Dark Matter: We Can’t See It, but We Know It’s Out There.

It's surprising to note that even in 2019, more is unknown than known about the actual composition of our universe.

For a long time, scientists have believed that everything in our universe--including us--was made of protons, neutrons and electrons, the building blocks of atoms. But—and there’s no nice way to say this—we’ve been completely wrong.

We now know that the visible universe--what we can see or observe with our eye or scientific instruments-- is only about 5% of the total mass of the universe. So what’s the other 95%? It appears to be composed of a mysterious, invisible substance called dark matter and invisible energy scientists call (not all that creatively) dark energy.

Looking for something we can’t define is obviously hard to do. We normally would want to use light to see things, but dark matter and dark energy can’t be seen in the ordinary light spectrum nor by any form of electromagnetic radiation.  They don’t directly interact with ordinary visible matter either.

So far, we don’t even have a single piece of experimental evidence that proves the detection of dark matter particles. Scientist working in the field think that dark matter is mostly likely made up of an entirely new elementary particle outside the Standard Model.

Knowing all this, you’d be forgiven if you asked: how do scientists know dark energy and matter even exist in the first place?

The answer is simple: gravity. All objects with mass have their own gravitational field. Scientists have been able to observe and measure the gravitational effects of dark matter and dark energy on objects they can observe. Studies suggest that galaxies, the large clusters of millions of stars, spin much faster than expected based on their visible matter.  Furthermore, galaxies move faster in clusters than expected. Scientist can calculate the “missing mass” responsible for these motions. The missing mass is dark matter. They can’t see it, but they know it’s there.

Scientist try to make sense of this missing mass by developing a theoretical model with the cosmological observations.  Fitting such models gives them an estimate of the composition of the universe. These estimates suggest that our universe is composed of 5% of the visible normal matter, about 27% with dark matter and about 68% with dark energy.

What dark matter actually is, is a field of current and future research. Several scientific groups are currently attempting to create dark matter particles in the lab. Scientists at CERN’s large hadron collider are among those leading the way.

Albert Einstein was the first to hint about the invisible matter and energy of the universe.  In his equations, he discovered a parameter known as the “cosmological constant,” which we now know to be synonymous with dark energy. Einstein called the cosmological constant his “biggest blunder,” thinking it an error. Now, however, we know that one of history’s smartest thinkers was right all along. At least, we think he is. After all, there’s still so much of our universe left to discover!

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