Starting at the beginning might be going back a bit far. But starting later will only mean having to explain what was before. Or what will be over and over again. When people start talking about time and time travel, well it's like listening to Kamala Harris.

For the record. I am an adamant supporter of time travel. I have nothing against it and have actually witnessed it first hand. So I do know it is factually true, you can time travel.

What do people use to bring about time travel. Generally some mechanical, nowadays electronical components and energy.

What about the paradoxes of time travel. I hear the typing in my head already. Telling me, those are solved by the timelines.

Time travel to influence the present. Or the pasts future.

Is there ever a time. When travelling back in time is not nefarious.

Let's start with the last one first.

The why to travel back. What would you do if you had a chance to travel back in time. To select the place and time. Many answers come with that question. Many of them are observational only. To witness some event. Others to be part of the event or the event itself.

I am unsure if there is a difference between those two.
Witnessing an event might appear on the surface to be the lesser chance of interference.

To change an event in history and alter the lives of millions of people. If not billions. Will bring about a timeline that you were not born in. The further you go back in history and make a change. The greater the chance you will not be born.

There comes the parallel world's theory.

Okay, let us entertain the idea of the parallel worlds. Each time you make a choice there is a split in the parallels. An addition track to travel along opens up. Any person moving back in time. Does not actually travel back in time. But jumps to a parallel world at a different time. The same space, just a different time. Yes, the same space is in a different world. It is still earth though.

So someone from 2030, jumps back to 2020 and Trump still does not get elected in 2020. This proves time travel is not possible back in time. Because history still shows Trump did not get elected in 2020. That or the prevention of Trump not getting in only happens ion the new world created.

Where does the energy come from to create this spontaneous new world and its surrounding galaxy and universe?
In this new universe. Where did all of the new people come from?
If you jump from one timeline to another. What would give anyone the notion that everything up until that point had the same end results? You would just jump to a developed world.

Then take in to account. you are moving your own entity through time. When you arrive at that time. Unless you have reversed time for at least the galaxy. Chances are you will end in empty space or inside an object. The smallest chances are of landing safely on a surface.

Travelling faster than the speed of light will not bring you back in time either. It is no different to breaking the sound barrier. You are just breaking a higher speed. Breaking the light speed barrier. Doing this releases massive amounts of energy, not consume. Travelling faster than light just means you get there faster.

If you can go back in time and forward in time.
Can you go sideways in time?
In the classical dimensions. If you are on any surface of the dimensions. You have two options of movement. Using a sphere you can go back/forth, up/down, left/right. Then they add time. Time we can only go one way.

While yes it does act as a measurement system. Just like the others. It us only travelled one way unlike the others.