After 35 Years, Another Message Sent From Arecibo 249
0xdeadbeef writes "Two weeks ago, MIT artist-in-residence Joe Davis used the Arecibo radio telescope to send a message to three stars in honor of the 35th anniversary of the famous Drake-Sagan transmission to M13 in 1974. It was apparently allowed but not endorsed by the director of the facility, and used a jury-rigged signal source on what will now be known as the 'coolest iPhone in the world.' The message encoded a DNA sequence, but no word yet on whether it disabled any alien shields. You can get the low-down on Centauri Dreams: Part 1, Part 2."
Re:Wishful thinking (Score:5, Informative)
We could never pick up a radio signal from an alien civilization because the power of a signal from a point source drops off exponentially..
Umm..... its not a "point source" its a spherical reflector..... the whole point of the construction of big antennas is to allow you to do precisely what it is you friend appears to believe is impossible.
We now return you to your usual /. chaos
Re:Wishful thinking (Score:5, Informative)
Oddly, we just solved this problem in E&M class. If you had antennas with 80 dBi gain at both ends and a megawatt of power, that would be sufficient to transmit 10^5 bits per second over a lightyear gap with a received power level above the thermal noise floor (e.g. the antenna does enough work on the receiver to flip a bit). Raise the distance to 100 lightyears and reduce the gain to 73 dBi (e.g. Arecibo) and you lose 5.5 orders of magnitude in bit rate. Up the power to three megawatts (not hard to imagine) and you get back half an order of magnitude. So the achievable rate over 100ly using only current Earth technology at both ends is about a bit per second. Useless, perhaps, but not technically impossible.
Re:Wishful thinking (Score:5, Informative)
Re:iPhone? (Score:3, Informative)
But they did use an iPhone.
Re:Wishful thinking (Score:2, Informative)
+3 Interesting, huh?
This (and some previous, as well as some following) comments, have absolutely no clue whatsoever about E&M radiation. If you don't know, don't post.
The strength of electromagnetic radiation drops off as the square of distance. (As long as you're far enough away to ignore "near-field effects", which for the astronomical distances we are talking about, they can very well be ignored.)
It is always the square of the distance no matter what antenna geometry, gain, feed, or other technological measure is employed. It is not exponential (as stated by a previous post). They do not degrade "less slowly" as stated in the parent post. (And - "less slowly" - does that mean they degrade more faster?)
I swear, I hardly ever post here, but I'm going to have to create an account just so I can reply to all the erroneous understandings of E&M that get modded up. I expected this readership to be better than that.
Re:Wishful thinking (Score:2, Informative)
No. The signal strength is 1/(r^2). Exponentially would be 1/(c^r), where c is some constant and r is the radius. Exponentially means r is in the exponent, not the base.
Re:Wishful thinking (Score:5, Informative)
As it is a linear partial differential equation, all solutions to the wave equation and equations of its type are governed by what is known as the "fundamental solution" or "Green's function" of the equation. In the case of wave type equations(in 3 or more dimensions), this solution will be a delta function type solution which decreases inversely with distance from the source. Squaring its amplitude to obtain energy gives an inverse square energy decrease.
It must be stressed that all solutions of the wave equation, no matter what the sources, or boundary or initial conditions, must all be functions derived, more or less, from convolutions of the fundamental solution with the source terms. You cannot escape the inverse square behaviour of wave propagation over long distances with finite wave sources. The fundamental solution characterises all waves because of the linearity of the wave equation.
Now, there is a second fundamental solution for the wave equation; the so called "acausal" Green's function, which represents an inwardly collapsing wave, or by some conventions, a wave travelling backwards through time. Naturally, these waves are not considered in the context of the transmission of signals. Even if they were, these waves also display and inverse square relation for signal strength( going backwards in time of course).
This has been your daily mathematical public service announcement. Complaints to be directed to the Dean.
Re:They should have resent the original message. (Score:3, Informative)
Definitely, sending the same message repeatedly is better than sending multiple messages in different encoding schemes. However:
The Arecibo message was designed to be as easy as possible to decode, it would be possible to do so with just a pencil and paper.
Designed, sure. I recall reading that it was nigh-impenetrable in practice, and it flip-flops between ways of encoding the same data at various points (e.g. it introduces a scheme for writing binary in limited space in the first part, then ditches it in favour of just extending the space in the second) which is hardly conducive to understanding. It should've been edited, then retransmitted. That way it would still stand out, but it would give some clues as to what it's actually meant to say.
Re:Just don't take any calls (Score:5, Informative)
Pointless Calculation...
What if they tried to send the exact same information to a neighbor, using Verizon wireless...
As a text message:
Base Pairs in DNA: 3,080,000,000
Total # Characters 6,160,000,000.00
Text Message Limit 160
# Text Messages: 38,500,000.00
Rate per Text Message: $0.20
Cost: $7,700,000.00
Using Verizon's 1.99/MB data rate:
Megabytes Data 770
Cost Per Megabyte $1.99
Total Cost $1,532.30
Mailing a Baggy full of sperm:
44 cents.
Seeing the look on your neighbor's face when she opens her envelope:
priceless