1. Subscribersonhouse
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    15 Aug '15 22:39
    Famous phrase from Enrico Fermi, if there are aliens, where are they, why haven't we seen any sign of them?

    The SETI project seems to me to be doomed to failure but of course a negative result is still useful.

    Consider the expanding sphere of human activity in RF, say about 100 years or so of detectable RF from Earth. So that represents a wavefront 100 light years across where the leading edge is now about 100 light years from Earth. If we had radio telescopes on a planet 100 LY from Earth, we could detect our own radio waves.

    We see however, the reduced usage of RF for TV and communications. Now cell towers transmit maybe 100 watts aimed to the horizon and so not much of that gets out of the atmosphere so it looks like the next 100 years or so will have less and less RF energy sent into space and say 100 years from now, we all switch to IR instead of RF for everything.

    So now we will have a wavefront of about 200 light years in depth from beginning to end. So that wavefront flies through space and maybe reaches the other side of the galaxy in say 30,000 years. So in that time some alien develops radio telescopes but say they are too early by a couple thousand years, so our wavefront goes right by them undetected. Or the other scenario, 50,000 years later, a civilization develops radio telescopes, but now our signal has come and gone thousands of years earlier and in both cases, no detect.

    Here on Earth, we would have to be very lucky to come across a detectable RF signal from any civilization in the galaxy because they may have gone through the same technological development that we are undergoing right now, so THEIR signals have come and gone or we are too early by say 10,000 years, both cases, no detect.

    So That is my analysis of why we will most likely never detect an RF transmission from aliens in our galaxy or any other galaxy for that matter.
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    16 Aug '15 00:32
    There is a recent [ish] long post on Wait But Why on the Fermi Paradox which is kinda relevant
    [and quite interesting].

    http://waitbutwhy.com/2014/05/fermi-paradox.html

    One of the points it discusses is hat the search for extra-terrestrial life/intelligence can potentially
    tell us about the possibility [and location] of a 'great filter' that ends development of life/civilisations
    before they can become galaxy spanning mega civilisations.

    If it's behind us that's great, we're unique [or incredibly rare] in getting past it and can happily expand
    into the universe to our hearts content.

    If it's ahead of us then maybe we should be working out what it is before we reach it and become just another
    failure to pass it [and go extinct].


    Which seems to me to be kinda important information to have.
  3. Subscribersonhouse
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    16 Aug '15 02:59
    Originally posted by googlefudge
    There is a recent [ish] long post on Wait But Why on the Fermi Paradox which is kinda relevant
    [and quite interesting].

    http://waitbutwhy.com/2014/05/fermi-paradox.html

    One of the points it discusses is hat the search for extra-terrestrial life/intelligence can potentially
    tell us about the possibility [and location] of a 'great filter' ...[text shortened]... e to pass it [and go extinct].


    Which seems to me to be kinda important information to have.
    It would seem we would have to develop faster than light craft to physically find the remains of dead civilizations before we could figure out that conundrum. If civilizations are destined in general to only last 1000 years or so and maybe 1 million years max to extinction then we would be extremely hard pressed to ever find ANY evidence of such civilizations. Not impossible I suppose but very difficult indeed. Maybe in a few hundred years we can have such things as telescopes that use the gravitational focus effect of our sun as a lens a million kilometers wide or some such, I envisioned and did the math for just such a device but you have to be at the right place to do it, namely at least 80 billion kilometers on one side of the sun looking past the sun for your object at interstellar distances, probably first achieved at radio frequencies.
  4. Cape Town
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    16 Aug '15 07:43
    Originally posted by sonhouse
    So That is my analysis of why we will most likely never detect an RF transmission from aliens in our galaxy or any other galaxy for that matter.
    Your analysis seems to be flawed. You seem to assume that all aliens will develop exactly as we have - and exactly as you predict we will in the future. Why make that assumption?
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    16 Aug '15 12:12
    Originally posted by sonhouse
    It would seem we would have to develop faster than light craft to physically find the remains of dead civilizations before we could figure out that conundrum. If civilizations are destined in general to only last 1000 years or so and maybe 1 million years max to extinction then we would be extremely hard pressed to ever find ANY evidence of such civilizatio ...[text shortened]... the sun for your object at interstellar distances, probably first achieved at radio frequencies.
    Why are we assuming that advanced civilisations only last such a short time span?

    Also what do you mean by that?

    The Roman civilisation didn't last very long... But that's not because humans went extinct,
    that civilisation was replaced by others.

    Take this quote from the article:

    One hypothesis as to how galactic colonization could happen is by creating machinery that can travel to other planets, spend 500 years or so self-replicating using the raw materials on their new planet, and then send two replicas off to do the same thing. Even without traveling anywhere near the speed of light, this process would colonize the whole galaxy in 3.75 million years, a relative blink of an eye when talking in the scale of billions of years:


    Which I view as being very conservative.

    It is evidently possible for non-intelligent species to survive tens or hundreds of millions of years.

    I don't see any inherent reason why an intelligent species [and it's presumably at least as intelligent
    offspring] can't last at least that long, if not longer.

    We are already potentially looking at developing the technology to become biologically immortal and
    be able to design and build improved bodies and increase our intellectual abilities.

    We also have the rudiments of the technology needed to sustain ourselves and our technology for
    hundreds of millions of years with solar and nuclear power.


    Assuming that there isn't some hostile alien species that likes to wipe out any and all competition.
    The only serious threats to our civilisations lasting million of years are a natural disaster wiping us
    out before we get off the Earth. Unfriendly AI. Or we wipe ourselves out in a war of some kind.

    Given that I don't currently see any of those as inevitable, I don't believe that such short half-lives for
    galactic civilisations are warranted.
  6. Subscribersonhouse
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    16 Aug '15 13:46
    Originally posted by googlefudge
    Why are we assuming that advanced civilisations only last such a short time span?

    Also what do you mean by that?

    The Roman civilisation didn't last very long... But that's not because humans went extinct,
    that civilisation was replaced by others.

    Take this quote from the article:

    [quote]One hypothesis as to how galactic colonization could h ...[text shortened]... evitable, I don't believe that such short half-lives for
    galactic civilisations are warranted.
    But we don't see evidence for those robots or anything else. It seems to me if it could happen it will happen. It didn't happen so maybe that is because it can't happen for some reason or other. Maybe there is a limit as to how well robots can self reproduce or something. My analysis is certainly flawed, but we ARE undergoing a transformation in technology and it seems to me the same thing would happen to any intelligent civilization valuing technological growth.

    It seems clear to me a sentient but low tech society would first have to master fire, first to use it and then to make it anytime. So it seems any primitive society, I don't care if they look like cats or crabs, they would still have to go from chemical energy to nuclear energy at some point in their development. You aren't going to find a society going directly from just using fire found in a forest to nuclear energy in one step.

    You need to develop metallurgy first and that can be easily done with chemical energy.

    That is assuming a life form similar to ours in that they would have an oxygenated atmosphere. If they didn't, they might never even advance to the fire stage.
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    16 Aug '15 14:21
    Originally posted by sonhouse
    But we don't see evidence for those robots or anything else. It seems to me if it could happen it will happen. It didn't happen so maybe that is because it can't happen for some reason or other. Maybe there is a limit as to how well robots can self reproduce or something. My analysis is certainly flawed, but we ARE undergoing a transformation in technology ...[text shortened]... to me the same thing would happen to any intelligent civilization valuing technological growth.
    Well this depends on where the 'great filter' is.

    You are basically assuming that the filter is ahead of us, and that any and all civilisations
    that reach our stage get wiped out by this filter.

    But what if the filter is behind us?

    In that case, we might be the first [perhaps only] species to get to this point.

    Perhaps the 'great filter' is forming life in the first place.

    OR

    Perhaps the 'great filter' is developing life more complex than bacteria.
    It took an incredibly unlikely set of circumstances to allow eukaryote complex life forms to
    occur, and it took something like 3.5 billion years to happen on the Earth.

    Perhaps that step is so rare that it has either never happened before, or where it did happen
    some other disaster [like major comet strike, near-by supernova, runaway climate change,
    atmosphere loss, etc] intervened before intelligent spacefaring life could evolve.


    In which case all other life in the galaxy would likely be like bacteria in form.

    However if we discover that that both life and complex life is common, then it becomes much much harder
    to find a credible 'great filter' that lies in our past.

    At which point we do have questions as to what the filter in our future might be and how we can get past it.
  8. Cape Town
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    16 Aug '15 17:34
    Originally posted by sonhouse
    It seems to me if it could happen it will happen.
    Which is a totally irrational position to hold.

    If on average, one planet per galaxy develops life forms that spread, then we would have a reasonable chance of not encountering one. There could still be plenty of civilizations out there that do not spread but do transmit something detectable by SETI.
  9. Subscribersonhouse
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    16 Aug '15 19:55
    Originally posted by twhitehead
    Which is a totally irrational position to hold.

    If on average, one planet per galaxy develops life forms that spread, then we would have a reasonable chance of not encountering one. There could still be plenty of civilizations out there that do not spread but do transmit something detectable by SETI.
    What if WE are the aliens, getting ready to enter a phase of our existence where such robotic probes self reproduce into the galaxy and we are the ones who do it but say 1000 years from now?

    RF wise, there have only been two possible detection's that have shown up on anything from radio telescopes and those were one off signals so there would be no way of knowing if they were just our own signals bouncing off the moon or some such.
  10. Cape Town
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    16 Aug '15 20:49
    Originally posted by sonhouse
    RF wise, there have only been two possible detection's that have shown up on anything from radio telescopes and those were one off signals so there would be no way of knowing if they were just our own signals bouncing off the moon or some such.
    Yes, but the reality is that we haven't looked very hard. There could easily be thousands of civilizations in the galaxy transmitting as much rf as we do now and we would not have detected them. There could also be thousands transmitting in different from us in different frequencies or different amounts. We will not know until we look. It is ridiculous to try and make conclusions without looking and it is illogical to make conclusions beyond statistical ones based on our very limited results so far.
    As for life (and not intelligent life) we haven't even ruled it out on a single solar system body - and we have hardly taken more than a cursory look at most solar system bodies.
  11. Subscribersonhouse
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    16 Aug '15 21:26
    Originally posted by twhitehead
    Yes, but the reality is that we haven't looked very hard. There could easily be thousands of civilizations in the galaxy transmitting as much rf as we do now and we would not have detected them. There could also be thousands transmitting in different from us in different frequencies or different amounts. We will not know until we look. It is ridiculous to ...[text shortened]... lar system body - and we have hardly taken more than a cursory look at most solar system bodies.
    Unless our technology is developed to a degree we can only now dream about, we will ALWAYS be in the position of just doing a cursory search of stars, there are just too many of them, like what, a million or so within just a couple hundred light years? The way it works now, you have to spend some time on a single star to build up detection of photons of various frequencies, you can't just go, Ok, let's spend one second on each star, it doesn't work like that.
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    17 Aug '15 02:07
    Originally posted by sonhouse
    Unless our technology is developed to a degree we can only now dream about, we will ALWAYS be in the position of just doing a cursory search of stars, there are just too many of them, like what, a million or so within just a couple hundred light years? The way it works now, you have to spend some time on a single star to build up detection of photons of var ...[text shortened]... quencies, you can't just go, Ok, let's spend one second on each star, it doesn't work like that.
    Well given that we have telescopes at the moment simultaneously viewing hundreds of thousands of stars....
  13. Cape Town
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    17 Aug '15 05:59
    Originally posted by sonhouse
    Unless our technology is developed to a degree we can only now dream about, we will ALWAYS be in the position of just doing a cursory search of stars, there are just too many of them, like what, a million or so within just a couple hundred light years? The way it works now, you have to spend some time on a single star to build up detection of photons of var ...[text shortened]... quencies, you can't just go, Ok, let's spend one second on each star, it doesn't work like that.
    You only need a few pixels on a ccd to monitor a star at a given frequency. As noted by googlefudge Kepler continuously monitors the brightness of 145,000 stars and has been very successful at finding planets.
    It will be a long time before we can really look at the spectra of large numbers of planets, but it is not so much the quantity as the resolution that is the issue.
  14. Subscribersonhouse
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    17 Aug '15 11:33
    Originally posted by twhitehead
    You only need a few pixels on a ccd to monitor a star at a given frequency. As noted by googlefudge Kepler continuously monitors the brightness of 145,000 stars and has been very successful at finding planets.
    It will be a long time before we can really look at the spectra of large numbers of planets, but it is not so much the quantity as the resolution that is the issue.
    That is optical measurements. I am talking about RF detection, detecting radio waves from technologically advanced civilizations around other stars. Those signals are very weak, you have to have your radio telescope on a subject for a significant length of time, the longer you look, the more photons you collect, photons in this case could be a wavelength of meters or millimeters, they are still photons.
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    19 Aug '15 09:02
    Of course there are life in our galaxy, in my opinion. I mean outside our own planets, that is.

    But what is the probability that life evolves into a technological state where we, with todays technology' can detect them with radio waves?

    Our planet is 4,600 million of years. Only the last 100 years or so we have been using radio waves for communications. How many years further will we be using radio based technology? That is a matter of optimism or pessimism about our technological future and it is an interesting question. I say that 100 or even 1,000 years out of 4,600 million of years is a very tiny fraction.

    I would say that civilisations in our galaxy is very rare. The probability that there are anymore than ours today is pretty low, in my opinions. The L parameter in Drake's famous formula is very low. Intelligence have to survive its infance in order to be old enough to perform space travels.

    Do I share this opinions with others? Comments?
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