Popularized in the 1989 film Back to the Future II, the iconic hoverboard has eluded us for almost 20 years. There have been prototypes such as the Hendo hoverboard, but sadly, they are not feasible for transportation. It is unlikely that we will ever get to see the kind of hoverboard that allows us to travel on any surface.
While we indeed have air transportation (see: planes), we might never get to have our own flying cars. The reason is not impossibility but logistics. We can barely manage with ground traffic, noise, accidents, and regulations. It would be highly dangerous to have two-ton machines of death flying above our heads.
Time travel was popularized by the 1895 novel The Time Machine by H.G. Wells. Since then, we have dreamed of traveling to the past to correct mistakes or to obtain information. Sadly, although theoretically time travel to the future is possible (traveling at the speed of light), traveling to the past is not even theoretically possible. Even if traveling to the past were possible, we don’t have a frame of reference of how the universe moves, so even jumping one-second to the past could leave you floating somewhere in the orbit of Jupiter.
Human interstellar travel
This point is more about our mortality than our technology. We do have the technology to launch things to space and even have them move for a very long time. We have sent probes to Mars, and we may one day send humans as well.
However, the distances become astronomical very quickly. The center of our own galaxy Milky Way is about 26 thousand light-years away, to which we would have to travel at the speed of light for 26 thousand years to reach.
The end of the world
Every time someone has said the world would end, it didn’t. Make no mistake, the world will one day end. It’s just a matter of when and how. But don’t be discouraged, the Earth will most likely still be standing long after humanity has gone extinct.