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Unformatted text preview: 73. The strategy is to ﬁnd the speed from E = 1533 MeV and mc2 = 0.511 MeV (see Table 383) and from
that ﬁnd the time. From the energy relation (Eq. 3845), we obtain
v=c 1− mc2
E 2 = 0.99999994c ≈ c so that we conclude it took the electron 26 y to reach us. In order to transform to its own “clock” it’s
useful to compute γ directly from Eq. 3845:
γ= E
= 3000
mc2 though if one is careful one can also get this result from γ = 1/ 1 − (v/c)2 . Then, Eq. 387 leads to
∆ t0 = 26 y
= 0.0087 y
γ so that the electron “concludes” the distance he traveled is 0.0087 lightyears (stated diﬀerently, the
Earth, which is rushing towards him at very nearly the speed of light, seemed to start its journey from
a distance of 0.0087 lightyears away). ...
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This note was uploaded on 11/12/2011 for the course PHYS 2001 taught by Professor Sprunger during the Fall '08 term at LSU.
 Fall '08
 SPRUNGER
 Physics, Energy

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