The Oregon Vortex
February 20, 2001 12:22 AM Subscribe
The Oregon Vortex is a nice place to visit if you enjoy places where things roll uphill and things change size base on their position. Many have tried to figure it out. Physicist John Lister spent forty years there only to burn all his notes.
When is someone going to let the vortex genie out?
Great article, southisup.
I'm curious about why these skeptics get so bitchy, though.
posted by lbergstr at 2:46 AM on February 20, 2001
I'm curious about why these skeptics get so bitchy, though.
posted by lbergstr at 2:46 AM on February 20, 2001
I think it's because $6.50 might be too much for the entertainment provided.
The Discovery channel did a segment about it that brought it to my attention.
It's sort of like knowing how most of the Copperfield disappearing object kind of magic is based on the Poggendorf illusion. It just doesn't feel like it's worth spending cash on.
Next time I'll do more then a casual search for skeptics. So I'm running out of reason's to go to Oregon again.
posted by john at 4:48 AM on February 20, 2001
The Discovery channel did a segment about it that brought it to my attention.
It's sort of like knowing how most of the Copperfield disappearing object kind of magic is based on the Poggendorf illusion. It just doesn't feel like it's worth spending cash on.
Next time I'll do more then a casual search for skeptics. So I'm running out of reason's to go to Oregon again.
posted by john at 4:48 AM on February 20, 2001
> I'm curious about why these skeptics get
> so bitchy, though.
Maybe they are just tired of watching frauds make lots of money ("Admission is $7 general, $6 for those age 65 and older, and $4.50 for those ages 5 to 11.") from the sort of cretinous tourist who would pay to see a pathetic sideshow rather than spend that time somewhere beautiful.
Or maybe they're just grumpy.
posted by pracowity at 4:55 AM on February 20, 2001 [1 favorite]
> so bitchy, though.
Maybe they are just tired of watching frauds make lots of money ("Admission is $7 general, $6 for those age 65 and older, and $4.50 for those ages 5 to 11.") from the sort of cretinous tourist who would pay to see a pathetic sideshow rather than spend that time somewhere beautiful.
Or maybe they're just grumpy.
posted by pracowity at 4:55 AM on February 20, 2001 [1 favorite]
The Oregon Vortex was explained a long time ago. The phenomenon is real but not inexplicable under the laws of physics.
It's a localized gravitational anomaly caused by a concentration of particularly dense mass below the ground. The center of the Vortex is at the gravitational center. The reason all the buildings are built the way they are is that the people who built there didn't understand what was happening, and they used bubble levels to get "vertical" and "horizontal" on the buildings -- only the levels were lying. Like compasses, a bubble level isn't measuring what people think it is. A compass doesn't point to the rotational axis of the Earth; it points to the magnetic North/South which is actually offset a bit. Equally, a bubble-level doesn't match the terrain but rather points along the lines of gravitational influence. In both cases the tool ordinarily gives the answer we want, which is why we use them. But sometimes they don't, and then the results will seem strange.
These kinds of things happen all over the world only they're usually much larger and less intense, so that they're not perceptible to the naked eye. The big ones have been mapped pretty well, though, because they cause low-earth-orbit satellites to change orbit. For a system like GPS, which requires the satellites to stay in precisely known orbits, they constantly have to fiddle using thrusters to keep them in the predefined orbits. Any continental mass does this and mountain ranges do it particularly well.
The Vortex is interesting as being one of the few places where the effect is particularly strong and localized, to the point where its effects happen on a human scale and are visible to the naked eye. It is counter-intuitive but not counter to the laws of science. We've evolved with an intuitive sense of gravity as being "down", so when "down" isn't actually toward the center of the earth it seems strange and wonderful. But in this as in so much else about physics, our native intuition is wrong. There's nothing unnatural about the Oregon Vortex; and it should be enjoyed for what it is.
posted by Steven Den Beste at 5:35 AM on February 20, 2001 [2 favorites]
It's a localized gravitational anomaly caused by a concentration of particularly dense mass below the ground. The center of the Vortex is at the gravitational center. The reason all the buildings are built the way they are is that the people who built there didn't understand what was happening, and they used bubble levels to get "vertical" and "horizontal" on the buildings -- only the levels were lying. Like compasses, a bubble level isn't measuring what people think it is. A compass doesn't point to the rotational axis of the Earth; it points to the magnetic North/South which is actually offset a bit. Equally, a bubble-level doesn't match the terrain but rather points along the lines of gravitational influence. In both cases the tool ordinarily gives the answer we want, which is why we use them. But sometimes they don't, and then the results will seem strange.
These kinds of things happen all over the world only they're usually much larger and less intense, so that they're not perceptible to the naked eye. The big ones have been mapped pretty well, though, because they cause low-earth-orbit satellites to change orbit. For a system like GPS, which requires the satellites to stay in precisely known orbits, they constantly have to fiddle using thrusters to keep them in the predefined orbits. Any continental mass does this and mountain ranges do it particularly well.
The Vortex is interesting as being one of the few places where the effect is particularly strong and localized, to the point where its effects happen on a human scale and are visible to the naked eye. It is counter-intuitive but not counter to the laws of science. We've evolved with an intuitive sense of gravity as being "down", so when "down" isn't actually toward the center of the earth it seems strange and wonderful. But in this as in so much else about physics, our native intuition is wrong. There's nothing unnatural about the Oregon Vortex; and it should be enjoyed for what it is.
posted by Steven Den Beste at 5:35 AM on February 20, 2001 [2 favorites]
The late, great arblog offered up this link a while back to a definitive debunking of the mystery spot phenomenon. If you haven't been to one it's well worth a visit -- there's nothing quite like stepping inside an illusion.
posted by sudama at 5:54 AM on February 20, 2001
posted by sudama at 5:54 AM on February 20, 2001
> caused by a concentration of particularly dense mass
> below the ground.
And above.
No, that's meaner than I want to be. But no misreading of any damned spirit level ever led to the construction of a building as askew as this one. It seems much more likely that the level of spirits in the builder's blood was a bit high.
posted by pracowity at 7:59 AM on February 20, 2001
> below the ground.
And above.
No, that's meaner than I want to be. But no misreading of any damned spirit level ever led to the construction of a building as askew as this one. It seems much more likely that the level of spirits in the builder's blood was a bit high.
posted by pracowity at 7:59 AM on February 20, 2001
Now this is a mystery spot. I remember seeing a story on "In Search Of..." years ago about this Latvian immigrant who had built huge stone structures singlehandedly. Search "Leedskalnin" on Google for loads of links. I think something explainable was going on here, but it has definitely become a favorite topic among the pseudoscience crowd, who believe it proves all sorts of antigravity and magnetic field theories. Here are a few more links: 1,2,3,4,5
I particularly like #5, as it illustrates how zany some people get when they become consumed with this stuff.
posted by gimli at 8:36 AM on February 20, 2001
I particularly like #5, as it illustrates how zany some people get when they become consumed with this stuff.
posted by gimli at 8:36 AM on February 20, 2001
Just reminds me of the MI-6 base built inside of the half-capsized QEII in Hong Kong Harbor ... as depicted in The Man With the Golden Gun. One of my favorite sight gags of the series, played deadpan.
posted by dhartung at 8:54 AM on February 20, 2001
posted by dhartung at 8:54 AM on February 20, 2001
Pracowity, the building in your article isn't at the Oregon Vortex.
posted by Steven Den Beste at 8:58 AM on February 20, 2001
posted by Steven Den Beste at 8:58 AM on February 20, 2001
It was the Queen Elizabeth in the bond film, the QEII is still afloat.
posted by Markb at 9:09 AM on February 20, 2001
More information on the aforementioned Poggendorf illusion, including a kewl little Java applet that demonstrates the effect.
posted by kindall at 9:35 AM on February 20, 2001
posted by kindall at 9:35 AM on February 20, 2001
It's sort of like knowing how most of the Copperfield disappearing object kind of magic is based on the Poggendorf illusion.
Does that include Copperfield's "Disappearing Statue of Liberty"? I'm trying to figure out how the Poggendorf thing could explain that, but I don't see how.
posted by dnash at 10:21 AM on February 20, 2001
Does that include Copperfield's "Disappearing Statue of Liberty"? I'm trying to figure out how the Poggendorf thing could explain that, but I don't see how.
posted by dnash at 10:21 AM on February 20, 2001
Actually, that's QE2, as QEII sits on a throne in Windsor Castle, while the boat just happens to be the second one by Cunard named Queen Elizabeth. :) This is why their next boat will be the Queen Mary 2.
Yeah, the problem with acribing special properties to the location of these mystery houses is that one of them is at Knott's Berry Farm... And it strikes me as really unlikely that something that anomalous just happened to sit there until a theme park was built right on top of it! :)
posted by aurelian at 10:32 AM on February 20, 2001
Yeah, the problem with acribing special properties to the location of these mystery houses is that one of them is at Knott's Berry Farm... And it strikes me as really unlikely that something that anomalous just happened to sit there until a theme park was built right on top of it! :)
posted by aurelian at 10:32 AM on February 20, 2001
Dnash,
I think thats why Copperfield stays in business. Knowing the idea behind the illusion is one thing, the technique is another story.
posted by john at 1:06 PM on February 20, 2001
I think thats why Copperfield stays in business. Knowing the idea behind the illusion is one thing, the technique is another story.
posted by john at 1:06 PM on February 20, 2001
Steven, you're just yanking our chains, right? You don't really believe that "localized gravitational anomaly" thing, right?
posted by rodii at 3:28 PM on February 20, 2001
posted by rodii at 3:28 PM on February 20, 2001
rodii, gravitational anomalies significant enough to affect orbiting satellites and sensitive navigational instruments do indeed exist. They are caused by variations in the earth's density. Here is a pretty good explanation.
posted by gimli at 4:50 PM on February 20, 2001
posted by gimli at 4:50 PM on February 20, 2001
Sure they do. But localized in this way, and strong enough to affect objects as massive as people? No.
Let's say we bury a bunch of neutronium in Gold Hill, Oregon. This has to be massive enough that it offsets the gravitational attraction of the entire earth and pulls "vertical" askew by 5 or 10 degrees. This means it will be *extremely* massive and close to the surface, and that every plumb bob within (some radius) in going to be skewed from the normal in the direction of the anomaly. Is such an effect observed? No. All the effects point in the same direction, not consistent with a "spherical" gravitational field. In addition, there should be an inverse-square falloff. But the neighbors don't report the effect, do they? Is the city of Gold Hill built on a slant? And not just a slant, but a gradually decreasing slant as you move away from the "anomaly"?
Steven's story is a good yarn, but he's too smart to believe it. This is a purely perceptual illusion. You can try out "gravitational anomalies" like this in your friendly neighborhood science museum.
posted by rodii at 5:28 PM on February 20, 2001
Let's say we bury a bunch of neutronium in Gold Hill, Oregon. This has to be massive enough that it offsets the gravitational attraction of the entire earth and pulls "vertical" askew by 5 or 10 degrees. This means it will be *extremely* massive and close to the surface, and that every plumb bob within (some radius) in going to be skewed from the normal in the direction of the anomaly. Is such an effect observed? No. All the effects point in the same direction, not consistent with a "spherical" gravitational field. In addition, there should be an inverse-square falloff. But the neighbors don't report the effect, do they? Is the city of Gold Hill built on a slant? And not just a slant, but a gradually decreasing slant as you move away from the "anomaly"?
Steven's story is a good yarn, but he's too smart to believe it. This is a purely perceptual illusion. You can try out "gravitational anomalies" like this in your friendly neighborhood science museum.
posted by rodii at 5:28 PM on February 20, 2001
You're right, rodii. I have no doubt that the Oregon Vortex is nothing more than a funhouse gag. I posted before rereading what Steven had said regarding the error in bubble levels. I'd have to see that to believe it!
posted by gimli at 6:05 PM on February 20, 2001
posted by gimli at 6:05 PM on February 20, 2001
Rodii, what I wrote was the truth as I know it. In the center of the Vortex it's possible to stand a broom up and let go without it falling down. The reason is that at the center, the direction "down" all around there pushes towards the center; it's slanted slightly. So standing vertically is the lowest potential for the broom. Any attempt to lean is "going up" and thus requires energy which isn't present unless someone nudges it.
See this picture; the black lines show an exaggerated view of the effective "down" at each point. (This effect was, I believe, confirmed by shining a levelled laser beam through as a reference and comparing it to a bubble level.)
And large-scale gravitational effects are very real. It's the reason that satellites typically carry about a quarter of their weight in fuel. They have to have their orbits constantly adjusted to keep them where we want them using small rocket motors. Most satellites reach the end of their lives when they run nearly out of fuel, even if the electronics still work. At that point, LEO satellites use their last fuel to descend into the atmosphere to burn up. Geosynchronous satellites use their last fuel to enter an elliptical parking orbit which has been designated as a graveyard because it would require too much delta-V to hit the planet. (All of this is done under ground control.) It's a sufficiently rare event for a satellite to become useless for non-fuel reasons that it usually makes the news.
The use of perceptual illusions happens at a lot of these kinds of attractions (like the one in the Bay area), but the Oregon Vortex not only uses perceptural illusions but also has a very real phenomenon -- albeit completely within the laws of physics. The two are not mutually exclusive.
posted by Steven Den Beste at 9:13 PM on February 20, 2001
See this picture; the black lines show an exaggerated view of the effective "down" at each point. (This effect was, I believe, confirmed by shining a levelled laser beam through as a reference and comparing it to a bubble level.)
And large-scale gravitational effects are very real. It's the reason that satellites typically carry about a quarter of their weight in fuel. They have to have their orbits constantly adjusted to keep them where we want them using small rocket motors. Most satellites reach the end of their lives when they run nearly out of fuel, even if the electronics still work. At that point, LEO satellites use their last fuel to descend into the atmosphere to burn up. Geosynchronous satellites use their last fuel to enter an elliptical parking orbit which has been designated as a graveyard because it would require too much delta-V to hit the planet. (All of this is done under ground control.) It's a sufficiently rare event for a satellite to become useless for non-fuel reasons that it usually makes the news.
The use of perceptual illusions happens at a lot of these kinds of attractions (like the one in the Bay area), but the Oregon Vortex not only uses perceptural illusions but also has a very real phenomenon -- albeit completely within the laws of physics. The two are not mutually exclusive.
posted by Steven Den Beste at 9:13 PM on February 20, 2001
> The two are not mutually exclusive.
No, you're right, they're not. Someone could be sitting on a wonder of nature and decide to screw it up with ugly idiocy, because you can sell tickets to ugly idiocy. See the US side of Niagara Falls, for example.
But strictly concerning this vortex stuff: you really, really believe what you write? You swear that you and your postings here are not just a pair of long-winded trolls? Because you're wrong, and I just want to know whether you're sincerely wrong or just hoping to mess with us.
Here's a very simple way to know that these vortexes don't exist, without any of us even having to go and look: imagine they did exists. Imagine they really worked the way their owners and barkers and ticket-takers and postcard salesmen say they do.
Such places would be declared state or national parks, they would be studied by real scientists and talked about in real mainsteam journals, they would be visited by famous people, and so on. They would not be tourist traps on the scale of roadside 'alligator farms' in Florida.
posted by pracowity at 11:12 PM on February 20, 2001
No, you're right, they're not. Someone could be sitting on a wonder of nature and decide to screw it up with ugly idiocy, because you can sell tickets to ugly idiocy. See the US side of Niagara Falls, for example.
But strictly concerning this vortex stuff: you really, really believe what you write? You swear that you and your postings here are not just a pair of long-winded trolls? Because you're wrong, and I just want to know whether you're sincerely wrong or just hoping to mess with us.
Here's a very simple way to know that these vortexes don't exist, without any of us even having to go and look: imagine they did exists. Imagine they really worked the way their owners and barkers and ticket-takers and postcard salesmen say they do.
Such places would be declared state or national parks, they would be studied by real scientists and talked about in real mainsteam journals, they would be visited by famous people, and so on. They would not be tourist traps on the scale of roadside 'alligator farms' in Florida.
posted by pracowity at 11:12 PM on February 20, 2001
I don't think anyone is disputing that large-scale gravitational effects are real. Small-scale gravitational effects, however, are not, at least not with the power to affect highly massive bodies like, uh, bodies.
What pracowity said. Come on, I know we have some real physicists here. I'm too lazy (and rusty) to do the math. but take a look at the relative masses of the earth and a broom, how much mass it would take to pull that broom 5 degrees out of line, and the other effects a mass of that magnitude would have. Unless there's some kind of directional gravity, it just can't happen.
posted by rodii at 6:29 AM on February 21, 2001
What pracowity said. Come on, I know we have some real physicists here. I'm too lazy (and rusty) to do the math. but take a look at the relative masses of the earth and a broom, how much mass it would take to pull that broom 5 degrees out of line, and the other effects a mass of that magnitude would have. Unless there's some kind of directional gravity, it just can't happen.
posted by rodii at 6:29 AM on February 21, 2001
But from the viewpoint of a physicist there isn't anything interesting about the Oregon Vortex. From the viewpoint of a geologist it might be interesting to try to figure out what the high density mass is and how it was formed. It's certainly not something that justifies a National Park; we're not talking about Yosemite or Yellowstone here.
Rodii, all gravity is directional. And there's no theoretical problem with localized gravitational anomalies; all it requires is a large dense mass.
posted by Steven Den Beste at 7:26 AM on February 21, 2001
Rodii, all gravity is directional. And there's no theoretical problem with localized gravitational anomalies; all it requires is a large dense mass.
posted by Steven Den Beste at 7:26 AM on February 21, 2001
I'm with rodii. I'd like to see just how large and dense this mass would have to be to overcome or deflect the earth's gravity in a localized area. My suspicion is that it would have to be incredibly dense and compact. The deflection of satellites can be explained by mountain ranges and mineral deposits. Localized, near-earth effects are a whole different kettle of fish. If it did exist, I think it would merit a national park. Physicists and geologists would be all over it and the funhouse would would have been removed.
posted by gimli at 8:12 AM on February 21, 2001
posted by gimli at 8:12 AM on February 21, 2001
Copperfield's Statue of Liberty illusion was done with a huge turntable, by the way. As in, a turntable big enough for the audience and cameras to all be sitting on. He put up the curtain, turned off the lights, and rotated everyone to face out towards nothing. Then he removed the curtain, and the lights pointed out at where the Statue wasn't (with helicopters circling above).
It's in the book Big Secrets. Or Bigger Secrets, or Biggest Secrets. I have all three, and I forget which stuff is in which one. They're a great read, all by William Poundstone.
Count me among those who can't believe that SDB is really that gullible about the "increased gravity spot" thing...
posted by beth at 3:49 PM on February 21, 2001
It's in the book Big Secrets. Or Bigger Secrets, or Biggest Secrets. I have all three, and I forget which stuff is in which one. They're a great read, all by William Poundstone.
Count me among those who can't believe that SDB is really that gullible about the "increased gravity spot" thing...
posted by beth at 3:49 PM on February 21, 2001
Rodii, all gravity is directional.
F = Gm1m2/d2
Where's the directionality?
posted by rodii at 5:12 PM on February 21, 2001
F = Gm1m2/d2
Where's the directionality?
posted by rodii at 5:12 PM on February 21, 2001
"F" is a vector, not a scalar.
posted by Steven Den Beste at 6:26 PM on February 21, 2001
posted by Steven Den Beste at 6:26 PM on February 21, 2001
"F" is a vector, but we're dealing with a third "m". We need to find out what the value of this third "m" needs to be in order to have an observable influence on "F". I think. God, I'm rusty.
posted by gimli at 7:32 AM on February 22, 2001
posted by gimli at 7:32 AM on February 22, 2001
Yes Steven (sigh) F is a vector, but gravity is not directional in any sense that concerns us here. The F on any two particles is not going to be parallel (except in the trivial case in which they and the center of gravity of the attracting body are collinear). If you draw a sphere (or whatever shape the "equipotential surface" is) around the attracting body, the force from that body will be normal to its surface, right? And spheres are curved, not flat, right? (That is, "equipotential surfaces" are closed.) So if it *appears* that their local "down" is parallel (the "gravity is directional" case) , the attracting body must be very far away, far enough that the curvature of the sphere is unnoticeable, and every other body at that same large distance will be equally attracted to the "anomaly."
But this isn't what you're claiming. You're claiming the effects are localized (to the Mystery Spot) *and* parallel (so various people can stand "at a slant" at various points in space). But if the sphere is small (your "localized gravitational anomaly"), local "down" will be different depending on where you're located, and people on the other side of the Mystery Spot are going to leaning at a different funny angle. They're not. If the sphere is big enough so that this effect is negligible, than the Mystery Spot effects are going to be felt over a wide area, and people on the other side of Gold Hill, Oregon are still going to be leaning at a different funny angle. They're not.
Really, all this is obvious, and I apologize for belaboring it. If it's obvious to a Bear of Very Little Brain like me, I should think it's trivially obvious to a smart engineer like Steven, which is why I say he's yankin' our chains.
posted by rodii at 8:41 AM on February 22, 2001
But this isn't what you're claiming. You're claiming the effects are localized (to the Mystery Spot) *and* parallel (so various people can stand "at a slant" at various points in space). But if the sphere is small (your "localized gravitational anomaly"), local "down" will be different depending on where you're located, and people on the other side of the Mystery Spot are going to leaning at a different funny angle. They're not. If the sphere is big enough so that this effect is negligible, than the Mystery Spot effects are going to be felt over a wide area, and people on the other side of Gold Hill, Oregon are still going to be leaning at a different funny angle. They're not.
Really, all this is obvious, and I apologize for belaboring it. If it's obvious to a Bear of Very Little Brain like me, I should think it's trivially obvious to a smart engineer like Steven, which is why I say he's yankin' our chains.
posted by rodii at 8:41 AM on February 22, 2001
I've already said that what I'm posting here is sincere. Gravity is directional, which means it points at something. At any given point in the universe except at the bottoms of gravity wells, there is a single direction which is "down", and all other directions are "not down". "Down" is the direction such that if you move in that direction you yield the maximum amount of increased kinetic energy per distance moved. It comes from conversion of potential energy. "Up" is the vector inverse of "down". But "down" is controlled by all nearby masses; there's nothing sacred about the vector which points at the mathematical center of the nearest large object and "down" may not point in that direction.
Everyone knows that the tides are caused by the gravity of the moon and sun. But consider what that means: it means that "down" for various parts of the ocean varies as a function of where the moon is; it's not just controlled by the earth. "Down" changes constantly as the earth rotates and thus the relative position of the moon changes.
The formula for gravity is in fact a bit simplistic because it assumes that the masses are mathematica points. Under some circumstances it's possible to pretend that a non-point mass is a point located at its center of gravity, but that only works if the distance to the mass is drastically larger than its actual diameter. Once you're within three or so diameters of the mass, it's necessary to decompose it. In other words, to really get the right answer you can't treat the earth as a single mass; you have to treat it as a billion small masses all at slightly different locations (say, every 5 mile cube making up the volume of the earth), and compute the gravitational force each of those billion masses exerts on you or whatever you're trying to calculate the force for.
Each of those decomposed masses yields a force vector (and rodii, it really is directional) and the total force is the vector sum of all of them. If you use the scalar sum you'll get the wrong answer.
If the Gravitational formula was inverse linear, the effects of the actual locations of all those decomposed masses wouldn't matter much. But inverse square changes everything, so that close masses disproportionately add to the overall vector sum. As a result, if one of those decomposed masses is particularly dense and particularly close, it can disproportately influence the vector sum, controlling not just the magnitude of the vector but also its direction. That's what mountains do to satellites, and that's what's going on at the Oregon Vortex. The technical term is mascon (mass concentration, at least regarding the moon) and if you're near one but off to the side of it, it will locally influence the direction of "down" so that the vector doesn't point to the center of gravity of the Earth (essentially the mathematical center of the body, though not quite).
Despite Newton's great achievement in finding the universal law of gravitation, gravity is easily the least well understood of the four forces. General Relativity says that gravity isn't really a force at all, but rather a side effect of curved space. While GR has made important predictions which turned out to be true, it also has made some which are wrong. So that book is open yet; the real answer is probably similar to GR but different in certain important regards. For the moment, GR is the best theory of gravity available but it's known to be incomplete.
But the math involved in applying gravity to specific circumstances is still fiendishly complex and not at all well understood. If the universe contains exactly two masses and if their starting positions and velocities are known, then it's possible to build formulas which will yield their positions and velocities at any arbitrary time in the future. But as soon as you toss a third mass in, no solution is known. (Let alone the real universe which has quadrillions of masses.) The only solution known is brute force simulations, with all the drawbacks of cumulative error implicit in the approach.
There's a very well understood example, which probably can't happen in the real universe, which demonstrates that you can't always use the "point at the center of gravity" approach. Suppose that someone builds a mathematically perfect hollow sphere with the mass of the sun, and suppose you're inside it. What direction will you fall?
Intuitively you'd expect to fall towards the mathematical center of the sphere, since that's the center of gravity. In actuality there is no force on you at all, and you won't fall in any direction whatever. The gravitational forces always balance; the vector sum always has a magnitude of zero irrespective of where you are inside the sphere. This can be proved mathematically, and it's a lesson taught in every physics class about gravity that I ever took to make sure that people don't always assume that masses are points.
In a mission filled with astounding finds, the single most astounding find of the Voyager mission was the extremely complex structure of Saturn's rings. They still haven't explained them. It's known to be the result of gravitational influence of Saturn's moons, but no-one knows how yet.
In the meantime, mascon's are well understood and not mysterious, and they can indeed cause very localized influences. The effect is not strong and it doesn't explain everything at the Oregon Vortex (much of it is due to suggestion and optical illusion, as mentioned). But suggestion and optical illusion won't explain why a broom will stand on end without falling over at the very center of the Vortex. A localized mass concentration explains that quite nicely.
posted by Steven Den Beste at 1:12 PM on February 22, 2001
Everyone knows that the tides are caused by the gravity of the moon and sun. But consider what that means: it means that "down" for various parts of the ocean varies as a function of where the moon is; it's not just controlled by the earth. "Down" changes constantly as the earth rotates and thus the relative position of the moon changes.
The formula for gravity is in fact a bit simplistic because it assumes that the masses are mathematica points. Under some circumstances it's possible to pretend that a non-point mass is a point located at its center of gravity, but that only works if the distance to the mass is drastically larger than its actual diameter. Once you're within three or so diameters of the mass, it's necessary to decompose it. In other words, to really get the right answer you can't treat the earth as a single mass; you have to treat it as a billion small masses all at slightly different locations (say, every 5 mile cube making up the volume of the earth), and compute the gravitational force each of those billion masses exerts on you or whatever you're trying to calculate the force for.
Each of those decomposed masses yields a force vector (and rodii, it really is directional) and the total force is the vector sum of all of them. If you use the scalar sum you'll get the wrong answer.
If the Gravitational formula was inverse linear, the effects of the actual locations of all those decomposed masses wouldn't matter much. But inverse square changes everything, so that close masses disproportionately add to the overall vector sum. As a result, if one of those decomposed masses is particularly dense and particularly close, it can disproportately influence the vector sum, controlling not just the magnitude of the vector but also its direction. That's what mountains do to satellites, and that's what's going on at the Oregon Vortex. The technical term is mascon (mass concentration, at least regarding the moon) and if you're near one but off to the side of it, it will locally influence the direction of "down" so that the vector doesn't point to the center of gravity of the Earth (essentially the mathematical center of the body, though not quite).
Despite Newton's great achievement in finding the universal law of gravitation, gravity is easily the least well understood of the four forces. General Relativity says that gravity isn't really a force at all, but rather a side effect of curved space. While GR has made important predictions which turned out to be true, it also has made some which are wrong. So that book is open yet; the real answer is probably similar to GR but different in certain important regards. For the moment, GR is the best theory of gravity available but it's known to be incomplete.
But the math involved in applying gravity to specific circumstances is still fiendishly complex and not at all well understood. If the universe contains exactly two masses and if their starting positions and velocities are known, then it's possible to build formulas which will yield their positions and velocities at any arbitrary time in the future. But as soon as you toss a third mass in, no solution is known. (Let alone the real universe which has quadrillions of masses.) The only solution known is brute force simulations, with all the drawbacks of cumulative error implicit in the approach.
There's a very well understood example, which probably can't happen in the real universe, which demonstrates that you can't always use the "point at the center of gravity" approach. Suppose that someone builds a mathematically perfect hollow sphere with the mass of the sun, and suppose you're inside it. What direction will you fall?
Intuitively you'd expect to fall towards the mathematical center of the sphere, since that's the center of gravity. In actuality there is no force on you at all, and you won't fall in any direction whatever. The gravitational forces always balance; the vector sum always has a magnitude of zero irrespective of where you are inside the sphere. This can be proved mathematically, and it's a lesson taught in every physics class about gravity that I ever took to make sure that people don't always assume that masses are points.
In a mission filled with astounding finds, the single most astounding find of the Voyager mission was the extremely complex structure of Saturn's rings. They still haven't explained them. It's known to be the result of gravitational influence of Saturn's moons, but no-one knows how yet.
In the meantime, mascon's are well understood and not mysterious, and they can indeed cause very localized influences. The effect is not strong and it doesn't explain everything at the Oregon Vortex (much of it is due to suggestion and optical illusion, as mentioned). But suggestion and optical illusion won't explain why a broom will stand on end without falling over at the very center of the Vortex. A localized mass concentration explains that quite nicely.
posted by Steven Den Beste at 1:12 PM on February 22, 2001
Interesting but not very convincing. I had those physics classes too, and understand how the "center of gravity" approach is an approximation of a very large number of vector sums. I still don't see anything in the above except "it could happen." And I can't see how it would apply to the broom example unless the falloff was pretty damn steep--the force is so strong on one end of the broom that falling over would actually take a relative expenditure of energy?
Got any citations on this (no offense, but the mascon link is pretty unenlightening)?
(By the way, I don't think it's correct to say that general relativity says that gravity "isn't really a force at all", or is "merely a side effect of curved space." If GR is correct, a description of gravity as spacetime curvature and a description of gravity as a force would have to have the same structure mathematically. If we can't see those as compatible, that says more about our ability to conceptualize than about the physics--or so Feynman would say: the question isn't whether "it's a force" or "it's curvature", but "is this
posted by rodii at 1:47 PM on February 22, 2001
Got any citations on this (no offense, but the mascon link is pretty unenlightening)?
(By the way, I don't think it's correct to say that general relativity says that gravity "isn't really a force at all", or is "merely a side effect of curved space." If GR is correct, a description of gravity as spacetime curvature and a description of gravity as a force would have to have the same structure mathematically. If we can't see those as compatible, that says more about our ability to conceptualize than about the physics--or so Feynman would say: the question isn't whether "it's a force" or "it's curvature", but "is this
posted by rodii at 1:47 PM on February 22, 2001
Steven & Rodil:Will one of you just go there and stand a broom on it's end? Please?
posted by davidgentle at 8:27 PM on February 22, 2001
posted by davidgentle at 8:27 PM on February 22, 2001
Is that some kind of cryptic English insult? HUH? *mumble*
Metafilter ate my last paragraph. I know you're dying to know what the rest said but I can't remember the details. It was brilliant, though, I remember that. Put this whole issue definitively to rest, it did.
posted by rodii at 8:45 PM on February 22, 2001
Metafilter ate my last paragraph. I know you're dying to know what the rest said but I can't remember the details. It was brilliant, though, I remember that. Put this whole issue definitively to rest, it did.
posted by rodii at 8:45 PM on February 22, 2001
The MetaFilter Vortex eats parts of posts? Which way does the gravity have to pull in order to have that effect?
Growing up in Columbus, Ohio (home of Ohio State University and party to the notorious Michigan-Ohio State football rivalry), all schoolchildren were educated on the Midwest's own peculiar gravitational anomaly. Q: Why do all the trees in Ohio lean north? A: Because Michigan sucks. So the existence of these kinds of "vortexes" have been anecdotally documented for decades.
posted by kindall at 3:01 AM on February 23, 2001
Growing up in Columbus, Ohio (home of Ohio State University and party to the notorious Michigan-Ohio State football rivalry), all schoolchildren were educated on the Midwest's own peculiar gravitational anomaly. Q: Why do all the trees in Ohio lean north? A: Because Michigan sucks. So the existence of these kinds of "vortexes" have been anecdotally documented for decades.
posted by kindall at 3:01 AM on February 23, 2001
Rodii, when I said "GR says that gravity isn't really a force" that's not really something that comes out of GR as much as a later interpretation based on a new theory of what a force is. According to current theory, forces are the result of exchange of particles: the photon for EM, gluons for the strong force, and the intermediate vector boson for weak force.
GR says that no particle is exchanged for gravity -- which would mean that gravity isn't really a "force" according to the current definition of force. This is an active area of research, because physicists hate asymmetry and they'd really love to add the graviton to the stable of particles. Unfortunately, they're probably going to have to accept that gravity is different since it's the only one of the forces which does curve space. There's no experimental evidence for the graviton; the only reason to suspect its existence is by analogy.
In the more collocquial sense of force as a way in which two or more objects interact, clearly gravity is a force.
posted by Steven Den Beste at 6:32 AM on February 23, 2001
GR says that no particle is exchanged for gravity -- which would mean that gravity isn't really a "force" according to the current definition of force. This is an active area of research, because physicists hate asymmetry and they'd really love to add the graviton to the stable of particles. Unfortunately, they're probably going to have to accept that gravity is different since it's the only one of the forces which does curve space. There's no experimental evidence for the graviton; the only reason to suspect its existence is by analogy.
In the more collocquial sense of force as a way in which two or more objects interact, clearly gravity is a force.
posted by Steven Den Beste at 6:32 AM on February 23, 2001
Yes, that's what the disappeared part of my post was about. But the search for the Higgs boson means there are more fundamental things going on too. But we digress. . .
posted by rodii at 6:46 AM on February 23, 2001
posted by rodii at 6:46 AM on February 23, 2001
My new philosophy:
If a broom doesn't fall in the woods, but there's nobody there to see it...
posted by gimli at 7:31 AM on February 23, 2001
If a broom doesn't fall in the woods, but there's nobody there to see it...
posted by gimli at 7:31 AM on February 23, 2001
« Older The new Mahir? | Newer »
This thread has been archived and is closed to new comments
posted by jjg at 12:49 AM on February 20, 2001