Time After Time
The oldest enigma of humanity has always been time, its perpetuity and ambiguity.
The enigma of time, is a conundrum of life which has plagued poets and philosophers from the beginnings of civilized thought. For life is lived in time and without time there is no life, but each one lives in his own time on his own time.
Running against time, is sine qua non with situations in which we must do or finish something very quickly because we only have a limited amount of time to do it. With only hours or days before an event or a happening, we find ourselves in a race against time.
Thus,a race against time is a situation in which something has to be done very quickly: It's a race against time to get things finished before something sets in.
Whereas, a race against the clock, is when you do something against time, you do it as fast as possible and try to finish it before a time deadline. When people do something against the clock, the time they take to do it is usually recorded, in order to find which person or attempt is the fastest.
To make time, is to cause an amount of one's time to be available to do something for or with others no matter how busy or short of time one is.
Time is the indefinite continued progress of existence and events that occur in apparently irreversible succession from the past through the present to the future.
Time in physics is defined by its measurement of what a clock reads. In classical, non-relativistic physics it is a scalar quantity and, like length, mass, and charge, is usually described as a fundamental quantity.
Physics of Time
Physics is the only science that explicitly studies time, but even physicists agree that time is one of the most difficult properties of our universe to understand. Even in the most modern and complex physical models, though, time is usually considered to be an ontologically “basic” or primary concept, and not made up of, or dependent on, anything else.
Quantum mechanics revolutionized physics in the first half of the 20th Century and it still represents the most complete and accurate model of the universe we have. Time is perhaps not as central a concept in quantum theory as it is in classical physics, and there is really no such thing as “quantum time” as such.
Most physicists agree that time had a beginning, and that it is measured from, and indeed came into being with, The Big Bang some 13.8 billion years ago. Whether, how and when time might end in the future is a more open question, depending on different notions of the ultimate fate of the universe and other mind-bending concepts like the multiverse.
The so-called arrow of time refers to the one-way direction or asymmetry of time, which leads to the way we instinctively perceive time as moving forwards from the fixed and immutable past, though the present, towards the unknown and unfixed future. This idea has it roots in physics, particularly in the Second Law of Thermodynamics, although other, often related, arrows of time have also been identified.
Absolute Time
The scientific study of time really began in the 16th Century with the work of the Italian physicist and astronomer Galileo Galilei, and continued in 17th Century England with the work of Isaac Barrow and Sir Isaac Newton. In non-relativistic or classical physics (the physics of Galileo, Newton, Maxwell, etc), time has always been considered one of the fundamental scalar quantities, along with length, mass, charge, etc (a scalar quantity is one that can be described by a single real number, usually with measurement units assigned). It was also considered to be absolute and universal, i.e. the same for everyone everywhere in the universe.
Newtonian Time
According to its most famous proponent, Sir Isaac Newton, for example, absolute time (which is also sometimes known as “Newtonian time”) exists independently of any perceiver, progresses at a consistent pace throughout the universe, is measurable but imperceptible, and can only be truly understood mathematically. For Newton, absolute time and space were independent and separate aspects of objective reality, and not dependent on physical events or on each other.
It should be pointed out, though, that the Newtonian version is still a very good approximation of what time is and how it behaves in the world we actually live in and experience.
Relativistic Time
Since Albert Einstein published his Theory of Relativity (the Special Theory in 1905, and the General Theory in 1916), our understanding of time has changed dramatically, and the traditional Newtonian idea of absolute time and space has been superseded by the notion of time as one dimension of space-time in special relativity, and of dynamically curved space-time in general relativity.
It was Einstein’s genius to realize that the speed of light is absolute, invariable and cannot be exceeded (and indeed that the speed of light is actually more fundamental than either time or space). In relativity, time is certainly an integral part of the very fabric of the universe and cannot exist apart from the universe, but, if the speed of light is invariable and absolute, Einstein realized, both space and time must be flexible and relative to accommodate this.
Although much of Einstein’s work is often considered “difficult” or “counter-intuitive”, his theories have proved (both in laboratory experiments and in astronomical observations) to be a remarkably accurate model of reality, indeed much more accurate than Newtonian physics, and applicable in a much wider range of circumstances and conditions.
The real paradox, though, as Einstein explained it, arises from the fact that (because there is no “preferred” frame of reference in relativity) we could just as easily consider the traveller in the spaceship as the one remaining at rest, while the Earth shoots off and back at close to the speed of light.
Time Travel
Arguably, we are always travelling though time, as we move from the past into the future. But time travel usually refers to the possibility of changing the rate at which we travel into the future, or completely reversing it so that we travel into the past. Although a plot device in fiction since the 19th Century (see the section on Time in Literature), time travel has never been practically demonstrated or verified, and may still be impossible.
Time travel is not possible in Newtonian absolute time (we move deterministically and linearly forward into the future). Neither is it possible according to special relativity (we are constrained by our light cones). But general relativity does raises the prospect (at least theoretically) of travel through time, i.e. the possibility of movement backwards and/or forwards in time, independently of the normal flow of time we observe on Earth, in much the same way as we can move between different points in space.
Time travel is usually taken to mean that a person’s mind and body remain unchanged, with their memories intact, while their location in time is changed. If the traveller’s body and mind reverted its condition at the destination time, then no time travel would be perceptible.
Quantum Time
In the first half of the 20th Century, a whole new theory of physics was developed, which has superseded everything we know about classical physics, and even the Theory of Relativity, which is still a classical model at heart. Quantum theory or quantum mechanics is now recognized as the most correct and accurate model of the universe, particularly at sub-atomic scales, although for large objects classical Newtonian and relativistic physics work adequately.
If the concepts and predictions of relativity are often considered difficult and counter-intuitive, many of the basic tenets and implications of quantum mechanics may appear absolutely bizarre and inconceivable, but they have been repeatedly proven to be true, and it is now one of the most rigorously tested physical models of all time.
Theoretical physicist Stephen Hawking has suggested that the fundamental laws of nature themselves, particularly the idea that causes always precede effects may prevent time travel in some way.
Some interpretations of time travel, though, have tried to resolve such potential paradoxes by accepting the possibility of travel between “branch points”, parallel realities or parallel universes, so that any new events caused by a time traveller’s visit to the past take place in a different reality and so do not impact on the original time stream. The idea of parallel universes, first put forward by Hugh Everett III in his “many worlds” interpretation of quantum theory in the 1950s, is now quite mainstream and accepted by many (although by no means all) physicists.
Copenhagen Interpretation
One of the main tenets of quantum theory is that the position of a particle is described by a wave function, which provides the probabilities of finding the particle at any number of different places, or superposition. It is only when the particle is observed, and the wave function collapses, that the particle is definitively located in one particular place or another. So, in quantum theory, unlike in classical physics, there is a difference between what we see and what actually exists.
The Copenhagen interpretation of quantum mechanics, mentioned above, is not however the only way of looking at it. Frustrated by the apparent failure of the Copenhagen interpretation to deal with questions like what counts as an observation, and what is the dividing line between the microscopic quantum world and the macroscopic classical world, other alternative viewpoints have been suggested. One of the leading alternatives is the many worlds interpretation, first put forward by Hugh Everett III back in the late 1950s.
According to the many worlds view, there is no difference between a particle or system before and after it has been observed, and no separate way of evolving. In fact, the observer himself is a quantum system, which interacts with other quantum systems, with different possible versions seeing the particle or object in different positions, for example. These different versions exist concurrently in different alternative or parallel universes. Thus, each time quantum systems interact with each other, the wave function does not collapse but actually splits into alternative versions of reality, all of which are equally real.
Quantum Gravity
Quantum gravity, or the quantum theory of gravity, refers to various attempts to combine our two best models of the physics of the universe, quantum mechanics and general relativity, into a workable whole. It looks to describe the force of gravity according to the principles of quantum mechanics, and represents an essential step towards the holy grail of physics, a so-called “theory of everything”.
Many different approaches to the riddle of quantum gravity have been proposed over the years, ranging from string theory and superstring theory to M-theory and brane theory, supergravity, loop quantum gravity, etc. This is the cutting edge of modern physics, and if a breakthrough were to occur it would likely be as revolutionary and paradigm-breaking as relativity was in 1905, and could completely change our understanding of time.
Imaginary Time
While looking to connect quantum field theory with statistical mechanics, theoretical physicist Stephen Hawking introduced a concept he called imaginary time. Although rather difficult to visualize, imaginary time is not imaginary in the sense of being unreal or made-up. Rather, it bears a similar relationship to normal physical time as the imaginary number scale does to the real numbers in the complex plane, and can perhaps best be portrayed as an axis running perpendicular to that of regular time. It provides a way of looking at the time dimension as if it were a dimension of space, so that it is possible to move forwards and backwards along it, just as one can move right and left or up and down in space.
Despite its rather abstract and counter-intuitive nature, the usefulness of imaginary time arises in its ability to help mathematically to smooth out gravitational singularities in models of the universe. Normally, singularities (like those at the centre of black holes, or the Big Bang itself) pose a problem for physicists, because they are areas where the known physical laws just do not apply. When visualized in imaginary time, however, the singularity is removed and the Big Bang functions like any other point in space-time.
Exactly what such a concept might represent in the real world, though, is unknown, and currently it remains little more than a potentially useful theoretical construct.
Time and the Big Bang
The general view of physicists is that time started at a specific point about 13.8 billion years ago with the Big Bang, when the entire universe suddenly expanded out of an infinitely hot, infinitely dense singularity, a point where the laws of physics as we understand them simply break down. This can be considered the “birth” of the universe, and the beginning of time as we know it. Before the Big Bang, there just was no space or time, and you cannot go further back in time than the Big Bang, in much the same way as you cannot go any further north than the North Pole.
As theoretical physicist Stephen Hawking notes in his 1988 book A Brief History of Time, even if time did not begin with the Big Bang, and there was another time frame before it, no information is available to us from that earlier time-frame, and any events that occurred then would have no effect on our present time-frame. Any putative events from before the Big Bang can therefore be considered effectively meaningless (or at least the province of philosophical speculation, not physics).
The Arrow of Time
Time appears to have a direction, to be inherently directional: the past lies behind us and is fixed and immutable, and accessible by memory or written documentation; the future, on the other hand, lies ahead and is not necessarily fixed, and, although we can perhaps predict it to some extent, we have no firm evidence or proof of it. Most of the events we experience are irreversible: for example, it is easy for us to break an egg, and hard, if not impossible, to unbreak an already broken egg. It appears inconceivable to us that that this progression could go in any other direction. This one-way direction or asymmetry of time is often referred to as the arrow of time, and it is what gives us an impression of time passing, of our progressing through different moments. The arrow of time, then, is the uniform and unique direction associated with the apparent inevitable “flow of time” into the future.
The idea of an arrow of time was first explored and developed to any degree by the British astronomer and physicist Sir Arthur Edington back in 1927, and the origin of the phrase is usually attributed to him. What interested Edington is that exactly the same arrow of time would apply to an alien race on the other side of the universe as applies to us. It is therefore nothing to do with our biology or psychology, but with the way the universe is. The arrow of time is not the same thing as time itself, but a feature of the universe and its contents and the way it has evolved.
Psychological Arrow of Time
A variant of the causal arrow is sometimes referred to as the psychological or perceptual arrow of time. We appear to have an innate sense that our perception runs from the known past to the unknown future. We anticipate the unknown, and automatically move forward towards it, and, while we are able to remember the past, we do not normally waste time in trying to change the already known and fixed past.
Stephen Hawking has argued that even the psychological arrow of time is ultimately dependent on the thermodynamic arrow, and that we can only remember past things because they form a relatively small set compared to the potentially infinite number of possible disordered future sets.
Anthropic Principle
Some thinkers, including Stephen Hawking again, have pinned the direction of the arrow of time on what is sometimes called the weak anthropic principle, the idea that the laws of physics are as they are solely because those are the laws that allow the development of sentient, questioning beings like ourselves. It is not that the universe is in some way “designed” to allow human beings, but merely that we only find ourselves in such a universe because it is as it is, even though the universe could easily have developed in a quite different way with quite different laws.
Thus, Hawking argues, a strong thermodynamic arrow of time is a necessary condition for intelligent life as we know it to develop. For example, beings like us need to consume food (a relatively ordered form of energy) and convert it into heat (a relatively disordered form of energy), for which a thermodynamic arrow like the one we see around us is necessary. If the universe were any other way, we would not be here to observe it.
Time is a necessary parameter in order to describe observed changes in three dimensional space, dx/dt, dy/dt, dz/dt. If there were no observable changes in the (x,y,z) contour map of the world (including us as contours also) there would be no time parameterization needed.
These changes are an experimental fact and to start with the day and night clock was used to define the parameter. Clocks can be anything that consistently reproduces periodically the same (x,y,z) for a specific location/point.
This is classical time. Special relativity and even more General Relativity are a different story with much more sophisticated mathematical modelling.
That said, if the essence of time was too complicated for you grasp, try to define or redefine what a moment in time is!
Food for thought!