Abstract
We argue that if everything there is in the world is physical, then time has an objective direction. If the fundamental equations of motion are time reversal invariant we show that the direction of time cannot be explained by anything else in physics (e.g. the direction of processes in time) and therefore must be added to physics. We further argue that the direction of time gives rise to both the thermodynamic and the psychological arrows of time (whenever they exist), and that it is necessary in order to construct a meaningful Past Hypothesis in statistical mechanics.
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Notes
- 1.
We focus here on velocity reversal in kinematics, and we do not address the significance of the symmetry of other theories under velocity reversal. In particular we do not discuss the fact that in order for a particle to return from B to A, if its evolution from A to B was affected by a magnetic field, one needs to reverse not only the velocity but also the field. See discussions on this topic in for example Albert (2000, Chap. 1), Earman (2002), Malament (2004) and Arntzenius and Greaves (2009).
- 2.
One may wonder how to express precisely this reversal, in particular whether the double reversal of sings result in a velocity with the same sign as in the original forward evolution. The answer is that this depends on some conventions, (see our 2012, Chap. 4).
- 3.
One way in which we come to have this knowledge is by memory. But by this we do not mean that we define the events that we remember to be in the past: this is characteristic but not analytic. It is physically possible given the laws of classical mechanics for example to remember events that occur in the future. See our (2012, Chap. 10), and compare Hawking (1985, 1988).
- 4.
Of course this may not be true, but here we wish to assume that everything in the world is physical. Also there are various views about how precisely this physicalist idea should be cashed out, but our argument does not depend on how these differences will be resolved.
- 5.
We assume here that there is a well-defined notion of an instantaneous state that includes velocity. For various approaches to this question, see Arntzenius (2000).
- 6.
- 7.
Not of time reversal; as we have shown these are physically distinct notions despite their mathematical equivalence.
- 8.
- 9.
Feynman (1967), p. 116.
- 10.
- 11.
The fact that we have memories of the past answers Price’s (1996) charge of a double standard since the symmetry between the past and the future is broken. Nevertheless it is a contingent fact that we remember the past rather than the future, but we shall not go into this issue here (see footnote 3 and Hemmo and Shenker 2012, Chap. 10).
References
Albert, David. 2000. Time and chance. Cambridge: Harvard University Press.
Arntzenius, Frank. 2000. Are there really instantaneous velocities? The Monist 83: 187–209.
Arntzenius, Frank, and Hilary Greaves. 2009. Time reversal in classical electromagnetism. British Journal for the Philosophy of Science 60(3): 557–584.
Brown, Harvey, and Jos Uffink. 2001. The origins of time-asymmetry in thermodynamics: The minus first law. Studies in History and Philosophy of Modern Physics 32(4): 525–538.
Callender, Craig. 2003. Is there a puzzle about the law entropy past? In Contemporary debates in the philosophy of science, ed. C. Hitchcock. Oxford: Blackwell.
Earman, John. 2002. What time-reversal invariance is and why it matters. International Studies in the Philosophy of Science 16(3): 245–264.
Earman, John. 2006. The Past Hypothesis: not even false. Studies in History and Philosophy of Modern Physics 37: 399–430.
Feynman, Richard. 1967. The character of physical law. Cambridge, MA: MIT Press.
Hawking, Steven. 1985. The arrow of time in cosmology. Physical Review D 32(10): 2489–2495.
Hawking, Steven. 1988. A brief history of time. London: Bentam Press.
Hemmo, Meir, and Orly Shenker. 2012. The road to Maxwell’s Demon. Cambridge: Cambridge University Press.
Malament, David. 2004. On the time reversal invariance of classical electromagnetic theory. Studies in History and Philosophy of Modern Physics 35B(2): 295–315.
Price, Huw. 1996. Time’s arrow and Archimedes’ point: New directions for the physics of time. New York: Oxford University Press.
Acknowledgements
This research has been supported by the Israel Science Foundation, grant number 713/10, and by the German-Israel Foundation, grant number 1054/09.
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Hemmo, M., Shenker, O. (2016). The Arrow of Time. In: Dolev, Y., Roubach, M. (eds) Cosmological and Psychological Time. Boston Studies in the Philosophy and History of Science, vol 285. Springer, Cham. https://doi.org/10.1007/978-3-319-22590-6_9
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