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December 26

Plate tectonics: When did America and Asia collide?

When did America and Asia collide in their current positions? In other words: When did the first land bridge between America and Asia after the split of Laurasia come into existence? --KnightMove (talk) 00:20, 26 December 2011 (UTC)[reply]

According to Beringia, it first formed about 35,000 years ago, though there may have been earlier connections during the Age of Dinosaurs, and again at perhaps some 55 million years ago. --Jayron32 01:51, 26 December 2011 (UTC)[reply]

Maybe there's a slight correction needed there. Didn't the dinosaurs disappear 65 million years ago? HiLo48 (talk) 02:08, 26 December 2011 (UTC)[reply]

So corrected. --Jayron32 03:02, 26 December 2011 (UTC)[reply]

Also note that the land bridge that formed 35,000 years ago had little to do with plate tectonics. The continents were in essentially the same position they are now, but lower sea levels (due to much of the ocean water being sequestered in glaciers and ice caps during the ice age) exposed the shallow area of the Bering Straight. StuRat (talk) 04:01, 26 December 2011 (UTC)[reply]

The northwestern part of Asia actually belongs to the North American Plate. The boundary between the Asian and North American plates runs through Siberia, and is pretty fuzzy, because the two plates are tightly locked together in that zone. The land bridge is not a tectonic feature, just an area of the continent so low in elevation that it sometimes falls below sea level. Looie496 (talk) 04:31, 26 December 2011 (UTC)[reply]

You mean the northeastern part of Asia. Bo Jacoby (talk) 06:35, 26 December 2011 (UTC).[reply]

Uh, right, thank you. Looie496 (talk) 14:16, 26 December 2011 (UTC)[reply]

Thanks for your answers so far, but the question remains unresolved yet. --KnightMove (talk) 21:31, 26 December 2011 (UTC)[reply]

Take a look at some geographical features in the area: Sakhalin Island, the Chersky Range and the Gakkel Ridge. Bedrock from orogens may hint at the age, and thus the timing of collision. ~AH1 ^(discuss!) 02:45, 27 December 2011 (UTC)[reply]

Well, you actually asked two distinct questions. Presuming the one you are really interested in is the timing of the plate collision, the answer is really not clearly known. Those two plates are currently wedged together so tightly that there is no identifiable fault between them, so even the location of the boundary is not clearly known -- and the fact that it's in remote Siberia means that research has been limited. My guess based on plate reconstructions is that they collided about 150 million years ago, but that's only a guess. Looie496 (talk) 16:48, 27 December 2011 (UTC)[reply]

All of these baby plates at the edges of landmasses have got me wondering if there aren't more babies located in the middle of the ocean where we just haven't looked that much. Hcobb (talk) 23:24, 27 December 2011 (UTC)[reply]

For most of the ocean it seems pretty unlikely, but there are a few dozen candidates, most of which are discussed at List of tectonic plates#Tertiary plates. Looie496 (talk) 17:02, 28 December 2011 (UTC)[reply]

See also Continental fragment. Small blocks or terranes may also form from island arcs when they become accreted to a continental block. Mikenorton (talk) 17:14, 28 December 2011 (UTC)[reply]

Parallactic mount

What is the difference between the equatorial mount and parallactic mount[1] of a telescope? Is the latter one a disused synonym only? (I know the meanings of parallax and parallactic angle.) - 80.98.99.154 (talk) 00:24, 26 December 2011 (UTC)[reply]

I'm mostly guessing here, but I think that parallactic mount is a calque from German parallaktische Montierung and it identifies a native German speaker.--Itinerant1 (talk) 08:07, 26 December 2011 (UTC)[reply]

Well, I will ask this at the German Wikipedia, too, thanks for the idea. But: Did anybody else see using this phrase nowadays? - 80.98.99.154 (talk) 17:52, 26 December 2011 (UTC)[reply]

Complex exponentiation

If a, b, and c are complex numbers, does $(a^{b})^{c}=a^{bc}$ ? If so, is there a proof or is this an axiom? The article on exponentiation wasn't too clear on this. Thanks. 65.92.7.9 (talk) 04:48, 26 December 2011 (UTC)[reply]

Shouldn't this be posted on the Math Desk ? StuRat (talk) 04:51, 26 December 2011 (UTC)[reply]

Yes, and worse, the article does discuss it. Sorry, my mistake. 65.92.7.9 (talk) 04:59, 26 December 2011 (UTC)[reply]

Resolved

Sex in space

Would it be possible for two people to have sex in space? Whoop whoop pull up (editing from my iPod, which won't let me log in) — Preceding unsigned comment added by 24.107.228.243 (talk) 15:23, 26 December 2011 (UTC)[reply]

I believe a person with your obvious intelligence, experience and savoir faire does not need an answer to this. Have you nothing bettwr to do today. Richard Avery (talk) 15:28, 26 December 2011 (UTC)[reply]

I believe a person with obvious intelligence does not fear to answer a question like this. - Orion 8 (talk) 17:47, 26 December 2011 (UTC)[reply]

Please see our article Sex in space. -- 203.82.82.134 (talk) 15:30, 26 December 2011 (UTC)[reply]

Not under docking maneuvers ? :-) StuRat (talk) 17:14, 26 December 2011 (UTC)[reply]

Thank you! — Preceding unsigned comment added by 24.107.228.243 (talk) 16:43, 26 December 2011 (UTC)[reply]

The sex in space article used to say that brief parts of a porn film had been filmed in zero-g (on a diving aircraft) - see this old revision - so this shows it's physically perfectly possible. There's no discussion on the article's talk page why this actually useful information was removed to make way for another useless "in popular culture" section. Testovergian (talk) 20:35, 26 December 2011 (UTC)[reply]

Good catch! It was lost in this tidying. While the collapse of most movie mentions into a single sentence was reasonable, the one that shows actual penetrative sex in actual zero-g deserves separate mention. Unfortunately, the original space.com reference is a dead link, but here is a WayBack link. -- 203.82.82.134 (talk) 01:08, 27 December 2011 (UTC)[reply]

The page uranus_experiment_000516.html says the scene in the movie "The Uranus Experiment: Part Two" was filmed by flying an airplane to an altitude of 3300 meter and doing a steep dive. The filming process was particularly messy from a technical and logistical standpoint. Budget constraints allowed only for one 20 second shot time window with the actors Sylvia Saint and Nick Lang. In the milton_interview_000516.html, the president and CEO says "You would not want to be afraid of flying, that's for sure!" and that 3D from Massive Attack and Liam from The Prodigy did the soundtrack. And russian_sex_studies_000316.html Lyubov Serova a leading IBMP specialist in the field of procreation in the conditions of spaceflight says "After a period of adaptation for weightlessness, people will not need any special devices, like elastic belts or inflatable tubes to have sex in space," and "We study the impact of weightlessness on the reproductive function of male and female bodies by using mammals as test subjects, particularly rats,". The overall conclusion is that sex in space is not a physical problem, and that individuals driven enough to embark on space flight won't be distracted by sex. Electron9 (talk) 10:01, 30 December 2011 (UTC)[reply]

Virgin Galactic that will offer 200 000 USD tickets for 6 minutes of zero-G at 100 km altitude refused a 1 million USD offer in 2008 to allow filming of a sex movie during zero-G. [2] Electron9 (talk) 10:51, 30 December 2011 (UTC)[reply]

Neanderthals

If a cloned Neanderthal were raised from birth by humans, how well would they fit in to modern society? How would they compare to modern humans in terms of appearance, strength, intelligence, etc.? --108.225.115.211 (talk) 22:15, 26 December 2011 (UTC)[reply]

Surely one very important issue would be language. Do we have enough information about Neanderthals to know whether they had reasonably advanced language capability? ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:30, 26 December 2011 (UTC)[reply]

I agree that language would be the main problem. I doubt if they could hold a conversation. In particular, I doubt if they could make the same sounds we make. And even if they could, they likely lacked the ability to use grammar. So, "I am hungry" would, at best, come out as "food me" or "me food".StuRat (talk) 00:56, 27 December 2011 (UTC)[reply]

See [3]. They had the capacity because they had their own language anyway (only "the nature of which is debated"), and if raised from birth by modern humans (remember, Neanderthals were human, too), they would learn to use language just as other babies do. -- Jack of Oz ^{[your turn]} 02:24, 27 December 2011 (UTC)[reply]

Neanderthal anatomy says they were shorter, more robust and much stronger. The reconstruction in the article indicates they wouldn't look out of place in a neighborhood bar or football game (or in one). Clarityfiend (talk) 23:35, 26 December 2011 (UTC)[reply]

I had a professor who used to tell me the pilgrims would die immediately if subjected to today's air pollution. I'd assume something similar for neandethals. Hot Stop ^UTC 02:05, 27 December 2011 (UTC)[reply]

I doubt your professor's statement, and would point out that even if it were true, it doesn't mean that a pilgrim (or Neatnderthal) zygote in utero subsequently born in "today's air pollution" would have any difficulties resulting therefrom. - Nunh-huh 02:59, 27 December 2011 (UTC)[reply]

I also doubt that claim. There hasn't been remotely enough time since the industrial revolution for any significant evolutionary changes in humanity. It's possible we're most used to respiratory irritants, but that would just mean the pilgrims would have a nasty cough for their first few weeks here. --Tango (talk) 15:26, 27 December 2011 (UTC)[reply]

If the air we breathe in big cities were so different from air in ancient times, wild animals would die when brought to a big city. 88.8.76.47 (talk) 16:06, 27 December 2011 (UTC)[reply]

Neanderthals could well be sucked up by gangs for their muscle. That or if they hobnob with sone of the numbskuls around where I live, no-one would notice the difference... Heck froze over (talk) 20:51, 27 December 2011 (UTC)[reply]

All modern European and Asian human populations (excluding African populations) are believed to have a certain amount of Neanderthal genetic admixture (1-4%) from contact during migrations out of Africa. In short, Neanderthals wouldn't look particularly out of place. Contrary to early depictions of them as brutish ape-men, they are humans sharing 95.5-99.9% of modern human genes having only diverged 300,000 years ago. They are adapted for the colder climates of their native range - southern Europe and the Mediterranean area - having pale skin and hair coloration and big noses. The most visible differences would be the longer skull at the back (the occipital bun), heavier brows, and a receding chin contrasting with the more neotenized modern human skull features (i.e. modern humans have skulls that are more child-like). Their brains are slightly larger than that of modern humans (but the same or slightly smaller when compared proportional to their body size), they had advanced tools, language, and culture. See Neanderthal admixture theory and Neanderthal Genome Project.-- Obsidi♠n Soul 01:31, 29 December 2011 (UTC)[reply]

Bike

is it true that no physics cant explain how a bicycle works? this is based on an article i saw on cracked.com MahAdik _usap 22:44, 26 December 2011 (UTC)[reply]

Our article Bicycle and motorcycle dynamics might answer your question. Hot Stop ^UTC 22:50, 26 December 2011 (UTC)[reply]

I'm not so sure that I would take something at cracked.com to be a serious claim. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:23, 26 December 2011 (UTC)[reply]

AFAIK, they do have references and its not original work. MahAdik _usap 01:13, 27 December 2011 (UTC)[reply]

Presumably this is the article in question. Most of them are fine, other than the caveate that "just because we don't 100% know everything doesn't mean we know nothing, or that we don't have mind-numbing data on the subjects in question." #5 is "How a Bicycle Works". It does have references. The essence is not so much "we have no clue" than it is "there have been a variety of theories and have been found wanting in terms of a physical explanation of what it stays upright." Which is essentially what the dynamics article above says as well: "Several factors, including geometry, mass distribution, and gyroscopic effect all contribute in varying degrees to this self-stability, but long-standing hypotheses and claims that any single effect, such as gyroscopic or trail, is solely responsible for the stabilizing force have been discredited." The question is whether there is an ultimate single factor or not to be found, I suppose. --Mr.98 (talk) 02:02, 27 December 2011 (UTC)[reply]

It seems that we don't know what exactly makes a bike so stable, since a simplified bicycle with very small wheels is stable on its own, without a rider. It may be a high centre of gravity, but ultimately some articles describe the invention of the bicycle as a quirk of some sort. ~AH1 ^(discuss!) 02:17, 27 December 2011 (UTC)[reply]

It doesn't seem like a mystery, to me. The bicycle is only stable while in motion, and this is because the wheels act like flywheels or gyroscopes, which resist any change in direction when spinning. This is a consequence of Newton's "an object in motion stays in motion (in the same direction), unless another force acts upon it". StuRat (talk) 06:39, 27 December 2011 (UTC)[reply]

Did you read the already linked article above, Stu? The article Bicycle and motorcycle dynamics states, in part, "long-standing hypotheses and claims that any single effect, such as gyroscopic or trail, is solely responsible for the stabilizing force have been discredited." (bold mine for emphasis). Which is to say that while the Gyroscopic effect you note is but one of the effects responsible for the stability of two-wheeled vehicles like bicycles, no one single effect, including that effect, is responsible in isolation for the stability of bicycles. Rather, as that article makes clear, it is the interplay of several effects, all of which contribute, and none of which is solely responsible, which make bikes stable. --Jayron32 06:45, 27 December 2011 (UTC)[reply]

Popular science writers often conflate problems that are difficult to explain in simple terms with problems that have no known solution. This is because popular science writers are rarely engineers; they know little of the techniques, practices, or the mode of thinking that an engineer would use to analyze any problem, including bicycle dynamics. In fact, engineered stability and dynamic control theory is very well developed, theoretically grounded in very robust mathematical physics, and tempered by many years of engineering practice. A bicycle, as a machine, pales in comparison to, say, a particle accelerator or a spacecraft, yet scientists and engineers seem to do just fine designing and stabilizing those devices - mechanically, electronically, and to very great degrees of precision.

First, we need to define the question. "How does a bicycle work" can mean many things. A bicycle works because a human presses on a pedal that is geared to a drive wheel, and energy is transferred to the motion of the bicycle. "How does a bicycle remain upright" is a more challenging question, but it's still not phrased as an engineer would think about the problem. Let's try this: "Can we construct an equation of motion that defines the attitude/orientation of a bicycle as a function of several relevant parameter?" The answer is, clearly, yes; any third-year physics or engineering student can do this, with various opinions about which parameters are important. Once we have this equation, we can write it in a special case form to study the tilt of the bicycle - that is, whether the bicycle is deviating from an upright angle. Through sensitivity analysis, we can ascertain, correctly, the exact parameters that contribute maximally to the bicycle's tendency to remain upright. I expect this would be a highly parameterized, many-input multivariable equation - probably a mess to work with on paper. Because we have powerful computers, we can trivially simulate a pole-zero analysis for the bicycle, as a function of each parameter: bicycle dimensions, wheel size, flywheel moment of inertia, bicycle mass and distribution, fork, trail, displacement due to steering. We can even simulate parameters that would be impractical to change "at runtime" on a real bike: maybe we can make the trail length vary with speed, for example. (Somebody once simulated changing the shape of an airplane wing in-flight, so our robo-bicycle should be easy by comparison). We can play with all of these parameters and determine which of these many factors contribute to stability - a mathematical exercise, but not an impossible one. At the end, we can analyze tradeoffs - aesthetic, economic - and of course, bear in mind that axial stability is not the sole objective in bicycle design - and make our final report to our bicycle design-lead.

The point is, system stability analysis is complicated. It requires solutions to several multivariable math problems, and requires certain conceptual insights that many people do not understand. But, it is well within the reach of modern engineering and science to totally and completely model and simulate the mechanical dynamics of a bicycle. Nimur (talk) 16:09, 27 December 2011 (UTC)[reply]

There's the crux of the problem; the distinction between "this is very difficult to explain this to someone without the proper training so they could understand it" and "we don't know". Far too often, people hear the former, and translate that as the latter. --Jayron32 16:13, 27 December 2011 (UTC)[reply]