Wikipedia:Reference desk/Archives/Science/2015 January 4

= January 4 =

Brain damage
Is it possible to cause brain damage by looking at an image? specifically a fractal image? Maybe I have watched too many science fiction shows, but I recently glanced at a strange image that caused my to go into a cold sweat. I found the image on Tor when I searched TorFind for my username "fractal618" I found the following link to a strange image (http://6lw4pg2wsy475d7q.onio n/processed/fc7f14caa618b178c8a95028337076528a651b88b5dac4b98de125d6dd82d089) If an image can cause neurophysical damage what might possible methods of healing be? meditation? herbal remedies? sleep? I realize this may sound a little silly, but it is a topic i have wondered about in the past. Thanks in advance Fractal618 (talk) 03:54, 4 January 2015 (UTC)
 * We cannot offer diagnoses or advice. Please contact a physician. μηδείς (talk) 04:41, 4 January 2015 (UTC)

You need to rewrite questions like this significantly if you don't want to sound totally crazy. why don't you at least upload the image somewhere so we can have a look? Of course, moving images can cause seizures in people who have epilepsy, so in theory images can have effects. There's a kind of image that if you stare at, even weeks later you will see it as being purple (or green) despite it being black and white. Overall though I would say the idea of causing "brain damage" from looking at an image is absurd, and you're obviously misinterpreting. (I don't see any request for medical advice in your question, and see no problem with answering it here.) Upload your image to imgur or something and link to it here. — Preceding unsigned comment added by 212.96.61.236 (talk) 06:40, 4 January 2015 (UTC)
 * When this question becomes answerable, the OP should see BLIT (short story). Tevildo (talk) 10:41, 4 January 2015 (UTC)
 * If you want to see the image and don't use Tor, you could always use a Tor2Web proxy e.g. http://6lw4pg2wsy475d7q.tor2web.org/processed/fc7f14caa618b178c8a95028337076528a651b88b5dac4b98de125d6dd82d089 http://6lw4pg2wsy475d7q.tor2web.fi/processed/fc7f14caa618b178c8a95028337076528a651b88b5dac4b98de125d6dd82d089. Nil Einne (talk) 13:48, 4 January 2015 (UTC)
 * It just looks like a Welsh dresser to me, but my brain is probably fairly abnormal to start with. :) Tevildo (talk) 14:23, 4 January 2015 (UTC)
 * Rorschach test and Op Art might also be relevant articles. Tevildo (talk) 14:28, 4 January 2015 (UTC)
 * Nil, your link doesn't work. Is  it so much to ask to upload an image to imgur, this takes literally 18 seconds from start to when you post the URL here.  THanks. 212.96.61.236 (talk) 07:20, 5 January 2015 (UTC)


 * It is hard to prove a negative in biology, but there is no precedent for the idea of an intrinsically damaging image, except of course for the occasional unshielded welding arc and similar bright or UV-rich sources. Psychologically there is a recognized post-traumatic stress syndrome, but this depends on the reaction to an image rather than the image itself.  For example, viewing two little girls butchered on a table will be near routine for a coroner, but might cause PTSD in their unexpecting father.  As with all psychology, one can question to what degree PTSD is damage rather than adaptation - obviously, the person beginning to come down with PTSD is supposed to run away as fast as his feet will take him, not finish out an eighteen-month tour because some bureaucratic paperwork says to, and I would be inclined to lay most of the blame on that rather than the image proper.  Now in theory virtually any image (or none) could cause sensations of fear capable of causing long-term trauma under the right circumstances; compare demonic possession and popular notions of voodoo.  With enough effort the subjective can seem objective, but there's nothing objective behind it. Wnt (talk) 15:13, 4 January 2015 (UTC)
 * See talk. μηδείς (talk) 20:39, 4 January 2015 (UTC)
 * I meant to refer to single images, not video, but Medeis correctly points out photosensitive epilepsy reacts to flashing video. Wnt (talk) 21:50, 4 January 2015 (UTC)

Llamas or alpacas?
Some months ago I uploaded at Commons and named it "Llamas at Shiprods", but since then I've been looking at photographs of both llamas and alpacas and now I'm not so sure. Is there a South American or a zoologist who can give me an authoritative answer? --Antiquary (talk) 18:40, 4 January 2015 (UTC)


 * The basic difference is size - llamas are much larger than alpacas, which are roughly sheep-sized whereas llamas are as tall as adult humans. Unfortunately there is nothing in the photo to indicate scale. It could be useful if you have any other information that can help deduce the size of these animals. Roger (Dodger67) (talk) 19:09, 4 January 2015 (UTC)


 * Nor is there anything to indicate scale in the other two photos I have of them, and my memory's a little vague too. But since they live half an hour away I'll go and check on their size tomorrow.  Thanks for that. --Antiquary (talk) 19:59, 4 January 2015 (UTC)


 * We used to feed the llama they kept at the local farmer's market about 15 times a summer for years until it died, and these look too small for adult llamas. It would be odd to have such a large group of juvenile llamas of the same size.  But I think your best bet is to contact "shiprods" (we don't have an article on that) and ask them.  I am sure they will know, given these are obviously not a flock that just wandered onto the property.  Or maybe someone will know a determinative diagnostic test.  In any case, I'd get in contact with the proprietor.


 * There is, of course, this very famous two-minute Llama documentary, but it is probably not a reliable source.


 * μηδείς (talk) 20:56, 4 January 2015 (UTC)


 * I'm not an expert on South American species, but the ears look more like alpaca ears. Llamas' ears look like bananas!  Also, the area is well-known for its alpacas, see here.    D b f i r s   21:06, 4 January 2015 (UTC)
 * I agree, they are alpacas. Their coats are typically more curly like that. Llamas have straighter coats, usually. But there are all kinds of breeds so don't quote me. 68.14.230.243 (talk) 23:31, 4 January 2015 (UTC)
 * The proprietors of that farm aren't on good terms with those of mine so the personal approach could be a bit tricky (Sussex is like that – see Cold Comfort Farm). Having taken another look at the beasties I find that even the largest is only the size of a large sheep as far as the body goes.  That long neck does bring some of them up to close to my height (I'm 5' 8"), but even so I think we can all agree they're alpacas, so I'll have the file  at Commons renamed.  Thanks to all. --Antiquary (talk) 11:51, 5 January 2015 (UTC)
 * Thanks! Looks like a great story, I have ordered the movie of Cold Comfort Farm for my mother. μηδείς (talk) 19:00, 6 January 2015 (UTC)
 * Wikiquote will give you an idea of the style, though they leave out the famous darkly repeated line, "There's something nasty in the woodshed". --Antiquary (talk) 19:51, 6 January 2015 (UTC)
 * Alpaca. Polypipe Wrangler (talk) 04:00, 8 January 2015 (UTC)

If I claim something has a 90% chance of happening the next day
Can I be proven wrong? If it doesn't happen, that just means that we are within the 10% of it not happening.--Noopolo (talk) 19:39, 4 January 2015 (UTC)
 * But if you start making such claims everyday and the your predictions prove to be wrong in say 90% of cases, nobody will take you seriously after that. Ruslik_ Zero 19:47, 4 January 2015 (UTC)


 * If you are talking about weather forecasting, I once heard it explained that when they say there is a 60% chance of rain tomorrow in a local postal code they mean that looking at the historical weather records that most matched the prevailing patterns right before the predicted day, on 60/100 of those following days it did rain. Now we also have all sorts of things like weather modelling for hurricane tracks, and predictions based on a consensus of models.


 * Your question as stated however, just seems like an invitation for debate which we have no grounds to answer with a reliable source. You seem to want to know if you can deceive people, and I suspect you know how good you are at that.  If you don't, you'll need to take a survey not only of those people who talk to you, but also of those who have ceased to talk to you, and ask their opinion. μηδείς (talk) 21:06, 4 January 2015 (UTC)


 * If you claim there will be a 90% chance some particular extraordinary thing will happen, and it doesn't, then, since extraordinary claims require extraordinary evidence, I would challenge you to show how you calculated that 90% chance, and I could then disprove your method. StuRat (talk) 22:05, 4 January 2015 (UTC)
 * Note that the original question doesn't say anything about the claim being "extraordinary". RomanSpa (talk) 08:54, 6 January 2015 (UTC)


 * This is basically a math question. Looking at it simply, the number of correct predictions should follow a Poisson distribution.  At some point though, a person has to evaluate the relative probabilities of a null hypothesis that you are lying vs. the odds that you were simply unlucky, which I think involves some degree of a priori assumption of your honesty.  Normally in science we don't get a specific frequency with which a drug cures a disease or the like, and so we simply look for "statistical significance", but this isn't quite the same situation as that.  In any case, a single lone prediction that is never repeated is, by its nature, outside the realm of scientific evaluation, and in the end a humanistic judgment will tend to vary by the author and his belief in whatever means you say inspired your prediction. Wnt (talk) 22:09, 4 January 2015 (UTC)


 * (ec) The technical term in forecasting for what you are asking about is the "calibration" -- as in: whether or not your probability assessments are well-calibrated. Typically, for something like weather forecasting, you can look back over all of the forecasts made e.g. for a whole year, which are likely to include a number of things predicted with 90% probability.  Depending on what fraction of those forecasts turned out to be correct, you can then estimate the probability (or a confidence, if you're a frequentist) as to whether you may be systematically over-estimating or under-estimating the robustness of your forecast, if you're assessing probabilities of 90%.   You may even be able to identify particular types of conditions under which the probability estimates appear to be systematically off -- though beware that such retrospective in-sample pattern spotting, once the data are in, can be notoriously deceptive.  Jheald (talk) 22:33, 4 January 2015 (UTC)


 * Even with a single data-point I can still sometimes use some of the machinery of probabilistic inference -- particularly if I have two distinct hypotheses to compare -- for example, suppose my alternative to your model was simply a 50/50 chance of the thing happening or not happening. Then the fact of it not happening one time out of one would represent a Bayes factor of (0.5 / 0.1) = 5.0 against your model -- a Bayes factor on the borderline between "barely worth mentioning" and "substantial", according to Harold Jeffreys.   The Bayes factor means that if beforehand I was predisposed to give odds of 5-1 on in favour of your model, eg because of my initial regard for your capability and previous good work, I should revise those odds to evens following the prediction failure.


 * (If, on the other hand, if your prediction had succeeded, that would have given a Bayes factor of (0.9 / 0.5) = 1.8 in favour of your model -- a small positive confirmation, so I should have revised my initial odds of 5-1 in favour up to 9-1 in favour.) Jheald (talk) 23:03, 4 January 2015 (UTC)


 * The traditional method of scoring probability forecasts is the Brier score. The Brier score can be decomposed to give more detailed information on the probability distribution of the forecasts relative to the observations, especially the reliability and resolution. (Historical note, not in any RS that I'm aware of: Brier was a modest guy, and insisted on calling this the "P-score" rather than the "Brier score." One day he was talking to someone and realized they were confusing P-score with Peace Corps. So he finally relented and accepted the name Brier score.) Short Brigade Harvester Boris (talk) 23:00, 4 January 2015 (UTC)


 * You might be interested in our article on Probability interpretations or the Stanford Encyclopedia entry, Interpretations of Probability. The short answer to your question is no, you cannot be proven wrong simply according to whether the prediction happens or not. Your claim about 90% could be proven wrong on other grounds, however, depending on the exact topic. IBE (talk) 06:26, 5 January 2015 (UTC)

What if someone conjectures that there is a 90% chance of something happening, but that is a physical impossibility. As soon as he realizes this his confidence drops to 0%, but he does not reveal his realization. The next day, as he already knew, it did not actually occur (easy enough since it is a physical impossibility). Was his first proclamation wrong then? Or was it correct, because it reflected his 90% confidence at the time?

Note that I can actually think of an easy way to make this scenario quite realistic. A mathematician learns that his friends are about to announce a big proof of an open conjecture. He knows they've probably proven it's true, and given that they're respected mathematicians, and the paper was circulated in a small audience, he thinks that when they announce the next day, there will be an 80% chance that no major flaws are found and in fact it is a proper proof of the conjecture. So, he tells his other friend that there is an 80% chance that the proof that would be announced the next day is valid. Meanwhile, that night our hero receives an email from a distributed networking application he was working on. He was just messing about, but set it to try to find a counterexampple. He was shocked to find that it did, in fact, offer a counterexample. The conjecture was therefore wrong. His confidence drops to 0% - or whatever his confidence is in his calculations - since with the existence of a counterexample, whatever proof the mathematicians thought they had discovered for the conjecture is meaningless. As he checks the counterexample more and more carefully, or with collaborators, he will be more and more sure that there is a 0% chance of a correct proof of the conjecture being published the next day; since it is, in fact, false. 212.96.61.236 (talk) 07:17, 5 January 2015 (UTC)


 * Again, just check the Stanford article I linked above. Your best bet would be to read the stuff on subjective probability. Your argument sounds perfectly fine; it just depends on your interpretation of probability. It sounds to me like you are using a subjective account, in which case the original 80% was not wrong, just based on less information. Probability always depends on a lack of information, since that is exactly the information we gain when we discover the outcome. IBE (talk) 07:49, 5 January 2015 (UTC)


 * There is a basic "sanity test" for predictions of this kind. If, for example, you examine all the cases in which some event was given a probability of 60%, then the predicted events ought to occur on approximately 60% of those occasions (plus or minus the statistical error range).  If the predictions fail this test, they are miscalibrated.  (I believe that many weather prediction systems fail this test badly.) Looie496 (talk) 14:55, 5 January 2015 (UTC)


 * Looie that is interesting, but can you give a reference? For example, in the interpretation where it is a confidence in belief, it doesn't really matter if it fails every time?  For example, suppose mathematicians throughout history were asked what the probability is that (whatever) is true.  In fact once the truth is known - e.g. look at some of these - http://divisbyzero.com/2010/08/18/mathematical-surprises/ then 100% of the predictions were false that claimed otherwise.  So, it's like, are you saying if for 300 years people predict 80% that something will turn out to be a certain way, then if it isn't, all those must be wrong?  So, it's not so simple I think!   it's an interesting sanity test but a reference would be nice :) 212.96.61.236 (talk) 16:44, 5 January 2015 (UTC)
 * The thing is, a mathematical claim is either true or false, probability has nothing to do with it*, the truth is only in terms of entailment from the axioms of a formal system. There is a difference between an event_(probability theory) and the truth of a formal claim. So a statement about "X theorem is 90% likely to be true" is a very different statement from "There is a 50% chance this coin toss will be heads." Probability theory is an axiomatic branch of formal math, but we use words like luck and chance and odds in other ways in natural language. So you won't find any formal mathematical treatment of probabilities of mathematical statements being true, but you will find formal treatments of things that are well modeled (or at least intuitively described) by random variables. If you want a formal treatment of belief statements, then you may want to look into modal logic, specifically alethic modality and epistemic modality - Epistemic probability is just a redirect to our Bayesian page, but this highlights the crux of the matter, see frequentist for the complementary interpretation, as well as the links from IBE above.
 * *Of course this depends a bit on the interpretation and the epistemology that we're working in. The point remains, however, that there is not any one treatment of probability (either formally, or in terms of interpretation) that can include all the subtle differences in meaning that occur in phrases from natural language. (P.S. a ref for Looie's description is law of large numbers. The key thing to note is that Looie's description and the LLN apply only to events and experiments (with their formal definitions from probability theory), and does not apply to statements like "The continuum hypothesis is 90% likely to be true.") SemanticMantis (talk) 18:21, 5 January 2015 (UTC)
 * SemanticMantis, OBVIOUSLY I meant a proof within a given axiomatic system. E.g. under ZFC+ what are the chances that P=NP?  Mathematicians can give a probability, given their confidence.  Another example would be, before the 4-color theorem was proved, what were the chances that it was true (under the standard axiomatic systems etc).  It was already very high (99%+) and a counterexample (where 5 colors were required) would have been absolutely shocking.  That turned from 99%+ to 100.000% when the proof was verified.  (and now should be 100.00000%, as it's well-verified.)
 * I also gave a very vivid account of a specific way to interpret a math probability: what are the chances that a proof published tomorrow will be accepted by the math community as valid, given that you know and respect the authors and the paper was circulated in private? (but you have not seen it). Again, you can give a probability!  212.96.61.236 (talk) 22:58, 5 January 2015 (UTC)
 * Remember we don't know what you do and don't know :) My main point was that the truth value of a mathematical claim is not an "event" in the sense of classical probability theory. As such, my belief is that the example statements are more the domain of modal logic than mathematical probability theory. SemanticMantis (talk) 15:06, 6 January 2015 (UTC)