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:
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.
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 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.
@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