Why do the order of Lorentz transformations matter?

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SUMMARY

The order of Lorentz transformations significantly affects the resultant transformation matrix, as demonstrated when applying a Lorentz boost in the x direction with velocity v followed by a boost in the y direction with velocity v'. This non-commutative property arises because the set of all Lorentz boosts does not form a group, unlike spacetime translations which do form a commutative group. In contrast, space rotations, such as those represented by the SO(3) group, do not exhibit commutativity in all cases, highlighting the unique characteristics of Lorentz transformations compared to Galilean transformations.

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  • Understanding of Lorentz transformations and their mathematical representation.
  • Familiarity with group theory, particularly the concepts of commutative and non-commutative groups.
  • Knowledge of matrix multiplication and properties related to matrix operations.
  • Basic understanding of spacetime concepts in the context of special relativity.
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  • Research the mathematical properties of Lorentz transformations in special relativity.
  • Study the structure and properties of the SO(3) and SO(2) groups in relation to rotations.
  • Explore the implications of non-commutativity in physics, particularly in quantum mechanics.
  • Learn about the relationship between Lorentz boosts and spacetime intervals.
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Physicists, mathematicians, and students of theoretical physics who are interested in the implications of Lorentz transformations and their mathematical foundations in special relativity.

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lets say you apply a Lorentz boost in the x direction with velocity v and a Lorentz boost in the y direction with velocity v'. Why does it makes that the order in which you apply the transformations affects the resultant transformation matrix? These are two independent directions, so shouldn't you be free to apply the transformations in whatever order you want. Interestingly, I get the transpose matrix when I reverse the order of application. Why does that make sense? In the Galilean system, the order does not matter, right?
 
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Well, the set of all Lorentz boosts don't even make up a group, not to mention a commutative group. Or think about it this way: do matrices generally commute under multiplication ?

Spacetime translations form a commutative group. Space rotations don't form a commutative group, but they form a group.
 
dextercioby said:
Well, the set of all Lorentz boosts don't even make up a group, not to mention a commutative group. Or think about it this way: do matrices generally commute under multiplication ?

Spacetime translations form a commutative group. Space rotations don't form a commutative group, but they form a group.

What is an example of two space rotations that are not commutative? They do form a group in two dimensions, correct?
 
By space rotations i meant just that, "space" rotations, i.e. the SO(3) group. The plane rotations, or SO(2), form an abelian group, since one can show that SO(2)\simeq U(1), with the latter group being abelian.
 
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I see. Thanks.
 

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