Curiosities of Quantum Physics

The quantum world is totally different from the macroscopic world. At subatomic scales, the laws of physics work in a non-deterministic way, that is, things may or may not happen according to a probability distribution.

Although not fully understood, Quantum Theory is known to be very accurate. Thus, most of his predictions, even the oldest ones, have been experimentally proven with the arrival of new technologies.

The quantum world reserves some oddities. How about meeting some of them?

Curiosity #1 – Quantum Superposition

One of the strangest properties of Quantum Mechanics is, of course, quantum superposition. This property makes it possible for a quantum particle to be simultaneously in two or more possible states . However, this will only occur if the state of that particle has not yet been determined.

For example, if there were a quantum door, it could be open , closed , or even open and closed at the same time. This last possibility, however, would only exist if you could not observe, or even touch, this door. If you were to somehow interact with this “quantum gate”, the superposition would simply cease to exist. In this way, nature would collapse the state of the door to the two possibilities of the classic situation: open or closed .

→ Schrödinger’s cat

For not understanding or not accepting the idea of ​​quantum superposition, one of the most influential physicists of Quantum Mechanics, Erwin Schrödinger, proposed a paradox that became known as “ Schrödinger’s cat ”.

Schröedinger’s thought experiment is paradoxical, that is, it has errors in its formulation.

In this thought experiment, the physicist suggested that we imagine a cat locked in a box perfectly isolated from the outside. Inside this box, in addition to the cat, there would be a radioactive atom, which could or could not undergo a decay and emit radiation, depending on the quantum probabilities by which it was governed. Along with that atom, there would be a mechanism that would release a poison capable of killing the cat.

The proposal is simple: if the cat is locked inside the box, according to the superposition, can we say that it is simultaneously alive and dead ? And if we open the box, would one of these states collapse?

This situation elaborated by Schrödinger, however, has some conceptual errors and does not meet the precepts of quantum superposition, so it is a paradoxical experiment. In this case, for the quantum superposition to arise, it would be necessary for there to be no transfer of information between the inside and the outside of the box, which would only be possible in an ideal situation.

Curiosity #2 – Wave-particle duality

The wave-particle duality is due to quantum superposition . Every quantum particle, such as protons, neutrons and electrons, can behave either as a particle or as a wave . For this to happen, it is enough that we do not know how to determine its nature.

If it is possible to detect the particle or the frequency of the wave, nature will be in charge of choosing the most probable state for that situation. This is why, in some phenomena, electrons behave like waves and, in others, like particles.

Curiosity #3 – Quantum Measurements

Did you know that by measuring the position of a quantum particle, you end up determining where it should be? Since everything in the quantum world has a probability of happening, a quantum particle can be anywhere in space. That’s right: anywhere!

Before being observed, the particle had many open possibilities, each with its probability. By trying to locate it, however, you make it cease to exist right there, in that position. From then on, only one of the possible positions is chosen.

At this point, you may be wondering how the quantum particle “knows” that it has been observed. It’s simple: in order for us to observe it, it is necessary to illuminate this particle. For this, it is necessary to emit at least one photon in its direction, which is later recovered, bringing information about the whereabouts of this particle.

The conclusion we can draw from quantum measurements is that they fundamentally depend on who makes the measurement and how it is made. The reason for this, however, is unknown.

Fun Fact #4 – Quantum Entanglement

Undoubtedly, quantum entanglement is one of the most curious phenomena in Quantum Mechanics. The state of a quantum particle is determined by a complex mathematical entity called a wave function. In some cases, it is possible to make two particles of a quantum nature share the same wavefunction, starting to behave as if they were a single particle.

Some experiments have been done to test quantum entanglement. In one, a set of entangled photons was split into two parts. Half of them collided with a frame that had an image of a cat, and the others were reflected by a mirror before reaching the frame and subsequently sent to a nearby detector.

To the astonishment of the researchers, the image captured by the detector showed the cat in the frame that had been hit by the first photons. This happened because the first group of photons interacted with the image, capturing its color, absorption, reflection and polarization information. As these photons were entangled with each other, information was instantly transmitted between them.

The experiment in question was carried out by a team of five scientists led by Brazilian scientist Gabriela Barreto Lemos , at the University of Vienna, Austria.

Apparently, entangled particles are able to share information with each other instantly, regardless of the physical separation between them.