Wormholes can be a difficult concept for people to understand. Time wormholes are theoretical rips or warps in time within the universe but have never been proven to actually exist. These types of wormholes would allow you to instantly go from one point in time in the universe to another.
Thinking about this concept may be against common sense at first, but if you can think of our universe in dimensions - three dimensions of space and one dimension of time - it is possible to make sense of wormholes.
In my article Understanding the Possibility of Space Travel Through Wormholes, I explain how a wormhole might look to a two dimensional subject within a three dimensional world as their two dimensional world is folded and connected at two different spots within its space. I highly recommend reading that article first in order to make sense of the concept when it is applied to time.
We only have one dimension of time. In terms of space, it would be referred to as "length" of time. Thinking of our dimension of time, it would be in a straight line. Now we would have to think in time in terms of a two-dimensional universe. Basically, it would be just like that two dimensional piece of paper in my space travel example. If you were to take a piece of paper and start drawing on it, you realize you can draw anywhere. Left to right, up and down etc. Now imagine this concept it terms of time. If you were to fold that piece of paper into a cylinder and continue to draw on it, constantly looping around, to an observer in our one-dimensional world of time you are going from one point in time to the next.
Unlike space travel there is an extra consideration of time travel and that is the prospect of paradoxes when travelling backwards in time. If the human race mastered time travel in the future, why are we not seeing them come back to our time right now?
It's a scientific impossibility to have a cause before an effect. For instance, you couldn't go into the past and kill your younger self. There are two theories which would prevent people from going back to the "real" past. The first one is that when you travel back in time, you are going to the past which is just like the real past in every which way, except it exists in another dimension or universe where you cannot create any paradoxes. The other theory states that any wormhole created as a window to the past would be destroyed by feedback from radiation. The "present" radiation would get looped in with its own "past" radiation and destroy the tunnel before anyone could go through it, making it impossible to travel back in time.
There is one way to look into the past without actually going there. We are doing it right now every time we look out into space with a telescope. Light is limited by its speed. A galaxy that is a billion light years away would be seen from earth how it was a billion years ago. If we were to build a mirror that reflects light a billion light years away, we could theoretically see how the earth looked two billion years ago, assuming it was ever possible to create something that can see the earth in great enough detail from two billion light years worth of distance.
Refer to my other articles if you are interested in reading about:
The possibilities of extraterrestrial life existing within our solar system
What UFOs could really be