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Q & A: Relativistic transformations of electric and magnetic fields

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Most recent answer: 11/03/2012
Q:
ok..heres one problem....i am inside a train,,the train is moving..and there is one electron inside a train ..and i am looking at that electron..in my perspective the electron is not moving and (as my high school teacher told) only moving charged particle creates magnetic field...so i will not see any magnetic field..but suppose my friend is looking that electron sitting outside the train..then he will see a magnetic field is created...then here is a problem...what is happenning in reality..is there a magnetic field or not,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,does a independent reality exist??
- aawaz (age 17)
pokhara,kaski,nepal
A:
Your facts are correct:  you see only a static electric field whereas your friend sees a combination of electric and magnetic fields.   There is no problem because there is a relativistic transformation between the train system and the ground system that mixes up the E and B fields.  Your friend sees both a magnetic field whose value is given by the standard Maxwell equations as well as an electric  field . 
See:
for details. 

LeeH

Just to address your last question, yes, an independent reality exists in the following sense: certain physical properties are the same regardless of which reference system you use to describe them. These "invariants", however, are not the familiar variables such as E and B but rather combinations of them. Basic physical outcomes (does a particle bump into another one or not) are invariant aspects of that independent reality. /Mike W.

(published on 11/03/2012)

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