C-ship

C-ship: Exploring special relativityHere’s what I’ve been doing the last week.  I’m not going to call this a Saturday night science post lest I find myself on a treadmill like at the other place, and besides it’s Sunday morning and before long the silly clock changing thing will kick in.  I’d hoped to wrap this up hours ago, but little did I expect that a bizarre confluence of IPv6, Gmail anti-spam filters, and obscure sendmail.cf configuration parameters would devour my entire day.

In 1995, I posted C-ship, in which I used a notional ship able to accelerate at a constant rate of up to 100 metres per second per second and ray-traced images and animations to provide an intuitive sense of how one perceives spacetime when travelling at a substantial fraction of the speed of light.  My inspiration in this was the Mr Tompkins stories by George Gamow, in which physical constants such as the speed of light and Planck’s constant were set to values near the human experience to illustrate how physics behaves at the scale of the very large and very small.  I’d hoped to use virtual reality to provide a visceral sense of such a world, but that was far beyond the technological capability of the time (and apparently the imagination of developers today), so I settled on a more static presentation.

The update brings all documents up to contemporary Web standards (XHTML/HTML5) and embeds animations and audio which previously required separate applications or plug-ins directly within Web pages.  Typography uses Unicode characters, and equations have been re-rendered to be more readable.

Enjoy your voyages on C-ship.

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25 Responses to C-ship

  1. 10 Cents10 Cents says:

    Thanks, John. That C is for Cents’ Ship, right?

  2. MLHMLH says:

    Which came first: the ship, the contraction or our own drlorentz?

  3. 10 Cents10 Cents says:

    It is amazing the ingenuity of people who had to come up with solution in the “stone age” of technology.

    I often think about how fast a ship can go if it has a constant acceleration. It can start off slow but over days it would be really going. The thing is how do you stop when you are going that fast. A really big parachute?

    • John Walker says:

      >> I often think about how fast a ship can go if it has a constant acceleration. It can start off slow but over days it would be really going. The thing is how do you stop when you are going that fast. A really big parachute?

      You just turn around at the half-way point and decelerate to a stop at the destination. This costs you remarkably little subjective (ship’s) time. See the “Trans-Lattice Shuttle” for an example.

      http://www.fourmilab.ch/cship/shuttle.html

      • 10 Cents10 Cents says:

        How does one turn around at that speed? In space is it easy to rotate when you are going that fast? Was this done in the command module and LEM rendezvous?

        • John Walker says:

          >> How does one turn around at that speed?

          Since there’s no air, speed with respect to anything is irrelevant. The only time which way you’re pointing matters is when you fire a rocket, which needs to be oriented to achieve the desired thrust vector.

          >> In space is it easy to rotate when you are going that fast?

          Again, speed doesn’t matter. The energy required to rotate depends only upon the moment of inertia of the object, which in turn depends upon its mass and shape.

          >> Was this done in the command module and LEM rendezvous?

          Yes—this was called the “transposition and docking maneuver”. Here is a video about the procedure.

          https://www.youtube.com/watch?v=Ac47IgC39m8

          This is actual film and video of the maneuver from Apollo 15. The video title is incorrect; the maneuver was not done in Earth orbit, but rather after leaving orbit en route to the Moon.

          https://www.youtube.com/watch?v=-1W_VYCzics

  4. BrentB67BrentB67 says:

    That was a great experience just traveling through the links on the site.

  5. JJJJ says:

    How interesting! I will check it out when I have some time. Thanks for posting.

  6. 10 Cents10 Cents says:

    I never thought about using water as a shield. Water in its ice form is very hard but not as hard as pykrete.

    • John Walker says:

      > I never thought about using water as a shield. Water in its ice form is very hard but not as hard as pykrete.

      Strength doesn’t really matter; at these velocities it’s just a question of absorbing and dissipating energy. If you are travelling close to the speed of light, the impact of a one microgram interstellar dust particle releases the energy of about 19.5 kg of TNT. The energy is radiated isotropically, and the part which impinges on the ship will be absorbed by and vaporise the ice. How much ice? Well, for a rough estimate take the sum of the enthalpies of fusion and vaporisation of water, 2590 kJ/kg, assume half the energy is absorbed by the ice shield (the rest being radiated away from the ship into space), and we get around 17 kg of the shield lost for each microgram dust impact.

  7. 10 Cents10 Cents says:

    I never knew a ping pong ball could go this fast. “Put your hands up, Brent. I have a vacuum. You too Vald.”

    https://www.youtube.com/watch?v=ONjlDPKdiVU

    • Vald the MisspellerVald the Misspeller says:

      Yeah, a perfect vacuum — between the ears, hence the IQ of absolute zero. (Don’t take it personally … wait, what am I saying, you can’t, you’re a sock.)

      By the way, that thing wouldn’t be much good for concealed carry. Where would you hide the compressor?

  8. Trinity WatersTrinity Waters says:

    Thanks for the time you spend creating such powerful reading pleasure for us, John!

    • Vald the MisspellerVald the Misspeller says:

      *

    • Trinity WatersTrinity Waters says:

      I need to amend this comment!

      I went through the whole program and it was enlightening. Understanding the concepts of classical physics and then the relativistic complications, similar to the quantum stretch I discovered after chemistry, are one thing in the intellectual realm, but the videos embedded here gave me a much improved understanding. I knew how to manipulate and use Convolution Integrals and Eigen vectors for years before a light went off one day and the construct became visual for me. So it is with time/space now. Thanks again.

  9. Whiskey SamWhiskey Sam says:

    The great benefit of the internet age for me is being able to sit back and watch (or take part in) discussions like this where you can pick the brain of someone like John.

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