Astronomy’s biggest misconception

💥 The basic idea amateurs and professionals still get wrong.

with Ethan Siegel • April 25, 2026

---

Greetings readers,

In all the Universe, humanity has come to understand many phenomena at a deep and profound level, but the general public, and even many experts, remain misinformed about how they work or whether those phenomena even exist. Examples abound in modern times, including about such important topics as dark matter, dark energy, cosmic inflation, the Big Bang, and type Ia supernovae. But the biggest misconception in all of astronomy is even more basic and fundamental: how stars work. You can ask Wikipedia, a leading LLM, or even many professional astronomers questions like: Why do stars shine? What holds them up against gravitational collapse? What sets a star’s temperature and brightness? Or when do stars turn on? When you ask, you’re likely to get the same (incorrect) answer to all of them: nuclear fusion. The fact is that “the birth of a star” doesn’t even come from achieving the ignition of fusion reactions in the star’s core, but rather from reaching an equilibrium state.

We also debuted another exciting issue at Big Think: the Energy issue, where I contributed a story on the energy required for interstellar travel and why antimatter is the only realistic option to get us there. On cosmic scales, a brand-new test of dark matter vs. MOND has come out, with the large-scale structure of the Universe and the CMB combined leading to a test on distance scales of hundreds of millions of light-years. It’s no surprise that, once again, dark matter has passed the test, while MOND fails it spectacularly. And when it comes to our quest for a theory of everything, there’s a sober possibility we truly must face: that the quest itself may be fundamentally wrongheaded, with heaps of reasons to support that line of thought.

The next time I write to all of you, it’ll already be May, so enjoy this week of April’s offerings, and stay tuned for even more cosmic news from the Universe here on Starts With A Bang!

All the best,
Ethan

---

ASK ETHAN

Ask Ethan: What’s the biggest misconception in astronomy?

In any field, misconceptions run rampant: things that “everyone knows” but don’t align with experts’ understanding of reality. In astronomy, the stakes are especially high, as our understanding of the Universe depends on getting it right. While misconceptions abound about the expanding Universe, the Big Bang, inflation, dark matter, and supernovae, the most misunderstood topic is the simplest: the stars themselves. Here’s what most people miss.

If you have a burning question about the Universe,
email startswithabang@gmail.com!

COSMIC PUZZLE

The idea of “theories of everything” may be fundamentally wrong

For more than 100 years, the holy grail of science has been a single framework describing all forces and interactions: a theory of everything. While early ideas like Kaluza-Klein fell short of our quantum reality, concepts like electroweak unification, GUTs, supersymmetry, and string theory point toward a tempting conclusion. But our Universe offers no evidence for them; only our wishful thinking does. Other attempts exist, but are they all without merit?

---

---

BALANCED BIRTH

Star birth doesn’t come from ignition, but from equilibrium

Throughout the Universe, the same story unfolds: a cloud of gas contracts, fragments, and forms clumps that grow into protostars, which gain mass and become full-fledged stars. This process is ubiquitous, with sextillions of stars now populating the observable Universe, powered by nuclear fusion. But igniting fusion doesn’t mark a star’s birth, and fusion alone isn’t why stars shine so brightly. The real story is only a little more complex, and it’s time you learned it.

---

FUEL PARADOX

Only antimatter provides the energy we need for interstellar travel

With Artemis II now complete, humanity has traveled farther from Earth than ever before, beyond the far side of the Moon by thousands of kilometers. But reaching other worlds in our Solar System, or exoplanets beyond, will require far more efficient propulsion than chemical rockets. The most efficient energy source, in theory, reaches 100%, and only one fuel can achieve it: matter-antimatter annihilation. Here’s why it’s the ultimate dream, and how we might get there.

---

THEORY CLASH

Dark matter passes a new cosmic test, while MOND fails

While a wealth of astrophysical evidence supports dark matter, it has yet to be directly detected, leading some to consider modifying gravity instead. Ideas like MOND remain popular, but they make different predictions than dark matter on large scales. In a new study, scientists have observed the kinetic Sunyaev-Zel’dovich effect on cosmic scales and tested both frameworks. Dark matter passes. MOND doesn’t. Here’s what that means.

---

Ethan Siegel, Ph.D., is an award-winning theoretical astrophysicist who's been writing Starts With a Bang since 2008. You can follow him on Twitter @StartsWithABang.

Get more Big Think content:
Big Think | Mini Philosophy | Big Think Books | Big Think Business