Extended Classic: Cosmic Queries: General Astrophysics 101

Image Credit: University of Warwick / Mark A Garlick

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Now extended with 12 minutes of Neil, Bill Nye and Steven Soter swapping their personal Carl Sagan stories in the “Cosmic Crib.”

Curious about general astrophysics? Then join us for class this week as Professor Neil deGrasse Tyson and teaching assistant Leighann Lord explain some of the basics. Discover why everything in the universe spins (and how you can test the theory of Conservation of Angular Momentum with a plate of spaghetti), how the gravity from a black hole can affect light even though light has no mass, and why we can be so sure that the universe is 13.7 billion years old. You’ll learn about dark matter and dark energy, the difference between weight and mass in planetary measurement, and why our galaxy isn’t expanding even though our universe is. Find out how we know that our solar system was formed as the result of a super nova, and whether a planet could orbit 4 suns. Plus, Neil trash talks Edwin Hubble and explains how NASCAR cars can steer in a straight line without crashing on a curved track.

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  • Jim

    So lets say a little orb is orbiting around you at 1 mph, but was rotating faster than the speed of light, would this object travel back in time?

  • I’ve played with geodesics on curved manifolds. I believe Dr. Tyson is incorrect, the Nascar racer would need to turn left. Unless the curves were banked at 90º (in other words, vertical walls).

    • Calvin

      I think your forgetting about the natural left you would get from gravity.
      also they do turn left, however I think that’s due to them exceeding the speeds the banks are designed for. (also the cars are set up to turn left on their own)
      with a 90 degree bank I think you would need to steer right, not left to fight off the gravity pull, unless your car was fast or had enough downforce (relative to the racing surface) to fight off the gravity pull with sheer momentum. (for instance an f1 car has enough downforce at 200+ mph to run upside-down)

      • A geodesic is the shortest path between two points on a manifold. If the manifold is flat Euclidean space, straight lines are geodesics. If on a spherical surface, geodesics lie along great circles. Also cylinders can have geodesics that lie on circle (this is what I’m thinking of when I mention walls with a 90º bank).

        Banked roads on Nascar tracks are fragments of a cone. You can’t follow a geodesic on this manifold without eventually leaving the track. You need to turn left to avoid going off the track.

        Tracks are banked so the net acceleration vector is closer to perpendicular to the race track. In this regard gravity comes into play. But earth’s gravity is pretty irrelevant when it comes to the geodesic on a banked curve.

        Given enough mass, gravity can bend geodesics into a circle. This is at 1.5 the Schwarzchild radius. Again, not relevant to an earthly race track.

        • HI all. Jeff from StarTalk here.
          I thought I’d just share this link to an article in Jalopnik that references this issue. The folks at Jalopnik (which describes itself as: “a news and opinion website about cars, the automotive industry, racing, transportation, airplanes, technology, motorcycles and much more. We aim to cover these things with an honesty, transparency and cheerful belligerence that can’t be found anywhere else.”) at first took issue with a series of tweets Neil did about NASCAR, after which, Neil explained in great detail the math behind his assertions. In the end, Jalopnik was more than satisfied with Neil’s points, which are included here. While this does not specifically reference the full breadth of your conversation, I think you guys might find it worth checking out:

          • Yes, if the tire’s coefficient of friction is about 1, Tyson is correct that 165 mph is the maximum speed cars could take the banks at the charlotte speedway. Faster and the so called centrifugal force would take the car off the track. But what is the so called centrifugal force but inertia in a rotating frame? And an inertial path is a path along geodesic. So Tyson seems aware that a car’s path on the banked curves isn’t a “straight line from the car’s point of view”.

            And the context of the discussion is the path of light in our space time manifold (starting at the around 33:30 of the above podcast). And light follows geodesics along our space time manifold. Tyson is not correct if he maintains a geodesic on the banked path can avoid going off the track. I’m disappointed he’s saying this.

            Also Tyson’s 165 mph max speed in the jalopnik article was also wrong. He started his calculations with a wrong assumption. In a Nascar race it is common for the coefficient of friction to be greater than one. Racers can go more than 165 mph on the turns and they do have to turn left.

  • G

    I have wondered for some time about the banking on race tracks. Thanks, Neil for finally giving me an answer! 🙂

  • Chris Arnold

    vap holes eblackerate?

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