What we know and don't know about gravity

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WHAT do we know
And we don’t know
About gravity

Anyone who has read I. A. Efremov’s novel “The Andromeda Nebula” remembers the iron star - the “horror of astronomers”, which with its enormous attraction captures bodies flying past.

Even more amazing celestial lenses have to be the stars predicted by German astronomer Karl Schwarzschild. The gravitational forces near such stars are so strong that the light emitted by them cannot move beyond the immediate vicinity of the star. And a ray of light sent from afar to such a star will never be able to reach its surface. Some kind of strange gravitational mousetrap! But, despite all the necessity of such celestial bodies, the theory predicts their existence with a sufficient degree of rigor.

It would seem that the gravitational forces of the present are accustomed and harnessed, so that a person should have known everything about them that interests him a long time ago. It’s so simple: let’s put a stone on a scale and measure the force with which it is attracted to the Earth! But, having thought about the nature of such a phenomenon, we immediately find ourselves captive to unresolved issues.

In fact, why do any two bodies always attract each other and not repel under the influence of gravitational forces? Why can’t we isolate ourselves from the forces of gravity, just as a curtain separates us from the sun’s rays? What is the nature of the invisible
dim “springs” that attract bodies even very far from each other? There are many questions related to gravity that science has not yet been able to answer.

But we already know a lot. In 1687, Isaac Newton discovered the law of universal gravitation, which made it possible to understand how celestial bodies move. The next important step in understanding gravity belongs to Albert Einstein. In 1916, he created the so-called general theory of relativity, which is commonly called the theories of space, time and gravity. This theory forced scientists to shift their views to such important physical concepts as space and time. Newton believed that the properties of space and the passage of time do not depend on the surrounding bodies. Einstein proved that the heavier the body, the more the space near it is curved and the slower the time in its vicinity. Space, time and gravity turned out to be not independent of each other, but it is not easy to designate test. But its significance in modern physics is exceptionally great. Therefore, what new popular science book devoted to this topic (and there are very few such books) promises to arouse more interest.

We will talk here about some books that cover various problems of the modern theory of gravity.

A much simpler and more accessible presentation of the fundamentals of the theory of gravitation

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is contained in the popular book by M. Gardner, “The Theory of the Relative Length of Millions,” published in 1966 by Atomizdat. The fifth chapter talks about the main initial postulate of the theory - the equality of the gravitational and inertial masses of any body - confirmed with a great degree of accuracy by specially performed experiments. Chapter six describes the views of modern physics on gravitational forces as a result of changes in the geometric properties of space and time under the influence of gravitational masses. Chapters (7, 9 and 10) are related to various cosmic problems related to the theory of gravity. They consider different versions of the model of the Universe and discuss in detail questions about the so-called “red shift” - a change in the color of celestial objects under the influence of their movement, which occurs at enormous speeds.

A much more modern description of space problems can be found in a small brochure by academician V.L. Ginzburg, “How the Universe is Structured and How It Develops in Time,” published by the Znanie publishing house in 1968. (This brochure is based on three articles by the author in the magazine “Nuka and Life” Nos. 1, 2, 3 for 1968.)

First, the author talks about the first cosmological models of the Universe, which were proposed even before the creation of the general theory of the relative length of millions. Then, after a brief description of the main special and general theories of relative length, he examines new models associated with this theory. According to Einstein’s model, the Universe forms a closed three-dimensional sphere that does not change over time. In the model of the Soviet scientist A. A. Friedman, the Universe is either expanding or contracting. In Lemaître’s model, the Universe at some stage replaces its development, as if frozen in immobility, and then begins to rapidly expand again.

In L. Ginzburg provides interesting data on radio galaxies that are located at distances of about 5-8 billion light years from Earth. Their study tells us about the processes that took place at a time when there was not only the Earth, but, apparently, the Sun as well.

In 1969, the Nuka publishing house published P. Bergman’s popular science book “The Mystery of Gravitation.” The author of the book was an employee of Einstein for several years.

Bergman includes in his book all the main issues related to the modern theory of gravity. The book has three chapters: I. Newtonian physics and the special theory of the relative length of terrine. II. General theory of relative terrine length. III. Latest achievements. The book contains a commemorative account of the fundamental theories presented by his effective and unsolved problems on which physics has been working in our days.

Schwarzschild stars, gravitational collapse, the recent discovery of mysterious celestial objects “quasars”, cosmic radio emission telling us what the Universe looked like billions of years ago, and much more, no less interesting, describes the first cosmological models of the Universe, which were proposed even before the creation of the general theory of the relative length of millions. Then, after a brief description of the main special and general theories of relative terrine length, he considers new models associated with the modern theory of gravity. According to Einstein’s model, the Universe forms a closed three-dimensional sphere that does not change over time. In the model of the Soviet scientist A. A. Friedman, the Universe is either expanding or contracting. In Lemaître’s model, the Universe at some stage changes its development, as if STANCE in immobility, and then begins to expand rapidly again.

In 1969, the Nuka publishing house published P. Bergman’s popular science book “The Mystery of Gravitation.” The author of the book was an employee of Einstein for several years.

The author strives to help the reader. He puts all the basic calculations into a special mathematical supplement, and places at the end of the book a small explanatory dictionary of the most difficult and understandable terms. And yet, in some parts the book remains difficult to understand for high school students. True, there are many paragraphs in it that are accessible to a much less prepared reader. There are especially many of them in the third and final chapter of the book.

The books we have listed contain a whole world of new ideas and facts, future experiments, discovered and undiscovered phenomena and laws. And whoever touches this world will certainly receive great satisfaction.

V. A. Leshkovtsev