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Comment by jerf | Hacker News Reader

It depends on whether you want to stay grounded in real-world physics, or if you want to spin off on flights of fancy.

If you want to stay in real-world physics, at the moment there is no reason to expect any civilization to use anything other than electromagnetic radiation for communication. Other than the low speed of light, which is a characteristic of the universe that it does not seem to allow any faster-than-light communication so it's not specially a disadvantage for EM, electromagnetic radiation basically has every characteristic you're looking for in a communications medium, and there's little reason to believe even an advanced civilization would use something orders of magnitude worse on numerous dimensions simply because maybe they can. This is for much the same reason that we could transport everything in our civilization by people carrying things around on Segways, but we don't, because why would we deliberately choose something suboptimal?

If you want to go off on flights of fancy, then anything is possible, but there's no way to say anything useful about it.

The "grounded in reality" answer is subject to change as our understanding of physics improves, but at the moment I wouldn't say there's any particular reason to expect this answer to change much. Even on the crazy fringe frontiers of real science, I am not aware of any candidates for communication any better than EM.

Most of the whacky ideas proposed as alternate methods fail by orders of magnitude vs EM. Might you be able to build a better neutrino detector than we can? Maybe, but it's still easier to build EM detectors, and EM emitters, by a lot. Gravity waves? Why on not-Earth would anyone spend the massive, massive amounts of energy required to do that, very klunkily and with very low bandwidth, when for literally a trillionth of a trillionth of a trillionth of a trillionth the energy expenditure you could use EM, and get higher bandwidth to boot and better reusability to boot? Quantum entanglement and teleportion are non-starters, because they both require a conventional channel to work at all, and the best tool for that communication is EM.

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Even with EM, they could have a highly advanced encoding format which is barely detectable about the random noise floor (spread spectrum like). US army uses these kind of techniques to make the signal both hard to detect and hard to jam.

Who knows how far you can push this, maybe to the point where it's essentially impossible to detect the signal if you are not the intended target.

Most signals would presumably also be highly targeted. The narrower the beam you are sending, the less energy is required to send the information. Unless aliens cheap out on antennas or prefer to waste lots of energy on broadcasting in all directions, we are very unlikely to be in the path of their communication beams.

Energy is very abundant by E = mc^2, so what we consider "wasting energy" they may not even consider.

The average web page is bigger than the original DOOM download, about 2/3 the size of War and Peace. In an era before Gutenberg, when monks copied books my hand, I wonder if anybody mused that nobody would "waste" the equivalent of 750 pages to communicate "please log in using your email and password."

You need to consider that you're sending a message over millions of light years. You'd need a a power output comparable to a star to be visible across that distance if you didn't focus your message (because, obviously, stars themselves do it!)

If you want to do it you might as well use the star itself it won’t be that hard to encode a message into the light emanating from the star itself you only need a sufficiently large polarizer or anything else capable of modulating the light coming form the star.

Any civilization that would need to communicate even across a few 100 light years would be capable of doing so.

That's an interesting idea (and something touched on in The Dark Forest[1], which is pretty good just for a peek into hard sci-fi through the lens of another culture).

How large an area would you need to cover to accuratly dim a star's output to an array at another star, say 100 light years away, if you positioned yourself towards the edge of the solar system? Is this cost effective, or any faster than using targeted EM?

1: https://en.wikipedia.org/wiki/The_Dark_Forest

>How large an area would you need to cover to accuratly dim a star's output to an array at another star, say 100 light years away

Jupiter-sized is good enough for some 3700 light-years with 2016-era technology [1]. We know because that's one of the current methods of detecting exoplanets [2].

[1] http://www.sci-news.com/astronomy/kepler-1647b-circumbinary-...

[2] https://en.wikipedia.org/wiki/Methods_of_detecting_exoplanet...

On the other hand Kepler 37b is only slightly bigger than the moon and its 200 l/y away.

Planetary transistion detection isn’t just a question of size (of both the star and the planet) and it’s orbit but also of alignment of the orbit of the planet, the orbit of earth and the two systems.

Now with a predetermined communication array the alignment isn’t a problem more so you can use a light shield at the receptor similar to StarShade which will be used to block the light from the star allowing Kepler to image the planets directly to block the majority of the light from the star which would reduce the required size of your transmitter further.

It’s quite likely that over a distance of even a few 100 light years with a modulator as small as a few 100 km across might be sufficient.

The problem with communicating across even a few hundred light years is that everybody's bored and gone to do something else before the response arrives.

You'd need a spectacularly static civilisation to engage in any meaningful communication over the timespans involved.

Maybe not bidirectional communication per se, but it’d still be pretty valuable to receive a live feed of what the other civilization was up to hundreds of years ago. Especially for things like scientific advances and important works of literature – but I suspect people would also be interested in the day-to-day trivia. I mean, as an individual I’m already largely powerless to influence any of the events I read about in the newspaper, but I still read the newspaper.

Besides, if you’re an AI or an uploaded brain, you can send yourself over a communications link. That’s pretty valuable, regardless of whether you ever intend to return!

How much do you pay attention to the live feed of news from Mauritius? (If you live anywhere close to that country, or have ties there pick a different country on a different continent). Somewhere in my family history is the towns where my family immigrated to the US from, but I don't care at all about news from those towns.

The news in my town is of interest to me, nobody else would care about the latest live music at the local stage.

Science might be of interest, but the problem is both cultures will work in parallel, so we can assume that majority of advances one planet discovers are discovered by the other planet in the mean time.

The nearest star (which might not even have a habitable planet) to earth is too far away for science collaboration other than the "here is new type of signal we are sending your way, see if you get it", and even then you take the risk that the other planet chooses to not listen for whatever reason (it wouldn't surprise me if some theory require this level of cooperation). It is close enough that some "we are studying this lead, so you probably want to look at something different to avoid duplicate work".

As we get farther and farther from the other planet collaboration is less and less useful. You quickly reach a point where the planets can advance faster by duplicating effort than talking to each other (other than as a much latter verification of current theories)

Of course if we colonize a planet 100 light years away you can assume a few hundred years of the colonists working hard to establish the colony and so getting science and technology feeds from Earth will be useful since then they can make a copy of widgets without having to design it from scratch. Eventually they will get established and start producing their own science locally, and soon the feed will be useless and not of interest.

This reminds of the time I first visited US. As an Indian, the first world infrastructure and living standards had me in awe.

After going back to India, merely showing things to people on Google Maps was an experience of its own.

People went like: Do people in other countries, live that well?

I'd fathom when we see some advanced civilization we would probably react the same way.

If I were an AI or uploaded brain, I'd copy myself over the communications link, fully expecting to diverge into two distinct individuals.

That's a very young-civilization perspective. 100 years seems like a long time to us because it's approximately 1% of the age of our civilization. But it's possible that civilizations that are hundreds of millions of years old exist. To such civilizations 100 years would be a flash in the pan.

Also keep in mind than until recently on earth we used transmission mechanisms for long-on-earth distances that were closer to the order of magnitude of 100-year transmission time (a few months) than to present transmission time (a few milliseconds).

>But it's possible that civilizations that are hundreds of millions of years old exist. To such civilizations 100 years would be a flash in the pan.

I don't know if it is possible for a civilization to connect the past to the present over such long periods of time. The individuals in each generation would have to pick up, use and pass on all the information that came before.

Our capacity to take past information into account, individually and collectively, is very limited, even if it gets stored somewhere. We can see that in many debates on here where arguments of the past are repeated many times over without younger participants having any awareness of what's been said before.

We can compensate for that to some degree by continuously retelling old stories. But relearning old stuff necessarily competes with new information for our limited mental capacity and so old information inevitable degrades over time.

Even religions, where there is a strong emotional incentive to retell old stories, are struggling mightily with even understanding what the original authors meant by the words they used and how to apply any of it to the current situation.

I think for a civilization to retain its collective memory over much longer periods of time requires completely different individuals. It requires individuals that are able to grow their mental capacity at the same pace as the amount of accumulated information grows.

If you consider the combinatoric explosion, this is unimaginable in a biological organism based on evolution and ultimately even in an AI.

I also want to add that age-wise we might be pretty old. Our galaxy (13B) solar system (5B), our planet(4.5B)are pretty old considering the Big Bang happened 14B year ago.

Definitely in civilization time that leaves a lot of room for a few milion years here and there, but still, we could be the oldest and most advanced (at the same time I do hope there is a civilization out there less eccentric and egocentric as ours...)

100 years doesn't seem like a long time to me because of the age of our civilisation or species, it seems like a long time to me because of the lifespan of our species. I certainly can't communicate at all on a 200 year RTT, as I'll be dead and forgotten before I get an answer.

If it's communication, that implies a two-way exchange of ideas. The galactic equivalent of blogging would be like all such communications: typically of more interest to the sender than the receiver.

If we assume a long-lived species that can receive a response within its lifetime, we must also assume that during the intervening time little enough of the context has changed that the answer is still relevant. That means a species and a civilisation that has extremely little change over hundreds of years.

This is what I mean by an extraordinarily static civilisation.

(But if it's so static, what could possibly be said that has material bearing on anything? :-)

That is the first time I've ever thought about that particular obstacle to EM technologies as a means of hyper-distant, bidirectional, purposiveful communication between advanced civilizations. I've always thought of EM (Radio/Communication Technologies) as potential tools to confirm specific sources/locations of other intelligent life as well as possibly their purported agenda/intention/lifestyle/threat-level? (or level of intelligence and even to develop [flawed but useful, a.i. based] predictive algorithms of their future likelihood of physical contact/threat and/or their rate of scientific advancement, based on analysis of numerous factors including their encoding used, past broadcasts compared to current, means of broadcast, etc. Etc. Etcetera.) [STRICTLY LIMITED TO/AT the time of the broadcasts, not at the time we receive them... BIG DIFFERENCE IN ASSUMING THAT THE TWO ARE THE STILL THE SAME!]. Never in my wildest dreams, would I consider us as humans advanced enough to ACTUALLY RESPOND (IN WAY THAT WAS COMPLETELY SAFE, FORETHOUGHT, LOGICAL, CALCULATED, MORAL, AND MUTUALLY-BENEFICIAL!). We shouldn't knowingly, directly communicate or reply to forces beyond our wildest comprehension, for what we wish to be a dream for the future of mankind could quickly turn to its worst nightmare, if we are not careful, moral, loving, prudent, and conscientious. We should not have the audacity to treat our supposed Galactic neighbor(s) based on behavioral assumations, if we ever resort to treating them any way whatsoever, which until we reach a far greater point of advancement (both materially, defensively, socially, scientifically, technologically, and, in all honestly, Spirtually) I advise against, 100% completely. Just my take. Learn what we can without exposing ourselves.

The diameter of Sun is 4.5 light-seconds. This is the lower bound for Sun-sized polarizer switching, as whatever switching process is it has to propagate at below speed of light. Which gives a really poor communication bandwidth even compared to a human Morse operator.

Radio is much better bet.

Never underestimate the bandwidth of a truckload of hard disks.

Latency hardly matters when the majority of the lag is the 100 light year leg: you first spread out your whole message to the surface of the filter with a high bandwidth distribution medium. Then each section of the filter switches in sync, encoding the message without relying on a real-time input from a central location light seconds away

Is it necessary to use the star one is orbiting around?

Why not use an array of smaller polarizers that can be modulated when they block the path of a bright but less adjacent star’s light to the recipient?

what you are saying could also be: other civilizations would do the same as we do. send small unmanned drones into space, and not just signals. they are much slower, but allow much more information and better reaction time, if the onboard logic does that. and they are not mistaken for something else, as in this case.

Can't you delay the signal sent to the center-parts of the polarizer relative to the edge? I think the panel would appear to switch all at once to somebody far away. Seems like this would increase the bandwidth.

Problem is, a star is curved, with the limb being over two light-seconds farther away from an observer than the center. Sure, you can switch the whole surface of the star as fast as you like, with bandwidth limited by how accurately you can synchronize the switching components. An advanced civilization might be pretty good with attosecond-level stuff, but the signal gets spread out over seconds regardless of the synchronization superscience you apply.

You can phase the switches and "aim" the star's signal at a point in the sky. Lower-frequency modulation can get signals to observers not on the direct line, at a lower bandwidth, and you can probably sweep these. Worst case you can blink the whole affair slowly; a star with a five second light curve is going to be pretty interesting.

It would take 2.25 seconds for a clock signal to propagate throughout the polarizer, but, after that, all distinct elements could sync up for whoever is perpendicular to the transmitter and blast away at whatever bandwidth the signal transitions allow.

You don't need to place the polariser right next to the sun; you can use a smaller disc to modulate it's output in one direction.

Like the way the earth is large enough to block the sun on the entire moon during a lunar eclipse.

If your shield is smaller than the star's diameter, you have a penumbra effect. Rather than stellar occlusion, at a sufficient distance you have a stellar transit.

Building a static support for your polariser might also prove challenging.

Ah, yes of course. Though if your disc is large enough, such a transit should still be detectable.

You're trying to detect the modulation, not merely the transit.

Your noise floor is now vastly greater.

They could be basically the same - during each transit you could either let the light through or block it.

Now you've decreased bandwidth to orbital period.

I missed the part about some minimum speed, but it's still flexible in regards to how many levels or frames per transit you use. The point is really to be able to communicate at all - without using a star's light it's basically impossible after a certain distance.

There is that "something is better than nothing" element.

I've also been thinking of whether or not some sort of stellar laser or maser might be possible. Modulating a narrow, tightly focused beam.

If you haven’t read Liu Cixin’s Rememberance of Earth’s Past trilogy you might really enjoy it.

I’m totally ignorant in this so my question could be half baked but what exactly are you saying?

By polarizing light, do you mean that a device would intercept the photons escaping from the sun and then changing their wavelength to encode a message similar to Morse code?

Or do you mean something else entirely?

Edit: a word

A polarizer only allows light of certain polarity (the "direction" the waveform oscillates, think sunglasses or 3D glasses, or the polariser in your LCD screen) to pass through.

https://en.wikipedia.org/wiki/Polarization_(waves)

But it doesn't have to be polarization just any easy modulation of the light, polarization is just easy to do since all you need is a huge polarizer and a few reaction wheels.

Think about planetary transitions; we can detect those quite easily this is how we find exoplanets these days, in fact we can fairly accurately identify the composition of the planet's atmosphere and the atmosphere is a fairly thin slice of the entire planet's silhouette.

So the only thing you need to do is to position a sufficiently big object it doesn't have to be even that big (still huge in our scale but something in the range of 100's or even 1000's of kilometers across would likely be sufficient the radius of the earth is only 6300KM~ and we can detect planets smaller than the earth AFAIK, and it can be as thin as a solar sail and considering we already build satellites with antenna that unfold to the size of a few football fields it might be possible even with our current level of technology or something not that far off) because you take advantage of the distance between planetary systems that object needs to be able to modulate the light it can be polarization, abstraction, color filtering.

To put it simply make a huge ass thin TFT LCD let the sun act as a backlight and put it in a stelar synchronous orbit from the vantage point of the star system you want to communicate with so it would always appear in line between it and your local star and blink your messages away.

If you want to go for the golden star then build a huge ring which also is capable of acting like lense this can allow you to have a communication array which can also direct the signal in a relative narrow beam.

It doesn't even have to be that huge if it's further away from the star.

Then you’re back into having a narrow transmission beam

Thank you for that reply. Makes a lot of sense.

> intercept the protons escaping from the sun

Minor typo: you mean "photons".

Solar wind too though.

Thanks. Corrected.

A polariser filters light whose electric field is oriented in a particular direction.

Like modern 3D glasses.

Seems to me that the size of the star would be a problem. Assuming the process of actually building stuff large enough to cover a star is solved, how do you control the polarizer to get any reasonable bandwidth? The light emitted from one side of the star will be shifted in time relative to the light emitted from the other side, in anything other than a very narrow beam. Targets outside of this beam will not really receive much of a signal due to interference.

I had this rough question (i.e., while entertaining causes as elaborate as a Dyson sphere, considering that a star might intentionally be used to send a low-information rotating signal like a lighthouse or signal/Morse lamp out along a plane) after the news about Tabby's star broke. I.e., I emailed it to Tabetha (no response; didn't expect one).

And I just imagined an Elsevier-like alien company controlling the broadcast bitstream for an entire star.

"...mit $700 trillion to renew your subscription to PubStar. Sol System, please remit $700 trillion to renew your subscription to PubStar. Sol System, please remit $700 trillion to renew your subscription to PubStar. Sol Sys..."

This is precisely why using neutrinos would be an attractive idea - the signal could travel over extremely long distances with very little diffusion/attenuation. (I.e., as long as you have a narrowly focused beam, to control dispersal, the beam itself won't be weakened by any intervening debris.)

> Energy is very abundant by E = mc^2

While we can expect a sufficiently advanced civilization to be in control of vast sources of energy, we need to consider losses, because nothing can be 100% energy-efficient. If sending data to the next node of your intergalacticnet requires you to deal with a Hiroshima per second of waste heat, yours is not a particularly attractive communication channel.

And, unless you have a very large heat exchanger, you are vulnerable to side-channel attacks where a third party can detect the heat you need to dissipate.

Perhaps instead of waste they are worried about, it's detection. Instead of broadcasting everywhere and letting all the swarm devouring aliens know where you are, doing a highly focused beam is far less likely to get detected.

Surely any species that manages interstellar travel will have a much easier time growing sentient beings to eat on their own planet(s), rather than going to other solar systems, lifting the people there out of their gravity well into space, and consuming them?

Wouldnt heavily advanced civilization wanted to remain silent? If they know they are less sophisticated aliens out there like us humans, then for sure there are civilizations more advance than they are. I suspect they are not interested of sending their own signal to someone who could anihilate them with a push of a button (even higher civ.)

In Carl Sagan's Contact (the book, not the very good movie), Ellie is on the life-extension station with SR Hadden and about to land back on earth after the accident. I can't find the exact quoted exchange but it goes something like:

Hadden: Ellie, when you find them and talk to them, be VERY careful. These folks are old and their tolerances for risk may be alien to us.

Ellie: Well they sent us the Message, they obviously want to chat

Hadden: With beings that may be immortal or close to it, what we may consider a sure-fire bet may seem like an impossible risk to them. When they offer you something, you take it, you hear?

If someone can find the actual quote, thank you!

The closest approximation I can find is pp. 292--293. (I don't have a copy and haven't read it in about twenty years, so there may be a better approximation available.)

Hadden and Ellie have a brief discussion about the potential to market dying in space as a "really nifty last indulgence", whereupon Hadden segues to the topic of immortality and says the following:

"Now, I'm not bringing this up so I can boast. I'm bringing it up for a practical reason. If we're figuring out ways to extend our lifespans, think of what those creatures on Vega must have done. They probably are immortal, or close enough. I'm a practical person, and I've thought a lot now about immortality. I've probably thought longer and more seriously about it than anyone else. And I can tell you one thing for sure about immortals: They're very careful. They don't leave things up to chance. They've invested too much effort in becoming immortal. I don't know what they look like, I don't know what they want from you, but if you ever get to see them, this is the only piece of practical advice I have for you: Something you think is dead cinch safe, they'll consider an unacceptable risk. If there's any negotiating you get to do up there, don't forget what I'm telling you."

(Please forgive transcription errors.)

https://books.google.com/books?id=Q6o51-W_z8MC&lpg=PP1&dq=sa...

Perfect! Yes, this is the passage I was thinking of. Thank you!!!

The only civilizations we have known definitely show that contact involving a great technological difference is usually a disaster for the less advanced people. https://en.wikipedia.org/wiki/Fermi_paradox#It_is_dangerous_...

Scarcity is an important factor. Today, primitive societies (mostly) safe from Western conquest because they simply don't have anything we want.

That's more about selection bias than about anything that's inherently different about advanced societies today. There were primitive societies that did have valuable things [1], and they were all destroyed or conquered very soon after contact with more powerful societies, and they remain vulnerable to outsiders as soon as they come into possession of something of value. When gold was discovered on the land of uncontacted Amazonian tribes, for example, this happened: https://www.theguardian.com/global-development/2018/aug/22/a...

This is a pretty essential point that I think changes the calculus of contact quite a bit. A civilisation capable of visiting us at a reasonable expense to themselves would presumably have much easier access to near unlimited astroids/moons for automated mining.

So unless they really prize rare meat or have other illogical goals you wouldn't expect any aliens to visit us until its as easy for them as it is for us to take a transatlantic flight... I wonder if they're also arguing that they should stay silent to preserve our culture instead of curing our diseases etc.

The Dark Forest (Three Body Problem) explores this

Via video game, no less. Well, simulation-y video game. Sort of.

I thought we could Van Eck phreak the aliens.

Makes you wonder what they call Van Eck phreaking.

Gardan's Steelyard?

No wait, that's something else.

clearly Saunt Eck's inverted speely.

That's a very good point. When we first started listening for alien signals, we assumed that of course aliens would have TV and radio. In the few decades since then we have mostly switched to digital TV which has much more efficient (looks more like noise) encoding, and a trend of moving away from broadcast to YouTube, Netflix and podcasts is also evident (using both higher efficiency encoding and much lower transmit powers). And developments like 5G are intended to accelerate this development by using even higher coding efficiencies and shorter distances/lower power, as well as beam steering to directly target the receiver. Perhaps civilisations only typically use broadcast communications for <100 years, a mere blip at galactic scales.

Something like FHSS (https://en.wikipedia.org/wiki/Frequency-hopping_spread_spect...), not only a low level of signal is spread throughout a board frequency range, the central frequency is also changing many times per seconds, synchronization and decoding is only possible if the CSPRNG key is known. The signal of interplanetary communication is also highly directional.

I guess an alien civilization has much better ideas to avoid detection.

There's a difference between successful real-time decoding, and just determining from a full-spectrum recording whether it is the case that a signal exists, even if its behavior is unpredictable.

The point of spread-spectrum signal is that it's indistinguishable from noise unless you know the key.

With frequency-hopping you still have spikes in the spectrum around the frequencies you hop between, but with most modern systems you no longer have anything distinctive to find.

It's not indistinguishable from noise, if it is powerful enough to be received at all. If you filter based on the background noise threshold, you will discover a signal that quickly jumps frequencies in a pattern that is unpredictable without knowing the secret key. If frequency hopping is all that is used, you could even recombine the pieces to put the original message back together again. But in any case it will be very plainly obvious that the signal exists. A radio with a hardware limitation of only tuning to a specific frequency at a time would be unable to pick up on it, and would only hear transient blips as the signal enters and leaves the channel, which is what people mean when they say spread spectrum "looks like noise".

You could defeat this analysis by actually broadcasting noise on all frequencies, so the transmission frequency is indistinguishable, assuming the encryption used is also indistinguishable from a random oracle. But now you have a noisy point source in the sky, even if you can't decipher the contents of the message.

Succinctly put, obfuscation techniques like frequency hopping spread spectrum are tactical techniques that try to hide transmissions from actual radios in widespread use, not hide the existence of the radio signal in some physical sense. FHSS radio transmissions look like noise sources, not silence. Which is basically what SETI is looking for -- sources of radio noise unexplained by our understanding of astronomy.

It is possible for the signal to be below the background noise. For example, GPS works this way. Sonars on submarines do the same thing, they send out a noise-like signal that can be detected only if you know what to correlate it with. There's always some noise to hide the signal in.

This isn’t true. If the signal was below the noise threshold, and no mechanism provided for detecting noise separately (as twisted pair provides, for example) it would be literally impossible to separate signal from noise. That’s what the noise threshold means.

GPS is not below the level of background noise. Not is sonar.

what if there exist ultimate limit to knowledge itself and laws of universe that can be discovered? it would imply that any civilization that reaches that point will have nothing to gain from communication with other civilizations.

How would you know that you have reached the limit of knowledge?

You probably wouldn't be able to for sure but if you had no more unexplained phenomena around then you'd probably have a reasonable idea.

Of course that only applies to the laws of physics. You'd still have an effectively infinite universe of maths, geography, biology, etc. to explore.

You would still not know. Maybe there is a branch of physics that you're simply biologically not equipped to even perceive, comprehend or understand in the slightest. Maybe not. The point is that you can't know. Not too long back, people thought gravity as entirely newtonian and couldn't imagine that gravity could behave like waves. Or that particles can exist as both particle and wave.

IMO the limit of knowledge is simply the limit of information you can cram into a region of space without it collapsing into a blackhole because of that.

No matter how hard you try, you cannot teach a mouse to learn french. That is why.

That's more a reason why knowledge is unlimited; a mouse is incapable of understanding french, but knowledge of french does and can exist, so the mouse doesn't know everything. There is a biological but not inherent limit.

There's also the possibility that some ET's may want to be known, and are sending out an easily-detected beacon.

That might be our best hope.

I have a half-baked idea that some alien planet's marketing team is probably using pulsars as an advertising stunt. "Relax on Risa" and the like. I don't know how one would go about modulating a pulsar's output, but pulsars are seen everywhere.

Maybe a modified star lifting process could work to change the pulsars pulse rate? https://en.wikipedia.org/wiki/Star_lifting

Sounds like a trap...

Yeah, who in his right mind would broadcast his position to all the possibly much more advanced, resource-hungry and expansive species out there? ;-)

Perhaps someone with a very strong conviction that they are already the most advanced, resource-hungry, and expansive species out there ;)

The Borg have become lazy indeed.

I would make all my planet's tech based off of sewage.

Borg Drone 8 of 200: "Nothing to Assimilate here...time to go assimilate Risa".

But how do we know our concept of an easily detected signal isn't merely a product of how our technology evolved?

I think it's worth investigating and looking for signals because it does find interesting phenomenon, I'm just very skeptical we'll ever find intelligent life doing so.

> how do we know our concept of an easily detected signal isn't merely a product of how our technology evolved?

Because 150 years of investigation very very very strongly implies that electromagnetism is one of the most powerful of a very short list of fundamental forces.

Even then you have to ask "How long do ETs live?"

Listening for radio signals is way, way cheaper than broadcasting. It might be fair for an advanced civilization to fire up its transmitter for one year every thousand, and transmit a dense "welcome to the universe, here are our civilization's greatest achievements" message to all the listening civilizations. Running a listen-to-the-sky antenna for 500 years is still vastly cheaper and easier than what the advanced civilization has to do to transmit the message, and transmitting constantly is kinda hella wasteful.

I think the idea is not whether we could speculate in a useful way about an FTL or otherwise seemingly impossible phenomenon that we are not yet aware of. It's more about the probability that phenomena and technologies that are far beyond our current understanding can exist or not. In all likelihood we would have the intelligence and technology of ants relative to a million year old civilization. We shouldn't limit what is possible in this universe to what ants are able to comprehend and achieve. Even without such an argument, we only need to look at what we thought was possible 500 or 1000 years ago, and extrapolate forward that in all likelihood our currently understood limitations of physics will all but be irrelevant in 1000 years.

Agreed that it's a flight of fancy to speculate on these yet unknown capabilities, but that doesn't mean they aren't highly likely to exist.

I don't see it that way. 100 years ago we had a million questions about physics, and lots of fundamental values were a mystery. Today the fundamental values have all been measured to a high degree, and we have a few questions about physics and lots of them epistemological.

If in 1M years we have a different view about the universe it won't be because we were wrong about physics today. It will be about something underlying or outside physics?

Every kind of matter that we know about makes up less than 5% of the believed matter in the universe. What's the rest? "Dark matter" and "dark energy" which are effectively empty placeholders. We know almost nothing about them, and yet they're the overwhelming majority of what exists.

Maybe they'll turn out to be boring and useless. Maybe they have even more complex interactions than ordinary matter does. About all we can say today is that there's a mystery 20x more massive than all known matter.

'Almost nothing' is not quite right. We know the fraction to 3 or 4 decimal places. 'What it is' may still be a question but we know precisely what it does

Describing the amount there is and that it exerts gravitational pull says almost nothing about it, assuming it's as complex as anything else in the universe.

We also know that, other than via gravity, if it does interact with matter or EM radiation at all it does so spectacularly weakly.

Erm, seriously?

Or do you only mean classical, newton physics?

Because as far as I know, (quantum) physic is far from explained. Shure we do know a LOT more than we did 100 years ago, but I doubt we have fewer questions. I even suspect it can never be fully understood. Some basic principles, yes. But if the universe is infinitely big and small and it seems it is, there is no full understanding nor resolving all questions. I thought that mindset died out allready. Because before quantum mechanics etc. physicist actually did thought they allmost solved all questions. And then: oh. There might be more ...

I thought the whole idea behind quantum physics is that the universe is NOT infinitely small and that the minimum size / amount is a quantum.

Not at all! -> https://physics.stackexchange.com/questions/9720/does-the-pl...

Sometimes I wonder, how confident were our ancestors when they thought fire was an element, or when the Egyptians made mummies and hoped they would come back to life. Did they have the same level of confidence as we do today? That the "fundamental values have all been measured to a high degree"?

If that's the case, then we can be as wrong as they were.

We don't know what we don't know.

That doesn't imply that we don't know what we do know, however.

It doesn't seem likely that everything we've observed, discovered and experimentally verified about the universe since the beginning of recorded history is simply wrong, or that our level of ignorance about the nature of reality remains constant regardless of the data amassed.

We have absolutely no idea whether the universe or its complexity are infinite. With that out there, it leave the possibility that no matter how much knowledge we amass, it's at best infinitesimal in comparison to all that is possible to know, and at worst, our models will be completely contradicted by some new knowledge that puts previous learning in a different context.

The set of all primes is also infinite, but that doesn't mean it's possible to find an even prime number greater than 2... the universe can be infinite but that doesn't imply the laws governing it are also infinitely varied.

My point was not to state the truth but to show the possibility. Unlike prime numbers, the historical pattern is that our model of reality has changed fundamentally several times.

An easy, however unlikely, example of what could change it again is to find out we are in a simulation.

> nature of reality remains constant regardless of the data amassed.

It does not remain constant. But it remains indeterminable. Ie we can say we know something about the universe. But we cannot say we know x % of the universe simply because we have no way of knowing what 100% is...

We do know that we don't know what we don't know though, which should hopefully reduce the urge to make overly confident statements about the limits of reality.

>Agreed that it's a flight of fancy to speculate on these yet unknown capabilities, but that doesn't mean they aren't highly likely to exist.

It's just as likely that there are constraints on what is possible that we are not aware of. Take Newtonian physics for example. It turns out physical systems are significantly more constrained by relativity than Newton would have supposed. Relativity makes less possible, not more.

We might assume that super advanced civilizations can do things based on our understanding of physics, but we might be wrong. A Newtonian physicist might assume an advanced civilization could accelerate rockets to arbitrarily fast speeds and get to the nearest star in less than 4 years, but would have been wrong.

A Newtonian physicist would also have known that it would take an awesome amount of fuel to accelerate to very high speeds. Being unaware of nuclear power they would have concluded that it's utterly impossible to go fast enough to reach even the nearest star in reasonable time frames.

At 1 g of sustained acceleration you do get to nearby stars in a number of years.

The big impact of relativity is that less time passes on the ship.

> Relativity makes less possible, not more

That's not strictly true. Before relativity, time dilation was not know to be possible.

> Agreed that it's a flight of fancy to speculate on these yet unknown capabilities, but that doesn't mean they aren't highly likely to exist.

Right, but since we have no scientific basis for figuring out which capabilities those would be, the reasonable guess is that EM is the best means of communication. It's more likely that we've figured out some basic physical limitations, even if there exists technologies within those limitations far beyond what we've though up so far.

Sure, and as I mentioned in my comment, I agree there isn't much value to speculating what these unknown phenomena or technology are. But, the value to recognizing that there is non-zero probability that they exist prevents us from making overly confident statements such as "the reason we haven't seen radio signals from other civilizations is because we are the only intelligent species in the universe"

This is for much the same reason that we could transport everything in our civilization by people carrying things around on Segways, but we don't, because why would we deliberately choose something suboptimal?

In some high profile military simulation exercises, the "Iran" side used motorcycle couriers to side-step the "US" advantage in signals intelligence. Perhaps other civilizations which manage to survive know something that prompts them to use highly directed, highly efficient spread spectrum technologies which are very hard for us to detect?

Perhaps the universe is much more dangerous for intelligent beings than we know in our youthful naivete as a species?

Besides emissions security, perhaps there's the equivalent of "never underestimate the bandwidth of a station wagon full of mag tapes" (with, say, a lattice of atoms of different types instead).

Perhaps other civilizations which manage to survive know something that prompts them to use highly directed, highly efficient spread spectrum technologies which are very hard for us to detect?

Perhaps the universe is much more dangerous for intelligent beings than we know in our youthful naivete as a species?

This is terrifying.

"The Three-Body Problem" (& its sequels) are a fantastic exploration of this terrifying idea.

I don't think it's really worth considering as a realistic reason for societies choosing suboptimal technologies, but maybe some sort of Skynet scenario is possible, or something more like Frank Herbert's Butlerian Jihad[1].

https://en.wikipedia.org/wiki/Butlerian_Jihad

"had been a semi-religious social upheaval initiated by humans who felt repulsed by how guided and controlled they had become by machines:"

Boy, that rings true right now. I kind of hope that happens.

Yeah in the books the universe life is kinda shitty for tens of thounsands of years because of the restrictions on "thinking machines". It is pretty much a blanket ban on much above a 80s level non networked pc. Anything that breaks it is pretty much black market good or used an excuse for military take over by a stronger feudal house. All automation pretty much requires a human in the loop. Also any machine a "in a image of a man is banned" also pretty much a prosthetics will get the owner killed. The Dune universe is a dystopic hell hole for anyone not a member a noble house or an administer for Chom mega-corp.

i feel this is too hyperbolic in the wrong direction. there is clearly more beyond our current knowledge of physics, so why is it beyond the realms of reality to assume that something in that subset of all knowledge is useful? we didn't even know of the possibility of gravitational waves a century ago and just confirmed their existence. so why is it reasonable to say they couldn't possibly be useful for communications?

in dealing with the eventuality of alien civilizations, we must open our mind. it is certainly probable they communicate in ways we can't understand, even if they are simply evolutions of our current communication methods.

I agree with your praise of EM. But hypothetical aliens might want to explore some trade-offs. The game we are playing is to find some advantage in the known physics of a medium even if we know of no practical way to create and detect those signals.

Neutrinos spring to mind: we can't work with them because they don't interact with matter. But if you had some technology that could interact with them, you would have the advantage that nothing in the natural world screens them much.

Even if that technology was much more cumbersome than radio, aliens might have special cases uses for it (e.g. for signalling to and from their secret base at the centre of the Earth).

Neŭtrino detectors are coming along nicely! For example, see this paper on the compact COHERENT detector, which is theoretically portable!

https://arxiv.org/pdf/1708.01294

It can only detect neutrinos <50 MeV but still, wow.

Production, modulation and beam forming (and then demodulation and background removal) is a significant challenge, but neutrinos have many advantages for signaling for a galactic civilization, such as not needing to worry about occlusion.

To me the most straightforward thing to think about is EM waves at frequencies we can only imagine. Very different sources and detectors from what we have, therefore the radiation is undetectable to us (also very line-of-sight), but still the same physics in terms of the properties-of-the-universe required. I would imagine this increase would be developed for the same reason we have gone from KHz to GHz in a hundred-odd years: The higher the frequency the more information you can transmit per second.

So, you're thinking those cosmic rays are really symbols in an alien modulation scheme? Quasars are really light houses...?

Ha ha yeah that would be scary-cool-- the cosmic charts showing black holes to avoid and such.

The issue with high frequency communication is the power needed to sustain it, since energy goes up as wavelength decreases.

I suspect that's not the biggest issue. Developing the tech to create a and detect a modulated wave at these frequencies is way bigger, IMHO. You might be using nuclei as detectors, for example.

But in my imagination I can see this being solved.

Maybe it looks something like this:

https://www.technologyreview.com/s/611977/get-ready-for-atom...

Yeah- maybe using a nuclear version of this ("Rydberg nuclei?"). Thanks for the link!

Or perhaps we are a only advanced civilization in the known universe and other civilizations are using some lo-tech method of communication like creating sounds or fire signals. Add we are looking for only high-tech modes of communications.

Thanks, I am now imagining interstellar smoke signals. I feel like that's pretty unlikely, though. :X

I'm assuming parent meant they're communicating across their own world using those forms, and we should be looking for timed puffs of smoke :)

Fantastic - but at what interval? Our lives may be measured in years, while another life form may measure itself in eons. How rapid must their oscillators be to download their own equivalent of Netflix? 1E-08 Hz? (Can we detect such slow oscillations? Is there a minimum timescale for consciousness?)

Using an SDSSD¹ they wouldn't need to tune to any specific oscillation. Just collect the data and start Fourier-ing it to find the signal.

1: Software-Defined Smoke Signal Detector

But we didn't suspect EM radiations existed until we started understanding electricity, magnetic fields, etc. What else do we not suspect exists today but will be obvious in 50 years?

We knew light existed long before we understood electricity and magnetic fields, even those had observable effects to us long before we discovered them.

That is because we could "see" it. Imagine if we were not able to see. Could we have known the existence of EM?

Or think if we were not able to hear. Could we have imagined the sensation of sound, or the concept of music?

Human beings are so pathetically stupid that they think that their intelligence and sensory capability are at the limits of what is possible.

>That is because we could "see" it. Imagine if we were not able to see. Could we have known the existence of EM?

Probably, it has a number of physical effects, like heating up the areas that it hits, there is probably quite a lot we could have deduced about light with no eyesight, as long as we lived somewhere EM existed had a noticeable effect, which is just about everywhere.

> Or think if we were not able to hear. Could we have imagined the sensation of sound, or the concept of music?

Of course not, but that wouldn't prevent us from understanding the concept of pressure waves.

> Human beings are so pathetically stupid that they think that their intelligence and sensory capability are at the limits of what is possible.

What? We know our sensory understanding has sever limits, no one that graduated the third grade thinks our sensory capability are at the limit's of what's possible. Everyone that has ever seen an x-ray knows this. To quote Brother Cavil:

I don't want to be human! I want to see gamma rays! I want to hear X-rays! And I want to - I want to smell dark matter! Do you see the absurdity of what I am? I can't even express these things properly because I have to - I have to conceptualize complex ideas in this stupid limiting spoken language! But I know I want to reach out with something other than these prehensile paws! And feel the wind of a supernova flowing over me!

> as long as we lived somewhere EM existed had a noticeable effect, which is just about everywhere.

You should have understood that I meant otherwise. Of course, if we could notice the effect of EM, that could trigger an investigation eventually leading to the discovery.

>we know our sensory understanding has sever limits...

Did you really think I implied that no one knows the limits of our built in senses? When I said sensory capabilities I meant the stuff we can sense, directly or indirectly (By indirectly, I mean by the help of another device, to make it very clear).

> You should have understood that I meant otherwise. Of course, if we could notice the effect of EM, that could trigger an investigation eventually leading to the discovery.

Can you suggest an environment conducive to life that isn't exposed to EM radiation? Life itself creates EM radiation.

> When I meant sensory capabilities I meant the stuff we can sense, directly or indirectly (By indirectly, I mean by the help of another device, to make it very clear).

I can't prove God doesn't exist either, but that doesn't make it logical to conclude that we will one day be able to harness the power of God for FTL communications, but this is what you're expecting. If there are fundamental forces left to be discovered then they are not having any observable effect on the world, making them unlike all other fundamental forces. This makes them unlikely to ever be discovered.

>Can you suggest an environment conducive to life that isn't exposed to EM radiation? Life itself creates EM radiation.

There is nothing in the definition of "life" that warrants an ability to observe EM radiation or create it for that matter..By the way, what is the definition of "life" that you are using here?

>there are fundamental forces left to be discovered then they are not having any observable effect on the world..

So just because we haven't discovered something, does it mean that that thing is not observable at all? We are still discovering "things" in our own body, let alone in the entire world. The fallacy that human beings are capable of detecting every observable (by observable, I did not mean observable with our current tech) phenomena in this world is exactly what I was indicating before.

> By the way, what is the definition of "life" that you are using here?

An incredible loose one. Basically any process remotely complicated enough to call life would be producing infra red radiation at least. From there the evolutionary pressure to be able to sense it is huge. Eyesight on our own planet could have evolved to see heat long before sunlight.

Unexplained physics today is primarily down to dark energy and dark matter.

The good news is that collectively they represent about 95% of the universe. So, that's a huge quantity of phenomena that we can't currently explain!

The bad news is that we have no local evidence for either; they only seem to have measurable effects over cosmic distances. So that implies that, even if we fully understand them, it's unlikely we will be able to harness the mechanisms to accomplish things at the scale of our civilization.

And--neither provides any evidence of FTL effects. So it's even less likely there is some amazing new form of FTL communication hiding in them.

How about soliton pulses in a plasma? Isn't interstellar space mostly plasma? Its still EM radiation. Such pulses can survive incredible distances undiminished, and they are point-to-point (not broadcast). So other civilizations might be using this, and we'd never notice unless we got between them and their target by accident

And of course it would be compressed or encrypted or both. So it would be indistinguishable from noise (as mentioned in other replies)

> And of course it would be compressed or encrypted or both. So it would be indistinguishable from noise (as mentioned in other replies)

The perennial optimist in me thinks that that all the work on cracking Tor is finally going to pay off when we can decipher alien's sending each other selfies.

No reason to assume that they use the same encryption schemes we do.

Well Geoff Goldblum made that assumption, and he was able to scp his files straight into an alien workstation soooooo

I put "soliton pulses in a plasma" in a search engine and everything that came back was well above my head.

Does anyone have a link to something that explains this in plain language?

In a plasma (or certain nonlinear media) a wave will not diminish in size. Its why waves in shallow seas can go for hundreds of miles unchanged, why light pulses in fibre optic cables can cross the ocean bottom without diminishing to noise. These waves are called solitons. It was my EE Professor's (Lonngren) favorite research topic back in my undergraduate days

Perhaps, if it gets a sequel, this (or similar) will be revealed as the cause of the "event" in _Seveneves_?

I think neutrinos would be viable with real world physics. They can go through anything which would be pretty useful and you can direct it easily.

We don’t have an easy way to detect them but a more advanced civilization might.

That's the paradox, isn't it? You want something that doesn't interact with matter until to reaches the detector, where you want it to interact as much as possible.

That's not a paradox, it's just the property that good communication medium should have.

EM waves have this property thanks to effect of resonance in the reciever. Neutrinos will have this property (but better) once we learn how to emit and detect them efficiently.

Wanting two opposite properties simultaneously is paradoxical requirements.

And no, resonance isn’t the reason for EM. Faraday cages are not resonant, and they block (certain frequencies of) EM. Neither are lenses, and they make directional detection of EM much easier. And, honestly, I’m not sure what the right word is for individual photons being absored by atoms or molecules.

EM is a fundamental force. Everything interacts by fundamental forces, even neutrinos, but even though I think neutrino communication is cool and potentially useful in limited circumstances, it’s not reasonable to just assert that aliens will be chatting interstellar with them. EM is about the best you can get for interstellar because there’s nothing in the way to block it. Neutrinos are what you would use if there is a lot of stuff in the way — like, say, a planet or a star — and you benefit from the slightly lower lag time of going through it instead of bouncing around it, or you can’t go around it because thing you’re talking to is in the middle of it.

Even if you posit that super advanced alien technology can make wormholes, the only way you’re going to get anything other than light going through them is if they turn out to be really small and it’s better to have a high energy electron (=small DeBroglie wavelength) beam going through them.

> You want something that doesn't interact with matter until to reaches the detector,

Axions [1]!

[1] https://en.m.wikipedia.org/wiki/Axion

In transiting space, the problem is far more the detecting than the getting through tings.

Space is mostly not-things.

(With some interesting exceptional cases.)

I'm not aware of any useful neutrino lensing mechanisms, either.

> flights of fancy

It seems presumptuous to dismiss the entirety of non-Standard Model physics thusly. Axions [1] are one of my personal favourites.

[1] https://en.m.wikipedia.org/wiki/Axion

>If you want to go off on flights of fancy, then anything is possible, but there's no way to say anything useful about it.

I would guess, though I could be completely wrong, that a civilization that both had access to far more advanced 'sci-fi' level technology and wanted to broadcast it's existence would also have an understanding of the technology other civilizations would have access to and would choose to broadcast using numerous 'ancient' technologies that more privatize civilizations could pick up on.

When we sent probes out into space to broadcast ourselves, we realized we couldn't just write a message in English and as such tried to send numerous different ways of conveying information, some linguistic and some not.

> Even on the crazy fringe frontiers of real science, I am not aware of any candidates for communication any better than EM.

There is one, and it is essentially

> people carrying things around on Segways

Electromagnetic radiation must obey the inverse square law. It spreads spherically through space, so required power for a given SNR raises with distance squared.

Moreover, there are severe interference issues. Once you have several systems communicating on the same bands you get more noise in the relevant frequency bands.

Unlike waves which don't self-interact (i.e. obey the superposition principle, are linear), matter is coherent. If you shoot a hard drive at a distance galaxy (with greater than escape velocity), it may take significant time to get there, but you can travel arbitrarily far for essentially the same energy, as a first approximation.

Of course, as a second approximation there is necessity of guidance/control (because of finite motor precision, target uncertainty, etc), but also the possibility of harvesting energy or photon momentum from stars en route.

Aside from the expansion of the universe there's no theoretical limit as to why a sufficiently advanced probe couldn't propagate information arbitrarily far (if it "refuels" periodically, then its total energy usage is proportional to distance, i.e. linear, but launch cost stays bounded).

In the worst case (perhaps for cosmically large distances) it'd need to colonize a planet en route to rebuild a pristine copy of itself.

"Never underestimate the bandwidth of a station wagon full of tapes hurtling down the highway."

–Andrew Tanenbaum, 1981

https://what-if.xkcd.com/31/

"The only way to actually reach the FedEx point is if transfer rates grow much faster than storage rates. In an intuitive sense, this seems unlikely, since storage and transfer are fundamentally linked—all that data is coming from somewhere and going somewhere (...)"

https://en.wikipedia.org/wiki/Sneakernet

EM doesn't have to spread spherically. There is such a thing as directional antennas, spotlights, or even lasers. Yes they spread too, but throwing a hard drive at distances on the scale of light years isn't going to be precise either. Go far enough and you won't hit the galaxy you wanted to.

Directional antennas still obey the inverse square law, because the beam still diverges as it travels. So the amount of energy that you spend sending the signal gets spread over a larger and larger area, meaning that at any given point in that beam, the signal is weaker and weaker, until it gets lost in the noise.

And even lasers diverge. An ideal laser has some minimal divergence that is inherent and cannot be overcome (if I understand correctly, it's because diffraction is non-zero even in vacuum). A true Bessel beam doesn't diverge - but it does not have a boundary, and hence requires infinite energy.

In order to achieve a Rayleigh length (effectively the "range") that is smaller than the distance from Earth to the nearest star, a (visible) laser should be approximately 40 kilometers wide. The effective range scales as the square of the beam waist, so you can communicate with the Andromeda galaxy using a laser just a little smaller than Neptune.

> Go far enough and you won't hit the galaxy you wanted to

This can be solved, in the limit of large distances (i.e. many galaxies away), by the aforementioned method of refueling/rebuilding/re-guiding along the way. But between each galaxy there's a vast, barren chasm to cross with little resources, I concur.

Wait, why is Quantum Entanglement a non-starter? How does that require a conventional channel? Once you have the two entangled, assuming you have some way to change the state of one with out breaking the entanglement, then how is that not enough for communication?

You still need to transfer a message using a classical channel to actually communicate anything. Remember, there is no known way to communicate faster-than-light.

https://en.wikipedia.org/wiki/No-communication_theorem

Following this rabbithole lead me here, which explained it in a way that made sense to me: https://www.lesswrong.com/posts/DY9h6zxq6EMHrkkxE/spooky-act...

Just in case anyone else is struggling with this, as I was :)

Good article! This part makes me laugh though

>Here's something that, as a kid, I couldn't get anyone to explain to me: "Why can't you signal using an entangled pair of photons that both start out polarized up-down? By measuring A in a diagonal basis, you destroy the up-down polarization of both photons. Then by measuring B in the up-down/left-right basis, you can with 50% probability detect the fact that a measurement has taken place, if B turns out to be left-right polarized."

He must have been a pretty smart kid...

Geeze that's a lot of words to explain something so simple.

Lets say you use pure energy to create a particles with a non zero spin (substitute a charge if spin is confusing) that immediately separate from each other at high speed. The rules of the universe demand that the sum of the spins (or charges) equals 0: eg if one is an electron the other must be a positron. So now you have two particles flying towards you and me, but no one in the universe knows which is which except possibly the particles themselves, so we say they are entangled. If I look at the particle coming towards me I have no way of knowing if I will see a positron or a electron. When I do look, I know what you will see if you look. Which is nice, but no information has passed from me to you. Instead have both learnt something new. The definition of communication is you pass some knowledge you knew before the process started onto me. (In fact we learnt the same thing.)

The word entanglement seems to imply if one particle changes the other undergoes a corresponding change. Whether that's true or not is a bit of a mystery. In any case it doesn't matter how it happens. Even if there was a "global variable" and even if it suddenly changed value when one of us observed it, merely observing it destroys the entanglement. So yes we both learnt something new and maybe it was communicated faster than the speed of light, but we now know the first observation doesn't communicate any information we knew before. And because observing it destroyed the entanglement no new information can be transmitted.

The way I understand it is that you still need a CLK signal, entanglement is the DATA pin. The primary purpose of entanglement is privacy. A sufficiently advanced species may choose to use entanglement to hide from the rest of the galaxy, and the CLK radio burst could be made to look suspiciously like natural phenomena (FRBs).

However, a major point of contention is that humanity occurs far too soon in the life of the universe. It has taken life on Earth 3.5 billion years to evolve to us, that means that there have been just under 4 epochs of human evolutions in the age of the universe (and just over 1 epochs of human evolutions in the age of Earth). Chances are, using sci-fi nomenclature, that we are the "ancients." We have quite a lot to get done for those that follow.

Because once the particles are entangled, one has to be moved by conventional means to the destination while the other stays behind.

Which is still extremely useful for things like probes.

Instant comm's to Mars rover or even voyager.

Of course no ones figured out how to make use of entanglement for information transfer.

Pops up a lot in Sci-Fi, reading Three-Bodied Problem now and the aliens sent "sophons" basically probes the size of protons at near the speed of light to earth from Alpha Centauri, they arrived in a few years while their invasion fleet will take 400 years to get here. The sophons spy and interfere with earth communicating with aliens via quantum entanglement.

> Of course no ones figured out how to make use of entanglement for information transfer.

Saying "no one's figured it out" is misleading because it creates the impression that it's an engineering problem to be solved.

According to our best understanding of quantum mechanics, the laws of physics fundamentally do not permit faster-than-light communication, whether through entanglement or any other mechanism.

Well, of course they don't. How would you even begin to build a simulator for something like that?

Communications overhead between the nodes is bad enough as it is.

Our understanding of the model is thought to be quite poor. Further, we should not ever mistake the model for reality or attempt to fit data to predictions. The cosmos might not be anthropomorphic.

The no communication theorem is not the no communication hypothesis, it's actually a math proof. You start from the principles of quantum mechanics (unitarity, etc), define what you mean by entanglement (non-factoring states), and prove it's not possible to use those states to win the communication game. This is an aspect of quantum mechanics that we understand extremely well.

I was trying to imply that its probably the best avenue for research, and also we may never figure it out, might be a dead end.

However I would say the reason it is used so much in sci-fi is it currently the one way we can cause action at a distance faster than light, which is so tantalizingly close to communication.

I wouldn't say we're close to FTL transfer of information in any meaningful way. In particular,

> we can cause action at a distance

is not true, either.

>is not true, either.

I didn't think this was settled and depends on your interpretation of QM: https://en.wikipedia.org/wiki/Action_at_a_distance

…and on your precise definition of "action and a distance", yes.

But there is something like standard textbook quantum mechanics which most physicists subscribe to, i.e. the Copenhagen interpretation, and while I'm not saying this is the interpretation everyone should follow and believe in (in fact, there are good reasons to be dissatisfied with this interpretation), the term "action at a distance" was coined in the context of the Copenhagen interpretation, so I think should therefore also be interpreted in this context.

Now, Copenhagen is a local and non-realist theory, the latter of which meaning among other things that the wave function is not believed to be an object of reality. Therefore, in this interpretation, the collapse of the wave function is merely a tool for predicting the outcome of a measurement and not something that's believed to actually happen. The same thing goes for an "instantaneous collapse" at a distance — this action does not exist in reality.

I know there is probably going to be someone who objects to me saying that Copenhagen is non-realist and local. But those people will have to explain to me how they would bring the actual existence of the wave function and its collapse into agreement with relativity and, in particular, with different observers who come to different conclusions about when the wave function collapses. For instance, for one observer, it might be Alice who causes the wave function to collapse and, thus, Bob to measure a certain outcome but then there is always going to be another observer who will say the exact opposite, namely that Bob caused the collapse. So, essentially, if you really think the wave function is an object of reality, all hell breaks lose.

Needless to say, even if you completely disregard these issues and still want to think of Copenhagen as a realist but then necessarily non-local theory (in which case I'd say you should really give your theory a different name), this is all just splitting hairs because the only thing that matters is that there's no FTL transfer of information. This is the only experimentally verifiable statement we can make.

There is no reason to think quantum entanglement could be used for FTL communication. The theory which gives us entanglement also proves (mathematically) it can't be used for communication.

Sure, but you could still create a two way walkie talkie that couldn't be eavesdropped on and would allow faster than light communication this way, theoretically.

You can make it secure from mitm with this but it doesn't allow ftl. You can't use the entangled particles themselves to do the communication since you cant control how the superposition collapses when you measure it. This allows you to get two streams that nobody but you and the party knows but they're fundamentally random and unpredictable, you can't encoded information into it, just use it as a one time pad essentially.

But that in itself is a signal, right?

Say you have two sets of two entangled particles, all four particles in similar states. You have one particle from each set, your partner has the corresponding particles in the sets.

You check both particles you have, and:

- if both particles have similar state, then your partner hasn't checked any of their particle states, because neither have collapsed.

- if one particle has collapsed and is in a different state than the other particle, then you know your partner has at least checked the state of one of particle sets, possibly both.

If you partner is 50 light years away and checks it only seconds prior to your check, then they are signalling you at faster-than-light travel, right?

But you have to communicate the states of each other's particles (as far as you can tell random noise) to compare/contrast and glean influence, so it's only suitable for encryption of classically transmitted messages.

Think faster-than-light XOR ;)

Got it, so the state is random for all particles until it is measured by your or your partner, afterwhich the other particle state is known. But the act of measuring or the decaying doesn't tell you when (or if) they measured it because the state never changes, it just becomes known.

It's not random; it's a superposition.

It is perhaps less nonsensical (in a "common sense" way) to think of it in terms of the many-worlds interpretation. The moment you have created the photons, you have forked the universe - but observers on both sides are still identical in both worlds, because they haven't done anything that'd allow them to figure out which universe they're in. So for each observer, we treat both "versions" of that observer as one and the same.

Now, when one of the observers measures their photon, they figure out which fork they're in. And then in that universe, the other observer measuring it will also get the same result, of course, proving that they're also in that same universe. And in the other universe, the second observer will get the opposite result, again, proving that they're in that other universe. But neither measurement actually caused anything to happen, nor did they get any information about the opposite observer in their universe as a result of it.

Nope, you couldn't. From all the experiments and theory we have on entanglement, you can't use it to communicate faster than light.

abdullahkhalids has the correct answer. Even if you have the entangled particles already in place, you can't communicate with them.

The real proof is that if you could, we'd already have this technology and high-speed traders would already be using it. If it could exist, we have all the tools to build it; it's far simpler than even a 4-qubit quantum computer, which we've also built. We don't have it because entanglement can't be used that way.

First, you have to transport one of the entangled pair to your remote location.

> assuming you have some way to change the state of one with out breaking the entanglement

Second, this isn't possible.

When you measure the entangled pair, you know they'll be correlated: if one is A, the other is B, and vice versa. But when you measure one of the particles, you have no idea if you're going to get A or B. You don't have a way to force the entanglement to go a direction you want. So it doesn't serve as a communication channel.

> assuming you have some way to change the state of one with out breaking the entanglement,

This isn't possible. Not only is it quantum mechanically impossible to change the state of one without breaking the entanglement, it is quantum mechanically impossible to observe the state of one of them without breaking the entanglement. Remember that in quantum mechanics "interacting," "changing the state," and "observing" are all the same thing.

Can you know whether or not a particle is currently entangled? With observation of only 1 of the entangled particles?

Say you had millions of entangled particles, you ship their companions to the other end of the galaxy. You now have a million bit array to encode data into for 1 time use?

I’m guessing you can’t know whether a partical is currently in a state of entanglement...

EDIT: my question has already be asked & answered several times...one such example: https://physics.stackexchange.com/questions/207169/can-i-tel...

>which is a characteristic of the universe that it does not seem to allow any faster-than-light communication

Great answer, but do you have more information on this?

I thought quantum entanglement allowed for teleportation of information at faster-than-light speeds. Yes, there is the original information being parcelled and shipped at slower-than-light speeds, but the individual act of disentangling particles can act as a faster-than-light signal.

Information is defined in such a way as it may never travel FTL.

When entangled particles reveal their states, they do not at that point in time transmit any new information. The information was actually encoded into the entangled pair which travelled at less than light speed to that destination.

I imagine this answer is probably unsatisfying and counterintuitive to you, as it is to me.

Great answer, but do you have more information on this?

PBS SpaceTime. The Speed of Light is not about Light: https://www.youtube.com/watch?v=msVuCEs8Ydo

They could just high focus beams of extremely energetic photons or even gamma ray transmitters with encoding that’s basically “noise” because we grew and evolved around it. There was one theory for Tabby’s star that it was basically a transmission beacon and we happened to see the transmissions because we are in the line of sight.

> Maybe, but it's still easier to build EM detectors, and EM emitters, by a lot.

It's easier to build paperclip factories than iphone factories but we are awash in both and some people own more iphones than paperclips.

Why on earth would you build EM emmiter if by bit more effort you could have device for unobstructible communication?

This is a very panglossian statement. You just recited a version of the "Best of all worlds" fallacy.

so the sun could not be a complex communication device? programmed by "someone" billions of years ago...

I don't know if I'd describe the speed of light as "low", more like the universe is really, really big

Things would be a lot simpler if it were faster though :)

Consider a modern cpu running at 3ghz. It can retire some instructions on every cycle. Light can travel one mm in that time. That means the part of the core that decodes the incoming stream of insns is effectively outside the lightcone of the part that retires instructions.

I make it 100mm, not 1mm.

A related point is that we can't just make a single CPU do more computations per unit time by making the CPU bigger because the finite speed of electricity (which is upper bounded by the speed of light), determines the largest size of the CPU before the different paths that electricity takes through the CPU logic gates become out of sync.

Then the speed of light is still not slow, cpus are just really fast. Point being, everything is relative, and lightspeed isn't necessarily the limiting factor.

c * (3 ghz)^-1 ~= 10 cm

You don't sound like you do a lot of distributed/network programming. The speed of light is achingly, infuriatingly slow.

Here's a faster than light issue I have:

Take a really weak light source. Aim it at a beam splitter, say, at 45 degrees to the line of the light. Assume that the light source is so weak that typically we get a photon only one a second or so (not strictly necessary for the idea).

Then each photon (there are standard claims that could also use an electron, proton, neutron, etc. but all photons travel at the speed of light, and using just light we don't have to worry about the electric charge of an electron or proton) has a quantum mechanical wave function. From the lessons we get from Young's double slit, the Michelson-Morley experiment, the Mach-Zehnder interferometer, the Fabre-Perot interferometer (right, my ugrad physics prof liked optics!), we believe at the beam splitter the wave function becomes two parts, one part continuing straight through the beam splitter and the other part going off at 90 degrees.

Now sit and have a brewski or two; finish a physics Ph.D.; get married; have a lot of kids; get them all through college; and, I omitted, for the beam that went through the beam splitter, have it bouncing around in a box full of perfect mirrors or resting in some Bose-Einstein condensate, and then get out a very sensitive photo detector and try to detect the photon.

Okay, for a perfect beam splitter, have a 50% chance of detecting the photon. Suppose we do, or, suppose we just in the beginning did this stuff for 1000 individual photons and pick one of the photons where we do get a detection from the part of the wave function close to us (the other half of the wave function is way past the nearest star by now).

So, we get our detection. We know the energy we get, just proportional to the frequency of the light. So, our detector gets it all -- the wavelength, the frequency, the momentum, the energy, maybe the polarization. Fine.

Now, folks, what the heck happens to the other half of the wave function, the half that went 90 degrees and by now is part way out of the galaxy?

No sense in saying that half just disappeared. For one, ET way out there 50% of the time could detect the photon. For another, we could have a mirror out there and have that half of the wave function return to us and do a Young's double slit or Michelson-Morley experiment where both parts of the wave function definitely get involved. So, no saying that the half of the wave function nearly out of the galaxy doesn't matter.

I know; I know; that half of the wave function gets old and tired, goes de-coherent, etc., but such stuff raises other little issues such as conservation of energy. So let's assume that, even after all these years, both parts of the wave function are still nice and healthy just like they would have been in Young's double slit, the Michelson-Morley experiment, etc. Besides we believe we can detect photons 13.8 or so billion years old, and, really, some of those may have their wave functions, from being deflected here and there for all those years, in multiple parts.

But we know also that we and ET can't both detect the photon. So, that part of the wave function out there with ET can't just do its own thing -- with us and ET, there will be exactly one detection.

Okay, when we get the detection, supposedly the other half of the wave function, some light years out there where ET is, disappears, folds up, evaporates, leaves town, becomes null and void, instantly, just as soon as we make our detection. So, sorry guys, that looks like an instantaneous effect (I didn't say communications) over a distance of light years. So, the naughty boy in his room running the simulation for our universe, as soon as we detect the photon, has to run around all over the whole darned universe and clean up any stray pieces of the wave function of the original photon, and there may be thousands of those. During this clean up, the whole simulation (think of a data base problem!) has to stop. So, the simulation has to run all over the universe or a lot of it in zero time -- that's an effect infinitely fast!

I know; I know; this is not faster than light travel for us, but it looks like faster than light travel for the naughty boy's universe simulation program.

Now from this, what can we say about how the quantum fields we believe in actually have to work? Is there something?

E.g., suppose both we and ET have really sensitive gravitational wave detectors and, thus, can detect each of the two pieces of the wave function as they pass by. Uh, the photon has to feel gravity and also create gravity, and, thus, BOTH parts of the wave function have to create gravity. So that part of the wave function that ET gets MUST create a gravitational wave as it passes by and MUST create a gravitational wave as it disappears instantly as we detect the photon. We're getting close to faster than speed of light something or other ...!

Okay, suppose ET is 10 light years away and we want to spend the next 10 years setting up an instantly fast communications channel.

We agree to send one bit a second.

We use the beam splitter, ..., etc. as above.

If we are using our elecgtro-magnetic detector, the for each photon we have not detected, ET gets both a gravitational wave detection and a photon (electro-magnetic) detection.

For each photon we do detect, ET gets neither the gravitational nor the electro-magnetic detection.

If we put our detector in the path of our half of the wave function, then we get a detection half the time which means that half the time ET gets neither a gravitational nor an electro-magnetic detection.

If we do not have our detector in front of our half of the photon, then ET always gets the gravitational signal and half the time gets the electro-magnetic signal.

So, suppose each second (since when we started spending 10 years setting up the communications channel) we sent 1000 photons a second.

Now for one of those seconds, if we are using our electro-magnetic photon detector, ET gets about 500 gravitational wave detections and 500 electro-magnetic detections. If we are not using our photon detector, then ET gets 1000 gravitational wave detections and 500 electro-magnetic detections. So, once we have spent 10 years setting up the communications channel, we can communicate at data rate of 1 bit a second with ET instantly.

I don't really believe it, but first cut it looks that way!

Now each second, we either put our detector in the path of our half of the wave function or we don't.

> BOTH parts of the wave function have to create gravity

Nope. Wave function obeys gravity but it does not create gravity. Gravity is created by matter/energy and wave fuction is not that.

The energy of the photon must generate gravity and must be somewhere, e.g., covered by the non-zero parts of the wave function.

Staying grounded in current physics is not a good idea. Humans are primitive and other civilizations capable of traveling the solar system is not.

Its like if you would ask a human 500 years ago how he think aliens would travel. He would say something likely in that age according to his understanding. We are exactly the same.

I think the parent meant -- or a least a steelman of the point would be -- whether there could be some kind of particle/field/force/form-of-energy we're missing out on that could be used to communicate (even if slower than light), and whether there's some way to rule that out. I don't think that's dismissable as being a flight of fancy any more than the existence of radio waves would have been in 1500.

"I don't think that's dismissable as being a flight of fancy"

What else would a flight of fancy be other than imagining something that we currently have absolutely zero evidence for?

I have no problems with flights of fancy. I like sci-fi quite a bit. I do have a problem with people not realizing they're taking flights of fancy. At the moment, as I said, I am not aware of anything even on the fringes of science that would permit a superior communication technology over EM, and I'm as informed as you can expect a layman to be about the holographic universe idea, violations of the standard model, various dark matter theories, hypotheses about various possible spatial deformations permitted in general relativity that may have started at the big bang, and everything else. There's not a lot of reason to expect something to pop up that's going to be better than light. At best, you could hope to tie it, because it's frankly already nearly perfect, and I wouldn't even hold out a lot of hope for that.

> I am not aware of anything even on the fringes of science that would permit a superior communication technology over EM

In another comment you mentioned things such as gravity waves, neutrinos, etc. You also mentioned that these things are far more expensive to generate than EM. I think those particular facts are "engineering problems to be solved" rather than just fundamental laws, yea? I never fired off a neutrino, I know you need a sun or a particle accelerator to do it, so I get why it's considered expensive, but is that inherent?

They didn't think particles could be proven as indistinguishable until they realize the laws of physics depend on it and therefore you could test for it.

I don't think it's a comparable flight of fancy to ask about whether there's a way you could detect unaccounted-for energy within some region that isn't one of the usual suspects.

Yes, there's always the "what if our understanding is completely broken", but your comments here feel way too uncharitable and dismissive, willing to equate the two kinds of questions.

"I don't think it's a comparable flight of fancy to ask about whether there's a way you could detect unaccounted-for energy within some region that isn't one of the usual suspects."

I gave you one interpretation of what I mean by flight of fancy already, which doesn't match what you seem to be reading it as.

The problem with the question about where stuff could be hiding is that, as I said, I'm as up-to-date as you can expect to be on this stuff for a layman, and I'm not aware of any "unaccounted for" energy that might be useful for communication. It is not known whether "dark energy" is simply a violation of conservation or if it is perhaps coming from somewhere else, but it doesn't seem useful for communication either way, and I'm not aware of any other places where energy is not accounted for.

Indeed, note all the modern articles are discussing how we are in precisely the opposite situation, and that's the problem for physicists today, that we do seem to have all the energy accounted for and there's nowhere else for physics to be hiding, which is a massive problem because we know we're not done yet.

At the moment, hypotheses about such things would be based on zero evidence. Again, I'm pretty comfortable calling that "flight of fancy". Maybe someday one of them will be correct. But the vast, vast majority of "flights of fancy" are not. Like that stupid "first they laugh at you, then they fight you, then you win" quote that everybody reads as if it's some sort of inevitability. In reality, what happens is that "they laugh at you, end of story" is the dominant case. There is no path of causality where simply because they're laughing at you you're inevitably on the path to winning. The ability to imagine in an incredibly hand-waving way that maybe something exists is not the slightest bit of evidence that it does.

> The problem with the question about where stuff could be hiding is that, as I said, I'm as up-to-date as you can expect to be on this stuff for a layman, and I'm not aware of any "unaccounted for" energy that might be useful for communication.

I'm aware you're not, and explained an example of a non-trivial, responsive answer which would differentiate between the "unknown" and "reasonable to rule out" case. "No, there is a way to measure the total amount of energy flux, across all sources, through a region and it rules out the possibility of undiscovered forms of energy passing through us without us knowing."

Similarly, if someone asked about whether Conservation of Momentum could be wrong, I would point out Noether's Theorem and how it falls out as a result of linear translational invariance of the laws of physics and thus has a higher barrier to disprove and what that would have to look like. I wouldn't just call their question a flight of fancy.

No one deserves ridicule for curiosity or asking which state the science is currently in.

All of your responses just come off to me as attempts to ridicule legitimate questions, so I don't feel comfortable engaging further.

>What else would a flight of fancy be other than imagining something that we currently have absolutely zero evidence for?

Exactly, but that was spirit of OP's question.

I do think that the fact that we can rewind our own history and find examples of technologies that were unimaginable at some more distant point in our history as something more than "absolutely no evidence."

> What else would a flight of fancy be other than imagining something that we currently have absolutely zero evidence for?

It would be a flight of fancy to argue for or imagine a specific one, but it's not a flight of fancy to say, "hey, there's probably forces and particles out there we don't know about or understand yet". Hell, it would be obscenely arrogant not to acknowledge that.

I'm going to take a stab at phrasing the question in terms of a simple yes or no answer. Do you believe it is possible that there exists a physical phenomena that, if described to you right now, would clearly be a "flight of fancy", however would in fact turn out to be real? Note I'm not asking you to state what that phenomena is or to "imagine" anything at all. Just that it can be ruled out that anything is really left to be discovered. Just as though it were the year 1500 and someone described radio waves to you. Because if you say no, that seems awfully confident that science has basically discovered every significant aspect of physical reality, it's just the small details left. The same attutide would have existed hundreds of years ago.

"Do you believe it is possible that there exists a physical phenomena that, if described to you right now, would clearly be a "flight of fancy", however would in fact turn out to be real?"

Yes, of course.

I think those of you who are finding your feathers ruffled need to go back to the initial post. The question is, do you want to answer the question based on current science, or do you want to imagine whatever you want to be the case? Both are valid options. But pick one. You do nobody any favors when you try to blurrily flick back and forth on a whim.

And the truth is, if you are going to just imagine whatever you like, there isn't much interesting to say about it precisely because anything could be true. Could aliens be communicating by getting high on DMT and have found a way to use DMT entities to transmit real, useful messages? Sure, whynot, but what's there to say about that?

By contrast, we can discuss what real science currently has to say about what aliens may be doing. Current science says there's not much reason to expect anything but EM. If you find that unfortunate somehow, that's a psychological thing, not a scientific thing.

Or, at least, we COULD discuss what real science has to say about it if people didn't immediately pop up with the equivalent of "But what about DMT-entity-based communication???!?" every single time.

Good answer, except for the last part. I think there is not much reason to expect we will detect aliens using anything other than EM, because that is all we know. But for all we know they could be sending messages to other galxies by communicating with the outside makers of the AI Elon Musk thinks created the universe.

Your turn: Yes or no, is "communicating with the outside makers of the AI Elon Musk thinks created the universe" something we have zero evidence for? Is that not reasonably categorized as a "flight of fancy"?

If yes, why do you expect to be able to say anything sensible about it? And why are we apparently obligated to discuss it despite explicitly setting up a premise of "let's discuss things using the physics we know?"

This is failing on the most basic level of philosophical discussion here. We are allowed to discuss "If X, then Y" without being obligated to also discuss "if ~X", nor is it a reasonable philosophical objection to "If X, then Y" to say "Well, what if not X?" It is a reasonable objection to disprove X and prove the whole "If X, then Y" conversation is thereby vacuous, but if you can disprove science as it stands today, this is hardly the place to do it.

(I'd also point out I did discuss "what if ~X" even so. It's just that if we're going to assume anything we like, we can get any answer we like. There's a profound sense in which there isn't much to say at that point.)

> Your turn: Yes or no, is "communicating with the outside makers of the AI Elon Musk thinks created the universe" something we have zero evidence for? Is that not reasonably categorized as a "flight of fancy"?

absolutely

> If yes, why do you expect to be able to say anything sensible about it?

I said somehting I think was sensible, which is that we have no way of knowing such a thing.

> And why are we apparently obligated to discuss it despite explicitly setting up a premise of "let's discuss things using the physics we know?"

We are not. We are obligated to acknowledge we don't know everything, which you admitted to by stating that sure, something that's a flight of fancy today could someday prove to be true, hence, there are possibly things we don't know. We of course cannot do anything with that, because we have no way to know.

> This is failing on the most basic level of philosophical discussion here. We are allowed to discuss "If X, then Y" without being obligated to also discuss "if ~X", nor is it a reasonable philosophical objection to "If X, then Y" to say "Well, what if not X?" It is a reasonable objection to disprove X and prove the whole "If X, then Y" conversation is thereby vacuous, but if you can disprove science as it stands today, this is hardly the place to do it.

all I wanted to state was that there may be things that prove to be true which if we were to hear them today, we would only be able to conclude they are flights of fancy and nothing more. and we agreed. I'm not attempting to make the "how do you know X doesn't exist?" argument because there's no X that has been suggested except for an intentionally ridiculous example. I'm more making a comment on what seemed to be your absolute certainty that electromagnetic energy is definitely the only way any intelligent life form would ever communicate across distances, science has successfully and provably ruled out any other possibility.

From Littlewood's Miscellany:

"Schoolmaster: 'Suppose x is the number of sheep in the problem.' Pupil: 'But, Sir, suppose x is not the number of sheep.' (I asked Prof. Wittgenstein was this not a profound philosophical joke, and he said it was.)"

Well, we already know that we don't know what dark matter is. Something might be hiding in there which is useful for communication.

We do not know what dark matter is, but we do know several things it is not. Among the things that it can not be is terribly strongly interacting with itself. We know this because dark matter appears to surround galaxies with spherical halos, rather than in discs. If it did strongly or even moderately self-interact, it would also be in the disc, because that's precisely why normal matter galaxies are in a disc.

So this excludes, for instance, the idea that there are dark matter civilizations using dark matter machines to send some sort of dark communication that we can't see.

It is not quite impossible to eliminate the possibility that there is some sort of dark radiation we could eventually create and detect. There's currently no particular reason to believe such a thing is possible, but it is not currently excluded necessarily. Whatever forces dark matter interacts with could have its own radiation. But it is difficult to imagine in what way this would be superior to EM-based communication, because, again, EM is just so perfect for communication that it's hard to beat.

It's the question people don't want to deal with because they're too busy being "gee whiz golly gosh" about the possibilities... in what way is this other communication method going to be better than EM? Dark matter communication would quite likely look in practice a lot like neutrino communication does today. It's already possible. We know that because we've built it. We don't call it a transmission method, though, because the bandwidth is soooo atrocious that it's reasonably approximated by "0 bits per second", so we just call it a "detector".

We know one way in which it would be superior - very low interaction rates which ordinary matter which would mean much longer propagation ranges.

And their difficultly is a bonus in itself - if you want to hide your communications as much as possible.

Cost is not always the only metric to optimize. Even today, people try to use quantum entanglement to create communication channels where snooping is detectable.

"very low interaction rates which ordinary matter which would mean much longer propagation ranges."

EM already propagates across the known universe.

"And their difficultly is a bonus in itself - if you want to hide your communications as much as possible"

It is unlikely that such hiding is going to be more effective than existing spread-spectrum techniques, which can already put your communication arbitrarily close to the noise floor, and already exist.

Of course, if you're going to leave science behind you're then going to hypothesize what aliens may have done to somehow break through the noise floor so that's not an option, and, well, this is what I mean by pick one; either use science, or imagine whatever you like, but don't mix the two. There's no reason to believe that the noise floor is penetrable and lots of mathematical reasons to believe it very much isn't.

> EM already propagates across the known universe.

I meant it in the sense that EM will be attenuated by gas clouds and solid matter due to the high interaction rate of EM, while neutrino (or presumably dark matter) much less so.

If it doesn't interact with gas clouds how do you build an efficient detector to receive it?

Since we are allowed to step outside the realm of current known physics I imagined what if we could produce a yet discovered energy that could travel faster then light and could also pass through matter. And lets for the sake of this hypothetical discussion say that we could prove there is no possible way to produce this energy without doing it intentionally, ie intelligent life producing it. I also picture this energy interacting only with itself in a way we can detect(it flashes or something). We could build an emitter and watch for the flash. Since it only interacts with itself and only is produced intentionally and not all over the universe occuring naturally we would know we have detected someone else sending the signal.

But then you have the issue that the communication doesn't actually interact with the detector you've built to receive signals.

> electromagnetic radiation basically has every characteristic you're looking for in a communications medium

Communication by electromagnetic radiation suffers from the fact that the radiation diffuses indiscriminately in all directions. Consider two models of "communication" -- in model 1, messages are sent by lighting a lantern and waiting for the other party to see it, and in model 2, messages are sent by propelling a less wave-like rock into the other party.

Model 1 is faster. But in model 2, my messages don't get broadcast to the entire world as I send them, all the energy I put into sending the message goes into delivering it (whereas most of the energy given off by the lantern is wasted), and if I start throwing rocks at my friend, that will not in general interfere with the rocks thrown between you and your friend.

"Communication by electromagnetic radiation suffers from the fact that the radiation diffuses indiscriminately in all directions."

While lasers technically do not need to be beam-like, I would point out that beam lasers do exist, as well as many other directional effects, as seen in flashlights and such.

It is a bizarre alien race that people are hypothesizing that apparently uses whatzamamagic communication that we currently can't even conceive of, but aren't capable of building the things we already know how to build that can provide very good directionality today. A very particular sort of powerful.

Beam lasers exist and stay narrow on the scale that we use them. They are tighter flashlights. Turn on any flashlight and the rapid diffusion of its light will be extremely apparent.

And I'll note that I responded to the comment "electromagnetic radiation basically has every characteristic you're looking for in a communications medium", with no mention of aliens at all. It is not true that electromagnetic radiation basically has every characteristic you're looking for in a communications medium.

There is a fundamental difference between a laser and a concentrated flashlight–lasers are coherent while ordinary light is not and cannot be made so no matter how much you focus it.

Lasers still diffuse; they are not fundamentally different in that sense. In the signaling sense of "is the light there or not?", whether it is coherent, or would be coherent if it was there, is not relevant to anything.

Lasers don't technically "diffuse", they spread out due to diffraction inside the beam itself. So they are much, much easier to better to in a reasonably directed beam.

Other than stars etc., I don’t think know any genuinely omnidirectional light sources. Even other substellar objects emit non-isotropically because they aren’t spherically symmetric. And at most frequencies, light doesn’t diffuse much.

To put it another way: lasers, lenses, parabolic dishes.

> Other than stars etc., I don’t think know any genuinely omnidirectional light sources. Even other substellar objects emit non-isotropically because they aren’t spherically symmetric. And at most frequencies, light doesn’t diffuse much.

In what cases does it matter that stars are not symmetrical enough to emanate light omnidirectionally? Stars are pretty close to isotropic.

That’s my point. They — stars and some stellar remants — are basically the only thing which are isotropic. Everything else is directed, has some gain over isotropic in the peak direction/s.

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