4 ms·

I'm no expert in this field, but aren't the existing assumptions around time being independent at the slice we want to take a major reason why QM and General R

I'm no expert in this field, but aren't the existing assumptions around time being independent at the slice we want to take a major reason why QM and General Relativity can't be reconciled? If so, that would seem like a good reason to look at alternative ideas in this space.

naasking 5y ago
I think that's more or less correct. GR suggests "time" isn't independent, we instead have 4-dimensional "spacetime". The idea that future inputs can influence past configurations can be perfectly sensible in this context. It's like a restricted form of consistent closed timelike curves. There was some development in this direction years ago: The Logic of Quantum Mechanics Derived from Classical General Relativity, https://arxiv.org/abs/quant-ph/9706018 https://arxiv.org/abs/quant-ph/9706018
- myridium 5y ago
  Why is GR required? Already in standard QFT (Minkowski metric; flat spacetime; special relativity) the propagator 'violates causality'. Although that phrasing is misleading; it doesn't mean there's any logical inconsistency. 'The future affects the past' you might say. Yes, well, all information about the future is derivable from information about the present. So actually those 'future influences' are determined by the present. In the same way, 'locality' is almost a moot concept, because the analyticity of fields implies that the value of fields at remote locations is determined entirely by the field locally.
  - naasking 5y ago
    Maybe GR isn't required. It seems like the simplest path to understanding how this could work for those who aren't familiar with QM though.
  - bollu 5y ago
    I don't follow the comment about analyticity. I thought fields were real analytic, which meant one needed to use a power series to expand them, which has a potentially infinite amount of information in the Taylor coefficients? So I don't see how the local data "effectively" captures non local information.
evanb 5y ago
I think you may be over-simplifying. We have relativistic quantum-mechanical theories, and we can formulate quantum field theories on curved background spacetimes.
- Koshkin 5y ago
  But isn't the spacetime of SR flat?

naasking 5y ago

I think that's more or less correct. GR suggests "time" isn't independent, we instead have 4-dimensional "spacetime". The idea that future inputs can influence past configurations can be perfectly sensible in this context. It's like a restricted form of consistent closed timelike curves. There was some development in this direction years ago: The Logic of Quantum Mechanics Derived from Classical General Relativity, https://arxiv.org/abs/quant-ph/9706018 https://arxiv.org/abs/quant-ph/9706018

myridium 5y ago
Why is GR required? Already in standard QFT (Minkowski metric; flat spacetime; special relativity) the propagator 'violates causality'. Although that phrasing is misleading; it doesn't mean there's any logical inconsistency. 'The future affects the past' you might say. Yes, well, all information about the future is derivable from information about the present. So actually those 'future influences' are determined by the present. In the same way, 'locality' is almost a moot concept, because the analyticity of fields implies that the value of fields at remote locations is determined entirely by the field locally.
- naasking 5y ago
  Maybe GR isn't required. It seems like the simplest path to understanding how this could work for those who aren't familiar with QM though.
- bollu 5y ago
  I don't follow the comment about analyticity. I thought fields were real analytic, which meant one needed to use a power series to expand them, which has a potentially infinite amount of information in the Taylor coefficients? So I don't see how the local data "effectively" captures non local information.

evanb 5y ago

I think you may be over-simplifying. We have relativistic quantum-mechanical theories, and we can formulate quantum field theories on curved background spacetimes.

Koshkin 5y ago
But isn't the spacetime of SR flat?