The case against dark matter – d-brief gas monkey


Physicists are painfully aware of the fact that spiral galaxies are spinning faster than they should be, given the amount of matter — and therefore, gravity — they contain. At the speed that some of them are spinning, current theory says that the stars, planets, dust, and other matter should be flung off into space. Because they are not, physicists have hypothesized that “dark matter” we cannot see or otherwise detect is causing the extra gravitational pull, keeping these galaxies together. This matter is said to account for about 25 percent of the universe, but Verlinde believes that there may be another answer that can account for the deviations between the expected and observed rotation curves.“What is observed is that the deviations that we see in the rotational curves of galaxies, which is just derived by looking at the matter that we see, always seems to occur at one particular acceleration,” he says.

That particular acceleration happens to play an important role in the relationship between a galaxy’s distance and the speed with which it’s moving away from our own, which is governed by the expansion of the universe, known as Hubble’s Law. A 2017 paper by Alexandre Chaloum Elbeze in the Journal of Modern Physics outlines how the expansion rate of the universe, or H 0, is linked through a new parameter, which he calls E 0, is linked to the rotation curves of galaxies measured by astronomers.

“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.

“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

“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.”

“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.”