More detail on the non-causality poll...

I'd expect adherents to quantum mechanics to choose "sometimes".

Since QM appears to introduce uncertainty (probabilistic) in place of causality (deterministic) (i.e., it moves from certainty toward randomness), I don't see why a deeper dive couldn't move entirely to randomness (non-causality).

Non-causality appears to be a generalization of nonlocality (or perhaps complimentary to it).

Because of the results of the Bell test experiments, there appears to be renewed interest in explicit theories of nonlocality (e.g., extentions of de Broglie–Bohm theory) to make QM more palatable.

I think the development of a construct for a non-causal extent with causality emergent at macroscopic levels (or emergent at the quantum/macro interface) could serve the same purpose, but I haven't been able to find anything on that.

*** Does anybody know of anyone who is working on that? ***

Here are some more hashtags to cast the net a bit wider. (feel free to comment even after the poll is complete):

#einstein #bohr #causality #spacetime #belltest #epr #paradox #light

#atom #atoms #electron #proton #quark #neutron #electricity #stem #technology

#cern #matter #energy #higgs #particle #lorentz #simultaneity #lightcone

#physics #QM #relativity #gravity #time #space

@Pat

Very interesting. I'd like to make three points regarding this.

1. The Schrödinger equation is perfectly deterministic. The "wavefunction" evolves causally, including interactions. Indeterminacy appears only in the act of measurement, which then forces a probabilistic interpretation of the wavefunction. If measurement is not involved, quantum evolution is as deterministic as a classical one.

2. Shouldn't measurement be nothing more than an interaction? Measuring devices, scientists operating measuring devices are all made of matter that obeys QM. So if the equation of motion (describing interactions) is deterministic, where do probabilities come from? This is the most frustrating property of QM. But even in a measurement, we don't simply lose all traces of causality. The outcomes of a measurement still depend on the way the system is prepared. We get a random outcome *from a set of allowed outcomes*. This set is determined by the way the system is prepared and how the measurement is made. So, causality is still present, but in a more relaxed sense, maybe.

3. Can science, or any organized thought for that matter, be done without a temporal order of events? If causality is macroscopic only, how did we manage to still make sense of the microscopic world if there is no temporal pattern to begin with? It seems to me that causality (maybe in a broad sense) is inescapable.

Thanks for your post!

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That first paragraph is not a simple one. I think it helps to separate the apparatus of quantum mechanics (which we all agree upon) from its interpretation. The theory doesn't really say much about the source of the probabilities, just that they exist. We can see that the defining aspects of quantum mechanics manifest themselves only in a measurement. We have two mutually-incompatible laws of evolution in quantum mechanics: 1. a perfectly deterministic, causal evolution equations (unitary in math terms), and 2. a probabilistic, acausal (non-unitary) wavefunction collapse. These two are opposite to each other. It's not a simple statement that the probabilities are intrinsic and not just an effect of measurement. For all we know, probabilities have no place in any part of quantum mechanics other than in a measurement.

Connecting measurement to consciousness is okay, maybe. But it doesn't tell us much. Consciousness is a material phenomena, whatever it is, it's still "made of" particles that should obey quantum mechanics. It's yet another interaction obeying the Schrödinger (or Heisenberg) equation; where does the collapse come from? We cannot dismiss the defining property and problem of quantum mechanics this way. At least not until we have a complete (even conceptual) model of how this works.

Regarding causality and probability, I don't feel like I can say anything useful at the moment, so I'm gonna leave it where it is.

About spacetime, I was not referring to the symmetry of the metric tensor (in Einsteins relativity, the metric tensor is always symmetric). I was referring to the Lorentzian signature of spacetime (the temporal component of the metric has an opposite sign to the spatial components of the metric). This is just math for "time only goes forward", kind of. So the preservation of causality is baked into relativity. That's what I meant by space and time are not perfectly symmetric. It's not simply a 4 dimensional thing. It's more of a 3+1 dimensional thing, one of them has a distinct character from the other three.