People are prety fond of saying how aliens will someday watch our broadcast TV programs, which makes sense as radio waves are photons, are quickly making their way out into interstellar space, etc. Lets assume the aliens figure out how to build a NTSC decoder television (yeah I know they would need a coherent signal to figure this out but lets play along), will they really be able to watch these shows? Wouldn’t the signal break up and become weaker the farther it travels? I can’t imagine it being much more than background radiation after 100,000 years of travel.
How about a closer example? If I was on the surface of a planet in the Alpha Centuri system could I watch 1996 season television with the technology we currently posses?
In more than a couple SETI press releases I’ve read that we don’t have a radio powerful enough to send a message that could be received by remote (don’t remember how far)alien civilizations. I’m sure the same rule applies to TV too.
Side question: How difficult would it be to reverse engineer a television by just detecting the signal? Would our encoding cause all sorts of problems or is it pretty straight forward stuff?
NTSC is not straightforward. But neither is it encrypted. I’d say that a determined entity could figure it out enough to get a good idea of what we sent.
Good point, Horse.
I’d guess it depends on how much ability we want to assume the ET’s have. Given that TV is EM radiation, it would suffer from the inverse square law, so the signal would be very weak by the time it got to another star. I wouldn’t know where to begin with crunching the numbers, but my WAG is that it would be stronger than background radiation. Maybe not much, but again, how much can the aliens do? Maybe they can detect a signal that weak, maybe not.
Same reasoning applies to reverse engineering the TV.
Well that was an informative post.
Isn’t it the regularity of the signal that is the key, not the actual decoding and observation of the TV shows themselves.
Too bad if all they get is I Love Lucy, or Married with Children.
Some science fiction writers, and more recently some members of SETI have speculated that a laser would be the best way of keeping a signal from degrading over interstellar distances.
Radio Frequency electromagnetic waves are electrons.
It is not that alien civilizations could decode complex signals. Rather the concept is that they would reconize that the electronic signal was from an intelligent source.
as to reverse engineering a TV, it seems it would be more difficult than we would allow. for instance, a radio signal and a television signal are both modulated electromagnetic radiation, but the former outputs to a diaphragm to cause sound wave vibrations, whereas the latter changes the the values for an electron gun’s rastering onto a phosphorescent screen. how the hell are aliens going to know how to reverse engineer that particular outputting device?
even worse, what if they don’t see in RGB?
Radio waves are NOT electrons, they are photons (although they are typically produced by moving electrons). Aliens on Alpha Centauri with our detection technology would not even be close to being able to detect any of our incidental transmissions, although they would be able to detect a signal from a laser (or more likely maser-- Same idea, different frequency). A maser signal isn’t broadcast, but it doesn’t need to be; we only really need to get the signal to stars, not to the vast empty spaces between. If you ask me, the problem with SETI is that we’re doing too much listening, and not enough talking… What if the rest of the Galaxy is doing the same?
As to interpreting the signals: TV might be difficult, but reverse-engineering radios would not only be easy, but likely unneccessary. Most radio signals are not encoded or encrypted in any way, and it’s likely that they use the same basic design for radios already. Remember, it wasn’t that long ago that building crystal radios was a common grade-school hobby.
I am curious, Chronos, what is your educational level?
My MS is in Electronics and Instrumentation.
Yes, radio would be very easy. TV audio is AM, BTW.
From carnivorous plant:
It is not that alien civilizations could decode complex signals. Rather the concept is that they would reconize that the electronic signal was from an intelligent source.
Now there is the problem right there. We are assuming that television signals and content can serve as the basis of our intelligence. We should question that.
Actually I’ve been rather dumb, but dumb like Michelson and Morley. An electromagnetic wave is a wave that travels in a vacumn. No photons, electrons, no ether.
You mean whether television program content indicates intelligence? I think the techology would indicate intelligentce. Content is obviously argued about between people of the same culture, so aliens thinking I Love Lucy or Citizen Kane is intelligent is really a moot point.
Wave-particle duality, carnivorousplant… Light (including radio waves) can be considered to be photons or waves. In the case of radio, it’s usually more convenient to consider it a wave, but there’s still a duality.
And since you asked, I’m currently working on my Master’s and Ph.D. in physics.
Chronos-
Well, cool. We can both agree that there in no ether, right?
Are you saying that all electromagnetic radiation can be cosidered to be photons in the sense that it is a wave?
Well, sure. Duh. I yield to the physics Student.
We can also argue dx verus delta x, if you would like.
er, I’m no physicist, but aren’t radio waves part of the EM spectrum which includes x-rays, gamma rays, and visible light, all of which consist of photons? (Or can be considered as photons, taking duality into account?) At least that’s what it says here in Beyond the Mechanical Universe by Olenick et.al. (1986)
Also Wouldn’t TV signals dissipate to much to be of any use by the time they got to Proxima Centauri, let alone to any more distant stars?
Yes. Yes. Yes. If a civilization were looking for such things, as SETI is, they would read these faint signals and see that an intelligent civilization existed.
First, Robert Preston lies to me in Music Man making me believe that I can play an instrument by the think method.
Now you guys tell me he was lying in The Last Starfighter , when the kid beat the video game? You mean there was no message beamed to some distant civilization, that it just dissipated along the way.
Bunch 'o Grinches ::grumble::
Larry, you are exactly right. The only difference between the EM radiation you see and the EM radiation you tune in on a crystal set is the wavelength (as it’s commonly thought of in broadcasting). And, yes, the ionizing radiation (commonly gamma radiation, sometimes x-rays) that causes cancer falls into the same category, just bounds higher frequency/more energy per photon. And, in the case of talking with ETI, we should broadcast loud and clear on hydrogen’s natural radiant frequency. It’s pretty quiet, and most intelligent civs would recognize hydrogen as being pretty fundamental, and its radiant frequency to be the place most others would broadcast at, simply because there is a low level of noise there. As for current radio systems, AM is much easier to broadcast and recieve than FM is. In AM, you only need the fundamentals of radio transmission and reception, as they both can be simple vibration detectors, the function crystals once served. Crystals, quartz in the standard crystal set IIRC, can be set to vibrate in tune with a sound or electromagnetic signal. In transmission, the vibration of a crystal or magnet varies the amount of current flowing to an antenna assembly. In reception, the antenna feeds a fluctuating current through another vibrator, which vibrates in sync, varying either another electrical current or making sound waves. In FM you need more advanced circuits, which is why FM stations were scarce until tubes gave way to transistors. Not that ETI will decode our signals anyway, or have to. The very fact of their presence will be enough.
Well, they’ll have to do at least some decoding. If they just see a stream of 22 cm radiation (the hydrogen hyperfine line), without any information content, then they’ll most likely just assume that they’re seeing a big cloud of hydrogen. In order to indicate intelligence, there has to be some sort of signal. Of course, that signal could potentially be very simple; remember the movie Contact? The first alien signal there was a series of pulses representing the first 32 (?) prime numbers: It’s a simple enough message to transmit, but mathematically sophisticated enough to prove that it’s some(one/thing) intelligent transmitting it.
As for wave/particle duality: The general rule of thumb is that things behave like a wave if the wavelength is long, and like a particle if the wavelength is short-- The definitions of “long” and “short” depend on the apparatus you’re using. Hence, radio frequencies (with very long wavelengths) are typically considered waves, gamma rays (short wavelengths) are typically considered particles, and visible light (in between) will often be described as either.
Yes, carnivorousplant, I agree that there’s no ether, but there just might be quintessence. Ether is ironic stuff; the original Greek word actually means “ever-moving”, because the stars (made of ether, of course) perpetually revolved around the Earth; but by the time of M&M, it had come to mean that which was always at rest. Fun, eh?