Fumfer Physics 39: Anthropic Principle, Cosmic Scale, and Why We Live in the Middle

Scott Douglas Jacobsen and Rick Rosner explore whether the ratio between the observable universe and the smallest physical scales carries deeper significance. Rosner situates the question within the anthropic principle: observers necessarily arise in regions and eras compatible with simple life. Humans exist near an active star, within the universe’s luminous core, because complex or long-lived civilizations would occupy very different energetic regimes. Rosner extends this reasoning to human history itself, noting that the present era contains the largest concentration of humans who have ever lived, making it statistically unsurprising that we find ourselves “now.” The result is not cosmic centrality, but observational inevitability.

Scott Douglas Jacobsen: When you look at those maps of the size of the observable universe, what we see—those structural, spatiotemporal limits—are bound by the speed of light. What we can observe is based on the apparent age of the universe, the speed of light, how far it can travel, and the expansion of space itself. But is there any importance to the ratio between the observable diameter of the universe and the smallest meaningful scales in physics?

Rick Rosner: People have noted.

Jacobsen: We are right in the middle of it.

Rosner: Yes, people have noted that there are evocative ratios that echo other ratios in physics—for example, in coupling strengths. There are these questions about why we are in the middle.

Jacobsen: Why are we in middle reality? Why are we in the middle of the universe’s magnitudes?

Rosner: For one thing, for life to exist—simple life like us—if you look at the possible ages of civilizations, human civilization is often said to have begun around 10,000 years ago. The universe is about 13.8 billion years old. Stars can burn for around 10 billion years.

It is possible to imagine civilizations that have existed for millions, or even hundreds of millions, of years. Compared to them, we would be young and simple. A civilization that has existed for 20 million years would be unimaginably complex by our standards.

But we are simple. We get essentially all of our energy from simple sources. All the energy on Earth ultimately comes from sunlight. It gets converted into other forms, but it is still sunlight.

Simple life emerges on a planet—a rocky body in orbit. We are very close to nature. We are not an engineered civilization of the far future. For us to exist in our simple form, we need to be part of the active center of the universe, orbiting an actively burning star.

So why are we in the center of the universe? Because of the anthropic principle: we necessarily find ourselves in a universe, and in a region of that universe, that is compatible with life. Otherwise, we would not be here.

The universe we observe is one in which life can exist. If there are many possible universes, we necessarily find ourselves in one that permits life. Likewise, if there are many possible locations within a universe from which observations could be made, we have to be observing from an active region—near a star—because without orbiting a star, we would not exist. That is why we are in the middle of things, in that sense.

There is also a demographic argument used to ask why we exist at this particular point in human history. Why are we not cavemen? Why are we not living during the Renaissance?

The argument—admittedly not a tight one—is that over the history of humanity there have been on the order of 110–120 billion humans, with roughly 8 billion alive now. If you sampled a human at random across all of human history, the present era represents the single largest concentration of humans. That makes it statistically more likely, compared to most earlier periods, that you would find yourself living now.

It is a somewhat wobbly argument. It does not necessarily imply that there will be fewer humans in the future. I do not know. But arguments of that kind exist.

Rick Rosner is an accomplished television writer with credits on shows like Jimmy Kimmel Live!, Crank Yankers, and The Man Show. Over his career, he has earned multiple Writers Guild Award nominations—winning one—and an Emmy nomination. Rosner holds a broad academic background, graduating with the equivalent of eight majors. Based in Los Angeles, he continues to write and develop ideas while spending time with his wife, daughter, and two dogs.

Scott Douglas Jacobsen is the publisher of In-Sight Publishing (ISBN: 978-1-0692343) and Editor-in-Chief of In-Sight: Interviews (ISSN: 2369-6885). He writes for The Good Men Project, International Policy Digest (ISSN: 2332–9416), The Humanist (Print: ISSN 0018-7399; Online: ISSN 2163-3576), Basic Income Earth Network (UK Registered Charity 1177066), A Further Inquiry, and other media. He is a member in good standing of numerous media organizations.