Wikipedia:Reference desk/Archives/Science/2015 November 5

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November 5

Does this concept describe virtual reality, or does it describe 3-D movies?

I'm writing a sci-fi story. Here is a concept I'm describing:

"If someone wanted to visit Hawaii without leaving home, that person could still see Hawaii, but first, the person's eyes would have to be covered with two displays (one for the right eye and one for the left eye), each display showing live action moving images (one for the right eye and one for the left eye) of life, like, someone at home could be able to see, for example, Hawaiians surfing. The image of the right eye and the left eye combine to form a single image."

I don't know what my concept is an example of, though. One person told me I was describing virtual reality. Another person told me I was describing 3-D movies. I don't really know the difference between virtual reality and 3-D movies. So is my concept an example of virtual reality or 3-D movies? VRtrooper (talk) 06:28, 5 November 2015 (UTC)

Your technology (variations of which exist, I should mention, so it's not altogether sci-fi) shares elements of both 3-D displays and virtual reality. The relevant articles you are going to want to look at are Stereopsis, binocular vision, virtual reality and 3D film. In short, in normal vision, the human visual system constructs a three-dimensional representation of the surrounding environment by comparing two essentially 2D image maps formed by stimuli acting upon the retina of each eye. The thing is, the pattern recognition capabilities of the brain are such that it can extract a three-dimensional representation even from a two-dimensional projection (hence the effect of a regular television or cinema screen and numerous forms of optical illusion). 3-D movie technology attempts to augment this perception by introducing more depth to the image it projects and allowing one to adjust their angle of perception to the stimuli. This can be accomplished in numerous ways; perhaps the most common in the history of 3D-cinema is to form a 2D projection to which the color has been altered in such a way that, when the viewer wears glasses with two lenses that filter different wavelengths of light, each eye is given a somewhat different set of stimuli, even if each is focused on largely the same point in space. The effect leverages binocular vision and allows for the perception of depth from an image which actually consists of optical stimuli on a flat plane. Depending on how your headset was designed, it could leverage similar effects, though probably through different mechanisms than colour filtration. In any event, any headset displaying a visual representation of a simulated or pre-recorded environment which the user could interactively engage with would be considered a form of virtually reality, which is basically defined by that form of interactivity. Snow ^{let's rap} 06:54, 5 November 2015 (UTC)

The Stereoscope has been around for about 200 years, and a 3-D film is simply a moving-picture version of the same idea. ←Baseball Bugs ^{What's up, Doc?} carrots→ 09:14, 5 November 2015 (UTC)

• Real world devices that use this idea include the Virtual Boy, Oculus Rift and the Virtuality. Smurrayinchester 09:35, 5 November 2015 (UTC)

Or Google Cardboard and your cell phone. --Stephan Schulz (talk) 13:49, 5 November 2015 (UTC)

The difference between a 3D movie and virtual reality is that in the latter you get to decide where to go. That's why the latter is a "reality" rather than just a 3D image. I don't think that wearing a headset or using inertial sensors or even having 3D is actually a requirement of virtual reality, since people have been using the term loosely for a very long time (and hey, your virtual avatar might be a Cyclops! Come to think of it, having the people with old/simple equipment appear as cyclopes would explain their uncoordinated blundering, and just be kind of cute), but certainly some would insist on it. Wnt (talk) 13:52, 5 November 2015 (UTC)

Q: What is cyclopes' favorite reference? ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:07, 5 November 2015 (UTC)

It is a fuzzy line between 3D video and true Virtual Reality. In a 3D movie (or TV), the display covers some area of a wall of the room - and appears as a "window" into a 3D virtual world. In the ideal of VR, you have a StarTrek-like "holodeck" which is indistinguishable from reality...but our present technology is far from being that good. With a typical VR headset, there is also a 'head tracker' - a device that measures where your head is pointing - the computer figures out where your head is pointing, then generates pictures that are both 3D *and* representative of the virtual world you're standing in. The effect is that no matter where you look, what you see is the virtual world. With 3D TV/Movies, when you look away from the screen, all you see is the wall of the real room that you're in. The effect can be quite convincing with very high end VR equipment - but on cheaper consumer-grade devices, it's more of a novelty than a convincingly "real" experience. Beyond that, you can add various control devices that also track the position of your hands, perhaps individual fingers even...and perhaps also your feet - so that when you look at your hands through the VR goggles, you see computer-graphics hands that are in the right place. This stepwise approach to making more and more real effects can include things like little balloons mounted into the fingers of gloves that the computer can inflate and deflate to give you a feeling of 'touch' when you grasp a virtual object...these are in no way convincing, but they allow a lot more subtle control in the virtual world. I've worked on systems that attempted to add smells and other effects such as wind blowing in your face, etc, etc. SteveBaker (talk) 02:49, 6 November 2015 (UTC)

Australian Spider Identification

Hello, I was wondering if someone could help me identify what species this spider belongs to. I do know that the photograph was taken in Darwin, Northern Territory, Australia and that it's a huntsman spider, possibly of the genus Heteropoda. Any help would be greatly appreciated.

Americanfreedom (talk) 06:56, 5 November 2015 (UTC)

I'd lean towards Holconia: [1], [2], [3], [4], [5] Snow ^{let's rap} 07:30, 5 November 2015 (UTC)

Here we go, would you like to buy him some companionship? Actually, don't; one will very likely try to eat the other, but this newest image/phenotype does seem to suggest that your specimen is likely to be a variant of Holconia immanis, or a very closely related species. Snow ^{let's rap} 08:13, 5 November 2015 (UTC)

Age of the Universe

I read that the Universe is c. 13 Billion years old, and that our Sun is c. 4.6 Billion years old. I also understand that there are Suns/Stars that are c.10 Billion years old. Considering the time taken to form suns, followed by planetary solar systems, and the time taken to form Galaxies, and that the death of a star is where (I am informed) the heavier elements are distributed, the relative lifespan of the Universe and Stars appear not to make sense. Explanation please? — Preceding unsigned comment added by 79.134.38.231 (talk) 07:29, 5 November 2015 (UTC)

The death of a star only causes heavy elements to be distributed if the star dies in a supernova explosion. The stars that undergo these explosions are very large ones. But the larger a star is, the less time it lives. The very large stars that become supernovas do not last billions of years, but much less, perhaps only 10 million years. --70.49.170.168 (talk) 07:59, 5 November 2015 (UTC)

Yep. The article Stellar population explains a bit more. The oldest star whose age is fairly certain is SM0313: at about 13 billion years old, it's nearly the same age as the universe. However, it's a "K dwarf" – fairly small and cold compared to, say, the sun. Supergiants and hypergiants, which are the really big and hot stars, only live a few million years. There have been many generations of supermassive stars blasting metals throughout the galaxy. Smurrayinchester 08:40, 5 November 2015 (UTC)

Also, since certain heavier elements catalyse fusion processes, earlier stars (in particular population III stars), which are poor in metals (in the astronomy sense), start fusion slower and at higher densities, thus allowing stars to become a lot larger before ignition, when radiation pressure clears the environment and accretion stops. Thus, population III stars are hypothesised to have been, on average, very large, and hence short-lived. --Stephan Schulz (talk) 13:47, 5 November 2015 (UTC)

If you want more details, I highly recommend Crash Course Astronomy. --71.119.131.184 (talk) 09:41, 5 November 2015 (UTC)

As per Stellar population, the idea is that early on, it was easy to form huge stars that supernovaed fast. These burst into supernovae and salted the galaxies with heavy elements. Even so, the older stars are more metal-poor than the new stars, because the process continues. Wnt (talk) 13:47, 5 November 2015 (UTC)

BTW when people here say "metal" they don't mean an actual metal, but rather any element heavier (i.e. more protons) than helium. So carbon and oxygen are "metals" in this context. Ariel. (talk) 16:46, 5 November 2015 (UTC)

estimated time to cure hepatitis A infection

OP curiousMahfuzur rahman shourov (talk) 16:18, 5 November 2015 (UTC)

See Hepatitis_A#Treatment. In short, forever. Hepatitis A cannot be cured, only its symptoms managed. --Jayron32 16:26, 5 November 2015 (UTC)

@Jayron32: That article says 1-3 weeks in children, 2-6 months in adults. Wnt (talk) 18:00, 5 November 2015 (UTC)

That's not the length of time the disease infects you, that's the time the symptoms are evident. The disease "flares up" for periods, and goes into remisssion for periods. A person is not cured of the disease merely because the symptoms have subsided for a time. --Jayron32 19:51, 5 November 2015 (UTC)

Hepatitis A is a self limiting disease that resolves on its own without any specific treatment in ~6 months. After that it is actually "cured" in sense that virus has completely disappeared from the body. The resolution results in life-long immunity. Ruslik_Zero 20:19, 5 November 2015 (UTC)

Yes, of course. I was confusing it with it's more chronic cousins, like Hepatitis C. Mea culpa. --Jayron32 20:34, 5 November 2015 (UTC)

(EC) I think Jayron2 may be getting confused with Hepatitis B and C (and perhaps some of the others). Both of these can result in chronic conditions. See Viral hepatitis and [6]. Hepatitis A does not (see the earlier refs) and nor is it a retrovirus which integrates in to the genome or have a long term latency phase (like say the varicella zoster virus). So once it's gone (which as was said may in some cases be 6 months or even a year), it's gone. Kariskwilson's point below is also relevant, there's not that much you can do to treat the symptoms or to speed up recovery beyond the basics (including those related to the symptoms like avoiding overtaxing the liver), and waiting for your own immune system to fight off the infection and body to recover from the symptoms. (As to whether to say you're "cured" this is to some extent a matter of semantics. Are you "cured" of a cold or flu? And in those cases you can I think have a greater effect on the symptoms.) Nil Einne (talk) 20:46, 5 November 2015 (UTC)

Hepatitis A can not be cured. In summary the definition of "cured" means to relieve symptoms of something in some way. The exact definition can be found at http://dictionary.reference.com/browse/cure. Also, the condition and effect of the disease can be lessened with medication and giving the body or the liver time to rest From things like medication or alcohol. sources and more information about what I have provided for you can be found on the following websites. http://www.mayoclinic.org/diseases-conditions/hepatitis-a/basics/treatment/con-20022163. there is no specific medication that can cure this disease but there are different thing that are natural things you can try and medication that will help in the healing process. The source for this information and more information I what I've written can be found at http://www.emedicinehealth.com/hepatitis_a/page7_em.htm.Kariskwilson (talk) 18:48, 5 November 2015 (UTC)

In any case, Hepatitis A can be prevented with the Hepatitis A vaccine. Get it if you can, unless you know you have immunity. --71.119.131.184 (talk) 20:34, 5 November 2015 (UTC)

Incidentally, if you've had Hepatitis A after the age of 11, you are forever after unable to donate blood (in the US and Canada, at least, and presumably elsewhere). 64.235.97.146 (talk) 21:09, 5 November 2015 (UTC)

Recovery from Hepatitis A can take anywhere from several weeks, to several months. Those most vulnerable to the infection are generally very old, sick or young. There is no specific treatment for hepatitis A and vaccines are available internationally. Jdulsky (talk) 23:27, 5 November 2015 (UTC) http://www.ncbi.nlm.nih.gov/pubmedhealth/PMHT0022975/ http://www.cdc.gov/hepatitis/hav/ http://www.who.int/mediacentre/factsheets/fs328/en/

• Yes, see your healthcare provider. If you do not already have Hep A, (as well as Hep B) you can get vaccinated. The test and the vaccination were both free for me, since the insurance company would rather prevent it than deal with the sequelae. μηδείς (talk) 01:06, 6 November 2015 (UTC)

This user has been indeffed for troling

Actually the editor was blocked because they either lack the competence to edit wikipedia, or they are trolling. Nil Einne (talk) 17:33, 8 November 2015 (UTC)

Where can I get information about the the rotation degrees of the Atlas around the axis?

I've searched many articles and I didn't find. I just want to know how many degrees is ability of the atlas to rotate around the axis dent. 78.111.187.141 (talk) 17:08, 5 November 2015 (UTC)

What 'Atlas' do you mean? This or may be this? Both cam rotate around an axis. Ruslik_Zero 20:13, 5 November 2015 (UTC)

He means the biological one Ariel. (talk) 20:44, 5 November 2015 (UTC)

Finasteride mechanism.

Finasteride inhibits 5 Alpha Reductase (5 AR) which is responsible for converting Testosterone to DHT which inturn is responsible for male pattern baldness. How much 5 AR does 1 mg Finasteride inhibit ? 5 AR converts 5% of Testosterone to DHT so if we increase Testosterone through sexual indulgence, exercise etc... we will be providing more facility for increase in DHT right ? So if 1mg Finasteride reduces 5 AR by x amount then the remaining (v-x) amount of 5 AR will still convert T into DHT and the amount of T increased by some activity or the other will still produce enough DHT to attack hair follicles right ? Please do give a quantitaive explanation if possible! — Preceding unsigned comment added by 175.101.24.136 (talk) 17:31, 5 November 2015 (UTC)

It gets complicated. I was going to go through according to the IC50, but it's more complicated than that - there's a Type I 5alpha reductase and a Type II. [7] It inhibits Type II, which produces 2/3 the testosterone, 100x better than type I. So a practical dose is probably, approximately, going to block a bit under 2/3 the testosterone production. But there's some tissue specificity - same paper says the prostatic DHT drops 90% with that treatment, so apparently DHT isn't in equilibrium throughout the body. So the type II that takes it in the shorts is prostate, seminal vesicle, epidydimis, hair follicle; the type I is in scalp sebum gland, liver, muscle, brain. The IC50 according to this is 5.9 nM in prostate, 310 nM in scalp. But then there's turnover ... takes two weeks for the enzyme to recover... and note the rodent results and human are different...

In reality, this is very much going to be settled empirically, not theoretically. Whatever dose is determined to work for a particular application with tolerable side effects is what people will use. Wnt (talk) 18:17, 5 November 2015 (UTC)

You're awfully interested in male-pattern baldness. Have you actually read our article? The only lifestyle factors with a well-demonstrated link to promoting male-pattern baldness are being overweight/obese, sedentary lifestyle, and chronic stress. So avoid those, which you should do for a million other reasons anyway. I'm getting a vibe of "I'm planning to take drugs without a doctor's recommendation because I think they will prevent hair loss", which is definitely a thing you should not do. If there is something else you're trying to learn, how about just asking it straight out instead of a bunch of vague questions about testosterone and drugs and hair follices? --71.119.131.184 (talk) 20:22, 5 November 2015 (UTC)

Assume good faith - the question is just interesting. It's interesting to see transgenders talk about it - there are probably biological insights to be learned regarding their inability to regrow the lost hair or the question of whether gynecomastia can be separated from it. I'd also love to see more research into He Shou Wu, despite occasional trouble with it. Still, a good rule for human biology is Don't be the science project. Let somebody else be the science project and watch what happens. :) Wnt (talk) 22:33, 5 November 2015 (UTC)

Homoromantic Asexual Men and Chocolate Allergen?

I've known two asexual men in my life who nevertheless tended toward other men. Both were allergic to chocolate. There's no correlation, is there? Theskinnytypist (talk) 19:27, 5 November 2015 (UTC)

No. --Jayron32 19:56, 5 November 2015 (UTC)

Do you have any sources for that, or is it pure speculation ? StuRat (talk) 05:18, 6 November 2015 (UTC)

Sorry, I must have thought I was you for a second. this turns up no significant cross section of information about the two random facts noted by the OP. I can't even find anyone aside from the OP who has proposed that there could be a connection. --Jayron32 16:52, 6 November 2015 (UTC)

Absence of proof is not proof of absence (of a link), so your answer is useless. Much better answers are below. StuRat (talk) 20:48, 8 November 2015 (UTC)

There could potentially be a correlation, but correlation is not causation. Two factors being linked does not necessarily mean either causes the other. Here is a website with some amusing illustrations of this. --71.119.131.184 (talk) 22:31, 5 November 2015 (UTC)

There's almost certainly no data on this - and in biology, if you don't have the data, you really don't know the answer. I'd bet money it's coincidence, but no more than I could comfortably lose. Wnt (talk) 22:35, 5 November 2015 (UTC)

(ec)Correlation does not imply causation necessarily. However identifying that the reasoning behind an argument is flawed does not imply that the resulting conclusion is false, so according to Popper we must admit the OP's alternative bold hypotheses to scientific investigation:

• Hypothesis A: Homoromantic asexuality causes chocolate allergy.
• Hypothesis B: Chocolate allergy causes homoromantic asexuality.

More than the two samples collected by the OP will be needed to lend more confidence to A or to B than already exists in the

• null hypothesis: !A AND !B

The latter predicts that wider sampling under controlled conditions will yield a standard Cauchy distribution which is the distribution of a random variable that is the ratio of two independent standard normal variables and has the probability density function

$f(x;0,1)={\frac {1}{\pi (1+x^{2})}}.\!$

Bestfaith (talk) 22:41, 5 November 2015 (UTC)

That math is great, but the math that matters is your odds of getting a Golden Fleece Award in the improbable event you actually get a research grant to study homoromantic asexual men. I am not expecting data soon. Wnt (talk) 22:49, 5 November 2015 (UTC)

Thanks, everyone, for helping me out! :) And too bad the second commentator was anonymous, because that website was hilarious! Theskinnytypist (talk) 23:35, 5 November 2015 (UTC)

What about:

• Hypothesis C: both are caused by some as yet unknown factor? (The poster formerly known as 87.81.230.195} 185.74.232.130 (talk) 14:43, 6 November 2015 (UTC)

• There is of course Hypothesis D: there is no connection, correlation, or causation between the two at all. The null hypothesis should be the default stance for any proposition. People can propose any two random facts, like "Do more people born on Tuesday have blue eyes". Unless and until evidence is presented which would support the proposition, the null hypothesis should be the default and standard answer to the proposition, without need for further proof. --Jayron32 16:54, 6 November 2015 (UTC)

Why do feces contain more dangerous bacteria than vomit?

They have both been in the stomach and exposed to digestive bacteria so why do feces contain more? ScienceApe (talk) 22:22, 5 November 2015 (UTC)

The stomach contains few if any bacteria. Your stomach is filled with acid partly in order to kill pathogens that might come in. Only a few acid-resistant bacteria can survive the environment, one notable species being Helicobacter pylori, which causes most ulcers. Your gut flora live mostly in the large intestine. --71.119.131.184 (talk) 22:25, 5 November 2015 (UTC)

Remember that the gut is actually designed to grow bacteria (people depend on vitamins they generate). And the contents have had longer to grow bacteria, wanted or unwanted, at the far end. And the bacteria have evolved to spread via feces, not via vomiting, because usually they go out the rear. (Fecal-oral route) Wnt (talk) 22:37, 5 November 2015 (UTC)

Designed? Bazza (talk) 16:38, 6 November 2015 (UTC)

Well, maybe this guy turned me into an anti-evolutionist yesterday. Or maybe the smart money is on trying to purge incorrect ways of speaking in preparation for a Ben Carson presidency. But honestly, my call is that something can be "designed" by an AI, which is not a conscious process, so why not by evolution? And really, we can't actually say that conscious thought doesn't use an evolution-like process in designing something. Wnt (talk) 12:49, 7 November 2015 (UTC)