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Author Topic: How Slow Can Light Get ?  (Read 3207 times)

Offline neilep

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How Slow Can Light Get ?
« on: 01/07/2009 17:56:25 »
Dearest Lightologists,

How are ewe today ?  I am well, kids are taking exams and stuff...which is nice !

As a sheepy, I of course am fascinated by the speed of light. Light is my all time favourite particle/ray thing that makes my candles work and enables me to woo ewe's under a full moon. It's like...well great !

Look, here's some light stuff right here :



Some Light, Doing What Light Does Yesterday !!

Nice eh ?...being delivered for a party special-effect next Tuesday.

Now we all know that light is well fast...even faster than a horsey or a cheetah...and they are well fast !

As I understand it, light in a vacuum travels at a constant speed !..That's nice. I took my Hoover, opened it up and voila !! light was there travelling between all the bits of dust & stuff...it was well constant !..I measured it with a tape measure and by counting !..so..it must be right.


However, I recently heard that when not in a vacuum, light can slow down......my question (Finally !)..is..how slow can light get ?....can light go really slow ?..can it even stop ?

As a firm believer in empirical study I snuck into my neighbours house at 3am this morning and whilst he was happily under the influence of some chloroform (which he delightfully let me force him to inhale)...I glued about a hundred candles all over him and then lit them up !...well....as the wax melted...he moved alright !!...and he moved very fast !!..despite him being blindfolded he still found his way into the walk in closet that I had filled with fireworks and pushed him into........and instead of slowing down he sped up !!..hmmmm  ! I have some doubts here.


Perhaps ewe can shed some light on this paradox and help me know how slow light can go !


Hugs and shmishes



mwah mwah mwah !


Neil
Something That I always wanted to know
Not how fast in fact, but how light can go slow !
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Offline lightarrow

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How Slow Can Light Get ?
« Reply #1 on: 01/07/2009 20:17:21 »
 

Offline neilep

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How Slow Can Light Get ?
« Reply #2 on: 02/07/2009 10:12:24 »
THANK EWE chum,

fascinating stuff !
 

Offline LeeE

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How Slow Can Light Get ?
« Reply #3 on: 02/07/2009 15:54:33 »
While storing the pulse was pretty clever, the photons weren't actually stopped.  The article actually uses the term 'stored' and this is closer to the truth of what they achieved.
 

Offline neilep

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How Slow Can Light Get ?
« Reply #4 on: 02/07/2009 17:49:12 »
So, If I take some slowed down light and release it into a vacuum will it speed back up again ?
 

Offline lightarrow

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How Slow Can Light Get ?
« Reply #5 on: 02/07/2009 19:16:04 »
So, If I take some slowed down light and release it into a vacuum will it speed back up again ?
The article I linked says so...  :o
 

Offline JP

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How Slow Can Light Get ?
« Reply #6 on: 02/07/2009 22:30:34 »
So, If I take some slowed down light and release it into a vacuum will it speed back up again ?
The article I linked says so...  :o

So let's say there's this sheepy running through a field.  Then in the middle of the field he hits a patch of mud and runs reaaaaaaaaaaly slow through it.  When he comes out of the patch of mud he speeds up again and keeps running. 

That's pretty much what the light's doing. 
 

Offline LeeE

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How Slow Can Light Get ?
« Reply #7 on: 03/07/2009 00:18:41 »
Lol - nice one jp  :D
 

Offline syhprum

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How Slow Can Light Get ?
« Reply #8 on: 03/07/2009 03:42:33 »
Light pulses can of course be stored in mirror walled cavities but not for long!, how long can the pulses be stored in this system and do they lose intensity before being released ?
 

Offline Don_1

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How Slow Can Light Get ?
« Reply #9 on: 03/07/2009 08:00:56 »
Taking the above into consideration, would 'slow light' have any measureable effect on the distances (in light years) between us and some of the distant celestial bodies.

For example, a visible galaxy has been measured at 1 billion light years distance. Can we be sure that light from this galaxy has not, say 300 million years ago, passed through a large meandering gaseous cloud, which slowed down the light, giving the impression that the galaxy is 1b light years away, when in fact, had the light not been slowed it would have reached us in 0.9 billion light years? Also, could any such event have any effect on red shift?
 

Offline syhprum

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How Slow Can Light Get ?
« Reply #10 on: 03/07/2009 08:08:06 »
I understand that the gas has to be at a very low temperature much less than the CMBR.
 

Offline JP

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How Slow Can Light Get ?
« Reply #11 on: 03/07/2009 17:50:26 »
Most things that the pulse could run into that slow it would end up leaving some measurable imprint on the pulse, so you could tell it had hit something and probably account for it.  If you could slow light down without altering it, and then let it go on its way again, it could make Doppler shift calculations inaccurate, since you can't account for the X years it spent traveling "slowly."  This wouldn't effect the redshift though.

There are mechanisms to get a red shift that isn't due to a Doppler effect, for example http://en.wikipedia.org/wiki/Wolf_effect .  No one knows how common these are, however.
 

Offline neilep

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How Slow Can Light Get ?
« Reply #12 on: 03/07/2009 19:12:55 »
So, If I take some slowed down light and release it into a vacuum will it speed back up again ?
The article I linked says so...  :o

DOH !!...Thanks *le ashamed for missing that bit*
 

Offline neilep

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How Slow Can Light Get ?
« Reply #13 on: 03/07/2009 19:17:05 »
So, If I take some slowed down light and release it into a vacuum will it speed back up again ?
The article I linked says so...  :o

So let's say there's this sheepy running through a field.  Then in the middle of the field he hits a patch of mud and runs reaaaaaaaaaaly slow through it.  When he comes out of the patch of mud he speeds up again and keeps running. 

That's pretty much what the light's doing. 

Ewe've seen me running in fields haven't ewe ?  except that's it's not mud that slows me down !!! 
 

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How Slow Can Light Get ?
« Reply #13 on: 03/07/2009 19:17:05 »

 

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