Author: Carl Sagan
I find the topic of space and the cosmos quite fascinating and Sagans book was a really accessible way to learn more about our universe, even considering it was published in 1980. I would love to read an updated version of this book with up to date information after over forty years of progress.
He covered a lot of topics. From chapters about various planets in our solar system, to deep dives on what stars are and how they are born and die, to discussing interstellar travel.
I still struggle to wrap my mind around the concept of special relativity and how when we speed up and approach the speed of light, time slows down for us, which is called time dilation. Time actually slows every time we speed up, even if we are just jogging, but the impact is so minor we wouldn’t notice it. But very precise clocks have been able to pick up the slowing of time on airplanes. Time dilation depends on your relative motion to others, but that is where I start to lose understanding. If time slows down for you relative to others, how is it that if you travelled near the speed of light for a long time, say 3 years, you would only age those 3 years, but everyone else will have aged decades in that 3 years of travel at the speed of light? I guess I struggle to wrap my head around how time and light are related. A ray of light from the sun leaves the sun at the speed of light. If you were to be able to travel faster than that light, you would essentially be in front of the light, and be able to see “back in time” because you are ahead of the light. But does your body not still age naturally while you are ahead of that light? I think I am getting confused about what “time” means in this instance. Anyways, big questions for another day.
Sagan dedicated a number of pages to interstellar travel and various ways we might explore more of the universe which was a cool section as well. One proposal for travel is a sort of “interstellar ramjet” which scoops up diffuse matter (mostly hydrogen atoms) that float between stars, and accelerates those atoms into a fusion engine and ejects them out the back of the ship. The hydrogen would be used both as fuel and as a reaction mass, presumably for energy for the ship. An issue with this though is that in deep space, there is only about one atom per every ten cubic centimetres, so for the ramjet to scoop up enough hydrogen, it would need a big vacuum/scoop at the front of the ship that would be hundreds of kilometres wide. And further complicating things, as the ship reaches relativistic velocities, the hydrogen atoms will be moving at close to the speed of light, and if the ship wasn’t designed carefully, the ship and the people on it will be fried by these rapidly moving cosmic rays. Wild stuff.
There was some interesting conversation on ways to explore the depths of space. Wanting to explore a star 4.3 lightyears away would take 43 years if we managed to travel at 10% the speed of light. At those lengths of time and beyond, resources become an issue. It makes me think that if we wanted to explore further and further out into space, we’d need some sort of chain of resources stretching from earth, that connect to hubs, perhaps near places we can extract more resource/energy like a star or a planet, and then launch further expeditions from. When they launched the James Webb telescope, I read that they parked it at what is called a Lagrange point which is a place where the gravity of two nearby bodies offset each other and allows the object between them to sit at rest. I thought of it as essentially a parking spot in space, where your telescope or other spacecraft would not just drift off. Maybe we need to park supply stations, etc at Lagrange points throughout our galaxy and beyond to act as resupply stations for deep space expeditions. Unfortunately, unless we can very quickly figure out how to travel very very fast (close to the speed of light), I won’t be alive to witness too much deep space exploration.
Overall, an inspiring and accessible book on space that I think is very worth reading.