can the speed of light go twice as fast?

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Offline i_have_no_idea

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can the speed of light go twice as fast?
« on: 12/10/2005 20:18:23 »
Hi my friend asked me this question "what if you were on an object (hypothetically) going at the speed of light and you sat on top and turned on a flash light what would happen to the light coming out”, this is like if you are in a car going 20mph and you throw a baseball out the window at 20mph then the baseball is moving at 40mph, but light ,according to Einstein, is the universal speed limit and nothing can go faster but can light go twice as fast?

p.s. If possible the light coming out of the flash light would have to be going 1,341,233,258 miles per hour.
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Offline Ultima

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Re: can the speed of light go twice as fast?
« Reply #1 on: 12/10/2005 20:37:15 »
It would appear to travel away from you at the speed of light, but it's still only going at the speed of light. I think thats right anyway we've had this thread over and over, so I doubt the really cool guys who know all the crazy physics will reply to this. I suggest doing a search for "speed of light" there is some good explanations floating around of varying degrees of crazy mathsynous. I think the basic idea is that light always appears to travel at the same velocity regardless of the observer's velocity.... I have no idea if im right this is a guess from my patchy memory glancing at previous threads.
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Offline Solvay_1927

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Re: can the speed of light go twice as fast?
« Reply #2 on: 13/10/2005 00:42:43 »
Phil, welcome to the forum.

There's loads on this forum (as well as across the internet) about this and similar relativity-related questions - where have you been hiding??

One example is:
http://www.thenakedscientists.com/forum/topic.asp?TOPIC_ID=2641

Matt(ultima) - when you say "really cool guys", i assume that's an ironic way of saying "sad anoraks"? [:)]


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Offline i_have_no_idea

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Re: can the speed of light go twice as fast?
« Reply #3 on: 14/10/2005 00:23:44 »
I figured it would be faster to just ask you than to search.
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Offline Sandwalker

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Re: can the speed of light go twice as fast?
« Reply #4 on: 20/10/2005 17:50:42 »
This question is very similar to one of Albert's, his included a mirror!

Its due to spacetime being 'flexible' the faster you go the slower your time passes, to an external observer, and space (in the direction of travel) gets denser (and mass gets heavier!).

The overall effect to the traveller is that he experiences the light travelling at c but 'in the durection of travel' in contracted space, this is in direct proportion to the time dilation seen below.

The external observer sees the light also traveling at c but the traveller existing in a slower spacetime frame.

The light emiting from the torch will be red shifted to the external observer due to its frequency being slowed by the time dilation.

« Last Edit: 20/10/2005 17:59:06 by Sandwalker »
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Offline tweener

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Re: can the speed of light go twice as fast?
« Reply #5 on: 21/10/2005 03:53:17 »
I'll jump in here.  The light coming out from the torch would appear to recede from you at the speed of light.  Of course you would feel like you were stationary.  Now, if you were traveling close to the speed of light relative to another observer, they would see you traveling away at the speed of light, and the light bean you generated traveling at the speed of light.

Light always travels at the speed of light.  The position of the observer is always the "relative" position to which it is measured.  That's why its called the theory of relativity.

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Offline Kerala

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Re: can the speed of light go twice as fast?
« Reply #6 on: 21/10/2005 09:26:13 »
In fact, the speed of light can vary : if it is inside a material.
What is constant is the speed of light in a vacuum.

In your experiment, indeed, YOU would see light going away from you at the speed of light, AND an outside observer would see both you and light going away at the speed of light...

In fact, the word "see" is even wrong, because that's not what you would see, but what the true speed of light would be in all those frames : always the same.
But what you SEE is different, because you have, on top of it, to take into account the time it takes for light to travel from, for example, a moving ship, to the observer. By the way, to "see" light, either it goes right away into your eye, or, to "see" a ray of light which doesn't arrive straight into your eye, the light has to be diffracted at some point and part of it diverted in the direction of your eye (like when you make a lot of dust in front of a laser ray to make it visible).

I hope what I write is understandable...

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Offline McQueen

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Re: can the speed of light go twice as fast?
« Reply #7 on: 30/10/2005 09:13:02 »
This is one of the truly amazing things in Physics and it perplexed scientists everywhere until Einstein , decided that , that was that, and proposed that the speed of light was constant. What does this mean. Suppose you have a stationary light bulb the speed at which that light is moving towards you is 300000Km/sec . Suppose that the light was still stationary and you were travelling towards it at 100,000 Km / sec. What should the speed of light be? 300,000 + 100,000km/sec = 400,000km/sec. Wrong it will still be 300,000km/sec. The same would apply if you were moving away from the light source at 100,000km/sec. The speed of light would not be 200,000Km/sec , it would still be 300,000Km/sec. So the speed of light is always constant regardless of your own speed and whether you are moving to , or away from it. This is not how ordinary objects behave. If you were in a car moving at 60Km/hr and another car is approaching at 70km/hr. The cumulative speed would be 130km/hr. Similarly if you were moving away from each other,the difference in speed would be 10km/hr and so on. What do you think ?
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Offline DoctorBeaver

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Re: can the speed of light go twice as fast?
« Reply #8 on: 31/10/2005 03:03:19 »
McQueen - If a humble psychologist may be permitted to poke his nose in, in your instance of the cars, there would be a tiny time distortion. The experiment where 1 of a pair of synchronised atomic clocks was taken in a plane and, on return, was slightly different to the 1 that had remained stationary, proved that, even at fairly modest speeds, the dilation can be measured. The faster one travels, the more pronounced the distortion becomes.

I know this subject has been covered many times, but there's something I have not seen asked before. Imagine there were only 2 objects in the entire universe, 1 being stationary & the other travelling at C. If the travelling object passed the stationary 1 then from the perspective of either it would be impossibe to tell which of them was stationary & which moving. However, the stationary 1 would age more quickly than the moving 1. If Einstein had been on the moving object (yeah, I know that nothing with mass can reach C but bear with me) & at some point, due to the curved geometry of spacetime, again went past the stationary object, he may have concluded that travelling at C would have exactly the opposite effect to that which he actually conceived; i.e. that for an object travelling at C, time passes more quickly. Would his relativistic equations therefore have been completely arse-about-face?

I'm sure there's a profound point lurking in there somewhere but I'm buggered if I can coax it into coming forth in my poor, addled brain [:(]
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Offline Sandwalker

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Re: can the speed of light go twice as fast?
« Reply #9 on: 31/10/2005 10:55:24 »
Dr B - I think it depends on initial conditions and forces applied.

If both started in the same spacetime frame travelling at similar speeds relative to each other, and then one having a force applied changing its spacetime frame (Perhaps this is the root of inertia) then you would be able to measure differences, from the initial conditions.

We have no relationship between your two objects until there light cones connected, it would be from this point that we might examine changes (forces applied) to there relative spacetime frames.

but I could be wrong!

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« Last Edit: 31/10/2005 11:00:35 by Sandwalker »
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Offline i_have_no_idea

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Re: can the speed of light go twice as fast?
« Reply #10 on: 01/11/2005 00:41:22 »
I thank all of you for your input and Dr. B that was very interesting what you said about the two objects in existance, I've never thought of it that way.
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Offline McQueen

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Re: can the speed of light go twice as fast?
« Reply #11 on: 03/11/2005 19:11:15 »
Doc
I was referring to how puzzling the speed of light must have been to Scientists before Einstein introduced the postulate of the constancy of the speed of light. Naturally once this was accepted , it meant that the theory of relativity , wherein ,the contraction and lengthening  of time and objects became significant also won widespread acceptance.
« Last Edit: 03/11/2005 19:15:44 by McQueen »
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Offline DoctorBeaver

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Re: can the speed of light go twice as fast?
« Reply #12 on: 03/11/2005 21:09:21 »
My uni lecturers hated me because I was always looking at things from a different perspective & asking awkward questions. I think they respected me for that at the same time, though [:D]
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Offline DoctorBeaver

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Re: can the speed of light go twice as fast?
« Reply #13 on: 03/11/2005 21:11:27 »
Sandwalker - In the instance I cited, I was assuming that the observer (Einstein in my example) popped into existence when the object he appeared on was already travelling at C. Therefore there would be no need for any external force

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Offline DoctorBeaver

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Re: can the speed of light go twice as fast?
« Reply #14 on: 03/11/2005 21:13:30 »
& here's another 1. If spacetime really is curved, photons will eventually come back whence they originated. Does that mean that if we wait long enough we will eventually see ourselves as we were n number of years ago? [:D]

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Offline DoctorBeaver

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Re: can the speed of light go twice as fast?
« Reply #15 on: 03/11/2005 21:15:12 »
McQueen - sorry, I misunderstood what you meant


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Offline Ylide

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Re: can the speed of light go twice as fast?
« Reply #16 on: 11/11/2005 12:16:11 »
Does anyone have a link to the experiments dont a year or two ago where a doped medium was produced in which the light traversed the pathway through the medium at a value of c whose velocity was greater than that of c in a vaccum.  

Random FTL factoid:  Speeds greater than c can be measured in media where the refractive index slows c to a value less than a fast-moving particle.  Google the Cherenkov Effect.



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Re: can the speed of light go twice as fast?
« Reply #17 on: 11/11/2005 20:57:35 »
quote:
Originally posted by DoctorBeaver

& here's another 1. If spacetime really is curved, photons will eventually come back whence they originated. Does that mean that if we wait long enough we will eventually see ourselves as we were n number of years ago? [:D]

We learn from history that we do not learn from history.
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The simple answer is, as far as we can tell, no!

The universe is expanding (or so they say), so light leaving our planet would have ever further to travel, and so while it will keep going, it will have ever further to come back.

http://www.news.harvard.edu/gazette/2002/01.10/01-universe.html
quote:

Eventually, the rate of expansion will approach the speed of light, 186,321 miles a second. As far as scientists know, nothing can move faster than that in a local area. But over the gigantic scale of the universe, galaxies moving at close to the speed of light can separate at a relative speed that exceeds the universal limit. At this point, light coming from distant galaxies never catches up to telescopes on Earth because the planet is moving away too fast.



If this is happening to galaxies that are today visible, you can imagine the problems of something trying to circumnavigate the universe.

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Offline DoctorBeaver

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Re: can the speed of light go twice as fast?
« Reply #18 on: 11/11/2005 21:38:50 »
But just hang on a minute. As an object approaches c, the slower it appears to move to an outside observer (isn't that why an object entering a black hole would appear to freeze at the event horizon?), Therefore the faster those galaxies travel, the slower we would see them moving & therefore gain the impression that the expansion was slowing down! And if all that is true, how do we see anything accelerating - as a car pulled away from traffic lights, it should appear to slow down! AAAARRRRRGH I think I'll stick to psychology, it's not quite so baffling [xx(]
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another_someone

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Re: can the speed of light go twice as fast?
« Reply #19 on: 11/11/2005 23:07:36 »
quote:
Originally posted by DoctorBeaver

But just hang on a minute. As an object approaches c, the slower it appears to move to an outside observer (isn't that why an object entering a black hole would appear to freeze at the event horizon?), Therefore the faster those galaxies travel, the slower we would see them moving & therefore gain the impression that the expansion was slowing down! And if all that is true, how do we see anything accelerating - as a car pulled away from traffic lights, it should appear to slow down! AAAARRRRRGH I think I'll stick to psychology, it's not quite so baffling [xx(]



That is not my understanding of things.  From what I can understand (which is not much at all), you are confusing speed with acceleration.  It is not that the faster you go, the slower you appear to go; but that the faster you go, the slower your rate of acceleration, until your acceleration approaches zero as you approach the speed of light.  Thus, as you get to the speed of light, it is not that your speed appear slower, but that your apparent acceleration being zero, you cannot appear to travel any faster.

I think the problem with black holes is that the light itself has to climb out of the black hole, thus the image you see is very very out of date (and, ofcourse, once the object gets below the event horizon, the light never manages to climb out of the black hole, and so you never get to see that bit – the the last image you see is where the object is just at the event horizon, but even that image takes literally forever to reach you).

Maybe I'm talking absolute rubbish (I often am), but that is as I understand it.

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Offline Solvay_1927

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Re: can the speed of light go twice as fast?
« Reply #20 on: 12/11/2005 01:41:09 »
quote:
Does anyone have a link to the experiments dont a year or two ago where a doped medium was produced in which the light traversed the pathway through the medium at a value of c whose velocity was greater than that of c in a vaccum.


Here's a couple of links - but they're both from 2000 - does anyone have anything more recent, or with more details?
http://news.bbc.co.uk/1/hi/sci/tech/841690.stm
http://www.abc.net.au/science/news/stories/s154610.htm
 

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Offline DoctorBeaver

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Re: can the speed of light go twice as fast?
« Reply #21 on: 12/11/2005 13:58:14 »
Another_someone - I'm not confusing speed with acceleration. Speed is a function of acceleration whereby at any given point in time the speed of an accelerating object has increased from that at any earlier point in time.
The experiment with the 2 atomic clocks (1 in a plane, the other stationary on the ground) showed that from the point of view of the stationary 1, time for the moving 1 had passed slower. At c, this effect reaches its maximum conclusion & to an outside observer, time would cease to pass for the moving object. If no time appears to pass then to the outside observer that object must appear to be stationary.
Oooh, how I love playing with logic in a non-logical world! [:D]
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another_someone

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Re: can the speed of light go twice as fast?
« Reply #22 on: 12/11/2005 15:21:37 »
quote:
Originally posted by DoctorBeaver

Another_someone - I'm not confusing speed with acceleration. Speed is a function of acceleration whereby at any given point in time the speed of an accelerating object has increased from that at any earlier point in time.



Speed is a function of acceleration and time, but it is still a different thing (a little like saying that prices and inflation are related, but a drop in inflation, until it becomes deflation, does not mean that things are getting cheaper, it just means they are not getting more expensive as quickly as they were before).

quote:

The experiment with the 2 atomic clocks (1 in a plane, the other stationary on the ground) showed that from the point of view of the stationary 1, time for the moving 1 had passed slower. At c, this effect reaches its maximum conclusion & to an outside observer, time would cease to pass for the moving object. If no time appears to pass then to the outside observer that object must appear to be stationary.
Oooh, how I love playing with logic in a non-logical world! [:D]



As I understand it, and it is not exactly clear to me what you meant in your statement (maybe I'm just not reading it properly), the clock that flew on the plane was running slower.  It did not make the plane appear slower to the outside world, but it would make those inside the plane think that everything outside the plane was happening much quicker (you might say that this is the same as people on the outside thinking that what was happening inside the plane was happening too slowly, but it does not alter the speed of the plane itself).

Thus, if a person were accelerated up to the speed of light, they would stop ageing, and to them, the entire lifespan of the universe would pass by them in an infinitesimally short time, but they would still only (to the outside observer) be travelling at the speed of light, no more and no less.  You might say that if time stops for the person who is travelling at the speed of light, that is tantamount to their perceiving that they are travelling at infinite speed, but that is their perception, not the perception of someone of the outside.  Ofcourse, one might say that if they believe they are travelling at infinite speed, then they would also believe that the outside world is travelling at infinite speed relative to them, and thus not constrained by the speed of light – that is where I get lost.

That, at least, is my naïve understanding of relativistic effects.

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another_someone

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Re: can the speed of light go twice as fast?
« Reply #23 on: 12/11/2005 16:00:58 »
quote:
Originally posted by another_someone

Thus, if a person were accelerated up to the speed of light, they would stop ageing, and to them, the entire lifespan of the universe would pass by them in an infinitesimally short time, but they would still only (to the outside observer) be travelling at the speed of light, no more and no less.  You might say that if time stops for the person who is travelling at the speed of light, that is tantamount to their perceiving that they are travelling at infinite speed, but that is their perception, not the perception of someone of the outside.  Ofcourse, one might say that if they believe they are travelling at infinite speed, then they would also believe that the outside world is travelling at infinite speed relative to them, and thus not constrained by the speed of light – that is where I get lost.



Sorry, I must be suffering from Alzheimer's, I am being an utter idiot.  OK, my excuse is that it was many years/decades ago when I last looked at the equations for special relativity (I never did try and understand general relativity).

Although the person travelling at the speed of light sees time on the outside speed up, to the point where his own time appears to stop; he also sees the distances on the outside shrink – so everything on the outside is happening infinitely fast, but is also infinitely small, so the speed over distance still remains at the speed of light and no more.


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Offline Solvay_1927

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Re: can the speed of light go twice as fast?
« Reply #24 on: 12/11/2005 23:56:42 »
quote:
The experiment with the 2 atomic clocks (1 in a plane, the other stationary on the ground) showed that from the point of view of the stationary 1, time for the moving 1 had passed slower. At c, this effect reaches its maximum conclusion & to an outside observer, time would cease to pass for the moving object. If no time appears to pass then to the outside observer that object must appear to be stationary.



DrB, if you're driving past me at the speed of c, I see you as travelling at the speed of c.  But if I could focus on your watch as you drove past me, it would appear to me that your watch has stopped - it wouldn't be ticking anymore.  So no, you don't appear stationary, you appear to be going very fast but with a broken watch!
That's my understanding of relativity, anyway.


As for my links in my last posting above ... has anyone looked at these?  I'm interested to know if they're valid. (Have the experiments been verified and repeated?)  Because I find them a bit confusing - I don't understand why the results DON'T violate relativity theory. They seem to suggest that FTL (faster than light) signalling) IS possible through certain mediums.

Can anyone shed more light (excuse the pun) on these experiments?

Solvay.


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another_someone

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Re: can the speed of light go twice as fast?
« Reply #25 on: 13/11/2005 01:03:59 »
quote:
Originally posted by Solvay_1927

As for my links in my last posting above ... has anyone looked at these?  I'm interested to know if they're valid. (Have the experiments been verified and repeated?)  Because I find them a bit confusing - I don't understand why the results DON'T violate relativity theory. They seem to suggest that FTL (faster than light) signalling) IS possible through certain mediums.

Can anyone shed more light (excuse the pun) on these experiments?

Solvay.


"Eagles may soar, but weasels don't get sucked into jet engines."



Had a brief look, but don't say they make a lot of sense to me either.

One comment one should be aware of:

http://www.abc.net.au/science/news/stories/s154610.htm
quote:

So, while the New Jersey researchers showed that a pulse can be shown to go faster than a speed of light, they have not managed show that a message can be transmitted at that speed.



On the other hand, there are already a number of quantum effects that seem to cause problems for speed limits imposed by C – one of them being particle entanglement.

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Offline ukmicky

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Re: can the speed of light go twice as fast?
« Reply #26 on: 13/11/2005 01:52:45 »
Hi  Paul

As usual don’t quote me, but I think I’m sort of right.

If they were to send information along with the pulse then they would be violating the rules,however i think you will find they are sending a smooth pulse of laser light which cannot contain information. If they were to include information in the pulse like a semaphore the pulse would no longer be smooth and the frequency changes would be too sharp for the type of chamber they are using to process. Therefore einsteins relativity theory remains intact.[:)]

I think quantum entanglement also runs into the same information hurdle as effects moving at superluminal speeds run into the uncertainty principle making it impossible to control any signals, and because you dont know what your going to get untill you observe it




Michael                                      
« Last Edit: 13/11/2005 02:30:51 by ukmicky »

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another_someone

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Re: can the speed of light go twice as fast?
« Reply #27 on: 13/11/2005 05:54:52 »
quote:
Originally posted by ukmicky

I think quantum entanglement also runs into the same information hurdle as effects moving at superluminal speeds run into the uncertainty principle making it impossible to control any signals, and because you dont know what your going to get untill you observe it



Looking at http://fergusmurray.members.beeb.net/Causality.html (and I only understand a fraction of what they are saying), it seems that you are partly right.

It seems, as far as I can understand, that there are some proposed mechanisms using entanglement that might be able to deliver superluminal information transfer, but nothing yet that has been demonstrated in practice.

quote:

Although it seems as if the Bell inequality, at least as it is usually presented, does not give us the convincing reasons for believing in the non-locality of physics which it has often been claimed to, it may be that there are other reasons for believing in non-local causes.  Greenberger, Horne and Zeilinger (1989) have presented a scheme which avoids the criticisms I have presented, and if correct really seems to leave no room for a local interpretation.  However, this scheme has not yet been tested experimentally.
The GHZ scheme uses three particles rather than two, and measurements of spin rather than polarisation.  The particles are sent out in different directions, and one of two sorts of spin measurement is made on each – call the first type X and the second type Y.  The measurements are made in one of four combinations:  Either every particle will be asked X, or two of the particles will be asked Y, and the other one X.  Quantum mechanics predicts a 100% probability that if only X measurements are made, an odd number of the particles will be found in the ‘spin-up’ state, whereas if two Y measurements are made, an even number of particles will be measured as ‘spin-up’.  The theory says nothing about whether the odd number will be 1 or 3, or the even number 2 or 4.
In this arrangement (assuming it is not eventually disproved, either by experiment or by the unlikely discovery of a theoretical error) it seems to be truly impossible to find a local explanation for the correlations; if each particle were to decide in advance what it will answer in response to the two questions, a single run of the experiment would stand at least a one in four chance of showing results that are in conflict with quantum mechanical predictions.
Another area of quantum theory which may be irreconcilable with locality is the Aharonov-Bohm effect, whereby particles travelling through a field-free region are influenced by a nearby magnetic field.  Richard Healey18 argues that the apparent non-locality of this effect is closely analogous to that manifested in violations of Bell’s inequality.


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Offline Solvay_1927

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Re: can the speed of light go twice as fast?
« Reply #28 on: 13/11/2005 23:06:30 »
I understand what you're saying, Someone and Michael.  But I'm still not convinced.  Maybe I'm just misunderstnding the experiment described in the earlier links above.

My understanding is that you have a container (containing ultra-cold caesium gas) which is, say, 30cm thick.  If a person on the left side of this container switches on a laser (of the right wavelength) at time t=0, a person on the right of the container sees light starting to come out his side at t<1 ns (ie. less than 1 nanosecond later).  But light in a vacuum would take a full nanosecond to traverse 30cm.

So you've got a "signal" being communicated faster than light. (The signal isn't a complicated message, it's just a simple "the laser has been switched on".  Like a binary 0/1 communication.)

Like I said, maybe I've misunderstood the experiment.  That's why I'd be interested in whether anyone has a more detailed explanation of what this experiment was about. (And why can't I find any references to this experiment dated later than 2000? Did they realise they'd made a mistake and quietly brush this false result under the carpet?)

Help.

Solvay.


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another_someone

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Re: can the speed of light go twice as fast?
« Reply #29 on: 14/11/2005 00:49:33 »
quote:
Originally posted by Solvay_1927

I understand what you're saying, Someone and Michael.  But I'm still not convinced.  Maybe I'm just misunderstnding the experiment described in the earlier links above.

My understanding is that you have a container (containing ultra-cold caesium gas) which is, say, 30cm thick.  If a person on the left side of this container switches on a laser (of the right wavelength) at time t=0, a person on the right of the container sees light starting to come out his side at t<1 ns (ie. less than 1 nanosecond later).  But light in a vacuum would take a full nanosecond to traverse 30cm.

So you've got a "signal" being communicated faster than light. (The signal isn't a complicated message, it's just a simple "the laser has been switched on".  Like a binary 0/1 communication.)

Like I said, maybe I've misunderstood the experiment.  That's why I'd be interested in whether anyone has a more detailed explanation of what this experiment was about. (And why can't I find any references to this experiment dated later than 2000? Did they realise they'd made a mistake and quietly brush this false result under the carpet?)

Help.

Solvay.


"Eagles may soar, but weasels don't get sucked into jet engines."



As I understand the document, it says that the back of the pulse exceeds the speed of light, but not the front of the pulse.

There seems a strange comment that the back of the pulse overtakes the front of the pulse.  I'm not sure if this is meant literally, or just a very loose way of saying that the back of the pulse is moving faster than the front of the pulse, and so catches up with the front of the pulse (i.e. the pulse is compressed).  If it is just that the pulse is compressed, and the information within the pulse is consequently garbled, then neither using the pulse front as a signal (which is still only travelling only at the normal speed of light), nor looking at the pulse contents (which are garbled) will give you any meaningful information quicker than it would take light to travel through the medium.  It is only if they meant what they said literally, about the back of the pulse actually overtaking the front (i.e. the pulse arrives back to front) that one might ask whether actual information (the knowledge of the existence of the pulse of light)  is travelling faster than the speed of light.

Do you know of any document that clarifies whether the back of the wave arrives at the output before the front would have expected to have arrived under normal speed of light conditions?

Even if the pulse arrives back to front, if the back of the pulse does not arrive at the exit point before the front normally would have (it seems to be the case, from what I read, that the front of the pulse is also slowed down, just and the back speed up), it would still not allow information to travel faster than the normal speed of light, even though it would (as clearly is the case they are talking about) still mean that the back of the pulse has exceeded the speed of light in order to get to the front; but taking the pulse overall, and the information about the pulse, it would still not have travelled at superluminal speed.
« Last Edit: 14/11/2005 02:56:58 by another_someone »

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Offline ukmicky

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Re: can the speed of light go twice as fast?
« Reply #30 on: 14/11/2005 04:40:38 »
To another someone

Firstly Relativity is taking about information in light and not pure light. it’s there fault why there is all this confusion because they don’t explain themselves properly.

secondly all their measurements are group velocity and not front velocity.
They measure when the central fat part of the wave leaves the starting blocks and crosses the line,(group velocity) not the very front information part. (front velocity)

so yes what you’re saying is right
The wave basically changes shape squashing up like a spring as the central fat pure light part of the wave travels faster than c and catches up to and can even pass the front information part which is travelling at c.[:)]



Michael                                      
« Last Edit: 27/05/2006 17:45:20 by ukmicky »

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Offline Solvay_1927

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Re: can the speed of light go twice as fast?
« Reply #31 on: 14/11/2005 13:37:10 »
Thanks michael & someone, that clears it up for me - I can stop worrying about it now and get back to worrying about more trivial things (like whether I can pay the mortgage this month, for example).

Solvay.

(P.S. I'm still interested if anyone can find any other web link references to this experiment, so I can understand it better.)


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Offline ukmicky

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Re: can the speed of light go twice as fast?
« Reply #32 on: 14/11/2005 20:24:03 »
Hi paul
The problem is over the years there have been many experiment along the same lines.
The first link is a long read but should awnser all

http://www.phy.duke.edu/research/photon/qelectron/pubs/SFLProgressInOptics.pdf
http://www.chtm.unm.edu/AA_NEWS_STORIES_DATA/NEWS_ITEMS/mojahedi_story.html




Michael                                      
« Last Edit: 14/11/2005 20:25:06 by ukmicky »

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Offline Solvay_1927

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Re: can the speed of light go twice as fast?
« Reply #33 on: 14/11/2005 21:39:07 »
Thanks Michael, these look very helpful.

One more question.  I've not read all of the first link yet (as it looks like that may take some time!), so I don't know if this question is covered in there, but ...

Could the experiment (in principle, at least) be done with such low intensity lasers that you're only getting a few (or even a single) photon passing through the apparatus at a time?  And if so, would the result be different?  (Does group velocity vs phase velocity still apply to individual photons?)

Or should I just go away and read up on this because my question just proves that I don't understand physics yet? [:)]


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Offline ukmicky

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Re: can the speed of light go twice as fast?
« Reply #34 on: 14/11/2005 23:02:02 »
originally posted by solvay
Thanks Michael, these look very helpful.

One more question. I've not read all of the first link yet (as it looks like that may take some time!), so I don't know if this question is covered in there, but ...

Could the experiment (in principle, at least) be done with such low intensity lasers that you're only getting a few (or even a single) photon passing through the apparatus at a time? And if so, would the result be different? (Does group velocity vs phase velocity still apply to individual photons?)

Or should I just go away and read up on this because my question just proves that I don't understand physics yet?
 

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NO maybe I should just go away and read up on this because your question just proves that I don't understand physics yet? [:D]

I don’t think any of the articles do answer your question; however it is possible to release and measure the speed of a single photon. Whether or not it would be possible in this particular experiment I don’t know. A few years back I looked into this same subject and at that time that was one of the questions I believe scientists were asking. I believe there were unresolved problems in regards to how to interpret the results if it worked. I have no idea whether the experiment has been tried yet.[:)]


Michael                                      
« Last Edit: 14/11/2005 23:07:26 by ukmicky »

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Offline ukmicky

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Re: can the speed of light go twice as fast?
« Reply #35 on: 14/11/2005 23:13:24 »
paul
Here's another article that a bit easier and quicker to read but still gives detailed info into the experiment.

Michael                                      

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Offline Solvay_1927

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Re: can the speed of light go twice as fast?
« Reply #36 on: 15/11/2005 12:35:54 »
Er ... is it written in invisible ink? [:p]

(Which reminds me of a question that I heard some time ago: How do you tell if you're out of invisible ink?[:D])
 

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another_someone

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Re: can the speed of light go twice as fast?
« Reply #37 on: 15/11/2005 13:13:23 »
quote:
Originally posted by Solvay_1927

(Which reminds me of a question that I heard some time ago: How do you tell if you're out of invisible ink?[:D])




Is the answer that you can see what's been written?[:o)]

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Offline ukmicky

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Re: can the speed of light go twice as fast?
« Reply #38 on: 15/11/2005 19:42:00 »
arrrhh,sorry about that http://physicsweb.org/articles/world/13/9/3

Michael                                      

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Offline Solvay_1927

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Re: can the speed of light go twice as fast?
« Reply #39 on: 16/11/2005 12:57:11 »
Michael - many thanks, this is really useful.

Someone - if only life were so simple.  The other problem I have with invisible ink is ... how do you know you're not writing on top of something you've written previously?


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