After the Big Bang when the Universe was a dense fireball it began to cool. It now has an average temperature of about 3 K, but there was a time when it had a temperature of about 273 K and 373 K. In other words, the average temperature of the cosmos was just the right temperature for liquid water to exist. Since liquid water is necessary for life as we know it, this raises an interesting question. Could life have arisen in the early Universe? 

This period is known as the habitable epoch of the early Universe, and it existed between 10 to 17 million years after the Big Bang. While it was the right temperature for liquid water during that time, that doesn’t mean that liquid water existed. The first elements of the Universe were primarily hydrogen and helium. To produce oxygen necessary for water, very young large stars would have needed to fuse oxygen in their core, then exploded as a supernova within the first 10 million years of the Universe. If such a thing did occur, it would have been extremely rare. Forming water from oxygen and hydrogen is pretty easy in space, but there would need to be sufficient water and other matter for it to gather in liquid form, rather than vapor.

Then there is the issue of time. The epoch itself only spans 7 million years, which isn’t nearly long enough for complex life to evolve (at least if Earth is a reasonable example). Add to this the fact that life also needs other elements like carbon and nitrogen in addition to water, and it doesn’t look particularly likely.  It is, however, and interesting example of how life might have arisen in ways we wouldn’t expect. We think of life as evolving around a typical star when the Universe was already billions of years old, but in the earliest cosmological moments it’s possible that life, uh, found a way to arise.

In a recent paper presenting the idea, the purpose was not to argue that such early life was likely, but rather as a discussion of the anthropic principle.  The anthropic principle comes in many forms, but one of the more controversial versions argues that if the various parameters of the cosmos were different then life wouldn’t arise. It’s almost as if the structure of the Universe was specifically tweaked for life to exist. But if life could arise in the early Universe, in period radically different from the present Universe, then it shows that life isn’t as delicate as we might think. A different set a cosmic parameters could allow for life to arise in radically different ways.

While I don’t think it’s likely life appeared just a few million years after the Big Bang, it is an interesting idea. It’s also a great example of why we shouldn’t presume that the story of life on Earth is the only story life could have.

Paper: Abraham Loeb. The Habitable Epoch of the Early Universe. International Journal of Astrobiology 13 (4): 337–339 (2014) doi:10.1017/S1473550414000196

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Everything you experience is experienced from your personal perspective. That seems like a rather obvious statement, but it also applies to humanity as a whole. Everything we experience in the universe is from our point of view. Cosmologically that view is a very narrow window. Humanity has only been around for a moment of cosmic time. We see the heavens from the vantage point of a small rock orbiting a medium star. Our comprehension of the universe is framed by the biases of our primate minds.

It is this idea that is encapsulated by a philosophical idea known as the anthropic principle. Of all the ideas in astronomy and cosmology, the anthropic principle is perhaps the most controversial. Despite its name, there are in fact several variations of the anthropic principle.

The Weak Anthropic Principle states basically what I summarized in the first paragraph. Our view of the universe is not random. It is biased by the fact that we are observing it. For example, we observe a universe that is billions of years old because it takes billions of years for planets to form and life to evolve.

The Weak Anthropic Principle is simply a reminder that we shouldn’t read too much into observations that seem special. I live in the United States, so a random sampling of people around me finds that most speak English as their first language. I can’t presume however that humans speak English as their first language, because my sample is biased by my location. Someone living in Japan would find that most people speak Japanese.

The Strong Anthropic Principle is more controversial. It states that the universe as a whole must have conditions necessary for life such as ours to exist. For example, gravity in three spatial dimensions allows for stable planetary orbits, but gravity in four-space doesn’t. If the universe had expanded more quickly than it did, then stars and galaxies wouldn’t have formed. Too slowly and it would have collapsed back on itself.

On the one hand the strong principle is rather obvious. If the universe was too different from the way it is (gravity too strong, speed of light too small, etc.) then we wouldn’t be here. But this fact is sometimes used to argue a stronger version of the principle. Specifically, the fact of our existence means the universe must be fine tuned to a set of conditions that allows us (or a similar sentient species) to exist. This idea was first proposed by Brandon Carter in 1974, and it has stirred controversy ever since.

But that’s a story for another day.

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