Backwards causation: Is there any proof really against it?

[mach567]

I feel like this a stupid question, but nonetheless it has to be asked. I am not saying I believe in backwards causation. However, is there any test(or thought experiment) that can disprove it. It says that information can move back in time, as long as a paradox is not created. So time-travel to the past can only occur if it creates what is supposed to happen in the future. Not saying I believe it...but is there really a way to disprove this?

 

[DrChinese]

No stupid questions here.

There is nothing inconsistent with backwards causation as a QM interpretation relative to experiment. There are experiments that distinctly "imply" this, as a matter of fact.

Experimental Nonlocality Proof of Quantum Teleportation and Entanglement Swapping, Thomas Jennewein, Gregor Weihs, Jian-Wei Pan, Anton Zeilinger

See page 5, "... seemingly paradoxical situation ..."

 

[Bill_K]

Say event B happens after event A. Did A cause B, or did B cause A, or did they both cause each other? Since you've specified that "time-travel to the past can only occur if it creates what is supposed to happen in the future", there is no difference in these three interpretations. Under this restriction, backwards influence is indistinguishable from forwards, and therefore unnecessary.

 

[DrChinese]

Say event B happens after event A. Did A cause B, or did B cause A, or did they both cause each other? Since you've specified that "time-travel to the past can only occur if it creates what is supposed to happen in the future", there is no difference in these three interpretations. Under this restriction, backwards influence is indistinguishable from forwards, and therefore unnecessary.

A past context and a future context are necessary to make a QM prediction. We arbitrarily call the past context the setup and the future context the observation. But as the reference shows, that ordering can be reversed.

 

[dm4b]

You may want to check out the TSQM (Time Symmetric) formulation of QM.

http://arxiv.org/abs/0706.1232

It's got an interesting twist on "retroactive" influences.

Although, as I understand it so far, it in no way allows causality, as we typically think about it, to be violated. You ain't going to use TSQM to kill your grandfather ;-)

 

[ThomasT]

I feel like this a stupid question, but nonetheless it has to be asked. I am not saying I believe in backwards causation. However, is there any test(or thought experiment) that can disprove it. It says that information can move back in time, as long as a paradox is not created. So time-travel to the past can only occur if it creates what is supposed to happen in the future. Not saying I believe it...but is there really a way to disprove this?

No way to disprove it. No empirical reason to believe it. Lots of empirical reasons to not believe it.

 

[DaveC426913]

Say event B happens after event A. Did A cause B, or did B cause A, or did they both cause each other? Since you've specified that "time-travel to the past can only occur if it creates what is supposed to happen in the future", there is no difference in these three interpretations. Under this restriction, backwards influence is indistinguishable from forwards, and therefore unnecessary.

Are you saying that, even if we could get a cause to precede an effect, it is indistinguishable?

Forgive my naivete (As I may not understand what you're getting at) but, surely we could set up an experiment that showed time-reversed causation as distinguishable from ... uh ... time forward causation.


Two switches and two lights. A switch operator who cannot see the lights, and an observer.

Experiment starts.
Light 2 turns on.
A pause.
Operator picks a switch at random and closes the circuit. He has chosen switch 2.

Without going into how we got the causal reversal to work, we can definitely determine that effect preceded cause.

 

[Phrak]

A past context and a future context are necessary to make a QM prediction. We arbitrarily call the past context the setup and the future context the observation. But as the reference shows, that ordering can be reversed.

What's a 'context'?

 

[Forestman]

Here is a similar thread on the question at hand.

https://www.physicsforums.com/showthread.php?t=482032

 

[ExecNight]

Ah ,the age old Chicken or the Egg question in disguise =)

Imho never try to prove a negative. Its useless, it has many examples.

 

[haael]

If forward and backward causation are indistinguishible, then I have another question: are closed time loops proven/disproven? And if you fear loops to much, are "zigzaks" possible?

Suppose you have 3 events: A, B and C. Say, they are ordered in time: A before B, B before C. Now is it possible that A causes C, then C causes B? If cause and effect can be swapped, then this is no different from A and B both causing C.

 

[DaveC426913]

Entropy is going to be a strong indicator of cause and effect.

No one is going to conclude that a puddle of milk on the kitchen floor has contracted to shove a randomized pile of glass shards into a glass shape and then launch it up onto the counter.

 

[haael]

Entropy is going to be a strong indicator of cause and effect.

Yes, but let's talk about the most microscopic level, where everything is reversible.

Someone here said that cause and effect can always be swapped. Yes, it can, when we have only one cause and one effect.

Suppose that we have 2 particles collision (event A). From this collision some other particle flies out, then it decays into other 2 particles (event B). Event A is a cause and event B is an effect. If we stopped event A from happening, event B wouldn't ever appear. However, we can swap A and B and say that 2 latter (anti)particles collided at B, created the intermediate particle that decayed into 2 former particles at A. If there's no A, there's no B. If there's no B, there's no A. Everyting is symmetric.

But suppose we have 2 spatially separated events: A and B. From these events, 2 particles follow and they collide at C. Then, A is a cause of C and B is a cause of C. We can also say that A and B are effects of C.

But can we say that B is an effect of A?

Can we reverse only the B->C process, still holding A->C?

There was a topic here that quantum entanglement has been teleported in time. I think this is an example of such a time travel.

 

[DrChinese]

What's a 'context'?

Measurement settings participate in a context. These can be values at various points in time. They can be spacelike separated (outside of a spacetime cone). In the example I provided, Alice and Bob (never in the other's lightcone) are detected BEFORE the decision is made to entangle them (via entanglement swapping). The detection of Alice, of Bob, and the decision to entangle them are all part of the context.

So I guess I am saying that we usually call the setup what happened in the past, and the observation what happens later. But that "can" be arbitrarily changed as to order without in any way affecting the QM predicted outcome. (Which is what is shown in the reference.)

 

[DrChinese]

And a general comment: even in the time symmetric interpretations, the last temporal event observed always ends up being a random outcome {+1, -1} or similar which cannot be heralded except by signals from the past.

 

[ExecNight]

1997 Game 5, Kasparov vs. Deep Blue

1.Nf3 d5 2.g3 Bg4 3.Bg2 Nd7 4.h3 Bxf3 5.Bxf3 c6 6.d3 e6 7.e4 Ne5 8.Bg2 dxe4 9.Bxe4 Nf6 10.Bg2 Bb4+ 11.Nd2 h5 12.Qe2 Qc7 13.c3 Be7 14.d4 Ng6 15.h4 e5 16.Nf3 exd4 17.Nxd4 O-O-O 18.Bg5 Ng4 19.O-O-O Rhe8 20.Qc2 Kb8 21.Kb1 Bxg5 22.hxg5 N6e5 23.Rhe1 c5 24.Nf3 Rxd1+ 25.Rxd1 Nc4 26.Qa4 Rd8 27.Re1 Nb6 28.Qc2 Qd6 29.c4 Qg6 30.Qxg6 fxg6 31.b3 Nxf2 32.Re6 Kc7 33.Rxg6 Rd7 34.Nh4 Nc8 35.Bd5 Nd6 36.Re6 Nb5 37.cxb5 Rxd5 38.Rg6 Rd7 39.Nf5 Ne4 40.Nxg7 Rd1+ 41.Kc2 Rd2+ 42.Kc1 Rxa2 43.Nxh5 Nd2 44.Nf4 Nxb3+ 45.Kb1 Rd2 46.Re6 c4 47.Re3 Kb6 48.g6 Kxb5 49.g7 Kb4 ½-½

So can someone explain how move 49 can be the cause of move 46?

And is move 49 a random event when observed? Or can it be interpreted backwards how the board came to this?

 

[DrChinese]

... So can someone explain how move 49 can be the cause of move 46?

And is move 49 a random event when observed? Or can it be interpreted backwards how the board came to this?

To continue your analogy, which is not exactly the best...

Move 49 is a participant in the context which leads to move 46. There are other participants as well. In addition, move 46 appears random until you learn the entire context. Then it may reveal previously unknown correlations. And you cannot learn this until move 49 at the earliest.

 

[ThomasT]

So can someone explain how move 49 can be the cause of move 46?

And is move 49 a random event when observed? Or can it be interpreted backwards how the board came to this?

What DrC said about context. Also, wrt "And you cannot learn this until move 49 at the earliest", it's generally true that given the rules and goal of chess it's possible to predict with certainty the outcome of some games from certain positions (forced mates). I don't think that's the case with the game we're considering, so DrC's statement applies.

The context of chess includes a well defined finite domain within which there are well defined rules including a well defined finite conclusion or spatial configuration of the pieces limiting the evolution of play. The well defined conclusion (or goal of the game) is parsed into not so well defined goals (spatial configurations of the pieces) which are compared and evaluated by the players via the weight given them via the particular evaluative process they might employ. These evaluative processes are precisely defined in computer chess program algorithms. Wrt humans, they're, historically, not so clearly defined (different players have different characteristic styles), but as more and more top players use chess programs to analyze and direct their play stylistic differences become less discernible.

Anyway, what this means is that the moves of chess players aren't random given the context, and that, in a certain looser sense of the word 'cause', we might say that Kasparov's move 46 'caused' his move 49. But in the strictest sense of the word 'cause', which is what we're concerned with here, and which is what DrC is talking about, the cause of move 49 can only be traced to Deep Blue's move 48 (or, more precisely, the configuration following Deep Blue's move 48).

In fundamental theoretical physics, the general equations of motion aren't constrained by a general dynamical law specifying a necessary direction of time evolution in accordance with our sensory observation of an arrow of time. In certain mathematical treatments time reversal is possible, as well as backward in time travel. But the science provides no empirical evidence for that, and lots of empirical evidence to suggest the contrary. So, solutions in accordance with time reversal (advance waves, certain interpretations of qm, etc.) and travel backward in time (CTC's of GR) are generally disregarded.

Note: I'm not an expert. I reply to posts/threads and write what I write to help sort things out for myself. Any criticisms, corrections, clarifications and/or elaborations are very welcome.

 

[ExecNight]

I know its not the best analogy for the reasons you have described. But what comes to my mind is, we have been finding answers about the universe looking only at the move 46. Considering move 46 is now, and move 1 is the Big Bang.

What makes me think no-no in this topic is, i can't understand how a chaotic background can create something that's not. When we take the atomic universe its exactly like a chessboard. Everything has its limits, every piece acts as expected.

But when we go beyond down to Quantum Mechanics there is chaos, probabilities. Well this maybe wasn't a scientific post at all. But analitic part of my brain finds only two solutions to these problems.

Either the quantum universe and the macro universe are not in relation enough to affect each other for an observable outcome, or what we know about Quantum Mechanics is somehow flawed (for the time being. Or you can change that to what i know is)

 

[DrChinese]

Either the quantum universe and the macro universe are not in relation enough to affect each other for an observable outcome, or what we know about Quantum Mechanics is somehow flawed (for the time being. Or you can change that to what i know is)

"Flawed" is one of those words that conjures an image that can be misleading.

The Bohmian Interpretation supplies a "missing" explanation via a hypothetical guide wave. Yet there is no useful information to be gained from such. I do not believe that we will discover a way to get past the limits of the HUP, nor is such even possible. But hey, that's just my take.

 

[ThomasT]

I know its not the best analogy for the reasons you have described. But what comes to my mind is, we have been finding answers about the universe looking only at the move 46. Considering move 46 is now, and move 1 is the Big Bang.

What makes me think no-no in this topic is, i can't understand how a chaotic background can create something that's not. When we take the atomic universe its exactly like a chessboard. Everything has its limits, every piece acts as expected.

But when we go beyond down to Quantum Mechanics there is chaos, probabilities. Well this maybe wasn't a scientific post at all. But analitic part of my brain finds only two solutions to these problems.

Either the quantum universe and the macro universe are not in relation enough to affect each other for an observable outcome, or what we know about Quantum Mechanics is somehow flawed (for the time being. Or you can change that to what i know is)

What DrC said. And I'll add:

We can infer that the submicro and macro universe are "in relation enough to affect each other for an observable outcome" because there are observable outcomes. They're just, taken individually, random. Conjecturing that an underlying reality must be evolving randomly because instrumental behavior is random is unwarranted.

Backward extrapolations from conjectures about the state of the current universe based on scientific observation to states of the universe at a time that we have no access to aren't, strictly speaking, science.

Also, wrt the current universe, there's no "quantum universe" to go "beyond down" to. QM is a mathematical construction that's compared to instrumental behavior. No more and no less. Attempts to solve the measurement problem in QM (Schrodinger equation is time symmetric and deterministic, measurements are irreversible and probabilistic) are obviated once it's realized that they involve making standard QM into something that no scientific theory can ever be, ie., a theory about an underlying reality that we have no direct sensory access to and hence no qualitative apprehension of.

Science has only to do with our sensory experience, and all of physical science assumes, at least tacitly, causal determinism. This is why CTC's, advance wave solutions, etc. are disregarded even though there's no way to prove they don't exist.

 

[byron178]

is there evidence for the existence of kerr black holes?

 

[GODISMYSHADOW]

I feel like this a stupid question, but nonetheless it has to be asked. I am not saying I believe in backwards causation. However, is there any test(or thought experiment) that can disprove it. It says that information can move back in time, as long as a paradox is not created. So time-travel to the past can only occur if it creates what is supposed to happen in the future. Not saying I believe it...but is there really a way to disprove this?

I have a question that's even more stupid. Is the past "unique?" Perhaps there are two slightly different pasts that could result in the present, and one is just as valid as the other.

That might explain the arrow of time, anyway. Time moves in the direction from cause to effect because the entropy of the universe is increasing. Precise information about one past isn't there. It isn't anywhere.

 

[DrChinese]

I have a question that's even more stupid. Is the past "unique?" Perhaps there are two slightly different pasts that could result in the present, and one is just as valid as the other.

You could say that. There is an interpretation, in fact, called Consistent Histories. Try googling:

consistent histories interpretation quantum mechanics

 

[dipstik]

People make moves to gain future advantage all the time. I think this is a poor analogy.

 

[Edward Solomo]

Are you saying that, even if we could get a cause to precede an effect, it is indistinguishable?

Forgive my naivete (As I may not understand what you're getting at) but, surely we could set up an experiment that showed time-reversed causation as distinguishable from ... uh ... time forward causation.

Entropy. If an observer somehow reverses the arrow of time, his actions must create an increase in entropy, which would result in a decrease in entropy for observers going forward in time, violating the second law of thermodynamics.

 

[K^2]

Localized time reversal is entirely possible. In a small enough system, provided that it's isolated, you can even have causality violations. The problem is that time flow seems to be "contageous". As soon as such a system interacts with the larger environment, it gets time order of larger environment. In the end, it's all about the entropy. Larger entropy wins, and keeps on increasing.

If you need the reason for initial choice of time direction, universe expansion seems to be the culprit. In principle, it doesn't matter if it's expanding or collapsing, but larger universe has more available states, hence higher entropy, and hence the arrow of time towards expansion.