[Ryan Mercer]

Ryan Mercer  asked the Naked Scientists:
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What would be the ideal method of contacting a technologically similar extraterrestrial race say less than 1 light year from us (sattelite network, outpost, exploration craft, what have you, just assume less than a light year out from within our own solar system to 1 light year). Would radio be ideal? From what I gather even lasers in the UV or even x-ray nanometer spectrum would still be incredibly dispursed at distances even as far out as Mars' average distance from Earth...
 
I'd think radio also because it would be far easier to detect with significant dispersion unlike visible like spectrum lasers, but not knowing the capabilities of our own equipment for detecting IR, UV, & x-ray might an array of diodes of one or all of the 3 be far easier to identify/detect/notice than radio?

What do you think?

[graham.d]

Hi Ryan. This is a bit hypothetical in that there is nothing within 1 light-year that would be likely to harbour intelligent life. If it were a spacecraft then the extraterrestrials would clearly be more advanced than us. Another question would be whether the aliens wish to be contacted assuming that, for some reason they were not aware of us (this is unlikely given this scenario).

If they were at a very similar technological level to us, radio may be a good way to get their attention. It would have to be simple pulsed signalling though, just to show that there was some intelligence affecting a signal in the radio spectrum. And be on some frequency band where we think they may be monitoring.

You have to think that our galaxy has been around for a long time (many billions of years) and that, even if life is very, very common, there is very little chance that we will stumble on a race whose level of development is within plus/minus 100 years of where we are now. If any race has made it close to us by some craft, they will be an older race than ours, and the probability is by a lot (maybe many milions of years). If they did not want to be noticed, we probably would not have a hope of detecting them.

[joepierson]

Any race probably emits RF for only a few thousands years in their history before moving on to whatever is next, so you not only have to be pointing at the right star but you have to point at it during a small window of a few thousands years out of billions. A better bet would be to examine the planet visually (as best you can with powerful space based telescopes), examine the atmosphere and what not for unnatural signs/events.

[Phractality]

Radio telescopes, presently have a far superior resolving power than optical telescopes. That is because of the way many dishes are combined in a phased array nearly as wide as Earth. If we figure out how to do the same with optical telescopes, the resolution should be trillions of times better than radio telescopes.

If communication via quantum entanglement (QE) is ever achieved, it would be far superior to any form of light-speed communication. However, QE has its own limitations; it not suitable for reaching out beyond where humans have already been.

There is no good way of contacting a technologically similar extraterrestrial race. Any race that happens to be 1 light year from Earth had to have travelled many light years to get there, which means they are technologically far superior to us. At best, they're like Christopher Columbus, and we're los Indios. We had better hope they overlook our planet and keep on going. Any signal we send to them will likely be interpreted as, "Free human burgers; all you can eat."

[imatfaal]

And you cannot transmit information faster than light - so a QEntangled system would max transmit at a speed we can already achieve.

[CliffordK]

Hi Ryan. This is a bit hypothetical in that there is nothing within 1 light-year that would be likely to harbour intelligent life. If it were a spacecraft then the extraterrestrials would clearly be more advanced than us.

It is my belief that if we chose to send a spaceship to Proxima Centauri (4.2 light years away), then we essentially have the technology to do so today. 

It would take a monumental effort, but it could be done.

It would also take a very long time to arrive.  Perhaps a 1000 year voyage.  And communication from the destination would be a welcome diversion.

EM spectrum communication, or perhaps Gamma, would be as good as anything for communication.  The goal would be to find a wavelength that is independent enough from the background stellar radiation (thus visible light would be out).

One might set up a couple of frequencies.  One frequency for some kind of test/attention signal.  Beep Beep Beep...  Send them CNN on one frequency.  And, a third frequency hoping to foster 1 on 1 communication. 

Perhaps send redundant transmissions on separate frequencies using various radio, TV, analog, and digital standards.  Hopefully intelligent life would be able to detect the difference between analog and digital and choose which they chose to decode first.

Mathematical series, Fibonacci, and etc are great at saying "here we are", but really don't convey much actual communication.

The biggest problem would be the delay.  1 year for the signal to travel 1 light year.  2 years for round-trip communication.  It would certainly make a question-answer or any kind of diplomacy difficult.

I would select a single language for all communication, and resist the temptation of sending a bit of English, some French, some Russian, and some Chinese...  it would be far too confusing.  Also resist the temptation of sending the aliens old episodes of Star Trek with captain Kirk for risk of creating some kind of "Galaxy Quest" miscommunication.

Also, keep in mind that we are unlikely to see a space ship one lightyear away without first detecting it with something else such as a radio signal, so one might choose to use the same communication method that they are using, while we would dedicate significant effort to decode the incoming signal.

[Ryan Mercer]

While there might not be anything as close as I stated, and yes they are probably more advanced, I'm just looking at it hypothetical to determine the best means of communication for such distance. Traditional radio, pulsed visible light, IR, x-ray, etc. What's going to hold up best over those distances and be the most reliable?

[CliffordK]

We've maintained contact with the two voyager probes for 1/3 of a century with obsolete equipment running under low power with radio.  And, with the combined effort of all the satellite dishes (on half the world), and a few very large dishes we could blast it with a quite a powerful signal, as well as having very good listening coverage.

However, in a sense, all EM spectra are similar, except for background contamination.

[Ryan Mercer]

We've maintained contact with the two voyager probes for 1/3 of a century with obsolete equipment running under low power with radio.  And, with the combined effort of all the satellite dishes (on half the world), and a few very large dishes we could blast it with a quite a powerful signal, as well as having very good listening coverage.

However, in a sense, all EM spectra are similar, except for background contamination.

Yes but how much data are we capable of sending it with any one single range (not a large array of antennas/dishes facing it), and what would the date integrity be like?

I'm thinking along the lines of what could we put on an average size satellite, launch into orbit to get away from atmospheric distortion/absortion, and what would be the most ideal spectrum to use for communicating a distance under a light year.

I'm going at this as purely what-if.

Assume there is a craft say .5 light year out that is known about and it needs to be sent say 5gb of data with absolutely no loss in data. Assume the target craft is a sphere 1/20th the size of our moon.

I'd imagine x-ray would be the best, no? I know they have x-ray emitting diodes now they are developing... would visible light be just as effective, or perhaps IR?

[graham.d]

With today's technology I would reckon the simplest communication method is radio transmission using a widely spaced array of large dishes. There are quite a few about that are used mainly as interferometric receivers (for radio telescope work). The technology to encode and modulate data, broadcast with high power, is all well understood.

Modulation of a laser may work but the laser would probably have to be in satellite based to avaoid atmospheric dispersion and then getting adequate power may be problematic even if this could be easily done with today's high power lasers.

You phrased your question in broad terms so most people cannot understand the range of problems you are considering. Are the aliens expecting to receive data or are you trying to get their attention? This determines how complicated or simplistic the encoding of the data should be and the type of modulation. Providing there is time to communicate what you are trying to do and how you are going to do it (in simple terms with simple signalling) then it is not hard to produce a modulation scheme and data encoding to send any amount of data. Any data loss can be mitigated with a sufficiently sophisticated Error Correction System. Having established a link it would be easy for the receiving party to optimise their receiver and have a focussed antenna.