My Blog

Mindblown: a blog about philosophy.

  • Spiral Structure

    Learning Objectives By the end of this section, you will be able to: Astronomers were able to make tremendous progress in mapping the spiral structure of the Milky Way after the discovery of the 21-cm line that comes from cool hydrogen (see Between the Stars: Gas and Dust in Space). Remember that the obscuring effect of interstellar dust…

  • The Architecture of the Galaxy

    Learning Objectives By the end of this section, you will be able to: The Milky Way Galaxy surrounds us, and you might think it is easy to study because it is so close. However, the very fact that we are embedded within it presents a difficult challenge. Suppose you were given the task of mapping…

  • Thinking Ahead

    Today, we know that our Sun is just one of the many billions of stars that make up the huge cosmic island we call the Milky Way Galaxy. How can we “weigh” such an enormous system of stars and measure its total mass? One of the most striking features you can see in a truly…

  • Gravitational Wave Astronomy

    Learning Objectives By the end of this section, you will be able to: Another part of Einstein’s ideas about gravity can be tested as a way of checking the theory that underlies black holes. According to general relativity, the geometry of spacetime depends on where matter is located. Any rearrangement of matter—say, from a sphere…

  • Evidence for Black Holes

    Learning Objectives By the end of this section, you will be able to: Theory tells us what black holes are like. But do they actually exist? And how do we go about looking for something that is many light years away, only about a few dozen kilometers across (if a stellar black hole), and completely…

  • Black Holes

    Learning Objectives By the end of this section, you will be able to: Let’s now apply what we have learned about gravity and spacetime curvature to the issue we started with: the collapsing core in a very massive star. We saw that if the core’s mass is greater than about 3 MSun, theory says that nothing…

  • Time in General Relativity

    Learning Objectives By the end of this section, you will be able to: General relativity theory makes various predictions about the behavior of space and time. One of these predictions, put in everyday terms, is that the stronger the gravity, the slower the pace of time. Such a statement goes very much counter to our intuitive…

  • Tests of General Relativity

    Learning Objectives By the end of this section, you will be able to: What Einstein proposed was nothing less than a major revolution in our understanding of space and time. It was a new theory of gravity, in which mass determines the curvature of spacetime and that curvature, in turn, controls how objects move. Like all new…

  • Spacetime and Gravity

    Learning Objectives By the end of this section, you will be able to: Is light actually bent from its straight-line path by the mass of Earth? How can light, which has no mass, be affected by gravity? Einstein preferred to think that it is space and time that are affected by the presence of a large mass; light beams,…

  • Introducing General Relativity

    Learning Objectives By the end of this section, you will be able to: Most stars end their lives as white dwarfs or neutron stars. When a very massive star collapses at the end of its life, however, not even the mutual repulsion between densely packed neutrons can support the core against its own weight. If the remaining…

Got any book recommendations?

Get In Touch