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I had the Relativity conversation with my 16 year old this past weekend, as he is taking AP Physics.
Yeah, he couldn't wrap his mind around it. Honestly, I can't say I understand it very well. I get that C (speed of light) is C in all reference frames. What I do not understand is for a spaceship traveling at C, the forces being transmitted between the atoms from stern to bow are unable to catch up to the next forward atoms. Hence time dilation, at least for those forces being transmitted "forward" in the ship's reference frame.
However, what happens to those forces being transmitted bow to stern or "backward" in the ship's reference frame? Would those forces be "dead stopped" in an external reference frame? Yet travel at C from bow to stern in the ship's reference frame? What does that mean for the ship if those forces are only being transmitted one way?
Or, as I very much suspect, do I just not have a clue as to how it really works. I always thought that "time dilation" was simply the inability of forces being transmitted from atom to atom. As those forces are limited to C and they are attempting to catch up to another atom also traveling at C. With that said, those forces are transmitted in multiple directions, not just the vector the ship is on.
Ok, another one of my very few brain cells just committed suicide and I'm not drinking anything, so I'll stop now.
My understanding is that it's impossible for a spaceship or anything else with mass to actually reach the speed of light. It can only approach it. Only massless energetic waves like light and radiation can travel at the speed of light.
Your understanding is correct.
Relativistic mass increases the faster the moving object gets. That in turn means more energy is required to accelerate an object the closer it gets to the speed of light.
Fun fact: the speed of light is not as absolute as it might seem when looking at relativistic effects. In media with a refraction index above 1 (only perfect vacuum has a refractiom index of 1), the speed of light equals 1/(refraction index).
For light moving in water that results in a speed of light of around 3/4 the speed of light in vacuum.