Star Trek: The physics behind blowing up a planet
MAY 29, 2009
DOI: 10.1063/PT.5.023379
SCI FI Wire : In the latest Star Trek movie , a series of planets collapse when a black hole is created inside the planet’s interior. Scientist and science fiction writer Wil McCarthy calculates how tricky would it be to completely destroy a planet. As McCarthy says:
According to McCarthy because of the small size of the black hole created in the movie, objects such as rubble “would be banging and grinding against one another for years” before they reached the black hole’s event horizon. Hence the destruction of a planet in Star Trek, which takes up only a few minutes of screen time, would be unrealistic in the ‘real’ universe.
“Destroying a planet takes time. They’re big, dense objects, and destroying one is not like popping a balloon or even vaporizing a city with nukes... Even if you drop a bomb or fire a death ray powerful enough to reduce a whole planet to rubble, you still have the problem of gravity; that rubble is going to stay where it is, or at worst, fly apart and then fall back together again.
The resulting planet would be loose rather than solidâmdash;picture a pile of sand or a dump truck full of gravelâmdash;but it would still be round, it would still have gravity, and you could still orbit your spaceship around it.
In the case of an explosion, the energies involved are colossal. The Earth (for example) weighs 6 billion quadrillion tons, and even if we ignore the force required to break it into small pieces, we still need to accelerate every scrap of it to escape velocityâmdash;over 10,000 meters per secondâmdash;in every possible direction, to overcome their collective gravity and keep them from falling back together again. That means almost a quadrillion quadrillion gigajoules of kinetic energy. That’s the equivalent ... of the total heat output of the sun for three full decades.”
© 2009 American Institute of Physics
