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New form of light discovered


seeder

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Physicists discover a new form of light

Physicists from Trinity College Dublin's School of Physics and the CRANN Institute, Trinity College, have discovered a new form of light, which will impact our understanding of the fundamental nature of light.

One of the measurable characteristics of a beam of light is known as angular momentum. Until now, it was thought that in all forms of light the angular momentum would be a multiple of Planck's constant (the physical constant that sets the scale of quantum effects).

Now, recent PhD graduate Kyle Ballantine and Professor Paul Eastham, both from Trinity College Dublin's School of Physics, along with Professor John Donegan from CRANN, have demonstrated a new form of light where the angular momentum of each photon (a particle of visible light) takes only half of this value. This difference, though small, is profound. These results were recently published in the online journal Science Advances.

Read more at: http://phys.org/news/2016-05-physicists.html#jCp

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I knew this one was a bit of a mind bender...... hence the lack of replies!

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And there goes the notion that Planck units are the smallest units which cannot be divided any further.

We need an alternative to reductionism because there is no evidence or logical proof that you cannot keep dividing things into smaller and smaller quantities.

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Theoretical physicists since the 1980s have speculated how quantum mechanics works for particles that are free to move in only two of the three dimensions of space. They discovered that this would enable strange new possibilities, including particles whose quantum numbers were fractions of those expected. This work shows, for the first time, that these speculations can be realised with light.

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And when the machines breaks the tech barriers to become much more technologically advanced they'll be getting results that are finer and the quantum number fractions will be further reduced and such minds will be further boggled ...

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On 5/21/2016 at 1:54 PM, RabidMongoose said:

And there goes the notion that Planck units are the smallest units which cannot be divided any further.

We need an alternative to reductionism because there is no evidence or logical proof that you cannot keep dividing things into smaller and smaller quantities.

Firstly, I think you're getting Planck "units" and "lengths" mixed up. A Planck length is the smallest measure of distance where time and gravity are relevant and where the concept of "distance" actually means anything. Planck units are a set of universal constants.

Secondly - I can't see how this idea does away with the Planck length. This isn't reductionism.

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On 21/05/2016 at 1:54 PM, RabidMongoose said:

 

seeder said:

 

And there goes the notion that Planck units are the smallest units which cannot be divided any further.

We need an alternative to reductionism because there is no evidence or logical proof that you cannot keep dividing things into smaller and smaller quantities.

Further to what Emma has said, how angular momentum is measured in photon's is via a formula - the attribute mentioned is technically, and more correctly, called the spin angular momentum and is found when a stream of photons comprising a "beam" of light all have the same circular polarisation (i.e. they spin around the beam axis in the same direction) - not via a direct measurement, so it was always possible (although previously considered unlikely) to be able to calculate values less than any of the Planck constants. This is similar to how charge is calculated in various sub-atomic particles, some of which are calculated to have a "half-charge".

It would be intuitive to suppose this "half-charge" is actually the singular value, and those particles which are referred to as having a "whole charge" then should actually have a charge value of 2 - but science in this case (and in the case of the angular momentum of photons) is counter-intuitive, nevertheless all the formulae for calculating such attributes are still relevant and "correct".

Edited by Leonardo
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This finding is interesting, but does not change the theory of Quantum Mechanics nor have any influence on Planck units.

The rules for "allowed values" of angular momentum in quantum mechanics originate - like all of the rules for any "allowed value" - from the boundary conditions of the system.

In a 3D system, the projection of any angular momentum associated with motion along any axis must be integer multiples of the reduced Planck's constant.

However the total angular momenta of a beam of line is a 2-dimensional system, because the momenta cannot project along the direction of travel (basically because nothing can go faster than the speed of light). This changes the boundary conditions and consequently changes the quantization laws.

The author's published manuscript is available here: http://advances.sciencemag.org/content/2/4/e1501748.full. Note that standard quantum mechanics is used to explain their experimental findings.

Finally, this research does not affect the well-established nature of the photon as a gauge boson with an intrinsic spin angular momentum of 1.

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