The Anthropic Principle states that the universe’s parameters suggest that it was built to support life. However, some scientists find this conjecture ultimately non-falsifiable, as humans—being intelligent life—can’t refute it.
Now, a new study suggests a theoretical test that could potentially prove the Anthropic Principle false if certain conditions—including cosmic expansion, axions, and dark matter—are met.
Scientists still have many outstanding questions on all of these topics, so the test isn’t possible at the moment. But it could one day help prove—or, at the very least, provide strong evidence for—the notoriously untestable principle.
When you go through the long laundry list of things that need to happen for life to emerge in the universe—let alone our Solar System—it’s easy to entertain the idea that maybe the universe is just purpose-built to support intelligent life.
This idea—first proposed by English physicist Brandon Carter in 1973—is known as the “anthropic principle,” or AP, and its purpose is to explore the question of whether the universe we live in is fine-tuned to play host to life. This idea has been formulated a couple different ways over the years. Weak AP asserts that because humans are observing the universe, it must have evolved to support the emergence of intelligent life. Meanwhile, a harder take on the idea says that the universe had no choice but to evolve in a way that intelligent life could emerge. Things get even more philosophical, and even religious, when hard AP advocates invoke a designed purpose to the universe.
Related Story
Many experts have disregarded AP, stating that because the conjecture can’t be proven falsifiable, it’s not really scientifically useful. However, a new study published in the Journal of Cosmology and Astroparticle Physics theorizes a way to experimentally test this previously untestable assumption.
The key to this test is understanding that there do seem to be universal constants that make intelligent life—or, at least, the chance at intelligent life—possible. For example, incredibly tiny changes to Planck’s constant or the gravitational constant could make life impossible throughout the universe.
This study focuses specifically an ultralight axions, also known as “fuzzy” dark matter. According to the two authors—Nemanja Kaloper (an astrophysicist from UC Davis) and Alexander Westphalb (a particle physicist at the Deutsches Elektronen-Synchrotron (DESY) in Germany)—through future observations of this theoretical particle, discrepancies between theory and reality could help elucidate the viability of AP. In order to falsify AP, scientists in the future would need to prove that cosmic inflation occurred, that axions exist, and that dark matter is not made of axions.
Related Story
“Our specific example is the first case where the anthropic principle might actually fail the test, as opposed to simply declaring that it does not apply,” Kaloper said in a press statement. “The point is, that the presence of high-scale inflation and ultralight axions with masses m > 10-19 eV would imply that dark matter ‘must’ be an axion: for typical initial conditions, we’d end up with way too much dark matter, and we’d desperately need the anthropic principle to constrain it.”
Of course, scientists haven’t been able to satisfy any one of these test’s criteria, let alone all three. But if initial assumptions are correct, this example could help prove—or, at the very least, supply strong evidence for—the Anthropic Principle. If AP is conversely proven false, Kaloper suggests that “different rules govern the initial conditions” of the universe.
“The real theory of cosmology,” Kaloper said, “might be more complicated than we thought.”
Headshot of Darren Orf
Darren lives in Portland, has a cat, and writes/edits about sci-fi and how our world works. You can find his previous stuff at Gizmodo and Paste if you look hard enough.