When it comes to explaining gravity, Einstein's theories of relativity are the gold standard. That doesn't mean they're perfect, however. For instance, in order to account for the large-scale movements of galaxies under Einstein's theories, scientists have had to postulate the existence of dark matter, a mysterious, undetectable substance that purportedly must make up as much as 80 percent of all matter in the universe.
But now there's a new theory on the block that's based on the idea that the universe is a hologram, and it doesn't require dark matter or its elusive cousin, dark energy, to explain gravity on a larger scale, reports Phys.org.
The idea, proposed by Erik Verlinde, renowned expert in string theory at the University of Amsterdam, is that gravity is not a fundamental force of nature, but instead an emergent phenomenon. This is a subtle but crucial distinction. In the same way, temperature is also not a fundamental force, but rather a phenomenon that arises from the movements of particles.
So if gravity is emergent, like temperature is, that means it must be emergent from something. But from what? This is where Verlinde borrows from the holographic principle. His theory suggests that gravity is emergent from fundamental bits of information that are stored in the fabric of spacetime itself.
Why this theory matters
It might sound a bit kooky, perhaps Matrix-like, but the theory nevertheless carries a lot of explanatory weight. In 2010, Verlinde published an article demonstrating how Newton's famous second law, which describes how apples fall from trees and satellites stay in orbit, can be derived from this principle. In his latest work, he has extended the idea to include an explanation of large-scale gravitational events like the movements of galaxies. That's important, because those are movements that give Einstein's theories some trouble.
For instance, to make sense of why the outer regions of galaxies rotate as fast as they do around their galactic centers using the theories of relativity, scientists have had to posit the existence of a substance that has yet to be detected: dark matter. In fact, they've had to posit a lot of the stuff. Dark matter would have to make up as much as 80 percent of all matter in the universe.
Just because it hasn't been detected yet doesn't mean dark matter doesn't exist, but its elusiveness poses a problem. So Verlinde's theory has a powerful advantage in that dark matter is not required. This is the principle of Ockham's Razor, the idea that, all things being equal, the simpler answer tends to be the correct one.
"We have evidence that this new view of gravity actually agrees with the observations," said Verlinde. "At large scales, it seems, gravity just doesn't behave the way Einstein's theory predicts."
Verlinde's theory is also convenient in that it's more compatible with quantum physics, a well-tested and fundamental branch of physics that nevertheless doesn't jibe with Einstein's theory of gravity.
"We might be standing on the brink of a new scientific revolution that will radically change our views on the very nature of space, time and gravity," claimed Verlinde.