Time is the indeterminate continuing progress of existence and events that takes place in a seemingly irreversible sequence from the past through the present to the future, intervals between them, and to quantify the rate of change of quantities in material reality or in the future conscious experience.Time is often referred to as the fourth dimension along with three spatial dimensions.

**What is Space Time?**

Space-time is a mathematical model that combines space and time into a single idea called a continuum. This four-dimensional continuum is known as the Minkowski space. The combination of these two ideas helped cosmology understand how the universe works on a large scale (eg, galaxies) and on a small scale (eg, atoms). In non-relativistic classical mechanics, the use of Euclidean space rather than space-time is good, since time is treated as universal at a constant rate of passage that is independent of an observer’s state of motion. In a relativistic universe, however, time can not be separated from the three dimensions of space. This is because the observed rate at which time passes depends on the speed of an object relative to the observer. In addition, the strength of a gravitational field slows the timing of an object as seen by an observer off the field.

** What is Quantum Time?**

In the first half of the twentieth century, a whole new theory of physics was developed that has superseded everything we know about classical physics, and even the theory of relativity, which is still a classic model. Quantum theory or quantum mechanics is today considered to be the most accurate and accurate model of the universe, especially at subatomic scales, although classic Newtonian and relativistic physics work well for large objects. If the concepts and predictions of relativity (see Relativistic Time section) are often considered difficult and counterintuitive, many of the basic principles and implications of quantum mechanics seem absolutely bizarre and unthinkable, but they have repeatedly proven to be true and it is now one of the most rigoroustested physical models of all time.

**Quanta ** One of the implications of quantum mechanics is that certain aspects and properties of the universe are quantized, i.H. They consist of discrete, indivisible packets or quanta. For example, the electrons orbiting an atom are in certain fixed orbits and do not slip any farther or farther away from the nucleus as their energy levels change, but jump from one discrete quantum state to another. Even light that we know to be a type of electromagnetic radiation that moves in waves is also composed of quanta or light particles called photons, so that light has both aspects of waves and particles, and sometimes likea wave and sometimes a good thing behaved like a particle (wave-particle-duality). An obvious question would be: is time divided into discrete quanta? According to quantum mechanics, the answer seems to be “no,” and time actually seems smooth and continuous (contrary to popular belief, not everything is quantized in quantum theory). Tests have been carried out with sophisticated timing equipment and pulsed laser beams to observe chemical changes that occur in very small fractions of seconds (up to a femtosecond or 10-15 seconds), and in this area time certainly seems smooth andto be continuous However, if the time is actually quantized, it’s probably at the Planck time (about 10-43 seconds), the smallest possible amount of theoretical physics, and probably forever beyond our practical capabilities. It should be noted that our current knowledge of physics is incomplete, and according to some theories that combine quantum mechanics and gravitation into a single “theory of everything” (often referred to as quantum gravity – see below), there is a possibilitythat time could actually be quantized. A hypothetical chronon unit has been proposed for a suggested discrete time amount, though it is not clear how long a chronon should be.

**Copenhagen interpretation **

One of the most important principles of quantum theory is that the position of a particle is described by a wave function that provides the probabilities of finding the particle at any number of different locations or overlays. Only if the particle is observed and the wave function collapses, the particle is definitely in one place or another. So, unlike classical physics, quantum theory makes a difference between what we see and what actually exists. In fact, the observation affects the observed particle. Another aspect of quantum theory is the uncertainty principle, which states that the values of certain pairs of variables (such as the position of a particle and its velocity or momentum) are not known exactly, so the more precisely one variable is known, the less accurate the other can be This is reflected in the probabilistic approach of quantum mechanics, which is very alien to the deterministic and particular nature of classical physics. This view of quantum mechanics (developed by two of the founders of quantum theory, Niels Bohr and Werner Heisenberg) is sometimes referred to the Copenhagen interpretation of quantum mechanics. Since the breakdown of the wave function can not be reversed and all information related to the initial possible positions of the particle contained in the wave function is substantially lost as soon as it is observed and collapsed, the process is considered to be time-limited.which affects the so-called “arrow of time”, the one-way street of time that we observe in daily life (see section The Arrow of Time).

Some quantum physicists have developed a theory that time is indeed an emergent phenomenon, resulting from a strange quantum concept known as constraint.Here, different quantum particles effectively share an existence even though they are physically separated, so that the quantum state of each particle can only be described relative to the other entangled particles. The theory even claims to have recent experimental evidence from experiments by Ekaterina Moreva stating that observers do not detect any change in quantum particles (ie, time enemies “do not appear”) until they become involved with another particle

**Interpretation of many worlds **

However, the above-mentioned Copenhagen interpretation of quantum mechanics is not the only way of looking at it. Frustrated by the apparent failure of the Copenhagen interpretation to address issues such as what counts as an observation and the dividing line between the microscopic quantum world and the macroscopic classical world, other alternative views have been proposed. One of the most important alternatives is the interpretation of many worlds that Hugh Everett III first presented in the late 1950s. According to the many worlds, there is no difference between particles or systems before and after they are observed, and no separate way of development. In fact, the observer itself is a quantum system that interacts with other quantum systems, with various possible versions seeing the particle or object at different positions, for example. These different versions exist simultaneously in different alternative or parallel universes. Each time quantum systems interact with each other, the wave function does not collapse but splits into alternative versions of reality, all of them equally real. This view has the advantage of preserving all information from wavefunctions so that each individual universe is completely deterministic and the wavefunction can be advanced and regressed further. Under this interpretation, quantum mechanics is NOT the underlying reason for the time arrow.

**Quantum Gravity **

Quantum gravitation or quantum theory of gravitation refers to various attempts to combine our two best models of physics of the universe, quantum mechanics and the general theory of relativity, into a functional whole. It is intended to describe gravity according to the principles of quantum mechanics and represents a significant step on the way to the holy grail of physics, a so-called “theory of everything”. Quantum Theory and Relativity, though in most respects coexist happily, seem fundamentally incommensurable with intangible events such as the Singularities in Black Holes and the Big Bang themselves, and their own control over the very nature of time itself. Over the years, many different approaches have been proposed for the puzzle of quantum gravity, ranging from string theory and superstring theory to M theory and Brant theory, to supergravity and loop quantum gravity. This is the newest state of modern physics, and if it came to a breakthrough, it would probably be just as revolutionary and paradigmatic as the Theory of Relativity of 1905, and could completely change our understanding of time Every theory of quantum gravity has to deal with the inherent incompatibilities of quantum theory and relativity, not the least of which is the so-called “problem of time” – this time has a different one in quantum mechanics and general relativityMeaning. This is best illustrated by the Wheeler-DeWitt equation developed by John Wheeler and Bruce DeWitt in the 1970s. Their attempt to unify relativity theory and quantum mechanics has resulted in time essentially disappearing completely from their equations, suggesting that time does not exist at all, and that the universe is timeless at its most basic level. In response to the Wheeler-DeWitt equation, some have concluded that time is a kind of fictional variable in physics and that we may confuse the measurement of different physical variables with the actual existence of something we call time.

** Imaginary time**

When theoretical physicist Stephen Hawking tried to combine quantum field theory with statistical mechanics, he introduced a concept he called imaginary time. Although it is difficult to imagine anything, imaginary time is not imaginary in the sense of unreal or invented. Rather, it has a similar relationship to normal physical time as the imaginary number scale to the real numbers in the complex plane and may best be represented as an axis that is perpendicular to regular time. It offers the possibility of viewing the time dimension as if it were a space dimension, so that one can move forward and backward just as one moves in space to the right and left, or up and downcan move. Despite its abstract and counterintuitive nature, the value of imaginary time is its ability to mathematically help offset gravitational singularities in models of the universe. Usually, singularities (such as the one in the center of Black Holes or the Big Bang itself) pose a problem for physicists, as they are areas where the well-known laws of physics simply do not apply. In imaginary time, however, the singularity is removed and the Big Bang works like any other point in space-time. What exactly such a concept might be in the real world, however, is unknown, and currently it remains only a potentially useful theoretical construct.

Source:wikipedia and exactlywhatistime