The possibility of travelling through time, either to the future or the past, has perplexed scientists, nerds, and people who regret their life decisions for centuries. Although it seems theoretically possible, there are so many variables which physics and common sense deem impossible.
Let’s say, years in the future, you discover that your grandfather was responsible for putting adverts on Spotify. It’s the future now, and now five adverts play between every song, even with Premium. You decide that the only way forward in life is to go back in time to kill your grandfather so that he never makes Spotify adverts. You go to the nearest time machine (because it’s years in the future remember?) and travel back to when your grandfather is 18. However, if you kill your grandfather, your father will never be born, which means you’ll never be born, and that sucks because you’re awesome. So surely it’s impossible to kill your grandfather, because then you’ll never exist to kill him in the first place? That’s called an ‘inconsistent causal loop’.
Maybe, because of this paradox, this means that any efforts to kill your grandfather are always thwarted, because otherwise you couldn’t exist to be there to kill him – at the critical moment, your gun jams, or you get struck by lightning, or you trip over your shoelace. That’s the post-selective model of time travel. Or maybe you’re in a ‘consistent causal loop’, and your fate is predetermined – when you go back in time, you realise that your grandfather is actually a pretty cool guy, and you have some beers and show him your phone with Spotify, and show him how annoying ads are. You also mention that he made millions off it, which is how you could afford to use the time machine. That means your whole life is a time loop, and your travelling back in time is the whole reason your grandad got the idea for Spotify ads and in the first place. But then that’s a ‘bootstrap paradox’ – Spotify ads (and the phone you brought back with you) hadn’t been invented yet, so how could it possibly exist without having been invented? That means that the invention of Spotify is the result of an infinite cause-effect loop, and essentially all your fault.
Head hurt yet? Mine too. Spotify ads aren’t the end of the world – vinyls are better sound quality anyway, and they make your friends think you’re interesting.