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Author Topic: Is the ''viscosity'' of light 0 unless there is impeadance?  (Read 1048 times)

Offline Thebox

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Is the ''viscosity'' of light 0 unless there is impeadance?

Z=m?

c=|Z|∠θ?

« Last Edit: 01/06/2016 18:51:37 by Thebox »


 

Offline Bored chemist

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No.
Viscosity is the ratio of the rate of momentum flux to the velocity gradient.
Since the velocity is constant it doesn't have a gradient and the ratio is meaningless.

The impedance of free space is a few hundred ohms
https://en.wikipedia.org/wiki/Impedance_of_free_space
 

Offline Thebox

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No.
Viscosity is the ratio of the rate of momentum flux to the velocity gradient.
Since the velocity is constant it doesn't have a gradient and the ratio is meaningless.

The impedance of free space is a few hundred ohms
https://en.wikipedia.org/wiki/Impedance_of_free_space

Ok, but when a word is in quotation, ''viscosity'' , it does mean exact strict definition.

A soup is ''thinner'' than a sauce, is light ''thinner'' than a soup?

And space has impedance, huh? 
 

Offline Colin2B

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Ok, but when a word is in quotation, ''viscosity'' , it does mean exact strict definition.
Usually putting something in quotes indicates it is not a strict definition, but for clarity it would be better to explain rather than let people guess.
 

Offline puppypower

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In the spirit of the analogy of viscosity, one might argue that changes in space-time can change the viscosity of light. For example, if space-time contracts, light becomes more viscous, with the blue shift due to adding heat to the light, due to higher viscous shear, at constant speed.

If you took an agitator at constant speed. First we stir pure water. Next,  we add corn starch to the water to thicken the sauce. The constant speed of agitation will now see more viscous drag, heating the sauce; blue shift in the infrared. If we could then remove the corn starch and lower the viscosity back to water, lower viscous shear would result in less heating; red shift.   

Based on this the viscosity of light would be zero at infinite wavelength where space-time is fully expanded. In black hole, the opposite is true with the viscosity of the light reaches a maximum. 
« Last Edit: 02/06/2016 12:07:38 by puppypower »
 

Offline Thebox

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Based on this the viscosity of light would be zero at infinite wavelength where space-time is fully expanded. In black hole, the opposite is true with the viscosity of the light reaches a maximum.

Resistance changes the ''viscosity'' of light, we only ''see'' observable light when light is interacting with 'matter', a denser cloud has more resistance than a ''fluffy'' white cloud. A dark cloud is the ''absence'' of light, I base the viscosity of light to be zero because light passes through things and into things, however things do obstruct light and create a ''viscosity'' of light in the things , light is ''captured'' by things?

 
 

Offline Bored chemist

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Is the zubzub of light zero?
Well, that depends on what you mean by zubzub.
Without a definition, the question is meaningless.

"Is the ''viscosity'' of light 0 ?"
Well, that depends on what you mean by "Viscosity".
Without a definition, the question is meaningless.
If you use the conventional meaning of the word- and life is often easier if you do, then the answer is "no".

If you want to use a different definition, then you really need to say what definition you mean.
 

Offline evan_au

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Quote from: TheBox
the ''viscosity'' of light

Viscosity has to do with a change in velocity. For normal matter, a change in velocity means a change in kinetic energy.

So the essential characteristic of viscosity is that it leads to dissipation of energy - it transforms "higher" forms of energy (eg kinetic energy) into "lower" forms of energy (eg heat).

However, every time someone measures the speed of light in their laboratory, it still comes out as "c". So the speed of light does not change.

If you measure the speed of light in a distant location (eg close to a star), it may come out as less than "c". But when it rises out of the gravitational well and returns to your laboratory, you will again measure the speed as "c". So it has not lost any energy. This occurs because the energy of light is reflected in its frequency, and not in its velocity.

Viscosity happens because matter interacts with matter. But light in a vacuum does not interact with other light (unless you get to extremely high energies).

So as I understand it, light does not experience viscosity.
 

Offline Colin2B

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Ω
Viscosity happens because matter interacts with matter. But light in a vacuum does not interact with other light (unless you get to extremely high energies).

So as I understand it, light does not experience viscosity.
I suppose the closest you could get to a viscosity would be when light interacts with matter such as glass and slows down. But even then there there is no interaction between light and other light (except in some nonlinear optical effects) and certainly never in a vacuum (with the exception you mention).
 

Offline Thebox

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I suppose the closest you could get to a viscosity would be when light interacts with matter such as glass and slows down. But even then there there is no interaction between light and other light (except in some nonlinear optical effects) and certainly never in a vacuum (with the exception you mention).

Yes Colin when the ''light'' is compressed it gains ''viscosity'', also when an object absorbs ''light'' , the ''light'' then contained within the object gains ''viscosity'', it becomes ''thicker'', the objects increases in it's ''positive'' entropy.
 

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