Why does time have to be a complex (Minkowski metric)?

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Discussion Overview

The discussion revolves around the use of complex time in the context of the Minkowski metric within special relativity. Participants explore the mathematical and physical implications of representing time as a complex variable, the derivation of the Minkowski metric, and the historical context of these concepts.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant notes that working with a four-dimensional space requires time to be treated as a complex variable, leading to the Minkowski metric where the time component is negative.
  • Another participant suggests that the use of a complex time coordinate is a convention that simplifies calculations, particularly in relation to the Lorentz transformation, and questions the physical significance of this representation.
  • A reference to the Bondi k-calculus is made as a method to understand how the signature of the metric arises.
  • There is a repeated mention of Hermann Minkowski's formulation of time as ##x_4 = ict##, with a participant expressing curiosity about its continued teaching in modern contexts.

Areas of Agreement / Disagreement

Participants express differing views on the necessity and significance of using complex time in the Minkowski metric. While some acknowledge its mathematical utility, others question its physical relevance, indicating that the discussion remains unresolved.

Contextual Notes

Some claims rely on specific interpretations of mathematical conventions and historical developments, which may not be universally accepted. The discussion also reflects varying levels of familiarity with the underlying concepts and terminology.

feryopo
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I am studying special relativity, and I found that you have to work with a four dimensional space, where time is a complex variable. If you do so, you end up with the Minkowski metric, were the time component is negative and space components are positive (or vice versa). My questions are, why do we have to work with a complex time component, what is the physical meaning of time being complex and mathematically how can you deduct the Minkowski metric?
Thank you very much in advance.
 
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Welcome to PF;
You will learn to discard this notation and use an object called the metric tensor instead.
Minkovski coordinates uses a complex time coordinate because of work done by Poincare, that the 4D euclidean metric had to subtract time-squared, where the usual pythagorean approach would suggest adding time squared. This makes lorentz transformaton look like ordinary rotations as opposed to something weird and mysterious.

There is no special physical significance to the time component being represented as a complex number - the convention is exploiting the properties of complex numbers to shortcut some maths. The physics is the Lorentz transformation.
 
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##x_4 = ict ## was the invention of Hermann Minkowski in 1907 (published in 1908). I wonder why people still teach it nowadays.
 
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dextercioby said:
##x_4 = ict ## was the invention of Hermann Minkowski in 1907 (published in 1908). I wonder why people still teach it nowadays.
The Law of Relativistic Inertia? o0)
 
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