While we owe it to gravity, to keep our feet firmly grounded on Earth, it is due to magnetism that devices like electric generators, motors, fans, hard drives and countless other electronic gadgets help make our life comfortable. Both magnetism (as one aspect of the electromagnetic force) and gravity are two fundamental forces of nature, which mold matter at the microscopic and macroscopic scales. Gravity is the force which determines the large-scale structure of space time by clumping together matter from planetary scales to galactic clusters, determining the ultimate fate of the universe. On the other hand, at microscopic scales, electromagnetic force determines atomic structure, determining the properties of materials. While the force of gravity felt by a particle is purely dependent on mass, electromagnetic forces are mediated by charge. Through this ScienceStruck article, I present a magnetism vs gravity comparison, which will illuminate the major differences in the nature of these two force fields that pervade nature.
What is Magnetism?
Magnetism is the tendency of any material to react to any applied magnetic field with attraction or repulsion. For example, when a magnet is passed over iron nails, they stick to it due to attraction. All substances are either diamagnetic (repulsed by applied magnetic field), paramagnetic (weakly attracted by applied magnetic field) or ferromagnetic (strongly attracted to applied magnetic field) in nature.
Every magnetized object has two poles, which are labeled as north and south poles (as they are attracted to the north and south poles of the Earth's magnetic field). Like poles of magnetic objects repel each other, while unlike poles attract. The Earth itself behaves like a large magnet, with the magnetic north and south poles directing compass needles towards them. The magnetic property of a substance arises due to the orbital motion of electrons around the atomic nucleus and intrinsic spin angular momentum.
In fact, wherever there's an electric current, there is a magnetic field. The degree to which magnetism is expressed in a material is largely dependent on the electronic configuration of its constituent atoms. More the number of unpaired electrons in an atom, more is the probability of the atom showing magnetism. Every atom of the material is a small magnet. In most materials, these small magnets are aligned in such a way, that they cancel each other out. In some ferromagnetic materials like iron, these small atomic magnets tend to be well aligned in the same direction, giving rise to pronounced tendency to be magnetized.
All conductors with an electric current flowing through them, have a magnetic field around them, making them 'electromagnets'. Magnets are used in countless electronic gadgets like audio speakers, doorbells, computer hard drives and in the construction of 'Magnetic Levitation (Maglev) trains'. Most importantly, electric power generation is made possible by the giant magnets placed inside power plant dynamos. After that brief overview of magnetism, let us move over to gravity.
What is Gravity?
According to the now discarded Newtonian theory, gravity is the universal force of attraction felt by every piece of matter, exerted by other forces of matter. Newton's law of gravitation states that every particle of matter gets attracted to every other piece of matter by a force which is directly proportional to the masses of the two particles and inversely proportional to the square of the distance between them. Though Newton's theory has been tested experimentally and can successfully predict macroscopic movement of satellites and planets quite accurately, it does not confirm with the special theory of relativity, which defines the structure of space time.
Einstein provided an alternative which effectively demolished the old Newtonian idea of gravity as an 'action at a distance' force and replaced it with an entirely new paradigm. Gravity is no longer recognized as a force! What we feel as a gravitational force is the result of the curvature of space time induced by the presence of matter in it. Space time itself bends because of the presence of matter and it influences the trajectories of 'free falling' particles within it!
It is not possible to explain the 'General Theory of Relativity' here, but that's the central idea of gravity which it presents. To put it in simplest words, 'Matter Tells Space How to Bend and Space Tells Matter How to Move'! For a better understanding, refer to the marvelous book by Bernard Schutz, titled 'Gravity from the Ground Up: An Introductory Guide to Gravity and General Relativity'.
Magnetism Vs. Gravity
So, how are magnetism and gravity different? For starters, magnetism is affected by the electronic configuration or charge of atoms, while gravity is independent of charge. All objects that have a mass, feel the tug of gravity, irrespective of whether they are charged or uncharged. Magnetism may cause objects to be attracted or repelled from each other, while gravity only works as an attractive force. The attraction or repulsion of magnetic field is dependent on 'poles', while gravity has no preferences to charge or poles. The only property of matter that qualifies it to be attracted by gravitational force is its mass.
Magnetism is a property of matter, while according to general theory of relativity, gravity is the property of space time itself. Magnetism depends on the electronic configuration, temperature and orientation of atoms of a material, while the force of gravitation only depends on the mass of the material. Magnetism can be 'turned off' by disrupting the orderly arrangement of magnetic domains in a material through heating, but gravity can never be 'turned off' as it's a property of space time itself.
Still gravity is weaker than the electromagnetic force (and hence magnetism). The force between two objects attracted by magnetism is far greater than the feeble gravitational attraction between them. However, gravity becomes stronger as particles attracting each other, become more and more massive and hence it determines the structure of large celestial objects like stars and galaxies.
Thus, gravity and magnetism are vastly different from each other as forces. While gravitation keeps our world tethered in an eternal orbit around the Sun, the magnetic field of our planet, provides a sheath which protects us from bombardment of cosmic radiation. Hope this article has stimulated your curiosity about gravity and magnetism enough, to make you delve deeper into the workings of these two phenomenal forces of nature.