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Albert Einstein's theory of gravity is generally explained in a wrong way


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Showing 1-3 of 3 posts in this discussion
Initial post: Feb 16, 2011, 8:30:00 AM PST
Rasih Bensan says:
About the misrepresentation of Albert Einstein's theory of gravity.

The way many physicists explain Albert Einstein's theory of gravity in TV and DVD documentaries, the way they write about it in books for the general public raises many questions and requires clarification.

In summary, according to these physicists Einstein stated that gravity is the warping of space - time by a massive object having considerable mass such as the sun. The planets orbit the sun because they have to follow the warping ( curvature ) of space-time around the sun. Other stars in the universe which have planets also warp space in their vicinity. By the same reasoning the moon and artificial satellites orbit the Earth, and many planets in the Solar system make their moons orbit them by warping the space-time around themselves with their great masses. Smaller objects such as asteroids generate very weak gravity because their masses are small and therefore warp the space-time around themselves very little. In fact some physicists even say that according to Einstein gravity was not even a force like Isaac Newton claimed it was. To demonstrate this, these physicists stretch a table cloth or a nylon sheet with gridlines, put a ball in the middle of the cloth / nylon stretch. The weight of the ball creates a dent in the strethed cloth. In this demonstration the stretched cloth represents the fabric of space-time, the ball in the middle represents the sun and the dent in the cloth is supposed to be the warping of space-time by the mass of the sun. Then the demonstrator rolls some smaller balls which rotate several times on the cloth around the ball placed in the middle. This is supposed to represent the orbiting planets following the curvature of space - time around the sun. And this is gravity. You can see this demonstration on many documentaries about Einstein and even in the BBC movie named Einstein & Eddington. In the movie, the famous British Astronomer Arthur Eddington does the demonstration with a tablecloth, a loaf of bread as the sun and an apple as an orbiting planet. As is known Arthur Eddington proved Einstein's theory that gravity bends light by photographing the shift in the visible position of the stars aligned behind the sun in the sky during a solar eclipse in 1920.

This interpretation of Einstein's General Theory of Relativity about Gravity raises many questions & objections in the mind of the careful analyst / thinker. Moreover, the demonstration of gravity with the stretched tablecloth representing space-time and the balls representing the sun and planets and the dent in the cloth representing the warp of space-time by a massive body and saying that according to Einstein this is what gravity is all about has a major flaw and is a poor analogy with the Solar System.

The objections / questions below are not to Einstein nor to his theory of gravity, but rather to the way it is explained by some physicists to the general public.

1) How can space-time be warped ? You can warp a malleable substance such as a sheet of aluminum or plastic or any flexible matter. But how can the sun or any massive object warp the space-time around it ? Space-time is not matter, it is emptiness, nothingness. How can nothingness be warped ? There is nothing to warp. Space is full of many particles at sub-atomic scale such as cosmic radiation, solar wind etc. But they are not space-time, they exist in space-time like bigger objects such as the stars and planets do. Space itself is emptiness, nothingness, it is not a substance. How can nothingness be bent or warped by a massive object ?

2) What makes the planets orbit the sun ? According to this interpretation of Einstein's theory of gravity planets orbit the sun because they have to follow the curvature in space-time created by the sun's mass around itself. OK then if gravity is not the force of attraction between objects having a mass like Isaac Newton said it was, what made the planets start to orbit around the sun in the curved fabric of space-time in the first place? Before the planets and the sun formed they were a giant cloud of gas rotating around its axis and held together with the force of gravity.

3) What about Newton's apple ? When Newton's apple falls from the tree onto the ground is it because the Earth's mass has warped the space-time around itself and the apple has to follow that curvature towards the Earth ? If gravity is not a force of attraction but merely the warping of space-time what pulls the apple towards the Earth ? What holds us humans on the surface of the Earth and prevents us from flying off into space if not the attractive force of gravity of the Earth's mass ?

4) Double standard about what gravity is . After having dismissed Newtonian Theory of gravity as proven wrong by Einstein, that it is not a force but a mere warping of space-time, the same physicists talk about gravity as a force elsewhere contradicting themselves. For example when they talk about the holy grail of physics, the quest for the Grand Unification Theory of Forces of Nature. That is a theory of everything that will hopefully someday unite the 4 fundamental forces ; nuclear strong force, nuclear weak force, electromagnetic force and the force of gravity under one unified theory. But while explaining Einstein's theory of gravity they had dismissed gravity from being a force. Now they say it is a force, the weakest of the 4 forces.

5) The table cloth demonstration is flawed In the table cloth and balls demonstration of the alleged Einstein's theory of gravity, what creates the dent in the middle of the stretched cloth ? It is the weight of the ball placed in the middle of the cloth. In other words the force of Earth's gravity pulls the ball down towards the center of the Earth. The ball's mass does not mysteriously warp the cloth under it. The sun is not pulled down in space-time like the ball on the table cloth is. Therefore the ball on the cloth can not be an anology for the sun in space-time.

6) Trying to reconcile unreconcilable interpretations Many times we hear / read that Einstein did not prove Newton's theory of gravity wrong, that they are both right in their own domains. To justify this it is said that satellite / space technology uses Newtonian theories of force, mass, acceleration and gravity to calculate rocket trajectories, satellite orbits etc. with great accuracy. And that this demonstrates that Newton's theory of gravity is still valid. On the other hand as Einstein's theory of gravity is explained gravity is dismissed from being a force ( force defined as an influence on an object to set the object into motion or change its motion ) and redefined as the warping of space-time by a massive object in it. Perhaps Newton's theory of Gravity can be reconciled with Einstein's but not with this kind of interpretation. Gravity is either a force or it is not. It can not both be a force and not be a force . At best one of the interpretations is true the other false. They are contradictory statements and therefore can not both be true.

7) Einstein's theory of gravity is not taught in middle and high schools

After almost 100 years after Einstein published his General Theory of Relativity on gravity, most middle school and high school science and physics lessons still only slightly mention if at all Einstein's theory of gravity. They devote the gravity subject almost entirely to Isaac Newton's theory of gravity. Even though Einstein's discovery that gravity is the warping of space - time has been widely accepted for almost a century it is amazing that schools around the world still stubbornly limit their lessons to Newton's theory.

Conclusion

Einstein most certainly was right in his theories including that of gravity and he replaced some misconceptions in Newtonian theories but the way these are explained by some physicists to the general public suffer from the flaws summarized above. Any physicist aiming to explain these to the general public should make sure that these points are dealt with effectively. Otherwise confusion on these subjects will continue.

In reply to an earlier post on Mar 28, 2012, 5:48:01 AM PDT
I think you misunderstand some of the semantic and the analogies they are using.

First of all, lets clear something up--space IS more than nothing. It isn't a "substance" in a classical sense, but it has properties, and can be warped, stretched, contracted, etc. A perfect visual demonstration of this is gravitational lensing--why is the light passing by very massive objects warped? Because the space(/spacetime) around the object is warped, and that is what light travels through. The same basic phenomenon is what causes redshift--the stretching of wavelength from distant objects. This demonstrates another aspect of how space is more than "nothing"--space itself is expanding. Sometimes faster than light. Space is also the only absolute frame of reference when it comes to velocity. This is partially the essence of special relativity--you can't travel faster than light relative to ANYTHING. If light travels at the speed of light if you are standing still, or if you are heading toward it at .9999x the speed of light.

A good example of space itself having properties--spin in a circle. What is pulling your arms away from your body? The answer, as crazy as it sounds, is warped spacetime.

As far as gravity not being a force, there is some basis to this--Gravity is a force unlike the other fundamental forces of nature (strong/color force, weak nuclear force, electromagnetism) because all of those forces act on an atomic level, according to very different laws, and use "force carriers" like photons or gluons. These are fundamental interactions between the objects and particles themselves, irrespective of spacetime. Gravity does not have a force carrier, it does not signify an energy exchange, it is simply an emergent property of spacetime. However, it does have an attractive interaction akin to the other forces, and so in that sense, it IS a force, just with a very different mechanism.

"It can not both be a force and not be a force" That is very black-and-white thinking, and doesn't take into consideration that there are different definition for the word. Some people call them "fundamental interactions" rather than "fundamental forces". It may be a force like the other 3, but it is in a category all its own.

As far as "disproving Newton", this is hogwash. He merely added to the understanding of gravitation. Although, the equations of general relativity are more precise at calculating orbits, trajectories etc. For example, using simple celestial mechanics, the orbit of mercury could never be predicted with exact precision--it came extremely close. However, general relativity was able to predict it perfectly. The equations of general relativity ARE used for satellites and other spacecraft. We may be able to get by on Newtonian calculations in some instances, but they have to be so precise, that general relativity is needed. It is simply more precise, more exact, and more thorough.

As far as the "following the path of warped spacetime", this is not just true for orbits, but for all of the attractive properties of gravity. It's like a pit in the sand--you either fall into it, spin around the edges, or reach enough velocity to escape. This analogy is very simplified, but it helps illustrate the mechanism behind all gravitational interactions--orbits, acceleration due to gravity (newton's apples), time dilation, gravitational lensing, black holes, etc.

So Newtonian and Einsteinian physics are NOT mutually exclusive. Einstein did not overturn Newton. Newton never attempted to explain what caused gravity, so the idea of warped spacetime does nothing to overturn Newton. Classical mechanics, classical optics, electrodynamics, celestial mechanics etc. MUST be understood in order to understand any more advanced physics like relativity or quantum mechanics. These newer sets of laws DO NOT overturn the old ones, but merely are a more advanced, precise, and elegant means of understanding the causes and making predictions about these interaction and phenomena. Believe me, if you ever want to take a course in relativity, you'd better get a really good grasp on Newtonian physics first. That's like trying to learn Calculus without an understanding of Algebra or Trigonometry. Calculus doesn't prove the other two wrong, but it builds on them and the end result is very different.

Posted on Sep 7, 2012, 8:36:51 PM PDT
Thanks, y'all. This is fun to read.
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