In the episode "Second Chances", some kind of transporter "accident" causes Riker to split into two people. To beam Riker back, two transport beams of Riker were created to ensure his pattern could get through the planet's "distortion field". The two beams were supposed to be "recombined" back on the ship before re-materializing.
But instead one beamed back aboard safely while the other beam reflected back and rematerialized back on the planet. Eight years later they find the second Riker.
According to the episode, Will asks which one of them is real and Dr Crusher answers that they "both are". But I'm not sure if that makes the most sense.
Other possibilities are:
- One of the two is real and a continuation of the "original Riker". The other is a DUPLICATE.
- BOTH are duplicates. The original Riker is DEAD! And if so it is very possible that whenever someone transports, it is their DUPLICATE that rematerializes. The original is DEAD!
This episode strongly suggests that transporters are capable of "creating" new life out of thin air essentially. And if so, then it also stands to reason that it is also destroying life as well!