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QUESTION OF THE DAY
Can decisions made in the future affect the past?

Retrocausal Quantum Theory

This theory isn’t saying signals can be communicated from the future to the past.
Retrocausality means that when an experimenter chooses the measurement setting with which to measure a particle, that decision can influence the properties of that particle in the past, even before the experimenter made their choice.
A decision made in the present can influence something in the past.
In order to explain observations that distant particles immediately know what measurement is being made on the other, the only viable explanation was that the particles are influencing each other even when separated by large distances.
By allowing for the possibility that the measurement setting for one particle can retrocausally influence the behavior of the other particle, there is no need for action-at-a-distance—only retrocausal influence.

Any quantum theory that assumes that:

  1. the quantum state is real
    ~and~
  2. that physical processes can run forwards and backwards while being described by the same physical laws
    …must allow for retrocausal influences.

Research suggests the quantum state is real.
Allowing for retrocausality may provide insight into this question.
Allowing for this openness regarding the reality of the quantum state is one of the main motivations for investigating retrocausality in general.
Reversing a process is not only possible but the probability of occurrence is the same whether the process is going forward or backward.
The 'no-retrocausality' assumption requires that they are different.
Do we keep time symmetry or no-retrocausality?
We can't have both.
Since time symmetry appears to be a fundamental physical symmetry, it makes more sense to allow for retrocausality.
Doing so would eliminate the need for action-at-a-distance and it would still be possible to explain why using retrocausality to send information is forbidden [no transgression of the Second Law of Thermal Dynamics].
Having retrocausality enables us to collapse several puzzles into just one.
The existence of an arrow of time has to be accounted for by thermodynamic arguments.
It is a feature of the boundary conditions of the universe.
The inability to signal into the past in a retrocausal universe could also come about from special boundary conditions and doesn’t need to be a law of physics.
If retrocausality is a feature of the quantum world, it would have vast implications for physicists' understanding of quantum theory. Retrocausality may be one of the missing pieces that makes quantum theory complete. The idea is an interpretation of observations rather than the making of new observations.

Zteph 7 July 29
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this is hysterical, there is no such thing as past or future. time is a measurement, it measures change. an inch doesn't exist until you have an inch of something. rope, wood, space.
same is time. if nothing ever changed, there would be no "time"

It is funny, figure some think too much. If you drop a rock, doesn't matter how fast you pick it up, you still dropped it. The idea of where you drop it next is just your perception. Your brain works through electricity, that's where you find the quantum.

@MilesPurdue agreed for the most part, I've never been able to get on board with a lot of the theoretical bits because a lot of the time there are basic questions you have to ignore in part or in whole to arrive at the theory. no thanks.

Do you consider 'now' to be time? If not, what is it?

@Zteph sure, now could be considered time the same way a foot is located inside a yard.

@solopro What is this 'now' inside if past and future don't exist?

@Zteph oof... this is going to take some doing.... now doesn't exist inside anything... it was an illustration meant to help you understand.

@solopro If it's like a foot inside a yard, how does that bring understanding if it doesn't exist inside anything? You contradicted yourself.

@Zteph ok well you don't know how illustrations work... i don't think this relationship is going to work out.... i do appreciate the interest tho !

@solopro illustrations only work if they actually represent what is. Doesn't your illustration, by your own admission, fail in that regard?

@Zteph nope

@solopro

  • a foot IS inside a yard
    1st claim: "now could be considered time the same way a foot is located inside a yard"
    Contradictory claim: "now doesn't exist inside anything"

@Zteph so I was thinking about why you are having such a hard time with this... you can't possibly be this confused by a simple metaphor... or at least I'm hoping not, so maybe we should take a step back.... what does it mean, in your own words, to measure ? I think that will go a long way toward getting us on the same page.

@solopro to find the appropriate amount for a specific need, whether it be distance, time, or property.

@Zteph great ! so if I asked you to bring me an amount... what would you bring me ?

@solopro Where did I say a distance or time amount is bringable?

@Zteph why would it not be bringable ?
surely if you can bring me lumber, or 6 feet of lumber, its possible to just bring the 6 feet...not the lumber

@solopro Because only three dimensional objects can move a distance in space [travel]. We can measure both the distance it travels and how long it takes to travel. If you're trying to claim that distance and time don't exist, you'd never be late for a meeting.

@Zteph ahh ! therein lies the confusion.... you are conflating the characteristic with the unit of measure for that characteristic.
example, you can't have a kilogram of empty space because the characteristic the kilogram measures isn't found in space. the measures for that characteristic are distance / volume / etc.
its the characreristic that exists, not the measure.
the unit of measure exists insomuch as an idea can exist, but its an arbitrary construct thats simply been standardized.
but the fact remains that you'll never be able to take a handful of degrees, ball it up, and hurk it at someone.
if you are going to try to drag me down the rabbit hole of what it means to exist and can a thought exist ... no thanks I been there... its such a gauntlet of stupidity

@solopro Every measurement is standardized, including pounds, ounces and tonnes. That doesn't help your case.

@Zteph omg, this is hysterical ! not only is that exactly what it does, it underlies exactly why its true.

@solopro I can bring you a pound of sugar, but a pound is an agreed-upon unit. You made an argument that if it's agreed-upon, it has no actual reality.

@Zteph correct ! it doesn't exist in and of itself, thats why we all have to agree to it. things that do exist don't need agreement or approval. its why Pluto is such a controversy, it exists on its own, but we have to agree whether or not it measures up to be called a planet.

@solopro Being that units are agreed-upon is for the sake of communication [both parties understand how much of something they're speaking of]. That doesn't mean there isn't any of that which units are used to measure.

@Zteph also correct.. it is the trait or chracteristic that is real. the unit of measure is made up for the purpose of communication.

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