Wikipedia:Reference desk/Archives/Science/2006 November 12

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November 12

Standard voltages

Where does the five-volt TTL operational voltage figure come from? Is it from the parts originally used in the first TTL circuits (and hence somewhat arbitrary), or is there a more physical/practical engineering reason for it? Virog^{It's not}_{my fault!} 04:41, 12 November 2006 (UTC)

It is the nominal supply voltage (actually 5v +/- 0.25V) that will guarantee a logic low of < 0.8 v and a logic high of between 2.0 V an 5 v with all the tolerances of the circuit and output loading etc. It does depend upon the internal design of the logic gates. See TTL and Digital circuit for more info.--Light current 21:14, 12 November 2006 (UTC)

Ah, I did read those already, and am quite familiar with digital logic. I was just curious as to how 5V was chosen - was it due to the parts used to prototype the first TTL circuits, or for a physical reason? Virog^{It's not}_{my fault!}

I think Light current did answer the question, if somewhat obliquely. Remember, for reasons of minimising power consumption, you want the lowest operating voltage that will still let your logic circuits operate reliably and quickly. I think that 5V was about the lowest voltage that ordinary TTL logic gates (with multi-emitter inputs, so-called "totem-pole" outputs, etc.) could utilize and still produce an adequate noise margin.

Similarly, you'll recall that the older RTL tended to use 3.6 volts.

I didnt know that! But there again it was before my time 8-)--Light current 16:26, 13 November 2006 (UTC)

I know how you feel; when TTL first came out, I know that I said "5 volts? Why 5 volts? Why not good-old 6 volts? Why 5?" But nowadays, of course, we're used to all sorts of odd voltages, and lower with each succeeding CMOS generation.

Atlant 14:09, 13 November 2006 (UTC)

That makes sense. I guess LC did answer my question - serves me right for reading the reply at 1AM =O) Virog^{It's not}_{my fault!} 16:12, 13 November 2006 (UTC)

Well only by chance! User:Atlant puts this in context and mentioned the important subject of power consumption which I ignored! 8-)--Light current 16:25, 13 November 2006 (UTC)

Capacitor

How does one build a capacitor? This is not for another half-baked idea like using human fat as an alternative fuel source. This is for a home project; don’t ask for the details. -- THL 05:23, 12 November 2006 (UTC)

Try using two pieces of aluminum foil, with each piece connected to one terminal of a battery. You can roll up the aluminum foil to make the capacitor smaller; read http://sci-toys.com/scitoys/scitoys/radio/homemade_radio.html (roughly halfway down the page, "Building your own capacitors") for details. --Bowlhover 05:30, 12 November 2006 (UTC)

You'd need some sort of dielectric between them unless they were far apart.

Would that work with AC current? Also, would copper plates work better? I need to build up a fair amount of voltage for this, and I need to minimize resistance. I have access to large amounts of rubber, so the insulator won't be a problem. -- THL 11:12, 12 November 2006 (UTC)

If it matters, I'm wiring this from a generator that I made myself, so it won't be out of a plug. I will be hooking the wires up directly to wherever they need to go. I have already built the generator and it works, but I need way more power than it generates. I only need it for an instant, however, so a capacitor would be perfect. -- THL 11:26, 12 November 2006 (UTC)

From the questions you asked, it seems you might have some misunderstanding about how capacitors work. People here may be able to help you better if you provide more details about your project. I am not an expert in electrical power, but capacitors are not the only way to provide a power reserve. Would a flywheel be an option for what you want to do? --71.244.101.6 15:52, 12 November 2006 (UTC)

AC current will flow through a capacitor as if it doesn't exist. The capacitor will charge up, but you can't access the charge unless you isolate the capacitor and connect it to an electric device. Is that what you want? --Bowlhover 22:55, 12 November 2006 (UTC)

Has the OP looked at our page on capacitor yet ?--Light current 00:11, 13 November 2006 (UTC)

I have looked at the page on capacitors. My father and brother both work for major electric companies, and they said that capacitors are often used to dam electricity and build up voltage in the same way that a dam blocks water and pressure builds up behind it. That is what I need to do. I need a fair amount of voltage for a very short time, and they said a capacitor would be the best choice for that purpose. Basically, I need around 500 volts of electricity for less than a second, and I would like to use a capacitor to do this. If you all know of a better alternative I'm listening, but if not I need to know of the best way to build a capacitor, and how to use it to dam electricity. My family doesn't know how to build them, or how to use it for that purpose, but they know that they are used for that purpose. Cheers, -- THL 04:35, 13 November 2006 (UTC)

Indeed, as you would basically be generating an RC circuit, with the thing you need to apply voltage to becoming your resistor. The easiest way to get a capacitor is to buy them; it's hard to build a capacitor with a dielectric constant high enough for it to be small. If size is not a constraint, though, use two aluminum (or any other metal) plates, and wax paper in between, and allow it to charge for a long time before discharging.

Also, remember that your capacitance is inversely proportional to the separation between your plates; so, you can put some weight on it and make your capacitor stronger. Titoxd^(?!?) 04:44, 13 November 2006 (UTC)

Sweet, thanks. One last question, aside from precious metals what would be the best metal for me to use? I must build this thing from scratch; I have no choice. I'm not doing anything illegal, but the parts that I would have to buy would look very suspicious. A metaphor so this can make more sense, I have a cold and I'm going to have to clean a house. I need certain ratios of certain cleaning products, and large amounts of Sudafed; what I'm doing is totally innocent, but the cashier at the store will think I'm running a meth lab and turn me in. That is the position I'm in. -- THL 05:07, 13 November 2006 (UTC)

Use kitchen foil (aluminium). Maybe greaseproof paper or (better) polyethylene or polycarbonate sheet as the dielectric (insulator). Please be very careful when you have connected the capacitors to your generator as at 500V they may hold enough charge to kill you (depending on the capacitance ).

--Light current 05:14, 13 November 2006 (UTC)

I'm going to take the appropriate precautions. Actually, I forgot to ask the most important question. How would I set it up to dam the electricity, and then release it? I couldn't understand the RC current page. I'll be hooking the capacitor up to my generator, and releasing the electricity into a nail. I'll be running wire to the nail. Cheers, -- THL 05:34, 13 November 2006 (UTC)

Well to large extent this depends upon the sort of generator you are using. If its a Wimshurst machine or Van de Graaf generator these will have a high output resistance and so the capacitor should be connected from the output to earth forming the RC circuit to store up the energy. You are also going to need a high voltage switch to release the energy from your capacitor into the nail. THis is going to be rather tricky cos you want it to be safe to operate. You might consider a relay but I suppose you dont have any lying around! It is just possible that you may get a spark gap to operate at around 500 V dc but the gap will have to be very small. Are you tring to melt the nail?--Light current 07:09, 13 November 2006 (UTC)

The questions sound like you have only a vague idea of the physics of electricity. If you know nothing about capacitors and very little about electricity, then you should not be working with capacitors charged to 500 volts, since they are quite capable of killing a person. When you say you will take precautions, I wonder how you would know what the proper precautions are. They are likely more severe than you would suppose. A capacitor of large capacitance connected across AC voltage will conduct a large displacement current and may fail or damage the generator. The capacitive reactance which limits the flow of AC current is $X_{C}={\frac {1}{\omega C}}$ where omega (ω)is equal to 2*pi*the frequency. A capacitor connected in an AC circuit might retain some unpredictable amount of voltage if the AC source were suddenly disconnected. DC could be obtained from an AC source by a bridge rectifier circuit. A capacitor connected actoss DC will charge up to the supply voltage, and will discharge across any available conductive path, or back through the generator winding if the generator stops. Diodes can control the direction of flow and resistors can limit the maximum current. A high school physics book can make a lot of things clear to you without going too deeply into the complex mathematics of how the circuits work. That said, a capacitor such as described would have one sheet of conductor attached to the positive supply and one to the negative supply, with an insulator (dielectric) between them. The dielectric must be thick enough to withstand the applied voltage with a sizeable safety margin. Books such as the "Handbook of Chemistry and Physics" or physics textbooks list the dielectric constants of various materials, and the thickness needed to withstand a certain applied voltage. A thinner dielectric means higher capacitance but lower voltage withstand. A thicker dielectric means a higher voltage withstand, but lower capacitance. Different dielectrics (plastic, glass, mica, waxed paper, oil, electrolytic chemicals) have different insulating abilities and dielectric constants. A larger area means a higher capacitance. A home made capacitor might fail by arcing between the conductors as a hole is burned through the dielectric, or by arcing between metal portions where the wires connect to the conductors. The dielectric between the conductive surfaces must not have any gaps or cracks or pinholes or thin spots. Remember that stored energy is inherently dangerous: it can shock and cause burns or cardiac arrest leading to injury or death. It can arc and catch fire, or it can explode. Commercially made capacitors are likely to work out better than a home made unit. Edison 16:59, 13 November 2006 (UTC)

This is an experiment tailor made to kill people. Please do not do this without adequate profesional supervision. 500 volts, if it can be sustained for even a 1/10 of a second across any reasonable resistor is enough amps to kill. Unless you have enough capacitance, you're playing with a giant generator, which given that you're asking these questions, is enough wattage to start serious fires. I have significant and strong safety concerns. JBKramer 17:10, 13 November 2006 (UTC)

I don't understand much about the physics of electricity, but my father and brother will be the ones doing the work. I'm just building it. They are paid to work with wires that are carrying 500,000v of electricity while they are hanging upside-down on a daily basis. They can handle themselves with 500v of electricity ;) They'll be inspecting my connections, how well I wired it, ect. They just don't know how to build capacitors, so they told me to do it. Anyway, all I have to do is get a charge around 500v to the nail, and they are taking care of the rest. We are not trying to melt the nail; we would just use a torch for that. My generator is a large, large coil of copper wire, surrounded by magnets. Like the kind a lot of high school physics teacher build for demonstrations, but it weighs around 50 lbs. I need to wire that up to the capacitor, dam the electricity to build the voltage, and connect the capacitor to the iron nail. My brother said he would wire the switch for releasing it himself, so I don't have to worry about that. At this point all I need to worry about is wiring the generator to the capacitor, and then the capacitor to the nail in such a way that the capacitor can dam the electricity. By the way, I've been forgetting to thank you all. Thanks for everything, and thanks in advance for this. Cheers, -- THL 22:54, 13 November 2006 (UTC)

If you connect one capacitor to one generator, the voltage on the capacitor will only be as great as the voltage produced by the generator. One way around this is to charge several capacitors wired in series, disconnect the generator, then throw switches to connect the capacitors in series. --Gerry Ashton 02:54, 15 November 2006 (UTC)

Alright, thanks everybody. -- THL^CCD 06:38, 15 November 2006 (UTC)

I think you mean connect them for charging in parallel (10 caps each at 10v) and then discharge them in series (10 caps in line makes 100v). Not that I encourage 'playing' with hazardous voltage, so DON'T TRY THIS AT HOME! In reference to the topic at large, to do what you are describing simply and effectively you need to use an inductor in a charging circuit. This can take a relatively low voltage over a period of time and turn it into a very brief period of very high voltage. To accomplish this from scratch, you will need a generator, a rectifier, a capacitor, and an inductor. I will leave the details to you hoping you will realize the potential hazards during construction. --Jmeden2000 20:23, 15 November 2006 (UTC)

Alright. I have trouble understanding articles that are mostly equations with minimal explanation, so I may be back with new questions. Cheers, -- THL^CCD 21:58, 15 November 2006 (UTC)

Graphs

Hello all. I have an exam tomorrow and this just came to me now.

120|
   |
   |
   |       /---------------------\
   |      /                       \
80 |     /                         \ 
   |    /                           \
   |   /                             \
40 |  / 
   | /
   |/
----------20-------40-------60----80-------

Now this is a displacement/time (time is x axis). Now, i am asked to draw the velovity time graph. is this drawn like

----------                _____________   or    
                                              /-----\
           --------------                    /       \

Please help. My textbook is worthless and i need this information quickly. Thanks in advance. Cuban Cigar 11:18, 12 November 2006 (UTC)

(edit) the graph looks real stilted. it goes diagnol up, straight horizontal, diaganol down. im just looking for rough shapes.

Here's a quick rundown on linear motion to help you for your exam. Before we can do anything, we need to decide on an axis. This is the straight line that we will be moving along. It might be forewards/backwards, east/west, up/down, whatever. Once we've got our axis, we choose an origin (a "zero" point), and a direction to call "positive". As an example, if I'm considering the motion of a train rolling along a straight strack over the course of 30 seconds, my axis would be along the track, a good origin will be the spot where the front of the train was at the start of the 30 seconds, and a good positive would the direction the train is moving.

Now that we have set up a way of measuring things, we can analyse motion. Remember that as things move, their displacement (position, with respect to the origin) will be changing. Their velocity is the rate of change of their displacement. So if our object's displacement is remaining constant (not changing at all), then it must have zero velocity. If the displacement is getting higher, then the object is moving in the positive direction, so it must have positive velocity. If the displacement is getting lower, then the object is moving in the negative direction, so it must have negative velocity.

Remember that positive velocity means "moving towards the positive end", not "moving away from the origin", and similarly for negative. An object which starts with displacement -10, and then over a few seconds moves through -9, -8, -7, etc, has a positive velocity, because it is travelling towards the positive numbers. Hopefully this helps you understand what you're looking at with these graphs. Maelin (Talk | Contribs) 12:14, 12 November 2006 (UTC)

With lack of figures I can't do the calculations involved in order to have the correct gradients and positions, but this image shows the general shape your graph should look like:

The first part shows a constant velocity since the first part of the displacement graph is straight. The middle part shows no velocity, because the displacement graph shows no change in displacement. The end part shows a negative constant velocity since the displacement graph shows the vehicle travelling back to the origin (so must be going in an opposite direction, hence opposite velocity, to the way it went in the first part). RevenDS 12:28, 12 November 2006 (UTC)

I should also add that since velocity has both magnitude and direction, you must indicate the third part of the graph to be below the x-axis. If you are asked to draw a speed-time graph, then your original guess is correct. RevenDS 13:03, 13 November 2006 (UTC)

Psychology

Like to find out 2 main questions that i concern now...

1) How does psychology affect us? 2) Each and every part of a living thing has muscles which are linked to the brain, but how does it work to tell us something?

Thanks alot...

Love, Joeline

(1) See psychology.

(2) See nervous system.

Come back an ask a more specific question if there is anything you still don't understand. Love. --Shantavira 13:39, 12 November 2006 (UTC)

Anaerobic fermentation with yeast.

I am wondering as to the effect a different type of sugar,mainly, glucose, fructose, lactose and sucrose, have on the amount of carbon dioxide, produced by the process of fermentation and the physiological explanation for this. Thank you in advance for your comments and suggestions. —Preceding unsigned comment added by 81.156.30.13 (talk • contribs)

Is this a homework question? Ultimately, only monosaccharides can undergo biochemical fermentation. One mole of glucose, for example, will always yield two moles of ethanol and two moles of carbon dioxide. However, polysaccharides like sucrose can be converted to glucose and fructose by the enzymes in yeast, and then the resulting sugars are what ferment. From sucrose, you get a mole of glucose and a mole of fructose. These two moles will then yield four moles of ethanol and four moles of carbon dioxide. --Russoc4 16:43, 12 November 2006 (UTC)

Global warming, man made?

• Isn't it a bit far fetched to suggest that a natural climate condition could have been affected so quickly by human actions? A few people driving around in modern SUVs isn't exactly going to affect a thousand year old cycle of climate change on the earth, I mean there used to be an ice age, and it's been getting warmer since, and now it's dry and arid, obviously there haven't been human beings living there the whole time doing it, so why attribute it to human actions? It seems like this was more of an excuse for Al Gore and the Bill Clinton / Howard Dean crowd to get the federal government involved in the personal affairs of Americans, then a serious study in climate change. So the question, in light of current science, does Gore's theory of 'Global Warming' still hold water?--Dusty Bowls 20:02, 12 November 2006 (UTC)

Dear Dusty Bowls, that's quite a loaded question, and I suspect you wont find a unanimous answer. Before we get into specifics, did you read Attribution of recent climate change and Scientific opinion on climate change yet? ---Sluzzelin 20:12, 12 November 2006 (UTC)

You're basing your conclusion on intuition, not science. A subjective feeling of far-fetchedness is not a proper tool for evaluating the likelihood that a theory explains some phenomenon. I'm sure someone from the Biblical times would find it far-fetched to imagine a machine capable of doing calculations a billion times faster than a human can and yet takes up no more space than an apple. --71.244.101.6 21:18, 12 November 2006 (UTC)

CO₂ concentrations over the past 400,000 years.

If you look at the graph on the right you will see that the concentration has increased very much over the past 200 years. Of course CO₂ isn't the only gas contributing to global warming, but I wouldn't say that humans have nothing to do with it. - Dammit 21:47, 12 November 2006 (UTC)

Al Gore doesn't have a theory of global warming as he is a politician not a scientist. Politics is much more interested in redistributing or protecting wealth so all of the research is tainted (both for and against global warming). --Tbeatty 21:50, 12 November 2006 (UTC)

I regularly read scholarly articles in Science et al. that do provide ample evidence, using dozens of different metrics & techniques, that there is a global warming trend. The most dramatic warming has occurred since the industrial revolution and seems to be causally linked to the great increases in greenhouse gas production via the burning of fossil fuels. It's a pretty established scientific consensus that

1. global warming is real

2. humans play a significant role in its progress

3. the consequences could be drastic and may be irreversible

The debate over #1 is largely closed, with essentially only right-wing thinktanks and such denying it is real, although there are some scientists with arguments against anthropogenic causes worth noting. #2 is a big question as to the proportion of "blame" to lay on us (IMO, it's too much finger pointing & too little action--what does it matter if we're responsible for 95% of the warming or 40%? It's still a significant amount...). #3 is where the real energy should be spent: what are the consequences of the trend & what can (reasonably) be done to slow/stop/reverse the trends. -- Scientizzle 21:53, 12 November 2006 (UTC)

Hmm? I regularly read scholarly articles in Science et al. that do provide ample evidence using dozens (more) of different metrics & techniques, that there is a global warming trend. Assuming a time frame, this is indebatable (no snide comments!). It's for sure. The debate is, and is centered around a few vital questions: how much? what is the cause? how strongly does CO₂ as a GHG's affect (logarithmic) the global mean temperature? Most disagreements not dripping science are either politically-, or economically-based and we should kill them we should not give them that much respect for those reasons. X [Mac Davis] (DESK|How's my driving?) 08:15, 13 November 2006 (UTC)

"A few people driving around in modern SUVs isn't exactly going to affect a thousand year old cycle of climate change on the earth" A few SUVs aren't going to affect the Earth, but how about millions of people driving millions of SUVs? Let's not forget the factories that release huge amounts of carbon dioxide. Carbon dioxide is a greenhouse gas that's very effective in keeping Earth warm; imagine what would happen if the amount currently in the atmosphere is doubled.

Let's imagine, shall we? Oh, it's making me giddy! But we can't. How about don't imagine, and we use data? I like that idea even better.

CO₂ is growing exponentially[1] Agree? I'm not about to go fetch the data and stick it in Mathematica at 2 am. Let's just eyeball it and it'll be a secret. ;) Wait, you believed me? Maybe I was wrong. Maybe it's a linear trend[2] eh? Or maybe we could just take into account that the relation of CO₂ and it's GHG effect is a logarithmic correlation, not linear. That greater the ppm value, the less effect you add on. In fact, the graph looks like this. Take for instance, the very high estimate of Charnock & Shine— rounding, from 0-20 the y coordinate is 6, Δ_y=6! From 20-40 y=8, or Δ_y=2. From 40-60, y=8.2? Δ_y= 0.25 You get the idea. The potential planetary warming from a doubling of atmospheric carbon dioxide from pre-Industrial Revolution levels of ~280ppmv to 560ppmv (future guess to the way we're going) is generally estimated at less than 1 °C. The point is, yes the more CO₂ you add the greater the GHE if you don't change anything else (then again, conservation of mass) but it isn't as scary as it sounds, because the more you add the less it counts. X [Mac Davis] (DESK|How's my driving?) 08:15, 13 November 2006 (UTC)

"The potential planetary warming from a doubling of atmospheric carbon dioxide...is generally estimated at less than 1 °C" Really? Have a look at our climate sensitivity article. The Earth's temperature will rise by 1.5 to 4.5 degrees if CO2 levels are doubled. The average of 1.5 and 4.5 is 3.

"it isn't as scary as it sounds, because the more you add the less it counts" So what? As you yourself admitted, pretty soon the amount of CO2 in the atmosphere is going to be doubled. Isn't a 3-degree rise in the temperature bad enough? Right now the average temperature has only risen half a degree, yet we're already noticing some of the effects. --Bowlhover 00:57, 14 November 2006 (UTC)

Two millennia of mean surface temperatures according to different reconstructions, each smoothed on a decadal scale. The unsmoothed, annual value for 2004 is also plotted for reference.

"I mean there used to be an ice age, and it's been getting warmer since, and now it's dry and arid, obviously there haven't been human beings living there the whole time doing it, so why attribute it to human actions?" Because, as the graph on the right shows, the temperature has been increasing drastically over the past century and a half. Now, Earth is warmer than it has ever been in the past two millenia. Do you think it's a coincidence that this warming started when human CO2 emissions started increasing rapidly?

"It seems like this was more of an excuse for Al Gore and the Bill Clinton / Howard Dean crowd to get the federal government involved in the personal affairs of Americans" But the vast majority of scientists around the world (not only in the U.S.) believe human activities are causing global warming. Unless you believe Bill Clinton can force every scientist in the world to believe in something that goes against the evidence, I don't see how global warming can be an "excuse" concoted by the U.S. government.

"that's quite a loaded question, and I suspect you wont find a unanimous answer." If Dusty Bowls asks scientists rather than us, I'm sure he will get a very nearly unanimous answer: humans are causing the Earth to heat up. --Bowlhover 22:53, 12 November 2006 (UTC)

The idea that "scientists know what is going on and we don't" makes me think appeal to authority, credentialism, and bastardization. And, as shown in our last discussion, paleoclimatology is a very rough field. There is a lot of guessing and we aren't exactly sure what is going on because we're dealing with quite a bit of stuff. Every possible tiny little biological and chemical cycle, quantum physics, the Earth's albedo, solar insolation, cosmic rays... it is all rather crazy. X [Mac Davis] (DESK|How's my driving?) 08:23, 13 November 2006 (UTC)

I agree, Bowlhover. I guess I remembered a similar question provoking a rather lengthy and decidedly multianimous debate here. ---Sluzzelin 01:06, 13 November 2006 (UTC)

Right. But it seems that this time, Mac Davis (the main supporter of the "global warming isn't due to humans" position) doesn't want to debate with us anymore. --Bowlhover 05:34, 13 November 2006 (UTC)

Whoa whoa whoa! What are you talking about? I'm on wikibreak and have got a lot of work to do. That's a low blow man. One day late... why I oughta! I'll see what I can do for you though. ;) And I think you've mischaracterized my position, if I have one. I'm just a guy that likes to read paleoclimatology and has formed my own conclusions after of course speaking with experts on the subject rather frequently. If you were to put me into a camp, although sometimes it seems like "faction" is better for this subject, I would advise you to make it "skeptical of an anthropogenic CO₂ global warming (AGW)." Thanks for putting me in quotes though to make me sound silly! X [Mac Davis] (DESK|How's my driving?) 05:57, 13 November 2006 (UTC)

The difficulty is not in proving that the changes are happening, but in pin-pointing whether that cause is by humans or not. A graph showing a rise in the past 200 years (or so) is not proof that the affect is CAUSED by humans, rather proof that changes are happening.

Additionally science is not a consenseus community, it is a community in pursuit of evidence to proof/disprove their claims. Of course the more scientists that agree on something the more likely that theory/argument is accurate, but by virtue of numbers alone this again is not proof.

All this is, however, an aside. The question with regards to climate change is whether we try to stop it, or whether we try and prepare to live through it. Nobody seems to produce in the media any benefits to global warming, yet with such vast change being undertaken there will be winners and losers. The question of human influence is down to the weight of human influence (is it all humanity's fault or has natural change had an impact too?). The technical questions are where scientists come in, but the world-impact questions are not the remit of science, they do not have the sufficient expertise in population management/technological development/world politics etc. etc. to work. ny156uk 23:17, 12 November 2006 (UTC)

Why do we need proof that the recent rise in temperature has been caused by humans? Strong evidence is good enough. I know science is not a consensus community, but there has been no evidence suggesting that the recent rise in global temperatures isn't due to human activities. --Bowlhover 00:57, 14 November 2006 (UTC)

Nice post. X [Mac Davis] (DESK|How's my driving?) 08:15, 13 November 2006 (UTC)

If the average global temperature starts rising at the same time as the amount of human-produced carbon dioxide starts rising, I would consider that as pretty strong evidence that the former is due to the latter, since carbon dioxide is a greenhouse gas. Of course this is not a proof; nothing in science can be conclusively proved. But if you add wood to a fireplace, and you feel hotter, wouldn't you assume that you feel hotter because of the extra wood? --Bowlhover 00:13, 13 November 2006 (UTC)

Don't make me start breaking out the logical fallacies Bowlhover— let's just say cum hoc ergo propter hoc. :) X [Mac Davis] (DESK|How's my driving?) 08:15, 13 November 2006 (UTC)

If an event, A, happens directly after another event, B, then this provides evidence that B causes A. I know it doesn't prove it, but what if you know for sure that B can cause A, because you've seen it happen before? Adding to the example I gave in my previous post, let's say you add more wood to a fireplace than you've ever added before. You know that your room will get warmer, because it got warmer all the previous times you've added wood. Also, the best scientific theories predict that your room will get warmer. Sure enough, you feel much hotter after a while. Will you assume that your heated up because of the extra wood, or will you assume that it's simply a coincidence that your room gets unbearably hot right after you add a ton of wood to the fireplace? What if a Wikipedia editor came to you and insisted that you're commiting the "cum hoc ergo propter hoc" logical fallacy? Will you listen to him? --Bowlhover 17:12, 13 November 2006 (UTC)

Whether or not humanity has caused the changes to happen is in the past. What matters now is what is making the problem worse. We know that vehicles emit CO₂. We know that factories emit CO₂. We know that global warming is getting worse, has the potential to change the world as we know it, and is currently in the process of doing so. We know that CO₂ makes global warming worse. We know that global warming has the potential to become self sustaining, assuming that it hasn't already. All of this we know. What matters in the here and now is what we should do about it. Lowering CO₂ emissions will slow the problem down, and that is better than not doing anything, but the real question is can/how do we reverse global warming. -- THL 05:50, 13 November 2006 (UTC)

"We know that CO₂ makes global warming worse." This implies global warming is a problem, a problem in which we will all die (or suffer horribly). If I'm not mistaken, global warming should have been happening since CO₂ started going up, somewhere around a hundred years ago (and it probably has). In fact, there should have been a ΔT spike in the 40s. Since we haven't gone through a global warming like this before, or in a high enough state of development to realize what is going on, I don't think we could nail down the cost-benefit analysis very close at all (although there have been a few crazy ones, most notably the most recent one from Britain), and definitely won't be able to think up the effects of any mean change in global temperature. Richard Muller at Berkeley doesn't think global warming is bad at all.[3] X [Mac Davis] (DESK|How's my driving?) 08:15, 13 November 2006 (UTC)

Just because mankind has never been through a global warming before, it doesn't mean that nobody knows what's going to happen. (As an example, even if no hurricane has ever hit a particular city before, we can be sure that there will be damaged buildings, flooding, power outages, etc. if one does hit.) The weather can be forcasted accurately, and weather forcasting uses roughly the same science as global-warming-forecasting. For example, Antarctic ice melting will increase the sea level, which will cause flooding in low-lying areas. Is flooding a good thing? You decide. --Bowlhover 00:57, 14 November 2006 (UTC)

There is a 30 year lag in climate behaviour from CO2 changes. It's been well established. Just wait til we start experiencing the weather 30 years down the track that we're creating today. Climate change from human sources was predicted, and now it's clearly happening. —Pengo ^{talk · contribs} 14:13, 13 November 2006 (UTC)

Well established 30 years eh?[4]

So there was an enormous CO₂ spike in 1910 then? If, in the 40s there was a CO₂ spike, why exactly does the temperature keep going down? Your mentioning of lag brought up an interesting possibility I just thought of. If CO₂ ppm goes up why does ΔT wait? Observe[5] Can you read that graph and infer anything? I would say Perhaps ΔT, ΔCH₄ ppm, and ΔCO₂ ppm are all related, and one or more influence each other. What if temperature influenced CO₂? I know that right now we're kind of talking about the around doubling of CO₂ (eyeballing) from the pattern in the last 650,000 years. Also, the solar insolation graph stuck on top looks pretty suspicious... X [Mac Davis] (DESK|How's my driving?) 20:37, 13 November 2006 (UTC)

"If CO₂ ppm goes up why does ΔT wait?" Because it takes a long time to warm up the whole planet. If you erect a greenhouse and close the door, does the temperature increase immediately after you close the door? No, it will take a while. Releasing huge amounts of CO2 can increase the temperature because it traps heat. But the trapped heat has to warm up the land, and then it has to warm up 1.3 billion cubic kilometres of water (so that the ocean doesn't keep the global average temperature down). How long do you think this will take? One day?

"What if temperature influenced CO₂?" I don't get what you mean. Are you trying to say that 200 years ago the temperature started rising for absolutely no reason, which then caused humans to pollute the atmosphere? If you're saying that a rise in temperature will cause more CO2 to be released by nature, which process would be reponsible for this? Carbon dioxide is, for certain, a greenhouse gas that can warm the planet up. --Bowlhover 00:57, 14 November 2006 (UTC)

If your models predict that the normal state of affairs will change, and then it does, in the way they predicted, then that is usually a pretty strong support for the models. And it isn't Gore's theory. It's a scientific theory. Gore merely refers to it. And he isn't quite the only one. From a scientific point of view there may not be absolute certainty, but then there never is. From a political point of view, if scientists say there is a possibility that things are going to go horribly wrong, then one should at least stop and think. Risk is chance times effects. If the effects are potentially disastrous, then even if there is a small chance, one should take action. If the chances come close to certainty then one should take action really fast. Especially if there are longlasting after-effects. DirkvdM 10:28, 13 November 2006 (UTC)

To come back to a few points... That X happens and then Y happens is not evidence that X caused it without taking into consideration many other factors. To use your wood-example, if at the same time as you were putting wood into the fire someone was turning up the thermostat, you would see a rise that in temperature caused by more than one factor, but on reading purely the wood and heat you would link the wood and not consider other factors that may have added to the issue.

"even a small chance, one should take action". This is quite wrong. In a risk-averse society maybe, but in our world we take actions that have a 'small chance' of catastrophe everyday. We drive a car and risk a crash, we cross the street and risk a crash, we smoke and risk lung disease. The cure to global warming lies in more than just prevention, but in alteration too. It is nigh on stupid to claim that global warming will be the end of civilisation as we know it - too many idiots in the past have proclaimed things will get worse - and the further respectable science goes down this doom-sayer route the more it sounds like religion.

All of this, agian, leads to nothing. The problem is there - we have a wealth of evidence showing change and predicting future change. Until it is seen that the solution has to balance social-allowance, economic-viability and scientific recommendations we will get nowhere. Tell people he world will end tomorrow if they don't stop driving and most will sit waiting for the end of the world. Tell them they can help make a simpler and perhaps better tomorrow by reducing their mileage, or switching fuel type and maybe, just maybe, they'll change. Add in tax-incentives and regulation and what do you have? A coherent policy on how to overcome the problem of climate change. The end of the world isn't scary, losing what advancement has brought me is. ny156uk 17:58, 13 November 2006 (UTC)

"To use your wood-example, if at the same time as you were putting wood into the fire someone was turning up the thermostat..." But you're sitting in the room that has the fireplace. If someone turned up the thermostat, you would know. There is no evidence that anyone touched the thermostat, just like there's no evidence that anything other than human CO2 emissions have been warming up the planet. --Bowlhover 00:57, 14 November 2006 (UTC)

That isn't true. There are indications that the world would have been warming up without human intervention. But the rate at which the climate is changing is way off the scale. What normally happens in at least thousands of years is now happening in decades. Such a fast change is unprecedented (afawk).

ny156uk, I said even if there is a small chance. Not a minute chance. The chances of getting killed when crossing the road are negligible. Even in a whole lifetime, the chances of getting killed in a car accident are about 0.5%. The chances of global temperature rising several degrees is considerable higher. A one or two degree rise is even close to certainty. Also, individually we have no choice but to cross the road if we want to get on with our lives. But, say, driving a car with a much smaller engine will barely affect our quality of life. As will voting for a climate-friendly party (if that is an option where you live). DirkvdM 06:18, 14 November 2006 (UTC)

The addition I made to the wood example is, I feel, correct: See correlation implies causation. That A (wood added) occurs in correlation to B (heat output) does not definitively mean A causes B. The caveat is this - you need further evidence to show that other factors are not at play.

In the real world this is a different matter. I have no idea whether nature has an impact on global warming alongside human-input, but I believe that as many potential avenues must be explored before we can call the explanation to be coherent.

Dirkvd...Sorry it was a poor example, though it does open up questions about risk-management and everybody has their own idea of cost/benefit analysis. Voting for a climate-friendly party is your choice, but a single-issue party is not able to run a government until it matures - it can, however, influence how the major parties operate. ny156uk 17:31, 14 November 2006 (UTC)

Please reread all my previous posts; I've argued against the "correlation implies causation, therefore we can't assume anything from the temperature record" argument two times already. --Bowlhover 00:36, 15 November 2006 (UTC)

The fire-wood example is a bit better if one doesn't know if putting wood on a fire will produce more heat, but has a theory about it, tries it and finds that indeed it does. That may not gove one certainty, but it's a bloody good indication. Sientifically speaking, yes we have to explore all possibilities before we can say for certain. Well, that's not quite right because in science there is never any certainty. But we must make sure we don't die in our ivory tower and in practise act long before we have any certainty. And why would a climate friendly party have to be a one-issue party? DirkvdM 08:15, 15 November 2006 (UTC)

Winners from global warming ?

Obviously many will lose, but who will win ? One country that comes to mind is Canada, who won't suffer as much as many other countries because most of it's major cities (Toronto, Montreal, Quebec City, Ottawa) are not on the ocean (Victoria, BC being a major exception). Canada could also benefit by the opening up of the Northwest Passage, formerly blocked by ice most of the year. Also, the vast northern tundra could change into productive cropland with enough of a temperature increase. Similarly, Russia might benefit. StuRat 04:51, 13 November 2006 (UTC)

Acutally "losers" from current environmental restrictions is perhaps more striking. One example, cheap and efficient refrigeration keeps food from spoiling. Considering there is starvation in the world, their money went to buy more expensive refrigeration instead of more food. I've seen estimates in millions of lives. There are lots of poor choices being made because of the shrill cry of global warming.--Tbeatty 05:58, 13 November 2006 (UTC)

Actually, Canada is losing at the moment, as it has to invest in ships and submarines for patrolling its huge (!) coastline in the north which will be subject of much interest (the famous Northwest passage). -- 85.179.10.106 10:00, 13 November 2006 (UTC)

In a 'globalised world' (sorry if that sounds odd :) ) a country's ecomomy depends to a large extent on other countries' economies. If your trade partners do bad, you will do bad. As to the local effects, two things should be kept in mind. Firstly, the warming is global, but regionally there could be cooling. An extreme example is the shutdown of thermohaline circulation, which could cause Northern Europe to freeze over. Secondly, the change will be unpredictable, so until it 'settles' (if it does) farmers won't know what to grow, resulting in bad harvests (and food shortages and hunger if you can't import from elsewhere because they had a bad harvest too). But what's possibly worse is that what the climate settles into will probably be more extreme. Just like heated water starts to boil (sorry about the slightly lame analogy), a heated atmosphere will result in more violent weather, with greater extremes. Storms will probably be more violent (hurricanes like Katrina will become commonplace) and one year may be too dry, while another year may see heavy downpours. This is probably the greatest threat, alas often ovelooked. Farmers rely on the weather being somewhat predictable. If it isn't, food shortages will result, irrespective if locally there is warming or cooling. Also, global warming means sea levels will rise and that will affect almost all civilisations since humanity largely lives at coastal areas and, again, that's where one finds most agriculture because of the deposited fertile soils. So the land that will disappear will be of the most valuable kind. Unless the thermohaline circulation shuts down and the ice will absorb a lot of water. But then we've got another problem (apart from this not being very nice for Europe). Ports will no longer be at the coast, causing transportation problems. Probably not as serious as the losing of land, but still a problem that will take a long time to overcome and cost a lot of money. Our societies are based on the status quo and if that changes, the way our societies are arranged no longer makes sense. And the change will cost us. DirkvdM 10:28, 13 November 2006 (UTC)

You can both win and lose if your partner does poorly. The question is whether the world economy goes downwards, or your regions. There will be short term difficulties from changes in power, but other nations can win as others lose. Farms wise the growing of harvests/food can be done in virtually all conditions and unless climates are changing rapidly from one year to the next there is no reason change cannot be acted quickly and efficiently (particularly if it is regularly happening they will become more efficient over time). This would mean it is likely that foodstuffs would go up in price though.

Just because the sea-level rises doesn't mean there we cannot cope. Population movement and development of systems to control/react to sea levels are not impossible to create or develop.

The cost to society of major upheaval is evidently large, but if the cost of reducing emissions is higher which do we choose? The world is going to have to come to terms with some big changes I am sure, but it is hardly the first time in history. We had nations almost bankrupt and ruined by 2 world wards in under 50 years. Our technological development will not go backwards, the difficulty will be in keeping the pace of change we have seen. It is far better that we have achieved the things we have in the past 200 years than to have prevented them from happening because of future issues.

The sentiment over global-warming/climate change is depressing reading. Few have faith in humanity, ingenuity and downright resiliance. I tend to believe we have what it takes to get through this, but that it will indeed be one of the toughes dilemmas we have encountered. But a world war that took 60 million lives, and one just before that took what 9 million (or thereabouts) our world is truely well adjusted to horrific atrocities occuring. Lets hope that we can minimize/eliminate it this time round. ny156uk 18:13, 13 November 2006 (UTC)

So your idea is to not reduce CO2 emissions and watch what happens. But reducing the emissions is definitely not more expensive than evacuating whole cities and spending more money for food because it's more expensive. The poor polar bears will drown because there's no more ice floes to rest on, and many other species will also have a tough time coping with the changing environment. --Bowlhover 00:57, 14 November 2006 (UTC)

Ny156uk, you say "unless climates are changing rapidly from one year to the next". But that is precisely the problem. (Also note that a rapidly changing climate really means 'no climate'.) And we probably can cope, but there will be a transitional period that may turn out very nasty (possibly around when I am an old man, so maybe I should strive to die young). And unlike the two world wars, this will be truly global. No Marshall plans for any nation because all others will have their own problems. The cost of adapting now or adapting then would have to be weighed against each other, with the problem that the latter will be mere guesswork. But something that is a certainty is that fossil fuels will run out. So we will have to come up with alternatives. So we have no choice to invest in that. So why not do it now and leave the remaining oil for other purposes it might turn out to be handy for in future technologies? I agree that we can solve this, but the problem is that hardly anything is happening so far. The free market will only step in when big profits can be made and it will be too late then. DirkvdM 06:42, 14 November 2006 (UTC)

Dirkvd, Until it is economically viable (or politically necessary) we will not change our behaviours. Fossil fuel will not run out - simplistically speaking the price will go so high that development of alternatives will be viable/lucrative and thus developments will be made, previously unworthwhile finds will become worthwhile investments/etc. etc. The cost of adapting now for the future is no more known than what the cost will be in the future, specifically because you cannot be sure of the exact benefits changes will bring.

This is not a call for non-action this is a call for rational action. Make changes where we can and help make it economic to change for the better and/or tax the habits you want to reduce. Direct funding into development and prevention, focus on ways of improving what we do and also improving the accuracy of the science. Do all these things we will (and to some degree already do), and the world will be better for it. But do not expect people to make their lives measurably worse, because few will regardless of the 'scale' of the potential disasters. In short be realistic about what is achievable and push the boundaries where you can. ny156uk 17:31, 14 November 2006 (UTC)

THC stopping sounds like it could never happen. There will always be change in the differences in temperature, density, and salinity. Through all the ice ages and warm periods in the recent past (myr I'm referring to) there has always been a circulation, it is in the data. Things move, period. The THC will change, and has been changing forever, just like currents in the atmosphere. If you can, prove me wrong. X [Mac Davis] (DESK|How's my driving?) 20:37, 13 November 2006 (UTC)

I won't. You're right. The THC has changed before. With catastrophic results. DirkvdM 06:42, 14 November 2006 (UTC)

I meant that it has never stopped. It only changes. X [Mac Davis] (DESK|How's my driving?) 16:57, 14 November 2006 (UTC)

I'm not interested in debating this, Mac. Post a new question if you feel the need to disprove global warming so badly. My question was who would benefit from global warming, not whether or not THC will end. StuRat 21:01, 13 November 2006 (UTC)

I'm not out to "disprove" it, I'm just being critical of parts of it. X [Mac Davis] (DESK|How's my driving?) 16:57, 14 November 2006 (UTC)

Another thought, would Greenland become usable ? If so, this could be a huge boon to it's owner, Denmark, who would increase their usable land area some 50X. StuRat 21:01, 13 November 2006 (UTC)

No luck there either. From the article: "If the Greenland ice sheet were to completely melt away, sea levels would rise more than 7 m [] and Greenland would most likely become an archipelago." The Netherlands, Bangladesh and Florida would have disappeared long before that. DirkvdM 06:42, 14 November 2006 (UTC)

Has it ever completely melted away? Bangladesh, ha! Everytime it's monsoon season or a typhoon comes by they go underwater. The Netherlands is pretty damn good at keeping the water out though :) X [Mac Davis] (DESK|How's my driving?) 16:57, 14 November 2006 (UTC)

"Bangladesh, ha! Everytime it's monsoon season...they go underwater." And you're using this to argue we shouldn't try to stop global warming? If sea levels rise, even more of Bangladesh will go underwater even more often, killing many more people. --Bowlhover 00:36, 15 November 2006 (UTC)

Funny, if something hasn't happened before, you say "Ha, see, it can't happen" and when it has happened before you say "Ha, see, it has a different cause". DirkvdM 08:15, 15 November 2006 (UTC)

Sorry if it's been mentioned already (I don't have the time/am too lazy to read through everything) but oil companies would probably benefit. I remember recently reading that 1/4 of the world's oil is lying, untapped, in inhospitable places such as Antartica. With all the ice melting, oil companies could easily begin extracting that oil too, and keep making money. --Saxsux 19:24, 15 November 2006 (UTC)

gastroenterology

is Barrett gastric metaplesia in the esophagus a precancerous lesion?

In short, yes. See Barrett's esophagus for details. - Nunh-huh 21:55, 12 November 2006 (UTC)

Barrett's esophagus refers to intestinalization of the esophageal mucosa. We know that (1) Barrett's itself carries a very low rate (but still extant rate) of malignant transformation and that (2) gastric metaplasia carries a lower rate than intestinal metaplasia. Most gastroenterologists recommend surveillance 2-4 years for Barrett's, with increased surveillance or treatment if there is dysplasia. -- Samir धर्म 03:54, 14 November 2006 (UTC)

Gabapentin

I work at a pharmacy and I noticed that a lot of people get benzodiazepines for their anxiety. I was reading the gabapentin article and it mentioned that it was made to mimic the GABA nuerotransmitter, which from what I learned the more you have, the calmer you are. So why aren't more people prescribed gabapentin and are prescribed benzodiazepines? Is it not as effective?

IANAD, but if you read the article carefully, the studies that have been done on gabapentin as a mood stabliser don't exactly appear to have a roaring success. --Robert Merkel 02:31, 13 November 2006 (UTC)

Because Gabapentin (despite it's name) doesn't act on the GABA receptor. Instead it binds to the α2δ subunit of a voltage-dependent calcium channel in the central nervous system and acts as an analgesic used especially in chronic pain. Mmoneypenny 10:37, 15 November 2006 (UTC)

List of minority-opinion scientific theories

I'm looking for some other scientific theories which have not gained traction, but have not been disproven, to add to the recently created list of minority-opinion scientific theories. So far we don't have much beyond string theory and the alternative to the Out-of-Africa model. —Pengo ^{talk · contribs} 22:48, 12 November 2006 (UTC)

Several of the interpretations of quantum mechanics fit this description. For instance, bohmian mechanics. Also I think a few of the dinosaur extinction hypotheses fit this description. I'm a little worried about this being a general "science" list. I think most theories in social psychology and sociology fit this description. In fact, the list might quickly become unmanageably large if "theory" is taken broadly enough. --best, kevin [kzollman][talk] 23:38, 12 November 2006 (UTC)

• Cold fusion. StuRat 04:37, 13 November 2006 (UTC)

String theory isn't exactly what I would call falsifyable. -- 85.179.10.106 10:10, 13 November 2006 (UTC)

I guess it makes the prediction that it will someday make a prediction :) —Pengo ^{talk · contribs} 16:28, 13 November 2006 (UTC)

I would call it a protoscience. X [Mac Davis] (DESK|How's my driving?) 16:59, 14 November 2006 (UTC)

Leaving aside conspiracy theories and pseudoscience, some serious minority theories I have read in recent years (sorry I do not have citations handy): One minority opinion theory is that humans were in North America long before the Clovis culture era dating from Folsom points, like 20,000 years ago versus 13,500 years ago. Another is that North America was first settled by Solutrean people from northern Europe before people came from Siberia. Another is that Neanderthals interbred with modern humans. Another is that a meteor hit the moon during the middle ages and the impact was witnessed by monks in Europe. Another is SETI, that we should be able to detect radio signals from intelligent beings on planets orbiting other stars with present technology. Another is that genetically modified plants and animals pose a great danger to our survival, due to the modified genes making their way into other species, like a gene for herbicide resistance added to a cultivated grain crop jumping to the genome of weeds. Another is that global warming is NOT a threat to our survival and is not caused by human activities. Another is that condoms do not reduce the spread of sexually transmitted diseases, and that abstinence education is the best way to prevent undesired pregnancies and STDs among young people. Edison 17:21, 13 November 2006 (UTC)

The Aquatic Ape Hypothesis never took off. 88.96.134.245 12:12, 15 November 2006 (UTC)