What is the Relationship Between Energy and Time in Different Frames?

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Discussion Overview

The discussion revolves around the relationship between energy and time in different reference frames, specifically focusing on the transformation of energy as described by the equation E' = gamma * (E - p.v). Participants explore the derivation and implications of this transformation in the context of special relativity.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions the derivation of the energy transformation equation E' = gamma * (E - p.v) and seeks clarification on its origins.
  • Another participant suggests that this transformation arises from the definition of energy as the "zeroth" component of the momentum four-vector, drawing a parallel to time as the "zeroth" component of the position four-vector.
  • A further response reiterates the relationship between energy and time transformations, indicating that E' can be expressed similarly to how time transforms under Lorentz transformations.

Areas of Agreement / Disagreement

Participants present multiple viewpoints regarding the derivation and interpretation of the energy transformation equation. There is no consensus on a definitive explanation, and the discussion remains open to further exploration.

Contextual Notes

The discussion does not resolve the assumptions underlying the transformation equations, nor does it clarify the mathematical steps involved in deriving the energy transformation from first principles.

chewwy
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something which seems so fundamental that i can't find anywhere that derives it is the following:

E' = gamma * (E - p.v)

where E is the energy in one frame, p the momentum, v the relative velocity of the other frame, and E' the energy in the other frame.

i.e. energy transforms like time. i can't quite see where this comes from though.. help?
 
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It comes from the fact that energy is the "zeroth" component of the momentum four-vector (p_0, p_1, p_2, p_3) = (E/c, p_x, p_y, p_z), just like time is the "zeroth" component of the position four-vector (x_0, x_1, x_2, x_3) = (ct, x, y, z).
 
Welcome to PF!

Hi chewwy! Welcome to PF! :smile:

(have a gamma: γ :wink:)
chewwy said:
energy transforms like time. i can't quite see where this comes from though.. help?

Yes, it's because (E,p) is defined as the derivative of (t,x),

so E' = γE - γ(p.v),

just as t' = γt - γ(x.v)
 
jtbell said:
It comes from the fact that energy is the "zeroth" component of the momentum four-vector (p_0, p_1, p_2, p_3) = (E/c, p_x, p_y, p_z), just like time is the "zeroth" component of the position four-vector (x_0, x_1, x_2, x_3) = (ct, x, y, z).

okie doke. thanks everyone!
 

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