Beyond/within the realms of possibility
Definition 1 of 1
Pro Tip 1/3Cultural Nuance
This phrase is often used to discuss future events, expressing varying degrees of uncertainty or hope. 
Becoming a professional athlete is within the realms of possibility for a dedicated person.
Pro Tip 2/3Subtle Doubt
When used in 'within the realms of possibility', it may imply something is possible but not guaranteed. 
Finding a cure is within the realms of possibility, though it may take years.
Pro Tip 3/3Skepticism
Saying something is 'beyond the realms of possibility' can carry a tone of skepticism or disbelief. 
Living on Mars is currently beyond the realms of possibility.