Friday, 8 April 2016

Technical Terminology

Hard sf writers use technical terminology which many of us skip past, e.g.:

"'Total delta v of about two and a half c, Newtonian regime. Customarily, during the war, they'd boost to one-half c...they'd strike and return with the extra half light-speed available for high-powered maneuvers in between.'"
(Man-Kzin Wars III, pp. 220-221)

How much does the layman understand?

v is velocity;
c is light speed;
v for material bodies has to be lower than c in relativistic space;
however, higher values of c can exist in mathematics, e.g., e = mc2;
so, if delta v can be two and a half c, then what is delta v?;
we can google but cannot understand the Wiki article which, at a superficial glance, does not seem to explain delta v's higher than c.

I am not about to pursue this issue further. However, Anderson fans with scientific training might be able to help.


  1. Delta v means change of velocity; a rocket can carry an amount of fuel sufficient to achieve a certain change in velocity. Short of an FTL drive which for now remains fictional, a spacecraft cannot travel faster than light. These fictional, although still STL ships apparently carry enough fuel for a total change in velocity of two and a half times the speed of light, c. That is, the ship can accelerate to half of c, then decelerate down again, use up to half c's worth of delta v in maneuvers, then, in order to return to its base, accelerate up to half of c, and decelerate down again.

    I hope this helps

    Best Regqrds,
    Nicholas D. Rosen, B.A. in Physics, M.S. and Ph.D. In Materials

  2. Nicholas,
    Thank you. Very helpful. You can understand my puzzlement at a "delta v" apparently higher than c but you have explained it as a simple addition of velocities used at different stages of the journey.

    1. Thank you for your kind words.

      Best Regards,