SCIENCE ODDS AND ENDS— PHYSICS

PAULI EXCLUSION PRINCIPLE The **Pauli exclusion principle **is the quantum mechanical **principle **which states that two or more identical fermions (particles with half-integer spin) cannot occupy the same quantum state within a quantum system simultaneously.

HEISENBERG UNCERTAINTY PRINCIPLE **Uncertainty principle**, also called **Heisenberg uncertainty principle **or indeterminacy **principle**, statement, articulated (1927) by the German physicist Werner **Heisenberg**, that the position and the velocity of an object cannot both be measured exactly, at the same time, even in theory.

MAXWELL EQUATIONS **Maxwell’s equations **are a set of partial differential **equations **that, together with the Lorentz force law, form the foundation of classical electromagnetism, classical optics, and electric circuits.

4 LAWS OF THERMODYNAMICS The **4 Laws**. Zeroth **law of thermodynamics **â€“ If two **thermodynamic **systems are each in thermal equilibrium with a third, then they are in thermal equilibrium with each other. The first **law**, also known as **Law **of Conservation of Energy, states that energy cannot be created or destroyed in an isolated system. The second **law of thermodynamics **states that the entropy of any isolated system always increases. Third law of thermodynamics â€“ As temperature approaches absolute zero, the entropy of a system approaches a constant minimum.

FORCES IN NATURE According to the present understanding, there are **four **fundamental interactions or **forces**: gravitation, electromagnetism, the weak interaction, and the strong interaction.

3 LAWS OF MOTION The second **law **states that the acceleration of a body is equal to the force acting upon it divided by the body’s mass. **Newton’s **first **law **states that every object will remain at rest or in uniform **motion **in a straight line unless compelled to change its state by the action of an external force. … The **third law **states that for every action (force) in nature there is an equal and opposite reaction.

LAW OF GRAVITATION Newton’s **law **of universal **gravitation **states that a particle attracts every other particle in the universe with a force which is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers.

2 THEORIES OF RELATIVITY Albert Einstein, in his **theory **of special **relativity**, determined that the laws of physics are the same for all non-accelerating observers, and he showed that the speed of light within a vacuum is the same no matter the speed at which an observer travels. **Albert Einstein’s **general theory of relativity is one of the towering achievements of 20th- century physics. Published in 1916, it explains that what we perceive as the force of gravity in fact arises from the curvature of space and time. **Einstein **proposed that objects **such **as the sun and the Earth change this geometry.

QUANTUM MECHANICS the branch of mechanics that deals with the mathematical

description of the motion and interaction of subatomic particles, incorporating the concepts of quantization of energy, wave-particle duality, the uncertainty principle, and the correspondence principle.

ENTROPY a thermodynamic quantity representing the unavailability of a system’s thermal energy for conversion into mechanical work, often interpreted as the degree of disorder or randomness in the system.

CONSERVATION LAWS **Conservation law**, also called **law of conservation**, in physics, several principles that state that certain physical properties (i.e., measurable quantities) do not change in the course of time within an isolated physical system. In classical physics, laws of this type govern energy, momentum, angular momentum, mass, and electric charge. In particle physics, other conservation laws apply to properties of subatomic particles that are invariant during interactions.

SCHRODINGER’S CAT A **cat **is placed in a room that is separated from the outside world. A Geiger counter which counts the amount of radioactive decay and a little bit of a radioactive element are in the room. … **Schrodinger **says that according to the Copenhagen Interpretation, as long as the door is closed, the **cat **is dead and alive.

SCHRODINGER’S EQUATION The **Schrodinger equation **is used to find the allowed energy levels of quantum mechanical systems (such as atoms, or transistors). The associated wave function gives the probability of finding the particle at a certain position. … The solution to this **equation **is a wave that describes the quantum aspects of a system.

BERNOULLI PRINCIPLE In fluid dynamics, **Bernoulli’s principle **states that an increase in the speed of a fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid’s potential energy.

PASCAL PRINCIPLE **Pascal’s law **(also **Pascal’s principle **or the **principle **of transmission of fluid-pressure) is a **principle **in fluid mechanics that states that a pressure change occurring anywhere in a confined incompressible fluid is transmitted throughout the fluid such that the same change occurs everywhere.

LORENTZ FORCE the force that is exerted by a magnetic field on a moving electric charge.

QUANTUM ELECTRODYNAMICS a quantum field theory that deals with the electromagnetic field and its interaction with electrically charged particles.

QUANTUM CHROMODYNAMICS a quantum field theory in which the strong interaction is described in terms of an interaction between quarks mediated by gluons, both quarks and gluons being assigned a quantum number called color.

QUANTUM GRAVITY **Quantum gravity **(QG) is a field of theoretical physics that seeks to describe **gravity **according to the principles of **quantum **mechanics, and where **quantum **effects cannot be ignored, such as near compact astrophysical objects where the effects of **gravity **are strong.

STRING THEORY In physics, **string theory **is a theoretical framework in which the point-like particles of particle physics are replaced by one-dimensional objects called strings. It describes how these strings propagate through space and interact with each other. On distance scales larger than the string scale, a string looks just like an ordinary particle, with its mass, charge, and other properties determined by the vibrational state of the string. In string theory, one of the many vibrational states of the string corresponds to the graviton, a quantum mechanical particle that carries gravitational force. Thus string theory is a theory of quantum gravity.

ARCHIMEDES PRINCIPLE **Archimedes**‘ **principle **states that the upward buoyant force that is exerted on a body immersed in a fluid, whether fully or partially submerged, is equal to the weight of the fluid that the body displaces and acts in the upward direction at the center of mass of the displaced fluid.

THEORY OF EVERYTHING A **theory of everything **(**ToE**), final theory, ultimate theory, or master theory is a hypothetical single, all-encompassing, coherent theoretical framework of physics that fully explains and links together all physical aspects of the universe.Â Finding a **ToE **is one of the major unsolved problems in physics.

HIGHER DIMENSIONS Ten **dimensions **are used to describe string theory, eleven **dimensions **can describe supergravity and M-theory, and the state-space of quantum mechanics is an infinite- **dimensional **function space. The concept of **dimension **is not restricted to physical objects.

SPACE CURVATURE In general relativity, the **curvature ****of ****spacetime **is expressed by the Einstein tensor in the Einstein field equations.

These tensor equations determine how spacetime (represented by a manifold) is warped by the presence of mass-energy (expressed in the stress energy tensor), producing the apparent phenomenon of gravitation as a fictitious force. The curvature is highly significant in cosmology, as the shape of the universe affects its ultimate fate.

ELECTRONUCLEAR FORCE Gravity had separated from the **electronuclear force **at the end of the Planck era. During the grand unification epoch, physical characteristics such as mass, charge, flavour and colour charge were meaningless. The grand unification epoch ended at

approximately 10^36 seconds after the Big Bang.

STANDARD MODEL The **Standard Model **of particle physics is the theory describing three of the four known fundamental forces (the electromagnetic, weak, and strong interactions, and not including the gravitational force) in the universe, as well as classifying all known elementary particles.

CASIMIR EFFECT The **Casimir effect **is a small attractive force that acts between two close parallel uncharged conducting plates. It is due to quantum vacuum fluctuations of the electromagnetic field. The **effect **was predicted by the Dutch physicist Hendrick **Casimir **in 1948.

BOSE EINSTEIN STATISTICS In quantum **statistics**, **Bose**–**Einstein statistics **(or more colloquially BOSE **statistics**) is one of two possible ways in which a collection of non- interacting indistinguishable particles may occupy a set of available discrete energy states at thermodynamic equilibrium.

BOSE EINSTEIN CONDENSATES A **Bose Einstein condensate **(BEC) is a state of matter of a dilute gas of bosons cooled to temperatures very close to absolute zero. Under such conditions, a large fraction of bosons occupy the lowest quantum state, at which point microscopic quantum phenomena, particularly wavefunction interference, become apparent.

PLASMA PHYSICS Plasma physics is the study of a state of matter comprising **charged particles**. Plasmas are usually created by heating a gas until the **electrons **become detached from their parent atom or molecule.

SUPERCONDUCTIVITY the property of zero electrical resistance in some substances at very low absolute temperatures.

QUARKS any of a number of subatomic particles carrying a fractional electric charge, postulated as building blocks of the hadrons. Quarks have not been directly observed, but theoretical predictions based on their existence have been confirmed experimentally.

STRANGE PARTICLES a subatomic particle classified as having a nonzero value for strangeness.

BOSON a subatomic particle, such as a photon, that has zero or integral spin and follows the statistical description given by S. N. Bose and Einstein.

MUON The **muon** from the Greek letter mu used to represent it) is an elementary particle similar to the electron, with an electric charge of 1 e and a spin of 1/2, but with a much greater mass. It is classified as a lepton.

lepton A **lepton **is an elementary, half-integer spin (spin 1/2) particle that does not undergo strong interactions. Two main classes of **leptons **exist: charged **leptons **(also known as the

electron-like **leptons**), and neutral **leptons **(better known as neutrinos).

PION. Each **pion **consists of a quark and an antiquark and is therefore a meson. **Pions **are the lightest mesons and, more generally, the lightest hadrons. They are unstable, with the charged **pions**.

GLUON a subatomic particle of a class that is thought to bind quarks together.

OMEGA MINUS The **Omega **baryons are a family of subatomic hadron (a baryon) particles that are represented by the symbol. Î© and are either neutral or have a +2, +1 or 1 elementary charge. They are baryons containing no up or down quarks. **Omega **baryons containing top quarks are not expected to be observed.

J/PSI The J/PSI (**J**/**psi**) meson or psion is a subatomic particle, a flavor-neutral meson consisting of a charm quark and a charm antiquark. Mesons formed by a bound state of a charm quark and a charm anti-quark are generally known as “charmonium”.

HIGGS BOSON The **Higgs boson **is an elementary particle in the Standard Model of particle physics. First suspected to exist in the 1960s, it is the quantum excitation of the **Higgs **field, a fundamental field of crucial importance to particle physics theory.

GRAVITON In speculative theories of quantum gravity, the **graviton **is a hypothetical elementary particle that mediates the force of gravitation in the framework of quantum field theory (QFT).

TACHYON The term “**tachyon**” was coined by Gerald Feinberg in a 1967 paper titled “Possibility of Faster-Than-Light Particles.

CHAOS **Chaos **theory is a branch of mathematics and it is focused on the behavior of dynamical systems that are highly sensitive to initial conditions. … This behavior is known as deterministic **chaos**, or simply **chaos**.

EINSTEIN FIELD EQUATIONS The **Einstein field equations **(EFE; also known as **Einstein’s equations**) comprise the set of 10 **equations **in Albert **Einstein**‘s general theory of relativity that describe the fundamental interaction of gravitation as a result of spacetime being curved by mass and energy.

EQUIVALENCE PRINCIPLE a basic postulate of general relativity, stating that at any point of space-time the effects of a gravitational field cannot be experimentally distinguished from those due to an accelerated frame of reference.

BERNOULLI THEOREM Bernoulli’s theorem. Bernoulli’s theorem, in fluid dynamics, relation among the pressure, velocity, and elevation in a moving fluid (liquid or gas), the compressibility and viscosity (internal friction) of which are negligible and the **flow **of which is **steady**, or laminar.

UNIFIED FIELD THEORY a theory that describes two or more of the four interactions (electromagnetic, gravitational, weak, and strong) previously described by separate theories.

W AND Z PARTICLES **W and Z bosons **are a group of elementary **particles**. They are **bosons**, which means that they have a spin of 0 or 1. Both had been found in experiments by the year 1983. Together, they are responsible for a force known as “weak force.

ANTIMATTER molecules formed by atoms consisting of antiprotons, antineutrons, and positrons. Stable antimatter does not appear to exist in our universe.

TIME TRAVEL Forward time travel, outside the usual sense of the perception of time, is possible according to special relativity and general relativity, although making one body advance or delay more than a few milliseconds compared to another body is not feasible with current technology. As for backwards time travel, it is possible to find solutions in general relativity that allow for it, but the solutions require conditions that may not be physically possible. Traveling to an arbitrary point in spacetime has a very limited support in theoretical physics, and usually only connected with quantum mechanics or wormholes, also known as Einstein-Rosen bridges.

SPACETIME the concepts of time and three-dimensional space regarded as fused in a four-dimensional continuum.

PARALLEL UNIVERSES There actually is quite a bit of evidence out there for a multiverse, an infinite number of other **universes **besides our own.

MULTIVERSE There are at least five theories why a multiverse is possible, as a 2012Space.com article explained

1. We don’t know what the shape of space-time is exactly. One prominent theory is that it is flat and goes on forever. This would present the possibility of many universes being out there. But with that topic in mind, it’s possible that universes can start repeating themselves. That’s because particles can only be put together in so many ways. More about that in a moment.

2. Another theory for multiple universes comes from “eternal inflation.” Based on research from Tufts University cosmologist Alexander Vilenkin, when looking at space-time as a whole, some areas of space stop inflating like the Big Bang inflated our own universe. Others, however, will keep getting larger. So if we picture our own universe as a bubble, it is sitting in a network of bubble universes of space. What’s interesting about this theory is the other universes could have very different laws of physics than our own, since they are not linked.

3. Or perhaps multiple universes can follow the theory of quantum mechanics (how subatomic particles behave), as part of the “daughter universe” theory. If you follow the laws of probability, it suggests that for every outcome that could come from one of your decisions, there would be a range of universes, each of which saw one outcome come to be. So in one universe, you took that job to China. In another, perhaps you were on your way and your plane landed somewhere different, and you decided to stay. And so on.

4. Another possible avenue is exploring mathematical universes, which, simply put, explain that the structure of mathematics may change depending in which universe you reside. “A mathematical structure is something that you can describe in a way that’s completely independent of human baggage,” said theory-proposer Max Tegmark of the Massachusetts Institute of Technology, as quoted in the 2012 article. “I really believe that there is this universe out there that can exist independently of me that would continue to exist even if there were no humans.”

5. And last but not least as the idea of parallel universes. To go back to the idea that space-time is flat, the number of possible particle configurations in multiple universes would be limited to 10^10^122 distinct possibilities, to be exact. So, with an infinite number of cosmic patches, the particle arrangements within them must repeat â€” infinitely many times over. This means there are infinitely many “parallel universes”: cosmic patches exactly the same as ours (containing someone exactly like you), as well as patches that differ by just one particle’s position, patches that differ by two particles’ positions, and so on down to patches that are totally different from ours.

BLACKBODY RADIATION An object that absorbs all **radiation **falling on it, at all wavelengths, is called a **black body**. When a **black body **is at a uniform temperature, its emission has a characteristic frequency distribution that depends on the temperature. Its emission is called **black-body radiation**.

CHERENKOV RADIATION **Cherenkov radiation**, also known as Vavilov, **Cherenkov radiation **(VCR) is electromagnetic radiation emitted when a charged particle (such as an electron) passes through a dielectric medium at a speed greater than the phase velocity of light in that medium.

GUAGE THEORY **Gauge theory **studies the group of transformations, or Lie group, that leaves the basic physics of a quantum field invariant.

QUANTUM ZERO EFFECT **Quantum **Zeno **effect**. The **quantum **Zeno **effect **(also known as the Turing paradox) is a feature of **quantum **mechanical systems allowing a particle’s time evolution to be arrested by measuring it frequently enough with respect to some chosen measurement setting.

YANG MILL THEORY **Yang**–**Mills theory**, in physics, a generalization of Scottish physicist James Clerk Maxwell’s unified **theory **of electromagnetism, also known as Maxwell’s equations, used to describe the weak force and the strong force in subatomic particles in terms of a geometric structure, or quantum field **theory**.

INERTIA a property of matter by which it continues in its existing state of rest or uniform motion in a straight line, unless that state is changed by an external force.

5TH FORCE In physics, there are four conventionally accepted fundamental **forces **or interactions that form the basis of all known interactions in nature: the gravitational, electromagnetic, strong nuclear, and weak nuclear **forces**. The search for a fifth force has increased in recent decades due to the discovery that most of the mass of the universe is accounted for by an unknown form of matter called dark matter. Most physicists believe that dark matter is some new undiscovered subatomic particle, but some believe that it could be related to an unknown fundamental force. It has also recently been discovered that the expansion of the universe is accelerating, which has been attributed to some new form of energy called dark energy, which some speculate could be due to a fifth force.

ANTIGRAVITY In the real world of peer-reviewed studies, corporate-funded labs and general relativity, however, “**antigravity**” is a dirty word. Gravity, you undoubtedly remember, is the attractive force between objects. It holds you to the planet and keeps the planet orbiting around the sun. Many scientists strongly believe that antigravity isn’t possible, given what we know about the universe and the laws that govern it. So for now, all those amazing antigravity gizmos are going to have to remain within the realm of science fiction.

QUANTUM GRAVITY **Quantum gravity **(QG) is a field of theoretical physics that seeks to describe **gravity **according to the principles of **quantum **mechanics, and where **quantum **effects cannot be ignored, such as near compact astrophysical objects where the effects of **gravity **are strong.

CALABI YAU MANIFOLD In algebraic geometry, a **Calabi-Yau manifold**, also known as a **Calabi Yau space**, is a particular type of manifold which has properties, such as Ricci flatness, yielding applications in theoretical physics. Particularly in superstring theory, the extra dimensions of spacetime are sometimes conjectured to take the form of a 6-dimensional Calabi-Yau manifold, which led to the idea of mirror symmetry.

SUPERSYMMETRY In particle physics, **supersymmetry **(SUSY) is a theory that links gravity with the other fundamental forces of nature by proposing a relationship between two basic classes of elementary particles: bosons, which have an integer-valued spin, and fermions, which have a half-integer spin.

SUPERGRAVITY In theoretical physics, **supergravity **(**supergravity **theory; SUGRA for short) is a field theory that combines the principles of supersymmetry and general relativity. In **supergravity**, supersymmetry is local (in contrast to non-gravitational supersymmetric theories, such as the Minimal Supersymmetric Standard Model).

VIRTUAL PARTICLE In physics, a **virtual particle **is a transient fluctuation that exhibits some of the characteristics of an ordinary **particle**, but whose existence is limited by the uncertainty principle.

FALSE VACUUM In quantum field theory, a **false vacuum **is a vacuum that exists at a local minimum of energy and is therefore not truly stable. This is in contrast to a true vacuum, which exists at a global minimum and is stable. A **false vacuum **may be very long-lived, or metastable.

QUANTUM VACUUM In **quantum **field theory, the **quantum vacuum **state (also called the **quantum vacuum **or **vacuum **state) is the **quantum **state with the lowest possible energy. Generally, it contains no physical particles. Zero-point field is sometimes used as a synonym for the **vacuum **state of an individual quantized field.

LOOP QUANTUM GRAVITY **Loop quantum gravity **(**LQG**) is a theory of quantum gravity, merging quantum mechanics and general relativity. It is an effort to unify gravity in a common theoretical framework with the other three fundamental forces of nature. It is the leading competitor to string theory. LQG begins with relativity and tries to add quantum features, while string theory, conversely, begins with quantum field theory and tries to add gravity.

GRAND UNIFIED THEORY A **Grand Unified Theory **(GUT) is a model in particle physics in which, at high energy, the three gauge interactions of the Standard Model which define the electromagnetic, weak, and strong interactions, or forces, are merged into one single force.

FEYNMAN DIAGRAMS In theoretical physics, **Feynman diagrams **are pictorial representations of the mathematical expressions describing the behavior of subatomic particles. The scheme is named after its inventor, American physicist Richard **Feynman**, and was first introduced in 1948.

BARYON a subatomic particle, such as a nucleon or hyperon, that has a mass equal to or greater than that of a proton.

MESON a subatomic particle that is intermediate in mass between an electron and a proton and transmits the strong interaction that binds nucleons together in the atomic nucleus.

PARITY LAW This conservation of **parity **implied that, for fundamental physical interactions, it is impossible to distinguish right from left and clockwise from counterclockwise. The **laws **of **physics**, it was thought, are indifferent to mirror reflection and could never predict a change in **parity **of a system.

SYMMETRY LAW In physics, a **symmetry **of a physical system is a physical or mathematical feature of the system (observed or intrinsic) that is preserved or remains unchanged under some transformation. A family of particular transformations may be *continuous *(such as rotation of a circle) or *discrete *(e.g., reflection of a bilaterally symmetric figure, or rotation of a regular polygon). Continuous and discrete transformations give rise to corresponding types of symmetries. Continuous symmetries can be described by Lie groups while discrete symmetries are described by finite groups (see Symmetry group). These two concepts, Lie and finite groups, are the foundation for the fundamental theories of modern physics. Symmetries are frequently amenable to mathematical formulations such as group representations and can, in addition, be exploited to simplify many problems. Arguably the most important example of a symmetry in physics is that the speed of light has the same value in all frames of reference, which is known in mathematical terms as PoincarÃ© group, the symmetry group of special relativity. Another important example is the invariance of the form of physical laws under arbitrary differentiable coordinate transformations, which is an important idea in general relativity.

M THEORY **M**–**theory **is a **theory **in physics that unifies all consistent versions of superstring **theory**. The existence of such a **theory **was first conjectured by Edward Witten at a string **theory **conference at the University of Southern California in the spring of 1995.

BRANE THEORY In string **theory **and related **theories **such as supergravity **theories**, a **brane **is a physical object that generalizes the notion of a point particle to higher dimensions. **Branes **are dynamical objects which can propagate through spacetime according to the rules of quantum mechanics.

NOETHER’S THEOREM Noether’s theorem is an amazing result which lets physicists get conserved quantities from symmetries of the laws of nature. Time translation symmetry gives conservation of energy; space translation symmetry gives conservation of momentum; rotation symmetry gives conservation of angular momentum, and so on. This result, proved in 1915 by Emmy Noether shortly after she first arrived in Goettingen, was praised by Einstein as a piece of “penetrating mathematical thinking”. It’s now a standard workhorse in theoretical physics.

GAMMA RAYS penetrating electromagnetic radiation of a kind arising from the radioactive decay of atomic nuclei.

LAGRANGIAN MECHANICS In each case, a mathematical function called the **Lagrangian **is a function of the generalized coordinates, their time derivatives, and time, and contains the information about the **dynamics **of the system. No new physics is introduced in **Lagrangian mechanics **compared to Newtonian **mechanics**.

HAMILTONIAN MECHANICS **Hamiltonian mechanics **is a theory developed as a reformulation of classical mechanics and predicts the same outcomes as non-Hamiltonian classical mechanics. It uses a different mathematical formalism, providing a more abstract understanding of the theory. Historically, it was an important reformulation of classical mechanics, which later contributed to the formulation of statistical mechanics and quantum mechanics.

LEPTONS A **lepton **is an elementary, half-integer spin (spin 1/2) particle that does not undergo

strong interactions. Two main classes of **leptons **exist: charged **leptons **(also known as the electron-like **leptons**), and neutral **leptons **(better known as neutrinos).

GUAGE BOSONS in particle physics, a **gauge boson **is a force carrier, a bosonic particle that carries any of the fundamental interactions of nature, commonly called forces. Elementary particles, whose interactions are described by a **gauge **theory, interact with each other by the exchange of **gauge bosons **”usually as virtual particles.

STATISTICAL MECHANICS the description of physical phenomena in terms of a statistical treatment of the behavior of large numbers of atoms or molecules, especially with regard to the distribution of energy among them.

HALL EFFECT the production of a potential difference across an electrical conductor when a magnetic field is applied in a direction perpendicular to that of the flow of current.

TELEPORTATION **Teleportation **or teletransportation is the theoretical transfer of matter or energy from one point to another without traversing the physical space between them. It is a common subject in science fiction literature, film, video games, and television.

WORMHOLES a hypothetical connection between widely separated regions of space-time.

PLANCK TIME AND LENGTH The Planck length is the scale at which classical ideas about gravity and space-time cease to be valid, and quantum effects dominate. the smallest

measurement of length with any meaning. And roughly equal to 1.6 x **10****-35 ****m **or about 10-20 times the size of a proton. The Planck time is the time it would take a photon travelling at the speed of light to across a distance equal to the Planck **length**. the smallest measurement of time that has any meaning, and is equal to **10****-43 ****seconds**.

SYNCHOTRON a cyclotron in which the magnetic field strength increases with the energy of the particles to keep their orbital radius constant.

POINT ZERO ENERGY **Zero-point energy **(**ZPE**) or **ground state energy **is the lowest possible energy that a quantum mechanical system may have. Unlike in classical mechanics, quantum systems constantly fluctuate in their lowest energy state due to the Heisenberg uncertainty principle.

NEGATIVE MASS Nobody knows whether **negative mass **can exist but there have nevertheless been plenty of analyses to determine its properties. In particular, physicists have investigated whether **negative mass **would violate various laws of the universe, such as the conservation of energy or momentum and therefore cannot exist.

QUANTUM TUNNELING **Quantum tunneling **or **tunneling **(see spelling differences) is the **quantum **mechanical phenomenon where a particle tunnels through a barrier that it classically could not surmount.

GRAVITY WAVES When atomic particles collide, they may disrupt one another’s **wave **patterns and may form new particles such as a neutrino. The amount of vibrational energy in a neutrino is equal to the amount of energy lost when an atomic particle decays.

LIGO The **LIGO **Scientific Collaboration (LSC) is a group of scientists focused on the direct detection of gravitational waves, using them to explore the fundamental physics of gravity, and developing the emerging field of gravitational wave science as a tool of astronomical discovery.

COSMIC RAYS a highly energetic atomic nucleus or other particle traveling through space at a speed approaching that of light.

NEUTRINO a neutral subatomic particle with a mass close to zero and half-integral spin, rarely reacting with normal matter. Three kinds of neutrinos are known, associated with the electron, muon, and tau particle.

SUPERSTRING THEORY **Superstring theory **is an attempt to explain all of the particles and fundamental forces of nature in one **theory **by modeling them as vibrations of tiny supersymmetric **strings**.

KALUZA KLEIN THEORY In physics, **Kaluza**–**Klein theory **(KK **theory**) is a unified field **theory **of gravitation and electromagnetism built around the idea of a fifth dimension beyond the usual four of space and time. It is considered to be an important precursor to string **theory**. … The five-dimensional metric has 15 components.

D BRANE M-theory is not just populated by strings, but also by membranes called **D-branes**. These are multi-dimensional surfaces that move through the eleven dimensions of M-theory. We can have D-branes of up to nine spatial dimensions (though that’s a little hard to visualise)! A point is a D0-brane, a string a D1-brane, a sheet a D2-brane and so on. Eleven-dimensional M- theory can look exactly like ten-dimensional string theory. This happens when one of the eleven dimensions is extremely small and circular. A two-dimensional D-brane wrapped around this extra dimension will look like a cylinder. But if the circular dimension is tiny then this cylinder will be very thin. As a result the D-brane will appear to be a one-dimensional string moving in ten dimensions.

WHITE WHOLE The complete Schwarzschild geometry consists of a black **hole**, a **white hole**, and two Universes connected at their horizons by a **wormhole**. The negative square root solution inside the horizon represents a **white hole**. A **white hole **is a black **hole **running backwards in time.

**Quantum entanglement **is a physical phenomenon which occurs when pairs or groups of particles are generated or interact in ways such that the quantum state of each particle cannot be described independently of the state of the other(s), even when the particles are separated by a large distance—instead, a quantum state must be described for the system as a whole.

ASTRONOMY—

ARIZONA IMPACT Meteor Crater Barringer Crater

**Meteor Crater **is a meteorite impact crater approximately 37 miles (60 km) east of Flagstaff and 18 miles (29 km) west of Winslow in the northern Arizona desert of the United States. Meteor Crater lies at an elevation of about 1,740 m (5,710 ft) above sea level. It is about 1,200 m

(3,900 ft) in diameter, some 170 m (560 ft) deep, and is surrounded by a rim that rises 45 m

(148 ft) above the surrounding plains. The center of the crater is filled with 210 240 m (690 790 ft) of rubble lying above crater bedrock. The crater was created about 50,000 years ago during the Pleistocene epoch, when the local climate on the Colorado Plateau was much cooler and damper. The area was an open grassland dotted with woodlands inhabited by woolly mammoths and giant ground sloths.

IMPACT 66 MYA The **Cretaceous Paleogene **(**K Pg**) **extinction event**, also known as the **Cretaceous Tertiary **(**K T**) **extinction**, was a mass extinction of some three-quarters of the plant and animal species on Earth that occurred over a geologically short period of time, approximately 66 million years ago. It was caused by a massive comet or asteroid impact, estimated to be 10 km (6.2 mi) to 15 km (9.3 mi) wide, 66 million years ago and its catastrophic effects on the global environment, including a lingering impact winter that made it impossible for plants and plankton to carry out photosynthesis. With the exception of some ectothermic species such as the leatherback sea turtle and crocodiles, no tetrapods weighing more than 25 kilograms (55 lb) survived. It marked the end of the Cretaceous period and with it, the entire Mesozoic Era, opening the Cenozoic Era that continues today.

DARK MATTER **Dark matter **is a hypothetical type of **matter **distinct from ordinary **matter **such as protons, neutrons, electrons, and neutrinos. **Dark matter **has never been directly observed; however, its existence would explain a number of otherwise puzzling astronomical observations.

DARK ENERGY a theoretical repulsive force that counteracts gravity and causes the universe to expand at an accelerating rate.

EARLY UNIVERSE 13.75 billion years ago – The Big Bang – It is not known what triggered the Big Bang. Cosmologists believe a process called inflation happened in the fraction of a second after the Big Bang. There was a strange type of vacuum energy that caused the the universe – the volume of space itself – to expand by a factor of 1078 in a fraction of a second.

One second after the Big Bang – The universe was made up of fundamental particles including quarks, electrons, photons and neutrinos. The universe continued to expand, but not as quickly as during inflation. As the universe cooled, the four fundamental forces in nature emerged: gravity, the strong force, the weak force and the electromagnetic force. Protons and neutrons began to form. The temperature of the universe was around 1032 Kelvin.

3 minutes after the Big Bang – Protons and neutrons began to come together to form the nuclei of simple elements. The temperature of the universe was still incredibly high at about 109 Kelvin. 24,000 years after the Big Bang – For the first time there was more matter than energy in the universe.

380,000 years after the Big Bang – The temperature of the universe had cooled to about 3000 K. Electrons began to combine with hydrogen and helium nuclei. High energy photons from this period rushed outwards. The early universe was so hot, that as it has expanded and cooled, the highly energetic photons from that time have had their wavelengths stretched tremendously. The cosmic microwave background we observe today is evidence of what the early universe was like. The temperature of the cosmic microwave background is now only a few degrees above absolute zero and radiation left over from this period has wavelengths of about 1 mm which is in the microwave range of the electromagnetic spectrum. This cosmic microwave radiation is what astronomers study with telescopes like Planck and others.

1,000,000,000 years after the Big Bang – The pull of gravity began to amplify irregularities in the gas in the universe. As the universe expanded, pockets of gas became more dense and and stars began to ignite. Groups of these stars became early galaxies. Many of these stars were much larger than the most common stars today.

3,000,000,000 years after the Big Bang – Many small galaxies merged to form larger ones. Often these mergers were so violent that the stars and gas collapsed and formed black holes. The gas flowing into these black holes became hot and glowed brightly before it disappeared into these black holes. This light was bright enough that is can be seen across the universe. These bright lights are called quasars.

6,000,000,000 years after the Big Bang – Large, short lived stars ended their lives in supernova explosions that distributed heavy elements such as nickel, gold, silver, and lead into the universe.

8,000,000,000 years after the Big Bang – Our Sun and Solar System began from a cloud of dust and gas in a spiral arm of the Milky Way galaxy.

9,200,000,000 years after the Big Bang (about 4,500,000,000 years ago) – the Earth formed. 13,750,000,000 years after the Big Bang – Now.

FATE OF THE UNIVERSE

THE BIG RIP

In this model, if the universe’s density is found to be less than critical density (the boundary value between open models that expand forever and closed models that re-collapse), the expansion of the universe will continue, as well as the accelerating expansion that is driving the galaxies apart at high speeds. If the density of the universe ever becomes equal to its critical density, it will continue to expand, but the expansion would eventually start to decrease gradually.

THE BIG CRUNCH

The Big Crunch is thought to be the direct consequence of the Big Bang. In this model, the expansion of the universe doesn’t continue forever. After an undetermined amount of time (possibly trillions of years), if the average density of the universe was enough to stop the expansion, the universe would begin the process of collapsing in on itself. Eventually, all of the matter and particles in existence would be pulled together into a super dense state (perhaps even into a black hole-like singularity).

THE BIG SLURP

In this model, if the Higgs Boson particle weighs in at a certain mass, it could indicate that the vacuum of our universe may be inherently unstable, perhaps existing in a perpetual metastable something that has been discussed at length many times before. If this were the case, our universe might experience a catastrophic event when a bubble from another alternate universe appears in ours. If said bubble exists in a lower-energy state than our bubble. the universe could be completely annihilated.

THE BIG FREEZE

Another popular scenario for the end of the universe that relies on deciphering the true nature of dark energy is the Big Freeze (also referred to as Heat Death or the Big Chill). In this scenario, the universe continues to expand at an ever-increasing speed. As this happens, the heat is dispersed throughout space while clusters, galaxies, stars, and planets are all pulled apart. It will continue to get colder and colder until the temperature throughout the universe reaches absolute zero (or a point at which the universe can no longer be exploited to perform work).

QUASARS a massive and extremely remote celestial object, emitting exceptionally large amounts of energy, and typically having a starlike image in a telescope. It has been suggested that quasars contain massive black holes and may represent a stage in the evolution of some galaxies.

NOVAS Novae and Supernovae. A **nova **is an explosion from the surface of a white-dwarf star in a binary star system. A **nova **occurs when the white dwarf, which is the dense core of a once- normal star, steals gas from its nearby companion star.

NEUTRON STARS a celestial object of very small radius (typically 18 miles/30 km) and very high density, composed predominantly of closely packed neutrons. Neutron stars are thought to form by the gravitational collapse of the remnant of a massive star after a supernova explosion, provided that the star is insufficiently massive to produce a black hole.

GRAVITATIONAL SINGULARITY A **gravitational singularity **(sometimes called a spacetime **singularity**) is a term used to describe the center of a black hole where **gravity **is thought to approach infinity. In the center of each black hole is a **singularity**, a point where infinite density develops as spacetime approaches it.

COSMIC INFLATION In physical **cosmology**, **cosmic inflation**, cosmological **inflation**, or just **inflation**, is a theory of exponential expansion of space in the early universe.

QUARK NOVA A **quark**–**nova **is the hypothetical violent explosion resulting from theconversion of a neutron star to a quark star. Analogous to a supernova heralding the birth of a neutron star, a **quark nova **signals the creation of a quark star.

HYPERGIANT **Hypergiants **are the largest **stars **in the universe, even larger than supergiants. The largest known **hypergiant **was NML Cygni, which is about 1,650 times wider than the Sun. It is one of the extreme luminous supergiant **stars**. The pulsating red supergiant UY Scuti is probably larger still.

MAGNETAR A **magnetar **is a type of neutron star with an extremely powerful magnetic field. The magnetic field decay powers the emission of high-energy electromagnetic radiation, particularly X-rays and gamma rays.

EXOTIC STAR a new class of **star**, one that has an **exotic **stellar engine that would emit mostly hard-to-detect neutrinos instead of photons of light like regular **stars**. These objects, dubbed “electroweak **stars**,” are plausible because of the Standard Model of physics.

GAMMA RAY BURSTS In gamma-ray astronomy, gamma-ray bursts (GRBs) are extremely energetic explosions that have been observed in distant galaxies. They are the brightest electromagnetic events known to occur in the universe. Bursts can last from ten milliseconds to several hours. After an initial flash of gamma rays, a longer-lived “afterglow” is usually emitted at longer wavelengths (X-ray, ultraviolet, optical, infrared, microwave and radio).

WHITE HOLES In general relativity, a **white hole **is a hypothetical region of spacetime which cannot be entered from the outside, although matter and light can escape from it. In this sense, it is the reverse of a black hole, which can only be entered from the outside and from which matter and light cannot escape.

MANY WORLD INTERPRETATION The **Many**–**Worlds Interpretation **(MWI) of quantum mechanics holds that there are many worlds which exist in parallel at the same space and time as our own. the hypothesis states there is a very large perhaps infinite number of universes, and everything that could possibly have happened in our past, but did not, has occurred in the past of some other universe or universes.

SEYFERT GALAXIES a galaxy of a type characterized by a bright compact core that shows strong infrared emission.

WOLF RAYET STAR **Wolf Rayet stars **are a normal stage in the evolution of very massive **stars**, in which strong, broad emission lines of helium and nitrogen (“WN” sequence), carbon (“WC” sequence), and oxygen (“WO” sequence) are visible. Due to their strong emission lines they can be identified in nearby galaxies. Wolf-Rayet stars represent a final burst of activity before a huge star begins to die. These stars, which are at least 20 times more massive than the Sun, live fast and die hard.

HYPERNOVA A **hypernova **(alternatively called a collapsar) is a very energetic supernova thought to result from an extreme core-collapse scenario. In this case a massive star (>30 solar masses) collapses to form a rotating black hole emitting twin energetic jets and surrounded by an accretion disk.

MULTIVERSE The **multiverse **(or **meta-universe**) is a hypothetical set of various possible universes including the universe which we live in. Together, these universes comprise everything that exists: the entirety of space, time, matter, energy and the physical laws and constants that describe them. The miscellaneous distinct universes within the multiverse are called the “parallel universes”, “other universes” or “alternative universes. The concept of multiverses is mentioned many times in Hindu Puranic literature, such as in the Bhagavata Purana: Every universe is covered by seven layers” earth, water, fire, air, sky, the total energy and false ego each ten times greater than the previous one. There are **innumerable universes **besides this one, and although they are unlimitedly large, they move about like atoms in You. Therefore You are called unlimited (Bhagavata Purana 6.16.37)

KILONOVA A **kilonova **(macronova or r-process supernova) is a transient astronomical event that occurs in a compact binary system when two neutron stars or a neutron star and a black hole merge into each other.

PARALLEL UNIVERSES—there exist parallel universes, exactly like our universe. These universes are all related to ours; indeed, they branch off from ours, and our universe is branched off of others. Within these parallel universes, our wars have had different outcomes than the ones we know. Species that are extinct in our universe have evolved and adapted in others. In other universes, we humans may have become extinct.

YELLOW SUPERGIANT STAR—A **yellow supergiant star** is a star, generally of spectral type F or G, having a supergiant luminosity class (e.g. Ia or Ib). They are stars that have evolved away from the main sequence, expanding and becoming more luminous.

**Yellow supergiants** are smaller than red supergiants; naked eye examples include Canopus and Polaris. Many of them are variable stars, mostly pulsating Cepheids such as δ Cephei itself.

HAWKING-PENROSE SINGULARITY THEOREM—a set of results in general relativity which attempt to answer the question of when gravitation produces **singularities**. It states under which circumstances **singularities** are inevitable in general relativity.