Slow Light????

[xelasnave]

Slow light.. is not C constant some sort of rule that can not be broken one is at first prompted to ask...


However the researchers point out.......

Slowing light this way doesn't violate any principle of physics. Einstein's theory of relativity places an upper, but not lower, limit on the speed of light.





http://www.cosmosmagazine.com/news/841/scientists-slow-light-speed-internet

I thought this may be interesting

alex

[xelasnave]

From Harvard U so it must be good....

http://www.news.harvard.edu/gazette/1999/02.18/light.html

alex

[xelasnave]

At the end of the HU gaz.....
..... (things)...are already being set up to slow light speed even more, to one centimeter (less than a half-inch) a second. That's a leisurely 120 feet an hour.

They said it not me

alex

[Glenhuon]

I seem to remember recently where scientists have actually stopped photons for a fraction of a second. can't remember the source though.

Bill

[Max Vondel]

The speed of light 299,792.458 km/sec is in a vacuum. Light slows down when it travels through different media. For example light slows when travelling through glass. Were it no so, then refractor telescopes and eye glasses would be impossible. The speed of light is relative to the refractive index of the material. For example the refractive index of light in diamond (the slowing down) is responsible for the nice colours and hence the price of this form of carbon. Your best bet is to check out some 1st years physics books as they nicely illustrate refractive indexes and light speed changes in assorted media
:)

[xelasnave]

Thank you Peter for the input.
I felt the research takes the matter a little beyond refraction as covered at the basic level of 1st year physics ....which was the reason I posted in fact.
alex

[xelasnave]

I think light slows in glass by approx 33% (light slows to approx 66% of speed in a vacuum in glass...) yet in the research program they are slowing it to 16% of its speed in a vacuum. That is a dramatic difference to what we have listed in the refractive index...

alex

[Max Vondel]

The slowing I think you are refering to is related to low temperature plasma physics and quantum mechanics. Articles have appeared in New Scientist and similiar publications. I wasn't being demeaning when I suggested the 1st year physics book in relation to the refractive index. If you have taken offense, I appologise unreservedly.
:)

[xelasnave]

No no:eyepop: ...no offence taken I thought you missed my point on the basis I was unaware of refractive index and I can see why with the introduction:D.
You can not offend me I am all most folk critise me for and more:whistle:... I accept personal responsibility for the slack way and the simplified way I post.
I read about it some time ago when I was looking at the Bose condensate stuff (and that certainly relates to the areas you suggest) but when I saw it this time given the chat on similar matters I thought I would post... I dont think folk think of light as having any speed but C and that C was selected for constant... but it is not.

alex:):):)

[Miaplacidus]

Not that it's related to the article, but I am quite sympathetic to MOND and the tired photon hypothesis. It must be quite exhausting, travelling at c all the time. When I was looking at some far off quasar once I remember thinking how those poor photons, which had been travelling uninterrupted for nigh on 13 billion years before obliterating themselves on my unworthy retina, could barely crawl through my cornea and over the inner edge of my iris. Oh, the darlings...

[xelasnave]

Tired or not I wonder how many photons there be to the cubic meter...there would be photons from everywhere ... I like to imagine the many sources and how at any place there must be a representation of everywhere even if each object only contribute one single photon there would be a few.

Tired light... it will meet fiece opposition but I often wonder if the background radiaition could be tired light from beyond where we can imagine light could come from... if you see what I mean.

MOND I am not really sure what is says exactly really so I will read up on it again... anything gravity related I like.

alex


alex

[bojan]

C is defined as the speed of light in vacuum.
And, it is a constant..

[xelasnave]

Well we need a V as well for the other mediums.
I was wondering Bojan how did they work out the speed of light considering when it was arrived at men did not have the vacuum of space to work in...
I will have a look today if I can fit it in my otherwise lazy planned day.

alex

[bojan]

C appears as a constant in Maxwell's equations (they describe the behaviour of electromagnetic field).
Have a look here:
http://en.wikipedia.org/wiki/Electromagnetic_wave_equation
It depends on e0 and u0, electrical and magnetic permeability constants of vacuum, presented and explained in a table lower on the page.

Not as simple as :cheers: eh ;)?



And, we do have V for other mediums, but this is not fundamental, nor it is a constant.
BTW, by knowing electric and magnetic properties of the medium, the velocity of light in it can be calculated with the same formula (v=1/SQRT(e0*u0)). of course, the medium have to be transparent too, and obviously those relations will not cover the issue of transparency, for this there are others.
So, optical behaviour (refraction index) of media are determined by their related electromagnetic properties.. strange but true.

[xelasnave]

Bojan thank you so much for all that...you know you have got me thinking that there may just be something in this math appraoch that is useful.

I really do appreciate you taking the time to help me and I can assure you your time is not wasted on me ...

alex:):):)

[maksutover]

Light can be slowed down (I think) when it traverses through a Bose-Einstein condensate (weird state of matter at 10^-9 Kelvin).

[acropolite]

I think there was some mention of this in the BBC documentary series Absolute Zero.

[xelasnave]

Yes I feel you are correct as I spent some time at one time reading about the interesting things surrounding the Bose-Einstein condensate and what you say seems to sit well. Actualy I should go back and read about it again it has been so long it will seem brand new to me..I am an old man with an older memory so it will seem new again:lol::lol::lol:

alex:):):)

[Mombat]

Lol this is like revision for me from first year physics.
I have a question though when matter reaches the event horizon of a black hole what exactly happens to it i know that it is stretched out by the lorentz factor as it speeds up due to the black holes gravity but what happens to it after that. Is it the massively compressed due to gravity and it coalesce into a single point at the center of the black hole or is it converted to energy due to the forces acting upon it?

Sorry if that was confusing i hope someone can understand and possibly shed some light on it.

[xelasnave]

I can not answer that I have not yet accepted they are what we have theorised them to be:lol::lol::lol:

Probably depends to a degree who you ask. Steven Hawkin has proposed radiation can escape but I think I saw something that may not be in favour.

I would imagine (and this is unsupported and pure speculation) that there would possibly be a process where it progresses from spagggtfication to vapourisation and the mass spread around as it compresses... in other words it seems that if you threw in a brick it would purverise well before compression and the forces would by such that radiation will no doubt be generated I think as exotic rays as oppossed to heat...however as the idea goes nothing can escape including radiation... Mr Hawking has shown however radiation can escape but I think it does not necessarily come from matter being eaten as such...but on his idea it seems there is room for a black hole to evaporate... again I am not sure that is currently popular.

Anyways I thought all we know goes out the door on the "inside" of a black hole..beyond the event horizon as they say...so how can we descibe what is going on. I wonder if nuclie are packed as if they are marbles in a jar...or packed like soap bubbles stacked in the same jar..with out marbles that is... or does it become some sort of soup made of quarks and stuff...

But the a black hole equates I think to a singularity which has interesting qualities such that matter and time are really different to what we can understand.

alex:):):)

[Mombat]

Yeh i think that is the general hypothesis. I think if i do remember correctly which remains to be seen that black hole does radiate energy as photons and such and that a small black hole say less than a solar mass will eventually shrink and disappear. However black holes of this size are yet to be identified although theorised to have been created early on in the universes history, but that even the smallest should only now be disappearing. to be honest i don't know how much of this i am remembering correctly.

In a massive black hole however say the one said to exist at the centre of our galaxy they have a constant source of matter which they absorb, increasing their mass so that they absorb more "energy" than they radiate off. If this is the case then will the black hole at the center of our galaxy eventually engulf the milky way.
What happens then though? Is the great attractor to which our own local group, and supercluster is speeding towards an enormous black hole which will engulf our galaxy or perhaps by then our milky way black hole. If this is the case could that be what our Universe ends up being a series of immense balck holes seperated by distances beyond which gravity cannot over come the expansion of space time. Bearing in mind that i am talking about a timeline of several times the age of the current universe.

That was confusing even to me. :D

[xelasnave]

Very interesting Mombat I am out of my depth with all this but I share my views ... Cosmology is not set in stone there is still some stuff to work out so think away...


U]If this is the case then will the black hole at the center of our galaxy eventually engulf the milky way.[/U]

I doubt it but who knows.
I think that black holes clean out the material available to them and observations I have read support this.. but it suggested to me that the influence of the black hole in effect left an eaten out region. AND I think a black hole has little gravitational influence outside that region ...but my point is, it therefore seems not a case where stuff is banked up waiting to drop in....which does not present a picture of eventual disappearance of the galaxy down its own black hole.



Is the great attractor to which our own local group, and supercluster is speeding towards an enormous black hole which will engulf our galaxy or perhaps by then our milky way black hole.

Well at those scales it is difficult to image it is attraction that is producing the move we observe... without doing the sums I bet we would find difficulties in determing attraction is doing all we observe... for mine to understand what we observe I feel we need an extenal influence at the scales you mention... pretty big...in fact very big... consider the distance spread for the region that appears related and then how any message of gravity could produce such unison...maybe it is dark energy that is holding all of that in place but I think there may be a problem in establishing gravitational relationships and explain them using current theories.

Sorry my mind is not in gear yet.


If this is the case could that be what our Universe ends up being a series of immense balck holes seperated by distances beyond which gravity cannot over come the expansion of space time.

Well one of the reasons I like push gravity ...is gravity will always rule and not see the Universe you consider.

I can not consider that the Universe will "suck" all matter to certain spots (black holes) such that the voids that remain are absent of all forces....and if you think it through that is what your hypothetical can only lead you to. The black holes will have all the matter .... mmm if nothing can escape a black hole how does the message of gravity make it...is that not curious?

Whatever the voids that remain maybe they will have no light or gravity... in fact nothing in the absolute meaning of the word. Sounds silly but that is to only result if we extrapolate to a situation where there be only black holes...what else can be on their outside??

Still if we consider what came before the BB maybe where you are going is correct...maybe finally all the black holes gather into one (man how long for everything to come home to unite as one) and as one we have a new singularity to set the seen for a new BB... if it is to go this way even starting right now how long would it take the universe to finally colapse...with out a reverse inflation theory ...trillions of years to the power of 50... so we are either very young in the scheme of things or its never going to happen...

Bearing in mind that i am talking about a timeline of several times the age of the current universe.

Take some time to think about ruffly how much time... first how big is the Universe at the moment...well we get all figures from infinite (forget that if using the big banf model) to about 160 billion light years...I dont know if that is the diameter of us as a sphere or a disk or what but just think using the force of attraction to bring all that back to one place with take "ages"...but as we observe the universe is still expanding so we would be looking at some time before we even saw a turn around....maybe the great attractor is a sign that the tide has changed;)...you may have something here:D...dont worry about a longer time line than you feel comfortable with just work out how long that time line may be... ruff of course.:whistle:

That was confusing even to me.
Well you are embracing interesting concepts and this is not the stuff one brings up when chatting about the footy so dont worry..and you seemed very lucid to me.:thumbsup:

alex:):):)