Is a revolution coming in physics?

Is a revolution coming in physics?

Galaxy Universe Gravity Spacetime

What is dark matter? Does it even exist, or do we just need an adjustment to our theory of gravity?

What is dark matter? It has never been observed, yet scientists estimate that it constitutes 85% of the matter in the universe. The short answer is that no one knows what dark matter is. Over a century ago, Lord Kelvin offered it as an explanation for the speed of stars in our own galaxy. Decades later, Swedish astronomer Knut Lundmark noted that the universe must contain far more matter than we can observe. Since the 1960s and 1970s, scientists have been trying to figure out what this mysterious substance is, using increasingly complicated technology. However, a growing number of physicists suspect that the answer may be that dark matter does not exist at all.

The backstory

Scientists can observe distant matter in several ways. Equipment such as the famous Hubble telescope measures visible light while other technologies, such as radio telescopes, measure non-visible phenomena. Scientists often spend years collecting data, then analyze it to get the most out of what they see.

What became very clear as more and more data came in was that the galaxies were not behaving as expected. The stars at the outer edges of some galaxies were moving much too fast. Galaxies are held together by the force of gravity, which is strongest at the center where most of the mass is. Stars at the outer edges of disk galaxies were moving so fast that the force of gravity generated by the observable matter there couldn’t have stopped them from flying off into deep space.

Scientists thought that there must be more matter present in these galaxies than we can currently observe. Something had to keep the stars from flying away, and they called it something dark matter. They couldn’t really say what properties it might have, except that it must have gravitational pull, and there must be quite a few. In fact, the vast majority of the universe (a whopping 85%) must be dark matter. Otherwise, the galaxies could not have stayed as long as they seem to. They would have separated because there would not have been enough gravity to hold the trillions of stars in place.

When it comes to science, the problem with something you can’t observe is that it’s hard to say much about it. Because dark matter does not interact with the electromagnetic force – which is responsible for visible light, radio waves and X-rays – all of our evidence is indirect. Scientists have tried to find ways to observe dark matter and make predictions based on theories, but without much success.

A possible solution

Newton’s theory of gravity explains most large-scale events quite well. Everything from the first pitch in a Yankees game to the movements of the constellations can be explained using Newton’s theory. However, the theory is not infallible. Einstein’s theories of general and special relativity, for example, explained data that Newton’s theory could not explain. Scientists still use Newton’s theory because it works for the vast majority of cases and has much simpler equations.

Dark matter has been proposed as a way to reconcile Newtonian physics with data. But what if, instead of a reconciliation, a modified theory is needed. This is where an Israeli physicist named Mordehai Milgrom enters. He developed a theory of gravity (called Modified Newtonian Dynamics or “Mond” for short) in 1982 which posits that gravity works differently when it becomes very weak, such as at the edge of disk galaxies.

His theory is not content with Explain the behaviors of galaxies; this predicted their. The problem with theories is that they can explain just about anything. If you walk into a room and see the lights are on, you can develop a theory that cosmic rays from the sun are hitting hidden mirrors in the right way to illuminate the room. Another theory could be that someone flipped the switch on the light. One way to separate the good theories from the bad is to see which theory makes better predictions.

A recent analysis by Mond shows that it makes significantly better predictions than standard models of dark matter. This means that, while dark matter can explain the behavior of galaxies well enough, it has little predictive power and is, at least on this front, an inferior theory.

Only more data and debate can settle the account of dark matter and the World. However, Mond coming to be accepted as the best explanation would shatter decades of scientific consensus and make one of the universe’s most mysterious features much more normal. A modified theory may not be as sexy as dark, unseen forces, but it may just have the advantage of being better science.

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