Names of 4-Vector Norms & Physical Quantities

In summary: Lorentz invariant norm of the four-potential and four-current. This is because their physical meaning depends on the distribution of charges and currents. In other words, the norm is proportional to the charge or current density in a particular frame. Additionally, vectors are invariant under coordinate system transformations, and their norm remains unchanged unless a different norm is used. In summary, the norm of every vector is an invariant, but there are no specific names for the Lorentz invariant norm of the four-potential and four-current.
  • #1
speeding electron
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Are there names for the Lorentz invariant norm of the four-potential and four-current? I assume that they are invariant under the transformations. Also, is it true that any physical quantities which form a four-vector have an invariant quantity associated with them (i.e. the norm of the corresponding four-vector)? Thanks.
 
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  • #2
Vectors are invariant under changes of the coordinate system (what you probably mean by tranformation). Only their representation as a linear combination of the base vectors changes (as an inverse to the changes of the base => contravariant vectors). As the vectors (do not confuse a vector with it´s representation (t,x,y,z)) remain unchanged so is their norm - unless you switch to another norm/metric for some reason.
Or in short: Yes, the norm of every vector is an invariant.

About the name: I´m not sure if there´s a special name for it but if you talk about "Lorentz metric" (note that the norm derives from the metric) I think people will know what you talk about - but beware that the sign-convention for this metric might vary.
 
  • #3
speeding electron said:
Are there names for the Lorentz invariant norm of the four-potential and four-current? I assume that they are invariant under the transformations. Also, is it true that any physical quantities which form a four-vector have an invariant quantity associated with them (i.e. the norm of the corresponding four-vector)? Thanks.
No. There are no names for them. The main reason being is that their physical meaning will depend on the particular distributions of charges/currents. I.e. if there exists a frame in which there are no charges present but there is a non-zero current density then the norm is proportional to that current density. If, on the otherhand, there is a frame in which there is no current density but there is a charge density then the norm is proportional that charge density.

Pete
 

FAQ: Names of 4-Vector Norms & Physical Quantities

What are 4-vector norms?

4-vector norms are mathematical tools used to measure the magnitude or size of a 4-vector in four-dimensional space. They are often used in physics and engineering to describe physical quantities.

What are physical quantities?

Physical quantities are properties or characteristics of a physical system that can be measured or described using numerical values. Examples include mass, velocity, and electric charge.

How are 4-vector norms related to physical quantities?

4-vector norms are used to measure and describe physical quantities that have four-dimensional components, such as energy-momentum or electromagnetic fields. They provide a way to quantify these quantities in a consistent and mathematically rigorous manner.

What are some common 4-vector norms used in physics?

The most commonly used 4-vector norms in physics are the Euclidean norm, Minkowski norm, and Lorentz norm. These norms differ in the way they account for the time component of the 4-vector and are used to describe different physical phenomena.

How are 4-vector norms used in practical applications?

4-vector norms are used in a variety of practical applications in physics and engineering, such as in relativity, electromagnetism, and quantum mechanics. They provide a mathematical framework for describing and analyzing physical quantities and their relationships in a consistent and precise manner.

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