Can you determine the next number in the below sequence?
$1.0 , 4.0 , 6.9 , 9.0 , 10.8 , 12.0 , 14.0 , 16.0 , ?$
Bonus: Determine the next number that comes after '?'
Note: I'll post some hints if nobody gets the answer.
Hint #1: You won't get the relationship between the numbers by calculating.
Hint #2: These numbers have some relationship with science.