Extraterrestrial Civilizations: Problems of Interstellar Communication (1971)
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The idea was to use the Wu experiment [1] and the lack of conservation of parity (= there is a difference between left and right, and you can explain which is which) but was a bit taken aback by the question.
Interestingly the first thing that popped in my mind was the peptide torsion direction (one of them is preferred in terrestrial life) and I started to wonder about alien abductions etc., and I fortunately got back on track with down-to-earth physics (thanks Ms Wu!)
Over the last century, our own radio technologies have undergone a continual progression in efficiency and data rate. Imagine someone with the latest radio technology from 1920 trying to monitor our civilization's progress. By 1950, a lot of things seem to become undecodable (FM), and shortly after that a lot of carriers seem to simply disappear. Assuming they manage to lock on to the frequency-modulated edge of a suppressed carrier in the 1970s, things start to switch to a multitonal digital encoding. Then round after round of increasingly complex digital encodings with error correction and encryption, with larger and larger symbol rates and symbol set sizes. Frequencies climb into the thousands of megahertz. Hundreds of thousands of carriers are used in parallel.
By the early 21st century it's unlikely our 1920s engineer can even detect radio signals from devices like a modern cellphone even if they had it in the lab with them -- and they blatantly transmit high power beacons in the open to find other devices. Too low power, too high frequency, data encodings based on mathematics not even invented yet. Even if detected, there would be no obvious modulation, and it would look a lot like a white noise emitter.
Maybe it's not worth even attempting until the receiving civilization would be able to decode more than just a few bytes from a signal that could be affordably transmitted from a single star.
MeeeaaouuuW!
As for entangled pairs, which I presume you imply by quantum communication, it really isn’t a hidden dimension with magical properties of superluminal communication, it just implies that two particles can have shared/correlated quantum states (assuming you can keep coherence). The coherence requirement basically means that the longer a particle is exposed to the normal world, the bigger the chances of some kind of stray interaction with other particles or forces, that will break entanglement. Further, for using this for anything, we’ll need to store the local particle for the duration of flight of the emitted one. That is also a technical problem of some magnitude if the distances are light years.
The short answer is that we don’t even come near to monitoring all “propagators” let alone all possible encoding schemes for these, for SETI.
https://www.forbes.com/sites/chadorzel/2016/05/04/the-real-r...
P.S. It's really funny to see forbes as a source of science.
I'm happy there are at least some universal constants like absolute zero or the max possible temp or planck length.
And as for anything FTL, I hear it breaks the rules of causality and that seems to be a big no-no and is indeed impossible.
The physics we have at any given time is tested through experimentation, and has proven effective and accurate to some degree. Within those parameters it's verified.
So skepticism of current physics makes sense to a point, we know it's not complete, but we also know that in a massive range of many complex and sophisticated tests it turns out to be precisely accurate. That's got to count for something.
Testability is a strength not a weakness, it means we know for sure what the limits of our understanding are. Outside the domain of science we have no such heuristic, so we have no idea whether or to what extent anything we think up bears any relation to reality whatsoever.
Do you have an alternative?
So far the only quantum communication we've done over distance is via photons, which are still photons.
On the other hand, it could be that they advanced to the age of using EM waves not too long ago, which means their signals are still on the way and we'll probably detect those in the future.
The fact that the universe seems to be totally natural, without any intelligent interference is more concerning. No megastructures or evidence that our solar system has been visited.
Genuinely curious - why does that worry you?
If the universe is neutral or friendly to civilizations, then we should expect to find someone out there in fairly short order. The universe is so large, even if there’s only a one in several billion chance of a particular solar system birthing a civilization, there should be a few others besides us already in the Milky Way.
If there’s not anyone else, the best case is that we are simply the first (this is my personal bet). Worse scenarios include civilizations simply fail and die after some time, or that one “predator” civilization kills off any other civilizations it finds before they can become a threat.
This would be odd given that 95% of the stars to ever be created in our universe have already been made. https://nautil.us/issue/104/harmony/the-universe-already-mad...
To think that with billions of stars, each with at least one planet, intelligent life only happened on one planet (the Earth) means intelligent life is super rare, even if life in general happens on many planets.
This means if we get hit by an asteroid or don't get passed the Great Filter, the only ones who "think" about this universe and give a meaning to it will be gone forever.
The rough idea is that the galaxy seeming insanely quiet could potentially imply that it's rare for life to reach a level which we can easily detect; space-faring, multi-planetary, capable of astro-engineering, etc.
If that is the case, it might be that there is a "Great Filter" which tends to knock these civilizations back into their stone age, or kill them outright. Maybe it's nuclear weapons, or grey goo, or biological experiments that break containment, or an AI that decides to kill its makers, or even just conventional wars that stunt their growth, etc. Generally, some kind of technological development or societal event that leads to that civilization going/staying dark to the galaxy.
The potentially worrying question is: have we passed the Great Filter? Or is it still somewhere in our future? There are any number of things that might kill or stunt humanity in its crib, before we spread out far enough to be able to persist.
And even then, how long is it going to be before a nuclear holocaust on Earth would no longer effectively cripple humanity, even if we've colonized the solar system and could nominally survive it? Or imagine AI-infused grey goo that spreads throughout the solar system.
There may also be more than one Great Filter.
1. it offers no testable predictions
2. it explains everything, yet explains nothing
I’d go further and say they require such a being, despite us having reason to believe such a being is not compatible with our understanding of how the universe actually works.
Just as the existence of an all powerful eternal being doesn’t seem compatible with what we know about what’s possible in the universe, I have severe doubts that a simulation of the fidelity we observe in our existence is practical to build in our universe.
It certainly isn't. You can't simulate three atoms using two atoms. There's no reason another universe has to abide by the same rules as ours, though. It's not something anybody should actually worry about but it's about as scientific an idea as string theory is.
That's not necessarily a ringing endorsement ;)
At least string theory has lead to some very powerful and productive mathematical techniques, if little in the way of actual physics.
If we can invoke other universes, then we're kissing Occam's razor goodbye and we're in magical fairy land territory.
As a biologist I'd love it if they found life (that was totally seperate from Earth life) somewhere else in the solar system, but if we do it's one less great filter.
Aliens have been all over the newsfeeds lately. Fermi Paradox this, Drake Equation that, Oumuamua, tictacs, yada yada. All is speculation (except tictacs: disinformation).
Suppose we encountered actual aliens. What could we reasonably expect, from what we know? By the numbers, for us to encounter them at all, these aliens will have to have been around for millions of years. To keep a culture we would recognize going for millions of years, they cannot be primitives like us, fresh from the muck. Nothing we make lasts. Its members have to be better-architected than would evolve the old-fashioned way.
To be that old, each was designed by somebody designed by somebody designed by somebody, untold generations deep. They only reproduce by designing a successor, and only die by choice, or embarrassment. Probably little in the outside universe is as interesting as what they are doing on their phones. Although architected to co-exist, each is custom-designed, as alien to one another as to us. Such hyper-evolved aliens won’t be interested in talking with us; if they care enough, they might probe us.
So, who is left?
o o o - Pace - o o o
We evolved in water, cells moving charges across bi-lipid membranes. This went on for eons until one invented photosynthesis and liberated oxygen, an apocalypse for almost everything alive. Then the Earth froze over solid for an eon. Survivors learned to tolerate and then to use the oxygen, and eventually to sustain bigger, more complex cells that connected up into plants and animals that took to eating one other. And, here we all are.
Yet, for all our common heritage, life on our world works at many different paces. Insect brains, microns across, process bits a thousand times faster than ours. Starfish creep, brainless, for all the world like nibbling aquatic Roombas, but in time-lapse playback, they are visibly as aggressive and territorial as any chihuahua. Sequoias live for thousands of years, and seem to be doing nothing, yet they share the world with everything going a thousand or million times faster.
There is nothing compelling about our own pace. We got here by a long series of accidents. Others will have had different accidents. A world could be as big and old and complicated as ours, but with everything alive on it a thousand or million times slower than us. They might do what we do, more or less, but just take longer at it.
o o o - Slow Worlds - o o o
Slow brains evolve differently. Where there is no rush, nerve cells need not be packed tightly together. It’s safer to distribute them. Radically fewer can do the same job, because they have no need to work all in parallel. A cell not immediately needed to think with can do something else useful, meantime. Our brains are about as big as we could afford until just recently. Slow brain-stuff is cheap. There is little pressure to limit it. Slow creatures can afford to be very, very smart.
Landing on a slow planet, we would find a whole world frozen in mid-step. They might move by putting down roots in front and taking them up behind. If we dared to cut one down, nothing inside would resemble a brain.
Such a civilization could last for millions of years, and still be as young, vigorous, and naive as ours, still interested in other young, vigorous civilizations. There is nothing to keep them from inventing mathematics, lasers, fusion drives. Spaceships. Their first spaceships would have to blast off at speeds like ours, and so be controlled by computers. Like ours.
But for a slow people, the vast chill void between stars is no barrier. There is time for a nap on the way. Electromagnetic signals transmitted between their stars need not be intensely bright. A photon now, another later gets the message across fast enough. The great civilizations that have spread across the galaxy, over untold eons, will be slow people. They are who might visit. They are who might blink lasers at us.
Slowly.
o o o - Contact - o o o
If we are interested in signals from galaxy-spanning civilizations, we are going about it all wrong. SETI looks for signals modulated at our speed. Signals too slow are systematically ignored. We miss all the action.
But, maybe we can find aliens closer to home. Sequoias do not seem to have brains, but they wouldn’t. Galactic elders, when they finally notice, might be unhappy to find we cut them all down.