Grains of Sand

What does Carl Sagan, Neil DeGrasse Tyson, Jim Al-Khalili, and Morgan Freeman have in common? 

They have mentioned in documentaries this powerful, thought provoking statement:

"There are more stars in the Universe than grains of sand in all of the beaches in the world."

Why are they saying this? We know for sure that we cannot count the actual number of grains of sand in the beaches where we live. But all the beaches in world? That would be an enormous figure if that is achieved. But we know it's impossible. So what is this with stars and sand?

It turns out, we need a thought experiment to grasp this idea. Let's just say that you are in a spaceship, and you are outside the Milky way galaxy - our home galaxy. Your ships computer scanned the galaxy and tried to count the number of stars. And the computer figured that the Milky way has approximately 300 billion stars. 

Now imagine your spaceship is capable of travelling to the very depths of the cosmos and the computer was able to get an estimate on the total number of galaxies in the known, observable universe. And that estimate is close to 100 billion galaxies. If each galaxy has around 100 billion stars for example, and there are 100 billion galaxies (estimates from the Hubble Telescope in 1999 puts it around 125 billion and it is slowly increasing as new technologies are invented), then how many stars there might be in the known universe? The numbers would be so, so huge we cannot even comprehend how large the numbers would be.

Jim Al Khalili 

 Morgan Freeman

 Carl Sagan

Neil DeGrasse Tyson