Gravitational anomalies across Illinois, Indiana and Ohio: red means higher than average, blue is lower than average
- The law of gravity may be universal, gravity itself varies considerably across the earth.
- Most factors can be mathematically accounted for; local geology is the odd one out.
- Bouguer gravity anomaly maps like these show regional gravitational variation.
Apple and tree
Isaac Newton's apple tree at Woolsthorpe Manor, Lincolnshire. In the background: the house where he was born.
Image: arthurmarris, CC BY-SA 3.0
What a weird place this planet is. But especially southern Illinois, according to this map of gravity anomalies across three Midwestern states.
Gravity is what made the apple fall from a certain tree (in Woolsthorpe, Lincolnshire), causing Newton to wonder why it fell down straight. But the law of universal gravitation he formulated (and published in 1687) by way of explanation is a lot less uniform than you'd think.
For gravity does vary across the earth, meaning Newton's apple has a slightly different weight in various other parts of the world and falls at slightly different speeds. That's due to a combination of four factors.
- First, there's a latitudinal effect. The earth is not perfectly round: it's flatter nearer to (and flattest at) the poles and bulges more towards (and most along) the equator. As a result, the distance from the earth's center to sea level is 13 miles (21 km) greater at the equator than at the poles. The latitude you're at has an effect on gravity, with polar and equatorial extremes: Newton's apple (and you) weigh 0.5% more at the poles than at the equator.
- Secondly, there's a rotational effect. That difference in gravity between the poles and the equator is only partly due to gravity itself; it's also caused by the fact that the earth spins faster at the equator.
Invisible elevations
Bouguer gravity anomaly map of Illinois, Indiana and Ohio. Red means higher than average anomalies, blue means lower than average ones.
Image: USGS
- Then there's an altitudinal effect. Earth's gravitational pull depends on your distance from its center. Gravity diminishes with altitude – but again, with fairly limited effect. If you're 16,400 feet (5 km) up a mountain, you weigh 99.84% of what the scales would say at sea level.
- Fourth differentiator: the tidal pull of the moon and sun. Although this has visible, repetitive and significant effects – the ebb and flow of sea levels – the variations this causes in the earth's gravity are very small indeed.
- Final factor: an area's geological makeup. The density of certain rock types has an effect on the force of gravity. Areas with higher subsurface rock density have higher than average gravity, and vice versa. Mountains increase gravitational density, ocean trenches decrease it. The effect is usually not greater than 0.01%.
While the first four factors can be compensated for mathematically, it's the local geology which produces random gravity anomalies of the kind mapped here.
This is a Bouguer gravity anomaly map, showing gravity variations resulting from lateral density variations in the earth. It looks like a relief map of invisible elevations and imperceptible depressions, grouped together in plateaus and peaks of higher-than-average pull and valleys and troughs of lower-than-average gravity.
Global anomalies
Of course, gravity anomalies are not exclusive to Illinois, Indiana and Ohio. Here's a gravity anomaly map of the entire earth, in two hemispheres.
Image: NASA
The Bouguer (pronounced boo-gay) gravity anomaly is named after French scientist Pierre Bouguer (1698-1758), a prodigy who succeeded his father as professor of hydrography at the tender age of 16. Among his many discoveries was the fact that small regional variations in the earth's gravity field could be related to the varying density of subterraneous rocks in the subsurface.
The values on this map are expressed in milligals, 1/1000th of a Gal (short for Galileo), which is the unity of gravity, equal to 1 cm/sec2. Positive anomalies (i.e. greater density than average) occur in areas colored red. Negative anomalies (less density than average) are found in areas colored blue.
It looks like Newton's apples weigh a bit more in southern Illinois than they do on average, and a bit less in central Indiana and large parts of Ohio. While these anomalies may only account for variations in decimal points, the difference is big enough to have measurable effects: these gravitational anomalies cause the sea to bulge in certain places, and throw pendulum clocks out of sync.
What's the anomaly in your neck of the woods? Check out this page at the International Gravimetric Bureau.
Strange Maps #999
Bouguer gravity anomaly map found here at the USGS. Map of global gravity anomalies found here at NASA's Earth Observatory.
Got a strange map? Let me know at strangemaps@gmail.com.
Does science tell the truth? The answer to this question is not as simple as it seems, and my 13.8 colleague Adam Frank took a look at it in his article about the complementarity of knowledge. There are many levels of complexity to what truth is or means to a person or a community. Why?
It's complicated
First, "truth" itself is hard to define or even to identify. How do you know for sure that someone is telling you the truth? Do you always tell the truth? In groups, what may be considered true to a culture with a given set of moral values may not be true in another. Examples are easy to come by: the death penalty, abortion rights, animal rights, environmentalism, the ethics of owning weapons, etc.
At the level of human relations, truth is very convoluted. Living in an age where fake news has taken center stage only corroborates this obvious fact. However, not knowing how to differentiate between what is true and what is not leads to fear, insecurity, and ultimately, to what could be called worldview servitude — the subservient adherence to a worldview proposed by someone in power. The results, as the history of the 20th century has shown extensively, can be catastrophic.
Proclamations of final or absolute truths, even in science, shouldn't be trusted.
The goal of science, at least on paper, is to arrive at the truth without recourse to any belief or moral system. Science aims to go beyond the human mess so as to be value-free. The premise here is that Nature doesn't have a moral dimension, and that the goal of science is to describe Nature the best possible way, to arrive at something we could call the "absolute truth." The approach is a typical heir to the Enlightenment notion that it is possible to take human complications out of the equation and have an absolute objective view of the world. However, this is a tall order.
It is tempting to believe that science is the best pathway to truth because, to a spectacular extent, science does triumph at many levels. You trust driving your car because the laws of mechanics and thermodynamics work. NASA scientists and engineers just managed to have the Ingenuity Mars Helicopter — the first man-made device to fly over another planet — hover above the Martian surface all by itself.
We can use the laws of physics to describe the results of countless experiments to amazing levels of accuracy, from the magnetic properties of materials to the position of your car in traffic using GPS locators. In this restricted sense, science does tell the truth. It may not be the absolute truth about Nature, but it's certainly a kind of pragmatic, functional truth at which the scientific community arrives by consensus based on the shared testing of hypotheses and results.
What is truth?
But at a deeper level of scrutiny, the meaning of truth becomes intangible, and we must agree with the pre-Socratic philosopher Democritus who declared, around 400 years BCE, that "truth is in the depths." (Incidentally, Democritus predicted the existence of the atom, something that certainly exists in the depths.)
A look at a dictionary reinforces this view. "Truth: the quality of being true." Now, that's a very circular definition. How do we know what is true? A second definition: "Truth: a fact or belief that is accepted as true." Acceptance is key here. A belief may be accepted to be true, as is the case with religious faith. There is no need for evidence to justify a belief. But note that a fact as well can be accepted as true, even if belief and facts are very different things. This illustrates how the scientific community arrives at a consensus of what is true by acceptance. Sufficient factual evidence supports that a statement is true. (Note that what defines sufficient factual evidence is also accepted by consensus.) At least until we learn more.
Take the example of gravity. We know that an object in free fall will hit the ground, and we can calculate when it does using Galileo's law of free fall (in the absence of friction). This is an example of "functional truth." If you drop one million rocks from the same height, the same law will apply every time, corroborating the factual acceptance of a functional truth, that all objects fall to the ground at the same rate irrespective of their mass (in the absence of friction).
But what if we ask, "What is gravity?" That's an ontological question about what gravity is and not what it does. And here things get trickier. To Galileo, it was an acceleration downward; to Newton a force between two or more massive bodies inversely proportional to the square of the distance between them; to Einstein the curvature of spacetime due to the presence of mass and/or energy. Does Einstein have the final word? Probably not.
Is there an ultimate scientific truth?
Final or absolute scientific truths assume that what we know of Nature can be final, that human knowledge can make absolute proclamations. But we know that this can't really work, for the very nature of scientific knowledge is that it is incomplete and contingent on the accuracy and depth with which we measure Nature with our instruments. The more accuracy and depth our measurements gain, the more they are able to expose the cracks in our current theories, as I illustrated last week with the muon magnetic moment experiments.
So, we must agree with Democritus, that truth is indeed in the depths and that proclamations of final or absolute truths, even in science, shouldn't be trusted. Fortunately, for all practical purposes — flying airplanes or spaceships, measuring the properties of a particle, the rates of chemical reactions, the efficacy of vaccines, or the blood flow in your brain — functional truths do well enough.
A Dadaist artist is painted with the ashes of burned banknotes during the financial crisis.
In a world gone mad, what can the few sane people left do? What can someone say when there are no words that seem up to the job? How can anyone hope to express ideas so terrible when doing so will only reduce those ideas?
These are some of the things that inspired the Dada movement, and in its absurd, surreal, and chaotic nonsense, we find the voice of the voiceless.
The origin of Dadaism
Dada was a response to the madness of World War I. Reasonable, intelligent, and sensitive people looked at the blood and mud graveyards of the trenches and wondered how any meaning or goodness could ever be found again. How can someone make sense of a world where millions of young, happy, hopeful men were scythed down in a spray of bullets? How could life go back to normal when returning soldiers, blinded and disfigured from gas, lay homeless in the streets? Out of this awful revulsion, there came one bitter voice, and it said: "Everything is nonsense."
Dada is the art of the nihilist. It smashes accepted wisdom, challenges norms and values, and offends, upsets, and provokes us to re-examine everything.
And so, the Dada movement expressed itself in absurdity. Tzara, the closest you get to a Dadaist philosopher, put it like this: "Like everything in life, Dada is useless. Dada is without pretension, as life should be." Dada rejects all systems, all philosophy, all definite answers, and all truth. It is the living embrace of contradictions and nonsense. It seeks "to confuse and upset people, to shake and jolt". It aims to shout down the "shamefaced sex of comfortable compromise and good manners," when actually "everything happens in a completely idiotic way."
In short, Dada is a response to the world when all the usual methods have broken down. It's the recognition that dinner party conversations, Hollywood blockbusters, and Silicon Valley are not how life actually is. This is a false reality and order, like some kind of veneer.
The Dada response to life is to embrace the personal and passionate madness of it all, where "the intensity of a personality is transposed directly, clearly into the work." It's to recognize the unique position of an artist, who can convey ideas and feelings in a way that goes beyond normal understanding. Art goes straight to the soul, but the intensity of it all can be hard to "enjoy" in the strictest sense.
Where is this Dada?
For instance, Dada is seen in the poems of Hugo Ball who wrote in meaningless foreign-sounding words. It's in Hausmann, who wrote works in disconnected phonemes. It's found in Duchamp's iconoclastic "Fountain" that sought to question what art or an artist really meant. It's in Hans Richter's short film "Ghost before Breakfast," which has an incoherent montage of images, loosely connected by the theme of inanimate objects in revolt. And, it's in Kurt Schwitters' "psychological collages" which present fragments of objects, juxtaposed together.
Dada is intended to shock. It's an artistic jolt asking, or demanding, that the viewers reorient themselves in some way. It is designed to make us feel uncomfortable and does not make for easy appreciation. It's only when we're thrown so drastically outside of our comfort zone in this way that Dada asks us to question how things are. It shakes us out of a conformist stupor to look afresh at things.
The paradox of Dadaism
Of course, like all avant-garde art, Dada needs to address one major problem: how do you stay so provocative, so radical, and so anti-establishment when you also seek success? How can maverick rebels stay so as they get a mortgage and want a good school for their kids? The problem is that young, inventive, and idealistic artists are inevitably sucked into the world of profit and commodity.
As Grayson Perry, a British modern artist, wrote: "What starts as a creative revolt soon becomes co-opted as the latest way to make money," and what was once fresh and challenging "falls away to reveal a predatory capitalist robot." With Dada, how long can someone actually live in a world of nonsense and nihilistic absurdity?
But there will always be new blood to keep movements like Dada going. As the revolutionaries of yesterday become the rich mansion-owners of today, there will be hot, young things to come and take up the mantle. There will always be something to challenge and questions to be asked. So, art movements like Dada will always be in the vanguard.
Dada is the art of the nihilist. It smashes accepted wisdom, challenges norms and values, and offends, upsets, and provokes us to re-examine everything. It's an absurd art form that reflects the reality it perceives — that life is nothing more than a dissonant patchwork of egos floating in an abyss of nothing.
Jonny Thomson teaches philosophy in Oxford. He runs a popular Instagram account called Mini Philosophy (@philosophyminis). His first book is Mini Philosophy: A Small Book of Big Ideas.
