Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.
All observation indicates that the universe is relative. There is no absolute position because there is no center. One way it is often explained is that no matter where you are in the universe, you appear to be in the very center of the universe. So, everything is relative to where you are. 199.15.144.250 (talk) 11:35, 15 October 2015 (UTC)[reply]
This is a little confusing, but if you work through it carefully, it's not that difficult. A lot of explanations talk about the surface of an expanding balloon, but to me that introduces irrelevancies like whether or not the universe is finite. It works just fine in a (more intuitive) infinite universe.
We don't need three dimensions; the point is the same in one dimension and it's easier to talk about.
So imagine an infinitely long rubber band, stretching out to infinity in both directions, and marks on it at intervals of one mile.
Now start to stretch the rubber band, in such a way that every mile becomes two miles over the course of one hour.
Let's say you're standing on one of the marks. You'll see the mark to your left move away from you, at an average speed of 1 mi/hr over the first hour. Similarly, the mark to your right will move away at the same speed.
The mark two miles to your left will end up four miles away from you, so it has to move 2 mi/hr averaged over the first hour. And so on.
Now, here's the point: What does it look like from the point of view of someone standing on the mark 100,000 miles to your right?
It looks exactly the same. So you can't tell whether your mark is the center, or whether that one is, or any other on the whole infinite rubber band. --Trovatore (talk) 20:50, 15 October 2015 (UTC)[reply]
There are no ends; it's infinite in both directions. You have to imagine the rubber band stretching, but what is stretching it is not really relevant to the thought experiment. --Trovatore (talk) 20:57, 15 October 2015 (UTC)[reply]
You're right that the balloon analogy doesn't work, because a balloon, whether expanding or not, still has a "center". So the one-dimensional object you're postulating doesn't have a "center", or something like a zero point as a number line does. Right? ←Baseball BugsWhat's up, Doc?carrots→ 21:01, 15 October 2015 (UTC)[reply]
So for the balloon case, you're not actually supposed to be considering anything but the surface of the balloon. It's two-dimensional, not three-dimensional. There is no "center of the surface of the balloon".
The balloon may work better for some people. I introduced the infinite rubber band to make it clear that the question does not depend on whether the universe is finite or infinite. An infinite expanding universe, with a Big Bang and everything, works just fine.
You can pick a point of the rubber band and say it's the center if you like, but the point is that any other point you picked would have worked just as well.
Well, of course in any analogy, you have to be able to figure out which elements are important to the argument and which ones are extraneous. In the case of the balloon, the important thing is that the surface is two-dimensional. At any point on the balloon, you can only travel in two independent directions, and remain on the balloon.
The balloon is embedded in three-dimensional space, but the embedding is extraneous, except insofar as it allows you to comfortably apply your spatial intuitions about what balloons are like. For the purposes of the analogy, the space in which the balloon is embedded does not exist. There is no inside or outside, there is only the rubber of the balloon itself. --Trovatore (talk) 00:38, 16 October 2015 (UTC)[reply]
I believe that phrase is used for this concept in some of the popularizations, yes. It doesn't correspond to the mathematical notion of an unbounded set, though. It's more like "without boundary" than "without bound"; that is, there is no point where you can't go farther. --Trovatore (talk) 06:27, 19 October 2015 (UTC)[reply]
Absolute zero is not part of the universe. It cannot be reached. You can get really really close, but you cannot reach it. You can only reach temperatures relatively close to it - but everything is usually very far away from it. 199.15.144.250 (talk) 14:10, 15 October 2015 (UTC)[reply]
Proving that rotation is absolute is one of the ways that we ended the debate about who goes around who. Two methods are Foucault Pendulum and Coriolis Force. And notably both can tell you if you are rotating without access to anything external (i.e. you can be a closed box and still tell), you don't need to compare yourself relative to anything else because rotation is absolute, not relative. Ariel. (talk) 21:34, 15 October 2015 (UTC)[reply]
Sure. But you're talking about measuring it. It depends on what you really mean by "tell". If I knew nothing about the workings of the universe, I could absolutely "tell" that the universe was revolving around the earth. ←Baseball BugsWhat's up, Doc?carrots→ 23:20, 15 October 2015 (UTC)[reply]
Two bodies orbiting around a common barycenter. Supposing the bodies tied by a rope to hold them together (rather than gravity, which is ignored in this example), the rope is under tension if the bodies are rotating. By "tell" I think you mean interpret? An essential component of interpretation is observation (measurement) and with that to take care to not cherry-pick the data and extrapolate too heavily from it. In this case, centripetal acceleration causes internal tensions in bodies, such as when a string is made taught when two balls are attached and are spun about each other; their inertia pulls the string taught. Thus if we were always blind and therefore could not ever see the stars we might very well have inferred Earth's absolute rotation simply from its oblong shape. See Issac Newton's bucket argument. However Ernst Mach and other physicists such as Max Born have argued that we should only infer a relative rotation with respect to other masses, but still, tension should arise due to inertia even if there is practically no other mass present. Nevertheless, we now know that we are always moving with respect to the Cosmic Microwave Background rest frame. -Modocc (talk) 00:19, 16 October 2015 (UTC)[reply]
The person knowing nothing about the workings of the universe could be invited to rebut a Sagnac interferometer that purports to measure local absolute rotation assuming only invariance of the speed of light, or to explain why in the Hafele–Keating experiment there is a difference of 207 ns in the times taken for a relay of pulses to circumnavigate the world depending whether their path is westward or eastward. Bestfaith (talk) 00:49, 16 October 2015 (UTC)[reply]
One is an observable phenomenon which was described after data was collected to do so. The other was an ancient philosophical concept developed by Greek thinkers with no real use of experimental or observational science. --Jayron3203:48, 16 October 2015 (UTC)[reply]
The above statements are correct, but keep in mind that the use of the terms aether and atom are matters of convention. We could start calling the vacuuum energy the aether tomorrow or start denying that chemical atoms are the smallest particles tomorrow if we wanted to. The issue is simply that modern atomic theory turned out to be predictive, why the aether of absolute Newtonian space turned out to be false. At the time of Michelson-Morley they could simply have redefined "aether" but physicists chose to declare the word itself disproven. The same thing applies with Pluto. μηδείς (talk) 04:09, 17 October 2015 (UTC)[reply]
The MAIN difference is the question that the hypothesis is trying to answer. The Luminiferous aether was proposed as a solution to the problem of how light propagates though supposedly "empty space", that question was answered instead by relativity, electromagnetic radiation does not require a medium to propagate, not even vacuum energy, vacuum energy addresses completely different questions. Vespine (talk) 22:17, 19 October 2015 (UTC)[reply]
None or all. There is no Rambo movie called "The Specialist". That is a Stallone movie, but not a Rambo movie. So, this falls into a logical division by zero where you tend to approach zero or infinity in most cases. 199.15.144.250 (talk) 11:33, 15 October 2015 (UTC)[reply]
I don't think an explosion of C-4 looks like much of anything, unless in slow motion. At normal speeds a car packed with C-4 is just there and then gone, replaced with a large, expanding cloud. StuRat (talk) 02:57, 18 October 2015 (UTC)[reply]
Here is an excerpt from a webpage discussing the antidepressant imipramine:
"Oral: absorption occurs in the small intestine with little or no absorption in the stomach (Crammer et al., 1969; Gramm & Christiansen, 1975). Absorption is virtually complete (95%).
The peak plasma concentration occurs 2 to 6 hours after administration (Christiansen et al., 1967; Dencker et al., 1976; Gram & Christiansen, 1975). Food does not affect absorption, peak concentration or time to peak concentration (Abernethy et al., 1984)"
If the patient is fasting then there ought to be no stimulus for the stomach to empty in which case I'd expect a delay in the absorption of imipramine in a patient that has not eaten in some time which contradicts the Abernathy et al. findings. Does any "empty" stomach release its secretions into the duodenum regardless of the presence of food? Otherwise, I don't really get it. ----SeansPotato Business13:04, 15 October 2015 (UTC)[reply]
(EC) I'm not an expert on pharmocokinetics or gastic emptying, but I think you may actually have it in reverse. Gastric emptying may very well be faster without food [1][2]. This is presuming water is taken with the pill, which is common advice when taking tablets, and seems to also be advice for imipramine [3]. I presume the content you are quoting comes from [4] or similar which tell us Abernethy et al., 1984 is [5]. That source confirms that in that experiment, the tablets were taken with 100ml of water. Bearing in mind by earlier caveats, while I'm not sure if 100ml of water qualifies as large glass, I think there's still a fair chance it will be enough to trigger rapid emptying, although the pill will probably need to be broken down enough before it's emptied. As to why this didn't affect "time to peak concentration", or any of the other things, when there may be a difference in rate of emptying, bear in mind 2-6 hours is a fairly large range and the variance in gastric emptying probably isn't that high for the comparitive examples. If for example, the difference is only 30 minutes, it's possible this won't result in a statisticly significant difference. It's also possible the rate of gastric empying isn't a factor in the examples compared, and the pill being broken down sufficiently to be emptied is the limiting factor. Nil Einne (talk) 15:30, 15 October 2015 (UTC)[reply]
For someone who works out every day and eats something like 20% more calories than they need, what is a realistic rate of muscle gain in kg/year? What amount of fat will be created with that muscle?--88.81.124.1 (talk) 15:31, 15 October 2015 (UTC)[reply]
Oh dear. I consider these questions to be bordering on medical advice – which we don't give here. You would be better off consulting a sports-coach because you have a misconception. You probable already know a little bit about this so I will go straight to the quick. It is not calories that add muscle mass but the bodies ability to protein synthesis larger muscles due to exercise (and this is a slow process and depends on your own personal metabolism – so no figures of what to expect). One does not need to eat loads. One needs to exercise and eat a normal 'balanced diet'. Let one's own body tell you if it needs more food by 'making you' feel hungry. It is a bit like forcing more fuel into you car engine than it is designed for and expecting it to go faster, when all it does is to fart the extra energy out the exhaust pipe whilst coking up the cylinders. Hunger is the signal that your engine has gained a few extra cubic inches and now it wants more fuel. Protein before and after exercise helps but please, not any of these fancy expensive sports drinks. That also means you will not have to consider the fat/muscle ratio because you won't put on any fat. Of course, if you're wanting to became a Sumo, then eat loads more carbohydrates (rice) than your appetite requires. A good sports-coach should know all this.--Aspro (talk) 18:51, 15 October 2015 (UTC)[reply]
Per Aspro, the variables are too great to work out for any one person, as it depends on your workout levels and types of actvities, your specific diet (not just total calories), and most importantly, your particular metabolism, which we don't know. Also per Aspro, the best person to ask this of is to consult a Personal trainer, Strength and conditioning coach, nutritionist, etc. This is not the sort of stuff that you can just "get for free" as it requires someone who can monitor your performance and give you active feedback. --Jayron3219:10, 15 October 2015 (UTC)[reply]
If shorthand is faster, why not use is as a first writing system?
If shorthand is faster, why not use is as a first writing system? And, I think that Braille has some shortening possibilities too, which make it more efficient. Besides for the obvious historical reasons, are there any cognitive reasons for not using a more sleek coding system instead of "normal" English?--Bickeyboard (talk) 22:51, 15 October 2015 (UTC)[reply]
Think the short answer to that is, in order to understand and write short-hand (and I'm talking Pitman's but it applies to other stenography's in other languages) one has to be able to read and write English.--Aspro (talk) 23:27, 15 October 2015 (UTC)[reply]
Shorthand writing systems are based on phonics - what the words sound like. In written language we have many heterographs - words that sound the same but are spelled differently and have different meanings (there/their etc.) Arguably, the use of heterographs enhances our ability to avoid ambiguity and make use of the great power of expression and description that is available in our written languages. Shorthand, or any other system based solely on phonics, ignores heterographs. Dolphin(t)23:59, 15 October 2015 (UTC)[reply]
That makes sense, as the article indicates shorthand is normally as an intermediate step between dictation and typing. Hence you might spell "there", "their" and "they're" all the same way, but you would recall or know from context, upon typing it, which one was meant. ←Baseball BugsWhat's up, Doc?carrots→ 00:26, 16 October 2015 (UTC)[reply]
A number of people have used personal shorthand systems for writing diaries, without the intention of transcribing it later, famously Samuel Pepys and I found this recent discovery. However, this is really a type of encryption. As pointed out above, shorthand is a rather poor tool for communicating with other people. Alansplodge (talk) 08:11, 16 October 2015 (UTC)[reply]
Why don't we do feel the wind moving past our faces on the equator due to the rotation of the Earth?
Why don't we do feel the wind moving past our faces on the equator due to the rotation of the Earth. Radius at equator is 6378 km.Ther circumference is 40074 km. So the speed must be 1670 km/hour. A tiny cuboid of air has mass and inertia, so when it is spun round and round, it should retard and we should be able to feel it moving past our faces. 175.45.116.59 (talk) 23:09, 15 October 2015 (UTC)[reply]
The atmosphere rotates with the lithosphere. On a global scale, atmospheric air is viscous enough to be dragged along by the ground as the Earth spins. But, because it is still a gaseous fluid, the atmosphere experiences many complex effects, including (but not limited to) differential rotation, convection, and turbulence on the global scale. These effects contribute to prevailing winds and climate, and the local effects are what we call weather.
If you're looking for a great textbook, Aviation Weather is available in electronic form at no cost, and it has lots of nice cartoons that explain how wind works on a planetary scale. Chapter 1 (The Atmosphere) and Chapter 4 (Winds) are of particular relevance.
"To first order," the air near the ground is stationary relative to the ground; the air is co-rotating at the same rate as the rest of the Earth. In actual fact, any time there is any wind at all, this comically over-simplified explanation falls apart; the cause of the wind can be due to many reasons, but its most notable cause is differential heating.
You can also find lots of fascinating research on the topic of planetary atmospheres and their angular momentum: for example, here's an archived news brief from Goddard Space Flight Center on atmospheric perturbations that affect the rate of Earth's rotation. That article links to a bunch of other great climate science websites from NOAA and NASA.
Wind at the equator varies slowly between easterly and westerly in a cycle that repeats about every 28 to 29 months. Westerly wind is shown by positive (red) values in the graph. The maximum speed in either direction is much less than the Earth surface rotational speed and the average speed over the cycle is near zero. This is because the angular velocity of the Earth's atmosphere is the same as whole planet and what we experience as winds are periodic tidal waves and local turbulences. The Earth's rotation contributes only the small Coriolis effect which deflects air and water currents greater near the poles but is negligible at the equator. Bestfaith (talk) 00:08, 16 October 2015 (UTC) That chart is very high up, though. The equatorial troposphere is known for winds monotonously from the eastSagittarian Milky Way (talk) 01:26, 16 October 2015 (UTC)[reply]
For a full review article, explaining the science and the methodology, the authors of the website also cite this publication: The Quasi-Biennial Oscillation (2001).
