In the very heart of matter there is an immense world, made of billions and billions of particles, which escapes our senses and our intuition. A world in which the usual physical laws are not valid, but instead the more complicated and “mysterious” ones of quantum mechanics, a theory so paradoxical to surprise the same scientists who invented it. “Nobody really understands it,” said Richard Feynman, one of the most brilliant physicists of his generation, in 1965. In the following, we will take about what is quantum physics and answer many of your questions in doing so.
An Amazing World
And yet this theory works, because it describes the world of atoms and molecules with flawless precision. It also has many applications, from lasers to MRIs. In fact, some phenomena are suspected to be connected to it, like tunnel effect, to enable photosynthesis and then life.
Moreover, quantum mechanics, for its almost “magic” characteristics, has always attracted philosophers and scientists. Today it is entering in our “daily” culture, inspiring also books, movies and works of art. But what is this theory really? And why is it so important? Let’s go step by step.
Miracle Particles
Waves that behave like particles, particles that cross barriers like ghosts or that communicate with each other in a “telepathic” way… That’s the strange world that scientists found themselves in front of when they discovered quantum physics.
A major feature of this theory is quantization. This means that, in the microscopic world, physical quantities such as energy cannot be exchanged in a “continuous” way, like a stream of water from the tap that can be measured at will, but through “packages” called “quanta”… like water contained in glasses or bottles with a fixed volume.
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Because of this property, light is composed of energy corpuscles called “photons”; and even the atoms can absorb this energy only in packets: an atom, for example, can absorb or emit 1 or 2 or 3 or more photons, but not 2.7 photons or half a photon.
This is what happens in the photoelectric effect, where a metal hit by the right kind of light produces electricity: this phenomenon, which was discovered at the end of 800 and explained in 1905 by Einstein, is the foundation of the functioning of modern photovoltaic panels.
Wave or Particle?
The second “oddity” of quantum mechanics is the fact that – like Janus Two-Faced – all of the particles have a dual nature: “In some experiments they behave as corpuscles, in others as waves,” explains Giancarlo Ghirardi, professor emeritus of physics at the University of Trieste.
“An experiment that shows the wavelike nature of electrons is the double slit experiment: you put a sensitive screen in front of a double slit and observe that electrons impress the plate by forming interference bangs, just like the light does. Other experiments show instead that electrons are particles”.
Unpredictable
The classical physics is “predictable”: it is possible to calculate with precision the trajectory of a bullet or a planet. However, in quantum physics, the more precisely we know the position of a particle, the more uncertain becomes its speed (and vice versa).
The uncertainty principle says it, formulated in 1927 by German physicist Werner Heisenberg. If we want to describe the behavior of an electron in an atom, we can just say that it is located in a cloud around the nucleus, and quantum mechanics shows us the probability that, making a measurement, the electron is in a certain point.
Before measuring, the electron state is described by the set of all possible results: this is called superposition of quantum states. At the time of measurement, the electron “collapses” in a single state. This conceptual principle has an important aspect: in a certain sense, with their measuring instruments, scientists are involved in the creation of the reality they are studying.
Like Ghosts
One other bizarre quantum phenomenon is the tunnel effect, which is how particles can pass through a barrier like a ghost passes through a wall. “This is how the decay of radioactive substances is explained,” Ghirardi says. “The radiation released by these materials, in fact, is made up of particles that pass an energy barrier within the nuclei.”
Glowing Weaves
Everything is strange enough. But the strangest phenomenon of all is entanglement. Suppose we take two photons in a “superposition of states” – we can imagine them as coins spinning infinitely, displaying both sides (heads or tails) – and put them in entanglement, and then bring them to opposite sides of the universe.
In quantum mechanics, if we measure one of the two, and we get for example heads, also the other coin, instantly, cease to be in an indeterminate state: when we measure it (after a second or after a century) we are certain that the result will be heads. The two particles are like in… telepathic contact. Absurd? No, it is entanglement!
Like Star Trek
This astonishing feature can be used to realize quantum teleportation. “Let’s say we want to transfer a photon identified by its polarization state from a point A to a point B,” Ghirardi says.
“In order to do that you need to have, besides the photon to be teleported, two entangled photons, one in A and the other in B. Then you interact the photon to be teleported with the first entangled photon (the one in A) and you inform the observer in B the outcome of the operation, and in this manner you tell him how he must manipulate the second entangled photon to obtain an identical copy of the starting photon”.
Basically, the information of the starting photon are transferred in B because of the intermediation of entangled photons: actually it is a transfer of information, more than a transfer of matter as in Star Trek.
For this reason, teleportation is of great interest to scientists who are studying quantum computers of the future. These are computers in which qubits are processed instead of “bits” (sequences of “0” and “1”) of traditional computing: the benefit is that qubits allow to perform in a short time, “in parallel”, tasks that traditional computers would take years.
In this way, with an “n” number of qubits, the amount of computing routes that can be undertaken simultaneously is equal to 2N, that is 2x2x2… x2, n times: with fewer than 300 qubits would exceed the number of particles in the entire universe. Up to now, however, you can manipulate only a few qubits, and with great difficulty: the “magic” world of quantum computers is still to be explored.
Most recently, 2 physicists at the University of Queensland (Australia) have designed even the “temporal” teleportation, by applying entanglement to time instead of space, with the objective of making complex calculations possible. However, if it works, it would be the first real example of time machine, albeit a little different from how science fiction has always imagined it.
Quanta in Philosophy and Culture
However, quantum mechanics is not only weird and complicated. It also forces us to rethink the mental patterns to which we are used to, challenging our beliefs and offering new answers to questions that philosophers have been asking for a thousand years. Following are some examples. Stay tuned to learn more about what is quantum physics.
Is Destiny Predictable?
For example, how can one forget Maradona’s shots? The trajectory impressed on the ball was an admirable encounter of sport and physics. Nevertheless, if a hypothetical quantum “Golden Boy” would find an electron between his feet, he would not manage to kick it with the same precision. In fact, that “ball” would not follow the deterministic logic of shot-goal.
Because of the principle of superposition of states, in fact, it might be anywhere in the field, spreading like a fog in several places at the same time. Only after having been observed it would finally “collapse” in a precise point, possibly right in the net… the destiny, in short, is not predictable.
Everything the opposite of what the Greeks Leucians claimed in the 5th century BC. C. the Greeks Leucippus and Democritus, who believed that the world was made of atoms that move in the vacuum in a predictable way.
However, a century later, another Greek, Epicurus, assumed that there were random collisions between atoms with unpredictable consequences. The classical physics, in 800, appeared to give reason to the first two. Instead quantum physics, even if on completely different basis, is closer to Epicurus’ thought.
Does the Universe Exist Independently From Us?
Esse est percipi: the things, in order to exist, need to be perceived. The British philosopher George Berkeley claimed in the eighteenth century, according to which a ball or a tree do not exist in themselves, regardless of us: those that we perceive are the sensory stimuli that come straight from God. Moreover, the German philosopher Immanuel Kant, also in the 18th century, stated that we cannot know the world “as it is in itself” (defined by him as noumenon), but only what “appears”.
Two centuries later, quantum mechanics says something similar: to determine the position of a particle, for example, it is necessary to illuminate it… and then the particle, struck by light, splashes away. So we know where it is, but not where it will be after a moment.
In order to observe reality, in short, we have to “disturb it”: “According to Copenhagen interpretation” explains Giulio Giorello, professor of philosophy of science at Università Statale di Milano “quantum events are dependent on the presence of the observation apparatus that has to measure them”.
In fact, Einstein was not able to digest this aspect of the theory: he was persuaded that reality was well determined and independent from the observer. But nowadays experts are in favor of Copenhagen interpretation. Stay tuned to learn more about what is quantum physics.
What if the Effect Preceded the Cause?
A cornerstone of classical science is the rule according to which, in this world in which we live, each cause necessarily follows an effect: if you throw a stone at a window you break it, if you touch the fire you burn yourself.
In the 1700’s, the Scottish philosopher David Hume challenged this principle: even if every day two events follow each other, we must not consider this link a logical consequence, because it might be our association of ideas determined by habit.
The traditional science has never questioned the principle of cause and effect. However, quantum mechanics would seem to violate it, but it is not like that: the theory allows to calculate with certainty some aspects of particles evolution, but not everything (for the rest we must be satisfied to calculate the probability that a certain phenomenon happen). But under no circumstances the theory admits situations in which, for example, the effect precedes the cause or is disconnected from it.
Does Our Essence Extend to the Entire Universe?
When we navigate in Internet, the space seems to be sucked by a click of the mouse, within hyperlinks between systems that are thousands of km far from each other. In the sub-atomic world, in certain conditions, the same thing can happen: there are “twin” particles, connected to each other by the property of entanglement, that even if they are in opposite points of the universe would be able to communicate instantly with each other, acting as one.
This phenomenon, which is now demonstrated, breaks down one of the pillars of traditional physics: the principle of locality. So much so as to raise a doubt: are we living in an indivisible, dynamic whole, whose parts are interconnected as claimed in ‘600 the Dutch philosopher Baruch Spinoza?
In his “pantheistic” view, there exists a unique and infinite substance, a geometric order in which God and nature coincide (Deus sive natura, “God, that is nature”) as an internal cause of the whole. Stay tuned to learn more about what is quantum physics.
Nature Refuses the Void?
Natura abhorret a vacuo (“nature rejects emptiness”): this phrase dates back to the Middle Ages, but its concept is ancient: as early as the fourth century BC. C. The Greek Aristotle and his disciples were denying the existence of “a place where there is nothing”, where “it is not possible that even a single object moves”.
In the West, this taboo remained for thousands of years, and was even assimilated by the Church, which did not tolerate the existence of a place without God. Then the classical physics had shown that vacuum could be created, for instance by removing air from a container. It was also possible to create the “perfect vacuum”, that is a region of space completely devoid of atoms and light.
However, quantum mechanics has determined that this is not possible: even the “perfect vacuum” would include infinite energy fluctuations able to generate virtual particles that are born from nothing and disappear continuously in a very short time. In short, Aristotle, in a certain sense, was right.
The Reality Is Substance or Information?
Nowadays we are witnessing the triumph of information technology: texts, images, sounds and films travel over the Internet from one part of the world to another in the form of sequences of 0 and 1: the bits. These little digital bricks, an essential part of our lives, make us reflect: is reality formed by matter or by bits?
As the science fiction film Matrix tells us, we may live in a large electronic brain that simulates the world. The difference is that bits of quantum mechanics are different from the “classic” ones: they are named qubit and allow combinations (and logical operations) of a complexity without comparison in the world of traditional computer science. Stay tuned to learn more about what is quantum physics.
Is There a Theory Able To Explain Everything?
Physicists are searching for a Theory of Everything, capable of unifying everything: man and stars, small and big… will they succeed? Not certain, but the ambition is ancient. The Greek philosopher Pythagoras had already tried in the sixth century BC., giving numbers, the ultimate constituents of nature, the task of keeping the universe united.
However, today, the main goal is an evolution of the String Theory called “M-theory”. At the moment, more than a single theory, it is a system of 5 distinct theories that apply in different contexts.
We can compare it to a big map of the world: to represent faithfully the entire earth surface we need many small maps that, partially overlapping each other, show different aspects of the same landscape.
In this article, we tried to give an answer to what is quantum physics question, in a simple way. If you have any question, don’t forget to ask us in the comments section below.
