Eli5. How its possible for the light to travel constantly with out stop slowing down from the most old galaxies?
In: Physics
Because everything travels at 3×10^8 m/s through spacetime. Objects with mass have this ‘velocity’ pointing so they move entirely or mostly in the ‘time’ direction (a stationary object is moving at full speed through time, but not at all through space), while photons and massless particles are heading in the ‘space’ direction (really fast in space, not so fast in time).
Like a ship sailing North at a fixed speed, if it turns to point more Eastwards, its Northwards speed decreases as its Eastwards speed increases, but its overall velocity is unchanged. Here, ‘North/South’ is analgous to moving in time and ‘East/West’ is analogous to moving in space.
This quite nicely captures why space contraction and time dilation occur (though it does ignore all the details). Hopefully ELY5!
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