Hi Suppose an astronaut is accelerated to the speed of light (OK to one part in a million less than the actual speed of light ) and makes a journey to the event horizon of a black hole that is ,at the outset of the journey and hopefully also when he reaches it) 100 light year distant. At his destination he slingshots back in direction of the Earth and so arrives home after 200 years. How much time has elapsed in the spacecraft on the astonauts watch? What would be the corresponding answer if the speed attained by the astronaut was 50 %, 90% or 100 %(theoretically) of the speed of light? Many thanks.