Note: Just wanted to say, I'm less trying to talk about "FTL" and more so that we may just not be able to intercept, decode, or "see" the communications via our current technologies.
P.S. Thanks for the thoughtful replies.
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.
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.
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."
Any civilization that would need to communicate even across a few 100 light years would be capable of doing so.
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?
Jupiter-sized is good enough for some 3700 light-years with 2016-era technology . We know because that's one of the current methods of detecting exoplanets .
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.
You'd need a spectacularly static civilisation to engage in any meaningful communication over the timespans involved.
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!
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.
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.
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).
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? :-)
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.
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...)
Radio is much better bet.
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
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?
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.
Like the way the earth is large enough to block the sun on the entire moon during a lunar eclipse.
Building a static support for your polariser might also prove challenging.
Your noise floor is now vastly greater.
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.
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
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.
Minor typo: you mean "photons".
Like modern 3D glasses.
"...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..."
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.
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!
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.)
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.
No wait, that's something else.
I guess an alien civilization has much better ideas to avoid detection.
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.
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.
GPS is not below the level of background noise. Not is sonar.
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.
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.
That might be our best hope.
Borg Drone 8 of 200: "Nothing to Assimilate here...time to go assimilate Risa".
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.
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.
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.
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.
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?
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.
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 ...
If that's the case, then we can be as wrong as they were.
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.
An easy, however unlikely, example of what could change it again is to find out we are in a simulation.
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...
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.
The big impact of relativity is that less time passes on the ship.
That's not strictly true. Before relativity, time dilation was not know to be possible.
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.
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?
This is terrifying.
Boy, that rings true right now. I kind of hope that happens.
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.
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).
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.
But in my imagination I can see this being solved.
1: Software-Defined Smoke Signal Detector
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.
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!
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).
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.
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.
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.
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.
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.
Does anyone have a link to something that explains this in plain language?
We don’t have an easy way to detect them but a more advanced civilization might.
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.
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.
Space is mostly not-things.
(With some interesting exceptional cases.)
I'm not aware of any useful neutrino lensing mechanisms, either.
It seems presumptuous to dismiss the entirety of non-Standard Model physics thusly. Axions  are one of my personal favourites.
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.
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
"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 (...)"
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.
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.
Just in case anyone else is struggling with this, as I was :)
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.
>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...
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.
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.
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.
Communications overhead between the nodes is bad enough as it is.
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.
> we can cause action at a distance
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
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.
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?
Think faster-than-light XOR ;)
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.
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.
> 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.
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.
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...
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.
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.
PBS SpaceTime. The Speed of Light is not about Light:
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?
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.
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.
Nope. Wave function obeys gravity but it does not create gravity. Gravity is created by matter/energy and wave fuction is not that.
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.
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.
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?
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 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.
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.
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."
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.
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.
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.)
> 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.
"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.)"
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".
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.
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.
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.
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.
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.
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.
To put it another way: lasers, lenses, parabolic dishes.
In what cases does it matter that stars are not symmetrical enough to emanate light omnidirectionally? Stars are pretty close to isotropic.
If every civilization that invents a radio gets past this phase we are now very fast (as we are soon going to do) advanced civilizations don't bother to encode their messages in a way that we listen now (we look mostly for phase and amplitude encoding)
Photons carry both Orbital Angular Momentum (OAM) and Spin Angular Momentum (SAM) OAM is relatively recent discovery (1990's). They exist just not in the light beams level but also at the single-photon level (very surprising).
Detecting photons with orbital angular momentum in extended
astronomical objects: application to solar observations
Optical orbital angular momentum (2017)
Entanglement of the orbital angular momentum states of photons
We've had radio for just a little over 200 years and we've already realized its limitations. The fact that we can even speculate about quantum communication leads me to believe that radio is definitely NOT the end-all-be-all. If you scale human civilization into a 1 year time frame we invent radio at 3PM on December 31st. It's successor likely emerges January 2nd at the latest. Radio communication is likely a blip.
Radio is efficient over short terrestrial distance but horrible for long (galaxy scale) distance communication. If interstellar travel is feasible at all it will have to be at FTL speeds and an FTL communication system would be necessary.
If FTL is truly impossible then it doesn't seem like there is much point in listening since everything is so incredibly far it's irrelevant even on a species-level or planetary-level time scale. I believe that everyone at SETI must believe FTL is possible because otherwise it truly is a waste of resources.
Isn't this like saying every historian must believe in time travel? Just because you can't visit someone doesn't mean you can't learn from them.
Who is it that's speculating about quantum communication? Certainly not physicists. It's mostly just IFLScience!-class journalists seeing a term like "quantum teleportation" and assuming that it means start trek is real and write their articles based on that.
> I believe that everyone at SETI must believe FTL is possible because otherwise it truly is a waste of resources.
If everyone at SETI believes that mysterious FTL communication exists, then why do they spend all their time looking for EM signals?
If we detect radio signals in another galaxy but FTL is impossible who cares? The human species will be extinct before any interaction can occur. It's probable that whatever species sent them is already extinct because it's at least 3 billion years old.
If c is the ultimate speed limit there's really no point in looking anywhere else because everything else is so far away it's irrelevant.
We get generation ships, and if we are extremely lucky, we may have some very patient pen-pals, but warp drives, ansibles, and their attendant paradoxes are pretty unlikely to be features of this universe. Personally I prefer a knowable universe to a tourable one.
If FTL isn't possible then the end result of listening is simply the confirmation that something else exists and it stops right there.
Don't you think there's at least a little bit that could be learned by listening to alien communications from centuries ago, other than the fact that it exists?
If such signals were found, would you really stop reading at the headline "alien communication discovered"?
Why is that? Special relativity already demonstrates that space contraction at near light speed would allow interstellar travel at human scale duration, with the side effect of time dilation for moving observers.
Probably true on a species level, but you are vastly underestimating how long a planetary-level timescale is. A von Neumann probe could cover the entire Milky Way in relatively short geological time.
For inter-stellar communications of sufficient distance, some sort of massive object (i.e., a space ship) seems like the preferred method because it can go at almost the speed of light, but it doesn't spread out over distance, can make minor corrections to its course, visit multiple destinations, and do something such as return a message, learn about its surroundings, and so forth.
I'd guess that a civilization might go through a period where it is emitting lots of easy-to-detect radio signals, lasting maybe a century, so we have to catch them at just the right moment.
It relies on the same mentality as the Fermi Paradox: it expects that an advanced civilization will master so much energy that its waste should be visible from afar. Only recently have we started considering that efficiency, rather than wastefulness, may be the hallmarks of civilization.
But yes, everybody at SETI knows that what they are doing are stabs in the dark. It is like trying to find inhabited lands by looking for tam-tam songs along the coast or to check if there are lighthouses installed where people may have switched to GPS.
Still, if there are thousands of civilizations out there, you can bet on off-chances of detecting one. The odds are low but the rewards would be huge. Fewer discoveries would be as consequential as this one.
So then similarly, it seems possible that advanced intelligence could be screaming at us but we're too "simple" to be able to understand them or even be aware of their presence.
Quantum entanglement does not, as far as we know, enable superluminal transmission of information. "Teleportation" is implementation-dependent and at this point entirely science fiction. If you're going to rip something apart or non-destructively scan it, and rebuild it at the other end, which is the only "realistic" theory of how it might work, you either need to transmit the bits or the bits (heh) and then you're back to the same problem of information transmission.
Of course we don't know everything, but the discussion really ends there: we don't know what we don't know.
We don’t know that there is anything better, but given how much we don’t know it’s not unreasonable to consider that we might not have the technology to receive communications from more advanced civilizations.
I agree with you that RF is a good communication medium given what we know, I just don’t put much weight on our existing knowledge being all there is.
> Of course we don't know everything, but the discussion really ends there: we don't know what we don't know.
I think the guy I replied to asked about "theories" of alternatives, and there isn't really anything specific as far as I'm aware; there's just this vague philosophical notion that we don't know what we don't know. I don't think anyone's denying it (I certainly am not) but there is not much else to be said on the subject. Knowing that we don't know what we don't know doesn't help us make predictions about what we don't know.
This implies a common assumption among people: That any civilization out there is automatically going to be more advanced than we are.
If you believe that the universe started with the Big Bang, then (IMO), it's reasonable to believe that we all had pretty much the same amount of time to evolve and develop civilizations. Asteroid events notwithstanding.
To me, believing that all beings average about the same place in the development cycle, it makes sense to look for the signals we know, rather than the signals we don't know.
But I'm no scientician.
Also, I can't use language bi directionally with a plant no matter how hard I try. Maybe we're the plants. Maybe they don't have language.
So that window holding our current level of communication abilities is 0.15% to 0.05% of our species' age, and our species is in a similarly tiny window.
To the side now with assumption they might communicate chemically only between themselves... WHAT IF their clock rate is way slower than ours? Like snails, or plants. Their bitrate of communication would be undetectable to us, if they're way slower. I suspect it would be detectable if their rate is higher though.
That would mean most civilizations in our galaxy could be very much older than ours.
Radio only came about 100 years ago for us. Some new form of communication could be 100 or 1000 years out, which is no time at all on these scales.
But life as we know it requires small but essential smatterings of "heavier" elements like potassium, iron, calcium, etc. Seems like we may need one or more cycles of stars forming and dispersing these elements into the interstellar medium to then form a solar system with enough of these elements to have life "as we know it." (Not to mention having a rocky planet for the life to live on.)
Smoke signals will have been around for a lot longer than radio. Smoke signals will have been around for 99.9% of the timeline and then 0.1% radio before quantum. To an outside observer it would look like radio was just skipped.
If you scale human civilization into a 1 year time frame we invent radio at 3PM on December 31st.
Such a relatively instant means of communication would become the defacto standard. Antiquated EM methods and equipment would be forgotten. Noone would be listening for it, just as very few today would recognize semaphore flags, smoke signals, or telegraph codes.
Today we'd not be eligible to join that club. And if we choose to remain certain that it doesn't exist, our determined ignorance would keep us locked out. If we conclude that we aren't special, that there -must- be life elsewhere, then the only logical thing to do is to keep our minds open and keep looking for clues.
We can't ever decide that we know enough. A century ago, the Milky Way was the whole universe. A few more observations changed that forever.
Some of the details are lost like maintenance details, advanced fault finding etc, but the core remains.
After a century of radio and electricity it would be rather silly to only search for other signs of life on the new system of FTL communication we just discovered. It still gives no certainty that the candidate alien discovered the same defacto standard for FTL comms or that theirs will be recognisable.
Any rational search should try and encompass both and probably still emphasise the analogue as any advanced civilisation would very likely go through that phase first, just like we are. We'd be likely to catch more possibilities that way.
Being able to send a message at a million times FTL would make it really easy to send messages back in time.
Actually that is exactly what physics says. Anything with whatever mass, as its relative velocity is accelerated, approaches a mass of infinity as its velocity draws nearer to c. Information, on the other hand, has no mass ...
In the 1890s, Lord Kelvin stated that physics was essentially complete. m'Lord was oh, so wrong.
Care to try again?
We can only try our best with the current means we have available.
not a chance. Our own radio transmissions barely go past the solar system before going under the noise floor.
The book covers many many possibilities for how a civilization might try to communicate or get the word out from Von Neumann probes to leaving something in our DNA, which could easily last multiple millennia to monuments...etc etc. It also covers the search for life elsewhere like looking for reverse chirality DNA on Mars (basically there is no reason all DNA found on earth should curl one way and finding DNA that goes the other way strongly suggests it didn't come from us).
- use the lowest common denominator long range communication medium (like EM waves), not the most advanced technology available to them, and
- would broadcast it widely in spatial, temporal and spectral dimensions and not worry about efficiency
Quantum entanglement is rather about correlation and statistics, which is, hopefully, will be quite useful for some applications, but not for communication channel. Otherwise, it will ruin the current foundation of quantum mechanics.
I strongly recommend reading the book of Nicolas Gisin 'Quantum Chance' , which is quite good for the general audience to understand, what quantum entanglement actually means in the real life, i.e. in the physical experiment.
These SETI signals, if they were of intelligent origin, would be showing just how dumb these aliens are. To send a presumably fairly local signal in such a way that it wastes such vast amounts of energy that it can be picked up 3bil ly away would seem like a serious transmitter design flaw.
Say you want to communicate between 2 star systems all you need to do is to position say a polarizer between at the edge of each solar system such as that polarizer can obstruct a suffiently large portion of the star from the point of view of the system you want to communicate at say the edge of a solar system it won’t even have to be that big.
You use the polarizer to modulate the passing light and encode your message onto it.
The smallest exoplanet discovered is Kepler 37b it’s smaller than mercury.
And planetary transitions are hard to detect because they are very time sensitive if you put something in a solar synchronous orbit between two planetary system a thin polarizing sheet which can be as thin as a solar sail can easily serve as communication device.
Any civilization needing one would easily be able to drag an asteroid which should have enough raw material to build a polarizer a few 1000’s of KM in size.
The concept is used in the "The Three Body" trilogy.
For a civilization to survive and be qualified as being advanced, not only implies being smart enough to develop some technology but smart enough to know when NOT to use it. e.g.: let's not use nuclear warheads, let's not use grey goo, let's not communicate with possibly agressive alien civilizations.
Terence McKenna Psilocybin - Magic Mushroom Grower's Guide
This probably really should be five questions.
1. For an advanced civilization trying to communicate to other, unknown, civilizations like ours. In other words, intentionally trying to have our SETI folks notice them.
2. Similar, but trying to communicate with a civilization that their SETI folks have detected. E.g., they have picked up on our existence from our EM emissions and want to to strike up a conversation.
3. For an advanced civilization that spans multiple star systems, not intentionally trying to communicate with anyone else.
4. Similar, but only spanning multiple planets within one system.
5. Finally, for an advanced civilization that is only one planet, not trying to communicate with anyone else.
For #1-4, EM is the most likely answer for reasons numerous others have mentioned. For #3 and #4, the big issue would be power. If they are only intending internal communication they might not be putting enough power for us to pick it up unless they are close to us.
For #5, even if they have not discovered something beyond the physics we know, they might not radiate their EM in a way we can detect. For example, if they have a planet wide urban civilization they might have every building connected to a high speed wired communication system. The only wireless they use might be something like Bluetooth or low power WiFi that only needs to communicate within a single room of a building between their portable devices and that room's node on the wired system.
At a scienctific level no, but in science fiction you have devices like the 'subspace ansible' and similar things that allow FTL communications by using some sort of currently-undiscovered 'subspace'.
I actually remember in the mid 90's seeing, in the Weekly World News (a sensational tabloid for those unfamiliar) or its primary competitor at the time, mention of a intelligence agency that had laptop like devices that allowed for real-time encrypted communication anywhere on the world which was likely a spin on this idea (IIRC it was suggesting some sort of quantum entanglement where doing something to one would instantly cause the same to happen on the 'paired' device so you'd just type on one and it would instantly appear on the display of the other).
There's no valid reason to think something like this isn't possible, or even plausible. We didn't discover infrared until 1800, x-rays and radio until 1895.
There could very well NOT be anything that would allow for FTL/real-time communication over any distance but then again there could be. There could very well be some sort of radiation or similar particle that we've yet to discover too which might be the preferred means of communication for an advanced enough civilization.
Look how far computers have come since I was born in 1985. Look at other technologies like genome sequencing, the human genome project took 13 years and cost many millions but now you can do whole genome sequencing commercially with an 18 hour turnaround and hire your own whole genome sequencing out for 500$ with a 10-12 week turnaround. I know these examples don't compare but what I'm getting at is we are barely a technological species and who knows what possibilities exist for us.
Another interesting question is if they are EM radiation.
It should be the most efficient way to travel. Going from Turing machine to Turing machine, a virus with a really advanced universal exploit, impregnating civilizations like ours around the time they develop both radio tech and computers.
Civilizations with the capability to travel in that fasion would be dominant.
I mean, before we knew that radio waves exists we could not forsee the use of radio for communicating
so, I'd say that better ways of communicating relay on something that physics hasn't found yet (like, you know "that weird supersimmetry decay thing that only su-top quarks do when reacting with Stuff")
Likely we are searching for radio waves and light since that's the only thing we know how to communicate with.
Personally until we've figured out things like consiousness and dark matter/inflation etc I think the null hypothesis should be that there is unexplained stuff happening and thus it's likely advanced civilizations use something other than electromagnetic waves, just like we don't use smoke signals or fire beacons much for communication anymore.
Maybe there's another form of communication we haven't discovered yet that's so much faster and more efficient (like Star Trek's "subspace") that everybody else in the galaxy uses that instead. For them to send radio waves to Earth might be like us pointing Morse lamps at Alpha Centauri.
Trying to detect alien life by scanning the EM spectrum sure is inefficient. Maybe it's the best we can do, but if there were something better, I could totally see why we'd abandon plain old radio waves.
SETI would become search for extraterrestrial intelligence that that believes it's worth a shot to emit RF to contact less advanced civilisations that at the moment of recieving the signal will be in that small time window when they used RF for communication because they had nothing better.
The two dimensional lifeforms were unable to perceive three dimensions. Yet at the same time, the crew of the TNG struggled to understand them.
First, they have mass, hence travel slower than the speed of light, which means they are less effective.
Second, it is very hard to detect neutrinos, which means they are very bad communication medium.
We use lasers for quantum teleportation. There's no reason to believe it can be realised more efficiently without.