Hacker News Reader

Comment by changoplatanero | Hacker News Reader

It would be so exciting if they find life there

I'm glad they're careful not to oversell this finding, but it's a little discouraging how far we are from the phrase we want to hear:

"Mars has life"

"We've found past life on mars"

"Rover finds past life on mars"

"Rover finds hints of past life on mars"

"Rover detects hints of past life on mars"

"Rover detects carbon signature that hints of past life on mars"

"Rover detects carbon signature that may hint of past life on mars"

You would have to look for evidence of life in the first place if you wanted to find it. None of the rovers we have on Mars right now have the right instruments to do so. Exomars' Rosalnd Franklin will be the first.

https://solarsystem.nasa.gov/missions/viking-1/in-depth/

    Viking 1
    
    July 20, 1976: Lander touched down
    
    Scientific Instruments
    
    Lander
    1. Imaging System (2 facsimile cameras)
    2. Gas Chromatograph Mass Spectrometer (GCMS)
    3. Seismometer
    4. X-Ray Fluorescence Spectrometer
    5. Biological Laboratory
    6. Weather Instrument Package (Temperature, Pressure, Wind Velocity)
    7. Remote Sampler Arm

Not for me. Behind all those hedges is where the intrigue lies! I'd rather that than overselling a thrice-maybe as a positive.

>"Rover detects carbon signature that may hint of past life on mars"

If you expand the list to include all the geological stuff Spirit/Oportunity, Pathfinder and Viking found then slap a "you are here" on it we are much closer to the "earth" end of things than the "dead rock" end of things.

I hope they don't. It would be a very bad indicator for our future in the cosmos, making it far more likely that whatever great filter is out there, is in front of us still.

Not necessarily. Before the great filter, there's the jump to multi-cellular life. As far as we know, the symbioses with mitochondria bacteria only happened once, and is the progenesis of all multi-cellular life on earth.

So single-celled life may not be terribly uncommon throughout the cosmos.

> Before the great filter, there's the jump to multi-cellular life.

Well, the filter may exist prior to the jump to multi-cellular life. Finding early life on Mars would necessarily be bad because we would now be able to mostly eliminate that possibility, which means that the probability that the filter is ahead of us increases.

I disagree. While finding dead life on other planets decreases the probability of some filters, it also increases the probability of other filters.

For example, if we go to every planet in the solar system and see evidence of extinct multi-cellular life, but no sapient life, this would suggest that the filter is indeed behind us, and not in front of us.

I don't think this is right. It moves the filter forward from "no life" to "no intelligent life" (If we have a TON of examples – remember, we are also a data point. so even if we find 200 planets with dead multicellular life, we still have 1/200 making it to spacefaring — that's a huge % when extrapolated out to a galactic scale! It's a large enough % that I don't even find this to be a meaningful prior adjustment).

It also adds no information as to which, if any, filters are in front of us. How would "lot of dead fish" help us understand "do civilizations destroy themselves with nuclear weapons"?

I agree with the first part, but not the second. Agreed it would rule out some early filters. But for the second part, the ratio doesn't go to 1 in 200. That's not how the anthropic principle works. You're already assuming that the Earth is extraordinary oh, so you can't just put it in the data set. Instead you would look at 199 out of 199 planets where sapient life capable of making an observation failed to develop.

Agreed that it provides no data on future filters ahead of us

> Agreed that it provides no data on future filters ahead of us

This was my instinct, too, after reading both of your posts, but on reflection I think that it's unlikely to be no information.

If we instead found 199 examples of extinct complex life (say, fossilized rodent-like creatures), instead of extinct simple life, we all probably agree that this would increase the odds of the filter being in front of us.

Now, imagine gradually changing the example from extinct complex life (rodent-type creatures) and going down to extinct simple life. At what point in this thought experiment does it become "no data"?

I guess I agree that discovering extinct life is information about probabilistic filters in earths future. I But, it does have to be weighed against the newly observed data supporting filters humans have already past.

To take your example, as we keep finding rodent fossils, we become more confident that a filter exists between rat and rocket-men. As we go from 0 planets with rodent fossils to 1 trillion planets, the probability that this is the filter keeps going up.

That is to say, we are not only decreasing the chance of pre-rat filters, but simultaneously increasing the chance that the filter is in the rat stage.

Isn't that backwards? The great filter is meant to explain why we don't see extraterrestrial life, so finding it would be counterevidence for a great filter

It's correct. There is still a filter somewhere that explains the Fermi Paradox. So finding evidence of primordial life on Mars would just mean that the filter exists somewhere between that primordial life and somewhere ahead of us. That is bad, because it increases the probability that the filter is ahead of us by eliminating the possibility that the filter was behind that primordial life.

If we assume that the great filter is ahead of us, then we were already a better lower bound. If it's behind us, then who cares?

If it's at all possible that it's behind us (which I believe it is), then this finding would be bad, because it necessarily shifts probability density into our future. Probability density must sum to 1. So eliminating one large chunk of possibility will necessarily increase the odds that the filter is in our future.

Yes, thank you for fleshing out what I meant.

Unless, for example, we were to find Mars had and has single cellular life. That might increase the likelihood that the filter is at the single to multicellular phase by enough to offset the bad news that the filter is not the abiogenesis step.

> it necessarily shifts probability density into our future

why? if the filter is "move from unicellular to multicellular" it would have wiped out life on Mars but Earth somehow made it. It shows there's at least one step behind us which is "hard" (while showing there's another one which is "easy").

I think one thing to keep in mind is that we haven't been here for very long. And as a technological society that is able to be detected or detect something we have been here for something between 70 or 5 years or 0 years depending on the definition. So the great filter is something that hinders us to detect detectable civilizations. But we are at the moment not totally sure if we are already detectable.

So per definition the great filter has to be in front of us as long as we wouldn't be able to find ourselves.

"Dissolving the Fermi Paradox": https://arxiv.org/abs/1806.02404

>The expectation that the universe should be teeming with intelligent life is linked to models like the Drake equation, which suggest that even if the probability of intelligent life developing at a given site is small, the sheer multitude of possible sites should nonetheless yield a large number of potentially observable civilizations. We show that this conflict arises from the use of Drake-like equations, which implicitly assume certainty regarding highly uncertain parameters. We examine these parameters, incorporating models of chemical and genetic transitions on paths to the origin of life, and show that extant scientific knowledge corresponds to uncertainties that span multiple orders of magnitude. This makes a stark difference.

This paper seems to get posted in most Great Filter discussions now. I don't find it very convincing - or I'm not sure why it is worded so strongly. It seems ultimately like just another opinion piece dressed with a bit more math than the topic usually gets.

My statistics chops might just not be up to snuff, but the authors are ultimately just choosing their own numbers (probability distributions in this case) and plugging them in like everyone else.

We still don't know the values of those parameters. The Fermi paradox exists only given "optimistic" guesses for those parameters. The authors choose "pessimistic" distributions and declare the problem "dissolved".

Sandberg and Ord are based at the same institute as Bostrom who popularized the Great Filter, if that has any effect on your opinion of the piece. They tend to work on pretty wacky things mind you, I had a discussion with Sandberg on whole brain emulation once and Ord champions donating to fairly sci-fi sounding charitable organizations (including his own, the future of humanities institute).

The problem I personally have with the Fermi paradox is that it essentially works if you assume that every non-zero probability is one, and justify that with there being enough chances for life to get going that it's bound to happen. Except... there really isn't all that much slack.

Another point that I don't see addressed much is the possibility that interstellar travel may just simply be impossible: that building machines that can travel to other stars, let alone ones that are capable of hosting a colonization process, are just simply not within the realm of materials that can actually exist.

FTL travel may well be impossible but what could possibly make sub-light-speed interstellar travel impossible?

Only if it had evolved independently during this step. Which is not certain either because we know big asteroid impacts can transfer material to other planets.

But I think the whole Fermi Paradox is a bit chauvinistic. It's assuming all life is like us, and ending in a colonisation explosion. Like our way is the only possible way.

Maybe other aliens do manage to reach a balance with their environment instead of screwing it all up like we are doing? After all, never-ending growth is simply impossible. It always reminds me of Agent Smith's speech from the matrix :)

But we as humanity have a habit of defining things around us in our own terms. We thought earth had to be the centre of the universe. Perhaps here we're also wrong and most life is just not like us?

How do we know never-ending growth is impossible?

I don't think there's just one great filter.

I imagine there are various filters depending on the particular environment and circumstances.

Several are behind us already. Several are ahead.

The filter might also not be one in which a civilization goes extinct but one in which the civilization goes dark to any outside observers. What if the ultimate fate of any sufficiently sophisticated species is to harness their sun's energy to create and enter a pocket universe where the stars are still close enough together to travel between them at light speed?

This isn’t an original opinion, it’s taken from this paper:

https://www.nickbostrom.com/extraterrestrial.pdf

I hadn't seen this post, but I'm glad he agrees. It's not a hard opinion to reach independently when you work through the math.

And I believe Bostrom was just summarizing the Fermi Paradox

https://en.m.wikipedia.org/wiki/Fermi_paradox

it would be super ironic if it turned out earth life came from Mars or something :P

Beresheet Tardigrades floated over and are setting up camp to enact their revenge would be my bet.

Reply on news.ycombinator.com