Posted by: movieotaku | April 2, 2007

Gravity & Mass go *POOF!*

This was in my mail box since 2002 (Sorry Jon of UIUC, I’m sure you’ve graduated by now :-):

This is something I’ve been thinking about in Star Trek: Generations. Maybe it’s not such a huge blunder, but as a physics student I think that it’s neat.
When Picard and Data are in astrometrics, the Captain asks Data to list all of the effects of the star exploding. On the list is the fact that a starship had to make a course correction because the star was no longer there, and therefore its gravitational pull is gone. That is bull. The star may not be shining any more, and much of it may have blown off (which it wouldn’t have), but all of the mass is still in the general area of where the star was. That means that the gravitational pull is still there, and the ship can keep going on its same course

Also, changes in gravity propogate at the speed of light so the pull of gravity would still be felt by the ship for a while. Exploding stars lose some mass in a nova or supernova event as mass is converted into energy, but not that much. The large bulk of the mass is still in the immediate vicinity no further away than a sphere bounded by radius = ct (Speed of light * time since explosion)

When Data shows the path of the “nexus” through the second solar system, it shows the nexus missing the planet by at least a few million kilometers. When the second star is blown up, it happens only seconds before the “nexus” hits the planet. EVEN IF the star’s gravity went away, there would not be a very big change in the direction of the nexus in these few seconds, and certainly not enough for it to divert such a large direction.
ā€” Jon from UIUC

In this case, the gravitational pull of the star is assumed to be weak and that the change in trajectory would be in insignificant fractions of a degree, insignificant for seconds before impact that is. But you gotta admit, it did look cool.



  1. Unless the star’s mass was pulled through an extra-dimensional wormhole? (Yeah, its a reach but so is much of star trek)

    What bothers me most about the series (and most SF) with the exception of one solitary trek movie is that regardless how much battle damage a ship has taken, the artificial gravity never fails.

    • Well… that being one of the most important device for people to function, perhaps they have multiple redundancies?

      Also, that such realism is quite expensive and demanding script writers make this artificial gravity generator one of the most hardiest technology… šŸ˜›

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s


%d bloggers like this: