Slashdot Mirror
More Strange Bose-Einstein Condensate Behavior
Allen Varney writes "According to a story on EurekAlert, an arXiv preprint server paper titled 'Scattering of atoms on a Bose-Einstein Condensate' reports that atoms striking a BEC sometimes appears to leave before they enter. 'This doesn't imply a breaking of the light-speed barrier, time travel or anything overly exotic but is a property of waves being broken down into component parts and being reassembled slightly differently. [...] As an atom hits the BEC, it is absorbed into the collective state but still exists as a vibration. The vibration travels through the BEC but can escape as an atom once more. The study reinforces the similarity between atoms as waves and light as waves.' Slashdot has talked about supposed faster-than-light travel once or twice (or more) before."
I think Bose-Einstein condensates are used in the making and / or broadcasting of sitcoms and movies. You're watching a movie or sitcom, and you already know what's going to happen. My guess is that you've already seen it just slightly before.
... would a particle have been emitted anyway?
Ie: Is there enough information in the 'onset' part of the wave to cause the reconstruction of a particle at the other end, similar to the other 'faster than light' story? I'm betting there is.
While I'm ranting: Why does the dot keep posting stories about obviously-misinterpreted science news while ignoring *serious* news like the cure for 1/3 of cancers in mice from a week ago?
.f00Dave
"sometimes appears to leave before they enter"
Does this mean all those magicians are correct when they say the hand is tuly quicker than the eye ?
Seriously are they even close to certain that their detection methods are accurate or is this a side effect of the enviroment on the detection equiptment. Wouldnt be the first time.
Sig went tro...aahemmm.....fishing........
You know, I'd be surprised if more than a couple of /. readers actually understand that paper. I just read it, and its pretty hard core. Well over my head.
/. Then again, no-one actually reads the articles, anyway....
Amazing what gets posted on
Michael
There is no cryptographic solution to the problem where the intended receiver and the attacker are the same entity.
One minute you're striking a BEC, the next minute 10 seconds have gone by.
I am a Karma Library.
It looks like a BEC is something like a Borg Einstein Collective from the atoms' point of view.
-- Cheers!
Stephen Hawking explains these concepts marvellously in his book, A Brief History of Time. It's an easy read, but also very informative.
I have discovered a truly wonderful explanation of this phenomenon, which unfortunately the lameness filter will not let me post!
The first time I leanerd quantum mechanics, I didn't understant it.
The second time I learned quantum mechanics, I thought I understood it.
The third time I learned quantum mechanics, I knew I didn't understand it.
Lord, bless my users that they may stop being such fucking idiots!!
I know the discovery of the BEC won a Nobel prize.
I just wonder how many secrets studying BEC's will unlock. How many questions that can be answered.
May it prove to be a more momentous discovery than the transistor?
-- Sometimes you have to turn the lights off in order to see.
Just make sure it isn't heavy on math...
I disagree. Try to get a book that is really, really heavy on math. Because, in my experience, the only thing you might understand in quantum mechanics is the math. Doesn't matter if you're a fourth-grader or a physics professor.
Books that try to explain that stuff without giving the mathematical background tend to only give you that nasty feeling of believe.
I remember that something similarly shocking was published back then in 1948.
;-)
The article in question was:
"The Endochronic Properties of Resublimated Thiotimoline"
Let's give some credit to pioneers!
That's because the truly insightful comments left the thread before they were even entered.
Can somebody point me to where in the paper this is claimed ? If it's true then what happens if you destroy the atom going in just after the atom has come out ?
Well..
I could argue that, at the energy levels we live at, say, here on earth, there ARE such things as elementary particles, more or less.
The fact that if you raise the energy level high enough they break apart into different things.. well..
It's not really like a bunch of marbles stuck together. A few 'quarks' *become* a proton once the energy level drops far enough (and the right stuff is present).
Yes, it's all just a model, and we all know it's nto finished yet.. (and I suspect it never, ever will be. It's turtles, all the way down)
...What are those 5 balls on strings called?...where you lift one and ...
release it and when it hits the others the last one goes up. Lift two
two go up, three....three go up....etc..
Didn't read the article but the comments all seem to reminds me of this
ball-string device.
That's because the truly insightful comments left the thread before they were even entered.
Hey, thats unfair. I thought my comments were insightful. They just got modded up as funny.....
Michael
There is no cryptographic solution to the problem where the intended receiver and the attacker are the same entity.
Second, there's no "magic" in it. As they say in the article, the peak of the transmitted wavepacket appears before the peak of the incident wavepacket has reached the condensate.
At the beginning of the century (1914), Brillouin and Sommerfeld already showed that, when a plane EM wave with a sharp forward front propagating in vacuum is incident upon a transparent medium, its shape is changed and precursor waves form, with a velocity approaching c in vacuum, corresponding to the high-frequency components for which the (relative) permittivity goes to 1.
In excitable media (and I assume the same happens with atoms in a BEC) the effect is even more spectacular, because these fast components (or, as in this case, the leading edge of the pulse) can get amplified and then leave the medium before the "bulk" of the incoming pulse even enters it.
Moreover, before leaving the medium this "fast" pulse is split in two, and the reflected component can interfere destructively with the "lazy" pulse, wiping it out. Hence the "illusion". Needless to say, Einstein is still right :-)
I haven't got the first clue about "the scattering properties of a Bose-Einstein condensate held in a finite depth well", and I doubt many people here have.
/.
To prove my point, most of the mod'ed up comments here have been mod'ed as 'Funny', rather than 'Interesting' or 'Informative'.
Seems symptomatic of most hard science posts on
That's it. My post-pub waffle is over.
They will never know the simple pleasure of a monkey knife fight
This is because the math is clear, but all the physical interpretations of it are nonsensical...
Having read the paper (forgive me, I'm new here), I'd say the negative time effect is very similar to the FTL transmission results reported earlier. On page 6 of the paper, the caption to Figure 6 reads in part: Note the negative values of tau-sub e (the time spent inside the condensate region) in the region around ka ~/2: Wavepacket simulations show that here the peak of the transmitted wavepacket appears before the peak of the incident packet reaches the condensate. Now, IANA condensed matter physicist, but my best assessment of the effect is that it operates similarly to previously observed, similar phenomena of "FTL" transmission. The incident wave of light contains information for the entire wave embedded in the wavefront- so the peak of the wave is able to be reconstructed on the other side of the BEC, even though the peak itself has not reached the condensate yet. Essentially, since the entire wave of light is defined by a wavefunction, the entire wave can be constructed from the wavefront. Although the process can take zero or even negative time, it is not a violation of general relativity. The light itself propagates at the speed of light, as it must. Since the peak of the wavepacket is recreated before it is actually destroyed, it would seem to be moving faster than the speed of light. However, the information that completely describes this peak is embedded into the wavefront, which travels at the rather pedestrian speed of light (and for a BEC, it is almost pedestrian- the amazing dispersive effects have been shown to reduce c to around 38 miles per hour, an effective refractive index of over 17 million!). While something is technically traveling over a nonzero distance in zero or even subzero time, no unique information can be transmitted in this manner- since the peak is constructed from information in the wavefront, the peak must be composed of information contained in the wavefront. The wavefront is moving at the speed of light, and taking all of the information it has with it at exactly that speed. If we had an ultrafast and ultrasmall computer conceivably, we could dispense with the Bose-Einstein condensate and do this thing ourselves. The wavefront enters a detector, the information is broken down, and the hypothetical supercomputer we have at our disposal uses the information in the wavefront to calculate the wavefunction. It then spits out a wavepacket with characteristics identical to those of the incident packet, and does so before the peak of the incident packet even reaches the detector. The effect is somewhat analogous to the movement of lights on a scrolling theatre marquee. The scrolling itself can actually occur faster than the speed of light, but since the "information" is just a discrete on/off light, no useful FTL message can be encoded. In the same way, the wavefront carries information faster than the speed of light, but the information merely codes for the rest of the wavepacket! Thus, it is not a violation of relativity. If anything, it is an affirmation- the weirdness of quantum mechanics, what with the wave/particle nature of light, is weird in such a way that useful messages cannot be sent faster than the speed of light. On a completely different note, I was amused to see someone referenced in this paper that /.ers might recognize, if they had actually read the paper. On page 6, the authors propose explanations for this effect, and they suggest a many-body interference mechanism devised by Ray Chiao et al. Raymond Chiao, some of you may remember, is the physicist who had a /. story not long ago about the possibility of a gravitational Meisser effect for superconductors (Can Superconductors Block Gravitational Fields?).
"FDA staff reviewers expressed concern about the number of patients who were left out of the study because they died."
Yes, the math is not too advanced (for a grad student), but the notation is scary for somebody who hasn't seen it before. There is a lot of knowledge presupposed in that paper. For example, I am sure it is confusing as to why they would want to diagonalize the Hamiltonian when it wasn't mentioned that it was a matrix.
So, for those who are bewildered by the math, there is salvation: don't read the paper. I'm serious, just read the introduction and conclusion, and then try to glean some understanding of the figures and their captions. I often do that before I launch into the math to get a general idea.
This seems deep and mysterious, but it is just a trick. To understand the trick you just need to understand two terms and one concept.
Here is the first term. If you change something, your change will cause changes to propagate outwards. That rate is called the group velocity. This is the rate at which changes propagate, and cannot exceed the speed of light (thanks to Einstein).
Here is the second term. If you sit and watch the waves go by, the peaks of the waves have an apparent motion. That rate of motion is called the phase velocity. The phase velocity is the most easily measured apparent motion.
Here is the concept. After you have been sending a constant stream of waves for a while, the phase and group velocities have nothing to do with each other! In particular this paper just says that the phase velocity can be made negative, that is the waves look like they are moving backwards. Mildly amusing, but commonplace.
If you want to visualize this, draw a 2 vertical lines on a piece of paper. Those lines are light-weight plastic barriers. On either side you have water, and inside you have something else - oil say. Visualize a stream of waves coming from right to left. They hit the first barrier, part bounces, part goes in. They hit the second barrier, most bounces, part goes out. The part that bounces from the second to the first, well most bounces, part goes through. And back and forth we go.
The incoming wave train sets up a resonance in the middle third. Depending on the details of that resonance, the waves in the middle section may move forward, stand still (if you do it just right) or even go backwards. When they go backwards, ohmigosh, the wave is leaving before it goes in, we have waves moving backwards in time!
Amazing, isn't it? And isn't it astounding that when you stop the waves coming in, between the two barriers your waves keep on bouncing back and forth for a while, and most emphatically the stoppage does not arrive on the other side before you stopped?
Cheers,
Ben
I was quite surprised to see our paper on /. Please note, that the mentioning of negative transmission times is aimed at an audience who will not see this as a very spectacular thing. Hopefully fascinating, but not sensational! :) ). Whether this is a good thing for physics is not clear to me: Will it help recruitment of new students? Or will they be turned off and go and do "useful things"?
Concepts like faster-than-light tend to draw a lot of attention from the general public (well, at least part of it
So a Rottweiler, a Golden Retriever, and a Chihuahua are sitting in a bar, and an attractive French Poodle comes in, and goes "I'll make one of you very happy if you can use the words 'liver' and 'cheese' in a pick up line."
So the Rottweiler comes up and goes "I like liver, I like cheese, and I like you!"
The French Poodle goes, "No, that was really dumb."
So the Golden Retriever tries. "I don't like liver and I don't like cheese, but I do like you!"
And the French Poodle says, "No, that was equally dumb."
The Chihuahua, growing annoyed, walks up and says "Hey, liver alone, cheese with me!"
Isn't it 'interesting' and 'insightful' of you to post this non-sensational news.
A fool throws a stone into a well and a thousand sages can not remove it.