Would Headlights Work at Light Speed?
Why Physics Stack Exchange recommends it
Physics Stack Exchange users link it as a clear layman's introduction when askers are confused about why light's speed stays constant for every observer.
Recommended by 2 people across 3 different months, 2015 to 2021.
What it is
A Vsauce explainer by Michael Stevens that answers a viewer's question about what would happen if you drove at light speed and switched on your headlights. It walks through the constancy of the speed of light, relativity of motion and what "light speed" really means, with pointers to further reading and related MinutePhysics videos.
What people said
Strong rec yolo · 2020-10 · Physics Stack Exchange · on “Why can't light travel three days into the future then transmit that information back to us prior to us arriving at that position?”
Weird thing about light; it doesn't really follow Newtonian mechanics. So we can fire something in a specific position to where we will be such as some planes being able to shoot themselves down [LINK] . Light doesn't work that way. You see, position is relative. Light moves relative to us. Hence, if the light is a distance away from us today, it's still a distance away from us tomorrow (Even more weirdly; it will move away from us at constant rate, despite our speed). If you're completely unfamiliar with this topic, it's very unlikely that a written answer will be as clear as something like this [this video] (highly recommended for better understanding)
Recommends CircleSquared · 2015-07 · Physics Stack Exchange · on “If all motion is relative, how does light have a finite speed?”
I've often heard that Einstein shattered the notion of absolute motion (i.e. all things move relative to one another) and that he established the speed of light as being absolute. That sounds paradoxical to me; I cannot understand how the two concepts can be reconciled. Before going further, I'd like to say: 1) Over the years, I've seen many layman's explanations on these topics (including the nice YouTube video by Vsauce, Would Headlights Work at Light Speed? [this video] ) . I understand everything that's said (or, at least, I think I do). Just nothing I've found seems to address this apparent contradiction. 2) More recently, I've tried to find the answer on my own. That includes searching the
Recommends yolo · 2021-02 · Physics Stack Exchange · on “Different speed of light in two inertial frames and the relativity principle”
Your error is in the idea that because you are still and can see someone moving, everything that they see is slower. That's not quite the case. Weirdly, the light will move away from the two of you at the same rate. While your friend is moving, the world (from their perspective), is squashed; This conserves the speed of light. This may be an interesting video to help you grasp your head around it: [this video]
Cites Malthe Andersen · 2015-10 · Physics Stack Exchange · on “Observing light speed”
In this video at 3 min. there is an easy video picturing and explaining what happans in front of B, but how does that explain what happens behind B? [this video]