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Sister question to How do you communicate with antimatter beings?

Defining dark matter for this question

According to NASA, 27% of the universe is dark matter - and about 5% of the universe is normal matter. Dark matter is a substance that doesn't interact with electromagnetism. That means light passes straight through (it's invisible), and that matter may also be able to "phase" through it (it's intangible and won't take our sound waves, either).

We only know it exists because it interacts with gravity.

For this question, assume that a fifth fundamental force, "dark electromagnetism" exists, and that humans haven't detected it yet. In this world, it allows for "dark light" analogous to ours; it allows "dark elements"; and it allows dark molecular bonds. These maps actually show dark nebula, and some dark solar systems exist in places we haven't looked yet$^1$.

So aliens have arrived in the solar system, and they're made of the stuff.

We detected them$^2$ because their ships have large-scale gravitational effects (lensing, attraction of matter), and they're built with dark handwavium$^3$ that allows them to stay ship-shaped without collapsing into spheroids. They do not know we're here, just our planet, and they have a level of technology parallel to ours - except the giant, interstellar, physics-defying ships.

What are effective ways for our groups to communicate?

How can we get their attention, knowing we can't see each other or hear each other? What could we build or do to allow interaction and conversation between the groups?

$1$ This is my cop-out for the "dark matter doesn't arrange itself into stuff" findings.
$2$ If you have a better explanation please let me know, I don't know how else we'd detect them without answering the question of how we communicate with them.
$3$ Even the crazy physics-turned-on-its-head aliens have handwavium. It's trendy in 2017.

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    $\begingroup$ I thought Dark Matter particles if proven(directly) can never clump together... $\endgroup$
    – user6760
    Commented Jan 2, 2017 at 9:14
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    $\begingroup$ I don't think science-based is right here. For what we know, dark matter is so unlike ours we can't even make out what is it, how it behaves. If it's in form of particles, it seems to lack any chemistry we could understand. Dark matter beings are clearly not scientific, no way. $\endgroup$
    – Mołot
    Commented Jan 2, 2017 at 10:15
  • $\begingroup$ @user6760 I'm under the impression they're hard to manufacture $\endgroup$
    – Zxyrra
    Commented Jan 2, 2017 at 14:45
  • $\begingroup$ @Mołot science-based is for "... questions that require answers based in hard science, not magic or pseudo-science ..." which is possible with the given context, regardless of changes to science I made. Using scientific fact, you can still say "neutrinos still interact, so shoot some" or "make a big object with a big gravity well", or "learn how to arrange subatomic particles and make some dark matter" or "figure out how to detect gravitons and shoot some of those"; answers still can be based in hard science. $\endgroup$
    – Zxyrra
    Commented Jan 2, 2017 at 14:56
  • $\begingroup$ Zxyrra, you should post other questions to flesh out these uncertainty points you have (2, 1, and 3) $\endgroup$
    – Mindwin Remember Monica
    Commented Mar 30, 2017 at 13:20

2 Answers 2

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Both we and the aliens can interact with the weak nuclear force. So we need to send a message in particles that interact weakly. Neutrinos seems like the best option since we can manufacture them en-mass and send them in particular directions. For example in the OPERA experiment, the super proton synchrotron at CERN, Switzerland) was fired at carbon to generate pions and kaons (CERN Neutrinos to Gran Sasso). When these particles decay they produce mu-neutrinos and even some tau neutrinos, which were detected in Italy. They can be detected above the background coming from the sun.

We have to hope that they have on their ship something for detecting neutrinos (all interstellar dark matter spacecraft do, as it is a good way to avoid crashing into the gravity well of large "light matter" stars). So we send beams of neutrinos their way. At some point, Science officer K'cops notices that there is an anomalous level of neutrino emission coming from the third orbiting gravity well and concludes the existence of a planet with intelligent life, and with the assistance of Engineer Yt-to'cs builds a neutrino beam to respond with.

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    $\begingroup$ We can produce lots of neutrinos in given directions! This sort of surprises me. More information about this, please. $\endgroup$
    – a4android
    Commented Jan 2, 2017 at 11:57
  • $\begingroup$ This is really promising, and not the approach I expected. +1. However aren't neutrinos notoriously difficult to detect; won't we have to wait months between signals arriving? $\endgroup$
    – Zxyrra
    Commented Jan 2, 2017 at 14:42
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    $\begingroup$ Yes, and yes. There is a whole lot of handwaving going on here. Cern beamed neutrinos by accelerating pions down a 1km long tube, allowing them to decay as they went. That is not easily pointed! Why would the star ship be looking for mu neutrinos (I suggested it was to detect and avoid stars... well there is worse science in star trek.) Since we know nothing about "dark light" we can't use that to communicate. I have no idea how condensed dark matter would interact with baryonic matter. The neutrino is the only dark matter particle that we understand. $\endgroup$
    – James K
    Commented Jan 2, 2017 at 16:24
  • $\begingroup$ My only quibble with this is that it might be hard to distinguish these neutrinos from the normal background coming from, say, the Sun. And it's another step entirely to go from "There's a faint anomalous source of neutrinos" to "There's a faint artificial source of neutrinos, heralding intelligent life". $\endgroup$
    – HDE 226868 ♦
    Commented Jan 2, 2017 at 16:56
  • $\begingroup$ I don't disagree. My only defence is "there's worse science in Star Trek" However I think the discovery of a neutrino anomaly coming from a planet, if it were by some Spock-like miracle to be discovered, would be hard to explain, except by some form of intelligence. $\endgroup$
    – James K
    Commented Jan 2, 2017 at 17:10
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Well the way that we know about dark matter is by the gravitational effects it has. This is then a place to start generating our communication system. We are using our current levels of technology. OK, great. We can currently send things into space. We can also currently detect local levels of gravitation - .

Taking these two facts, and using some our own dontaskium (similar to alien's handwavium but light instead of dark) to generate the appropriate governmental and public support and funding for our venture, we do this:

  1. We start by pointing NASA's Deep Space Network at the appropriate point in our solar system. We move them if necessary. I don't know how long this will take. Now we can measure any gravitational-signal responses send back by the aliens.
  2. Then we come to the harder part. Generating the signal. So, gravity produces gravitational waves, as we have recently proved using two interacting black holes. Now I'm not going to suggest we create two black holes in our solar system (disclaimer: OK, I was going to suggest that we did that using our wormhole-generating technology until I read the question saying that we need to stick with current tech levels). However, those black holes were far away which is why they needed to be big to detect them. Can we get a similar effect by using smaller objects nearby? I have no idea, but since I haven't been paid yet as the lead scientist on this project, I'm going to say "Yes, with absolute certainty"!
  3. We make two Space JCBs. They are load-carrying spaceships.
  4. Then we fill up their load bins with heavy things (rocks, or lead, or uranium, or asteroids, or whatever is most fun).
  5. Now, the fun part. We send these Space JCBs to the point where we detected our aliens, and get them to play Space Chicken. We get these Space JCBs to fly towards each other, leaving only the tiniest of margins where they don't crash into each other. Their masses interacting will produce a gravitational wave, which since it's so close (or possibly inside) the alien spaceships, should be Super Easy to Detect™. However, for all these aliens know, that was just an asteroid crashing into another one, or however they explain common things occurring on the Light Side.
  6. So let's do it again. And again. And again. And again. But let's set up a specific pattern: a coding, if you will. Let's do one pass. Then wait. Then two passes. Then wait. Then three, and wait. Five, wait. Eight, wait. Thirteen, wait. Twenty-one, wait. I think you know what's next.
  7. That's right, back to one. This Fibonacci sequence was getting too long, so we'll stick to repeating this sequence up to twenty-one passes.
  8. Let's do this for an unreasonably long amount of time, or until the aliens notice, and our detector picks up some sort of coded activity in the wait periods - my hope is that our alien friends will start to pre-empt our numbers by filling in the wait periods, showing us that they are receiving our signals, understanding the sequence, and able to communicate back at us.
  9. ?
  10. Profit.
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  • $\begingroup$ Oh I just saw this was asked months ago. Still, fun work-through. $\endgroup$
    – Hugh Nolan
    Commented Mar 30, 2017 at 12:39
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    $\begingroup$ It's always good to answer questions, no matter how old they are. +1 from me $\endgroup$
    – Secespitus
    Commented Mar 30, 2017 at 12:41

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