How old is quantum physics

Knopf, How are atoms structured? According to the so-called old quantum theory, first enunciated by Bohr in and elaborated by Sommerfeld three years later, atoms consist of a tiny positive nucleus surrounded by negative electrons which orbit the nucleus like planets around a sun.

Nearly all the mass of the atom is concentrated in the nucleus. The number of electrons is given by the "atomic number" of the element. The electrons are held in their orbits around the nucleus by electrical attraction, similar to the gravitational attraction that holds the planets in their orbits around the sun in our solar system.

I tend not to agree with this, because many of the same concerns could be raised about calling electrons "particles," but it makes for a reliable source of blog conversations. This "door number three" nature of quantum objects is reflected in the sometimes confusing language physicists use to talk about quantum phenomena. The Higgs boson was discovered at the Large Hadron Collider as a particle, but you will also hear physicists talk about the "Higgs field" as a delocalized thing filling all of space.

This happens because in some circumstances, such as collider experiments, it's more convenient to discuss excitations of the Higgs field in a way that emphasizes the particle-like characteristics, while in other circumstances, like general discussion of why certain particles have mass, it's more convenient to discuss the physics in terms of interactions with a universe-filling quantum field.

It's just different language describing the same mathematical object. These oscillations created an image of "frozen" light. Credit: Princeton. It's right there in the name-- the word "quantum" comes from the Latin for "how much" and reflects the fact that quantum models always involve something coming in discrete amounts.

The energy contained in a quantum field comes in integer multiples of some fundamental energy. For light, this is associated with the frequency and wavelength of the light-- high-frequency, short-wavelength light has a large characteristic energy, which low-frequency, long-wavelength light has a small characteristic energy. This property is also seen in the discrete energy levels of atoms, and the energy bands of solids-- certain values of energy are allowed, others are not.

Atomic clocks work because of the discreteness of quantum physics, using the frequency of light associated with a transition between two allowed states in cesium to keep time at a level requiring the much-discussed "leap second" added last week. Ultra-precise spectroscopy can also be used to look for things like dark matter , and is part of the motivation for a low-energy fundamental physics institute.

This isn't always obvious-- even some things that are fundamentally quantum, like black-body radiation , appear to involve continuous distributions. But there's always a kind of granularity to the underlying reality if you dig into the mathematics, and that's a large part of what leads to the weirdness of the theory.

One of the most surprising and historically, at least controversial aspects of quantum physics is that it's impossible to predict with certainty the outcome of a single experiment on a quantum system. When physicists predict the outcome of some experiment, the prediction always takes the form of a probability for finding each of the particular possible outcomes, and comparisons between theory and experiment always involve inferring probability distributions from many repeated experiments.

There's a lot of debate about what, exactly, this wavefunction represents, breaking down into two main camps: those who think of the wavefunction as a real physical thing the jargon term for these is "ontic" theories, leading some witty person to dub their proponents "psi-ontologists" and those who think of the wavefunction as merely an expression of our knowledge or lack thereof regarding the underlying state of a particular quantum object "epistemic" theories.

In either class of foundational model, the probability of finding an outcome is not given directly by the wavefunction, but by the square of the wavefunction loosely speaking, anyway; the wavefunction is a complex mathematical object meaning it involves imaginary numbers like the square root of negative one , and the operation to get probability is slightly more involved, but "square of the wavefunction" is enough to get the basic idea.

This is known as the "Born Rule" after German physicist Max Born who first suggested this in a footnote to a paper in , and strikes some people as an ugly ad hoc addition. There's an active effort in some parts of the quantum foundations community to find a way to derive the Born rule from a more fundamental principle; to date, none of these have been fully successful, but it generates a lot of interesting science. Quantum entanglement the inseparable correlation of properties in objects — even when they are separated to a distance that they can no longer communicate by any known means.

This learning environment focuses on the first aspect: the matter-wave nature of massive particles, here in particular large and complex molecules. In Louis de Broglie formulated the idea that all material particles should also be described by a wave-particle duality, similar to quanta of light. Even electrons which had previously been considered as point-like particles with a well-defined mass, location and momentum should thus be assigned a delocalized wave function, which we interpret as a probability amplitude today.

Reid at the University of Aberdeen. It has become a cornerstone of modern quantum science and the basis for a highly precise theory of nature. Meanwhile, the physics of matter waves has found its way into many modern technologies , including electron microscopy, superconducting interference devices SQUIDS with applications as ultra-sensitive magnetic field sensors, neutron scattering in the materials sciences or atom interferometers as very precise sensors for gravitational and rotational acceleration.

The drawing shows sine waves that resemble waves on the surface of water being reflected from two surfaces of a film of varying width, but that depiction of the wave nature of light is only a crude analogy. Early researchers differed in their explanations of the fundamental nature of what we now call electromagnetic radiation.

Some maintained that light and other frequencies of electromagnetic radiation are composed of particles, while others asserted that electromagnetic radiation is a wave phenomenon. Ever since the early days of QM scientists have acknowledged that neither idea by itself can explain electromagnetic radiation. For example, the behaviour of microscopic objects described in quantum mechanics is very different from our everyday experience, which may provoke some degree of incredulity. Dirac brought relativity theory to bear on quantum physics so that it could properly deal with events that occur at a substantial fraction of the speed of light.

Classical physics, however, also deals with mass attraction gravity , and no one has yet been able to bring gravity into a unified theory with the relativized quantum theory. Reference Terms. The term "quantum mechanics" was first coined by Max Born in It can be explained by a model that depicts it as a wave. In classical physics these ideas are mutually contradictory.