Why take that as a given? Can you disprove the claim that some things happen instantly? Yes, because photons have zero rest mass. Photons don't have opinions. Travelling towards the Earth at the speed of light, like origin said. Yes. The main problem is that space will be expanding faster than the light can travel through it. Obstacles are a separate issue. The "stretching out" is a cosmological red shift. We already see that in the cosmic microwave background radiation and also in the red shifting of light from distant galaxies. That kind of response is common but not quite right. It tries to extrapolate from what you would see if you travelled at a speed very close to the speed of light to what would happen at the speed of light. But the associated maths breaks down at the speed of light, so that step that goes from 99.999999% of the speed of light to 100% of the speed of light is not truly applicable. Basically, a lot of physicists sort of fudge this when they're trying to communicate this science in popular forums. To understand why you can't really make the intuitive leap that is being made in the pop-science description requires that you actually study relativity, with the maths. Photons don't experience.