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
If you were standing in the bed of a pickup truck traveling 50mph, and you threw a ball forward at 30mph, you would measure the speed of the ball at 30mph. Me, standing at the side fo the road, I observe the ball traveling at 80mph, adding the speeds together. This makes sense for objects in motion.
The equation for speed is distance divided by time. For you, throwing the ball, it traveled 30ft in 1 second so that speed is 30ft/second. For me, it looked like it traveled 80ft, so I measured 80ft/second.
Light is measured the same way, distance divided by time. It’s been proven that if you’re traveling at 50% of light speed and you measure light’s speed as distance divided by time, you’re gonna get the same answer as me while standing still. How can this be? Well, the only answer is, your seconds must be slower than mine.
Carl Sagan actually did a [really great video](https://www.youtube.com/watch?v=PKE1WyEPdNA) explaining exactly why it has to be this way. Basically, for the universe to be logically consistent, there *has* to be a cosmic speed limit. And that limit is c.
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