Wikipedia:Reference desk/Archives/Science/2009 August 25

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August 25

Immunity to disease/infection/etc

As far as I understand it, your body keeps a sort of inventory of diseases that you've been sick from (colds, flus, etc) so that it can fight it off again the next time it shows up. Some are only kept in this inventory for so long, right? Why do some stay in this inventory while others do not? Dismas|^(talk) 00:38, 25 August 2009 (UTC)

Right? Not sure. If you're wondering why we can catch colds repeatedly, "At least 99 serotypes of rhinoviruses affecting humans have been sequenced." That is to say, there's a lot of potential for catching a superficially different cold. 213.122.42.252 (talk) 01:09, 25 August 2009 (UTC)

There are actually about 120 types of rhinovirus, the agent behind the common cold -- that gives you just enough for about 2 colds a year for 60 years. That's what the microbio professor said in dental school. As far as antibodies go (they are the entities your B lymphocytes produce to "remember" the various foreign antigens that present themselves to your immune system), they will last forever. That doesn't necessarily mean that the actual immunoglobulin protein particle lasts for 20, 30, 40 or 80 years, but rather, a circulating bunch of these guys will be produced by your memory cells (a type of mature B cell, as mentioned above) at all times, to combat any antigen (i.e. new foreign attack) that presents itself. I'm no immunologist, so I'm unsure exactly why boosters and other advanced techniques are necessary -- I think boosters serve to add to your body's protective potential, so that a defensive strike will happen faster and more strongly than otherwise. You can check out the above linked articles for more info. DRosenbach ^{(Talk | Contribs)} 01:55, 25 August 2009 (UTC)

Immunologic memory, the ability to respond to antigens previously encountered, persists for variable lengths of time depending on many factors, including the type and intensity of the initial stimulus (e.g. infection versus vaccination), the condition of the host (e.g. healthy versus immunosuppressed), the type and intensity of the initial immune response, and any re-exposure that might boost the initial response. Contrary to what DRosenbach said, B cells certainly don't live forever. The plasma cells (which are generally not considered B cells, because they lack many important characteristics of B cells) that produce most of our antibodies may live for decades, but even they slowly decay. Some T cell responses are so intense that they seem to last indefinitely, but most of them can be shown to wane, too. So, designing a vaccine, or understanding why some infections can be repeated in the same host, depends on a lot of nuanced conditions. --Scray (talk) 03:01, 25 August 2009 (UTC)

Contrary to what Scray said, I did not say that B cells live forever. What I did say was "As far as antibodies go (they are the entities your B lymphocytes produce to "remember" the various foreign antigens that present themselves to your immune system), they will last forever. And then I qualified that by stating I am not referring to actual proteins enjoying an existence of 60-100 years, but rather a cumulative, overlapping sort of "you will be covered for life" concept. DRosenbach ^{(Talk | Contribs)} 03:34, 25 August 2009 (UTC)

Sort of like saying "Sir, your circulatory system will last your entire life," even though blood cells die off after 3 months, endothelial cells die off after a few weeks/months, etc. It's the overlap -- like shingles. DRosenbach ^{(Talk | Contribs)} 03:44, 25 August 2009 (UTC)

Your use of the term "shingles" in this context is highly relevant (inadvertently, perhaps), since shingles (the medical condition) is due to waning immunity to a virus. --Scray (talk) 03:38, 28 August 2009 (UTC)

No, antibody responses wane over a period of years, and B cell clones are unique, not interchangeable like roofing shingles are. For example, the third injection of Hepatitis B vaccine results in greater durability (duration) of antibody titers, but they still wane over time. Antibody and cellular immune responses to Hepatitis C virus dropped below detectable levels two decades after accidental infection (PMID 10802716). --Scray (talk) 03:52, 26 August 2009 (UTC)

(EC) For things like the flu the virus mutates fast enough that resistance quickly diminishes since there will be new strains your body can't effectively recognise. This is one of the reasons why Influenza vaccines are only considered effective for about a year. The article provides some detail on this, as well as how the strains are chosen each year. Nil Einne (talk) 03:04, 25 August 2009 (UTC)

Inaccuracy of Significant figures

In chemistry class today, we were doing some practice problems on the use of significant figures, and on one of the problems to have the right number of significant figures, you had to lop off an entire 500,000 from the answer. To me, this makes the answer very inaccurate, and it made me wonder: when exactness is sometimes the matter between life and death, or the success of, say, a mission to Mars rides on accurate calculations, what is the point of significant figures? Also, are there any examples of times when using significant figures could cause fatalities that might be prevented by the non-use of significant figures, or even times when this has actually happened? Ks0stm ^(T•C) 02:08, 25 August 2009 (UTC)

In real life you would not "lop off an entire 500,000" unless the measure was so imprecise that the 500,000 was far less than the expected error. The point of significant figures (your teacher should be telling you this) is to avoid giving a false impression of the accuracy of the measurement. Suppose I estimate the height of a building by dropping a rock from the top and timing how long it takes to hit the ground. Suppose the time is about 3 seconds -- I do a calculation using the Earth's gravitational constant, and get a height of 144 feet. But if I give 144 ft as the answer, I'm misleading you, because that 3 second value really just means anything between 2.5 and 3.5 seconds. I will give you a more accurate impression of what I actually know if I say "around 150 feet, probably". Looie496 (talk) 02:18, 25 August 2009 (UTC)

500,000 may be well below the ability to measure accurately if you were, say, calculating the age of a star. If you can only estimate the age of a star to within, say, 50 million years one way or the other, and result which pretends to have an accuracy down to 500,000 years is bullshit. That's the point of significant figures; if the you are writing a non-zero digit in that place, what you are saying is "I know that this number really is THIS NUMBER". If you cannot say that for certain, than regardless of what your calculator tells you, you shouldn't write it down.

Look at it this way. Say I have a scale that measures to 0.01 grams accurately. Lets say that I measure exactly 50.00 grams of a sample, and then lets say that I want to divide my sample into seven equal portions. So I get out my calculator, and divide 50.00 by 7 and get 7.1428571428571428571428571428571. So, why do I not indicate that every sample is exactly 7.1428571428571428571428571428571 grams? Because everything after 7.14... is bullshit; because my measuring device cannot measure that small. Anything after the 0.00 mark is not significant. THAT is what significant digits means; its the fact that our numbers are limited by the precision and accuracy of our best measurements, and doing a simple mathematical operation cannot change how precise your numbers are. --Jayron32 03:01, 25 August 2009 (UTC)

Reminds me of the old joke : A tour guide is showing off some dinosaur bones and a student asks how old the bones are. The guide replies "One hundred million and three years.", The student is astonished. "How can you know the age of the bones with such amazing precision?", he asks. "Easy," replies the guide, "When I started working here they told me that it was one hundred million years old, and that was three years ago!" APL (talk) 03:24, 25 August 2009 (UTC)

But 7.14 * 7 = 49.98, and your scale is accurate enough that you know for a fact this is the wrong figure ... and so is 7.15 (which gives 50.05). So, 7.143 then. 213.122.42.252 (talk) 03:19, 25 August 2009 (UTC)

True, but which of your seven samples contains the extra bits that add up to the .02 loss? You cannot be certain; that's the inaccuracy of this. You know that a few of your samples will be VERY slightly heavy or VERY slightly light of the 7.14 figure; but you just cannot tell which ones are off and by how much, you just know its not enough to change the numbers on the scale. --Jayron32 15:31, 25 August 2009 (UTC)

I think part of the confusion relates to what we're discussing here. If you start off with 50.00g and have some magical (okay there are few situations where magic isn't required) way of dividing it by 7 then you end up with samples that you can say are 7.143g. IRL, there's no magic so commonly if you have 50 g and want to divide it by 7 what you would do would be to take 7 samples that are 7.14g using the scale Nil Einne (talk) 18:13, 25 August 2009 (UTC)

Note also that that in any scientific work where the amount of expected error is important, people don't rely on just quoting things to the appropriate number of significant figures -- those are just a rough indication of the expected error. If 3 seconds really meant that you were confident it was be between 2.5 and 3.5, you'd write "3 s ±0.5 s". Now 2.5, 3.0, and 3.5 seconds correspond to heights of 101, 145, and 197 feet (rounded to the nearest foot, but using a more accurate gravity value than Looie). Then the answer might be written as "149 ft ±44 ft"; here 149 was obtained by splitting the difference between the high and low numbers. But if it was felt that exactly 3 seconds was the most likely value, then the result might be written as "145 ft +52 ft -44 ft", showing specifically the expected error amount on the high side and the low side. --Anonymous, 03:08 UTC, August 25, 2009.

+/- factors are usually based on confidence intervals based on the number in the sample size; a single measurement does not really have a confidence interval, so in the case of a single measurement, such +/- factors are not usually reported. If you make 100 repetative measurements, the +/- factor would be different than 1000 repetative measurements, and the +/- reported should reflect that, based on the standard deviation from the mean value. With a stand-alone measurement, such statistical analysis is meaningless. However, stand-alone measurements are still limited by the precision of the measuring devices, and so still have significant digits... --Jayron32 03:16, 25 August 2009 (UTC)

The precision of the measuring device still may be such that a confidence interval is appropriate. If you can read it to within a quarter of whatever the appropriate unit is, then it's perfectly reasonable to record a reading as "42.25 ±0.25", and this is more useful than just writing it down with either 2 or 3 significant digits. (Of course, if you are recording a series of measurements, you won't repeat the ±0.25 on each one.) --Anon, 09:03 UTC, August 25, 2009.

(After edit conflict : Sig figs are not used for serious calculations in the scientific world. They're better than just punching numbers into your calculator blindly, but ideally you should be calculating the margin of error of your measurements, and then calculating the min value and the max value through your entire set of calculations. Surprisingly, sometime the answer you'd get by using significant figures is OUTSIDE the properly calculated min/max. In the "real world" significant figures are mostly just used for back-of-the-envelope type calculations. Great for quickly working something out on the whiteboard, but bad for sending someone to Mars. APL (talk) 03:21, 25 August 2009 (UTC)

The height of Mt. Everest was in the 1950s stated as "29,00229,003" feet. The actual best measurement, from a careful 1855 survey, was 29,000 +/- 3 feet, but for a century they expressed the height as "29,003 feet" to clarify that it was not "29,000 +/- 1000 500 feet." Strangely there have been several careful height measurements in the past few decades which give inconsistent heights which differ by more than their stated uncertainties. If I recall correctly, numerous physical constants such as the speed of light have been stated over the years with values which differ more than their stated uncertainties. The older measurements should have had stated uncertainties broad enough to encompass the more recent and more exact figures. But scientists like to claim their results are more precise than they really are. A lot of time in college science and engineering labs was wasted trying to measure things with greater accuracy than the crummy instruments permitted. Points were taken off if the "correct" result was not obtained,regardless of the fact that, say, a 3 mm high sine wave on an oscilloscope cannot be measured with high accuracy. Edison (talk) 04:10, 25 August 2009 (UTC)

The second question by the OP is the wrong way round. There are sure to be examples where the non-use of significant figures caused accidents that could have been avoided by proper use of significant figures. An example might be a diver who relies to the last second of his calculated air supply capacity 47.123 minutes when the calculation uses the oxygen tank pressure measured by a gauge that is accurate to only 5%. Cuddlyable3 (talk) 08:16, 25 August 2009 (UTC)

Adding a decimal point at the end of a number means it is ± 5, so "29,000." would be one way to specify it, although the actual error is ±2. The more difficult problem is how to specify 29,000 ±50 using significant digits. I've never much cared for significant digits, myself, and think ± values make a lot more sense. StuRat (talk) 14:34, 25 August 2009 (UTC)

You wouldn't be annoyed to see a paper give a value of 2528.41567 ± 108.64372? Looie496 (talk) 18:42, 25 August 2009 (UTC)

Haha. What about 2528.41567 ± (108.64372 ± 5.72318)? Dauto (talk) 20:03, 25 August 2009 (UTC)

It wouldn't annoy me in any case where that accuracy might be helpful. If they are giving the weight, in pounds, of a particular model of car, then that would be rather silly, yes. StuRat (talk) 15:46, 26 August 2009 (UTC)

Proper use of slide rules got around all these problems. And got us to the moon. Weepy.Moyer (talk) 18:55, 30 August 2009 (UTC)

Why old colour televisions with Cathode Ray tube show reddish colour when swithched on?

Yesterday when i was seeing television suddenly power went off and again came back suddenly. My television with cathode ray tube showed reddish effect.Why? —Preceding unsigned comment added by Sdbhadra (talk • contribs) 06:23, 25 August 2009 (UTC)

Could this be a phase error resulting in misalignment of the beam (e.g. hitting the wrong element of an aperture grille?) It seems plausible that on cold-start, temperature or voltage some other parameter is out of the steady-state value, resulting in a small phase-error in the timing of the raster-scan beam. Nimur (talk) 06:33, 25 August 2009 (UTC)

Colour TV CRTs have 3 beams for red, green and blue. Alignment of the beams is adjusted by "purity" magnets on the neck of the CRT; it is not a matter of signal timing. The overall colour cast of the picture is depends on the beam currents which are trimmed by 6 separate electrical controls i.e. one for each beam, bright and dark. The OP's reddish effect could be due to upset of these controls or uneven wear of the CRT guns. Cuddlyable3 (talk) 08:04, 25 August 2009 (UTC)

Most old TVs had manual adjustment knobs to correct for these problems. Usually, these were located under a panel or around in back of the TV. Look for a removable panel of some sort; you should find knobs that will allow for color, brightness, and contrast correction. --Jayron32 15:27, 25 August 2009 (UTC)

Is the issue transient (it came back reddish and then eventually equilibrated back to normal) or is it permanently changed after this event? DMacks (talk) 22:28, 25 August 2009 (UTC)

inadequate degaussing seems to blame

Jump the Moon

If I jump when the moon is directly overhead how much longer do I spend in the air? What about when it is on the horizon or directly underneath me? TheFutureAwaits (talk) 10:19, 25 August 2009 (UTC)

(all units below are in metric/SI units)

As an estimate, the acceleration due to gravity is 9.8m/s2 (I assume an average) , the moon weighs ~7.4x10^22 kg, and is at a distance of ~380x10^6 m

F=GM1M2/r^2

So acceleration on a mass =

a= F/M1=GM2/r^2 

which is (G=6.7x10^−11) :

6.7x10^-11 x 7.4x10^22 / 3.8x10^8 x 3.8x10^8
3.4 x 10^11 x 10^-16
3.4 x 10^-5

or 0.000034 m/s2 (no attempt made to avoid compound rounding errors)

Acceleration is a vector, so it can be added and subtracted to the mean acceleration

Giving an estimate of the min and max accelerations due to gravity of

9.8+/- 0.000034

As you can see the change is so small that it's not really work calculating the difference in times for the jumps.

Jump starts with velocity V , the time to accheive velocity -v (ignoring losses this is the velocity on landing) = 2v=0.5at^2

or t^2 = 4v/a

time = 2 sqrt(v/a)

Can you take it from there?83.100.250.79 (talk) 11:35, 25 August 2009 (UTC)

Interesting, what about the Sun? It's much heavier but also much further away. I wonder if athletes gain a performance advantage during the day versus at night? TheFutureAwaits (talk) 13:06, 25 August 2009 (UTC)

Actually I just tried the math with the sun's values and because the magnitude drops with the square of distance it's even less of an impact. TheFutureAwaits (talk) 13:17, 25 August 2009 (UTC)

Could a two body system exist where the phase of one would singnificantly affect the length of a person's jump? Say two large planets closely orbiting each other? TheFutureAwaits (talk) 13:17, 25 August 2009 (UTC)

I assume it COULD, but both planets would probably be terribly ripped apart due to the gravitational effects (see Jupiters Moon IO, or take the effect the moon has on the oceans and multiply it by 10,000. Chris M. (talk) 14:24, 25 August 2009 (UTC)

Plugging the moon's Roche limit (9496 km) into 79's math will give you ~0.054 m/s² of vert, so still not much. --Sean 15:08, 25 August 2009 (UTC)

That's because 79's math is wrong. He used the moon's bare gravitational atraction which falls with the square of the distance. He should have used the moon's tidal force which fall's with the cube of the distance. Dauto (talk) 16:58, 25 August 2009 (UTC)

The Earth (and anything on it) and Moon are in free fall with respect to each other, so they are weightless. I don't think the gravitational force of the Moon will have any impact at all. The tidal force on the other hand will, but the effect will be negligible compared to things like variations in the Earth's gravity in different places, atmospheric effects, etc.. --Tango (talk) 17:56, 25 August 2009 (UTC)

To expand on what Dauto and Tango said, the Earth is already experiencing acceleration due to gravity from the moon (or sun). Standing on Earth, the apparent gravitational acceleration caused by the moon (or sun) is the difference between the total acceleration due to gravity acting on the Earth (which is equivalent to the acceleration experienced at the center of the Earth) and the acceleration due to gravity acting on you (which is the acceleration experienced on the surface). This is the tidal force. Let R be the center to center distance, r the radius of Earth and M the mass of the moon (or sun), then the apparent acceleration to someone standing on the surface of the Earth directly under or directly away from the moon (or sun) is GM/(R±r)² - GM/R² or roughly 2GMr/R³ (in magnitude) if we take r << R which is the case here. For the moon that comes out to like 1.14×10^-6m/s² and for the sun 5.06×10^-7m/s². Rckrone (talk) 18:24, 25 August 2009 (UTC)

Which is about one ten millionth the Earth's surface gravitational acceleration. Variation between different locations on Earth is on the order of a few hundredths. --Tango (talk) 20:53, 25 August 2009 (UTC)

As to whether two bodies could exist where the phase of one (by which I assume you mean it's current location in the orbit) would significantly affect the gravity of the other, this would result in dual tidal locking, where one side of each body is always facing the other. Our Moon is already tidally locked to the Earth, but the Earth is not tidally locked to the Moon. I suppose if two such bodies had just come into proximity with one another (due to some interaction with a third, massive body, perhaps), then your scenario would present itself (along with massive quakes and/or tides) for a few million years before the two bodies became mutually tidally locked. StuRat (talk) 15:19, 27 August 2009 (UTC)

220v /230v/240v

Dear engineers ,

1. I have a query on line voltages . Pls reply the impact of using a 220v ballast in a 230v or 240v supply or vice versa especially in strret lighting using 400w/ 1000w sodium lamp .

2. also pls advise the impact if can use a 50 Hz ballast on a 60 hz circuit .

Thanks . —Preceding unsigned comment added by Npc123 (talk • contribs) 12:09, 25 August 2009 (UTC)

Answering question 1) The tolerances just aren't that tight. Read our article on Mains electricity, the section titled "Voltage levels" states that the voltage will vary by as much as 10% from the mean; so that a 230 V power supply really means anything from 210-250 or so. The fact is, the tolerances on what you are plugging in should allow for this; a light bulb will not explode over a 10% spike increase in voltage. It's just not that finicky. --Jayron32 15:25, 25 August 2009 (UTC)

I would expect 10% voltage variation to have an effect on bulb/ballast efficiency and lifetime. Edison (talk) 17:07, 25 August 2009 (UTC)

So exactly what effect would it have Edison? —Preceding unsigned comment added by 79.75.6.246 (talk) 23:12, 26 August 2009 (UTC)

Potential gain of irreversible, unidirectional, negative value time travel

If it is taken as a given that an average adult member of a civilized nation in 2009 has been transported back 200 years completely naked and without his time machine -- what would be the potential gain for the past civilization as it makes it ways towards the time period of the time traveler, if the average adult may know lots about the end products of technological advancement but not really so much about how to get there from scratch? Maybe he would know that penicillin kills bacteria and that it comes from bread mold, and I suppose that would give scientists a big head start. But to advance the people effectively, would saying things like "cathode ray tube" or "internal combustion engine" lead past scientists to anything if the time traveler can't explain anything about them? DRosenbach ^{(Talk | Contribs)} 12:21, 25 August 2009 (UTC)

The article on John Titor may be a start. --Cookatoo.ergo.ZooM (talk) 12:36, 25 August 2009 (UTC)

A Connecticut Yankee in King Arthur's Court would probably also be a good read. -- 128.104.112.102 (talk) 16:36, 25 August 2009 (UTC)

Does he have to be completely naked?  :) --Sean 12:57, 25 August 2009 (UTC)

Well, I added that in mid-writing so exclude the overwhelming benefit his clothes would play, as any one can describe seams, collars, textiles and buttons, but they would likely not be able to direct anyone on how to develop a bobbin, sewing machine, etc. based purely on knowledge without a physical example. His or her nudity was not a requirement as much as a lack of clothes. :) DRosenbach ^{(Talk | Contribs)} 13:40, 25 August 2009 (UTC)

I don't think you read my link, which would help more than buttons. --Sean 14:36, 25 August 2009 (UTC)

Haha -- you're right. I was in the middle of something and I thought it was a link to an article on nudity. :) DRosenbach ^{(Talk | Contribs)} 16:00, 25 August 2009 (UTC)

I think a person of modest intelligence could make an immense difference if he/she were believed and could manage to talk to the right people. However, arriving in a town, stark naked and babbling about time travel and the future could easily get you tossed into the nearest insane asylem with no chance of passing on any ideas whatever. Simple things like "Most diseases are caused by tiny animals that are too small to see" sounds like the babbling of a raving lunatic - but if described along with "Put some lenses together into a tube and you can see them" might help. But I think you'd want to be very careful about what things you described and in what order. 200 years ago, it would have been tough to manufacture many of the things you could describe. Even if you're a car mechanic who can explain every tiny detail about how a car works - that's of zero use if they can't make sufficiently accurate machine parts in a repeatable fashion.

The John Titor link above is a pretty good example of that. If Titor were indeed who he said he was - then pretty much everyone who mattered (including ALL of us here) would have dismissed him as a hoaxer or a loonie. SteveBaker (talk) 13:54, 25 August 2009 (UTC)

Indeed. The Victorians already knew plenty of basic science and had lots of vision and ideas. What they lacked was the technology to put some of those ideas into practice. The internal combustion engine was invented by François Isaac de Rivaz in 1806 but took 60 years before it could be produced in any numbers. The incandescent light bulb was invented in 1802, but not perfected until 75 years later. The electrical telegraph, invented in 1809, only went into commercial use in 1837. A Jacquard loom (invented 1801) embodies many of the concepts behind a modern computer, but the available technology could not be scaled up to produce mechanical computers. Gandalf61 (talk) 14:52, 25 August 2009 (UTC)

A couple more — diethyl ether and nitrous oxide (laughing gas) were both known before 1800, but didn't come into use as surgical anesthetics until the 1840s. (Unfortunately, the germ theory of disease and the idea of sterile surgical instruments didn't get kicked off until much later.) Really, though, we're well into the what-if games of science fiction. The problems of conveying scientific and engineering principles, along with the construction of the necessary infrastructure for technological development, are a staple of the time-travel genre. I recently read R.A. Lafferty's short story Rainbird, in which the protagonist is an early nineteenth-century inventor who repeatedly sends himself back in time (his final project is a time machine) to advise his younger self on what order he will need to invent things. If you're interested in knowing what the people of that era would understand, our articles here on Wikipedia can give you all manner of dates and places. TenOfAllTrades(talk) 15:10, 25 August 2009 (UTC)

The traveller would do well to gain the favor of someone with the resources to develop the things he has in his head and who is already an experimentalist. If you went back 200 years to London, you might swim to the docks and say you fell off a boat and had to shed your clothes to swim. Now clothed, go to the Royal Institution and volunteer to sweep up and assist for little or no pay, and gain the attention of Humphry Davy, who was at the forefront of electricity , physics and chemistry. You will be there 3 years before Michael Faraday would arrive in our timeline, and achieve about the same thing. But you can suggest many fruitful things to Davy, anticipating the discoveries Faraday would have made together with Davy a few years later, but you are in an alternative universe, so Faraday can go on to do other things. With a nudge, there could have been photography by 1810, telegraphy, telephones, phonographs and widespread use of practical generators powered by steam engines running incandescent electric lights and motors by 1820, radio, Xrays petroleum refining and internal combustion engines by 1830, airplanes, machineguns and practical submarines by 1840, and unfortunately nukes by 1900. Of course several other countries could have similarly been a fruitful field for introduction of science and technology. But you would get farther explaining an uptime gadget to an experimentalist with a scientific bent and resources than just going to a banker or politician with words. Depending on the era, one could have approached Franklin, Jefferson, Fulton, Joseph Henry, Volta, Westinghouse, Edison, or other experimentalists. Tesla (a hundred year ago) would likely not have been perturbed at all by a strange visitor with odd ideas. Get one uptime gadget working and making money or achieving fame for the patron, then work on the next one. Once you have made a name, there is less need for the downtime experimentalist. The bankroll is needed to pay the machinists, chemists, and glassblowers, as well as to pay for expeditions to remote lands to get minerals or biologicals needed for uptime gadgets, and a lot of time would be needed to get from the basic idea to a working gadget. Getting from the idea to the practical invention ate up an amazing amount of money. It would be very hard for the stranded uptimer to get the resources needed to make a working doodad, when by definition he starts with no resources and a presumption he has a screw loose. Edison (talk) 15:11, 25 August 2009 (UTC)

How did you estimate those dates, Edison? Sagittarian Milky Way (talk) 16:42, 27 August 2009 (UTC)

There are many, many examples of the abject failure of forward-thinkers (who might as well have been time travellers for all the good it did them): Babbage's Analytical engine would have been a perfectly useable computer - it would have propelled people forward into thinking of better ways to build such things, resulting (perhaps) in a much earlier arrival of modern computers and electronics onto the scene - and introduced the powerful idea of software as a way of formalizing algorithms in the same way that mathematics formalizes algebra, arithmetic, etc. Sadly, the guy with all the bright ideas was a terrible implementer and project manager and just awful at getting funding and such. If you tried to explain any of that stuff without those skills, your work would be a soon-forgotten novelty too. I was reading a book by the guy who made the replica of the (much simpler) Difference engine - and he showed conclusively that the machine could have been built with the available metalworking technology fairly easily. He also pointed out that none of the early developers of "modern" electronic computers had any idea of Babbages' earliers work...it was that completely forgotten!

The more I consider this question, the more I'm convinced that the problem would be entirely one of "getting the message across".

I'm reminded of an old Sci-Fi story (sorry - I forget who it was by or what it was called). A guy invents a one-time-use time-machine that can take him back by up to 500 years, keep him there for exactly 10 minutes and then bring him back to the present with no possibility of it ever working again - or ever being rebuilt (yeah - that's a bit contrived...but let's go with it). Knowing that he has only one shot at "fixing" history, he studies hard to see how to improve the lot of humanity and decides that taking a simple pocket calculator back in time and giving it to Sir Isaac Newton would relieve him of doing tedious calculations and enable him to get much more productive work done before he went "off the rails" and started flailing around with alchemy, crazy religious ideas, etc. The idea is that this one small act would improve the lot of man more than anything else he could come up with. What happens is that he materializes back in Newton's study with an impressive bang and a cloud of smoke - with one of those old red-LED calculators in hand. He shows it to Newton, and in an attempt to demonstrate its power, punches in '123+543' at random, hits '='...and the machine displays '666' in fiery red letters - thereby convincing Newton that this is the work of the devil and propelling him into his crazy religious ideas, alchemy, etc - exactly as per historical record. Such are the perils of this kind of endeavor!

SteveBaker (talk) 15:37, 25 August 2009 (UTC)

What was poor Newton going to do when the batteries ran out? Googlemeister (talk) 17:47, 25 August 2009 (UTC)

What if you gave Newton an iPhone, with the most useful parts of Wikipedia on it in screenshots and saved photos? You have 5 hours to use this, then it will be lost forever. ftocks fettings fafari flide to unlocke Sagittarian Milky Way (talk) 15:39, 26 August 2009 (UTC)

This must be a weird sticking point for SciFi writers. I've never read the story you just mentioned, but I'm sure that I've read a couple of other stories about time travelers or scientists with past-viewers that don't quite work right accidentally nudging Newton into insanity and/or occult research. APL (talk) 16:29, 25 August 2009 (UTC)

If you gave Newton a calculator, it's quite possible that he would not have gone on to invent integral calculus. Symbolic integration was invented to solve a class of physics problems that are very tedious to solve by successive additions (or as we call it today, numeric integration). --Carnildo (talk) 23:13, 25 August 2009 (UTC)

I would argue that what we should actually do is work for social progress (such as democracy), and not scientific progress. Otherwise, we might end up with Nazis who had nuclear weapons. It might even be good to retard scientific progress, in certain areas, if possible (tell the scientist about quantum mechanics, guaranteeing that they would all end up in insane asylums). :-) StuRat (talk) 15:43, 25 August 2009 (UTC)

"Otherwise, we might end up with Nazis who had nuclear weapons." -- As in the movie Philadelphia Experiment II? 98.234.126.251 (talk) 05:10, 26 August 2009 (UTC)

Yes, among many other sci-fi stories with a similar theme. StuRat (talk) 13:40, 27 August 2009 (UTC)

200 years ago would not put you before the invention of the internal combustion engine. But it would put you before it was easy to buy gasoline.

Instead of randomly giving scientists a head-start on things that you know for sure are going to be invented anyway, why not try to manipulate the order that things become practical and see if you can change which technologies go "mainstream".

My first thought was that perhaps you could reduce modern-day dependency on fossil fuels, but I'm not sure how. APL (talk) 16:06, 25 August 2009 (UTC)

You could do that by not helping with internal combustion engines but instead help with hydro-electric and windmill power generation (in particular, with the invention of the dynamo). I don't think solar cells were possible then, but passive solar heating certainly was. StuRat (talk) 16:32, 25 August 2009 (UTC)

I thought useful penicillin was first found on a moldy melon. Bread mold might turn out to be ergot, with hilarious results. 81.131.32.223 (talk) 17:23, 25 August 2009 (UTC)

I sit corrected. DRosenbach ^{(Talk | Contribs)} 21:30, 25 August 2009 (UTC)

As our articles Penicillin and Discovery of penicillin note, while the strain of Penicillium mold that was used for the first mass production of penicillin was indeed isolated from a moldy cantaloupe, penicillin itself (the identical chemical structure) was isolated prior to that from airborne contamination (Flemming's work). And while we can't be sure penicillin was the curative agent, traditional folk remedies used moldy bread, moldy oilcakes, and even warm soil to treat infections. So penicillin is found in bread mold - though, as you correctly point out, not all bread molds contain penicillin. -- 128.104.112.102 (talk) 21:51, 25 August 2009 (UTC)

I would just like to poke my head in to point out that the history of technology is very firm in showing that it is not just ideas that makes things work, but the creation of an infrastructure and overall context that is receptive to the idea. Thomas Edison gets a lot of credit for the light bulb; he ought to get more for developing the infrastructure of modern electricity. All the light bulbs in the world are useless if you don't have a system for powering them, and that doesn't come easy. As a lot of failed technologists have discovered, a good idea, by itself, doesn't do much, no matter how right it is. In medicine this is especially clear—even when it was rather conclusively demonstrated that cholera was a water-based illness, it took some many decades before physicians actually believed that was the case to the point that they would actually act on it. They stubbornly clung to their previous notions (that it was miasmatic, and was related to moral squalor) in part because that was the context of their medical worldview and their professional role ("don't drink the water" was not something that got them very much). (There is more detail on the cholera example in Rosenberg's The Cholera Years.) Over time, the incredibly simple explanation did, in fact, win out, and now it looks as terribly obvious as germ theory and so much else. But it took a lot of time, because people are rather stubborn lots... even being completely and demonstrably correct does not mean you will, in your lifetime, be recognized for it. --68.50.54.144 (talk) 23:30, 25 August 2009 (UTC)

Even the end of Cholera in London was by accident; the end of Cholera there is widely credited to the development of the London sewerage system, however the sewerage system was built under the mistaken belief that the smell of the sewerage caused cholera; by diverting sewerage from water supplies, the system largely helped clean up Cholera, but not for the expressed reason it was built. The history of science is filled with examples of people who got the right results for the wrong reasons. --Jayron32 23:44, 25 August 2009 (UTC)

Is that correct ? I thought John Snow conclusively demonstrated that cholera outbreaks were due to polluted water sources in his investigation of the 1854 Broad Street cholera outbreak. Bazalgette's London sewerage system was commissioned in 1858. Gandalf61 (talk) 13:41, 26 August 2009 (UTC)

Method of exhaustion may be seen as a form of calculus available 2 millenia early. Leonardo da Vinci's workshop with modern materials may have been a marvel unfathomable. However, without machines that make machines making machines, modern high technology is difficult. Mine some palladium if you please. Manufacture a 45 nm CPU (let alone the rest of the machine so you have something useful). One's knowledge of future events would be compromised by utilization of said knowledge (pardon the cartoons, but this exact premise is used in Beast Wars - the entire history of the future (up to a point many millions of years removed) is recorded on two disks... but one change and the rest would become fiction; unless you prefer your time travel Back to the Future style anthropomorphic). Also, Lord Kelvin - I can't seem to find the incident where later in life, he refused to amend his perceptions, holding back science (as it were) a few months. 69.255.26.5 (talk) 05:09, 26 August 2009 (UTC)

Your best bet would probably be social change. You could predict the downfall of Napoleon and his failed invasion of Russia. You could also predict his return to Paris for another go. That should buy you some credibility, and you could perhaps try to avoid some major mistakes made in the past. The problem is though, that then humanity would not learn from those mistakes (assuming humanity ever learns from its mistakes). Googlemeister (talk) 13:43, 26 August 2009 (UTC)

The problem is that predicting those things might prevent Napoleon from invading Russia, refuting the prediction. What you could do is claim to be a time traveller, write an encrypted message, and say that the key will be provided on a certain day. When the message is decoded on that day, its predictions would hopefully turn out to be right. --99.237.234.104 (talk) 14:15, 26 August 2009 (UTC)

The earlier in time you go, the more out of place you'd look if you weren't white. In addition, your English would get more and more strange to their ears, and theirs to yours. Would they stone a yellow human who appeared before they'd heard stories of them thirdhand or something through the Silk Road? Sagittarian Milky Way (talk) 14:00, 27 August 2009 (UTC)

I'm not at all sure this is true. Letting aside that there are places on Earth other than England, and letting aside that if you go back far enough you won't find white people anywhere, there's still a chance that you could parley your strange appearance into an explanation for your otherworldly knowledge but lack of status. APL (talk) 15:10, 27 August 2009 (UTC)

I was just saying if you were a race they'd never heard of before, death could be enough of a possibility to affect your destination for irreversible naked time travel. Spending the rest of your life running from and thsn hiding from humans in the woods and having to learn how to make fire does not sound funner than helping Davy. Even if you die, you might live awhile. Magellan lived for awhile but Medieval deformed babies were thrown down wells immediately. Either it'd be very good for your goal or very bad, possibly depending on local mythology and legend. It's hard to imagine they'd be indifferent. With the language, you'd be very disadvantaged until you could learn Middle English or Gutenburg's German or whatever. This would be important for time tourism but moot for this purpose though, as these problems wouldn't exist in the locations and time periods most interesting for seeing the effects of your knowledge flourish in the remainder of your lifetime. Sagittarian Milky Way (talk) 16:42, 27 August 2009 (UTC)

Lest Darkness Fall is a very good book about a guy in exactly this situation, sent back to Ancient Rome and stuck with the dilemma of trying to accelerate science despite lack of materials, not speaking the language, no one taking him seriously, his own incomplete knowledge, etc. Replay is another book that touches on the "what would be the best changes to make, and how would you gain credibility" questions. -Elmer Clark (talk) 08:06, 28 August 2009 (UTC)

human hermaphrodites

can a human hermaphrodite give birth or impregnat a woman ? —Preceding unsigned comment added by 123.208.128.220 (talk) 12:58, 25 August 2009 (UTC)

There are a broad range of conditions that fall under that term, with different impacts on fertility. See intersexuality for the details. --Sean 13:03, 25 August 2009 (UTC)

Recoil in a vortex launcher

Hi guys

Question: If i have an explosion driven vortex launcher and I shoot it at an object, what will happen due to recoil would it be tgus

Since the area of effect on the launcher in the explosion chamber is small in diametre (about 4 inches) and the area the vortex effects is larger (around 2 foot) the target will be moved further backwards than the launcher, since larger area and less force are better for moving objects and even though the launcher feels more kinetic energy it is over a much small serface area. (for example like a sail on a large ship. 100 psi focussed on 1 foot of the ship would not be as good for moving the ship as 0.3 psi focused on the 30 feet sail?

Thanks

Robin —Preceding unsigned comment added by 79.68.243.180 (talk) 19:57, 25 August 2009 (UTC)

How much farther back is the ship and how heavy is the ship? Dogposter 21:28, 25 August 2009 (UTC)

Who was "Lawrence" that named lots of southern African species in the early 20th century?

A person (presumably male) with the name (presumably surname) "Lawrence" seems to have done a lot of taxonomic work identifying species (e.g. spiders and lizards) in southern Africa (especially Nambia, Botswana and South Africa) around the 1920s. See for example 8 separate species on the List of Salticidae species K-M.

However I can't find who he was. Wikispecies article species:Lawrence is about George Newbold Lawrence an American ornithologist who lived from 1806 - 1895 and so isn't the right person. Thryduulf (talk) 22:36, 25 August 2009 (UTC)

Seems to be an R. F. Lawrence, if this then this google searches are anything to go by. --Tagishsimon (talk) 22:41, 25 August 2009 (UTC)

And here's an obituary. --Tagishsimon (talk) 22:44, 25 August 2009 (UTC)