Abstract
It seems appropriate now to turn attention to the most controversial issue related to the time machines—the time travel paradoxes. On the one hand, paradoxes seem to be something inherent to time machines (their main attribute, perhaps). On the other hand, the (supposed) paradoxicalness of time travel is traditionally the main objection against it and a good pretext for dismissing causality violating spacetimes from consideration. Recall, however, that in studying physics one meets a lot of ‘paradoxes’ (Ehrenfest’s, Gibbs’, Olbers’, etc.). Today they are just interesting and instructive toy problems. Our aim in this chapter is to examine the ‘temporal paradoxes’ and to reduce them to the same status. In particular, we are going to show that they do not increase the tension between the relativistic concept of spacetime and ‘the simple notion of free will’ (S. W. Hawking and G. F. R. Ellis (1973). The Large Scale Structure of Spacetime. Cambridge University Press, Cambridge) [76]. As a by-product, we shall reveal, in the end of the chapter, a curious relation between the geometry of a spacetime and its matter content.
... Loads of them ended up killing
their past or future selves by mistake!
Hermiona in [158]
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Notes
- 1.
The term was coined by Tadasana.
- 2.
In fact, this assumption is not that extravagant. I am not aware of a single strong argument against it. Note, in particular, that the apparent lack of contramotes in the everyday life and in astronomical observations is not an argument: the contramotes must be practically invisible to us comotes. Indeed, they almost do not radiate light. Instead, a contramote star, say, absorbs a powerful flux of photons emitted (for some mysterious reason) towards the star by other bodies.
- 3.
For a collection of such pseudoparadoxes see [138].
- 4.
We speak of the existence of the note and not of its appearance, because being a typical Cauchy demon, see Sect. 3 in Chap. 2, the note has always existed, without ever having come into being.
- 5.
In fact, they often are too complex even when consist of billiard balls, see [39, 127].
- 6.
As is known, ‘...either a tail is there or it isn’t there. You can’t make a mistake about it...’ [128]. The same is true for evolutions. So, we shall not speak of ‘self-inconsistent evolution’ or ‘trajectories with zero multiplicity’.
- 7.
For a technical description see Example 74 in Chap. 1.
- 8.
For a less trivial one see [65].
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Krasnikov, S.V. (2018). Time Travel Paradoxes. In: Back-in-Time and Faster-than-Light Travel in General Relativity. Fundamental Theories of Physics, vol 193. Springer, Cham. https://doi.org/10.1007/978-3-319-72754-7_6
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