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April 3

Gravity

Why does gravity keep the Earth going around the sun and not pull the Earth towards the Sun? 86.41.181.188 (talk) 02:16, 3 April 2012 (UTC)[reply]

Gravity does pull the Earth toward the sun. It is the conservation of angular momentum that keeps Earth at a fairly constant distance from the sun. Physicists say that there is an "effective radial potential energy field" as a result of the initial angular momentum of the Earth. In simple terms, we can say that this means an "effective force," centrifugal force, counteracts the inward pull of gravity; but if we want to correctly solve the equation of motion for Earth's orbit, we must be very careful in treating this "effective" force - it is a bit of a mathematical abstraction that only applies if we are considering just the radial component of motion. If we properly solve the movement of Earth in three dimensions, we do not need the "effective" centrifugal force; in fact, we see that it's just a mathematical trick to simplify a treatment of inertia. Nimur (talk) 02:26, 3 April 2012 (UTC)[reply]

No offence Nimur, but that's a heck of a confusing answer! ;) If the earth was standing still, it would get pulled into the sun, the reason it doesn't is beause it isn't standing still but has velocity in an orbit, which is a balancing act of sorts. The Earth's momentum is essentially what keeps it from falling "into" the sun, and the sun's gravity is what stops it from flying away from the sun, the two balance out and the earth keeps flying around in "roughly" the same path. The counter intuitive part might be that if this was happening in air, the earth would quickly loose velocity due to wind resistance and WOULD therefore spiral into the sun, but in space of course there is no air, so due to conservation of momentum the earth is speeding along now, not much slower then when it formed billions of years ago. Vespine (talk) 02:32, 3 April 2012 (UTC)[reply]

Actually, the orbit article has a section called understanding orbits which might be more help. Vespine (talk) 02:37, 3 April 2012 (UTC)[reply]

Sometimes, the explanation that is most simple to a physicist can be quite confusing to a non-physicist, because of the mismatch between each person's previously-acquired knowledge and baseline of understanding. Sorry if my answer wasn't very easily understood. At the very least, I hope it will encourage the OP to think in terms of energy, inertia, and the many different ways we can represent an object's position. Energy and inertia always follow the same rules, no matter how we measure the position. Nimur (talk) 03:29, 3 April 2012 (UTC)[reply]

If the OP attaches a ball to a piece of string and whirls it around his (or her) head he will have his answer. The tension in the string pulls the ball towards his hand, but the ball doesn't fall inwards so it collides with his hand! The inward force on the ball exactly matches the force required by the ball to travel in a circle - this required inward force is called the centripetal force.

In situations like this I find explanations relying on man-made concepts such as momentum and angular momentum are unsatisfactory. Eminent scientists have developed concepts such as momentum to help them calculate the magnitude of forces and the duration necessary to match their observations, but it cannot be said that the physical world acts in the way it does because of momentum. I concede the same can be said of fundamental concepts such as force and time, but I think a question of the kind we are dealing with is better answered with fundamental concepts, and the more fundamental the better, rather than more complex concepts such as conservation of angular momentum.Dolphin (t) 04:06, 3 April 2012 (UTC)[reply]

It seems like a man-made concept, and yet - angular momentum is the thing quantized by Planck's constant. Photons carry it in discrete amounts as particles go up and down in their orbits. In a sense, it's actually more fundamental than position or velocity, and someday, somehow, I think someone will create an intuitive model that explains why. Wnt (talk) 04:10, 3 April 2012 (UTC)[reply]

(ec - believe it or not this was written at the same time as the above) The cannon figure is a classic and useful example. But Nimur's explanation could be expressed more simply. Think of spinning a ball around on a string over your head. The string pulls straight in on the ball, so it doesn't do anything to keep it from going around and around. Only air resistance stops the ball from going around, and there's nothing like that in space, so ... a planet just goes around and around, even though gravity, like the string, constantly pulls in on it. Wnt (talk) 04:08, 3 April 2012 (UTC)[reply]

I've personally always thought the "ball on a string" analogy was terrible; sure the sum of forces is similar, but conceptually it's completely different. In my opinion, a better way to think about it is with those wishing well coin funnels that you see at malls and the like. Gravity is always pulling the coins downward towards the center, so if you just dropped the coin straight down it would fall right in. However, give the coin some tangential (sideways) velocity, it will "orbit" around the hole; if you somehow got rid of friction, the coin would never fall into the hole, but just keep "orbiting" around it, because the downward force is balanced out by the upward force provided by the curved side of the funnel. It's just like this picture of bikes on a slanted race-track; gravity may be pulling them down towards the bottom (center) of the race track, but their sideways velocity is great enough that gravity can't pull them down fast enough. If they stopped, of course, they would fall to the bottom of the track. (And if you've never played with one of those coin things, I feel sorry for your childhood). -RunningOnBrains^(talk) 07:08, 3 April 2012 (UTC)[reply]

I concur, isn't centripetal/centrifugal force a red herring in this? I'd always thought that, in reality, the Earth (along with all other bodies in the solar system) is continuously falling towards the centre of the Sun but has enough angular velocity to be continually missing the target. Blakk and ekka 13:37, 3 April 2012 (UTC)[reply]

Most physical phenomena can be explained satisfactorily using two or more explanations. I am not aware of any physical phenomenon that has only one correct explanation. In the case of the question above, I prefer an explanation using centripetal force and you prefer an explanation using conservation of angular velocity. The User who asked the original question will be able to comment on which explanation he prefers, but neither explanation is incorrect and neither is a red herring. Dolphin (t) 22:59, 3 April 2012 (UTC)[reply]

Newton's cannonball describes how a mass can be "missing the target". One can even demonstrate this orbital effect given a steel ball and a strong magnet. But as our article on gravitation touches upon, the Earth's orbit is not ascribed to a force, but to spacetime curvature due to the Sun's mass-energy. Thus, with Einstein's theories, gravitational forces are only analogous to the known centripetal forces due to boson interactions. But if Einstein's postulates are completely wrong (FWIW I believe I can demonstrate why these can be wrong or I would not bother with this line of reasoning), then gravity is simply another quantum matter phenomenon with extensive near-field-like bonds such that it is also attributable to a centripetal force interaction. --Modocc (talk) 16:46, 3 April 2012 (UTC)[reply]

Now that's a red herring. 112.215.36.183 (talk) 04:59, 7 April 2012 (UTC)[reply]

Underwater hand stand

When you do a hand-stand on dry land, the blood rushes to your head. Does it also do this if you're entirely submerged at the time ? If not, why not ? StuRat (talk) 04:48, 3 April 2012 (UTC)[reply]

Yes, it will. Gravity is exactly the same underwater as it is on dry land. The buoyancy from the water isn't going to have a significant effect on what happens inside your body. If you were deep enough underwater then the pressure might be a significant factor - fighter pilots wear g-suits which apply pressure to the legs and prevent blood from pooling there due to the high g-forces (standing upside down is essentially -1g, so it has a similar effect). If the water is applying pressure to your whole body, that may impact the flow of blood in a similar way (although it would be evenly applied, so it might all end up cancelling out). --Tango (talk) 05:48, 3 April 2012 (UTC)[reply]

The pressure gradient is greatest close to the surface which makes me wonder if it would then have a significant effect on the blood rushing down to your arms and head if you were doing a hand stand in a swimming pool, for example. I've done hand stands in pools before, but between trying to hold your breath and keep water out of your nose, it's hard to tell whether the blood is rushing to your head as much or not.. Vespine (talk) 06:07, 3 April 2012 (UTC)[reply]

Why is the pressure gradient greater close to the surface? I thought it was pretty much constant (it should increase slightly as you get deeper due to the increased density of the water, but that will be a very small effect). --Tango (talk) 11:19, 3 April 2012 (UTC)[reply]

For all practical purposes, the pressure gradient is constant. A scuba diver should worry just as much about nitrogen narcosis, lung hyperinflation, and other pressure effects, whether they rapidly ascend from 100 to 50 feet or from 50 feet to the surface. (Actually, you should worry more in the former case, because you're still far from help!). While water density can vary across thermoclines, haloclines, and a tiny tiny variation with depth due to fluid compressibility, these effects are all essentially negligible for practical purposes; the pressure of water is well-modeled by the linear fluid head equation. Our article is Pressure head, but I always use the baby-physics version: pressure = density × gravitational acceleration × depth. Assume constant g and density for all practical cases: dP/dh = ρg = constant. Nimur (talk) 15:00, 3 April 2012 (UTC)[reply]

You are correct in pointing out that the pressure gradient is constant, but lung hyperinflation (or air embolism due to pulmonary barotrauma) is much more of an issue while ascending in shallow water because of the much more rapid volume changes in a given amount of gas. Yes, dP/dh is constant, but for a given amount (moles or mass) of gas V ∝ 1/P so dV/dh ∝ P^-2 dP/dh. This is also why it is more difficult to maintain neutral buoyancy during a shallow dive than a deep one, as during a shallow dive a small change in depth results in a larger change in volume of the air in the diver's BCD, making the unstable equilibrium which is neutral buoyancy harder to maintain. Nitrogen narcosis here is a red herring, as it is not brought on by ascent. -- ToE 20:43, 3 April 2012 (UTC)Note that the "-2" exponent in dV/dh ∝ P^-2 dP/dh isn't quite fair when discussing lung hyperinflation, because while we are talking about a constant mass of gas expanding during a given portion of ascent, we are not dealing with an under-inflated lift bag (a dangerous thing due to runaway near the surface) where that same mass of gas makes the entire ascent, but instead with divers who may be intermittently holding their breath (a dangerous thing during ascent) so that there is a smaller mass of gas involved in the shallower depth ascent than there would be had they held their breath the whole way (an even more dangerous thing). This resetting of the volume brings the effect down to ∝ P^-1 due to the relative (as in fractional) pressure changes being greater at a lesser pressure for the same absolute pressure change. -- ToE 22:17, 3 April 2012 (UTC)[reply]

Sorry. "Narcosis" was incorrect. I meant "outgassing." It can be a problem for any ascent at any depth. Nimur (talk) 21:03, 3 April 2012 (UTC)[reply]

Ascent rates are limited at all depths due to DCS concerns, but while the old U.S. Navy tables were built around a maximum ascent rate of 60 ft/min, modern models often incorporate variable ascent rates, with slower ascent rates near the surface and more rapid ones permitted at depth, because while the rate of change of pressure with respect to depth is constant, it has a greater effect on off gassing at shallower depths because. For many of the mechanisms involved, such as microbubble growth, the issue is not the absolute rate of pressure decrease as much as it is the relative rate of pressure decrease. From a depth of 30 meters a diver must ascent 20 meters to reduce the absolute pressure in half, but need only ascent a further 10 meters (to the surface) to reduce the absolute pressure in half again. -- ToE 21:25, 3 April 2012 (UTC)[reply]

No, it will not. The issue of blood running to your head during a hand stand or the issue of a someone's feet swelling while standing at work all day is not so much that of the differing blood pressure between the head and the toe as much as it is the difference, between the head and the toe, in the relative pressure between the tissue and its surrounding environment. The atmospheric pressure does not differ sufficiently over a 2m change in altitude for this to be a factor on land, but in the water, which has roughly the same density as your blood, the pressure differential will be the same at your head as at your toes (regardless of your orientation), so you feet will not swell if you stand up and the blood will not run to your head if you do a head stand. This is the same mechanism which allows for compression stockings to alleviate swollen feet. They certainly don't work by lowering the blood pressure in the feet, but by compressing the feet they do lower the relative pressure between the blood in the feet and their surroundings (the atmospheric pressure augmented by the compression of the socks). -- ToE 21:53, 3 April 2012 (UTC) I do find that unless I exhale slowly through my nostrils during an underwater hand stand or somersault, water will run into my nose and on to my sinuses, resulting moderate discomfort.[reply]

We seem to have a disagreement. Shall we adjourn to the pool for a test ? StuRat (talk) 04:41, 4 April 2012 (UTC)[reply]

Some people already have. Telling which way is up can be a life and death thing for a scuba diver ... and they can have trouble doing so. Wnt (talk) 05:52, 4 April 2012 (UTC)[reply]

However, that doesn't directly address the question. Divers may become disoriented whether or not blood rushes to their head when upside down. StuRat (talk) 22:12, 4 April 2012 (UTC)[reply]

Well, outside the water you certainly know when blood rushes to your head... it would be a giveaway, wouldn't it? Wnt (talk) 23:15, 5 April 2012 (UTC)[reply]

Compared to all the other things going on, like the pressure differential in the water, that might not be very noticeable. StuRat (talk) 04:47, 6 April 2012 (UTC)[reply]

Sprained pelvises

How does one sprain one's pelvis? Human pelvis and sprain don't mention it, and the diagrams given at the human pelvis article don't show anything that I can recognise as ligaments or anything else (if such exist) that would be sprainable. Never heard of the idea until reading this article. Nyttend (talk) 05:22, 3 April 2012 (UTC)[reply]

That just says he injured his pelvis, not sprained it. It might have been a hairline fracture, for example. StuRat (talk) 05:29, 3 April 2012 (UTC)[reply]

Maybe not in this article, but it does indeed seem possible to sprain your pelvis. I believe it's the Sacroiliac joint that gets sprained. Vespine (talk) 06:13, 3 April 2012 (UTC)[reply]

I read it in a printed newspaper and linked to the story without reading the online version in detail; apparently the AP wire stories get slightly modified from newspaper to newspaper. Now I'm curious how my Google search terms found this story in the first place... Nyttend (talk) 11:14, 3 April 2012 (UTC)[reply]

One possibility is that the original version of the article at that link did say "sprained", but they have since corrected it. Unfortunately, they seem to be quite lax about online corrections, and often seem to fix problems without notification, in order to mask their incompetence. StuRat (talk) 18:15, 3 April 2012 (UTC)[reply]

Pencil sharpener

I have a metallic pencil sharpener on my desk made from magnesium (Checked by Energy-dispersive X-ray spectroscopy). I looked and found that the machining properties of extruded magnesium are a little better than that of aluminium. Is this the only cause to use the more expensive magnesium than aluminium? The people in the machine shop told me that turning housings for electronic devices is due to the higher risk of fire more complicated for magnesium. So you buy the better machining properties by safety problems.--Stone (talk) 08:09, 3 April 2012 (UTC)[reply]

Magnesium is also quite a bit less dense than aluminium (1.74 vs 2.70 g/cc). This is why it's used (alone or in alloys) where low weight is important: see this section of the article. I guess a light pencil sharpener is useful? --Colapeninsula (talk) 09:11, 3 April 2012 (UTC)[reply]

It is not a space flight pencil sharpener but a very ordinary one. So weight is no topic for that thing.--Stone (talk) 09:23, 3 April 2012 (UTC)[reply]

this video at 1:34 says magnesium is harder - http://www.youtube.com/watch?v=7Gco191pEag - I would think since you're constantly abrading against it with both carbon (inside the pencil) and wood, magnesium is simply higher-quality than aluminum. (I would think the softer it is, the easier/faster it wears away). Naturally it can be brittle etc and break off as well, but as a rule in such a situation I would think hardness would be the determining factor. The whole linked video is interesting btw and points to the fact that there are both aluminum and magnesium pencil sharpeners (in the same form, prob. same company). It also shows the fire risk you mention. 188.36.162.23 (talk) 12:14, 3 April 2012 (UTC)[reply]

The knife in the sharpener is made from steel, so the advantage is not that big.--Stone (talk) 13:39, 3 April 2012 (UTC)[reply]

I would think the rest of the groove wears away as well, since you're sticking the pencil in there with pressure and turning it around corkscrew like. After a while, you would think a harder material would retain the crisp groove better and just have a tighter sharpening experience. I mean, imagine it's wood. after a while the groove would be too big/loose for the pencil, and pushing it and turning wouldn't be eough, you would also need to angle it up toward the blade, and it would get closer and closer to feeling like you're just using a straight blade without the groove in the pencil sharpener holding the pencil tight and in form for you... --188.36.162.23 (talk) 13:43, 3 April 2012 (UTC)[reply]

I remember hearing about (but cannot find in our articles) NYMTA farecard readers having their metal groove worn down so much by rubbing of the paper(?) cards that the magnetic stripe tracks no longer aligned well with the read/write head. DMacks (talk) 15:21, 3 April 2012 (UTC)[reply]

You can see KUM's PR reason for using magnesium [1]. Someone here [2] suggests that perhaps magnesium is used as a sacrificial anode to keep the blade from rusting. This site [3] seems to have an entirely different reason for wanting magnesium pencil sharperners. Nil Einne (talk) 14:28, 3 April 2012 (UTC)[reply]

I got an email making clear that the machinability is the main point.--Stone (talk) 21:42, 7 April 2012 (UTC)[reply]

Male emotion

Why is it that males don't express emotions other than happiness or anger? Clover345 (talk) 20:31, 3 April 2012 (UTC)[reply]

They do. If you've never seen a male cry with sadness then you've never been to a funeral. If you've never seen a male worried then you've never been to court. If you've never seen a male compassionate then you've never been to a homeless shelter. Seems like you've led a pretty lucky life, congratulations! -RunningOnBrains^(talk) 20:43, 3 April 2012 (UTC)[reply]

Wow, what eloquence. Probably the best response I've ever rread on reference desk. 188.157.251.150 (talk) 21:11, 3 April 2012 (UTC)[reply]

Sarcasm meter is definitely spiking... If the asker wanted to know why males have a tendency to show their emotions less often than females, it is generally thought to be mostly societal pressure: men who have strong feelings of some emotions, particularly sadness are perceived as less masculine. In addition to social pressure, there is the simple factor of societal norms: children grow up mimicking those around them, and if they don't see other males crying then they certainly would be less likely to do so. It is thought that biology does not play as important a role as these factors (source). This should not be surprising, as the number of "feminine" men who frequently express emotions other than anger and happiness has certainly been on the rise due to the metrosexual movement and increasing societal acceptance of homosexuality, and I doubt this is due to some new wave of human evolution. -RunningOnBrains^(talk) 00:35, 4 April 2012 (UTC)[reply]

(same poster). No sarcasm, you handled the question incredibly well and eloquently. 188.157.46.184 (talk) 08:36, 4 April 2012 (UTC)[reply]

I guess I've been around the internet too long to recognize a genuine compliment. Thanks! -RunningOnBrains^(talk) 10:05, 4 April 2012 (UTC)[reply]

They definitely do. I definitely do, and my friends definitely do (male and female). Falconus^{p t c} 21:10, 3 April 2012 (UTC)[reply]

Males experience all of the same emotions females do, but they can be trained by their culture to avoid displaying them. Wikipedia has an article, Emotions and culture which may give some leads for further research. --Jayron32 22:13, 3 April 2012 (UTC)[reply]

Can't find it online, so I'll have to recite from memory, from a Shoe comic strip. Two birds at the lunch counter. One says, "How about the Cubs?" The other says, "Mmmph." The waitress says, "You men are all the same. You never talk about your feelings!" First bird says, "How do you feel about the Cubs?" Second bird says, "Mmmph." ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:48, 3 April 2012 (UTC)[reply]

Males can be just as affected emotionally by a "chick flick" as women. That is, they can be angry, confused, sad, and even deeply depressed. The only difference is that they experience these emotions prior to the actual movie, when first informed that they must attend. :-) StuRat (talk) 04:37, 4 April 2012 (UTC) [reply]

This is interesting. I have to say, honestly, I personally doubt that men really have as much emotion inside as women do. I mean, women seem to constantly dredge over stuff in their minds that in any man could be dispelled with even the lowest quality video game. But I can't even begin to guess how you'd analyze this... hmmm, maybe fMRI? Well, looking, men actually have bigger amygdalas then women, but use most of it for looking at pornos. ;) [4] Maybe this depends, in the end, on how "emotion" is defined and whether who defines it is a man or a woman. ;) Wnt (talk) 17:31, 4 April 2012 (UTC)[reply]

I think that you underestimate us. Just because I don't always show it or talk about it doesn't mean that my emotions can be dispelled by video gaming. I can think of a lot of stereotypes about women too, but most of the time I find that it's only that - a stereotype. Any truth to these stereotypes are probably dominated by cultural expectations - if I, a man, walk down the street crying, it looks a heck of a lot worse than if a woman does. That doesn't mean that I don't cry; it just means that culturally I'm not supposed to (so I'm probably more likely to resist/hide it). In fact, it feels very wrong to publicly admit here that I ever cry, even though none of y'all know who I am. As for other stereotypes (women are irrational, women hold grudges, women are emotionally instable), I think about my female friends, and note how very few of them fit any of those stereotypes. Falconus^{p t c} 22:37, 4 April 2012 (UTC)[reply]

Just replace video games with shopping and you've turned a meaningless male stereotype into a meaningless female one. There might be something more to it than just culture (differences may have evolved due to the different roles men and women played in hunter-gatherer societies), but I don't think there is any real evidence for men being less emotional than women. And, for the record, I enjoy romantic comedies and I suspect most men do, we're just culturally required to pretend otherwise. Well, I'm throwing off the shackles of oppression - Hugh Grant for the win! --Tango (talk) 05:27, 5 April 2012 (UTC)[reply]

Is the outside of single cell algae lipophilic or hydrophilic?

Or, are there algae strains that are lipophilic on the outside? If you would spray water with lipophilic algae in it on water that is covered with a layer of oil (perhaps a few inches thick), I guess all the algae would be trapped in the oil layer, making it easy to pump out algae-free water below the layer. Harvesting them would be a lot easier and cheaper than for example centrifuging. As algae don't form "drops" in water like fat does, the answer is probably simply "No", but then again there are algae containing very high oil percentages (like 70% of dry weight). They might be forced to leaking a little of it? Joepnl (talk) 22:04, 3 April 2012 (UTC)[reply]

AFAIK, all living cells, including algae, are encased in a phospholipid bilayer called the cell membrane, and I don't think there is a sufficient distinction between any species of algae, or indeed any eukaryote life, with regards to this level of structure. --Jayron32 22:08, 3 April 2012 (UTC)[reply]

Thanks, that's the (interesting) dissapointment I was expecting :) Joepnl (talk) 22:21, 3 April 2012 (UTC)[reply]

Whether the algae is hydrophilic or not depends only on the outer surface. I'd say that because algae almost always exist in water, it must be hydrophilic if not it will not be able to stay in water (not enough adhesion to water) and will always be pushed to one side (less repulsion from the water), so from this, I'd say the outer surface is hydrophilic. You method depends on the density of the algae I suppose Kinkreet^{~♥moshi moshi♥~} 12:41, 4 April 2012 (UTC)[reply]

All algae have a cell wall and many have other layers of mucilage and the like around that. I suppose you could find some strain/engineer a strain that produces a wall/sheath that can be easily be flocculated by adding some other chemical, maybe calcium ions or some special organic compound. This might grow faster than a species that stays aggregated( nutrient competition). Alternatively, you could engineer them to have gas vesicles/ magnetite particles( will need super high supply of iron for decent growth rates). Cheerio. Staticd (talk) 18:18, 4 April 2012 (UTC)[reply]

Thanks for your answers. I was hoping may be this would be the extremely simple algae harvesting method. These guys have found a solution without adding nasty chemicals (Hexane seems to be used a lot), but it's still too complicated IMHO. It feels pretty strange that growing algae is so simple, yet harvesting them is so complicated. Joepnl (talk) 23:59, 4 April 2012 (UTC)[reply]

A formal symbol for a postulated absolute rest frame?

What symbol or symbols, in a formal way as possible, would be best identified with the antithesis of Einstein's relative reference frame postulate? This absolute rest frame is not necessarily equivalent with the CMB rest frame, although it may very well be. With my work, the absolute rest frame is identified as the inertial frame for which identical clocks (that are distant from strong gravitational influences) tic with a maximal observed rate or, for unstable identical matter, decay with the fastest rates. When studying the observable clocks or matter with different velocities, matter with these maximum rates should be a subset of the entire lot. In my work, I need to reference this absolute rest frame quite a bit, and so if there is some symbolism in use that I could use or borrow from that would be helpful, otherwise I'm open to suggestions. --Modocc (talk) 22:34, 3 April 2012 (UTC)[reply]

When you're making your own stuff up, you can use whatever symbols you want for it. There are fairly standard ways of expressing special relativity, but if you're hypothesizing an alternative in which an absolute rest frame and time dilation coexist, you're really on your own as to how you want to express that. There is no widely-agreed-upon standard way to express that, because that's not a widely-agreed-upon idea. The harsh reality is that you aren't going to get any physicists to take your ideas seriously regardless of what symbols you use to express them, so you might as well just use whatever symbols make the most sense to you for your own exploration and enjoyment.

And there is no special frame of reference in which clocks tick at their fastest rate. Clocks are always measured to run the fastest in an inertial frame of reference in which the clock is at rest. A "moving" clock may run slowly as measured in your "lab" frame, but the clocks in the lab frame are running equally slowly as measured in an inertial frame of reference in which that "moving" clock is at rest. Red Act (talk) 23:57, 3 April 2012 (UTC)[reply]

For any given precision of measurement, such as incremental differences of, say, a hundred meters per second and directions of one arc secs, there are a limited number of possible velocities that can be measured. One of those velocities will be maximal with respect to rates when the observers compare them, such as with the Twin paradox such that one ages the fastest (only two velocities are compared, so its not very precise, but one can add more velocities with incrementally different directions and speeds... and one of these clones will age the fastest). For my model, I assume the existence of a classical Euclidean geometry for space (its not a Minkowski space) as well as an invariance for the simultaneity of events such that events that are simultaneous in one inertial frame are also simultaneous in other frames. --Modocc (talk) 00:28, 4 April 2012 (UTC)[reply]

There is no frame in which clocks tick the fastest. If you believe that there is, please describe in detail an experiment which could detect that frame, and I (or someone) will tell you what's wrong with the experiment. The experiment has to be one that could actually be performed, given an unlimited budget. I'll get you started: you probably want to launch a bunch of clocks at different speeds in deep space and measure their tick rates. The one with the fastest tick rate is the one closest to your state of absolute rest. What you need to do now is tell me how to measure the tick rates of the clocks. -- BenRG (talk) 00:55, 4 April 2012 (UTC)[reply]

There is already plenty of matter out there that is already moving at different velocities, and which do not tick any faster/slower because observers have accelerated their reference frames (thereby changing their own clock rates). Comparing observers that have different velocities after they have measured that matter with their different reference clocks you will find which observers have the fastest clocks relative to each other, based on measurements of that unaltered matter, for there is only one and absolute reality. With my model, there is no need to worry about seeming to measure a universe which is magically seeming to become an awesome pancake either, and the time dilation that we measure is entailed, as well as the inertial frame Lorentz corrections to the Doppler relation (which is necessary to accurately model the differences in measured wavelengths, frequencies and energies) and the transverse Doppler relation. I've got the basics pretty much covered or else I wouldn't be here asking this question about referencing the absolute rest frame which, with a couple of other reasonable assumptions, gives these results. Since only with my model, as oppose to relativistic models, this inertial reference frame is absolutely unique, I have used the capital U to represent it, and the U prime for any other inertial frame, but I'm not sure if U is the best available choice (and barring any alternative suggestions, I am thinking it is the best choice though). --Modocc (talk) 01:57, 4 April 2012 (UTC)[reply]

Just out of curiosity, is your absolute-rest frame a single inertial frame, or does it change according to the Hubble constant and gravity? A good absolute rest frame, to me, should be one defined so that most matter you encounter in the universe is <0.1c or so, no matter how far away. Wnt (talk) 17:35, 4 April 2012 (UTC)[reply]

Its a single inertial frame, either similar to or congruent with the CMB rest frame with which we are moving 627±22 km/s in relation to. I don't know what objects are at rest in the CMB rest frame, but it seems like a fairly good candidate. Of course, a velocity addition for light is entailed, which is contrary to relativity, but inertial frames other than the absolute rest frame are distorted mimics of it, yielding an apparent invariance, although the velocity addition for light can be accounted from data when the significant distortions are removed. --Modocc (talk) 23:07, 4 April 2012 (UTC)[reply]

So far as I know the "CMB rest frame" is something of a misnomer. So far as I know, if you are at rest with the CMB, and you look at a galaxy in a region that on average is receding from you at 1 km/s - if you went there, you'd have to accelerate by 1 km/s to be at rest with respect to that region's CMB. Otherwise this would be the one region in the cosmos where the CMB is not tremendously red/blue shifted depending on whether you're looking toward the "center" which we are close to. Wnt (talk) 22:01, 6 April 2012 (UTC)[reply]

I don't think the CBM rest frame changes to some local rest state, because the CMB originates from the distant past. Thus, supposing the CMB frame and U are the same, if you are at rest with it here because its radiation profile is isotropic, and your twin goes on a long journey, the twin must accelerate and decelerate such that the measured CMB radiation frequency profile becomes isotropic again and I would think that would happen only if you and your twin are not in relative motion when your twin has decelerated. I've more than one important project afloat, and wouldn't you know I got too cold last night from the drafts and my sinus pain is getting worse ... so I'll have to take time for tea... don't worry, I'll either swim or sink later. Thanks for the feedback. To a certain extent, I've always thought of U as a logical consequence based on what we do know from local measurements, thus I did not think of it as a prediction (I am a fish in my own paradigm) and not something that must be confirmed. Thus, I now better appreciate the fact that it is a testable hypothesis. Thanks again.

  --Modocc (talk) 15:46, 7 April 2012 (UTC)[reply]

Wikipedia:Reference desk/Archives/Science/2012 April 3

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