 So in Bob's reference frame, Alice is moving forwards at speed v when she emits those photons. So our Newtonian intuition tells us that in that case, the forward-facing photon would be emitted at speed c plus v, and the backward-facing one at c minus v. So in this case, let's calculate t1. Alice and friend 1 are initially separated by a distance lv over 2. And the photon and friend 1 are approaching each other at a speed c minus v plus v. And from this, we get a result similar to what we get in Alice's frame. However, this reasoning is not correct. Pause the video now and see if you can guess why. Okay, so the second postulate of relativity tells us that the speed of light is the same in all inertial reference frames. So even though Alice is moving at speed v, Bob measures the photons at traveling at c, the speed of light. So in this case, to calculate t1, Alice and the friend are initially separated by a distance lb over 2, and the light and the friend approach each other at a speed c plus v. For t2, they approach each other at a speed c minus v, because the friend is moving away from the light. In particular, while the two dunkings were simultaneous in Alice's frame, they're no longer simultaneous in Bob's frame.