Talk:Quantum mechanics

From RationalWiki
Jump to: navigation, search
Icon science.svg

This science related article has been awarded BRONZE status for quality. It's getting there, but could be better with improvement. See RationalWiki:Article rating for more information.

Copperbrain.png

I've made some modifications to this article:

  1. Separated the material on the quantization of photons from the quantization of bound energy states. At this level, photon energies and bound electron energies are both quantized, but for different reasons.
  2. Made it clear that only not all particles have quantized energy states. Unbound elections can take on any energy.
  3. Added notes on superpositions of states.
  4. Removed section describing uncertainty principle as "if you want to measure position accurately, you need a high-frequency photon which is going to change its momentum more". This is a common description, but fallacious, since it implies that the particle has a definite position and momentum at the same time, but we're just having trouble measuring it with the tools available. The particle doesn't actually have a definite position and momentum, but is in a superposition of states that give a range of both.

Vyzen (talk) 05:17, 17 January 2011 (UTC)

That description of the uncertainty principle is true considering something like the Copenhagen Interpretation. However, given that these interpretations make the fundamental mistake of assuming that quantum systems, underneath all that uncertainty stuff, must behave like classical systems, it is slightly dubious. The implication shouldn't be that the problem is in the instrumentation, for sure. Scarlet A.pngsshole 15:18, 17 January 2011 (UTC)

Am I the only one who is amused by the mention of Albert Einstein and Eliezer Yudkowsky in the same two-sentence paragraph? - LucidFox (talk) 08:20, 3 August 2011 (UTC)

Consciousness[edit]

While I'm skeptical about the Copenhagen interpretation, I should point out that its mainstream formulation has nothing to do with consciousness -- "consciousness causes collapse" is indeed is a fringe hypothesis. Observation, in Copenhagen terms, is defined as the point when a quantum system interacts with a classical measurement system. Where exactly the border lies between quantum and classical systems is ill-defined, which is the main problem here. - LucidFox (talk)

I realised there that someone had inserted a vague refutation of concious observation without actually explaining what it was. I really need to take a hammer and chisel to some of this. ADK...I'll vote your bomb! 11:45, 3 August 2011 (UTC)
@LucidFox - my understanding there are different versions of Copenhagen, "objective Copenhagen" vs "subjective Copenhagen". Objective Copenhagen is more popular than subjective Copenhagen. Objective Copenhagen does not treat consciousness specially, subjective Copenhagen does. Some say, "objective Copenhagen"=Schrödinger's viewpoint, "subjective Copenhagen"=Bohr's viewpoint. (((Zack Martin))) 12:08, 3 August 2011 (UTC)

In the conscious observation section, it says: "Well-known physicist and atheist author/apologist Victor Stenger argued against the Copenhagen interpretation in his book The Unconscious Quantum.". I don't know the book or Stenger, but seeing that conscious observation is more like a fringe interpretation for physicists (except for jokes like "I have two lectures at the same time." - "That's entirely possible, just take care that nobody sees you.") and only favored by religions and everybody who subscribes to quantum woo, I think that it should actually be "[...] Victor Stenger argued against the Conscious Observation interpretation [...]". --93.209.248.34 (talk) 22:16, 16 February 2015 (UTC)

@Maratrean 'subjective Copenhagen' sounds like MWI... also, any 'conscious-subjective' theory has the problem of not being of much/any practical use (if there is no objective reality, our whole notion of existence is flawed, which sets us back before 'I think, therefore I am', and it's difficult to try to argue for both objective reality and 'conscious-subjective' influence on it)

Configuration space[edit]

Many worlds comes from assuming configuration space is where physics happens, and seeing that the equations lead fairly simply to decoherence and separate worlds. So I wrote that and now I have to explain configuration space in a paragraph. Anyone want to give it a go? - David Gerard (talk) 13:38, 25 December 2011 (UTC)

Many-Worlds[edit]

I've added some critical comments to the section on the MWI. I felt it worth pointing out that MWI does face significant difficulties in the face of the work coming out of the quantum gravity world. It may also be worth adding some mentions of relational QM to the interpretations section, as such interpretations from my experience (this is an anecdote though so take it with a grain of salt) seem popular among foundational QM and quantum gravity researchers, because they preserve many of the strengths of Everett's original "relative state" project while avoiding some of the difficulties of MWI. Anarcho-fox (talk) 05:27, 9 August 2012 (UTC)

Yeah, I really don't buy the MWI. At least not in a literal sense. Scarlet A.pngmoral 09:53, 9 August 2012 (UTC)
There's nothing wrong with this, I know several physicists who are "fictionalists" about the "many worlds" of MWI - like "possible worlds," they think they are useful fictions. However, this is still an ontological/philosophical take on the question, and while there's nothing wrong with that, I wanted to show how the MWI runs into difficulties even on a purely scientific level, as there seems to be an increasingly popular meme along the lines of "MWI is for real hard-nosed rationalists who take the science seriously, while the other interpretations are for wooly-headed philosophers." Anarcho-fox (talk) 16:28, 9 August 2012 (UTC)
When you say there's a "hard-nosed rationalists" meme, you're not referring to this guy are you? Because his reasoning for favouring MWI is dubious at best. Scarlet A.pngnarchist 17:12, 9 August 2012 (UTC)
What exactly is wrong with EYs reasoning? He doesn't explain everything too intuitively, but I don't see any error in the reasoning (I don't know the actual equations though, so if you do disregard my judgement on this).

“Some scientists suspect that superposition states will vanish when quantum theory is further refined”[edit]

I can guess who these scientists are. Superposed states are a thing of primary importance if only as the fundamental cause of entangled states, but also for other reasons (see Stern–Gerlach experimentWikipedia's W.svg for example). A theory without superpositions is possible, but it just will not be a quantum theory. Incnis Mrsi (talk) 21:16, 30 October 2013 (UTC)

The main thing about superpositons is that they're not particularly magical, they're just an effect of wave mechanics. In that respect there's no need to refine them out of QM. Scarlet A.pngbomination 13:16, 31 October 2013 (UTC)
Of wave mechanics, ORLY? In the Shrödinger picture the linearity of equations is just some fact introduced without a good substantiation, but it agrees with experiments. Indeed, in observable-centered pictures states are functionals on observables and existence of both coherent superpositions and mixed states are consequences of the definition of a state. In finite-state systems pure states are yet simpler and the linearity follows just from the matrix nature of a Hamiltonian. I’d not say it is the wave mechanics that offers some particular insight about quantum superposition. Incnis Mrsi (talk) 13:58, 31 October 2013 (UTC)

Weird and Spooky[edit]

Should we include Einstein describing quantum entanglement as "spooky action at a distance" rather than just "spooky"? QuantumDudeI am beyond your understanding 15:57, 31 July 2015 (UTC)

Ape Brains[edit]

"Interpretations usually try to translate quantum physics into classical physics terms so our piddly ape brains can grasp it all". The problem as I understand it is that QM is inherently formulated in terms of our ape brains and explicitly invokes them when it talks about the subjective idea of "measurement". The point of the various realist interpretations is to try to bring QM back in line with the other branches of science, which try to provide an objective picture of the world.

Could you rephrase this point into coherent sentences please? CorruptUser (talk) 18:58, 6 September 2015 (UTC)

The point is that QM just straight up says "measurement causes collapse" without explaining what measurement is. The collapse postulate contradicts all the other laws of QM, which means that there is no quantum mechanical account of how measurement works as a physical process. The standard, Copenhagen way of dealing with this is to say that the wavefunction, and wavefunction collapse, is just a subjective thing invented by our ape brains, instead of something real.

I object to the idea that I have a brain. Scherben (talk) 15:13, 8 August 2017 (UTC)

Atomsol?[edit]

WTF is that word doing in the top line? An error?? Ithaca8 (talk) 18:00, 4 April 2017 (UTC)

Thanks for pointing that out, I corrected it. (In future you could just edit it yourself you know, if you turn out to be wrong it can always be put back). Christopher (talk) 18:07, 4 April 2017 (UTC)