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Author Topic: Do photons change speed in Empty Voids in the universe?  (Read 2045 times)

Offline Fluid_thinker

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Not sure it this is actually possible, but something i was thinking about.

If the empty voids in space are virtually empty of matter and dark matter etc...... and in theory the Cosmic Microwave Background radiation would be cooler in these voids.

Is it possible that particles, say photon's could or would change speed?

Could they speed up or slow down?


 

Offline Pmb

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Re: Do photons change speed in Empty Voids in the universe?
« Reply #1 on: 18/09/2013 17:42:23 »
Quote from: Fluid_thinker
If the empty voids in space are virtually empty of matter and dark matter etc...... and in theory the Cosmic Microwave Background radiation would be cooler in these voids.
You attempted to construct a logical form but failed in your attempt to do so. The logical form you were trying to write was of the type

If A and B then C

What you ended up with is something totally different. In fact its not even a logical statement. You really need to rephrase if before any sense can be made of it.

What you have so far is a statement of the form

If <a> and <b> and in theory <c> would be cooler in these voids.

That’s a meaningless statement. What you attempted to do was make a statement of the physical conditions that exist and with those statements ask

Quote
“Is it possible that particles, say photon's could or would change speed?

Could they speed up or slow down?

Since its not clear what the conditions are that exist then we can’t answer your question adequately.

For example, we don’t know whether you’re asking

“In a region of space which is devoid of matter but which contains a gravitational field then is it possible that within that region of space the photons can’t change their speed?”

or something else. If you’re answering this question and we assume that you’re defining “matter” in the same way Einstein did then no, it’s not possible.
« Last Edit: 18/09/2013 21:41:34 by Pmb »
 

Offline syhprum

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Re: Do photons change speed in Empty Voids in the universe?
« Reply #2 on: 18/09/2013 20:09:59 »
It is rather difficult to work out what "Fluid thinker" is really asking but I believe he is asking does the lower density of particles in voids have any effect on the speed of photons which is normally said to be c in a vacuum .
An interesting idea I would think very little but it might measurable by some subtle means.
 

Offline AndroidNeox

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Re: Do photons change speed in Empty Voids in the universe?
« Reply #3 on: 19/09/2013 22:28:55 »
The emptier the void, the closer to c the light will travel. Theoretically, any normal matter (as opposed to "dark matter") in the region through which the light travels will interact electrically with the light, just as it does in solid matter, slowing it. But, the effect would be amazingly tiny and I doubt that there would be a detectable effect even for vacuum as dirty as that within our solar system. But, technically, light would travel faster through those emptiest of voids... not slower.
 

Offline Soul Surfer

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Re: Do photons change speed in Empty Voids in the universe?
« Reply #4 on: 19/09/2013 22:29:43 »
The simple answer fluid thinker is NO.  Photons go at their fastest when there are no other particles around and photons go slightly slower in a gas but the density of particles in space is so low that it has no detectable effect on the velocity of light if it did the variable densities would cause the images of distant objects to be distorted like looking through bumpy glass.  in fact the only thing that does this over vast distances is large gravitational fields associated with large galaxies and dense clusters of galaxies and this is an exceedingly small effect
 

Offline alancalverd

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Re: Do photons change speed in Empty Voids in the universe?
« Reply #5 on: 19/09/2013 22:35:19 »
If the speed of light through interstellar matter is lower than in vacuo, we should expect to see Cerenkov radiation from the denser bits. Do we? 
 

Offline evan_au

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Re: Do photons change speed in Empty Voids in the universe?
« Reply #6 on: 20/09/2013 12:09:46 »
There are some detectors which look for Cerenkov radiation from cosmic rays striking the upper atmosphere; I guess the Earth's atmosphere qualifies as one of the denser parts of space?

However, Cerenkov radiation consists of light, generated by particles which are not light, exceeding the speed of light in that medium.
  • Can light generate Cerenkov radiation?
  • If it did, it would rapidly lose energy, and then be traveling at a speed slower than the speed of light in the local interstellar medium
Sorry if that sounds convoluted!
See http://en.wikipedia.org/wiki/Cherenkov_radiation#Physical_origin
 

Offline alancalverd

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Re: Do photons change speed in Empty Voids in the universe?
« Reply #7 on: 20/09/2013 17:35:35 »
Aha! You caught me! I don't expect a photon to produce Cerenkov radiation - light is simply refracted in a denser medium. But what about other particles? Space should be full of Cerenkov photons! 
 

Offline yor_on

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Re: Do photons change speed in Empty Voids in the universe?
« Reply #8 on: 21/09/2013 13:09:03 »
Sounds like tachyons to me :)

If we define 'c' as being lights speed in a vacuum, then that's it. you might want to argue that some 'vacuums' are emptier than others but the theory presumes a 'perfect vacuum' as far as I'm concerned. So, in a solid or a gas, can there exist minuscule patches of this perfect vacuum? If we use the argument of something getting magnified, a gravity for example getting 'flatter' the more you magnify some coordinate system then I suppose you can apply the same sort of thinking to what's inside a solid, magnifying it. Then again, I don't think light, necessarily, have to propagate to give us c', not mathematically. It should be enough with some logic principles defining a coordinate system, then find excitations under a arrow, measurably differing in position.
 

Offline yor_on

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Re: Do photons change speed in Empty Voids in the universe?
« Reply #9 on: 21/09/2013 13:17:21 »
The most intriguing thing to me, with assuming that you can apply a magnification to find a 'perfect vacuum' even in matter is that, if correct that is :), it should be valid for any and all points inside that coordinate system, if I'm thinking right here, just as it should be finding gravity 'disappearing', going down in scale.
 

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Re: Do photons change speed in Empty Voids in the universe?
« Reply #9 on: 21/09/2013 13:17:21 »

 

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