Try not to think of time-dilation in relation to "light travelling". Time dilation just means that time passes more slowly for you due to your speed relative to

Try not to think of time-dilation in relation to "light travelling". Time dilation just means that time passes more slowly for you due to your speed relative to an observer. So imagine you have an identical twin, and you leave on a Journey to a nearby solar system at say 0.9x the speed of light. Your twin stays on earth and for arguments sake you can say he is "stationary" in comparison to you. When you come back, he'll be much more "aged" than you. You had a clock on-board your craft, and it measured your trip as say "2 years". Likewise, your twin also had a clock and it measured your trip as having lasted "20 years". The clocks are not wrong. And trust me, this isn't some science-fiction type thing we're discussing. GPS satellites orbiting the Earth carry very accurate atomic-clocks, and they need to take time-dilation into account in order to compensate for the drift in values, simply due to the accuracy necessary for GPS. Just had a look on the wiki page, and the drift is approximately 38 microseconds per day. When I first encountered this concept in high-school randomly, I was quite shocked at how "non-complicated" the equation for it is. https://en.wikipedia.org/wiki/Time_dilation#Simple_inference_of_time_dilation_due_to_relative_velocity https://en.wikipedia.org/wiki/Time_dilation#Simple_inference... https://en.wikipedia.org/wiki/Global_Positioning_System https://en.wikipedia.org/wiki/Global_Positioning_System