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Surely quantum electrodynamics was so named as a play on Q.E.D.. Is there a nice succinct quote about this from the 1920s or so when it was being developed? Comet Tuttle (talk) 00:35, 27 October 2009 (UTC)[reply]
Mm... was it? I have never seen that claimed, even in books on the subject. --Mr.98 (talk) 00:59, 27 October 2009 (UTC)[reply]
I think that's just a coincidence. Dauto (talk) 03:39, 27 October 2009 (UTC)[reply]
I would not put it outside of the realm of possibility; after all these sorts of people are the same that gave us "strange" and "charm" for names of quarks; heck the name "quark" itself was intentionally chosen because it resembled a duck's quack and a seagull's call. They also gave us the name "gluon" because they "stick things together" (i.e. "glue"-ons). Physicists have their own brand of wit, so the connection between "quantum electrodynamics" and "quod erat demonstrandum" may have been more than a happy coincidence. I have no citations to say one way or other; I just would not be surprised if it were so... --Jayron32 03:39, 27 October 2009 (UTC)[reply]
Feynman definitely intended the parallel in his book. --antilivedT | C | G 04:19, 27 October 2009 (UTC)[reply]
I thought quarks were so named for "Three quarks for muster Mark" - a phrase from Finnegans Wake by James Joyce? In other words, as there were three flavours of them, something that came in threes were quarks... A quote to this effect from Murray Gell-Mann,the discoverer of quarks is given under Quark#Etymology .--TammyMoet (talk) 10:36, 27 October 2009 (UTC)[reply]
Joyce was using the "three quarks for Muster mark" in reference to three honks of a seagull; while Murray Gell-Mann used the term "kwork" in reference to a duck's quack. So he specifically picked the spelling from Finnegan's Wake since he liked the spelling better but ALSO had roughly the same meaning as his first word. --Jayron32 13:26, 27 October 2009 (UTC)[reply]
I don't put it outside the realm of possibility... I just haven't heard anyone claim it. They were using "Quantenelektrodynamik" as a name for it when Feynman was still in diapers, he doesn't have anything to do with the name... similarly, "quark" and its names are from a much later generation (the 1960s). Were Dirac and Pauli as funny with their physics? Not generally... --Mr.98 (talk) 14:40, 27 October 2009 (UTC)[reply]
If the speed of light through space is constant, regardless of the movement of an observer...wouldn't an individual be able to measure his movement through space (the combined velocities of the earth rotation, earths orbit, sun's movement through the galaxy, galaxy though universe, etc.) by the difference in the apparent speed of a light emitted by the user in various directions? That is, assuming that all of the above movements were lined up in the same direction at the time of measurement, wouldn't light appear to move faster from the observer when a beam is aimed to (for example) the West then when aimed to the East? I would think that the combined velocities would give a vector and velocity for the observer, and that it would be detectable by measuring the apparent speed of light (produced locally) from the perspective of the moving observer. I am referring to a local observation. I understand this has been seen as a red shift when observing incoming galactic light from a galaxy that is moving away from the observer. A Glass Bubble (talk) 00:52, 27 October 2009 (UTC)[reply]
No, the speed of light is, as you say, constant regardless of the movement of an observer, so it is exactly the same in all directions. --Tango (talk) 00:56, 27 October 2009 (UTC)[reply]
Got it, and I will go read the links (Thanks)...and not to be thick headed...but if it is the same speed in all directions through space, and I as an observer am moving (for the above reasons). Shouldn't I be able to detect that a beam shot from me towards my direction of movement is moving away from me (key from me) slower than if I turned around and shot a beam away from my direction of movement? I understand that an observer at close to the speed of light will start seeing a shift in the appearance of light directly approaching him, and warping of the light to his sides. I thought that this might be a theoretically detectable phenomenon at the velocities that you and I are traveling at.A Glass Bubble (talk) 01:04, 27 October 2009 (UTC)[reply]
I think you're still misunderstanding. It is simply that no matter how, when or where you measure the speed of light (in vacuum) - you always get the exact same answer. So, for example, if you measure the speed of the light coming from a far distant star in summer when (say) the earth is moving away from it in our orbit - and then again in winter when the earth is moving towards that same star - the speed of the light you measure coming from the star is exactly the same. Even though the relative motion of the earth was 100,000 km/hour away from the star in the first measurement - and 100,000 km/hour towards the star in the second measurement - so you might expect your instrument to read 200,000 km/hour different in the two cases - it won't - you'll get the exact same answer. Similarly - if we measure the speed of light from something like a comet when it's rushing towards us - it's exactly the same as when it's moving away. No matter what you do - any measurement of the speed of light in vacuum will produce the exact same numerical result. Light it quite different from everything else in that regard. If you measure the speed of sound waves or water waves or the speed of an oncoming car - it'll depend on how fast you are moving and perhaps on how fast the source was moving - but light is completely weird in that regard. SteveBaker (talk) 14:06, 27 October 2009 (UTC)[reply]
Strictly speaking, there's no real way to test the constancy of the speed of light with respect to special relativity. That is to say, special relativity doesn't hypothesize that the speed of light is the same to all observers, but rather it assumes as much. The real test then, is in all the other predictions made by the theory, as they all rest on this assumption. And indeed, special relativity has proven remarkably accurate in experiment after experiment, except in those that require the use of general relativity. But there were attempts to see if the speed of light varied with the reference frame, and you can read about those at Michelson–Morley experiment and Fizeau experiment (well, that second experiment is not quite about the reference frame, but still related). Someguy1221 (talk) 01:12, 27 October 2009 (UTC)[reply]
These questions get at the heart of some of the major problems with pre-relativity physics, and were the motivations for the development of special relativity. I suggest looking for a good introduction to topic to get an understanding of how exactly relativity deals with these problems. You could try Introduction to special relativity, but I'm not really sure how clear that article is. Googling "Introduction to special relativity" comes up with a bunch of stuff. Rckrone (talk) 20:16, 27 October 2009 (UTC)[reply]
It involves the warping of space and time. To put it simply, if you had two different observers moving at two different velocities looking at a snapshot of photon that was moving towards them, they'd both agree on how fast it was going, but not on how far away it was or even when the picture was taken. — DanielLC 05:18, 28 October 2009 (UTC)[reply]
I have trouble understanding how damping affects the period of an underdamped harmonic oscillator. I know that damping affects the amplitude of the oscillator, however, how would damping change the period (or frequency)?
I feel like the period should be unaffected because the angular frequency, omega, equals sqrt(omegazero^2-beta^2), which seems to me is a constant.
Note: omegazero equals the natural (undamped) angular frequency, and beta equals the damping coefficient.
As you said, the angular frequency is sqrt(ω02-β2), which is less than ω0, so the oscillation with damping is slower than without damping. The angular frequency is constant in time, which means that the period doesn't change while the oscillator is running, even as the oscillations become smaller. But it's not constant in β, which means changing the amount of damping will affect the period (more damping means longer period). Rckrone (talk) 02:44, 27 October 2009 (UTC)[reply]
Thanks for the response, but can you explain how beta is not constant? Thanks again. Steevven1(Talk) (Contribs) (Gallery) 06:01, 27 October 2009 (UTC)[reply]
β is constant for a particular oscillator. Your question was, if β is changed, will ω change? and the answer is yes. For example, suppose I have an undamped oscillator (β = 0) with an angular frequency of 1.0 rad/sec. Now I add a damping force with coefficient β = 0.6 rad/sec. The angular frequency now is sqrt((1.0 rad/sec)2 - (0.6 rad/sec)2) = 0.8 rad/sec. That's slower than it was without damping. Rckrone (talk) 19:12, 27 October 2009 (UTC)[reply]
The article Harmonic oscillator provides the equations for the damped case. Not using the beta symbol the underdamped frequency is where ζ is a constant called the damping ratio.Cuddlyable3 (talk) 12:36, 27 October 2009 (UTC)[reply]
With all the other GMO corn, rice, peanuts, etc. why not GMO hemp to get rid of the THC so hemp can be grown once again (in the US legally) and provide us with abundant fiber, food and fuel? 71.100.9.185 (talk) 04:52, 27 October 2009 (UTC)[reply]
Because there are other, less expensive, and better sources of fiber, food, and fuel than hemp. The whole "legalize hemp because it can be used for really useful things" is usually a cover for the fact that the most useful thing it can do is get you high. While I will not deny that hemp has been quite useful for many applications, it is not more useful than other substances for the same applications, which makes genetically engineering a THC-free hemp kinda pointless. For more reasons than one. --Jayron32 05:18, 27 October 2009 (UTC)[reply]
And what might those other reasons be? ...hemp grows virtually anywhere, can be grown and used to make fiber food and fuel easily by the grower - cutting out the middle and the end man, would end American dictatorship and restore the democratic right of Americans? ...and probably a lot more. 71.100.9.185 (talk) 06:31, 27 October 2009 (UTC)[reply]
You're really on a roll with your conspiracy theories recently. Here's a suggestion for you - find someone who's big into marijuana sorry, hemp legalization and argues the "we can make stuff with it!" point, then invite them to join you with a placard declaring your support for THC-less hemp bioengineering. I strongly suspect all of your vocal proponents will suddenly be nowhere to be found... because what they want is legal pot to smoke, not an alternative to cotton. 218.25.32.210 (talk) 07:37, 27 October 2009 (UTC)[reply]
Yes, still a conspiracy but this time on the part of potheads ...er people who like to wear hemp ...er because it does not have the same depressing connotation as cotton has with slavery. Get it? COTTON = SLAVERY, HEMP = FREEDOM. Freedom, man freedom. That's what its all about. 71.100.9.185 (talk) 11:05, 27 October 2009 (UTC)[reply]
Paper made from hemp being considerably more durable and longer lasting than wood pulp doesn't match Jayron32's description of the product being less useful.163.1.147.64 (talk) 12:25, 1 November 2009 (UTC)[reply]
Interestingly enough, hemp might be a good target for pharming use anyway, since there shouldn't be any native crops which could be cross-contaminated. The cultivation techniques are well known, and the plant's toxicity is, as far as I know, limited to the THC, which is a well-characterized and, in the grand scheme of things, well tolerated chemical. SDY (talk) 08:00, 27 October 2009 (UTC)[reply]
"why not GMO hemp to get rid of the THC?" => Most other sources of fiber rot (e.g. flax). Thanks to the THC hemp does not. DVdm (talk) 11:34, 27 October 2009 (UTC)[reply]
Ah, the complication for law enforcement. Who hasn't had someone who smoked pot do a 180 on you and if the are the skitziod type reveal their Jekyll personality? I say keep marijuana illegal except for use by qualified psychiatrists to treat psycho patients in the psyco ward or in their office. —Preceding unsigned comment added by Biggerbannana (talk • contribs) 16:04, 27 October 2009 (UTC)[reply]
As mentioned in Hemp, it is already legally grown in a number countries throughout the world. I believe that list is incomplete anyway it appears there are a number more countries from (old and not exactly a neutral source but no evidence it's inaccurate) although it's possible some of them it's more of a technically legal issue like the US rather then actually done in practice kind of thing. And as also mentioned there and elsewhere there are already varieties of hemp with low THC, according to this below 0.05% [1]. The EU evidentally allows anything below 0.3% while NSW allows below 1% [2]. Also from what I can tell from the article and [3][4][5][6] the situation in the US is unclear. It is legal in some states. Federal law technically allows it with special requirements including a Drug Enforcement Administration permit/license, but they've refused to issue them. It appears from my earlier ref this is being tested in court so the legal situation may be cleared up in the future. (Or maybe Obama will change things or stuff like this [7] will compel changes or Congress wil change htings [8].) In any case, I'm doubtful that the minimal amount of THC in hemp is the reason why some governments (including the US) are reluctant to allow hemp to be grown. Much more likely is because of the difficulty actually differentating varieties with a low THC and a high THC. As police in the Netherlands found out [9] when they destroyed a universities' crop. Clearly allowing anyone and everyone to grow hemp wherever they want is likely to be problematic if you want to prevent marijuana/cannabis varieties with high THC being grown. That's likely why in many countries were it is allowed it's still fairly regulated. But these countries trust their ability to ensure only low THC varieties are grown, the US Federal government or specifically the DEA apparently does not. Completely eliminating THC from hemp is not likely to help this. There's no real solution other then improving testing methods and convincing the government it is a practical to regulate it. Sure you could do something like make GFP hemp but illegal growers could likely replicate that presuming they can't just breed it in to their existing cultivars so it's not likely to be a useful strategy. Since the most interest in hemp appears to come from people like you who don't like GM plants, I also question the merits of even going down the GM route beyond perhaps proof of concept. BTW, who said that hemp isn't associated with slavery? [10][11](yes I'm aware it says slavery wasn't essential). Edit: Actuallying considering [12][13]List of Schedule I drugs (US)Controlled Substances Act and some of the earlier refs, I may be mistaken about the THC thing. I don't really know much about US law and I often find some of the stuff they do strange particularly when it comes to the interaction of state and federal law. It's possible that the reason why the DEA limit (or claim they can limit) the growth of hemp is because it contains THC which is a controlled substance therefore it you completely eliminated THC the DEA could not claim such a right. However given some of the refs particularly the food stuffs issue, I'm not convinced the DEA's claim is legit and it seems possible if there really is desire to control hemp the absence of THC is ultimately not going to stop them since the law could potentially be amended to control hemp even if it doesn't contain THC. Nil Einne (talk) 21:59, 27 October 2009 (UTC)[reply]
Maybe this example of hypocrisy being practiced by the US government would be the last straw for the American people... Biggerbannana (talk) 05:40, 28 October 2009 (UTC)[reply]
I'm surprised no one has mentioned the conspiracy theory-like but not totally crazy notion that DuPont worked to make hemp illegal, or nearly so, in order to make their nylon product more dominant. There's a brief mention of it at DuPont#Hemp. Pfly (talk) 09:14, 29 October 2009 (UTC)[reply]
According to our article on the tsar bomba, it states, "In terms of physical destructiveness, much of its high yield was inefficiently radiated upwards into space". Is this true? In addition, I did some research and there are concepts and designs for nuclear shaped charges that can direct the energy released by a nuclear explosion into a cone as small as 22.5 degrees. Would a shaped charge create additional ground damage if used in a similar high yield bomb? If so, how large should the cone be and at what altitude should it be detonated at to maximize ground damage if we assume the bomb is 50 megatons in yield. ScienceApe (talk) 06:21, 27 October 2009 (UTC)[reply]
The problem here may be in ft/sec propagation of the blast wave front. The main advantage of a shaped charge is to make the copper cone lining into a plasma and while so doing propel it more or less as a small diameter cylinder. A very high ft/sec blast wave might not allow for the cylinder to be formed properly or propelled in a linear or even cone shaped fashion. 71.100.9.185 (talk) 06:38, 27 October 2009 (UTC)[reply]
Again the problem with this is the power and speed of the blast. This thing would have to be as big as a stadium to achieve anything besides everything turning to plasma closer to the center of blast. 71.100.9.185 (talk) 11:36, 27 October 2009 (UTC)[reply]
According to those designs, the materials are supposed to turn into plasma. ScienceApe (talk) 15:53, 27 October 2009 (UTC)[reply]
I'm pretty sure that the article isn't referring to shaped charges. My guess is that what it's talking about is the high detonation altitude (4 km), since the Soviets really didn't want to blow away a lot of ground and create a lot of fallout. The fireball from the explosion was ~4.6 km, so they basically dropped it at the ground and missed. SDY (talk) 08:05, 27 October 2009 (UTC)[reply]
That really wasn't what I was asking. I know it wasn't shaped. ScienceApe (talk) 15:53, 27 October 2009 (UTC)[reply]
You can see from the Tsar Bomba videos that it was not shaped in any way—it was just a perfect sphere. The shaped charges used for Project Orion are miniscule in comparison to the Tsar Bomba. You could probably shape an arbitrary-sized explosion but the size of the casing and liner needed to shape it gets prohibitive—you aren't going to fit the resultant bomb onto an airplane. Anyway, what's the point of such a thing? Even the 50MT was an active of political demonstration, not a feasible weapon. There are basically no targets where a 50MT is better than a few 5MT, which are much more manageable. As you probably know, increasing yield of individual weapons generally just increases the wasted energy. --Mr.98 (talk) 14:17, 27 October 2009 (UTC)[reply]
Yes, I know the Tsar Bomba wasn't shaped. I know what the Tsar Bomba's intention was, and its impracticality, and I know 5MT bombs are more manageable. However, I simply want to know if a shaped charge would in fact increase the ground damage, and if so, what would the cone have to be and at what altitude it should be dropped at. Your last comment is what I'm after. If shaping a charge will reduce the energy being wasted in a large explosion. ScienceApe (talk) 15:53, 27 October 2009 (UTC)[reply]
I don't see why shaping it would not reduce the energy being wasted, since most of it would no longer be directed away from your target (as with the sphere, the top half basically just goes up, where there isn't anything to hit... maybe some of that reflects off of the atmosphere and comes back down again, but it's not very much). The problem, again, is that shaping 50MT is probably an extremely non-trivial task. Anyway, there's a question to me of whether "wasting" is really the right terminology here -- the goal is not really total efficiency, but a question of how much of a yield you want in one place at one time. Anyway, I understand that this is peripheral to your question. --Mr.98 (talk) 20:43, 27 October 2009 (UTC)[reply]
strange diversion on the topic of the morality of the free exchange of ideas. (I think.)
Freedom of useful information like the above is a wonderful thing. What is an efficient way of raping a person? Cuddlyable3 (talk) 12:23, 27 October 2009 (UTC)[reply]
Except that the barrier between someone raping someone else and someone building a hydrogen bomb is totally different. (Maybe seven nations have developed hydrogen bombs, ever. Compare that to how many rapists there are.) Only advanced nuclear states have the materials to build a hydrogen bomb (which requires already having a fission bomb, and sufficient understanding to use it in the most optimal way), and they aren't going to spend their billions on something they found on the internet. Even then, there is little evidence that suppressing information actually suppresses unwanted illegal activity—rather, many have argued that if more information is out there, more people know what sorts of unquestionable behavior to look for. --Mr.98 (talk) 14:10, 27 October 2009 (UTC)[reply]
I agree that the scale of the assaults is different when seen by the perpetrator, but whether they are so different when suffered by the victim depends on the victim's distance from ground zero. I suggest that states or organisations who are interested in leap-frogging nuclear weapon capability in fact do check Wikipedia as one of their sources of information. Responders knowing that can answer appropriately to the OP's request for bomb-making information. Cuddlyable3 (talk) 19:46, 27 October 2009 (UTC)[reply]
Er, no, it is not about the scale of the assaults, it is about the likelihood of them happening in the first place. Talking about h-bombs in a speculative way isn't going to help or hurt anybody, presuming that nobody on here actually works on them for a living. (And even then, I think one would find that what counted as "useful" information is far more technical than you and I would recognize.) --Mr.98 (talk) 20:43, 27 October 2009 (UTC)[reply]
Both nuclear bombing and rapes have happened. One cannot presume that either will not happen again. The OP has researched how to carry out the former and seeks numerical information to maximise the ground damage which is where people will be hurt. Judging by the links cited about shaped charge the OP's research has found the most detailed information that is publically accessible. There are certainly responders here who are qualified to add to that information. The free-access principle of Wikipedia means they cannot know who may use its public information. We live in a time of Nuclear proliferation where quantitative engineering details for making a nuclear WMD have to be limited by Need to know not "cool to know". Sean thank you for fascinating references. The Los Alamos Primer is part of mostly classified material whose historical significance is undeniable. High-energy physics encompasses much more of importance than how to destroy people so I don't see a good reason to ban that subject. Cuddlyable3 (talk) 22:06, 27 October 2009 (UTC)[reply]
First of all, as others mentioned above, a 50-megaton bomb has no uses outside of political saber-rattling, and shaped charges are not helpful for that. Second, shaped charges already exist. We're discussing their capabilities, not offering improvements to existing designs. Third, if you seriously think that any terrorist who can make a nuke doesn't already know EVERYTHING that we can possibly discuss here like the back of their hand, you're severely underestimating the difficulty of making a bomb. --99.237.234.104 (talk) 01:25, 28 October 2009 (UTC)[reply]
The Ref. Desk is not a chat room. Shaped charges are uninteresting to rapists. Limited access to fissionable material is one of the few difficulties left for rogue states and terrorists seeking to make a nuke. Technology such as shaped charges that are key to detonating a subcritical mass must be highly attractive to them. Look here. Every bad guy has an Internet connection. It would be naive to suppose nobody in emerging and wannabe nuclear-capable groupings Iran, DPRK, Al-Qaeda or any of these learns nothing from Wikipedia or the links so freely given here. That means us. Shaped charges certainly exist. Their quantitative design data for WMD use is neither in Wikipedia mainspace, Popular Mechanics or otherwise in public domain because this is on-going research data from Nuclear weapons testing. Sean you provided aerial views of Nagasaki that don't show its inhabitants. Here is one of the lucky ones.Cuddlyable3 (talk) 08:47, 28 October 2009 (UTC)[reply]
Not a chat room? You started it! In fact you , frequently start it. You're always first to jump in with a joke, even when the question isn't answered. Collapsing this off topic stuff.APL (talk) 12:51, 28 October 2009 (UTC)[reply]
Please ask on Talk page if you remain uncertain whether the Ref. Desk is a chat room. No joke was added to this thread so your reference to jokes is a comment on a contributor not a subject. I have made visible your "hidden" questions about rape since that allows them to be treated properly and hope you don't mind. I agree that there are several parameters for quantifying rape efficiency depending on the rapist's motivation. In analogy to the tsar bomba one's goal could be to cause maximum human devastation and noise for the purpose of intimidating others, inflicting disease(s) would be an acceptable secondary achievement. You should not ask a contributor's gender. Cuddlyable3 (talk) 11:14, 29 October 2009 (UTC)[reply]
So I did some weird light reaction with benzophenone. So in exciting from pi to pi-star, evidently fluorescence is kind of slow because the pi star electron, if we were to follow Schrodinger's equation classically, would have to go through a point of zero probability (the nucleus) in order to make the transition, right? So some quantum tunneling must occur.
However, in lab we also have "spin forbidden" reactions -- I assume this is a different kind of forbiddance? What is the difference between spin forbidden and classically forbidden? What is spin forbidden anyway, in layman's terms? (Or terms for a second year undergraduate.) Thanks! John Riemann Soong (talk) 08:58, 27 October 2009 (UTC)[reply]
SPin forbidden reactions would be ones that caused two electrons of the same spin to occupy the same orbital. I can't think of any off the top of my head (its been too long for me since I did this stuff), but there may be some transition states that cause the creation of such orbitals. --Jayron32 13:10, 27 October 2009 (UTC)[reply]
It's a bit more complicated than that. For a simple (that is, non-relativistic) case, which means for electrons bound to light atoms like C and H, the wavefunctions are products of spatial part and spin part. The electric dipole operator only acts on the spatial part. Thus, when spin part of the wavefunction of the electron that makes the transition is different in the initial and in the final state, the electric dipole operator matrix element between the initial and the final state is zero, and the transition is spin-forbidden. Now, I am deliberately oversimplifying it. For a really thorough explanation of the Selection rules for electron transitions in atoms and ions, see Theory of Atomic Structure and Spectra by Cowan. There must be a similarly voluminous textbook for transitions in molecules, too, but I am less familiar with the molecular transitions. The basis of the selection rules is the same in atoms and in molecules, of course. --Dr Dima (talk) 18:34, 27 October 2009 (UTC)[reply]
Hello,
I have had, just in the past month or so, small black worms (with antenna), crawling on my garage floor. They seem to just crawl in and die on the floor ( although one was crawling on the wall). I have just been vacuuming them up with my shop vac, but in a day or two, I have to do it again. I live in West Michigan. I am wondering (1) what are they and, (2) would they get into anything like the cars that are parked there?
I have been trying to find out what they are and, to this point, have had no luck!
Do they have any other coloration (e.g. red spots)? Do they have legs? (How many?) They sound like larvae of some sort, not worms, per se, but without a picture it's hard to make heads or tails of it. --Mr.98 (talk) 14:07, 27 October 2009 (UTC)[reply]
As Mr.98 says, much more details, or a picture, would be necessary for a meaningful answer. My own best guess would be millipedes or centipedes: there are around 10,000 different species of the former and 8,000 of the latter. They might also be the caterpillars of some local butterfly or moth; these do not have antennae (unlike the adult insects), but some have spines, horns or tufts of hairs that may be mistaken for antennae. To answer question (2) - if they can climb a wall (as all of the suggestions so far can) then they might be able to get inside a parked car (by climbing the tyres or dropping from above), but would probably have little motivation to do so. 87.81.230.195 (talk) 06:46, 1 November 2009 (UTC)[reply]
1.please tell me something about disaster preparedness fr eg: first-aid kit what to keep in it etc
please ans soon thank you —Preceding unsigned comment added by Advaitadd (talk • contribs) 13:51, 27 October 2009 (UTC)[reply]
You might check out our article on bug-out bag for one potential list. The answer depends on what kind of disaster you are preparing for—there's a sweet spot between "electricity goes out for a day" and "end of civilization" that most people are aiming for, given that the former doesn't really require more than a flashlight and some batteries, and the latter is not something you have much of a chance of surviving anyway. What you probably want, ideally, is "keep me afloat for a few days so that I can get the heck out of here if things are really going sour," with modifications depending on your particular local risks (e.g. whether you are on a flood plain vs. in an earthquake zone vs. wildfires, etc.). We also have an article on survival kits more generally—but these, IMO, are assume you are really going to survive long-term in such a situation, which I personally find unlikely. (Flee to higher ground, find help! That's about all I think one should be trying to do, not eke out some sort of The Road lifestyle.) --Mr.98 (talk) 14:59, 27 October 2009 (UTC)[reply]
I think you need to consider the kinds of disaster you are preparing for. If (for example) you live in a small town in tornado alley and you want to prepare for tornado season - then you need a good first aid kit - enough so you can help people out in the hour it might take for help to arrive. But if you were involved in the aftermath of hurricane Katrina - with the possibility of it taking an entire week for help to arrive in enough quantity - then food, bottled water - a way to hack your way out of your attic if you're trapped there - maybe a small inflatable boat. It really does depend on what kind of thing you think might happen. Consider also where you're going to be. You need loads of bottled water for surviving here in Texas - but perhaps that's not a consideration in the wilds of Alaska. Of course if you're planning some kind of extreme travel (trekking across Death Valley, skiing in the Antarctic, taking a mini-sub into the Marianas Trench) - then your plans for disaster will be MUCH more specific!
I would argue that from a day-to-day perspective, the Katrina type of problem is at the more extreme end of the scale. It's very rare for help not to arrive within hours to days in most places in the civilised world. In which case, perhaps you should consider things like a safe, waterproof place to keep important documents (copies of insurance policies, deeds for property, bank account details, etc) - pre-paid credit cards - some cash. Things that will help you when you're kept out of your home (or what remains of it) for weeks or more.
Survival experts often quote the following rules of thumb:
Humans cannot survive more than three hours exposed to extremely low temperatures.
Humans cannot survive more than three days without water.
Humans cannot survive more than three weeks without food.
So should you keep food in your emergency stores? Perhaps not. If you're not going to be rescued within three weeks - then you're in a lot of trouble! If we have to survive cold or wet weather then warm clothing might be more important. Will you need to make a shelter? A decent multi-tool (a Swiss Army knife or a Leatherman multi-tool) will give you huge advantages for a tiny amount of space/weight in your kit. A way to make fire (waterproof matches). Maybe a waterproof sheet and some rope to make an improvised shelter - a mylar foil blanket to keep yourself warm & dry. A first aid kit certainly wouldn't hurt - you should have one of those in your home and car anyway. When you have all of those immediate needs taken care of - then bottled water is your next priority - and only then consider some long-life food. Trail mix, jerky, energy bars.
What percentage of the brain is water, fat and protein? Generally people and sites quote: 70 or 76% is water, 60% is fat and 40% is protein. But, that adds up to over 100%, so what am I missing?Clb14a (talk) 15:25, 27 October 2009 (UTC)[reply]
Without knowing the answer, those numbers suggest that the 60 and 40 percent numbers exclude water. --Sean 19:34, 27 October 2009 (UTC)[reply]
A lot of weights in biology are measured dry - the water is driven off before measurement. Vimescarrot (talk) 20:58, 27 October 2009 (UTC)[reply]
This says that the makeup is 77 to 78% water, 10 to 12% lipids (fat), 8% protein, 1% carbohydrate, 2% soluable organic substances and 1% inorganic salts. That article is well referenced (those particular numbers come from: McIlwain, H. and Bachelard, H.S., Biochemistry and the Central Nervous System, Edinburgh: Churchill Livingstone, 1985) - so I think we can take these numbers are true. So if you remove the water, then the remainder is reasonably close to 60% fat, 40% protein - so I think TotoBaggins and Vimescarrot have nailed the reason for the confusion in what you read. SteveBaker (talk) 02:22, 28 October 2009 (UTC)[reply]
In water, suppose a crest and trough of equal magnitude travel towards each other and causes destructive interference, how is that, a short while later, that the crest and trough each *pop* out again and continue their own merry way as it will be if they had not met in the first place? Where did the *information* go during the destructive interference? another dimension?
does the same thing happen with matter and antimatter too? —Preceding unsigned comment added by 118.100.10.187 (talk) 15:34, 27 October 2009 (UTC)[reply]
With simple waves neither a crest nor trough travel unaccompanied. If two waves did perfectly interfere then they wouldn't carry on their merry way, they cancel out. --Digrpat (talk) 18:15, 27 October 2009 (UTC)[reply]
No additional dimensions are involved. The "information" at the instant that the water is flat is in the kinetic energy, or equivalently the momentum or the velocity of the water, depending on how you want to look at it. The potential energy of the gravity wave, which is determined by the position of all of the water molecules, may for an instant be as if the water was static. But in order to completely describe the water at that instant, you also have to describe the velocity of each of the water molecules. (There are also additional complexities involved due to water not consisting of point particles, but I don't think it's important to bring that up here.)
The annihilation of matter and antimatter is different, in that the annihilation process produces new, different particles. And there isn't an instant of time at which the old particles don't exist anymore, and the new particles don't exist yet. Once you get down to the level of quantum mechanics, you can't say exactly what's happening at a precise instant like that, because the Heisenberg uncertainty principle requires that an infinitely large amount of energy would need to be involved, in order to know exactly when something happened. Red Act (talk) 19:06, 27 October 2009 (UTC)[reply]
Why do most humans grimace when they're straining themselves?[edit]
Back off!
Such as when they're trying to lift something heavy or during a very large bowel movement? 20.137.18.50 (talk) 15:36, 27 October 2009 (UTC)[reply]
Well it could be evolutionarily beneficial because those heavy things may have been a predator or other human, and animals tend to show their teeth to warn attackers that they can bite. --Mark PEA (talk) 18:29, 27 October 2009 (UTC)[reply]
It's simply a result of tensing all the muscles of the face and jaw -- when you strain, pretty much every muscle in the body contracts to some degree. Looie496 (talk) 21:27, 27 October 2009 (UTC)[reply]
It seems rather unlikely that something like tensing your face while lifting something would exert any reproductive pressure on a population. "Ah, well, if Bob had only tensed his face while lifting that rock, he'd probably be alive by now..." We're getting into Just-so story territory here... --Mr.98 (talk) 01:42, 28 October 2009 (UTC)[reply]
It was just a speculative hypothesis, like much of evolutionary psychology. The fact is, a gene which makes one bare one's teeth when straining is more beneficial than one that doesn't, in the scenarios where the strain is caused by a predator/enemy on top of oneself. What isn't a fact is that natural selection favoured this, and Looie's answer is the much more likely explanation.
-∞ (Predator doesn't fear being bitten, kills prey)
's net utility:
> -0.1
-∞
The net utility obviously assumes that both conditions occur, which isn't an unreasonable assumption for >10,000 years ago seeing as animal-human and human-human attacks still occur to this day. I know it also seems to assume that grimacing will cause the predator to run away 100% of the time, which is clearly not the case. I still think it is worth it even if a fraction of predators run away.
Feel free to pick away at any flaws, and remember that I'm being hypothetical. --Mark PEA (talk) 11:43, 28 October 2009 (UTC)[reply]
It's really tough to know - but I guess another possibility is that this grimacing is proto-language - like smiling, crying, frowning and laughing. Before the ancestors of humans learned to speak - they would have used facial expressions just like dogs wag their tails in different ways to signify welcome (circular wag) or happiness (side-to-side wag). Perhaps the grimace in the context of someone lifting something means "This is really heavy - could you please come over and help me?". SteveBaker (talk) 12:23, 28 October 2009 (UTC)[reply]
Or maybe it's because the muscles in your neck actually contribute to the lifting of heavy weights. Try lifting something heavy without grimacing and you'll see what I mean. Conversely, try exerting a large force with your legs, with your back braced against a wall, and you won't feel such a strong need to grimace - although the tension in your back will affect your face to a lesser degree. --Heron (talk) 18:00, 28 October 2009 (UTC)[reply]
The stroke article is fairly comprehensive and has detailed sections on symptoms and possible treatments. --- Medical geneticist (talk) 16:18, 27 October 2009 (UTC)[reply]
Oh! ok, I didn't know it was a type of stroke.--Reticuli88 (talk) 17:14, 27 October 2009 (UTC)[reply]
Athero would refer to a "blood vessel," thrombotic would refer to a "clod of platelets," cerebral would refer to the upper most, paired lobes of the brain known as the "cerebrum" and infarction refers to a "blockage of a blood vessel." DRosenbach(Talk | Contribs) 23:22, 27 October 2009 (UTC)[reply]
Triceratops And Their Frills (And Also Stegosaurus)[edit]
If a triceratops were to somehow fall onto its back, would it have a problem getting back upright due to its frill? How about a stegosaurus and its plates, would it also have a problem? -WarthogDemon 16:00, 27 October 2009 (UTC)[reply]
Well, barring the plates getting stuck in the soil from falling off a ledge, wouldn't they help it right itself, as the frill and plates would prevent a creature from staying on its back and would instead roll it to its side? ~ Amory(u • t • c) 17:48, 27 October 2009 (UTC)[reply]
It is unreasonable to assume that there is a creature that evolved to be unable to roll over. Even Bender learned to get up off his back. -- kainaw™ 19:55, 27 October 2009 (UTC)[reply]
That source, which doesn't appear very reliable to my eye, doesn't state that the desert tortoise cannot right itself. It claims that desert tortoises cannot always right themselves, and it is suspiciously devoid of examples and references. Comet Tuttle (talk) 23:38, 27 October 2009 (UTC)[reply]
The point was that tortoises can get stuck depending on their shell shape and that it's unreasonable to state that actual reality is unreasonable. It's like saying that it's unreasonable that earthworms leave their flooded tunnels to get bloated and drown on rocks and eaten by birds and etc. when it happens all the time. It's like saying that it's unreasonable to assume that there is at least a single organism that cannot swim, because how would nature allow an animal to evolve into something so unfavorable - but I'm sure there are animals that drown (and that list, however short, might include caterpillars and some tortoises). DRosenbach(Talk | Contribs) 01:51, 28 October 2009 (UTC)[reply]
There is a huge difference between "having the possibility to get stuck upside down" and "being unable to roll over". If you rationalize that those two are equivalent, then we can pick anything that can happen sometimes and argue that it happens all the time. For example, why not argue that evolution sucks because humans always die in vehicles that humans invented and built. An obvious absurd argument - just as absurd as claiming that desert tortoises are unable to roll over because they sometimes get stuck upside down. -- kainaw™ 23:41, 28 October 2009 (UTC)[reply]
How do people know that the mad cow disease generally would not migrate to other non-ruminant species?
Chicken on modern farms are seldom observed by people. A chicken may only be examined once by people at hatching (sexing the chicken) and the second time in the slaughter house. If I have a little Old McDonald-styled farm, I would spend hours after hours watching my animals walk, run, eat. If a cow has become unable to walk, I would have noticed it. In contrast, a chicken farmer having a large industrial farm only check the chicken once a day. If a hen dies in the cage, he picks it up and send it to the rendering plant. I bet even if a chicken cannot work, it may not be observed before death.
In many countries, a dozen chicken are stuffed in a small battery cage. They are killed when they are about sex-weeks-old. I don't believe that you may notice any of their abnormal behaviors.
What may happen if I have a very large piece of land so I can grow one million free range chicken to their natural deaths? If I feed them with feeds made from mad cows and scrapie sheep and goats, would they show symptoms after a few years? -- Toytoy (talk) 17:37, 27 October 2009 (UTC)[reply]
The main way you would find out if your chickens are sick is to give a sample of them post-mortems, I think. I imagine that is being done. --Tango (talk) 17:43, 27 October 2009 (UTC)[reply]
Egg-laying hens in factory farms are kept about 1 1/2 years, and spongiform encephalopathy does eventually cause death, so perhaps it would be noticed by that route. Anyway, people eat an enormous amount of factory-farmed chicken -- including spinal cord tissue in the case of soups and stocks -- and there's no big prion-disease outbreak that needs explaining by a hypothesis of undiagnosed SE in chickens. --Sean 19:44, 27 October 2009 (UTC)[reply]
If chickens live at most 1.5 years for egg layers and much shorter time if intended for slaughter, then spongiform encephalopathy might not have time to manifest its behavioral effects. In humans, what is the incidence of mad cow/CJD and has it varied over the years? 24.12.190.7 (talk) 20:56, 27 October 2009 (UTC)[reply]
Many dog and cat food suppliers use livestock rendering as a main ingredient. Pet dog and cats may live for a decade or longer. They may eat the same brand of food for many years (prolonged consuming of the same ingredients). Many pet owners bring their pets to vets periodically. Despite the fact that extremely old dogs and cats are certainly too weak to walk, we do not see the global emergence of mad dog/cat diseases ... Does it imply that the species barriers are generally strong enough to stop a specific type of prion to migrate from this animal to that animal? -- Toytoy (talk) 03:13, 28 October 2009 (UTC)[reply]
We know that one of the major causes of the Mad Cow outbreak was that farmers were (perhaps unknowingly) causing highly processed left-over parts of cow carcasses back into protein that was been fed back to cows in their food supplements. The parts that were recycled were the things we don't eat - brain and spinal cord tissue - which is precisely the place where these prions are to be found in mad cows. Part of that was just sheer stupidity - it seems really obvious to me that cannibalism is going to cause diseases to spread - they should have thought of that. Worse still, cows are naturally herbivores - they don't have the digestive mechanisms to protect them from meat-born diseases.
Cats and dogs are both carnivorous - and (thankfully) we never feed them dog and cat parts - however indirectly. So neither of those major screw-ups that the cattle industry fell foul of could possibly affect cats and dogs. If a dog were to contract "mad dog" disease - it would eventually die - the body would probably be cremated or otherwise safely disposed of...there is simply no way for the disease to spread. You don't put dead dogs into dog food!
The case with chickens lies somewhat between those extremes. Chickens are naturally carnivorous - they eat all sorts of insects and worms and such - so they have a digestive system that's evolved to handle the problems that come up with eating meat. The less obvious question is whether left over chicken carcasses somehow get recycled into chicken feed. That was certainly possible in the past - and it seems quite possible that mad-chicken disease could have appeared in the past. But since we became acutely aware of the causes of the mad cow outbreak - I would assume that the feedstock chain is now likely to be very highly regulated to prevent dead chickens ending up inside chicken feed.
So, while it's not impossible for this to happen to chickens - I think the odds are considerably longer than they were with cows. SteveBaker (talk) 04:18, 28 October 2009 (UTC)[reply]
Most shockingly, this also can include dogs and cats. That's right, your pets could be cannibals. Fast Food Nation author Eric Schlosser writes, "Although leading American manufacturers promise never to put rendered pets into their pet food, it is still legal to do so. A Canadian company, Sanimal Inc., was putting 40,000 pounds of dead dogs and dead cats into its dog and cat food every week, until discontinuing the practice in June 2001.
However unlikely, some pet food companies might have used pet meat in their products. Since the majority of meat still has to come from fish and livestock, the concentration of any possible pet carcasses could have been small. And since pets eating "pet foods" might not re-enter the pet food chain when they die, their prions were unlikely to infect other pets. Take cats for example:
cat carcasses --> dog food --> dogs are unlikely to be infected
cat carcasses --> cat food diluted with other sources of meat --> cats are unlikely to be infected
cat carcasses --> cat food --> infected cats --> buried or cremated --> cause no further infection
Only #4 could result in the spreading of prion, I guess. -- Toytoy (talk) 01:49, 29 October 2009 (UTC)[reply]
It's definitely not implausible that pet food companies would use pet meat in their products if it were a cheap and available alternative to other meat, but that doesn't seem very likely. Where would the cat or dog meat be coming from? Pet owners don't sell their deceased pets' carcasses to meat vendors and I'm pretty sure animal shelters and pounds don't either. Rckrone (talk) 05:06, 29 October 2009 (UTC)[reply]
Were they from the puppy mills? -- Toytoy (talk) 09:13, 30 October 2009 (UTC)[reply]
From the Hippocratic Oath: "All that may come to my knowledge in the exercise of my profession or in daily commerce with men, which ought not to be spread abroad, I will keep secret and will never reveal." -- Scray (talk) 18:57, 27 October 2009 (UTC)[reply]
Sadly our article Hippocratic Oath is US Centric.. "Most Medicine schools administer some form of oath" as far as I know completely untrue in respect of every medical school in the UK for example, and I guess is unlikely outside the new world. I think Tango's answer is better --BozMotalk 19:07, 27 October 2009 (UTC)[reply]
My sister is a British medical student and I've never heard of any kind of oath for British doctors. --Tango (talk) 20:15, 27 October 2009 (UTC)[reply]
Used to in Hippocrates day in Greece maybe? Did they ever do this in the UK? It isn't mentioned in the history sections of the Royal Colleges websites as far as I can see. --BozMotalk 12:06, 28 October 2009 (UTC)[reply]
Found a slightly better reference in the letters section of the British Medical Journal suggesting the use of the HO in the UK ever is a myth: [14] --BozMotalk 12:11, 28 October 2009 (UTC)[reply]
Apparently it's also rare in Australia and NZ although a (small) majority of institutions do have a declaration of some sort [15]Nil Einne (talk) 21:11, 27 October 2009 (UTC)[reply]
For those (like me) who would check - it's been fixed to clarify that the statement applies to U.S. medical schools. -- Scray (talk) 11:20, 28 October 2009 (UTC)[reply]
What is GVO] pigmentation basically for when the primary color is green, orange, violet and secondary color is pink, yellow, blue. CYMK is use for printing and RGB is for light use.--209.129.85.4 (talk) 20:37, 27 October 2009 (UTC)[reply]
what s the meaning of energetically favorable? —Preceding unsigned comment added by Farahghannam (talk • contribs) 20:37, 27 October 2009 (UTC)[reply]
Thermodynamics and chemistry aren't my strongest subjects, but I'm pretty sure I know the right answer. An energetically favorable reaction is one that decreases the Gibbs free energy of the system. Energetically favorable reactions can occur spontaneously, whereas an energetically unfavorable reaction can only occur if it is coupled to a second, energetically favorable reaction. It's basically a result of the second law of thermodynamics. Red Act (talk) 21:12, 27 October 2009 (UTC)[reply]
A reaction is energetically favourable if it has a negative ΔH - if it gives out more energy than it takes in. However, it may not be _kinetically_ favourable - it may take place so slowly that it effectively doesn't occur. See particularly Chemical kinetics#Free energy, and Chemical thermodynamics. Tevildo (talk) 21:13, 27 October 2009 (UTC)[reply]
Really? I'm rather weak on thermodynamics, but if I Google "energetically favorable", the search results are all about ΔG, not ΔH. Chemical kinetics#Free energy also mentions ΔG, not ΔH. I'm probably wrong, but I'd be curious to hear a brief explanation as to why. Red Act (talk) 22:57, 27 October 2009 (UTC)[reply]
Also, some reactions that occur are endothermic. Doesn't that violate the idea of negative ΔH always being what's energetically favorable? Red Act (talk) 23:47, 27 October 2009 (UTC)[reply]
It usually means that the reaction has a negative ΔG. The second law of thermodynamics tells us that the ΔG of the universe is always negative in the forward time (that is, free energy is always decreasing on a universal level). Any reaction that itself has a negative ΔG then will occur spontaneously; while a reaction that has a positive ΔG will require you to basically "steal" free energy from elsewhere to occur, so that the ΔG is negative in total for the universe. RedAct is basically right here. Enthalpy is only important because exothermic reactions decrease free energy for the universe (moving energy from a concentrated state inside a chemical bond to a diffuse state as heat); but the key measurement in determining energetic favorability is ALWAYS ΔG. --Jayron32 05:53, 28 October 2009 (UTC)[reply]
A widely talked about topic on the internet - in fact if you type 'space expands' into google, it expands it to the topic 'space expands faster than light'! This was mentioned when someone was talking about the Big Bang during The Universe Season 4 Episode 4, and piqued my interest. I kind of understand the possibility of the physics behind the concept, but I can't help thinking that once again, scientists have come up with contrived physics to explain the rapid expansion of space at the very start of the inflationary model. Where else do we see this happening? Certainly nowhere now except in the realms of science fiction... Sandman30s (talk) 21:46, 27 October 2009 (UTC)[reply]
The main problem with attempting to understand this concept is the idea that the edge of space is a thing. That thing cannot travel faster than the speed of light. The problem is regarding that there is a "thing" called the edge of space. A better way to conceptualize it is as the surface of a balloon. It has no edge. If you walk around on it, you can walk forever without reaching that thing called "the edge of the balloon". At the beginning of the big bang, the balloon was very tiny. Within seconds, it expanded to a huge size. The expansion rate was faster than the speed of light if you attempt to place the balloon in another space all together. For example, if you blow up a balloon real fast, you can say that two opposite sides of the balloon are moving away from each other at a certain speed - but that speed based on the distance measured between the sides of the balloon. What we call the speed of light is measured on the surface of the balloon - not inside the balloon. So, referring to an expansion speed has very little to do with the speed of light. If that all makes sense, then working out how the expanding size and distance between objects on the surface of the balloon does not affect the speed of light relative to the surface of the balloon even when the balloon expands. -- kainaw™ 21:53, 27 October 2009 (UTC)[reply]
I thought the 'thing' is a particle within space-time, not an edge of space itself? Anyway, I understand what you're trying to say... thanks. Sandman30s (talk) 22:35, 27 October 2009 (UTC)[reply]
You are right. Even if there were an edge of space, it could expand faster than the speed of light. Objects cannot move through space faster than light speed, that doesn't say anything at all about the metric expansion of space. --Tango (talk) 22:38, 27 October 2009 (UTC)[reply]
If you're generally asking, "does inflationary theory seem a little ad hoc to anyone else?" the answer is, emphatically, YES, it is, and even the scientists recognize this, BUT the data it gives fits REALLY quite well with experimental results, so most cosmologists think that there is a lot to it, EVEN IF it seems a bit ad hoc (at least, at this stage—it is still being worked on and is a topic of active research). It is, incidentally, not the first time in the history of physics that a somewhat ad hoc explanation to solve a numerical problem has turned out to be both true and much more profound than was initially realized—Max Planck's invention of the quanta was just such a thing (Planck thought of it as a heuristic, a mathematical "trick" to get the right answers, and it was some time before he or anyone else realized that it was a real, fundamental property of the universe, one that had massive implications for physics). --Mr.98 (talk) 22:15, 27 October 2009 (UTC)[reply]
Yes I was asking exactly that. What do you mean by 'experimental results'? Sandman30s (talk) 22:35, 27 October 2009 (UTC)[reply]
I meant observational results, actually, not experimental. Sorry. There is some detailed discussion of the Observational status in the theory article. And just to amplify one other thing—appealing to Planck isn't meant to say, "this is fundamental and must be true." I don't know—I'm no cosmologist, and even they aren't sure. It could be a Planck-type thing, where it ends up being true, or it could turn out to be a cosmological constant type thing, where the idea is fundamentally wrong. But I think the scientists are currently happy with inflation because the observational evidence works out well and it's one of those deals where it gives you good results with only ONE big arbitrary assumption (inflation), rather than the ton of tiny, arbitrary assumptions that other theories require. That's my understanding of it, anyway, as someone who does not understand the math in the slightest. --Mr.98 (talk) 22:40, 27 October 2009 (UTC)[reply]
I don't understand why you say that inflation is ad hoc. All you need for inflation is general relativity and quantum field theory and a scalar field with some fairly unremarkable properties. Anyway, this isn't related to the original question. Inflation or no inflation, space doesn't expand faster than light, and you should be suspicious of the overall accuracy of any book or TV program that claims that it does. -- BenRG (talk) 22:55, 27 October 2009 (UTC)[reply]
I'd like to know why you think that. AFAIK "The Universe" makes use of some eminent cosmologists from top universities. The one who made that statement was Alexei Filippenko, American astrophysicist and professor of astronomy at the University of California, Berkeley. Sandman30s (talk) 10:41, 28 October 2009 (UTC)[reply]
I watched the episode (the big bang part of it, at any rate). Here's a transcript of what Alex Filippenko said:
"The 'bang' of the big bang is a time in the early universe known as inflation. The size of the universe went "whoosh"—it just expanded so quickly, doubled in size many times over a very very short interval of time. This incredible inflationary exponential state of expansion lasted only a tiny fraction of a second. A millionth of a millionth of a millionth of a millionth of a millionth of a millionth of a second."
Then there's some voiceover narration, and then:
"In fact, it expanded so quickly that it was faster than the speed of light. That's okay—that doesn't violate Einstein's theory of relativity. Space itself can expand faster than the speed of light. No particle can travel through space faster than the speed of light, but space itself can and does expand faster than the speed of light."
So let's look at inflation. In the diagram on the right, the curve to the right of the point marked "reheating" is a square-root curve; this is the expansion predicted by general relativity when the mass of the universe is mostly in the form of particles moving at relativistic speeds. The dotted line is the extrapolation of the square-root curve back to the point where it hits zero, which is called the "big bang singularity". That was the traditional model. In the inflationary model the universe is only dominated by relativistic particles back to the time marked "reheating", and before that it's dominated by a scalar field; according to general relativity, this gives an exponential expansion curve instead of a square root. This is not the only such transition in the universe's history; around 100,000 years later there was a transition from relativistic particles (t1/2 curve) to nonrelativistic particles (t2/3 curve) and right now we seem to be in the middle of a transition back to scalar field dominance (the famed accelerating expansion). Parts of this model may turn out to be wrong, but at any rate that's the present model.
The first thing you notice about the inflationary expansion is that it's much slower than the traditional big bang expansion (given by the dotted line). It is fast in absolute terms—in order for the inflationary epoch to solve the problems it was introduced to solve, the scale factor has to increase by a factor of at least 1025 or so, and this happens in a tiny fraction of a second. I can't remember how long it takes, but let's take Filippenko at face value and say that it's 10−36 second. A factor of 1025 in 10−36 second is fast, no question, but the traditional big bang expands by a factor of infinity (from zero to a nonzero size) in an even smaller time (less than a hundredth as long). You could argue that people are technically telling the truth when they say inflation is fast, but when it's part of a story that goes "inflation was introduced into the traditional big bang model, and inflation is really fast", no one is going to come away thinking "I bet the traditional big bang expansion that inflation replaced was even faster". I don't know where this fast-inflation narrative came from; it seems completely arbitrary.
Additionally, no one knows how long inflation lasted. The fact that you need an expansion factor of at least 1025 gives a lower bound, but the simplest inflationary models last enormously longer than that; they have no problem satisfying that lower bound, in other words. So anyone who says that inflation lasted for 10−n second, for any n, is making it up. Nobody knows. A lot of people understandably have the idea that if inflation ended 10−k seconds after the big bang then it must have lasted 10−k seconds or less, but as you can see from the diagram it doesn't work that way. Times quoted as "since the big bang" are measured from the traditional big bang singularity (by necessity, since the duration of inflation isn't known), so inflation starts "before the big bang".
I'm not sure what to make of the claims of faster-than-light expansion. There are two versions of this, one claiming that space always expands faster than light, and the other claiming that it only expanded faster than light during inflation. The former is presumably referring to comoving recession velocities, which can exceed c, but this really has nothing to do with faster than light motion, which involves a different kind of velocity. The best I can come up with for the latter is that it's referring to the presence of a cosmological event horizon during inflation; effectively the universe is partitioned into regions that can't communicate until after inflation ends. But that's not at all what your typical layperson will imagine as "space expanding faster than light". They will have in mind some kind of absolute background like Newton's absolute space, and space as a separate substance moving through that with a certain speed, and that bears no resemblance to reality.
Why did Alex Filippenko say those things? I don't know. Maybe I'll ask him. -- BenRG (talk) 15:18, 28 October 2009 (UTC)[reply]
Many thanks for the in-depth explanation. If the prof replies to your question, I'd love to know his answer. If that comment was tongue-in-cheek, maybe you should try to email him anyway! Keep me posted! Sandman30s (talk) 21:11, 28 October 2009 (UTC)[reply]
Er, I'm pretty sure the OP has made it clear that the ad hoc question is exactly what was meant by the original question (title be damned). What I mean by "ad hoc" is that the inflationary epoch was created to solve a problem of the previous existing theory. It is a "patch" to fix a cosmological model that otherwise doesn't work. You have a little period of really abnormal behavior, stuff that doesn't generally happen, and then things go back to normal again. (Why did the abnormal period start? Why did it stop? Unclear.) Yes, if you set all the fields up right, it works fine, but that's tautological (if you do what the theory says, the theory works). Historically it was conceived of as a "patch", and I have read scientists today who talk about it as a "patch". Still, as patches go, it works pretty well, in terms of observational results. The question is: is it physically real, or is it a mathematical fix? That's what I'm trying to get at up there. --Mr.98 (talk) 01:39, 28 October 2009 (UTC)[reply]
I just don't understand why you're singling out the inflationary epoch. The post-inflationary state that you describe as normal was pretty weird. The forces were unified, quarks were unconfined, there was some CP-violating process going on that resulted in the present-day dominance of matter over antimatter, etc. The accelerating expansion in the inflationary epoch doesn't happen by fiat, but because that's what general relativity predicts for a universe dominated by a scalar field. The transition to radiation-dominated expansion happens when the scalar field reaches a local minimum of its potential. The model was constructed to fit existing experimental data, but so was Newtonian mechanics. It also made predictions that were confirmed later (scale invariance of the CMB power spectrum). It's based entirely on well-tested theories, GR and QFT, and all it needs is a new particle. All of the alternatives to inflation require radical new physics. It's hard to test, but that's unavoidable—that era is hidden from us by 400,000 years of plasma. -- BenRG (talk) 16:02, 28 October 2009 (UTC)[reply]
I'm singling it out because I've seen others single it out, and because inflation was a rather later-comer to the Big Bang question. I'm not, as I indicated above, claiming that inflation is wrong or weird. But it was, at the time, perceived to be a hack, and there are still some of those who consider it to be one. I'm personally fine with that. Obviously if you have internalized a theory, it looks natural and non-hackish. --Mr.98 (talk) 13:28, 29 October 2009 (UTC)[reply]
I am not asking for medical advice here. I am asking about measurements.
I'm trying to learn what sort of time series data would be measured by a medical monitoring device that is stochastic or has the appearance of randomness?
Is there anything else, especially medical time series data that defies prediction efforts? =Axlq 21:49, 27 October 2009 (UTC)[reply]
Hmm...even after checking out the stochastic article linked above, I can't make a real grasp of it in order to give you any examples -- perhaps a few examples with the reasoning behind them would help those very familiar with medicine/science yet not so familiar with stochacism (if that's the noun form). DRosenbach(Talk | Contribs) 23:29, 27 October 2009 (UTC)[reply]
According to SOED: stochasticity noun, the property of being stochastic Mitch Ames (talk) 00:03, 28 October 2009 (UTC)[reply]
"Stochastic" is what statisticians say so they sound clever. It just means "random". --Tango (talk) 00:33, 28 October 2009 (UTC)[reply]
My sense is that in biostatistics (and some other disciplines), "stochastic" is used to emphasize more discretely random data (e.g. a random walk), as contrasted with more continuously random data. I'd agree that there's no bright line. -- Scray (talk) 01:44, 28 October 2009 (UTC)[reply]
Pretty much all continuous measurements can modelled as stochastic. Even if there is no randomness is the quantity itself there will be random error in the measurement. --Tango (talk) 00:33, 28 October 2009 (UTC)[reply]
Stochasticity is a very old but (no pun intended) inexhaustible subject of research in neuroscience. Neurons in the central nervous system do not respond in an exactly repeatable way to a repeated stimulus; some randomness is always present. In absence of a stimulus, spontaneous activity in neural networks - in vivo, in vitro, or simulated - is very often stochastic in its nature. --Dr Dima (talk) 00:38, 28 October 2009 (UTC)[reply]
From what I can put together after all of these explanations and exemplifications, I wonder if there are any measurements that are not stochastic -- I mean, height is probably not stochastic, but weight (to the gram, let's say) would be stochastic, wouldn't it? My point is that I didn't understand your question before, but I don't really understand it now, but for a different reason (because examples seem to abound to the extent that such a question is silly). Anyway, maybe I just don't understand it at all -- that's certainly a possibility. DRosenbach(Talk | Contribs) 01:36, 28 October 2009 (UTC)[reply]
(ec) Cost of service can be modeled stochastically. That is the basis of the entire health insurance industry - a particular individual's cost for healthcare is unknown (though can be modeled using prior knowledge about their health, and statistically analyzed as a member of a larger population). In truth, every data series can be modeled stochastically - some data is simply more "random" because the controlling parameters are less well-known. Nimur (talk) 20:28, 28 October 2009 (UTC)[reply]
OK, thanks for all the comments, but I think the answers are focusing more on semantics than the intent of my question. Suppose I have an algorithm to which I can feed a random-walk time-series signal, and that algorithm does something predictive with the input signal (for example, say it identifies data points that it predicts will be the beginnings and ends of trends). Now, I want to apply that algorithm to the field of medical monitoring devices. I'm looking for appropriate medical measurements that might benefit from this predictive algorithm. All I could think of were EEG measurements and (thanks for the correction) blood glucose measurements (which exhibit randomness because they are typically done at irregular times). =Axlq 18:23, 29 October 2009 (UTC)[reply]
The heartbeat has sometimes been used for this -- there is a degree of stochasticity in the series of intervals between beats. There are actually lots of variables showing a mix of structure and randomness -- eye blinks and eye movements are other examples. Looie496 (talk) 18:39, 29 October 2009 (UTC)[reply]
Where's a video of francium reacting with water? I looked on YouTube, but I couldn't find any. --70.245.188.147 (talk) 23:30, 27 October 2009 (UTC)[reply]
Hardly surprising. According to our francium article, The largest amount ever collected of any isotope was a cluster of about 10,000 atoms (of francium-210) created as an ultracold gas at Stony Brook in 1997. Wouldn't make much of a video. --Trovatore (talk) 23:32, 27 October 2009 (UTC)[reply]
But given the trend with the reactivities of other alkali metals, isn't francium reactive enough that even a mere 10000 atoms would cause a large explosion? --70.245.188.147 (talk) 23:45, 27 October 2009 (UTC)[reply]
Large? No. 10000 atoms is almost nothing. That's only about 1.6x10-20moles. And with anything that extremely hard to gather, they aren't likely to waste any of it making videos of it reacting with water. Red Act (talk) 23:57, 27 October 2009 (UTC)[reply]
Even if you converted the atoms completely into energy (E=mc^2 and all that) you would only get 0.0003 joules. That's not much of an explosion. --Tango (talk) 00:27, 28 October 2009 (UTC)[reply]
Fun fact: a single fissioning uranium atom will plink a grain of sand about an inch off the ground releases enough energy to make a grain of sand visibly jump, so 10,000 of those might be fun to watch. --Sean 02:27, 28 October 2009 (UTC)[reply]
Um, really? Let's do a quick estimate: A uranium atom weighs 235/(6e23) grams -- call that 4e-27 kg as we don't need much accuracy. If you could completely convert it to energy (which is off by three orders of magnitude) that would be about 4e-10 J. A grain of sand weighs at least a microgram, 1e-9 kg; to raise that one meter would take 1e-8 J, so to raise it one inch would take about 3e-10 J. So if fissioning converted all the mass to energy, you'd be in the ballpark. But as I say, that's three orders off (the Hiroshima bomb fissioned about 1kg of U-235, and its yield was the equivalent of about 1g of mass). --Trovatore (talk) 08:05, 28 October 2009 (UTC)[reply]
Maybe a single pair of annihilating uranium (anti)atoms? Still a fun fact. Someguy1221 (talk) 08:20, 28 October 2009 (UTC)[reply]
Fun facts are sometimes more fun than factual.
Dilbert: Studies show that numbers you make up are just as useful as the real ones.
Here's another point to consider, in case anyone wants to argue for nanogram "grains of sand" (I think those'd be more like dust motes, but whatever). The word "plink" suggests that the visible particle is going to be propelled into the air as a direct consequence of the fission, not by some complicated micro-winch powered by the fission. For that, as in a previous discussion of reaction drives in space, the limiting factor is not energy at all, but rather momentum. The momenta of the reaction products are very small; even if the upward-bound reaction products were all absorbed inelastically by the mote of sand, almost all of the energy would simply go into heating the mote, not lifting it. Imagine shooting a bullet into a boulder — as small as the velocity would be that corresponds to the bullet's energy, the boulder isn't going to move anywhere near that fast; almost all the energy would be simply dissipated.
OTOH if the sand mote is perfectly rigid and you get an elastic collision, then the mote will move slightly faster than it would from the inelastic absorption. But still not enough to notice — almost all the energy will be carried away by the reflected reaction products, and almost none will go into the sand mote. --Trovatore (talk) 08:48, 28 October 2009 (UTC)[reply]
What I have heard said, by physicists at various times, is that on average, U-235 fissions with about 200 MeV of energy, which is about as much energy to move a speck of dust noticeably. Notice that nobody said that fission itself actually moved it—you'd have to get all 200 MeV pointed in the right direction as kinetic energy, which isn't actually going to happen in real life. The nice thing about the speck-of-dust analogy is that then you (the teacher) say, "that's kind of a lot for ONE atom, no? Now if you increase that to 1kg of U-235, that's a LOT of dust—a whole city's worth!" and so forth. --Mr.98 (talk) 13:14, 28 October 2009 (UTC)[reply]
Here is my source for the claim. It actually says it will make the grain "visibly jump", which I misremembered as "jump an inch". I thought it was obvious that I meant "the energy of one fission event", rather than a proposed Atomic Sand Plinker, but have amended my statement just the same. --Sean 13:27, 28 October 2009 (UTC)[reply]
Well, when I write something, its meaning is almost always obvious to me :-). You can see, I hope, that a naive reader might suppose that if you had a plate made of U-235, and sprinkled sand on it, you'd every now and then see a sand grain move when a uranium atom captured an ambient thermal neutron. And that I think is completely wrong, for the reason I explained. --Trovatore (talk) 20:09, 28 October 2009 (UTC)[reply]
Re: obviousness, it reminds me of the Ignobel Prize committee awarding the prize for the water-memory homeopathy guy who "demonstrated to his own satisfaction that water retains information that can be transmitted over the Internet". :) --Sean 14:37, 29 October 2009 (UTC)[reply]
Yeah, but this isn't fission here. It's just oxidation in water; alkali metals tend to do so in a highly exothermic manner. The deal with Francium is, while in theory, it should be even more reactive than Cesium (to date, the most reactive observed metal), there has never existed in one place anything more than an exceedingly microscopic number of atoms. Even if every atom of francium that has ever existed on earth were dropped in water at the same time, it would likely not generate enough energy to fizzle. --Jayron32 05:42, 28 October 2009 (UTC)[reply]
The other problem with this idea is that Francium isn't stable. The most stable isotope has a half-life of just 22 minutes - so if you make your 10,000 atoms of the stuff - then take a break for coffee - you'll only have 5,000 atoms left when you get back! SteveBaker (talk) 12:17, 28 October 2009 (UTC)[reply]
In that case, put it in your accelerator and speed it up to near the speed of light before your coffee break so time for it will go more slowly as compared to your frame of reference. :) 20.137.18.50 (talk) 14:56, 28 October 2009 (UTC)[reply]
... but then its kinetic energy (+ other Taylor expansion terms) will swamp its rest-mass energy by many orders of magnitude, and any chemical reaction with water will be totally insignificant. Dbfirs 19:59, 28 October 2009 (UTC)[reply]
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