Wikipedia:Reference desk/Archives/Science/2009 January 22

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January 22

Aerated autoclaved concrete

Does anyone know how to make Aerated autoclaved concrete? —Preceding unsigned comment added by Elatanatari (talk • contribs) 05:24, 22 January 2009 (UTC)

The "Raw materials" section of its article explains it. DMacks (talk) 06:03, 22 January 2009 (UTC)

I meant more like the exact ratio of ingredients and the chemical processes that take place. --Elatanatari (talk) 01:28, 25 January 2009 (UTC)

Neat search tip: when you're looking for "how to make" something, try adding the word "patent" to your search terms. I did that and was able to find this. 152.16.16.75 (talk) 11:04, 25 January 2009 (UTC)

How to have a nightmare

Is there any way I can arrange to have a nightmare shortly before I need to get up in the morning, sufficiently intense that I'll rapidly become wide awake and fully alert, won't have to drag myself out of bed, and will be relieved to have returned to the real world, rather than disappointed as after a pleasant dream? NeonMerlin 06:01, 22 January 2009 (UTC)

I suppose a cassette player on an appliance timer, set to go off an hour before you wake up, with sufficiently spooky sounds on it, might work. StuRat (talk) 06:08, 22 January 2009 (UTC)

That's not really going to be reliable, because even if the tape could trigger nightmares, which is dubious, you've still got to synchronize it to your REM sleep cycles. If I recall correctly, REM sleep is the minority of your actual sleeping time. So that would very rarely work, if at all. APL (talk) 06:14, 22 January 2009 (UTC)

Our article on lucid dreaming may be of interest. --Jayron32.talk.contribs 06:18, 22 January 2009 (UTC)

(lyrics of Lucid Dreams by Franz Ferdinand removed) --Scray (talk) 12:22, 22 January 2009 (UTC)

When I was very young I convinced myself, in that way of children, that if I crossed my hands over my chest like a mummy while I slept then I'd have nightmares. And you know what? It worked very well—I had fantastical, nightmarish dreams whenever I set upon doing it. Later I tried to figure out why that might be, as it was obvious that any connections with mummies were only in my head, but that, of course, is quite a lot. I think the act of convincing myself that what I did would produce nightmares did, in fact, produce nightmares in some strange and subliminal way. I haven't tried it again for a long time, but it seemed to work even when I knew that it was just in my head—maybe something about the contrivance of it? I don't know. But hey, it's worth a shot—no harm if it doesn't work. --98.217.14.211 (talk) 15:42, 22 January 2009 (UTC)

Self-hypnosis it is, then. Julia Rossi (talk) 20:52, 22 January 2009 (UTC)

But with self-hypnosis, there's nobody there to stop you from clucking like a chicken. :-) StuRat (talk) 02:07, 26 January 2009 (UTC)

If you want to wake up at the best possible time then there are a few options available:

• http://www.happywakeup.com/en/index.htm
• http://www.sleeptracker.de/
• http://www.axbo.com
• http://www.reuters.com/article/technologyNews/idUSL0878172320070829

Isaac Asimov years ago noted the amazing ability of the brain to wake one up shortly before an alarm is to go off. He speculated that maybe (mechanical) alarm clocks made some small sound, or there was some alteration in their ticking shortly befre the alarm sounded. Without ruling out that hypothesis, I note that I have many times woken up a minute before a purely electronic alarm sounded at odd hours of the night, when I had to get up for some reason or other. I assert that it is possible to program the brain to wake you up at a particular time when there is something to be done. Edison (talk) 05:32, 23 January 2009 (UTC)

There is a much better modern explanation for Asimov's observation - which is that our conscious mind doesn't operate in "realtime" as we think it does. We are consciously registering events at least seconds (and possibly more) behind "realtime" and we're getting a highly edited version of events because the conscious brain simply doesn't have the bandwidth to handle all of that data. Our subconscious mind is doing ALL of the work and making our consciousness merely think that it's in charge. The subconscious edits the timeline to make all of this seem self-consistant and that means that since subconsciously we are collecting data BEFORE the alarm goes off - and long before the conscious mind needs to know about it - there is no problem with collecting some of the memory of events just beforehand and inserting those into the stream of events going to the conscious part. Like so many things in our world - the mind doesn't work the way common sense says it does and life is MUCH weirder than you'd think. SteveBaker (talk) 14:42, 23 January 2009 (UTC)

Asimov's explanation was exactly right for me, as I regularly woke up one minute before my alarm was set. It was a mechanical alarm clock with flipping cards containing the digits, and it did make a noticeably different click one minute before the alarm went off. The cat would also hear this, apparently, and pester me for breakfast. StuRat (talk) 15:50, 23 January 2009 (UTC)

Kramer: Alarm clocks? I never use 'em. Don't trust 'em.
Jerry: What do you do?
Kramer: I have a uh...mental alarm. I set my head for... quarter to seven and... (makes sound with the lips - "pop!") ...I get up!
Jerry: Always works?
Kramer: It never fails. .froth. (talk) 18:26, 23 January 2009 (UTC)

NeonMerlin, the answer is yes, and there are many ways to do it. One of the easiest ways to do it is to ingest the appropriate dosage of an OTC drug (but only under your doctor's supervision) that contains diphenhydramine (such as Benadryl) at least two hours before you go to sleep. An added bonus is to set the alarm for about 4am, wake up immediately, then go back to sleep. This will work if the dosage and alarm is set accordingly. Don't ask me why it induces nightmares, but it does. Although I don't have experience with it, another drug, Varenicline (Chantix), is said to have the same nightmarish effects, although this is by prescription only and should only be taken under the supervision of a physician. Eschewing this route, another thing that seems to cause nightmares in some people (although this is purely anecdotal) is pizza. I'm not entirely sure what the ingredient is, but it is apparently something in the tomato sauce, and probably can be traced to an herb or spice. You might try ordering a late-night pizza with extra sauce before you go to bed, as this also seems to be effective, but only causes nightmares in some people. Viriditas (talk) 08:14, 26 January 2009 (UTC)

Creation of unfeasably large nuclei through the quantum zeno effect

A question arose in freenode ##physics, where a fellow wondered if it would be possible to create through nucleosynthesis elements heavier than would normally be possible due to high decay frequency by forestalling decay with the quantum zeno effect: sampling (measuring) the state of the nucleus at a frequency high enough that the probability of decay is vanishing.

A precursory search reveals nothing relating to the application of the quantum zeno effect to heavy atomic nuclei. Theoretically, one would suppose, there is a limit for frequency of measurement at some function of the planck time, and thus at some point the probability of a quantum vacuum fluctuation somewhere within the nucleus occuring between measurements will break even. However, I am not mathematically-conversant enough to be able to calculate even roughly this limit.

Any thoughts? 86.157.24.150 (talk) 12:45, 22 January 2009 (UTC)

Except that functionally, rapid "sampling" is functionally equivalent to bombarding the nucleus with particles; there is no such thing as "passive observation" in the quantum world, which is why observation always effects the properties of what you are looking at; you can only observe BY altering the properties of the subject. So while you may think that you are delaying decay by simply watching the particle to make sure it doesn't decay, what you are really doing is delaying decay by adding lots of energy to the system in such a way as to cause the decay to take longer. Paradoxes in the quantum world only appear to be paradoxes if you make incorrect assumptions about the ability to make passive observations. Once you realize that ALL observation occurs only by changing the target subject, then the apparent paradoxes disappear. SteveBaker is much more conversant in these matters than I, so I am sure he will be able to direct you to a more quantitative explanation. --Jayron32.talk.contribs 18:05, 22 January 2009 (UTC)

A few comments. First, to 86.157: if it was a simple quantum tunneling (think Gamow model) then, yes, a measurement that localizes the tunneling particle to the volume inside the potential well (rather than outside) reduces the amplitudes of the continuum (outgoing wave) components of the wavefunction and thus hinders tunneling for a short while. That is the essence of the quantum Zeno effect. However, for superheavy nuclei there are many decay modes to be expected, and I don't think it is even remotely possible, with present-day technology, to measure the location of all the possible "fragments" of the superheavy nucleus. And you need to do this more than once, and without destroying the nucleus in the process... So, in brief, it does not look like a feasible experiment to me at present, although it may, in principle, become feasible at some point in future. And a side note: our article on quantum tunneling is quite incomplete, and does not nearly give a proper insight in terms of scattering theory or energy spectra. I won't have time to fix it anytime soon, but I probably will fix it eventually. Now, to Jayron: I'm not sure what you mean by "passive observation", but a concept of "null measurement" is well established in quantum mechanics. Think of lack-of-interaction as a measurement: a photon passed through the system without scattering; nothing happened to the system, but some information about it has been gained. --Dr Dima (talk) 19:45, 22 January 2009 (UTC)

That;s true, however such null measurements do not actually cause "spooky action at a distance", or quantum paradox, or the "quantum zeno effect" that the OP is refering to. After-the-fact information gathering is NOT the same as live sampling, which is what the OP is asking about. Think to the classic double slit experiment. Measuring the location at which the electrons hit the target is a "null measurement" and does not effect the behavior of the electrons as they pass through the slit; knowing where the last electron hit does not effect where the next one will hit (it is still random) any more than not knowing would. However, live sampling of the slits themselves, where you "watch" which slit the electrons go through DOES effect the electrons flight path, and thus affects the outcome of the experiment. What the OP is asking about is whether some sort of rapidly repeated sampling could some how affect the decay rate of the particles. If you only count the particles after they have decayed, then no it won't. If you set up a device to observe the particles as they decay, then yes it very likely CAN effect the decay rate; however its not the fact that information is obtained that matters. You could set up your obeservation equipment and then not collect the data; and the decay rate would be effected by the same as if you tabulated the data. Its not information collection that matters; its observation in this case. --Jayron32.talk.contribs 02:54, 23 January 2009 (UTC)

Your understanding of the term "null measurement" is incorrect. A null measurement is a measurement (i.e. something causing the measurement effect) that isn't associated with any (ordinary causal) interaction between the system of interest and your lab equipment. Measuring the location at which the electrons hit the target is not a null measurement, since the electrons do interact with the target. The classification has nothing to do with the time at which the measurement takes place. That really has no relevance in quantum mechanics. All that matters is what you learn about the system. The reason measuring the electrons at the target shows an interference pattern in the double-slit experiment is because that particular measurement doesn't tell you which slit the electrons went through. It's pointedly not because the measurement takes place after the electrons have already gone through the slits. There's no theoretical reason why a null (i.e. interaction-free) measurement can't cause the quantum Zeno effect just like any other measurement. -- BenRG (talk) 14:15, 23 January 2009 (UTC)

Effect of Sildenafil (Viagra)

I read the subject published on Wikipedia concerning Sildenafil,but I have a quistion which is: we know that Sildenafil is not recommended for the patient with cardiac problems, althought sometimes it's given as antihypertensive drug? Can you give me a simple explanation on how it can be use for this case.

Thank you —Preceding unsigned comment added by Ghost whispers (talk • contribs) 16:36, 22 January 2009 (UTC)

Sildenafil is well-known to reduce blood pressure. However Pfizer noticed an unusual side-effect when their male volunteers took the drug. ;-) Hence it subsequently became marketed for erectile dysfunction. Sildenafil is also used to treat pulmonary arterial hypertension. Axl ¤ [Talk] 17:38, 22 January 2009 (UTC)

Expanding universe

If the expanding universe is stretching space and, I presume time, and we and our measuring instruments are an inevitable part of this expansion, then how do we determine that it is expanding and the rate at which it expands? 196.2.124.251 (talk) 17:19, 22 January 2009 (UTC)

The size of a ruler (and other material objects) is not affected by the expansion of space. Dragons flight (talk) 17:29, 22 January 2009 (UTC)

Why are rulers not part of the expansion? 196.2.124.251 (talk) 17:36, 22 January 2009 (UTC)

Because the chemical bonds holding them together are stronger than the expansion. --Tango (talk) 17:44, 22 January 2009 (UTC)

That's not quite right. The expansion of the universe is not a force. When you think of something like a balloon expanding, the force (pressure) causes it to happen, and that force puts a strain on the chemical bonds holding the balloon together, actually altering the properties (like size and shape of the balloon). The expansion of the universe is a different sort of event entirely; what is expanding is the actual space between objects. Its not that the objects are being pushed away from each other by some unknown force; its that the space between the objects is actually ITSELF getting bigger. This expansion does not affect other forces except where those forces are themselves dependant on distance (i.e. inverse square law forces like gravity. For example, the force of gravity between two objects will decrease due to the increasing distance between them, but it is not counteracted by any applied "force"; if it were, you would see decreasing gravity effects to be GREATER than the increasing distance due to cosmological expansion, and you do not. --Jayron32.talk.contribs 17:57, 22 January 2009 (UTC)

While the expansion is not a force, it does require a force to overcome it. If that force isn't strong enough, the objects get further apart, if it is strong enough, they don't. --Tango (talk) 18:50, 22 January 2009 (UTC)

If the actual space between objects increases, then surely that would include the space between molecules and the space between atoms? Would the dimensions of the nucleus itself not also be affected? 196.2.124.251 (talk) 18:02, 22 January 2009 (UTC)

The size of objects is determined by chemical bonding. These bonds have a characteristic length and resist efforts to stretch or compress them. You can't use your hands to appreciably stretch a ruler, and for the same reason the expansion of the universe doesn't change the length of a ruler. The bonds simply return to their natural size after being perturbed. Dragons flight (talk) 18:11, 22 January 2009 (UTC)

(EC) No. As Jayron32 says, the expansion does not constitute a force, hence it does not enter into the equations governing stable structures held together by electromagnetic or gravitational forces. These forces keep the physical distances (that's the distances that enter e.g. Newton's and Coulomb's laws) between, say, the nucleus and the electron in a hydrogen atom or between the Sun and Earth, constant (I'm using simplified pictures of these things, of course). To describe the situation, you could say that these forces cause Earth to move through an expanding space, that motion balancing the expansion. Or you could say, equally appropriately and much simpler, that the space in the solar system or the hydrogen atom is, in fact, not expanding at all. What it boils down to is that the phrase "Space is expanding" is an imperfect rendition in plain language of what the mathematical equations of general relativity imply (in pretty much the same way as the expanding balloon is an imperfect model for the universe), and is indeed to some extent a coordinate-dependent concept. --Wrongfilter (talk) 18:18, 22 January 2009 (UTC)

Going back to the trusty balloon model, if the universe is like the surface of an expanding balloon, does that mean that objects on the surface, like a ladybug, will also expand when the balloon is blown up ? No. StuRat (talk) 18:46, 22 January 2009 (UTC)

The idea of only select portions of space being affected by expansion sits rather awkwardly. If the space between atoms, and in fact the dimensions of atoms themselves, had to change in step with universal expansion, then surely the changes would not be detectable by any measurement one could carry out? 196.2.124.251 (talk) 20:49, 22 January 2009 (UTC)

Yes, you are correct. If absolutely everything changes then it would be indistinguishable from a situation in which absolutely nothing changed. Please note though that changing "everything" would also requiring changing the force laws that depend on distance by a comparable amount. The idea that physical matter stays the same size is comparable to saying that the strength of the forces holding matter together are unaffected by the expansion. Dragons flight (talk) 20:57, 22 January 2009 (UTC)

Things changing by just the right amount so that everything still appears the same, is a notion that happened once before, isn't it? Michelson and Morley. 196.2.124.251 (talk) 21:28, 22 January 2009 (UTC)

More specifically, Lorentz's interpretation of Michelson and Morley (and the source of the Lorentz contraction that we still use today). --98.217.14.211 (talk) 23:25, 22 January 2009 (UTC)

The expansion of the universe is sort of like gravity—it is very weak over short distances, powerful over long distances. Compare that with, say, electromagnetism. You can observe that a tiny, tiny magnet easily contains more strength over a short distance than the gravity of the entire Earth. However the strength of the magnetic force quickly diminishes as you get away from the source. The expansion of the universe isn't going to affect things at scales that are governed by chemical bonds, electromagnetism, etc. But it'll affect things at big, big scales—entire galaxies moving apart from one another, staying internally ordered by the powerful shorter range forces. --98.217.14.211 (talk) 23:25, 22 January 2009 (UTC)

The idea of an expanding universe selectively affecting the spaces that make up its structure, doesn't fly well. The "internal ordering" at chemical, and for that matter quantum scales, is simply another way of saying that things don't seem to change at that scale, and what I'm saying is that is to be expected if everything changed proportionately, when we wouldn't be able to tell if there were a change, would we? 196.2.124.251 (talk) 04:50, 23 January 2009 (UTC)

See, that's the thing. The expansion of the universe is a measureable effect, so any conclusion that would lead us to not notice it (if, for example, our "rulers" were growing at the same rate as the expansion) is a faulty conclusion at the a priori level. It must be a bad understanding because it does not explain observation. So we need to come up with conclusions about what is happening that fit the observations... --Jayron32.talk.contribs 04:57, 23 January 2009 (UTC)

Well, strictly speaking, what has been measured is redshift, the rest is surmise 196.2.124.251 (talk) 05:15, 23 January 2009 (UTC)

"selectively affecting the spaces that make up its structure, doesn't fly well"—why not? All of the forces have limited ranges on which they act. I don't see why the expansion of space would be different. The expansion force (though I am aware it is not technically a "force") is so small and so slight on the micro level that it can't compete with the strong localized forces like the nuclear force or the electromagnetic force. Think about how powerful expansion of space would have to be to have any affect on the nuclear force—it just isn't going to happen. One way to think about it is as particles in a giant grid. Let's say the grid spaces double slowly and weakly over time. On the whole of the grid, the grid space increases. But localized groups of particles, tightly bound to each other, are going to stay together. The net result is that the spaces between the clumps of particles will change but the particles themselves will stay internally ordered, not because the doubling is "selective" but because it is far too weak to affect the powerful forces that maintain their internal organization. You don't have to postulate any selective or intelligent force here—just one that is weak on small scales. Again, consider the example of gravity and electromagnetism. A tiny magnet easily defies the entire gravitational force of the earth. But as a whole, on the aggregate, gravity is powerful enough to organize the entire solar system. Different scales do get affects by forces differently. --98.217.14.211 (talk) 11:27, 23 January 2009 (UTC)

The expansion is not just "not technically a force" it is quite simply not a force. Therefore it is not a small effect on small scales, it is no effect. --Wrongfilter (talk) 11:46, 23 January 2009 (UTC)

Quite so! The assumption that in some way forces (or some of them) would be immune to such an expansion, is bizarre. In dimensional analysis a force would be (mass x length)/(time x time). At its most basic level time could be measured by the orbital period of an electron around a proton. If the mass and the scale of an atom's components were to change as a result of universal expansion, then the forces in such a system - be they gravitational, electromagnetic or nuclear - would all seem to remain constant. Since we and our instruments are of the very same stuff we are examining, it is impossible to gain an outside perspective. 196.2.124.251 (talk) 12:23, 23 January 2009 (UTC)

But our instruments do detect the expansion. Your theory doesn't match observation, so it must be wrong. --Tango (talk) 12:30, 23 January 2009 (UTC)

It has an effect, that effect is just easily compensated for by other effects (due to actual forces). --Tango (talk) 12:18, 23 January 2009 (UTC)

Let's try again. Why does the Universe expand? We do not know. It expands because we observe it to expand. Peacock ("Cosmological Physics") expresses it as follows: "The Universe expands today because it expanded yesterday." When we solve Einstein's field equation to build a model of the Universe, we put the expansion in as an initial condition. The field equation admits solutions that are not expanding, solutions that are for instance contracting. But that doesn't conform to our initial conditions, hence we throw these solutions out and only keep those that are expanding at the present time. Expansion is not a dynamical effect, it is not part of the dynamical equations, and there is no necessity for space to expand everywhere and at all times. Whatever caused the Universe to expand initially is not known, and it is not relevant for this discussion. Now, consider for example a cluster of galaxies (whose structure is unaffected by anything except gravity): At some point in the past, the region occupied by the galaxies that now belong to the cluster was expanding, the distances between the galaxies increased, and the whole thing was well described by a Robertson-Walker metric. But because the matter density in that region was higher than the average, the expansion was reversed, so the region collapsed. As the local density increases due to the collapse, the Robertson-Walker approximation to the true local metric breaks down, and in fact the cluster virializes. Today, the metric in a cluster is anything but Robertson-Walker. Clusters form stable objects and space in clusters has forgotten that it once expanded a long time ago. --Wrongfilter (talk) 13:04, 23 January 2009 (UTC)

OK Let me try again too. Does the Universe expand? We do not know. Why do we think it expands? Basically because of our interpretation of redshift. Do we get redshift if and only if it is caused by recession? No, there are a number of redshift causes we know and doubtless many that we as yet don't know. Then why does the mainstream of astrophysicists and cosmogonists believe in an interpretation based on expansion? Largely because it is the flavour of the month and because of something called Cosmic Microwave Background Radiation which is considered the best argument ever in favour of a Big Bang and a consequent expansion. Does this mean there are dissenting opinions on expansion? Certainly! There are some great minds in the fields of cosmogony and theoretical physics who are not at all convinced by the circumstantial evidence supposedly supporting the Big Bang. Does this mean the jury is still out in this case? It most certainly does! 196.2.124.251 (talk) 13:40, 23 January 2009 (UTC)

There are many more phenomena than just redshift that are consistently described by relativistic cosmology (and the big bang, incidentally, is not part of the theory). Alternative models are welcome if they're sufficiently sensible. --Wrongfilter (talk) 13:55, 23 January 2009 (UTC)

Alright, name 4 great minds in physics or scientific cosmogony that don't believe in the expansion of the universe? Some people argue about the details, or dark energy, but I can't think of any that dispute the entire idea of expansion. Dragons flight (talk) 14:15, 23 January 2009 (UTC)

I've said it before and I'll say it again: the expansion of the universe is just objects moving apart. Forget general relativity and spacetime curvature, it's just plain old Galilean inertia. There's nothing mysterious about "the space between objects increasing". That's what happens when things move apart. There's nothing mysterious about the expansion applying to some things and not others. Just because some things are moving away from each other doesn't mean others can't be moving towards each other or maintaining a constant distance. There's nothing deep here except for the Galilean principle that objects don't need to be pushed to keep moving, and the cosmic inflation (or whatever) that gave them the initial separating velocity. When Peacock says "the Universe expands today because it expanded yesterday", he's expressing Galileo's principle.

The only exception to the above is a cosmological constant (if it's real, which isn't clear yet). It does behave like a force: like a centrifugal (not centripetal) force, in fact, but directed in all three dimensions instead of only in a plane perpendicular to a rotational axis. But this force is utterly negligible in ordinary situations compared to another force that people routinely neglect: the self-gravitation of your lab equipment. For a meterstick weighing one kg, the ΛCDM cosmological constant is trying to pull the ends apart with a relative acceleration of about 10⁻³⁵ m/s², while self-gravitation (Gm/r²) is trying to push the ends together with a relative acceleration of about 10⁻⁹ m/s². We don't have the technology to measure the self-gravitation of a meterstick to one part in 10²⁶. The cosmological constant is noticeable at large scales only because the overall density of matter in the universe is so low, about 10²⁷ times smaller than the density of air. -- BenRG (talk) 13:19, 23 January 2009 (UTC)

Viewing it as just standard Galilean inertia (incidentally, wasn't it Newton that talked about inertia? At least he's the one the law is named after, although that doesn't usually mean much.) only works for an infinite universe. If the universe is finite (a 3-sphere, say), it would be impossible for everything (on a large enough scale) to move away from everything else, there would have to be things moving together on a large scale, but we don't see that (we see Hubble's law instead). Now, it could just be our bit of the universe (ie. the 46 billion light year radius ball around Earth, or whatever the number is) where everything is moving outwards, but that would violate the Copernican principle. If what you're saying was the mainstream understanding, then people wouldn't still be wondering what shape the universe is (well, there are still plenty of options, but it narrows it down a lot). --Tango (talk) 14:29, 23 January 2009 (UTC)

Hubble flow is simply the inertia of galaxies and other matter evolving under general relativity following an explosive initial condition. The global curvature and/or closure of the universe requires general relativity to understand, but Galileo (or is it Newton?) provides a perfectly functional local understanding of Hubble flow as purely a manifestation of inertia. Incidentally, Hubble flow does not violate the Copernican principle. If you sit at any point defined to be (0,0,0) in space and observe that all matter is moving radially away from you with a velocity proportional to its distance, then one can rigorously show (after a change of coordinates) that an observer at any other point in space reaches exactly the same conclusion. Dragons flight (talk) 15:09, 23 January 2009 (UTC)

If you view it as space expanding, everyone sees the same, if you view it as objects moving through space, you don't. There is no way all objects can move apart when they are restricted to a finite and constant volume of space. --Tango (talk) 15:17, 23 January 2009 (UTC)

So why restrict them to a finite and constant volume? You need GR to get the time evolution and global properties right, but there is no local difference between saying "space is expanding" and "objects are moving apart". Dragons flight (talk) 15:40, 23 January 2009 (UTC)

Except that if the expansion were simply objects moving away from a big explosive force, then over time they would continuously decelerate due to gravitational effects. However, most measurements now show that the expansion is not decelerating, but actually speeding up! Its got to be something more than "moving apart because the big bang pushed everything out into empty space". It didn't push stuff into empty space, it CREATED that space, and is indeed still creating that space. The Big Bang was not an instantaneous event, it is a process which is still occuring. --Jayron32.talk.contribs 17:37, 23 January 2009 (UTC)

That's because of the cosmological constant, which adds an extra factor to the equations. That doesn't really effect what we're talking about. --Tango (talk) 17:42, 23 January 2009 (UTC)

Because, for all we know, the universe is finite. The global shape and compactness of the universe is an open question. --Tango (talk) 17:42, 23 January 2009 (UTC)

But at a sufficiently small scale those questions are irrelevant, because even if the universe is globally curved, it must still be locally flat. As it happens, to within our measurement ability, the entire visible universe seems to be "small" since we haven't been able to definitely identify any large scale curvature (or the universe may simply be globally flat and infinite). Also, the global issues don't change the observation that Hubble flow is locally equivalent to the inertial evolution of mass moving apart following an initial explostion. Dragons flight (talk) 21:47, 23 January 2009 (UTC)

The two theories are mutually exclusive, either space is expanding, or it isn't. Yes, they are indistinguishable on small scales, but we can distinguish them on larger scales and our observations (together with the Copernican principle) say it is space that's expanding. The mechanism is the same on whatever scale you are considering. --Tango (talk) 00:06, 24 January 2009 (UTC)

No, our observations say things are flying apart due to interia, embedding in and evolving under a framework of general relativity. That is what "the expansion of space" means physically. Such motion is perfectly consistent with the Copernican principle as mentioned above. I think you may have listened to one too many balloon analogies. The balloon analogy creates the impression the distances between all objects are being driven apart by some dynamical property of the universe. This is false. It is an incorrect understanding of Hubble flow, which is a fundamentally and observably an inertial process. Dragons flight (talk) 00:36, 24 January 2009 (UTC)

If the universe is a 3-sphere (which is one possibility that hasn't been ruled out, although observations put a lower bound on its radius), how can everything be getting further away from everything else unless more space is being created inbetween them? There is a maximum distance anything can be away from anything else, so once you reach that distance you have to stop moving apart, or you'll just start moving back together again from the other direction. --Tango (talk) 01:25, 24 January 2009 (UTC)

The size of a closed universe in GR is a manifestation of its curvature. Curvature in turn is locally a manifestation of mass density. The inertial tendancy of mass in our universe to be flying apart (due to the big bang) causes local curvature to decrease (assuming a closed universe) and this in turn would causes the global volume of the universe to increase. You have causation backwards I think. It is not that the universe gets larger and this forces things to fly apart, but rather it is because things are flying apart that we say the universe is getting bigger. The key point here isn't to fret about the impact of closure on the universe's evolution, but rather to realize that Hubble flow is a perfectly sensible classical and inertial solution once one starts with a Big Bang initial condition. Hence, even though GR does add wrinkles to the problem, it isn't necessary to invoke GR to broadly explain how or why things are flying apart. The answer to why we observe Hubble flow is simply because the universe is carrying forward its inertia following the Big Bang. Dragons flight (talk) 01:24, 25 January 2009 (UTC)

Dragons Flight, you are wrong. In fact, the expanding baloon analogy is quite good and the idea that the distances between objects is expanding due to a dynamic property of space (governed by GR) is the right one. The catch is the fact that the uniformly expanding universe is a solution to the GR equations obtained by assuming uniformily distributed mass and negligible proper velocities. Those assumptions are valid only for scales larger then galaxy clusters. Within galaxys due to virialization of the matter the correct solution (locally) is no expanssion at all Dauto (talk) 00:31, 25 January 2009 (UTC).

Thank you for your opinion Dauto, but I am not wrong. The easiest way to see this is by realizing that Hubble flow is a solution to the classical dynamics of a uniform and isotropic universe given the Big Bang initial condition. You lose the pressure term and the curvature term, but Newtonian gravity will otherwise given an identical expression for the evolution of the Hubble flow. General relativity adds corrections, but Hubble flow is at its heart a manifestation of classical inertia. There is no bogeyman somewhere blowing on the universe's balloon to make things move apart. Things move apart because they are carried by the inertia they recieved in the big bang. Dragons flight (talk) 01:24, 25 January 2009 (UTC)

Hubble flow as classical inertia gives results that match our observations in an infinite Newtonian universe, that doesn't mean it is correct. Consider a 3-sphere universe at a particular instant in time, what directions are all the bits of matter moving? There is no solution in which they are all moving apart, some of them have to be moving towards each other. That matter density decreasing would cause the universe to expand doesn't help if you can't get matter density to decrease in the first place. --Tango (talk) 16:29, 25 January 2009 (UTC)

If every local observer witnesses inertial Hubble flow in their neighborhood, then the space is expanding (inertially). The global observer might say that is impossible, as you do, by arguing that space is finite. The only way to reconcile this is to say that space is expanding. But don't you see the tautology, space is expanding (inertially) everywhere if and only if everyone witnesses inertial Hubble flow? (I have to be a little careful here because processes like dark energy lead to non-interial expansion, and in particular the local observer would then observe non-inertial flow.) The assumption of a Big Bang initial condition in a closed universe implies space is expanding in exactly the same way as it does in infinite Euclidean universe, since ultimately the shape of space is a composite of infinitely many local patches. The more interesting question is what happens in a portion of the universe where gravity has overcome Hubble flow and locally matter is collapsing? Is that part of the universe experiencing any expansion? No, that piece is collapsing. Again the evolution of the local shape of space is a reflection of the local mass dynamics. The (inertial) expansion of space is not merely opposed by gravity it is actually stopped in the local patch. Dragons flight (talk) 20:01, 25 January 2009 (UTC)

What is this space expanding stuff? (see Space/matter further down). That galaxies might be moving apart, one could understand even though the circumstantial evidence is highly suspect, but how does that make "space" expand? 196.2.124.248 (talk) 15:09, 27 January 2009 (UTC)

Highly suspect? Do you have a better explanation for cosmological redshift? --Tango (talk) 20:23, 27 January 2009 (UTC)

Foucault pendulum in Lost

I guess he was trying to find out where in the world he is with a foucault pendulum. Longitude is impossible to determine with it of course, but it got me thinking about latitude. The article says that the pendulum appears to take different amounts of time to return to its original floor-relative position depending on your latitude, so by measuring that time you can determine your latitude. But this is very confusing to me. Isn't the whole idea of a Foucault pendulum that the ball swings back and forth with no external forces except the top of the string getting pulled along with the rotation of the Earth (and gravity of course)? Doesn't that mean that when the rotation of the Earth brings it round 360 degrees back to its starting point that the swing of the pendulum should be the same as when it started? In other words, shouldn't the pendulum take the same amount of time on every latitude: 360 degrees in 1 day? 72.236.192.238 (talk) 18:37, 22 January 2009 (UTC)

Do yourself a favor, as I did: Stop trying to make scientific interpretations of events in LOST. It's all Hurley's dream anyhow :-D -RunningOnBrains 19:52, 22 January 2009 (UTC)

Yes yes lost is a bit out there (There are rules! Principally that time travel is impossible; second, that you can't change the past.. unless you say "please let this work" 3 times.) but I'm mostly asking about the pendulum. Hours of swinging my cell phone back and forth around my fist have only made me more confused. I really think that the pendulum should be "back where it started" relative to the ground at the end of the day, regardless of latitude, although I admit it must move at the poles and not move at the equator and don't understand what happens in between. It can't possibly have anything to do with Solar time can it? 72.236.192.238 (talk) 20:12, 22 January 2009 (UTC)

Latitude is easy to measure though. What's wrong with measuring the angle to which either Polaris or the Sun or any of the planets rises above the horizon? All of those things lie in the plane of the ecliptic - so you know the angle of your local horizon to that. You need to take account of the tilt in the earth's axis - and I suppose if you don't know what time of year it is, you might need to take both a daytime and a nighttime reading to get that. But that's WAY simpler than messing around with the pendulum. (And I agree that I don't see how it actually works) The trick is in figuring out longitude...but I don't see how the pendulum helps there. Unless you've got a pretty well detailed almanac or a perfectly synchronised clock - you're basically doomed. SteveBaker (talk) 19:54, 22 January 2009 (UTC)

It works because the precession of the plane of the pendulum in 24 hours is not 360 degrees, it is $360\cdot \sin \phi$, with $\phi \,\!$ being the latitude. The calculation is in the article, but to accept this result consider that the plane does not rotate at all at the equator, and there must be a smooth transition between that value and the 360° at the poles. Geometrically, if you're familiar with vectors, the rotation about the vertical that we're looking at here, is only a part of the angular velocity vector of the Earth (of magnitude 360°/24\,h), a projection of the latter onto the local vertical, which of course has a smaller magnitude, implying a slower rotation. And yes, I also find it difficult to actually picture what's going on here. --Wrongfilter (talk) 20:08, 22 January 2009 (UTC)

Hmmmm with your velocity vector analogy I just thought of sort of a way to picture it:

Forget the rotating frame of reference and the markings on the floor, and think of the pendulum as being fixed in space above the earth as the earth rotates below it. On the equator the pendulum just swings back and forth like the article says; the earth rotates below it but it doesn't affect the pendulum. But once you move north of the equator and become slightly more aligned with the axis of rotation, you can imagine the pendulum experiencing torque and starting to turn slowly. As you get to the pole, the pendulum's spin catches up with the speed of the earth until when the axis of rotation and the pendulum are perfectly aligned they're in sync. Now that's very easy to picture, and the jump to the torque being a fictitious force is almost as easy to accept, though not really to picture. 72.236.192.238 (talk) 20:31, 22 January 2009 (UTC)

Another thing just occurred to me to explain why the pendulum doesn't turn over the equator. Imagine a low pressure zone in the northern hemisphere, and air is rushing north to fill it. It moves in a straight line but the earth rotates under it, seeming to a ground-based observer that it's deflected it to the right. No matter which way you approach from it will deflect clockwise. But if there's a low pressure zone right on the equator, the earth isn't rotating under it! There's no coriolis effect at all because it's completely orthogonal to the only axis of rotation. 72.236.192.238 (talk) 20:54, 22 January 2009 (UTC)

I don't think that was a foucault pendulum on the show, since the pendulum wasn't on the island it was in Los Angeles I don't see the point of using it when GPS is available. That was some instrument they used to find the island so they could go back. Unless I missed some other pendulum on the show... -- Mad031683 (talk) 21:49, 22 January 2009 (UTC)

That it doesn't rotate at the equator can perhaps be seen best from that it will rotate in opposite directions at the two poles. Dmcq (talk) 23:25, 22 January 2009 (UTC)

Two quick points. Wrongfilter is right that a Foucault pendulum will tell you your latitude, but Steve is right that observing the sky is a much easier way to do it. As for what was shown on the show, I have no comment.

And one slower point. We usually think of the Coriolis effect as a fictitious force that appears to deflect an object's motion sideways on the Earth's surface. That's true as far as it goes, but there is also a vertical component. Because the effect is generated by the Earth's rotation, the "force" is necessarily felt in a plane parallel to the equator. There is a Coriolis effect at the equator -- but it's entirely vertical. (Imagine moving rapidly east along the equator so that your speed was added to the Earth's rotational speed. You would get slightly lighter. That is an upward Coriolis effect.) As your latitude increases, the Earth's surface comes nearer to being parallel to the plane of the equator. Therefore the horizontal component of the Coriolis effect increases and the vertical component decreases, becoming zero at the poles. This is also why the Foucault pendulum reveals your latitude: as seen from the Earth's rotating surface, it is the Coriolis force pushing it sideways with each swing the causes its plane to rotate, and at higher latitudes, the (horizontal part of the) force is greater. The vertical part, of course, has no effect on its plane.

--Anonymous, 05:47 UTC, January 23, 2009.

Incidentally, the vertical Coriolis effect is illustrated in Ringworld by a permanent sideways hurricane above a puncture. —Tamfang (talk) 18:47, 24 January 2009 (UTC)

Actually, they were trying to determine the location of something else. Remember that was Ben and that woman who had the pendulum and they weren't on the island. But who knows, maybe they have some sort of secret back door way of getting on the island where this room is located. But if you had a secret back door way of getting on the island, why would you need to know where it is located? A Quest For Knowledge (talk) 14:59, 27 January 2009 (UTC)

:: in gene notation

What does the notation something::something mean in regards to genes? E.g. spt10::KanMX6 ? ----Seans Potato Business 20:24, 22 January 2009 (UTC)

Googling for "double colon" genetics tells me that A::B designates a particular insertion of the B transposon within the gene A. --Sean's Utter Lack of a Potato Business 20:49, 22 January 2009 (UTC)

Its perhaps more typical in today's usage, that the double colon is used to denote a fusion gene has been engineered by inserting a sequence in frame behind, or in front of, a coding gene. So MC1R::GFP would indicate that you have a gene construct that has the Melanocortin 1 receptor gene sequence followed by the sequence for green fluorescent protein. The result, when the construct is expressed is a fusion protein. Rockpocket 06:44, 23 January 2009 (UTC)