Time travel is already possible

1. From the official NASA Hubble telescope website: 

"To examine the way the universe behaved in the past, astronomers look at extremely distant objects, such as supernovae in galaxies billions of light-years away. But how does that work? How can astronomers look out into space and see the universe back in time?

The answer lies in the speed of light. Light waves move very fast, about 186,000 miles per second (300,000 km/s). Light moves so fast that as you go about your daily life, it appears to travel instantaneously from one place to another ... 

In space, however, the distances are so immense that the time that light takes to travel is noticeable ...

Across our Milky Way galaxy, distances are measured in terms of how many years it takes light to travel. The nearest star is over four light-years away. So when we look at that nearest star, we see it not as it is today, but as it was four years ago. We are seeing the light that left that star four years previously and is just reaching us now ...

Very distant galaxies are billions of light-years away. At that distance, their light tells what the universe was like billions of years ago. Since the age of the universe is about 14 billion years, these distant observations allow astronomers to measure changes over the lifetime of the universe. So when astronomers look out into space, they are essentially also looking back into time."

2. International Space Station:

"To get ahead in life, spend some time on the International Space Station. Why? Well, according to the theory of relativity, astronauts on the ISS age more slowly due to the spacecraft’s high orbital speed. It’s called time dilation, and it means that when they return they’re a bit younger than they would have been—as if they’ve traveled into the future. (The effect is very small—it would take more than 100 years on the ISS to warp ahead by just one second.)"