# Retrocausality

## Recommended Posts

I've heard people discuss retrocausality(that causes in the future can change effects in the past). It seems to me if anyone could do this they would be a millionaire and here's why.

I've comprehended the ability to do this described in layman's terms like this. If you shoot particles through a double slit at a screen, whether u view them or not changes whether it has an interference pattern or not. So in order to predict the future and prove retrocausality you do the experiment 16 times and collect the data for each one store it away and then in the future you look at the experiments that are the binary number of the future lottery number. This will change each of those experiments to interference patterns and presently you will know what the lottery will be.

Can someone explain to me in layman's terms why people aren't doing this if this is what's going on in that double slit eraser experiment or expirements where people are saying retrocausality is possible.

• Replies 76
• Created

#### Popular Days

Well, I'm not very good at this, but since there are no takers, here's what other people think.

Retrocausality is any of several hypothetical phenomena or processes that reverse causality, allowing an effect to occur before its cause. (emphasis mine).

Apparently, nobody actually thinks effects happen before the cause since, you know, that sort of violates the whole concept of cause and effect. As I see, this is a theoretical model, that is to say a way of looking at something, not a way things actually happen.

As for your example I can't tell if it's bad, badly explained or I can't understand it right (It feels like you were trying to say something else). But in your example,

"If you shoot particles through a double slit at a screen, whether u view them or not changes whether it has an interference pattern or not".

I fail to see the time travel. Observing or not (likely) changes the outcome (uncertainty), but still, you have the shooting, the observing and the results that point to what you have done. It's quite linear.

Also, if any retro stuff happens it will be between emission and reception, storing data does little for time travel, as we all know. You could emit, wait, then in the future run after the beam an observe. But I feel like pointing out that the beam has no interference until observed, then it has when observed. There is little info there and no timetravel.

In addition, to store data you need to have data. To have data you need to observe. If you observe, then it has an interference pattern, no?

##### Share on other sites

Thanks, that's very clear Ndi.

In addition, to store data you need to have data. To have data you need to observe. If you observe, then it has an interference pattern, no?

This is exactly one of the questions I'm wondering. I assume the answer is that if you observe with a machine then it has an interference pattern and my thought experiment of retrocausality which enables someone to know the future means nothing.

However I've heard many people describe these quantum mechanics as though its not the machine but the person the conciousness that determines the outcome of interference and I interpreted one to mean it was possible to actually store the data and whether u looked at it later would determine whether it had an interference pattern before. I think this thought experiment of saving the data and looking at it later(if it doesn't work) shows that it is not the person or the conciousness that determines quantum mechanics but the machine.

I've been interested in this partly because I'm a hard determinist like Einstein, I think there is only 1 possible future, etc. I've been trying to find a way to either prove or disprove this and retrocausality is something which disproves it.

##### Share on other sites

I'd suggest you take a look at Bell's theorem and the experiments involving it.

##### Share on other sites

I've seen http://en.wikipedia.org/wiki/Bell's_theorem before and just as before I came to the same conclusion.

For Bell's theorem the correlation of spins calculated from QM makes perfect sense to me you don't even need these long explanations or complex math you can just picture it visually. So in my view the 2 entangled particles have opposite spin about an axis we do not know. When 2 people measure their own particle at the same axis with one axis 180 degrees you get a correlation of 1(always the same). At 90 degrees a correlation of 0(half the time its the same). And at 45 degrees a correlation of .71 because 3/4 the time its the same. Visualizing 2 spheres with opposite spins and comparing how often they have the same spin around a particular axis is not easy but it shows there is nothing "magical" going on. You could even describe this axis and spin as the hidden variables and correlation is perfectly described.

I'm still a bit confused what Bell is doing when he picks some other hidden variables and then gets a correlation of 1, -1, and 0 for the same 180degrees, 90 degrees, 45 degrees. It seems to me like Bell is picking bad hidden variables or has a limited definition of what a hidden variable can be? but I think I need to read more into it if I really want to explain why he's wrong if he's wrong. For now it just seems as though the results of correlation and spin in entangled particles are very simple and don't mean anything.

##### Share on other sites

One must note that the particles only have the spins when you measure them — you can't say the particle always had that spin. That's a huge deviation from classical thinking.

##### Share on other sites

[...] I've heard many people describe these quantum mechanics as though its not the machine but the person the conciousness that determines the outcome of interference

I don't really pretend to understand this stuff about particles and their various effects, but logic seems to dictate that interference is interference regardless of the nature of the observer.

If it isn't, then several scenarios lead to absurdity. For example, you record a pattern, but not look at the recording. Later, when you look at it, it is determined. This implies that the recording medium shifts in anticipation of your play button which is, basically, a showstopper. Unlike particles, I understand storage mediums.

Interference exists always because of the nature of the observed medium. It doesn't become a "pattern" until it is observed since the pattern is a "snapshot" of the phenomenon. This implies a fixed time and place (or a multiple of). Note I'm thinking of interference in terms of a light interference pattern here.

##### Share on other sites

Yeah, it's got nothing to do with consciousness. To be "observed" means to interact with something.

##### Share on other sites

Yeah, it's got nothing to do with consciousness. To be "observed" means to interact with something.

Is that not part of a current debate? I did not know the question had been settled.

##### Share on other sites

Is that not part of a current debate? I did not know the question had been settled.

In physics circles, I'm not aware of there being any debate. Do you have information to the contrary?

##### Share on other sites

how can anything be observed without the interaction of conscious humans? No consciousness means no observation. ???

Edited by bombus
##### Share on other sites

how can anything be observed without the interaction of conscious humans? No consciousness means no observation. ???

The word does cause confusion, but it just means interaction with something external. I think it comes from the initial Heisenberg thought experiments in a "how do we determine position and momentum at the same time" kind of thing, and would still apply in laboratory experiments (where, in the case of QM, it always means recorded by some type of machine, for obvious reasons). It is similar to the way we say that "no information can be transferred at faster than light," where "information" isn't limited to something understood by conscious beings.

##### Share on other sites

The word does cause confusion, but it just means interaction with something external. I think it comes from the initial Heisenberg thought experiments in a "how do we determine position and momentum at the same time" kind of thing, and would still apply in laboratory experiments (where, in the case of QM, it always means recorded by some type of machine, for obvious reasons). It is similar to the way we say that "no information can be transferred at faster than light," where "information" isn't limited to something understood by conscious beings.

Consciousness being interaction is an opinion of some physicists I think.

The results of any expts or measurements can only be recorded once a conscious observer is involved. A machine that records data has recorded nothing until the results are analysed by a conscious observer. There is no way out of this as far as I can see.

Edited by bombus
Consecutive posts merged.
##### Share on other sites

The results of any expts or measurements can only be recorded once a consciousness observer is involved. A machine that records data has recorded nothing until the results are analysed by a conscious observer. There is no way out of this as far as I can see.

You can do that indefinitely, but at that point you're no longer dealing with quantum mechanics. You're talking about philosophical sollipsism. "How do we know the machine has recorded something real until we look at it" vs. "How do I know the world doesn't disappear when I close my eyes." No difference.

##### Share on other sites

You can do that indefinitely, but at that point you're no longer dealing with quantum mechanics. You're talking about philosophical sollipsism. "How do we know the machine has recorded something real until we look at it" vs. "How do I know the world doesn't disappear when I close my eyes." No difference.

Yes, you are absolutely correct, one can do it indefinitely. But no-one can draw the line between when it stops being 'QM' and becomes solipsism? This is the big issue with QM and however unpalatable it will not go away by ignoring it.

In laymans terms, some physicists do choose to ignore it so have a different interpretaton of observation than those that do not.

As far as I am aware, the issue cannot be resolved by scientific experimentation. It's down to belief - which one could say has no place in science.

And there we are all stuck!

##### Share on other sites

So, in other words, you have ZERO real citations that there is this supposed "debate," you're just making stuff up based on your own (mis)understanding of the semantics, and you will just be ignoring swansonts question presented to you in post #10. Good to know.

##### Share on other sites

So, in other words, you have ZERO real citations that there is this supposed "debate," and you will just be ignoring swansonts question presented to you in post #10. Good to know.

OK, I will find some for you.

Maybe you can find me some citations that everyone is in agreement.

##### Share on other sites

Nope. I didn't make the claim. The onus is on you, bud.

##### Share on other sites

http://www.sciencedaily.com/releases/1998/02/980227055013.htm

Also, read up on John Archibald Wheeler and his Participatory Anthropic Principle (PAP):

http://en.wikipedia.org/wiki/Interpretations_of_quantum_mechanics#Participatory_Anthropic_Principle_.28PAP.29

A quote from the following page proving the debate - see for yourself: the Many Worlds Iinterpretation is just one of many.

MWI removes the observer-dependent role in the quantum measurement process by replacing wavefunction collapse with quantum decoherence. Since the role of the observer lies at the heart of most if not all "quantum paradoxes," this automatically resolves a number of problems; see for example Schrödinger's cat thought-experiment, the EPR paradox, von Neumann's "boundary problem" and even wave-particle duality. Quantum cosmology also becomes intelligible, since there is no need anymore for an observer outside of the universe.

http://en.wikipedia.org/wiki/Many-worlds_interpretation#Wavefunction_collapse_and_the_problem_of_interpretation

That will do. There's enough here to prove that the subject is open to debate.

##### Share on other sites

My point, though, was that there's nothing especially quantum mechanics-y about those doubts. There's no more reason to suspect that it it's not there until a conscious being looks at it than it is for classical physics, or everyday life. You say "choosing to ignore it" as if quantum physicists in particular are ignoring some possibility especially relevant to them. But in the exact same way, every one of us goes about our daily lives under the implicit assumption that the world is still there when we're not looking, and that objection can always be raised, no matter what the subject.

With QM, "observation" is indeed special in a way that in some ways parallels that idea, but the "observation" means interaction with something external, not awareness by some conscious mind particularly. In fact, you could argue that it specifically doesn't mean that, as the only conscious minds we know of (humans) have no way of directly observing quantum phenomena.

##### Share on other sites

My point, though, was that there's nothing especially quantum mechanics-y about those doubts. There's no more reason to suspect that it it's not there until a conscious being looks at it than it is for classical physics, or everyday life. You say "choosing to ignore it" as if quantum physicists in particular are ignoring some possibility especially relevant to them. But in the exact same way, every one of us goes about our daily lives under the implicit assumption that the world is still there when we're not looking, and that objection can always be raised, no matter what the subject.

With QM, "observation" is indeed special in a way that in some ways parallels that idea, but the "observation" means interaction with something external, not awareness by some conscious mind particularly. In fact, you could argue that it specifically doesn't mean that, as the only conscious minds we know of (humans) have no way of directly observing quantum phenomena.

But wasn't it QM experiments (double slit and all that) that brought the issue of observation into sharp relief? Before then it was just a philisophical question (falling trees making noises in woodlands etc). QM suggests that such philosophical thinking could have some basis in reality.

Can you direct me to a definition of observation with regard to QM? I'm happy to be corrected.

##### Share on other sites

But wasn't it QM experiments (double slit and all that) that brought the issue of observation into sharp relief? Before then it was just a philisophical question (falling trees making noises in woodlands etc). QM suggests that such philosophical thinking could have some basis in reality.

QM does indeed make some previously purely academic philosophical questions a more practical concern. Physics has a history of doing that to philosophy and mathematics. However, consciousness doesn't particularly enter into it, although certainly many (mostly non-scientists) have tried. One issue is similar to the tree in the forest, though "someone around to hear it" is replaced with "something that will be different depending on whether or not it has fallen" or some such. It is reminiscent of but not the same as the original...

##### Share on other sites

Thanks, but thats a link to [an] 'observable' not 'observation'. There is a subtle but important difference. The page doesn't tackle the issue directly.

FYI, the role of consciousness and observation/measurement in Qm is being discussed here:

http://www.physicsforums.com/archive/index.php/t-126077.html

Merged post follows:

Consecutive posts merged
QM does indeed make some previously purely academic philosophical questions a more practical concern. Physics has a history of doing that to philosophy and mathematics. However, consciousness doesn't particularly enter into it, although certainly many (mostly non-scientists) have tried. One issue is similar to the tree in the forest, though "someone around to hear it" is replaced with "something that will be different depending on whether or not it has fallen" or some such. It is reminiscent of but not the same as the original...

I get what your saying - the trouble is that the intention of the measurement in the double slit experience affects the outcome. If you try to see which slit the electron actually goes through it behaves as a particle, if not it behaves as a wave. The act of observation affects the outcome. This is not the case in classical physics.

Edited by bombus
Consecutive posts merged.
##### Share on other sites

I get what your saying - the trouble is that the intention of the measurement in the double slit experience affects the outcome. If you try to see which slit the electron actually goes through it behaves as a particle, if not it behaves as a wave. The act of observation affects the outcome. This is not the case in classical physics.

Not really, though. It's the physical set up of the experiment, not the intention of the experimenter. If you have a device that measures which slit it goes through, all you're doing is forcing an external interaction at an earlier point, and that external interaction forces it to be one place or another. Measurement requires interaction, and interaction causes change.

If you put a brick wall across the road to measure whether a car goes by, whether or not you choose to "measure" (i.e., build the wall) will certainly affect the outcome, but it would be an odd way of phrasing it to say that your free will caused the car to crash. The car crashed because there was a wall in the way.

There is, of course, an important difference between car and electron, which is the point of the experiment. When there's no "wall" in the way of the electron and thus no difference in the external world until it hits the second screen, it turns out it went through both slits. When there are walls in the way, you're forcing an interaction and thus a wave collapse sooner, and so it has to be in one place or the other. Freaky. But consciousness still doesn't enter into it.

## Create an account

Register a new account