Hawking's Brief Answers to the Big Questions: Is Time Travel Possible?

Summary: Time travel claims sixth place in 10 inquiries collated by theoretical physicist Stephen Hawking into Brief Answers to the Big Questions.

artist's 1998 representation of passage by a hypothetical spacecraft with a negative energy induction ring through a traversable wormhole: NASA Glenn Research Center/Les Bossinas, Public Domain, via NASA

The final work, posthumously published through Bantam Books Oct. 15, 2018, by a world-renowned theoretical physicist acclaims time travel as sixth among 10 questions about the universe's origins and relationships to humans.

Stephen Hawking (Jan. 8, 1942-March 14, 2018) brings up "closed time-like curves" through Chapter 7's "Is Time Travel Possible?" in Brief Answers to the Big Questions. Science fiction calls for space and time warps through extra dimensions to carry cargo and crew to certain spaces, or future and past times, and back. Earth-surface triangles; Euclid's (from Greek Εὐκλείδης, Efkleídis, "renowned," 325-270 B.C.?) flat-surface, straight-line triangles; saddle-shaped surface triangles respectively come to more than, precisely, less than 180 degrees.

Euclidean geometry explains the Earth's flat, three-dimensional space of down-up, east-west and north-south directionally at right angles to one another in a triangle of 180 degrees.

Curved spaces fit into Bernhard Riemann's (Sept. 17, 1826-July 20, 1866) mathematical descriptions in 1854 and Albert Einstein's (March 14, 1879-April 18, 1955) general relativity theory.

Special relativity in 1905 gathered three-dimensional space of distance, latitude and longitude and fourth-dimensional time into space-time, gauged similarly by non-moving, but differently by moving, observers. Its application, at less than light's 186,282.398-mile (299,792.458-kilometer) speeds per second, has eight- and 50,000-year round-trip travel respectively to the nearest star and Milky Way center. General relativity in 1915 identified space-time as curved, distorted, warped by its inclusive energy and matter and implied semi-bent light and radio waves near the Sun.

Kurt Gödel (April 28, 1906-Jan. 14, 1978) in 1948 joined general relativity field equations and an albeit non-expanding universe of rotating matter into time travel backward.

Curved, distorted, warped Gödel and cosmic-string universes respectively keep the small cosmological constant too large and stretchable, super-long, thin backward-curled, backward-traveling strings in 1.1023-octillion (100-billion-billion-billion-tonne) tension.

Big-Banged and time-travelling universes respectively lacked curved, distorted, warped space-time and launch shortcut, time-travelling, tube-like wormholes by loading negative-mass matter and negative-energy density into saddle-shaped surfaces. The electromagnetic, gravitational, quantum Uncertainty Principle militates against simultaneously well-defined positions and speeds for paired antiparticles and particles moving together, apart and together for mutual annihilation. The Casimir effect nets indirect, virtual observations of paired antiparticles' and particles' negative and zero energy densities respectively between and outside two close, parallel metal plates.

Experimental evidence in bent light of curved space-time and Casimir effect confirmation of negative-warped, saddle-shaped space-time offer apparent support to time travel through warped, wormholed space-time.

The co-author with Roger Penrose of The Nature of Space and Time Sept. 22, 2015, presents the alternate-path alternative-histories approach after return from time travel forward.

The repeat-story, unblocked-path consistent-histories' approach qualifies as more like Richard Feynman's (May 11, 1918-Feb. 15, 1988) sum-over-histories approach than David Deutsch's alternative-histories approach. The sum-over-histories approach resists, under quantum theory rules, one unique history since "the universe has every single possible history, each with its own [greater, lesser] probability." Hawking's Chronology Protection Conjecture stops time travel backward in warped space-time by sustaining virtual articles as closed-trajectory particles with large densities and energies and low probabilities.

Special relativity and M-theory respectively suggest time travel at swifter than the speed of light and at mix-ups of curved, warped seven-dimensional and flat, four-dimensional space-times.

Phenomenon of gravitational lensing involves distortion of light from background galaxies by a nearer galaxy cluster's gravitational field warping of space-time; gravitational lensing by Abell 370, a galaxy cluster located 5 billion light years away, manifests as arcs and streaks of background galaxies' stretched images; image credit NASA, ESA/Hubble, HST Frontier Fields: European Space Agency (europeanspaceagency), CC BY SA 2.0 Generic, via Flickr

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Image credits:

artist's 1998 representation of passage by a hypothetical spacecraft with a negative energy induction ring through a traversable wormhole: NASA Glenn Research Center/Les Bossinas, Public Domain, via NASA @ https://www.nasa.gov/centers/glenn/multimedia/artgallery/art_feature_001_CD1998_76634.html

Phenomenon of gravitational lensing involves distortion of light from background galaxies by a nearer galaxy cluster's gravitational field warping of space-time; gravitational lensing by Abell 370, a galaxy cluster located 5 billion light years away, manifests as arcs and streaks of background galaxies' stretched images; image credit NASA, ESA/Hubble, HST Frontier Fields: European Space Agency (europeanspaceagency), CC BY SA 2.0 Generic, via Flickr @ https://www.flickr.com/photos/europeanspaceagency/34332264821/

For further information:

Hawking, Stephen. 2018. "[Chapter] 6: Is Time Travel Possible?" Brief Answers to the Big Questions. New York NY: Bantam Books.

Hawking, Stephen. "Chronology Protection: Making the World Safe for Historians." In: Stephen W. Hawking, Kip S. Thorne, Igor Novikov, Timothy Ferris and Alan Lightman, The Future of Space-Time. Introduction by Richard Price. New York NY: Norton Paperback, W.W. Norton & Company, 2003.

Hawking, Stephen; and Roger Penrose. 2015. The Nature of Space and Time. With a New Afterword by the Authors. Princeton NJ: Isaac Newton Institute Series of Lectures, Princeton University Press.

Marriner, Derdriu. 18 October 2018. "Hawking's Brief Answers to the Big Questions: Scientific Literacy." Earth and Space News. Thursday.
Available @ https://earth-and-space-news.blogspot.com/2018/10/hawkings-brief-answers-to-big-questions.html

Marriner, Derdriu. 25 October 2018. "Brief Answers to Big Questions: Divine Creation, Scientific Creation?" Earth and Space News. Thursday.
Available @ https://earth-and-space-news.blogspot.com/2018/10/brief-answers-to-big-questions-divine.html

Marriner, Derdriu. 1 November 2018. "Cosmological Beginnings in Hawking's Brief Answers to Big Questions." Earth and Space News. Thursday.
Available @ https://earth-and-space-news.blogspot.com/2018/11/cosmological-beginnings-in-hawkings.html

Marriner, Derdriu. 8 November 2018. "Intelligent Life in Stephen Hawking's Brief Answers to Big Questions." Earth and Space News. Thursday.
Available @ https://earth-and-space-news.blogspot.com/2018/11/intelligent-life-in-stephen-hawkings.html

Marriner, Derdriu. 15 November 2018. "Hawking's Brief Answers to the Big Questions: Predictable Futures?" Earth and Space News. Thursday.
Available @ https://earth-and-space-news.blogspot.com/2018/11/hawkings-brief-answers-to-big-questions.html

Marriner, Derdriu. 22 November 2018. "Hawking's Brief Answers to the Big Questions: Black Hole Interiors." Earth and Space News. Thursday.
Available @ https://earth-and-space-news.blogspot.com/2018/11/hawkings-brief-answers-to-big-questions_22.html