# What happens when light stops?

Discussion in 'Physics & Math' started by Xelios, Dec 1, 2001.

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1. ### RickॐValued Senior Member

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3,336

Actually i took the whole idea from general theory of relativity.
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the fight of two balls can be represented in two dimensions,now we can use the third dimension as space time.they both assumedly advance in X-axis.both the balls will have the same curavture in space time.the earth has caused a curved dimple in nearby space-time.each is following a geodesic.neither of them is experiencing the gravititional force,each is doing what comes naturally,in a curved space.

we usually tend to think abou light travelling in straight lines,but general theory of relativity disproves the fact.here's how.
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according to theory of relativity(general)the effect is only due to the fact that light travels a hell lot faster.the flash of light to origin to the landing place of the balls would be so quick thats its path would be indistinguishable from the X-axis itself.the curvature of it in space-time would be same as that of balls.,thus paths of balls and beams of light are geodesics in space time curved by earth.any further clarifications and comments would be welcome.
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bye!

3. ### Chagur.Seeker.Registered Senior Member

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James R ...

Was not that the point I was making ... or attempting to make?

5. ### SeekerOfTruthUnemployed, but LookingRegistered Senior Member

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Crisp,

What about the slowing of light in a Bose-Einstein Condesate? It is possible to slow light down to very slow speeds, on the orders of miles / second in such material and it has even been proposed that if you create a BEC and then spin it somehow that you could potentially create a light "black hole" in which the ligth could not escape because its velocity in the medium would be slower than the rotational velocity of the medium.

7. ### CrispGone 4everRegistered Senior Member

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1,339
Hi SeekerOfTruth,

"What about the slowing of light in a Bose-Einstein Condesate? It is possible to slow light down to very slow speeds, on the orders of miles / second in such material and it has even been proposed that if you create a BEC and then spin it somehow that you could potentially create a light "black hole" in which the ligth could not escape because its velocity in the medium would be slower than the rotational velocity of the medium."

In theory (if you consider the wave nature of light) you could do that yes, but that wouldn't mean that the light inside has "stopped" (eg. the photon is at rest, v = 0 and not v = c/n where n is the refraction index of the medium). Light is still propagating inside the medium, but slower than usual. On the other hand, it could be a bit problematic if you use the photon description of light: once a photon is absorbed by a boson of the BEC the boson moves forward and emits the photon again, so in that way I don't immediatelly see how the light could "lag" behind the matter. I guess the experiment should be done and tell us more about the nature of light

Bye!

Crisp

8. ### James RJust this guy, you know?Staff Member

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Chagur:

zion:

If two balls are travelling at different speeds, they <i>must</i> have different worldlines. For example, if we graph their position, <b>x</b> against time <b>t</b>, then the gradient of the line on the graph at any point is equal to the ball's speed. Different speeds mean different gradients and therefore different lines for the two balls.

9. ### Mr. Greality.sysValued Senior Member

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5,190
Chagur,

Does the pulse of photons exiting the B-E condensate contain the same photons that initially entered it, or does the exiting pulse contain new photons recontructed from wavelength & pulselength information stored within the condensate while it was opaque to photons?

Does what usually happens to photons when they encounter conditions of severe opacity also occur within B-E condensates?

What role, if any, is played by electrons within the condensate that might affect the identities of photons when during the experiment the condensate is suddenly made to again become opaque?

Take care.

10. ### Chagur.Seeker.Registered Senior Member

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Gee, Mr. G ...

Darned if I know ...

Have you tried a Google search?

Take care

11. ### Mr. Greality.sysValued Senior Member

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5,190
Chagur,

Yes, I googled and still I'm left with my original suspicion that the photons coming out are not the same as went it, that indeed the originals were absorbed, converted into stored above-ground-state information that was then reconverted into new photons to permit the condensate to return to (truer) ground state.

I can't do the math so I am left with offering the innuendo.

12. ### James RJust this guy, you know?Staff Member

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Mr G, I think you are right. A BEC, when it comes down to it, is just another bunch of atoms, so it acts in many ways just like any bunch of atoms. (In other ways it acts more like <i>one</i> big atom, of course.)

13. ### Chagur.Seeker.Registered Senior Member

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Gee, Mr. G ...

I would say: BINGO!

If for no other reason than
which is what James R referred to in a prior post.

As far as
I can not think of a reasonable alternative.

Take care.

PS Wonder if thinking of photons as distinct entities rather than
energy which can be 'reconstructed' from the original information
doesn't contribute to the seeming problem? Just a thought.

Last edited: Dec 5, 2001
14. ### StryderKeeper of "good" ideas.Valued Senior Member

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13,105
I'm still going to say "Photoelectric effect".

15. ### Mr. Greality.sysValued Senior Member

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Re: Gee, Mr. G ...

<<...If for no other reason than...reconstructed...>>

Um, I wasn't basing my argument on simple semantics. Too easy.

I said previously that electrons stop only when they are absorbed by electrons. You then offered that they can also stop in Bose-Einstein condensates (slowed, anyway). So, I responded that Bose-Einstein condensates contain electrons and then further implied that photons entering such condensates will encounter electrons that will absorb them. To which you had a google's reply.

I also am quite aware that photons are not particles but packets of bundled interfering waves that could constructively interfer with the Bose-Einstein condensate wave function(s) and be represented within it by short-term wavefront interference patterns.

I was probing you, not the condensate.

16. ### Mr. Greality.sysValued Senior Member

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And no, I'm not an alien and you'll have to supply your own probative anal reward.

17. ### Chagur.Seeker.Registered Senior Member

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Gee, Mr. G ...

Now that we've 'probed' each other

Just so you understand where I'm at (not that you necessarily care) ...

No problem with your initial, 12/01 0908hr., response:
"It gets absorbed by an electron."

But then, when at 2139hr. you stated in a subsequent post:
"... the photon (apparently frozen in place within the sodium atom) ... "
The old antenna started vibrating and I responded.

Take care.

PS Use of expression 'antenna vibrating' metaphorical!

I herewith state under penalty of perjury:
I am not and never have (to the best of my knowledge) been an alien.

18. ### machaonRegistered Senior Member

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733
When light stops

It looks both ways, and if nothing is coming, continues.

19. ### nanokRegistered Senior Member

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Re: Gee, Mr. G ...

I read an article in Scientific American called "frozen light" where it told about slowing light to the speed of a bike just like that article,

they were even able to store information in the light and when it got back up to speed it still had the info intact, though the longer they kept it the more it degraded,

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21. ### Joeblow93132Guest

Who says a photon doesn't have mass? It does have mass but it is different than regular matter. Regular matter creates a unipolar gravitational field at all sides. A photon, on the other hand, has a bipolar gravitational field, an anti-gravitational pole facing forward and gravitational pole facing back. That is how it's able to accelerate to light speed.

Tom

22. ### James RJust this guy, you know?Staff Member

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<i>A photon, on the other hand, has a bipolar gravitational field, an anti-gravitational pole facing forward and gravitational pole facing back. That is how it's able to accelerate to light speed.</i>

Do you have a reference for where I can read up on that theory? I'm unfamiliar with it.

23. ### Joeblow93132Guest

James R,

There is no theory, it's just an assumption I made. I figured that a photon needs to create a force to accelerate. Since the electric and magnetic field of a photon are at right angles to the motion of the photon, it can't be them. It would have to be the gravitational field , since a photon reaches light speed in space where no other fields are present except the gravitational field. Now if you assume it is gravity that causes the photon to accelerate, you would have figure out the structure of the gravitational field around the photon. The only way a particle could accelerate to light speed using it's gravitational field would be if it's gravitational field was bipolar.