Is it realistic to suppose an alien civilisation 60 light-years away could now be receiving tv transmissions of "I Love Lucy"?

This site says emphatically not, but my brother say ET could easily do it if he wanted to. Please settle the argument, somebody!

ADDED 11th July: Just to clarify, my brother is prepared to assume ET's detection facilities could be incredibly good (i.e. - receiver array as wide as a planet or larger, focussed exactly on the earth), and almost infinite processing power to separate signal from noise.

In short, the question comes down to whether there's some upper limit on how close ET would need to be, before 'background noise' would overwhelm any feasible attempt at detection. I don't know enough about information theory to even know whether such a limit can be proven to exist, let alone whether it can be calculated to an actual value.

  • It's very unlikely that a undirected signal is still correctly receivable after 55 light years. It's original power would be spread over a sphere with a radius of 55 light years. You can easily imagine that its long gone below the background noise. Jul 10 '11 at 9:31
  • How strong is the background noise? Is it equally strong everywhere? Jul 11 '11 at 1:10
  • @user unknown: I don't think it's a matter of just comparing signal strength to noise. More processing power could identify an information-modulated signal even against higher background noise. Jul 11 '11 at 2:21
  • @FumbleFingers: No. In the absence of any error correction, even the tiniest bit of noise will cause some corruption of the signal. If Forward Error Correction is used, the amount of FEC determines the maximum tolerable noise. (See also Shannon–Hartley theorem)
    – MSalters
    Jul 11 '11 at 11:35
  • @MSalters: I don't like to be lazy, but I doubt my maths is up to ferretting out the truth on this one, even with your link. Is it mathematically possible to establish a maximum distance beyond which no feasible detection equipment (coupled to effectively infinite processing power) could abstract usable information from those early high-powered broadcasts? I mean purely on the basis how 'background noise' comes to dominate the issue. Jul 11 '11 at 14:20

Actually, your brother is right. The answers here all are for Earth-class facilities, which indeed are inadequate for the task. But planet-sized, or even smaller antennas, can do the trick out to anywhere our signals have gotten so far.

I've written up (with some reasonably detailed computations) what would be possible with alien-class facilities, and they could watch our TV if they wish to. See


  • I'm sold on this! The "factor of a million" in the current top answer is in fact small beer in the context we're talking about. I think our "useable within a single box" computer processing power has gone up by significantly more than that in the last 50 years, which is a mere blink of an eye (who's to say ET didn't start evolving towards intelligence / technology millennia or even millions of years before us?). But the main reason I switched my "accept" is your point about exploiting the redundancy of hundreds/thousands of repeats (which obviously would apply in spades to "I Love Lucy" :) Mar 30 '12 at 22:39
  • 1
    This answer does not seem to have a valid source...
    – Ephraim
    Apr 3 '12 at 3:04
  • Do you have any sources to back this up? Also, you should include all the relevant information in your answer, not in a link.
    – HDE 226868
    Sep 30 '15 at 1:51

Note: Since the link in the question actually gives a good answer I'll use it.

From Seth Shostak (SETI Institute), via Space.com:

The first episode of "I Love Lucy" was broadcast sometime on October 15, 1951.

[The signal] is still going. Every day, that first installment passes through an additional 4 thousand trillion trillion trillion cubic kilometers of the cosmos.

Given that stars in our galactic neighborhood are separated by about 4 light-years, it's easy to figure that roughly 10 thousand star systems have been exposed to "I Love Lucy" in the past five decades.

That may suggest a high Nielson rating, but the chance that extraterrestrials are now hooked on 1950s television is low.


Imagine that there are alien couch potatoes 55 light-years away who, bored with their own Fall lineup, have constructed a LOFAR-style antenna (a telescope consisting of 25 thousand tent-shaped antennas spread across Holland and Germany) in hopes of picking up "I Love Lucy's" debut.

OK, how strong is that signal by the time it reaches our putative alien audience at 55 light-years distance?

Not very. The megawatt broadcast washes over ET's world with a power density of about

  • 0.3 million million million million millionths of a watt per square meter,

which is not exactly a scorching signal.

Could their LOFAR-style antenna find that carrier, thereby indicating that a program was on the air?

Well, engineers have computed that at the frequency of VHF television, LOFAR will have an effective collecting area similar to that of the 305-meter diameter Arecibo antenna in Puerto Rico.

That's big. That's brawny. But not brawny enough. In our SETI experiments at Arecibo, we could find a signal if it were about 0.1 million million million millionths of a watt per square meter.

That number, you will notice if you count up the words, is a million times bigger than the "I Love Lucy" carrier at 55 light-years. The aliens' LOFAR would be inadequate to detect the broadcast by a factor of a million, a not entirely negligible amount.

Simply stated: LOFAR couldn't hear it.

LOFAR would only be able to find TV signals comparable to ours from a distance of much less than one light-year!

From Radio Leakage: Is anybody listening?:

Hypothetically, assume that the Arecibo telescope was put on the back of a starship making its way into deep space.

If it was possible to point the telescope back towards Earth, how far could the starship travel and still be able to detect terrestrial electromagnetic radiation leaking into space?

Neglecting atmospheric effects:

  • An AM radio broadcast could only be detected out to 0.0074 Astronomical Units (AU).
  • FM Radio could be detected out to 5.4 AU.
  • A 5 Megawatt UHF television picture could be detected out to 2.5 AU, although the carrier wave could be detected much further; out to 0.3 light years.

(1 light year ~ 63,000 AU )

The SETI FAQ says:

Detection of broadband signals from Earth such as AM radio, FM radio, and television picture and sound would be extremely difficult even at a fraction of a light-year distant from the Sun.

For example, a TV picture having 5 MHz of bandwidth and 5 MWatts of power could not be detected beyond the solar system even with a radio telescope with 100 times the sensitivity of the 305 meter diameter Arecibo telescope.

From PopSci:

Frank Drake, the father of SETI, worried that the switch from analog television and radio signals to digital cable and satellite radio would render Earth invisible to aliens looking for other life.

... as more and more people receive their media beamed down to them from digital satellites, not up to them from analog radio towers, that signal slowly fades away, drastically reducing the chance that aliens might detect our tiny blue rock.


  • Okay, thanks. I was undecided/sceptical myself, but I'm pretty well convinced now. More importantly - so is my brother, and if he hadn't tried to big up ET's ability to eavesdrop I wouldn't have given it much credeence at all. Now I'm happy to think the chances of ET hearing us in the near future are vanishingly slim. Plus if ET did find us and respond in kind, it would be a long time before we could pick up any signal he might send to us! Jul 10 '11 at 16:08

Obviously all calculations based on inverse square law (i.e. strength of a signal is inversely proportional to the square of distance) is proof enough. But I'd like to remind you of few more factors:

  • TV signal back then was VHF, and Earth's troposphere and ionosphere will reflect VHF waves at acute angles back to the surface. See: http://www.df5ai.net/Material/articles3.html
  • Given that, only signal which goes practically straight up has chance to leave the Earth's atmosphere;
  • Characteristics of dipole antenna (which happen to be the kind of antennas that were used for TV broadcast at the time), practically prevents any signal to travel straight upwards.

Another argument, would be that the Earth is in a constant movement. It's spinning around it's axis at 360°/24h, which means that Earth spins 7° during one episode of "I Love Lucy". Also Earth travels around the Sun at angle velocity of 360°/365¼d. Note, that few degrees off might not seem much, but at a distance of 55 light years 1° off translates into 1 light year off.

  • Hi @var. I agree on all counts except the last point, really. We might rotate, but the waves are emitted uniformly in all directions (more or less), and therefore the only effect the receivers would see is a doppler effect. The rotation argument would apply if the waves were unidirectional, like a laser, but in that case the inverse square law would not apply as long as the waves are coherent (and therefore do not disperse over a larger area as radius increases).
    – Sklivvz
    Jul 12 '11 at 13:12
  • +1 for the useful observation about earth's spin. But I'm not sure about the '1° translates to a light year. Surely the drop in signal strength between 90° and 89° would not be so great as to matter to ET? The difference in the amount of earth's atmosphere that a signal would have to 'punch through' at 89°would be a tiny fraction of a percent less than at 90°, no? Jul 12 '11 at 13:13
  • @Ski: between unidirectional and omnidirectional there is whole range of possibilities. Even if Earth would have no atmosphere, antenna relatively close to the surface (comparing to Earths curvature), would at most give you 180° Effects of atmosphere limit that further. If Earth happens to be rotated India/Middle East side towards you, the signal from USA will be completely blocked by Earth itself.
    – vartec
    Jul 12 '11 at 14:06
  • @var: true, but an omnidirectional signal in close proximity to earth surface would still be visible ~12h/day to someone at 55ly, no? In other words, depending on the direction and the latitude, we "see" any particular star for ~12h/day (and all year long)--so it stands to reason that someone in that star's direction would "see" us for just as long.
    – Sklivvz
    Jul 12 '11 at 14:33

Transmission of uncollimated TV and radio background signals seems to die out after 1 lightyear source:http://www.davidbrin.com/SKEPTICcontactperils.pdf first page, second paragrph

  • 3
    Please make this answer more than a link.
    – Sklivvz
    Jul 10 '11 at 9:15
  • The bit about 1 lightyear is only mentioned in passing, with no figures or substantive argument to back it up, so I can't really go for this answer, sorry. It's an interesting link though, thanks. Jul 10 '11 at 16:13

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