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

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.

September 8

Big Bang & Star(s)

1. List of things/matter(s) that are found in a nebula now i.e. relative to the things/matter(s) in the universe found when gravity first started drawing things/matter(s) together into large scale structures.
2. Correct me if I’m wrong: When quasars were forming in a transparent place, were population III stars forming in front, middle and in the tail, since it’s a large scale structure forming altogether, creating clouds such as HHobjects and bok globules dust and gas…? I can’t recall where I read, that the large scale structure we are talking about, population I stars are forming in the milky way galaxy's tail – measuring from the centre of the galaxy to its farthest end (tail) – population II stars have formed in the middle and (I guess) population III stars formed along with the centre star of the galaxy, in the front, after the so called halo.
3. What’s the ultimate state of a star? Does it decompose?

Space Ghost (talk) 05:42, 8 September 2015 (UTC)

Gravity always has been "drawing things together". So take a look at Big Bang and maybe Big Bang nucleosynthesis. I can't quite make out your second question. Different stellar populations are defined by their metallicity, generally assumed to correlate to the time of formation, not their location (earlier stars have lower metallicity because the interstellar medium is enriched over time by heavier elements - see Stellar nucleosynthesis). As for the third question, it depends on your definition of "ultimate" and the type of the star. Typical endings are white dwarfs (or eventually black dwarfs), neutron stars and supernovae. Ultimately, all matter may decay - see Ultimate fate of the universe. --Stephan Schulz (talk) 07:53, 8 September 2015 (UTC)

---

I'm gonna tell you a secret i.e., I'm thinking of a hypothesis i.e. 'Big Bang' occured from a 'supernova', excluding 'gravity' from the 'primodial atom' ofcourse by keeping 'gravity' and 'dark energy' as 'primary forces' available from beforehand in 'space', but I need clarifications in order to call it a hypothesis.

1. View this diagram, this is of a population I star. I require information of population II and III stars for analysis. I also require information of their temperatures (each phase) - I already know the temperature of population I stars.
2. I don’t understand the following image. What’s the step by step process shown in this image?

Space Ghost (talk) 20:10, 8 September 2015 (UTC)

Why do you think that image is of a Population I star? As far as I can tell, its so schematic that it could be any large mass star. Your idea of the Big Bang is not really compatible with our current understanding. In particular, there is no "primordial atom" that explodes into space, but rather space itself that suddenly expands. Have you looked at Stellar population? Temperature of a star depends, significantly, on mass and stage in the life cycle, so stars from different populations will all have a wide range of temperatures. The second image your reference shows not one, but two(or two and a half ;-) processes (which are mostly continuous - the various "steps" are just for illustration). Both processes start in the middle, in the star-forming nebula. On the left, there is a counterclockwise cycle illustrating the evolution of a low-mass star like our sun, which goes from a protostar to a main-sequence star, then turns into a red giant, shedding a lot of its outer shell as a planetary nebula, then turns into a white dwarf and eventually a black dwarf. Inside that larger circle is a secondary cycle, showing the life cycle of a red dwarf (a star which is so small that convection keeps the material homogenous throughout its long long long lifetime). It will eventually turn directly into a wide dwarf, without a red giant phase. On the right, there is a clockwise cycle showing the evolution of a high-mass star, turning into a red supergiant, and then a supernova, which ejects a lot of the star's material into the interstellar medium and may leave behind either a neutron star or a black hole or not very much. --Stephan Schulz (talk) 21:38, 8 September 2015 (UTC)

3) As far as the ultimate fate of an ordinary star, see proton decay. If this occurs, it would indeed cause stars containing those protons to break down. StuRat (talk) 02:38, 9 September 2015 (UTC)

I understand what you both are saying, I'm gonna re-read all the articles, I'm pretty sure what I'm searching for won't be their... Thank you (both) for whatever you guys helped me with so far...cleared a few things... Regards. -- Space Ghost (talk) 06:22, 10 September 2015 (UTC)

Relationship between temperature and latitude

1. In January, the correlation between temperature and latitude is very strong[1], but in August [2], that relationship is much weaker. What causes this huge difference?

2. Does this difference exist in other places in the northern hemisphere?

3. Does the same effect, except reversed, happen in the southern hemisphere? My other car is a cadr (talk) 04:28, 8 September 2015 (UTC)

For your first question, I don't know the specific answers, but I expect it is being caused by one or more of: a) warm air moving NW from the Gulf of Mexico; b) the geography of the Southern / Southeastern USA being such that it absorbs more heat than the surrounding country; c) various mountain ranges in the west blocking east-west air currents. Regarding your 2nd and 3rd questions, similar things do happen elsewhere in both N and Southern hemispheres, but they depend on specifics of the regional geography and so the S isn't simply a mirror-image of the North. The Monsoon and El Niño, for example, are both caused by differernt part of the world heating up asymetrically. Iapetus (talk) 14:03, 8 September 2015 (UTC)

I think you're basing your premise on visual inspection of these charts. That's not a great way to compute correlations!

All sorts of factors affect peak temperature. Latitude determines insolation; but other factors that affect peak temperature include the altitude, prevailing winds, proximity to large bodies of water... review our article on climate.

I would not conclude anything about the relationship between latitude and peak temperature until I saw a little bit more statistical analysis. Here's a simple worked example of a multiple variable regression analysis for a statistics class at University of Florida: Temperature vs. Latitude and Elevation. To apply this methodology to the massive dataset available from Daymet, you'd need to do a little bit more work! But at least we could conclusively evaluate whether the correlation is weaker or stronger in summer, without letting the color-scales and complex visual shapes interfere with the data analysis.

Nimur (talk) 14:08, 8 September 2015 (UTC)

Over the course of a year, the maximum insolation (i.e. energy from the sun) varies from the Tropic of Cancer to the Tropic of Capricorn as seasons change from summer to winter in the Northern hemisphere. The change in insolation as one moves away from the latitude of maximum insolation is roughly proportional to the cosine of the angular distance between your current latitude and the latitude of maximum energy. Because the cosine function is flat for small angles, if you are close to the Tropic of Cancer in NH summer, there is relatively little effect of latitude changes. Hence the North American dependance on latitude in August is weaker than the North American dependance on latitude in January when all of North America is far from the Tropic of Capricorn. Does that make sense? So the answer to your second question is yes, and the third question is also yes. Though as Nimur describes, there are a variety of other affects that will go into determine the weather at any particular location, and not every location will reliably follow a simple "relative angle of the sun" rule. Dragons flight (talk) 16:24, 8 September 2015 (UTC)

Another point is that the jet stream retreats to the north in summer and extends farther south in winter. Thus, terrain effects and regional circulation patterns can have relatively large effects in summer, whereas in winter the large-scale movements of air masses tend to dominate. Notice for example that in summer the effects of the Rocky Mountains are obvious in creating an east-west temperature gradient (say, along the gradual elevation rise from Kansas to Colorado) whereas in winter the effects of the mountains are more smeared out. Short Brigade Harvester Boris (talk) 02:51, 9 September 2015 (UTC)

Theory of Relativity-Space Warp

As per relativity theory, mass warps the space. Because of the warping object can not travel in straight line as they are pushed toward massive body. Thus warping dictates the travel path, what was earlier understood as gravitational force. Now, I want to ask, if the massing body warps the space in a peculiar fashion, why then a 2 objects traveling at different velocity, following the same path while approaching the heavy body will have different paths after it comes under the influence of that body. Say, a body traveling at lesser speed may fall in to it, while other traveling at greater velocity may escape. — Preceding unsigned comment added by Steamline098 (talk • contribs) 11:50, 8 September 2015 (UTC)

This should be explained at Geodesics in general relativity, but that article is written in accordance with the usual Wikipedia style for math articles, which is to say, lots and lots of math and absolutely no comment about what it means, starting with what the alpha and beta are in the first equation and continuing in that vein right through to the end. General relativity is no easy subject in the first place, and we're definitely not helping. Wnt (talk) 12:08, 8 September 2015 (UTC)

On close reading of the question, this "conundrum" actually has nothing to do with general relativity! Two objects traveling inertially in orbit cannot follow the same path if they have different velocities. That's ordinary mechanics, not general relativity! Some orbit trajectories, even in conventional non-relativistic treatments, are insufficient to escape a gravity well.

If we throw in extra details to account for relativistic effects of very massive objects, the math only gets harder... but if our OP is stumbling over qualitative, conceptual problems associated with the easy version of the math, all hope is lost for bringing in extra complexity. As Wnt remarked, our article on this topic expects some familiarity with prerequisite physics and mathematics. If you need a refresher, you can click on the wiki-links, but if you're learning this all for the first time, reading Wikipedia isn't going to turn you into a physicist.

Addressing Wnt's remarks more generally, some knowledge requires prerequisite study. In the case of advanced physics, it is widely accepted that the prerequisites entail many years of mathematical preparation. One cannot understand advanced physics without advanced math. There isn't anything we can do about this: if we remove the complicated math, what is left is basic conceptual physics, which is not suitable for analyzing relativistic orbital trajectories.

Nimur (talk) 15:21, 8 September 2015 (UTC)

@Nimur: as I said, to begin with, they simply don't define their variables. I'm sorry, but I don't think "perquisite study" should include having to go somewhere else to find out what those are. Beyond this, the math may be complex but the problem with Wikipedia's math articles isn't really the math, but the failure to explain it in a more meaningful way. Wnt (talk) 00:02, 12 September 2015 (UTC)

The original poster gave an argument that objects moving at different speeds must follow the same paths in GR, and asked what was wrong with it. Saying "it isn't true in Newtonian gravity" doesn't answer that. -- BenRG (talk) 16:25, 8 September 2015 (UTC)

It's spacetime that's warped, not space, and it's the path in spacetime that matters. Objects moving at different velocities always have different paths in spacetime (the velocity is a direction in spacetime). -- BenRG (talk) 16:25, 8 September 2015 (UTC)

Ben has explained it above but I try and explain it again. From the wiki page of General Relativity

Phenomena that in classical mechanics are ascribed to the action of the force of gravity (such as free-fall, orbital motion, and spacecraft trajectories), correspond to inertial motion within a curved geometry of spacetime in general relativity; there is no gravitational force deflecting objects from their natural, straight paths. Instead, gravity corresponds to changes in the properties of space and time, which in turn changes the straightest-possible paths that objects will naturally follow.

1 It is spacetime (and not space) that is curved around a massive object. The curvature is caused by the rest mass of the massive object.

2 Any object moves at an angle through spacetime. If the object is at rest, it only moves through time in spacetime. If an obeject is moving at a velocity then it moves through both time and space at an angle. Therefore two identical objects (from the same starting point in space) moving at two different velocity will move through spacetime at two different angle (this is true whether the massive object is around or not). Thus it is impossible for the two identical objects to follow the same path in spacetime if they have different velocity.

3 With a massive object "warping" the spacetime. Two identical objects with different velocity (starting from the same starting position) will have two different angles in spacetime. One object may escape from the orbit of the massive object while the other object may spiral into the massive object.

175.45.116.66 (talk) 00:19, 10 September 2015 (UTC)

Calculating the price of things that are never the same

How can I calculate the market price of things like used cars, or real estate, where no two units are exactly the same. Even if a building has flats that are internally the same, they will have different views, or be on a different floor (and hence, not be the same totally). How does statistics deal with it? --Yppieyei (talk) 12:11, 8 September 2015 (UTC)

What would be the point of trying to lump all types of cars together? You would get a meaningless number. You would also need to take into account the age of the car and the class (such as economy, mid-range, luxury, etc.) ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:57, 8 September 2015 (UTC)

Well, it's not about lumping them together, but about calculating the inflation in a sector. You are right that lumping together economy and luxury class is not very meaningful. In the same way that's not very meaningful to lump together two economy cars that have different mileage or year. Hence the question, how to make price indexes in markets where products are unique? Add to the two categories above also the art market. There must be a way of dealing with this statistically, and analyze how much each feature weights in the price.--Yppieyei (talk) 13:07, 8 September 2015 (UTC)

This is what averages are for. There are many different averages to work with, such as mean (what most people call "average") and median (which is more meaningful when the distribution is not a perfect bell curve). You also want to look at standard deviation (how much variation is there in the average). As long as you are very clear about what you are measuring, such as stating "I am looking at the mean average, which increases by 4% while the standard deviation decreases by 1%", you will be making a meaningful statement. If you are like politicians or news agencies, you make idiotic statements like "the increase in home prices doubled over the last three years" - what does that REALLY mean? 209.149.115.219 (talk) 13:17, 8 September 2015 (UTC)

I am afraid that an average won't be enough here. What if people start buying a better car, or a better house due to economical growth? Your economy class car will still cost the same (or even less, or only a little bit more), but your average car would cost much more, since people are buying luxury class now. The same applies to flats.--Yppieyei (talk) 13:27, 8 September 2015 (UTC)

Wikipedia has an article on Valuation (finance). In cases where the asset value is unclear, there is room for negotiation. Prices that are too high preclude sales; that affects market volume and market liquidity. These are two other parameters, other than price, that market participants might care about. For example, I could offer my car for sale at a low price and sell it this afternoon; I could offer it at a high price and perhaps find a buyer within three months. There is no straightforward way to tell me what "the" price of my car is: it must be estimated, with the intent to drive a particular condition for sale. Analogous logic applies to sale prices for real estate, labor wages and salaries, service contracts, luxury goods, and generally any other non-fungible asset: price is one of many variables that can be adjusted to affect market conditions; or price can be left to equalize by market forces while sellers adjust other parameters like time-to-sale or sales-volume.

One can pursue an advanced degree, and obtain a very competitive job, by studying price behavior in non-fungible marketplaces. Nimur (talk) 14:31, 8 September 2015 (UTC)

"puruse" a degree?

(EC) This actually applies to a lot of things. Even something like potatoes will depend on the type and quality. Plus even if you specify the exact type and quality etc, most of the time there's no reason why it's super meaningful that this sort of potato has gone up because it's less in demand now than it was before so far fewer people are producing them and they're a more speciality item. Since you mentioned inflation, AFAIK most agencies world wide do use averages (although it is fairly complicated how to decide precisely what goes in to the basket, what to weight it, and how to measure the price). Take a read of our Consumer price index for example, or the page on the US one United States Consumer Price Index [3]. Note in particular, the fact that you take in to account people what people are paying for now is differebt from what they were paying for in the past is AFAIK a feature and not a bug when it comes to such indices. (Although I think you've also greatly over simplified how things change. For example in a number of countries, houses might be more luxurious in some ways then they were 50 years ago, but often due to smaller families and other factors, they are also smaller, with smaller yards etc. Luxury is also a real fussy concept. 50 years ago, a heat pump or air conditioner may have been expensive enough that it was a real luxury to have in your home. May be not so much nowadays.) Nil Einne (talk) 14:40, 8 September 2015 (UTC)

{at|Nil Einne}People paying for a different product is something to be dealt with. I didn't say it's a bug, nor I oversimplified, since I was not analyzing a solution to the problem, just describing the problem to be solved. Calculating how inflation is affecting your concrete assets implies much more than looking at gov indexes. Nimur above is spot on, and the Valuation (finance) + concept of "non-fungible goods" are what I needed to dive deeper.--Yppieyei (talk) 15:27, 8 September 2015 (UTC)

Valuation for physical items (cars, houses, etc...) tends to use averages (as I mentioned above). I work with real estate rentals. We need to know how much we can get for rent before placing something on the market. That is valuation - what is the value of the rental - and knowledge of the relationship between value of a rental property and the actual monthly rental cost. I cannot compare a specific townhouse to itself to get a value. I can't even look at "comparables" - which is a real estate myth used to increase/decrease the cost of a home as needed. What I do is I look at every historical value for a property (sales, rentals, taxes paid, etc...). I take the mean and median average for every property in the area. I compare the property to all the other properties in the area. It may end up being 5% above mean and 12% below median (as an example). I also have a trendline. It may have been at mean and 20% below median two years earlier. Then, I look at actual rentals in the area and compare rental to value for those properties. I will end up with something like rental=value/120. In this case 120 is the factor I need. It will have variance also. If it is a large variance, such as 90 to 150, the area is likely going downhill fast (someone is renting at far too low, bringing in low income renters, causing existing renters to leave) or it is being gentrified (houses are being improved and rent is increasing faster than value has been updated). In those cases, I need to look at the house and decide to go low or high. It is almost always a tight figure, such as 112 to 118. That will result in a very narrow rental margin of something like $950-%975/month. The point being - it is all averages. I do not pick one specific house and use some weird formula to make it comparable to another. I only care about the average money being transferred for sale or rent or taxes, ignoring the type, size, or age of the property. 209.149.115.219 (talk) 18:48, 8 September 2015 (UTC)

If you only want to look at the value of your property rather than general inflation (which is what your older comment implied) then you need to look at things differently but as the IP, Nimur and Jayron32 have said, you're still looking at this wrong. What you actually care about is the value of your property rather than simply inflation. You need to properly understand what you're trying to do, before you have any hope of achieving it. (As various people have mentioned, concentrating simply on the size, rooms etc is also a mistake, in reality the location of the property will make a very big difference. It's also important to understand the state of the market, in some cases the will be much more variability in the price then in others and this will generally matter to you. Similarly in some cases you should expect to have to wait longer to sell then others. And for real estate, there isn't just the sale price, but also what you will make in rent, if you're renting the property. If it's owner-occupier it gets even more complicated. And we haven't even touched vehicles where the age of your vehicle will have a significant effect on the value, particularly initially. When you are talking about the real world, these things matter. Even if you're running a business, you can't just let your stock sit around waiting for a decent price, let alone if you're just an individual and have a reason you need to sell your property. ) And yes, you will always be using averages, even if you have to be specific about what averages you are looking at. Nil Einne (talk) 00:33, 9 September 2015 (UTC)

Do the following:

1) Separate the items into classes of similar items. For cars, you might look at a particular year and model of car, with all the same options, and, in the case of used cars, the same mileage and evaluation of condition. Web sites like Kelly Blue Book help with this part (the VIN will give you most of that info). For houses, do something similar, although they don't fall into classification categories quite as well.

2) Aggregate all those items in the same category together, then compare the change in price over time. You end up with statements like "Three bedroom single-unit homes in the city of X increased in median value by Y % over the last Z years". StuRat (talk) 16:32, 8 September 2015 (UTC)

• In real estate, the ability to value properties depends on what are called "comparables", while no two houses are identical, certain facts about the property (square footage, condition, improvements made by home owners, lot size, etc.) will all go into the ability to value a house. A real estate appraiser would start with a base price based on floor space of house and/or the size of the lot. Then they would add or subtract value based on, for example, having a rebuilt kitchen, or a swimming pool, or needing a roof replaced, etc. All the prices are based on prices of similar houses in a similar neighborhood. This allows them to give a house it's initial value, which may then go up or down depending on market conditions (if the homeowner receives several offers, the initial price goes up. If the house sits on the market with no offers, the price may go down). --Jayron32 16:58, 8 September 2015 (UTC)

Fat goalkeeper to occlude goal?

Is it possible that a football club could hire a person so fat that they could occlude the goal as a goalkeeper? Do any such fat people exist? Given their limited mobility, there could presumably be no very large gaps. 192.41.131.250 (talk) 15:58, 8 September 2015 (UTC)

No human has ever been 8 yds wide! 217.158.236.14 (talk) 16:05, 8 September 2015 (UTC)

(ec) That's the problem with that plan. The goal is 8 yards (24 feet or 7.32 m) wide. Nobody is that fat. StuRat (talk) 16:08, 8 September 2015 (UTC)

It would be even harder if "football" had meant the American or Canadian kind. The goalposts you see here are only about 6 yards (6 m) wide, but they start 10 feet (3 m) above the ground and go up from there. Good thing our football doesn't use goalies. --65.95.178.150 (talk) 00:39, 9 September 2015 (UTC)

Somewhat related, here are some discussions of the potential value (or not) of large goalies in hockey, which has a much smaller goal - [4] [5]. SemanticMantis (talk) 16:09, 8 September 2015 (UTC)

Just a note — hockey doesn't point where you think. It's a sort-of DABCONCEPT article about various sports that are called "hockey", along the lines of football. You need the link to ice hockey. --Trovatore (talk) 19:19, 8 September 2015 (UTC)

An ice-hockey goal is 6 feet wide...the waist measurments of the morbidly obese are not widely documented - but we do know that Michael Hebranko was one of the heaviest people in the world (at 900lbs) - and his waist measurement was 110 inches. Assuming his waist was roughly circular, he'd have a diameter of 35 inches - a little under half what would be needed to fill the ice-hockey goal mouth. Even if he was completely flattened out - you still can't span a 72" goal with two layers of his 110" circumference skin.

So no, not even in ice hockey. To double the waist diameter, you'd probably have find someone four times heavier...the heaviest person on record was an estimated 1400lb - but the heaviest actually recorded weight was around 1000lb - there are absolutely no 3,600lb people!

Not going to work...unless you find a sport with a much smaller goal. (Maybe Rollerball (1975 film)!) SteveBaker (talk) 00:46, 9 September 2015 (UTC)

Sheffield United did actually have a goalkeeper whose primary skill was in his bulk! Fatty Foulkes --TammyMoet (talk) 19:01, 8 September 2015 (UTC)

A little unfair to Fatty, Tammy. If bulk had been his primary skill, I doubt he would have played for so long for such prominent teams, including England. {The poster formerly known as 87.81.230.195} 185.74.232.130 (talk) 13:58, 10 September 2015 (UTC)

Basketball centers are usually the largest and least mobile players that serve the purpose you suggest. But a shortstop accomplishes a similar dunction by being one of the smaller players. There's always going to be a range and domain such that various combinations of size and speed are more effective at guarding a specific area. Ice hockey is interesting as virtually all the skaters are in a vary narrow range of weight and height without a lot of extremes. --DHeyward (talk) 00:56, 9 September 2015 (UTC)

Zdeno Chara may have something to say about that. --Jayron32 01:00, 9 September 2015 (UTC)

Off Topic but amusing: In the earliest days of cricket, there was no law stipulating the width of the bat. One enterprising team brought out a bat that was the entire width of the pitch. Akld guy (talk) 06:53, 9 September 2015 (UTC)

Not the width of the pitch: that would have needed a bat 10 feet wide! Just the width of the wicket: 9 inches.--Phil Holmes (talk) 08:06, 9 September 2015 (UTC)

Yes, my mistake. In some countries 'wicket' is interchangeable with 'pitch' and I jumped to the larger of the two. Still, a 9 inch wide bat would defend the stumps quite well. Akld guy (talk) 08:44, 9 September 2015 (UTC)

Nope. It would defend the wicket, which is comprised of the stumps and the bails. Rather like saying that a goalkeeper tries to stop the ball hitting the goalposts (which is what makes the goal) when they actually try to prevent it from entering the goal (the entity itself).--Phil Holmes (talk) 09:11, 9 September 2015 (UTC)

Use of the word wicket to describe the pitch might be frowned upon by pedants in the cricket world, but it is very common, even amongst cricket players and commentators, and the term sticky wicket has entered the general language. Dbfirs 19:40, 9 September 2015 (UTC)

Civil engineering

Do civil engineers rarely go out on site other than site engineers? 90.192.100.180 (talk) 21:50, 8 September 2015 (UTC)

I don't understand your question. Site engineers are (often civil) engineers that work on site. Civil engineer is the professional title, site engineer is the task assigned within a company.--Scicurious (talk) 22:30, 8 September 2015 (UTC)

I believe they are asking if civil engineers not assigned the task of site engineer still need to visit the work site. StuRat (talk) 02:41, 9 September 2015 (UTC)

It would be rare for a civil engineer NOT to go out on site. Civil engineering activities are rarely based in a laboratory, engine room, power generation station etc. They are mostly based "outside"; therefore the civil engineer observes those activities by going out on site. Dolphin (t) 07:49, 9 September 2015 (UTC)

So, maybe the question was: if a civil engineer is not a site engineer (that means, not part of the site management team), does he rarely go on site?`1234--Scicurious (talk) 15:45, 9 September 2015 (UTC)

Seems to me it would depend on the specifics of the job, company practices, personality (hands on approach..), and standards and regulations. Ssscienccce (talk) 14:20, 10 September 2015 (UTC)