It's hard to say "never" to something like time travel, simply because we don't understand the universe well enough to give a definitive answer. Right now, it's a hard "no" on Doc Brown's DeLorean, sure, but who knows what the future holds? Speaking of which, if time travel ever becomes a thing, it might only be to the future, as this video from RealLifeLore explains.
As detailed in the clip, there already exists a "soft" way to test for time travellers able to journey to the past. Hold your own party, just as Stephen Hawking did in 2009, but only send the open invite afterwards.
FYI, you can stop watching after the 5:40-mark, the rest is just advertising.
No one showed up to Hawking's soiree, which means either time travel to the past is impossible, or no one from the future was keen on the scientist's choice of hors d'oeuvres.
There's also the Grandfather Paradox, wherein one can't go back and assassinate there own grandfather, which would prevent them from being born and of course, committing the aforementioned murder.
While the video can't definitively rule out time travel, it does put forward a decent argument for why zipping into the past is unlikely. I don't really buy the idea of "time police", but I am a fan of the Novikov self-consistency principle. Basically, if time travel to the past was possible, someone would have turned up at Hawking's party. But they didn't, so it isn't.
It's kind of unsatisfying, but if we can't explain how something could work logically, it's hard to make it happen practically.
This article has been updated since its original publication.