Light Speed Lag

Light is fast. Very, very fast. You may think the TayGayVay is fast, but that's just peanuts to light.

Problem is, space is big. ReallyBig.

The time a radio wave takes to "bounce" off a satellite in geosynchronous orbit is perceptibly long, long enough to make fluid conversation over such a "circuit" difficult. The round-trip time for a radio signal between Earth and the Moon is even longer.

So a phone conversation with Jupiter (assuming there's anyone there you could call) would be a practical impossibility.

PostalChess is another matter. I go first. P-K4. (Good. I'm not the only who prefers the traditional notation to algebraic. e4, sheesh! -- djbr)

See "2001: A Space Odyssey (1968)" - which does a really good job of showing the inconveniences of communicating over increasing distances - out to Jupiter, in fact. ;-> [ISBN: B00000J2KZ] (and others) [http://www.amazon.com/exec/obidos/ISBN%3DB00000J2KZ/portlandpatternrA/]

So what's the light lag between Earth and Mars? I know it must vary as our orbits go in and out of phase...

Mars has an orbital radius of about 1.5AU, which means that its distance to the Earth varies from about 0.5AU to 2.5AU. One AU is about 500 light seconds, so the light lag between Earth and Mars ranges from 500s (8m20s) round-trip to 2500s (41m40s) round-trip.

One way to solve the "phone conversation" problem is to avoid having a dialog, but rather have two simultaneous monologues. Each side doesn't stop talking, but continuously gives new information. Any query will be answered in due time, but no one stops to wait for an answer.

IsaacAsimov had this exact solution in one of his stories, inspired by the protagonist's mother talking to her friends - a set of monologues, with answers to questions inserted as they were received. -- PeteHardie

Anyone who uses IRC gets used to funny interleavings of question/answer, but it works reasonably well. (Though, the real lag on IRC isn't the transport time - it's the typing time.)

The trouble with that idea is that most people have trouble listening when they're also talking, so most of the conversation will get lost. And if they pause to listen when they hear the other person talking, they'll quickly get tangled up, since the talking periods are not of equal length.

That's why you WriteNotTalk?.

Oh, by the way -- this is how a number of communications protocols work, too. Token Ring is like this, as is a handful of others I can't recall right now. Genesis for instruments may be one, can't remember.

You know, I'd really like to see a science fiction film where some big conspicuous activity takes place over a couple of minutes, then the hero jumps into an FTL ship which really is an FTL ship, not one that drops into hyper/super/ultra/round-the-back-so-it-doesn't-count space and zooms away, watching the big conspicuous activity happening backwards.

That happened in at least one episode of the old SpaceNineteenNinetyNine series.

Only this isn't really what special relativity predicts should happen. FTL allows for travel backwards in time, but the actual movement is neither forwards nor backwards. This sort of thing is much less cool when it isn't grounded in the physics. Also, I imagine someone should be concerned about which signals from the activity will reach the craft.