According to David Lewis, the grandfather paradox is a valid argument. A causal loop necessarily involves backward causation. Here are some of the leading time travel theories, delving into the fourth dimension and space-time. 5 Bizarre Paradoxes Of Time Travel Explained December 20, 2014 Peter Christoforou Astronomy Lists , Time & Time Travel 48 There is nothing in Einstein’s theories of relativity to rule out time travel , although the very notion of traveling to the past violates one of … The A-series of time can make sense of backward time travel. The River of Time. Le Poidevin, Robin. Oxford: Oxford University Press, 2005. He discusses temporal parts , personal identity, causation and causal loops, free will, and the complications arising from our many different modal concepts. However, even hundreds of years prior to now, philosophers have tried to understand the implications of time travel and possible effects. Novikov, Igor.
Lewis, David. “The Paradoxes of Time Travel.” American Philosophical Quarterly 13 (1976): 145-152.
All theories of causation assume that the cause precedes the effect (in external time). “On Some Alleged Paradoxes of Time Travel.” Journal of Philosophy 72 (1975): 432-444. PHIL 100 Paper 6: Lewis' Grandfather Paradox Solution (Topic 2) Time travel is a phenomenon which no one that we know of, has discovered even in our advanced modern day society. Travels in Four Dimensions.
 While not the first philosophical discussion of time travel, David Lewis’s classic 1976 essay “The Paradoxes of Time Travel” popularized the subject in metaphysics. Horwich, Paul. In “The Paradoxes of Time Travel” (1976d), Lewis discusses the many complicated philosophical issues about time travel. For a recent philosophical discussion of time travel—an excellent summary of several facets of the debate, as well as some new developments—see Wasserman (2018). Traveling through time — possible in theory — is beyond our current technological capabilities.