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Because of momentum conservation laws, the creation of a pair of fermions (matter particles) out of a single photon cannot occur. However, matter creation is allowed by these laws when in the presence of another particle (another boson, or even a fermion) which can share the primary photon's momentum. Thus, matter can be created out of two photons.
In physics, motion is when an object changes its position with respect to a reference point in a given time. Motion is mathematically described in terms of displacement , distance , velocity , acceleration , speed , and frame of reference to an observer, measuring the change in position of the body relative to that frame with a change in time.
Inertia is the natural tendency of objects in motion to stay in motion and objects at rest to stay at rest, unless a force causes the velocity to change. It is one of the fundamental principles in classical physics, and described by Isaac Newton in his first law of motion (also known as The Principle of Inertia). [1]
[8] [9] [10] Active matter is a relatively new material classification in soft matter: the most extensively studied model, the Vicsek model, dates from 1995. [11] Research in active matter combines analytical techniques, numerical simulations and experiments.
The universe, as represented by the average motion of distant galaxies, does not appear to rotate relative to local inertial frames. Newton's gravitational constant G is a dynamical field. An isolated body in otherwise empty space has no inertia. Local inertial frames are affected by the cosmic motion and distribution of matter.
Despite the close relationship between math and physics, they are not synonyms. In mathematics objects can be defined exactly and logically related, but the object need have no relationship to experimental measurements. In physics, definitions are abstractions or idealizations, approximations adequate when compared to the natural world.
The current density of the observable universe is of the order of 9.44 · 10 −27 kg m −3 and the age of the universe is of the order of 13.8 billion years, or 4.358 · 10 17 s. The Hubble constant, H 0 {\displaystyle H_{0}} , is ≈70.88 km s −1 Mpc −1 (The Hubble time is 13.79 billion years).
The CPT theorem implies that the difference between the properties of a matter particle and those of its antimatter counterpart is completely described by C-inversion. Since this C-inversion does not affect gravitational mass, the CPT theorem predicts that the gravitational mass of antimatter is the same as that of ordinary matter. [5]