I asked a student in class: “What percentage of the universe can we actually see?” Most answers: “50%? 80%?” The correct answer is about 5%. The remaining 95% is made up of dark matter and dark energy [1].
Dark Matter — 27%
When we observe the rotation speeds of galaxies, visible matter alone cannot explain them. Stars at the outer edges of galaxies are rotating too fast. Vera Rubin confirmed this observationally in the 1970s, concluding that an invisible mass — dark matter — must exist [1].
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Dark matter does not interact with light. We can only observe its gravitational effects. In class, I compare it to an “invisible hand” [2].
Dark Energy — 68%
In 1998, teams led by Riess and Perlmutter independently discovered that the expansion of the universe is accelerating [3]. This discovery earned the Nobel Prize in Physics. The unknown force driving this acceleration is called dark energy.
Science That Admits What It Doesn’t Know
The message I emphasize most to students: the beauty of science lies in admitting what we don’t know. We can explain remarkable things with the 5% of the universe we understand, while remaining ignorant of the other 95%. That is scientific humility.
The Value of This Topic as a Teacher
Dark matter and dark energy are topics that ignite students’ curiosity. “Teacher, so what exactly IS dark matter?” “We don’t know yet. Maybe you’ll be the one to find out.” That answer makes their eyes light up [4].
Disclaimer: This article is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider with any questions about a medical condition.
Your Next Steps
- Today: Pick one idea from this article and try it before bed tonight.
- This week: Track your results for 5 days — even a simple notes app works.
- Next 30 days: Review what worked, drop what didn’t, and build your personal system.
Last updated: 2026-03-16
About the Author
Written by the Rational Growth editorial team. Our health and psychology content is informed by peer-reviewed research, clinical guidelines, and real-world experience. We follow strict editorial standards and cite primary sources throughout.
References
- Trimble, V. (1987). Existence and nature of dark matter in the universe. Annual Review of Astronomy and Astrophysics, 25, 425-472.
- Tarbuck, E. J., & Lutgens, F. K. (2017). Earth Science. Pearson.
- Riess, A. G., et al. (1998). Observational evidence from supernovae for an accelerating universe. The Astronomical Journal, 116(3), 1009.
- National Research Council. (2012). A Framework for K-12 Science Education. National Academies Press.