it never really made sense to me how you could travel the same distance in less time if the airplane isn’t going any faster. how is the time reduced?
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While the other comments are correct that they can find jet streams, the jets also can just straight up fly faster. Jets don’t cruise with the throttle wide open at max speed. Broadly, there are two kinds of drag that a plane has to deal with: parasitic, and lift-induced. Lift-induced drag goes *down* as the plane goes faster through the air because the wings produce the same amount of lift with a lower angle of attack as speed increases.
Parasitic drag *increases* as the plane goes faster. This is the air getting bunched up in front of the plane without enough time to get out of the way. As the plane goes faster, the air has less and less time to get out of the way, so more gets bunched up and drag increases. [Here is a graph](https://en.wikipedia.org/wiki/File:Drag_curves_for_aircraft_in_flight.svg) of the two kinds of drag as airspeed increases. The most efficient airspeed is at the bottom of the curve that shows total drag.
Being at either end of the curve means that you’ll need to increase the throttle to maintain your speed. Note that at very low speeds you could max out the throttle *without* going faster. To fly at that low speed, the angle of attack has to be very high, close to stalling, and extra power gets wasted as drag. To fly faster, the angle of attack has to be lowered – which, predictably, means the plane will temporarily lose lift and drop. This is a very dangerous configuration for the plane to be in: if airspeed drops for whatever reason, the plane will stall and since the throttle is full open, there is no option other than to lose altitude, which is undesirable for hopefully obvious reasons.
Regardless, the point is that the plane uses the least amount of fuel while traveling at the speed where the curve is the lowest. The pilot *can* fly faster, though, at the cost of burning more fuel. Sometimes, that’s exactly what the pilot does: increase speed and accept that it will cost the airline more by burning more fuel than they need to.
Another option is to request a higher altitude from ATC. The shortest path is always the straightest line so all of the planes flying between certain airports want to be following the same line. Having established corridors also helps with navigation, making it easier for planes to safely navigate to their destination. Very long flights like transoceanic flights want to jump into the same jet streams to take advantage of the boost available. To maintain safe separation between planes, air traffic control assigns each plane its own altitude. Planes typically want to fly higher, because the air is thinner and there’s less drag. Yes, there’s also less oxygen for the engines, so the engines lose efficiency, but the net effect is that higher means less fuel burned. That changes the total drag curve mentioned above by reducing the effect of parasitic drag. If the pilot can get clearance for a higher altitude, they can increase the throttle and fly faster while staying in the most efficient part of the drag curve.
TL;DR: The plane *can* just fly faster, sometimes.
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