Wikipedia:Reference desk/Archives/Science/2010 January 6

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January 6

How the hell do people get AIDS?

While reading the article on AIDS I came across a chart the listed the chances of getting HIV based on a particular type of contact with an infected source. If the person I am having sex with has AIDS, I only have a 5 in 10,000 chance of getting it...and considering that the HIV infection rate in the US is less than 1 percent, it would mean statistically I could have sex with a random person 200,000 times before I get AIDS. I think there is a better way of saying this. Obviously I could get it after one time, but I think that statistically if I have unprotected sex 200 000 times, I would be just as likely to get HIV as not. So...how do people get AIDS??? Is everyone else just getting laid *way* more than I am? XM (talk) 06:50, 6 January 2010 (UTC)

The error in your assumption is that the distribution of HIV-positive people is uniform, when it clearly is not. Certain (cultural/ethnic/income/sexual orientation/age) subsets of any population have infection rates many times higher than the overall average. Conversely, certain subsets have rates many times lower. 218.25.32.210 (talk) 06:56, 6 January 2010 (UTC)

To make an extreme example - you could (probably) have all the unprotected sex you wanted with Mormon Octogenarians in Salt Lake City and never approach the likelihood of contracting HIV that someone in Sub-Saharan Africa has after one encounter. 218.25.32.210 (talk) 06:59, 6 January 2010 (UTC)

Look at it from the point of view of disease propagation. In order to spread HIV only needs to infect, on average, slightly more than one person for every person that it kills. Given that the median time to death for an untreated HIV infection is 10 years, most of which time is asymptomatic, it is not so crazy to think that an HIV+ person can manage to have enough sex to infect at least one other person. Add to that higher infection rates from the (mostly) historical problem of contaminated blood transfusions and the ongoing problem of sharing needles by drug users, and it it is not that hard to see why HIV continues to spread even though it does not do so very easily. There are about 40000 new HIV diagnoses per year in the US. There are also about 450000 Americans known to be living with HIV (according to the CDC). Given a ten-year prognosis, if they were all untreated, HIV/AIDS would have already come close to a standstill since about 1/10 of the known cases would be expected to die each year. So, we've made progress. Hopefully we'll eventually see new infection rates fall as well, but we aren't there yet. Dragons flight (talk) 09:20, 6 January 2010 (UTC)

why 5 in 10,000? Why not just say 1 in 2,000? (or is there some reason we can't reduce the fractions?) 194.221.133.226 (talk) 09:30, 6 January 2010 (UTC)

You can reduce it. It's just that the chart in HIV happened to scale everything in per 10000 event terms. Dragons flight (talk) 10:12, 6 January 2010 (UTC)

I would surmise that the robustness of your immune system has a lot to do with transmission probability. I mean, it's pretty obvious isn't it. :) Vranak (talk) 11:26, 6 January 2010 (UTC)

So this 5:10,000 (1:2,000) chance is per time you have 'normal' unprotected sex. If you do so at an 'average' rate of 2.5 times per week (I believe that's about the rate for humans in their sexually active years) then you're doing this 142 times per year. So your chance of getting the disease is now 1:14 per year. Over 14 years of sexual activity - you odds of getting the disease are close to a certainty. Do this experiment for me. Take two normal 6 sided dice. Roll them and add up the numbers. If it comes up '4' you just got AIDS...now roll them again - if it comes up '4' you get AIDS next year...keep rolling the dice. How many years did you get away with it? Of course, you could easily roll a 4 the first time...bad luck...you might get away your entire sexually active life without ever rolling a '4' but it's not really likely is it? SteveBaker (talk) 14:15, 6 January 2010 (UTC)

Also looking at the source quoted [1] 0.04% rises by a factor of ten-ish if your partner has started developing any symptoms, either of you had genital ulcers or it is male-male intercourse. I guess checking the gender of your partner is the onyl one of these you'll be sure of. The only friend I knew who was confident about the risks being small died in 1997 leaving a three year old daughter. --BozMo talk 14:30, 6 January 2010 (UTC)

To be specific, 1 in 2000 is the reported risk for a male to receive HIV from penis-to-vagina intercourse with an HIV positive woman. That last bit is highly relevant. If you limit your partners and have confidence in their disease-free status, then you can greatly reduce your odds of infection. Of course if you have sex three times a week with a different stranger each time, then your odds of infection go way up. Dragons flight (talk) 14:47, 6 January 2010 (UTC)

Additionally, circumcised males vastly reduce their chances of contracting HIV via sexual transmission because of the reduction of mucous membrane surface area. DRosenbach ^{(Talk | Contribs)} 23:49, 6 January 2010 (UTC)

I think it is important to emphasise that it reduces the chances, it doesn't eliminate them. (I know you didn't say otherwise, but I don't want anyone to misunderstand you.) --Tango (talk) 01:57, 7 January 2010 (UTC)

Properly using a condom of course reduces the chances even more Nil Einne (talk) 05:11, 8 January 2010 (UTC)

Climate Change and work done by Professor Cox at Princeton University USA

Perhaps Peter Robert Cox (apologies if I have the name wrong) of Princeton University USA could look at a global warming problem for me? It involves the spreading of the weight of the earth as we move around in space, our spinning, our magnetic field orbiting our sun. I put the question to Professor Cox, what happens to Earth, when our ice changes to liquid and the magnetic fields change? Where will the equator be? where will the 8 meters (i believe you mentioned as an estimate) of water level be? how many hundreds of millions of we humans will be effected? i.e. thats if we don't start to address the problem that many be no longer then a centry away from happening? When we go into the next iceage, where will the "new ice caps form? ...think thats enough for the moment haha.....have much more though.

Wouldn't the main problem facing the human race be the distribution of excess water as opposed to carbon emissions? first and foremost water distribution across the globe to dry but fertile areas of the land mass to enable the mass planting of forests and crops, that would not otherwise survive without the water. Wouldn't that be the first problem to tackle? By changing the effect of more water in our seas to a plus you then can tackle the continuing effects of carbon emittions through the use of the water? You could also address the sea level by redirecting rivers back inland, the mass closing off of rivers across the globe that flow into the sea (the greenies would hate me, but i'm one myself). Create inland canals, storage areas for water across the globe, redirect human population from the cities to the inland water storage areas. Create towns and cities where the water supply is. Also harvesting sea water from the oceans as the human water supply will lesson the impact of the melting of the icecaps. The more the icecaps melt the more the sun's heat will pentrate the earth,(less reflection) therefore the meltdown of the ice may occur faster then we estimate. I would appreciate it if you could let me know what you think. If you have time you may contact me at <email>. Regards I like you work todate. Barry Harrison <phone> —Preceding unsigned comment added by 203.51.38.97 (talk) 07:29, 6 January 2010 (UTC)

Phone and email removed from public post for the protection of privacy. Dragons flight (talk) 07:40, 6 January 2010 (UTC)

• Hello and welcome to the the Wikipedia Reference Desk. This is a free service intended to help answer visitor questions. Volunteer(s) will be along shortly to attempt to address the questions you asked. However, you should be aware that we do not have any special connection to Peter Cox of Princeton, and we do not generally forward questions to outside parties. In addition, answers to questions will be posted directly on this board and we do not generally provide answers by email or phone. Dragons flight (talk) 07:49, 6 January 2010 (UTC)

• The oceans cover about 70% of the surface of the Earth. If you want to reduce sea level by one meter, you would need to flood all the land to an average depth of more than 2 meters. The Greenland ice cap that will, if completely melted, cause about 7m of sea level rise, now is kilometers thick. What's more, all that extra water is unlikely to end up where you want it. There is no guarantee that now dry areas will receive more water (although some may). On the other hand, despite a higher sea level and likely higher overall precipitation, some areas may dry up further. --Stephan Schulz (talk) 12:26, 6 January 2010 (UTC)

Indeed - we have no connection to Princeton - if Mr Cox happens to be a Ref Desk volunteer (it's hard to tell with all of the psudonyms around here!) then he might answer - but the odds of that are pretty small! Let me break up your many questions to make them easier to address:

1. "what happens to Earth, when our ice changes to liquid and the magnetic fields change?" Firstly, the business of the magnetic field 'flip' is nothing to do with global warming. Many scientists believe we are due for such an event sometime soon because they have historically happened on average once every 300,000 years - and it's been 750,000 years since we last had one. However, the 300,000 years figure is only an average - sometimes the earth goes for millions of years without such a flip - so the probability of it flipping in our lifetimes is not very significant. So the two events are not correlated. However, when the magnetic field flips, it "briefly" (in geological time) turns off much of the earth's protection from solar radiation - which would be "A Bad Thing".
2. "Where will the equator be?" - right where it is now! Our compasses would all point in the opposite direction - but that doesn't affect the path of the earth around the sun or our axial tilt (which determines where the equator is). It's only the magnetic field direction that flips - not the entire planet. All of that water sloshing around also cannot make a difference - the earth is well over a million meters across and the sea level rise is "only" 5 to 20 meters - so this is a negligable change to the shape and balance of the earth - nowhere near enough to make an appreciable change to our orientation with respect to the sun.
3. "where will the 8 meters (i believe you mentioned as an estimate) of water level be?" - everywhere that is currently less than 8 meters above sea level. If you own ocean-front property...well, it's gonna be under 8 meters of water. If you live 100 meters above sea level - then the ocean will be closer - but you're not gonna get wet.
4. "how many hundreds of millions of we humans will be effected?" - That's hard to estimate. One problem is that we don't know the extent of the problem. The number "8 meters" that you are quoting is an estimate. Other estimates range from about 2 meters to about 20 meters. Clearly, the number of people who are affected will vary immensely between those two extremes. However, this word "affected" is a tricky one. When the climate changes, every human on the planet is "affected" somehow. So the answer is "All of us"...the real question is not "How many?" but rather: "To what extent?".
5. "i.e. thats if we don't start to address the problem that many be no longer then a centry away from happening?" - it's already happening. The polar ice is visibly reduced - polar bears are going extinct - glaciers around the world are vanishing. People living near large bodies of ice and snow are experiencing rapidly rising river levels - and will soon be witnessing dramatically reduced river levels when it's all melted. This is happening TODAY. Arguably the disaster that struck New Orleans with hurricane Katrina is at least in part due to global warming because the intensity of hurricanes is worsening.
6. "When we go into the next iceage, where will the "new ice caps form?" - Well, we might have been due for an ice age over the next few thousand years - but it's not gonna happen. Global Warming is not the kind of thing that causes ice ages!
7. "Wouldn't the main problem facing the human race be the distribution of excess water as opposed to carbon emissions?" - well, there are other effects too - that CO2 will dissolve in the oceans forming carbonic acid - so the acidity of the oceans will rise and that will have other deleterious effects. But certainly the most obviously apparent effect will be the rise in ocean levels. But the increased temperature is having other effects too - the migration of animals, the places where temperature-sensitive plants will grow is changing. There are many, many other effects that are not directly related to sea level rise. I very much doubt that we've explored all of the problems we're going to see - the world is just too complex for that.
8. "first and foremost water distribution across the globe to dry but fertile areas of the land mass to enable the mass planting of forests and crops, that would not otherwise survive without the water. Wouldn't that be the first problem to tackle?" - Sadly, no. The water is flowing out of the ice caps into the ocean. The ocean is very salty. When the ocean levels rise, that doesn't increase the amount of fresh water available for watering fertile areas of the world! To the contrary, the inundation by the sea kills off crops and makes it impossible to grow plants close to the water in flatter areas. There aren't many (if any) trees that grow well in salt water.
9. "By changing the effect of more water in our seas to a plus you then can tackle the continuing effects of carbon emittions through the use of the water?" - It's not a "plus" - it can't be changed into a plus. It's a gigantic minus! In fact, the rise in ocean levels results in lighter colored parts of the world being covered by darker colored water - that actually INCREASES the amount of absorption of heat from the sun and accelerates the entire process.
10. "You could also address the sea level by redirecting rivers back inland, the mass closing off of rivers across the globe that flow into the sea (the greenies would hate me, but i'm one myself). Create inland canals, storage areas for water across the globe, redirect human population from the cities to the inland water storage areas. Create towns and cities where the water supply is." - well, rivers flow downhill and empty into the ocean. When the oceans rise by (let's say) 10 meters - that's a lot like lowering the heights of all of the hills and mountains by 10 meters and making them shorter by whatever distance the ocean gets closer. That makes using rivers that much harder. But redirecting a long river is a matter of moving gargantuan amounts of dirt and rock...it's very difficult to do on a large scale. I don't think that's really a viable plan. Besides, the water has to go somewhere - even if humans use it, the waste water has to go somewhere. The amount of water produced by the melting of the ice caps is unbelievably huge - you couldn't remotely come close to digging enough lakes to hold it all!
11. "Also harvesting sea water from the oceans as the human water supply will lesson the impact of the melting of the icecaps." - not by any measurable amount. Again, even a modest 2 meter rise in ocean levels would require us to build (say) 12 meter lakes over half the surface of the land to hold it all - and dumping 12 meters of dirt and rock over the remaining half! It's a totally infeasible way to handle the problem. You have to get a grasp of just how huge the oceans are...they cover 70% of the earth's suface - when that much area increases in depth by even a few meters, the increase in volume is spectacular. The oceans cover 360,000,000 square kilometers - multiply that by 2 meters and you get 7,200,000,000,000,000 cubic meters of water. Seven million CUBIC KILOMETERS. Imagine a cube of water half a mile high by half a mile wide...that's a mind boggling thing...more water than a really REALLY large lake. Now imagine seven million of those. That's how much water we have to get rid of at a minimum. The worst-case estimate is for around a 20 meter rise - which is 70 million cubic kilometers. Digging 70 million vast lakes and redirecting our rivers to fill them is beyond crazy!
12. "The more the icecaps melt the more the sun's heat will pentrate the earth,(less reflection) therefore the meltdown of the ice may occur faster then we estimate." - yes, but scientists who are working on the problem are well aware of that issue. There are others that make matters worse too. Water (like most materials) expands when heated. As the planet warms up, the amount of expansion of the water in the oceans right now is enough to produce massive flooding - even if the ice caps didn't melt. Then there are a bunch of other effects - the possible melting of the deep ocean "methane clathrate" deposits - which would dump a bunch of methane into the atmosphere. Methane is an even worse greenhouse gas than CO2 - so that would make matters MUCH worse!

It's good that you're thinking about this - I wish everyone would do that - and ask questions about the bits they don't understand. SteveBaker (talk) 13:52, 6 January 2010 (UTC)

Regarding point 2, actually if you remove 20 m worth of sea level from Greenland and West Antarctica, the redistribution of mass is expected to shift the Earth's rotation axis about 500 m. Not much compared to the 40000 km circumference, but still very measurable and enough to have secondary effects on the distribution of meltwater. Dragons flight (talk) 14:25, 6 January 2010 (UTC)

Regarding number 6, one of the problems with many models of climate change and global warming is that they predict larger swings between climatic maxima and minima. In simpler terms, while on average the world may be getting warmer, there will likely also be greater variation between the hotter hots and colder colds; so that one symptom of global warming may be some "ice ages" of a few decades or a few centuries, followed in rapid succession by some very hot decades or centuries. Rather than gradual changes of slowly warming up or slowly cooling down, we may anticipate wild swings and unpredictable changes from year to year or decade to decade. The climate-change-deniers like to point at this sort of thing and say "See, you don't know what you are talking about, because you don't know whether its going to be warmer or cooler" Actually, that's kinda the point. In a world with stable atmospheric levels of greenhouse gases, then the system is more predictable. With the rapid changes in atmospheric chemistry we have been experiencing over the past century or so, the system becomes chaotic in ways that make it harder for us to prepare for it. See also Runaway climate change which touches on some of these issues, and also discusses some historical examples of periods in the past when we had wildly variable climate. --Jayron32 18:49, 6 January 2010 (UTC)

Regarding point 3: the extra increase in sea levels may well be uneven. You could have a semi-permanent sea surface height anomaly stretching from Jakobshavn Isbrae to Boston, for example. Changes in ocean currents would also affect local sea levels, as is the case in the Pacific where the sea levels are around half a meter higher in the west than in the east due to the Walker circulation and cold Humboldt Current. Global warming may well disrupt these ocean currents, causing more sea level rise than in others. Also, the effects of erosion from sea level rise, storm surges and tidal action could cause unstable cliffs to fall into the ocean, and the effects of subsidence in some areas will have an effect on this as well, while in other places isostatic rebound will negate most of the sea level rise. Seawater filling into large depressions will have the effect of temporarily displacing some of the rise in sea levels. Also, sea level rise estimates depend on the timescale on which the changes are forecast. Normally the forecast is for the next 100 years, and during this period sea level rise could be anywhere from half a meter to two meters, but "tipping points" could pass, for example the Greenland Ice Sheet (7 m) or the West Antarctic Ice sheet (6 m) collapsing that would result in higher sea levels in a relatively short amount of time.

Regarding point 4: if I recall correctly, a 10-metre rise in sea levels would displace roughly 640 million people based on present-day populations. Since much of the change will be occuring in developing nations, that number over 100 years could easily be far higher. Here is a map roughly showing the projected sea level rise innundation for units up to 14 meters, but "flooded" areas not connected to another flooded area that meets the present-day ocean will likely not be flooded at that sea level. Sea level rise is not the only threat, for there is also desertification, water/food shortages, and even resource wars that would displace more people. Billions of climate refugees is a distinct possiblity.

Regarding point 5: global warming is occuring now, and many thousands of species have already gone extinct. But we often don't hear about the human aspect of the damage, where in developing nations food and water shortages are already having an effect on populations. The Second Chadian Civil War and Darfur crisis, for example are sparked by water shortages. In Kenya, gunfights have broken out over evaporating waterholes and families have resorted to sending their daughters to prostitution as farming no longer produces enough food and charcoal doesn't make enough money. Right now, global ocean currents are slowing down due to a combination of climate oscillations likely stemming from global warming that have allowed cold Arctic air to flood deep into the interior of Northern Hemisphere continents. This situation is getting worse as the current state of El Nino progresses.

Regarding point 6: global warming is not likely by itself to trigger another ice age, but the shifting of ocean currents could easily plunge Western Europe into a much colder climate. However, another long ice age is likely inevitable, as Earth's orbit around the sun does not change, and we still undergo Milankovic cycles, and negative feedbacks are likely to take over once the driver of global warming, an increase in greenhouse gases, ceases to increse. Not to mention other possible effects like the eruption of the Yellowstone Caldera that would plunge the planet into a state of colder climate.

Regarding point 7: there will be on average more precipitation, but more of it will fall over the oceans and less over continental interiors. This threatens water supplies for many places around the world, for example around the Colorado River basin. The 2007 book Dry Spring (ISBN 1551928140) addresses this issue for a timeframe of within the next 25 years, mostly for North America.

Regarding point 8: see saltwater intrusion. ~AH1^(TCU) 00:08, 10 January 2010 (UTC)

Anti nuclear anti bodies

what is anti nuclear anti bodies? —Preceding unsigned comment added by 59.92.141.29 (talk) 07:52, 6 January 2010 (UTC)

See our article Antinuclear antibodies. --Thomprod (talk) 12:35, 6 January 2010 (UTC)

Rice type

Is there a rice or rices that will grow in salt marshes and moderate climate? 71.100.3.13 (talk) 08:06, 6 January 2010 (UTC)

Pokkali Rice grows in salt marshes, but I don't know how warm it needs the climate to be. --Sean 15:32, 6 January 2010 (UTC)

Rice also grows in Northern Ontario, I think. ~AH1^(TCU) 20:57, 9 January 2010 (UTC)

Physics and Chemistry

I'm in a joint physics and math undergraduate program now, but I'm thinking of switching into a joint physics and chemistry progam instead (this program is still primarily intended for physics students). I've done a quick googling of condensed matter physics (which the program intro lists as one of the areas falling within the intersection of physics and physical chemistry), and while it is apparently the most active area of research in physics, most of the work I've found seems to be experimental rather than theoretical, and I'm really only interested in doing theoretical work. But at the same time, it also appears that the same is true in other disciplines of physics, such as particle physics (although this may be due to the ineffectivness of my google-searching). Is it just me, or is there little important theoretical work left to be done in physics? If not, what fields of physics (other than string theory and the like) are active areas of theoretical research, and what sort of research could I look forward to if I went into physics and chemistry? Thanks. —Preceding unsigned comment added by 173.179.59.66 (talk) 09:29, 6 January 2010 (UTC)

From time to time it may seem that physics is pretty much all wrapped up and that "the great advances lie in the tenth decimal place" (anyone got a source for that quote?), but I think it's unlikely. The universe is bound to hit us with some big surprise some time soon. Quantum gravity still needs some work. — PhilHibbs | talk 14:51, 6 January 2010 (UTC)

A A Michelson, Light Waves and their Uses, University of Chicago, 1903. [2]. Michelson presented the quotation _as_ a quotation (that is, he appears to be quoting someone else), but there isn't a definitive source for an older version. "Sixth place of decimals", incidentally. Tevildo (talk) 18:00, 6 January 2010 (UTC)

There is theoretical work done in all areas of physics, and experimental work in nearly all areas. That said, a great deal of the theoretical work gets done by people that would generally be classified as experimentalists because their primary work is to collect new data and only a minor portion of their time goes towards developing the theoretical understanding of that data. True theorists, i.e. people who never manage experiments are relatively less common. My experience would suggest there are probably three or four experimentalists for every pure theorist. And its a distinction that has been muddied in recent years with the advent of computer technologies for theoretical modeling. Someone who designs computer models to predict the properties of new chemical compounds would probably be called a theorist though such a person might be closer to an experimentalist in many ways. There are several reasons that pure theorists are less common. For one it is harder. The easiest experimental projects are little more than exercises in applied technology, where one can produce useful science through the repeated application of straight-forward (though technically challenging) processes. That alone can be enough to justify a career if done well. By contrast, a theorist's career depends on developing a legacy of useful and novel insights. The path to doing that is far less obvious. Secondly, it tends to be easier to justify funding things than funding people (even though people can be considerably cheaper). For example, throwing a million dollars at the characterization of high temperature superconductors seems sure to produce something tangible at the end. By contrast, throwing $100k at a theorist to think about loop quantum gravity may or may not ever be useful. Even at the graduate student level it is much easier for experimental projects to offer financial support to students than for theorists to do so.

Because of such factors as those above, I would say that many students with theoretical leanings still end up getting involved in experimental work. And let's not kid ourselves, there is a lot of theory that can go into experiment design and data analysis if that is what one chooses to do. The kind of people that go into physics theory these days (with some exceptions) tend to be very talented mathematicians who coincidentally tend to be terrible at experimental work. There certainly still is a place for a people with a deep understanding of mathematics and birds-eye view of physics, but its not any easy field to get into or do well at. If you are dropping the math double out of a dislike for math (rather than say a love of chemistry) then you probably wouldn't much like modern theoretical physics anyway since it is extremely oriented towards mathematics.

You are right that condensed matter physics is an active area of research. In part this is because it has a relatively large number of near-term applications, far more so than more basic lines of research, and hence condensed matter can more easily attract funding from commercial interests looking for practical solutions in addition to the general funding available for basic research. Most theory done in condensed matter these days is probably of the computer modeling kind (i.e. predicting and explaining material properties through modeling). Deep theoretical insights, such as BCS theory still occur, but would be relatively rare.

At the intersection of physics and chemistry, in addition to condensed matter (see also physical chemistry, materials science), you also have problems in designing new compounds and synthesis processes (a subset of so-called chemical physics), and also applications to areas like biophysics and medicine with the understanding of cellular processes (you'd need to get involved with biology to go those directions). Dragons flight (talk) 15:17, 6 January 2010 (UTC)

First off, thank you for the swift and detailed response.

Now, I don't have an aversion to math at all, but I found some of the math courses I was taking to be a bit tedious. For instance, I had a class in algebra, dealing with fields and rings and so on, and I really couldn't see how it would have any application in physics, so I decided to drop the math part of my program. Right now I'm either switching into pure physics or phys and chem, and I would appreciate any imput as to which one I should pursue. And at the same time, I'm not reluctant to do experimental work, I just don't want to end up just doing experiments, in a way that detaches me from the real physics. Ideally, I would like to spend most of my time thinking about physics in an armchair with some paper and a pen, rather than filling in experimental holes. I looked into this chemical physics business, and from the wikipedia article it appears that this remains a field with theoretical questions to be probed. But looking at some articles published in chemical physics journals, it seems most of the practitioners are chemists, rather than physicist. Are either of these assements correct? Finally, these pure theorists you mention; are they found in all subfields of physics, or just in string theory, loop quantum gravity, and so on? Much thanks. —Preceding unsigned comment added by 173.179.59.66 (talk) 23:09, 6 January 2010 (UTC)

Well, first the bad news, field theories in the mathematics sense are massively important for cutting edge particle physics and string theory, and to a lesser degree quantum mechanics in general. Take a look at Standard Model and gauge theory. Now, of course, there is a lot of ground in the advanced theory of algebras that physicists never use, but the parts that do get used are essential and can get quite deep. In fact, Edward Witten, a leading string theorist was awarded the Fields Medal (the highest prize in mathematics) for the development of new mathematical techniques and theorems needed to understand string theory.

There are theoretical positions in all areas, but far more in the areas of string theory, particle physics (and its cousin particle astrophysics), quantum mechanics, and general relativity. In large part this is because these are areas that are highly amenable to further advancement through mathematics alone. If you really want to be a paper and pen type of theoretical physicist, then the easiest path is to master the deep mathematics relevant to one or more of the highly theory-inclined specialties. By contrast, areas like biophysics, geophysics, chaotic dynamics, fluid dynamics, and ultra-low temperature physics tend to skew towards experimentalists (though you can find theorists in those areas too). Things like condensed matter, cosmology, and thermodynamics are more intermediate.

With respect to the chemistry, I think chemical physics probably is more chemists than physicists (though certainly not exclusively so), and yes there are avenues for theoretical work. In principle, the foundations of chemistry are entirely described with early twentieth century quantum mechanics. In practice, almost no system involving more than two components can be solved exactly, so there is a lot of computational modeling and theoretical approximations in the hope of making useful predictions. And of course condensed matter added a whole further level of complexity. Being able to predict the properties of substances not yet synthesized is both an art and a science.

Personally, I would recommend figuring out what it is about physics that you love and follow that direction as much as you can. Making a career as a theorist is hard and competitive. Unless you love what you do it is unlikely that you will manage to put in the time and dedication necessary to be really good at it. Maybe chemistry does that for you, and maybe not. Maybe it is the mystery of the universe stuff, and you really should pursue string theory, or cosmology, or something. Or maybe you just like having interesting problems to solve, but don't really care about the field they are in (a not uncommon condition for physicists). In that case, you might consider leaving academia entirely; industries like management consulting actively hire physicists (at BS, MS and PhD levels) as technical problem solvers. It's much more lucrative but still caters to the urge to solve problems. Dragons flight (talk) 03:06, 7 January 2010 (UTC)

So are most physicists required to know a computer language or not? Sagittarian Milky Way (talk) 17:27, 6 January 2010 (UTC)

"Most"? Absolutely. Not all professors do, but it would be quite unusual for a new physics PhD not to be able to program at least within a scripting language like Matlab if not also in a compiled language like C++. Dragons flight (talk) 19:00, 6 January 2010 (UTC)

The article Computer literacy gives a good general account of what is expected. Cuddlyable3 (talk) 21:17, 6 January 2010 (UTC)

Regarding the original question, I strongly recommend taking a graduate level introductory quantum mechanics course before making a final decision, if you can. It's needed for just about any advanced theoretical physics or chemistry, and after taking it you'll have a much better sense of where you want to go. Looie496 (talk) 21:55, 7 January 2010 (UTC)

LMC/SMC Not orbiting Milky Way?

http://www.astronomynow.com/news/n1001/06SMC/

This article claims that "Astronomers have recently discovered that the Magellanic Clouds don’t orbit the Milky Way, but are merely passing through our neighbourhood with an entourage of smaller dwarf galaxies in tow." Can someone point me at the evidence for this please? --TammyMoet (talk) 11:04, 6 January 2010 (UTC)

http://arxiv.org/abs/astro-ph/0703196 Dragons flight (talk) 11:13, 6 January 2010 (UTC)

Thanks for this. From the abstract, though, there seems to be no support for Astronomy Now's assertion. Is there anything else? --TammyMoet (talk) 12:33, 6 January 2010 (UTC)

Sure - it's right there in the very first sentence of the abstract: "Recent proper motion measurements of the Large and Small Magellanic Clouds (LMC and SMC, respectively) by Kallivayalil et al (2006a,b) suggest that the 3D velocities of the Clouds are substantially higher (~100 km/s) than previously estimated and now approach the escape velocity of the Milky Way (MW).". If the Magellanic clouds are moving at anything close to the escape velocity of the Milky Way, they cannot be in orbit around it. Hence they will pass through our Galaxy and causing who-knows-what devastation along the way. Obviously, individual stars in each group will be disrupted in different ways - it could easily be that some of "our" stars will be captured by one or other of the Magellanic clouds - and that some of their stars will be captured by us - and all of the galaxies involved will have their nice symmetrical shapes splattered in all directions - but for sure the Magellanic clouds can't simply be in a nice gentle orbit around the Milky Way if they are moving faster than the escape velocity. But even at close to the escape velocity, there is no chance of a nice, clean orbit. A more appropriate term would be "train wreck" ! SteveBaker (talk) 13:06, 6 January 2010 (UTC)

Thanks Steve, but I still don't see how this means they can't be in orbit around the MW - even if it's a messy, chaotic and rapid orbit, it's still an orbit! And what about these "smaller dwarf galaxies"? What are they? They're not mentioned. I've not managed to find any dwarf galaxies which are recognised as being part of the LMC/SMC system. The SEDS page [3] gives about 4 globulars which may have been associated with the Canis Major dwarf, but doesn't mention any around the Magellanic Clouds. --TammyMoet (talk) 14:46, 6 January 2010 (UTC)

Escape velocity, by definition, means they're not in a periodic (or even pseudo-periodic) orbit. --Tango (talk) 14:51, 6 January 2010 (UTC)

What makes you think they will collide with the Milky Way? While they could have escape velocity towards us and will go through us and escape in the other direction, the abstract doesn't say that's the case and I would have thought it would mention it if it were the case. --Tango (talk) 14:51, 6 January 2010 (UTC)

To clarify, that's the paper with the unexpected measurements showing the LMC/SMC to be near escape velocity for the Milky Way (so possibly unbound). Everything else is probably the consequence of filtering the science through press releases and underqualified science reporters. Dragons flight (talk) 15:00, 6 January 2010 (UTC)

(sighs) I guess you're right there - I've had a good look round and can't see anything giving the Magellanic Clouds any entourage! I'm still confused though. If something is moving greater than escape velocity, that means it will escape the gravitational field of the larger object right? If something is moving slower than escape velocity, that means it will not escape the gravitational field of the larger object right? OK so they may not be orbiting us, but the lower-than-escape-velocity speed should mean they will eventually fall towards us, and be captured? It's interesting to see that many websites still claim they are satellites of the MW. Perhaps they're waiting for measurements which show that the direction of movement is not around, but through. --TammyMoet (talk) 15:13, 6 January 2010 (UTC)

If the speed is lower than escape velocity then they will be in a roughly elliptical orbit. The statement about them not being in orbit is just in the event that the speed is greater than escape velocity. If they are in a (psuedo-)periodic orbit then they are captured, that's what the words means, that doesn't mean they will collide with us, though - that would only be the case if the orbit is so eccentric as to make the perigalacticon (closest approach) less than the sum of the radii of the two galaxies, and I see nothing in the abstract to suggest that is the case. --Tango (talk) 16:08, 6 January 2010 (UTC)

However, it is likely that the two Magellanic Clouds will not escape the Milky Way's gravity by the time the Andromeda Galaxy collides with ours, so the combined gravity will likely be greater and draw in the Magellanic Clouds. ~AH1^(TCU) 20:50, 9 January 2010 (UTC)

catalytic dehydrogenation

Suppose I have a starting reagent that when dehydrogenated, has thermodynamic stabilisation because of aromaticity or extended conjugation of the product. Are there any selective reagents to facilitate oxidation or hydride transfer? If selectivity isn't a requirement -- e.g. it's a hydrocarbon, will bleach or hydrogen peroxide work? John Riemann Soong (talk) 11:22, 6 January 2010 (UTC)

There are several dehydrogenation reactions (especially easy if product is aromatic, for example cyclohexadiene→benzene; "aromatization" reactions should give you lots of literature hits), but I don't know of good catalytic ones. DMacks (talk) 17:41, 6 January 2010 (UTC)

I'm trying to design a transfer hydrogenation reaction... only I need to work backwards from most literature reactions (most people want to hydrogenate, I want to dehydrogenate). Does catalytic dihydroxylation with osmium tetroxide work with aromatic rings? I was thinking of a cyclodiene-like intermediate, with the expulsion of H2... maybe into a hydride acceptor like cyclooctatetraene. John Riemann Soong (talk) 23:55, 6 January 2010 (UTC)

OsO₄ doesn't easily touch benzene; RuO₄ might (heck, that oxidizes diethyl ether → ethyl acetate quantitatively!). But your whole process is confused by mixing up different types of "oxidation". Inserting oxygen is quite different than removing hydrogen. Searching for "catalytic dehydrogenation" gives many hits, there are many proprietary ways of doing it, which should tell you something about the ease of a novice getting it to work using simple chemistry or reverse-engineering an easy forward reaction. DMacks (talk) 16:49, 7 January 2010 (UTC)

Cursus honorum

Moved to Wikipedia:Reference desk/Humanities. --Stephan Schulz (talk) 13:20, 6 January 2010 (UTC)
The following discussion has been closed. Please do not modify it.
I see in the article cursus honorum there are various sequential steps and positions of public offices. Would it be fair to say these are the following and in this order? Military Tribune Quaestor Aediles Praetor Consul Proconsul Governor Censor Tribune of the Plebs Princeps senatus Magister Equitum (Master of the Horse) - 2nd in command (like a Vice President) Dictator From approximately what time range did this apply?--Doug Coldwell talk 12:53, 6 January 2010 (UTC) In what way is this a science question? Can I suggest you take this to the Humanities reference desk - the people there are much more capable of answering questions of a historical nature. All we're able to tell you is that the people who held these offices evolved from small shrew-like mammals and while in office they fully obeyed ALL of the laws of thermodynamics! SteveBaker (talk) 12:59, 6 January 2010 (UTC) What we can also tell you is that you should read your sources. In particular, Governor: "Though not part of the Cursus Honorum...". Also, a governor is usually a proconsul or a propraetor at the same time - one being a rank, the other a position. Censor: "After a term as consul, the final step in the Cursus Honorum was the office of censor" - which implies that all the later positions are not part of the c.h. In particular, as long as (non-thermodynamic) laws mattered, the plebeian tribune had to be a plebeian, while for quite a while the cursus honorum was reserved to aristocrats. --Stephan Schulz (talk) 13:11, 6 January 2010 (UTC) Yikes!!! I thought I was on the Humanities Desk. My mistake.....--Doug Coldwell talk 13:19, 6 January 2010 (UTC)

Spots on Betelgeuse, or just an imaging artifact?

APOD today has a nice picture of Betelgeuse. The text mentions the two bright spots, but it seems to me that there are bands of brightness across the image, some bands are horizontal and the others are diagonal about 30 degrees clockwise from vertical. Where these two sets of lines overlap, there are the bright spots. So, could the bright spots just be an artifact of the imaging process used? — PhilHibbs | talk 13:21, 6 January 2010 (UTC)

Possible, but highly unlikely. You're talking about an image that's been in the hands of numerous professional astronomers, including those who originally decided to construct the image. I think they'd know to account for imaging artifacts before claiming and publishing results. — Lomn 13:29, 6 January 2010 (UTC)

I agree with Lomn. Optical interferometry is very tricky business and requires considerable processing to get an image. What's more likely is either that the bright bands are an imaging artifact due to the (real) bright spots, or the bright bands are related to a real, but unmodeled, structure of the star. If you look at the journal article, the bottom panel of Figure 8 shows the sorts of artifacts associated with this interferometric image; a single point source would be split up into at least 5 spots with some streaks. The researchers don't just look at the image and decide what's there; they model a bunch of things might be there, subject those models to the same observational artifacts, and compare that to the data... whatever model best reproduces the data is their "answer" for what's on the star. The authors found a 2-spot model to work well, but freely admit that "Although the 2-spot model catches most of Betelgeuse surface brightness complexity and can be considered a fair description of the object spatial brightness distribution, going further requires even smaller and fainter details (as images in Fig. 8 show) thus probably showing the complexity of the star surface." -- Coneslayer (talk) 13:51, 6 January 2010 (UTC)

I see, so it is more likely that the bands are an image artifact caused by the spots than vice versa. Thanks. — PhilHibbs | talk 14:45, 6 January 2010 (UTC)

By the way, recent observations also suggest that Betelgeuse's diameter has shrunk 15% in the past 15 years. This could be an indication that the stellar activity is increasing and that a supernova could possibly occur in the near future. ~AH1^(TCU) 20:34, 9 January 2010 (UTC)

Decay

How have elements with relatively low half lifes not all decayed by now, considering the earth is 4.5 billion years old and before that no telling how long the elements were floating around in space 98.20.192.49 (talk) 14:02, 6 January 2010 (UTC)

Well, for one thing, you can have an element with a very long half life that decays into an element that has a short half life. The decay of the first maintains a supply of the second. -- Coneslayer (talk) 14:12, 6 January 2010 (UTC)

Similarly, other sources produce radioactive (and non-radioactive) isotopes. Carbon-14, for instance, is primarily generated by cosmic rays entering the atmosphere. — Lomn 14:15, 6 January 2010 (UTC)

Same with tritium which can be created by cosmic rays knocking bits from nitrogen nuclei. Googlemeister (talk) 20:59, 6 January 2010 (UTC)

But he's right; this is the reason that there isn't a lot of Californium in the Earth's crust. Comet Tuttle (talk) 20:43, 6 January 2010 (UTC)

Indeed. There are no transuranic elements with half-lives of more than a few million years (ie. about 1000 less than the age of the Earth) so there is no long-lived isotope that can decay into the shorter-lived ones, which means the shorter-lived ones are simply not found in nature. (There are some very minor exceptions due to very small amounts of those elements with the few million years half-lives surviving and the possibility of atoms increasing their atomic numbers through beta decay, but those just give isotopes in trace amounts.) --Tango (talk) 01:52, 7 January 2010 (UTC)

Muonic matter armour?

Could a stable, super-dense material ever be made of muonic matter or any other exotic atoms? And even if they were unstable, what if the muons were constantly replaced in the material (possibly made of normal matter) by some sort of "muon generator?" Also, is there any other form of exotic matter which might be a candidate?Trevor Loughlin80.2.193.221 (talk) 14:38, 6 January 2010 (UTC)

In any meaningful, grounded-in-science sense, no. There's nothing in the question that doesn't require firkins of handwavium. We also note that muonium behaves quite like hydrogen. — Lomn 15:14, 6 January 2010 (UTC)

It would take about 4×10²² W to generate 1 kg of muons at a rate fast enough to match the decay rate. For those keeping track all of human civilization uses about 1×10¹³ W. Dragons flight (talk) 15:27, 6 January 2010 (UTC)

We might need to work on the efficiency of our muon generator then. Googlemeister (talk) 15:55, 6 January 2010 (UTC)

Dragons flight has calculated a lower limit which assumes 100% efficiency. The lifetime of a muon is about 2 microseconds, which means replacing all of your muons half a million tmies each and every second. The energy equivalent of 1 kg of mass is about 9×10¹⁶ joules. Multiplying those numbers gives you your energy input per second (in watts) — assuming that all of the energy you put in is converted directly to muon mass. If you had access to that kind of energy (equivalent to detonating ten million one-megaton nuclear bombs every second) you'd be far better off pointing it at whatever was attacking you.

Incidentally, if you were able to generate all those muons, the wearer of the armor would almost instantly be incinerated by the heat from their decay. TenOfAllTrades(talk) 23:32, 6 January 2010 (UTC)

What if we make the armour spin around you really fast so the time dilation extends the lifetime? Or find some way to turn existing matter into muons, rather than creating them from raw energy? Or have very short wars? You just aren't being imaginative enough! --Tango (talk) 23:40, 6 January 2010 (UTC)

The energy cost for accelerating the shield up to a speed where time dilation becomes relevant is comparable to the energy cost of constantly replacing the muons. Plus, you're going to bleed horrific amounts of energy through synchrotron radiation. Again, if you had a way of accelerating significant masses to relativistic speeds, you'd be better off pointing them at the enemy. If pigs could fly, we could make flying pigs — but they don't. TenOfAllTrades(talk) 03:46, 7 January 2010 (UTC)

I think the centrifugal force would rip the armour apart long before it it reached relativistic speeds, actually. I was joking - I thought the final idea of having short wars (by which I meant wars of less than a microsecond) made that clear. --Tango (talk) 18:01, 7 January 2010 (UTC)

Flesh covered android?

Whilst the human-like intelligence depicted in the "Terminator" movies is quite a long way off being achieved, would an android covered with tissue engineered living flesh be possible with present day technology? And would this be within the reach of an amateur scientists using home equipment?Trevor Loughlin80.2.193.221 (talk) 14:46, 6 January 2010 (UTC)

Apparantly you can cut a cactus in half and then fasten it back again with a piece of metal, and the cactus still lives. So you could see if you could cover a robot in cacti perhaps. I do not know if you could combine cacti flesh from different cacti. Another possibility would be mould. Or do I mean mold? 78.146.51.13 (talk) 15:38, 6 January 2010 (UTC)

Not possible with current technology. It will probably take another 20-50 years of advances in biotech to get to that stage--not that there is actually any good reason to do it, though. Looie496 (talk) 16:33, 6 January 2010 (UTC)

Covering an android with human flesh seems like it might stall in the institutional review board phase. You would have to provide a pretty convincing reason why this would be a good idea. (If you're working alone in a garage, you can circumvent that kind of bureaucracy, at the expense of the support and organizational expertise that a large research institution provides). Nimur (talk) 17:30, 6 January 2010 (UTC)

Would "I want to build the most realistic sexbot ever - and we can all make billions off of this!" be a good enough reason? :) --Kurt Shaped Box (talk) 22:16, 6 January 2010 (UTC)

Only in Japan. --Tango (talk) 23:42, 6 January 2010 (UTC)

Only? Clarityfiend (talk) 02:28, 7 January 2010 (UTC)

There has been a lot of work on trying to make robots that look "human"—always with plastic flesh, though. The results are impressive though they are well inside the uncanny valley yet. The uncanny alley article has some links to such projects. --Mr.98 (talk) 17:59, 6 January 2010 (UTC)

If you want to use animal or human flesh then you would need the internal organs to keep the flesh alive. Vegetable or fungal flesh would be much more practical, as suggested above. For a fungal-flesh covered android, all you would need to do would be to cover the android in damp bread and let nature take its course. 78.146.51.13 (talk) 19:48, 6 January 2010 (UTC)

Current technology to use animal flesh on an android is not currently possible for the reasons state above, but some of the current test models such as eveR-1 have a pretty decent synthetic flesh. Googlemeister (talk) 20:56, 6 January 2010 (UTC)

This kind of question comes up once in a while in conjunction with the X-men character "Wolvarine" (whose bones have supposedly been replaced with metal). This is essentially the same problem that you are contemplating. The biggest problem is that bones are not simply inert lumps of support structure. They also are the source of new blood cells. Without proper bones - there is no way for blood to work - and without that, no flesh. SteveBaker (talk) 23:37, 6 January 2010 (UTC)

"Wolverine" and his bones weren't replaced, but rather partially coated, with the adamantium. How are we ever going to develop razor wielding super soldiers if we can't even cover the basics??? Of course, the question really is - where do the claws go when they retract? Having them sit on top of the bones of his forearm is ju-u-u-st this side of believable (for a superhero), but how they get through all his wrist bones is a bit tricky (or else his wrists should be about twice as thick as normal). Matt Deres (talk) 17:55, 7 January 2010 (UTC)

Special dreams

While dreaming, it is difficult to impossible to read. I heard rumours that some people can not even see colours in dreams. Mostly, it is difficult to recognize visual details. But then, there are dreams when reading is easy, when you can see and recognise every stroke of each letter. All details are (or seem to be) visible, colours are bright even exalting the waking state. Is there a name for that? 93.132.156.195 (talk) 16:36, 6 January 2010 (UTC)

Maybe Lucid dreaming or dreaming may have info for you. --Jayron32 18:35, 6 January 2010 (UTC)

Not really. Lucid dreaming is something different (being aware that so. is dreaming). While I myself, the most parts I can remember from those dreams, am aware that I am dreaming, the dreaming I described above holds elements especially uncommon to dreams that could mislead to take it for reality even more than common dreaming. 93.132.156.195 (talk) 20:19, 6 January 2010 (UTC)

Not sure of the term, but I have found that I can read in most of my dreams, but the part of the brain that is able to recall what I have read does not seem to work right when dreaming, so is it really considered reading if you can not remember it 15 seconds later? In any case, if a term for this has not yet been coined, perhaps you could write a paper and name the phenomenon after yourself? Googlemeister (talk) 20:53, 6 January 2010 (UTC)

I'd just call it a vivid dream. I used to meditate and visualise a lot when I was groing up and sometimes I used to have such vivid dreams I would remember details from them when trying to recall things that really happened. I sometimes actually found it difficult to say for certain whether a particular memory I had was of a dream or of reality!! This was mostly when I was groing up, it hasn't happened to me for a long time now. Vespine (talk) 23:06, 6 January 2010 (UTC)

Vivid dreams often occur in lucid dreams, and REM sleep may produce this type of vividity. However, I remember in some of my dreams that if I look away from the text, the text changes thereby making it difficult to read properly or recall what I'm reading. ~AH1^(TCU) 20:30, 9 January 2010 (UTC)

• Once I had a lucid dream that had the same vividity of reality. Obviously, take this as just a personal experience.--Mparu (talk) 16:18, 10 January 2010 (UTC)

Exploding olive oil

Earlier tonight, we finished a glass bottle of olive oil. Because it's prettier, we then refilled it from another, plastic bottle (of olive oil). An hour or two later there was a loud bang, and I went through to discover that the bottle had exploded, blowing the bottom clean off, and with a crack running along one of its corners (it's roughly cuboid-shaped). It wasn't near any sources of heat, and wasn't especially warm to the touch when I checked. What happened?! 94.168.184.16 (talk) 21:06, 6 January 2010 (UTC)

Well that certainly sounds pretty bizarre. About the only thing that I can think of is that the bottle had a knock when it was nearly empty, causing a small crack to develop and that when the bottle was refilled this caused the crack to propagate until failure occurred. You could look at the surface of one of the pieces of the bottle to see if there is any sign of an initial crack. Mikenorton (talk) 21:13, 6 January 2010 (UTC)

The culprit will most likely be either overpressure inside the bottle, or a temperature gradient that the bottle could not handle. From what I understand, olive oil has a high heat required to turn into vapor, so unless you were storing your bottle somewhere hot, like near a fire (you said this was not so), this would not seem likely unless your oil had a significant amount of some contaminant like dry ice (highly unlikely unless you regularly keep your plastic bottle of oil in deep freeze). That leaves a temperature gradient, which seems equally unlikely as that would also most likely involve a source or high (or perhaps low) heat. Only other idea I have is that there was some kind of slow chemical reaction between the oil residue, and the new oil. Honestly, I would hope not, because if I chose to eat both of those oil brands, I would not want that reaction to occur within my stomach. Googlemeister (talk) 21:34, 6 January 2010 (UTC)

Could a mouse have knocked it over? 67.243.1.21 (talk) 22:14, 6 January 2010 (UTC)

This doesn't answer your question but I regularly refill glass oil bottles (not because they are pretty but because I often by large quantitities in plastic bottles or cans and the smaller glass bottles are easier to use) including at least once IIRC an olive oil bottle with olive oil but have never had an explosion yet. I do usually clean and rinse the bottle and then let it dry properly first. Nil Einne (talk) 23:25, 6 January 2010 (UTC)

You said "wasn't especially warm". Does that mean it was warmed (or cooled) by something? Because that could do it. A square bottle might have some stress in it from the way it was manufactured, and maybe you hit it or something which released the stress. Check out Prince Rupert's Drops for a spectacular example of that. Ariel. (talk) 00:32, 7 January 2010 (UTC)

All I can say is that olive trees are revered in Greece and perhaps they and their fruits have some interesting properties as a result of being adapted to rather harsh, arid conditions. Vranak (talk) 11:38, 7 January 2010 (UTC)

It may have been due to temperature differences between the old and new oil, particularly if you kept the old bottle in the fridge and the plastic bottle not in the fridge. It may have been the air in the bottle warming up and expanding. (I do not know if oil changes volume with temperature). Or it may have been due to the glass equivalent of metal fatigue perhaps. See also Thermal shock and Liberty bell. 78.151.131.82 (talk) 21:06, 7 January 2010 (UTC)

• I agree; if you use cold oil to refill bottles, than you tap them and keep them at room temperature you will have an expansion causing an increment of internal pressure, wich may result in an explosion. Olive oil it is known to explode.--Mparu (talk) 17:30, 10 January 2010 (UTC)
  • By the way, here (in Tuscany) paesants use to sell olive oil using kilos instead of liters; this indicates that oil tends to vary its volume.--Mparu (talk) 17:34, 10 January 2010 (UTC)

Experiments in making ginger beer found that square cross-section bottles break easily from internal pressure. Polypipe Wrangler (talk) 02:52, 9 January 2010 (UTC)

butter churning

I watched "Catch me if you can" and was intrigued by the story about a mouse who fell into a pail of creme and churned it into butter so it could escape. It occurred to me, is it possible for a mouse to do that? In other words, what energy input is required to convert 2 liters of creme into butter, and is a mouse capable of supplying sufficient energy to do this before it drowned? For the purpose of this, we can assume a temperature of creme most charitable for the mouse provided it is between 5C and 25C. If this question is too complicated for a decent answer, what would be a good way to determine this experimentally without killing the mouse? Googlemeister (talk) 21:23, 6 January 2010 (UTC)

This isn't a particularly scientific answer but having whipped cream before (IIRC never by hand thankfully) and nearly churned it to butter too I highly doubt it. Particularly since it's likely to get harder as it churns it as the viscosity increases. In fact, I'm not even sure how it will work, all that will happen even if the mouse could do it would likely be a mouse stuck in butter (or more likely nearly butter) since I somewhat doubt the mouse could escape the butter once it is churned. More charitably, the mouse may not need to make butter. The surface tension of whipped cream may be enough for the mouse to escape so it won't have to churn it to butter, although I still doubt it would be possible.Nil Einne (talk) 23:19, 6 January 2010 (UTC)

My recollection of churning butter myself (I only did it once with a hand-cranked rotating barrel contraption - and that was a long time ago) is that its a long and exhausting process - I'm 100% sure a mouse couldn't do it. But there is another major hole in the story. When you churn milk into butter - you don't turn the entire volume of milk into solid butter - rather you separate the fat as butter from the water leaving a rather watery milk called "buttermilk". The butter forms little blobs that you have to skim out of the churn and squeeze to get rid of the remaining liquid. So the mouse (at best) dumps a lump of butter into the bottom of the churn and drowns in the remaining liquid. SteveBaker (talk) 23:26, 6 January 2010 (UTC)

Um, the butter will float not drop to the bottom. Ariel. (talk) 00:28, 7 January 2010 (UTC)

Yeah - just about...it's not very different in density than the buttermilk. But still - it's not one solid lump - you get bunch of loose curds that have to be scooped, drained and squished into a patty. Even a little mouse couldn't climb on it. SteveBaker (talk) 01:29, 7 January 2010 (UTC)

Actually, in many circumstances, you'll eventually get a single largish blob of butter rather than individual curds; they all agglomerate together, although the single lump will still contain entrained buttermilk that needs to be pressed out. The trick for the mouse, though, would be to manage to get to the top of the buttery island without the island capsizing and dumping the mouse back into the drink. I think the mouse would do better if it tried to climb out while it was all still very stiff whipped cream. ;-) Atlant (talk) 01:08, 12 January 2010 (UTC)

It did sound like one of those happy stories with a moral that has no scientific basis, but not having made butter (or whipped creme) I did not realize how difficult it was. Googlemeister (talk) 14:47, 8 January 2010 (UTC)

Palm Trees in Eastern Coast, USA

Where do palm trees start naturally growing on the US Eastern coast? --Reticuli88 (talk) 21:30, 6 January 2010 (UTC)

OR here, but I have seen them as far north as Norfolk/Virginia Beach, but those could have been planted and not natural, and the ones I saw did not look terribly healthy. Googlemeister (talk) 21:36, 6 January 2010 (UTC)

Palmetto trees grow as far north as Southeastern North Carolina. I'd guess that's about the northern limit. --Jayron32 21:37, 6 January 2010 (UTC)

It could be warmer temperatures due to the Gulf stream. 78.146.51.13 (talk) 23:16, 6 January 2010 (UTC)

Sound of sloshing water in home heating system

A week ago, the outside temperature fell to around 20-30 °F from being 30-40 °F the previous week. The heating system, which works through vents at the bottom of the walls, for my apartment stopped working in the middle of the night. I called my apartment manager, and I used a portable electric heater until the next day, when a repairman came and fixed the heating system. I have no idea what he did exactly since the heating unit is down in the basement, to which I have no access.

Everything seemed to be working fine -- the apartment is warm again -- except now whenever the heating system starts up (that is, when the temperature falls below the thermostat's setpoint), I hear the sound of sloshing water in the walls. The sound of sloshing water stops after a few seconds, but while the heater is running, I occasionally hear sounds that I would describe as perhaps a small brook or stream. I am sure I never used to hear these sounds of water before the heating system failed and was repaired.

Also, this I am not so certain about, but I think that the vents may take longer to get hot than they used to, and that when I touch the vents, the metal does not get as hot as it used to. But unlike the case with the sounds of water, I am not totally sure that the metal is less hot (I think it might be, but I am not sure) (even if the metal is less hot, the apartment is still being heated to the setpoint of the thermostat).

I don't see any water leaking anywhere. What do these sounds of water, which I never used to hear previously, mean? Do I need to be worried that something is wrong?

—Lowellian (reply) 21:34, 6 January 2010 (UTC)

If one has central heating with radiators (where water is pumped around a circuit to radiators in each room) then it's common for the plumber to introduce air to the system when working on it, which produces just the sound you describe. One can easily remove this by bleeding radiators with a special key. But it sounds like you have one of those naff blown-air heating systems popular in north america, so I guess it's air in the heat-exchanger pipes instead (and again it should have a bleed valve). Or it's ghosts. -- Finlay McWalter • Talk 22:33, 6 January 2010 (UTC)

If it's air, is this bad? —Lowellian (reply) 22:36, 6 January 2010 (UTC)

Not in moderation, it's just annoying. At least for the radiator-kind (and surely the other kind) there's a feed from the water main that tops off the water if any escapes (from leaks or plumbing-works), which fills the system up. Here is a page about bleeding radiators and here for here for system valves. But if it's an apartment then you might as well get the apartment complex handyman to do it (it shouldn't need a plumber). -- Finlay McWalter • Talk 22:47, 6 January 2010 (UTC)

You were not clear if you have radiators, or air heat. I'll assume radiators. Air is kinda bad because it can cause a slight amount of rust. But also air prevents the hot water from flowing properly, so the radiators would not be as hot. After service which opens the pipes (I'm going to guess he replaced the water pump) you will need to bleed all the radiators. Then after the system runs for a while (and the dissolved air comes out) you will need to bleed the radiators on the top floors. You need a special radiator key to bleed them, it has a square hole in it, and they are not hard to find, any hardware store should have it. Be aware after you bleed the radiators it takes a while for the pressure to build up again - usually you need a full off/on cycle. You might only be able to bleed half a radiator at a time. I'm very very surprised the service man did not say, or do, anything about it. BTW, if this is a multi-unit apartment, you will have to bleed all the radiators in the whole building to get rid of the noise, also if you don't your apartment will always be hotter than the others. Ariel. (talk) 00:00, 7 January 2010 (UTC)

When you bleed the air out of a radiator with the special key mentioned, air hisses out, then a little stream of water squirts out until you shut the flow off with the key. The system should automatically replenish the water in the room where the furnace is. A radiator that is not full of hot water obviously puts out less heat than one full to the top. Edison (talk) 20:12, 7 January 2010 (UTC)

Two more questions:

1. Will the presence of air pockets raise my heating bills?
2. Will this problem go away by itself (will the air escape on its own)?

—Lowellian (reply) 21:00, 8 January 2010 (UTC)

It might because the heating will be less even, so you might overheat one area because a different area is not getting the correct amount. Also heat transfer from the radiators will be worse. I would not expect much impact though, I'd be more worried about not having enough heat for the coldest days. Note: this is only if you have a lot of air, like half a radiator, a tiny amount at the top won't hurt (but probably also doesn't make noise). If the water level is really low, you'll have no heat at all.

The air will never escape. If it did it means you have a leak, and water would escape too.

That said, some systems have air removal devices. But they are installed near the boiler (in the basement), and since air rises, it will never get to the device. Those devices are meant for tiny bubbles carried along with the water. The don't help for large amounts. If they could have removed the air they would have by now.

Bleeding radiators is very easy. Just hold a paper cup, or paper towel (the water is black and metallic sometimes when it comes out) under the spout and open the key, listen (or feel) for the hiss of air, wait for water to spurt out, then close it, pause for a bit and do it again. It's easiest (most pressure) when the system is hot (but don't burn yourself). Ariel. (talk) 21:38, 8 January 2010 (UTC)

Well, the thing is, as I stated earlier, I don't have access to the basement. And my apartment manager would probably insist on anything being done having to be done by a repairman, so I don't want to insist on calling a repairman back if there's no real problem.

And here's the other strange thing: after the heater was repaired, for three or four days, I would definitely hear the sloshing every time the heater started, and I would also occasionally hear those brook/stream sounds I described earlier. And then, today or yesterday, those sounds stopped for the most part (the sounds do still occur from time to time, but much less than before). That's why I'm asking if the problem could have somehow fixed itself.

—Lowellian (reply) 00:31, 9 January 2010 (UTC)

You don't need access to the basement. The radiators are in your apartment. The water (air) levels in the various radiators has probably leveled out, so you don't hear the water moving around so much. And yes, some bubbles probably were removed by the air removal device I mentioned. I would still bleed them though, if you are willing to buy one of those keys (it's probably just a few dollars), it's very easy, and you don't need a repairman or anything. Ariel. (talk) 00:04, 10 January 2010 (UTC)

Possibly (assuming that it is a sophisticated system without normal radiators) there is some form of automatic air trap (at the highest point, up near the roof) to eliminate air, and this has now done its job, though there is still the risk of pockets of air being trapped unless the pipework is very carefully designed. Dbfirs 02:42, 10 January 2010 (UTC)

If there was such a device it would have removed the air by now. They work fast, and air rises immediately. Ariel. (talk) 06:09, 10 January 2010 (UTC)

... provided that the pipework is very carefully designed. Dbfirs 10:26, 11 January 2010 (UTC)

Life sensors

In Star Trek, the sensors can somehow detect the locations and numbers of living organisms. It can't be by heat or electric fields, because those can both be generated by natural phenomena. Is there any scientific plausibility to this? I'm aware that Star Trek is fiction, but many of the other concepts (phasers, antimatter fuel, etc.) have at least some scientific basis. --75.50.48.130 (talk) 22:13, 6 January 2010 (UTC)

Pheromones? CO2 emissions? The above in conjunction with either of these two? --Kurt Shaped Box (talk) 22:22, 6 January 2010 (UTC)

Real scientists look for the signatures of chemicals associated with life, such as methane on Mars. All that tells you is that there is (probably) life, and maybe how much, but not where, and not what. -- Finlay McWalter • Talk 22:36, 6 January 2010 (UTC)

(ec)These sensors are ridiculously inconsistent, even in-universe. The number of times that sensors detect life on a planet before the Enterprise or Voyager even reach orbit are too numerous to count. Yet, they seem to be totally unable to detect intruders, stow-aways, or others on board the same ship in numerous episodes. Rack it up to poetic license, grab a copy of the Nitpicker's Guide to `Trek, and forget about the details. Nimur (talk) 22:38, 6 January 2010 (UTC)

Telepathy and such work in Star Trek, so maybe the life signs detector is based on the same concept. Ariel. (talk) 23:54, 6 January 2010 (UTC)

StarTrek is about story, plot and characters. The technology is quite blatantly allowed to do whatever the story needs with little regard for science. If it's inconvenient for a character to return to the ship - there will be a transporter interference problem from some randomly named mineral deposits on the planet. If it's convenient to be able to transport someone aboard an enemy vessel, it works - if you wanted to beam a large nuclear weapon onto the enemy ship then you can't because you can't beam through shields or you can't beam at warp speeds...except when you can. Hence it's inconsistent, impractical and frequently impossible. Even the simple stuff like the communicator badges they all wear. Sometimes they have to tap the badge in order to place a call - other times they just speak. Ditto with answering calls. When they speak commands to the computer - it's not always clear that they are definitely talking to it. A system like that would result in a computer that picked up random orders from unintended bits of conversation all the time! But none of this matters because it's not that kind of a SciFi show. SteveBaker (talk) 01:24, 7 January 2010 (UTC)

The weirdest thing with the combadges is that they know who you are about to open a channel to before you say it, since the channel is already open and the intended recipient can hear you say "Picard to Riker" (or whatever). Now, that in itself isn't too strange - we know combadges can read minds otherwise the universal translator could never work - but why bother saying it if the combadge already knows? --Tango (talk) 01:43, 7 January 2010 (UTC)

That's actually not too big of a problem. See Buffer (telecommunication). The combadge could keep a 5-10 second recording, and when it hears a "connect" command, simply replays the recording of "Picard to Riker" over the com channel. Ambiguous commands to the computer are slightly more difficult to explain, but remember that Star Trek computers have highly advanced artificial intelligence systems. If you as an intelligent audience member can tell that the command was intended for the computer, then the AI probably would be able to too. That said, most of the Enterprise is usually run by highly powerful plot devices. -- 128.104.50.40 (talk) 23:16, 7 January 2010 (UTC)

I thought of a buffer but it seems to me that there is no buffer at least over long periods since they seem to respond very fast. In fact sometimes even over small intervals it seems there is no buffer. For example, if you say "Picard to Riker", Riker often seems to respond instantly (Riker here), this wouldn't work if the AI only plays back the message to Riker after you finish saying the Riker. Over longer intervals , I guess perhaps the computer slowly reduces the buffer. I don't know if the artificial intelligence in Star Trek is that great. Sometimes it shows some great ability, but for example it often needs to ask dumb stuff it should be able to guess or know or otherwise asks or specifies too much detail. E.g. if you want a glass of water it needs to ask what temperature and e.g. Data, one of the smartest AIs of all doesn't seem to be able to learn not to overspecify detail. There are better examples but it's been a while since I watched Star Trek. Nil Einne (talk) 00:43, 8 January 2010 (UTC)

There are real life life sign detectors. They are used to detect illegal immigrants hiding in the backs of lorries and work by detecting heartbeats (Google will find you details if you ask nicely). --Tango (talk) 01:43, 7 January 2010 (UTC)

Right, but they are looking for a different kind of aliens on Star Trek, most of the time. The device that the Enterprise is equipped with is called Everything_Sensor :) --Dr Dima (talk) 05:58, 7 January 2010 (UTC)

Why not just use visual cues? You can go with infrared, that's probably the most straightforward. Vranak (talk) 11:35, 7 January 2010 (UTC)

I read somewhere that if you could look closely at them one of the health indicators that move up and down in star trek is labelled 'Blue Cross'. :) Dmcq (talk) 14:07, 7 January 2010 (UTC)

[found it at imdb], it said 'medical insurance remaining. :) Dmcq (talk) 17:53, 7 January 2010 (UTC)

"Life sensors" did not detect life on Mars, but they didn't detect any in the deserts on Earth, either.[4] ~AH1^(TCU) 20:20, 9 January 2010 (UTC)

Reacting vicinal diols with formaldehyde hydrate (methanediol)

Or better yet ... methylene chloride ... can I count on the rapidity of intramolecular reactions and the driving force of distilling water to get a dioxy five-membered ring? John Riemann Soong (talk) 23:31, 6 January 2010 (UTC)

Also, all solutions I've seen of formaldehyde have been aqueous... essentially since the diol is acting like a protecting agent, how would side reactions be minimised? Is a solution of formaldehyde in methylene chloride viable, or do you have to use a protic solvent to prevent the formaldehyde from evaporating? John Riemann Soong (talk) 23:38, 6 January 2010 (UTC)

The 40% aqueous solution works. Or also you can use paraformaldehyde (no water, so you do not have as much equilibrium problem). If you really want water-free formaldehyde (either as the gas or dissolved in some other solvent, the usual way is by thermal cracking of paraformaldehyde—heat the solid in a still-pot, the gas comes out and you can bubble it into a cooled solvent, or even directly through your reaction mixture. A more efficient way is to start with dimethyoxymethane. A non-acidic way is to use dibromomethane with a base (S_N2 reactions). Beware, the methylene-acetal protecting group is very hard to remove. DMacks (talk) 16:43, 7 January 2010 (UTC)