Anyway, I was wondering about two particles moving at or near the speed of light colliding into each other

if two objects head straight at each other, the speed that they run into each other is the two speeds added together

a car going 30mph colliding head on with a car travelling at 70 mph results in both cars experiences a 100mph collision

so if two photons moving at the speed of light collide "straight" into each other, shouldn't their collision exceed the speed of light?

The answer is, unsurprisingly, no

but the reason why eludes me after reading a few different sources on it

if someone has a source explaining it that is made for a dumb person like me feel free to share, please

just going by my existing physics education, i can think of two different explanations for why the answer is no

1 is because realistically, it's impossible for objects with mass to achieve the speed of light, and you need mass in order to collide with something

but if we ignore that fact and pretend we're in a universe where that's possible, explanation 2 is because the colliding objects don't actually experience the combined speed of both objects. they experience the equivalent force of hitting something at that speed

and 3. the speed of light is not relative

due to time dilation, they would not collide at more than the speed of light

despite both going at 0.9c

thank you, those explanations make sense to me