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Lorentz Transforms + Relativity of Simultaneity

  1. Mar 28, 2009 #1

    I'm studying special relativity this semester and stumbled onto a couple of problems. These have nothing to do with my homework or anything, they're just a couple of things I thought up. Since I have little contact with my teacher (it's an online course), it'd probably be a good idea to put them here. I'm sorry if this is the wrong forum, but again this isn't homework but questions on the topic.


    Person A sets up, in the lab frame, a string of collinear firecrackers evenly spaced one meter apart. Person B is in the rocket frame, traveling parallel to the firecrackers at speed .5*c. A sets off the firecrackers so they all go off the same time, her frame. To B, the distances every two consecutive firecrackers are lorentz contracted to 1*sqrt(1 - .5^2) .866 meters. So after the first flash of light reaches him, the next one should arrive after 1/(1 - .5) 1.73 seconds. Is this correct? If not, what did I accidentally add or leave out? Does this demonstrate the relativity of simultaneity?


    We'll define A to be gamma. We have a lab frame (with coordinates x
    and t), and a rocket frame (with x' and t'). In the lab frame, there
    are two points, x1 and x2. The distance between them is dx. In the
    rocket frame, the two points are at locations A(x1 - vt) and A(x2 -
    vt). Therefore, in the rocket frame dx' is A*dx.

    Now, we place a bar between those two points of length dx. It Lorentz
    contracts to length dx/A as observed in rocket frame. So the space
    increased to A*dx and length of the bar in that space decreased to
    1/A * dx. Is this all correct, or am I missing something here?



  2. jcsd
  3. Mar 29, 2009 #2

    Well, you have to add the relativity of simultaneity, i.e. the time transformation [tex]\gamma(t-vx/c^2)[/tex].

    For example, we have 2 firecrackers starting simultaneously at the coordinates x1=0, t1=0 and x2=1m, t2=0.

    What are the coordinates (both space and time) of those two events in the rocketframe?

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