Maria Goeppert-Mayer was one of only two women to win the Nobel prize for physics thus far, the other being Marie Curie. And yet her name isn’t anywhere near as well known as Marie Curie’s. She also worked on the Manhattan Project and spent time during her long career with Enrico Fermi, Max Born, Edward Teller, and many other physics luminaries.
She was “other” in another way too. She followed her husband from university to university, and due to prevailing rules against hiring both husband and wife, often had to take a non-faculty position, sometimes even with no salary. Yet being the other, or plus-one, seemed to give her what every pure scientist desires, the freedom to explore. And explore she did, widely. She was always on the cutting edge, and all the time working with the leading luminaries of physics. For a scientist, her story reads like it’s too good to be true, which is what makes it so delightful to read about.
Hold out your hands in front of you, palms forward. They look quite similar, but I’m sure you’re all too aware that they’re actually mirror images of each other. Your hands are chiral objects, which means they’re asymmetric but not superimposable. This property is quite interesting when studying the physical properties of matter. A chiral molecule can have completely different properties from its mirrored counterpart. In physics, producing the mirror image of something is known as parity. And in 1927, a hypothetical law known as the conservation of parity was formulated. It stated that no matter the experiment or physical interaction between objects – parity must be conserved. In other words, the results of an experiment would remain the same if you tired it again with the experiment arranged in its mirror image. There can be no distinction between left/right or clockwise/counter-clockwise in terms of any physical interaction.
The nuclear physicist, Chien-Shiung Wu, who would eventually prove that quantum mechanics discriminates between left- and right-handedness, was a woman, and the two men who worked out the theory behind the “Wu Experiment” received a Nobel prize for their joint work. If we think it’s strange that quantum mechanics works differently for mirror-image particles, how strange is it that a physicist wouldn’t get recognized just because of (her) gender? We’re mostly here to talk about the physics, but we’ll get back to Chien-Shiung Wu soon.
The End of Parity
Conservation of parity was the product of a physicist by the name of Eugene P. Wigner, and it would play an important role in the growing maturity of quantum mechanics. It was common knowledge that macro-world objects like planets and baseballs followed Wigner’s conservation of parity. To suggest that this law extended into the quantum world was intuitive, but not more than intuition. And at that time, it was already well known that quantum objects did not play by the same rules as classical objects. Would quantum mechanics be so strange as to care about handedness? Continue reading “There Is No Parity: Chien-Shiung Wu”→
The Greek philosopher Plato is well known for his allegories and metaphors. Of particular interest is his Allegory of the Cave, which appeared in The Republic, written around 380BCE. In it, Plato describes a group of prisoners which are chained to a wall within a cave, and have been all of their lives. They have no direct interaction with the world outside of the cave. They only know of the world via shadows that are cast on the wall opposite of them. For the prisoners, the shadows are their reality. Though you and I know the shadows are only a very low-resolution representation of that reality.
Theoretical physicist Steven Weinberg, a Nobel Prize winner who works out of the University of Texas at Austin, once likened himself to a prisoner in Plato’s cave. We are forever chained to this cave by the limitations in measurements we can make and experiments we can perform. All that we can know are shadows of the reality that exists in the sub-atomic world. We can see the shadowy figures lurking in our math and as wisps of misty vapor trails in our cloud chambers. We attempt to pierce the veil with the power of our imagination and draw nifty looking charts and animations depicting what our mind’s eye thinks it can see. But in the end, we are all trapped in a cave… staring at shadows. Reflections of a reality we can never truly know.
In our last Quantum Mechanics article, we introduced you to the idea of quantum electrodynamics, or to put it more simply — quantum field theory. In this article, we’re going to explore how QED lead to the prediction and eventual confirmation of something known as the Higgs Boson, also known as the God Particle. As usual, we’ll aim to keep things as simple as possible, allowing anyone with a curious mind to know what this God particle talk is all about. Like so many things in the quantum world, it all started with an unexpected outcome…
The story of Schrodinger’s cat is well known, and one of quantum theory’s most popular phrases on the world stage. You can find his cat on t-shirts, bumper stickers, internet memes and the like. However, few know the origins of the cat, and how it came into being. I suspect many do not understand it beyond the “dead and alive at the same time” catchphrase as well. Not surprisingly, it was Einstein who was at the center of the idea behind Schrodinger’s cat. In a vibrant discussion between the two via letters across the Atlantic, Schrodinger echoed Einstein’s concerns with the following:
Contained in a steel chamber is a Geiger counter prepared with a tiny amount of uranium, so small that in the next hour it is just as probable to expect one atomic decay as none. An amplified relay provides that the first atomic decay shatters a small bottle of prussic acid. This and -cruelly- a cat is also trapped in the steel chamber. According to the wave function for the total system, after an hour, sit venia verbo [pardon my language], the living and dead cat are smeared out in equal measure.
This was the first mention of Schrodinger’s cat, and one would not be incorrect in stating that this paragraph from a letter was where the cat was born. However, the original idea behind the thought experiment was from Einstein and his loathing of the wording of the Einstein-Podolsky-Rosen (EPR) paper. He expressed his frustrations with Schrodinger with a few simple examples, who then catapulted it into his famous paradox . In this article we’re going to explore not so much the cat, but the meaning behind the thought experiment and what it is meant to convey, while keeping it simple enough for anyone to understand. So next time you see it on a t-shirt, you will be able to articulate the true meaning and know the real Schrodinger’s cat.
Richard Feynmann noted more than once that complementarity is the central mystery that lies at the heart of quantum theory. Complementarity rules the world of the very small… the quantum world, and surmises that particles and waves are indistinguishable from one other. That they are one and the same. That it is nonsensical to think of something, or even try to visualize that something as an individual “particle” or a “wave.” That the particle/wave/whatever-you-want-to-call-it is in this sort of superposition, where it is neither particle nor wave. It is only the act of trying to measure what it is that disengages the cloaking device and the particle or wave nature is revealed. Look for a particle, and you’ll find a particle. Look for a wave instead, and instead you’ll find a wave.
Complementarity arises from the limits placed on measuring things in the quantum world with classical measuring devices. It turns out that when you try to measure things that are really really really small, some issues come up… some fundamental issues. For instance, you can’t really know exactly where a sub-atomic particle is located in space. You can only know where it is within a certain probability, and this probability is distributed through space in the form of a wave. Understanding uncertainty in measurement is key to avoiding the disbelief that hits you when thinking about complementarity.
This article is a continuation of the one linked above. I shall pick up where I left off, in that everyone agrees that measurement on the quantum scale presents some big problems. However, not everyone agrees what these problems mean. Some, such as Albert Einstein, say that just because something cannot be measured doesn’t mean it’s not there. Others, including most mainstream physicists, say the opposite — that if something cannot be measured, it for all practical purposes is not there. We shall continue on our journey by using modern technology to peer into the murky world of complementarity. But first, a quick review.
One can be reasonably certain that when the title of an article includes the phrase “The Nature of Reality”, thought provoking words must surely lie ahead. But when that same title seems to inquire about a gentleman’s socks, coupled with an image of said gentleman’s socks which happen to be mismatched and reflect very loud colors , one might be moved in a direction which suggests the article is not of a serious nature. Perhaps even some sort of parody.
It is my hope that you will be pleasantly surprised with the subtle genius of Irish physicist [John Bell] and his use of socks, washing machines, and a little math to show how we can test one of quantum physic’s most fundamental properties. A property that does indeed reside in the very nature of the reality we are a part of. Few people can say they understand the Bell Inequality down to its most fundamental level. Give me a little of your time, and you will be counted among these few.
The philosopher in the street, who has not suffered a course in quantum mechanics, is quite unimpressed by the [Einstein-Podolsky-Rosen] correlations. He can point to many examples of similar correlations in everyday life. The case of Bertlmann’s socks is often cited. Dr. Bertlmann likes to wear two socks of different colours. Which colour he will have on a given foot on a given day is quite unpredictable. But when you see that the first sock is pink you can be already sure that the second sock will not be pink. Observation of the first, and experience with Bertlmann, gives the immediate information about the second. There is no accounting for tastes, but apart from that there is no mystery here. And is this [Einstein-Podolsky-Rosen] business just the same?
John Bell began his now famous paper with the above paragraph. The Bell Inequality started off like so many other great theories in science – as a simple thought experiment. Its conclusions were not so simple, however, and would lead the way to the end of Einstein’s idea of local hidden variables, and along with it his hopes for a deterministic universe. In this article, we’re going to look at the Bell inequality in great detail. Our guide will be a chapter from Jim Baggots’ The Quantum Story, as it has one of the best descriptions of Bell’s theory I’ve ever read.