On Jan 28, 2005, at 12:19 AM, Nelson Helm wrote: > I read that persons standing on the sidewalk below hear Big Ben, the > bell at the Houses of Parlement, after Australian listeners to the > BBC. Signal goes to Australia at speed of light, in less time than to > sidewalk at speed of sound.
Being my usual persnickety self, I checked the facts, and you're right. (Google knows everything!) Big Ben is 106 m tall, so it takes the sound about 0.3 s to reach the ground at 340 m/s. The mean circumference of the earth is 12,742 km and the speed of light in a vacuum is 299,792,458 m/s. As a worst case, Australia is halfway around the world, so use 6500 km as the distance from London to Australia, giving 0.02 s as the time to get there. Light is quick, but not quick enough to help satellite broadband. A satellite in geostationary orbit is 35,768 km above the equator. It takes at least 0.12 s to get a signal there. Since we're talking round-trip time, this is about a quarter second to squirt something up there and get it back. I've tried satellite broadband. It works great for downloading big files because once the file starts coming, it comes really fast. Using a terminal is pretty frustrating because the echo of what you've typed takes at least a half second to appear. Complex Web pages are made up of dozens, or even hundreds of little pieces. You can watch in slow motion as your computer requests them and they arrive. The satellite broadband companies are fighting the latency by caching commonly requested pages so they can send all the pieces at once without waiting for the individual requests. Email is OK because you just get it all in one shot, so the half second isn't noticeable. | The next meeting of the Louisville Computer Society will | be January 25. The LCS Web page is <http://www.kymac.org>. | List posting address: <mailto:macgroup at erdos.math.louisville.edu> | List Web page: <http://erdos.math.louisville.edu/macgroup>
