Quantum Laws: Where Do They Show Up?

Quantum laws become obvious in the quantum world, where small particles, atoms, and tiny scales tell us about reality. For instance, when gas is heated and observed through a prism, distinct lines of different colors are formed due to the quantum leap. This phenomenon, along with other behaviors of particles at microscopic levels, provides evidence for the existence and significance of quantum laws.

Electrons and their behaviour

Electrons are subatomic particles with a negative elementary electric charge. They are attracted to the positively charged nucleus of an atom and revolve around it, occupying the majority of the atom's volume. They are generally thought to be elementary particles because they have no known components or substructure. Electrons have a mass of approximately 1/1836 of a proton.

Electrons are found in specific locations outside of the nucleus. The shell in which an electron resides indicates its energy level: those closer to the nucleus have less energy, while those further out have more. Electrons closest to the nucleus have the lowest amount of energy, and as the distance between electron and nucleus increases, so does the energy of the electron. There is more space for electrons to orbit in the outer shells, so they can hold more electrons than the inner shells. The outermost electrons of an atom reside in the valence shell and are called valence electrons. These electrons form ionic and covalent bonds with other atoms.

Electrons are involved in many applications, such as tribology, electrolysis, electrochemistry, battery technologies, electronics, welding, cathode-ray tubes, photoelectricity, photovoltaic solar panels, electron microscopes, radiation therapy, lasers, and particle accelerators. They also play an essential role in numerous physical phenomena, such as electricity, magnetism, chemistry, and thermal conductivity.

Electrons exhibit properties of both particles and waves. They can collide with other particles and can be diffracted like light. The wave properties of electrons are easier to observe in experiments than those of other particles like neutrons and protons because electrons have a lower mass and hence a longer de Broglie wavelength for a given energy.

The English physicist J.J. Thomson discovered the electron in 1897 during investigations of cathode rays. Thomson's discovery of electrons, which he initially called corpuscles, played a pivotal role in revolutionizing knowledge of atomic structure.

Light and electron interactions

Recent studies have employed advanced techniques such as electron energy-loss spectroscopy (EELS), cathodoluminescence spectroscopy (CL), and photon-induced near-field electron microscopy (PINEM) to investigate light and electron interactions at the nanoscale. These techniques provide insights into the complex dynamics of electron-light-matter interactions, offering unique prospects for various applications, including quantum information processing.

The interaction between light and electrons can be either spontaneous or stimulated. When a swift electron passes through or near a specimen, its time-varying evanescent electric field can induce optical material excitations, resulting in energy exchange. This process is spontaneous in nature, and the energy transferred can be measured using EELS. On the other hand, CL spectroscopy detects the induced radiative polarization states in the far field, allowing for the study of radiative transitions.

PINEM, on the other hand, involves using swift electrons to probe the near field of a material illuminated by an intense laser. This technique enables the investigation of stimulated energy-gain and energy-loss transitions as electrons absorb or emit photons at the laser frequency. The population of these sidebands varies with the near-field integral along the electron trajectory and the statistics of the incident light, providing insights into the spatial and temporal characteristics of light and electron interactions.

Furthermore, the interaction strength between light and electrons depends on the incident electron velocity. Theoretical analyses and numerical simulations have shown that lower electron energies, typically in the keV range, result in stronger coupling with the optical near fields. This is because slower electrons can better match the phase of the optical field, maximizing the interaction.

In conclusion, light and electron interactions are a fascinating aspect of quantum mechanics, offering insights into the behavior of particles at the nanoscale. By employing advanced experimental and theoretical techniques, researchers are unraveling the complex dynamics of these interactions, leading to a deeper understanding of quantum phenomena and potential applications in quantum information processing and nanotechnology.

Atomic theory

Quantum mechanics is a fundamental theory that describes the behaviour of nature at and below the scale of atoms. It is the foundation of all quantum physics, which includes quantum chemistry, quantum field theory, quantum technology, and quantum information science. Quantum mechanics can describe many systems that classical physics cannot.

The laws of quantum mechanics become obvious at the quantum level, where small particles, atoms, and tiny scales tell us about reality. Quantum systems have bound states that are quantized to discrete values of energy, momentum, angular momentum, and other quantities, in contrast to classical systems where these quantities can be measured continuously.

The modern atomic theory, proposed by English chemist John Dalton, is a fundamental concept that states that all elements are composed of atoms. Atoms are the smallest unit of matter that can take part in a chemical reaction. Dalton's atomic theory was based on three laws of chemical combination: the Law of Conservation of Mass, the Law of Definite Proportions, and the Law of Multiple Proportions.

The Law of Conservation of Mass states that in a chemical reaction, matter is neither created nor destroyed. The total mass of the products remains equal to the total mass of the reactants.

The Law of Definite Proportions states that in a given type of chemical substance, the elements are always combined in the same proportions by mass. For example, when different samples of isooctane are analyzed, they are found to have a carbon-to-hydrogen mass ratio of 5.33:1.

The Law of Multiple Proportions states that if two elements form more than one compound, the ratios of the masses of the second element that combine with a fixed mass of the first element will always be ratios of small whole numbers. For instance, nitrogen forms several oxides, and the ratios of the relative weights of the two elements in each compound are small whole numbers.

Dalton's atomic theory was a powerful development as it explained the three laws of chemical combination and recognized a distinction between the fundamental particle of an element (atom) and that of a compound (molecule). However, Dalton's theory had some drawbacks. For example, atoms can be further subdivided into protons, neutrons, and electrons, proving that atoms are not indivisible. Additionally, not all atoms of the same element are similar in all respects, as some elements have isotopes with different masses.

The quantum world and its scale

The quantum world deals with the behaviour of matter and energy at the smallest scales of energy and distance, probing the fundamental building blocks of nature. This includes the study of subatomic particles like electrons, photons, and atoms, which make up our everyday world but operate according to different rules at these minuscule scales.

Quantum laws become apparent when examining the behaviour of these tiny particles and the peculiar rules that govern them. For instance, electrons don't follow the same rules as larger objects, they can act like waves, and their behaviour is governed by probabilities rather than certainties. This wave-particle duality is a fundamental concept in quantum mechanics, highlighting the dual nature of particles like electrons, which can exhibit both wave-like and particle-like properties depending on the context.

The quantum world operates at incredibly small scales, far beyond our everyday experience and perception. At these tiny scales, the rules of classical physics break down, and the strange and unpredictable nature of quantum mechanics takes over. Here, particles can exist in multiple states simultaneously, and their positions and momenta can only be described in terms of probabilities.

The quantum realm is where the concept of a "quantum leap" becomes significant. This refers to the abrupt change in an electron's energy state within an atom, jumping from one energy level to another without passing through the intermediate states. This behaviour is in stark contrast to the gradual changes observed in our macroscopic world and underscores the unique nature of quantum systems.

The scale at which quantum laws dominate is so minuscule that it's beyond the direct observation of even the most powerful microscopes. Scientists employ advanced tools and techniques, such as scanning tunnelling microscopes and electron microscopy, to indirectly observe and manipulate quantum systems, providing valuable insights into this hidden realm.

Inventions powered by quantum mechanics

Quantum mechanics is a fundamental theory that describes the behaviour of nature at and below the scale of atoms. Quantum mechanics can describe many systems that classical physics cannot. Most theories in classical physics can be derived from quantum mechanics as an approximation, valid at large (macroscopic/microscopic) scales.

Lasers and Telecommunications

The fibres used in telecommunications are classical, but the light sources used to send messages down fibre optic cables are lasers, which are quantum devices. The key physics of the laser is contained in a 1917 paper by Einstein, which introduces the idea of stimulated emission, where an atom in a high-energy state encountering a photon of the right wavelength is induced to emit a second photon identical to the first.

Atomic Clocks and GPS

The Global Positioning System (GPS) is another application that is critically dependent on quantum physics. Smartphone navigation is enabled by the Global Positioning System, a network of satellites each broadcasting the time. The GPS receiver in a phone picks up the signal from multiple clocks and uses the different arrival times from different satellites to determine the distance from each of those satellites. The computer inside the receiver then does some math to figure out the single point on the surface of the Earth. This trilateration relies on the constant speed of light to convert time to distance. Light moves at about a foot per nanosecond, so the timing accuracy of the satellite signals needs to be very precise. Each satellite in the GPS constellation contains an ensemble of atomic clocks, which rely on quantum mechanics.

Magnetic Resonance Imaging (MRI)

The central process in an MRI machine is called Nuclear Magnetic Resonance (but "nuclear" is a scary word, so it's avoided for consumer medical processes). It works by flipping the spins in the nuclei of hydrogen atoms. A clever arrangement of magnetic fields lets doctors measure the concentration of hydrogen appearing in different parts of the body, which in turn distinguishes between a lot of softer tissues that don't show up well in traditional x-rays.

Computers and Smartphones

The entire computer industry is built on quantum mechanics. Modern semiconductor-based electronics rely on the band structure of solid objects, which is fundamentally a quantum phenomenon, depending on the wave nature of electrons. By understanding this wave nature, we can manipulate the electrical properties of silicon. Stacking up layers of silicon doped with different elements allows us to make transistors on the nanometer scale. Millions of these packed together in a single block of material make the computer chips that power all the technological gadgets that are so central to modern life.

These are just a few examples of inventions that are powered by quantum mechanics. There are many other applications and technologies that utilise the principles of quantum mechanics to function and provide us with valuable tools and insights.

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