Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Spacetectonics on 13/02/2013 16:30:18
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How light behave in very low speed? what physical property of it changes?and what happen if it stop(0KM/H)?
Cheers
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It doesn't. The question doesn't make sense.
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In empty space, light always travels at the speed of light, hence the name the speed of light.
However, if light interacts with matter, the total time it takes a pulse to travel through some material can be made slower due to this interaction. There is a research area called slow light that seeks to find ways to make the speed of light very low due to light-matter interactions. One hope is that this could allow light to be stored more efficiently and enable computers to use light instead of electrons.
Edit: And they have apparently "stopped light" and later restarted it, essentially storing it within matter for a time. (see links at http://en.wikipedia.org/wiki/Slow_light)
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Theoretically light is at 0 km/s at the event horizon of a black hole, although it may not be observable.
The speed of light is also dependent on the medium it is in. C is measured in a vacuum.
There is reasearch into Slow Light (http://en.wikipedia.org/wiki/Slow_light), often being tested in a Bose–Einstein condensate (http://en.wikipedia.org/wiki/Bose%E2%80%93Einstein_condensate)
According to this article, the researchers may have in fact been able to stop, or pause the progression of light. (http://www.photonics.com/Article.aspx?AID=28520)
One theory is the light is being absorbed and re-emitted. Have they verified whether polarized light maintains its polarization under these conditions? What about resuming its previous frequency once released? Tight focus of a laser beam?
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Yes, I believe they maintain all the properties of the incident photons. Otherwise you could just stick a detector there, measure the pulse, and send out a similar pulse with an attached laser at a later time and call it stopping light. :p
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Theoretically light is at 0 km/s at the event horizon of a black hole, although it may not be observable.
Have they verified whether polarized light maintains its polarization under these conditions? What about resuming its previous frequency once released? Tight focus of a laser beam?
Thanks CllifordK,
I wish to add a question !
In particular what about "SAM"? (spin angular momentum of light )
What happen to it when light beam stops?! :)
Cheers
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Is not properly "light" which has been slowed down or stopped, but the speed at which light is generated by the medium.
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Light is always at 'c'. There is no way you ever will be able to measure it locally at any other 'speed', except in a acceleration. The reason to that last is explained through the equivalence principle in where the light takes a 'bent path' through SpaceTime due to gravity, and a uniform acceleration is equivalent to a gravity according to Einstein. At the Even Horizon it may be perceived as being 'stopped' and 'red shifted' into oblivion by a far observer outside the 'gravitational pull', but locally measured it should still act at 'c'.
It all depends on your scaling factor what you might define as a 'local measurement'. Make it small enough and SpaceTime can be seen as flat, meaning no gravity. And there it 'propagate' at 'c'.
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Theoretically light is at 0 km/s at the event horizon of a black hole, although it may not be observable.
What Happens to light in a black hole?Nobody knows, because the known laws of physics do not apply in the center of a black hole. :)
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The reason to that last is explained through the equivalence principle in where the light takes a 'bent path' through SpaceTime due to gravity,
And what happen if we consider what has been known to us as" dark matter" as "strange behavior of gravity"? yes/no?just an idea! :)
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The interesting thing to me with stopping light is that you could see it as a pure information storage. And looking at it that way the condensates, in their turn so 'still/unmoving' as humanly accomplish-able, still retain the full information of this 'photon propagating'. What I'm saying is that as there is no 'motion' to the system, how does it retain the perfect exact description?
You might assume it a result of probability theory :) And would be correct. But that builds on our former observations put into a mathematical system as I think, describing probabilities of outcomes. But does it explain how a 'unmoving system' knows a polarization? Let us assume that we inject a photon into a condensate in where it disappear. What was the interaction storing this information?
The condensate should be in a 'super position' if cooled down as I think, does the injected photon change this?
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You mean that we should make dark matter and gravity equivalent? Maybe? Dark matter is what theorists think allowed galaxies to form from particles, becoming stars, becoming solar systems, becoming galaxies. Dark energy is used to explain a expansion. But 'gravity' don't exist on its own as far as I know, so what you then would have to assume seems to be some deformations/distortions on the room time geometry locally, pushing or pulling particles together. It all depends on what defines a universe, one view same for us all or unique (local) views, gathered together into a universe by 'light', being the force and information carriers. The simplest explanation should be one universe, same for us all, but relativity disagrees with that one when it comes to 'room and time' in where all descriptions you make become local definitions.
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You might assume that in its 'light existing' moment the universe had no real 'size', although energy indeed should be able to create gravity. When particles are created they must involve gravity though, and as I think then, that gravity might also define the room we see? Which are a lot of 'mights' in two sentences :) but it would fit a purely local interpretation, maybe? In where gravity and mass could be seen as being 'inseparable' phenomena, creating/defining the room they need to exist in, for us observing it. That way, particles by necessity will 'gravitate' towards each other at the same time they create the 'room time' we observe locally measured. But this fits 'new theories' much better than here :)
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In a way it's close to the idea of relativistic mass created through acceleration as it assumes the same sort of non intuitive phenomena, able to define a local gravity through a mere uniform acceleration, or if you like, changing your coordinate system. Then a acceleration would be a expression of a distorted room time geometry too. And yes, I will have to write about this one, it's perfectly suitable for me :) Nice idea ST ::)) At least it makes some sense to me, not that that say all that much :)
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It also have to do with how you define relativistic mass. Something moving in a circular motion around a center has a relativistic mass, even if uniformly moving (keeping a same speed). That's because it 'breaks' its natural velocity (speed and direction combined) at all times, constantly changing its direction. To change direction involves a acceleration as I think of it.
(Ahem, better expressed, breaking a geodesic always involves a acceleration. My reasoning holds if you define a uniform paths 'velocity' as following a geodesic, which can be seen as the 'straightest path' in a non-euclidean universe. And let this be a lesson to you, never reread what you once wrote, or you will find yourself changing almost all, of what you once thought of as 'self-explanatory':)
But uniformly moving objects in geodesics, do they have a relativistic mass? If you can't decide their motion, how can you decide their velocity? and without a velocity there should be no increase in relativistic mass, as I gather it? It's a important point to make I think.
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I better rewrite that one :) It's not about velocities really. What I mean is that all uniform motions must become equivalent in form of describing a relativistic mass. But as all uniform motion only are uniform until you change course, using velocity to describe it seems appropriate to me.
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And looking at it that way 'motion' becomes suspect, don't you think? We seem to have two definitions of it. One we call 'relative motion' in where you are free to define 'what moves', relative some other object, not involving any added 'forces' as 'gravity', due to whatever velocity you define. Then we have all sorts of accelerations, not only uniform, that must be considered adding a relativistic mass, and a 'gravity', if I'm thinking right here.
But then we have the fact that we can define different uniform velocities, giving 'motion' as a concept a existence outside those two definitions. Only a acceleration can create that local 'gravity well' though.
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And, by the way, it also makes me think about momentum and how we define that as having a direction?
Does it?
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I'm not sure about this though, as a acceleration create a relativistic mass, equivalent to its speed (kinetic energy) in the end becoming infinite limiting the speed to just under 'c'. Can't you assume that this will hold true for a uniform motion too? But then it comes back to uniform motion, and there we have no proofs I know for local changes due to your increased velocity, as long as we're talking measuring uniform motion?
It once again comes down to how you expect the universe to be/act for me. As a whole expression? Then it should exist in a uniform motion too as I suspect, as it should be a redistribution of a 'defined total energy' of the universe. But if it is a strictly local definition that holds then it's not you that change, but your relation to the universe around you. If one trust measurements to define what is 'real', that is?
(The point I'm trying to see, and understand, myself here :) is that it's easy to define a energy to something, as long as you do it relative something else. But when it comes to locally measuring a difference, due to a uniform motion, all such 'change' disappear, as I understands it. Relativity is indeed about needing two frames of reference, and then measure.)
If I was to put it into a context I would define two identical systems (closed particle chambers), uniformly moving relative some third part, defined as 'inertial' and so being 'still'. Then you accelerate a electron inside each identical particle chamber, using identical 'force', and measure as it hits the detector.
Now, the particles relativistic mass will increase due to what velocity you give the electron, but if we now also measure the chambers uniform motion relative that third part, defined as 'unmoving', would different uniform motions of the chambers themselves also give us different detector results (locally measured)? If they would, then the chambers uniform motion must play a part in defining the electrons 'energy', assuming identical setups.
But if it doesn't have any influence?
And I don't expect it to have any.
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or if you like, changing your coordinate system. Then a acceleration would be a expression of a distorted room time geometry too. And yes, I will have to write about this one, it's perfectly suitable for me :) Nice idea ST ::)) At least it makes some sense to me, not that that say all that much :)
Thanks for your comments Yor_on,go ahead your writing! :)
Yes I think there Will be a room in new theories, soon:))
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It doesn't. The question doesn't make sense.
Why? Does the light born everytime at 300.000km/s ready and steady?
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Hey
When an object approaches the speed of light, it gains infinite mass, and hence slows down. Then why doesn't light become a victim of infinite mass?
Cheers
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It doesn't. The question doesn't make sense.
Why? Does the light born everytime at 300.000km/s ready and steady?
Yes.
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Yes
No, because its impossible. Also that info its not written in any books.
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Yes
No, because its impossible. Also that info its not written in any books.
It's not necessary to write it, light doesn't accelerate. If light had mass, it could be a problem, but it doesn't have...
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@ lightarrow
Well, I think that your 'answer' is way too too simplistic. Don't you?
For example, you may consider when a photon borns and its own genesis (if there's one...)
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@ lightarrow
Well, I think that your 'answer' is way too too simplistic. Don't you?
For example, you may consider when a photon borns and its own genesis (if there's one...)
A photon is not a tiny corpuscle which "starts" from a point. We had a lot of threads about it, look for them.
Anyway, what a photon really is and how it behaves it's not a simple subject, so you can't have a simple answer.
Have a look to this interesting document:
stochastix.files.wordpress.com/2008/05/what-is-a-photon.pdf
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Hey
When an object approaches the speed of light, it gains infinite mass, and hence slows down. Then why doesn't light become a victim of infinite mass?
Cheers
Because that expression only holds for particles which have finite proper mass (aka "rest mas") and not for particles which have zero proper mass. The relativistic mass is defined as m = p/v which is finite for light and infinite for particles with non-zero proper mass.