not just because it solves the measurement problem. Conventionally, physics regard interacting fundamental particles’ existence as reality. Yet if collapse upon irreversible processes is true, it implies that all meaningful reality depends on physical changes.

                        Developing from this is the final solution, a relatively recent approach called “consistent-histories”. In this approach, different situations can be explained with various “histories”, sets of outcomes representing reality. We can choose whichever histories we prefer, provided that they are “consistent”, meaning they must have valid probabilities. Only consistent histories describe the situation accurately. So we can choose history sets which are consistent but not in superposition, avoiding the measurement problem. Irreversible changes are involved in that they are thought to produce consistent histories. Although seemingly promising, consistent-histories have a catch. Simply put, consistent histories may not necessarily reflect actual reality, even if it comprehensibly explains a situation.

                        Rae then ends the book with his opinions on each of these solutions. He rejects the consciousness approach, as he believes that objective reality exists. The author also expresses doubt of the size-criterion approach’s feasibility, unless experiments produce conclusive proof. For Many-Worlds, the problems involving probability must be resolved before it can be seriously considered. Conversely, Rae thinks that the combination of irreversible processes and consistent-histories approach is the most promising solution. Based on what we can actually observe, we work backwards to find suitable, reasonable interpretations. Rae is also willing to accept physical changes as actual reality so as to use this approach. But ultimately, all the problems in quantum physics have no conclusive solution. Further studies must be done to ascertain what is illusion or reality.

                        Personally, many of these quantum physical ideas and arguments are quite abstract. This realm of physics seems just as philosophical as it is scientific. Regardless, it is fascinating how such ideas can lead to ambiguous situations so contrary to conventional physics. On the various solutions themselves, my conclusions are mostly in line the author’s. Yet I do not have any preferences, as none have particularly strong proof.

Confounding Reality

                        On a general note, it is interesting how quantum physics confounds our sense of reality. In science, we typically tend to get more specific when we look at increasingly basic levels. For quantum physical situations, however, we get apparently indeterminate results. This led physicists to devise theoretical solutions, which then led to questions on reality‘s significance. Usually we loosely assume reality as everything that we can see. Yet with atoms, superposition, and the measurement problem, we can really start doubting what is actually real. As such, work in quantum physics might help us scientifically define what constitutes a meaningful reality.

                        Quantum physics is certainly abstract, but it is our most advanced study of existence’s fundamental levels. An understanding of our universe shall be complete only with at least some rudimentary knowledge of this field. As such I shall definitely pay attention to any quantum physical developments in the future.


                                                                                                                                                                  Mike Ko
                                                                                                                                                                  ( 1,382 words )

 

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