[amelius]

Sorry, I don't get it.

Imagine you are on a rubber ruler. You can move at most 1 mark per second on the ruler. This is true regardless of how much the ruler is stretched or compressed.

So to move from mark 1 to mark 100 will always take the same time at top speed, regardless of any stretching/compression.

[cglan]

Don’t take my word at all, but I think in your analogy you can’t imagine it as you’re only allowed to go 1 ruler tick a second, but imagine you can only move 1mm per second. If you compress the rubber ruler you traverse more ruler per second than before while still going the Same speed

[dotnet00]

The idea is similar to how we detect gravitational waves in interferometers, when space gets compressed, the distance the photon has to travel shrinks slightly.

To take your ruler example, if you compress it by 1mm, you can traverse its entire length traveling 1mm less than before, thus, from the reference frame of someone who can't see that you've compressed the ruler, you've traveled slightly faster.