FRONTIERS OF THEORETICAL PHYSICS AND EXISTENTIAL RISK: Time Travel, Parallel Universes, Extraterrestrial Life, Dark Matter, and the Future of Life on Earth

This comprehensive review examines five interconnected frontiers in contemporary physics and existential risk analysis: the theoretical possibility of time travel and its associated paradoxes, the search for extraterrestrial life and habitable exoplanets, the multiverse hypothesis and parallel universes, the dark matter enigma, and existential threats to life on Earth. We analyze time travel through the lens of general relativity, examining wormholes, closed timelike curves, and temporal paradoxes including the grandfather paradox and causality violations. The search for extraterrestrial intelligence is evaluated through recent exoplanet discoveries, the habitable zone concept, and SETI initiatives. The multiverse hypothesis is explored across its various formulations, from inflationary cosmology to quantum many-worlds interpretation, with particular attention to philosophical implications. Dark matter evidence is critically assessed alongside alternative theories including modified gravity frameworks. Finally, we examine natural extinction events, technological threats including artificial intelligence and nuclear warfare, and gradual environmental collapse scenarios. This interdisciplinary synthesis demonstrates how theoretical physics, cosmology, and risk analysis converge to address fundamental questions about the nature of reality and humanity's long-term survival prospects.