Do the Laws of Physics Forbid the Operation of Time Machines
Earman (John), Smeenk (Christopher) & Wuthrich (Christian)
Source: PhilSci Archive website
Paper - Abstract

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Author’s Abstract

  1. We address the question of whether it is possible to operate a time machine1 by manipulating matter and energy so as to manufacture closed timelike curves. This question has received a great deal of attention in the physics literature, with attempts to prove no-go theorems based on classical general relativity and various hybrid theories serving as steps along the way towards quantum gravity.
  2. Despite the effort put into these no-go theorems, there is no widely accepted definition of a time machine2. We explain the conundrum that must be faced in providing a satisfactory definition and propose a resolution. Roughly, we require that all extensions of the time machine3 region contain closed timelike curves; the actions of the time machine4 operator are then sufficiently “potent” to guarantee that closed timelike curves appear.
  3. We then review no-go theorems based on classical general relativity, semiclassical quantum gravity, quantum field theory on curved spacetime, and Euclidean quantum gravity.
  4. Our verdict on the question of our title is that no result of sufficient generality to underwrite a confident “yes” has been proven.
  5. Our review of the no-go results does, however, highlight several foundational problems at the intersection of general relativity and quantum physics that lend substance to the search for an answer.

Contents
  1. Introduction
  2. Time travel5 and its paradoxes
  3. Operating a time machine6
  4. Chronology protection and no-go results for time machines7 in classical GTR
  5. No-go results using semi-classical quantum gravity
  6. No-go results from quantum field theory on curved spacetime
  7. No-go results from Euclidean quantum gravity
  8. Conclusion

Comment:

Text Colour Conventions (see disclaimer)

  1. Blue: Text by me; © Theo Todman, 2018
  2. Mauve: Text by correspondent(s) or other author(s); © the author(s)



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