One thing to look at is how is the theory formulated. Standard QM seems to build its Hilbert space of wave functions from functions over R^3N. It has a Hamiltonian built out of the notions of that space. So configuration space seems pretty crucial. But configuration of what? If you say particles with positions do not exist, then what exactly is the relevance of this space? What is the primitive stuff whose behavior can be right or wrong from our perspective?
It is also odd to say that position cannot be measured. We can tell in an experiment whether something ended up over there or over here. It would be reasonable to then try to have a theory that correlates the position measurements with something that has a position. Now it is not necessarily the case that there has to be such a thing, but it seems like a reasonable first step.
We can even see trails of particles in cloud chambers and the like. Why is that an IPU?
I will grant that it does not have to be the case that the only possible explanation is that of particles with position. But it certainly seems like if there is such a theory (and, of course, there is), then it would seem reasonable to consider it as quite plausible.
It also helps to ask you what is real in your theory. Are wave functions real? They certainly can't be measured in their entirety. Are operators the real thing? We don't measure them, but rather get something close to their eigenvectors/eigenvalues. Are those real?
Many worlds is the closest version with nothing added, but even that requires some kind of mass density function to make explicit connection with our lived experience. While it doesn't add too much in the way of extra mathematical structure in the theory (integrate over the wave function in a certain way: https://arxiv.org/abs/0903.2211 ), the implication in terms of what it says reality is actually like certainly involves a heck of a lot of IPUs.
> If you say particles with positions do not exist, then what exactly is the relevance of this space?
That's a good question. The real answer is that no one actually knows. I think this is actually the biggest mystery in QM. But let me start with this, because I didn't make myself clear:
> It is also odd to say that position cannot be measured.
When I said that Bohmian positions are an IPU I did not intend that to mean that particle positions can't be measured. Obviously they can. The IPU-ness of Bohmian positions has to do with their ontological status, not their epistemic status. On Bohm's theory, a particle position considered along some axis is a real (in the mathematical sense) value, which is to say, it contains an infinite amount of information. But this information cannot be accessed in the same way that information stored in (say) a book can. I can open a book, even a book with an infinite number of pages, to any page and start reading it, and having read any page, I can go back and read that same page again. The information stored in Bohmian positions doesn't work that way. The laws of physics somehow conspire to hide all that information so that it can only be accessed serially and non-repeatably. The first time you measure a particle's position you get the most significant bits of its position. Those are then lost forever. You can never measure them again. The next time you measure a particle's position you get the next most significant bits of what that particle's position originally was, and so on. But you can never go back and do a second experiment to verify that the result you got for any of your measurements was actually correct and not a result of experimental error.
So the much-vaunted determinacy of Bohmian mechanics is not a reflection of the determinacy of the underlying metaphysical reality. It is really nothing more than a rhetorical trick. All the randomness is still there, it's just "pre-computed" and stored in particle positions in a way that it can only be accessed so that the world behaves exactly as if it were "really random" (whatever that means).
This same kind of trick is made manifest in a thought experiment [https://www.mathpages.com/rr/s9-07/9-07.htm] proposed by Kevin Brown. He points out that, if pi is normal (which is almost certainly is) then all of the results of all experiments ever conducted could be produced by a "cosmic Turing machine" computing the digits of pi. (See the two paragraphs beginning with "Even worse, there need be no simple rule of any kind relating the events of a deterministic universe.") Bohmian positions have exactly the same ontological status as the cosmic Turing machine. Only the window-dressing is different.
> It also helps to ask you what is real in your theory. Are wave functions real?
The key to identical particles is understanding the configuration space properly. Basically, instead of ordered n-tuples (R^3N), one can use sets of size n whose elements are points in R^3. This immediately eliminates everything except the "symmetric" wave functions. To get the anti-symmetric functions needed for fermions, one needs to extend the theories under consideration a bit. One could use a covering space approach, demanding a suitable projection of the trajectories downwards or one can approach it from the perspective of having a twisted bundle for the value space of the wave function, one in which it looks locally like complex-valued wave functions, but globally it has a parallel transport action that leads to sign change around a closed path that suitably permutes the set.
The nice thing about the parallel transport point of view is the extension to spin. Again, it will look locally like the usual tensor product, but by using an index set for the tensor product being just the set of positions itself, one can again get a non-trivial parallel transport that does just what one would expect.
This is what restricts the permissible wave functions.
One reference for this is my own thesis from about 20 years ago:
There were some papers that were published from that, but they mainly focused on the general topological story rather than having very much in the way of identical particles.
One thing we never did accomplish from this point of view was explaining why fermions went with half spins and bosons integer spins. But at least we did get it reduced to just the two choices.
Hidden variables theory was not disproved. Local hidden variables theory was disproved, but, actually, all local theories of any kind whatsoever that say that experiments have definite results have been disproved.
EPR is the argument that showed any local theory agreeing with the results of quantum experiments must have hidden variables. Bell showed that any hidden variable theory must be non-local. Conclusion: theory is non-local.
Many worlds escapes this by not having definite results of experiments or anything else. Since anything that could happen does happen, there is no need for non-local communication to achieve the (non)results.
Bohmian mechanics is a mathematically consistent theory (uniqueness and existence proven for a wide range of Bohmian systems) and it gives rise to an explanation of the quantum formalism. One can choose to dismiss because of prejudice, but there is no mathematical or physical reason to do so. Its biggest flaw, being nonlocal and thus philosophically (not actually) incompatible with relativity, is what Bell established as having to be the case for any theory with results.
The story with quantum field theory is more questionable, but there is a perfectly fine setup with creation and annihilation of particles, thereby being compatible in spirit with much of QFT. The biggest problem is that technically QFT has problems with having a well-defined wave function. But there have been Bohmian inspired methods of solving that problem, basically using boundary conditions that respect the preservation of probabilities under annihilation and creation.
I have been upgrading (and porting to new machines) a Mac account starting in 2008 on a white macbook (2006?), transferred to a 2009 iMac, and then transferred to a 2017 iMac. Never had issues until Catalina.
Catalina finally made me do a completely fresh install with transferring data files as the only touch from the old system. Since the fresh install, it has worked perfectly, but before that the system would randomly keep repeating the last typed character. I could not live with that behavior.
Also got a new MBAir 2020 (Catalina) and that has been perfectly fine and solid as well.
They are using the linearity to say that the effect is not magnified as it would be classically, but it is in the context of repairing damage done by a measurement.
A book to read, though older, is Tyranny of Kindness and it expands on the plight in vivid detail of our current system.
The article is an anecdote, but it tells the narrative of how the current setup is pretty difficult for people, particularly single mothers with children. They are already at the mercy of people and find no help for charity. In the article, it even mentions how the family that gets supported moves out of their subsidized apartment. It also mentions how brutal the current system is in terms of cutting off benefits.
By making sure each person has their minimum needs met, one can then have a better chance at having support for solving big problems that require government which requires popular support.
There are schemes for UBI which don't actually cost much more than we are spending. It can just be reallocation with more clawback in taxes. If one wants to.
There may also be ways to rearrange the labor if insufficient people wan to step up. For example, there are places where garbage trucks lift trash cans to dump into them. If that is too difficult, one could setup dumpsters at the end of neighborhoods and have a truck that goes dumps that stuff into it. So more work for the individuals.
Similarly, if there were not people to clean offices, then have the office workers do it (assuming there are offices, of course).
For things that are really essential and cannot be done away with, the cost would go up. It seems reasonable to pay more for vital services. That may mean higher taxes or some other payment arrangement, but it is only regressive if the taxes are done in a regressive way.
A UBI would change the job market. But whether it is a distortion or fixing some externality cost that was distorting the market is certainly debatable.
Keep in mind that the book that is from, Humankind, while a hope filled book (I enjoyed it thoroughly), makes the point that when we get together, the bonds between people can lead them to do horrendous things to others. Our power to cooperate is our superpower and our kryptonite.
It is also odd to say that position cannot be measured. We can tell in an experiment whether something ended up over there or over here. It would be reasonable to then try to have a theory that correlates the position measurements with something that has a position. Now it is not necessarily the case that there has to be such a thing, but it seems like a reasonable first step.
We can even see trails of particles in cloud chambers and the like. Why is that an IPU?
I will grant that it does not have to be the case that the only possible explanation is that of particles with position. But it certainly seems like if there is such a theory (and, of course, there is), then it would seem reasonable to consider it as quite plausible.
It also helps to ask you what is real in your theory. Are wave functions real? They certainly can't be measured in their entirety. Are operators the real thing? We don't measure them, but rather get something close to their eigenvectors/eigenvalues. Are those real?
Many worlds is the closest version with nothing added, but even that requires some kind of mass density function to make explicit connection with our lived experience. While it doesn't add too much in the way of extra mathematical structure in the theory (integrate over the wave function in a certain way: https://arxiv.org/abs/0903.2211 ), the implication in terms of what it says reality is actually like certainly involves a heck of a lot of IPUs.