UK launches Search for ExtraTerrestrial Intelligence Research Network

Jul 05, 2013
The Lovell Telescope at Jodrell Bank inspired the first proposals to search for radio signals from extraterrestrial civilizations. Credit: Anthony Holloway, University of Manchester

(Phys.org) —A network has been launched to promote academic research in the UK relating to the Search for ExtraTerrestrial Intelligence (SETI). The UK SETI Research Network (UKSRN) brings together academics from 11 institutions across the country. The network's Patron is the Astronomer Royal, Professor Martin Rees. UKSRN will present current activity and consider future strategy in a session and panel discussion at the National Astronomy Meeting in St Andrews on Friday 5 July.

UKSRN (www.seti.ac.uk) covers a broad spectrum of research topics, including potential methods for detecting signals, the linguistic challenge of deciphering messages, the probability of an extraterrestrial civilization interacting with Earth and the longevity of civilizations.

Dr Alan Penny, the coordinator of UKSRN said, "We hope that the existence of the network will excite interest from people in the UK astronomical community that have been thinking about SETI and encourage them to contribute their work. In this session at NAM, we are presenting the whole range of UK SETI activities to the community and hope that it will promote a wider understanding of, and activity in, this subject."

Dr Tim O'Brien from The University of Manchester's Jodrell Bank Observatory will describe the capability of the UK's recently commissioned e-MERLIN array of seven for SETI projects and report on progress in initial test observations.

The first proposal to search for from extraterrestrial civilisations was actually inspired by the construction of the Lovell Telescope at Jodrell Bank," said O'Brien. "We went on to take part in the SETI Institute's Project Phoenix from 1998 to 2003, searching for signals from about a thousand nearby stars. At that time the equipment required to sift through the data was expensive and unusual, but our modern telescopes are potentially capable of conducting these type of observations as a matter of course."

The e-MERLIN array, which includes the Lovell Telescope, is connected by optical fibres and spread over 217 km from Jodrell Bank to Cambridge. This multi-telescope approach offers potential for distinguishing true extraterrestrial signals from interference generated here on Earth, a key problem for all radio SETI projects.

O'Brien is excited about future prospects, "It's early days for this new SETI work at Jodrell but we think that using e-MERLIN, and future facilities such as the Square Kilometre Array, we could make an important contribution to the search for intelligent life elsewhere in the Universe."

Dr John Elliott of Leeds Metropolitan University is a researcher on the nature of communication: how language structure can be identified, and methods for subsequent decipherment and dissemination. He has analysed over 60 human languages, which cover all the different types of systems, as well as non-human communication, such as robots and dolphins. Elliot believes that by understanding our analytical capabilities for communication, we can develop strategies for extra-terrestrial message discovery and understanding.

"Suppose SETI succeeds and we detect a technological beacon. Any message is unlikely to be written in Martian English, so standard decipherment/decryption techniques used by the military and security agencies are not going to help much. To put the challenge into context, we still have scripts from antiquity that have remained undeciphered over hundreds of years, despite many serious attempts," said Elliott.

Elliott's research focuses on whether there is something unique to communication phenomena, irrespective of the source, that makes them distinguishable from other signals in the universe.

"By looking beneath the surface veneer of the arbitrary sounds and symbols used, we can 'see' the language machine itself: its mechanisms, constraints, and evolutionary forces of efficiency and compromise that shape it. By understanding these structures, it should be possible to glean information on the intelligence of the message author," said Elliott.

Back in 1950 during a conversation on SETI, the physicist, Enrico Fermi, posed the question 'Where is everybody?' The paradox between the high estimates for the probability of the existence of extraterrestrial civilizations and the lack of contact or evidence remains a key area of SETI research. Dr Anders Sandberg, of the Future of Humanity Institute at Oxford University, is investigating the question of how far away in space and time a civilization could start and still have a chance of interacting with Earth today.

"If this were a very limited range, the Fermi question, "Where are they?" would be easy to answer: they couldn't have got here yet. However, we show in our paper that, beyond a certain technological level, civilizations can spread not just across their own galaxy but across enormous intergalactic distances. This is mostly limited by how fast their devices are and the expansion of the universe. There are millions or billions of galaxies from which a civilization could have reached us, if it were established early," said Sandberg.

Sandberg and his colleagues have concluded that the answer to the Fermi question is more extreme than normally thought. "If life or intelligence is rare, it must be millions or billions of times rarer; if advanced societies wipe themselves out, or decide to not go exploring, they need to converge to this outcome with extremely high probability, since it only takes one that escapes this fate to fill the universe," said Sandberg.

The work of Dr Austin Gerig, senior research fellow in Complex Networks at the University of Oxford, estimates the fraction of civilizations in the universe that are long-lived and analyses the human race's prospects for survival.

Dr Gerig said, "We know that (1) we exist and that (2) our birth number within our civilization is approximately 70 billion (i.e., approximately 70 billion people were born before us). From such little information, we can reasonably, and perhaps surprisingly, conclude that (1) many other civilizations exist and that (2) most of these civilizations are small, i.e., most will die out before producing trillions of people."

Gerig and his colleagues have focused on a specific consequence of this reasoning, called the 'universal doomsday argument': long-lived civilizations must be rare because if they were not, we would find ourselves living in one.

"If most civilizations are small, then our own civilization is likely to be small, i.e., it is likely to die out within the next few centuries. Our research indicates this is the case, but that our estimates of survival are greater than previously thought using a more traditional form of the doomsday argument," said Gerig.

Duncan Forgan, from the Royal Observatory Edinburgh, is looking at the possibility of detecting large structures built by civilizations orbiting other stars. The transit method of detecting extrasolar planets involves measuring the dip in starlight as a planet passes in front of its star. The Kepler Space Telescope has detected a whole host of new exoplanets using the transit technique, and there are many future telescopes and missions lined up to succeed it. Forgan has investigated whether the obstruction of the stellar disc by a large orbiting structure would make a detectable difference in the shape of the lightcurve of an exoplanet transit.

"I looked at one type of megastructure, which is essentially a very large mirror. The mirror reflects the star's own radiation and produces thrust, much like a sail produces thrust from wind. This thrust could be used to move a civilization's host star from its 'natural' orbit if it posed some harm to the civilization, for example a dangerous close approach to another star or dust cloud," said Forgan.

Forgan's study showed that a giant mirror of this type would leave a characteristic trace in exoplanet transit data, which could be detectable with the next generation of telescopes.

"While the odds of seeing megastructures are probably very low, we will soon have a huge archive of exoplanet data to search for these objects – at no extra cost to SETI scientists. We may detect the presence, or remains, of an alien civilization that felt the need to move their star!" said Forgan.

Explore further: New mass map of a distant galaxy cluster is the most precise yet

More information: www.seti.ac.uk/

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MrGrynch
2.3 / 5 (13) Jul 05, 2013
Considering our current level of technology, it seems silly that we're looking for radio/laser signals. We should be looking for modulated neutrino streams. This would be an ideal communication mechanism since neutrinos can pass through most matter in its path undisturbed.
philw1776
2.1 / 5 (9) Jul 05, 2013
Glad we're looking Contributed $ to Planetary Society SETI in Harvard MA, radio & optical. However I expect null result. I don't think there's a tech civilization even as far as the Virgo cluster and maybe the observable universe. Let's observe & prove me wrong!
MrVibrating
1.1 / 5 (9) Jul 05, 2013
At the level of sentient experience, i believe all multicellular organisms process all information as modulation of factor-of-two symmetry.

This is axiomatic as all other frequency relationships are by definition more complex, and processing costs energy.

In short: the metadata we assign to relationships between spatial frequencies has an informational 'zero point' at all factors of two of a given fundamental. It's a form of channel convergence inherent to multicellular processing, correlating signal to network entropies.

It seems to me the most fundamental substrate from which perceptual information is constituted.

In other words, if our prospective ET cousins are multicellular, they'll be subject to the percept of octave equivalence, and accordingly their communicative bandwidths will be around one or two octaves wide, using 2f to represent zero.

We should be looking for signals bound to octave bandwidths, because these are the signature processing channels of complex life.
LarryD
1.6 / 5 (9) Jul 05, 2013
We have no idea of what we are talking about here. If this, if that and so on...and what IF they, ET, are already here? In the sci fi realm there's much I feel, 'I wouldn't like THAT knocking on my door'. IF, IF ET exists then we must also assume that, just as we are, some will be 'good' and some 'evil' (no religious idea intended) so sending out signals and CD's about life here is a bit risky.
I feel that we need to deal with this issue right here on Earth first. We all realise that some govs are hiding something from us (UFO's and the like) and we need to open that 'box' first, just how we do it is another question. But IF govs already have the answer, 'yes', then we needn't search the sky and IF it is 'no' then okay we can debate whether or not searching the cosmos is worth it.
Then there is the question of 'multiverse', other 'dimensions' (macro or compactified). IF, IF these exist and ET is in these then our signals etc might not get through.
bipolarbear
4.6 / 5 (8) Jul 06, 2013
Considering our current level of technology, it seems silly that we're looking for radio/laser signals. We should be looking for modulated neutrino streams. This would be an ideal communication mechanism since neutrinos can pass through most matter in its path undisturbed.

Neutrinos also have a nasty habit of passing through most of neutrino detectors in their path undisturbed.
CaptainSlog
1.6 / 5 (10) Jul 06, 2013
Does extra-terrestrial include extra-dimensional? Are the realms of dark matter and dark energy included in term extra-terrestrial?
PhotonX
2.5 / 5 (4) Jul 06, 2013
Does extra-terrestrial include extra-dimensional? Are the realms of dark matter and dark energy included in term extra-terrestrial?
Presuming that by "extra-dimensional" you actually mean alternate universes. I doubt that most people include these, though strictly speaking we should. After all, it's all hypothetical. AFAIK there's no empirical evidence at this point that multiverses, dark matter, or dark energy even exist, so it's academic whether we wrap them in or not. I know that a character in Stephen Baxter's scifi book "Exultant" feels confident that dark matter life exists, but that opinion is based on the principle of mediocrity because life had become known to be common in baryonic matter ('real' matter), and of course they had by then (20,000 years in the future) come to know with certainty that dark matter itself exists. Until those things become known, it seems rather pointless to concern ourselves with potential dark matter life.
antialias_physorg
3.8 / 5 (6) Jul 06, 2013
Couple of issues with the content of the article:

1) Search in the radio bands:
WE don't even use broadcasts anymore because it is much more efficient to send directed transmissions. Why are 'advanced' aliens always considered more stupid than us? (Apart from the fact that using radio is probably the dumbest form of interstellar communication)

2) Linguistic analysis is futile as WE don't even send unencrypted messages. You think aliens send BROADcasts AND unencrypted messages? You must be out of your minds.

3) Civilization spread: If you can live anywhere (or survive in space) WHY would you spread to other planets? If you're basically immortal WHY would you spread (i.e. multiply) at all?

The paradox between the high estimates for the probability of the existence of extraterrestrial civilizations and the lack of contact

Given our own history in this regard I can see why an advanced civilization would not contact a less advanced one (whatever for?)
alfie_null
5 / 5 (2) Jul 06, 2013
Assume an omnidirectional transmission. Calculate how much power would be required for us to be able to detect it (assuming some range of distances). Come up with some rationale for why some E.T. civilization would do this? Presumably for their own use?

If you'd like to stuff information into that transmission, be aware it costs. And efficient modulation starts looking like noise.

Or assume a directed transmission. Still a lot of power, but less. Assumes they want to talk to us, which means they are able to detect us. How? By our radio transmissions? Note we don't yet have the capability to do that (detect a civilization like us) at stellar distances.
geokstr
1.5 / 5 (8) Jul 06, 2013
Considering our current level of technology, it seems silly that we're looking for radio/laser signals. We should be looking for modulated neutrino streams. This would be an ideal communication mechanism since neutrinos can pass through most matter in its path undisturbed.

Or tachyons, assuming they even exist, or could figure out how to look for them.

Neutrinos also have a nasty habit of passing through most of neutrino detectors in their path undisturbed.

We just haven't figured out a decent way to detect them yet.

Remember, we've only really been doing this science thing in earnest for a hundred years or so. It's hubris to believe that we know anything yet, really. In fact, at this point there is probably far more that we don't even know we don't know than what we know we don't know.
geokstr
1.5 / 5 (8) Jul 06, 2013
If an intelligence was old and powerful enough, it might be that pulsars and other exotic stars are just their homing beacons, warning signs, and traffic signals. Clarke's third law: "Any sufficiently advanced technology is indistinguishable from magic." Or maybe even indistinguishable from what we might call "god". (Full disclosure: I'm an atheist.)
zorro6204
4 / 5 (3) Jul 06, 2013
Yeah, I totally agree with some of the other comments, we've only been using radio for a little over a century, and we're probably about to stop. And we think we can catch another civilization just in that brief period where they were using electromagnetic radiation to communicate? It's an unlikelihood piled on an unlikelihood, it makes no sense at all to spend precious science money on such an ephemeral prospect.
LarryD
1.7 / 5 (6) Jul 06, 2013
I'm basically referring to my earlier post. I don't intend to turn this into a UFO debate but it does have connection to SETI. I know that most UFO reports are either misidentification, hoax etc. But even scientists agree that a very small portion lack explanation. Those craft that make almost instant 90 deg turns at speed are just not common ordinary aircraft! But are they of ET origin? Take the Roswell incident for example (Arabela, actually). What happened there to make the US military restrict the town (but only after it was reported). Was it ET? Was it some secret gov experiment that went wrong (no, not balloons)? Or was it some other almighty gov 'cockup'. Whatever happened there is still classified as are many more 'incidents'. Get an answer to these and then we can decide whether SETI is a good idea or not.
No, multiverse and extra dimensions are not the same. One implies other 3D universes, perhaps similar to our own, but somewhere out (cont.)

LarryD
1.8 / 5 (5) Jul 06, 2013
(cont.)
of range of our instruments. Extra dimensions imply hyper volumes (tesseract etc) and where our laws of physics might need some adjustment. Newton's law of gravitation would be of the form G(m1m2)/r^(2+d) where 'd' is the extra but there are other possible forms. We might be on the surface of a hyper-sphere.
At the other extreme there might compact extra dimensions at the quantum level.

MrVibrating
1 / 5 (5) Jul 06, 2013
Assume an omnidirectional transmission. Calculate how much power would be required for us to be able to detect it (assuming some range of distances). Come up with some rationale for why some E.T. civilization would do this? Presumably for their own use?

If you'd like to stuff information into that transmission, be aware it costs. And efficient modulation starts looking like noise.

Or assume a directed transmission. Still a lot of power, but less. Assumes they want to talk to us, which means they are able to detect us. How? By our radio transmissions? Note we don't yet have the capability to do that (detect a civilization like us) at stellar distances.


Such attempts might be purely prospective, however, rather than evidence-lead - perhaps just on the basis of promising stellar properties for example. And perhaps there's some quiet corner of, say, the neutrino-sphere that might overcome much of the limitations of the EM-sphere.

Re. obfuscating complexity, see my prior post...
Hermanx
3 / 5 (4) Jul 06, 2013
The first decoded message has arrived. It says:

EXTERMINATE, EXTERMINATE, EXTERMINATE

Newbeak
not rated yet Jul 07, 2013
All interesting comments here.One has posted an argument I like to make regarding SETI's attempt to detect ET radio transmissions: What are the odds that there is (actually was,if they live a couple of hundred light-years away) a civilization at our level who is trying to communicate with radio? I think it is a Star Trek fantasy that you will find dozens of alien cultures roughly equivalent to humanity in technological terms. I am glad none of my tax dollars is being spent on faith based SETI projects.Wikipedia says they are a non-profit organization,with no government involvement.
kevin_hingwanyu
1 / 5 (4) Jul 07, 2013
[
Sandberg and his colleagues have concluded that the answer to the Fermi question is more extreme than normally thought.
] . . .
In terms of radio SETI the Milky Way is too large, the detectable radii for radio signals for civilization of Earth scale is merely few ten(?) light years. The capability of radio SETI is still too low ?

[
The e-MERLIN array, which includes the Lovell Telescope, is connected by optical fibres and spread over 217 km
] . . .

Is it true that adding more telescopes covering larger areas and distances could increase the overall sensitivity and reduce most interference from Earth providing that the topology of the telescopes is ideal ? I guess the sophisticated contemporary pc technology can simplify and or divert most physical obstructions (hardwares of the instruments) which may solve the physical problems indirectly in 'easier' ways. I guess if the curvature of (the surface of) the Earth is not a problem then it may add more telescopes to the array.
. . .
kevin_hingwanyu
1 / 5 (4) Jul 07, 2013
. . .
I guess the locations of the antennae and the geometry of the array may be allowed higher degree of 'irregularity'. (That is,) Is it possible that computer software can handle 'irregular' (for example, in sense of the symmetries in locations, distances, signal strengths and timings) telescope array ? The possibility to add telescopes at 'irregular' locations (and altitudes) can change a lot of constraints. The most obvious are the costs.

When computer software can align data or signals from every telescopes in the array (maybe even the shape of the array is 'irregular'), then computers may not need to process the astronomical numbers in real time. That is, the number of antennae of the array can grow rapidly (with relatively lower costs) without too much considering the speed of computer and network (connectivity).

Maybe it does not demand the computing speed to scale up when it adds more instruments at mundane (or irregular) positions to increase the areas and distances.
. . .
kevin_hingwanyu
1 / 5 (5) Jul 07, 2013
. . .
Although it seems off topic, how scientists say about Crop Circles ? (The phenomena of) Crop Circles involve many many aspects. For some extraordinary Crop Circles it is difficult to explain, and what else.
LarryD
3 / 5 (2) Jul 07, 2013
Another point is that IF one assumes the universe is expanding (and I know some post names don't agree that it is) then the age (BB, if one agrees with BB) is about 13.7 bil l.y. But that refers to what em has reached us. During that time the universe has expanded even more and will be doing so as we write. this COULD mean that our signals will never reach ET that are in the expansion.
Newbeak
not rated yet Jul 07, 2013
Another point is that IF one assumes the universe is expanding (and I know some post names don't agree that it is) then the age (BB, if one agrees with BB) is about 13.7 bil l.y. But that refers to what em has reached us. During that time the universe has expanded even more and will be doing so as we write. this COULD mean that our signals will never reach ET that are in the expansion.

That would mean they are expanding faster than light,which would violate Einstein's speed limit.
LarryD
3 / 5 (2) Jul 07, 2013
Newbeak, some theories suggest ftl because they say there is evidence that the 'horizon' expansion is accelerating with Dark Energy being a candidate reason. Another idea was that at the BB expansion was a great deal ftl and that the 'horizon' is slowing but remains flt.
A more conservative view might be to think of two galaxies on opposite sides of the 'horizon' both moving at light speed. As they are moving away from each other light signals from one never reaches the other.
But light v limit is perhaps more about information transfer. For example Tachyon particles. These remain hypothetical but as long as they remain ftl there is no problem with SR. And don't forget that within light theory itself individual amplitudes are ftl but cannot carry information.
Greenwood
5 / 5 (2) Jul 08, 2013

1) Search in the radio bands:
WE don't even use broadcasts anymore because it is much more efficient to send directed transmissions. Why are 'advanced' aliens always considered more stupid than us? (Apart from the fact that using radio is probably the dumbest form of interstellar communication)

2) Linguistic analysis is futile as WE don't even send unencrypted messages. You think aliens send BROADcasts AND unencrypted messages? You must be out of your minds.


1) SETI isn't looking for broadcasts it's looking for intentional attempts to contact other life, we do this. Radio is not dumb at all, galactic emission is low and absorption is low.

2) The intentional part of transmission is key. We have sent unencrypted files.

3) You don't understand the motivations of aliens, you're guessing. They don't have to think like you.
antialias_physorg
1 / 5 (1) Jul 08, 2013
If an intelligence was old and powerful enough, it might be that pulsars and other exotic stars are just their homing beacons, warning signs, and traffic signals.

Don't you think that an old/powerful intelligence might not use stuff that isn't blocked by the next dust cloud?
Photons seem woefully inandequate fo communication purposes in any regard. With the types of energies a civilization like ours can mount, the signals will be undistinguishable from noise before it even reaches the next star.

That would mean they are expanding faster than light,which would violate Einstein's speed limit.

Expansion isn't limited by the speed of light. If the acceleration (as currently measured) of the expansion continues then we'll eventually be facing a Big Rip (and before that a time when there will be nothing in the night sky but stars fom our own galaxy)
antialias_physorg
1 / 5 (1) Jul 08, 2013
You don't understand the motivations of aliens

All the more reason not to send any signals, don't you think?

I'm guessing that they will be either more or less advance than us (which seems a reasonable assumption).
Less advanced: not much of a target (as they aren't sending anything and are incapable of receiving anything we send).
More advanced: Nothing to gain for them from contactong us. And if they want to watch...well..if you go birdwatching: do you try to make contact with the bird? Certainly not.

If we want to find out what's out there we should go andhave a look - as sneakily as possible. It's preferrable to scout the field before putting a big "we're here" neon sign up. And even if aliens have dfferent motivations - THAT simple piece of logic can't even escape them.
Guy_Underbridge
not rated yet Jul 08, 2013
...before putting a big "we're here" neon sign...

"we're here" = "50¢ Luncheon Special"
LarryD
1 / 5 (1) Jul 08, 2013
antialias_physorg, really backs up what I said what I posted a couple of days ago. Maybe elsewhere 'nature' favoured another species.
Fleetfoot
not rated yet Jul 08, 2013
Photons seem woefully inadequate for communication purposes in any regard. With the types of energies a civilization like ours can mount, the signals will be undistinguishable from noise before it even reaches the next star.


With tight beams (i.e. large, space-based antennas), EM is adequate, but incidental radiation would equivalently be negligible, we could only pick up a beacon aimed at us. If an advanced species were trying to attract the attention of a newcomer, it would be logical for them to use the simplest mechanism.

Expansion isn't limited by the speed of light. If the acceleration (as currently measured) of the expansion continues then we'll eventually be facing a Big Rip ..


Only if the equation of state for dark energy has w < -1, also known as "phantom energy". The Cosmological Constant has w = -1 exactly so you get a de Sitter solution with eventually a constant Hubble Length.

http://en.wikiped...overview
MaiioBihzon
2.3 / 5 (12) Jul 08, 2013
The energy, the cost, for getting from one star to another is not trivial. A crewed interstellar mission should be thought of as a planet's Wonder of the World, along the lines of the Great Wall and the Pyramids of Giza. Not something to be tried without a clear and definite goal in mind, a goal and benefit reaching well beyond simple exploration.

The life here did not develop independent of the evolution of our galaxy; it is part of that evolution, a product of it. The same holds for any life existing elsewhere in the Milky Way. Our planet orbited its host star for 4 billion years before technological beings appeared. Technological civilizations surely exist. But they may not be numerous or star-faring. Yet.

Elites running civilizations anywhere are not likely to welcome contact from beings from other worlds. They would ~ correctly ~ regard such beings as a threat, to be rejected if possible.

Also, extraterrestrials could visited a million years ago. Many possibilities.
LarryD
not rated yet Jul 08, 2013
MaiioBihzon, yes, but two other important aspects also. Even if the velocity was a considerable fraction of light speed (or accel. g's) no matter how short the onboard time food or sustenance must be available for the trip. If it were us we know what we need and it would have to be taken or produced on board. So stations or colonies would be necessary around our solar system to provide supplies.
The other point is that machines break down so the less moving parts for the drive engine the better. If one is on a ship way outside the SS and the main drive can't be repaired, well...
If we have such problems then ET might have similar.
'..Also, extraterrestrials could visited a million years ago. Many possibilities.' This point I covered in my earlier post. Zeus, Apollo and all the others might have been Star Trekkers but there's no proof. Some ancient drawings suggest beings from the sky...but it's speculation.
If govs know better then they say so and save the rest of us a lot of bother.
antialias_physorg
1 / 5 (1) Jul 09, 2013
it would be logical for them to use the simplest mechanism

Which would be, I think, a probe. A probe would only be marginally slower relative to a beam the further out they are, as you can accelerate stuff to near light speed given enough time (and even just using photovoltaics and starshine as your energy source if you have to).
It might take years/decades to get close to c, but if the distance is 1000 light years that's a negligible difference compared to the flight time of photons.

The problem with a tight beam is that it requires that someone actively sets up a listening post at the receiving end, looks in EXACTLY the right direction and tunes it to the right frequency - all of which is stuff that a sending species has no control over.

A probe, on the other hand, is rather hard to ignore and can contain any number of means to make itself obvious (and, if needed, can wait around until it's sensible to make contact).
Fleetfoot
not rated yet Jul 09, 2013
It might take years/decades to get close to c, but if the distance is 1000 light years that's a negligible difference compared to the flight time of photons.


No problem, you have to send out probes first to build the comms network across which the probe can return its data ;-)

You also need the probes to find potential targets with which to communicate.

The problem with a tight beam is that it requires that someone actively sets up a listening post at the receiving end, looks in EXACTLY the right direction and tunes it to the right frequency - all of which is stuff that a sending species has no control over.


However, for one species to use for their own purposes, it is cheap and easy. That's why we shouldn't expect to overhear interstellar comms not intended for us. If we sent a probe to Alpha Centauri, that's how we'd get the data back to the Solar System. There's no need for anything more sophisticated.
antialias_physorg
1 / 5 (1) Jul 09, 2013
No problem, you have to send out probes first to build the comms network across which the probe can return its data ;-)

Well, the probe can tight-beam back home. IT at least knows someone is listening ;-)

That's why we shouldn't expect to overhear interstellar comms not intended for us.

And even if we do - if these comms aren't encrypted I'll lose faith in the universe as a whole.

And decrypting something if you don't know the crypting algorithm (in the unlikely event it is even hackable) AND the language is an excercise in futility.
Fleetfoot
not rated yet Jul 10, 2013
No problem, you have to send out probes first to build the comms network across which the probe can return its data ;-)

Well, the probe can tight-beam back home. IT at least knows someone is listening ;-)


That works within a few light years, a few tens at most, but to get data back from a hundred light years away (never mind the core or the far side), it will be necessary to relay via intermediate systems. That network would get built as the fleet of probes moves slowly out from home because they would need to make the shortest trips possible to be able to repair flight damage at each stop.
antialias_physorg
1 / 5 (1) Jul 10, 2013
To get good data back it's probably even better to have the probe gather data and then fly back.

It's the old problem: Yeah, we have nice internet lines and good connectivity from, say, New York to San Francisco - but for amount of data per hour transmitted a train loaded with BluRay discs still beats that easily and it's not prone to dropped packets.

With interstellar distances it can be a lengthy procedure to request a 're-send' if a packet happens to be corrupt/missing. Especially since the nature of noise en route cannot be easily predicted like for short distance routes on Earth (or even interplanetary).
GSwift7
1 / 5 (1) Jul 10, 2013
Let's pretend that you are the Fleetfoot people and the Antialias civilization, and I'm the Mighty Swift Empire (muahahaha). The three of us are advanced and we have regular communications. Each individual grass plant on the Earth represents a habitable planet and each ant colony is a lower level civilization amongst those planets.

So, did you guys notice the ant colony 54 feet north of the big rock in front of Madison Wisconsin's Town Hall? I think they're a previously unidentified species.

I tried to communicate with them by drawing a picture on a piece of paper with crayons, because that's the simplest form of communication I can think of. If we leave an Iphone for them, do you think they'll respond?

We should try to warn them that their ant hill is built in the middle of a State highway. How can they not notice the cars going over them?!?!

Oh well, never mind, you guys should bring the kids over for BBQ.
GSwift7
1 / 5 (1) Jul 10, 2013
Hey, very off topic, but probably something most people here would get a kick out of. My brother bought me a copy of a PC game called Kerbal Space Program.

It's still kinda a beta version, but it's cool as heck. You assemble rocket parts to try to build a working space mission of your choice. As of now, it's a simple sandbox simulator, without any real game mechanics. There's no score or money or missions to do. You just build whatever you want and try to fly it, and your 'solar system' seems to be persistent, so you can put up space stations and Mun (their pun on moon) bases and such. I don't want to post a link to Steam's retail page here, but here's a link to the wiki page about it:

http://en.wikiped..._Program

I've just started playing it, and it's fairly complex and difficult. If you decide to give it a go, be prepared to search the web for tips and buy a notebook to take notes with. Like I said, you've gotta be a true geek to like this, so enjoy. :)
Fleetfoot
not rated yet Jul 10, 2013
To get good data back it's probably even better to have the probe gather data and then fly back.


True, someone did a calculation a few years back that suggested that's the case, however, you pay for the throughput with greatly increased latency (centuries instead of years).

amount of data per hour transmitted a train loaded with BluRay discs still beats that easily and it's not prone to dropped packets.


Fire those discs through space at 1% of c and most will arrive with holes in them and quite a few won't get there at all.

With interstellar distances it can be a lengthy procedure to request a 're-send' if a packet happens to be corrupt/missing.


FEC and packet interleaving would help too, one bit per day per packet means dropouts have little impact and you don't wait for a repeat request in ARQ, send multiple copies as a matter of course.

http://en.wikiped...rrection
Fleetfoot
not rated yet Jul 10, 2013
It is informative to consider how the signal quality scales with the comms relay size. The simple example is to assume a geodesic sphere. Each plate is a separate transmit/receive element and multiple beans can be formed using a synthetic aperture technique. For a reasonable angle of incidence, probably half the visible area of the sphere can be used.

If the error rate is too high, double the diameter. That quadruples the number of transmitting elements and hence transmitted beam power (though each element still transmits the same power). It also doubles the Rayleigh Length of the beam and quadruples the illumination at the target. If the same design is used at each relay, the receiving area is doubled and, from the point of view of the receiver, the area of background sky contributing thermal noise is reduced by four as well. Overall, that's a factor of 64 improvement of SNR. For any given range, throughput and BER, it wouldn't be hard to calculate the station diameter required.
GSwift7
1 / 5 (1) Jul 11, 2013
You're not accounting for the relavence of the data upon reaching its destination. With this time scale, would the message be important to the people receiving it? (if there's anyone there at all)

Would anyone maintain an outdated receiving station for thousands of years, waiting for a message that might never come? The technology you'd be listening for would be so old that you would need to go to a museum to decode the digital compression. Reading documentation written by the original project team would be like reading ancient Egyptian scrolls, as our languages would change significantly in that amount of time.
antialias_physorg
1 / 5 (1) Jul 11, 2013
@Fleetfoot:
It rellay depends what kind of noise we're dealing with (in earthbound systems this is true as well. A stochastic bit flipping requires an entirely different approach to error correction than a blockwise data corruption e.g. due to lightning strikes).
You can harden your data transmissions against many types of errors. Redundancy and resending data certainly helps. But in every case you're adding (sometimes massive) amounts of extra data, which means your information transmission rate drops through the floor.

Especially stochastic processes can be nasty since their effect goes linear with the distance. At some point this will actually overtake the capability to add corrective data (as you have to safeguard against the corrective data bits being corrupted, too). If you have stochastic noise on the line then there is a maximum distance beyond which you just can't go (given a fixed power for the sender. Of course you can always up your SNR by pumping in more energy)
antialias_physorg
1 / 5 (1) Jul 11, 2013
This is why I think it's better to return the probe. Yes: even the memory in a probe can get corrupted by the occasional stray cosmic ray. But a probe can continually keep checking its data (and immediately use error correction to mitigate any such bit flips). So it would need much less complicated error correction methods (and hence can store more useful data)

A sent signal can't do this. It just accrues errors until received, and you have to pray that the error correction scheme employed is enough for you to extract the message.

With this time scale, would the message be important to the people receiving it?

That really depends on how long lived the sending/receiving entity is. If you live for millions of years a signal that takes 1000 years isn't particularly problematic. And I hardly think that there is anything happening at solar system X to which solar system Y must react with any urgency.
GSwift7
1 / 5 (3) Jul 12, 2013
That really depends on how long lived the sending/receiving entity is. If you live for millions of years a signal that takes 1000 years isn't particularly problematic. And I hardly think that there is anything happening at solar system X to which solar system Y must react with any urgency.


Yeah, a general survey would be one of the only practical reasons for doing anything like that at all. Kinda just keeping tabs on who is where and what they are doing. Kinda like, oh look, Earth's dinosaurs appear to have died off, or hey, that planet has ice age problems.
Fleetfoot
not rated yet Jul 13, 2013
You're not accounting for the relavence of the data upon reaching its destination. With this time scale, would the message be important to the people receiving it? (if there's anyone there at all)


When we use a telescope to look at a start 10,000 light years away, we see it as it was 10,000 years ago. This would be no worse but the data would have been collected in system.

A distance to a hub in the Alpha Centauri system could be transponded very accurately and used for parallax measurements with a 4 light year baseline. Proper motions and accelerations of stars could be measured with transponded distance accuracies.

The technology you'd be listening for would be so old that you would need to go to a museum to decode the digital compression.


As new coding schemes are devloped, they get loaded locally and propagate out. Returned data can be up-converted en route so each hub only needs the latest and previous schemes with one conversion algorithm.
Fleetfoot
not rated yet Jul 13, 2013
A stochastic bit flipping requires an entirely different approach to error correction than a blockwise data corruption e.g. due to lightning strikes).


Certainly, and there's work to be done finding the best codes but the DSN already has this problem on a smaller scale.

But in every case you're adding (sometimes massive) amounts of extra data, which means your information transmission rate drops through the floor.


Not so with interleaving, spreading a millisecond packet over a month would virtually eliminate burst errors but not greatly impact latency.

If you have stochastic noise on the line then there is a maximum distance beyond which you just can't go (given a fixed power for the sender. Of course you can always up your SNR by pumping in more energy)


Precisely. A robust network in our region needs links around 20 light years, just size the hubs for that requirement and your desired SNR. The bigger the hub, the more power it intercepts from its star.
Fleetfoot
not rated yet Jul 13, 2013
This is why I think it's better to return the probe. Yes: even the memory in a probe can get corrupted by the occasional stray cosmic ray. But a probe can continually keep checking its data (and immediately use error correction to mitigate any such bit flips). So it would need much less complicated error correction methods (and hence can store more useful data)


But that needs on-board power, a signal just propagates.

A sent signal can't do this. It just accrues errors until received, and you have to pray that the error correction scheme employed is enough for you to extract the message.


Errors don't accumulate, the SNR depends on the received signal strength and the equivalent temperature of the background seen by the receiver which is typically 10 to 100K. Look at the charts under "Multiwavelength Milky Way" on this page:

http://www.astro...._mw.html

As long as each hub can reconstruct the data from the FEC, distance is not a problem.
antialias_physorg
1 / 5 (1) Jul 13, 2013
Errors don't accumulate

I think they do. Consider that any dust particle in between can cut out a block of a very tight beamed transmission (by scattering that part of the photons of the transmission that impacts on them). The number of intervening dust particles goes roughly linearly with the distance. (it's only roughly linearly as the medium isn't uniform and the closer to the destination you get the wider the beam is - so that dust particles have to be increasingly big to cut entire parts of the transmission)

For the SNR part you're right. But that still means you need a pretty hefty power source in order to overcome any kind of interstellar distances. Can't find the article right now, but I do seem to recall someone calculating that our terrestrial (TV, radio) signals heading outward are below the resolution possibility of even theoretically optimal amplifiers more than 2 light years out (which is a bit of a relief, if you ask me).
Fleetfoot
not rated yet Jul 13, 2013
For the SNR part you're right. But that still means you need a pretty hefty power source in order to overcome any kind of interstellar distances.


Suppose you construct a geodesic sphere with plates that are 1m^2. At e.g. 0.5AU each plate facing the Sun would collect ~5kW. A similar plate facing outwards might radiate 500W at 10% efficiency. The total power only depends on the sphere diameter which would be several km to get the required Rayleigh Length (depending on signal wavelength). The receiver mustn't see the target star so the beam has to be ~0.2AU diameter at full range!

I do seem to recall someone calculating that our terrestrial (TV, radio) signals heading outward are below the resolution possibility of even theoretically optimal amplifiers more than 2 light years out


That's right but those are nearly omnidirectional whereas we are talking about a very narrow beam and CW power levels in the terrawatt range, perhaps four orders of magnitude higher than TV.
Fleetfoot
not rated yet Jul 16, 2013
Errors don't accumulate

I think they do. Consider that any dust particle in between can cut out a block of a very tight beamed transmission (by scattering that part of the photons of the transmission that impacts on them). The number of intervening dust particles goes roughly linearly with the distance.


It's only linear as long as overlaps are negligible after which it is exponential. However, that's a reasonable approximation or we wouldn't even see the stars, the ISM would be opaque!

(it's only roughly linearly as the medium isn't uniform and the closer to the destination you get the wider the beam is - so that dust particles have to be increasingly big to cut entire parts of the transmission)


They don't cut out bits of the transmission (in time), just shadow bits of the beam. Bear in mind it has to be hundreds of metres or perhaps km wide to have an adequate Rayleigh Length. The vast majority of the beam would pass between the dust particles unhindered.