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Comment by panda-giddiness | Hacker News Reader

I don't think you really groked your parent's comment. Asking why we don't see |dead> + |alive> states is like asking why we don't measure states of definite Jx when measuring Jz -- you're simply measuring in the wrong basis.

So why do we measure only states of |dead> or |alive>? I don't know; maybe it's evolutionarily advantageous (those simultaneously dead and alive beings sound quite bothersome). Regardless, it's irrelevant -- evidently we are only capable of making measurements in the basis {|dead>, |alive>}, so naturally that's all we'll ever see. Of course, that restriction by itself doesn't make the |dead> + |alive> state less real, only unobservable when you're coupled with the system.

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I admit I haven't really groked it, but the author of the article hasn't groked it either (why these 2 states are special - is the main question he's asking). I'm not a physicist, so the following question might be naive. Suppose there are 2 entangled particles - one goes to Andromeda, another - to Earth. Somebody on Andromeda (for whom the evolution has different "priorities", for we are talking about a totally different world) measures. They detect a glorph, so due to entanglement, we are guaranteed to detect a hibble when we measure. But we can't detect a hibble (by your theory). What gives?

For electron spin, a hibble detector would be a magnet rotated 90 degrees relative to an up detector. For photon polarization it would also be a filter rotated 45 degrees relative to an up-filter. Talking about it in the abstract conceals how easy it would be to realize the experiment.

So you agree with the theoretical possibility of somebody in Andromeda seeing a cat in the glorph state (dead & alive)? If not, then why can they (in theory) see the particle in the glorph state?

There's nothing theoretically impossible about building a detector that measured a cat's dead or alive state obliquely (in the "glorph basis"), and if you did it, the machine would look something like this: it would disassemble the cat without learning much about it, and then measure a lot of things that didn't tell you whether it was dead or alive.

Here is where the problem arises practically: The cat has an enormous number of particles, and (naturally) exists as a vector in an exponentially large number of dimensions. Observing whether it is alive or dead is a measurement along an axis that you get the equipment for by default. On the other hand, building a machine that can take arbitrary measurements of millions and millions of particles would naturally give it so much freedom within that giant space of possible axes that the smallest misalignment would take you away from the glorph basis.

However you look at it, this "special basis" we live in remains a mystery. One unorthodox way to address it is to speculate that our position/velocity in the Universe is special. It might be that by moving at a speed close to the speed of light, the astronaut could observe the glorphs, but he will turn into a glorph himself and cease to exist as a human before he can observe anything. I know, it sounds crazy and contradicts the principle of equivalence. But, as Matthew Cook pointed out, the principle of equivalence of all bases is broken is QM anyway. Please think about it. :-)

> Observing whether it is alive or dead is a measurement along an axis that you get the equipment for by default.

The questions is why position is the preferred basis that ‘you get the equipment for by default’ - if that’s what you mean.

If you accept things like space and time as a given, it is not so hard to see why. When you are measuring many-particle systems the easiest thing to do is measure each particle individually, with detectors that interact with small numbers of them. That privileges the basis that separates out particles over those that we would describe as entangled combinations. Carrying that over to the cat picture requires noting that most of our measurements of the cat, like reflecting photons off of it, interact strongly with individual particles in a way that separates them by spatial location.

This takes us back to my original point, which is that although the consequences of space seem mysterious in a perspective so abstract that there is no space, they no longer seem so mysterious when you include other facts about physics, like about particles and fields. I am aware that there are some attempts underway to figure out how space could come about as a consequence of quantum stuff, but even they add extra behavior on top of the postulates of QM in order to plant the seed, so to speak, that spacetime grows from.

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