No Intelligent Aliens Detected In Gliese 581

astroengine writes "Using an Australian very long baseline array (VLBA) of three radio antennae, the first very long baseline interferometry (VLBI) campaign has been carried out on a SETI target star: the famous Gliese 581 red dwarf. However, after 8 hours of observing the star — thought to play host to six exoplanets, two of which are in the star's 'habitable zone' — no alien signals were detected. This result isn't surprising, as the likelihood of us stumbling across intelligent aliens living in the Gliese 581 system transmitting radio is extremely slim, but it does validate VLBI as a very exciting means of using the vast amount of exoplanetary data (coming from missions such as the Kepler space telescope) for 'directed SETI' projects."

Comments

Re:proof?

[gstrickler]

If they're not smarter, better, or more civilized than we are, why would we want to meet them? Dealing with all the idiots here is more than enough, I don't want to have to deal with alien idiots too.

Correction: no signals detected

[Chemisor]

Having no detectable radio emissions does not preclude possibility of a civilization. Our civilization's emissions are already mostly in spread-spectrum format, which is by design indistinguishable from noise unless you know the encryption key. The transmitters we do have usually do not radiate omnidirectionally; that would be wasteful. Antennas are designed to cover the intended audience and minimize leakage outside of it, which makes detecting their radiation unlikely at any appreciable distance.

Futhermore, natural inverse square weakening of the signal makes the signal fade into the background before leaving the solar system anyway. Our TV and radio transmitters are not going to be heard outside the solar system. It is no coincidence that our satellites communicate with highly directional dishes. Directed signals are the only ones that will make it to the next star, so what SETI is really looking for is aliens who are actively broadcasting toward Earth. I don't know why they would be doing such a dumb thing, but who knows, maybe they are a not-too-intelligent life.

Re:Correction: no signals detected

[thegarbz]

That's not quite true. Some of our signals are spread spectrum, but the vast majority of licensed bands are still the age old single peak and often at insane output powers. These are very easy to distinguish from background noise, and as often is the case you could simply apply a 25kHz bandwidth and pick one of a few common coding methods and listen right in. The actual use of encryption for radio communication is rare when you're looking at the entire spectrum used over a planet. Hell if you exclude WiFi and satellite TV it's incredibly rare when you look at any major city too.

On that note satellites have pointed dishes because they are incredibly weak. They have to be, it's not like we have power stations up there powering them. When talking to a satellite we're trying to pick out a whisper from an asthmatic across a noisy room. We attempt to make our ears highly directional and filter out other conversations and he in turn cups his mouth to get his little voice that bit higher. That's not what these SETI projects are looking for. They are looking for aliens who have set up multi-Gigawatt transmitters all over their planet, just like we have. The equivalent of a rave happening somewhere else in an otherwise quiet rural town.

Also the directionality equation incorporates both the receive and transmit paths. You could have a perfect unit gain transmitter sending power out equally in every direction and still pick it up line of sight from anywhere you want with a theoretical infinite gain receive antenna pointed in the right direction, providing there's no louder signal source in your frequency of interest in the way. VLBI which is what they are using here provides an incredibly amount of gain at the receive side. Lots of really good signal analysis from multiple dishes result in us using a theoretical dish with a size and gain that could not realistically be constructed.

Some real geniuses came up with these designs and I'm willing to bet they know their antenna theory enough to think that it would be possible to detect a sufficiently advanced civilisation who take a similar evolutionary route that we take.

Re:Correction: no signals detected

[Chemisor]

the vast majority of licensed bands are still the age old single peak and often at insane output powers

I wouldn't call a few kW insane. Only the largest transmitters in the world go into the megawatt range; the vast majority are things like wifi, which are small and weak, at
They are looking for aliens who have set up multi-Gigawatt transmitters all over their planet, just like we have.

You obviously don't know much about transmitters. There are no multigigawatt transmitters anywhere in the world. The most powerful transmitter in the world is the Roumoules transmitter in France, which outputs 1.4MW, three orders of magnitude less than you think. It is notable that only its longwave broadcasts can be heard past 100km, because those reflect off the ionosphere. At night, the medium waves can do that too and so can be heard farther.

Notice that most of that radiated power will be reflected from the ionosphere and won't even make it as far as Earth's orbit. But for argument's sake, let's assume a full half of the signal makes it through. The antenna is somewhat directional, though the wikipedia article does not specify the beam width. Let's be generous and say it's a cone 30 degrees wide.

This cone will form a moving beam across the sky as the Earth rotates. A 30 degree beam will illuminate any particular star in its path for 2 hours each day. The study in the article we're discussing listened only for 8 hours, which is too short to always catch it.

Even if the signal is not reflected from the atmosphere, it will be significantly attenuated. Let's say 1MW makes it through. Gliese 581 is 20 light years away, ~2e17m. The base of the radiated cone is 2e17*tan30=1e17. The area of the base is pi*1e17^2=3.75e34. 1MW/3.75e34m2 = 2.67e-29W/m2.

Minimum detectable signal with a 1kHz bandwidth is -144dBm of the 1mW reference signal. That's 4e-15W. As a dumb estimate, we can calculate that 1.5e14m2 of continuous antenna area would be necessary to receive such a signal. That's approximately equal to the cross section of the Earth.

Of course, that's if the signal can be received at all. At low levels like that electrons in the antenna are unlikely to absorb anything at all. The ground state energy, for example, is 13eV = 2e-18J, 11 orders of magnitude lower than the signal per square meter. I find it difficult to believe that any excitation can occur here.

Re:Validation?

[mbone]

This result isn't surprising [...] but it does validate VLBI as a very exciting means

I'm a little confused as how a negative result validates the excitement-quotient. Or how this could even be validated in a more meaningul sense -- there's no way of checking the data. Maybe it was a false negative and there's oodles of aliens there.

The biggest technical problem in radio SETI is RFI. A signal from the star in question would have a very specific Doppler shift between the VLBI antennas, different from the relative Doppler shifts from any terrestrial RFI, even spill-over from a satellite. You can still have a saturated receiver if the RFI is too strong, but that is less of problem (it's easy to detect), and VLBI really reduces the chance of a false positive to almost nil. You also don't need an actual signal to show that this technique works.

Re:Are you guys stupid or something?

[RubberDogBone]

This is true. Nearly all of what we have ever broadcast has been trashed into junk RF by the time it passes through our own heliopause. Voyager 1 and 2 are helping us learn that it is a fantastic filter aggressively scrubbing and sterilizing radio. Perhaps only a few terrifically strong military radar signals or intentional interplanetary signals (i.e. the powerful Arecibo transmissions) might have made it through. Decades of TV and radio have not. For practical purposes, our Sol system is silent. We are not emitting potent enough repeating signals of the sort we ourselves are seeking.

It is logical to expect a similar result for other planetary systems where something like a heliopause exists. RF would be trashed and never make it into interplanetary space.

For even more discouragement, remember that most of life on Earth does not use radio. A planet teeming with life might yet have nobody emitting even weak signals. Radio derives from the human need to communicate, constantly. Especially while driving. It is entirely possible that another similarly advanced species might not have that need to talk talk talk and entertain at a distance.

Anyway, the universe is a very big place. It's a long way down the road to the pharmacy, but that's nothing compared to the universe. Most of it is empty. On average, we don't actually exist at all. Sigh.

Re:Are you guys stupid or something?

[Jappus]

You might want to reread that quote from Adams. He did not express any of the erroneous formulas that you stipulate. Here's the full quote in all its glory:

It is known that there is an infinite number of worlds, but that not every one is inhabited. Therefore, there must be a finite nuber of inhabited worlds. Any finite number divided by infinity is as near to nothing as makes no odds, so if every planet in the Universe has a populations of zero then the entire population of the Universe must also be zero, and any people you may actually meet from time to time are merely the products of a deranged imagination.

So what he's actually saying is this:
X = # of worlds;
Y = # of inhabited Worlds;
X = infinite;
Y = finite;
infinite number >>> finite number (infinity has a higher magnitude than any finite number)
It follows: X/Y = 0 - epsilon, where epsilon approaches 0 infinitely close.
Thus: Average density of life per world so close to zero, that it functionally IS zero (remember, just like: 0.99999... = 1)

Summary: Any life one sees must be the product of a deranged mind. You could even go so far as calling it imaginary.

Actual summary: Expressing humorous quotes in terms of maths is exactly what it takes to take the humour out of them.