# In SI units, its value is approximately 6.67 × 10–11.

The fictitious force that acts in the above example is called the Coriolis force, after the French physicist Gaspard Coriolis, who first described this effect. Interestingly, it is the Coriolis force that determines the direction of rotation of cyclone vortices, which we observe in images obtained from meteorological satellites. Initially, air masses begin to rush in a straight line from areas of high atmospheric pressure to areas of low atmospheric pressure, but the Coriolis force makes them spiral in a spiral. (You might as well argue that the air currents continue to move in a straight line, but as the Earth rotates beneath them, it seems to us on the surface of the planet that they are moving in a spiral.) Let’s go back to the example of throwing a ball from the pole to the equator. It is easy to understand that in the Northern and Southern Hemispheres, the Coriolis force acts on a moving body in directly opposite directions. That is why in the Northern Hemisphere, cyclone eddies seem to be swirling counterclockwise, and in the Southern Hemisphere – clockwise.

Hence comes the popular belief that the water in the sewer openings of bathtubs and sinks in the two hemispheres rotates in opposite directions, allegedly due to the Coriolis effect. (I remember when I myself was a student, the whole group, including one Argentine, spent more than one hour in the men’s room at the Faculty of Physics at Stanford University, watching the streams of water in the sink, hoping to confirm or disprove this hypothesis.) In fact, While it is true that the Coriolis force acts in the opposite direction in the two hemispheres, the direction of the swirling of the water in the funnel is only partly determined by this effect. The fact is that water flows for a long time through water pipes, while currents are formed in the water flow, which, although it is difficult to see them with the naked eye, continue to swirl the water stream even when it pours into the sink. In addition, similar currents can be created when water flows into the drain hole. It is they who determine the direction of movement of water in the funnel, since the Coriolis forces are much weaker than these currents. In ordinary life, the direction of swirling water in the drain funnel in the northern and southern hemispheres depends more on the configuration of the sewer system than on the action of natural forces.

However, nevertheless, a group of experimenters was found who had the patience to repeat this experiment in "clean" conditions. They took a perfectly symmetrical spherical sink, removed the sewer pipes, allowing water to pass through the drain hole freely, equipped the drain hole with an automatic shutter that opened only after any residual currents in the water had calmed down – and they saw the Coriolis effect in action! Several times they even managed to see how the water, first under a weak external influence, twisted in one direction, and then the Coriolis forces took over, and the direction of the spiral changed to the opposite!

On the decline of his days, Isaac Newton told how it happened: he was walking in an apple orchard at his parents’ estate and suddenly saw the moon in the daytime sky. And right there, before his eyes, an apple came off the branch and fell to the ground. Since Newton at this very time was working on the laws of motion (see Newton’s laws of mechanics), he already knew that the apple fell under the influence of the Earth’s gravitational field. He also knew that the Moon does not just hang in the sky, but revolves in an orbit around the Earth, and, therefore, it is affected by some kind of force that keeps it from falling out of orbit and flying in a straight line away, into open space. Then it occurred to him that, perhaps, it is the same force that makes both the apple fall to the ground and the moon to remain in near-earth orbit.

To fully appreciate the brilliance of this insight, let’s briefly return to its background. When the great predecessors of Newton, in particular Galileo, studied the uniformly accelerated motion of bodies falling on the surface of the Earth, they were sure that they were observing a phenomenon of a purely terrestrial nature – existing only near the surface of our planet. When other scientists, such as Johannes Kepler (see Kepler’s laws), studied the motion of celestial bodies, they believed that completely different laws of motion operate in the celestial spheres than the laws governing motion here on Earth. The history of science testifies that almost all arguments regarding the motion of celestial bodies before Newton boiled down mainly to the fact that celestial bodies, being perfect, move in circular orbits due to their perfection, since a circle is an ideal geometric figure. Thus, in modern terms, it was believed that there are two types of gravity, and this idea was firmly entrenched in the minds of people of that time. Everyone believed that there is terrestrial gravity acting on an imperfect Earth, and there is celestial gravity acting on a perfect heaven.

Newton’s insight was precisely that he combined these two types of gravity in his mind. From this historical moment, the artificial and false separation of the Earth and the rest of the Universe ceased to exist.

The results of Newton’s calculations are now called Newton’s law of universal gravitation. According to this law, a force of mutual attraction acts between any pair of bodies in the Universe. Like all physical laws, it is clothed in the form of a mathematical equation. If M and m are the masses of two bodies, and D is the distance between them, then the force F of the mutual gravitational attraction between them is equal to:

F = GMm / D2

where G is the gravitational constant determined experimentally. In SI units, its value is approximately 6.67 × 10–11.

There are several important remarks to be made about this law. First, its action explicitly applies to all physical material bodies in the Universe without exception. In particular, you and this book are now experiencing equal and opposite forces of mutual gravitational attraction. Of course, these forces are so small that even the most accurate of modern instruments will not detect them, but they really exist, and they can be calculated. In the same way, you experience mutual attraction with a distant quasar, tens of billions of light years away from you. Again, the forces of this attraction are too small to be instrumentally registered and measured.

The second point is that the gravitational force of the Earth at its surface equally affects all material bodies located anywhere in the world. Right now, gravity, calculated by the above formula, is acting on you, and you really feel it as your weight. If you drop something, it will, under the influence of the same force, rush to the ground with equal acceleration. Galileo was the first to experimentally measure the approximate value of the acceleration of gravity (see Equations of uniformly accelerated motion) near the Earth’s surface. This acceleration is denoted by the letter g.

For Galileo, g was simply an experimentally measured constant. According to Newton, the acceleration of gravity can be calculated by substituting the mass of the Earth M and the radius of the Earth D into the formula of the law of universal gravitation, remembering that, according to the second law of Newtonian mechanics, the force acting on a body is equal to its mass multiplied by the acceleration. Thus, what for Galileo was simply a subject of measurement becomes for Newton the subject of mathematical calculations or predictions.

Finally, the law of universal gravitation explains the mechanical structure of the solar system, and Kepler’s laws describing the trajectories of the planets can be derived from it. For Kepler, his laws were purely descriptive – the scientist simply generalized his observations in mathematical form, without giving any theoretical foundations to the formulas. In the great system of world order according to Newton, Kepler’s laws become a direct consequence of the universal laws of mechanics and the law of universal gravitation. That is, we again observe how empirical conclusions obtained at the same level turn into strictly substantiated logical conclusions during the transition to the next stage of deepening our knowledge of the world.

The picture of the structure of the solar system, arising from these equations and uniting earth and celestial gravity, can be understood with a simple example. Suppose you are standing at the edge of a sheer cliff, next to you is a cannon and a pile of cannonballs. If you simply drop the core from the edge of the cliff vertically, it will begin to fall down vertically and uniformly. Its motion will be described by Newton’s laws for uniformly accelerated motion of a body with acceleration g. If you now shoot a cannonball in the direction of the horizon, it will fly – and will fall in an arc. And in this case, its motion will be described by Newton’s laws, only now they are applied to a body moving under the influence of gravity and having a certain initial velocity in the horizontal plane. Now, as you load the cannon with a heavier cannon and fire it over and over, you will find that as each subsequent cannon is ejected from the barrel at a higher initial velocity, the cannonballs fall farther and farther from the base of the cliff.

Now imagine that you have loaded so much gunpowder into a cannon that the speed of the cannon is enough to fly around the globe. If we neglect the air resistance, the core, having flown around the Earth, will return to its starting point at exactly the same speed with which it originally flew out of the cannon. It is clear what will happen next: the core will not stop there and will continue to wind circle after circle around the planet. In other words, we will get an artificial satellite orbiting the Earth, like a natural satellite – the Moon. So, we gradually moved from describing the motion of a body falling exclusively under the influence of "earth" gravity (Newtonian apple) to describing the motion of a satellite (Moon) in its orbit, without changing the nature of the gravitational effect from "earthly" to "heavenly". It was this insight that allowed Newton to connect together the two forces of gravitational attraction that were considered different in nature before him.

The last question remains: was Newton telling the truth on the declining days of his days? Did it really happen that way? Today there is no documentary evidence that Newton really dealt with the problem of gravity in the period to which he himself relates his discovery, but documents tend to get lost. On the other hand, it is generally known that Newton was an unpleasant and extremely meticulous person in everything related to securing priorities for him in science, and it would be very in his nature to obscure the truth if he suddenly felt that his scientific priority was at least something- then it threatens. Dating this discovery to 1666, while the real scientist formulated, wrote down and published this law only in 1687, Newton, in terms of priority, gained an advantage for himself in more than two decades.

I admit that some of the historians will get a blow from my version, but in fact, this question does not bother me much. Be that as it may, Newton’s apple remains a beautiful parable and a brilliant metaphor describing the unpredictability and mystery of man’s creative knowledge of nature. Whether this story is historically accurate is a secondary question.

After the discovery of Hubble’s Law, most astronomers adopted the Big Bang theory – the concept that the universe was formed in the past persuasive argumentative essay examples from a point. However, in the 1940s, a group of astrophysicists led by Fred Hoyle proposed an alternative theory.

The main idea of ​​this theory is this: as galaxies move away from each other during the Hubble expansion, new matter is formed in the increasing space between them. The newly formed matter eventually self-organizes into galaxies, which, in turn, will move away from each other, freeing up space for the formation of new matter. Thus, the observed expansion was consistent with the concept of a "stationary" universe, which retains its overall density and does not have a single point of formation (the presence of which is assumed by the Big Bang theory). But at the same time it was required to accept without proof a new concept of the process of the formation of matter.

Several astronomers supported the theory of a stationary universe until the mid-1960s. The main advantage of this theory was its philosophical side. It was argued that the theory is consistent with the Copernican principle that our world is not unique, and does not single out a particular moment in time as the main one.

Arguments against the theory soon began to emerge. First, precise laboratory experiments have failed to reproduce the formation of matter. Second, and more importantly, new discoveries in cosmology – such as the cosmic microwave background (see Big Bang) – have shown that many phenomena in the universe can be explained in terms of the Big Bang scenario, but not in the theory of a stationary universe. For example, when powerful telescopes were able to look deeper into the Universe and thus penetrate into its past, it became clear that all the most distant galaxies are young, not yet formed systems. This is exactly what was expected from the Universe, which emerged as a result of the Big Bang, but did not agree with the stationarity picture in any way. In the end, most defenders of the theory of a stationary universe, overwhelmed by this counterargument, simply gave up.

However, one legacy of this theory has survived to this day – the term "Big Bang" itself. Hoyle originally suggested it to laugh at his opponents, and he was probably very surprised when they enthusiastically accepted the term.

It is difficult to imagine an absolute emptiness – a complete vacuum that does not contain anything. Human consciousness seeks to fill it with at least something material, and for many centuries of human history it was believed that the world space was filled with ether. The idea was that interstellar space is filled with some kind of invisible and intangible subtle substance. When Maxwell’s system of equations was obtained, predicting that light propagates in space with a finite speed, even the author of this theory himself believed that electromagnetic waves propagate in a medium, just as acoustic waves propagate in air, and sea waves propagate in water. In the first half of the 19th century, scientists even carefully worked out the theoretical model of the ether and the mechanics of the propagation of light, including all kinds of levers and axes, supposedly promoting the propagation of vibrational light waves in the ether.

In 1887, two American physicists – Albert Michelson and Henry Morley – decided to jointly conduct an experiment designed to prove once and for all to skeptics that the luminiferous ether really exists, fills the Universe and serves as a medium in which light and other electromagnetic waves propagate. Michelson had unquestionable authority as a designer of optical instruments, and Morley was famous as a tireless and infallible experimental physicist.