Lumpy Earth---gravity's effects on us?
February 18, 2006 9:56 AM   Subscribe

Gravity/Life/SocietyFilter: So the Earth is all lumpy, with more or less gravity in some places. Has anyone ever corroborated it with life/social/world things? Many questions inside...

--is life worse there for people or better?
--is a place like the Middle East, which has seen almost continual strife since recorded history a place of denser gravity? or of the opposite? (it's also the where civilization first developed) or was it lighter and now heavier?
--have breakthroughs in various fields tended to happen in lighter places or heavier? have wars? have long stretches of peace? have healthier populations? etc?
--was the change from the Dark Ages to the Renaissance a result of the lightening of gravity in the area?
--does it have any effect on us? i would think it would, no? Is there a depressing or generally bad effect of more gravity on us?

We're very much creatures of our environments, and there are places with lots of energy and buzz (NYC, Bombay, etc), and places that are sleepy and quieter, even when geography matches (Pittsburgh, or Amsterdam, etc). And we're affected by things like the moon and its movements, and by sunshine and the weather and pressure, etc.

Why not gravity too?
posted by amberglow to Science & Nature (33 answers total) 1 user marked this as a favorite
Response by poster: and also: are people grumpier in places with more gravity, like they are in places with less sunlight? is there more crime? is there more suicide? or the opposite?

(hopefully this is making sense)
posted by amberglow at 10:02 AM on February 18, 2006

Red = more gravity, blue = less.
posted by public at 10:06 AM on February 18, 2006

Considering pretty much all of Africa has similar readings to most of the east coast of the USA, I'm going to go out on a limb and say there's no correlation.
posted by public at 10:09 AM on February 18, 2006

Well, you can do this yourself. Here's one of the maps (this one is taken from several decades of satellite data):

A quick look suggests that gravity is lower in (some) areas covered by ocean. Population seems not to correlate with gravity (look at India and China), even if the gravity is higher near Indonesia.

And other than population mass (which would be swamped by the mass of the earth anyway), I can't see any mechanism that would connect social conditions to gravity. We'd have to postulate that happy thoughts are significantly lighter than heavy thought. Since mass is conserved despite state transformations, I don't see this as possible.

The fluctuations are probably caused by the shape of the earth; the earth is a massy object, and it's not a perfect sphere. Not by the feelings of the naked apes roaming the earth's surface.
posted by orthogonality at 10:10 AM on February 18, 2006

Would 60 millionths max difference in local gravity have any effect at all?
posted by A189Nut at 10:11 AM on February 18, 2006

Response by poster: even tiny amounts of sunlight have an effect on mood and health--why not gravity?
posted by amberglow at 10:13 AM on February 18, 2006

I would imagine that the difference is relatively minute between a red area and a blue area but I'd be interested to see some numbers. Micro-gravity has noted effects on the body and there are studies ongoing specifically about how the brain holds up in such environments (see here). However, to my knowledge there's never been a test about the effects of too much gravity.
posted by saraswati at 10:14 AM on February 18, 2006

Preview, dammit, preview
posted by saraswati at 10:14 AM on February 18, 2006

Response by poster: We'd have to postulate that happy thoughts are significantly lighter than heavy thought. Since mass is conserved despite state transformations, I don't see this as possible.

It's not that, but that our environments have an enormous effect on us and our lives, and on society and its development and highs and lows.
posted by amberglow at 10:15 AM on February 18, 2006

There's a pretty massive different between a micro-gravity environment and a 0.0006% variation from 1G.
posted by public at 10:16 AM on February 18, 2006

Response by poster: It's sorta like the fact that for women who live or spend tons of time together, their menstruation tends to sync. Something makes that happen, and it shows how attuned we are to things around us, no? (i'm not at all saying that gravity does that--i don't want to derail)
posted by amberglow at 10:18 AM on February 18, 2006

Biological organisms tend to be pretty sensitive to certain chemicals so it's not that surprising that women's menstrual cycles can end up in sync. Unless the tiny variations in gravity caused certain chemical reactions to behave differently (which I very much doubt it would) then we have no innate mechanism to detect gravity. The cochlea isn't *that* sensitive.
posted by public at 10:21 AM on February 18, 2006

Might as well consider the effects of altitude on attitude. Is someone living in Denver (Mile High City) more or less cheerful than someone living in Death Valley (lowest point in the US)? Gravity is lower in Denver (farther from the Earth's center), but so is the oxygen content of the atmosphere. Denver is more crowded, but Death Valley has more lonely, flesh-eating mutants.

It's a puzzler, that's for sure.
posted by SPrintF at 10:23 AM on February 18, 2006

Response by poster: public, if we're "pretty sensitive" to chemicals (and sunlight, and weather, and nutrition, and really everything i can think of), why not to even small fluctuations in gravity? Gravity is not only a cochlear thing.

SPrint, altitude does have effects on us--most people live at or near sea level, no? Life is harder the higher you go, and resources aren't as available as they are nearer the coasts, thus affecting development and stuff. See cultures in the Himalayas as compared to cultures along any coast, for just one example. (and i would say mood is affected as well--there's more light higher up, i think)
posted by amberglow at 10:31 AM on February 18, 2006

Amberglow: The reason why you won't find significant effects attributable to gravity is that a) the significance of the variation is pretty low, and b) any changes are likely to be correlated with other factors that are much more important.

Take, for example, altitude (which oddly enough seems to negatively correlate with gravity, if the map is any judge– the mountainous regions of the Andes, Rockies, Himilayas, etc. have redder tints than the sea level places) is a much more important factor on human life than the gravity. If you were looking for something more likely to be affected, you should look for variations in bacterial growth or in single-cell organisms and viruses. As plants have different ecologies based on micro-altitude changes (as small a difference as one foot can lead, in some places, to totally different plants), they might also be more likely to be affected. Something as big as humans? The differences are likely to be incredibly small. You might as well be trying to track variations in nitrogen content or ionization.
posted by klangklangston at 10:44 AM on February 18, 2006

Oh, sorry, I misread amberglow's arrow of causation.

The effect is too slight to be noticeable, I'd guess. And an organism has no motivation to notice; I can't see how noticing minute gravity differences gives any advantage to fitness, so selection won't care about it. But I could be wrong.
posted by orthogonality at 10:47 AM on February 18, 2006

Response by poster: i wondered about altitude too when i saw the map--is it where plate/earthquake fault lines are that have more gravity? (and why?)

Has anyone correlated gravity with those other factors tho? It seems like it would be a piece of the puzzle to me, since everything else is.
posted by amberglow at 10:50 AM on February 18, 2006

The scales on those images has been greatly exaggerated so that it is visible, but the actual change in gravity is miniscule, on the order of parts per billion.

As an example, the scale in that image goes from -60 mGal to 60 mGal. So even from the darkest blue to brightest red would be a difference of about 120 mGal, with most variations being far lower. But even 120 mGal difference in 'g' is equivalent to a change in altitude of only 400 meters. So the variations in gravity due to the composition of the earth is essentially just insignificant noise compared to the effect of altitude on gravity. So you might as well be asking "does altitude have an effect on society," which has already been addressed. But of course I think you could argue that effect is going to be primarily due to air pressure and logistical constraints (roads, etc) rather than the extremely small change in gravity.
posted by Rhomboid at 10:57 AM on February 18, 2006

Response by poster: So we are not even able to notice the difference at all in any possible way at all, long- or short-term?
posted by amberglow at 11:02 AM on February 18, 2006

Again, to Newtonian approximation (which is totally reasonable in this case), the force of gravity correlates inversely with the squared distance between you and the center of mass of the planet. This distance is so closely approximated by altitude that there's no point in differentiating. There are just too many other factors correlated with being at high altitude / lower gravity to piece out the affects of gravity. These include climate differences, decreased partial pressures of gases (thinner atmosphere, lower oxygen content), varied agriculture, limitations in transportation and communication, and the millenias of anthropological variations that have developed as a result. Thinking abstractly, these other variables have a far greater degree of variance than the force of gravity which would suggest that it's direct effects are probably minimal if any.
posted by drpynchon at 11:47 AM on February 18, 2006

Amberglow: it's not some mysterious property of having more gravity in different locations for no apparent reason. It looks like most of the red spots are mountain ranges: more Earth, more mass, more gravity.
posted by awesomebrad at 12:48 PM on February 18, 2006

It's useless to make suggestions and postulate ideas here. The only thing that would be conclusive is some sort of real scientific study. Not everyone's pot-induced what-if scenario bullshit that everyone's been laying out so far.
posted by cellphone at 1:23 PM on February 18, 2006

Response by poster: I can't believe there haven't been any. Wasn't this a big deal when it was discovered that it wasn't uniform?
posted by amberglow at 1:36 PM on February 18, 2006

True, cellphone, but without these "pot-induced what-if-scenarios," where may we start with such scientific studies? I don't think that the only people qualified to create hypotheses are scientists. Remember that before the days of modern science and technical methods and equipment, all people had to go on was reason and ideas. Sure, they made a lot of mistakes, but does that mean that it wasn't worthwhile?

Surely any answer that someone gives here will be unsubstantiated at best, and logically absurd at worst, but I still think it's worth the time to think about.

I'm surprised at how much amberglow has had to defend his/her own curiousity about this. It seems to be a valid idea to think about.

The obvious first idea would be to postulate that more gravity makes for more serious people, right? After all, they do have more forces pushing down on their heads, so they would be less likely to have their "heads in the sky." Any other pot-induced what-if-scenarios?
posted by zhivota at 1:37 PM on February 18, 2006

The only thing that would be conclusive is some sort of real scientific study. Not everyone's pot-induced what-if scenario bullshit that everyone's been laying out so far.

What did you expect? Pot-induced what-if scenario bullshit questions elicit pot-induced what-if scenario bullshit answers.
posted by jjg at 1:49 PM on February 18, 2006

Best answer: The lumpiness is due to more than just mountains here and oceans there. The anomalies provide a window into the dynamic operation of the forces within the earth. If there were no dynamic forces there would be no anomalies. The earth is a deformable plastic and on the geologic timescale all gravitation lumps would have evened out like silly putty.

For example look at the central parts of North America and Africa in the map above. Note that it is light green exactly like parts of the pacific ocean that are thousands of feet lower. So what about the "extra" mass of the continents? Why don't you see a red spot in the middle of North America? That is because the continents are composed of less dense rock that floats on the mantle like an iceberg in the ocean. The continents, just like an iceberg, consist of exactly the same amount of mass as the material it is displacing. If there were no dynamic forces, the entire earth would be an even light green color in the map with no mass anomalies, just like an ocean of icebergs.

So what about the yellow spot over the Rocky Mountains? That is because the Rockies are a relatively young mountain range that has been shoved up by mantle currents in a collision of tectonic plates. This causes a temporary excess of mass. This is similar to the ice ridges that form in the Arctic ice pack when wind and currents blow two sheets of ice into each other.

Notice that the Appalachian Mountains do not have a mass anomaly. These mountains were formed long enough ago that they have sunk back down to the floating equilibrium level.

And what about that dark blue area in eastern Canada? This seems to indicate a lot of missing mass. This is a result of the last Ice Age in which thousands of feet of ice were piled on the continent. The weight of this ice caused the dense mantle to ooze out to the sides and create a depression. The ice then melted in the blink of an eye in geologic terms and the crust has yet to rebound to the equilibrium level. It is as if we have a high-speed snap shot of the crater just after a pebble was tossed into a pond.

The lumpiness of the gravity anomaly map is an indication that powerful forces are still active within the earth, temporarily disturbing equilibrium.
posted by JackFlash at 1:54 PM on February 18, 2006

Response by poster: so eventually that Canadian depression will fill in?

and--it's a sign of planetary health that these things are all active, no?
posted by amberglow at 2:21 PM on February 18, 2006

The Canadian depression has been rising for 10,000 years and will probably continue to rise for another 10,000. The current rate is about 1/2 inch per year for an eventual total of about 1500 feet. The technical term is isostatic rebound.

The corollary to this filling in is that the lump that was formerly squeezed out to the edges by the glacier subsides as it flows into the depression. For example, Glasgow which was covered by glaciers is rising while London, which was not, is sinking.

I wouldn't use the anthropomorphic term "health" to describe this activity, but is certainly makes things more interesting than say, the moon.
posted by JackFlash at 3:46 PM on February 18, 2006

It's useless to make suggestions and postulate ideas here. The only thing that would be conclusive is some sort of real scientific study. Not everyone's pot-induced what-if scenario bullshit that everyone's been laying out so far.

Do you have a sister?
posted by Brian James at 4:00 PM on February 18, 2006

Response by poster: thanks, Jack
posted by amberglow at 8:15 PM on February 18, 2006

No surprise to me that China and India are in the blue zones. People weigh much less than rocks.
posted by flabdablet at 10:14 PM on February 18, 2006

The gravity low of India and the Indian Ocean is one of the most negative gravity anomalies on earth. It is believed to be caused by the movement of the Indian sub-continent. India used to be separated from Asia by the Tethys Ocean, lying far to the south. The Indian plate moved northward at high speed, in geologic terms, ramming into Asia and forming the Himalayas. It is believed that the fast moving Indian plate left a trough behind it in the mantle like the wake of a boat, forming the prominent dark blue gravity low you see on the map. This trough represents a groove of about 600 meters depth which should eventually fade away over time as the mantle flows back in and returns to equilibrium.
posted by JackFlash at 11:12 PM on February 18, 2006

That was all awesome, JackFlash. Thanks!
posted by five fresh fish at 11:36 PM on February 18, 2006

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