The substance of the bread and wine are transformed. But the physical aspects (accidents) are the same. They remained the same because it was the same with Christ, his body was human, material. But he was God at the same time, but if you saw him you would see a man like any other.
In the Eucharist three things happen : sacrifice, resurrection and glorification.
It's a kind of time travel because it's not a different sacrifice but the same one at the Cross. Because that was an eternal act, the eternity in Catholicism it's not an infinite amount of time but a timeless moment. The sacrifice of the Lamb goes eternally to future and past in our spacetime.
Way before Einstein the Eucharist already have the concept of relative time. Even if one does not believe in this it must have to admit that this was a very sophisticated concept to be created so long ago.