Wednesday, September 2, 2020

Tim Anderson - How the illusion of an objective reality creates time travel paradoxes

Quantum information theory resolves the grandfather paradox but questions our belief in an objective reality.


When down the pub with friends years ago someone might ask how did he know if any of us were actually here, he might be generating the whole reality? It was a popular thought years ago, that we might be living in a computer simulation. I always dismissed all this as nonsense, but perhaps we are all here, with each one of us creating our own reality. Physics keeps getting weirder. 


The alternative explanation is that there are no objective realities but only your subjective reality. Frank Ramsey, Oxford mathematician, philosopher, genius by all accounts and contemporary with Bohr, was one of the early proponents of the idea that probability is a subjective game where our beliefs, the knowledge we have available to us, determines what is real. The very idea of things existing and ascribing logical values such as true, false, or probabilities to such things as coin flips is entirely a mental exercise. Instead, what you observe in a coin flip is a cacophony of sense impressions that your mind orders into logical statements such as heads and tails. The probability of either one is likewise all in your mind. Although he was no quantum physicist, his ideas were at odds with the predominant, Bohr/Einstein viewpoint of a single objective universe. His work has led to a major modification of the Bohr hypothesis to create Quantum Bayesianism (QBism), a subjective interpretation of quantum mechanics that does not invoke additional universes but also does not indicate we have a single objective reality either.

In a QBist or Ramseyan quantum universe, reality is composed of a set of beliefs and information that you hold in your mind. Out there, outside the mind there is no reality, no true, no false. Thus, having realities that are inconsistent between different people, even paradoxical, is entirely possible, even the norm. All probable outcomes are the results of bets that each individual makes with the universe. God doesn’t play dice with the universe. You play dice. In a Ramseyan interpretation, reality is more like a virtual reality game that your mind generates for you from sense impressions. You make bets on what will happen and then interpret the results based on what you bet. The idea that you might have different objective realities based on different probable outcomes is nonsense because you created those outcomes in your head in the first place. Going back to the highway analogy, if you get off your highway and get onto another in your game and change things, even if it looks like you are changing your own past, it is still all just your own personal experience. There is no possibility of paradox because your own life is a linear progression of bets, one after another, and likewise for everyone else. The only reality is your reality and any observation of reality you make is a quantum measurement (according to the universality of quantum physics) but is subject to your interpretation. To quote Christopher Fuchs of Quantum Bayesianism:

Medium 

How the illusion of an objective reality creates time travel paradoxes

7 comments:

Peter Pan said...

So death, taxes, weights and measures are subjective realities?

Kaivey said...

No, they are real.

Matt Franko said...

Weights and measures are NOT real they are abstractions....

3 pounds of bananas: the 3 is an abstraction, the pound is an abstraction and the bananas are real...

Science people create the abstractions to deal with the real...

In a similar way Artists create the figurative to deal with the literal...

The problems arise when we employ Artists to deal with the real using the figurative... it doesn’t work that way obviously...

Matt Franko said...

The Artists end up reifying the abstractions (they think the abstractions are REAL) because they don’t understand the abstraction... the abstractions can only be understood via rigorous training in their application...

So you have an abstraction of a banks Reserve Assets which is an abstraction in Accounting Science and then the unqualified Artists employed there think they are REAL and go all around all over the place saying stupid shit like “banks lend out the reserves! ... banks lend out the reserves!“ as if the abstraction were REAL...

You see it every day...

Peter Pan said...

Do weights and measures meet the standard of objective reality?

I'm not concerned if concepts are deemed abstract or not.

Weight can be experienced thanks to our senses, so we understand it better than say capacitive reactance.

Matt Franko said...

Your conflating force and weight (mass)...

F=ma

You don’t feel weight you feel force...

Peter Pan said...

Try holding a pumpkin at zero acceleration. e.g. 50 Kg x 0 m/s^2 = 0 N

So what are you sensing? It's weight.

People also 'understand' they need to apply force to throw objects, as opposed to just holding them stationary. Sensory perception may be misleading, yet it is distinct to conceptual thinking.