Skip to comments.Quantum causal relations: A causes B causes A
Posted on 10/03/2012 4:33:24 PM PDT by LibWhacker
One of the most deeply rooted concepts in science and in our everyday life is causality; the idea that events in the present are caused by events in the past and, in turn, act as causes for what happens in the future. If an event A is a cause of an effect B, then B cannot be a cause of A. Now theoretical physicists from the University of Vienna and the Université Libre de Bruxelles have shown that in quantum mechanics it is possible to conceive situations in which a single event can be both, a cause and an effect of another one. The findings will be published this week in "Nature Communications".
Although it is still not known if such situations can be actually found in nature, the sheer possibility that they could exist may have far-reaching implications for the foundations of quantum mechanics, quantum gravity and quantum computing.
Causal relations: who influences whom
In everyday life and in classical physics, events are ordered in time: a cause can only influence an effect in its future not in its past. As a simple example, imagine a person, Alice, walking into a room and finding there a piece of paper. After reading what is written on the paper Alice erases the message and leaves her own message on the piece of paper. Another person, Bob, walks into the same room at some other time and does the same: he reads, erases and re-writes some message on the paper. If Bob enters the room after Alice, he will be able to read what she wrote; however Alice will not have a chance to know Bob's message. In this case, Alice's writing is the "cause" and what Bob reads the "effect". Each time the two repeat the procedure, only one will be able to read what the other wrote. Even if they don't have watches and don't know who enters the room first, they can deduce it by what they write and read on the paper. For example, Alice might write "Alice was here today", such that if Bob reads the message, he will know that he came to the room after her.
Quantum violation of causal order
As long as only the laws of classical physics are allowed, the order of events is fixed: either Bob or Alice is first to enter the room and leave a message for the other person. When quantum mechanics enters into play, however, the picture may change drastically. According to quantum mechanics, objects can lose their well-defined classical properties, such as e.g. a particle that can be at two different locations at the same time. In quantum physics this is called a "superposition". Now an international team of physicists led by Caslav Brukner from the University of Vienna have shown that even the causal order of events could be in such a superposition. If - in our example - Alice and Bob have a quantum system instead of an ordinary piece of paper to write their messages on, they can end up in a situation where each of them can read a part of the message written by the other. Effectively, one has a superposition of two situations: "Alice enters the room first and leaves a message before Bob" and "Bob enters the room first and leaves a message before Alice".
"Such a superposition, however, has not been considered in the standard formulation of quantum mechanics since the theory always assumes a definite causal order between events", says Ognyan Oreshkov from the Université Libre de Bruxelles (formerly University of Vienna). "But if we believe that quantum mechanics governs all phenomena, it is natural to expect that the order of events could also be indefinite, similarly to the location of a particle or its velocity", adds Fabio Costa from the University of Vienna.
The work provides an important step towards understanding that definite causal order might not be a mandatory property of nature. "The real challenge is finding out where in nature we should look for superpositions of causal orders", explains Caslav Brukner from the Quantum Optics, Quantum Nanophysics, Quantum Information group of the University of Vienna.
Unintented consequences are a fact of life.
“How can you be in 2 places at once when not anywhere at all?”
How many frames of reference were you using? An outcome is still a singular event; the WTC is still gone, for example.
If a video game programmer can code superposition into a game what would it look like? And of course our Creator can easily “code” superposition into our existence. (If you haven’t guessed already.. I know nothing about physics and very little about science in general.)
“But if we believe that quantum mechanics governs all phenomena...”
The key phrase. Quantum mechanics is an attempt to explain the behavior of subatomic particles and the forces that act upon them. If the theory works, it’s provisionally true. But this doesn’t mean we understand quantum behavior as it really is, just that we have an explanation of the quantum behavior that we have observed in experiments, which is an infinitesimally small proportion of all quantum behavior.
So it’s “Bob & Carol & Ted & Alice” or “Alice & Carol & Ted & Bob” depending on your “perspective”...
Nah; that was Schrödinger’s brain cells.
That’s easy when you work for the Department of Redundancy Department.
One is used to moving a video game character through space; now imagine that the character can move just as easily through time. Time is just another “direction” in which the character can move. So, from the character’s perspective, what is a cause, and what is an effect? If the character moves backward through time, the “effects” come before the “causes”. Now consider the subjective philosophical perspective of the game character...it would likely see a cause-effect relationship as being a duality, not a fixed, one-way relationship.
Hidden in Plain Sight Kindle Edition is 99 cents. The author is Andrew Thomas.
It helps, I think, if you've been exposed to quantum and relativity for awhile, and are either in awe or puzzled that the two regimes don't reconcile.
The other stuff I've been reading is heavy on string theory, which is sort of interesting and aims to put some more meat on what Mr. Thomas is getting at; and books about "dark matter" and "dark energy." Very strange physical world we live in, in many many ways.
This reminds me of Borges’ masterful “Tloen, Uqbar, Orbis Tertius”:
So should I get a Obama phone or not?
You seem to be reading material similar to what my older brother reads. He’s a virtual wealth of conversation when it comes to the deeper things of science and discussing them in layman’s terms.
and if things are in parallel universes, they aren't the same thing anyway
Strange? As opposed to what, familiar? Physical? As opposed to what, mental? Relax, everything will be all right.
How would you know?
I used two. I showed the proof to a fellow grad student in math whom I respected. He said I must’ve made a mistake somewhere but couldn’t find it.
if you are on the foo stam you can already get obama phow
Any married guy could have told you that.
It could make you rich. Or getting rich could make you buy one. Your choice.
Physically would that be similar to recursion? Here a video character's actions could be influenced by his actions in each successive execution; but unlike "Ground Hogs Day" the video character could change the future? Eventually it does reach the desired end.
That was a really great story!
I’m more confused now than I never was.
I wonder what the chances of that are.
"strange" as in doesn't follow intuition or common sense. Like, if your mother took a fast ride, she could come back and be younger than you are. One of my favorite remarks about physicists is that the closer they look, the more the stuff they are looking at disappears. Or, that what we think of as "solid" stuff is about 99.999999999999999% empty. (I guessed at the number of trailing nines there, but it's in the right neighborhood).
Agreed, thing will turn out fine. I read physics just because I find it interesting. I like music too.
These guys were a lot of fun. Most of them had served in WWII or the Korean War and every day was a breath of fresh air for them ~ even the crotchity ones.
So they had a feel ~ a real personal feel for probability.
Their hobbies were either dabbling in quantum physics, or figuring out what the structure of the elements was all about ~ plus visiting the Wailing Wall in Jerusalem as soon as that could be done. WWII had done things to their life's links that were simply incredible.
So, smart guys, right attitude, and well experienced in everything. Each one of them had his own interpretation for the Schroedinger Cat theorm. In fact, that little tale fell right in the middle of a sampling algorithm dilemma they'd come up with ~ which is very simple. When you have an ongoing continual process and you need to reach in and take a snapshot of just a second of time and something comes up that prevents you from doing so, what is the correct prophylaxis to take another sample at another time that will PROBABLY (Within some degree of certainty) replace the lost data?
Remembering that each little 1 second snapshot is going to represent hours of work and thousands of pieces of mail down the road as the typical second is structured for total agency operating costs, can you just wait 5 and try it again? Or is it more complex ~
These people consciously killed Schroedinger's cat every day ~ usually several times ~ because there's the answer to the question of when can you repeat your action and get the same result?
As I recall it if you kill the cat you can never repeat the action, so you gotta' leave the cat alone!
Decades later more advanced string theory theoreticians are getting more deeply into this problem ~ so I follow that stuff just in case one of them comes up with a better solution than just out and out killing the cat ~ the only action that allows you to stick a (new) kitty back in the box and strive for a different, but otherwise identical, result.
Then there's a whole school of thought with thousands of members who dispute the relevance of that cat to anything.
It will be the ultimate cruelty if we are never given a glimpse of the mystery.
He's with you on that Schroedinger's cat thing. Your opening the box isn't relevant to the outcome. He makes real good sense of the question of "what constitutes observation?"
Quantam crap is total horse manure.
Quantum mechanics throws a monkey wrench into that idea.
I am positive a conscious observer of some kind was required to bring the universe into existence. Nothing occurs in the quantum universe without a conscious observer. Calling that observer "God" would not be outrageous.
sounds like the author of the Harry Potter books was on occasion not writing about “magic” but instead reflecting quantum physics (whether she realized it or not)
the more humans know, the larger becomes the body of knowledge we are aware that we don’t know
the “undiscovered” universe (that portion of creation we either have no knowldge of or no understanding of or admittedly incomplete understanding of) seems to keep expanding as fast as what we do know grows - like peeling an onion with infinite layers
Ah, so the math is finally showing them that time has variable expressions, not merely linear. The planar nature of temporal reality has been right before them for a long time, in the phenomenon of quantum non-locality. Wait until they discover the volumetric nature of time. That should ruffle their ‘e’ ...
“When I was a graduate student, I proved the temporal order of events was relative; i.e., whether event A precedes event B or B precedes A in time depends on the frame of reference of the observer.”
I taught a class in intro relativity and quantum mechanics for two semesters. When it came to that stuff I needed to stick strictly to the book or I would confuse myself due to that problem so much that it was really a danger that I would completely mess up my students. Frame of reference stuff seems like it should be so elementary until you start really getting into it, then it can become impossibly obtuse.
If nobody did I would have :-)
That explains a lot doesn't it? LOL
One more reason I don't eat at the Peking Moon!
Yep, that's why I never told anyone else about it. I figured I had probably just made a mistake somewhere, though my friend couldn't find it, if so. And for the life of me, neither could I. Still, there was no way I was going to waltz off to one of my professors and suggest I had found something new! It's too easy to make a mistake and not realize it. Then you look like an idiot. Strange in a way because that's what math and physics are all about: making a million mistakes. That's how we learn. But you better not make that one or you're through.
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