Wikipedia:Reference desk/Archives/Science/2008 December 28

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December 28

What is the minimum amount of heat it takes to burn you?

I realize that the confines of this question are rather vague, but please bear with me as I try to give further specifications.

For example, when the average person touches a hot stove top, he or she immediately jerks away his or her hand. So, in a sense, my question is what is the minimum temperature the stove top needs to be in order to cause the human reaction. Nkot (talk) 03:27, 28 December 2008 (UTC)

Heat is relative. So, it isn't a minimum amount of heat. It is a minimum difference of heat you are looking for. If you soak your hand in cold water for a bit and touch a "warm" stove, it will feel very hot. If you soak your hand in hot water for a while and touch a "warm" stove, it will feel cool. -- kainaw™ 03:29, 28 December 2008 (UTC)

In fact, it's even more complicated than that. I saw an exhibit with coils of metal that could be brought to different temperatures, and it turns out that if you have alternating warm and ice-cold coils, the combination feels hot. It's as if there are some receptors that sense warmth, and other receptors that sense extreme temperature (either hot or cold), and if you have alternating warm and cold coils, both receptors are excited. —Keenan Pepper 04:41, 28 December 2008 (UTC)

According to our article "Withdrawal reflex", interneurons in the spinal cord pass a signal from pain or heat sensors in the hand directly to motor neurons to pull the arm back. The sensing organs are known as nociceptors, I suppose from the Latin for "noxious". According to that article, exactly how the reflex is triggered is unknown, but "Nociceptor#Thermal" says "The first [thermal nociceptor] to be discovered was TRPV1, and it has a threshold that coincides with the heat pain temperature of 42°C." --Milkbreath (talk) 03:47, 28 December 2008 (UTC)

Interesting article, but doesn't 42C seem a little too low to be the kind of reaction I am talking about?Nkot (talk) 04:49, 28 December 2008 (UTC)

It does sound low but isn't 70-80 degrees enough to kill bacteria? When reading the question I thought if you were cold enough 50-60 degrees could feel very hot. Also a small child will feel the effect of reddening or burning much stronger than an adult. If you spend too much time indoors, 40 degrees in the sun for a couple of hours will burn you easy. ~ R.T.G 11:25, 28 December 2008 (UTC)

But, 80 degrees is not enough to trigger an involuntary "that's hot" reaction for a normal human at normal body temperature. A "warm" shower is above 100 degrees. Below 100 is considered cold. Below 90 degrees is considered very cold. So, 70-80 degrees would produce a "damn that's cold" reaction, not a "that's hot" reaction. However, as I noted above, if the person getting into a 70 degree shower just got out of a tub of ice, the 70 degree shower would feel hot. -- kainaw™ 14:58, 28 December 2008 (UTC)

Fahrenheit and Celsius, friends. A human will get a "damn that's hot!" reaction to about 60C, but 60F is chilly. ~ mazca ^t|c 15:26, 28 December 2008 (UTC)

Indeed I had a real WTF moment when reading Kainaw suggestion 80 degrees isn't going to trigger a 'that's hot' reaction Nil Einne (talk) 09:47, 3 January 2009 (UTC)

Oh, I don't know. That temperature corresponds to about 108 degrees Farenheit, which could be uncomfortable if you take into account the phenomenon Kainaw and Keenan discussed above. And the way I understand the article, and I'm pretty sure I don't very much, you're not going to find a single threshold temperature that will cause the reflex, because it relies on a combination of triggers from various receptors in the limb, our TRPV1 being just one of them. It could be, for example, that TRPV1 is there only to help prevent false alarms, which would be deuced inconveient. --Milkbreath (talk) 15:56, 28 December 2008 (UTC)

60C is 140F, so that's hot enough to burn. The fact that staying in the sun on a hot day might give you a burn has to do with ultraviolet radiation, not heat. Staying in the heat will not give you a burn pain reflex, but it might cause heat stroke. ~AH1^(TCU) 17:27, 28 December 2008 (UTC)

I think I found what I was looking for here (at the very bottom of the page). Specifically, for a "uncoated metal" where the period of contact is one second, a burn will be caused by temperatures of 70C or greater. Nkot (talk) 19:03, 28 December 2008 (UTC)

I've always used 66ºC (150ºF) as a reference. My hand can tolerate that temperature (barely) and so I can estimate from there. hydnjo talk 22:05, 28 December 2008 (UTC)

"Ba humbugi"

Apparently this is a snail found on the island Mba (here)- could someone give a taxonomy (family / class) for this species? Nadando (talk) 08:15, 28 December 2008 (UTC)

Sounds like Humbug to me. 93.132.189.157 (talk) 10:22, 28 December 2008 (UTC)

No 'apparently' about it, there is a snail with this name on a Fiji island. Apart from confirming its existence [1]I can only suggest contact with Oceanic snail experts. Richard Avery (talk) 11:14, 28 December 2008 (UTC)

According to Alan Solem's original description (search for "Type species. Ba humbugi"), it's in the family Charopidae. Note that Solem has given gave other odd names to species of gastropods—see Aaadonta and Zyzzyxdonta, for example. Deor (talk) 16:22, 28 December 2008 (UTC)

Changed verb form above, since it appears that Solem, erstwhile curator of the Division of Invertebrates at the Field Museum in Chicago, died in 1990. Deor (talk) 17:17, 28 December 2008 (UTC)

In the lower orders where the new species to be named can outnumber the taxonomist's imagination, they will sometimes turn to whimsy, as seen in List of animals named after celebrities. --Sean 14:05, 29 December 2008 (UTC)

Freesat, free satellite, DVB-T, DVB-S and satellite dish mounting

Hi, I have a new TV and am looking at free satellite broadcastings. I wonder a few things which are not covered in the info available hopefully someone around here knows a bit about it (maybe once they are finished new years but ask now anyway). My new TV can receive digital. I am led to beleive it recieves Freeview and am sure it does but it does not say Freeview on it (says DVT for digital and AVT for normal aerial) so, it does not say Freesat on it either (I am in Ireland so Freesat is available here). Freeview is called DVB-T and Freesat is called DVB-S. Is my TV built in DVB-T Freeview decoder capable of decoding DVB-S? Shouldn't I be able to hook a dish up to it directly and just tune in what I want without buying a special box? Also wondering if anyone has experimented or knows of putting a dish in a loft? I am in an upper flat so would need to climb 30ft to my outside wall but can get into my loft easy. Shouldnt a dish work ok if put in the loft? Happy new year :) ~ R.T.G 11:02, 28 December 2008 (UTC)

Very very few TVs sold in the UK and Ireland right now are Freesat/DVB-S capable, and those few that do explicitly say "freesat" on them. So you surely need a special box. [I'll mention in passing that I've tried both, and that the Freesat service was inferior to Freeview, and the picture quality (over SCART) from my cheapo freesat box was much worse than both digital and analog terrestrial TV. Your results may, of course, vary]. Yes, it is possible to put a special satellite antenna inside a roof space, but doing so requires a specific antenna and can be done only depending on the construction of the roof. I don't know about other places, but in Scotland the building regulations say that external satellite dishes can't be fitted higher than 3 (or is it 4) storeys - beyond that the danger of them blowing off and killing someone is felt to be too high. So when new blocks of tall flats are constructed, they're fitted with a high-gain satellite antenna inside the roof space - I guess they specifically locate this in relation to a skylight or radio-transparent roofing panel, so as to not block the signal. I'd say this requires a professional install, and indeed fixing an external antenna so high as you describe is probably better left to someone who does that a lot too. Local TV installer companies should be able to supply and install the dish, and run the cable into your living room, for maybe 200 euros. 87.113.77.112 (talk) 17:38, 28 December 2008 (UTC)

My roof is the standard pine wood frame and stone based tiles. As I am on a coastal hill I must get a decent aerial for the local channels but some of these Freesat kits dont cost much more with a Sky type dish. Any quotes I saw for supply and fitting started at 400 euro and sourcing the cheaper kit myself for less than 100 makes it a bit much. Maybe I will fit it in the loft to see. It gets fairly windy around here lol. ~ R.T.G 23:50, 28 December 2008 (UTC)

Psychoactive drugs and human survival

Would it ever have been in the human species' survival interest to evolve, or not to evolve, an immunity to all psychoactive drugs? NeonMerlin 17:02, 28 December 2008 (UTC)

Chocolate can kill many animals and birds, and we also seem to be developing some protection against alcohol. I can't see any problem about immunity developing eventually for things like cannabis or ecstasy if people keep abusing them in such quantities but speculation is frowned on by WP refdesk. Dmcq (talk) 19:43, 28 December 2008 (UTC)

I wonder if chocolate is toxic to humans too - with the only difference being that due to our species' size, a human would need to eat a much larger amount (perhaps more chocolate than could be consumed in one sitting) before any ill effects occurred? --Kurt Shaped Box (talk) 01:38, 29 December 2008 (UTC)

That's an easy one: the major psychoactive component of chocolate is theobromine, which has an LD50 of about 1000mg/kg, or 80g for an 80kg human. Theobromine is approximate 0.5% (w/w) sweet chocolate and 0.15% (w/w) of milk chocolate ^[2], so the amount of to kill 50% of 80kg humans would therefore be 16kg of sweet and 53kg of milk chocolate. An interesting note: the LD50 of theobromine in dogs is significantly lower than humans (300mg/kg)^[3], but it would take about 60g/kg and 200g/kg of sweet and milk chocolate, respectively, per kg of the animal to be 50% fatal. – ClockworkSoul 02:08, 29 December 2008 (UTC)

Consider this: psychoactive drugs work by a vast number of mechanisms to affect how the CNS functions. For example, cocaine, MDMA, and LSD all increase the effects of dopamine in the brain, but do so via completely different mechanisms: cocaine inhibits serotonin reuptake, MDMA induces serotonin release, and LSD mimics serotonin. The same target can even be effected with similar effects by different mechanisms: ethanol and barbiturates are both agonists of the GABA receptor GABA_A but interact with different sites on the same receptor. There are dozens of neurotransmitters, each with one or more receptors that can be interfered with in some way. Considering the incredible number of drugs and variety of mechanisms, I would say that it's really, really, really unlikely that such a general immunity could evolve. – ClockworkSoul 01:47, 29 December 2008 (UTC)

And further to Clockwor's explanation the effects of psychoactive drugs either mimic or trigger natural processes that in their original form and intensity are rather essential or useful. Consider e.g. Parkinson's disease which is related to Dopamine which Clockwork cited. If you'd get something like that as a trade off for immunity to LSD or cocaine then I don't think evolution would favor that result. A human or animal that couldn't sleep or would constantly be in a state of "fight or flight" because it's "immune" to serotonin would end up dead pretty fast. 76.97.245.5 (talk) 10:26, 29 December 2008 (UTC)

Psychoactive drugs are generally present in plants to kill or frighten off animals that might eat them. It's therefore likely that in an area where many plants produce psychoactive drugs, organisms could evolve to deal with them. However this would have to take place in an ad hoc way, and immunity to everything is unlikely bearing in mind the costs it would have (mentioned above). Humans may have evolved their tolerance to alcohol because it is found in rotting fruit (and is largely tasteless and hard to detect), but if you have enough food it's easier to develop an aversion and just not eat the nasty chemicals: people are reluctant to eat bitter flavours, which stops us consuming many alkaloids (though many people can tolerate caffeine-full coffee). --Maltelauridsbrigge (talk) 15:52, 29 December 2008 (UTC)

Regarding psychoactives in plants, you could argue that we have partial immunity to some drugs, i.e. DMT, as monoamine oxidase in the gut prevents any significant concentrations from reaching our CNS (of course us clever humans found the plant that contains MAO inhibitors and mix them with DMT-containing plants). In fact first pass metabolism, P-glycoproteins and the blood-brain barrier could be considered an immunity to psychoactives, just not every one of them. --Mark PEA (talk) 19:25, 29 December 2008 (UTC)

Humans seem to have already evolved to tolerate higher doses of the poisons that appear on mouldy cereals. Compared to other animals anyway. I looked up ergot and ergotism but couldn't find this info.Polypipe Wrangler (talk) 11:34, 31 December 2008 (UTC)

chemical reactions

Are there any cool chemical reactions that I cause with things i might find in my house such as cleening suplize or cooking in gredence. Please dont give me any chemical reactions that will get me in trouble from my parents or blow up the house thanks. --76.235.179.169 (talk) 19:31, 28 December 2008 (UTC)

Read the article about toast to learn about the Maillard reaction. That shouldn't blow up the house and has the added benefit of having a tasty result. hydnjo talk 19:44, 28 December 2008 (UTC)

On this subject, Alton Brown's Good Eats program used to delve deep in to the chemical explanations for all of the cooking he did. For example, the Pancake Episode (2) may give you some insight into pancake chemistry - flour proteins, different types of fats and oils, baking soda, etc. "1 cup buttermilk + 1/4 teaspoon baking soda = enough carbon dioxide to lift 1 cup of flour"... Nimur (talk) 20:09, 28 December 2008 (UTC)

Adding household vinegar to baking soda releases lots of carbon dioxide. You can use this reaction to power a small "jet" boat. -- Flyguy649 ^talk 19:49, 28 December 2008 (UTC)

A pretty classic and cool thing is a non-Newtonian fluid, which you can create simply by adding corn starch into water -- so it's a cheap and completely harmless thing to do. (I believe a ratio of one part corn starch, two parts water will produce the desired results.) I don't know about you, but the idea of a liquid that turns into something resembling Play-Doh when you sequeeze it and runs right past your fingers when you relax your grip always blows my mind a little bit. It's not really a chemical reaction, though, but what the hell. -- Captain Disdain (talk) 02:39, 29 December 2008 (UTC)

I had trouble understanding your question, at first. Then I realized you meant "cleaning supplies or cooking ingredients", not "cleening suplize or cooking in gredence". StuRat (talk) 10:10, 29 December 2008 (UTC)

Baking soda boats are fun: take half a walnut-shell, fill with baking soda, add a short piece of straw, seal with a thing bit of playdoh or putty or wrap in aluminum foil, leave one end of the straw sticking out. Put it in water with a few drops of lemon juice in it. Your boat will fizz around. Magic color changes also can be fun: boil some water with a couple of leaves of red cabbage and put the liquid in a glass. It will turn red if you add lemon juice or vinegar. Write something with lemon juice on a piece of paper and let it dry. If you ask an adult to heat the paper over a candle the writing will turn brown. These sites have some more ideas [4] [5]. Not exactly a chemical reaction, but also fun [6]. Mix fresh green peas (not frozen or canned), 1/2 apple (peeled and cored) and 2 tablespoons of brown sugar in a blender. Have people close their eyes and sniff it, it will smell like strawberries. 76.97.245.5 (talk) 11:12, 29 December 2008 (UTC)

The red cabbage juice experiment is also a fun way to identify acids and bases: [7]. StuRat (talk) 13:15, 29 December 2008 (UTC)

Can I have some more Sun Conure advice, please?

How far does a Sun Conure usually fly every day in the wild, on average? At her last checkup, the veterinarian said that my SC was getting quite tubby, so I'm trying to get her to fly a lot more than she does at the moment. How far are they supposed to be able to fly before they get out of breath? --90.240.153.26 (talk) 19:37, 28 December 2008 (UTC)

I'm rather skeptical that you could possibly get a captive bird to fly as much as a wild bird. You will likely also need to restrict food quantities. Also, do they have low calorie bird food ? StuRat (talk) 10:02, 29 December 2008 (UTC)

Following EC:

Don't have info on their range in the wild, but if you'd like to give your bird more exercise, put some toys in the cage. Apart from ropes and things, you can DIY puzzles from wooden rings and balls and bells from your pet store or a crafts store (make sure the wood isn't treated with harmful chemicals if you use the latter). There are also standard parakeet toys available, but lots of birds find those boring. (Same problem as with little kids, cats etc. the stuff you spend oodles of money on is less interesting than a pot and a spoon or a crumpled up bit of paper.) A fresh branch for climbing and tearing off leaves and bark can also be both entertaining and energy consuming. Wrapping nuts in paper (check with your vet which types are safe, newspaper is definitely not recommended) before you feed them is also an idea that will make your bird spend a few calories before gaining them. 76.97.245.5 (talk) 10:05, 29 December 2008 (UTC)

You people look all the same to me!!

I started coming into contact with a number of asians lately, and I have to say that I do find them harder to distinguish. My question is: is this due to minor variations in appearance or does the brain get better at picking off differences of a race you are familiar with? Bastard Soap (talk) 21:27, 28 December 2008 (UTC)

I think it's experience. In countries where "non-asians" grow up with asians in the community, the "non-asians" have no problems picking the asians apart. I think you do not grow up with asians in your community. If you do not believe me, try picking penguins apart. 122.107.203.230 (talk) 21:43, 28 December 2008 (UTC)

Hi. I am inclined to say it's the latter, but I'm not 100% sure. Maybe you are having a harder time finding distinguishing caracteristics, since most north Asians have the same hair colour, eye colour, skin colour, etc, while Caucasians might have different hair an eye colours, freckles, etc. I think it's the same reason why sheep can tell each other apart but humans have a harder time doing so (by the way, I'm definitely not imagining things, your text is single spaced while my answer is double spaced in the edit window, but not anymore, because edit conflict). ~AH1^(TCU) 21:46, 28 December 2008 (UTC)

It's not a very politically-correct thing to say (I don't think that it's said with any malice, to be fair) - but I've definitely heard (white) people saying that they find it difficult to distinguish one black man from another. Personally, I think it's just a case of lack of familiarity with the facial characteristics of races other than your own. Then again, how many times have you been walking down the street and mistaken a person of your own race for someone else you vaguely know and had to double-take? --Kurt Shaped Box (talk) 01:34, 29 December 2008 (UTC)

Here's a simple test: ask a group of white persons from New York City and from rural Ohio whether they are able to easily distinguish between members of different ethnicities. I'll bet you dollar to donuts the you'll get far more affirmative responses from the New York group than the Ohio one. – ClockworkSoul 02:25, 29 December 2008 (UTC)

Well, if comparing to everyone in Asia, including Russians and Saudis, I'd say no. However, if you meant Orientals, I'd be more inclined to agree. If we limit a comparison of, say Chinese with Europeans, two groups of approximately the same population, I'd definitely say there's more variation in the Europeans. The Europeans have every hair color there is, including red, blond, brown, and black, while the Chinese pretty much only have black hair. The Europeans have every hair texture, including straight, wavy, and curly, while the Chinese pretty much only have straight hair. The Europeans also have more eye colors. So, based on these attributes, I'd say it's fair to say there's more variation amongst Europeans. Now, one could argue that I chose those attributes which vary more for Europeans, but, in this case, which attributes vary more for the Chinese ? If they had a variable number of fingers, or something like that, then I would accept that argument. StuRat (talk) 09:57, 29 December 2008 (UTC)

Yes, I would argue that you've been very selective in your attributes. An example of an attribute that varies more amongst the Chinese than among Europeans is skin pigmentation. I suspect also, the general shape of the face. mike40033 (talk) 04:49, 4 January 2009 (UTC)

Cecil Adams did a column on this. 24.91.45.12 (talk) 16:53, 29 December 2008 (UTC)

StuRat, it's a matter of cultural conditioning; in fact, and your own response above lists facial variations that you have been conditioned to notice. In other ethnicities, they notice other things, like hairline position, eye placement, cheekbones, lips, etc. A friend of mine from Laos once complained to me that "you white people look all the same." Sure, white people have a greater variety in their hair texture, hair color, and eye color — but those aren't the cues he was conditioned to look for, because in his ethnic group hair and eyes aren't perceived as differentiating features (people dye and perm their hair and wear colored contacts in his country too, so those features are useless anyway, he'd say). ~Amatulić (talk) 22:43, 29 December 2008 (UTC)

You seem to have ignored the last two lines of my post. In order to argue that Chinese don't "look more alike" than Europeans, you need to list some identifying characteristics that vary more for Chinese, just as I listed some that vary more for Europeans. Otherwise, we get that Europeans vary more for some characteristics, and by the same degree for others, which still leaves Europeans as varying more when you average those characteristics out. As for the argument that you can't identify people based on hair or eyes, as those can be changed, so can facial features, with make-up or plastic surgery. StuRat (talk) 15:32, 30 December 2008 (UTC)

Skin tone IMHO varies more in Chinese then it does in Europeans. It's also worth considering who we're talking about. Europeans is actually a very broad ethnic group. Chinese by which people probably mean Han Chinese is likely a less variable group then Europeans. Also I doubt you have enough evidence to rule out there being greater variance in facial features or even eye colour (brown eyes can actually vary a lot in colour). In other words, while you may be correct, you haven't presented close to enough evidence to suggest you are. The Cecil Adams column is a decent read Nil Einne (talk) 09:43, 3 January 2009 (UTC)

Skin colors vary more for Chinese than Europeans ? Europeans vary from extremely white in the Nordic countries to quite dark in Italy and Spain. And you say that the brown eye color of Chinese varies more than the blue, green, brown, and black eyes of Europeans ? I don't understand how that's possible. I was attempting to compare contiguous regions with similar populations, regardless of the ethnic groups contained therein. But, in any case, both Europe and China contain many ethnic groups. As for limiting the Chinese to the Han, there's no need to do that, go ahead and include Mongolians, Tibetans, and even Koreans, etc., if you think that will make a difference. Now, as for you wanting proof, what part of my statements exactly do you find to be questionable ? That many Europeans have blue eyes ? That almost no Chinese do ? Give me some facts that you dispute and I'll try to find some proof. StuRat (talk) 19:24, 3 January 2009 (UTC)

Oh wow! A speculation-fest!! Can I join in too? I think it's entrirely experiential. You get better at picking differences between (apparently) similar objects with practice:

• Ask any pathologist how s/he differentiates between similar cell types - many will respond "they look different."
• We have 2 (unrelated) black cats at home, they're both skinny and have yellowy-green eyes. We've had them both for about 10 years and to my wife and I they're like chalk and cheese to look at, but our kids (who are younger than the cats) and other family & friends who've known them as long have trouble telling them apart.
• Anyone who's ever hired a car can probably relate to the problem of not being able to differentiate your hire car from similar model cars of the same colour.

Happy NY! Mattopaedia (talk) 03:17, 1 January 2009 (UTC)

As we grow, we learn to distinguish faces based on certain features. Each person uses a different set of features to distinguish faces. For someone unfamiliar with Asian faces, or African, or Caucasian faces, members of that group "all look the same". I lived in Asia for a while, and on several occasions, had conversations with locals that went like this. Someone says - "That guy (referring to a Caucasian male) looks a bit like that other one." Then I look at the two, and seeing no resemblance, reply "not really." The phenomenon is both ways.... modulo Hollywood, of course....... when I was younger, I kept a beard. Then came a day I decided to get rid of it. I asked people to try to imagine what I would look like without a beard. Some had no trouble (call them group A), others just couldn't imagine it (call them group B). Of course, these are two ends of a spectrum. When I finally shaved it off, I got a range of reactions. Interestingly, the people in group B typically said "Oh my God, is that you? I can't believe it. You... you look completely different". The poeple in group A would say, after chatting normally to me for half an hour "You've changed something, haven't you. Is it your glasses?" My theory is that some people used the beard (or lower face) as a cue, others didn't. And these "experimental subjects" were all from the same ethnic group.... mike40033 (talk) 04:42, 4 January 2009 (UTC)

Methane clathrates, global warming, and such

Hi. Back in September, we found out that "peliminary findings" indicate that methane clathrates in the Siberian Arctic Ocean were melting. Now, what does that actually mean, and is there any chance that they aren't melting? If these are "peliminary" findings, then will they be confirmed, and when? I'm currently reading a book (four years old) that lists three possible scenarios with severe global warming: 1. The collapse of the ocean thermohaline circulation; 2. The collapse of the Amazon; 3. The release of the methane clathrates. The book lists the third one as the "least likely to occur this century"! So how could it be occuring now? Also, why haven't I heard of this on the news on TV? In fact, I only know one other person in real life who already knew about this before I told them about it. If the thermohaline circulation freezes the Norwegian sea, will the clathrates have less time each year to release, or will the melting of the whole Arctic Ice cap in summer (which could occur as early as 2013, from a LiveScience article) trigger a longer window? Also, this always confuses me: If the freshwater released by the Arctic could disrupt the Gulf Stream, how come it is supposed to "plunge Britain and Scandinavia into an ice age"? I mean, if the Arctic sea ice is going to melt anyway, then this will only have an effect in winter, since then the ice cap could extend to cover the North Atlantic between Greenland and Scandinavia in winter, which currently does not happen. Also, I have a hypothesis (and no, I'm not asking for opinions, just if it is valid), that the slowing and possible colapse of the thermohaline will cause smaller semi-permanent high and low pressure zones, that warm currents will flow near the surface, disconnected with cold currents, which will flow at lower depths, that this will cause a warming of the Humboldt current, which will therefore bring rain rather than fog, which will un-desert the Acatama, which will in turn solve Peru's water crisis. Also, a question about the Great Lakes. How much sea level rise is needed in order for either salt or brackish water to seep into the bottom of Lake Ontario (remember that salty and brackish water are denser than fresh, therefore it can seep into the St. Lawrence from underneath while fresh water remains on top or estuary, and therefore what is the bathymetric maximum height above sea level of the depth of the seafloor of the St. Lawrence river). Thanks. ~AH1^(TCU) 21:39, 28 December 2008 (UTC)

Sorry, no time to answer all of this, but read Methane clathrate particularly the section on climate change. As to why it's not a hot news item, apart from affecting other factors that influence global warming and thus keeping those deposits from melting there isn't anything we can do to prevent it AFAIK. You can't very well build freezers around it to keep it cold. So news focuses on things we can influence like emissions of greenhouse gases from industrial sources. The Gulf Stream moves warm tropical water from around the Bahamas to the North Sea. If you compare the temperatures there to the Hudson Bay which is at about the same latitude you'll see the North Sea gets heated by the waters from the Gulf Stream. If the poles melt, cold fresh water will flow into the salty sea and drive the salty water down. This will disrupt the convection pattern and change or even reverse the flow of the Gulf Stream. Since there will no longer be warm water from the tropics warming Europe, it's going to get colder there although this is an effect of Global warming. This has been shown by running models of the earth looking at possible effects of various climate factors.76.97.245.5 (talk) 09:33, 29 December 2008 (UTC)

As far as Lake Ontario goes, the St. Lawrence Seaway descends from 73 m a.s.l. to 46 m at the International Rapids section. Rapids generally being fairly shallow, this implies a minimum rise in sea level of 46 metres, so I'd think we're OK for a while yet.

On the cooling of Europe bit, while I've seen the prevailing theories, I've also seen the statement that there will be a Gulf Stream as long as the winds blow, since it is surface wind which creates the current, so I'm a little confused on that one. Franamax (talk) 23:59, 29 December 2008 (UTC)

@Framax If you look at Gulf Stream the wind action is only part of a rather complex mechanism that creates this specific convection pattern (contributing part of the North Atlantic Deep Water to be precise). As far as "there will be a Gulf Stream as long as the winds blow" that phrase is pretty much out the window since the Gulf Stream stopped for 10 days in 2004 to everyone's surprise. (Don't know if the winds stopped blowing ;-) One of the problems with making climate predictions is that there are natural patterns, both large scale and long term as well as local and short term, that either get emphasized or offset by global warming. Since human activities such as agriculture depend on lots of factors remaining stable (e.g. rainfall, temperature, planting seasons) within very small margins, one could say "any change is bad change". Lisa4edit (talk) 02:12, 30 December 2008 (UTC)

Do photons lose energy?

Does the red shift noted as galaxies rush away from our own represent any loss of energy in the photons, and if so, where does the energy go? --Halcatalyst (talk) 22:20, 28 December 2008 (UTC)

First, I should note the distinction between redshift from the Doppler effect due to "actual relative velocity" ("comoving velocity") of galaxies, and the redshift due to the expansion of space (see Hubble's law). From the wording of your question, I am fairly sure you are referring to the latter. The short answer is, the energy of redshifted photons goes into gravitational energy. However, since the theory of general relativity indicates that the gravitational field is more accurately represented as the metric of space. Basically as the light traverses a region of expanding space, it gives up some of its energy to the structure of space. If you happen to be fluent in 4-dimensional GR tensors, stress-energy tensor is the relevant concept. --Bmk (talk) 00:50, 29 December 2008 (UTC)

Oh right - I neglected to specifically answer your first question - yes, redshifted light has lost energy - it has a longer wavelength than when it was emitted, so its energy is lower. --Bmk (talk) 01:00, 29 December 2008 (UTC)

Are the photons then converted into gravitons? --Halcatalyst (talk) 04:24, 29 December 2008 (UTC)

No, I wouldn't say the photons are converted into gravitons. Gravitons are at best a theoretical possibility. It's currently not known whether gravitons are a valid way to describe gravity. A simplified answer to your question is that the energy of the photons is transferred from electromagnetic energy to the "energy of the shape of space". Unfortunately, a more accurate answer requires knowledge of general relativity. --Bmk (talk) 06:51, 29 December 2008 (UTC)

I believe the Hubble's law is due to the Doppler effect. If this is correct, there is no gain in energy. You are simply observing the photon from a different point of reference. It would be like jumping and asking what could possibly have given the Earth enough kinetic energy so that it's moving away from you at many feet per second. — DanielLC 03:27, 30 December 2008 (UTC)

There's only one kind of redshift in general relativity and only one kind of relative motion. Your description is correct and so is Bmk's. Redshift is often divided into "gravitational", "cosmological" and "Doppler" redshift, and the last might even be further divided into a quasi-Newtonian Doppler shift and a special relativistic "correction" to that, but general relativity makes no such distinctions. -- BenRG (talk) 05:46, 30 December 2008 (UTC)