"Strong" means that the evidence is reported as credible by mainstream press and/or is accepted by at least a large minority of relevant scientists (e.g. 1 in 3).
"Evidence" can be direct (e.g. the physical recovery of alien bacteria from Mars) or indirect (e.g. telescopic observations of technosignatures). Evidence can also be of the past existence of aliens, such as fossils.
"Aliens" are defined liberally. This market counts anything that is arguably non-earth-originating life as aliens. This includes both intelligent and non-intelligent beings, non-carbon-based biology, and things, such as viruses, for which there is controversy over their status as life.
If there is uncertainty in applying the resolution criteria, I will resolve the market using reasonable judgement.
Related questions
I want to believe 👽🛸 .. scary tho
We've been seriously searching for aliens since the 1960s and haven't found anything yet after 63 years, so that puts the "base rate" at about 1,6% per year. With 7 years until 2030 that puts the "base rate" at 11.2%.
Robin Hanson who claims to be an expert on the "prior probability of aliens" (based on his grabby aliens model) claims that the chance that their are aliens nearby are 1/1000 (although I can't remember exactly what he meant).
The UAP sightings while evidence for aliens, doesn't seem like enough evidence to warrant more than a 5:4 likelihood ratio.
All things considered the probability we spot aliens is well below 20%
@moyamo bet YES as a hedge against species destruction. Everyone is focused on the wrong x-risk boogeyman. I want to believe 👾
@shorty I don't get it.
1. You bet YES.
Aliens arrive.
You get internet points.
The aliens terraform our atmosphere to suit them, killing all earth life.
???
Profit???
@moyamo Most of those years since the 1960s were spent without technology like the JWST capable of gathering spectroscopic data from exoplanet atmospheres. We weren't even capable of detecting exoplanets at all until the 90s. Any calculation that assumes our technical capabilities have been constant since the 1960s is going to mislead you.
@whenhaveiever True, but our past and future observations aren't really dependent, since all accumulated negative evidence is (some) evidence that our future observations will also turn out negative. The amount of this evidence does of course depend on how likely it is we'd actually find evidence of aliens assuming said evidence/aliens exist, which in turn depends on our level of technology/current methods of observation. That's hard to sus out, as is the rate of tech improvement and everything else pertinent to this question, but it's not obvious to me the straight base rate calculation is an underestimate rather than an overestimate.
And other methods such as grabby aliens seem to indicate the chances are even lower. Since I'm not aware of any obvious tremendous tech advances relevant to searching for aliens coming in the next decade-ish, and grabby aliens style reasoning at minimum indicates we're almost certainly not about to meet an interstellar civilization, the bulk of the likelihood seems like it should come from simply continued observations of distant exo-planets. That and discovering non-carbon based life in our solar system, but, you know, that seems almost irrelevant.
I would vote no a bit stronger on this, but I just made my account today and I'm not yet sure I want to lock up that much mana until 2030.
@DavidHiggs (good news! Manifold gives you 2% of all your committed mana back daily by taking a loan against your investments, which you pay back when the market resolves or you exit your position. so your mana won't be locked up here forever, but it's still a good idea to not put all your mana into one basket, especially a long term one)
@DavidHiggs I agree that the bulk of the likelihood comes from observation of exoplanets (though a significant part also comes from the growing acceptability of discussing aliens as a reasonable hypothesis), and in this area JWST really is a game-changer. For the first time, we are getting spectrographic data on the atmospheric composition of Earth-sized exoplanets. There are entire categories of biosignatures and technosignatures that we were incapable of detecting up until last year that are now within our reach.
The grabby aliens hypothesis as I understand it supports the null finding from previous SETI, since a communicative interstellar civilization would have to be grabby and so would already be here. But it's silent on the existence of the same kind of life Earth has—we're not yet grabby, but an alien JWST could've detected our oxygen, methane, etc at any time in the last few billion years.
@whenhaveiever I think the Grabby Alien model does account for non-grabby civilizations and Robin Hanson's estimate was that the model predicts a 1/1000 chance that there is a nearby non-grabby alien civilization (or something like that). I can't remember if the 1/1000 included "alien bacteria" or only "space-faring non-grabby aliens"