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Comment by ianai | Hacker News Reader

I fear that the “it’s never aliens” credo was taken to the pathological case. Nothing can be life so why look for it? Nothing can be life, so any really complicated scenario not involving life must be true, always.

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But they are looking for it. Science demands evidence for your claims. If x could be due to a, but also b, c, d, maybe e, you can't say x = a until you've proved that x ≠ b, c, d, e.

Conversely you can't say x != a until you've proven x = b or c, d, e. Which is GP's point if I understood correctly.

"However improbable", Sherlock Holmes is often brought up in cases like this...

That's contingent on eliminating the impossible.

the scope of which begs a complete understanding of the possible

That quote always rubs me the wrong way. To reach certainty through deduction you need a closed domain. Assume Holmes is 100% correct about the information he has, and he has three suspects, two of whom he ruled out. Does that mean the third did the deed? No. There may be information Holmes does not have and there is really no way for Holmes to know he does not have that information.

Holmes does appear to be operating under the closed-world assumption: https://en.wikipedia.org/wiki/Closed-world_assumption

The fastest way isn’t to eliminate the other possibilities, it’s to find a unique test for a that can’t be met by any of the others. Bear in mind that your list of alternative causes may be very long and each require large amounts of work to eliminate.

I too find it strange that multiple landers have been sent to mars since Viking, ostensibly looking for evidence of present or past life, and have yet have carried no tests for it. I find the best way to find something is to look for it.

The authors suggest testing for chiraliry in an LR test. Life creates certain “handed” organic molecules while purely chemical reactions do not. They said there’s already designs for flight ready tests. NASA just needs to include it in a mars mission. But they have no plans to do so.

This significantly increased my frustration with NASA.

I thought life on earth favoring a particular chirality was supposed to be primarily because of like common ancestors and stuff. If you flipped the chiralities of everything, would stuff no longer work? Or, I guess really my question is, would it be nearly impossible for life on another planet to use the opposite chirality instead?

The test is not for right chirality, it's for any preferred chirality. Non-life is half and half at random.

Ah, cool, thanks

Life on our planet does. Doesn't mean that's the case everywhere else. Or even anywhere else, for that matter.

In the "swapping spit" scenario, we the aliens and they are us.

If genetic material did travel in either direction, it would be easily verified.

There is life on Mars -- JPL just doesn't want to tell us. Follow this logic: 1) two planets in habitable zone - both spontaneously cause life; 2) then many or most habitable zone planets have life; 3) Of the trillions of stars in our galaxy, there must be multitudes that have hosted intelligent life; 4) we don't hear SETI signals; 5) that means SETI must have snuffed themselves out with some super-technology; 6) ergo, cannot tell the masses, because they will freak out knowing that we are all doomed, including all our offspring.

> they will freak out knowing that we are all doomed, including all our offspring

Um, sorry to break it to you but the horse has left the barn in regards to future prospects.

Things may get pretty shitty for them, but if I could wager on such a thing, I'd wager on the species surviving.

who would you collect from if you wagered against, and how would you take it with you?

One could say we are already collecting from our offspring.

Basically Pascal's wager:

https://en.m.wikipedia.org/wiki/Pascal%27s_wager

The wager is problematic for both sides. There's no end-point in which someone who was wagering for could collect.

We already know we’re all doomed. The sun bakes us in somewhere around 5 billion years.

I think the scuttlebutt is the sun gets increasingly brighter and strips off all the earths hydrogen in about a billion years.

Oh no my 401k retirement fund isn’t going to last that long

Earth will become inhabitable faster than that. The timeline at

https://en.wikipedia.org/wiki/Timeline_of_the_far_future

is thought provoking.

That’s more than enough time to colonize most of the galaxy.

I wonder if Type 3 civilizations might engulf their star in a Dyson Sphere to block out light and make it harder to find. A dark forest where the life-bearing trees aren’t even visible.

The thing about that is all the energy from a star is still being radiated, just in infared. So if this was true a IR telescope should see a star like object with no visible light but a large amount of infared emitted.

Apparently Dyson spheres can be undetectable with IR telescopes:

https://www.tillett.info/2016/08/03/carnot-efficient-dyson-s...

People have looked. There are some candidates that have not been ruled out, but are not particularly promising. Do a Google Scholar Search for "IRAS dyson spheres" and you'll get oodles of papers describing attempts, new places we might look (I recall one suggesting they might all be surrounding the galaxy's central blackhole), current theoretical limits of our ability to search, new methods we might use to find them, etc.

The biological plausible explanation is that there simply has not been enough time for other civilizations to form up. It took us 4 billion years to reach civilization from primordial goo. Apparently not many planets remain habitable that long. It does not matter if you have a trillion planets if they don't remain stable long enough.

In all the vastness of the universe, “we were the first” is a stupendously implausible hypothesis compared to “we were the only”.

If "we were the only" is true so is "we were the first" ...

However, there exists or has existed one planet with the first civilization ever.

And the odds that it’s us are astronomically even longer than the odds that I’m going to win the next Powerball, and I’m probably not even buying a ticket.

it's not even entirely a given that we are the first, as it's unlikely any evidence of a small tribe of sentient dino villagers for example would persist to the present day.

Like a petal on the flower, or an apple on the tree, it's likely that planets fruit at about the same time.

But on the universes timescale, a slight variance could still be thousands of years or more. So maybe there is life in some distant reaches of the universe, who are +/- a thousand years from our level of development. Their signals simply haven't reached us yet, or ours them.

Suggested reading: Rare Earth: Why Complex Life is Uncommon in the Universe by Peter D. Ward and Donald E. Brownlee. The basic premise is that complex life is incredibly rare, because only through a series of effectively chance events, did complex life happen on Earth.

Even if each of those events were actually inevitable, planet size, radiation received from host star, exact chemical makeup of atmosphere/oceans and any number of other variables could affect the time scale for a planet to fruit.

I did not imply at any point that we were the first, or only. Perhaps in our galaxy. I don't know if we could ever find out about civilizations in other galaxies.

There are a 100 billion galaxies. I'm ready to guess each has at least a few planets theoretically capable to sustain life for long enough.

It is also stupendously implausible that our civilization arrives at all in a mere 14 billion years, considered against the gazillions of years in the potentially infinite lifespan of the Universe. Yet here we are.

If it is difficult for civilizations to develop, then our existence is so implausible already that being the first is not such a leap.

It seems quite implausible that JPL would have sufficient confidence that things would play out as you say (everyone freaks out because everyone is convinced by this line of reasoning) to deny themselves a rather good opportunity to get people excited about space exploration.

Here's what I think:

1. ET life formed and vanished so quickly that they didn't even get to the stage where they generate electromagnetic signals.

2. ET life formed and got to generate EM waves, but:

- they're either too far from us that we haven't detected those waves yet;

- they only recently got to this stage and the signals they produce have not reached us yet;

- or both.

3. ET life formed way sooner than we did; figured out how to generate EM waves, and then vanished entirely. So, any signals of their civilization they must have sent out there have already reached earth, but before we began listening for such signals.

4. Then again, since there are practically infinite number of planets with habitable conditions for ET life, statistically speaking, we must have already received a signal from at least one of them.

Which leads me to this:

5. ET life doesn't exist, because the universe as we know it is most probably a simulation inside a computer and the computational resources can only render so many different objects at a time. (This is serious stuff, researchers have already proposed methods for verifying this: https://www.washington.edu/news/2012/12/10/do-we-live-in-a-c...).

Earth level EM waves are indistinguishable from background noise pretty quickly thanks to the inverse square law. And we've been reducing emissions, not increasing them, as we shift to cell networks rather than one to many broadcast networks of old.

It also depends on your definition of live.

The best broad test to look for life would be to look for an entropy source.

I think it's because when it is actually alien life the expectation is it will be obvious. If we are splitting hairs to find it we probably haven't found it yet.

the keyword here is expectation. that expectation may be misguided.

Obvious? A colony of fungus setting up a new home on your own foot isn't even necessarily obvious—humans are constantly surprised by what turns out to be terrestrial life, so it's completely unreasonable to expect extraterrestrial life to be obvious when we see it.

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