It is already happening--in a limited form. It is well-known we can see due to light reflecting the objects around us and being processed by the retina and brain, it forms images that we use to navigate in the world. The speed of light equals approximately 300,000 kilometers per hour, so in our everyday life, we receive information about the surrounding world without any delay. However, in space, which is almost endless (compared to our habitual scales) the speed of light is not enough to cover vast distances instantly; sometimes the light travels thousands or even millions of years before it reaches Earth. This means that some of the stars we can see above our heads may actually not be there already; the light emitted by them needs so much time to reach our eyes (or telescopes) that during this period, the star itself could have had collapsed, and what we see its ghost--light, emitted a long time ago. So, in this sense, we travel back in time whenever we look into the night sky. At the same time, any other means to travel in time are yet unknown to humanity.