Could future humans return to the past?
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What would it mean for our sense of free will and moral responsibility if descendants could reach back and alter the choices that produced them?
Summary
Mainstream physics treats backward time travel as mathematically conceivable in some relativistic spacetimes, but not as an established engineering possibility. Closed timelike curves and time-machine proposals encounter questions about physical admissibility, quantum effects, stability, causation, and the extreme resources required. The lack of observations means the answer remains open rather than confirmed.
- General relativity is compatible with some spacetimes containing closed timelike curves, so the equations alone do not rule out backward time travel.
- The existence of suitable mathematical solutions does not demonstrate that a time machine can be built or operated in our universe.
- Modern discussions address the grandfather paradox through consistency constraints or other restrictions on what travelers could do.
Source mix
3 of 4 institutional
- 3 Journals & institutions
- 1 Other / unclassified
Deeper Insight
A serious skeptical reading argues that backward time travel is not merely technologically difficult but conceptually or physically incoherent. It emphasizes the improbable coincidences required for a single consistent past, the possibility that preserving the past while changing the present is logically inconsistent, and the absence of visitors. These arguments challenge feasibility but do not settle the physics conclusively.
- Some analyses argue that classic backward-time-travel scenarios are extremely improbable because records and dispositions would need to align through remarkable coincidences.
- One published argument claims that the assumption that zero change to the past implies zero change to the present is logically inconsistent, making past travel pseudoscientific.
- A philosophical position holds that travelers to the past cannot do otherwise than what they in fact do, limiting their ability to alter events.
Sources · 8
- 3 Journals & institutions
- 1 Other / unclassified
What do these mean?
- Journals & institutions. Published in a peer-reviewed journal, or from a university, government body, court or other institution.
- Other / unclassified. A site we have not classified yet. This says nothing good or bad about it.
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Time Travel (Stanford Encyclopedia of Philosophy)
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American Philosophical Quarterly | Vol. 54 No. 2 | ARTICLE: Nicholas J. J. Smith: I'd Do Anything to Change the Past(But I Can't Do "That") | PDF Document
Other
American Philosophical Quarterly Volume 54, Number 2, April 2017 ©2017 by the Board of Trustees of the University of Illinois ## I’d Do Anything to Change the Past (But I Can’t Do “That”) Nicholas J. J. Smith Abstract This paper addresses a worry about backwards time travel. The worry is that there
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