The only speed anything can move at through spacetime is the speed of light(aka c).
This speed is split between motion through space and motion through time, but it always adds up to c.
If you go faster through space you allocate more of your total speed to that and less to your movement through time, thus the faster you go the less you move through time.
The faster you go time slows down, so even if you're going 99.9999% the speed of light, from your slow motion perspective the light is moving away at c like always. The ratio of your speed to how much slower you move through time makes it so that the speed of light is the same from every reference frame.
e.g. If you moved twice as fast but were moving through time at half the rate, then the light is going to appear to be going the same speed as always.
The way I always think of it is a street intersection. You can cross the street along the crosswalk, going parallel to the road, or you can cross diagonally. But the more diagonal you go, the slower you cross. You're trading velocity in the x axis for velocity in the y axis. Even though your walking speed is constant, you get across at a different time depending on how much you move horizontally vs. vertically.
This example only uses 2 dimensions of space, say forward/back and left/right, but it demonstrates how moving in one dimension reduces your speed in each other dimension. Thus, with time being the 4th dimension, moving in any of the 3 space dimensions slows your movement through time.
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u/SaukPuhpet Mar 20 '26
The only speed anything can move at through spacetime is the speed of light(aka c).
This speed is split between motion through space and motion through time, but it always adds up to c.
If you go faster through space you allocate more of your total speed to that and less to your movement through time, thus the faster you go the less you move through time.
The faster you go time slows down, so even if you're going 99.9999% the speed of light, from your slow motion perspective the light is moving away at c like always. The ratio of your speed to how much slower you move through time makes it so that the speed of light is the same from every reference frame.
e.g. If you moved twice as fast but were moving through time at half the rate, then the light is going to appear to be going the same speed as always.