- #1

aliens123

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In Robert M. Wald's

The energy of a particle as measured by an observer - present at the site of the particle - whose 4-velocity is ##v^a## is defined by

$$E=-p_a v^a$$

Thus, in special relativity, energy is recognized to be the "time component" of the 4-vector ##p^a.##

Is this a typo? We get the following:

$$E=-p_a v^a$$

$$E=-p_a(m \gamma) v^a / (m\gamma)$$

$$E=-p_a p^a /(m \gamma)$$

$$E = - (-m^2) / m \gamma)$$

$$E= m/\gamma \neq m \gamma = p^0.$$

__General Relativity__he writes on page ##61##:The energy of a particle as measured by an observer - present at the site of the particle - whose 4-velocity is ##v^a## is defined by

$$E=-p_a v^a$$

Thus, in special relativity, energy is recognized to be the "time component" of the 4-vector ##p^a.##

Is this a typo? We get the following:

$$E=-p_a v^a$$

$$E=-p_a(m \gamma) v^a / (m\gamma)$$

$$E=-p_a p^a /(m \gamma)$$

$$E = - (-m^2) / m \gamma)$$

$$E= m/\gamma \neq m \gamma = p^0.$$

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