About Dark Matter Day

What is Dark Matter Day?


On and around October 31, 2017, the world celebrated the hunt for the unseen—something that scientists refer to as dark matter. Local events organized by institutions and individuals around the planet explored its mysteries, and highlighted the experiments that could bring us closer to solving them. Since then, Dark Matter Day has become an annual celebration with labs around the world taking part. Stay tuned for information about Dark Matter Day 2023.

Less than 5 percent of the total mass and energy in the universe is the stuff we know about: like stars, planets, galaxies, and gases.

Dark matter makes up about 85 percent of the total mass of the universe, and about a quarter (26.8 percent) of the universe’s total mass and energy. Almost 70 percent (68.3 percent) of the universe’s mass and energy is composed of dark energy, another big mystery to scientists that is causing the accelerated expansion of the universe.

It’s Everywhere

All of the things that we can see in the universe only accounts for about 5% of all the matter in the universe. Around 95% of our universe is unknown to us. It exerts influence on what we see, but we can’t see or touch it. We call it, ‘dark matter’.

It’s Invisible

Dark matter is completely invisible to us. We have no way of seeing it because it doesn’t interact with light.

It Binds Galaxies

According to our current understanding of physics, something is holding galaxies together as they spin faster than we expected. Either there is some sort of unseen matter or force holding it together or our understanding of gravity and physics needs to be corrected. Either way, the hunt for dark matter will change how we see the universe.

It Distorts Space

When we observe distant galaxies, they appear distorted or stretched. This ‘gravitational lensing’ is caused by some unseen matter’s gravitational influence bending light around those galaxies.

Dark Matter Day is a globally recognized celebration of this cosmic riddle. It is sponsored by the Interactions Collaboration, an international community of particle physics communication specialists. Dark Matter Day was recognized around the globe on Tuesday, Oct. 31, 2017, as a day of intrigue and inquiry into the true nature of dark matter. Local events featured science experts, activities, and film presentations.

While Dark Matter Day was celebrated for the first time that year, it is not the first worldwide event to raise awareness about dark matter. In December 2010, for example, SISSA (the International School for Advanced Studies) in Trieste, Italy, organized Dark Matter Awareness Week to broadly share information about dark matter with scientists working in many different fields.

What Is Dark Matter?

There’s more to the universe than we can see. In fact, there’s a lot about universe that we can’t yet explain.

Dark matter, which we have so far only detected through its gravity-based effects in space, makes up about 85 percent of the total mass of the universe. So there’s a BIG part of the universe that we don’t know much about. We’re not sure if dark matter is made up of undiscovered particles, or if it can be explained by tweaking the known laws of physics. Solving the mystery of dark matter is considered one of the most pressing pursuits in particle physics and could teach us much about the history and structure of our universe.

Plan an Event

Want to plan a Dark Matter Day event in your community?

A local event could be:

  • A tour of a laboratory where dark matter research is conducted.
  • A screening of a dark matter-themed planetarium show or film.
  • An online chat or Q-and-A with a dark matter expert.
  • An in-person talk by a dark matter expert or experts.

We can help get you started!

Get Resources

This website includes resources that can help you find and connect with local dark matter experts, plan a program, and share your event with the world:

Frequently Asked Questions

Q: Why is dark matter so important that it has a dedicated day?

A: Dark matter is the glue that holds galaxies together, but we don’t know what it is. Understanding its true nature could explain its origins, evolution, and overall structure in the universe. The search for dark matter at the furthest reaches of the universe, and also at scales smaller than atoms, is one of the hottest pursuits in physics today, and whatever we learn about dark matter will be a discovery for the ages.

Q: Who is organizing Dark Matter Day and why?

A: The Interactions Collaboration, a global group of particle physics communicators, wants to give a voice to the silent, unseen, and massive presence of dark matter. The collaboration conceived of the Dark Matter Day—planned on and around October 31—to highlight the multitude of scientific experiments and theories that seek to resolve dark matter’s makeup and mechanisms. Dark matter is everywhere and all around us, and you don’t need a PhD to appreciate the impact it has on our cosmos. The goal of Dark Matter Day is to illuminate this cosmic mystery and share the exciting scientific adventure with everyone.

Q: Why is Dark Matter Day on October 31?

A: Some parts of the world celebrate the unseen—including all things ghostly, enigmatic, spiritual, and even spooky—with traditions such as Halloween, Day of the Dead, All Saints’ Day, and All Souls’ Day on or around October 31. Dark Matter Day is timed around these holidays as a way to call attention to the elusive, mysterious, and ethereal nature of dark matter. Scientists haven’t yet directly observed it though we know it’s there because of its observed gravitational effects on ordinary matter, such as the rotation speed of galaxies and the movement of galaxies within clusters. Dark matter seems to “hide” in plain sight and doesn’t play by the known rules of physics. Its like a costumed trick-or-treater who rings the doorbell and then dashes away, and scientists are trying to unmask it!

Q: Why should I host or attend a Dark Matter Day event?

A: Dark Matter Day events will seek to inspire, educate, and inform a global audience—from school-age children to the science-curious public, as well as active and aspiring scientists—about the importance of experiments and theories that seek to solve the universe’s dark matter mystery and to better explain its role in shaping the universe. The ultimate aim is for Dark Matter Day events to drive more international support and rally more brainpower for the dark matter experiments and theories that ultimately will lead to a discovery of epic proportions. And you can play a pivotal role in this effort by hosting an event detailing the history and progress of the hunt for dark matter or by attending a local event planned in your community.

Q: Do I need a science degree to attend a Dark Matter Day event?

A: Nope! Dark Matter Day events are designed for people of all ages, professions, and educational backgrounds. All you need is an inquisitive mind and thirst for knowledge.

Q: Why isn’t there a Dark Energy Day or a Multiverse Day or a String Theory Day or a Black Hole Day to learn about other important mysteries and scientific theories?

A: Dark matter is one of the most vexing mysteries in modern physics, so we decided to focus on this one for now. But there are many more mysteries of the universe that scientists are also pressing to solve. We encourage you to participate in other educational and informational events, too, that shed light on the importance of unraveling the universe’s other mysteries.

Q: Is Dark Matter Day an annual event?

A: Yes. It is now an annual event.

Contact Us

Contact us: darkmatterday@interactions.org.