valid strain frowned

It was a time of magic. Superstition ruled the world. A dark time. After the empire and before the age of reason.
It was a clouded time. When life was nasty brutish and short.
William McLarty was born into this time with a magical power so dangerous that by the time he was in his early teens, everyone, from the church to the king's men wanted him dead.
William was cursed with an awful power.
William could think.
Nearly 1000 years later, one of William's decendents was having lunch with a collegue from the laboratory when the curse manifested itself again.
"So Jack, get it like this, if time is like a cloud of probability with the present like an endlessly moving point of maximum collapse, then it should be possible to travel in time without affecting causality," said Bill McLarty.
"Come on Bill, even if what you say is theoretically possible it would still be impossible in terms of the energy needs of such a device," said Jack, Bill's co-researcher at the laboratory.
"Oh, so it takes a lot of energy to travel in time?" said Bill.
"Enormous quantities, and huge machines," said Jack.
"Are you sure?" said Bill.
"Absolutely," said Jack.
"So where's the big machine moving us in time now?" said Bill.