Book: A Brief History of Time by Stephen Hawking. Rating: ⭐️⭐️⭐️⭐️.

Nice book but not that simple for those who are not engaged with physics. That’s not a problem with the book, IMO, physics is complicated.

The pacing of the book is really good. He starts with the basics of physics and how paper after paper it is changing. It’s interesting how Stephen Hawking puts himself as part of that story, not the center of it.

I knew the Doppler Effect before this book, but for some reason, I was only applying it for sound and not for light. It was quite interesting to see the explanation of how we measure other stars via the light they emit. The redshifting effect because of the Doppler Effect is something I never thought about and was a good experience.

I have to say that it was quite hard to read (listen, in my case). I decided to not listen at 2.0x as I usually do and even though I had to move back many times to be able to get “in the flow”. I don’t have too many notes for this book and I think it’s related to the fact that I can’t explain some ideas I had without adding the whole context to it. To be able to add full context, I would need to understand some other contexts that are not clear enough.

I will probably read it again in the future.

Here are my personal notes:

  • Aristotle had a thought that the earth is round because the shadow of the moon would be an ellipsis if it was sharp
  • Isaac Newton not only proposed a theory of how objects attract each other but created all the complicated math to validate it
  • Newton came to the idea of gravity when he was in contemplating mood. It’s not when an apple hit his head
  • The city of God book, Saint Augustine
  • A theory can be disproved by falsifying just one of its hypothesis
  • When an object is not acted upon any force, it will keep moving in a straight line. It’s the first law of Newton
  • Acceleration is smaller the greater the mass (big engine in a heavy car)
  • Newton thought that time and space were two separate things
  • Time is not constant anymore. Now we consider the speed of light as constant and calculate time using it
  • Different elements absorb different specters of life. By using this information we can determine the elements present in that star’s atmosphere
  • The Doppler effect also applies to light. If a source star is moving away from us, its color tends to be redder, since the waves are reaching us faster and fave frequency is how we see colors. The same happens with sound waves, the sound changes related to distance (cop sound)
  • All measurements we have from galaxies are red shifted, which means that they are moving away
  • The farther a galaxy is from us, the faster it’s moving
  • The current evidence we have shown that the universe will probably expand forever but we’re are not 100% sure of that. If we have enough gravity to hold the expansion, the universe may start to compress
  • Hubble discovered that the universe is expanding
  • Why does the universe look so similar whatever direction we look?
  • The initial state of the universe must have been very well chosen to result in what we have now if the theory of a hot big bang is right. There are many explanations for this fact, not only “god”, but also multiple universes, each one having its own configuration and we can only exist in the ones who reach this form/state
  • Mathematics is what we use to describe our experiments. It doesn’t make sense to question what is real or not (talking about real and imaginary time)
  • The disorder increases in time because we measure time in the direction where the disorder increases 🤔
  • Science became too technical for philosophers in the past centuries
  • Galileo fought the church to be able to spread his ideas on science