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.
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.
Rasih, you raise some good points. When I was in public school over 30 years ago, physics classes were taught as though little new information was discovered after the days of Newton. That's possibly because the math required to do the calculations of Relativity is beyond the level taught in school, but I think also because we don't notice relativistic effects at speeds significantly < C. Keep in mind that when NASA (for example) calculates trajectories of rockets, probes, satellites and celestial objects, they are using the old fashioned Newton laws of motion, because even fast-moving rockets and space rocks don't go anywhere close to C.
But even in my 1970s-era high school classes, they were making us aware that space isn't just nothingness and that it does have a fabric that can be warped. That's what anyone teaching the subject has to be clear on -- that despite appearances, "empty" space isn't really empty, and even has a small amount of vacuum energy.
Dear Bob, I already said in my note that I am aware space is filled with particles, radiation and force fields. I also know that Einstein himself talked about the warping of space - time. But that still leaves the question of what it is that is being warped unanswered. I am not claiming that Einstein was wrong nor that space - time can not be warped. I just think that the non - physicist public must be explained clearly what exactly is being warped. It is not the particles, radiation nor force fields that permeate in space that are alleged to be warped, it is the fabric of space-time itself. Therefore, we need to be explained what this fabric is made of. Because if the fabric is just space, not the particles etc. in it, then we are implying that nothingness is being warped which is impossible. How can nothingness be warped ? There must be something to be warped. I don't intend to claim the existence of ether which was proved not to exist long ago by the Michaelson - Morley experiment. The reason why I raise this point is that in the many books and documentary films I read / watched about this no phycisist ever explained to the public what this fabric is made of. I am eagerly waiting to be acknowledged by an expert on the field. I think books and documentaries on the subject should explain to the public what this fabric is made of otherwise it is not very convincing.
Rasih, I think the reason physicists don't provide a more thorough explanation of the malleability of space-time is that it isn't something that can be directly observed. As I'm sure you know, the most direct observation anyone can point to is measuring bent starlight during a solar eclipse.
Keep in mind that very few people have the type of high-level math training needed to fully understand how space-time bends, and thus to understand that it really is something, and not just the empty stage described by Newton.
So you may be right that nobody gives a good explanation, but there may not be a good explanation to be had that doesn't involve deriving the equations of General Relativity. Heck, most people think physics works like in Roadrunner cartoons, where the coyote runs in a straight line off a cliff before falling down at a 90 degree angle. And don't get me started on the people who think the earth is 6000 years old.......
Bob, contrary to popular belief, explanation of Einstein's concepts does not require high level math. I read many biographies about Einstein. He himself stated that he was not a mathematical genius but rather deeply interested in the secrets of nature. Einstein's method was creative imagination. His famous "thought experiments" such as riding along a light beam, being pulled by a being in space and others have led to many concepts in his special and general theories of relativity. In fact, biographies say Einstein was not good in maths at school. He later learned non - Euclidian Space Geometry to incorporate gravity into his theory and develop the General Theory of Relativity. Certainly, all his concepts can be represented mathematically and Einstein did so afterwards. But he relied on his thought experiments involving no math to develop these concepts. If space-time is nothingness stripped of the particles, radiation and force fields in it, this has nothing to do with mathematical complication. I have had similar answers before : you have to be very good in math to understand the fabric of space-time. I don't buy that argument. I think people even physicists just accept the concept of warping of space-time without thinking about what it really is. Bending of light in the famous Arthur Eddington solar eclipse observation of 1920 is shown as proof of the bending of space - time. OK, it is bent. But what is it exactly that is being bent ? Moreover, perhaps it is the light beam from the star that is bent, not the fabric of space-time around the sun.