Review of the Concept of Time in Physics

Time as Motion

In Classical Mechanics (branch of physics dealing with macroscopic objects), past and future play the same role in the description of the motion. The equations of motion are symmetric in time. If you record the motion of an object in videotape and play it backwards, in principle, you cannot tell whether the object is moving forward or backward in time. More precisely, the motion of an object moving backward in time is described by the same equations.

Time as Irreversibility

We don’t get younger, we get older. This is an irreversible process. If we heat part of an object and isolate it thermally the temperature of the object will eventually become uniform. This is an irreversible process.

For a long time physicists thought that this irreversibility was caused by “initial conditions” but now almost all physicists accept the fundamental nature of the irreversibility. In physics irreversibility is known as the “second law of thermodynamics”.

The intrinsic randomness of the microscopic world which is described by Quantum Mechanics may be causing the irreversibility at the macroscopic level.

Time as irreversibility is sometimes known as the “arrow of time”.

Time as Evolution

In biology and sociology, time is seen as evolution. In evolution the move is towards higher levels of complexity which means that randomness is decreasing. In the irreversible process of heat diffusion the randomness is increasing. Life in general and evolution in particular seems to be reversing the arrow of time.

There is another word for randomness: entropy. Nature maximizes entropy. All organisms eventually die. Life opposes this natural process. Life emerges when Consciousness allows itself to be confined by nature. Consciousness allows the confinement as part of the cosmic play but escapes the imprisonment through life. Such is the cosmic play.

Evolution is an expression of Consciousness at a higher level. Speaking of higher level function, Consciousness also allows nature to destroy the non-working structures whether they are organisms or societies. This is a very important point.

Some physicists extrapolate the “nature maximizes entropy” principle to the cosmic scale and say that the universe will end up in the so called “thermal death”. They are completely wrong about this conclusion. There are many other possibilities. Our physical universe may be just one of the countless other physical universes. If one of them dies others will continue. Our physical universe may stop expanding, and start shrinking. Another possibility is that the black holes in this universe may be the Big Bangs in other universes. New baby universes may be emerging from black holes. There are countless other possibilities. Besides, all physical universes exist within the Mind of God (Cosmic Mind). There is nothing outside of the Cosmic Mind. There are mental and spiritual realms within the Cosmic Mind. When you consider the big picture the statements like “thermal death of the universe” sound so childish.

Time as Dimension

In 1754 d’Alembert mentioned that time appears as a geometrical parameter in dynamics. Lagrange called dynamics a 4-dimensional geometry in 1796. These early notions found their full expression in Einstein’s theory of relativity (1905 and 1915).  Einstein’s theory of General Relativity (1915) unites space and time but it cannot unite spacetime with matter. In that theory matter is a separate reality and it distorts spacetime causing gravitation. In Einstein’s theory,  time appears as the fourth dimension of spacetime, others being the length, width and height of a volume of space.

Einstein did not invent the term spacetime and he was not particularly fond of this terminology. Others, Minkowski especially, interpreted Einstein’s theory in the mathematical language of geometry and physics community started to refer to that geometrical entity as spacetime. Einstein eventually accepted the spacetime terminology.

Einstein’s theory of General Relativity predicted that time slows down

  • for those clocks zipping around at great speeds
  • for those clocks experiencing strong gravity

relative to the clock which is at rest and experiencing less gravity. A “clock” can be an inanimate or animate object including humans. These predictions have been experimentally verified.

Information Physics the New Frontier

I would like to bring your attention to a new development in physics. Kevin H. Knuth is one of the pioneers in this new branch of physics. This is radical new approach to physics and it may result in a new understanding of the physical time. In Kevin H. Knuth’s words:

“At this point in time, two major areas of physics, statistical mechanics and quantum mechanics, rest on the foundations of probability and entropy. The last century saw several significant fundamental advances in our understanding of the process of inference, which make it clear that these are inferential theories. That is, rather than being a description of the behavior of the universe, these theories describe how observers can make optimal predictions about the universe. In such a picture, information plays a critical role. What is more is that little clues, such as the fact that black holes have entropy, continue to suggest that information is fundamental to physics in general. In the last decade, our fundamental understanding of probability theory has led to a Bayesian revolution. In addition, we have come to recognize that the foundations go far deeper and that Cox’s approach of generalizing a Boolean algebra to a probability calculus is the first specific example of the more fundamental idea of assigning valuations to partially-ordered sets. By considering this as a natural way to introduce quantification to the more fundamental notion of ordering, one obtains an entirely new way of deriving physical laws. I will introduce this new way of thinking by demonstrating how one can quantify partially-ordered sets and, in the process, derive physical laws. The implication is that physical law does not reflect the order in the universe, instead it is derived from the order imposed by our description of the universe. Information physics, which is based on understanding the ways in which we both quantify and process information about the world around us, is a fundamentally new approach to science.”

You can read the rest of Knuth’s paper at

My favorite books on the concept of time 

About Time: Einstein’s Unfinished Revolution” by Paul Davies, Simon & Schuster (1996), ISBN: 0684818221 / 9780684818221

The Voices of Time: A Cooperative Survey of Man’s Views of Time As Expressed by the Sciences and by the Humanities” by J.T. Fraser, Univ of Massachusetts Pr (1981),  ISBN: 0870233378 / 9780870233371

From Being to Becoming: Time and Complexity in the Physical Sciences“, by Ilya Prigogine, W H Freeman & Co (Sd) (1981), ISBN: 0716711087 / 9780716711087

The Fabric of the Cosmos: Space, Time, and the Texture of Reality” by Brian Greene, Vintage (2005), ISBN: 0375727205 / 9780375727207

Physical Origins of Time Asymmetry” by J.J. Halliwell, Cambridge University Press (1996), ISBN: 0521568374 / 9780521568371

Asymmetries in Time: Problems in the Philosophy of Science (Bradford Books)” by Paul Horwich, The MIT Press (1987), ISBN: 0262580888 / 9780262580885

The Art of Being and Becoming” by Hazrat Inayat Khan, Omega Publications (2005), ISBN: 093087241X / 9780930872410

On Space and Time“, by Shahn Majid Eds. (Alain Connes, Michael Keller, Roger Penrose, John Polkinghorne, Andrew Taylor), Cambridge University Press (2008), 052188926X / 9780521889261

The Road to Reality: A Complete Guide to the Laws of the Universe” by Roger Penrose, Vintage (2007), ISBN: 0679776311 / 9780679776314

About Suresh Emre

I have worked as a physicist at the Fermi National Accelerator Laboratory and the Superconducting Super Collider Laboratory. I am a volunteer for the Renaissance Universal movement. My main goal is to inspire the reader to engage in Self-discovery and expansion of consciousness.
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