The special theory of relativity, put forward by Albert Einstein in 1905, is one of the most influential theories in the field of theoretical and practical physics of the 20th century. Any physicist knows it, but how can it be explained to those who have nothing to do with science? Are there things and phenomena observed in everyday life that could demonstrate this revolutionary theory in action?
Theory of relativity
Formulated by Albert Einstein in 1905, the scientific theory of relativity suggests that:
- all physical processes are the same everywhere, and the laws of physics are observed in any environment;
- there is a maximum speed of propagation of interactions that cannot exceed the speed of light;
- space and time are homogeneous.
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The theory explains the behavior of various objects in space-time, which makes it possible to predict everything from the existence of black holes, in which Einstein himself could not believe, to gravitational waves. Relativity seems deceptively simple, but it’s not entirely true.
Influence of the theory of relativity
The theory of relativity explains not only such amazing phenomena as gravitational waves and black holes, but also how space-time is perceived differently depending on the speed and direction of movement of objects.
If the speed of light is always constant, this means that for an astronaut moving very quickly relative to the Earth, seconds pass more slowly than for an observer from Earth. Time essentially slows down for the astronaut.
But we don't necessarily need a spaceship to observe various relativistic effects. In fact, there are many cases where the theory of special relativity, designed to improve Newtonian mechanics, manifests itself in our daily life and the technologies we use regularly.
Electricity
Magnetism is a relativistic effect, and if you use electricity you can thank relativity for making the generators work.
If you take a conductor and expose it to a magnetic field, an electric current is generated. Charged particles in a conductor are exposed to a changing magnetic field, which forces them to move and creates an electrical current.
Electromagnets
The work of electromagnets is also perfectly explained by the theory of relativity. When a direct current of electric charge passes through a wire, the electrons in it drift. Usually the wire appears to be electrically neutral, with no positive or negative charge. This is a consequence of the presence in it of the same number of protons (positive charges) and electrons (negative charges). But if you place another wire next to it with a direct flow of electricity, the wires attract or repel each other, depending on the direction in which the current moves in the wire.
If the current moves in the same direction, the electrons from the first wire “perceive” the electrons in the second wire as stationary (if the electric charge is of the same strength). Meanwhile, in terms of electrons, the protons in both wires are in motion. Due to the relativistic shortening of the length, they seem to be located closer to each other, thus, along the entire length of the wire, there is more positive charge than negative. Since the same charges are repelled, the two wires also repel.
The current traveling in opposite directions causes the conductors to attract.
Global Positioning System
For the most accurate GPS navigation, satellites must take relativistic effects into account. This is due to the fact that, despite the fact that the satellites move much slower than their maximum speed, they still move fast enough. Satellites send their signals to ground stations. They, like the GPS navigators of cars, smartphones and other devices, experience higher acceleration due to gravity than satellites in orbit.
To achieve perfect accuracy, satellites rely on super-accurate clocks to tell times down to nanoseconds (billionths of a second). Since each satellite is 20,300 kilometers above Earth and travels there at about 10,000 kilometers per hour, a relativistic time difference of about four microseconds per day appears. Add gravity to the equation and the number rises to about seven microseconds. This is about 7 thousand nanoseconds.
The difference is quite large: if no relativistic effects were taken into account, the GPS navigator would be mistaken by almost 8 kilometers on the very first day.
Noble color of gold
Metals appear shiny because the electrons in their atoms move between different energy levels or orbitals. Some photons of light hitting a metal surface are absorbed and then emitted by a longer wave of light. Most of the visible light rays are simply reflected.
The gold atom is very heavy, so the electrons in the nucleus move fast enough, resulting in a significant relative increase in mass. As a result, the electrons revolve around the nucleus in a shorter orbit with more momentum. The electrons in the inner orbitals carry a charge that roughly coincides with the charge of the outer electrons, respectively, the absorbed and reflected light is characterized by a longer wave.
Longer wavelengths of light mean that some of the visible light that would normally just be reflected has been absorbed by atoms, and that portion is at the blue end of the spectrum. This means that the light reflected and emitted by gold is closer to the longer wavelength spectrum, that is, it has more yellow, orange and red, and almost no shortwave blue and violet.
Gold is virtually erosion resistant
The relativistic effect seen on electrons in gold is also the reason that the metal does not corrode and reacts poorly with other elements.
Gold has only one electron in the outer electron shell, but despite this, it is even less active than calcium or lithium, which are similar in structure. The electrons in gold are heavier and therefore located closer to the nucleus of the atom. This means that the most distant outer electron, most likely, will be among the "own" electrons in the inner shell, than will begin to react with the outer electrons of another element.
Liquid state of mercury
Like gold, mercury also features heavy atoms with electrons orbiting close to the nucleus. Hence follows a relative increase in velocity and mass due to a reduction in the distance between the nucleus and the charged particle.
The bonds between mercury atoms are so weak that mercury melts at lower temperatures than other metals, and is generally liquid in most of the cases it is observed in everyday life.
Old TVs and Monitors
Not so long ago, most televisions and monitors were cathode ray devices. A cathode ray tube is a device that reproduces an optical image by firing electrons in beams or beams of rays onto a luminescent surface with a large magnet. Each electron creates an illuminated pixel after it hits the back of the screen. Electrons are launched at a high speed equal to about 30% of the maximum speed or speed of light.
For a functional optical picture to be formed, electromagnets installed in the apparatus in order to direct electrons to the required part of the screen had to take into account various relativistic effects so as not to disrupt the entire system.
Hope Chikanchi