Darkness does not travel at any speed.
Darkness is decribed as a lack of light, therefore darkness in itself does not exist. Think about it when you enter your house at night and it`s dark, do you remove darkness or do you add light?
The human mind need to name what wich is not ( darkness, cold ...) Yes it's easier in a conversation to talk about cold rather than the lack of heat, but here again cold does not exist, it is a non-precense of heat. When you go outside and you feel the cold, it's not the cold that is getting inside your body it's the heat from your body that is escaping. Here again to refrigirate something you do not add cold you remove heat(from the air that you blow inside the fridge).
As for the car travelling at the speed of light, No one has the answer because no one can attempt the experiment. In theory (mine) the headlight you be on but you would not be able to see it because you are traveling at the same speed. It`s like if you fire a pistol and at the same time you propell the pistoll at the same speed as the bullet, the bullet will never get out of the cannon, therefore you fired but no bullet came out so it gives the impression(from a perspective) that you did not fire the pistol. However the person standing in the trajectory of the pistol will know it all too soon that you did fire that pistol.
For the pistol in outer space, the bullet would go on till it came close enough to a space body that would alter it`s trajectory and finaly make the bullet impact somthing. So in order to make travel pretty far you would first need to go ouside our solar system (because pretty little escape our gravity) and then fire on a pre-calculated trajectory that would not come close enough to any stellar mass to alter the "flight" of the bullet and yes it could go on forever.
Magic recipe : No friction, No gravity.
"I'm Ugly and you're not!"
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