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

Are there simultaneous moments?

  1. Jun 5, 2013 #1
    Are there simultaneous moments?

    I know that relitivity states that demetion is proortional to velocity ant that mass is also demension of time but the real question is are nearness values absolute? Is there such a thing as objective nearness in strict time?

    Thought experiment: A species travels into the past on an asteroid while skimming the atmosphere of planet X are the two events simultaneous?
     
  2. jcsd
  3. Jun 6, 2013 #2

    ghwellsjr

    User Avatar
    Science Advisor
    Gold Member

    Sorry, I can't understand any of the foregoing.

    Now this part, I think I understand what you are asking.

    Two events are simultaneous if their Coordinate Times in a particular Inertial Reference Frame (IRF) have the same value. If you transform the coordinates of the two events into another Inertial Reference Frame the two new Coordinate Times may be different and so the two events in this other frame are not simultaneous. However, some other pairs of events may be simultaneous.

    Here is a spacetime diagram depicting a species on an asteroid (in red) skimming the atmosphere of planet X (in blue). The asteroid is traveling at 0.8c. The dots represent Proper Time intervals of 1 microsecond. Key to understanding this type of spacetime diagram is that any object in motion will be Time Dilated, meaning that the dots are placed farther apart.

    We consider the time of closest approach to have a coordinate value of 0 and we start the scenario 6 microseconds (usecs) for each object before that to show the approach and 6 microseconds after that to show the trajectory of the asteroid past the planet. We are considering the speed of light to 1000 feet per microsecond. Here's a diagram for an IRF in which the planet is at rest:

    attachment.php?attachmentid=59322&stc=1&d=1370503338.png

    Notice that the event corresponding to the red asteroid's time of -3 microseconds is simultaneous with the blue planet's time of -5 microseconds since they both happen at the same Coordinate Time of -5 microseconds. We could say the same thing with regard to the two events occurring at the Coordinate Time of 5 seconds.

    Now we want to transform all the coordinates of the events in this first IRF into an IRF where the red asteroid is at rest and the blue planet is moving past it in the opposite direction:

    attachment.php?attachmentid=59323&stc=1&d=1370503338.png

    Now we see a symmetrical new set of coordinates in this frame. Again, the events at Coordinate Times of -5 and +5 microseconds have dots for each object that are simultaneous with each other.

    I want to show you one more diagram for an IRF in which both objects are traveling in opposite directions at the same speed, 0.5c:

    attachment.php?attachmentid=59324&stc=1&d=1370503338.png

    Now because the two objects are traveling at the same speed, they are Time Dilated by the same amount and so their clocks remain in synch with each other. This means that any two events corresponding to the same Proper Time for both objects will also have the same Coordinate Time values and therefor are simultaneous.

    Thus, simultaneousness is a coordinate effect which depends on the IRF you chose to describe, analyze, and depict your scenario. Transform to a new IRF and you can change all the simultaneous events.
     

    Attached Files:

  4. Jun 6, 2013 #3

    Mentz114

    User Avatar
    Gold Member

    I've corrected this to what I think you mean, but it is confused and not answerable.

    Travelling into the past is not considered possible so this is also not answerable. But if it did happen, how can an event in the past of another event be simultaneous with it ?
     
  5. Jun 11, 2013 #4
    OK what I'm saying: relativity makes time distance off the delta time-cone, which is to say there is only one kind of distance, which is informational on the non-euclidian time dimension. But time is also the engine of mass-energy entropy, so, can you simulate relativistic mass-velocity interactions without each photon having its own separate clock? I mean, what is a photon? Is its velocity really just its intertial rest frame, which is the speed of light? How can a photon be equivalent to a velocity delta? Is mass made out of photons? Do photons warp space-time? Were do the photons go on a light powered rocket? How do you clean ice-cream off a computer? and where are my keys?
     
  6. Jun 11, 2013 #5

    Dale

    Staff: Mentor

    Are you perhaps a non-English speaker using a machine translation tool like Google translate? I can't understand your sentences.
     
  7. Jun 11, 2013 #6

    ghwellsjr

    User Avatar
    Science Advisor
    Gold Member

    I don't think so. Look at his other thread:

    www.physicsforums.com/showthread.php?p=3918710#

    And look at the last two questions in this thread.

    Maybe one of his kids got a hold of his computer.
     
  8. Jun 11, 2013 #7
    Oh DaleSpam, :smile: you're far to familiar with SR to "understand" what "time" as an "engine" is supposed to mean.


    time is part of the geometry of spacetime. Entropy "plays out" on time & length, there really isn't anything that time "does", it merely allows more "room" much like a greater length offers more room.

    Consider specifically the length part. Length requires exactly what you are asking; "Are there simultaneous moments?". Yes there definitely are, much like the end points of a meter stick are simultaneous.

    The end points of that meter stick are simultaneous in spacetime* (read both in space & time), if there is then relative motion between you and the meter stick it will contract in the direction of motion, or take an amount of time to traverse a length of one meter. read about c & how time length are defined to learn more.

    With all that said note there is no casual connection between any two points* simultaneously. or better said there is no instantaneous casual connection between any two points*. As in there is no casual connection between the end points on a meter stick, despite calling them simultaneous, this is inescapable.

    *separated in spacetime
     
  9. Jun 11, 2013 #8

    Mentz114

    User Avatar
    Gold Member

    A photon does not need a clock, just an odometer because Δt2 = Δx2
     
  10. Jun 11, 2013 #9
    wait a minute, it's a continuum; that mass less "bit" must do both simultaneously :tongue2:

    Odometer & clock are synonymous at c :smile: Like your equation says (or assume it does, I cant read math)
     
    Last edited: Jun 11, 2013
  11. Jun 11, 2013 #10

    Dale

    Staff: Mentor

    OK, whether it is intentional or not, nothing beneficial can come from discussing word salad.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Are there simultaneous moments?
  1. Criteria of simultaneity (Replies: 15)

  2. Simultaneity question (Replies: 10)

Loading...