9 ms·

Would Sol look obviously inhabited on the radio spectrum? This is a common sci-fi trope (“Contact”), but I have no idea whether it’s actually true that our rad

• wyldfire 5y ago
  What if they had an array similar to the one used in "Contact" to receive the response?
• fermuch 5y ago
  Our radio waves have traveled for about 200 light years. Proxima centauri, our closest star, is located at 4246 Light years from us. Very, very unlikely that someone can hear us, even if they tried. Space is huge.
  • gpderetta 5y ago
    I think your Alpha Centauri distance is off by 3 orders of magnitude :) Edit: I think there are thousands of stars within 200ly of Earth.
    • _q8zh 5y ago
      Here's an interactive 33ly radius model: https://gruze.org/fly_10pc/ https://gruze.org/fly_10pc/ - left click + drag, mousewheel, right click. Could be more efficient, but this interactive does the trick; shows how loaded our neighborhood is. Going to hamburger menu -> settings -> show labels brings it to a crawl, though filtering objects helps that a bunch. Showing only stars with known planets is rather interesting.
      • BoxOfRain 5y ago
        This is really cool! Definitely going to be a time sink for me!
  • ajakate 5y ago
    Proxima centauri is actually ~4 light years away. Space is really big, but there are a handful of stars in relative vicinity of us (under 250 ly) https://en.wikipedia.org/wiki/Proxima_Centauri https://en.wikipedia.org/wiki/Proxima_Centauri http://www.icc.dur.ac.uk/~tt/Lectures/Galaxies/LocalGroup/Back/50lys.html http://www.icc.dur.ac.uk/~tt/Lectures/Galaxies/LocalGroup/Ba...
  • deleted 5y ago
    [deleted]
• ortusdux 5y ago
  The inverse square law really dilutes out most signals - https://www.quora.com/How-far-do-radio-signals-travel-into-space-before-they-degrade-to-a-degree-beyond-being-possible-to-be-detected https://www.quora.com/How-far-do-radio-signals-travel-into-s...
• ThomasWinwood 5y ago
  As I understand it the amount of time we were tossing radio into space was quite brief, and more modern radio traffic is directed at the ground (since after all if you're leaking signals into space you're wasting power). One of the papers cited in the OP argues that a good indicator that there's something interesting about a planet is the combination of molecular oxygen and methane in its atmosphere - the former is a strong oxidiser, while the latter is a reducing gas, so there's some dynamic system producing free methane in the atmosphere.
• mandevil 5y ago
  From the 1960's to the present, the Ballistic Missile Early Warning System radars have been broadcasting enormous amounts of coherent power on specific, non-natural frequencies into outer space: if we were to detect a signal like that we'd almost certainly determine it was artificial. You can see the list of stars which would have recently started seeing the first glimpses of the BMEWS Line radars here: https://en.wikipedia.org/wiki/List_of_star_systems_within_55%E2%80%9360_light-years https://en.wikipedia.org/wiki/List_of_star_systems_within_55... Obviously many other radars (DEW, Hen House, etc.) are doing the same thing, but BMEWS has continuous operation and power on its side.
  • rootusrootus 5y ago
    I hope that little forest of stars is not just dark, but actually empty.
  • zardo 5y ago
    How far away will the signal be detectable above the background noise?
  • giantrobot 5y ago
    In theory yes but in reality Earth rotates and orbits the Sun. Any particular observer outside our solar system has a very low probability of catching any one of those beams at the moment it's photons are reaching them. There's also little chance of those beams will ever hit the same observer. The inverse square law also means that a potential observer would need to be in a relatively small radius from our system.
  • rimliu 5y ago
    And those signals have travelled 60 light years. Our Galaxy is 100 000 ly accross…
• ChuckMcM 5y ago
  I would guess, "probably not" for a variety of reasons. First, the ionosphere bounces a lot of radio traffic right back down to the planet, amateur radio operators (like me) use that to talk to stations farther away on planet but it doesn't go into space. Second the frequencies that do travel through the ionosphere are typically aimed at satellites (geosynchronous or lower) and are scaled to have a level of power that gets there reliably but without an overly large margin for error. Third, the Sun is a very "noisy" source of RF energy and someone looking this way at us would also be looking at the Sun as well (if you're looking at transits). In terms of radio frequencies that they could perhaps analyze it would require a lot of filtering. The analysis we've done on transiting planets so far is based on spectroscopy using the star as a huge light source and looking for how that light is filtered by the 'edges' of the planet. (so through the atmosphere of the planet). If they are doing that, then the change in atmosphere composition over the last 1000 years seems like it would be detectable.
  • nawgz 5y ago
    > the change in atmosphere composition over the last 1000 years seems like it would be detectable Interesting to think what conclusions would be drawn in these scenarios. Obviously atmospheric composition has drastically changed over the eons - I wonder what sort of civilization could detect these kind of longterm changes, and if they wouldn't have better observational capabilities than what we assume here given they have persistent knowledge over "long" timespans
    • kadoban 5y ago
      I _think_ even just seeing Oxygen (in O2 form) should be fairly suggestive, because it's not stable in the presence of a whole bunch of other things.
      • perihelions 5y ago
        And the CFC's would be definitive proof. https://arxiv.org/abs/1406.3025 https://arxiv.org/abs/1406.3025
• DamnInteresting 5y ago
  If you'll excuse the self-link, I have written about this at length: https://www.damninteresting.com/space-radio-more-static-less-talk/ https://www.damninteresting.com/space-radio-more-static-less... In short, even our largest, most sensitive radio telescopes are far too small to detect omnidirectional (e.g., FM radio) leakage from Sol's nearest celestial neighbor. Unless an exoplanet directs a coherent radio beam at Earth, we'd need an antenna larger than the planet to detect a signal amid the noise.
• oh_sigh 5y ago
  To put it generally: How far could we be from each other and still detect ourselves?
• credit_guy 5y ago
  No, our radio emissions would not be trivially detectable. In fact they would be phenomenally difficult to detect even from our nearest stellar neighbor, Proxima Centauri. If you take the most powerful BBC antenna [1], then a James Webb-sized telescope placed near Proxima Centauri, and pointing straight at the Earth would receive less than 5 photons per second from that antenna. Here's the calculation, in case you're curious: one light year is about 10^16 meters; a sphere of radius 4.25 ly has an area of 2 10^34 m2. The BBC antenna emits in the 200 kHz band, so a single photon has an energy of (plank const) x (frequency) = (6.6 10^-34) x (200 10^3) = 1.3 10^-28. The antenna has a power of 500 kW, so that translates into 3.8 10^33 photons per second. That means at Proxima's distance each square meter will be crossed by a photon about once every 5.4 seconds. The James Webb telescope has a receiving area of 25 m2, so you end up with a bit less than 5 photons per second. [1] https://en.wikipedia.org/wiki/Droitwich_Transmitting_Station https://en.wikipedia.org/wiki/Droitwich_Transmitting_Station
  • deleted 5y ago
    [deleted]
• belter 5y ago
  They are trying to communicate with us with Quantum Entanglement. Until our physics progresses, so as to understand that Quantum Entanglement does not limit you to transfer of information at the speed of light, we are considered a level IV Civilization. The current agreement is that level IV Civilizations should stay "Uncontacted" : https://en.wikipedia.org/wiki/Uncontacted_peoples https://en.wikipedia.org/wiki/Uncontacted_peoples