Wikipedia:Reference desk/Archives/Science/2010 March 28

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March 28

Stomach Cancer Genome

Our article on Stomach cancer includes an un-cited sentence: "China being member of International Cancer Genome Consortium is leading efforts to map stomach cancer's complete genome." (last sentence; causes)

What does this mean? I thought most cancers were uncontrolled growths forming as a result of genetic damage. This sentence seems to imply that this type of cancer is either of a specific genetic form, or similar to a virus. NByz (talk) 04:00, 28 March 2010 (UTC)

Cancer has many genetic causes, but they're probably looking for oncogenes that are linked to those particular cancers. Sometimes there's a genetic predisposition to cancer, and I'm guessing the ICGC is trying to find either oncogenes or proto-oncogenes in the human genome. SDY (talk) 09:15, 28 March 2010 (UTC)

[1] which seems high up on a Google (albeit not Bing) search for 'cancer genome' should be of relevance, particularly the part on research as would International Cancer Genome Consortium and [2]. Incidentally, the wiki-article is already linked to from the stomach cancer article (as has been for at least a week) and the ICGC homepage is already linked to from the ICGC article. While they don't go into detail on China's stomach cancer efforts, they do provide a general idea of what the ICGC's efforts entail and what is generally meant by a cancer genome project in general which appears to be the source of confusion/uncertainty here.

As an example of some of the work that's part of the Chinese efforts, you may want to take a look at the work of You-Yong Lu [3] who is listed as one of China's representatives to the ICGC. Also Henry Yang who is probably this guy [4] [5]. An investigation of the BGI website [6] [7] may also yield information on relevant research.

Nil Einne (talk) 09:48, 28 March 2010 (UTC)

The basic idea is that there are some genetic mutations which are often associated with particular cancers and large scale genome sequencing of cancer cells followed by comparison to the reference human genome will allow the "mutational spectrum" of different cancers to be defined. This could lead to better diagnostic categories based on cancer genotype rather than merely phenotype (histology etc.), paving the way for treatments targeted at particular mutations. Looking at the mutations associated with particular cancers in lots of samples will also hopefully give some insight into which mutations are causative or "driver" mutations, and which are merely the result of the cancer disease process ("passenger" mutations). Equisetum (talk) 10:30, 28 March 2010 (UTC)

Where to start with extreme theoretical physics?

"Okay, what is the definition of a blackhole? Okay it has an event horizon- what's that?" So I click the link titled event horizon, "An event horizon is where you have to be going faster than the speed of light to break free of the gravitational pull of a black hole- or gravitational or quantum singularity... What's a normal singularity?" etc etc etc... Where do I start? Rather than back tracking to what i want, why can't i go forward? Rather than asking about everything on the page, how about understanding it and taking the next step so that i can understand things from the beginning? Here's where wikipedia goes wrong- you have to click a billion and one links before you get down to understandable parts of a complex topic... the beginning. So what would i have to search to begin with the very basics of say, a Riemannian Manifold? Or a black-body? Singularity? Euclidean Space? Don't make me keep listing them... I'm 14 so no i can't just take a course at uni, believe me i would if i could! —Preceding unsigned comment added by SamitaEJ (talk • contribs) 10:58, 28 March 2010 (UTC)

I'll take you at your word: here's an MIT physics course open to you right now. --Tagishsimon (talk) 11:13, 28 March 2010 (UTC)

May I direct you to Gerard 't Hooft's page on this subject : http://www.phys.uu.nl/~thooft/theorist.html . 83.134.157.187 (talk) 12:29, 28 March 2010 (UTC)

The problem is that Wikipedia is an encyclopedia, not a textbook. It doesn't necessarily have great ways to go through topics in the same way you would a book. Personally, I recommend getting a book! There are many excellent books on physics out there that lead you through this stuff in any interesting way, at any level of detail you desire. --Mr.98 (talk) 13:23, 28 March 2010 (UTC)

I recommend Stephen Hawking's work as being very readable - accessible to the average person who has some scientific knowledge - and a good introduction to the topics. --TammyMoet (talk) 13:49, 28 March 2010 (UTC)

If you really want to get to grips with a subject, do it the same way you would at school. Start from the basics (in the UK we have GCSEs, then A levels, then university) so you could read individual guides for the first two levels which can give you a good basic understanding of the topic, then go on to read books which expand on the details. Regards, --—Cyclonenim | Chat  14:52, 28 March 2010 (UTC)

There is a problem with technical articles at Wikipedia, that they tend to be written by, and for, experts in the field. Some concepts are inherently complex, so there's no easy way to explain them. But others aren't all that complex. A black hole can be described quite simply: "A black hole is where so much matter is packed into such a small space that the gravity causes it to pull itself down to a single point, called a singularity, and nothing, even light, can escape from a roughly spherical region around it, called the event horizon.". Now, our black hole article isn't bad, but the opening paragraph does go into the "general theory of relativity", the "deformation of spacetime", a "perfect black body in thermodynamics", the "theory of quantum mechanics", and "Hawking radiation". That's probably a a bit much for the average person to take in at once. I'd leave those details until later. StuRat (talk) 15:07, 28 March 2010 (UTC)

Read up a bit on the gravitational singularity, and ring singularity if you have time, and white hole for the opposite of a black hole. ~AH1^(TCU) 16:23, 28 March 2010 (UTC)

If you're prepared to struggle a bit, Roger Penrose's The Road to Reality is worth looking at. The first few hundred pages cover the mathematical background for the rest, which aims to be a pretty complete introduction to modern physics. At 14 the mathematics will probably be very difficult for you, nevertheless you might get a lot out of it, especially if you've got somewhere you can go for help (e.g. the ref desk!). I wish I'd had the book when I was that age. Tinfoilcat (talk) 17:05, 28 March 2010 (UTC)

+1, it is a good book (and can be had for next to nothing). If nothing else it will show you how important mathematics is for physics. 131.217.255.213 (talk) 23:51, 28 March 2010 (UTC)

Next on my reading list in this vein is Richard Feynman's Six Not-so-easy Pieces (ISBN 978-0140276671). I mention that because, although it doesn't contain any black holes, it does, from what I have seen of it so far, take you a long way in that direction, while possibly being an answer to your question "Where do I start?". (But, thanks to this thread, I have added Penrose's book to my personal reading list.) Brian Greene called general relativity (where the prediction of black holes came from) the "crowning jewel" of classical physics. I don't expect it to be easy!

I agree with your point about Wikipedia. It does not do as well as other encyclopedias in meeting a general reader where he comes from in topics of mathematics and physics (it does seem to beat most others in depth and breadth of coverage.) Maybe collaboration will change that over the years, though I doubt it will soon beat the top flight of popular science books and documentaries. One example is a recent BBC Horizon programme (popular science on TV) where Brian Cox explained a 'waterfall' analogy of a black hole, trashing the well known belief that objects are torn apart as they cross the event horizon. It is hard for Wikipedia to match that.

--Hroðulf (or Hrothulf) (Talk) 14:07, 31 March 2010 (UTC)

I wasn't aware of Wikipedia's Introduction to general relativity. Perhaps that will also help. It is not as straightforward or vivid as the relativity chapter of Brian Greene's The Fabric of the Cosmos (ISBN 0713996773. Greene uses characters from The Simpson's instead of rigorous mathematics, and actually brought to life the simple special relativity equations that I found so hard to understand at university.) However, the Wikipedia introduction does cover more ground.

wikibooks:Introduction to Astrophysics/Black holes also seems relevant.

--Hroðulf (or Hrothulf) (Talk) 15:09, 31 March 2010 (UTC)

The Russian Sleep Experiment

Is this real, and is it verifiable enough to be included in any Wikipedia articles? ~AH1^(TCU) 13:50, 28 March 2010 (UTC)

It doesn't seem anything like a true story, to me. The subjects obviously would have died with their internal organs removed like that. Also, there have been plenty of real sleep deprivation studies to know what happens. The paranoia part seems right, but not the rest. StuRat (talk) 14:43, 28 March 2010 (UTC)

It's clearly fiction. There is no way anyone could survive that, even with some fancy stimulant gas. --Tango (talk) 15:08, 28 March 2010 (UTC)

But the "freeing the internal madness" part sounds somewhat plausible, as certain circumstances could perhaps allow the subconscious mind to dominate one's actions. ~AH1^(TCU) 16:19, 28 March 2010 (UTC)

But why would you think your subconscious mind is suicidal ? It evolved, just like the conscious mind, based on the survival of the genes most likely to bring about the survival of the genes. Thus, being suicidal isn't a winning strategy. I can imagine the higher reasoning part of the brain ceasing to function, leaving you in an animal state, but those "animals" would still have a sense of self-preservation. StuRat (talk) 19:42, 28 March 2010 (UTC)

|||as a point i'd like to say this reminds me of a situation in the animated movie "dead space downfall" where a woman proceeds to tear away at her own flesh... watch it, you'll see what i mean. ~wolfee

CCTV cameras in the 1940's Union - that's suicidal. At least they didn't write of ipods and cellphones :)) NVO (talk) 22:29, 30 March 2010 (UTC)

The subtitle is "The best short story I've read" and the opening blurb says "Don’t know who wrote this or where it came from. My brother emailed me a link to it and I was completely immersed in it. Kudos to the author. If you know the author or any other works by this person, please leave me links in the comments, I would love to read more from this person." The only real question is what could possibly have made you think there was even the slightest chance this was real, let alone a reputable source to base articles on? No offence, but it says flat out that it's a story; why is there any confusion? Matt Deres (talk) 18:41, 28 March 2010 (UTC)

What a load of complete bullshit. Honestly - not one single part of that rings true or has even fractional basis in known science. Zombies created in Russian death-camps. Sheesh! It's obviously fiction. Ignore it...and DEFINITELY don't write a Wikipedia article about it without a heck of a lot of reliable-source references. SteveBaker (talk) 23:06, 28 March 2010 (UTC)

Obviously fiction, and the writing's not stellar (The story would be a lot punchier if they left out that explanation in the next to last paragraph.) , but it's still a fun story. It comes from a long tradition of sci-fi/horror about what happens to people when they stay awake for ridiculous periods of time.

Spoilers for short story linked above : I didn't catch this until I saw it pointed out in the comments, but check it out : Of the original five test subjects, one is killed by the other subjects, one dies when his spleen is stepped on, one died on the operating table when he was anesthetized, one of them dies mysteriously when he falls asleep, and two of them are shot by a researcher.

APL (talk) 05:15, 29 March 2010 (UTC)

Dust Bowl

Dust from the Dust Bowl can be found in major cities across the East including New York City. In addition, tons of Dust Bowl topsoil was dumped into the Atlantic Ocean. Why was the soil carried east to the Atlantic rather than west to the Pacific? Lamb99 (talk) 16:06, 28 March 2010 (UTC)

Prevailing westerlies generally carry airborne dust eastwards at the latitude of the United States Midwest. Further south in latitude however, the Saharan Air Layer is carried westwards by trade winds. ~AH1^(TCU) 16:15, 28 March 2010 (UTC)

Okay, thank you. Lamb99 (talk) 16:49, 28 March 2010 (UTC)

Boob.

Lowering tone as I stir drink mix

Why when I stir a drink mix into water does the sound of the stirring lower in tone until it reached an equilibrium? Actually, I'm not sure the drink mix has anything to do with it, though I haven't tried it with plain water. My guess is that as you're stirring, air is being forced into the liquid and this changing the tone until no more air can be incorporated. Just a guess. Looking for a real answer.--162.84.128.153 (talk) 17:36, 28 March 2010 (UTC)

The rotational force of the liquid increasingly builds pressure against the inside wall of the glass. This pressure also increases the density and makes it harder for the glass to oscillate resulting in a lower tone. Just as a thin piece of metal will have a high frequency when struck; I thicker piece will have a lower.

We've had this question before and I'm not sure we've ever had an entirely reliable answer. You may find this discussion and this Straight Dope article interesting, though. --Tango (talk) 17:57, 28 March 2010 (UTC)

Hmmm. This is very strange. First, there's all this stuff in the past discussion about hot liquid. This is an everyday phenomenon for me and cold liquid is at issue (well tap water temperature). No need for anything hot. Second, no tapping on the outside is going on. Just the sound of the stirring and the spoon making noise off the inside of the glass. This happens whenever I am mixing (I am completely addicted to Crystal Light) and it doesn't matter one wit what vessel I use. Second, people kept taking about the tone rising. The tone lowers. I just tried an experiment with interesting results. I tried it with Crystal Light, then I tried it without. With the mix there was the normal effect. With just tap water, the same effect was present but not as strong. And here's where it gets interesting, if I fill the glass and let it sit for a few minutes, the effect goes away entirely, regardless of whether I use the drink mix or not. So, there certainly is much of this that is related to the gas present as I fill the glass from the tap coming out of solution (the opposite of what I suspected when I first posted).--162.84.128.153 (talk) 18:46, 28 March 2010 (UTC)

You beat me to it. That's just what I was going to say about air bubbling out as it sits or is stirred. This is especially true if you have an aerator on your faucet. StuRat (talk) 19:35, 28 March 2010 (UTC)

Personally, I don't believe the "air bubbling out" theory - it doesn't fit all of the facts we've heard over the years - and I can't reproduce the conditions where the effect "goes away" after these bubbles have supposedly escaped. I suspect (without proof) that we're hearing the result of doppler shift in the sound due to the motion of the liquid. But this question has come up at least three times in the last year - and there is no solid science to explain the effect that I'm aware of. This would make a great study for someone with access the the right equipment. SteveBaker (talk) 22:50, 28 March 2010 (UTC)

Could it be that the frequency of the stirring sound is related to the relative speed of the stirrer in the liquid? The liquid was stationary when you first started stirring it. After a while, its has caught up with the stirring so the stirrer is no longer moving as fast relative to the liquid. --173.49.14.137 (talk) 11:43, 29 March 2010 (UTC)

I think that the properties of the solution are changing as the sugar, flavoring, etc. are dissolved, so it transmits sound differently. --98.221.179.18 (talk) 20:18, 29 March 2010 (UTC)

will bleach oxidise hemiacetals?

Suppose that all the OH groups on a sugar ring have been protected except the OH group on the anomeric carbon (since it easily undergoes exchange). It possible to oxidise this selectively unprotected OH group to an ketone, with mild conditions and bleach? I am hoping the anomeric effect will actually promote the reaction and make the OH group more reactive than normal, allowing me to use bleach under very mild conditions without oxidising anything else. Ideally my yield would be >70%. John Riemann Soong (talk) 18:11, 28 March 2010 (UTC)

Bleach (especially under acidic conditions) can oxidize secondary alcohols. Not sure if being anomeric helps or hurts: for the normal (not hemiacetal in equilibrium with an aldehyde), I think the mechanism is E2-like, with from anomeric H coming off and its σ bond becoming the carbonyl π). That mechanism doesn't work unless there is an exchangeable H on the O, so an acetal or other ether would not react rapidly.DMacks (talk) 19:00, 28 March 2010 (UTC)

Oops, I meant hemiacetals. Bleach is too weak of an oxidant to oxidise C-H bonds, right? What about the potentially activated C-H bonds on the other side of the acetal-ethoxy oxygen? Also the largest issue I'm worried about is the bleach oxidising the other alcohol in the straight-chain form... which would give me a dialdehyde...

Essentially, I'm trying to convert a hemiacetal into a cyclic ester. This should be more favourable than forming dialdehyde product, right? John Riemann Soong (talk) 19:46, 28 March 2010 (UTC)

That's actually the question I answered:) Your real problem is keeping the sugar-ring in the closed (hemiacetal) form. If it opens, you risk oxidizing the aldehyde to acid, and that is a very easy process (basis for the many chemical tests for reducing sugars). Bleach doesn't touch alkanes, and I do not think (based on mechanism) that it would touch a carbinol hydrogen (the H on a C, where that C is attached to an O as ether or hydroxyl)--except when it is an OH group. DMacks (talk) 14:09, 29 March 2010 (UTC)

Hold on, bleach oxidises aldehydes? I thought it just oxidised pri/sec alcohols. (okay, also amines into chloramines, but we don't have to worry about that here...) John Riemann Soong (talk) 04:41, 30 March 2010 (UTC)

No, I don't know if bleach does oxidize aldehydes. But if it does, your major problem is not "ring opens, primary alcohol oxidizes to aldehyde" but instead "ring opens, aldehyde oxidizes to acid". Either way, it's a problem. But it's a different problem. One way, you have to consider primary vs secondary-alcohol/hemiacetal oxidation rates, other way you have to consider secondary-alcohol/hemiacetal vs aldehyde oxidation rates. In general, aldehyde→acid without also oxidizing alcohols is very easy to do. And the specific bleach oxidation mechanism looks to me like it could work well on aldehydes also. Try this experiment: take some simple aldehyde, some simple secondary alcohol, and some simple primary alcohol, and try to oxidize each with bleach under the same experimental conditions. See if each one reacts, and approximately how rapidly. DMacks (talk) 15:06, 30 March 2010 (UTC)

Anyone know about Victoria building and guttering?

Is it possible that the downpipes carrying rainwater off the roofs of our house simply sink about 3 metres vertically into the ground and then soak away directly into the foundations/ watertable? Did they do that? --BozMo talk 19:55, 28 March 2010 (UTC)

Unlikely. A downspout concentrates the volume of rainfall collected from a large area into a single spot. The permeability of the ground to water, however, is limited. If you merely buried the downspout in the ground (whether 3 meters deep or half a meter or whatever), the water would simply back up in the downspout until the gutter overflowed, thus defeating the purpose.

If you ran the downspout down into a dry well you'd constructed, on the other hand, it would work quite well. Such wells tend to get clogged with silt and other material after a while, however, and stop working. After 100 years I can imagine that it might be largely indistinguishable from soil. —Steve Summit (talk) 20:57, 28 March 2010 (UTC)

Ok, thanks. There has been a problem with ground water flooding into the cellars in the last couple of decades. I assumed it was to at least below the cellar level originally. I guess a silted up dry well is a possible cause. I could divert the downpipes fairly easily so perhaps I should just do it. --BozMo talk 21:21, 28 March 2010 (UTC)

(ec)It depends a lot on the type of ground conditions you have whether such a soakaway (as we call dry wells in the UK) would be effective long term. I live on river gravels over chalk and I reckon that the water table is a long way down, as we have a completely dry unlined cellar. I think that under those conditions it would work (the down side is that it makes growing stuff in the garden during dry summers a pain). Mikenorton (talk) 21:25, 28 March 2010 (UTC)

However they probably don't mix very well with cellars. Mikenorton (talk) 21:27, 28 March 2010 (UTC)

Yes, this arrangement is common in the area where I live, but the water is usually ducted away from the foundations before being allowed to sink into the ground. As Steve says above, silting-up is a problem, and it is possible that the original underground drain has collapsed. Dbfirs 21:30, 28 March 2010 (UTC)

We are on real Suffolk clay (chalky boulder clay to geologists). We live right at the top of a hill but the moat and pond in our garden stay full and have been 5 m apart with 1m difference in water depth since about 1150 AD without one draining into the other (the moat isn't around our house, it is the site of a medieval hall). But the cellar used to be dry: indeed even thirty years ago it had electrics and central heating fitted which is not sensible today. So something has silted or blocked I guess. --BozMo talk 21:33, 28 March 2010 (UTC)

Sounds like a great place. You must have a sanitary sewer or a septic tank, and you could always direct the water there (although it might not be legal to drain it into the sewer in some places, and it might overflow a tank). The most obvious solution is just to have some maintenance done to remove the generations of silt built up in the dry wells. StuRat (talk) 22:01, 28 March 2010 (UTC)

As far as I know, one should never divert rainwater or other runoff water into either a septic tank or a sanitary sewer. The former is a significantly bad idea; the latter is (as Stu mentioned) illegal in some/many/most jurisdictions. —Steve Summit (talk) 13:46, 29 March 2010 (UTC)

Well, there is the combined sewer. While I agree that they are a seriously bad idea, they seem to be widespread in certain areas, anyway. In South-Eastern Michigan we pretty much have to close all the lakes and beaches when there's a heavy rain, and the basements of all homes in low lying areas flood with sewage, because of combined sewage overflow: Combined_sewer#Mitigation_of_CSO_Impacts_in_United_States. StuRat (talk) 18:41, 30 March 2010 (UTC)

Some houses use a cistern to store rainwater. I would think you would know if you had one of those, however. Googlemeister (talk) 14:00, 29 March 2010 (UTC)

Some options for what to do with rainwater coming out of downspouts:

• You could put a French drain under the downspout which directed the water elsewhere. A french drain is basically a trench filled with gravel. The large pore space between the gravel makes an effective means of containing and/or diverting water. Some French drains also contain a semi-permiable pipe to direct the collected water away towards a more desirable area.
• You can bury some flexible piping and use that to direct your water, used by itself or in connection with a French drain, it can be very effective. Years ago I had a problem with my downspouts washing away a flower garden; so I dug a trench across my yard to an overgrown area, and installed something like this corrugated black plastic pipe, covered it back again with dirt and grass, and and it works great. Its been in the ground almost 7 years, and it has never clogged or backed up at all. I have three downspouts (roughly 1/4th of the water from my roof) all directing their water into a pipe 4 inches in diameter, and it runs underground down a slope that has about a 1-2 foot drop over about 30 feet, and its plenty to direct all of the water away from the house. The entire project took a Saturday, a buddy, and a case of beer.
• You can collect the water and reuse if for gardening. The article Rainwater tank contains some examples of rainwater collection barrels and tanks.

Just some ideas. --Jayron32 14:47, 29 March 2010 (UTC)

Some buildings take the water to the gutter of a nearby road. But roads can get built up over time blocking the outlet. (I have excavated near an old road and found the old piping no longer going to the road). Polypipe Wrangler (talk) 01:15, 30 March 2010 (UTC)

Turnover number

Do you know the turnover number (or deactivation/poisoning velocity) of a CuCl2-based catalyst (i.e. "Deacon catalyst")? --Aushulz (talk) 22:10, 28 March 2010 (UTC)

If there was a giant hole through the Earth...

Ok lets say that the Earth (or some other large solid planet) had a solid core, and we drilled a great big hole from one side of the Earth, through the centre, and out the opposite side. What would happen if you jumped down this hole?--92.251.136.245 (talk) 22:20, 28 March 2010 (UTC)

If you jumped in the hole, when you reached the middle, you would be in the center of gravity, so you would not fall anymore. --The High Fin Sperm Whale 22:26, 28 March 2010 (UTC)

But surely momentum would carry you towards the opposite side? And if you were in the middle, would you be floating?--92.251.136.245 (talk) 22:28, 28 March 2010 (UTC)

Without air resistance, you'd speed up, falling to the center, and then start slowing down again, making it just far enough to poke your head out the other side (assuming the Earth is a perfect sphere here), and the process would repeat forever. With air resistance, you'd quickly reach terminal velocity, so you wouldn't make it very far past the center. However, since air resistance is a bigger deal the faster you move, you'd probably oscillate back and forth for a long way near the center. Paul Stansifer 22:36, 28 March 2010 (UTC)

See the several times this same question has been asked and answered previously, for example, Wikipedia:Reference desk/Archives/Science/2008 November 19#What if we cut a hole through Earth?. DMacks (talk) 22:31, 28 March 2010 (UTC)

If we were to build a colony on an asteroid or small moon, that might actually be an efficient way to transfer items from one side to the other. As a practical matter, you might want to build an elevator shaft with a magnetically "levitated" car, so the people or objects wouldn't keep hitting the sides. StuRat (talk) 22:40, 28 March 2010 (UTC)

There have been many discussions of this in the past - and the consensus is that outcome depends entirely on the assumptions you make.

From most realistic assumptions to least:

1. The hole would fill up with molten lava and other materials faster than you could dig it. So you can't construct such a hole.
2. In order to prevent this collapse, we'd have to line the tunnel with something - but there is no material we have that could survive the temperatures and pressures involved.
3. Even if we imagine such an 'unobtainium' material to make a liner with, the hole would fill up with air. At the pressures you'd get towards the center of the hole, the air would liquify and block the hole that way.
4. So you'd jump in and as the air density increases towards the center of the earth, then either:
   • You'd be crushed by the pressure.
   • If you wore some kind of pressure-resistant suit then you'd eventually float like a balloon at some distance before you got to the center.
   • If you put enough weights onto the suit then you'd slowly sink to the bottom of the liquified air and arrive at the center of the earth - where you'd feel no gravity at all.
5. If you could pump the air out to make a nice hard vacuum throughout the hole - then you'd obviously suffocate on the way down...so you need to wear a space-suit.
6. If you get rid of all of these annoying issues, then you'd still be bouncing off the sides of the hole all the way down due to coriolis forces - so the friction would slow you down to an eventual stop at the center of the earth - where you'd float freely and feel no gravity.
7. To solve that problem, we'd have to drill through the axis of rotation (ie from pole to pole).
8. With only gravity acting on you, you'd have to enter the hole at a very precise vertical angle to avoid hitting the sides on the way down.
9. Assuming you get around ALL of those issues, then there is no friction in the hole - so what would happen is this:
   • In your spacesuit, you jump into the hole at the North Pole. Since you are falling, you feel no gravity from the instant your feet leave the ground - you fall all the way towards the center of the earth, getting faster and faster - so fast in fact that you overshoot the center and start to slow down. You finally stop just as your head pops up above the surface at the south pole - then you fall all the way back again, through the center and back out to the North Pole. This happens over and over again until someone or something intervenes to helps you out!

SteveBaker (talk) 22:41, 28 March 2010 (UTC)

How would one calculate the pressure at the center of the Earth in an Unobtanium tube exposed to the atmosphere? It seems counterintuitive that air pressure gets higher and higher as you descend below the surface, since gravity should decrease steadily, due to some of the mass being above you and a smaller amount below you. At the same time, though I admit that the "column of air" above the point would get higher and higher, which would seem to increase the pressure. And wouldn't the temperature have to be lowered to get air to liquify? Edison (talk) 16:36, 30 March 2010 (UTC)

Surely you would move less and less each run and evenutally remain stationary in the centre?--92.251.136.245 (talk) 22:47, 28 March 2010 (UTC)

Only if there was some friction acting on you. For instance if you were bouncing off the sides, or there was some air. ... But, as Steve mentioned, if there was air, it would increase in pressure until some parts of the tunnel were actually filled with liquid air. APL (talk) 23:04, 28 March 2010 (UTC)

You'd need a lot more air to liquify in the center than you would to slow you down a bit with each pass. If we pumped out all the air we could, to get as close to a vacuum as possible, we would still be slowed appreciably at those speeds we would reach near the center. StuRat (talk) 23:54, 28 March 2010 (UTC)

1) What is the diameter of this hole?

2) I find there to be too much disbelief to suspend to presume one's head would always be the body portion 'popping' out the other side. DRosenbach ^{(Talk | Contribs)} 00:06, 29 March 2010 (UTC)

It's possible to control your spin, even in a vacuum. Cats don't use wind resistance to land or their feet. — DanielLC 06:25, 29 March 2010 (UTC)

I think a more interesting question involves a lined (with unobtainium) perfectly straight and regular cylindrical hole through the center of the Earth containing absolutely nothing (a vacuum). A lead sphere is released from beneath the cap of one end of the tunnel (at the surface of the Earth). Would the sphere oscillate indefinitely or would it eventually come to rest at the center of the Earth? Let us say that the tunnel was drilled from pole to pole to eliminate the Coriolis forces that SteveBaker presciently pointed out. Bus stop (talk) 00:24, 29 March 2010 (UTC)

Well, the axis moves around a bit, so I guess if you waited long enough the ball would end up hitting the sides and slowing down. --Tango (talk) 00:30, 29 March 2010 (UTC)

Precession of the equinoxes takes tens of thousands of year, though. I suspect that before that effect you would see something similar to tidal forces, whereby the passing lead sphere would warp the shaft inward, ever so slightly increasing the pull of gravity towards the sphere. As the sphere would be continuously moving past this bulge, it would tend to slow the sphere down, over time. StuRat (talk) 00:35, 29 March 2010 (UTC)

The lead ball would emit gravitational waves to slow down, but the time scale of that dwarfs everything you mentioned. — DanielLC 06:25, 29 March 2010 (UTC)

I'm not talking about precession of the equinoxes - I believe that is the axis moving relative to the distant stars, not the Earth. I'm talking about polar motion, which happens over a much shorter timescale. --Tango (talk) 13:01, 29 March 2010 (UTC)

Instead of a straight shaft down the axis, why not drill a curved shaft at the equator? APL (talk) 00:41, 29 March 2010 (UTC)

Entering at the equator one's momentum would be conserved. Comparable to ice skaters who bring their arms to their bodies to increase their rate of spin one will rotate progressively faster than the Earth as one falls. A tunnel must have the shape shown for one not to touch its sides. Cuddlyable3 (talk) 14:44, 29 March 2010 (UTC)

What type of curve? Would the two ends of the curved tunnel represent the two ends of some diameter of the Earth? Bus stop (talk) 01:01, 29 March 2010 (UTC)

Imagine you moving back and forth as the Earth spins. The path you draw on the Earth would be the shape of the curve. It looks kind of like a flower. Since a day isn't perfectly divisible by the time it takes to make one lap, the "petals" of the flower would never quite line up, so you'd have to keep digging until you eventually just hollow out the entire equator. — DanielLC 06:25, 29 March 2010 (UTC)

Sounds like the line inscribed by a Spirograph. Bus stop (talk) 14:47, 29 March 2010 (UTC)

I'll bet that you could make it evenly divisible by starting the passenger some distance above ground level. APL (talk) 16:24, 29 March 2010 (UTC)

Regarding the picture, that can't be right. I think your path would be some kind of oval. You wouldn't spiral towards the center. You'd pass around it. Compare it to an elliptical orbit. — DanielLC 07:36, 30 March 2010 (UTC)

You're right; in an inertial reference frame, your path would just be an elliptical orbit. The path using the rotating earth as a reference frame would be different; it probably would look a bit like a spiral. The picture is certainly not correct: the path would not hit the center of the earth, and it would begin perpendicular to the surface of the earth. (The picture may be accurate for something dropped straight into the earth that wasn't traveling along with the earth's rotation at the surface.)71.240.196.243 (talk) 14:03, 30 March 2010 (UTC)

This entire question has blown my mind thoroughly. Is there a book or a website or even a really long article about an Earth-spanning hole that I can read to sate my interest? ZigSaw 01:54, 31 March 2010 (UTC)