Atomic Orbitals Imaged 53
joshv writes "Ever think that physics professor was smokin dope as he described those mysteriously shaped clouds of electron probability floating around atoms? Here's proof. Someone has managed to image atomic orbitals using X-ray crsytallography." The story's from Scientific American; very cool stuff. This may be old hat to physics grads, but it's interesting to us laypeople. ;-)
Heisenberg talks about the uncertainty principle (Score:1)
The page is nice to read too, by the way.
controversy (Score:1)
Of course. There's bound to be controversy when a new theory/idea is introduced which, if true, would cause a drastic change in currently held theology in that field.
I imagine that I wouldn't be ready to jump at this new information and hold it concretely until someone else had worked on it as well, and produced the same result. Of course, I do find it intriguing, but, since I'm not an expert in this field, and I certainly don't understand the processes of which they speak, I can't throw my opinion of that around.
I just think it's interesting, but they should, if they rewrite the books, show this as a new theory, but that, as before, they aren't 100% sure that they're right.
Re:Yes, Yes. But where are the PICTURES? (Score:1)
Re:bah (Score:2)
What is looking? Some process that gives you information on the object you look at. On the physical level this exchange of information turns down to an fundamental interaction. And those change the state of the observer and the object.
Copper Fab Process (Score:1)
Does this have anything to do with the Copper interconnect process being used by IBM, Motorola, and (next year) AMD?
Re:Philosophical Questions Still Not Resolved (Score:1)
But where do the choices come from? Is it a result based on some physical states somewhere (like a computer program that takes a certain decision given a certain input) then it is determined, the opposite seems to be something truly random, so we can't speak of a decision anymore. Does not fit into logic, in my opinion.
In the sense of Hofstadter I would say that we have no chance to solve these issues until we understand what a "self" is and find some mathematical (thus logically consistent) model for it.
Re:A couple of points (Score:1)
This is true, but worthless, because the wavefunction can never be known (and is complex). All that can ever be observed is the square of the wavefunction, the probability distribution of the quantum state described by the wavefunction. If you think about this for a bit, you realise that this prevents you from ever being able to make any predicitions at all using QM.
The meaning of life is: (Score:1)
*) Maby it was NON-entalpy, i always get that wrong.
LINUX stands for: Linux Inux Nux Ux X
Re:Not new (Score:1)
What I see in your image is a 2D density image. The "new" story has 3D reconstructions. Gives a whole new dimension to the whole thing....
Roger.
Re:Funny... (Score:3)
To be truthful, probably 99% of the physists out there are either doing the work at the quantum level (and thus can be called physical chemists), or work at the extreme macroscale (that is, universal scale), and thus can be called astrophysists.
Almost everything in between was solved by Newton way back when, and Einstein in the early part of this century, except for the connection between a 'small' number of molecules (on the order of 1 to 10^10) and the quautum theory level. And that's the job of chemistry :-)
Re:Philosophical Questions Still Not Resolved (Score:2)
The problem we have here is that we try to extrapolate a statement from basic physics, from very simple, idealistic situations, like the path of a particle to very complicated situations, like the free will of an intelligent being. Very easy to be victim to improper generalization.
Example: I am able to write a program for a computer, that pretty much gives determined output, despite the fact that all particles making up my box are subject to the Heisenberg principle.
Of course a cosmic particle might flip some bit, or all particles (and thus my box) might show up on Mars in a second, that is all perfectly legal under present known laws of physics, just extremly unlikely.
Re:The article doesn't inspire confidence... (Score:3)
Thus, I suspect that the details in this SciAm are about as deep as they are in the Nature or Science article, just rewritten to a slightly lower reader level (not too low, mind you, just low enough for the scientific layman to understand). Yes, you should expect contriversy about it. If I remember correctly, the Cold Fusion project of years back underwent a similar treatment. And if you look at the Nobel prizes in Chemistry or Physics and note where the first reported mention of the work occured, I'd expect that you'd also find contrivesry as the idea was tossed around the scientific community.
Now, there is one last point: both Science and Nature are what are known as peer-reviewed journals: before you can publish in those, your article is subjected to critism from at least 3 experts in the field (these experts are anonymous). If they find something fishy or questionable, they'll ask you to fix it , or not approve the article for publication. The fact that it DID get published means that at least 3 experts agree with the results and how the researchers got to them. However, another cavaet - from a chemistry standpoint, this result makes me want to shout horray, as it proves something that's only been shown to work in theory. It's rather easy to ignore possible problems in the mechanics of the experiment for a result like this.
However, now that the technique is out there and reported, you'll see others trying to repeat this, and within 6 months, we'll know if we have the next cold fusion, or the next Nobel-prize winning award.
Re:Philosophical Questions Still Not Resolved (Score:1)
One of the things that this paper made me wonder about is the implications of the exitence of the present moment. It seems to me that the simplest reason for there being a present moment is that the future is in some sense indeterminate. Whether this means that we have free will or not is an open question (could be only God does or everything could be random and we are rats in the maze) but worth considering. At any rate, the fact that we can percieve the present moment to me argues strongly that we are active in it. If this is really the way that reality is structured, I would be very leery of someone claiming that evolution would not find it and make use of it.
The situation may even be more subtle than my poor description above. Suppose that the future is inteterminate but constrained in some manner. The present moment might not be a point but have some sort of width described by a Poisson-type weighting and different possible futures get to vote, but the further out you go the less say a future has. One of the possibilities opened up by this model is some variation on Teilhard de Chardain's infamous "Omega Point" teleological God.
This model of cognition may also allow us to appreciate the concept of infinity by doing an infinite number of back and forth transactions in a finite amount of time. Sort of what Penrose was trying to say, but with a somewhat different mechanism.
Anyway. I am a mathematician, not a philosopher or a physicist, (although I play one on TV, much to the chagrin of my brother the experimental physicist!)
Re:Philosophical Questions Still Not Resolved (Score:1)
For example you are trying to decide a particular model of car to purchase. This mysterious someone used their skill to slow down a cosmic ray, 10 years ago. That cosmic ray passes through your brain, lights up a neuron (ok, simplistic here) and changes your decision.
While convoluted, to a lay person such as myself, it appears possible. Between this and the Uncertainty Principle (Which I believe proves that any Supreme Being must live in annother Universe, because I don't believe in Supernatural powers)
Any thoughts, takers?
Re:Philosophical Questions Still Not Resolved (Score:1)
Re:Philosophical Questions Still Not Resolved (Score:2)
IMO, and that of others, this simply doesn't work. It assumes that (1) quantum mechanics is complete and correct, which is far from proven, (2) that for some reason statistical smoothing doesn't happen in synapses, (3) these variation are amplified, due to the 'chaotic' nature of the brain, and (4) that randomness == free will. To be honest, I see no evidence that this *could* work. OTOH, this may be a good thing.
Free will, as most people define it, is about making free choices; that is, being able to choose one alternative over another. By its very nature, this isn't 'free' in the same way that electrons are 'free'. My choices are determined by who I am, by my ethos, my history, my culture, my beliefs, my passions. They aren't random selection, but utterly determined expressions of my will.
What you are looking for is pure freedom, but the only way to find that is to abandon everything else we believe about freedom: that we make choices, as opposed to selections simply being 'made' on their own. Heidegger wrote about this in Being and Time--I don't have it handy, but his point, IIRC, was that the more we understand Being, who we are, the more we understand how valuable, even wonderful, that psychological determinism is: it makes our choices ours, and gives them meaning and purpose.
Re:Group vs Molecular Orbitals (Score:1)
Can't judge the state of computational chemistry. I have not heard of any big success stories.
Physicists however, especially particle physicists, depend very much on computing.
Or engineering. I did finite element modelling for solving heat diffusion problems, where computations save lots of money because it is cheaper to find out at the desk that some casting of a gas turbine blade won't succeed than after doing this for real with a furnace etc.
Yes, Yes. But where are the PICTURES? (Score:1)
Re:Orbitals NOT observed! (Score:1)
This is a difference map; the subtraction of a density distribution constructed from the fit of a basis set (the presumed orbitals) to the observable structure factors (the observed scattering) - however obtained - from a model distribution constructed from the superposition of atoms in chosen (and hopefully appropriate) states. The later distribution is entirely arbitrary.
Re:Group vs Molecular Orbitals (Score:1)
I believe that some BIG success stories in computational chemistry are just over the horizon. Chemical and Engineering News had an article several months back (April 26, 1999 p. 24) about the use of computational chemistry as a Chemical Engineering tool.
Also, take a look at this article about modeling SiON chemical vapor depositon [msi.com] on the Molecular Simulations, Inc. (MSI) web site.
Re:The article doesn't inspire confidence... (Score:1)
Well, they may not have been in this work, but X-rays certainly can be focused. See, for example, the Chandra image of Cas A [nasa.gov].
It doesn't get much more focused than that!
Funny... (Score:1)
And now, like physics (and relativity) someone has the means and the technology to find out the truth, and force those lazy professors to rewrite the books and think again.
Man, I'm glad I'm in computer science, and can contribute to the 'means and technology' side without having to think too much.
Not new (Score:2)
spelling (Score:1)
Re:Atoms in Molecules (AIM) (Score:1)
(I forgot to add :-)
The article doesn't inspire confidence... (Score:5)
The X-ray and electron beams are not combined, they are collected separately, and the information is combined.
Moreover, the principle difficulty has been completely ignored. Electron beams can be focused to produce a direct image. X-rays cannot be focused for imaging purposes (although crude focussing to concentrate a beam is just possible). As a result, you only get a diffraction pattern with no phase information. The image must be reconstructed by Fourier transformation [york.ac.uk], which needs the phases. (There is a strong analogy with optical holography, in which a reference beam must be interfered with the diffracted beam to obtain phase information, but with x-rays the coherence length is too short to get a reference beam).
The trick is to use the phases from the low resolution electron image, and some mathematical relationships to reconstruct the missing phases in the high resolution image, which will show your electron orbitals. The problem is unless the statistics are treated very carefully, all you get is an image which confirms the assumtions of the model you used to get the relationships with which you reconstruct the phases.
The mathematical techniques were just coming on line in X-ray crystallography in 1996 and there was still considerable debate back then over their correct application. So there is a fair possibility that these results are correct, but I would suspend judgement until they have been scrutinised for a year or two.
Re:Not new (Score:1)
(That is using resolution as defined in crystallographic terminology, it might be used differently in STM).
resolution (Score:1)
Although it does not show the same detail as the results in Scientific American (and by no means is the experiment I did a novel thing - it was practically the first thing done after the STM was invented) it does demonstrate something about the shape of orbitals; namely that the electrons are not just aranged spherically around each atom.
It can be seen that the hexagonal arrangement here includes a maximum at the centre of each hexagon - this would not be observed if only spherical orbits were present.
disclaimer - I was not trying to suggest that this experiment (a tiny part of a third year project at uni) was comparable to that of the scientists in SA - only that theirs is not the first experimental evidence of orbital shapes. That much was done many years ago.
Atoms in Molecules (AIM) (Score:5)
That such a treatment is possible, is not obvious, nature could have been that way, that one had to treat the whole system (like solving the wave equation for all particles at once) in order to make any useful statement at all.
Read this article on Atoms in Molecules [mcmaster.ca] by Richard Bader to find out more.
Bader claims that the study of the Laplacian (2nd spatial derivative) of the electron distribution leads to a natural spatial decomposition of a molecule.
Have a look at these great pictures [nasa.gov] for some simulations based on that AIM theory.
I am still surprised, that during my physics studies, I heard nothing about that treatment. You get exposed to Feynman of course, but Schwinger's formulation of quantumn electro dynamics I knew only as possible but not practical alternative. Very interesting to see Schwingers approach [mcmaster.ca] at the heart of this AIM theory.
Re:Philosophical Questions Still Not Resolved (Score:1)
In classical mechanics one learns that the conservation of energy is a consequence of a corresponding symmetry, here the invariance of the system under time (= it should not matter if you do the experiment today or tomorrow).
Thus looking sharply, energy can't be conserved througout the universe, because the universe changes.
I wonder if cosmologist take such effects into account in their models.
Re:The article doesn't inspire confidence... (Score:2)
My concern was the appalling reporting, which contained several statements which were factually wrong (and clearly physically impossible), and failed to consider the reliability of the results at all. The real facts were obviously read and then re-written by someone who didn't understand what they were reading.
When I find Sci-Am reports wrong facts in a field I do know, it shakes my faith in what they write about other fields where I am reliant on their layman-explanations.
The work is already published in Nature, where I don't doubt there is an accurate account of the techniques. But I'll wait for the top statisticians in the field to comment, because it is really, really easy to bias this sort of result unintentionally by an inadvertant assumption: There have been several wrong results of this type published before.
Re:Not new (Score:2)
Philosophical Questions Still Not Resolved (Score:3)
The answer for me has always been found in Heisenberg's (sp?) uncertainty principle. He states that you can never know the velocity and the position of an electron at the same moment. What this means to me is that no matter how deep or how complete our physical understanding is, there will always be some bit of uncertainty, if only on the minutest level, that allows us to operate as if we had free will. To me, free will is necessary for me to view my life as a worthwhile pursuit.
Thus, while we can now picture the movements of electrons physically, in doing so, we disturb their velocity and Heisenburg's uncertainty principle is still valid. Therefore, while this may have increased our understanding of the universe, it has not destroyed what I feel is the basic necessity for the pursuit of life: free will.
Re:Philosophical Questions Still Not Resolved (Score:2)
understand the quantum nature of time. David Deutsch's excellent book, "The fabric of reality" does a very good job of explaining quantum time, and its concequences for parallel universes, free will and quantum computation.
A couple of points (Score:1)
The particles don't have precise Newtonian position and velocity. But that is not because the particles are not deterministic, it is because the Newtonian idea of infinitely fine grained space doesn't match reality.
Instead of space being made up of completely independent points, at the finest scales there is considerable mutual information between a point and it neighbours. So it no longer makes sense to speak of an event or a particle at a point -- what's going on at that point shares information with what is going on nearby. That's why particles are described by spread-out wavefunctions (and why the universe has a smaller information content than it first appears, with Heisenberg's equation connecting the local information density/resolution to how much mass or energy there is around).
But the wavefunctions evolve deterministically (Schroedinger's equation etc).
(Note: quantum 'measurement' events don't actually represent abrupt changes in reality -- they represent abrupt changes in our modelling of the rest of reality, of which the particle is not independent. So our modelling of the uncertainty about the particle must also change abruptly.)
Quantum mechanics doesn't have the indeterministic evolution you wanted. But even if it did, that still wouldn't give you free will. If every action you took in a Newtonian universe was conditioned on the roll of a die, that would be indeterministic, but you wouldn't have free will. The die would be in command.
On the other hand, if Laplace's calculating god could know the position of everything in a Newtonian universe apart from the material contents of your head, there would be no predictability. The unpredictability that 'you' impose on the rest of the world is your true freedom.
Re:H2+ is Sexy! (Score:1)
I thought it was evidence for... (Score:1)
Re:Funny... (Score:1)
I do agree with you that chemistry is a lot like physics. Chemistry has been described (by me (-: )as a specialisation of the physics of the behaviour of the electron.
Free will: explicable via physics, or memetics? (Score:2)
And this is, of course, the nub of the matter. Because a being that does not believe in free will is unlikely to survive, we could have simply have evolved the whole 'consciousness' memeplex without it actually having to exist.
Or maybe not. Maybe it does exist. Maybe it's something to do with quantum effects. Dunno.
So, for now, we get on with living, yeah?
Okay...
--
Group vs Molecular Orbitals (Score:1)
The point surely is that if we consider interactions between atomic orbitals slowly being 'turned on' as a perturbation (the infamous hypothetical black box controller), then there are strong interactions between say orbitals on adjacent bonding atoms. The independent atomic orbitals are a approximation; so it is very sensible to think of joint orbitals, representing chemical bonds or functional groups.
Going to the next level, we can now (conceptually) allow the functional-group orbitals to become aware of each other. This means further interactions, so a truer picture (at least at the level of a single electron linearisation) is that the molecule has molecule-wide electron orbitals. But in practice these interactions are much weaker, so taking them into account via the full quantum mechanics makes little difference to the overall electron density distribution.
Also, although the molecular orbitals are the right solution for a well isolated molecule doing its own thing, in practice chemists are often more interested in reactions & mechanisms. These involve applying local perturbations to the electrons' environment which are much stronger than the comparatively weak interactions between the groups; so taking group orbitals as a conceptual base is a better and more appropriate first-order approximation than molecular orbitals.
But in other cases, Molecular Orbitals are the more useful conceptual approximation -- eg for thinking about electron transfer between different levels, which is the basis for the beautiful biological miniaturised electron tunnelling spectroscopes [ucl.ac.uk] that give us the sense of smell in our noses.
Re:Philosophical Questions Still Not Resolved (Score:1)
You have restated everything I said: randomness isn't a choice, the alternative is determinism. I take the latter, with the caveat that the determinism at work in the mind is far more complex that we can understand at this point. Determinism doesn't mean simplicity or predicability, by any means, only that the past has influence on the present.
As for Hofstadter, its been argued, convincingly, that we cannot form a mathematical conception of the mind (note: the mind, not the brain). Mathematics is simply too limited to encompass the subject; this is the same reason no one attempts to create mathematically complete models of metaphysics. Logic can explain a lot about the world, but it is still part of that world--a small subset of reality that can no more explain the whole picture than we can explain neuropharmacology using the tools of psychology.
bah (Score:1)
Re:Group vs Molecular Orbitals (Score:1)
True. In FEM you can enmesh your geometry with different elements, using elementwise different base functions. For our problems however we stuck to finer enmeshments rather than using higher order polynomials as base functions.
Once you get to that point, you're not so far from any other methods for solving the equations.
In the end it is solving large linear systems that have band structure, solving linear equations on the surfaces of the elements and solving nonlinear eqautions if you need information within the elements.
BTW for 1 dimensional problems Finite Differences and Finite Elements yield the same systems of linear equations.
The more important issue is that the variational conceptual perspective is equivalent; but does it actually help the thoughts ?
If you pick up a FEM book by a mechanical engineer (like Oden), they often derive their variational formulations (calculating mechanical stress for example) not from a mathematical point of view, but from a reasoning along mechanical laws (minimization of energy, d'Alembert's principle of vanishing virtual work). So it seems to help them (and annoys the more mathematical folks :)