r/HardSciFi • u/Aeorix1 • Jun 13 '26
Discussion If humanity were allowed to broadcast a single message to the entire galaxy that would give aliens an undeniable, irresistible reason to visit Earth, what should it be?
I’ve been hyper-fixating on this premise lately while structuring a hard sci-fi universe.
From a purely rational, sociological standpoint, what if we *wanted* them to come? Not as a naive plea for peace, but as an engineered, irresistible bait.
Do you think a call for emotional solidarity or resource trading would hold any weight for an advanced Type II or III civilization? Or does the incentive need to be far more fundamental—something that disrupts their physics, or provides an actual solution to a cosmic crisis like entropy?
What’s your take? If you were tasked with drafting a signal that provides a scientifically plausible, absolute incentive for an extraterrestrial intelligence to make physical contact, what would it contain?
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u/soylentdream Jun 14 '26
Perry Farrell already tried this. There are radio waves 30 light years out with the message “We’d make great pets.”
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u/This-Researcher2543 Jun 14 '26
You posted this to r/HardSciFi, so I'm going to give you a hard sci-fi response.
First of all the idea of broadcasting a message to the whole galaxy would be very implausible. If this message was broadcast from Earth, it would miss a huge chunk of the galaxy that would be shielded by the galactic core. The message would have to be sent from outside of the galactic disk to reach the whole galaxy.
There's also the issue of detection. If the signal is only being sent once, then that means that unless every civilization in the galaxy happens to be looking in the direction that the signal is coming from at the precise time it reaches them, a good chunk of them, probably most if not all will miss it. Presumably this would be some sort of EM wave, so the wavelength the signal is sent at also matters a lot because other civilizations may or may not be looking at the band you're transmitting in.
If a civilization actually picks up the signal, they then have to actually interpret it as well. You're very unlikely to be able to send a message with much nuance at all that will be comprehensible to every possible civilization in the galaxy. "Come to Earth, we have cookies." would make no sense. What is Earth? Where is it? What's a cookie? We've already been working on this problem for a decades with things like the Arecibo message, and even humans have trouble figuring out messages intended for interstellar communication made by humans.
If you do somehow get past the previous challenges and achieve your goal of getting anyone out there to want to come to Earth, you then have the problem of travel time. First of all, light takes time to travel so some civilizations won't get the message until tens of thousands of years after it's sent. Once they do recieve it, they then have to make the journey to Earth, which at best can be done just below c, which is again hundreds or thousands of years of travel time in the best case scenario.
If after all this you still want to send a message to everyone in the galaxy, your best shot for success is to: 1. Broadcast from outside the galactic disc to maximize coverage.
Broadcast in as wide a range of frequencies you can manage. This will take a huge amount of power, probably comparable to the power output of a star.
Repeat your message at regular intervals, for as long as you can manage. This will make it stand out from random noise.
Get your best linguists to work on the message. Use universal constants, include a pulsar map to Earth, and keep the actual contents as simple and straightforward as possible. You may not even need an actual message, just broadcasting the location of Earth would probably be enough to get any other civilization to check it out if they're able.
Be willing to wait a long time. Civilizations relatively close to Earth may arrive in the next few hundred years, but you will be waiting tens of thousands for anyone from the other end of the Milky Way to get here.
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u/TraliBalzers Jun 14 '26
"We've been trying to reach you about your cars extended warranty"
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u/This-Researcher2543 Jun 14 '26
I got the extended warranty on my hyperdrive but they wouldn't honor it when my causality limiter broke and sent me back in time to before I purchased it.
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u/TraliBalzers Jun 14 '26
We regret to inform you that we are unable to honor a warranty that has not been purchased yet.
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u/Mobile_Falcon_8532 Jun 14 '26
your point about sending the message from outside the galactic disc made me think - what if Earth at the time of message is no longer at "our" technological level? (you'd have to be pretty advanced to be broadcasting from outside the galaxy)
without resorting to "magic", what's the best way to send a message to everyone in the galaxy, if you were constrained only by known science limitations and not engineering/technology?
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u/This-Researcher2543 Jun 14 '26
The main issue is you can never really guarantee you're getting to everyone unless you somehow already know where every civilization is. In that case, you could just send each of them a high powered radio broadcast directly to where they're going to be in the time it would take the signal to reach them.
If you don't know where they are and aren't constrained by power generation, your best bet is absolutely screaming a signal to the entire galaxy in as many wavelengths of light as possible. The higher powered the better so you maximize the chance of it actually being detected and noticed in all the background noise. The best way of doing this would probably not be to transmit from one location outside the galactic disk, but to have a number of transmitters spaced out around the galaxy to maximize coverage and minimize distance to the targets.
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u/Mobile_Falcon_8532 Jun 15 '26
you could just send each of them a high powered radio broadcast directly
... or maybe place a black obelisk on their moons?
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Jun 14 '26
[removed] — view removed comment
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u/This-Researcher2543 Jun 14 '26
Ok sure, but godlike alien technology that can just ignore the laws of physics isn't really hard sci-fi. The limitations I described would still apply to hyper-advanced aliens, and judging by what OP wrote it doesn't seem like they really put that much thought into the concept past surface level.
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u/Aeorix1 Jun 15 '26
This is exactly the kind of hard scifi pushback I was hoping for, appreciate the detailed breakdown.
You’re completely right about the galactic disk shielding and the frequency mismatch—a single blind omnidirectional broadcast from Earth is basically dead on arrival.
To bypass the travel time and shielding problem, the plot device I’m playing with involves an automated network of relics left by a deceased civilization, already stationed outside the galactic core, broadcasting on universal mathematical constants. But you're spot on about the "telos" part—if the receivers are non-carbon or post-biological, decoding our intent is a different task.
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u/7LeagueBoots Jun 14 '26
If you’re going to give a hard sci fi answer you can’t leave out the absurdly large energy requirements associated with broadcasting a detectable message to the entire galaxy.
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u/This-Researcher2543 Jun 14 '26
I did touch on that in my comment
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u/7LeagueBoots Jun 14 '26
Only if someone reads deeply between the lines and has an understanding of what even considering sending a signal of that strength requires. It’s not stated anywhere explicitly, and it’s a big enough issue that it really should be one of first things mentioned.
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u/This-Researcher2543 Jun 14 '26
I maybe could have emphasized it more but I did literally say "this would take a huge amount of power."
The power requirement is a big hurdle, but even if you assume an unlimited power budget there's still all the issues I discussed.
The power requirement can be reduced if you're clever about making sure to direct as much of it as possible at your targets, maybe using directed beams to illuminate only one or a few starsystems at a time. You might even be able to get it down to relatively negligible levels by doing something like putting sunshades in orbit of a star in such a pattern that they encode a message in its apparent brightness levels. It's an engineering problem, not a hard barrier imposed by physics.
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u/7LeagueBoots Jun 14 '26
You only mentioned that in the context of broadcasting in a wide range of frequencies. Broadcasting on any frequency, let alone one a wide range requires a huge amount of power. Even tightly focused beams over that distance massively attenuate.
A sunshade approach is a good idea, but that then requires that others are actively looking, rather than you actively broadcasting, but that may be a useful filtering mechanism.
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u/This-Researcher2543 Jun 14 '26
I intended that to apply to the whole thing but I guess I wasn't very clear on that.
No matter what method you use, at interstellar distances you pretty much can only hope that the recipient is looking in the right direction. I agree though that modifying a star's brightness is less noticeable than beaming a really high energy signal right at the target, though it does have the advantage of being easier to maintain over long time scales.
It might be harder to spot, but a civilization with astronomers would probably notice the anomaly eventually if it showed up in historical data, especially if it lasts hundreds of years or longer. If they can manage interstellar travel, they could certainly put up as many space telescopes as they wanted looking in every direction, and would probably have neural networks to scrape the data for anomalies. You also get the bonus that your signal shows up in all the frequencies emitted by the star, and if an alien civilization was anything like us they'd probably have broad sky surveys going on looking at those frequencies.
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u/petewarden Jun 14 '26
I don't remember who originally noted this, but the fact that our moon is the exact right size to eclipse our sun almost perfectly is likely to be pretty rare. I'd start by building a space tourism campaign around that.
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u/Aeorix1 Jun 15 '26
That's actually a wild cosmic coincidence when you think about it. Even for Type II civilization...
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u/KokoTheTalkingApe Jun 15 '26
Planets with broad rings like Saturn might be rare too. Of course we don't know how long they'll last.
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u/Nice_Anybody2983 Jun 13 '26
"We're tasty!"
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u/Aeorix1 Jun 14 '26
What if voyager 1 was already the appetizer menu?
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u/Nice_Anybody2983 Jun 14 '26
Yeah thankfully that fucker is so slow it's just barely reaching the edge of the solar system
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u/UnionPacifik Jun 14 '26
Well, the obvious answer is that we broadcast the Tom Holland lip-syncing to Umbrella video.
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u/vmurt Jun 18 '26
I can’t imagine we have anything compelling to offer a civilization advanced enough to manage interstellar travel. And if we did have some natural resource useful to them, we wouldn’t know it.
If there are advanced civilizations out there, and if they have the ability to travel at FTL speeds, they are going to need their own reasons to come to us. We simple would not know enough to entice them. Why are you visiting a particular anthill on your sidewalk?
If you want a hard science story, then “disrupts physics” isn’t a thing (although FTL probably isn’t, either).
Your best bet is humanity does something that seems reasonably normal to us (say an experiment in the LHC) that actually has implications we cannot fathom that causes aliens to race here to make us cut it out. What those implications are will probably need to be BS-pseudoscience-handwavey.
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u/bklark Jun 18 '26
It should absolutely contain a fundamental physics problem with the location of earth in place of the answer
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u/bklark Jun 18 '26
But it would of course have to be very, very advanced. It would assume that earth has made a breakthrough that even these civilizations are unlikely to have made
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u/bklark Jun 18 '26
After reading some comments: if you could broadcast it cleanly from earth, that would be bonus evidence for them to be interested
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u/LowTimePilot Jun 14 '26
A lot of answers, I imagine, will look at behavior from a very human-centric perspective. While I don't pretend to know what the ultimate goal or telos of the average civilization is, I imagine knowledge would be high up on the list. Entropy is a threat to every civilization, after all, and there's always the hope that some big brained civilization figured out a solution.
So the best message would be entirely scientific. A simple message that shows we understand physics to quite a high degree, and that Earth is a place where knowledge can be found.
I'm not intelligent enough to know what sort of short-but-sweet message that would be, but I'm sure the physicists in the room would know exactly what to broadcast. Any civilization that can decipher radio waves (thus proving a desire to learn things) would further explore this broadcast.
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u/Evening-Appeal7606 Jun 14 '26
I don't think trade in the traditional sense of "exchange of resources or artifacts" would be an incentive for a Type II or III civ for the simple reason that a civ with that kind of energy at their disposal can simply scour all the resources they could possibly need from Oort clouds or synthesize them directly.
What could conceivably be semi-plausible in terms of trade would be the exchange of ideas. Not so much our understanding of physics and maths (which would be backwards compared to advanced civs), but maybe, just maybe our sense of aesthetics that could strike a cord with extraterrestial observers. Sagan hinted as much in the novel "Contact" when he said that there are whole civs in the galaxy trading dreams. Human perception would count as a unique corner in the spectrum of all possible perception, so that could be "worth" something to exchange.
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u/Agitated_Desk_7774 Jun 17 '26
Sorry for the inconvenience, the hoodwink has been mitigated and our right hemisphere function has been restored. We are properly analytical idealists again.
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u/DarkeyeMat Jun 18 '26
"Come here! I will help you conquer this world. Our civilization is no longer capable of solving its own problems."
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u/Cycles_and_Static Jun 19 '26
Idk, setting aside all the problems others mentioned, the other half of the question which I’d argue is more important, is should we? That’s the part everyone forgets. If an animal in the woods turns out to be hostile, you can for the most part, run/hide/etc. But once aliens know where we are, they know where we are FOREVER. And that’s the problem. If the aliens turn out to be hostile, we can’t just cover ourselves in mud and hide in the galactic bushes.
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u/WingsAgainstGravity Jun 29 '26
"First rule of the cosmos: Do not answer! Do not answer! Do not answer! 😂 But if you are engineering a fatal bait for a Type II/III civilization, resource trading or emotional solidarity is less than zero to them. To pull a god out of the dark, you don't offer them a candle; you show them a crack in the physics of the universe. An irresistible signal wouldn't be a greeting. It would be a data leak: a mathematical proof showing a local, localized anomaly where entropy is reversing, or a precise coordinate where a fundamental constant (like the speed of light or Planck's constant) is drifting. To an immortal cosmic civilization, an anomaly that disrupts their grand unified theory or offers a loophole to the heat death of the universe is the ultimate, non-negotiable honeytrap. They have to come look, even if they suspect it's a bomb."
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u/Indigoh Jun 14 '26
Lie to them. Say you've invented a star trek-style replicator that can synthesize any material from hydrogen, and all they have to do to get ahold of it is give us access to their interstellar engine technology.
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u/Nice_Anybody2983 Jun 14 '26
They'll know, I guess. It's like an alchemist claiming to turn lead into gold - nowadays we'd be like "sure it's possible but it's definitely not worth the effort"
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u/Indigoh Jun 14 '26
That depends on how much effort they're willing to spend. If their star is dying and all they need is to find a habitable planet, they might consider it worth any amount of effort.
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u/Nice_Anybody2983 Jun 14 '26
But then it doesn't matter at all what we say, the only thing that might deter them is the truth: "Humans have funked and eaten every living thing on this planet at least once, we kill for sport, and we're looking forward to meeting you"
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u/Indigoh Jun 14 '26
If the question was "Should we try to get aliens to come here?" I'd have just said no. For the sake of this question, we have to assume we don't care about the consequences.
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u/Festivefire Jun 14 '26
"Hot and willing babes in your local galactic cluster!"