Fabio Costa
University of Vienna
Tue, 02 Oct 2012 20:40 CDT

A new framework for quantum mechanics which does not assume a pre-existing global time. It demonstrates the possibility for two agents to perform a communication task in which it is impossible to tell with certainty who influences whom.
This press release is available in German.

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.



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.

Publication:

"Quantum correlations with no causal order"
Ognyan Oreshkov, Fabio Costa, Caslav Brukner. Nature Communications.
DOI: 10.1038/ncomms2076.

Funny...I was just thinking about this the other day. I think there are many A causes B causes A scenarios we can look at. The one I was thinking about is the brain-state. It is a fact that the electrical activity of the brain causes a magnetic field to exist, but experiments have shown that manipulation of this field has a profound effect on thought (hence an effect on the synapse in the brain). It seems to me that the field brings more order & control to the chaotic firing of neurons, but the order that it might bring arises from the semi-ordered(?) chaos of the synapses in the first place. Apparently brain function is the result of a sort of closed-loop feedback. So what do we think with, the cells or the field they generate?...Obviously both.

We are now left to wonder which came first, the chicken or the egg? The correct answer now appears to be that since each causes and is an effect of the other, neither could have been first and the question is therefore nonsensical.

This is crap. Nature very much DOES have examples of superimpositions and supraprecendencies. For instance, the University of Vienna preceded the foundation of the Univedrsityh of Bruxelles library, yet, after the migration of the University's identity and physical manifestations, and after the renaming of their collective unit, the members of the Universite Libre de Bruxelles are still at the University of Vienna.

This is a clear case of that, which the group of three of he University of Vienna desparately denies has been demonstrated, although theoretically it is possible.


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Edit: seriously speaking, this makes sense. So far the phenomenon that has given rise to this type of thinking, only viewed the paradox of events starting before they had been caused, in explanative theories of time jerking off. Now we have a different approach, which is that causation is not linear and consecutive.

next we will have an angle of how reason is not.

But to me it talks about the same event. It just gives different explanations.

Which is good, in the sense that humanity is trying to wrap its nose (ie. what science knows) around the mind-bending nature of quantum mechanics.

This is a new one, and I applaud it. QM has always been a science that came up with hopelessly counter-intuitive theories, some of which are "proven" or have evidence to support it, which made man need to warp his own mind to make sense of it.

The truth is it can't be made sense of, and that is the beauty of quantum mechanics. It is a micro physical world, with its completely unique featurs, wholly different from the macro physical world, and either of the two worlds will never be able to fully understand the other.

I just fear that some not-so-hot theorist will force the laws of one of these worlds to apply to the other of these worlds. This might lead to trouble, as only very uninitiated people don't know that the two worlds have a boundary, and some things, laws, and methods of executing events can never cross the border between them.

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Edit: famous last words. I am saying as if I had had devine precognition of the findings of science in the future of today. Maybe they will show how the two world's laws, method of events, etc., can cross.

In fact, it is never possible to know precisely which one or the other truth of science as we perceive it, we would need, and which of them we would not need, to reevaluate in the future, and how many of them.

Feedback loops are not the same as atemporal causal relations. Related but not the same.

However, your post immediately made me think of an excellent book I read called, "I am a strange loop". Which goes into great detail about these very ideas regarding cognition requiring feedback loops in order to better explain choice.

You should check it out!

obviously, the egg... the first chicken wouldn't be there until hatched... something other than a chicken laid the egg, and then the first chicken was here... evolution is a ***** that way...

The confusion between the micro and the macro universe has led many to form specious religious views based on quantum mechanics, but the money still flows from the gullible.

We know that changing magnetic fields creates electricity and changing electrical fields creates magnetism. (Maxwell's equations verify this) Figuring out what started it would give me a mega-headache.

It is because of cause and effect that we believe there is such a thing as time because the movement of things and the effects of things acting upon other things are the temporal markers that give us time.

When you get to a point within consciousness where A causes B causes A, you have gone beyond perceptions of a space-time and you have entered into the singularity where everything “happens” at once.

Time and space is all about consciousness. Everything is all about consciousness.

I thought everything was all about energy and vibration JB . . you changing things up? New Guru? New Book?

What you call the physical universe is all about energy and vibration.

I'll use dehydration as an example. The main reason someone will get dehydrated is because of not enough fluid intake. Which is the reason why they hook you up to an drip full of I.V fluid in hospital. However, if you fill yourself up with more fluids at home, then you could save yourself the trip to hospital. Hot weather is also a cause of dehydration. Over-heated houses, offices, shops, also a cause.