Newton’s Theory Obsolete, Einstein’s Holds Good, But Need for More Comprehensive ‘Theory of Gravity’

Do we really understand what gravity is? Newton tried to understand it and formulated the gravitational laws. Newton’s laws of gravitation once appeared in his most glorified book—“Mathematical Principle of Natural Philosophy” in 1600s, went almost unchallenged for a period of three centuries. Then came Einstein with his special theory of relativity, where Newton’s concept of gravity was thoroughly questioned. After more than a century since Einstein came up with his relativity theory, scientists believe that world needs more comprehensive theory to understand what gravity is. They are saying that as of now, Newton’s laws can be ruled out and Einstein’s theory holds good. But, that’s not enough; we need more to understand gravity more comprehensibly.

Andrea Ghez and her team at University of California, Los Angeles (UCLA), USA, have been studying the supermassive black hole at the center of our galaxy, the Milky Way. They have tested Einstein’s Theory of General Relativity near this monstrous black hole. The team has published their findings in Science recently. Ghez, one of the lead authors of the study quoted to have said — “Einstein’s right, at least for now. We can absolutely rule out Newton’s law of gravity. Our observations are consistent with Einstein’s general theory of relativity. However, his theory is definitely showing vulnerability. It cannot fully explain gravity inside a black hole, and at some point we will need to move beyond Einstein’s theory to a more comprehensive theory of gravity that explains what a black hole is.”

Ghez’s team studied the orbiting of the star SO-2 around the massive black hole. SO-2 takes 16 years to complete one round around the black hole, and it now about to complete one round. They tested whether Einstein’s theory of general relativity gives the full understanding of how gravity behaves near the supermassive black hole whose mass is almost 4 million times the mass of the sun.

The key data that the research has is from the analysis of the spectra. The spectra here could be visualized as the rainbow of light received from stars. These spectra show the intensity of light travelling from the star and offer extremely important information about the stars. Spectra also show the composition of the star.

The spectra from the star SO-2 were collected at the W M Keck observatory in Hawaii using a spectrograph built at UCLA. These spectra revealed the details of the star’s motion in a precision that was not attained earlier.

The spectacular observation that Ghez and her team could make was regarding the co-mingling of space and time near the supermassive black hole. The co-mingling of space and time is the hallmark that pertains to Einstein’s concept of gravity. On the other hand, Newton’s concept of gravity space and time cannot co-mingle, they are separate.

Einstein’s theory describes gravity as a geometric property of space and time or spacetime. He proposed that celestial objects such as sun or the Earth change the geometry of spacetime and this change gives rise to what we perceive as gravity. In Einstein’s understanding of gravity, there does not exist anything like a gravitational force, rather it’s the changing of spacetime. On the other hand, going by Newton’s understanding of gravity, we have to believe that there always exists a force between two objects, the gravitational force.

The space-time co-mingling near the massive black hole at the centre of our galaxy reaffirms Einstein’s correctness in understanding of gravity and about the universe. Previously as well, gravitational waves had been detected as theorized by Einstein. This finding won the Nobel Prize in Physics in the year 2017. Whereas Newton’s concept of gravity wherein the space and time separate from each other, could not be visualised in the study of gravity near black holes.

To become a universal law, any physical theory must be applicable everywhere in the universe, including the black holes. Findings the congruity of Einstein’s theory, but not Newton’s, in the case of black holes led the scientists to proclaim the rule out of Newton’s theory of gravity. Einstein’s theory also showed vulnerability despite its correctness in understanding something very fundamental of physics as the gravity. The future of astrophysics has much a lot to do for developing a better understanding about gravity.