Change the comma after time machine to a period and capitalize However.
Did you spot the typo? Change turnign to turning.
I suggest changing have managed to create to just have created.
Scientists have created the world’s first time machine. However, it can only send messages to itself in the past. Within seconds of the machine being turned on, messages of warning begin to flood in from the future.
(Ah, quantum entanglement… This scenario is plausible, you know.)