He argues that the time travellers will have to find a different technology than the traversable wormholes (TW).
The large wormholes are impossible classically because they would violate the positive energy theorem. Quantum mechanically, there could be loopholes that make them possible. However, Lenny Susskind argues that
- the energy must be conserved locally, and therefore the energy eaten by the throat is exactly zero
- because we know the energy exactly, we can't know the moment in which the object jumped into the wormhole - by the energy-time uncertainty relation
- consequently, you should have the same probability to reappear from the second throat at any moment, which does not seem like if you reappear at a particular moment of the history of the Universe
