4 ms·

Please bear with me, but how is this true? If we're in an airplane going 250 m/s - it also takes me 2 hours to fly to NYC. The air around the plane is windy, t

Please bear with me, but how is this true? If we're in an airplane going 250 m/s - it also takes me 2 hours to fly to NYC. The air around the plane is windy, the air inside is still. Now we're in a spaceship headed from the earth to the moon & it's going to take us 3 seconds. We've agreed ahead of time it takes 1.5 seconds for light to go from the earth to the moon. C is the speed at which light moves, and we're taking 2x the amount of time light would. The air inside is still. But we're still going fast. How could it be that we are not approaching the speed of light? What do you make of time dilation at higher speeds if we aren't approaching the speed of light at all, ever?

JdeBP 2y ago
It's the stumbling block that everyone has grasping this stuff, and it's rooted in the old faulty kind of speed calculations. Speeds don't add like you think. There are many ways to grasp this, and one has to try several of them to find an intuitive explanation that works for onesself; but one way is to consider that you, in your spaceship (as long as you are coasting along with no rockets firing, and aren't performing orbit/deorbit burns) are, in your frame of reference, at rest. Your speed is zero. You haven't approached anything at all, and light is still whizzing away from you at c. Indeed, it's Terra and Luna that are experiencing time dilation as far as you are concerned, because they are the ones with the high speeds. * https://www.youtube.com/watch?v=Zkv8sW6y3sY https://www.youtube.com/watch?v=Zkv8sW6y3sY (FloatHeadPhysics addressing this in another way: there are a other approaches still) Accelerate at the beginning and end of your trip over to Luna, and of course general relativity comes into play and things get more complicated. What many gedankenexperiments get wrong is that usually there's only a short period of burning the rockets, in the real world. So for most of your trip in the rocket you aren't burning propellant and are in an inertial frame of reference. No inertial frame of reference approaches the speed of light/causality, by postulate 2 of special relativity, and one is always at speed zero in one's own inertial frame of reference.

JdeBP 2y ago

It's the stumbling block that everyone has grasping this stuff, and it's rooted in the old faulty kind of speed calculations. Speeds don't add like you think. There are many ways to grasp this, and one has to try several of them to find an intuitive explanation that works for onesself; but one way is to consider that you, in your spaceship (as long as you are coasting along with no rockets firing, and aren't performing orbit/deorbit burns) are, in your frame of reference, at rest. Your speed is zero. You haven't approached anything at all, and light is still whizzing away from you at c. Indeed, it's Terra and Luna that are experiencing time dilation as far as you are concerned, because they are the ones with the high speeds. * https://www.youtube.com/watch?v=Zkv8sW6y3sY https://www.youtube.com/watch?v=Zkv8sW6y3sY (FloatHeadPhysics addressing this in another way: there are a other approaches still) Accelerate at the beginning and end of your trip over to Luna, and of course general relativity comes into play and things get more complicated. What many gedankenexperiments get wrong is that usually there's only a short period of burning the rockets, in the real world. So for most of your trip in the rocket you aren't burning propellant and are in an inertial frame of reference. No inertial frame of reference approaches the speed of light/causality, by postulate 2 of special relativity, and one is always at speed zero in one's own inertial frame of reference.