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Comment by macu | Hacker News Reader

taking another of many possible perspectives, here is a strong case for hoping that we don't find life on Mars: http://www.nickbostrom.com/extraterrestrial.pdf

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"There may be no signals from space, yet those with their antennas tuned to more anthropomorphic wavelengths are sure to pick up a buzz of social signaling in people’s attitudes towards the search for extraterrestrial beings. Such social background noise might in fact be one of the main obstacles to intellectual progress on many big picture topics."

I first apologize for being an obstacle to intellectual progress.

I then pose the question:

Is it impossible for Venus to have harboured some form of life (sentient or not) involved in a carbon cycle not unlike ours, hundreds of billion years ago, except (or perhaps similarly...) due to one of the "Great Filter" probability barriers, the life on the planet eventually produced a runaway greenhouse effect, which leads to the current state of Venus today (and over hundreds of millions of years, wiping all obvious traces of life)?

Summary: Author hopes we don't find life on Mars because if it's dead that provides an ill omen for the human race. He thinks if life on Mars wasn't sustainable then he repeats the whole argument that there must be some reason why advanced civilizations can't manage to get off the original rock they're assigned to and that's why we haven't seen any other intelligent life.

Which in itself is a bit weird. Mars and Earth formed in the same solar system, from an orbital disk around the same sun. Similar conditions and building blocks.

Surely whatever improbability would be diminished because of this?

The probabilistic evidence is a bit more indirect, and depends on anthropics:

Since we don't see galaxy-spanning, highly advanced civilizations, there seems to be some combination of factors that prevents planet-bound dirt from turning into them. If those factors are primarily after our stage of development between dirt and galactic civilization, that's Very Bad News, because we shouldn't expect to get extraordinarily lucky. If those factors are primarily before our stage of development, that's reasonably good news, because we've already made it past the hard part.

Seeing bacteria isn't as bad as seeing the ruins of a civilization just past our stage of development. But it does move the probability-mass forward more than if we just found dirt.

There's so many things that can go wrong, during the period needed for advanced intelligent life to evolve. Add to that the inherent difficulty of moving between solar systems. Space is vast, and we're not really making that much noise. I don't see a big paradox here?

Nick Bostrom's reasoning is more complex, but yes, you nailed the summary perfectly. Even shorter: The more complex life on Mars we are going to find, the more we as human race are doomed, says Bostrom. Because as Bostrom wrote in TimGebhardt words: "there must be some reason why advanced civilizations can't manage to get off the original rock they're assigned to" and if there is life on Mars, it could be everywhere in the universe. Nick Bostrom's reasoning: If life could start everywhere else, why haven't we detected it, yet. I think Nick Bostrom should have focused more on the time and randomness factor. Maybe there was life in our galaxy, but they visited us before humans have lived. Or we have been visited (think peruvian desert drawings), but before we as human race were as advanced as we are today and they left our boring planet to visit another galaxy. There are probably more than 170 billion (1.7 × 1011) galaxies...

If the Orion project in the 1960s hadn't been stopped, we might have viable interplanetary colonies already. Also, if NASA hadn't poured most money into the shuttle (and hence had a reason to kill competing projects, for job security) the space exploration/colonization would be much further along.

Even now, we might be less than 50 years from independent colonies, if lower costs for space launch finally "take off" with Musk.

This implies that if there is some common reason (e.g. a physics experiment with unexpected outcome) that exterminates budding civilizations, it ought to have already happened (and we were lucky) -- or it is something big enough to blast a whole solar system.

Edit: It would be interesting with percentage chance evaluation of the possibility that the Shuttle project doomed humanity to extinction...?

It may be a slight cause for concern if we find extinct life on Mars, but for it to be too much of a worry, you have to make quite a lot of assumptions. There are plenty of other explanations for the Fermi paradox that don't include a great filter, and this argument only applies if the life we found was dead rather than possibly still present microbiological life. And it's also assuming the life here and on Mars wasn't seeded from the same place, but Earth was the only hospitable planet.

My view is that it's likely/possible the universe is has quite a lot of life. However, since all evidence suggests the universe had a beginning, between abiogenesis, evolution, and the universe/galaxy/planet being in a state hospitable to life, it might always take a very long time to get the state we're in now, just as it did on this planet. It's quite possible that there are billions of planets with life in some stage of evolution, but few of them are significantly more advanced than our planet's life. Even if there are a smaller number of super-advanced civilisations, they may only have been broadcasting for a few hundred thousand years, and we may not be in range of that, or pointing our antennae at the right place to pick up the very weak signals. Even if they have discovered FTL travel, it would conceivably still take an extremely long time for them to visit every planet in the universe. Even if they have visited Earth in our historically documented timeline, they may not have been interested enough in what they saw to stop by and have a chat. Worse, if they have discovered FTL, they're probably not using radio broadcasts any more.

But that doesn't mean that life is uncommon, or even that there isn't some intergalactic federation of civilisations, just that any given civilisation being significant enough to notice or be noticed happens rarely. I would be far more worried about extra-terrestrials being hostile than non-existent (see Stephen Hawking's views on the matter).

Really, most of these sort of arguments feel quite similar to a bunch of humans sitting around a hundred thousand years ago, discussing with their tribe that they are probably the only humans on the planet, since no other more advanced cultures have communicated with them yet. Even though they haven't discovered any efficient means of transport to actually explore the Earth yet...

Interesting, but signs of (extinct) life on mars could have been seeded from earth.

Bit of a tangent, but does anyone know of a service where I can copy in a pdf url and get a rough approximation of the content as plain text html?

Here we go: http://viewtext.org/article?url=http%3A%2F%2Fwww.nickbostrom...

I'm really paranoid about loading unfamiliar websites up (I've got a version of Chrome with js and plugins disabled that I use for random links), and pdfs are still a bit of a concern as an attack vector. It looks like this viewtext.org will come in handy.

</tangent>

Not a URL but arguably more useful:

    $ curl http://www.nickbostrom.com/extraterrestrial.pdf | pdftotext - -

Don't forget the two dashes, as it doesn't default to reading stdin, and doesn't default to writing to stdout when instructed to read from stdin.

Also, pdftotext is part of poppler in Arch and poppler-utils in Debian.

Embarrassingly enough, I'm a Python dev on Win7 - now you know why I'm so paranoid. :)

Thanks anyway, though.

Then, PDFMiner comes to mind. Pure python, so slower but no C/native dependencies.

The instructions work fine with cygwin on windows btw, pdftotext is in the poppler package.

EDIT: Reading comprehension problem -- you wanted clean HTML. I thought you meant you wanted an HTML5 viewer.

  - - -

This is nice:

https://docs.google.com/viewer

Example using this PDF:

https://docs.google.com/viewer?url=http://www.nickbostrom.co...

Clean, light, and doesn't require a GA login.

Usually the vacuum's functionality of scribd is used, but it seems to not work at this moment http://www.scribd.com/vacuum?url=http://www.nickbostrom.com/...

I paste the complete url into Google search, then hit "Quick View" on the first result.

Damn, I have no time reading his entire article right now, but it looks very interesting.

seems a leap to treat life on Mars as totally independent of life on Earth.

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