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It's about signal and noise. Let's say there is a civilization out there, and we know about each other and want to talk. We point a big parabolic antenna at eac

It's about signal and noise. Let's say there is a civilization out there, and we know about each other and want to talk. We point a big parabolic antenna at each other and start exchanging radio massages. That's what we are doing with Voyager right now, we point some high-gain antennas at each other and talk. At the rate of 7.2 kb/s [1], or one quarter of the bandwidth of the old dialup connections. But Voyager is close, stars are far. The closest star is about 2000 times farther than Voyager 1. Radio waves decay with the square of the distance, so if a Voyager-size antenna were to transmit towards us from 2000 times farther away, we'd get a signal 4 million times weaker. So, our friends out there need a much bigger antenna than the one on the Voyager, and we need them to point it straight at us, and we need them to blast a mighty strong radio signal towards us. We should also point a bigger antenna at them (the one we point at Voyager is 70 meter wide, not really a toy). Somehow between their bigger antenna and our bigger antenna, we need to overcome the 4 million decay factor. If our friends are 10 times farther away from us than Proxima Centauri, then we need to overcome another factor of 100. But, our friends out there don't know about us, and they don't set up a mighty large antenna and align it perfectly in our direction. They simply chatter locally using radio waves, in many cases, their antennas are pointing towards their intended receivers, and not randomly towards some exoplanet far far away (the Earth). SETI never had a chance to find anything. [1] https://voyager.jpl.nasa.gov/mission/spacecraft/instruments/hga/ https://voyager.jpl.nasa.gov/mission/spacecraft/instruments/...

baxtr 6y ago
Yes, I agree. Just note, that this is assuming however, that no alien civilization has developed any vessels that would bring them closer to use, e.g. in our solar system so we could detect their signals
- VBprogrammer 6y ago
  Even the focus on on radio is potentially misguided. Perhaps there are alien species who's home planet is under some heavy fog so they have evolved to see the reflection of radio waves, to then go bouncing high power radio signals around could potentially blind themselves so they have evolved some other means of distant communications. That's just one failure scenario, if you took a Wifi signal and could somehow transport it back in time 100 years and blast it out at 1000 times the normal energy how long would it take past us to notice?
  - dTal 6y ago
    I think even 100 years ago, a kilowatt microwave transmitter would probably draw attention to itself by the way that eggs explode and cups of water boil when near it.
    - nradov 6y ago
      You would have to stand right next to a 1kw microwave transmitter to notice any heating effects. That wouldn't help you locate it at any distance.
    - VBprogrammer 6y ago
      Fair point. Call it 60w or even 1w if that feels better. It's still many orders of magnitude over what you would be receiving across space from another solar system. Also, for mild amusement, your comment reminded me of this video https://www.youtube.com/watch?v=b9UO9tn4MpI https://www.youtube.com/watch?v=b9UO9tn4MpI
deleted 6y ago
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CryptoPunk 6y ago
The more significant 'silence' is the fact that every star in the Milky Way galaxy has not already been colonized and turned into a Dyson sphere. Species with language and toolmaking capabilities seemingly grow in technological sophistication at an exponential rate, so on the geological timescale, will quickly acquire space flight, grow to populations of trillions, harness the resources of their star system, then move onto settling a new star, and so on.
- bena 6y ago
  Why do you believe that? You're making the assumption that the problems involved with prolonged space travel are solvable with the time and resources we have here. It could not be. It could be too expensive to colonize beyond the immediate area. If even the immediate area can be colonized. There's also the assumption that there's going to be a good reason to make a non-returnable investment. Because, at some point, that's what it is. The speed of light is a limit we have not even come close to exceeding, much less approaching. And even if we do, and the people on the ship, time dilation, yadda, yadda. It does not matter. The people on Earth will still experience time normally. It taking the ship no time at all does not matter if it takes 1000 years on Earth. Or even 50 years. The return has to be phenomenal or the cost negligible.
  - CryptoPunk 6y ago
    I assume the cost of settling other stars would become negligible at some point. If our solar system becomes a Dyson Sphere, and we have a population of thousands of trillions of people, I can't imagine how launching laser propulsion spacecraft that can travel at 0.2c toward other stars wouldn't be easily within reach of any moderately wealthy coalition of space enthusiasts. You're right though. I haven't actually done a careful estimate of the resources required vs the resources available to a Type II civilization. If the former is significant relative to the latter, and there is no Return that can motivate that magnitude of an investment with the type of investment structures that will evolve on a solar-system-wide economy - where investment time horizons have no need to be extraordinarily long - then maybe interstellar colonization is not inevitable.

baxtr 6y ago

Yes, I agree. Just note, that this is assuming however, that no alien civilization has developed any vessels that would bring them closer to use, e.g. in our solar system so we could detect their signals

VBprogrammer 6y ago
Even the focus on on radio is potentially misguided. Perhaps there are alien species who's home planet is under some heavy fog so they have evolved to see the reflection of radio waves, to then go bouncing high power radio signals around could potentially blind themselves so they have evolved some other means of distant communications. That's just one failure scenario, if you took a Wifi signal and could somehow transport it back in time 100 years and blast it out at 1000 times the normal energy how long would it take past us to notice?
- dTal 6y ago
  I think even 100 years ago, a kilowatt microwave transmitter would probably draw attention to itself by the way that eggs explode and cups of water boil when near it.
  - nradov 6y ago
    You would have to stand right next to a 1kw microwave transmitter to notice any heating effects. That wouldn't help you locate it at any distance.
  - VBprogrammer 6y ago
    Fair point. Call it 60w or even 1w if that feels better. It's still many orders of magnitude over what you would be receiving across space from another solar system. Also, for mild amusement, your comment reminded me of this video https://www.youtube.com/watch?v=b9UO9tn4MpI https://www.youtube.com/watch?v=b9UO9tn4MpI

deleted 6y ago

[deleted]

CryptoPunk 6y ago

The more significant 'silence' is the fact that every star in the Milky Way galaxy has not already been colonized and turned into a Dyson sphere. Species with language and toolmaking capabilities seemingly grow in technological sophistication at an exponential rate, so on the geological timescale, will quickly acquire space flight, grow to populations of trillions, harness the resources of their star system, then move onto settling a new star, and so on.

bena 6y ago
Why do you believe that? You're making the assumption that the problems involved with prolonged space travel are solvable with the time and resources we have here. It could not be. It could be too expensive to colonize beyond the immediate area. If even the immediate area can be colonized. There's also the assumption that there's going to be a good reason to make a non-returnable investment. Because, at some point, that's what it is. The speed of light is a limit we have not even come close to exceeding, much less approaching. And even if we do, and the people on the ship, time dilation, yadda, yadda. It does not matter. The people on Earth will still experience time normally. It taking the ship no time at all does not matter if it takes 1000 years on Earth. Or even 50 years. The return has to be phenomenal or the cost negligible.
- CryptoPunk 6y ago
  I assume the cost of settling other stars would become negligible at some point. If our solar system becomes a Dyson Sphere, and we have a population of thousands of trillions of people, I can't imagine how launching laser propulsion spacecraft that can travel at 0.2c toward other stars wouldn't be easily within reach of any moderately wealthy coalition of space enthusiasts. You're right though. I haven't actually done a careful estimate of the resources required vs the resources available to a Type II civilization. If the former is significant relative to the latter, and there is no Return that can motivate that magnitude of an investment with the type of investment structures that will evolve on a solar-system-wide economy - where investment time horizons have no need to be extraordinarily long - then maybe interstellar colonization is not inevitable.