Is time travel possible?

Yes, time travel into the future is real. You are doing it right now, at one second per second. The surprise is that the rate is not the same for everyone. A clock that moves fast ticks slower than one at rest. A clock deep in gravity ticks slower than one higher up. Einstein’s theories of relativity predicted both effects, and scientists have measured them many times.

The effect is tiny in daily life. Astronaut Scott Kelly spent a year on the International Space Station, moving much faster than people on the ground. Compared with his twin brother on Earth, he aged 5 milliseconds less. That is less than the blink of an eye. But it is real, and your phone depends on it. The clocks inside GPS satellites tick at a different rate than clocks on the ground. Engineers must adjust for it, or the system would not work.

Why do people ask about time travel? Some grew up on movies and novels about time machines. Some want to know if the past is really gone. Some wonder if they could fix a mistake or see someone again. These are fair questions, and science fiction has often asked them well.

Travel into the past is the hard part. Einstein’s theory of gravity allows some very strange shapes of space and time on paper. In some of them, a path can loop back to its own past. But every such case needs things no one has ever found, like a spinning universe or a tunnel through space held open by a strange kind of material. Stephen Hawking suspected that the laws of physics block these loops. Nobody has proven him right or wrong.

So the honest answer has two parts. Forward: yes, measured. Backward: nobody knows yet, and no one knows how to build a machine for it.