The hunt is on for a dark force of nature

Getting dark: Scientists believe that dark matter will be found at the edges of galaxies. © NASA

Is the search worth it? Scientists are launching an experiment to find a mysterious fifth force of nature. If they find it, it will give us an insight into the unseen world of dark matter.

At a lab near Rome, a group of physicists have begun a search for a mysterious “dark force”. It might sound a bit like Star Wars — the experiment is even named Padme — but this is no science fiction. (The name has nothing to do with Luke Skywalker’s mother; it stands for Positron Annihilation into Dark Matter Experiment).

In fact, the scientists in question are searching for insight into one of the most fundamental questions of the universe: what is in it?

“At the moment, we don’t know what more than 90% of the universe is made of,” researcher Mauro Raggi explained to The Guardian. All of the atoms and particles that we can see account for just 4%.

Most scientists believe that the rest is a “dark world” of dark matter and dark energy. Very little is known about it, besides its gravitational effects.

Padme will be searching for a “dark force” that links the dark world and the one that we see.

The experiment will fire antimatter at a wafer-thin diamond, just a tenth of a millimetre thick. In most cases, the antimatter will disappear, producing two particles of light (known as photons) in its place. However, if a dark force exists, every now and then a “dark particle” will be produced instead. The scientists will not be able to see it — but they will notice the missing photon. They might even be able to work out the dark particle’s mass.

At the moment, we only know about four fundamental forces of nature. There is gravity, which keeps your feet on the ground and the planets in orbit. Then there is electromagnetism, which interacts with light and electricity. Then strong force, which keeps atoms together, and weak force, which is involved in radiation.

If it exists, this fifth force will be the dark equivalent of electromagnetism. But nothing is certain — in fact, the chances of finding it are incredibly slim. “We are shooting in the dark in every sense,” said Raggi. “But if you are shooting, you at least have a chance.”

Is it really worth all the effort?

May the force be with you

It is pointless, say some. Why spend all this time looking for something we cannot see, cannot use, and have little hope of finding anyway? Some scientists are sceptical that dark matter even exists, instead arguing that we should modify our theories of gravity and the matter that we can see and touch.

Of course it is worth it, argue others. If it is successful, the experiment will open a window to a vast world that we know nothing about. The potential for discovery is unimaginable; just think of everything that happened after we found the forces of gravity, electricity, and then radiation. A dark force would be just as significant. Let’s hope we find it.

You Decide

  1. Do you think that a dark force exists?
  2. Will anything change if it does?

Activities

  1. Dark matter is more famous for what we don’t know about it than the things we do know. Write a list of questions you would want to answer if you were a scientist.
  2. Draw a diagram which explains the four fundamental forces of nature in as much detail as you can.

Some People Say...

“The most beautiful thing we can experience is the mysterious. It is the source of all true art and science.”

Albert Einstein

What do you think?

Q & A

What do we know?
When scientists observe galaxies, they come to an alarming conclusion: there is simply not enough stuff there for gravity to hold them together. And yet gravity is holding them together. This means that there must be something else present which is heavy enough to stop them from flying apart — something that we cannot see. Scientists call this extra stuff dark matter.
What do we not know?
What it is, how it works, where it comes from, or anything else about it. We are not even 100% sure that it exists, although so far most of the evidence suggests that it does. But if it does, we do not know whether the dark world is entirely separate from the world we see, or whether there is a dark force that interacts between them. That is what the scientists in Rome are looking for.

Word Watch

Lab
The National Institute for Nuclear Physics.
Dark matter
This is thought to make up roughly a quarter of the universe, and to be related to galaxies. (See the Word Watch for “gravitational effects”.)
Dark energy
This is thought to make up around 68% of the universe, and to be related to its expansion.
Gravitational effects
For example, stars at the edge of a galaxy ought to be travelling more slowly than those at its centre. However, this is not the case — they all travel at roughly the same speed. One explanation is that dark matter is lurking around the edges.
Antimatter
Particles which correspond to “ordinary” matter. In this case, the experiment will use positrons, the antimatter to electrons.
Modify
Changing our theory of gravity would, for example, be an alternative solution to the galaxy problem explained in the “gravitational effects” Word Watch. However, scientists who argue for this are still in the minority.

Subjects

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