What does the “arrow of time” stand for?
Author(s)
Etienne Klein
ABSTRACT
One hundred and thirty years after the work of Ludwig Boltzmann on the interpretation of the irreversibility of physical phenomena, and one century after Einstein's formulation of Special Relativity, we are still not sure what we mean when we talk of “time” or “arrow of time”. We shall try to show that one source of this difficulty is our tendency to confuse, at least verbally, time and becoming, i.e. the course of time and the arrow of time, two concepts that the formalisms of modern physics are careful to distinguish. The course of time is represented by a time line that leads us to define time as the producer of duration. It is customary to place on this time line a small arrow that, ironically, must not be confused with the “arrow of time”. This small arrow is only there to indicate that the course of time is oriented, has a well-defined direction, even if this direction is arbitrary. The arrow of time, on the other hand, indicates the possibility for physical systems to experience, over the course of time, changes or transforma-tions that prevent them from returning to their initial state forever. Contrary to what the ex-pression “arrow of time” suggests, it is there-fore not a property of time itself but a property of certain physical phenomena whose dynamic is irreversible. By its very definition, the arrow of time presupposes the existence of a well- established course of time within which – in addition – certain phenomena have their own temporal orientation. We think that it is worth-while to emphasize the difference between sev-eral issues traditionally subsumed under the label “the problem of the direction of time”. If the expressions “course of time”, “direction of time” and “arrow of time” were better defined, systematically distinguished from one another and always used in their strictest sense, the debate about time, irreversibility and becoming in physics would become clearer.
One hundred and thirty years after the work of Ludwig Boltzmann on the interpretation of the irreversibility of physical phenomena, and one century after Einstein's formulation of Special Relativity, we are still not sure what we mean when we talk of “time” or “arrow of time”. We shall try to show that one source of this difficulty is our tendency to confuse, at least verbally, time and becoming, i.e. the course of time and the arrow of time, two concepts that the formalisms of modern physics are careful to distinguish. The course of time is represented by a time line that leads us to define time as the producer of duration. It is customary to place on this time line a small arrow that, ironically, must not be confused with the “arrow of time”. This small arrow is only there to indicate that the course of time is oriented, has a well-defined direction, even if this direction is arbitrary. The arrow of time, on the other hand, indicates the possibility for physical systems to experience, over the course of time, changes or transforma-tions that prevent them from returning to their initial state forever. Contrary to what the ex-pression “arrow of time” suggests, it is there-fore not a property of time itself but a property of certain physical phenomena whose dynamic is irreversible. By its very definition, the arrow of time presupposes the existence of a well- established course of time within which – in addition – certain phenomena have their own temporal orientation. We think that it is worth-while to emphasize the difference between sev-eral issues traditionally subsumed under the label “the problem of the direction of time”. If the expressions “course of time”, “direction of time” and “arrow of time” were better defined, systematically distinguished from one another and always used in their strictest sense, the debate about time, irreversibility and becoming in physics would become clearer.
Cite this paper
Klein, E. (2010) What does the “arrow of time” stand for?. Natural Science, 2, 212-219. doi: 10.4236/ns.2010.23033.
Klein, E. (2010) What does the “arrow of time” stand for?. Natural Science, 2, 212-219. doi: 10.4236/ns.2010.23033.
References
[1] Davies, P.C.W. (1974) The physics of time asymmetry. University of California Press, berkeley-losangeles. [2] Hawking, S. (1994) The no boundary proposal and the arrow of time. In Halliwell, J., Pérez-Mercader, J., Zurek, W., Ed. Physical origins of time asymmetry. Cambridge University Press, Cambridge. [3] Haddad, W.M., Chellaboina, V. and Nersesov, S.G. (2005) Thermodynamics: A dynamical systems approach. Prince-ton University Press, Princeton. [4] Horwich, P. (1987) Asymmetries in time, MIT Press, Cambridge. [5] Klein, E. (2005) Chronos, How time shapes our universe. Thunder’s Mouth Press, New York. [6] Price, H. (1996) Time’s arrow and archimedes’ point. Oxford University Press, new tork. [7] Prigogine, I. (1980) From being to becoming. Freeman, W. H. San Francisco. [8] Reichenbach, H. (1956) The direction of time. University of California Press, Berkeley. [9] Sachs, R.G. (1987) The Physics of time reversal. Chicago University Press, Chicago. [10] Savitt, S., Ed. (1995) Time’s arrows today, recent physi-cal and philosophical work on the direction of time. Cambridge University Press, Cambridge. [11] Zeh, H.D. (1989) The physical basis of the direction of time. Springer Verlag, Berlin.
[1] Davies, P.C.W. (1974) The physics of time asymmetry. University of California Press, berkeley-losangeles. [2] Hawking, S. (1994) The no boundary proposal and the arrow of time. In Halliwell, J., Pérez-Mercader, J., Zurek, W., Ed. Physical origins of time asymmetry. Cambridge University Press, Cambridge. [3] Haddad, W.M., Chellaboina, V. and Nersesov, S.G. (2005) Thermodynamics: A dynamical systems approach. Prince-ton University Press, Princeton. [4] Horwich, P. (1987) Asymmetries in time, MIT Press, Cambridge. [5] Klein, E. (2005) Chronos, How time shapes our universe. Thunder’s Mouth Press, New York. [6] Price, H. (1996) Time’s arrow and archimedes’ point. Oxford University Press, new tork. [7] Prigogine, I. (1980) From being to becoming. Freeman, W. H. San Francisco. [8] Reichenbach, H. (1956) The direction of time. University of California Press, Berkeley. [9] Sachs, R.G. (1987) The Physics of time reversal. Chicago University Press, Chicago. [10] Savitt, S., Ed. (1995) Time’s arrows today, recent physi-cal and philosophical work on the direction of time. Cambridge University Press, Cambridge. [11] Zeh, H.D. (1989) The physical basis of the direction of time. Springer Verlag, Berlin.