QUANTUM REALITY AND APPEARANCE
2016/2017, Semester 1
University Scholars Programme (University Scholars Programme)
Modular Credits: 4
Can physics allow us to know the reality of nature or does it merely tell us how nature appears? Or for that matter, what are the limits of knowledge in physics, constrained as it is to giving responsible proof for the claims it makes? The enquiry into
what we can know
can be traced back to the philosophy of Ancient Greece. In pre-Socratic times there was a fundamental disagreement between Protagoras and Democritus on the issue of realism. Protagoras held that all we can know are the sensations that we receive. He maintained that we can know nothing of what is out there causing these sensations. Democritus, on the other hand, insisted that “things” exist separately from our perception of them.
Fast forward to the mid-1920s and the jury is still out on this issue. Based on developments in quantum physics, Niels Bohr, an indisputable giant of early 20
century physics, decreed that
“… it is wrong to think that the task of physics is to find out how nature is. Physics concern what we can say about nature.”
For Bohr our observations
the reality that we are observing. Albert Einstein, on the other hand, maintained that “
Physics is an attempt conceptually to grasp reality as it is thought independently of its being observed.
” This dispute became what is now called the Bohr-Einstein debate.
In 1935, in his bid to hold on to his concept of reality, Einstein (with collaborators Podolsky and Rosen) launched his most scathing attack on quantum theory by declaring that it was incomplete. Using a property of quantum systems, called entanglement, he demonstrated that there were elements of reality that were not captured by quantum theory. Bohr fairly quickly produced what he claimed to be rebuttals of Einstein’s claims. Although many accepted that Bohr had prevailed, the argument by Einstein and his collaborators (EPR) was relegated as a paradox in quantum mechanics.
It was not until the mid-60s that a seminal paper by John Bell provided a first hint that the deadlock between the two viewpoints could be broken. He showed that if reality was assumed in the way that Einstein did, one could, in principle, subject this notion to an experimental test. Writing down, what is now called Bell’s inequalities, he showed that if these inequalities are violated then one has to abandon Einstein’s brand of realism. The results of this test only emerged in the early 80s when Alain Aspect and collaborators showed that the inequalities are indeed violated.
But as one starts to draw the curtains on this debate, other interpretations emerge that attempt to salvage realism by reinterpreting quantum theory. So the saga continues…. In this module students will be taken through a journey that showcases the developments and the key ideas that have shaped our current views on reality (or lack thereof).
This is a Inquiry-Tier module offered under USP’s structured collection of multi-disciplinary modules. Aimed at exposing students to various aspects of scientific inquiry, this module examines issues related to
and its counterpart,
In this module, s
tudents will be brought through a general framework for thinking about these issues lensed from both Philosophy and Physics. Specifically, students will
appreciate and understand the philosophical underpinnings of the notions surrounding reality and appearances;
examine what constitutes the scientific method and scientific reasoning;
learn how quantum theory is used in understanding the behaviour of subatomic particles; and
examine how the interpretations of quantum theory bear on the issue of reality and appearances.
Principally, the pedagogical components will be divided into four units:
UNIT 1 - Philosophical Underpinnings (2 weeks)
The discussions here will examine the ontological and epistemological questions that one is faced with in describing nature. Here, discussions will be grounded in the basic approach to scientific enquiry that constitutes the Scientific Method. This will include, among other things the Aristotle’s Inductive-Deductive approach where observations play a fundamental role in knowledge generation. This will be contrasted with Plato’s orientation which favors the contemplation of abstract ideas over sense experience in deriving knowledge. The key distinctions between rationalism and empiricism will also be discussed.
UNIT 2 – The Formalism of Quantum Mechanics (4-5 weeks)
Starting with a mathematical prelude, that covers some basic notions of linear algebra, this unit will bring students through the formalism of quantum mechanics. Two key questions that underlie the formalism will be expounded, namely, (a) what are the possible measurement results of an observable? and (b) what are the probabilities associated with these outcome? These will be addressed using the polarization states of photons as an example.
Unit 3 – The EPR – Paradox and Bell’s Inequalities (3- 4 weeks)
This unit will examine the Complementary Principle and the underlying Copenhagen interpretation of quantum mechanics (positivism). These discussions will then center on Einstein’s attack on Complementarity. Bell’s inequalities and their implications on the notion of realism will follow, leading up to experimental tests for these inequalities.
Unit 4 – Other Interpretations of Quantum Mechanics (2-3 weeks)
This concluding unit will examine alternative interpretations to the Copenhagen Interpretation. Here students will be introduced to De Broglie’s pilot wave scheme where the quantum particles are regarded as real particles moving in a real field (the pilot wave). The associated Bohm theory will also discussed as a popular alternative which requires a violation of special relativity. If time permits, the many-world interpretation of Everett will also be discussed. Their bearing on the issue of reality will also be elucidated.
The assessment scheme for this module is as follows:
Tutorials (group assignments) - 40%
Individual assignments (2 Essays) - 60%
Not applicable to USP modules.
Workload Components : A-B-C-D-E
A: no. of lecture hours per week
B: no. of tutorial hours per week
C: no. of lab hours per week
D: no. of hours for projects, assignments, fieldwork etc per week
E: no. of hours for preparatory work by a student per week