Verlinde believes that this is an indication that he is on to something.

“That fact kind of hints that it has something to do with the Hubble expansion [of the universe], which at present is due to the presence of dark energy,” he says.

The Hubble constant describes the observed accelerating expansion of the universe. This acceleration is unexplained, but has been attributed to “dark energy,” which Verlinde says can be used to explain away the idea of dark matter.

“Dark energy is quite an important part of my theory,” Verlinde says. “I don’t do away with everything that’s called ‘dark,’ I just explain what is what we now call ‘dark matter’ by thinking about what the influence of dark energy would be, and that [dark energy] actually gives the same effect.”

It should be noted that Verlinde is tackling the problem with dark matter from a specific point of view as a string theorist and is working to fit it into that perspective. Mark Van Raamsdonk, a professor of physics at the University of British Columbia, says that this method should be approached with caution.

“This possibility is intriguing, but as far as I’m aware, it’s not based on a precise model that is mathematically consistent,” Van Raamsdonk says. “Rather, he’s using his intuition to piece together a set of ideas and provide a story for how things might work. He is a very accomplished physicist, so I think his intuition is worth paying attention to.”

Early Days

So far, the ideas that Verlinde confidently stand by have proven to be mathematically and observationally valid — at least, as far as galaxy rotation curves go. The real project will be building a theory that describes more than the rotation of galaxies. Sabine Hossenfelder, a research fellow at the Frankfurt Institute for Advanced Studies, says that a major challenge will be describing the evolution of the early universe.

Currently, theories that incorporate particle dark matter correctly predict the observed temperature variations in the cosmic microwave background. “Unfortunately, Verlinde’s emergent gravity model does not allow the necessary analysis [to prove its validity] — at least not yet,” she wrote in a Forbes article.

Verlinde is aware of the young theory’s shortcomings, but is confident that he can address them in the future.

“I only focused mostly on trying to explain these rotation curves, but dark matter has been used in many other parts of trying to understand the early universe,” Verlinde says. “I have to develop an explanation of how galaxies form, but also these fluctuations in what we see in the cosmic microwave background. If I want to describe the evolution of the universe, I have to calculate much more what is happening on longer timescales. That is the next step for me.”

Searching For Support

Pitching this idea around the world has been quite a task for Verlinde. Given that the idea goes so strongly against popular belief, he has only a handful of allies even amongst his own teammates.

“I have to sell my ideas to various audiences, not just to cosmologists and people that are dealing with dark matter in other ways, but also my string theory colleagues,” he says.  “I think people are slowly starting to see the advantages of the logic of my reasoning.”

“There is a lot of work still to be done, but I think this is a better theory than to just assume that there is dark matter. Because if dark matter has so many forms in which people can imagine it’s there, and there are a zoo of those theories and nobody really knows which one it is, maybe all of those are wrong indeed.”

Regardless of how Verlinde’s theory fares overall in the pursuit of understanding, the outcome has some exciting prospects.

“In any case, trying to understand the implications of these new connections between gravity and [quantum] entanglement, is very exciting and many of us are working hard to see where this will lead,” Van Raamsdonk says. “Even if Verlinde’s specific explanation for dark matter doesn’t turn out to be correct, we are already learning new things about gravity and black holes, and I’m optimistic that we will learn something exciting about cosmology, dark energy, or the Big Bang.”