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Cake day: June 1st, 2023

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  • Energy use increases with bpm, change in pressure (systolic - diastolic) and the stroke volume (amount of blood pumped per beat).

    Note that there is also an inverse relationship between stroke volume and bpm because the faster the heart beats, the less time for blood to return to the heart for the next beat.

    That said, heart “strength” is more about reserve capacity (ie ability to ramp up when necessary) than energy efficiency. It’s like comparing a Ferrari to a Corolla: at 100 mph the former can still increase its power whereas the latter is getting near its limit.

    So if the Ferrari has a “car attack” and suddenly loses 50% of its max speed then it can still keep up on the highway, the Corolla maybe not. That’s more important than which one is more energy efficient.


  • Well, if the second photon is in a new, weird superposition then the first photon must also be in the same new, weird superposition. Again, I don’t that’s compatible with Copenhagen given that the first photon no longer exists.

    Note by the way that 50% y+ and 50% y- is how all photons start. So if that’s also the final state then there is no reason for it to prefer any detector over the others.


  • Entangled electrons are entangled in all directions. If you measure one along any direction, you can completely predict the measurement of its pair in the same direction.

    In other words, measuring one along X and its pair at Y is equivalent to measuring one along X and then measuring the same one again at Y (accounting for the sign shift in the pair, of course).


  • In the electron example, if the two electrons are entangled then the wave functions must be the shared. The new superposition for the second electron would therefore be shared with the first electron. So if you measured the second electron along z+ and got up, then if you measured the first electron again, this time along z+, it would give down.

    Likewise if the twin photon is still in superposition, then the first photon is also in superposition. Which is hard to accept in the Copenhagen interpretation, given that the first photon has been absorbed. If absorption doesn’t completely collapse a wave function, then what does?



  • Most of what you perceive as “taste” is just using your sense of smell on food within the mouth, where it is very close to smell receptors.

    To isolate taste informally, pinch your nose, stick your tongue out, and put food directly on the tongue when it’s outside your mouth. You’ll find that by itself your tongue can’t distinguish many flavors, that’s why everything tastes terrible when you have Covid or a bad cold.




  • When the first photon hits the screen and collapses, that doesn’t mean its twin photon collapses too.

    Yes, it does. By definition, entangled particles are described by a single wave function. If the wave function collapses, it has to collapse for both of them.

    So for example, an entangled pair of electrons can have a superposition of up and down spin before either one is measured. But if you detect the spin of one electron as up, then you immediately know that the spin of the second electron must be down. And if the second electron must be down then it is no longer in superposition, i.e. its wave function has also collapsed.


  • Right, but in order to get the observed effect at D1 or D2 there must be interaction/interference between a wave from mirror A and a wave from mirror B (because otherwise why would D1 and D2 behave differently from D3 and D4?).

    And that’s a problem for some interpretations of QM. Because when one of the entangled photons strikes the screen, its waveform is considered to have “collapsed”. Which means the waveform of the other entangled photon, still in flight, must also instantly “collapse”. Which means the photon still in flight can be reflected from mirror A or mirror B, but not both. Which means no interaction is possible at D1 or D2.


  • There are even plenty of questions, like the delayed-choice quantum eraser, that have already been solved

    No, it has not been solved. At least not solved to the satisfaction of many physicists.

    In one respect, there is nothing to solve. Everyone agrees on what you would observe in this experiment. The observations agree with what quantum equations predict. So you could stop there, and there would be no problem.

    The problem arises when physicists want to assign meaning to quantum equations, to develop a human intuition. But so far every attempt to do so is flawed.

    For example, the quantum eraser experiment produces results that are counterintuitive to one interpretation of quantum mechanics. Sabine’s “solution” is to use a different interpretation instead. But her interpretation introduces so many counterintuitive results for other experiments that most physicists still prefer the interpretation that can’t explain the quantum eraser. Which is why they still think about it.

    In the end, choosing a particular interpretation amounts to choosing not if, but how QM will violate ordinary intuition. Sabine doesn’t actually solve this fundamental problem in her video. And since QM predictions are the same regardless of the interpretation, there is no correct choice.


  • Even once you understand that the uncertainty principle is not the same as the observer effect, I think it’s still mysterious for the same reason that “the wavefunction is the only thing that exists” is mysterious.

    If anything, it’s more mysterious once you understand the difference. People are more willing to accept “Your height cannot be measured with infinite precision” than “Your height fundamentally has no definite value”, but the latter is closer to the truth than the former.