by S. Prasad Ganti

On a recent long flight to India, I saw a documentary titled “How does the Universe work”. I am summarizing the notes I took down from this fascinating piece. How did the universe evolve from such a tiny beginning to what it is today? 

The present day universe looks like a cosmic web. Given below is an artist’s rendering, courtesy Max Planck Institute of Astrophysics. It consists of galaxies or clusters of galaxies connected to each other via thin long filaments consisting of dark matter and gases. 

This could have been a picture of interconnected neurons in a brain. Or roads in a city or across cities themselves. Or a cobweb ! It appears to be random and unplanned growth. But it is a network of lumps connected by filaments. 

The universe formed about 13.8 billion years ago from a tiny spec in a process called the Big Bang. The tiny spec was intensely dense and hot. The explosion it created led to the creation of space itself. And the time started ticking thereafter. After the aftermath of the explosion settled down after 380,000 years, atoms started forming resulting in elements Hydrogen and Helium. Bulk of it being Hydrogen with little quantities of Helium. Ironically I learned that anything other than Hydrogen and Helium are known as “metals” to astronomers. For example, Argon the gas would be a metal !

The universe in those ages was very small. Nowhere compared to the huge volume we have today spanning billions and billions of light years across. Like how human civilizations started with small groups of people growing into towns and cities much later.  

In an infant universe, it was the dark matter which created the lumps and filaments structure. This dark matter is what is invisible to us but the effects of its gravitational pull are felt. Regular matter and lighting of the web came later after the initial skeleton was built. In as little as 250 million years after the Big Bang, stars had metals.And these are the oldest stars we see today. Metals would have been formed in ancient stars older than the oldest we see today. Those ancient stars when they died would have been the raw materials for the next generation stars we see today. The conclusion is that the first generation stars died too early for us to be observing them today. 

We know by observation that massive stars glow very brightly and die soon. The medium size stars like our Sun are relatively dim and last longer, like 10 billion years. The speculation is that the first stars were1000 times more massive than our Sun. Which means they were as big as extending the size of the Sun to the orbit of Jupiter, engulfing Mercury, Venus, Earth and Mars and the asteroid belt. Massive stars die in giant explosions called supernovas. There would have been a lot more supernovas in the earlier universe. The metals got cooked pretty early in the life of our Universe.

We do not find such huge stars in our Universe today. Something like dinosaurs not existing anymore !

The filaments in the web are known to contain vast swaths of hydrogen clouds. Dark matter feeds these gases to galaxies for star formation. The dying stars then make a contribution to the super massive black holes at the center of the galaxies. Super massive black holes formed just 900 million years after the Big Bang. Seems like the baby started running, not just crawling, very early !

There were a lot more stellar and galactic collisions in the early Universe. Since the early Universe was very small and there was not much room to move around without bumping into each other. 

The expansion of the Universe happened all along and is said to be accelerating today. Dark energy is supposed to be responsible for this expansion. The dark energy arises from “nothingness” in space. Speaking at a quantum level, the particle and virtual particle pairs get created and destroyed all the time leading to dark energy. 

Not bad for capturing a few interesting things on a flight ! The more we find, the more intriguing it becomes. Just a way of telling us that we are just beginning to scratch the surface !