1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

I Faster than light

  1. Dec 30, 2015 #1
    Hello i love physics and would love to learn more about it.
    I stumbeld upon a wikipedia page called faster then the speed of light
    And if you look at 3.1 it seems to be prooven
    Could someone with knowledge of the topic explain this to me and tell me al about it
    Thx in advance
  2. jcsd
  3. Dec 30, 2015 #2
  4. Dec 30, 2015 #3


    User Avatar
    2017 Award

    Staff: Mentor

    The first question is "what type of velocity do we measure?". Take a laser pointer, point at the moon and rotate it fast enough: the dot of the pointer can easily "move" from one side to the moon at a speed faster than the speed of light. That is not the speed of any real object, however, and it cannot be used to transmit information from one side of the moon to the other at this speed.

    The true limit applies to signal speed: how fast can an event at place A influence an event at place B? None of the experiments discussed there found superluminal effects here. Just nonsense.
  5. Dec 30, 2015 #4
    Welcome to PF!
    Just to expand on what mfb said, the limit of the speed of light applies to particles and mechanical disturbances (there is actually really good information about this on the FAQs, I believe under relativity). The dot on the laser pointer he mentioned is not a particle or object because it is an effect of the photons constantly traveling from the pointer to the moon, and those photons are effected by the speed of light limit.
  6. Dec 30, 2015 #5
    That depends on the definition of "object".
  7. Dec 30, 2015 #6
    Object meaning something made up of one or more particles, and we should not make this more complicated than it needs to be. I understand that it is not a perfect definition but it should do for this situation.
  8. Dec 30, 2015 #7
    That would mean that a black hole is not an object because it is made up of space time only.
    And it would mean that a dot on a crt-display is an object because it is made up of electrons and a fluorescent substance. And yes, I know that this also depends on the definition of "made up of".

    Than we should avoid imprecise terms.
  9. Dec 30, 2015 #8
    Good show! If an explanation ain't broke making it more complicated won't fix it. :wink:
  10. Dec 30, 2015 #9
    I'm sorry for my improper terminology, however I believe the OP gets what I mean. As I said, it is not a perfect definition, but it should do for this situation.
  11. Dec 31, 2015 #10


    User Avatar
    Staff Emeritus
    Science Advisor

    FTL travel isn't possible according to known physics, which is the only kind we discuss here at PF. Thread locked.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook