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February 14[edit]

Freezing point?[edit]

my wood shop has been at a constant temp below 26 degrees Fahrenheit for days there are several open containers of standing water but they do not freeze why is that. — Preceding unsigned comment added by 68.41.73.11 (talk) 00:40, 14 February 2014 (UTC)[reply]

Perhaps supercooling? Try stirring the containers and see if they freeze. If they doesn't work, try adding dirt or a small bit of ice. Nil Einne (talk) 02:47, 14 February 2014 (UTC)[reply]

If it didn't freeze at 24 degrees, not surprising that it wouldn't at 26. DMacks (talk) 02:48, 14 February 2014 (UTC)[reply]

How do you know it's been at that temperature constantly for all of that time? I think you should at least consider the possibility that you have a bad thermometer. Very clean water can super-cool and fail to freeze - but it seems unlikely that water just laying around a wood shop would be that clean...but it's the most plausible explanation if the thermometer is good. SteveBaker (talk) 02:56, 14 February 2014 (UTC)[reply]

Also, what are the containers on? If they are resting on the floor, it's possible the floor has a lot of stored heat energy, such as a large concrete slab is a very good insulator and can retain heat for long periods of time. Vespine (talk) 03:17, 14 February 2014 (UTC)[reply]

This exact question was asked within the last two weeks. μηδείς (talk) 18:54, 14 February 2014 (UTC)[reply]

Citation needed —Tamfang (talk) 08:46, 15 February 2014 (UTC)[reply]

DMacks already pointed out a very similar question had been asked by the same OP 2 weeks ago and also provided a citation, around the time I was replying (i.e. before any of this). Nil Einne (talk) 13:50, 15 February 2014 (UTC)[reply]

You won't have a constant and uniform temperature in your wood shop, unless it's hermetically sealed, surrounded by lots of insulation, and has been undisturbed long enough to reach equilibrium. Placement of the thermometer is an issue, walls will be colder than the middle of the room. Measure the temperature of the water instead. Ssscienccce (talk) 00:31, 15 February 2014 (UTC)[reply]

In natural sciences, does it make sense to ask why?[edit]

Are the questions about why the melting point of an element is the way it is, or why the speed of light it what it is, or why the mass of particles are what they are, meaningful at all? Or is it something that can only be answered with a paternalistic: "because it is." — Preceding unsigned comment added by OsmanRF34 (talk • contribs) 13:03, 14 February 2014‎

It's the single most important question. We don't always find an answer right away, but it often leads to great discoveries and inventions. See reason just for starters.--Shantavira|^{feed me} 13:38, 14 February 2014 (UTC)[reply]

I was not asking whether why some complex property is the way it is. H might be combined with O and we know why this is possible. But why coundn't the speed of light be something different from 299,792,458 meters per second? Does it make sense to ask the why of pretty basic properties? OsmanRF34 (talk) 13:41, 14 February 2014 (UTC)[reply]

Very much so. If you understand "why", you can extrapolate this into further theories.Zzubnik (talk) 13:46, 14 February 2014 (UTC)[reply]

The question is not why in general, but why basic stuff is the way it is. Of course, science will always ask why this or that, but is there a point where we can't ask why anymore? Could we reach some sort of axiom, where it doesn't make any sense anymore to ask why? OsmanRF34 (talk) 14:22, 14 February 2014 (UTC)[reply]

I don't think so, but if some sort of grand unifying theory of everything was discovered, and every single thing in existence could be calculated, then we might not need to ask why any more. However, I don't think mankind is capable of understanding everything, so there will always be a "why".Zzubnik (talk) 15:33, 14 February 2014 (UTC)[reply]

Just make sure you don't destroy the computer in the process.--Shantavira|^{feed me} 15:50, 14 February 2014 (UTC)[reply]

You might find Anthropic_principle interesting as an overview of the different types of "why" that we can ask, and the debates about where science ends and philosophy begins. OldTimeNESter (talk) 15:54, 14 February 2014 (UTC)[reply]

There are basically two ways of answering a "why" question: by giving a cause (what Aristotle called a proximate cause), or by giving a reason (what Aristotle called a final cause). It always makes sense to ask for the proximate cause of something, but it does not always make sense to ask for a final cause. Looie496 (talk) 16:07, 14 February 2014 (UTC)[reply]

Per Louie, the question "Why?" has to different meanings, and unless one is clear on which meaning, the answer is different. If you ask "Why is the sky blue?" What you mean is "By what mechanism is the sky the color that it is?" Natural sciences can totally answer those kinds of why questions. If you is instead ask a question like "Why did you hit your brother?" What you mean by that is "What was your purpose in hitting your brother." You don't really want to know how muscles and coordination and neuromotor activity work to make punching happen. You want to know the rationale,the purpose, the intent behind the action. Natural sciences don't do a good job of answering those questions. In simpler terms, if you ask "why am I here?" Science can give you the mechanism (evolution) but not the purpose. You'll have to look elsewhere for that answer; even if the answer is ultimately nothing, that is not a falsifiable question or answer and so lies outside of the realm of "science" to give you backing for. That doesn't mean it is an invalid question regarding the human condition, it just means you'll have to get your answer from somewhere else. A good read in this direction is the philosophy works of Stephen Jay Gould, especially Rocks of Ages which explores this very issue. --Jayron32 18:00, 14 February 2014 (UTC)[reply]

If we limit ourselves to the answers of why "pretty basic properties" are certain values, then yes, it makes a lot of sense. As an example, one may well get a noble prize for figuring out for establishing, beyond the shadow of a doubt, why any really basic constant in physics is what it is. Not only does it make sense to ask these questions, but I have seen several of them asked, both at University and in sci-fi books. If they are answered by being reduced to something even more basic, they original "basic" property suddenly is no longer basic, and we have the next level of basic knowledge. DanielDemaret (talk) 14:02, 15 February 2014 (UTC)[reply]

What constitutes a medical diagnosis ?[edit]

Somewhat related to the above Q, let's say we have the various (cumulative) scenarios:

1) Patient goes to doctor with purple spots on his ankles. Nobody has ever seen this symptom before. The doctor diagnoses it to be a new "Purple spotted ankle disease" (or maybe he names it after himself or the patient). He has no idea what caused it or how to treat it.

2) 1000 (or whatever number would be sufficient to qualify it as a disease) such patients have been diagnosed.

3) The doctor has published in a reputable medical journal, declaring the symptoms and name of the disease, but still has no idea what causes it or how to treat it.

4) A way to treat the symptoms is found.

5) A way to cure it entirely is found, but the cause has still not been identified.

I'm guessing somewhere around step 3 it would qualify as a diagnosis. StuRat (talk) 17:23, 14 February 2014 (UTC)[reply]

Oh, if only we had, at our fingertips, some reference work, some encyclopedia, perhaps, that could help us define and explain what a diagnosis is... --Jayron32 17:47, 14 February 2014 (UTC)[reply]

► Differential diagnosis is closer to what you're looking for. ~E:71.20.250.51 (talk) 20:18, 14 February 2014 (UTC)[reply]

In practice, a MEDICAL diagnosis in a patients journal, a combination of symptoms is often given, rather than a cause. It SHOULD be a cause, preferably a cause which can be cured, but the physician is often required to write something without knowing the cause for sure - so he writes down symptoms, often in Latin. A true cause is often hard to find, and the true cause can be in several steps. I could give a lot of examples, but that would be outside the scope here. DanielDemaret (talk) 14:10, 15 February 2014 (UTC)[reply]

None of the five steps you mention are true causes, and therefore none are a proper diagnosis, but one has to write something in the box marked "diagnosis" all the same.DanielDemaret (talk) 14:12, 15 February 2014 (UTC)[reply]

Let me quote the first sentence of our Medical diagnosis article:

"Medical diagnosis (often simply termed diagnosis) refers to both the process of attempting to determine or identify a possible disease or disorder (and diagnosis in this sense can also be termed (medical) diagnostic procedure), and to the opinion reached by this process (also being termed (medical) diagnostic opinion)."

Hence, even step #1 is a diagnosis because the doctor has attempted to determine the disease - and delivered an opinion that ruled out all of the other causes of the spots. The statement "You definitely don't have any of the other 200 diseases that could be the cause of the spots on your ankles - so this is new to medical science." - is a diagnosis...albeit not a completely satisfying one. SteveBaker (talk) 15:44, 15 February 2014 (UTC)[reply]

Just to be picky, purple spots would be a sign not a symptom. Richard Avery (talk) 07:39, 16 February 2014 (UTC)[reply]

Early warning system for supernovas?[edit]

Is it possible, in principle, to detect a supernova(that is close enough to cause destruction to the earth) before the leathal radiation reaches us? It doesnt necessarily have to be detcted from the surface of the earth, it could be a detector in space. The best(vauge) Idea I have till now is a detector that uses gravitational lensing to shorten the path of its communication signal to earth. For context, I am trying to write a short story where future humanity is preparing for a catastrophic colapse of earth's ecosystem due to a nearby supernova. Diwakark86 (talk) 18:09, 14 February 2014 (UTC)[reply]

If your question is on how to incorporate this bit of technology into a good story, see Clarke's Third Law. Arthur C. Clarke knew a thing or two about writing in this area, and the entire point is to be believable, which is not to say the same thing as being correct. Whether a piece of technology is possible or not isn't as important as the author making the reader believe in its possibility, which is the point of Clarke's three laws. If you want to invoke gravitational lensing or any other actual scientific principle, that's fine, but the technical details needn't be explored to scrupulous detail. Remember, the characters in your story will either know and/or understand how the doofalators they use work, and the reader will accept that readily more than they will either a kludged-in but incorrect explanation or a scrupulously correct, but overly detailed digression into deep physics. --Jayron32 18:46, 14 February 2014 (UTC)[reply]

You might find the article on Betelgeuse interesting, since the star is perhaps quite close to nova, and we have been able to witness this buildup. You'll read suggestions it may have already gone nova, as it is about 500 light years away IIRC. Luckfully its poles face perpendicular to us, so we won't sprayed by a polar jet when it does go. μηδείς (talk) 18:51, 14 February 2014 (UTC)[reply]

As to the use of gravitational lensing to shorten the path...you may want to think carefully about the geometry of the situation. Our hypothetical deadly radiation is already following (essentially) a straight-line path from source to Earth—where would you place the detector, and what shorter path would its signal follow? TenOfAllTrades(talk) 18:56, 14 February 2014 (UTC)[reply]

I just had a vague notion rather than a concrete plan. I am asuming the radition doesn't cover all the points in earth's orbit. so the communcation signal would be aimed at a point before the earth reaches position in its orbit which is dangerous. Is this asumption wrong? If Betelgeuse's poles were pointed directly at the solar system would all of earth's orbit be covered in radiation? — Preceding unsigned comment added by Diwakark86 (talk • contribs) 19:22, 14 February 2014 (UTC)[reply]

The blast wouldn't be like a laser, as an ignorant layman, I expect it should widen as it travels. But orbital position might matter, were that the case--especially if the sun were eclipsing Betelgeuse, which I think does cross the ecliptic. μηδείς (talk) 20:01, 14 February 2014 (UTC)[reply]

You might look at Action at a distance (better known as "spooky action at a distance") and Quantum entanglement for ideas to develop a fictional device that could overcome the time/space problem of providing (near instantaneous) warning for a distant event. ~E:71.20.250.51 (talk) 19:34, 14 February 2014 (UTC)[reply]

Don't neutrinos escape the star in large amounts just before it explodes? Could neutrinos themselves alone cook us? μηδείς (talk) 20:01, 14 February 2014 (UTC)[reply]

I'll offer no opinion how much you want to trust it, but there is a what-if.xkcd about it. Yes, there is a ludicrous number of neutrinos coming out (think 10⁵⁷), and no, they can't hurt you unless you are actually inside the star when it goes supernova - in which case the neutrinos are not the biggest problem you'll be having that day. 88.112.50.121 (talk) 20:14, 14 February 2014 (UTC)[reply]

I don't know the facts here, but in the science fiction novel Iron Sunrise by Charles Stross, he has people in a space station in rather distant orbit being killed by the neutrino flux after the star is made to explode by "iron bombing" (that is, killing the fusion reaction by injecting iron into the star's core). Stross usually gets that sort of thing right. Looie496 (talk) 21:26, 14 February 2014 (UTC)[reply]

It's hard to see how a type I supernova (caused by accretion of material onto a dwarf star) could be detected before it blows, except on the basis of it's gravitational pull on its companion. But for a type II (caused by collapse of a massive star), I would expect that there would be a dropoff in radiation as the star exhausts its fuel, and also a change in chemical composition. Looie496 (talk) 21:26, 14 February 2014 (UTC)[reply]

During a Type II supernova (i.e. massive core collapse supernova with outer envelope), the core collapse is transiently shielded from view by the thick outer layers of the star which must be blown off. As a result, the neutrino flash created by the collapse will arrive about 2 hours before the gamma ray pulse becomes visible. Any Type II supernova close enough to do real harm to the Earth will generate a neutrino pulse that is blindingly bright at the existing neutrino detectors (e.g. IceCube). Assuming those scientists can quickly figure out what the hell they just saw, the Earth would have a couple hours to prepare. Can't do a lot in 2 hours, but perhaps it is better than nothing. Dragons flight (talk) 21:51, 14 February 2014 (UTC)[reply]

Well, that's enough time to go underground, if shelters were already built. Maybe there could have been some signs of a incipient supernova for some time, so the shelters would be built ahead of time, with the neutrino blast being the final sign ? Just how much protection would, say, a tenth of a mile of rock be against a gamma wave burst (or maybe a mile of water) ? StuRat (talk) 00:47, 15 February 2014 (UTC)[reply]

A tenth of a mile of rock would be plenty of protection against a worst-case scenario of a gamma-ray burst. 67.169.83.209 (talk) 20:03, 15 February 2014 (UTC)[reply]

If I'm reading Type II supernova#Core collapse and Carbon-burning process correctly, you may be able to get as much as a thousand years' warning by watching for a change in neutrino flux coming from the star -- as it starts burning heavier elements, neutrino production increases. That will give you time to build the shelters you need, while the neutrino flash of the supernova itself tells you it's time to enter those shelters. --Carnildo (talk) 02:25, 15 February 2014 (UTC)[reply]

With existing technology it is not possible to measure neutrino fluxes from the ordinary activity of individual stars (other than the sun). Dragons flight (talk) 02:55, 15 February 2014 (UTC)[reply]

Still, it's very much possible to predict which stars are close to the supernova stage, based on their evolution. 67.169.83.209 (talk) 20:03, 15 February 2014 (UTC)[reply]

How much warning would we get from the time when the neutrino flux from the supernova starts to diverge by orders of magnitude from the total background level of all other sources combined?

Also... I have a thoroughly groundless suspicion that the military has much, much better ways of detecting neutrinos than they admit. See [1] Just because they seem so blase about the nuclear weapons and material floating around, yet somehow they managed to nab that fellow driving across Germany. Speaking of which... does anyone know how open the existing neutrino detector projects are? Do lots of scientists wander in and out gawking at the equipment, or are they locked up pretty tight with people with security clearances in charge? I'm imagining them not being what they say they are, and while pretending to find a couple of events here and there, really compiling extensive triangulated tomography of all the radioisotopes on Earth, especially the moving sources. Wnt (talk) 23:07, 15 February 2014 (UTC)[reply]

Come on, Wnt, you know such conspiracy theories are much more fun when you give documentary citations to clips from Mel Gibson and Oliver Stone movies. μηδείς (talk) 00:17, 16 February 2014 (UTC)[reply]