Tag Archives: quantum physics

The Universe Revealed Through Modern Science

Physical laws have existed since the beginning of time, but they had to be discovered for science to become relevant. Scientific knowledge was built mainly by a series of small advances and adjustments, however, a few major discoveries by a few scientists have altered the course of the scientific endeavor. The age of modern science was pioneered by men like Copernicus, Galileo and Kepler. They began to examine the patterns in nature, and discovered that in some situations the workings of nature could be explained, and even predicted. They found that nature’s harmony was governed by physical laws, which were at least partly accessible to human comprehension. They studied the motion of objects on earth, and then turned their attention to the heavens. They charted the movement of the celestial bodies in great detail, and discovered that the motion of the celestial bodies could also be predicted. The gateway to scientific discovery had been opened—the universe would soon begin to reveal its most profound secrets.

In the early years, it was Isaac Newton’s insight that stood above all others. He discovered gravity as the force responsible for the motion of the moon and the planets. And as the story goes, the same force responsible for an apple falling from a tree. In 1687, he published the Principia Mathematica, where he disclosed his law of universal gravitation and the three laws of motion. It was a major breakthrough in advancing the scientific cause. Newton’s laws provided the foundation for what has become known as classical physics. For more than 300 years his equations have stood the test of time. In fact, Newton’s equations were all that was needed to plot the course that placed men on the moon. Although his equations provided an accurate mathematical framework (actually a very close approximation that was later revised by Einstein), Newton had no idea what mechanism was responsible for the effects of gravity. It is also believed that he regarded space, the arena of motion, to be absolute and unchangeable. He viewed time in much the same way.

It was not until the early 1900s when the mysteries of space and time, as well as the underlying causes of gravity, were addressed. Albert Einstein changed the course of history when he published his theories of special relativity (in 1905) and general relativity (in 1915). Einstein formulated that space and time are not absolutes, but have dynamic qualities associated with mass and motion. In fact, he described space and time as a unified whole, which later became known as space-time.

With special relativity, Einstein showed that measurements of time (and even distance) could differ for two observers, based on their relative motion. Time will elapse slower for someone in motion than it does for someone at rest. And the discrepancy in elapsed time will increase as the difference in the speed increases. In a sense, observers carry their own clock with them. This realization signifies another important point—that the observers would also disagree on what constitutes a given moment in time. One person’s now would be different from the other person’s now, yet both perspectives would be equally valid. Keep in mind, that it’s only when dealing with speeds approaching the speed of light or extreme distances that disagreements in time become significant. The effects of special relativity are not visibly apparent in the temperate conditions that exist here on earth; however, the earth is somewhat of an anomaly in comparison to the universe as a whole. With the universe, where extreme distances and speeds are commonplace, special relativity becomes important.

With general relativity, he showed that the effects of gravity are caused by the warping or curving of space (or space-time, but for simplicity I will use the term space). Heavy objects like planets and stars warp the fabric of space, thus creating the effects of gravity. It is similar to placing a heavy ball in the center of a trampoline. Any smaller balls placed on the surface will be drawn to the center, due to the surface being warped by the heavier ball. Bear in mind that a trampoline is a two dimensional representation of what is actually a three dimensional spatial fabric. It does, however, give us a clear visual analogy of how curved space participates in the motion of celestial bodies. In the case of planets and stars, orbits will develop when a stable balance is achieved. The earth can be thought of as moving in a straight line along a curved surface of space. Or as taking the path of least resistance along the distorted spatial fabric, which is created by the sun’s presence.

Another consequence of general relativity is that just as gravity curves space, it also curves time. But what does curved time mean? Similar to special relativity, where motion alters time, general relativity claims that gravity also alters time. When gravity exerts its influence time slows down. For instance, time passes a little slower on the surface of the earth than it does for objects high above the earth. A practical example of this effect is in the technology behind global positioning systems (GPS). The satellites that guide GPS devices have to account for both special and general relativity (general relativity producing the largest effect). The internal clocks of the satellites account for the fact that clocks on the earth’s surface run slower. If not for these adjustments, GPS devices would quickly become inaccurate; the coordinates on the ground would drift off by several kilometers each day.

Einstein’s relativity goes against our common sense perceptions, but apparently this is the reality of the universe. Einstein’s insights led to modern cosmology (the study of the origin and evolution of the universe), and our current view of the universe. Both classical physics (Newton’s view) and relativity (Einstein’s view) provide a deterministic framework. That is, if the present conditions are known, the past and future conditions can also be determined. That’s assuming that you have all the present data and the mathematical ability to do the calculations.

The next scientific breakthrough would be of a very different nature. In the mid-1930s a group of scientists were unlocking the secrets of the atom. In so doing, it led to the development of quantum mechanics. They found that the atomic and subatomic realms behave in ways that are very different from the world experienced at the larger scales. A whole new set of laws had to be developed to deal with the bizarre nature of the atom—laws that are partly governed by randomness and probabilities. Physicist Brian Greene describes the nature of quantum mechanics. He writes in The Fabric of the Cosmos:

 “…according to the quantum laws, even if you make the most perfect measurements possible of how things are today, the best you can ever hope to do is predict the probability that things will be one way or another at some chosen time in the future, or that things were one way or another at some chosen time in the past.”

The probabilities that are used in quantum mechanics are more fundamental than the probabilities that are assigned to everyday events. When we assign a probability to a game of dice or blackjack, it is based on our inability to calculate the precise conditions that will determine the outcome of the event—specifically, each roll of the dice or flip of the card. With quantum mechanics, however, even if we know all the present information possible, we still can not predict a future outcome with absolute certainty. Quantum physics describes a reality that is fundamentally uncertain, in which objects have no definite position, take no definite path, and even have no definite past or future.

Some experiments (known as the double-slit experiment and variations of it) have actually shown that a single particle, such as a light photon, can behave as if it simultaneously takes a number of different paths from a source to a target. It is debatable whether this really happens; nonetheless, outcomes are determined by the number of possible paths of the photon, whether or not they are all realized. The photon takes a definite position only when it is observed or measured (when it strikes the target). In between the source and the target, it can be thought of existing as a haze of possibilities.

This is partially explained by the idea that subatomic objects, like photons and electrons, exhibit both wave-like and particle-like properties. At times, a photon or electron can be described as occupying a wide region in space, and at other times described as occupying a single point in space. Depending on the variation of the double-slit experiment, a photon can sometimes behave like a wave and sometimes behave like a particle. Although it is not entirely clear how these results should be interpreted, physicists agree that our conventional sense of reality does not apply at the quantum level—even to a larger degree than Einstein’s relativity.

I know this all sounds absurd. Nevertheless, the predictions of quantum mechanics have produced results that are extraordinarily accurate. Quantum mechanical predictions are accurate in the sense that if a sufficient number of identical experiments are carried out, the totality of the outcomes will reflect the assigned probabilities. Yet each single experiment will generate a random and unpredictable outcome. Therefore, even with the most precise calculations possible, there is an unavoidable degree of uncertainty in quantum mechanics.

It has been said that nobody understands quantum mechanics, that even scientists that work with quantum mechanics don’t understand it. So if it’s not sinking in, don’t lose any sleep over it. In summing up: the renowned physicist Richard Feynman once wrote in The Strange Theory of Light and Matter “[Quantum mechanics] describes nature as absurd from the point of view of common sense. And it fully agrees with experiment.”

Once again our common sense is challenged by the laws of physics. From classical physics to the updating of relativity, and the weirdness of quantum mechanics, reality is proving to be difficult to grasp, as these theories give us very different views of reality. For this reason, there is a consensus among some physicists that there exists a deeper level of reality to the universe that remains undiscovered. They propose that there should be one theoretical framework that describes the universe, and not a fragmented view based on several partial theories. Einstein called this hypothetical theory a unified theory (also called the theory of everything). The quest for a unified theory became one of Einstein’s passions during his later years; however, it was not realized during his lifetime.

Today, physicists are still seeking the elusive unified theory. Our present understanding of the universe is based on the two major breakthroughs of the 20th century. 1) General relativity, which describes the large scale structures of the universe, like stars and galaxies. 2) Quantum mechanics, which describes the small scale structures, like molecules and atoms. These two theories have been very successful in their own right, but in some extreme situations they cannot be applied successfully. In some situations where large densities are compressed into a tiny region of space, an understanding of both the large and the small is required. But when general relativity is applied together with quantum mechanics, the theories fall apart. This becomes a major obstacle when trying to understand conditions such as the center of black holes and the origin of the universe where these conditions need to be considered. The big bang theory describes the events a fraction of a second after the beginning, but says nothing about the beginning or before. Without a unified theory, or a new theory altogether that can deal with this situation the cause for the origin of the universe will remain a mystery.

As we have seen, each new discovery has added a piece to the puzzle and our understanding of the universe has increased dramatically over the years. The ultimate goal of science can be nothing other than a complete understanding of the laws of nature, though it may be that mystery will forever be a part of the picture. In his 1988 book, A Brief History of Time, Stephen Hawking weighs in on the subject:

“But can there really be such a unified theory? Or are we perhaps just chasing a mirage?

There seems to be three possibilities:

1) There really is a complete unified theory, which we will someday discover if we are smart enough.

2) There is no ultimate theory of the universe, just an infinite sequence of theories that describe the universe more and more accurately.

3) There is no theory of the universe; events cannot be predicted beyond a certain extent but occur in a random and arbitrary manner.”

There may very well be limits to what humans are able to understand, but this should not limit our quest for knowledge. Where would we be today if some people hadn’t questioned conventional thinking and opened the door to greater discovery? It is due to the few who dared to challenge the beliefs of their time that many benefited. Not only in science, but in other domains as well, it is the quest for knowledge that paves the way for progress. This is the case for our lives, as well as humanity as a whole. No one knows how far we can go, and only time will tell. On this note, we can at least rest assured that the modern age of science has brought humanity out of the darkness of ignorance, and into the light of knowledge.

References: Brian R. Greene, The Fabric of the Cosmos (New York: Alfred A. Knopf, 2004), 10-11.

Richard Feynman, QED: The Strange Theory of Light and Matter (Princeton: Princeton University Press, 1988).

Stephen W. Hawking, A Brief History of Time (New York: Bantam Books, 1988), 165-166.



The Paradox of Wave-Particle Duality

blue light beam The wave-particle duality of light and other subatomic particles, such as electrons, is a central concept in quantum mechanics. The idea that light and elementary particles have both wave-like and particle-like properties is just one of a number of strange quantum realities. The quantum revolution, which began at the turn of the 20th century, has transformed our world from a technological standpoint. A century later the quantum laws underpin our modern technology. But scientists that were probing the atom in the early 1900s were simply trying to understand the nature of reality at the smallest scales. The challenges proved to be immense, mind-boggling and paradoxical. Wave-particle duality is one paradox that is still not completely understood.

The Photoelectric Effect

Albert Einstein is most famously known for the theories of special relativity, general relativity and the equation E=MC². However, in 1905 he won the Nobel Prize for his explanation of the photoelectric effect. Before Einstein, light was generally thought to behave like a wave, similar to a water wave. But there were some unsolved questions regarding properties of different colored light. Specifically, the ability of ultra-violet light to remove an electric charge from a metal plate (a phenomenon not observed with red light).

Photoelectric Effect

Photoelectric Effect

Einstein proposed that light was composed of packets of energy called quanta (later known as photon). These particles of light acted like miniature billiard balls, knocking the electrons off the metal plate. According to Einstein, the particles from the red light carried low energy, because red light has a low-frequency. Conversely, the higher frequency ultra-violet light contains higher energy particles, which were able to dislodge the electrons from the metal plate. With the analogy of the billiard balls, it was like the ultra-violet particles were heavier than the red light particles. Therefore, the heavy particles of light were able to knock off the electrons, while the lite particles could not.

Einstein’s explanation of the photoelectric effect showed that light was made up of individual particles. It opened the doorway to a new branch of physics. Although Einstein played a key role in the foundation of quantum physics, he never accepted the implications that the theory would eventually bear out. The idea that the quantum world was ruled by uncertainty, did not sit well with him. Einstein supported the classical view of physics, where precise predictions and conclusions could be made. Referring to the probabilistic foundation of quantum mechanics, Einstein said: “God does not play dice.”

 The Double-Slit Experiment

The discovery of the wave-particle duality of light was only the beginning of the paradoxes that would later emerge. A simple experiment, known as the double-slit experiment would overthrow any common sense notion of the quantum realm. The experiment worked as follows: An electron gun was set up to fire an electron beam through a barrier with two open slits. A full screen was placed a small distance behind the barrier. One would expect that the electrons that go through the slits would strike the background screen and produce two bands. However, the outcome showed not two, but a number of bands across the length of the screen; a striped pattern emerged.

Double-Slit Experiment

Double-slit Experiment

The electrons were behaving like a wave; the stripes were consistent with an interference pattern. This had already been observed in water waves. For instance, when two ripples in a pond meet they interfere with each other, causing the similar interference pattern that was observed with the electrons. Water is composed of individual molecules and together they combine to form a wave. Similarly, the electrons were exhibiting both wave-like and particle-like properties (this was also observed in light).

If this was not strange enough, the next step of the experiment would reveal a greater paradox. When the electron gun was allowed to fire one electron at a time, the screen in the back would eventually show the same striped pattern. How could single electrons produce an interference pattern? To point out how strange that was: it was like a single electron was passing through both slits at the same time, or like each electron was carrying information from the wave as it was passing through the slits.

Explaining the Impossible

Niels BohrDanish physicist Niels Bohr, one of the founders of quantum mechanics provided a possible explanation. It is known as the Copenhagen Interpretation. According to Bohr, the electrons that travel from the gun to the screen cannot be viewed as single point particles, but rather as a probability wave. In other words, an electron exists only as a spectrum of possibilities when it travels. It carries with it every possible path from the gun to the screen, including passing through the two slits at the same time. Only when it strikes the screen is the electron forced to take an exact position.

In this view, each electron will strike the screen at a different point, however, with a sufficient number of electrons the striped pattern will emerge on the screen. Whether the electrons are traveling in a continuous beam or as single travelers, the outcome will produce an interference pattern. Even if it is not completely understood, wave-particle duality is a fundamental property of the quantum world.

It is safe to say that Einstein and Bohr disagreed as to what is ultimately responsible for quantum uncertainty. For Bohr it was enough to apply a workable mathematical framework (based on probabilities), but for Einstein there must have been an undiscovered classical principle guiding the process. A century after Einstein and Bohr there is still no classical physical principle (one that agrees with common sense) that explains the uncertainty of quantum mechanics. However unsatisfying, it seems that Bohr’s explanation of the double-slit experiment is still as good as we have. Nevertheless, Bohr realized the gap between quantum mechanics and everyday experience, he said: “If quantum mechanics hasn’t profoundly shocked you, you haven’t understood it yet.”

In time, Bohr’s approach would lead to a revolution in technology. Even if exact outcomes cannot be known, physicists can calculate probabilities that will allow electronic devises to work. Similar to the double-slit experiment, even if the path of each individual electron cannot be known, the overall pattern can be predicted. Today, computers, mobile phones and GPS devices operate based on quantum mechanics.


References: The Secrets of Quantum Physics Episode 1 Einstein’s Nightmare BBC Documentary 2014. Published on Feb 28, 2015. https://www.youtube.com/watch?v=uV8oSgMhS54

Brainy Quote, 2001-2015. http://www.brainyquote.com/quotes/authors/n/niels_bohr.html

Brian Greene, The Fabric of the Cosmos.