[joeycastillo]

One thing that's always gotten to me about this distance is what it means for communication latency. Mars is 20 light-minutes away. If we sent colonists, communication would be a 40-minute round trip. No phone calls home, no way to have a chat with friends or loved ones; at best they could send a message, and wait 40 minutes for a reply. That's far away.

[MrBra]

if we could stretch a stick as long as the distance from earth to mars and use it to tap on mars ground something like a morse code to communicate, would that message be faster than a wifi message traveling at the speed of light?

[danielweber]

Does everyone come up with this idea independently, or is someone suggesting it? It's a very common retort to speed-of-light communications, but someone told me about it before I thought of it.

Anyway, your idea wouldn't work. If you press on one end of the stick, it would issue a pressure wave along the length of the stick near the speed of light (depending on its material), so you haven't gained anything.

[MrBra]

No I am guilty of having thought about it myself :) But I would like to know more about these kind of anti-common sense examples regarding this subject. Do you have a website or some search keyword to suggest? Thanks

[marshray]

No. As in air, the speed of sound in stick is still slower than the speed of light.

[MrBra]

no i think you did not understand my example.

[marshray]

You're talking about using a mechanical compressive wave in a medium to transmit information. Whether the medium is 'air' or 'stick', the rate at which such waves travel is generally called 'the speed of sound in [medium]'.

Wifi signals to Mars travel at the speed of light in a vacuum. This is faster than any mechanical wave because the changing forces of compression between the atoms in the medium must still obey the speed of light.

[MrBra]

mechanical compressive wave ,traveling at the speed of sound? Why do u introduce these? What has sound to do with my example? Imagine the stick not tapping on ground but just getting close. to it. Not an audio, but a visual way for the receiver to tell the 2 different singnal states. Then he'd grab his end of the stick and do the same. I am sure what you say is correct by itself but.. it feels there is just something from it that doesn't fit with my example.. Edit: reading again your comment and trying to understand what you say.. if i get it right then it's totally misleading to call it "speed of sound": it should be called speed of mechanical compressive waves

[anonymfus]

Like foreign country few hundreds revolutions of our planet around the Sun ago.

[Connaissance]

Good point. We have so forgotten how bad it used to be, that 40 mins seems so long. Kings weren't able to talk to their ambassadors in 30 mins, not that very long ago.