Australian Astronomers Make Interstellar Hologram

KentuckyFC writes "Australian astronomers say the way a beam of light from a pulsar is scattered by interstellar dust is analogous to the way a hologram is made. But to reconstruct an image of this dust, you've got to know what the light was like before it was distorted. With an impressive piece of computer optimization, these astronomers have worked out the 8000 coefficients that determine the light field and so have been able to produce an image of the interstellar medium (abstract on the physics arXiv)."

Astronomers make hologram?

[BadMrMojo]

To be fair, it sounds like the pulsar and the interstellar dust did all the hard work. The Australian astronomers just managed to notice it.

Re:Astronomers make hologram?

[Frozen Void]

Information(such as hologram) doesn't exist outside the context of conscious systems able to interpret it. Light doesn't carry the information, the patterns are arising from temporal changes in light.

Re:Astronomers make hologram?

[FooAtWFU]

Information(such as hologram) doesn't exist outside the context of conscious systems able to interpret it. Light doesn't carry the information, the patterns are arising from temporal changes in light.

Maybe from the Philosophical standpoint, but there are a variety of other uses of 'information', including some very specific ones in Physics, where it is strongly related to Entropy.

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[Frozen Void]

That hologram was created from temporal changes in the light captured(with guesstimates about the fields the light goes through), it didn't exist in the light.
Information in this case is an interpretation(or reification) of scientists parameters, light data, and correlation by computer into one hologram.

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[Retric]

No the information was in the light. "There's all kinds of infromation locked in this data." Finding out what that information is like decoding an encrypted transmission the information is still there but finding out what it is still takes effort.

There are year's worth of data from this object that's in the form of light that will one day reach the earth but is still in space for now. A specific picture they create may or may not accurately reflect the information stored in the light but at some level it

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[alexgieg]

Information (such as hologram) doesn't exist outside the context of conscious systems able to interpret it. Light doesn't carry the information, the patterns are arising from temporal changes in light.

Information (such as holograms) are as much reality as the material substrate which carries them. Light is absolutely real, as is the information carried by it. The perceived patterns are the form, temporal changes in quantifiable electromagnetic fields are the matter, qualified light being the resulting ontol

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[Frozen Void]

See http://slashdot.org/comments.pl?sid=435874&cid=22243868 [slashdot.org]

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[alexgieg]

That hologram was created from temporal changes in the light captured (with guesstimates about the fields the light goes through), it didn't exist in the light.

The hologram that was obtained from temporal changes in the light captured is a fair approximation of the original one that existed (and still exists) in the it. Or, to be more precise, it is the same hologram, but with differing accidents.

Information in this case is an interpretation (or reification) of scientists parameters, light data, and correla

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[Frozen Void]

Its only a model which doesn't exist without creating and observing it.
The map is not the territory
http://en.wikipedia.org/wiki/Map%E2%80%93territory_relation [wikipedia.org]

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[MozeeToby]

Perhaps "Astronomers Use Hologram-Like Effect to Determine Dust Cloud Structure" just doesn't have the same ring to it.

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[$RANDOMLUSER]

...developing an algorithm that can simultaneously optimise the eight thousand coefficients that describe the electric field.

Yeah. That's the easy stuff.

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[syousef]

To be fair, it sounds like the pulsar and the interstellar dust did all the hard work. The Australian astronomers just managed to notice it. ...Only if by notice it you mean develop new mathematical techniques for extracting the data. In the same way you might "notice" the orbit of mercury doesn't quite fit Newton's model of Gravity.

Genetic Algorithm

[MozeeToby]

I'm interested in knowing what kind of algorithm they developed to solve this problem. It seems to me like it would be an excellent application of genetic algorithms as it is essentially a giant optimization problem. I sopose that assumes that you can recognize correct results when you see them though.

Re:Genetic Algorithm

[jd]

Well, it depends on what exactly was optimized, but this is usually an iterative process where the next step is determined by herustics. So, yes, genetic algorithms would be fine for this. You keep going until whatever variable(s) you're optimizing hit a local minimum (the point at which herustics give up and decide all options will de-optimize the solution). You can either stop there or try another starting point to see if it produces a "better" result. If you keep going, then you've some stopping condition (eg: N successive runs in which no better result was obtained, or you have calculated more than some percent of the minima that system of equations would potentially allow for). If you've not calculated all potential minima, then ultimately "recognition" of correct results will be down to a gut instinct.

This assumes that the system can't actually be solved or reduced/simplified to one that can without losing too much accuracy. If you can solve it, then all you have is some basic matrix algebra on an 8000x8000 array. Non-trivial, sure, but 4Gb of RAM and a good gaming machine (you want fast maths) would be adequate to crunch such data. Alternatively, an analogue computer would be ideal for a problem like this, as you'd have far greater precision and far greater parallelization. It would also take far more space and cost far more, but the world economy could do with a boost about now.

Not always necessary

[mstahl]

It's not always necessary to judge if a given solution is the solution, because often determining the optimality of a solution is tantamount to computing that solution analytically (i.e., not using genetic or EC techniques). For genetic algorithms it's only really necessary to determine the relative optimality of two solutions so that you can compare them and pick the best ones of the group quickly.

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[hubie]

If you link through to the paper, it is right there. Essentially to reconstruct the hologram you need to know the form of the electric field from the source. To do this they have a model for it that has thousands of parameters. To determine these parameters they use the Newton method of optimization, which is an iterative method. You guess a form for the input and crunch through the numbers to get an output. You then compare your output to what you measure. A difference function is constructed to dete

Like crystallography

[sacremon]

It sounds like x-ray diffraction crystallography, where one has a pattern of scattering of an X-ray as it interacts with the atoms in a crystal. The difference here is that in the lab we tend to be dealing with regular crystals as opposed to presumably less organized clouds of dust. There have long been statistical methods for interpreting these data, called Direct Methods [wikipedia.org].