Okay so I know that this has been a prompt several times before on this sub, and this post is me giving one final shot at attempting to understand the intricacies.
My brain, due to lack of prerequisite/foundational knowledge or perhaps sheer stupidity, simply cannot comprehend the fact that a clock on Earth will tick faster than, say, a clock on Voyager II. I have two main questions, likely only surface level following your guys’ explanations:
1. What exactly is spacetime, and how do gravity and speed warp it? I’ve heard the ‘trampoline’ theory of time where objects with mass create a dip in spacetime that other objects of lesser mass ‘fall’ into. I’ve seen the visual, and I feel as though I’m missing something fundamental that explains exactly what it means to warp/create a dip in this ‘plane’ of space. How does that affect time?
2. What do you mean, “The speed of light is constant”? If you’re in a spaceship, hurtling through space at 50% the speed of light wouldn’t the light coming at you from the front of the spaceship be 50% faster than usual to you, and the light at the tail of the spaceship be 50% slower for you? And how the hell does this make it so you age slower than your twin brother on Earth? Why was one hour on planet Miller seven years on Earth in Interstellar? Help???
I don’t want to be stupid; being stupid really is my biggest fear in the universe. But how can I possibly wrap my brain around the concept of time, pretty much the only constant I thought there was in life, being not-so constant?
In: Physics
The speed of light is constant in all frames of reference. If you shine a light in a direction, and measure it, you’ll get 299,792,458 m/s. If you move in the direction of the beam of light, it’ll still move at that speed. It doesn’t matter how fast you move, or even which direction you go. It won’t change.
Now imagine you have a pulse of light bouncing between two mirrors. The time it takes for the light to travel from one mirror to the other is just the distance between the mirrors divided by the speed of light.
Now imagine that same setup, but it’s on a spaceship passing you to the side at a considerable fraction of the speed of light. The pulse of light isn’t just bouncing up and down. From your perspective, the light has to travel the distance between them while also traveling horizontally with the spaceship. You can use the Pythagorean Theorem to find out how far the light has to travel, with one leg being the distance between the mirrors, the other leg being the distance the spaceship travels in the time it takes the light to move between the mirrors, and the hypotenuse being the path the light takes. Of course, you don’t need to solve for anything to realize the light travels a greater distance than the distance between the mirrors.
Since the speed of light is the same in all reference frames, you will observe the light taking a longer time to move between the mirrors than someone on the ship watching the light pulse bounce up and down. You are measuring a longer amount of time between two events than an observer on the ship, so from your perspective, time is moving slower on the ship due to the ship’s motion.
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