| FastFourierTransform | Date: Sunday, 02.10.2016, 23:17 | Message # 1 |
 Pioneer
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| Usually in videogames like Age of Empires you have a map that you explore. The map is in shadow where you have no previous knowledge and the explored part figures exactly as it was when you where there. This is kind of like space exploration, where we have a "mental" map that includes high resolution images of some planets in the Solar System (some updated to changes), catalogues of millions of stars etc...
I'm very very interested in quantifying our knowledge and our ignorance in this matter (a thread was needed for this) and I think we can all contribute to find reliable sources that shed some light on the numbers involved. I'm not talking about our knowledgo of the laws of physics etc... just our exploratory knowledge in astrophysics as cartographers (coverage and detail of each map of a solar system body, number of comets catalogued, how many stars we think there are in the Milky Way compared with how many we have catalogued, etc...)
The purpose of this is in general having a comparison and a size perception of how much we know and how much we still have to explore in different parts of the universe at different scales.
But there is a second related purpose for this thread: quantifying the probability of the existence of exotic unknown objects (for example extraterrestrial artifacts or rarely occurring 1-in-a-billion natural phenomena) in our vicinity. I think is interesting to know exactly by how much is feasible that we have missed an alien probe in cislunas space for example, and what confidence do we have in extrapolating to the whole set (for example the Solar System) the things we have explored and the processes we have witnessed until now.
The subject is complicated and finding sources is a difficoult task. I'm very inexpert but I'm sure that users like Watsisname, HarbingerDawn and others more prepared than me, can come with great ideas and debates on this issue.
I will start the debate with a very interesting paper called "On the likelihood of non-terrestrial artifacts in the Solar System". I recommend reading it to all because is very easy to understand. It starts saying that "Extraterrestrial technology may exist in the Solar System without our knowledge. This is because the vastness of space, combined with our limited searches to date, implies that any remote unpiloted exploratory probes of extraterrestrial origin would likely remain unnoticed."
The key idea that the paper expresses is that of equation (7):
This equation assumes that prior to the exploration we have equal odds of H being true or the contrary being true: p(H)=50% and p(H)=50%. This is reasonable, this is the state of least information. We know nothing about the probability of the existence of alien probes to assume that is more plausible than them not existing.
There is one expresion for the case where the search conducted on VR is not adecuate to reveal an alien probe inside the explored volume: p(H|VR)=1/2=50% (if even searching you are not capable of seen it when it was there then you have no reason to assume nothing more than your prior odds of the probe being there: 50% chace). The other expresion, p(H|VR)=1/(2-VR/V) is for the case the partial search is based on a method that is in reality capable of detecting the alien probes (because of their specific characteristics, that are totally unknown).
In the paper the equation (7) is in fact much more specific: they imagine a search method consisting on taking a photograph of the exotic object (in their case an extraterrestrial artifact) with sufficiently high resolution as to allow identification of the object in the picture. This involves a lot of assumptions: the alien probe is visible in visible light (why not invisible?), the probe doesn't mimics anything know to us and therefore is inmediatly noticed when imaged (it could perfectly look like a rock but we assume is evidently artificial), etc...
In the paper the condition for one expression or the other is expressed in this way (for their specific search method): the object is detectable (not detected) by the search in VR is translated as the fact that the object has a size d greater than the size resolution of the camera R.
The article makes a good job on explaining the underlying theory for the estimation of this probability but makes a poor research on the actual VR we have effectively explored as to exclude the possibility of alien probes in the Solar System, for example. So here is where I think this thread should help.
I will start, in this first post, with the case of the Martian surface!
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Martian surface cartographic coverage and probability of undetected alien structures
So, Mars is the most explored planet in the entire Universe aside from Earth. The surface has been mapped with an enourmous precission and resolution. If there where alien probes or structures we would have noticed them by now for sure. In reality no as I'm going to show now.
Many spacecrafts have been sent to Mars but just a few have explored systematically the surface completing near full global searches in detail. This are Viking 1 orbiter, Viking 2 orbiter, Mars Global Surveyor (in particular the instrument: Mars Orbiter Camera - Narrow Angle or MOC-NA), Mars Odyssey Mission (in particular the instrument: Visible Sensor of the Thermal Emission Imaging System or THEMIS-VIS), Mars Express (in particular the instrument: High Resolution Stereo Camera or HRSC) and the Mars Reconnaissance Orbiter Mission (both Context Camera or CTX and the High Resolution Imaging Science Experiment or HiRISE).
All of this orbiters have made some images in resolutions higher than 100 meters per pixel. The most important instrument in terms of resolution is HiRISE aboard of the MRO with thousands of images with 0.25 m/px resolution (this means that you can see perfectly objects the size of an office desk on the surface of Mars), but sadly not even a fraction of the whole planetary surface has been mapped by the finnest instrument. The THEMIS aboard Mars Odyssey has covered with good resolution (18 m/px) nearly the entire globe (most extensive coverage) thanks to the long duration of the mission. CTX, also aboard MRO, has made the finest-extensive coverage maps (with not so high resolution as HiRISE but more than other spacecraft instruments and with not so extensive coverage as THEMIS but with sufficient as to beat the other spacecrafts). And HRSC aboard Mars Express has made a great job at making 3D stereographic models of the terrain in resolutions between 11 m/px to 100 m/px, covering much of the Martian globe.
By 2016 CTX had covered 85% of the martian surface with a resolution of 6 meters per pixel, and HiRISE with a resolution of 0.25 m/px to 0.5 m/px has covered only 2.4% of the martian surface. (please tell me if there are better sources or more updated ones).
In total we can say (source) that:
- 100% of Mars has been mapped with R>100m/px
- 99.85% of Mars has been mapped with R<100m/px
- 96.76% of Mars has been mapped with R<20m/px
- 2,4% of Mars has been mapped with 0.25m/px<R<0.5m/px
- nearly 0% of Mars has been explored with 0.0000125m/px<R<0.25m/px (resolution of cameras and magnyfying lenses aboard the Mars Science Laboratory, Mars Exploration Rovers, and other robotic landers).
Let's suppose now that extraterrestrial structures are automatically recognizable in an image where it can be seen (that's a lot of assuming considering the fact that the hundreds of thousands of images taken from the martian orbiters are not nearly scrutinized at all and considering there are enourmous chances of been confused with a rock formation or another natural object).
Let's also aknowledge something about pattern recognition and confidence with images as a function of their resolution (are there rigorous researches about what I'm going to say?):
Imagine we have a blue circle of diameter of 1 meter. Would camera with a resolution of R=0.5 m/px be able to resolve the object? and what about one of R=0.25 m/px?
As you can see in the figure above a 0.5 m/px resolution image (2X2 pixel image in the case of the figure) wouldn't at all allow you to tell what is there. You could probably say that there is something (if the color of the object contrasts with the sorroundings) but nothing about the nature or shape of that something (the circle could be a kid, a 1 meter boulder, everything...). With the 0.25 m/px resolution camera (4x4 pixel image) you can be sure there's something there but no understanding of the shape at all (it could be even a square instead of a circle). Just when you reach resolutions of around 12 cm/px you could start to say something about what it is and congeture if it is a circle indeed (the 8x8 pixel image). This is a problem.
Consider this simulated image of the Mars Polar Lander (a 4 meter wide object) as seen from the MOC-NA (1.5 m/px resolution camera) and the HiRISE (0.3 m/px resolution camera):
It's crear that even if you are searching for it and know the geometric shape of the object it is impossible to distinguish it from a boulder or other feature in the MOC-NA images and is quite imaginative to resolve the lander from the HiRISE image. The HiRISE image has pixels that are 13 times smaller than the lander itself and we are even here uncapable of telling with high confidence that the object is an artifact created by humans. If an alien takes an image like that would it be capable of understand that there is a man-made object there?
So I'm going to make another rought assumption: in order to tell if there is an extraterrestrial artifact in the image the artifact must be at least 10 times as big as the pixel size. So the HiRISE camera, for example, could barely make us aware of a 3 meter size extraterrestrial artifact on the surface of Mars.
So, now we go with the calculations:
Since there is a 0,15% of the martian surface that has not been imaged yet with better resolutions than R=100 m/px (it has with R>100m/px) we can say that an 8 to 10 meter-size extraterrestrial probe could perfectly be hidden in that 0,15% of the surface. But this is not very probable considering the fact that in the other 99,85% of the planet that has been imaged with better resolutions, we haven't found any (they would have to be actively hiding or there would have to be an improbable chance that we have skipped just the insignificant patch of the surface that has alien probes).
Using the equation of the first figure we can tell that the probability that there are 10 meter wide extraterrestrial objects on the surface of Mars right now that have been unnoticed is 0.1498% at least. Small, but surprisingly not extremely small.
What about smaller objects? A 3 meter size probe would only be detectable by the HiRISE instrument, but only 2.4% of the surface has been covered with it. An object like this could perfectly be exposed on the surface without us having noticed it. With all the Mars exploration we have done until now (all the orbiters and landers and Earth observations) we are just 0,61% more confident that there are no 3 meter sized alien artifacts or smaller on the surface of Mars, than we where before we even knew Mars was something. JUST 0,61% !!!!!!! We have not excluded at all the possibility in fact!. We are just slightly more secure about what we know in this matter.
If we where talking about alien artifacts of half a meter in size (not even in the reaches of the HiRISE) we would be uncapable of discovering it in even in the near future. The rovers have not detected one yet, but for the probability of them detecting one we would inmediatly assume that there are millions of objects like this over the whole planet (so that we sent a rover to a very small spot and we find one). So, the fact that the rovers (that could in principle see a half meter size alien object if they where at a maximum distance of 50 meters of it) have not detected anything like that means that we have gained in all the history of space exploration a 0.0000011% confidence that there are no half-meter size alien probes parked on the surface of Mars (I made the calculation considering that the total distance travelled by all the martian rovers has been of 65.6 km and with a strip of "alien probe detection" around them of 50 meters in each side; thus 6.57 km2 where the rovers have excluded half meter-size alien probes, or putted in another way the 0.0000045% of the surface of Mars). It could be full of artifacts and we wouldn't notice at all over millenias.
And all of this is considering just the surface of the most explored planet of all!!!! What if the probe is just buried 1 meter below the surface (something that could happend in very little time geologically speaking). We can't state anything about this objects not been there. We know so sooo little. What if the objects have an iiregular shape that totally can mimic a stone? The thermal radiation that THEMIS is capable of detecting is with the tens of meters in resolution in the infrared filters so there could be quite huge beasts over there still unnoticed.
This gets even worst when you consider the fact that for interstellar travel it's far more cheap, energy-efficient and strategic to send small probes than huge ones (large masses could be moved but you always could move more easily very small masses). This is something we ourselves are realizing. We are getting in the CubeSat exploration method (small satellites but in greater quantity) and Breaktrought Starshot aims to lunch interstellar nano-probes (1 cm to 10 cm size spacecrafts to explore other stellar systems).
If alien civilisations have sent to the Solar System this kind of nano-probes then there could be millions exploring each corner, even in LEO or in the surface of Earth there could be some and we couldn't notice them with current exploratory coverage of the planet (this is topic for another post so I hope we all contribute searching for how much resolution Earth has been mapped and wich parts are untouched by humans, the ocean floor unknowns etc...).
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| Watsisname | Date: Monday, 03.10.2016, 01:34 | Message # 2 |
 Galaxy Architect
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| Interesting topic.
It reminds me a lot of Russell's Teapot. Just as how we cannot disprove the existence of God, we cannot disprove the existence of a teapot orbiting somewhere between Mars and Jupiter. The purpose of the exercise is to show that the burden of proof is not on showing that something does not exist -- it's to show compelling evidence that it does, and the more phenomenal the claim, the more compelling the evidence should be.
Interplanetary teapots are cosmically less likely to exist than alien constructions. It is very hard to imagine a scenario where even one teapot would exist. But we could easily imagine many scenarios for which alien probes could exist. So we may take that idea quite seriously. The best we can do though is look at the results of surveys, and conclude that within the sensitivities of the surveys, we can rule out the existence of alien artifacts with such-and-such level of confidence. It's pretty easy to show that there are not large alien craft or whatever within the orbit of the Moon. If they were there we would see them. "Okay, but maybe they are cloaked." Or "maybe they are smaller." There is a maximum size that they could be before they would enter the range of sensitivity to surveys, and we cannot rule out the existence of objects below that size.
The evolution of sensitivity of observations over time are also as important as volume searched. An Earth-sized alien craft could have passed by Neptune 500 years ago and we would have missed it. A city-sized craft could have passed Mars 50 years ago and we'd have missed it. A thumb-drive size probe could buzz by the Moon tomorrow, and we would miss it.
So, we cannot possibly say that there are no alien constructions in the solar system, whether beyond Jupiter or on Mars or even closer to home. We can only speculate about how likely or unlikely they are to exist, and conclude that if they are there, then we haven't seen them, and can rule them out only within certain possibility-spaces. 
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| Banana | Date: Tuesday, 04.10.2016, 02:08 | Message # 3 |
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| Not to mention an alien structure could seem so utterly strange when compared to our technology that humans would not even consider the possibility of it having been created by undetected life. After all, an alien's mind could be unusual to a point where it couldn't be considered a mind by human standards. We Earthlings are so accustomed to our own ways of life that even outlandish fantasy could not compete with alien organisms and creations.
Hello.
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| Watsisname | Date: Wednesday, 05.10.2016, 23:42 | Message # 4 |
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| Watsisname | Date: Thursday, 06.10.2016, 05:20 | Message # 5 |
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| Solved the first part of the challenge question. With the premise of humans being the only technological civilization to have ever developed within 100 light years, then given observations of the frequency of Earth-like planets around Sun-like stars with Earth-like insolation, this would require the probability of technological development on such a planet must be:
This tells us that optimistic values for the chances of technological civilizations developing on suitable planets leads to the prediction that advanced life, or at least archaeology of advanced life, is common in our solar neighborhood. For us to be unique within the whole galaxy, we must assume far more pessimistic values -- less than one in 60 billion. Which in my view seems unreasonably low. For the universe, it must be as low as 10-24, which seems patently absurd. We can't possibly be the only life, or even technological life, to have ever existed, unless you are very pessimistic.
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| DoctorOfSpace | Date: Thursday, 06.10.2016, 05:43 | Message # 6 |
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| Quote Watsisname (  ) Which in my view seems unreasonably low.
That is where I would disagree, but I favor rare Earth considering all the variables that made humans possible.
Quote Watsisname ( ) or even technological life
I suspect its less than 1 per galaxy
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| Watsisname | Date: Thursday, 06.10.2016, 06:51 | Message # 7 |
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| I'm somewhere in between. I think it's a lot less than 1%, but cannot easily imagine it being so low as one in 60 billion or less.
Of course I have no sound observational basis for that, but that's the interesting thing about this exercise. It tells us how optimistic or pessimistic we must be about how commonly technological life develops on suitable planets to get a certain result, now that we have good constraints on the astrophysical parameters.
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| DoctorOfSpace | Date: Thursday, 06.10.2016, 07:02 | Message # 8 |
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| My issue stems from how long humans have stagnated, how there are other intelligent species on Earth but they are in the wrong environments, and how precarious technology is.
Think of what the Type 2 civilizations equivalent of knocking their coffee cup over might be. It just seems that as energy access continues to increase per individual the chances of self annihilation becomes increasingly more likely. Combine that with how long it took intelligence to evolve in the right environment and how Earth has all those specific variables that allowed that to happen, and the picture doesn't look good.
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| FastFourierTransform | Date: Saturday, 08.10.2016, 18:55 | Message # 9 |
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Pioneer
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| Quote Watsisname ( ) It reminds me a lot of Russell's Teapot. Just as how we cannot disprove the existence of God, we cannot disprove the existence of a teapot orbiting somewhere between Mars and Jupiter.
This is totally true. All of this calculations are just for curiousity not for science in reality. Science needs to put things as to be disproven. If we could formulate the problem in a sense where we could find an evidence of it been wrong then we would at least sure of something in this matter, but until then we only can manage to put upper and lower bounds to our expectations. We would have to explore each cubic nanometer of the universe to disprove the existence of other intelligent life but we should transform the question in one that can be answered by a single non-eternal experiment, one that could tell us that if something happens or exists then there can not be such intelligent life (the problem for that is that we ourselves exist).
Quote DoctorOfSpace ( ) That is where I would disagree, but I favor rare Earth considering all the variables that made humans possible.
I also would bet for the rare Earth. A probability lower than 10^(-24) of life arising per planet is so strange? I think we have to think about it more deeply. This number is incredibly small but very different from zero; life needs a series of prerequisites that we ignore in great extent, maybe the list is quite large, strict and demanding, much more than we can even imagine right now.
My interest is not necessarily focused on extraterrestrial artifacts (although I know it is a popular topic) but in all exotic objects. By this diffuse term I include things as complex and strange as life but not yet imagined or discovered, amazing geological structures, strange substances, crazy interactions, etc.... the idea is making a cosmic atlas of our ignorance.
In my next post I will talk about Earth. I'm searching for sources about unexplored places and their extent. Is quite complicated as a task so please help me if you know something. As I see, even Earth could have very close alien spaceships without our knowledge. This relates also with the Shadow Biosphere topic, we are uncapable of excluding it to exist within a the first kilometers of crust (for complex organisms) or even in our houses and enviroment (for microrganisms).
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