Powerful Radio Signal from Deep Space • Hacker News Board

Re: Powerful Radio Signal from Deep Space

#51

Post by anonsivalley652 » Wed, Feb 12, 2020, 11:39 PM UTC

richk449 wrote: post #24

agoodthrowaway wrote: post #4

One thing that I wonder is whether we could ever identify an alien communication signal as an alien signal is likely to be much more advanced. In that scenario, the alien civilization is likely to be able to send their signal at the Shannon limit. Additionally an advanced civilization is likely to be sending signals optically instead of over radio waves. But even if we assume radio waves, Shannon says that the you ca…

> But even if we assume radio waves, Shannon says that the you can send the most information when using a random code. As you approach the Shannon limit the signal becomes more noise-like as the encoding tends towards random. The waveforms we currently use for high data rate communications are already pretty close to the Shannon limit. I'm willing to bet the aliens will tolerate a 30% reduction in data rate if it mea…

Let's apply common sense.

0) First, would it be a good idea to announce your world's existence? Robotic explorers who might exist in your neighborhood might decide your world is worth harvesting or colonizing.

1) If yes, then wouldn't sending a high-power announcement signal need to be obviously unnatural, i.e., containing very little data? Short trains of pulses with pauses that count up in binary perhaps?

1.1) "Visible light" seems like an anthropocentric assumption because there's not necessarily a reason other entities couldn't sense microwaves, IR, UV or even possibly fissile radiation. Furthermore, cybernetic "evolution" seems like there would be many possibilities for different senses. Maybe there is something particular efficient about the visible spectrum, such as polarized laser light remaining distinguishable extreme distances?

2) If said entity wanted to send a little more data as well, wouldn't they use a slightly different carrier or modulation but it wouldn't necessarily reach as far? Or, send it, as mentioned, more slowly?

Re: Powerful Radio Signal from Deep Space

#52

Post by sliken » Wed, Feb 19, 2020, 7:55 AM UTC

giantrobot wrote: post #46

agoodthrowaway wrote: post #4

One thing that I wonder is whether we could ever identify an alien communication signal as an alien signal is likely to be much more advanced. In that scenario, the alien civilization is likely to be able to send their signal at the Shannon limit. Additionally an advanced civilization is likely to be sending signals optically instead of over radio waves. But even if we assume radio waves, Shannon says that the you ca…

The inverse square law pretty much guarantees we're not going to ever detect random emissions from some alien civilization. The only way to get discernible signals an interstellar distance is with highly directional transmissions. So if we were to ever detect a signal from an alien civilization it would be a deliberate one. There's properties of coherent signals that would stand out significantly from natural sources…

Depends what you call a signal. Imagine the earth was just a bit more focused on science, united, and thought a bit longer term (on the order of 100k years). Living sustainable, but curious and motivated to explore.

Imagine an earth where literacy, science, and peace were priorities. All countries joined a UN like organization and decided to spend 1% of the planets resources on exploring.

Assuming earth level tech and the next 1000 years of progress (.000007% of the life of the universe) we manage a ship/converted asteroid/similar that can travel for 500 years at 2% of the speed of light with some combination of power solar power lasers orbiting the sun, solar sails, nuclear power (ion, explosion and/or pulse), or antimatter. That gets us to the nearest 10 stars. Hard to say what earth technology will be like in 1000 years, but no new physics are needed. Would that be a huge ship with kitchens, gyms, entertainment etc? Or maybe just some autonomous AI with some genetic samples, some robots, and a 3d printer?

After another 1000 years things have improved further, and slowly spreading across the galaxy at a few % of the speed of light becomes ever more practical. Maybe just enough so that a 2nd solar system in the galaxy an start launching ships. Said 2nd solar system could make it dramatically easier for travel between those two systems since they could use a laser to help decelerate the incoming light sails.

Those huge solar arrays + lasers for pushing a large ship up to a few % of the speed of light make for a hell of a beacon. Even unintentionally it should be visible from quite a distance, even by astronomical standards. A ring of solar panels near a sun could provide considerably more power than is available on earth today, even crazy inefficient things like producing antimatter might become viable. Things like geo-engineering become feasible, some distant civilization might detect things like an implausibly quick change in the atmosphere of mars. Or unusually energetic particles coming out of ships trying to accelerate or decelerate to a few % of the speed of light.

As technology progresses we might even be able to focus the energy coming from the sun more directly to directly push ships to other stars. After all solar power -> laser is horribly inefficient.

Distant observers on the same plane as our solar system might even start to notice the particular pattern caused by the solar/whatever energy collection.

Earths atmosphere might start to exhibit unusual characteristics. Even nuclear propulsion becomes common and we start mining the outer reaches of the solar system that might exhibit some unusual characteristics.

Of course any similar civilization in the galaxy could similarly expanding and eventually the two civilizations would get close enough to notice each other, even without deliberate signals.

Re: Powerful Radio Signal from Deep Space

#53

Post by sliken » Wed, Feb 19, 2020, 8:19 AM UTC

anonsivalley652 wrote: post #51

richk449 wrote: post #24

Earlier quoted context omitted.

> But even if we assume radio waves, Shannon says that the you can send the most information when using a random code. As you approach the Shannon limit the signal becomes more noise-like as the encoding tends towards random. The waveforms we currently use for high data rate communications are already pretty close to the Shannon limit. I'm willing to bet the aliens will tolerate a 30% reduction in data rate if it mea…

Let's apply common sense. 0) First, would it be a good idea to announce your world's existence? Robotic explorers who might exist in your neighborhood might decide your world is worth harvesting or colonizing. 1) If yes, then wouldn't sending a high-power announcement signal need to be obviously unnatural, i.e., containing very little data? Short trains of pulses with pauses that count up in binary perhaps? 1.1) "Vis…

Seems unlikely. Assuming a civilization could send a force to take over earth from many light years away, what could they possibly find of use?

Any element is easier to get elsewhere (without such a big gravity well) and no monkey descendants grumpily lobbing nukes at ya.

Sure, maybe they would harvest the asteroids and small moons while ignoring our complaints over sent over radio waves. No direct impact on earth. Maybe they would zorch a few suspicious looking sats with high energy signatures while they sat in high orbit and observed.

If we particularly amused them, or they thought we were uniquely tasty they could just grab a few of us and figure out how to replicate us.

Maybe our internet and fascination with cat videos would amuse them, some advanced crawlers running on quantum computers (for those pesky prime number based encryption) might cause some serious, but temporary disruption.

Maybe they would install a world leader with orange hair to sabotage any world wide scientific progress to help ensure we don't make significant progress any time soon.

But the sci-fi troupes of stealing humans to eat or vacuuming up the atmosphere or oceans seems exceedingly unlikely.

If anything they might drop a blackhole into the sun to harvest 10% of the mass that falls in and is converted into energy. That way then can use the energy for something more useful. But if that was common we'd be seeing lots of other stars disappear strangely.

All in all seems rather egocentric to think any really advanced civilization would particularly care about us.

Re: Powerful Radio Signal from Deep Space

#54

Post by sliken » Wed, Feb 19, 2020, 8:46 AM UTC

sixdimensional wrote: post #29

Sci fi daydream here. What would it take for us to actually try to make such a signal ourselves in space? Really huge explosions? I suppose one weird way to see if they could be alien signals is see if we can imitate them. Of course, that would be no guarantee that we aren’t just making bird calls imitating the sounds of car alarms (or other birds for that matter). But, I mean, if we can detect these signals, if we c…

Well 1 watt across 1 Mhz for 1 second isn't a particularly power signal.

But 1 watt across 1 hz for 1 ns is a significantly more power signal that will propagate much better. In fact it's about 1e+15 times easier to detect. Hrm, maybe it's more like log(1e+15), but in any case it's quite helpful.

If we can get space based manufacturing working well we could start making solar powered lasers that orbit the sun. Ideally with a bot that self replicates. Say relatively small panels like 2 meters by 2 meters = 5444 watts (near earth orbit). Assume a 20% conversion ratio and some kind of energy storage. Maybe operate for a 1 ns per 10 minutes on a very narrow frequency with a particular target in mind. Time them all to transmit precisely so that the wave front reaches the target at precisely the same time.

5444 * 10 = 54,444 watt minutes * 20% conversion = 10,888 watt minutes. Released in 1ns would be as bright as 653,280,000,000,000 watts steady state. Obviously there are efficiencies and physical limits to consider. Although maybe not as much as you might think. For instance the worlds brightest laser is already 1 billion times brighter than the surface of the sun. Maybe settle for 1,000 times dimmer, but 1 million of them.

Make a few 1000 or a few million and you could easily outshine the sun for 1ns in a particularly narrow frequency. Ideally a frequency with minimum background noise and minimal absorption in the nearby interstellar mediums.

The system could also act as a defense system. Although given the solar -> energy storage -> laser inefficiencies not sure if the single frequency of the laser would be more effective than just a mirror.

Maybe count up the first 16 primes repeatedly to rule out any natural causes.

The three body problem uses some implausibly small amount of energy to get the sun to resonate in a way detectable from many light years away. Not sure that could work, but maybe a million sats could reinforce a natural resonance in the sun to accomplish similar. That would only be worth it if the sun acted like amplifier and not sure that's feasible.