Wikipedia:Reference desk/Archives/Science/2009 November 17

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November 17

Name of process in which complex material things appear from nowhere?

I've just forgotten this term, but I think it had "brain" in there somewhere. The idea is that in an infinite space, or infinite time, or both, you could have anything happen, including our world simply appearing out of nowhere 5 minutes ago. Myles325a (talk) 01:40, 17 November 2009 (UTC)

Infinite monkey theorem? Mitch Ames (talk) 02:06, 17 November 2009 (UTC)
(That's complex structured data of course, not real physical material) Mitch Ames (talk) 02:19, 17 November 2009 (UTC)

Maybe something to do with brane? DMacks (talk) 02:17, 17 November 2009 (UTC)

Boltzmann brain -- Coneslayer (talk) 02:26, 17 November 2009 (UTC)

OP myles back. Yep, it's Boltzmann's brain (or brane) alright. Thanks. Myles325a (talk) 03:06, 17 November 2009 (UTC)

'For God, all things are possible'. Vranak (talk) 17:06, 17 November 2009 (UTC)

Why is urea planar?

I've drawn the Lewis dot structure of urea, and I just don't understand how it can be a planar molecule with a double bond between the carbon and the oxygen. Why don't the two nitrogen atoms have tetrahedral structures? Is there a double bond that resonates among the O-C and C-N bonds? What's going on here? —Preceding unsigned comment added by 134.10.29.252 (talk) 05:08, 17 November 2009 (UTC)

If we're talking about the configuration of urea around the central carbon atom, it would be expected to be trigonal planar since there are no unpaired valence electrons (using one of the simplest approaches to molecular geometry). Of course, if you mean the amine groups, they will have tetrahedal configuration. So, the entire molecule is not planar, but the carbon is.Thanks Jayron32 for setting me straight below, sloppy work on my part. -- Scray (talk) 06:00, 17 November 2009 (UTC)

The lone pair on the amine nitrogens can enter into conjugation with the pi-bond in the C=O. Lone pairs are not confined to any one geometry, so the amines can take whatever geometry will produce the lowest energy configuration. In this case, the ability for the unbonded pair on the amines to enter into conjugation means that the amins will take on sp² hybridization, and the lone pair will occupy an unhybridized "p" orbital. As a result, the entire molecule will be planar. --Jayron32 06:13, 17 November 2009 (UTC)

To Scray: Its an easy mistake to make. If there is not a neighboring sp² carbon to conjugate with, then amines will take the standard tetrahedral sp³ shape, since that is the lowest energy configuration normally. However, the ability of unbonded pairs in the valence level to move freely, and thus change the geometry of the rest of the molecule, is what makes molecules like Imidazole planar (and thus aromatic) as well; the carbon-only analog, Cyclopentadiene, is clearly NOT planar or aromatic. --Jayron32 06:47, 17 November 2009 (UTC)

I was surprised you used Cyclopentadiene as an example - it seems less than "clearly" non-planar. Our article say's it's planar, as reflected in the Talk page discussion. -- Scray (talk) 12:00, 17 November 2009 (UTC)

The carbons are in a plane, but the hydrogens attached to the non-double-bonded carbon (the sp³ carbon) are not in that plane. Thus, while the ring part of the molecule is in the same plane, the whole molecule is not. This is different from Imidazole, where every single atom is in the same plane. --Jayron32 15:00, 17 November 2009 (UTC)

Resonance in amide functional groups is a pretty important thing...it's one of the reasons proteins are fairly stable (one of the most stable types of acyl group). The result—the C–N bond looks a bit like a double-bond—affects the geometry of protein backbones (like an alkene C=C, a C=N cannot rotate freely the way a single bond can). DMacks (talk) 07:00, 17 November 2009 (UTC)

What is a scientific body of national or international standing?

On Scientific opinion on climate change, we're trying to create a FAQ so the watchers and frequent editors don't have to answer the same questions over and over. One such question is What exactly is a "scientific body of national or international standing"? I've posted the answer I came up with here on the article's talk page. However, I am not a scientist of any kind, so I'm not sure if it's accurate. Any comments, suggestions, or feedback I can get from any scientists out there would be greatly appreciated.

An Academy of Sciences or a scientific society that maintains a national or international membership, and that is well-regarded within the scientific community could be said to be of "national or international standing." Discerning how well-regarded a particular scientific body is requires some familiarity with the scientific community. However, in general, this can be determined by the impact factor ratings of the body's journal as provided by Journal Citation Reports. The journals Science, from the American Association for the Advancement of Science, and PNAS, from the US National Academy of Sciences, are considered amoung the world's most influential and prestigious.[1][2][3]

Thank you.--CurtisSwain (talk) 10:14, 17 November 2009 (UTC)

Well, you may need to be clear whether you mean prestigious in terms of membership, or prestigious in terms of publications. The two are somewhat correlated but not synonymous. For example, NAS membership is highly selective, while membership (as opposed to "Fellow"-ship) in AAAS and most such scientific societies is essentially open to any graduate in the field. On the other hand NAS's sister societies National Academy of Engineering and Institute of Medicine, while being selective, do not publish any journal; while prestigious and high impact journals such as Cell (journal) and Nature (journal) are published by private companies. Finally, the prestige of a society depends on its relevance to a particular field; so IEEE may not be as well known as NAS and the Royal Societies, but when it comes to wireless communication standards, its opinion and publications are more relevant than theirs. Abecedare (talk) 10:37, 17 November 2009 (UTC)

For the UK, probably the best suggestion would the the Royal Society. --Phil Holmes (talk) 10:39, 17 November 2009 (UTC)

Yes, figuring out the best examples is easy - most national academies of science qualify. The question is where to set the lower level. Looking at a fairly harmless field, I'd say AAAI qualifies - what about AAR or FLAIRS? On the one hand, FLAIRS is a Florida group, but both AAR and FLAIRS organize internationally attended conferences. --Stephan Schulz (talk) 17:11, 17 November 2009 (UTC)

Your efforts are noble, but they may be in vain; essentially, you're trying to draw the bottom demarcation line of the "gray zone," which is inherently subject to debate. Take a look at Wikipedia:Reliable sources for previous consensus opinions about how to do this. Nimur (talk) 01:08, 18 November 2009 (UTC)

Wow, this is so cool that people have taken the time to help with this. Thank you. I think what Scientific opinion on climate change really needs is some sort of criteria for distinguishing a respected, legitimate scientific body (like those mentioned above) from one of dubious standing (like Oregon Institute of Science and Medicine). Is there a way to do that? It doesn't have to be perfect.--CurtisSwain (talk) 21:54, 18 November 2009 (UTC)

There are numerous problems with trying to categorise organisations in articles. But any smart reader would check out any organisations they don't recognise. Reading the linked article, it doesn't take a genius to figure what kind of organisation "OISM lists six "faculty members,"[1] but does not enroll students or teach courses." In any case, there may be merit to exclude organisations who's opinions carry no weight. And indeed there is no mentioned of the OISM in the article. Oregon Petition is in a see also that's all. But the merits of the petition have only limited connection to the organisation starting it. And the petition article does have criticism of the petition. And more importantly perhaps the intrinsic problems with any petition of scientists is documented in a number of places in wikipedia I'm pretty sure. E.g. Project Steve Nil Einne (talk) 07:12, 19 November 2009 (UTC)

Further digital television enquiry

This is a UK-related TV problem. I posted a few weeks ago about a solution for digital television in my home and had a useful answer, though not the one I was hoping for. I'm still finding it really hard to get objective information about the best solution for my needs. All I really want is to be able to get TV into several rooms in the house (3 rooms at least) in a way that different channels can be watched simultaneously. Only looking for the main free-to-air channels: BBC1 to 4, Channel 4, ITV. We already have digital co-ax running from a central point to those rooms, so distribution should in theory be possible. At the moment we are with Virgin Media and I have a quote for adding two extra digiboxes (installation plus extra subscription), but I want to work out if Freesat is a better option. Not considering Freeview due to poor reception in the area. At the same time, we want to replace two old analogue TVs with new ones. If we get a Freesat dish, then presumably we can distribute the signal around the house easily enough, either with the current (powered) connections, or with a distribution box that I have seen on the Maplins website? Then should the new TVs be Freesat TVs rather than normal digital TVs? They are much more expensive. I assume that normal digital TVs can actually be used in a Freesat system, since analogue ones can. But what about HD? Most sets sold at the moment are HD-ready, but will a typical HD-ready digital TV receive Freesat HD, either now or in the near future? Many thanks if you have borne with this long explanation and can understand where I have got to. The idea of queuing in Maplins for twenty minutes and then having to go through all this to one of their vendors is a bit daunting. Itsmejudith (talk) 11:44, 17 November 2009 (UTC)

I can't answer your query directly, but you may wish to have a look at Digital Spy forums: here's a link to the Virgin Cable one [4] --TammyMoet (talk) 12:23, 17 November 2009 (UTC)

And I Am Not An Expert, but my understanding is that with Freesat you need a tuner for every TV you want to use to view content. So if you have 3 rooms, then you will need a Freesat dish and LNB with at least 3 (I think 4 is common) outputs. These are distributed (I think with co-ax) to where the TV is. You can then either have a Freesat TV (they are more expensive because the satellite tuner is more expensive) or a "normal" HD one with HDMI in. If you get a Freesat HD tuner, I would expect it to have HDMI out, and so you connect them using that. You then have HD sent from the tuner to the TV where you can view it. If you don't have HD/HDMI on the TV, you could use SD with a SCART cable. Think this is accurate and Hope It Helps. --Phil Holmes (talk) 12:32, 17 November 2009 (UTC)

Does help, thanks both. I also spoke to the local Maplins store on the phone, and they are recommending buying a lot of equipment, so it may work out better to stick to Virgin in the short term at least. The devil you know... Itsmejudith (talk) 13:45, 17 November 2009 (UTC)

Bear in mind that TVs (e.g. Panasonic) are starting to appear which have both Freeview and Freesat receivers built-in. Bazza (talk) 14:13, 17 November 2009 (UTC)

Can confirm some correct data above - 3 TVs on Freesat need a dish with a Quad (4) or Octo (8) LNB (and a cable from the dish to each TV - you cannot split them!) A Freesat recorder also needs it's own cable (and if it's a dual tuner, then it needs 2 cables!) Most Freesat TVs have Freeview as well - hence the high price. Remember that when analogue goes off the digital signal will be much stronger - I'm on Lancaster at 200W, last year we lost a whole day's TV while they modified it to be able to go to 2kW on Dec 4th. Also note that a lot of TVs are marked as HD ready - but they only show 720p, only the more expensive ones will do 1080p. Also BBC & ITV intend to transmit a few HD channels on Freeview, but existing boxes/TVs might not be able to decode the signal without a software update. As you say, it may well pay to sit tight until the dust settles.  Ronhjones  ^(Talk) 19:53, 17 November 2009 (UTC)

To clarify, a 720p TV will still display a 1080 channel, just at the lower resolution. StuRat (talk) 22:55, 17 November 2009 (UTC)

The Mystery of Almond Milk

Hello! Almonds are pretty high in calories (nearly 200 per 1. 0z serving), like all nuts. So why is almond milk so low in calories? (30-50 cals per 8 0z. serving, depending upon brand). Since it's made from almonds, you'd think a cupful of almond milk would be about as many calories as a cupful of almonds, but it's not. O_o Anyone know why? 128.239.150.20 (talk) 12:43, 17 November 2009 (UTC)mimosa

It's not as much of a mystery as you might expect. The process produces an almond "pulp" that needs to be watered down to get the consistency of milk. This dilution reduces the fat by volume content. Fribbler (talk) 12:53, 17 November 2009 (UTC)

species diversity

How species diversity affect ecosystem —Preceding unsigned comment added by 61.2.193.124 (talk) 16:59, 17 November 2009 (UTC)

The more species you have the more complex food chain you get. The rest is very much depend on the kind of species, the enviroment they live in and etc. Humans proved time after time that they not fully understand how different ecosystems work (but they do know how to destroy them).--Gilisa (talk) 18:17, 17 November 2009 (UTC)

See Biodiversity. We have a brief article about the measure Species diversity too. Fences&Windows 00:41, 18 November 2009 (UTC)

Scar removal?

I was wondering if it was possible to remove a scar completely.

I know there are treatments to reduce the appearance of them but I was wondering if it is or if there might be potential with new medical technologies to remove scars completely.

Just emphasizing once again, if there is a way through plastic surgery or dermabrasion or something to remove a scar completely. If they are not too deep like the singer, Seal's and just look normal. —Preceding unsigned comment added by 139.62.167.186 (talk) 18:00, 17 November 2009 (UTC)

This sounds like a request for medical advice. The best person to seek to answer your question would be a dermatologist; without an actual live person to actually examine you, it would be impossible for anyone to make a determination on a correct course of action in your unique case. --Jayron32 19:07, 17 November 2009 (UTC)

That doesn't sound like a request for medical advice at all. He is asking if it is possible to do it, not wheather he should do it. I don't think it is possible. Dauto (talk) 19:33, 17 November 2009 (UTC)

Cosmetic surgery can do all kinds of things to reduce the visual impact of scarring, but I've never heard of anything that can remove them perfectly. --Tango (talk) 19:42, 17 November 2009 (UTC)

Given requisite time and resources, your body takes care of business. That includes scar tissue. It re-absorbs the collagen or something of that nature. Vranak (talk) 21:21, 17 November 2009 (UTC)

Really, because I have several scars, some of which I have had for 20 years or more. Googlemeister (talk) 21:35, 17 November 2009 (UTC)

This is why I also said 'resources'. Rejuvenative juices, if you will. Vranak (talk) 22:06, 17 November 2009 (UTC)

That's interesting Vranak. So what 'rejuvenative juices' are you talking about here. I also have a scar that is about 55 years old. Am I lacking some vital process in my body that should have corrected and repaired this or am I the same as the enormous majority of the human race who have life-long scars? Richard Avery (talk) 08:18, 18 November 2009 (UTC)

All I'm saying is that scars can be totally healed. That they commonly don't is not disproof that they can and do. Vranak (talk) 19:44, 18 November 2009 (UTC)

Mucosal scars are much easier to restore to virtual perfection than dermal scars -- you didn't specify type or location of scar. DRosenbach ^{(Talk | Contribs)} 17:36, 18 November 2009 (UTC)

See also, Scar#Treatments_for_skin_scars. "Currently no scar can be completely removed... all treatments will leave a trace." --Mr.98 (talk) 22:58, 18 November 2009 (UTC)

Flying birds that are very weak in the air

Which bird species, whilst being capable of flight is considered to be the worst, or weakest flier? I know that domestic chickens are technically able to fly but even without their wings clipped, they can just sort of flutter about four feet off the ground for a few seconds but I'm not counting these as they are not wild birds. --90.241.8.92 (talk) 18:12, 17 November 2009 (UTC)

Well, there are a large variety of birds that will not fly except when absolutely necessary. I don't know which is the weakest, but birds like peacocks and wild turkeys don't seem to be likely candidates for flying long distance. Falconus^{p t c} 19:20, 17 November 2009 (UTC)

I think you are looking for the albatross. It can glide extremely well, but it has a hard time with takeoffs. Googlemeister (talk) 19:30, 17 November 2009 (UTC)

I will second wild turkeys. Vranak (talk) 21:20, 17 November 2009 (UTC)

According to our article on wild turkeys, they are actually agile flyers, but don't fly far off the ground, and rarely for more than 400m.Falconus^{p t c} 21:28, 17 November 2009 (UTC)

Clapper Rail, Hoatzin. Fences&Windows 00:37, 18 November 2009 (UTC)

The Flying Steamer Duck is the only one of the four Steamer Duck species that can actually fly at all (hence its name): however (although our article doesn't mention this) while smaller specimens of the species can get themselves airborne, the largest and heaviest (usually adult males) cannot. More details can be found in this [5] post on Palaeontologist Dr. Darren Naish's excellent Tetrapod Zoology blog. 87.81.230.195 (talk) 11:29, 18 November 2009 (UTC)

Elevator stuck

A couple days ago, one of my friends was stuck on an elevator for 45 minutes. Apparently he and a large group got on on the first floor, and more joined on the second floor. It just stopped soon after. Unsurprisingly, 18 geniuses on board and 700lbs over the weight limit seemed to be a contributing factor. Anyway, my friend commented to me that it's good they didn't try to force the door open, because it may have caused the elevator to fall. The elevators break frequently here, so my guess is that they only told them that so that in the future they wouldn't try and damage the door mechanism. Surely the engineers would not have designed the safety catches to be dependent on closed doors? How does that work? Thanks, Falconus^{p t c} 18:17, 17 November 2009 (UTC)

Oh, I should mention that I am in the US. I know foreign elevators tend to be different. Falconus^{p t c} 18:20, 17 November 2009 (UTC)

Elevator#Cable-borne elevators is your friend: your suspicions are confirmed - the door thing is a canard. --Tagishsimon (talk) 18:21, 17 November 2009 (UTC)

Alright, thank you. That's what I thought. Now that statistic of 10000 out of 120 billion elevators having even minor anomalies is interesting. In this building, it seems someone gets stuck on an elevator weekly (usually it has little to do with overloading). Falconus^{p t c} 18:29, 17 November 2009 (UTC)

That's 120 billion elevator rides, not elevators. That many elevators would mean we would each have over 20, and I barely even own a dozen. :-) StuRat (talk) 22:43, 17 November 2009 (UTC)

Did your friend notice what was the weight rating and the person limit on the elevator? Edison (talk) 18:49, 17 November 2009 (UTC)

There is no posted person limit, but the weight rating is 2500lbs. I'm not sure if he noticed that or cared until they got stuck, at which point they decided to kill time by adding up everybody's weight. Apparently they totalled 3198lbs. Falconus^{p t c} 19:10, 17 November 2009 (UTC)

Might want to add up to a 5% error margin since a lot of people habitually under report. Googlemeister (talk) 19:28, 17 November 2009 (UTC)

If an elevator is overweight, it's supposed to stand and refuse to even close the doors. So how did they get stuck? It stopped midway? It closed the doors and wouldn't open them? The reason I ask is that it doesn't sound like being overweight was the reason they got stuck. If I were making an elevator I would add at least a 50% margin to the weight limit. Ariel. (talk) 21:47, 17 November 2009 (UTC)

I believe that it started to move and then stopped, leaving them stuck. It wouldn't surprise me though if it was just acting up anyway, because it does that stunt regularly (once a week or so) with only a couple people on it. It's somewhat ironic that these elevators are in the dorm of a very well respected engineering school, but yet they can't even figure out how to maintain them. Falconus^{p t c} 23:11, 17 November 2009 (UTC)

One thing that surprises me is that they don't just make it impossible to overload an elevator with people. For example, if the elevator is 5 feet by 5 feet, I figure it could hold at most maybe 25 people at 200 pounds each, so would make it able to haul 5000 pounds. If it could only haul 3200 pounds, then I'd make it only 4×4. Do they really expect people to start asking each other's weight and adding them all up, before they get on the elevator ? Of course, some idiot could still try to fill the elevator with heavy machinery or something, but at least the common case of too many people would be handled. StuRat (talk) 12:09, 18 November 2009 (UTC)

Presumably, the elevator company's customers are people who are building buildings. If you're trying to make your building as nice as possible (to satisfy your customer) are you going to choose the company that makes uncomfortably small elevators? APL (talk) 15:34, 18 November 2009 (UTC)

Well, if I were hiring an elevator company I sure wouldn't want them to give me elevators that won't work whenever they are full of people, would I ? I'd expect them to provide an adequate lift capacity for everyone who could fit in there. I'd also expect there to be safety regulations which would require this. StuRat (talk) 16:32, 18 November 2009 (UTC)

But for much cheaper, you could get ones that just don't work under the very rare chance that you put too many people in them. If money is no object, you could just get so many elevators people would never have to crowd onto them. — DanielLC 16:35, 18 November 2009 (UTC)

An elevator would have to be very uncomfortably tiny (relative to its weight capacity.) to make it impossible to over-stuff it. See Phonebooth stuffing. Any elevator designed this way would not be pleasant to ride. Normal elevators are usually strong enough to carry people when they 'fill' the elevator with reasonable personal space allowances, but not necessarily if you cram every cubic inch with human flesh. APL (talk) 21:17, 18 November 2009 (UTC)

I seem to recall reading that passenger elevators, for safety reasons, have to be able to stand at least 10x their rated weight. That is, for an elevator to be rated at 2500 lb, it must be capable of functioning safely with a 25,000 lb load. Freight elevators were said to have a 2-5x safety factor instead. Again, I can't remember where I read this, so I can't say it's definitely true, but I would be *very* surprised if the safety margin is sol slim that it can't stand an extra 3-4 people. -- 128.104.112.237 (talk) 17:32, 19 November 2009 (UTC)

I got stuck in an elevator in spain. I was jumping in it and it stopped.18:03, 19 November 2009 (UTC)

"Stand" is a relative term. It means that the cable won't break, the brakes won't fail, and the floor won't fall out of the car. It says nothing about the ability of the motor to lift the car: it's quite possible that the extra load will cause the motor to burn out (or a circuit breaker to trip), stalling the car halfway between floors. --Carnildo (talk) 01:42, 20 November 2009 (UTC)

What's the strongest acid and the strongest base?

What's the strongest acid and the strongest base? Are they known to be the strongest possible, or have there merely been no stronger ones found? --75.6.4.21 (talk) 22:04, 17 November 2009 (UTC)

Fluoroantimonic acid. Vimescarrot (talk) 22:22, 17 November 2009 (UTC)

I'd also like to point out the redirect, strongest acid. Which makes the link for strongest base a little annoying. Vimescarrot (talk) 22:23, 17 November 2009 (UTC)

The answer is somewhat ambiguous, and depends on the definition of 'base' one prefers. Is a base a material which produces hydroxide ions when dissolved in water (the Arrhenius definition), a material which is a proton acceptor (the Brønsted definition), or a material which can act as an electron pair donor in a chemical reaction (the Lewis definition)? You can find some useful discussion in our article on superbase, however. TenOfAllTrades(talk) 22:51, 17 November 2009 (UTC)

Not sure if it is strictly the strongest under all definitions, but tert-Butyllithium is the strongest I have ever worked with. Its particularly unpleasant stuff. --Jayron32 23:08, 17 November 2009 (UTC)

The strongest acid is actually helium hydride Which will add a proton to any other material (apart from a proton). Graeme Bartlett (talk) 01:37, 18 November 2009 (UTC)

That's pretty exotic stuff, though, considering that you can't even keep it in a jar, since it will protonate the material making up the jar. It is literally impossible to handle in any way, and all its properties, save basic spectroscopic properties, are only known theoretically, and not empirically. We can say that it exists, but there is almost nothing else that could be said about it. As far as a substance a person could reasonably consider to handle, the strongest acid would be HSbF₆. --Jayron32 04:38, 18 November 2009 (UTC)

Pretty exotic indeed. I hereby invent hydrogen hydride (H₃), which would even outclass helium hydride :-) DVdm (talk) 08:28, 18 November 2009 (UTC)

The article on this is H3+ or Trihydrogen cation, and it is a weaker acid, HeH⁺ will protonate H₂ to make H₃⁺. Neutral H₃ could only exist as an excimer as it is unstable in the ground state H₃ --> H₂ + H.—Preceding unsigned comment added by Graeme Bartlett (talk • contribs)

Dang, too late! Thanks for the information. DVdm (talk) 21:31, 18 November 2009 (UTC)

Perhaps you can turn your invention into a redirect! Your invention is actually a very common ion in space. Graeme Bartlett (talk) 21:34, 18 November 2009 (UTC)

The Spanish version of a H₃ article exists: es:Hidrógeno triatómico I suppose the English equivalent is triatomic hydrogen. Graeme Bartlett (talk) 11:55, 20 November 2009 (UTC)

Expansion of the universe

If we were to lay a rope from here to some distant galaxy and tie the end there, will it stretch and break because the distance increases but the electromagnetic force overpowers the expansion of the universe within the rope? Or will it just "lengthen" without stretching, expanding along the universe? --78.176.22.9 (talk) 23:12, 17 November 2009 (UTC)

The expansion of the universe is actually overcome quite easily by small forces such as gravity, the effect is not generally visible on anything smaller than the galaxy size; that being said, if you could attach such a rope to said galaxy and hold it to yourself, the two objects would be "bound" and thus would not be suject to the Metric expansion of space. There are some patrollers at these refdesks who hold that the so-called expansion of space isn't real; that its just the objects in the universe moving out into emptiness, but many cosmologists would disagree with that assessment. --Jayron32 00:18, 18 November 2009 (UTC)

So is that to say that the rope is strong enough that it could exert enough force accelerate an entire galaxy enough to overcome the expansion? Rckrone (talk) 00:30, 18 November 2009 (UTC)

In the light of what you have just said, does an object larger than galaxy-size expand within (along?) the space? The article states that the cosmological constant acts as a repulsive force even on individual atoms. So, am I right thinking that the rope that "binds" the galaxies together will be subject to tremendous forces? --78.176.22.9 (talk) 00:47, 18 November 2009 (UTC)

Tremendous forces, yes. But dark energy is largely irrelevant. You'd encounter tremendous force for the same reason that one sees tremendous force if you throw a lasso around a moving car. In other words, simply because it has a lot of momentum from it's existing motion and you are trying to stop it. Dragons flight (talk) 01:17, 18 November 2009 (UTC)

Attach a rope to anything that is currently moving away from you and there are only two outcomes. Either the rope exerts sufficient force to slow and stop the object it is attached to from moving further away (relative to you), or the rope breaks. Same holds at astronomical scales, except it is virtually certain your rope would break for any physically constructed rope. Dragons flight (talk) 01:02, 18 November 2009 (UTC)

Sorry, maybe I should rephrase the question, Forget the galaxies seperating and pulling the rope. Let's just have the rope. Does a rope or rod-like object millions of light years long expand/stretch ordinarily? I mean, does this object experience a force like being pulled from each end? Or does it expand "freely" without "being pulled", similar to relativistic length contraction? Like its "coordinates" moving or something? I'm not a native English speaker, I hope I made myself clear... --78.176.22.9 (talk) 01:33, 18 November 2009 (UTC)

Neither. It doesn't expand. Assuming you laid it out so that the rope was stationary to begin with (and ignoring the self-gravity of the rope) then it would stay that way. Dragons flight (talk) 01:38, 18 November 2009 (UTC)

The electromagnetic forces holding the atoms and molecules together would be more than enough to stop there being an expansion. Even if the rope were long enough for the two ends to be causally disconnected (that is, one end is not within the observable universe of the other end) it still wouldn't be ripped apart since the expansion on an atomic scale is tiny so it is easily overcome by the EM forces and if there is no expansion on small scales there can be no expansion on large scales, since the expansion between A and C is just the sum of the expansions between A and B and between B and C (assuming the points are in alphabetical order). --Tango (talk) 02:50, 18 November 2009 (UTC)

That doesn't seem quite right. The longer the rope is, the more either end is forced to accelerate in order for the rope to remain the same length. There's only so much acceleration the end of the rope can withstand before it simply breaks off. In other words, the very small amount of acceleration needed locally to overcome the tendency to expand is cumulative over the full length of the rope. Rckrone (talk) 03:21, 18 November 2009 (UTC)

Acceleration relative to what? What matters is acceleration relative to the bit of rope it is connected to, which is the bit right next to it. --Tango (talk) 03:28, 18 November 2009 (UTC)

Acceleration relative to a local inertial frame. Assume the first bit of rope is not accelerating in its frame (for example it's the center of the rope). The second bit of rope has to accelerate a little in its frame to stay next to the first bit. The third bit has to accelerate a little to stay next to where the second used to be, but the second bit is also accelerating away from the third bit due to the bond with the first bit, so the third bit has to accelerate twice as much to stay with the second bit. The fourth bit has to accelerate more, etc. Rckrone (talk) 03:46, 18 November 2009 (UTC)

A rope at rest will stay at rest. All local frames are equivalent and it doesn't need to accelerate anywhere. Now creating a rope at rest would be complicated since at least one end of the rope would appear to be moving very rapidly compared to the inertial frame of the local stars, but that's a problem of experimental design, not one of physics. All each bit of the rope knows is that it is at rest with respect to neighboring bits of the rope, and nothing about the expansion of the universe acts in such a way to change that. Dragons flight (talk) 05:22, 18 November 2009 (UTC)

Is it not the case that two very distant inertial objects that start at rest relative to one another will begin to move away from each other? I'm not an expert on cosmology, but that's the impression I got from articles like Metric expansion of space and Cosmological constant. I know there are still a lot of different theories, but I thought there was evidence that the expansion of the universe was accelerating, and not just caused by objects moving away from each other due to inertia. Is this incorrect? Rckrone (talk) 06:44, 18 November 2009 (UTC)

For Hubble expansion they never move. Cosmological constant type dark energy can be modeled as a psuedoforce $F={4\pi \over 3}Gm\rho r$ where ρ = 1×10⁻²⁵ kg/m^3. So at a megaparsec it is the same as applying an acceleration on the rope of order 1 ×10⁻¹² m/s^2, or thirteen orders of magnitude less than Earth's gravity. Any real rope would have sufficient tensile strength to resist such forces. So again, the ends wouldn't move appreciably (just enough to provide the tension to counter dark energy and then stop). Dark energy is only just observable if you consider objects at cosmological scales and assume if has been acting for billions of years. It is not a big force. Dragons flight (talk) 07:15, 18 November 2009 (UTC)

Ok thanks. I didn't realize just how tiny the acceleration was.

However, regarding the megaparsec rope, I think it still would not be able to withstand the kind of tension that would result. The acceleration necessary is small, but the mass that needs to be accelerated is pretty large. Suppose the density of the rope is 0.1 kg/m, then the masses being accelerated are of order 10²⁰ kg, and the tensions involved would be of order 10⁸ N, which is probably more than a rope like that can exert. On the other hand, a real rope has some elasticity. If it could stretch up to 10% of it's original length before breaking, it could be stretching for a billion years before it failed. Rckrone (talk) 19:09, 18 November 2009 (UTC)

Quite true. My answer below was predicated on a rope (tether) of length comparable to cosmological distances; a thought experiment similar to that in Davis and Lineweaver's paper. Such a rope is not something that could ever be constructed physically. The main thing is... expansion isn't a force that would make things expand or contract. Galaxies continue to expand by inertia. Local concentrations of matter easily hold together by their own gravity regardless of the tiny hypothesized pressure from dark energy to accelerate expansion; our galaxy does not expand, for example. —Duae Quartunciae (talk · cont) 07:38, 18 November 2009 (UTC)

Whether inertial objects that start out at rest relative to each other will accelerate away from each other depends on whether the rate of expansion is accelerating or not. The point is, as many people have been saying, is that the expansion of the universe is not a force that makes things expand. It is a description of the large scale motions. Galaxies expand away from each other not because they are being pushed, but because they they started out expanding away from each other. So what about a really long rope that DOESN'T start out expanding or contracting? Expansion is not a force to push on it and change it. However, there are forces to consider; forces that also work to change the rate at which the universe in general is expanding.

In the models of the universe before dark energy was inferred, it was thought that expansion was slowing due to the effect of gravity to pull everything back together again. In this case, the very very long rope initially at rest with respect to itself (zero rate of change of proper distance all along the rope, to get technical) would start to compress (the second derivative of proper distance along the rope is negative). With dark energy, there is a kind of pressure that accelerates expansion; if dark energy is sufficiently dominant (as it appears to be in the current epoch) then the rope will start to stretch.

This does get pretty technical. The best account is probably Davis, Tamara M; Lineweaver, Charles H.; Webb, John K. (2003), "Solutions to the tethered galaxy problem in an expanding universe and the observation of receding blueshifted objects", American Journal of Physics, 71: 358–364 {{citation}}: Cite has empty unknown parameter: |1= (help). —Duae Quartunciae (talk · cont) 07:06, 18 November 2009 (UTC)

Hmm.. what I understand from this is: The universe started with an initial push causing the expansion and that initial push exists no more. But we also have the dark energy, which pushes today and the expansion accelerates.

So, does the rope stretch? 78.176.22.9 (talk) 09:49, 18 November 2009 (UTC)

Yes; you can call the inflationary epoch the initial push; after which everything was flying away from everything else, and the space everything occupies increases in volume also. Once inflation shut down, the universe "coasts", with gravity working to slow the rate of expansion. But (apparently) there's still a tiny little bit of dark energy around, so that after 5 to 8 billion years or so, density has dropped enough that the effects of dark energy actually overcome the effect of gravitation from mass, and the expansion rate starts to accelerate again. Or at least, that's how it looks at present.

But as for the rope, it depends. As has been pointed out, dark energy is really really weak, up until you get to cosmological scales. pretty much any kind of force within a "rope" binding it together would be enough to hold it together just fine.... unless perhaps you have a rope hundreds of Megaparsecs long. The Davis and Lineweaver thought experiment may be more useful. Just think of the end points of rope. Take two galaxies, give them peculiar (local) motion so that the "proper" distance between them has a rate of change of zero, and then release them and just let them coast along with the rest of the universe. Ensure they are far enough apart that you can neglect gravity between them. You can image a rope between them if you like; but the question is, do they start to recede from each other, or remain at a fixed distance?

1. In the empty universe model, they remain always at the same distance from each other.
2. In a matter or radiation dominated universe, the expansion rate is slowing, and the two galaxies actually start to approach. In the long run, they pass through each other and then asymptotically approach the Hubble flow on the other side of the sky.
3. In a dark energy dominated universe (which is the present leading model), the two galaxies will start to recede from each other, with a very slow acceleration.

Full gory details in Davis and Lineweaver (2003). —Duae Quartunciae (talk · cont) 11:13, 18 November 2009 (UTC)

Thank you for your explanation. I found the the aforementioned article (or a summary of it, seven pages long). While the math is above my understanding, the rest isn't gory at all but pretty fun to read, with graphs and diagrams! Thanks again for your time! 78.176.22.9 (talk) 17:17, 18 November 2009 (UTC)

fermentation - what's the correct term for this?

Which is the correct term for one whose profession is fermenting? Fermenter OR fermentor? (I'm not interested in other synonyms) I already checked multiple dictionaries. ike9898 (talk) 23:25, 17 November 2009 (UTC)

This question stands a better chance of being answered at the Language Desk. You might try moving it over there. --Jayron32 23:46, 17 November 2009 (UTC)

Brewer. 75.41.110.200 (talk) 01:33, 18 November 2009 (UTC)

Narrower term of Brewer or Vintner. Graeme Bartlett (talk) 01:32, 18 November 2009 (UTC)

Dunno if it exists, but zymurgist would suit. From zymurgy. [6] --TammyMoet (talk) 11:05, 18 November 2009 (UTC)

It depends on what you're producing via fermentation. If it's beer you're a brewer, if it's wine you're a vintner, if it's bread you're a baker. If it's vinegar, cheese, or something else, then I'm not sure if there's a specific name, but the general terms zymurgist and zymologist might apply. StuRat (talk) 11:59, 18 November 2009 (UTC)

Thanks, but I said I wasn't interested in synonyms. ike9898 (talk) 18:53, 18 November 2009 (UTC)

It's also worth noting that there are a number of words that end -er and -or with no correct one. Adviser/advisor, for example. --Phil Holmes (talk) 15:45, 18 November 2009 (UTC)

Merriam-Webster does not indicate the usage of either word for the person doing the fermenting; they have fermenter as the organism that causes fermentation or an apparatus used in fermenting, and they indicate fermentor as an alternate spelling for the second definition only. The -or suffix is usually confined to meaning "a person who does X", while the -er suffix can be used in many other ways. As Phil Holmes indicates, there is likely no "correct" answer, and of the synonyms provided by others (although you clearly said you weren't interested in such) might be more precise. --LarryMac | Talk 16:04, 18 November 2009 (UTC)

Thanks, this helps! ike9898 (talk) 18:53, 18 November 2009 (UTC)

snowboard jump equation/formula

if i were to snowboard straight off an 8 foot tall ledge at about 7mph how far from the ledge would i land given there tas no wind and i rode right off the edge w/o jumping?. what would the formula be for this? ihave been trying to find it but all the equation i have found are extremly complicated. thanks for the help --99.89.176.228 (talk) 23:27, 17 November 2009 (UTC)

The vertical motion and the horizontal motion can be considered separately. In the vertical direction you start with no velocity, but there's acceleration from gravity pulling you down (about 32 ft/s²). Given that figure out how long it would take to fall 8 feet. In the horizontal direction you start with a velocity of 7 mph (you should probably convert that to ft/s), with no acceleration. Figure out how far that would get you in the horizontal direction during the time it takes to fall. Rckrone (talk) 23:41, 17 November 2009 (UTC)

(edit conflict)Everything has the same acceleration downward while falling thanks to gravity, and that is 9.8 m/s². In order to figure out how far you would land you need to first figure out how long you would fall for, which is given by the equation h=.5at² where h is the height, a is the acceleration due to gravity, and t is the time taken to fall. Make sure your units are correct! 9.8 m/s² is roughly 32 feet/s². Next, you just have to multiply your horizontal speed by the time you have to move before hitting the ground (again, making sure your units are the same - convert mph to feet per second) and then you'd have a good estimate! ~ Amory (u • t • c) 23:41, 17 November 2009 (UTC)

It's slightly more complex than that. All decent snowboard and ski jumps are sloping, usually quite steeply, in the landing zone, so as to minimize the impact. Jumping onto a flat is quit difficult, unpleasant, and dangerous, especially if you start with an 8 foot drop. So for a real answer, we would need a better specification of the slope. --Stephan Schulz (talk) 00:07, 18 November 2009 (UTC)

No i wouldnt jump the ledge onto flat ground so me and my friend were going to make a landing ramp. i needed to know the distance so that i dont missjudge the jump and miss the landing.I also needed to know this so that i can angle the jump to minimize the impact of landing. Is there a straight clear forward formula to find all these things out such as a formula i can enter into a graphing calculator?--99.89.176.228 (talk) 01:00, 18 November 2009 (UTC)

All the equations you need are found at Trajectory of a projectile. It is probably worth calculating the sensitivities to various parameters, if you are really building a ramp - i.e. "what would happen if you mis-estimate the slope by 10%?" "What would happen if you miscalculate the initial velocity by 10%? 50%?" This is called sensitivity analysis and can become very complex, but you can do a simplified version by varying your inputs to the formulae. This will help you design a safety factor into your ramp. Also keep in mind that simplified ballistic equations don't account for non-point-like, non-spherical humans - you have significant air resistance, rotational inertia, non-rigid dynamics, etc. All of this should be considered - at least, in the simplest sense, by having a robust safety factor. It would be a big error to assume that you will exactly land at a particular spot unless you are a small marble in a vacuum chamber launched by a precisely calibrated launcher at an exact velocity and angle. Nimur (talk) 01:18, 18 November 2009 (UTC)