Comment by abeppu
6 years ago
The ending of this makes it sound super clean. 3 ms * speed of light => ~560 miles. "It all makes sense!"
But ... isn't the speed of light through fiber actually like 2/3 of the speed of light in a vacuum? And that fiber isn't going to be laid out in a straight line exactly to the destination. So I think really there must have been a fair bit of uncertainty around that ~3ms to abort a connection.
The FAQ addresses this:
https://www.ibiblio.org/harris/500milemail-faq.html
The FAQ was more entertaining than the actual story!
Since the story has been posted umpteenth times, this is what should be posted these days. Very entertaining, thanks!
Yes! Thank you GP this too was my first time reading that follow-up FAQ.
My goodness, the questions people sent in. "I've never met a rich nitpicker" comes to mind.
Was gonna say. Speed of light through cables or fiber optics is roughly 2/3 the speed of light through vacuum. Also I don't see how it would know it has established a connection until the round-trip has happened. All in all, it probably waited more like 10 ms, if this story were true, which it probably isn't.
I am surprised that signals travel faster in copper (3c/4) than in fiber (2c/3), anyone has an explanation?
The number for copper is not a fixed quantity, it varies with the type of cable. Electric fields are outside of the copper wire, not inside. The copper conductor acts as a wave guide for the electromagnetic wave. So it turns out that things around the cable have an effect on the speed of propagation [1], particularly the insulator. Bare copper wire in a vacuum would be very close to c. In the case of fibre, the issue is index of refraction.
[1] https://en.wikipedia.org/wiki/Velocity_factor
And the time it takes to get to that fiber. It’s a fictive piece probably?