Why is No Backward Wavefront Possible?

  • Context: Graduate 
  • Thread starter Thread starter ronrknob
  • Start date Start date
  • Tags Tags
    Wavefront
Click For Summary

Discussion Overview

The discussion centers around the question of why backward wavefronts are considered impossible in wave propagation, particularly in the context of optics. Participants explore theoretical concepts, interpretations from literature, and the implications of different materials on wave behavior.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions the impossibility of backward wavefronts, suggesting that reflections in wave optics may imply backward propagation.
  • Another participant cites a book stating that there cannot be a backward flow of energy during wave propagation, asserting that secondary wavelets cancel out at points on a backward wavefront, leading to its non-existence.
  • A later reply emphasizes the need for proper citation of sources when referencing literature and introduces the concept of metamaterials, which can exhibit negative index of refraction, potentially allowing for backward wave behavior.
  • There is a suggestion that the original claim about backward wavefronts may apply to ordinary materials but may not hold for exotic materials like metamaterials.

Areas of Agreement / Disagreement

Participants express differing views on the existence of backward wavefronts, with some supporting the traditional perspective while others introduce the possibility of exceptions through metamaterials. The discussion remains unresolved regarding the general applicability of the claims made.

Contextual Notes

There are limitations regarding the definitions of wavefronts and the conditions under which backward propagation might be considered. The discussion also highlights the need for clarity in citing sources and understanding the context of claims made in literature.

ronrknob
Messages
2
Reaction score
0
Why no backward wavefront is possible?
 
Science news on Phys.org
ronrknob said:
Why no backward wavefront is possible?

This is puzzling. A "mirror" is a "wave optics" device, and a reflection is a "backward wavefront".

Zz.
 
In a book it is written
" there cannot be backward flow of energy during propagation of a wave..
and the resultant amplitude of all secondary wavelets at any point on a backward wavefront is zero.
The effects of secondary wavelets cancel out at all points except those lying on forward envelope. So a backward wavefront cannot exist.."

I'm not able to understand this thing
 
ronrknob said:
In a book it is written
" there cannot be backward flow of energy during propagation of a wave..
and the resultant amplitude of all secondary wavelets at any point on a backward wavefront is zero.
The effects of secondary wavelets cancel out at all points except those lying on forward envelope. So a backward wavefront cannot exist.."

I'm not able to understand this thing

In the future, you should start with this, and not the cryptic first post. Furthermore, in this forum, we require that you cite your source. So if you read it off a book, then the proper way to do this is to provide the author and title of the text.

What your book described is ordinary material, having a "regular", normal index of refraction. But if you are still asking on if it is possible to have a material producing a "backward" wave, then yes, it is. There are a certain class of "metamaterial" that produced a negative index of refraction, often also called left-handed material.

http://www.metamaterials.duke.edu/what-are-negative-index-refraction-materials

Note that these are more "exotic" type of material that are not usually cover in standard, optics text.

Zz.
 
Last edited by a moderator:

Similar threads

Graduate When should I analyze optical problems using ray tracing vs. wavefront analysis?
  • · Replies 12 ·
Replies
12
Views
2K
Undergrad How Do Different Wavefront Shapes Appear to the Human Eye?
  • · Replies 28 ·
Replies
28
Views
3K
High School How would one draw reflected wavefronts?
  • · Replies 9 ·
Replies
9
Views
2K
High School How do you explain a plane wavefront based on huygens' principle?
  • · Replies 2 ·
Replies
2
Views
2K
Graduate Interference of light by splitting the wavefront and recombining
  • · Replies 8 ·
Replies
8
Views
2K
High School Wavefronts: Understanding Wave Optics
  • · Replies 10 ·
Replies
10
Views
3K
Graduate How should the optical diffraction field be solved?
  • · Replies 8 ·
Replies
8
Views
2K
Undergrad Geometry of Cherenkov radiation
  • · Replies 4 ·
Replies
4
Views
1K
Undergrad Huygen Wavefront: Drawing a Tangent to Wavelets
  • · Replies 6 ·
Replies
6
Views
2K
Graduate Are holograms able to reconstruct wavefronts in all directions?
  • · Replies 4 ·
Replies
4
Views
2K