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Cosmic Communications

Cover story blurb: It's almost a 'given' that remote civilizations will try to contact us using radio waves. The search for extraterrestrial intelligence was first mooted by Giuseppe Cocconi and Philip Morrison 45 years ago ('Searching for interstellar communications' Nature 184, 844--846; 1959). Since then, 2 million years of CPU time has been given to SETI@home in the spirit of that paper: 'The probability of success is difficult to estimate: but if we never search, the chance of success is zero.' Christopher Rose and Gregory Wright propose a new take on extraterrestrial contact. It seems the 'Sounds of Earth' gold disks aboard Voyagers 1 and 2 (see cover, left) were on the right track. The message-in-a-bottle idea of sending physical objects across space is highly energy efficient, and we should search for artefacts in the Solar System now.

Nature Letter 431, pp.47--49, September 2, 2004 and Supplementary Information. Full size 9/2/2004 Nature cover picture (PDF). NSF (National Science Foundation) 3/10/2006 Discoveries feature story (local copy).

If the above blurb made little sense to you, some really nice descriptions of the work by really good science writers can be found here. Some even managed to drag the right words out of me during radio interviews (at least for the most part when they could contain my digressions and technospeak). Here's the Rutgers University press release.

My home page and Gregory Wright's (co-author) home page.



Basic Idea

Publications

PRESS COVERAGE

Acknowledgments  

Related

Quantitative Analogies  

Mass Information Density

Voicemail For ET?  

Cosmically Selfish Genes?

Cartoons  




Basic Idea

How will our first extraterrestrial civilization contact occur -- through radio waves or artifacts?
Strangely enough, we think artifacts may be more likely!

It turns out that it's often MUCH ( many many orders of magnitude ) better from an energy use perspective (and perhaps from others like message persistence at the destination) to write a message down in some medium and LITERALLY toss it to the recipient than it is to radiate the message electromagnetically -- assuming delay beyond light transit time can be tolerated.  This result has some implications for terrestrial communications, but the most impressive gains are for interstellar and intergalactic distances. So perhaps the SETI program should be sifting through dust/pebbles/rocks in addition to searching the electromagnetic spectrum for messages from "out there."

This work, an accidental outgrowth of work on terrestrial wireless, is pretty careful in assessing the energetics and provides outer bounds for the ratio of the energy necessary to deliver a message using "inscribed matter" to that for electromagnetic radiation -- and usually favors radiation by assuming such things as infinite bandwidth.

We also worry about directed radiation, aperture sizes, and the fact that there are many targets -- matter transmission STILL wins.

We've recently included the delivery problem (how do you slow the particle down at the destination), the construction problem (how much energy to construct the particle) and a version of the civilization communication problem (civilizations are almost certainly asynchronous owing to calamity -- celestial, like meteor strikes,  or competition/stupidity-induced). We'd wanted to wait to add these, but various referees felt these aspects were necessary to convince readers that evidence of ET might appear in grains of sand or on comets, meteors, etc..

We also recently considered the ballistic aiming problem since gravitational perturbations might serve to knock a package off course (the effect seems small).

Of course, if energy is no object (consider Freeman Dyson's "sun herding" or building what amounts to a giant blinker around a sun) our energy comparisons are irrelevant. But since such feats are not presently on our technical horizon, we have a bias in favor of worrying about energy.

Hopefully you'll find the work thought provoking, or at least amusing! Talks, publications and earlier "kitchen sink" versions of the work can be found below. Of particular note, some folks have found the following captioned pictures especially amusing.



Publications and Talks

Communication Theory Workshop 2013, Phuket Thailand Slides (pdf)

June 24, 2013

Northern NJ Junior Science and Humanities Symposium Slides (pdf)

March 19, 2012

CSEE Seminar, Universtiy of Maryland Baltimore County Slides (pdf)

December 9, 2011

Lunch Bunch Seminar, California Institute of Technology Slides (pdf)

October 25, 2011

iCORE Summit'06 Keynote Address Slides (pdf)

May 23, 2006

British InterPlanetary Society
Space Archaeology Conference '06 talk   slides (pdf)

May 10, 2006

Princeton University
ISS Seminar Series talk   slides (pdf)

Mar 9, 2006

Lawrence Berkeley National Laboratory
Lecture for the World Year of Physics Celebration. "Today at Berkeley Lab" announcement ( local copy).
Special thanks to
Saira Mian at LBL for creating the compelling and fun talk advertisement ( local copy).
Talk abstract and slides (pdf).

July 25, 2005

University of Texas at Austin
General Motors Wireless Networking and Communications Seminar talk   slides (pdf)

Feb 25, 2005

University of Texas at San Antonio EE   seminar talk slides (pdf)

Feb 24, 2005

Telcordia Midnight Seminar Series   talk slides (pdf) ( postscript)

Dec 16, 2004

Asilomar'04 Conference on Signals, Systems, and Computers talk and paper

Nov 9, 2004

Nature Letter 431, pp.47--49 and Supplementary Information

Sep 2, 2004

DIMACS Workshop on Storage talk

Mar 24, 2004

Crawford Hill Coffee Hour talk

Oct 21, 2003

VTC Fall 2003 talk and paper

Oct 8, 2003

Previous Drafts


Commentary, Press and Radio Coverage



Related Information

Web Sites

Some Information Payload Sizes

-- mostly lifted from Michael Lesk's (now rather quaint ) 1997 unpublished paper

Approximate Mass Information Density ( &rho ) of Common Storage Media

Illustrative Cartoons by Students!



Quantitative Analogies

Lift a sugar sack or detonate a 24 Megaton blast?

For an Arecibo-Arecibo radio communications example (without shielding or other costs for matter), the efficiency gain of inscribed matter over radiation is about 5 X 1015. So, if raising a 2kg mass (roughly a 5lb sack of sugar) one meter on earth were equated with the energy needed to deliver the matter, the relative amount of energy necessary to radiate the same message would be a 24 megaton nuclear blast.

If we include the extra costs for sending matter as in the paper, the relative efficiency drops to 108. Using the sugar sack raised one meter analogy again, the relative effort to send a radiated message would be like raising a 200,000 ton cruise liner about 1 meter on earth.

You'd need a spherical galaxy 10 times bigger than
the visible universe before radiation beats matter!

Radiation would seem to have an advantage since it covers more targets than a matter transmission. However, for radiation to be even remotely competitive with inscribed matter, the radiation has to be collimated (like a laser beam). The tighter the collimation, the fewer star systems (we're being "solar-centric" ) are illuminated -- and this requirement vitiates any "broadcast advantage" one might get with radiation. Said another way, if signals were sent isotropically (everywhere) in a spherical galaxy with uniform stellar density, even accounting for the fact that shielded messages would have to be sent to each and every star in a given volume, the relative efficiency of matter is so enormous that the breakeven galaxy size (where there are so many stars to reach that radiation again becomes more efficient) is about ten times larger than the visible universe!!!

How Long Is Long?

In the paper we say that owing to shielding, longer messages are favored over short "we exist" messages. One sharp journalist (Stefan Lovgren of National Geographic) asked the question of exactly how long is long in this context. For the Arecibo example at 10,000 lightyears, inscribed matter beats radiation for messages larger than 1014 bits -- about the size of the written information in the library of congress (see Michael Lesk's treatment).

How Well Can We Aim?

One question which arose is how well one could aim a particle using mostly ballistic transport. For grossly macroscopic particles, Heisenberg (uncertainty principle) is pretty much irrelevant, but more important, there will be random gravitational perturbations en route owing to the gravitational pull and somewhat random (unknown) placement of stars in our Galaxy. The effect of how well we can aim, however, seems relatively unimportant.



Musings

Cosmically Selfish Genes

If civilizations at any given stellar location are short-lived owing to various sorts of celestial, geological or self-inflicted calamity, there could be a survival benefit to seeding the cosmos with compelling records of a civilization in the hopes that it would be eventually adopted by other fledgeling civilizations (or subsumed by older ones). However, under the assumption of impermanence, literal biological seeding of likely habitats (similar to Crick's "panspermia") seems much more likely in that it confers a selective advantage -- of sorts. That is, those civilizations that seed may survive in some form, and those that don't may likely perish completely.

Here's a recent (6/30/2005) news article ( local copy ) on the idea that life is everywhere and might even turn up in the comets that NASA is currently stalking ( Wild-2, Tempel-1 ). I have a soft sport for comets as potential message delivery vehicles. They can release material during transit through the inner solar system and they are highly visible. However, for archival data messages, the annoying fact is that their orbits are only stable for a relatively short time -- tens of thousands of years as opposed to hundreds of millions. That doesn't leave the local denizens much time to attain the necessary technological sophistication to reach out and grab one. But if biological seeding is the aim, comets seem (at first blush) like a decent delivery method.

Of course, the context of the selfish gene is evolution, and since evolution implies mixing and competition, (more)

Is Life the Message?

Michael Crichton the novelist made exactly the point that life might be the message (and explicitly that it seems more efficient to send a package than to use electromagnetic radiation) in his 1969 novel The Andromeda Strain (pp.222-225 courtesy of Rich Howard).


Of Motes and Matter

One admittedly crazy image I cannot seem to shake is of arrays of computer chips using MEMS catapults to deliver info in lieu of optical/electromagnetic bus lines! Well, I nagged myself into doing the calculations. Specific scenario: wafer-to-wafer communication (10cm) at a speed of about 0.3m/s compared to IR laser communication assuming 5 micron radius apertures.

You work out the numbers and find that the matter efficiency ( &Omega ) figure is about &Omega = 5.2 X 10-14 &rho where &rho is the information density of the storage/transmission medium. So tossing little magnetic chits back and forth (see density figures above) would be about 5000 times more energy-efficient than laser communication. And if an STM tip were employed to inscribe the surface of an information carrier (like an SiO2 chit), the energy efficiency could be more than 1000 times larger still.

So, smart dust tossing inscribed dust may not be crazy after all!



There's One Born Every Minute

Sending voicemail to ET?

A recent article (local copy) in New Scientist profiles a now bybone service (racket!) whereby you call a "900" number to leave voice messages for ET to be beamed out into space using a satellite dish. New Scientist contacted me and since silence can imply complicity, I did the calculation. I suspect that customers of this service have little hope of getting their messages across. But people bought "pet rocks" in the '70s so perhaps there'll be a lot of takers.



Credit Where Credit Is Due:

A special note of thanks to Leslie Sage and the editorial staff of Nature who saw something of interest in an overlong and overmathy draft, and shepherded a newbie (me) through the Nature publications process from "presubmission enquiry" to the final paper. I would have formally thanked Leslie in the paper acknowledgements, especially since he made substantive contributions to the paper (for instance, the Voyager comparison was his idea), but it seemed to go against Nature's policy. Overall, this was the most enjoyable editorial experience I've ever had even if the paper had not "made the cut." Bravo Nature! But a special Bravo Leslie!!!"



In addition, without countless invaluable conversations with G.J. Foschini or N. Beaulieu's eye for potential and strong encouragement, I'd never have approached Nature with this work. Thank you both! I'd also like to correct two misprints which appeared in the paper acknowledgments. Special thanks are due to PAUL HENRY for being an invaluable sounding board early on, and to STAVROS TOUMPIS for careful reading of an early manuscript.


Christopher Rose and Gregory Wright.

Common Question: How did an independent consultant/astronomer and a college professor of wireless communications theory get together?

Answer: We're both part of the post-divestiture diaspora from the old Crawford Hill lab (Bell Labs Research) -- of Telstar and big bang background radiation fame.

Tripped over a non-functioning link? Please email Chris. No guarantees, but I'll try to get to it ASAP .



Last updated June 28th, 2013

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