Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Sending information faster than speed of light?

  1. Jun 21, 2013 #1
    Say I am in the middle of two people that are 2 lightseconds (we'll call this unit a distance that speed travels in 1 second) away from me. They are 4 lightseconds away from each other. So these two guys are my friends, and before they moved to 2 lightseconds away from me, I told them, if I am shining a red light at one of you, that means I am shining a green light at the other person.

    They tell me OK, and they move 2 lightseconds away from me. So I shine a red light at one of them, and a green light at the other. So the guy that sees the green light says "hey! the guy that is 4 lightseconds away from me is seeing the red light, and I only know this in 2 seconds!" VOILA! information have just traveled faster than the speed of light
  2. jcsd
  3. Jun 21, 2013 #2


    User Avatar
    Gold Member

    Come on. We all know the information came to him from 2ls away and took 2s.

    Of course, you could have lied, in which case it is disinformation.
  4. Jun 21, 2013 #3


    Staff: Mentor

    Correlation is not information. No information was sent 4 lightseconds. I.e. there is no way for the person at one end to use this method to encode a message to the person at the other end.
  5. Jun 21, 2013 #4
    aha! I set you guys up! I knew you were gonna answer that.

    Now to my next question. Whenever we receive information, how do we know that the information might not have changed regardless? maybe the light 10 billion lightyears away that we are just getting now might actually be a monster, that turns into light at some point that it crosses through the universe. After all, entropy says everything is possible, just the matter of chance, how often it is going to occur.

    Yea of course I am a person, and I can lie, and they will never know. Now, what if the two guys make a machine, that is maybe as accurate as any information can be. That when one side of the machine sends out a green light, the other side would send out a red one.

    How much more reliable are information from "nature" than information from something that can make choices? How do we know our "detectors" are not lying to us, and we might be getting false information?
  6. Jun 21, 2013 #5
    Oh man, so they can't communicate. Communication = information. Alright I get it, thanks.
  7. Jun 21, 2013 #6


    User Avatar
    Science Advisor

    This interpretation of entropy is news to me. I thought that even when entropy is considered, things still had to obey the laws of physics.

    It's always possible, of course, that what we think is a galaxy 13 billion light years away is just some joker holding up a picture of one.
  8. Jun 21, 2013 #7
    Bill_K I cracked up when I read this...I'm sure this "interpretation" of entropy is general in nature, and assumes the laws of physics do apply to the phrase "everything is possible", nearly to the point of your retort...why wouldn't they?

    And from a causality perspective it makes no difference if it is, presently.
    Last edited: Jun 21, 2013
  9. Jun 21, 2013 #8
    This thread lead me to read about "Physical Information"...wow physics is a ridiculously deep subject. Anyways, I suppose what you're suggesting is a "field" of physics. I can't understand it in the slightest :tongue2:
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook