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> It seems far more likely that objects like 'Oumuamua are relatively rare, and that means it likely came from someplace close by (if it came from farther away,
by komali2 8y ago
> It seems far more likely that objects like 'Oumuamua are relatively rare, and that means it likely came from someplace close by (if it came from farther away, the odds are even lower we'd ever see one).
Ok, it's on my list of things to do this year to actually learn how statistics work, but my naive reaction to this supposition, which I read is "the fact that we have encountered Oumuamua means that it's likely it didn't come from far away, because if it did, it's less likely we would have encountered it," is: We did encounter it. Just this one, ever. How can we draw any statistical information from that? Either we encountered it, or didn't, how does that have any bearing on the statistical probability of seeing it?
- nerbert 8y agoWe did encounter it during the short timeframe in which we would be able to detect it. Could be a once every 20 years occurrence, that would make it quite frequent.
- azeirah 8y agoI don't know much about statistics, but I can add that the time period matters. If we only started observing space yesterday, and saw it, it would be weird to say "it's rare", but we've been observing space for, I don't know, up to 400 years? (counting since invention of telescope, 1608)
- nkrisc 8y agoI don't think an object like this could have been spotted until relatively recently.
- polityagent 8y agoBut how recently have we developed the capability to: - observe this thing at all - accurately measure it's velocity and acceleration - understand that it's velocity and acceleration were unusual?
- KineticLensman 8y ago> but we've been observing space for, I don't know, up to 400 years? (counting since invention of telescope, 1608) We've been observing space 'forever'. Pre-telescope observers had quite accurate star maps (of the naked-eye stars, obviously) and were fully aware of the complex movements of the planets. Their models of the movements were good enough for predictions even if the underlying explanatory causal models were sometimes wrong.
- garmaine 8y agoThis type of object could only really have been seen when it was. It was picked up as part of a full-sky survey that year, the firsts time such a thing had been done at sufficient resolution to detect an object like 'Oumuamua. A number that I saw quoted earlier was that it is expected that around 3 of these things go through the solar system every day. This one just happened to be the one caught by the survey, which itself required a bunch of coincidences since it means catching multiple pictures of the same object in different locations so as to establish a trajectory, so an ability to detect is not just resolution, but also timing and orbital trajectory.
- joshuamorton 8y agoSay your prior is that something has a 1 in 1 million chance of happening in any given year. You start monitoring it. Year 1, the thing happens. Which is more likely: 1. You've encountered a 1/1,000,000 event 2. Your prior is incorrect and the thing happens more often than once every million years? Without more information we can't actually answer this question with certainty, but "re-evaluate your priors" would absolutely be a thing one might suggest in response to this event.
- bsder 8y agoUnfortunately, LIGO encountered the 1/1,000,000 almost as soon as it was powered on and they've been waiting for another one like it. Probabilities are funny things ...
- Blackbeard_ 8y agoI don’t understand this comment... It’s true that the first event occurred after only two days but ligo have 11 events over two running periods at this point. https://en.m.wikipedia.org/wiki/List_of_gravitational_wave_observations https://en.m.wikipedia.org/wiki/List_of_gravitational_wave_o...
- bsder 8y agoI was under the impression from an interview that the first event that LIGO caught was held up so long before release because it was such a stupidly rare occurrence.
- bjelkeman-again 8y agoEven as there are eleven observed events so far, that is from 2 trillion galaxies in the observable universe [1]. So at 100 billion stars per galaxy [2] a guesstimate is that we are talking about 200 billion trillion stars. Seems even divided by eleven it seems pretty rare. (Not sure if the detector can “see” all those stars though.) [1] https://en.m.wikipedia.org/wiki/Observable_universe https://en.m.wikipedia.org/wiki/Observable_universe [2] https://www.livescience.com/56634-how-many-stars-are-in-the-universe.html https://www.livescience.com/56634-how-many-stars-are-in-the-...
- pvg 8y agoWe're not 'drawing statistical information' from the observation itself, simply saying that if it is the case that such objects come from interstellar space and are relatively rare, it is more probable to encounter one that originated nearby than it is to encounter one that came from far away. With those assumptions, you can arrive at this conclusion without observing such an object at all.
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- flatline 8y agoFor a humorous take on what can be done with a sample size of 1: http://www.thebigalientheory.com http://www.thebigalientheory.com Certainly, any new information is going to radically adjust the posterior probabilities, but you can still make some tentative inferences.
- rocqua 8y agoA quick scan didn't reveal my favorite sample size 1 statistic. If you sample serial numbers starting from 1 and sample N, the best guess is that there are 2N examples. This was worked out in WW II for estimating tank production.
- madrox 8y agoHere's a quote by Feynman on the topic: “You know, the most amazing thing happened to me tonight... I saw a car with the license plate ARW 357. Can you imagine? Of all the millions of license plates in the state, what was the chance that I would see that particular one tonight? Amazing!” I believe what you're getting at is the Ludic Fallacy, which could probably apply here. That said, whether it's a fallacy in the science or in the reporting, it's hard to say. I have a degree in statistics, and I'd say I spent half the time learning stats, and half the time learning to use language precisely to avoid overgeneralizing stats. There's a really great TED talk about how even very educated people get it wrong when talking about stats: https://www.ted.com/talks/peter_donnelly_shows_how_stats_fool_juries?language=en https://www.ted.com/talks/peter_donnelly_shows_how_stats_foo...
- ALittleLight 8y agoSuppose you know nothing about license plates and I tell you that license plates work one of two ways, either every license plate reads "ARW 357" (it's just a meaningless tradition) or every plate has six randomly selected numbers and letters and there's equal probability that either explanation is true. THEN you observe a single car with a single license plate with the value "ARW 357". Does this single observation tell you anything about reality? I would argue that it does - it should strongly suggest to you that you're in the "every car is ARW 357" reality. Similarly, if you draw a ball from an urn and it's red, and you know you've drawn either from the "urn of red balls", or the "urn of one million green balls and one red one" you should be pretty confident you've drawn from the "urn of red balls". If one theory can explain your observations but the explanation is highly unlikely, and another theory explains your observations and the explanation is likely, the second theory is more likely to be correct all else equal.
- komali2 8y agoOk, this explanation makes a lot of sense. However, are we able to reduce down our understanding of "which universe we're in" in such simple terms? I think I'd understand better if I knew how long we've been capable of detecting oumuamuas.
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- mabbo 8y agoPresume I have a machine that, when you press a button, will either light up the red light bulb or the green light bulb. Usually, the red light bulb lights up, but the green bulb will if and only if one of the following two things are true: #1. The lottery ticket in your pocket is the winner of the big jackpot #2. It's raining. You press the button. The light bulb turns green. There's no windows to check for rain or internet to check for winning numbers. You have no further information beyond the fact that the light bulb turned green. Which is more likely to be the case: That you're now a millionaire, or that you should grab an umbrella as you leave? We know we saw 'Oumuamua (the green light). We now can construct many models for why we might see such results. The probability that we would see the results given the model (lotteries or rain) can be used to infer what the true model most likely is.
- jklinger410 8y agoIn this instance it seems like what's more interesting is what it possibly is rather than what it probably is.
- daveFNbuck 8y agoAnother way to state this would be that given our current understanding of the universe, most objects that get close enough for this kind of encounter will have a nearby origin.
- wcoenen 8y agoI'm not sure whether that sentence from the article actually makes sense. But to answer your question more generally: you start with some model, with one or more parameters for which you don't know the value. e.g. "the galaxy contains N uniformly spread out interstellar objects that are big enough to see if they happen to come within 1 AU of Earth." Then we start watching the sky, and after 10 years we see 1 such object. Then for each possible value of N, you could calculate the probability of observing exactly 1 such object during a decade. One particular value of N is going to give us the highest likelihood of getting that result. We call that value the "maximum likelihood estimate" for N.
- rjf72 8y agoLet's consider two scenarios: 1) Somebody starts flipping a coin they claim is fair. You're not sure whether or not that's true. It comes up with 10 heads in a row. 2) Somebody tells you there's a 1 in 10,000 chance of something happening each day. You're not sure whether or not this is true. It happens tomorrow. Which, if either, do you think has reasonable evidence to begin to doubt the claimed odds are the real odds? Which do you think is better evidence of the proposed claim being false? With the logic you expressed in your post you might suggest the first is better evidence of a false claim, but it's not. The odds a fair coin going 10 heads in a row is 1 in 2^10, or 1 in 1024. Even though it's 10 'events', it's ultimately just a 1 in 1024 happening if we assume a fair coin. By contrast the second event is about an order of magnitude less likely to have happened by chance. So even though the second event is only one happening, it's more likely that that event is not a 1 in 10,000 event than it is that the coin is not fair.
- bsder 8y agoWhile I do love the "ejected from another star" idea, the probabilities of something being ejected from another star in the correct direction AND being captured by our Sun is so vanishingly small that it's far, far, FAR* more likely to be a remnant of when our own star formed.
- Trombone12 8y agoWell, there is this entire science describing the universe and how it works you see, and that science makes certain prediction about things like how easy it is to kick something out of a star system and how likely a rock thrown in a random direction on the other side of the galaxy is to hit a our particular sun.
- Jeff_Brown 8y agoWhat we can say statistically is that, if there was no intention behind this object's trajectory, then it is more likely to have come from a nearby system. We can even say how much more likely. In fact, an argument that it's more likely to have come from somewhere nearby holds even if it was sent by design. Conscious beings are more likely to want to explore the stuff they can reach sooner, and they are more likely to succeed at reaching nearby things. But without knowing their engineering constraints and their preferences, we can't quantify that like we can the random ejection scenario.
- joe_the_user 8y agoI'd take issue a different way. It seems far more likely that objects like 'Oumuamua are relatively rare, and that means it likely came from someplace close by (if it came from farther away, the odds are even lower we'd ever see one). I'd rather look at the density of Oumuamua-like objects in space. First, it seems like these objects rarer than some things but dense enough for us to have seen them. Their "terminal density" comes when their rate of production managers to equal their rate of consumption. Who knows how they're produced but I'd assume they are consumed when they are gravitationally captured by a solar system - actually flying into a sun is much less likely I'd assume. Such gravitational capture is more likely if these objects are moving at a similar speed to the solar system they encounter. The one thing we know about Oumuamua is it seemed to speed up as it left the solar system. This factor might imply that the chances of capture wind-up very low. Now, the rate of production could be low and thus life-span could be high. A high lifespan implies this came from far away. I could be wrong on the consumption chances. But still, I think arguments about how far these travel would do better with such life span analysis than with the quote argument, whose implications are foggy imo. As to whether the thing is a product of alien intelligence? If the very low density analysis is correct, if such a thing could behave as Oumuamua did, then that too might be a good spacecraft design. Which is to say, the amount of information we have is low that making absolute answer seems pretty hard here.