Ask MetaFilter questions tagged with quantummechanics

You are not my quantum mechanic

Kid Charlemagne — Wed, 04 Nov 2009 07:57:42 -0800

I'm looking for something like Feynman's explanation for how a difraction grating works only for the absorbance of a colored chemical in solution. In biochemistry there is a technique where one measures protein concentration by looking at how much UV light the protein absorbs. Unfortunatly this technique doesn't see agregates (big blobs of amorphous protein) the same way it sees properly folded protein in solution.

The traditional explanation has to do with things being in the shadow of other things. But recently I've heard people making arguments about the wavelength of the light and how big the particles are. I can tell that both sides are way off base in terms of modern physics.

Can anyone point me at something that would explain this phenomenon the way it really happens, but with out too much (any) tensor calculus?

Can the Universe hold all of mathematics?

DU — Tue, 23 Jun 2009 05:33:29 -0800

Can the Universe hold all of mathematics? First assumption: The universe is finite in size and time. (Size, OK, but time is undetermined AFAIK.)

Second assumption: There is some scale below which information cannot be packed. At the planck scale, say. Put another way, there is a maximum information density to the universe.

These two assumptions imply that there is some maximum amount of information storable in the universe.

However, it is easy to prove on a number of fronts that mathematics has an infinite amount of information. The reals, for instance. Or, if that's not "information" in a strict sense, consider Godel's Incompleteness Theorem. It basically says that no matter how big the axiom list, there's always another one you can add.

Where is this information stored if not the universe?

Running this past an acquaintance of mine, he first suggested that while space was quantized, time wasn't. I countered by noting that General Relativity doesn't differentiate between the two.

His second attempt to wiggle free was to cloud the issue with a discussion of "creating" vs "discovering" mathematics. However, I think this is a red herring. Whether one creates or discovers, the information exists and had to come from somewhere. (There's a Conservation of Information principle, right? Entropy?)

Let's say I had a box. When I crank the handle, it applies Godel's method and pops out a new mathematical axiom that can't be proved from the existing list. *crank* P=NP! *crank* Riemann! *crank* Etc! I furiously scribble all these down at the tiniest scale possible.

At some point, the universe will be completely packed with information. I crank the handle one more time. And....?

Now that I think about it, how can such a box exist? There's much more information coming out of that box than the space(time) inside can hold. Is "raw information" leaking into the box from the universe? My understanding was that an "information generator" such as this box couldn't produce more information than it was "made of". That helpfully prevents the box from filling the universe up (whew!) but does not explain where all the information of mathematics is coming from.

Can I learn quantum mechanics?

Grundlebug — Sat, 30 May 2009 09:03:22 -0800

I'm reading Quantum: a Guide for the Perplexed and I'm enjoying the graphics, history and simplification of the math and science used to explain quantum mechanics. But I'm reasonably well versed in math and science - I took a year of college physics, linear algebra, and diff eq about ten years ago. Is there any chance of me learning to understand the equations and papers of Planck and Einstein that are the basis of QM? Are there any good books that could help walk someone like me through this stuff? Or am I stuck as a layperson unless I earn a degree in math or physics?

How are particles measured?

Citizen Premier — Thu, 11 Sep 2008 19:35:41 -0800

How are the attributes of atomic and subatomic particles measured? I guess you can't measure a particle without slamming something into it, right? How is this actually done?

Bonus: Is it this that forces us to use uncertainty in our current model? Does measuring a particle's location, say, change its momentum?

Why can't I move shit with my mind?

Nattie — Sat, 29 Mar 2008 06:18:51 -0800

On what grounds does one draw the line between quantum physics/mechanics and pseudoscientific claims about the powers of consciousness? I'm naturally skeptical of claims like the following that purport to be supported by quantum physics/mechanics:

- Telekinesis.
- Telepathy.
- Healing yourself with your mind, etc.

I don't know enough about quantum physics to understand where the reasoning goes south, though. When I read skeptical articles, they usually dismiss the claims by saying "they misunderstand the science," but they don't go into detail. That's what I'm looking for.

If it's helpful, these sort of things tend to take the idea that your consciousness acts on everything it observes and extrapolates from there.

Does it have something to do with the idea of a "conscious observer" not necessarily meaning "a human being with a conscious," depending on your interpretation of quantum mechanics? Is it conflating superposition with observer effect? Something else?

Are these claims actually possible in some "legitimate" interpretations but we're doubtful those interpretations are true? Or are all the claims based on misunderstanding?

I feel like I have a very vague grasp of these concepts, and whenever I try to pinpoint the flaw in reasoning my mind can't process it.

What the bleep do we know about weaponizing Quantum Mechanics?

basicchannel — Thu, 16 Nov 2006 00:10:28 -0800

Have humans' evil brains yet conceived of ways to weaponize the ideas and implications relating to Quantum Mechanics? It took roughly 30 years for humanity to weaponize General Relativity. It's been, what, roughly half a century since QM/QP has gained acceptance? This shocking lapse in evil human ingenuity can mean only one thing: I am ignorant to the various sundry DARPA projects that have been undertaken to solve this vexing problem! Please hope me MeFi!

Does Feynman's approach to QED render the observer problem moot?

unSane — Mon, 05 Dec 2005 10:05:16 -0800

This site: http://www.skepticreport.com/print/quantum-p.htm ...suggests that Feynman's 'sum over all histories' approach to Quantum Electro-Dynamics has sidestepped the well known 'observer problem' in quantum mechanics (exemplified by the Wigner's Friend paradox). Is this true? According to some conventional approaches to quantum mechanics, a waveform collapses when a particle is 'observed'. But the meaning of 'observed' is moot. According to the Copenhagen Interpretation is means something along the lines of 'interacts with a classical (as opposed to quantum) system'. But since all systems can be regarded as quantum in some sense, it doesn't really answer the question. In the Schroedinger's cat paradox, a cat whose survival or death depends on the decay of an atom is in a strange alive/dead superimposition-state until an observer opens a box. If you add a human being watching the cat to the room, and close the door ('Wigner's Friend') then the human being is likewise in a superimposition of states ('believing the cat is dead'/'believing the cat is alive') until the observer opens the door and observers him/her. But of course you can keep adding doors forever, until you finally require some ur-observer (God?) to observer the entire universe and force the waveforms to collapse.

Other explanations include the many-universes theory and the idea that consciousness itself somehow defines an 'observer'.

The Skeptic site claims that Feynman's approach of summing over all possible histories to arrrive at the probability of a particular event sidesteps the observer problem, but my understanding is that all it does is provide a neat way of calculating the probabilities to an arbitrary accuracy. Can somone help me?