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bernhard.rothenstein
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What is the simplest way to find out if a physical quantity is the component of a four vector? There are opinions that the Lorentz contracted length is not, the Lorentz dilate length being.
bernhard.rothenstein said:What is the simplest way to find out if a physical quantity is the component of a four vector? There are opinions that the Lorentz contracted length is not, the Lorentz dilate length being.
Thank you. Please have a look at the following lines.DrGreg said:A set of quantites form a 4-vector if they tranform via the Lorentz tranform. Thus if [itex]\textbf{X} = (ct, x, y, z)^T[/itex] and [itex]\textbf{X'} = (ct', x', y', z')^T[/itex] are coordinates for the same event in two different inertial frames (in "standard configuration", i.e. with aligned spatial axes and in relative motion along their common x axis), we can say this is a 4-vector because
[tex]\textbf{X'} = \Lambda \, \textbf{X}[/tex]
where
[tex]\Lambda = \left[ \begin{array}{cccc}
\gamma & -\gamma v & 0 & 0 \\
-\gamma v & \gamma & 0 & 0 \\
0 & 0 & 1 & 0 \\
0 & 0 & 0 & 1 \\
\end{array} \right][/tex]
"Lorentz-contracted length" doesn't satisfy this because the length is measured between two events that are simultaneous in the frame where the measurement is made. When you change frames, you also change events. The Lorentz transform applies only when you measure the same pair of events in two different frames.
Other examples of 4-vectors are
Energy-momentum... [tex]\textbf{P} = (\frac{E}{c}, p_1, p_2, p_3)^T = m\frac{d\textbf{X}}{d\tau}[/tex]
4-force...... [tex]\textbf{F} = \frac{d\textbf{P}}{d\tau}[/tex]
4-current..... [tex]\textbf{J} = (\rho c, j_1, j_2, j_3)^T[/tex]
electromagnetic 4-potential [tex]\Psi = (\phi, a_1 c, a_2 c, a_3 c)^T[/tex]
(See four-vector on Wikipedia.)
A four vector component is a mathematical concept used in the field of physics and special relativity. It is a set of four numbers that represent the position and direction of an object in space and time.
A four vector component is different from a regular vector in that it includes time as a fourth component, while a regular vector only has three components representing space. This allows four vector components to accurately describe the position and motion of an object in four-dimensional space-time.
A four vector component is usually denoted by a symbol with an arrow above it, such as A → or p →. It will also have four components, typically labeled as x, y, z, and t for space and time, respectively.
Four vector components are important in physics because they provide a way to accurately describe the position and motion of objects in space and time. They are used in special relativity, electromagnetism, and other areas of physics to calculate and describe physical phenomena.
Yes, four vector components can be used to describe any type of motion, as long as it occurs in four-dimensional space-time. This includes both linear and rotational motion, as well as motion at any speed, including the speed of light.