Douglas Adams, in his Hitchiker’s Guide to the Galaxy books, once suggested that falling was akin to an ingrained habit. If you could just forget about falling, you could defy gravity and fly. It works as a joke, but in real life gravity is pretty unforgiving.
So you can imagine my surprise when I came across “gravity deniers” trolling at Tara Smith’s Aetiology blog. Tara was dumbfounded that anyone could deny the so-called “germ” theory of infectious disease, since there has been so much evidence since Louis Pasteur’s time that bacteria, viruses, and single-celled parasites cause a wide variety of illnesses. Yet, it seems, just as there are souls who deny the connection between HIV and AIDS or the validity of the theory of evolution, there are some who deny that “germs” cause disease.
One of the commenters, jspreen, claimed that poverty caused disease, noting that poor people seem disproportionately more susceptible to infectious diseases than richer people. Someone else claimed that Pasteur had recanted his support of the germ theory on his deathbed. I commented that jspreen was confusing correlation with causation, and closed my comment with this snarky remark:
By the way, I heard that Newton confessed on his deathbed that gravity did not exist. He was dreadfully sorry he ever came up with the idea.
Little did I know that my snide remark would end up hijacking the thread. To wit, here is what a germ-denier named Wilhelm had to say:
Who wants to deny gravity? I do. There IS no gravity force, and Newton had it wrong. Just take a bag holding 10 pounds of whatever, and hold it with your arm stretched out in front of you. After a while, your arm muscles get tired. Not surprising, because you expended energy, resisting gravitation. But… what is the energy source that is responsible for this “gravitational force”? Shouldn’t that get depleted also? (Think of the 1st Law of Thermodynamics)
The earth has been around for a long time. If there was any energy depletion, we should have measured that somehow.
So what’s a force for which there is no energy source? Answer: A non-existing force.
Now, there are so many confused thoughts in those few sentences that it might take an entire course in physics to untangle the mess. I resisted the temptation to reply — difficult for a physics teacher.
Then after a few more comments more pertinent to Tara’s original post, a commenter named dot weighs in on the subject:
denying gravity – Is there anywhere to debate this? It looks fun.
For example: could, rather than being a ‘force’, gravity be the effect a mass has on spacetime (like the general relativity theory or gravity). If this is the case, rather than an object ‘falling’ (as in moving toward the ground due to gravity), the distance between the ground and the object could be getting smaller due to mass ‘bending the universe’: Objects we perceive as being held still are actually moving away from the ground at the same rate as the distance between the object and the ground is shrinking.
Of course this would also mean that unless another force is acting upon everything (i.e the force of big bang), the universe would be shrinking, not expanding.
Thats my theory anyway – its probably already been disproven.
Now dot comes closer to understanding the physics than wilhelm, but she’s still missing the barn by a country mile.
robster and I attempted some basic physics instruction at this point, but dot was unconvinced.
So then, wheatdogg & robster, where does the energy expended to keep the object from falling go? What form does the energy used take? After all, energy doesn’t just disappear.
Gravitational Potential Energy doesn’t account for objects that remain a static distance from the ground: the potential energy does not increase.
The graviton particle model may or may not explain it: that particles move between the object and the ground MAY indicate that the energy the arm expends increases the mass of the object, which in turn is transferred to the ground in the form of graviton particles. This could indicate that the mass of the planet is increased by gravity.
This is, of course, all conjecture as the theory of gravity provides good predictions but we do not currently know why it works.
I’m not getting into discussing ‘intelligent falling’ as, even if we can prove how gravity works, the religious people will just say thats god’s method for doing it just like with evolution: the single, universal and indisputable cause for everything approach.
(“Intelligent falling,” by the way, refers to an article in The Onion satirizing intelligent design.)
And later on,
Robster, what I meant by objects remaining a static distance from the earth was when you hold them at a static distance. If the energy is used for work and some is lost as heat, what work is that energy being used for if the object is being held at stationary distance from the ground, as the energy in the object is not changing (as Davis pointed out) but energy is being lost by the arm. Is it all heat?
Davis, that doesn’t answer Wilhelm’s point which I was referring to: why does your arm get tired after holding up a 10 pound object for a while? Where does that energy go if there is no change in that of the object?
Robster offers some more clarification, and then dot replies:
The arm works to hold the object, I’m not disputing that. What I am questioning is where does that kinetic energy go/what does it do if the object is not moving (i.e being held still). Yes muscle fibres move, but the kinetic energy doesn’t stop there.
Working from the assumption that gravity is a ‘force’ that pulls things toward it, the kinetic energy would go to counterbalancing that ‘force’.
My theory is that gravity, rather than pulling things toward it, it bends space so that the distance between the source of gravity and the bag is constanty getting smaller. The kinetic energy would be used to move the bag away from the ground rather than hold it in the same place, but would have the overall effect of keeping it in the apparent same place.
Either way you get tired and the bag does not fall.
(note: the “is it all heat?” comment was sarcasm (when in Rome, do as the Romans do))
As for the hook, I’ll work out an explanation, elasticity might be a good place to start.
Robster and I each posted another comment after dot’s last one, but I decided to work up a post here about the whole gravity denial thing.
Wilhelm seems to be a classic denier of all current scientific thought, be it germ theory or the standard model of particles and interactions. His convoluted comment tangles up fuzzy understandings of energy, thermodynamics, forces and gravity into a mush. Since he cannot reconcile his fuzzy understanding of physics as it is, he concludes that it must be wrong.
Dot, on the other hand, is not a denier, but a “misunderstander.” She’s got some of the concepts down, but imperfectly, so she can’t see the contradictions in her own explanations. She’s on the physics “short bus,” while Wilhelm just missed it entirely.
I suspect they are not alone. The American Association of Physics Teachers (AAPT), about 20 years ago, reported that less than 20% of high school graduates nationally had taken a course in physics before graduation. (The rate is now closer to 30% — still no great shakes.) Presumably, the other 70-80% may have had some physical science in middle school or in the 9th grade, which guarantees that they remembered none of what they were taught by the time of their graduation.
Physics is a tricky subject to teach. Like math, it can be very abstract while describing some very concrete things. We expect students to master physics in a year, but the truth is few students really understand the subject well enough after one course to discuss it authoritatively. They remember bits and pieces, and in time the bits and pieces get jumbled up with ideas pulled from other sources of information. We can well imagine how blissfully entirely unaware of physics concepts that other 80% is.
Energy is one concept in physics that has gotten completely fouled up by the popular press and new-age thinkers, who equate it with all sorts of esoteric, mystical concepts. Popular treatments of Einstein’s relativity, while usually very well done, leave some readers and viewers with a vague sense that gravity is an illusion, a result of the curvature of spacetime by massive objects like Earth, and that Newton had it all wrong.
So, Adams’ suggestion of forgetting about falling is a wry comment about that fuzzy concept of gravity-as-illusion. Einstein, though he suggested gravity was not per se a force, never recommended that people try to deny its effects. Things fall. Gravity sucks. It’s as easy as that.
Wilhelm, meanwhile, mangles the concept of energy to suggest that there must be some energy source powering the gravitation pull of Earth, much as burning gasoline powers a car’s engine. Since it appears Earth gets its “gravity power” from nowhere, a violation of the First Law of Thermodynamics, he concludes that gravity does not exist as a force.
If Wilhelm is correct, his feet need never touch the ground. He can fly around with Superman.
Dot later on also betrays some fundamental misconceptions about energy, forces and gravity, as well as a passing familiarity with general relativity. So robster and I tried to tutor her, perhaps with some success. We’ll see.
Physics (and I try to get my students to understand this subtlety) is a model of the “real” universe. Since Galileo’s and Kepler’s days in the early 1600s, we have built up a model of the universe that holds up remarkably well. Newton and Einstein had two diametrically different models of how gravity works, and the truth of the matter is that we still do not understand gravity as well as, say, magnetism.
Newton conceived of particles exerting forces on one another, either by contact or across distances, like gravitation. His laws of motion were a powerful tool in understanding how the universe works, but Newtonian physics has its limitations.
After Newton’s death, several scientists developed another model for the behaviour of the universe, the concept of energy. Unlike the nearly immediate acceptance of the Newtonian model, it took nearly 150 years for science to embrace the energy theory as valid. The “energists” had to accumulate sufficient evidence that their energy model gave the same results as the Newtonian model — the correspondence principle that knits the various fields of physics into a coherent whole.
Energy is defined as the capacity to do work. Work is the product of a component of a force moving an object along the direction of that component. Work equals the change in energy of an object or system. We always specify what we are doing work ON.
Notice the word, “moving.” Holding a 10-pound sack does not result in your doing work ON the sack. Gravity is also doing no work on the sack. No work means no energy change for the sack, and to address Wilhelm’s challenge, no energy “expenditure” by the earth. When the sack falls, the earth’s gravity does work on the sack, since it moves toward the ground. The earth moves imperceptively upward at the same time, as Newton’s Third Law predicts.
Energy is defined as the capacity to do work, not as the capacity to exert a force, as Wilhelm suggests. Forces, in fact, change the energy of objects and systems, not the other way around. Otherwise, we would have to scrap both Newton’s laws (which work really, really well 99% of the time) and the laws of energy, work and thermodynamics. I’ll let WIlhelm work out those details and eat my hat if he later wins a Nobel prize in physics.
Einstein, for his part, succeeded in turning Newtonian physics on its ear. His conception of gravity resulted from his earlier work with the effects of motion on time, space and matter. If you could travel at near-light speed, your observations of the world around you would be distorted. It would appear, for example, that external objects were curving around you as you approached them.
Special relativity dealt with constant velocities. General relativity dealt with non-constant velocities, accelerations, and gravitation. Einstein proposed that the attraction of two objects toward each other results not from a force they exchange but from the curvature of the space in which they exist.
The Sun, for example, with its 1030 kilograms of mass warps the space around it quite a bit. The planets are moving inertially through that space, as Newton’s First Law dictates, but the space is curved. So we see the planets follow elliptical paths. Light, meanwhile, must also curve as its passes by the Sun, since it has to travel through that same space. Einstein’s 1916 calculation of the deviation of starlight grazing the sun and its verification in 1919 during a solar eclipse propelled the fluffy-haired scientist into worldwide fame. As strange as it seems, space has shape, and objects move according to that shape, much as a ball rolls down a hill.
Now I think dot has picked up on some of these ideas, and perhaps Wilhelm too in his denialist fashion, but neither “gets” the big picture. A person with just a hazy sense of physical concepts cannot develop singlehandedly an entirely new model of physics. After 400 years of effort by countless men and women, physics as a science is pretty well undeniable. Gravity, specifically, is here to stay, folks, no matter how hard you try to forget it.