Cosmology and astronomy
Detectable civilizations in our galaxy 5
More reasons why we haven't detected anything yet. Created by Sal Khan.
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- Would archaeabacteria be able to survive gamma ray bursts?(25 votes)
- Well bacteria are able to withstand even the most deadly of events that would shatter our existance as a species. So they should be able to. So thus say a meteor comes and obliterates this planet, bacteria will come up out of the atmosphere and survive probably long enough for them to reach a new home and take root and create life anew.(20 votes)
- Let's say we hypothetically do receive a signal from a distant (10,000+ LY away) civilization. Since the galaxy, and the solar systems within it, is constantly moving through space, how would we even know the exact location the signal originated from? Do we possess technology that is advanced enough to predict shifts through the universe? Or, would we just have to take solace in the fact that we even discovered another detectable civilization at all?(6 votes)
- Actually you could hardly use the red shift to determine how far is the place of origin of communication signal, since it is not the spectrum of an element from the periodic table. So there might be a small problem there. Since it is supposedly a civilization that emitted the signal you could say there's an upper bound of the power used for the signal and then just calculate the attenuation and get an estimate of the greatest distance the signal could have originated. It won't be too precise though...(2 votes)
- Why is it that when you get closer to the center of the galaxy, or far away from from it that life gets harder to detect. What is the goldilocks effect?(4 votes)
- It isn't harder to detect, its harder for life to spawn. Closer to the center, the intense radiation from a large star density and a larger amount of big stars. In the outer areas, there is not a lot of heavy elements so it is much less likely for planets to form or for complex life to take hold.(6 votes)
- 3:45you mentioned that there are some theories that there has been massive extinctions on earth due to heavy bombardments of radiation (gamma-rays) from the center of the galaxy, and that this happens each 10 billion years. The Earth's tectonic plates shows that Earth's magnetic poles have reversed over time. A magnetic pole reversal could only happen if the magnetic field is exposed to a seriously heavy radiation so it would partially 'fail' and some how will be 'braked down' and drastically change. Now, Is It some how related to events predicted on late 2012, a magnetic pole reversal due to a heavy bombardment of gamma-rays from the center of the galaxy?(4 votes)
- Regarding the magnetic poles switching, that does happen, without any external force applied, on average every 450 000 years. Oh, and it's about 780 000 years since the last time.
Enjoy!: )(4 votes)
- If just 1 planet would develop a space traveling civilization, 'shortly' later all habitable planets around would have detectable civilizations.
Therefore should not be the question, are there more or less than one space traveling civilizations?(1 vote)
- Who says they should stop at habitable planets. They could make stations on airless planets or moons with sealed in air. Aliens could live and thrive there. Also, it is possible for aliens to terraform planets. This is the process of making uninhabitable planets habitable by converting its atmosphere to something the species can breath.(8 votes)
- Anybody else think that radiation, may be the force that drives evolution, because we know that radiation causes mutations, some of them are helpful, maybe, there are planets that just graze, radiation hot zones, that not all of the living intelligent life are wiped out, and the survivors get more benefits, of course that's assuming, that the initial population is high enough to be able to recover from the near sterilization ( depending on how much radiation they get hit in the hot spot) just a thought(3 votes)
- Radiaton is just another of the many factors in an organism's environment, and the theory of evolution is quite clear about the role of the environment - it matters a lot.(1 vote)
- Would a civilization that doesn't send out distinct (electromagnetic) signals even be detectable for us? For example through their "daily"usage of signal? Or are they too weal to reach us?(2 votes)
- Remember, the electromagnetic spectrum includes all detectable energy in the universe. This includes, light, gamma and x-rays, radio, everything. If a civilization did not emit regular and distinct signals of any kind, they would be undetectable as yet to us.
Further, you need to consider distance. We've only been listening for about the last 50 years, and transmitting only since the early 20th century. At best, we could detect an answering signal of a range of about 50-60 light years away. There are, however, over 50 star systems within just 16 lightyears. So there is a chance we've been detected, but it's still very slim. The chance that any response has been given or that 2 advanced civilizations live so close together in the same galaxy is very slim. Statistically speaking.(3 votes)
- Would archaeabacteria be able to survive gamma ray bursts?(2 votes)
- If directly exposed, no. Gamma rays destroy DNA and even the most hardy life would not be able to survive gamma rays in such quantity. However, archaebacteria has a habit of living deep underground which would muffle most of the burst, allowing them to survive. Assuming the burst doesn't strip away the planets atmosphere (by no means a guarantee), life deep in the ocean would also survive.(2 votes)
- why there will be more planets in the centre if the density is high?(2 votes)
- Lets just say we did find an exoplanet in the Goldilocks zone, and were able to send a colonization crew there. But because the planets are tons of light-years away, how would we know if the planets were still there? Maybe a asteroid slammed into the planet and destroyed it a long time ago, but we still haven't found out yet because the light from the system hasn't reached us yet.(3 votes)
- Most of the habitable exoplanets we have found are on the order of about 1000 light years away, some are a bit farther, a few are less than 50 light years away. Within a 1000 year time span, it is extremely unlikely that the conditions on the planet will have changed drastically. Over the past 500 million years, it is thought that only 5 major extinction events have occurred.(0 votes)
In the last video on the Drake equation we tried out some numbers we just made some assumptions that seemed reasonable at least to me and we got that there should be 12.5 detectable civilizations in the Milky Way Galaxy and I've talked about a bunch of reasons about why we are not detecting them but I left out one of the most obvious reasons that we are not detecting them and it was rightfully pointed out in the comments below that video and thats just the signal might be too weak if theres 12.5 if there's on the order of 10, 11, 12 detectable civilizations in our galaxy they could be quite far from us this isn't the Milky Way but this is a galaxy that probably doesn't look too different from our Milky Way we could obviously never get this vantage point of our galaxy well at least not for a while not unless we can travel quite far away from it but lets say we are over here you could imagine if the ten civilizations or the twelve civilizations are here, one, two, three, four there's probably a lot more at the center actually because that's where our density is higher so let me put it here so one, two, three, four, five, six, seven eight, nine, ten, eleven, twelve the closest of them might be tens of thousands of light years away from us and there might be a lot of stuff in between all sorts of crazy things happening stars exploding all sorts of signals that we are receiving and it might just be that the signals from those civilizations are too weak to reach us or that there is too much interference from all of the other craziness that's happening around the galaxy there's also these other reasons that I've talked about in the last video maybe they've gone beyond using radio as a form of communication and thats why.. or they never used it to begin with and that's why we don't even see them ever using it or they used if for a very short period a kind of transition period and maybe in a hundred years we'll discover the next best thing the other idea behind why we're probably or maybe why we might not be able to detect civilizations is that well there might be a lot fewer than ten when I did the Drake equation right over here I just made a bunch of assumptions none of these seemed crazy but I assumed a reality where you didn't have these kind of cataclysmic events in the galaxy at regular intervals but we know there are cataclysmic events that happen in our galaxy in other galaxies the one we know the most about although there are all sorts of things that we don't know much about are gamma ray bursts and these are still kind of trying to be understood GAMMA RAY BURSTS and you can watch the video on quasars those are essentially of highly energetic rays being released when all this material is being kind of absorbed into super massive black holes at the centers of galaxies that tend to be very very very often billions of light years away and gamma rays are one of the things that get emitted from those but you can also have gamma ray bursts within galaxies we believe maybe certain types of stars when they collapse into black holes you have this burst of gamma rays there might be certain kinds of neutron stars with the right properties that might every now and then release gamma rays and the view is is that if there is a civilization that is within a few thousand light years near one of these gamma ray bursts and its in wrong place its kind of in the path of the burst then its a good chance that those civilizations will be completely wiped out that those planets will become sterilized because there is so much radiation coming out from that gamma ray there's even some theories that some of the extinction events that have happened in Earth's history we are not talking about the dinosaurs we are talking about billions of years ago maybe a billion years ago or two billion years ago that these might have been caused by relatively local gamma ray bursts the theory is that these might hit earth on the order of once every billion years and if you think about the galaxy as a whole we're kind of in.. our solar system is orbiting the galaxy its kind of a nice distance from the center of the galaxy the closer you get into the center the higher densities of stars you have so you can imagine if earth gets hit with one of these gamma rays bursts every couple of billion years you can imagine something closer the center of the galaxy gets hit with these gamma ray bursts much much much more frequently just because there is more activity there there are more stars that are closer by more stars that are aging more stars that might be collapsing into black holes so the simple answer is we don't know there could be a thousand civilizations out there and we're not sophisticated enough to notice them just yet or there might be very very few because all of this craziness that happens in the galaxy or who knows there might be none although I find that kind of... that's not too exciting so I try not to think about that one