Cellular Phone Spectra and Earth's SETI Invisibility

astrobio writes: "How long will the Earth's technology be detectable to other worlds? From an article today by the Chairman of the SETI Institute: 'Not long, with shared transmission spectra. To transmit ever-increasing amounts of information, portions of the spectrum must be shared. This is only possible if signal strengths are reduced so that transmissions on the same frequency do not interfere with one another. The textbook example of this paradigm is the cellular phone system. This signal reduction means we are well on our way to becoming invisible.'"

Comments

Good.

[Violet Null]

Maybe now the three-eyed, ten-tongued aliens of Vega will be able to get some rest once we turn the noise down.

Bad intergalactic neighbors, that's what we are.

This is not a new theory

[eclectric]

SETI researchers have known this for a good while now. As we move from broadcast television and radio to digital formats, we will essentially be reducing and eventually completely shutting off runaway transmissions out into the cosmos. This is actually included in probability calculations in the success of SETI: you only have about 200 years in a given civilization in which to find them through their leftover radiation... after that time frame, there are certain signals (radio telescopes, for instance) that are detectable, but which don't travel in every direction.

One of the goals/projects of SETI is to keep transmitting data that appears to be from intelligent creatures... Prime numbers in binary is one proposed method. A simple SOS is even possible... anything that would look nonrandom.

Invisible?

[Rhombus]

Perhaps this is why we don't hear any radio transmissions from alien civilizations...by the time we thought to start listening, they've already refined their communications to the point where they're no longer detectable by us.

Sounds like it could be the death knell for SETI...

Re:Our signals may not be visible

[TRACK-YOUR-POSITION]

Geez no wonder I can't see the light from other stars anymore! All this time I was blaming pollutants.

Re:Great tech, but why from SETI?

[mberman]

SETI isn't proposing that we should use tech that doesn't broadcast as much as in the past. It's reporting that we already are. It's an unavoidable consequence of progress in radio communication. Just because SETI talks about it doesn't mean they think it's contributing to their cause.

This may be a Good Thing

[rpjs]

Because do we really want to let the universe know we're here? Contact with a more advanced civilisation might have unfortunate repercussions for us - look at the impact contact with the West had on so many indigenous cultures during the ages of exploration and imperialism.

And that's just assuming the ETs are benevolent and simply can't help having the effect on us that we have on a newly contacted tribe in the Amazon. What if the ETs are paranoid about competitor intelligences arising and have a policy of wiping out any new civilisation that pops its head up over the electro-magnetic parapet? That's one of the more pessimistic explanations for the Fermi Paradox.

Re:This may be a Good Thing

[Rhombus]

Good point....look at StarFleet...they have a specific rule against this sort of thing, and it gets broken about twice an episode. :P

Seriously, though, if we were to discover an alien race that was technologically inferior to us, I entertain no illusions as to how our species would corrupt and exploit them. Why do we assume that alien races technologically superior to us would be equally superior ethically?

Re:This may be a Good Thing

[dpilot]

Or read "The Forge of God" by Greg Bear, or the Galactic Center series by Greg Benford. The hazards of becoming visible. Maybe everyone else knows better.

Re:This may be a Good Thing

[whovian]

On the other hand, what if a civilization gets the idea of "aliens" for the first time by discovering patterned interstellar radio signals? It's an involuntary violation of the Prime Directive on our part. In the big scheme of the universe (whatever that may be) I don't think this is so serious.

On the other hand, that civiliation too would probably get sued under DMCA :P

Not True

[Perdo]

I thought of this years ago. Then realized I was wrong. How much power does your local AM radio station put out? 50,000 watts. Will the ammount of power required to broadcast to three states ever drop? Nope. How many 50,000 watt radio stations are there in the US alone? Over 8000.

Will XM sattelite radio change that? Has linux been able to break Microsoft's monopoly?

Re:Not True

[babbage]

Actually, almost all of the high power AM stations are required to throttle back at night so that they can't interfere with each other. During the day they have to pump out that much power to get through the Sun's radiation; at night the signals have no such interference and so have to operate at low power to keep from trampling each other. There are only a dozen or so AM stations allowed to broadcast at full power overnight as a result.

So, yeah. The amount of power required to broadcast to three states rises & falls every single day, and the amount of power used to accomplish this is adjusted accordingly :)

Another interesting angle is signal compression & encryption, both of which can make the signal sound like so much static. Will this make us more "invisible" too? Presumably a burst or stream of seeming gibberish might be distinguishable from true static if you know what you're listening for, but if not it could easily blend into the background noice. Conversely, if other civilizations are doing the same thing, picking up their signals could be very difficult -- much harder than just scanning for Betelgeusian episodes of "I Love Lucy"... :)

Re:Not True

[AJWM]

There are only a dozen or so AM stations allowed to broadcast at full power overnight as a result.

I suspect Denver's KOA (850 kHz) is one such. They certainly pump out 50 kW, and brag about reaching a 38 state (plus Canada and Mexico) area.

OTOH, one reason for the huge range is that the radio signal is reflected back to Earth by the Heaviside layer, reducing the amount of it detectable beyond the ionosphere.

We Should Build a Directional Ant.

[capt.Hij]

The examples of space going radiation given in the article are all point sources. The power per area for such sources should be exceedingly small for those sources within a relatively small distance. Perhaps we need to build directional antenae to make sure that we can be heard. Of course given the nature of directional antenae we should make sure that we build millions of them to make sure that they are pointing in the correct direction. (The down side of Fermi's dilema!)

What we need is a screensaver that will turn a monitor into a directional antena. Then everybody can then turn their monitor towards the heavens when their computers are not at work and let the screen saver then broadcast a message. This would be much more effective and much cheaper. This way we can do the broadcasting for a change and let those free-loading, beer swilling aliens take a turn trying to decode noise from space for a change. Why should we do all the work?

Re:A limited form of invisibility

[dzym]

There is no reason expect that oxygen is the basis for all life in the universe. The scientific community has become increasingly aware of small bacteria-sized creatures currently termed archaea. These creatures do not depend on photosynthesis for their nutrition but instead rely on varying and diverse elements (including some of the "heavy" ones) and presumably also do not require the existence of massive amounts of oxygen to survive/thrive.

Bottom line: don't assume that just because humans require oxygen to survive, that any other alien species must also, and that they would necessarily also search for oxygenated worlds.

Holy Shit Batman!

[capt.Hij]

Italy passed a new law regulating electromagnetic emissions in February, which sets a limit of six volts per square metre for inhabited areas. Residents in Cesano have complained that the eletromagnetic emissions in their homes sometimes exceed 50 volts per metre.

Wow! I thought the neighbors described in the article were whining until I got to this part. This is a staggering amount of radiation that they are pumping out.

I once spoke to some Air Force dudes about this sort of stuff, and they said that the big concerns were over endocerine systems. It would be very interesting to see if there are any problems with diabetes or other such diseases in the area. Sounds like a perfect test bed to see if e-mag emissions really can be harmful.

Of course the complication here is that if someone there gets sick, they can rest assured that the pope will be praying for them. It is probaly a bit tough to add such complications into your statistical models.

Re:A limited form of invisibility

[joto]

And this has exactly what to do with radio-signals?

Re:Our signals may not be visible

[ShavenYak]

The point of this is that a signal may only propagate outwards until the total mass behind it exceeds a critical value (the location of this is called the "event horizon" in an analogy to black holes). At that point its deflection will equal more than 90 degrees...i.e. it will not go any farther from its point of origin.

Obviously this limit, if it exists, is more than several billion light years, otherwise we wouldn't be able to see galaxies that far away. So I don't think this is going to affect SETI too much.

Moon transmitter.

[Yet Another Smith]

What the heck is stopping us from setting up a transmitter station on the far side of the moon which beams out as powerful a message as we want without interfering with terrestrial communications one bit.

You'd be able to broadcast a hemispherical signal in all the transmission windows no problem. You could broadcast with as much power as you can provide, and the moon would sheild earth-bound and even orbital communications systems.

Frequency Hopping and other Obfuscation

[ZahrGnosis]

Even if some extra-terrestrials can pick up our wireless communications, their ability to decipher it from noise may be limited because of new technologies, notwithstanding the power of our transmissions.

Consider the 2.4GHz range and frequency hopping. There's no way anyone picking up the earth's aggregate transmissions in that band would be able to decipher them, (frequency hopping is designed that way)... TV and AM/FM broadcast signals are relatively simple to decipher, having carrier signals that are quite regular.

I also understand that radio waves are fairly common in the universe, although not being at all the astronomer, I have no idea why. If our airwaves get too muddled, I imagine we won't look much different to a radio telescope than some other radio-prolific celestia.

Another question is, has this already happened somewhere else? I think I remember hearing that SETI's work, particularly their distributed computer search software would probably miss wide spread-spectrum FH radio technology and consider it white noise. Any word on that?