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When learning quantum mechanics, you have to let go of the commonly-held belief (often unknown to the holder) that everything in our world can be explained in t

When learning quantum mechanics, you have to let go of the commonly-held belief (often unknown to the holder) that everything in our world can be explained in terms of concepts that are familiar to us and our human-sized environment. You cannot reason your way through QM with classical analogies. You find the wave-particle duality confusing; why? Only because you cannot imagine a human-sized object that is both a particle and wave. Let go of both of those concepts - forget about particles and waves as you know them - and accept that QM objects fall into new ontological categories which do not map well onto any classical concept. This is fine! As a child, you learned new ontological categories all the time. Everything was alien to you. You've learned new categories before, and you can learn them again. If we cannot use the language of everyday experience to understand quantum mechanics, what can we use? The answer is math. We have found math to be an incredibly effective language for describing quantum mechanical phenomena. Superposition isn't really like a particle being "in two different places at the same time", it's a complex linear combination of state 0 and state 1. There are differences between those things, and the differences are fundamental to understanding quantum mechanics. A corollary to the inability to meaningfully explain QM with classical analogies is that all pop science dealing with QM is absolute, irredeemable garbage and always will be. Stop reading it.

goatlover 8y ago
Everett was a physicist. So was Einstein, Schrodinger, Bohm and DeBroglie. Not all physicists have been sold on the Copenhagen interpretation of QM, where classical concepts don’t apply. That’s just one interpretation.
- ahelwer 8y ago
  Classical concepts apply in neither interpretation. The math is the same, all that changes is how you interpret collapse.
  - Koshkin 8y ago
    To be fair, collapse is an interpretation...
    - red75prime 8y ago
      Isn't collapse what we observe? At least everything seems to behave like collapse is happening.
      - goatlover 8y ago
        A collapse involves imagining that the wave-function is a physical thing which resolves to having the properties of a particle when measured as such. It might be real, but the problem is nobody knows what the physical mechanism for a collapse would be.
      - blotter_paper 8y ago
        Everything also seems to behave like a split is happening. They are equally valid explanations, and neither has any supporting evidence that isn't shared by the other. We should probably assume the simpler explanation is more likely, but it's not even clear which explanation is simpler. :/
        red75prime 8y ago
        Doesn't a split require additional assumptions to get to the Born rule?
  - goatlover 8y ago
    Nothing is collapsing in MWI or Pilot Wave interpretations.
- Koshkin 8y ago
  But: if you do not calculate probabilities, what do you calculate?
  - goatlover 8y ago
    This dispute isn't about the probabilities or the math, it's about what the probabilities/math are modeling. Is it a non-classical wave-function woo that collapses, including backwards in time? Is it evidence for multiple realities? Is there a pilot wave or other hidden variables? Or is it mostly a matter of ignorance of the exact state of the quantum system, requiring us to use probabilities?
    - Koshkin 8y ago
      Consider particle decay: it's a fundamentally random event - there is not enough internal structure to suppose the existence of some internal timer, nor is there enough worlds to fill the eternity during which the particle can "choose" to decay at any moment.
danShumway 8y ago
Just to somewhat gently push back on this a little bit, math is probably not enough if you want someone to really get how quantum mechanics work at a fundamental level. So quantum superposition isn't just two things at the same time, it's a complex equation that combines the two states. Great. Except that non-math majors don't think of linear equations as a singular 'thing' that describes a state. That in itself is a huge paradigm shift for people like me. I'm not used to having an axis in an equation not refer to a continuous range that I can move through. There's a comic[0] on this springs to mind, that being able to plug equations into something is not the same as understanding it. Most tutorials or technical articles I read about quantum mechanics skip concepts and assume that showing the math is enough. In doing so, they skip all of the hard, useful parts of education and focus only on the language and terminology we can use to talk about something. I spent a lot of time in physics, statistics, and calculus where I understood the math and not the concepts. I graphed things in 4 dimensions before I encountered Flatland, but I didn't understand the 4th dimension before Flatland. I worked with complex numbers all the time in calculus, but I didn't start to understand complex numbers until years later when I started watching Numberphile. So I'm at least a little bit skeptical of claims that that quantum mechanics are different. We've had to build new paradigms to understand a lot of stuff in the past; concepts like infinity don't map to tangible analogies, but we can still build tutorials and scenarios that demonstrate interesting behaviors and properties. Right now the only people I can find trying to do that for quantum are the pop-science writers, and like you said they're mostly all crap. It's kind of frustrating. [0]: https://web.archive.org/web/20120206011811im_/http://zs1.smbc-comics.com/comics/20100620.gif https://web.archive.org/web/20120206011811im_/http://zs1.smb...
- ben_w 8y ago
  As you mentioned Numberphile, what do you think of the YouTube channel PBS Space Time? It helped me finally grok quite a few bits of physics that never made sense to me before.
  - danShumway 8y ago
    First time I've heard of them, so I dunno. I'll add them to the list though. :)
MisterOctober 8y ago
Non-physicist here - genuine question : do you consider, say, Feynman's pop books [QED and the like], Tony Zee's, Lee Smolin's, etc to be rubbish?
- ahelwer 8y ago
  For pop books I've only read Brian Greene. I don't think they were helpful for learning quantum mechanics; the reader just stumbles through bewildering scenario after scenario and has forgotten them all within a week.
  - Koshkin 8y ago
    Learning about the experiments that led to creation of quantum mechanics is helpful.
- improbable22 8y ago
  QED is great, I think it really gets across one way of thinking about these things. Agree with @ahelwer that Brian Greene isn't terribly useful. Have not read Zee & Smolin's popular books... but for what it's worth, Zee is a serious guy & writes great textbooks, Smolin is not.
gus_massa 8y ago
I totally agree, but I like bad analogies. There is a similar problem with Special Relativity and Classic Newtonian Mechanics. Let's pick an usual object like a pool ball. To understand it completely you must apply Special Relativity, but for everyday calculation you can approximate its behavior with Classic Mechanic and the approximation is good to play pool, throw it at a target and whatever you usually need. Moreover, you can apply all the theory of a Rigid Body and analyze how it rotates. The problem is that there are no rigid bodies in Special Relativity, because any change must affect all the ball instantly. So a rigid body is sometimes a very good approximation, but there are no true rigid bodies. In a quantum object in some experiments they can be approximated very well as a particle, and in other experiments they can be approximated very well as a wave. But this are only two good approximations that make the calculations much easier but are not the exact behavior of the object. I think that at the beginning of discovery of quantum mechanics nobody know what was happening and only know that some object were weird and sometimes they ware well approximated as particles and sometimes they ware well approximated as waves. Later they discovered the "true" nature of these object that sometimes can be approximated as a wave or as a particle, but it is much more difficult to explain to someone that doesn't want to learn the math.

goatlover 8y ago

Everett was a physicist. So was Einstein, Schrodinger, Bohm and DeBroglie. Not all physicists have been sold on the Copenhagen interpretation of QM, where classical concepts don’t apply. That’s just one interpretation.

ahelwer 8y ago
Classical concepts apply in neither interpretation. The math is the same, all that changes is how you interpret collapse.
- Koshkin 8y ago
  To be fair, collapse is an interpretation...
  - red75prime 8y ago
    Isn't collapse what we observe? At least everything seems to behave like collapse is happening.
    - goatlover 8y ago
      A collapse involves imagining that the wave-function is a physical thing which resolves to having the properties of a particle when measured as such. It might be real, but the problem is nobody knows what the physical mechanism for a collapse would be.
    - blotter_paper 8y ago
      Everything also seems to behave like a split is happening. They are equally valid explanations, and neither has any supporting evidence that isn't shared by the other. We should probably assume the simpler explanation is more likely, but it's not even clear which explanation is simpler. :/
      - red75prime 8y ago
        Doesn't a split require additional assumptions to get to the Born rule?
- goatlover 8y ago
  Nothing is collapsing in MWI or Pilot Wave interpretations.
Koshkin 8y ago
But: if you do not calculate probabilities, what do you calculate?
- goatlover 8y ago
  This dispute isn't about the probabilities or the math, it's about what the probabilities/math are modeling. Is it a non-classical wave-function woo that collapses, including backwards in time? Is it evidence for multiple realities? Is there a pilot wave or other hidden variables? Or is it mostly a matter of ignorance of the exact state of the quantum system, requiring us to use probabilities?
  - Koshkin 8y ago
    Consider particle decay: it's a fundamentally random event - there is not enough internal structure to suppose the existence of some internal timer, nor is there enough worlds to fill the eternity during which the particle can "choose" to decay at any moment.

danShumway 8y ago

Just to somewhat gently push back on this a little bit, math is probably not enough if you want someone to really get how quantum mechanics work at a fundamental level. So quantum superposition isn't just two things at the same time, it's a complex equation that combines the two states. Great. Except that non-math majors don't think of linear equations as a singular 'thing' that describes a state. That in itself is a huge paradigm shift for people like me. I'm not used to having an axis in an equation not refer to a continuous range that I can move through. There's a comic[0] on this springs to mind, that being able to plug equations into something is not the same as understanding it. Most tutorials or technical articles I read about quantum mechanics skip concepts and assume that showing the math is enough. In doing so, they skip all of the hard, useful parts of education and focus only on the language and terminology we can use to talk about something. I spent a lot of time in physics, statistics, and calculus where I understood the math and not the concepts. I graphed things in 4 dimensions before I encountered Flatland, but I didn't understand the 4th dimension before Flatland. I worked with complex numbers all the time in calculus, but I didn't start to understand complex numbers until years later when I started watching Numberphile. So I'm at least a little bit skeptical of claims that that quantum mechanics are different. We've had to build new paradigms to understand a lot of stuff in the past; concepts like infinity don't map to tangible analogies, but we can still build tutorials and scenarios that demonstrate interesting behaviors and properties. Right now the only people I can find trying to do that for quantum are the pop-science writers, and like you said they're mostly all crap. It's kind of frustrating. [0]: https://web.archive.org/web/20120206011811im_/http://zs1.smbc-comics.com/comics/20100620.gif https://web.archive.org/web/20120206011811im_/http://zs1.smb...

ben_w 8y ago
As you mentioned Numberphile, what do you think of the YouTube channel PBS Space Time? It helped me finally grok quite a few bits of physics that never made sense to me before.
- danShumway 8y ago
  First time I've heard of them, so I dunno. I'll add them to the list though. :)

MisterOctober 8y ago

Non-physicist here - genuine question : do you consider, say, Feynman's pop books [QED and the like], Tony Zee's, Lee Smolin's, etc to be rubbish?

ahelwer 8y ago
For pop books I've only read Brian Greene. I don't think they were helpful for learning quantum mechanics; the reader just stumbles through bewildering scenario after scenario and has forgotten them all within a week.
- Koshkin 8y ago
  Learning about the experiments that led to creation of quantum mechanics is helpful.
improbable22 8y ago
QED is great, I think it really gets across one way of thinking about these things. Agree with @ahelwer that Brian Greene isn't terribly useful. Have not read Zee & Smolin's popular books... but for what it's worth, Zee is a serious guy & writes great textbooks, Smolin is not.

gus_massa 8y ago

I totally agree, but I like bad analogies. There is a similar problem with Special Relativity and Classic Newtonian Mechanics. Let's pick an usual object like a pool ball. To understand it completely you must apply Special Relativity, but for everyday calculation you can approximate its behavior with Classic Mechanic and the approximation is good to play pool, throw it at a target and whatever you usually need. Moreover, you can apply all the theory of a Rigid Body and analyze how it rotates. The problem is that there are no rigid bodies in Special Relativity, because any change must affect all the ball instantly. So a rigid body is sometimes a very good approximation, but there are no true rigid bodies. In a quantum object in some experiments they can be approximated very well as a particle, and in other experiments they can be approximated very well as a wave. But this are only two good approximations that make the calculations much easier but are not the exact behavior of the object. I think that at the beginning of discovery of quantum mechanics nobody know what was happening and only know that some object were weird and sometimes they ware well approximated as particles and sometimes they ware well approximated as waves. Later they discovered the "true" nature of these object that sometimes can be approximated as a wave or as a particle, but it is much more difficult to explain to someone that doesn't want to learn the math.