The United States’ recent release of hundreds of previously classified Unidentified Anomalous Phenomena (UAP) cases — covering incidents from the 1940s to the present — and the publicity around Steven Spielberg’s new film Disclosure Day have intensified public belief that extraterrestrials might be visiting Earth. Polls in Australia, the United States and elsewhere now show roughly a third of people say they believe aliens are here. Yet scientists point to three strong reasons why visitors from other star systems are unlikely to be arriving anytime soon.
First, space is unimaginably vast. The nearest star, Proxima Centauri, lies about 4.3 light‑years away — roughly 40 trillion kilometres. With current human technology we travel at only a tiny fraction of light speed: the fastest spacecraft to date, the Parker Solar Probe, reaches around 191 kilometres per second, a speed that would still take on the order of 6,650 years to reach Proxima Centauri. Even if a ship could approach light speed, Einstein’s relativity means time would pass much more slowly for its travellers than for those back home. Small effects have been measured — for example, astronaut Scott Kelly returned from a year aboard the International Space Station a few milliseconds younger than his identical twin — but interstellar voyages would amplify this. Any voyagers who returned could find their home world centuries older, making such travel a one‑way displacement in time for the visitors.
Second, the energy and physical hazards of interstellar flight are extreme. As velocity increases, so does the energy required to accelerate a craft; at light speed mass and energy requirements become effectively infinite under known physics. Even at sublight speeds, collisions with sparse interstellar particles convert into intense radiation and heat at high relative velocities, threatening equipment and life. Proposed faster‑than‑light concepts, such as theoretical warp‑drive models, face their own unresolved technical and astronomical energy challenges. Faced with these costs and risks, it is reasonable to ask why an advanced civilization would expend enormous resources to travel here when any material or knowledge they might seek could likely be obtained closer to home.
Third, Earth’s biosphere is the product of billions of years of co‑evolution and is chemically particular. Oxygen, produced by ancient cyanobacteria about 2.4 billion years ago, makes complex life possible for us but is highly reactive and potentially corrosive to organisms shaped by other chemistries. While protective suits could mitigate hostile environments, many reported sightings and accounts of so‑called visitors do not describe such equipment, raising compatibility questions.
That does not settle the question of life elsewhere. Astronomers have now catalogued thousands of exoplanets across thousands of star systems, and our galaxy contains on the order of 100 billion stars — many with planets that could, in principle, be habitable. Searches for intelligent signals, led by projects such as the SETI Institute and Breakthrough Listen, have not yet produced confirmed detections, but researchers stress that absence of evidence is not evidence of absence. As a mid‑20th century note in Nature observed: if we do not search, the chance of finding other intelligence is effectively zero. Continued observation and study remain the prudent path forward.
Carol Oliver, Professor in Science Communication and Astrobiology, UNSW Sydney.
Original Source: https://www.unsw.edu.au/newsroom/news/2026/06/aliens-might-exist-but-there-are-three-reasons-why-theyre-not-visiting-us
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Publish Date: 2026-06-15 07:29:00
