Very simple thought experiment about time dilation: Let's say I have two clocks that are a substantial distance (light years) apart, at rest with respect to each other. The clocks are Einstein synchronized. Also, the clocks are specially designed to withstand any force or collision. However, if subject to a collision, they are designed to stop ticking, and will be "frozen" at the moment of the collision. Then I travel, in a large spaceship, past one of the clocks so that I and the two clocks are all in a line (Me, clock 1, clock 2). I then accelerate toward the clocks. I cease accelerating before reaching clock 1, and travel at a constant speed, a substantial fraction of c, directly toward both clocks. I get out my stopwatch. When my spaceship strikes clock 1, I start the my stopwatch, and maintain my velocity toward clock 2. Years later, when my spaceship strikes clock 2, I stop my stopwatch. I then pull my spaceship over (or not), get out, and peel both clocks off the front of my spaceship. Is the difference in time displayed on the clocks greater, less than, or the same as the time elapsed on my stopwatch between collisions? If they are unequal, then what about the principle of symmetry? To me, the clocks are moving. To the clocks, I am moving. If they are equal, then is "time dilation" just a visual illusion?