What are the odds of an alien invasion or first contact in your lifetime?
Evidence quality 4.5/5
Eight-dimension review score against the quality rubric . Each dimension scored 1–5.
- D1 Source grounding
- 5/5
- D2 Source authority
- 5/5
- D3 Arithmetic
- 4/5
- D4 Uncertainty
- 4/5
- D5 Scope
- 4/5
- D6 Prose
- 5/5
- D7 Perception honesty
- 4/5
- D8 Caveat completeness
- 5/5
Lifetime probability · lifetime, US adult
1 in 169,491,525
0.0000006% lifetime chance
range 1 in 10,000,000,000 to 1 in 1,000,000
≈ As likely as
Perceived
Alien invasion anxiety occupies a unique slot in the risk landscape: it is simultaneously taken very seriously by a meaningful fraction of the population and treated as a punchline by another. A 2021 Pew Research survey found that 65% of Americans believe intelligent life exists on other planets, and 51% say UFO sightings reported by military personnel are likely evidence of extraterrestrial life. Hollywood has spent decades training the public to think of first contact in dramatic terms — invasion, abduction, existential threat — rather than the more prosaic possibility of detecting a radio signal from a civilisation that may have died millions of years ago. The perceived probability is driven by cultural narrative, not by any evidence of contact.
Rough estimate: A majority of Americans believe intelligent alien life exists; a substantial minority considers contact plausible within their lifetime
Source: editorial intuition, not polled
Actual
~38% ex ante probability of zero other civilisations in the observable universe (Sandberg, Drexler & Ord 2018)
Earth, any detectable alien contact
Show derivation
This is necessarily speculative. Sandberg, Drexler, and Ord (2018) showed that when Drake-equation parameters are treated as distributions reflecting genuine scientific uncertainty rather than point estimates, there is a ~38% ex ante probability that humanity is alone in the observable universe — and a >50% probability that we are alone in the Milky Way. If we take the complementary probability (~62% chance of at least one other civilisation in the observable universe) and discount by the probability of overlap in time, spatial proximity within detection range, and mutual technological compatibility, the conditional probability of detectable contact within a single human lifetime drops to a number that is essentially indistinguishable from zero. The headline figure of ~1 in 170 million is a placeholder (native rate of 1/10 billion per year × 59 years ≈ 5.9e-9) that reflects the Sandberg et al. framing: not impossible, but far below any risk that merits practical concern. The uncertainty band is deliberately wide because the underlying parameters span dozens of orders of magnitude.
Caveats: This entry is inherently speculative. The normalised probability is a placeholde…
This entry is inherently speculative. The normalised probability is a placeholder derived from the Sandberg et al. 2018 framework, not an empirically measured rate. The uncertainty band spans four orders of magnitude because the underlying parameters (especially abiogenesis probability and civilisation longevity) are unconstrained by data. The entry treats "first contact" broadly — including detection of a radio signal, not only physical encounter or invasion. Even under optimistic Drake-equation parameterisations, the probability of contact within a single human lifetime is extremely low because of the vast distances and time scales involved. The entry is included as a calibration anchor: it places alien contact on the same probability axis as other risks so readers can see where it sits relative to things they actually worry about.
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Other risks with roughly the same likelihood — useful for calibration.
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Pick challenger
The question of extraterrestrial contact is unique in this catalogue because the base rate is not merely uncertain — it is epistemically unconstrained. The Drake equation, proposed by Frank Drake in 1961, was designed as a framework for estimating the number of detectable civilisations in the Milky Way, but its output is dominated by terms that no observation has yet measured: the probability of abiogenesis on a habitable planet, the probability that life evolves to intelligence, and the longevity of technological civilisations. Plug in optimistic values and you get millions of civilisations; plug in pessimistic ones and you get a number well below one. The equation organises ignorance more than it resolves it.
Sandberg, Drexler, and Ord (2018) addressed this directly by treating each Drake parameter as a probability distribution reflecting genuine scientific uncertainty rather than a point estimate. The result was striking: when the uncertainties are propagated honestly, there is a roughly 38% ex ante probability that humanity is alone in the observable universe, and a greater than 50% probability that we are alone in the Milky Way. This does not prove we are alone — it proves that “we should expect the universe to be teeming with life” was never a justified conclusion from the available evidence. The Fermi Paradox dissolves not because we have found the answer, but because the premise (that contact should be expected) was built on the false precision of point estimates applied to quantities that span dozens of orders of magnitude.
Even under the most generous parameterisations, the probability of detectable contact within a single human lifetime is vanishingly small. The distances are too large, the time scales too long, and the mutual-detection window too narrow for contact to be anything other than spectacularly unlikely on a per-lifetime basis. NASA’s exoplanet surveys have usefully constrained one piece of the puzzle — roughly 10-50% of Sun-like stars have rocky planets in the habitable zone — but the origin-of-life and civilisation-longevity terms remain as uncertain as they were in 1961. The entry sits near the bottom of the Likelier probability axis, several orders of magnitude below asteroid-impact death and in the same neighbourhood as a single-ticket lottery jackpot. It is included not because it is a practical risk, but because it is a useful calibration point for the kind of fear that feels large precisely because the brain has no data to anchor it to.
Claim ledger
Every number below is what each source reported, with the verbatim quote we relied on and how we arrived at our figure. Click any link to verify directly.
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[1] arXiv / Sandberg A, Drexler E, Ord T — Dissolving the Fermi Paradox
Dissolving the Fermi Paradox- Statistic
When Drake-equation parameters are treated as probability distributions, there is a ~38% probability of zero other civilisations in the observable universe and >50% in the Milky Way alone- Excerpt
“"We find a substantial ex ante probability of there being no other intelligent life in our observable universe, and thus that there should be little surprise when we fail to detect any signs of it." ”
- Source data from
- 2018-06-06
- Accessed
- 2026-04-18 · archived copy
- Calculation
- Sandberg, Drexler, and Ord (2018) is the most rigorous probabilistic treatment of the Drake equation in the literature. Rather than plugging in point estimates for each parameter (which produces the classic "there should be millions of civilisations" result), they used probability distributions reflecting actual scientific uncertainty for each factor — especially the probability of abiogenesis and the transition from simple to complex life. The resulting distribution for N (number of civilisations) spans many orders of magnitude and places substantial probability mass at N=0 or N=1. This is the basis for the headline: the best available probabilistic analysis suggests we may well be alone, which makes the probability of contact in any given lifetime vanishingly small.
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[2] NASA Science — Are We Alone in the Universe? Revisiting the Drake Equation
Are We Alone in the Universe? Revisiting the Drake Equation- Statistic
NASA overview of the Drake equation notes that modern exoplanet surveys have constrained some parameters but the origin-of-life and civilisation-longevity terms remain uncertain by many orders of magnitude- Excerpt
“"While astronomers have made progress quantifying some of the Drake equation's factors, the most important terms — such as how often life originates and how long civilisations last — remain deeply uncertain." ”
- Source data from
- 2024-06-01
- Accessed
- 2026-04-18 · archived copy
- Calculation
- NASA's overview provides the institutional context for why the Drake equation does not yield a useful point estimate. The Kepler and TESS missions have constrained the fraction of stars with Earth-like planets (now estimated at 0.1-0.5), but the abiogenesis and intelligence-evolution terms remain unconstrained by data. This confirms the Sandberg et al. framing: the uncertainty is not merely large, it is epistemically fundamental. Used here as an authoritative secondary source confirming that no scientific consensus exists on the probability of extraterrestrial contact.
- Independence
- NASA editorial overview; independent of the Sandberg et al. probabilistic analysis and the SETI Institute's operational search programme.
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[3] SETI Institute — Drake Equation
Drake Equation- Statistic
Frank Drake's original 1961 estimate yielded N=10 civilisations in the Milky Way; modern estimates range from <1 to millions depending on parameter choices- Excerpt
“"It is impossible to do anything more than guess at the probable longevity of other advanced civilisations." ”
- Source data from
- 2024-01-01
- Accessed
- 2026-04-18 · archived copy
- Calculation
- The SETI Institute — the organisation most invested in finding extraterrestrial intelligence — acknowledges that the Drake equation's output is dominated by the civilisation-longevity term (L), which is completely unconstrained by data. Drake's original 1961 workshop estimated N=10 with L=10,000 years, but L could be 100 years (civilisations destroy themselves quickly) or 10 million years (they do not). The SETI Institute's own assessment is that the equation is a framework for organising ignorance, not a tool for generating a reliable number.
- Independence
- The SETI Institute is the primary non-governmental organisation conducting extraterrestrial intelligence searches; independent of the Oxford/FHI group (Sandberg et al.) and NASA.