Gravity is a natural phenomenon by which objects and fields of matter endowed with mass or energy are attracted to each other.but two scientists struggled to prove whether it occurred instantaneously.
Newton thought that gravitation would occur instantaneously and propagate at infinite speeds. Einstein proved the opposite; lGravity is not instantaneous, but how did that result come about?
Is gravity instantaneous or does it have a velocity?
When Newton first formulated his theory, he imagined masses attracting each other, instantaneously, from any great distance throughout the Universe.
But it turns out that no signal, not even gravity, can travel faster than the speed of light: the cosmic speed limit for any and all particles and/or forces.
It turns out that, despite any intuitive thoughts we may have about how gravitation should behave, only experiments, measurements and observations can provide the answer to a physical question like this about reality.
This was demonstrated by Einstein when, after several failed attempts and approximations, he achieved something satisfactory in 1915 that was called the theory of general relativity. In this theory, the calculations are very complicated, but numerous examples show that the curvature of a region of space-time takes spread to other places. The gravitational waves themselves that are a disturbance of the gravitational field are not instantaneous and propagate precisely at the speed of light.
Everything starts with the speed of light
The first to try to measure it, at least according to legend, was Galileo. He set up an experiment at night, in which two people would each stand on top of adjacent mountain peaks, each equipped with a flashlight, style of the beacons of Gondor . One of them revealed his flashlight, and when the other saw it, he revealed his own flashlight, allowing the first to measure how much time had passed. Unfortunately for Galileo, the results seemed instantaneous, limited only by the speed of a human being’s reaction time.
The key breakthrough would not come until 1676when Ole Rømer had the brilliant idea of observing Jupiter’s large innermost moon, Io, as it passed behind Jupiter and reappeared from the giant planet’s shadow. Because light has to travel from the Sun to Io, and then from Io back to our eyes, there should be an observed delay from when Io geometrically leaves Jupiter’s shadow, until the light that arrives, bouncing off the Moon, , becomes observable here. on earth.
Rømer’s work influenced several important scientists of his time, including Christiaan Huygens and Isaac Newton, who devised the first (but mutually contradictory) scientific descriptions of light. But, it was Newton who managed to demonstrate that each massive object in the Universe exerted an attractive force on all other massive objects in the Universe, and that interaction was instantaneous and occurred without any delay.
This is how Newton formulated his law of universal gravitation, where the mathematical orbits he derived matched precisely the way the planets moved through space.
But Newton’s successes would not last forever. The first real clue came with the discovery of Special Relativity, and the notion that space and time were not actually absolute quantities, but that the way we observe them depends very intricately on our movement and location.
relativity appears
After Newton, various scientists discovered that the faster you move through space, the slower clocks seem to run and the shorter distances seem to be, that is, the distance contract and time dilates.
That is, in increasing quantities the closer we get to the speed of light, the more time differs. It was observed that unstable particles that decay with a specific half-life survive longer if they move at high speeds. This led to a revolutionary conclusion: space and time cannot be absolute, but rather relative for each unique observer, which differs from what Newton proposed.
The problem, according to Einstein, is that Newton’s entire picture must be discarded for the Universe to make sense. In a Universe where space and time are not absolute quantities but relative to any observer, gravity can no longer be seen as an instantaneous, straight-line force that connects any two points in the Universe. As a viable alternative, Einstein proposed an image in which space and time are interwoven into what he envisioned as an inseparable four-dimensional fabric.
This fabric would be deformed not only by the presence of masses, but by all forms of matter and energy, wherever and whenever they were located.
And, as a consequence of this, instead of the planets orbiting the Sun due to an invisible force, they simply move along the curved path determined by the curved and distorted structure of space-time.
A current logic
From a modern point of view, this makes sense, since any form of massless radiation (whether particle or wave) must travel at exactly the speed limit for all massless quantities: the speed of light in a vacuum.
It is for this reason that Newton’s original conception of gravitation does not hold up, since, after all, gravity is not an instantaneous force. Instead, the results agree with Einstein: gravitation propagates at a finite speed and the speed of gravity is exactly equal to the speed of light.