Are there reflections in the fourth dimension?

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The discussion centers on the concept of reflection in relation to dimensions, specifically the fourth dimension. A phase conjugate mirror is mentioned as a theoretical device that could reflect electromagnetic radiation backward in time, potentially rendering objects invisible. There is acknowledgment of military research into invisibility technology, though no significant breakthroughs have been reported. The definition of reflection is also explored, describing it as a linear transformation that alters one dimension while maintaining others. Overall, the conversation delves into the complexities of reflection in higher dimensions and its implications.
hydrostaticequil
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If so what does the reflection look like?
 
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hydrostaticequil said:
If so what does the reflection look like?
Physicists refer to three dimensions of space and one of time usually. I am not sure what you mean by "reflection."
 
What do you mean by the fourth dimension?
 
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hydrostaticequil said:
If so what does the reflection look like?
How will you make the mirror?

A "phase conjugate mirror" might reflect EM radiation, back the way it came, in effect backwards in time. That would cause things that reflect light or radar to cancel with themselves, becoming invisible. There has been military research into the field of making things invisible, but I don't think there has been any real success.
https://en.wikipedia.org/wiki/Nonlinear_optics#Optical_phase_conjugation
 
hydrostaticequil said:
If so what does the reflection look like?
I would define a reflection as a linear map that changes the sign in one dimension and keeps all other dimensions fixed. This is independent of the number of dimensions.
 

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