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Astronomers want to plant telescopes on the Moon. The lunar surface offers advantages for infrared and radio astronomy, despite the challenges. By Ramin Skibba, Inside Science | Published: Tuesday, January 19, 2021 Astronomers want to plant telescopes on the Moon | Astronomy.com (See the link there to a journal special issue exploring the idea.) I speculated about the possibility of detecting exo-civilizations optically in this Kerbal forum post: How large a space telescope do we need to see exo-civilizations? - Science & Spaceflight - Kerbal Space Program Forums In the discussion in that thread, someone suggested we would need a telescope 1.6 km across to see a visible disk of an Earth-sized planet at the nearest stars. But we might not need to be able to resolve a visible disk to be able to observe illumination of the exoplanet beyond that which would be expected on its nightside. In any case quite large telescopes could be made on the Moon if you used rotating liquid mirrors. This proposal is for one 100 meters across: Texans Want to Put a Big Ol' Liquid Mirror Telescope on the Moon But can they do it? And why even try? BY TIM CHILDERS NOV 18, 2020 https://www.popularmechanics.com/space/moon-mars/a34714863/liquid-mirror-telescope-on-the-moon/ On Earth there are limits to the size you can make a liquid scope because the rotating mirror surface and containment vessel creates wind currents that distorts the liquid mirror surface. But this would not be a problem on the airless Moon. So that raises a question: is there a limit on the size you can make such a mirror on the Moon? Another possibility would be to do the detection through radio telescopes on the Moon. The advantage of radio telescopes is they don't have to have a solid surface but can consist of a set of grid wires, as was done with the Arecibo telescope. And this is the approach taken for one plan for a radio telescope on the Moon: Apr 7, 2020 Lunar Crater Radio Telescope (LCRT) on the Far-Side of the Moon. Saptarshi Bandyopadhyay NASA Jet Propulsion Laboratory https://www.nasa.gov/directorates/spacetech/niac/2020_Phase_I_Phase_II/lunar_crater_radio_telescope/ So how big would a radio telescope have to be on the Moon to detect Earth-like radio emissions from a near-by star like Alpha Centauri? Note this is a different question than that studied for example by SETI. With SETI they assumed such a civilization was beaming radio emissions directed at us. Such searches have been negative. But in the scenario I'm considering, an advanced civilization is creating omnidirectional radio emissions just as a byproduct of conducting its advanced civilization. How large a radio telescope would we need to detect those? Robert Clark
Let‘s imagine that an alien spaceship or probe is coming in our solar system from interstellar space - How close would it have to be that we would be able to detect it and which methods could be used? Is there even a chance that we discover it until it has almost reached earth?
A team of scientists is investigating ways of detecting exo-civilizations aside from just radio signals as with SETI: JUNE 19, 2020 Does intelligent life exist on other planets? Technosignatures may hold new clues. by University of Rochester https://phys.org/news/2020-06-intelligent-life-planets-technosignatures-clues.html Two methods of detection mentioned in the article are detection from reflected light from solar panels or detection or pollution such as CFCs. However, even on our planet the number of solar panels would not be such that they would add appreciably to the Earth light. And CFCs presence might be short lived as it has been on our planet, having been banned. Could we instead detect the light on the night side coming from all the artificial lighting that would be used in a civilization? Some of the photos seen from space of the cities alit at night on Earth have been quite striking: Aug. 14, 2014 Space Station Sharper Images of Earth at Night Crowdsourced For Science https://www.nasa.gov/mission_pages/station/research/news/crowdsourcing_night_images How big would a space scope need to be able to see this in the Alpha Centauri system, for example? Robert Clark
So doing alot of reading about space-time lately and ran across this very appropriate quote yesterday. http://www.householdgigs.com/2016/05/05/fermi-paradox/ So the above is just coincidentally in my reddit stream this AM and I was reading down the list wondering why it was new science and I am reminded of the Ravolli quote, and I though if this is not an example of guessing then I don't know what is. How would I solve the problem. Before I got a few paragraphs down I realized that it was a dirty laundry list of guesses, many of them rather uninformed. So here is it, we have 1 example of sentient life. And we have been looking all over the cosmos and not seeing any other examples of life, and have not even found examples comparable to earth after studying 2400 exoplanets. So we have a data set of 1 and a possibility of less than 1:2400 or more. So lets look and see what the density might be. So if life on planets is X below the probability of observing 1 in 2400 is y (remembering that our observation of ourselves has an acute observers bias) The problem is there are no statistical tests that allow this. While most qualitative testing does not allow me to do this (to do it accurately I really need a >>32 bit computer), I can trick the fisher exact test into doing it by setting ratios like the actual is say billion over a million is roughly equal to 1000:1 odds. So lets see were this takes us. lets start by saying there are for every 1000 planets we have 999 with sentient life and 1 without. and we will step this ratio down by 10 each time. SL:Not 999 :1 P = 0 to the calculation limit of a 32 bit computer. 99:1 P = 0 " " 9:1 P = 0 1:1 P = 0 1:9 P < 1E-107 1:99 P < 1E-9 1:999 P < 0.4 1:9999 P < 0.3 1:99999 P < 1E-3 1:999999 P < 1E-5 Note: the estimates below are not really accurate because they test the computational limits of the computer, I could reduce these, but . . . . . . 1:9999999 P < 1E-7 1:9999999 P < 1E-9 1:9999999 P < 1E-11 As we can see the probabilities drop more slowly into the microscopic ranges on the low estimates relative to the high estimates of extraterrestrial life. What this means that if we have to entertaine a broad confidence interval, its going to stretch more quickly into the very low estimates of sentiency. Do we have to entertain such estimates? A historical analysis of the science suggests yes,the curve has been shifting down. First we examined ourselves and concluded it was 100%, then we discovered our 9 planets and it dropped to 1:9, then 100s of planets, now thousands of planets and the probability is falling each time, the reason it is falling is because of our bias. Where does observers bias come from and what is it? Our observations suffer from both observation and confirmation bias. The problem is only living sentients can be/create the observers can count sentient life, and there always has to be 1 observer an any observation of sentient life. In very crude sampling (such as 2400 planets out of galaxy that has a trillion planets), very low estimates can never exist because there would be no observer to observe a region that is devoid of life or sentient life. So lets say our observation limit is 100,000 light years, and the field of view has a 10,000,000 stars with transects and we pick up 3 planets with stars. If we do not see signs of life in 1:30,000,000 planets can never allow a statistic say 1000 times lower, even if that is the life's (or sentient life's) rate in the entire galaxy So the base assumption of science is that a potential something is nothing until something. We can flip that to the opposite if we observe a strict pattern, such as all flying birds have wings, if want to test a new set of flying birds then the null hypothesis is that they should have wings. Having one earth and no observations of planets, we assume that all planets should have life. Moving to the next higher level of observation, having studied the moon and many planets, we have yet to observe life elsewhere (though predict that one or two have life). In observing the planets and all the moons of our solar system we do not see evidence of sentient life. The mistakes that are made here in the argument is that we assume the current knowledge suffices to create the appropriate argument, and the revelation of new technique reveals that it is not. Its historic ignorance, the question is whether we are above historic ignorance on not in our answers. From this perspective we should argue that the naive state of a planet is not to have life or sentient life, that is our null hypothesis that needs to be disproven. Some may argue the point but if they do we then have all kinds of subjective qualifiers. Do we count moons, do we count large asteroids, what should be counted in the assessment of life. So lets say we only count planets that have atmospheres. How many planets have we observed that have atmospheres, . . .very few. What is the probability that life exists outside of earth, in this argument we can exclude earth, lets say we believe to be transplanted here by beings from another galaxy, an omniscient creature about intergalactic sentients and we know we are the only species in this galaxy from the next galaxy, we ask the question how many planets have evolved life in this galaxy. To improve information of the low estimate statistics, there is another statistical method which is to remove 1 and then re-analyze, this is often done with data presents with a few outliers. Lets suppose we remove the earth from the analysis, because the observer creates the bias, what happens. Assuming no evidence of life or sentient life on 2400 worlds how can we estimate? 1:9 P < 1E-109 1:99 P < 1E-10 1:999 P < 0.2 1:9999 P < 1.00 1:99999 P < 1.00 since now earth is one of 2400, the lost estimates can of very rare life can never go below 1:2400 (0.0042) which means that our probability slow on the low estimate side and essentially stops at 0.0042 This is because although the probability is high at the low end, of the 2400 observations we have a 1:2400 chance of removing the one earth, removing any of the other planets does not matter much, they are pretty much the same statistic. So this then gets into a qualitative sphere, how far could we observe life on other worlds if we could observer sentient life on other planets. Or to ask the basic question, do some of the observed planets have life and we simply cannot observe it, do some have sentient life and we are missing it? If another world has life did it evolve or did it commute? Asking these questions we can then ask how biased is the observations? Planet hunters are looking for earth like planets, not at all planets, what about moons around gas giants, don't they qualify, should not the total number of planets be more? And we cannot see all planets, only those that transect our Earth - star sight, many go unobserved. There is a size bias to the observation, certain stars cannot be observed because of solar flares during the observation window, etc. What have I done, I have improvised a confidence range containing 99.7 percent of estimate where there was none it runs from about 1:20 satellites (1:300 for sentients) to 1:1E23 for the observable universe. The number is sufficiently small to not require adjustment for the entire universe. There is some hideousness to the argument, because space-time obviates any considerations beyond about 2 billion light years. And in fact the observations constraint is limited to a pool about 1000 galaxies in our vicinity. This statistical observation therefore epitomizes the problem that the data used to describe the Fermi paradox is a guess, it has a huge confidence range that is created by an observation bias and no other positive observations. The argument exists but the quantification does not. Some here might argue, why have such a wide and useless confidence range. A nice reason is that the Fermi paradox has bred a plethora of guesses that have each a very low probability of being correct. The confidence range therefore contains data for all of them and does not interfere greatly with the likelihood that any given one is wrong or right. So for example how could you know if there are species wiping out upstart civilizations if, in fact, that sentients are so rare, such species would only have a space-time SOI of a few 100 million light years and you are outside of that range, they might exist, but you could never detect them. The correct answer to the Fermi paradox is that it (the argument) exists. This may seem like a denigration of the paradox, its not meant to be, its meant to be a denigration of the solutions. Whenever we have an object where it can be inserted into an 'it exists' class, but the supporting data is minimal, we have to be wary of the answers/solutions. Who told us this? About 1000 years of theological philosophy went unresolved until Occam's razor. The simplest answer here is that life is rare and sentient life is even rarer, but we do not know what degree or why because our sampling is too poor. The sampling maybe poor because there is roughly nothing to sample......only statistics, however poor, are permissible at this point, nothing else has relevance.