Is physics about to undergo a revolution?

galaxy universe gravitation 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, but scientists estimate it makes up 85% of the matter in the universe. The short answer is that nobody knows what dark matter is. More than a century ago, Lord Kelvin offered it as an explanation for the speed of the stars in our own galaxy. Decades later, Swedish astronomer Knut Lundmark determined that the universe must contain much more matter than we can observe. Since the 1960s and 70s, 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 there is no such thing Dark matter at all.

The backstory

Scientists can observe distant matter in a variety of ways. Devices like the famous Hubble telescope measure visible light, while other technologies like radio telescopes measure non-visible phenomena. Scientists often spend years collecting data and then analyzing it to make the best possible sense of what they see.

As more and more data came in, it became abundantly clear that galaxies were not behaving as expected. The stars at the outer edges of some galaxies were moving far too fast. Galaxies are held together by gravity, which is strongest in the center where most of the mass is. Stars at the outer edges of disk galaxies moved so fast that the gravity generated by the matter observed there could not have stopped them from flying into space.

Scientists thought there must be more matter in these galaxies than we can currently observe. Some gotta keep the stars from flying away, and they called that something Dark matter. They couldn’t really tell what qualities it might have, other than that it must have an attraction, and there must be quite a bit of that. In fact, the vast majority of the universe (a whopping 85%) must be made up of dark matter. Otherwise galaxies could not have existed as long as they seem. They would have dissolved because gravity wasn’t strong enough 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 difficult to say much about it. Because dark matter doesn’t interact with the electromagnetic force — 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 about it, but without much success.

A possible solution

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

Dark matter has been proposed to reconcile Newtonian physics with the data. But what if, instead of reconciliation, a modified theory is needed? Here is an Israeli physicist named Mordehai Milgrom. He developed a theory of gravitation (Modified Newtonian Dynamics or “moon” abbreviated) from 1982, which posits that gravity works differently when it becomes very weak, such as at the edges of disk galaxies.

His theory not easy to explain the behavior of galaxies; it forecast She. The trouble with theories is that they can explain pretty much anything. When you walk into a room and see the lights on, you can theorize that cosmic rays of the sun hit hidden mirrors in just the right way to illuminate the room. Another theory could be that someone flipped the light switch. One way to tell good theories from bad ones is to see which theory makes better predictions.

Recent analyzes of the moon show that it makes significantly better predictions than standard dark matter models. This means that while dark matter is reasonably good at explaining the behavior of galaxies, it has little predictive power and is an inferior theory, at least on this front.

Only more data and debate will be able to settle the score on Dark Matter and the Moon. However, accepting the moon as the best explanation would shake decades of scientific consensus and make one of the universe’s more mysterious features much more normal. A modified theory may not be as sexy as dark, unseen forces, but it may have the benefit of being better science.

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