Electromagnetic fields are created and only by all particles or objects that have an electrical charge. Remember that the electric charge can be of two different and opposite classes, positive and negative, with which they can neutralize each other. In addition, electric charges of the same sign repel and those of a different sign attract. Electric charges in motion give rise to magnetic fields, and if they are also accelerated (or decelerated) they produce electromagnetic radiation, that is, electromagnetic waves. Electric charges cannot be created, so we can only generate electromagnetic fields if we have electric charges at our disposal. In the case of magnets, the charges move inside them as small electric currents that generate the magnetic field.
To achieve electrical charges easily, without the need for scientific equipment, we can transfer electrons from some objects to others by rubbing, since the electrical charges of electrons (negative) and protons (positive) are half hidden in the atoms and molecules that make up these objects, and also in equal numbers, so they neutralize each other. As a result, the total electrical charge of everyday objects is equal to zero. The transfer of electrons from some objects to others by rubbing, and even just by contact, often occurs in everyday life and is called the triboelectric effect. We see this frequently in the case of certain materials, such as amber, plastics, and other synthetic materials. These acquire a negative electrical charge due to excess electrons, while nylon or wool, or our own hair, with which we rub the object, loses electrons and acquires a positive charge. A very attractive experiment consists of inflating balloons and rubbing them with the upper part of the head (own or someone else’s) in the area where we will place them on walls and ceilings by simple contact. Not only will we see how the balloons are “stuck” to the walls and ceilings (although not for long, depending on various factors) but we will also see all the creeps get in the friction zone, since they all acquire the same positive charge so they repel each other. We can also take a walk with one of the balloons carried by the house. As a result, we will be creating magnetic fields just by moving the balloon, and it will also emit electromagnetic waves, since when we walk we do not move at a constant and rectilinear speed, but we are accelerating and decelerating all the time.
Gravitational fields, on the other hand, are created by all particles or objects that have mass and / or energy, as can be deduced from Einstein’s equations of general relativity. So everything that exists creates gravitational fields, since everything has mass and / or energy, although these fields are extremely weak in the vast majority of cases and therefore undetectable. In fact, it is impossible to block or disguise a gravitational field, unlike what can be done with electromagnetic fields. This difference is due to the fact that electric charges can take two types of opposite values: positive or negative values, as we said, so that electromagnetic fields can be neutralized, but in the case of gravitational fields there is only one type of value; that is, there are no positive and negative masses with which a gravitational field can be blocked or disguised, there are only positive masses that produce gravitational attraction.
In theory, there could be a type of energy in the Universe, the energy of space itself, that generates gravitational repulsion instead of attraction.
The same happens with all known energies, since, like masses, they produce only gravitational attraction. However, there could be an exception, since, in theory, there could be a type of energy in the Universe, the energy of space itself, that generates gravitational repulsion instead of attraction. This possibility is also contemplated in Einstein’s equations, in a term known as the cosmological constant that could be responsible for the acceleration of the expansion of the Universe.
In conclusion, there is no technology to create, destroy or hide gravitational fields, which are generated directly by the mass and energy of everything that exists. The only thing we can do is increase or decrease the intensity of the gravitational field created by an object within our reach in a specific place. We can do this by adding or removing mass to the object, heating or cooling it, moving the object closer to or further away from that place, etc., since the intensity of the gravitational field at a point is proportional to the mass and energy of the object that produces it and decreases with the square of the distance to that object. As for gravitational waves, they are generated when masses accelerate (or decelerate), but they are so extremely weak that their artificial production is not going to be an object of interest at any time for our science and technology.
Beatriz Gato Rivera She is a doctor in Physics and a researcher at the Fundamental Physics Institute of the Higher Council for Scientific Research (CSIC).
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