Wikipedia:Reference desk/Archives/Science/2008 March 26

= March 26 =

Faster than light/Big Bang question
Whatever universe theory currently has scientific consensus (which I assume is based on the Big Bang model) seems to suggest that the universe is 13.73 billion years old and 93 billion light years in diameter. The Big Bang theory also states that the universe started from one point of infinite density. Therefore what seems to add up in my head is that the matter in this point which is now at the far reaches of the observable universe must have moved at least 46.5 billion light years in 13.73 billion years at most, which is faster than light. Is this the case, and if so how is moving FTL possible in this case? 212.49.210.38 (talk) 02:56, 26 March 2008 (UTC)
 * Take a read of this URL http://www.astro.ucla.edu/~wright/Dltt_is_Dumb.html which is the reference given to expalin the misconceptions in the time. The basic reason is that you cannot measure a distance between two point seperated so far in time.  At great distances the relationship becomes non-linear. Graeme Bartlett (talk) 03:13, 26 March 2008 (UTC)
 * (ec) See Observable universe. DMacks (talk) 03:14, 26 March 2008 (UTC)


 * Simplified explanation: the oldest photons that we can detect are the photons in the Cosmic microwave background radiation, which were emitted about 400,000 years after the Big Bang. It has taken those photons about 13.7 bn years to reach us. But in those 13.7 bn years the space between here and the places where those photons were emitted has expanded. It is possible for space itself to expand faster than light - the speed of light is only a limit for objects moving through space. So the places where these photons were emitted 13.7 bn years ago are now about 46 bn light years away from us, not because anything has moved, but because space itself has expanded. (Yes, yes, I know I haven't mentioned the cosmological constant, the changing value of the Hubble parameter, red-shift, the curvature of space, the difference between comoving co-ordinates and proper distance etc. etc. etc. - that's why I called it a simplified epxlanation) Gandalf61 (talk) 12:26, 26 March 2008 (UTC)


 * The explanation leaves the impression that if objects A and B are at points 1 and 2, 1 billion light years apart, then the "space" between them could "expand" to 4 billion light years in a period 1 billion years, somehow without objects A and B moving faster than the speed of light. Would this same process be applicable to 2 objects 1 light year apart, which could via "space expansion" become 4 light years apart in 1 year? Why couldn't Spaceman Biff use "space contraction" to travel between 2 planets 4 light years apart in 1 yea4 without travelling faster than the speed of light.  If the distance between points can increase via expansion, why is the process irreversible? Sorry for the simplistic question, but the usual explanations lead to such conjecture. Edison (talk) 13:44, 26 March 2008 (UTC)


 * If the planets are 1 light year apart when Biff sets out from planet A and Biff travels at the speed of light and we assume that the planets are stationary with respect to each other but the space between them is rapidly expanding then it will take Biff longer than 1 year to reach planet B. On the other hand, if planet B is 4 light years from planet A when Biff reaches it, then his journey will have taken less than 4 years, because of the expansion of space. To see the hypotehtical effects of a rapidly contracting space-time metric, I guess you could run the movie in reverse. All these times are in the frame of reference of both planets - in Biff's frame of reference, travelling at the speed of light, the journey takes zero time and he covers zero distance. Gandalf61 (talk) 14:53, 26 March 2008 (UTC)


 * You may want to read the article on the Alcubierre drive. — DanielLC 20:30, 26 March 2008 (UTC)


 * The quick answer as to why we couldn't use contraction of space to travel FTL is that we haven't found a decent way yet - various models have been proposed to do just that, but almost invariably they require at least one of two things: (a) thousands of times more energy than is available in the known universe, and (b) some unknown type of exotic matter that could somehow generate "negative energy". The Alcubierre drive apparently doesn't require much exotic matter any more, but it still needs some, and as yet there's no proof that such a thing even exists. Confusing Manifestation (Say hi!) 23:18, 26 March 2008 (UTC)


 * I am no expert by any means but my understanding is that shortly after the big bang the universe was indeed expanding much faster than the speed of light.Em3ryguy (talk) 00:24, 28 March 2008 (UTC)

Red cross society in Taiwan?
Hi, maybe this can be a sensitive issue. Since (the current elections in republic of china), among protests on tibet, etc. But i want to focus on the question putting aside any political blur.

Okay, basically, i have been trying to look here Category:Red Cross national societies, but i didn't get any clue about this
 * Is there a Red cross society in Taiwan (R.O.C) and in China (P.R.C)?, are those countries represented in one of them? or splitted?.

I really need to get a clue about this. Thanks in advance. --HappyApple (talk) 06:59, 26 March 2008 (UTC)


 * Taiwan appears to have a Red Cross Society, see . The graphic of the website identifies itself as "The Red Cross Society of the Republic of China".

Blood/urine tests
This is not a request for medical information, as you'll see. I had blood work/urine test last Saturday, and the doctor's office called today to tell me there's a "slight problem." They can't tell me what it is over the phone, and I'm not free for the next two days. I had already made an appointment to review the results this Saturday, so I'm worried that they called me now. Do doctors make these calls if it's just high cholesterol? Thanks. Imagine Reason (talk) 15:36, 26 March 2008 (UTC)


 * Quite possibly. If you have high cholesterol (the fact that a lot of people have high cholesterol doesn't lessen the problem) your doctor will want to advise you what you can do about it and possibly perform further tests.--Shantavira|feed me 15:50, 26 March 2008 (UTC)


 * Why would they tell you the results over the phone for free when they can make money if you come in for an appointment? I wouldn't worry yet.

72.211.184.40 (talk) 15:51, 26 March 2008 (UTC)


 * If the tests indicated anything that might represent an urgent medical problem then your doctor would have advised you to present yourself at the local emergency ward or after-hours clinic. Beyond that, it would be entirely inappropriate – not to mention futile – for us to speculate as to what your test results might mean.  TenOfAllTrades(talk) 15:53, 26 March 2008 (UTC)


 * That's not good. I'd rather it be cancer than AIDS! Imagine Reason (talk) 16:12, 26 March 2008 (UTC)


 * User:TenOfAllTrades/Why_not%3F - to further expand on TenOfAllTrades point! Good luck with your results. CycloneNimrod (talk) 17:44, 27 March 2008 (UTC)


 * I could be wrong, but I don't expect in most cases your doctor would have advised you to present yourself at the emergency ward or after-hours clinic for either AIDS or cancer (in other words, you shouldn't rule any of these out, although I'm not suggesting you expect them either). Urgent medical attention is something like 'you might be going to have a heart attack soon' or 'someone spiked your food with arsenic'. Nil Einne (talk) 18:29, 27 March 2008 (UTC)


 * " a slight problem" often means that the lab messed up the sample and needs another, so don't panic just yet.


 * Thank you, all. It turned out to be a "slight" liver function abnormality, although I'm immunized against Hep B and have not had a hep infection. Imagine Reason (talk) 02:07, 30 March 2008 (UTC)
 * Good to hear that it doesn't appear to have been anything major Nil Einne (talk) 17:34, 31 March 2008 (UTC)

Hail
Why does hail never seem to settle (unlike snow)? If and when it does settle, is there a name for it?--Shantavira|feed me 15:46, 26 March 2008 (UTC)


 * Possibly because, per the article, hail comes from thunderclouds, which require reasonably warm surface temperatures to form. Algebraist 16:01, 26 March 2008 (UTC)


 * Hail is little balls of ice, so can't compact much. The best you could get is to force the air between the hail stones out to form a solid sheet of ice.  This might happen if it's near freezing and you put a lot of weight on it, like by driving a car over it. StuRat (talk) 16:17, 26 March 2008 (UTC)


 * I may not understand the question, but what about this hail is not settled? [[Image:Hail_in_Bogota.jpg]]


 * Hail is the closest thing to snow here in the tropics. I don't think it settles into a deposit as it melts away even during the thunderstorm.-- Lenticel ( talk ) 23:34, 26 March 2008 (UTC)


 * I'm assuming that Shantavira is referring to the fact Given a little time, and maybe a little wind, A foot of light-fluffy snow can "settle" into half a foot of heavier snow. Hail, being rigid balls of ice, won't do that.  Or maybe he means to say "accumulate" in which case the answer is "Because hail shows up with above-freezing temperatures, so usually it melts instantly.  But sometimes it doesn't as in that photo. I don't know what you'd call that except 'hail, on the ground'." APL (talk) 06:49, 27 March 2008 (UTC)


 * There have been occasions of hail forming "drifts" due to floating along with runoff from the parent thunderstorm, even piling several feet high. - Running On  Brains  23:34, 27 March 2008 (UTC)

Regenerating Limbs
Has anyone heard any recent updates on the possibility of human limb regeneration just like the starfish?

Also, when our skin heals say from a cut, why does it not "remember" what that particular section of skin was before the cut? I mean is, why does it leave a scar? --Jonasmanohar (talk) 17:50, 26 March 2008 (UTC)


 * I don't think human ability to regenerate limbs is changing much. You may be interested in the article scar.  Friday (talk) 17:55, 26 March 2008 (UTC)


 * Depending on the severity of the wound, excessive deposition of collagen by fibroblasts at the expense of re-epithelialization (the epidermis) causes the scar.  Wisdom89  ( T |undefined /  C ) 21:05, 26 March 2008 (UTC)


 * The current edition of Scientific American has an article on the subject. --Gerry Ashton (talk) 21:40, 26 March 2008 (UTC)


 * See Regeneration (biology) as well. There are some human sections there. -- Lenticel ( talk ) 22:26, 26 March 2008 (UTC)


 * This was actually the featured article in Scientific American this month. Check it out, this might be what you're looking for. Mac Davis (talk) 23:21, 27 March 2008 (UTC)

Here is a news story about a man who managed to chop off a fingertip, and doctors regrew it. All it took was sprinkling on the wound a powder developed by Dr. Steven Badylak of the University of Pittsburgh's McGowan Institute of Regenerative Medicine. The powder was "a substance made from pig bladders called extracellular matrix." Edison (talk) 23:48, 27 March 2008 (UTC)

Intestinal Dysbiosis
Does anyone know where I can read valid information on Intestinal Dysbiosis? Is it anywhere in Wiki?
 * Our (inadequate) article is at dysbiosis. --Sean 18:41, 26 March 2008 (UTC)

global warming
what evidence that global warming is occuring, and what evidence is there that it isnt occuring?


 * See global warming and related articles. At this point there's little doubt that it's occurring- scientific disagreements are generally over the details these days. Friday (talk) 21:22, 26 March 2008 (UTC)
 * See in particular scientific opinion on climate change. It looks like it's now almost impossible to find scientists who deny that anthropogenic global warming is occuring and has been for some time. Algebraist 21:54, 26 March 2008 (UTC)
 * I'd like to cut in and mention that he wasn't asking for numbers of scientists, he was asking for evidence pro or con. Mac Davis (talk) 23:10, 27 March 2008 (UTC)
 * At this point most of the serious opposition has taken to arguing that it doesn't matter, or it isn't really caused by humans all that much, or that it can't be stopped, or that measures to stop it would be economically prohibitive, etc., with only the real fringe arguing that no change is happening at all. (At least, that's what I've noticed.) --Captain Ref Desk (talk) 21:58, 26 March 2008 (UTC)


 * The intersting data are those that indicate, not that global warming is happening (this is indisputable, but it could be a cyclic phenomenon), but that it's happening faster than it ever has before. Core samples of glacial ice at the poles, and analysis of fossilized pollen (thus indicating periodicity of tropical / temperate cycles over millions of years) indicate that the globe is warming more and faster than at any other point in at least a few million years since the Industrial Revolution.  At the risk of climbing upon a soap-box, it is frustrating as a scientist and an educator to hear people talking about "opinions" regarding global warming.  Everyone's entitled to their own opion.  But no one is entitled to their own facts.  Facts are facts.  One can argue that the data are corrupted or inaccurate, one can dispute the rigor of the methodology in collecting the data, one can even produce a contradictory data set.  But one cannot simply say that they don't believe in global warming, for example, without first accounting for the data that support it.  This is not an even-handed debate.  It really isn't a debate at all. Vance.mcpherson (talk) 16:29, 27 March 2008 (UTC)


 * No argument at all -- and I share your frustration about the "opinionization" of reasonable facts -- but for clarity, may I ask if you in fact meant "since the Industrial Revolution the globe is warming more and faster than at any other point in at least a few million years"? :-) —Steve Summit (talk) 02:47, 28 March 2008 (UTC)

Time on the moon
This maybe a strange (or even a rather dumb) question but I was wondering whether the moon has been divided in different timezones. For example: if you were to live on the moon on the place where Neil Armstrong made his famous small step, what time would it be when on earth it's 12:00 pm (GMT)?


 * No, it hasn't; there would be no reason. On the Apollo missions, I believe they simply used Houston local time, so 12:00 pm GMT would have been 7:00 am CDT during Apollo 10, 11, and 15; and 6:00 am CST during Apollo 8, 12, 13, 14, 16, and 17.  --Anonymous, 6:22:22 pm EDT = 22:22:22 UTC, March 26, 2008.


 * Bear in mind that the length of a lunar day is a little bit more than 27 Earth days. (The Moon doesn't turn very quickly on its axis.)  Time zones on Earth mean that the sun rises at about the same local time all around the world; people go to work, have lunch, return home, go to sleep, etc. at similar times by their local clocks.
 * On the moon, one would go through about two weeks of daily activities between local sunrise and sunset, and two more weeks of activity between that sunset and the next sunrise. You're not worrying about local sunlight as a cue to tell you (and your body) when to get up and when to go to sleep.  If you called your buddy on the night side of the moon, you wouldn't have to worry about waking him up; he's not going to stay in bed for two solid weeks.  It's much more convenient to not have time zones on the Moon&mdash;that way, you can do business with someone on the lunar farside and have everyone awake at the same time.  Up until now, there's only ever been one small group of Americans on the Moon at any given time, so they've simply stayed on Houston time&mdash;the local time zone that they were talking to on Earth.
 * The question of what local time will be chosen for use by permanent settlers on the Moon is still open. Will Russians insist on Moscow time for their moonbase while Americans use Houston or Washington?   TenOfAllTrades(talk) 23:03, 26 March 2008 (UTC)


 * Armstrong & co probably did use Houston time among themselves because they were in communication with Houston and that made sense in the context of the mission, which was only a few days duration. But they "came in peace for all mankind'', so we now generally use UTC time when referring to it; our article says that they "touched down on the moon at 20:17:39 UTC on 20 July 1969".  As for future settlements, regardless of which country's citizens do the settling, why on Earth (no pun intended) would they use a time system that applies only to the Earth for a heavenly body that, well, isn't the Earth?  That would seem to come from an attitude that the Moon is somehow part of the Earth, or at least owned by Earth.  It would be like American colonists of some newly discovered island in the Mediterranean making it run on Los Angeles time - absurd.

They'd have to establish a base meridian, probably the place where Armstrong & co touched down, and divide the Moon up into an appropriate number of zones, which wouldn't be 24, by the way. -- JackofOz (talk) 23:24, 26 March 2008 (UTC)


 * I object to the bit about "They came in peace for all mankind, so we use UTC." Wikipedia uses UTC because that's appropriately neutral Wikipedia style.  But anyone who remembers the event is likely to describe it in terms of their own local time zone.  --Anonymous, 04:09 UTC, March 27, 2008.


 * Objection noted. What you say is true for individual memories; but if asked, free of any other context, the exact date on which the first Moon landing occurred, a more accurate answer would be "It's arbitrary because calendars aren't defined on the Moon.  Even if we align it to the Gregorian Calendar used on Earth, it would still depend on which place on Earth you chose as the reference point, because Earth uses many different time zones, and it happened on 19 July 1969 in some time zones and 20 July 1969 in others.  As a compromise, scientists usually resort to UTC as a standard - but still arbitrary - way of expressing time, and work out the date accordingly.  On this basis, it happened on 20 July 1969". --  JackofOz (talk) 07:08, 27 March 2008 (UTC)


 * Having a time system based on the Moon's local day/night cycle doesn't strike me as a practical approach. The only reason we need time zones on Earth is so that local clock time follows our diurnal rhythm wich follows local solar time.  On the Moon, that just wouldn't happen&mdash;no one can stay away for two weeks and then sleep for two weeks.  On what basis, and for what purpose, would one create time zones on the Moon?


 * What new clock system would you propose? You can't alter the length of the second without creating massive headaches for every scientist and engineer on the Moon.  If you create a clock system or calendar based on the Earth second, you're stuck with having odd numbers of minutes in an hour or hours in a day to get the hour/day to line up with some natural cycle of the Moon's orbit or rotation.  Further, if the Moon isn't tied to a terrestrial clock, then the difference between lunar time and Earth time will be constantly changing&mdash;is noon here going to be in the middle of the 'night' on the Moon next week?  Three months from now?
 * Besides, the Moon is part of the Earth, as far as I'm concerned. It's stuck in our gravity well.  Unless we do something really blindingly stupid, the population of the Moon is always going to be a tiny fraction of the Earth's.  Why set up a time system that has no readily apparent benefit for the lunar colonists, and makes it more difficult for them to communicate and do business with the billions of people on Earth? TenOfAllTrades(talk) 00:27, 27 March 2008 (UTC)


 * That strikes me as more of an argument for fixing our own problems on Earth and not worry about ever colonising the Moon. We're obviously talking hypothetical here.  But for the sake of argument, if there were a permanent colony on the Moon, and if they used an Earth-based time system, how would that work?  It would have as much relevance as using the time system they use on Uranus.  The Moon doesn't have the same relationship with the Sun as we do, so diurnal patterns are out the window for starters, and the 24-hour clock which is based on the rotation of the Earth would be utterly confusing, counter-intuitive and hopeless.  I appreciate that our body clocks are more-or-less in line with the 24-hour clock, and they'd have to deal with the same problem that people from the tropics or the temperate zones experience when they go to the Arctic and have months of daylight and months of darkness.

Yes, they'd have to stay in communication with their Earth-bound colleagues, but that presents no greater an intellectual problem than Russians in Vladivostok communicating with their cousins in Kalinigrad, 14 (?) time zones away. There would have to be a system for converting the "time" at any moment in time at any point on the Moon's surface to the the corresponding moment of time at any point on the Earth's surface, and vice-versa. If they can get to the Moon and back safely, that would be child's play. -- JackofOz (talk) 01:02, 27 March 2008 (UTC)


 * Up above, someone asked, "why on Earth would they use a time system that applies only to the Earth?" Because we're creatures of habit, that's why, and we really like our units.  Units of time, for some reason, most of all: though systems of length and mass measurement have come and gone, the hour, minute, and particularly the second have been just about universal since they were invented (except for one short-lived experiment during the French revolution). My guess is that we'll be using hours, minutes, and seconds for quite a while after we have an Earth day to synchronize them to.  (And once we stop caring about days, the leap year and leap second problems will go away!)


 * In the far-future civilization described by Vernor Vinge in his novel A Deepness in the Sky, the hour and minute have fallen out of use as well, but the second is still going strong, and properly decimalized. A kilosecond is about 15 minutes or a quarter of an hour (a perfectly useful amount of time); a megasecond is about 11 days, and also perfectly useful (not too far from our week); and so forth.  It's not clear what they use for an absolute reference, but there's a delightful passage describing the origin they use for computer timekeeping:


 * Programming went back to the beginning of time. It was a little like the midden out back of his father's castle.  Where the creek had worn that away, ten meters down, there were the crumpled hulks of machines -- flying machines, the peasants said -- from the great days of Canberra's original colonial era.  But the castle midden was clean and fresh compared to what lay within [his own ship's] local net.  There were programs here that had been written five thousand years ago, before Humankind ever left earth.  The wonder of it -- the horror of it, Sura said -- was that unlike the useless wrecks of Canberra's past, these programs still worked!  And via a million million circuitous threads of inheritance, many of the oldest programs still ran in the bowels of the Qeng Ho system.  Take the Traders' method of timekeeping.

The frame corrections were incredibly complex -- and down at the very bottom of it was a little program that ran a counter. Second by second, the Qeng Ho counted from the instant that a human had first set foot on Old Earth's moon. But if you looked at it still more closely... the starting instant was actually about fifteen million seconds later, the 0-second of one of Humankind's first computer operating systems.


 * —Vernor Vinge, A Deepness in the Sky, ch. 17


 * —Steve Summit (talk) 02:21, 27 March 2008 (UTC)


 * No, no, and no. They kept time on the Apollo missions using Mission Elapsed Time, which starts at zero at liftoff. 98.201.87.17 (talk) 05:15, 27 March 2008 (UTC)


 * The question has been asked "for what purpose would we propose a new time system for the Moon ?". Obviously it couldn't guide our sleep/wake cycle, since we can't make that 27.3 Earth days long.  However, one purpose would be for adjusting solar panels which are aimed at the Sun.  Many such system are likely automated, but for those which must manually be adjusted (say a portable unit used by an exploration team), a daily adjustment, or perhaps twice daily adjustment, might be appropriate.  Knowing which lunar time zone you were in would help you determine how to aim it.  You would also need to know how far north or south you are.  Of course, you could just visually aim it at the Sun and ignore the math.  Perhaps the more serious issue is knowing when the Sun will set, depending on your lunar time zone, so you can get back to base for the 14 Earth day lunar night, when solar power will be useless.  Hopefully the base either has a sufficient capacity to store solar power over that period or uses nuclear power. StuRat (talk) 19:28, 27 March 2008 (UTC)

Medical equipment grounding
I have noticed that medical equipment seems to have a grounding terminal of some sort (the symbol is something like a circle within a triangle) which is separate from the normal earth ground. The ground (electricity) article doesn't mention anything about it, and I can't find it on commons:Category:Power supply symbols. What is that pin for? --cesarb (talk) 23:18, 26 March 2008 (UTC)


 * Is it a ground symbol within a circle? If so, this seems to indicate a connection to safety ground via the equipment. Usually, you will find that this terminal is connected to the metal casing of the instrument and therefore to the mains ground lead (and hence real ground). Such a terminal would allow the protective connections of transducers external to the equipment to be connected easily to safety (mains) ground. Say you had some gear that might tend to float to high or dangerous voltages, then connecting it to this terminal would prevent it. Simply, if you want a real ground connection, you have it here!  —Preceding unsigned comment added by 79.76.201.53 (talk) 02:17, 27 March 2008 (UTC)


 * No, it's the opposite: the circle is within the symbol. --cesarb (talk) 03:43, 27 March 2008 (UTC)


 * Are you in Brazil? What is an example of one machine that has this so we can look for a picture? When you say "grounding terminal", is it a female banana jack or a screw or what? How do you know that it is separate from the normal earth ground, and what does the "normal earth ground" look like? --Milkbreath (talk) 15:28, 27 March 2008 (UTC)


 * Lots of medical equipment can run from an internal battery, right? I wonder if these terminals are there to "tie together" multiple pieces of equipment that aren't plugged in to the mains, to prevent sparking, ground-loops, etc.  -- Coneslayer (talk) 15:35, 27 March 2008 (UTC)


 * (ec) Its not the symbol for signal ground shown in ground (electricity)? I don't know about medical equipment, but professional audio broadcast equipment commonly has a separate terminal for technical ground which is isolated from the safety ground connection.  This is so the studio or whatever can provide a 'clean' signal ground to the equipment free of the 'dirty' noise going down the safety earth wire due to power supplies and the like.  As I say, I don't really know much about medical instruments but I would guess they have a similar problem in that a small amount of noise on the ground connection can cause large errors in the readings.  When a technical ground is not available the signal ground would normally be linked to safety ground since this is better than nothing.  Most equipment I have come across have a terminal internally connected to safety ground immediately adjacent to the technical ground terminal in order to enable this linking to be conveniently easy and the manufacturer supplies the equipment with the link in place.  It is therefore good to go out of the box and only an installer who has a technical ground facility needs to mess with it. You could also try [Symbols.com on-line encyclopedia of symbols] which allows you to search by graphic symbol type as well meaning although I could not find what you describe.  Sp in ni  ng  Spark  15:45, 27 March 2008 (UTC)


 * Spinningspark is on the right track. There is a ground-loop connection on most of my medical equipment.  It is used to ensure that the signals from the equipment have the same ground reference.  This is important when using multiple machines to get a running history of data on more than one patient (primarily for studies).  Some machines are very susceptible to this, such as EKG machines.  It is not truly a ground because the wire I use to connect the machines couldn't handle the current if something were to spike.  There is still a real ground going to the power outlet. --  k a i n a w &trade; 16:03, 27 March 2008 (UTC)


 * Almost it; it's the one shown for signal ground but with an extra circle within the triangle. --cesarb (talk) 03:38, 28 March 2008 (UTC)


 * I think cesarb is describing the equipotentiality symbol (IEC 417, No. 5021), as shown here . It is a warning to the user that all terminals marked with the symbol are internally shorted together. For example, on an oscilloscope with BNC inputs, all the shields are usually shorted together. You might want to remind the user of this so that he doesn't try connecting the ground clips on his scope probes to different potentials. The symbol specifically does not mean that the point is grounded, although in practice it usually is. --Heron (talk) 10:58, 29 March 2008 (UTC)