His report of life there covers a wide range of topics, such as marriage in heaven ( where all angels are married ), children in heaven ( where they are raised by angel parents ), time and space in heaven ( there are none ), the after-death awakening process in the World of Spirits ( a place halfway between Heaven and Hell and where people first wake up after death ), the allowance of a free will choice between Heaven or Hell ( as opposed to being sent to either one by God ), the eternity of Hell ( one could leave but would never want to ), and that all angels or devils were once people on earth.

The single-photon annihilation of an electron-positron pair, + →, cannot occur in free space because it is impossible to conserve energy and momentum together in this process.

The reverse reaction ( in free space, without an atomic nucleus ) is also impossible for this reason.

Many agates are hollow, since deposition has not proceeded far enough to fill the cavity, and in such cases the last deposit commonly consists of drusy quartz, sometimes amethystine, having the apices of the crystals directed towards the free space so as to form a crystal-lined cavity or geode.

The ratio of the speed of the electromagnetic wave to the speed of light in free space is called the velocity factor, and depends on the electromagnetic properties of the conductor and the insulating materials surrounding it, and on their shape and size.

In large impacts, the expanding vapor cloud may rise to many times the scale height of the atmosphere, effectively expanding into free space.

At low pressure, there was enough space between the gas atoms that the ions could accelerate to high enough speeds that when they struck another atom they knocked electrons off of it, creating more positive ions and free electrons in a chain reaction.

The resulting free space, is commonly considered a security risk due to the existence of file recovery software.

: is a unit vector in the direction of r, p is the ( vector ) dipole moment, and ε < sub > 0 </ sub > is the permittivity of free space.

The formalism of diffraction can also describe the way in which waves of finite extent propagate in free space.

Beginning with Maxwell's equations in free space:

Telecommunications engineering focuses on the transmission of information across a channel such as a coax cable, optical fiber or free space.

Transmissions across free space require information to be encoded in a carrier wave to shift the information to a carrier frequency suitable for transmission, this is known as modulation.

According to Maxwell's equations, the speed of light in a vacuum is a universal constant, dependent only on the electrical permittivity and magnetic permeability of free space.

where is the charge density, which can ( and often does ) depend on time and position, is the permittivity of free space, is the permeability of free space, and is the current density vector, also a function of time and position.

Inside a linear material, Maxwell's equations change by switching the permeability and permittivity of free space with the permeability and permittivity of the linear material in question.

Maxwell's equations take the form of an electromagnetic wave in an area that is very far away from any charges or currents ( free space ) – that is, where and are zero.

There also exist planetary-mass objects that orbit brown dwarfs and other bodies that " float free " in space not bound to any star ; however, the term " planet " is not always applied to these objects.

Since the stored energy in the barrier is less than the energy stored in a barrier-free region of the same length due to destructive interference, the group delay for the energy to escape the barrier region is shorter than it would be in free space, which according to Winful is the explanation for apparently superluminal tunneling.

Some predictions of general relativity differ significantly from those of classical physics, especially concerning the passage of time, the geometry of space, the motion of bodies in free fall, and the propagation of light.

The preferred inertial motions are related to the geometry of space and time: in the standard reference frames of classical mechanics, objects in free motion move along straight lines at constant speed.

A simplified version of this is embodied in Einstein's elevator experiment, illustrated in the figure on the right: for an observer in a small enclosed room, it is impossible to decide, by mapping the trajectory of bodies such as a dropped ball, whether the room is at rest in a gravitational field, or in free space aboard an accelerating rocket generating a force equal to gravity.

In 1780, for example, Laplace and Lavoisier stated: “ In general, one can change the first hypothesis into the second by changing the words ‘ free heat, combined heat, and heat released ’ into ‘ vis viva, loss of vis viva, and increase of vis viva .’” In this manner, the total mass of caloric in a body, called absolute heat, was regarded as a mixture of two components ; the free or perceptible caloric could affect a thermometer, whereas the other component, the latent caloric, could not.

The Laplace number ( La ), also known as the Suratman number ( Su ), is a dimensionless number used in the characterization of free surface fluid dynamics.

* Solutions to the radial Schrödinger equation ( in spherical and cylindrical coordinates ) for a free particle

A transition from one state of minimal free energy requires some form of activation energy to penetrate the barrier ( compare activation energy and Arrhenius equation for the chemical case ).

The word " critical " refers to a cusp in the behavior of the differential equation that governs the number of free neutrons present in the fuel: if less than a critical mass is present, then the amount of neutrons is determined by radioactive decay, but if a critical mass or more is present, then the amount of neutrons is controlled instead by the physics of the chain reaction.

The Schrödinger equation, applied to the aforementioned example of the free particle, predicts that the center of a wave packet will move through space at a constant velocity ( like a classical particle with no forces acting on it ).

Using a uniqueness theorem and showing that a potential satisfies Laplace's equation ( second derivative of V should be zero i. e. in free space ) and the potential has the correct values at the boundaries, the potential is then uniquely defined.

Instead of also using E < sub > a </ sub >, however, the Eyring equation uses the concept of Gibbs free energy and the symbol * to denote the energy of the transition state.

The Dirac equation is superficially similar to the Schrödinger equation for a free massive particle:

Since E and P are defined separately, this equation can be used to define D. The physical interpretation of D is not as clear as E ( effectively the field applied to the material ) or P ( induced field due to the dipoles in the material ), but still serves as a convenient mathematical simplification, since Maxwell's equations can be simplified in terms of free charges and currents.

The Gaussian beam formalism begins with the wave equation for an electromagnetic field in free space or in a homogeneous dielectric medium:

Radio and antenna engineers use the following simplified formula ( also known as the Friis transmission equation ) for the path loss between two isotropic antennas in free space:

Young ’ s equation describes the contact angle of a liquid drop on a plane solid surface as a function of the surface free energy, the interfacial free energy and the surface tension of the liquid.

The mass flux equation in the free molecular regime is:

Mean free path is one factor that determines the temperature dependence for λ < sub > L </ sub >, as stated in the following equation

In quantum mechanics, the analogue of Newton's law is Schrödinger's equation for a quantum system, usually atoms, molecules, and subatomic particles ; free, bound, or localized.

Linearity: The previous assumptions only allow one to derive the equation for plane waves, corresponding to free particles.

" Robert Bloch has the android Ruk free himself by recalling how his cohort of androids had freed themselves from control by their makers, The Old Ones, long before, exclaiming " That was the equation!

Applying Gibbs free energy equation for reactions:

When c is very large and psi is slowly varying so that the lattice can be thought of as a line, this becomes the free Schrödinger equation:

The nearly free electron model rewrites the Schrödinger equation for the case of a periodic potential.

The equation fails at extremely low pressures and short wavelengths, due to dependence on the assumption that the wavelength of the sound in the gas is much longer than the average mean free path between gas molecule collisions.

In fact, this is a free Kleene algebra in the sense that any equation among regular expressions follows from the Kleene algebra axioms and is therefore valid in every Kleene algebra.