So, this is a very tricky question because time is an odd thing and we really don't understand it. Is it fundamental and continuous or discrete, or even emergent from an underlying fundamental process or is it just an illusion we have as creatures with a type of memory? Do we live in the philosopher's block universe? There are theories that predict all of the above and we really don't know.
That said, we have models and the most prominent is General Relativity which treats time travel as possible, both forwards and in reverse. See a formalized definition by it's actual name of
Closed Timelike Curves (CTCs). There are solutions and implementable ways of making it feasible, such as Frank Tipler's work but it relies on either an infinity or negative energy. Wormholes could do it, but again require exotic matter and energy levels that are huge. That said, these things are theoretically possible with our physical models, thus they are engineering solutions and humans/intelligence are great at this. Look at how the
Alcubierre Drive has gone from a theoretically possible solution to something we can actually physically imagine as the energy requirements are now 'only' on the order of a Jupiter-sized object (they used to be huge order of magnitude larger, so I mean this broadly, in a grand civilizational manner) in a few decades time for an example. That said there are some who believe things like even thought it's allowed, it will be prevented by the universe -- people believe all kinds of things.
To the future is simple and we've measured it and see the effects on precise atomic clocks that are in accelerating reference frames such as GPS satellites.
If you're interested, I can go into more detail, but it gets more tedious and you really need to dig into the mathematics and understand stuff like a Minkowski space and the Einstein field-equations. People here are name-dropping blackholes and such, but it's a bit more complicated in reality.
