What goes up, must come down. It’s really that simple. Grab a ball and toss it in the air. Bend your knees and jump. Pour any liquid from a cup. Gravity, as we know it, brings things back to ground level. The heavier the object, the quicker it falls. But that only describes what gravity does. That doesn’t tell us what gravity actually is. So what is gravity? What is gravity made of?
Ancient Indian and Greek philosophers first observed that objects would naturally fall toward the ground but this wasn’t put in its proper light until Isaac Newton and his law of gravity. As one of the four fundamental forces of nature, gravity is, “the force that attracts a body towards the centre of the earth, or towards any other physical body having mass.”
Centuries later, Albert Einstein solved a puzzle within Newton’s law with his theory of general relativity. Newton theorized that all objects exert a force which attracts other objects. This theory worked well for objects on Earth as well as the motion of planets. But it didn’t work for Mercury’s orbit around the sun.
Einstein knew that the planet’s orbit shifts over time. Mercury’s shifted faster than Newton predicted. Einstein offered a different thought. He said instead of this exertion of force, instead of these objects, planets, in this case, curve the fabric of space and time around them. This theory showed that the sun curves space so much that it distorts nearby orbits to include Mercury.
Einstein’s theory has been confirmed from over a century’s worth of experiments. But since that time, scientists have continued to study Einstein’s theory with the idea of taking that knowledge further than ever before. In fact, with the technology given to scientists today, they feel they will be able to show that Einstein’s theory has a point where it will break down.
University of California, Berkeley astrophysicist Jessica Lu said, “We now have the technological capacity to test gravitational theories in ways we’ve never been able to before. Einstein’s theory of gravity is definitely in our crosshairs.” So just as Einstein solved Newton’s puzzle, scientists want to put Einstein’s theory through more stringent testing.
Modern Science On What Gravity Is
In a study conducted earlier this year, scientists proved that Einstein’s gravity theory works, even up to the very edge of a black hole. This study focused on an enormous star S0-2 which is 4 million times larger than the sun and is in a 16-year orbit around a black hole. Scientists watched the light from S0-2 as it reached its closest point to the black hole. If Einstein’s theory was correct, the gravity from the black hole would stretch the light, turning its color from blue to red. Einstein was correct, the color changed.
Even with proving Einstein correct, scientists know at some point his theory will fall apart. Kip Thorne is a Nobel Prize-winning theoretical physicist at the California Institute of Technology and though he didn’t have a part in the study, he did offer his insight. “The curvature of spacetime is so extreme that Einstein’s general relativity fails. We don’t understand how it works when the thing you’re dealing with is extreme.”
This study moves scientists just a little bit closer to a possible new take on gravity. Columbia University astrophysicist Zoltan Haiman also was not part of the research but offered, “It’s definitely exciting,” he said. “It’s pushing the envelope. This is how we get to someplace where we discover [Einstein’s] theory no longer works.”
So, where do scientists go from here? Lu gave her outlook for the next 10 years, “We should be able to push Einstein’s theory of gravity to its limits and hopefully start to see cracks.” Pushing it to its limits is one thing, but a new theory altogether? “A new theory of gravity might help us understand how our own universe was born, and how we got to where we are today 13½ billion years later,” said Lu.
What Is Gravity Made Of?
One person who has already made waves with his view on gravity is theoretical physicist Erik Verlinde. It was ten years ago in 2009 that Verlinde developed a radical new idea about gravity. As reported by the Netherlands Organization for Scientific Research (NWO), Verlinde’s hypothesis states, “Gravity is not the invisible pulling force of Newton or the curved space-time of Einstein. Gravity arises due to the reallocation of information in the universe.” This was met with much harsh criticism from many critics accusing Verlinde of coming up with ideas just for the sake of it, not publishing enough, or providing no testable predictions. Others have embraced Verlinde’s theory and attempt to use it as proof of the validity of simulation theory.
While Verlinde doesn’t pay much attention to the criticism, he does say that since a lot has happened in the ten years he wrote his initial story, a rewrite may be forthcoming. “Over the past ten years, we have gradually learned a lot more about how you should talk about space and time information. I am seriously considering rewriting my story from 2009, but now formulated much more precisely. I think that could remove some of the skepticism that still exists.”
Theoretician Koenraad Schalm from Leiden University explained why scientists are so critical of Verlinde and he put the onus directly on the media. “That media hype sometimes gives rise to irritation among scientists. The headlines were about a new theory of gravity that had been discovered, whereas Verlinde had a hypothesis that still had to be elaborated and tested. The media simply do not understand that nuance, all they want is the next Einstein or Eddington on the front page.” Schalm did, though, offer an olive branch. “But don’t misunderstand me, it is incredibly difficult to have a really good idea in this discipline. So I have a lot of respect for Verlinde, because he has definitely given the field a new direction.”
Which way is up (or down) for gravity? Isaac Newton laid out the first set of rules and Einstein perfected them. The advancement in technology we see today allows us to further explore what those two brilliant minds gave to us. When it comes to understanding what gravity is, it’s quite obvious there are two vastly different schools of thought in play and it will be very interesting to see where these new theories lead us. One thing for certain though, again, what goes up must come down. What is gravity and what is gravity made of are questions we’re still on our way to understanding.