I've always had a problem understanding the theory of relativity. How could one second of travel time in a spaceship translate into 20 hours of elapsed time for someone on earth?

At 12pm a friend and I are standing in my backyard of my home. My friend sits down on a chair and waits. I get into my spaceship, turn on the engine and in 1 second I am 300000 km away because my ship flies at 300000 km/s. Why did my friend who was sitting still say I was gone for 20 hours?

Did it take me 20 hours to build up enough speed to travel for 1 second?

And yet is so simple

.

I think only a few people on this planet really get it ...

Einstein predicted it and @al infierno experiments have confirmed it.

http://www.alternativephysics.org/book/TimeDilationExperiments.htmhttps://www.space.com/42641-einstein-gravitational-time-dilation-galileo-probes.htmlTime is relative to the observer. The traveler is gone for 1 second but the person who stays behind has to wait 20 hours for his return.

This effect even occurs at much lower speeds (as mentioned in the article : after 6 months on the International Space Station (ISS), orbiting Earth at a speed of about 7,700 m/s, an astronaut would have aged about 0.005 seconds less than those on Earth.

Also : you can never reach the speed of light.

The mass of any object increases as the speed of the object increases. At 90% of the speed of light mass will approximately double, but at 99% of the speed of light the apparent mass will appear to have increased by about 7 fold. As we get closer to the speed of light the mass increases very dramatically until at the speed of light it would be infinite. To move something of infinite mass would require infinite energy and this is clearly not possible, hence nothing can travel faster than light.