Wednesday, September 2, 1998 Published at 20:06 GMT 21:06 UK
Time travel theory 'full of holes'
No jumping through time in the Tardis like Dr Who
Scientists appear to have dashed hopes that black holes might provide a way to travel around the universe by jumping through the fabric of space and time. Our science editor Dr David Whitehouse reports
Two Israeli scientists appear to have found out that if anyone tried to use a black hole this way they would be ripped apart.
A black hole is an object from which light cannot escape. It can be the extremely dense remains of a collapsed star.
Professor Stephen Hawking and Sir Roger Penrose showed that inside every black hole there is always a thing that scientists call a "singularity".
Here matter and also space and time is condensed to a point. The normal laws of physics break down.
If it was possible to go through the hole in a spaceship you could jump across the universe in an instant, or even emerge in a completely different universe.
Ripped to shreds
Tsvi Piran and Shahar Hod of Jerusalem's Hebrew University used computers to simulate both how a black hole forms and how the singularity behaves.
The simulations showed that an electrically charged black hole creates a new kind of singularity which forms an impassable barrier.
This work is not the final word on this idea. Many scientists say that even if it were theoretically possible to use a black hole this way it would be impossible to do so practically.