The classical world, governed by classical physics, might have felt more intuitive and certain. However, the 20th century’s revolutionary birth of quantum mechanics opened a way to the “quantum world”. This chapter investigates the evolving concept of “world”, especially exploring the special and general theories of relativity, with Wittgenstein’s philosophical view that the world is composed of facts, or the existence of states of things. Quantum mechanics has two essential principles: The Heisenberg uncertainty principle and the new Heisenberg uncertainty principle, where the former indicates the inherent uncertainty within the quantum world and the latter uncovers the certainty under some circumstances such as quantum entanglement. Quantum mechanics, while having multiple interpretations, is considered a relatively complete framework; however, its “counterfactuals”—scientific facts that defy classical expectations—can be challenging for the classical understanding. Additionally, the potential for “backward causality” under time symmetry conditions adds another level of complexity. These counterfactuals and the possibility of backward causality don’t contradict existing facts, but rather signal the expansion of our scientific scope and, potentially, a new scientific paradigm.
The classical world, governed by classical physics, might have felt more intuitive and certain. However, the 20th century’s revolutionary birth of quantum mechanics opened a way to the “quantum world”. This chapter investigates the evolving concept of “world”, especially exploring the special and general theories of relativity, with Wittgenstein’s philosophical view that the world is composed of facts, or the existence of states of things. Quantum mechanics has two essential principles: The Heisenberg uncertainty principle and the new Heisenberg uncertainty principle, where the former indicates the inherent uncertainty within the quantum world and the latter uncovers the certainty under some circumstances such as quantum entanglement. Quantum mechanics, while having multiple interpretations, is considered a relatively complete framework; however, its “counterfactuals”—scientific facts that defy classical expectations—can be challenging for the classical understanding. Additionally, the potential for “backward causality” under time symmetry conditions adds another level of complexity. These counterfactuals and the possibility of backward causality don’t contradict existing facts, but rather signal the expansion of our scientific scope and, potentially, a new scientific paradigm.
For over nine decades, quantum mechanics has profoundly shaped our understanding of nature, offering explanations for the stability of atoms, the formation of mole cules, the properties of materials, and phenomena such as light or radioactivity. It is essential to modern technologies—from microchips to lasers—and underpins the physics of elementary particles. Yet, despite its successes, it remains a deeply mysterious theory, confronting a central enigma: why does the quantum world behave so differently from everyday reality? Elements such as superposition and quantum entanglement—which allow particles to exist simultaneously in multiple states or remain interconnected regardless of distance—contradict classical world intuitions. This gap between microscopic and macroscopic behavior has given rise to what is known as the “measurement problem,” raising fundamental questions about the nature of reality. Diverging interpretations have led to two major schools of thought: anti-realism, promoted by Niels Bohr, which holds that reality depends on the observer and their interaction with measurement instruments; and realism, supported by Albert Einstein, which argues that quantum mechanics is incomplete and that eality exists independently of observation. Bohr’s complementary philosophy and Heisenberg’s uncertainty principle were central to the formulation of the “Copenhagen interpretation,” which became dominant in the 20th century. However, the persistent opposition of scientists like Einstein and Schrödinger inspired generations of physicists to seek a unification between quantum mechanics and relativity, culminating in new theories such as loop quantum gravity and string theory. Thus, the debate between realism and anti-realism remains alive, and philosophy continues to play a crucial role in exploring the new foundations of physics.
Modern scientists describe the universe in terms of two basic partial theories: firstly, the general theory of relativity proposed by Albert Einstein, and secondly, the theory of quantum mechanics. This theory introduces an immense reality and simultaneously creates complex questions for the world of physics. Quantum mechanics is an incompletable knowledge however scientists are finding the basic theories from this theory. They propose complex mathematical expressions from quantum mechanics to prove the basic law of atoms. Quantum mechanics is the entire knowledge of subatomic particles such as electrons, protons, and neutrons. Quantum mechanics reveals that what we see is just a part of a deeper reality. Then we can grasp from this theory that the material world is not the completed reality; there are other things beyond human physical senses. The concept of quantum mechanics describes particles that can exist in multiple states. The concept of quantum mechanics is directly proportional to contemporary world technologies. The super specialty of this theory is that scientists cannot be explained universe without quantum mechanics. The uncertainty principle of Heisenberg in quantum mechanics suggests that there are limits to what we can know about a particle state of an atom. Humans cannot yet find out what it looks like and how we can imagine the existence of subatomic particles in an atom. That was an unseen dynamite for humans' perspective observation of the material world.
In the 20th century, two new terms were added to the scientific lexicon: relativistic mechanics and quantum mechanics. The challenge to the concept of the absoluteness of space and time started at the end of the 19th century and gave birth to Einstein's special relativity theory in 1905. This unified space and time to a single entity, space–time, and we have been introduced to many new concepts such as time dilation, space contraction, mass–energy relation, and the space–time continuum in relativity theory. We have also learned that the highest possible velocity in this universe is that of light and that nothing in the universe can move faster than light. Einstein's general theory of relativity took into consideration gravitation and established the chronogeometric concept of gravity. Quantum mechanics developed by Bohr, de Broglie, Heisenberg, Schrödinger, and others gave us knowledge in the atomic and subatomic domain and led to the wave–particle duality of de Broglie, the uncertainty principle of Heisenberg, the wave mechanics of Schrödinger, and so forth. We have learned that three distinct chords are at the heart of quantum mechanics—granularity, relational, and indeterminism. Although quantum mechanics is a weird subject, as we will discuss, the modern physics is totally based on it.
Quantum mechanics has achieved unparalleled success as an operational theory, describing a wide range of experiments to remarkable accuracy. However, the physical foundations on which it rests remain as puzzling as they were a century ago, and a concise statement of the physical principles that underlie quantum mechanics is still outstanding. One promising approach holds that these principles should be formulated in terms of information, since many of the counter-intuitive effects in quantum theory concern questions such as what one can know about a quantum system and how the information encoded therein can be processed and distributed between parties. Another challenging feature of quantum theory is its incompatibility with the other cornerstone of modern physics, general relativity. In order to reconcile the two, one must identify and retain only the essential concepts and principles of each theory, and in the case of general relativity, causality has been identified as such a concept. This raises the question of how our classical understanding of causality must change when quantum theory is taken into account. In order to address these questions about information, knowledge and causality, I turn to the framework of causal models. In classical statistics, causal models explain the relations among a set of variables in terms of causal influences, which makes them a powerful tool for structuring our knowledge about complex systems and developing strategies for interacting with them. More importantly, the framework provides the conceptual underpinnings and mathematical methods for addressing questions about causation, information and knowledge in a rigorous manner. In this thesis, I develop a version of the classical causal models framework that is compatible with quantum theory and explore its physical implications. \n \n \nA first step is to define quantum versions of fundamental elements such as variables, conditionals and belief propagation rules. This allows one to consider the question of what one can come to know about a quantum variable from the point of view of causal modelling. The conditionals relating quantum variables are found to have a richer structure than their classical counterparts, which can be exploited for the task of discerning causal relations given limited data -- a central problem in classical causal modelling. The mathematical properties of quantum conditionals also establish a correspondence between various classes of two-party correlations, such as bound and distillable entanglement, and the types of causal structures that can give rise to them, which may become a useful tool for entanglement theory and quantum information processing. In the context of open quantum systems dynamics, quantum causal models provide a clear physical explanation of not completely positive maps and, more broadly, of non-Markovian quantum dynamics. Finally, I consider the possibility of non-classical effects in the way that different causal mechanisms are combined -- that is, non-classical causal structures. For the simple case of two causally ordered variables, I propose indicators that witness different classes of combinations of causal mechanisms, including a non-classical mixture, and describe an experiment realizing examples of the different classes. \n \n \nAs these results illustrate, the framework of quantum causal models provides both greater conceptual clarity and a comprehensive mathematical formalism for studying a diverse set of problems, ranging from foundational questions to applications in open systems dynamics and the exploration of non-classical causal structures, which are likely to feature in a future theory of quantum gravity. The material presented in this thesis is intended as a foundation and inspiration for further applications of quantum causal models.
Quantum physics, also known as quantum mechanics, is one of the most profound and successful theories in modern science, fundamentally transforming our understanding of the microscopic world. It governs the behavior of matter and energy at atomic and subatomic scales, where classical physics fails to provide accurate explanations. This review paper presents a comprehensive examination of the fundamental concepts of quantum physics, including wave–particle duality, quantum states, superposition, uncertainty principle, quantum measurement, entanglement, and quantum dynamics. The paper traces the historical development of quantum theory, reviews seminal contributions from key physicists, and analyzes major theoretical frameworks such as Schrödinger’s wave mechanics, Heisenberg’s matrix mechanics, and Dirac’s formalism. A systematic literature review of 25 scholarly sources is conducted to highlight the evolution, interpretations, and applications of quantum concepts. A comparative analysis of classical and quantum physics is provided to emphasize conceptual differences and paradigm shifts. The discussion explores philosophical implications, experimental validations, and emerging applications in quantum computing, cryptography, and quantum technologies. Finally, the paper concludes by summarizing key insights and outlining future directions for research and education in quantum physics.
This paper re-opens the debate on the failure of quantum mechanics to provide an understandable view of micro-reality. A critique is offered of the commonly accepted ‘Copenhagen Interpretation’ of a theory that is only a mathematical approach to the level of reality characterized by atoms and electrons. This critique is based on the oldest approach to thinking about nature for over 2500 years, known as Natural Philosophy. Quantum mechanics (QM) was developed over the first quarter of the 20th Century, when scientists were enthralled by a new philosophy known as Positivism, whose foundations were based on the assumption that material objects exist only when measured by humans – This central assumption conflates epistemology (knowledge) with ontology (existence). The present critique rejects this human-centered view of reality by assuming material reality has existed long before (and will persist long after) human beings (“Realism”). The defensive view that the micro-world is too different to understand using regular thinking (and only a mathematical approach is possible) is rejected totally. At least 12 earlier QM interpretations are critically analyzed, indicating the broad interest in “what does QM mean?” The standard theory of quantum mechanics is thus constructed on only how the micro-world appears to macro measurements - as such, it cannot offer any view of how the foundations of the world are acting when humans are not observing it - this has generated almost 100 years of confusion and contradiction at the very heart of physics. Significantly, we live in a world that is not being measured by scientists but is interacting with itself and with us. QM has failed to provide explanations: only recipes (meaningless equations), not insights. Physics has returned to the pre-Newtonian world of Ptolemaic phenomenology: only verifiable numbers without real understanding. The focus needs to be on an explicit linkage between the micro-world, when left to itself, and our mental models of this sphere of material reality, via the mechanism of measurement. This limits the role of measurement to confirming our mental models of reality but never confusing these with a direct image of ‘the thing in itself’. This implies a deep divide between reality and appearances. This paper proposes that it is the attempt to preserve continuum mathematics (especially calculus), which drives much of the mystery and confusion behind all attempts to understand quantum mechanics. The introduction of discrete mathematics is proposed to help analyze the discrete interactions between the quintessential quantum objects: the electrons and their novel properties. Additionally, several hidden major assumptions have been present in Classical Mechanics (represented by continuum mathematics) since its inception by Newton that are blocking progress and understanding of quantum mechanics. A related paper demonstrates that it is possible to create a point-particle theory of electrons that explains all their peculiar (and ‘paradoxical’) behavior without introducing the continuum mathematical ideas of fields or waves. * Surrey, B.C. Canada (604) 542-2299 spsi99@telus.net Version 1.195 10-07-2016 Begun 23-06-2008 {pp. 80, 70.4 Kw; 800 KB}