Wikipedia:Reference desk/Archives/Science/2015 October 8

= October 8 =

A Fourth Dimension
In my geometry class, we watched this video about dimensions. It had this city of two-dimensional shapes that weren't aware of a third dimension (can't remember the name of this particular film). It just got me wondering if there was a fourth dimension, and if our minds would be able to comprehend it. What could the fourth dimension be? The mind? Space? Something with the senses? Can we even begin to imagine what it could be? How could we discover it? Thanks.2602:306:CC43:A8A0:C8A1:D21E:F7DC:74C1 (talk) 00:12, 8 October 2015 (UTC)


 * There is a fourth dimension, time. Whenever you specify the location of an object, you need to include the 3 spacial dimensions but also the time, as the object won't be there permanently (although some things seems permanent, on a human timescale, so the time dimension is often omitted for things like mountains). StuRat (talk) 00:27, 8 October 2015 (UTC)


 * As far as I know, the problem with extra spatial dimensions is that they might be expected to consume particles, forces, and so forth. A radioactive atom breaks - the pieces go left and right, up and down, back and forth, why not zerk and krez?  But we see every particle come out, in normal 3D space, by seemingly normal laws of Euclidean physics.  In M-theory there is this idea that there are extra dimensions but they are "curled up", so you go the tiniest smidgeon of a nothing in them and you're back to where you started.  Sort of like beads on a string - they seem confined to a one-dimensional space but if you look really close you can see they are able to rattle back and forth a bit too, rotate etc.  But honestly I still don't really understand that, because wouldn't a particle looping around and round in a fourth dimension have energy diverted to its motion in that space that leaves it going too slow in regular space?  But since M-theory ties these states to various physical forces, I am probably missing the point. Wnt (talk) 00:47, 8 October 2015 (UTC)


 * In at least some of these models, possibly all, particles are spread evenly across the extra dimensions in a low-frequency (so also low-energy) mode, analogous to a transverse mode of a waveguide. To get something resembling motion in the extra dimension, you'd need to excite higher-frequency modes, but their energy is high enough that they haven't been seen in experiments.
 * Another type of extra-dimensional model has the particles (except the graviton) confined to a 3+1 dimensional surface in the higher-dimensional space. Apparently this sort of thing shows up naturally in string theory. -- BenRG (talk) 04:04, 8 October 2015 (UTC)


 * The OP may have seen the 2007 movie based on Flatland: A Romance of Many Dimensions an 1884 satirical novella by the English schoolmaster Edwin Abbott Abbott. Bestfaith (talk) 01:08, 8 October 2015 (UTC)


 * Zerk and krez? I am not even going to ask permission to steal that.  What a great thread.  I read Flatland back in the 80's when there was no non-public domain version of it.  Great thread.  Am off to look zerk and krezward for the 2007 film. μηδείς (talk) 01:25, 8 October 2015 (UTC)
 * ana and kata are sometimes used for the extra pair of directions. —Tamfang (talk) 09:52, 8 October 2015 (UTC)

As far as I can tell, all of you live in two dimensions. --Amble (talk) 02:18, 8 October 2015 (UTC)
 * Oh come on people. We're talking about geometry here, we DO have quite well defined Four-dimensional space in geometry. Also Tesseract is relevant here. Vespine (talk) 03:05, 8 October 2015 (UTC)
 * It's not clear that the OP is really talking about geometry. He/she asked what was "the" fourth dimension.  Many many people seem to think that's somehow a meaningful question.  I would ask those people, what is "the" first dimension?  Is it left/right?  Is it north/south? Or maybe galactic north and galactic south?  Up/down?  Forwards/backwards?  In any of those cases, what makes that the first one?
 * If you can't figure out what the first one is, how are you going to figure out the fourth one?
 * Ancient Greek geometry was all coordinate-independent. Then analytic geometry got people thinking in terms of Cartesian coordinates, and the coordinate-independent view had to be rediscovered and made precise and rigorous at some point in the history of differential geometry.  I wish we had an article on that but I am not able to find it.  General covariance touches on it but is not quite what I'm talking about. --Trovatore (talk) 03:34, 8 October 2015 (UTC)
 * Trovatore is exactly correct.
 * Furthermore, in mathematics, the term "dimension" has a specific meaning. Often, when real scientists and physicists talk about multiple dimensions, they are not talking about spatial coordinates.  This terminology frequently confuses readers of popular-science who have not formally studied mathematics and physics.  For example, we have an article on parameter spaces and configuration spaces.  Scientists may use the term "dimension" to represent one coordinate in these abstract or generalized models.
 * Nimur (talk) 04:10, 8 October 2015 (UTC)


 * StuRat mentioned spacetime and Vespine mentioned Euclidean four-space, but please note that these are not the same thing. Spacetime has a Minkowski geometry in which time has to be distinguished from the spatial dimensions.  Special relativity can be expressed as rotations between time and space, but they're not quite the rotations with which you're familiar. —Tamfang (talk) 09:52, 8 October 2015 (UTC)
 * Well, sort of. There are "timelike" and "spacelike" directions, and those can be distinguished in a coordinate-free way.  However, there is no distinguished "pure time" dimension. --Trovatore (talk) 18:25, 8 October 2015 (UTC)


 * We've answered this question several times before - and I've come to the following view. Let's lay out some assumptions and ground rules:
 * I'm assuming that we're taking a standard "3D" human with normal eyes and brain and dumping them into a world with four spatial dimensions and one time dimension.
 * This being the case, we need to imagine how our current visual system would react to being in this strange place.
 * Note that we have two eyes, spaced a little way apart in a direction determined by turning our heads.
 * Note that our retinas are not 3D "cameras" - they are (essentially) 2D cameras - we see a projective projection of the 3D scene onto a pair of 2D retinas.
 * We see a slightly different 2D projection of the three dimensional scene in each of our two eyes and we have to focus to make a sharp image on the retina - and the degree of focus, and the degree of adjustment between the two images to make them 'fuse' into a single image allows our brain to calculate an estimate the third dimension distance.
 * So what happens?
 * Well, for starters, in the 3D world, our eyeballs are solid walls with a hole in the front - this ensures that light only enters the eye through lens and iris. In a 4D world, light can cleanly bypass those solid walls and light from all directions would hit the retina.  This would effectively render us blind.  We'd see a uniform sea of light coming from all directions.
 * Imagine the 2D analogy. A circle in 2D completely surrounds the space inside it - but in 3D, you can shine a flashlight onto a 2D circle and light up its interior...and the same thing happens with a 3D sphere in a 4D world.
 * If instead we imagine that the spheres that are our eyes are hyperspheres in 4D - then what becomes of our retinas? If they remain as essentially 2D surfaces then what we'd see would be just like a projection of the 3D world into 2D...things would look entirely normal until you turned your head in the 4th direction - when you "turn your head" in the 4th direction - then the world would morph and shift bizarrely - but it would still look like our 3D world.
 * If we imagine that we magically have 3D retinas in 4D eyeballs - then we have to imagine how those retinas are connected to our brains. Our brains aren't large enough to incorporate all of data from the millions time greater numbers of light-sensing cells.   If you follow that direction of thinking then all bets are off.  In order to be able to see anything 'unusual' about the 4th dimension, we'd have to be fully 4D creatures - and we'd be very, very different.
 * So different, that it wouldn't be meaningful to call us human anyway.
 * Bottom line - it all depends on your assumptions about how we are in the 4D world. If unchanged, we can't see anything beyond a uniform bright blur - and if we're sufficiently changed, then it becomes meaningless to ask how we'd see things - because we wouldn't be remotely human and we can't imagine the answer.
 * 05:27, 11 October 2015 (UTC)


 * The question seems most likely to arise for a brain-in-vat who's given a 4D virtual environment, and virtual eyeballs. I imagine a space E³×S¹, where the extra dimension is initially such a tiny circle that variation of that coordinate has essentially no effect, but slowly grows as the subject gains familiarity until the circle is too long to notice the wrapping. —Tamfang (talk) 08:00, 11 October 2015 (UTC)

The differences between those two scenes allow us to (somewhat) deduce a distance in the direction that's perpendicular to the take one 2D image from each eye and combine them to produce a means to get an approximate idea of distance in that 3rd direction...the direction that's at right angles to the line joining our two eyes and in the general direction that they are pointing.
 * So

why is the Lasioderma serricorne called tobacco beetle, if he is eating everything?
I have read the article in german and I have 2 questions: The first is above and the second is: Reading the german and the english article does make me feel, like he is only eating tobacco products, not the pure plant himself when it is growing. Am I right? Because this would make my question even harder, why a beetle what isn´t living with the tobacco plant has got this name.. here is a 1:1 translate of the german part with google translate what this beetle is able to eat (I have not corrected it, just if someone wants to grew the article about Lasioderma serricorne) numerous foods, such as flour, dried fruits, such as dates and raisins, cereals, cocoa, coffee beans, spices and herbs, nuts, rice, animal-dried foods and other foods that chambers extended period in storage cabinets, and stored like. In addition, you will find the beetles also dried plants, as in herbaria, decorations and potpourris, in medicines, in insect preparations, in filling of furniture, paper mache and the binding glue of books. Thank you and greetings!--Hijodetenerife (talk) 05:48, 8 October 2015 (UTC)
 * is he able to eat the pure tobacco plant (like snails) or does him harm this scent of a blossoming tobacco plant? (such as mosquitoes or bees, for example).


 * Like any animal, tobacco beetles do all sorts of stuff. But they're notorious for one thing. It's like why we don't call him "Zorba the House Builder". InedibleHulk (talk) 06:05, 8 October 2015 (UTC)
 * The black carpet beetle is reddish brown and can live outdoors just fine. InedibleHulk (talk) 06:26, 8 October 2015 (UTC)
 * Same as this guy. http://www.naturespot.org.uk/species/black-clock-beetle 196.213.35.146 (talk) 11:57, 8 October 2015 (UTC)

any other answers?--Hijodetenerife (talk) 22:27, 8 October 2015 (UTC)


 * The tobacco beetle is so named because of the tremendous economic damage he incurs upon tobacco farmers. The beetle will eat either the leaves off the live plant, or the aging tobacco being stored in a warehouse. Tobacco beetles will also eat virtually any dried vegetable matter. I have not been able to find out who so named the beetle or when. I suspect that history is buried in an 18th century Latin or German manuscript. If you do manage to find some of the sources cited in the history section of this paper, maybe you could find out. Someguy1221 (talk) 23:46, 8 October 2015 (UTC)


 * The article doesn't answer a question. Does the tobacco beetle have a resistance to nicotine?  The nicotine alkaloid is commonly used as an insecticide, and it is plausible that the plant developed the production of the alkaloid precisely because it is a very good insecticide, and so would protect the plant from most species of insects.  I am conjecturing that this species of beetle has adapted to its environment by acquiring a resistance to the insecticide.  Maybe it was so named both because it causes economic damage to tobacco and because it was seen to be one of the very few pests that could cause damage to tobacco (since the plant protects itself otherwise by being poisonous.)  Robert McClenon (talk) 22:16, 9 October 2015 (UTC)

list of chemicals in blood that increase when a person goes into physical exertion mode
running, weight lifting, swimming etc compared to rest state. — Preceding unsigned comment added by Mahfuzur rahman shourov (talk • contribs) 15:52, 8 October 2015 (UTC)
 * The concentration of blood lactate is usually 1–2 mmol/L at rest, but can rise to over 20 mmol/L during intense exertion. Immune cell functions are impaired following acute sessions of prolonged, high-intensity exercise, and some studies have found that athletes are at a higher risk for infections. Athletes may have slightly elevated Natural killer cell count and cytolytic action, but these are unlikely to be clinically significant Bestfaith (talk) 18:04, 8 October 2015 (UTC)


 * Epinephrine - its concentration in blood can increase 10x during exercise. SemanticMantis (talk) 18:33, 8 October 2015 (UTC)

creatinine, cortisol, testosterone, do they increase? what other chemicals increase?Mahfuzur rahman shourov (talk) 04:58, 9 October 2015 (UTC)
 * I don't know much about this to be honest. But for each of the things you are interested in, check the WP article. For instance Cortisol and Cortisol give some info on the (wide) normal range in blood, and also indicated that aerobic exercise can increase blood cortisol. While "things that increase in the blood during exercise" is indeed an interesting category, I don't know of any place to find a comprehensive list. SemanticMantis (talk) 15:00, 9 October 2015 (UTC)


 * The muscles used in exercise are powered by oxidation of fats and carbohydrates using oxygen that is transported in red blood cells. A protein Hemoglobin in the blood cells binds with oxygen molecules in the lungs to form Oxyhemoglobin and on releasing oxygen returns to deoxyhemoglobin. A pulse oximeter (shown) can measure the amount of oxygen in a person's blood because oxyhemoglobin and deoxyhemoglobin have different absorption spectra. Bestfaith (talk) 17:27, 9 October 2015 (UTC)