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The Quantum Agent
Investigating how the quantum measurement process might be related to the emergence of intelligence, agency and free will.

First Things First: The Physics of Causality
Why do we remember the past and not the future? Untangling the connections between cause and effect, choice, and entropy.

Can Time Be Saved From Physics?
Philosophers, physicists and neuroscientists discuss how our sense of time’s flow might arise through our interactions with external stimuli—despite suggestions from Einstein's relativity that our perception of the passage of time is an illusion.

A devilish new framework of thermodynamics that focuses on how we observe information could help illuminate our understanding of probability and rewrite quantum theory.

Gravity's Residue
An unusual approach to unifying the laws of physics could solve Hawking's black-hole information paradox—and its predicted gravitational "memory effect" could be picked up by LIGO.

February 27, 2020

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Emergent Reality: Markus Müller at the 6th FQXi Meeting
By IAN DURHAM • Jan. 10, 2020 @ 19:55 GMT

At the 5th International FQXi conference in 2016, participants were given a marker and asked to write something on their conference badge that might serve as a conversation starter. It could be a bold statement or a single word. The only requirement, if I recall, was that it had to have something loosely to do with the theme of the conference (that is, the organizers didn’t want anyone putting random words like “potato” on their badges). In what I perceived as a show of defiance against certain elements in the community, I wrote “objective reality exists” on mine. No one noticed. To be fair, I don’t think anyone actually paid much attention to anyone else’s name tag. Nevertheless, in my own mind, it felt like I took a stand on something important (feel free to laugh at that).

I still firmly believe that objective reality exists in some form, but in the past few years, I have begun to think that the story may be a bit more complicated than I’d originally thought. I have always thought that there are aspects of the universe that are necessarily emergent and I have also long believed that “reality” is fundamentally relational in a certain sense. As an anonymous reviewer once wrote in Philosophical Magazine (which, despite its name, is actually a physics journal), science is the “rational correlation of experience.” That is, if we view science as uncovering the parts of the world that can be “objectively” known, then this knowledge is necessarily correlative and therefore relational.

To be clear, this does not deny that there is a reality outside of this correlative experience. It simply says that this experience is what constitutes an objective reality since it assumes that objectivity, in this sense, is common experience that can be rationally agreed upon. Certainly this is not a perfect definition, but there is an element of truth to it. Falsifiability only has real weight in a relational sense since it requires some kind of comparison.

At any rate, this all suggests a number of things. First it suggests that objective reality is emergent (though, again, it does not outright deny a more fundamental, non-emergent reality). But it also suggests that the very concept of objectivity requires observers of some sort. To put it another way, if science is the rational correlation of experience, then there must be observers whose experience is being rationally correlated.

In his talk at the 6th International FQXi conference, Markus Müller
Markus Müller at the 6th FQXi meeting in Tuscany.
pointed out that this suggests that perhaps the laws of physics themselves only apply at the observer level. The external world described by these laws would thus be emergent. Specifically what Müller suggests is that this objective external world must be an emergent approximation of something more fundamental but potentially inaccessible.

Müller’s work, which is developed in detail in a recent preprint, specifically makes reference to John Wheeler’s concept of “law without law” according to which there actually are no fundamental laws and the universe’s basic building blocks are random, possibly chaotic quantum phenomena.
Physicist John Wheeler, originator of the concept of
He begins by committing to the first-person perspective of observers as being fundamental. This is in contrast to most theories which take the third-person perspective representing “the world” to be fundamental. In other words, Müller does not assume that there is necessarily an objective, external world. Rather, he seeks to place the question “What will I see next?” at the center of the story. Using algorithmic information theory, he then proceeds to show that an objective, external world naturally emerges from a basic set of postulates that includes the first-person perspective under the guise of “observer states”. Specifically he shows that, in the presence of enough information, the first-person and third-person perspectives are equivalent; absent sufficient information, they are not. Müller goes on to show that switching to a fundamental first-person perspective can dissolve the famous Boltzmann brain problem from cosmology and can offer interesting insights into the brain emulation problem from AI.
Ludwig Boltzmann, who originally proposed the idea of Boltzmann brains.

To be clear, Müller isn’t necessarily making the claim that this is how the world works. He’s simply attempting to show that one can devise a self-consistent theory that begins with a first-person perspective and that then leads to an emergent third-person perspective. As with most physical theories, the aim is to chip away at our understanding of the world. In Müller’s case, it is to say that maybe we should reconsider how we formulate our theories, which overwhelmingly assume a third-person perspective.

As I mentioned before, though I firmly hold that objective reality in some form exists, I have come to realize that it may not come in quite as simple a form as I had originally thought. One of the reasons for the change in my thinking on this topic is my recent involvement in a program called Science for Monks and Nuns which aims to bring science to Tibetan Buddhist monastic communities. (Several FQXi members have been involved in this program including Tim Maudlin, George Musser, Howard Wiseman, and the late David Finkelstein.) Buddhist philosophy, like science, does not have a single, established view on reality. Rather it is divided into various schools of thought. One such school of thought, known as Cittamātra or Yogācāra, sometimes referred to as the “Mind Only” school, flatly denies the existence of an objective, external world. By contrast, Madhyamaka, also known as the “Middle Way”, posits that the external world is essentially one of co-dependent origination. That is, it posits that nothing has its own intrinsic nature. In other words, nothing has any meaning without reference to something else.
A Buddhist philosophy classroom at the Tibetan Government in Exile compound in Dharamsala, India.

In his FQXi conference talk, Müller employed the phrase “mind before matter” to emphasize the point that, in his model, the observer state is fundamental and gives rise to an objective, external world. His model seems to include elements of both the Mind Only and Middle Way schools of Buddhist philosophy. Similar to the Mind Only school, Müller’s model takes first-person perspective observer states as fundamental. However, his model allows for the mutually dependent emergence of a third-person external world in a manner that is reminiscent of the Middle Way’s co-dependent origination.

I want to emphasize that I am not an expert on Buddhism by any stretch. But my time working with the monks and nuns has changed my perspective on reality and I found the similarities with Müller’s purely scientific model to be striking.

At any rate, I think Müller’s model holds a great deal of promise for explaining the quantum/classical contrast. Perhaps the world really is fundamentally quantum and the objective reality of classical physics is an emergent phenomenon. It doesn’t make that reality any less real. It simply might be that it’s not fundamental.
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2019: The Physics Year in Review
By ZEEYA MERALI • Dec. 29, 2019 @ 19:47 GMT

As 2019 draws to a close, we're counting down some of the biggest stories in foundational physics and related fields.

Once again, items have been chosen by quantum physicist Ian Durham, of Saint Anselm College in New Hampshire.

In the first part of the rundown, Ian lists a few highlights that haven't quite made his top 5, but which are nonetheless noteworthy. I'll be posting his top 5 soon. Listen to the podcast and let us know, if you agree (or disagree) with his choices.

And in the second part, Ian completes his list -- and admits he struggled with which of top two should come in first.

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2019: Year in Physics Review Part 1 Beginning our countdown of the biggest stories of the year in physics, as chosen by quantum physicist Ian Durham.


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2019: Year in Physics Review Part 2: Concluding our countdown of the biggest stories of the year in physics, as chosen by quantum physicist Ian Durham.


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Consciousness in the Physical World: Call for Proposals
By DAVID SLOAN • Dec. 28, 2019 @ 16:56 GMT

We're happy to announce that we are opening a call for proposals to focus on 'Consciousness in the Physical World'. Generously supported by the Fetzer Franklin Fund, we're looking for ideas coming from a broad range of scientists on the nature of consciousness and what makes for a conscious agent.

Following on from our calls on intelligence and agency, this time the focus on consciousness aims to promote the use of the large swath of recently developed tools and ideas to look for new insights.

The complete timeline is available, together with an FAQ and some examples of ideas and questions.

We have around $1.8 million in total funding available, so get your thoughts and ideas together, build a proposal and head over to the application form.
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Undecidability, Uncomputability, and Unpredictability - FQXi's New Essay Contest
By DAVID SLOAN • Dec. 24, 2019 @ 22:34 GMT

At FQXi we're excited to launch our latest essay contest, with generous support from the Fetzer Franklin Fund and the Peter and Patricia Gruber Foundation. The topic for this contest is: Undecidability, Uncomputability, and Unpredictability.

For a brief time in history, it was possible to imagine that a sufficiently advanced intellect could, given sufficient time and resources, in principle understand how to mathematically prove everything that was true. They could discern what math corresponds to physical laws, and use those laws to predict anything that happens before it happens. That time has passed. Gödel’s undecidability results (the incompleteness theorems), Turing’s proof of non-computable values, the formulation of quantum theory, chaos, and other developments over the past century have shown that there are rigorous arguments limiting what we can prove, compute, and predict. While some connections between these results have come to light, many remain obscure, and the implications are unclear. Are there, for example, real consequences for physics — including quantum mechanics — of undecidability and non-computability? Are there implications for our understanding of the relations between agency, intelligence, mind, and the physical world?

In this essay contest, we open the floor for investigations of such connections, implications, and speculations. We invite rigorous but bold and open-minded investigation of the meaning of these impossibilities for reality, and for us, its residents. The contest is open now, and we will be accepting entries until March 16th.

Note: Despite a slight slip on the contest page, we aren't looking at time travel for essay entries! The real timeline is available which might be more helpful to those who don't have access to a flux capacitor.
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Watching the Watchmen: Demystifying the Frauchiger-Renner Experiment — musings from Lidia del Rio and more at the 6th FQXi Meeting
By GEORGE MUSSER • Dec. 24, 2019 @ 19:04 GMT

Credit: Lidia del Rio
Even by their usual excitable standards, the physicists and philosophers who study the foundations of quantum mechanics have been abuzz about a thought experiment first proposed in 2016 by Daniela Frauchiger and Renato Renner at ETH Zurich, and later published in Nature Communications (Frauchiger, D., Renner, R. Quantum theory cannot consistently describe the use of itself. Nat Commun 9, 3711 (2018)). A blog post about it by Scott Aaronson of the University of Texas drew nearly 300 comments, and sparks flew at the two most recent FQXi meetings. So it was high time for me to buckle down and make sense of the experiment.

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An amped up version of the Schrodinger Cat Paradox spells trouble for all quantum interpretations -- according to its architect Renato Renner. He tells Zeeya and Brendan how the controversial thought experiment works, and why he thinks it is bad news for fans of Many Worlds and quantum parallel universes, QBism, Collapse models and (less so) for Bohmian interpretations of quantum mechanics. But not everyone agrees.


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You can listen to a detailed rundown of the thought experiment for beginners, in which Renner talks through each step, on the podcast. He also describes the controversy his paper caused, and how fans of various interpretations of quantum mechanics—including Many World's, QBism, Bohmian mechanics and Collapse models—argue that the paradox actually supports their preferred model, while ruling out its rivals. But Renner, as you'll hear, disagrees, explaining that in his opinion, no current interpretation can provide a satisfactory way out of the paradox.

I've come up with my own way of describing it—vetted by Renner—and put it into the form of a quantum circuit that I've run on IBM's cloud quantum computer. Renner says it is the first experimental implementation of his experiment. (A closely related experiment proposed by Časlav Brukner of Institute for Quantum Optics and Quantum Information in Vienna has already been performed (Science Advances  20 Sep 2019: Vol. 5, no. 9, eaaw9832).) The interpretive dispute will no doubt rumble on. But what makes quantum physics fun is the journey, not the destination.

The experiment engineers a contradiction between third- and first-person views: the objective perspective that physics traditionally provides and the experience of an embedded observer. "In physics we try to build a theory of the world as seen from the outside, as God would see it," Renner's colleague Lídia del Rio said at this year's FQXi meeting in Tuscany. "But of course, to do this, we have only, as a basis, our own observations. We are always talking about the point of view of some observers, and the best we can do is talk to each other, compare observations, and try to build a consistent picture." In the Frauchiger-Renner experiment, observers find themselves weirdly unable to do this. "The agents will make some inferences about each other's results, which in the end will be contradictory," del Rio said.

These days, especially, it seems naïve to expect that we could reach consensus through dialogue. But et tu, physics?

Becoming One With Nature

As usually presented, the experiment involves a convoluted series of measurements and logical deductions. But stripped to its essence, all you are doing is measuring a pair of entangled particles in two different ways. Normally, the first measurement of a particle would disturb it, spoiling the second. But Frauchiger and Renner propose a trick to measure and remeasure the particle in its pristine state: combine a direct and an indirect measurement. One observer measures the particle, and another measures the first observer. The first measurement transfers the state of the particle to the combined system of particle and observer, making it available for a second look. Frauchiger and Renner argue that, in specific cases, the indirect measurement is just as good as a direct one.

So, this experiment has the feature that observers are themselves observed. In most presentations of the experiment, the observers are human beings, but they could be just particles. All they have to do is make a prediction on the basis of quantum theory, and, for Frauchiger and Renner's scenario, that is a simple logical operation. Swapping particles for people makes the whole business of observing-the-observer seem less mysterious and implausible. That said, it also lessens the philosophical puzzle, because only if the observers are people can they be said to have a first-person viewpoint.

This procedure requires four observers in all, two for each of the entangled particles. Let's call those making the direct measurement the "friends" and those making the indirect measurement the "Wigners," in homage to the physicist Eugene Wigner, who was one of the first to note that observing the observer is a useful test case for interpretations of quantum theory. If the particles are photons, the observers measure their polarization using a special light filter. The friends orient their filters horizontally, and the particle either passes through (0) or reflects off (1). The Wigners orient theirs diagonally, and again the particle either passes through (+) or reflects off (–). So, that's four results to compare:

1. What a friend saw for the first particle vs. what a friend saw for the second

2. What a Wigner saw for the first particle vs. what a friend saw for the second

3. What a friend saw for the first particle vs. what a Wigner saw for the second

4. What a Wigner saw for the first particle vs. what a Wigner saw for the second

The team creates and measures multiple pairs of particles to see the statistical trends. The particles are entangled in a way devised by Lucien Hardy of the Perimeter Institute in 1993. This state can be written in four equivalent ways corresponding to the above cross-comparisons:

1. |00> + |01> + |10>

2. |+0> + |+1> + |–1>

3. |0+> + |1+> + |1–>

4. |++> + |+–> + |–+> – |– –>

To write these is just an exercise in geometry, using the fact that diagonal is part horizontal and part vertical. I am neglecting the exact probabilities for these sundry outcomes; Hardy considered a range of values. What's important is that, in the first three formulas, only three of the four possible outcomes arise, whereas in the fourth all can occur. Hardy showed that such a pattern is hard to explain and seems to require some spooky coordination among the particles.

Frauchiger and Renner have a different aim. They don't seek to explain how the particles could exhibit this pattern, only what happens if they do. Because the first three formulas contain a restricted set of outcomes, a friend can sometimes be certain what a Wigner will see, and vice versa. Based on that, we can draw some conclusions for what they will see and surmise.

When the first friend measures 0, she can conclude the second Wigner will measure + (per #3).

When the second friend measures 1, she knows the first friend must have measured 0 (per #1) and concluded that the second Wigner will measure +. The second friend adopts this prediction as her own, on the assumption that if you know that someone knows something, you know that thing, too—a principle that philosophers call "closure."

When the first Wigner measures –, he knows the second friend must have measured 1 (per #2). He now adopts the friend's prediction.

But sometimes when the first Wigner measures –, the second Wigner will measure –, too (per #4). That violates the prediction. Paradox!

Winding Back the Clock

When critics such as Aaronson say Frauchiger and Renner got it wrong, they are not disputing that the experiment gives the results it does. It's the interpretation that riles them.

Many have latched onto the strange feature that the observers are themselves observed. Observation is not a passive operation, but a thoroughgoing alteration. In the course of doing their indirect measurement, the Wigners undo the friends' direct measurement and wipe their memory. The friends see something, then un-see it. To them, it is as though nothing has happened; when the experiment wraps up and everyone else goes out for after-work drinks, the friends are still sitting there asking, "When will the experiment start?" In some descriptions of the experiment, it's even worse: they enter a Schrödinger-cat-like state of complete ambiguity. This makes The Matrix or brain-in-vat scenarios look tame by comparison. It's one thing to imagine that our world is a virtual projection, another that someone could reach directly into our brains and decide what we think.

At the meeting in Tuscany, Aaronson and Raphael Bousso at U.C. Berkeley argued that if you can't trust in your own integrity as a reasoning agent, you shouldn't be surprised to encounter contradictions such as the one in Frauchiger-Renner. By screwing with the friends' temporal continuity, the experiment smashes the chain of logical statements. If someone has made an observation and then un-made it, you can't base any conclusions on that observation.

Renner and del Rio reply that the experiment is staged to avoid this problem. The friends do get wiped, but by that point, they have no further role to play in the experiment. Whatever they saw and concluded has already been incorporated into the analysis, and nobody refers to it again. Now, you might wonder, if their memory is wiped, then how can any record of their observation endure? This is the most critical part of the experiment. Most of the time, it is true that no record endures. But when the conditions I laid out above are satisfied—namely, when observers are able to make definitive predictions for one another—information lives on. That happens for one in six trials (given the specific Hardy state used by Frauchiger and Renner), and a contradiction arises in half those cases. Thus the experiment walks a line: in undoing an observation, it sometimes preserves a trace of it.

Making the Circuit

This can be illustrated by a quantum circuit—that is, an algorithm that can be implemented on a quantum computer. If you're new to quantum circuits, this section will probably make zero sense. The main takeaway is that the circuit shows how the observers don't need to be humans. Also, the circuit lays bare the sequence of events and the conditions under which information can endure, allaying some of the skeptics' misgivings.

I've implemented the circuit using Quirk, an online quantum simulator created by Craig Gidney in Google's quantum-computing group. (Gidney has his own circuit version of the Frauchiger-Renner experiment.) You can run and modify the circuit for yourself.

I'm attaching a PDF version of this circuit to this post. If you scroll down to the bottom of the post, you can click "Quirk_circuit.pdf" to open a larger version, so you can more easily see the details.

Here, the observers are abbreviated F1 and F2 (the friends) and W1 and W2 (the Wigners). The first two wires (horizontal lines) are qubits representing the entangled particles. The next two are flags indicating whether a given observer is able to make a firm prediction. The following two are the actual predictions. Although we have four observers, we need only two sets of wires, since we track only two observers at a time. The bottom wire is a workspace where observers compare their results and confirm they are entitled to make the inferences they do—an aspect of the Frauchiger-Renner experiment that tends to get overlooked.

Quirk has a nice set of probes—colored green or cyan—that show the qubit values and their correlations at any stage nondestructively. The two boxes with four little yellow circles are custom operations to create or manipulate the Hardy state. The rest of the symbols are standard quantum circuit symbols.

The steps in the procedure are:

1. Hardy state preparation

2. F1 measures particle 1. If 0, F1 is able to make a firm prediction—namely, that W2 will measure + (0). Otherwise F1 assigns equal probabilities to + (0) and – (1).This gives formulation #3 of the Hardy state.

3. F2 measures particle 2. If 1, F2 is able to make a firm prediction—namely, that F1 measured 0. Otherwise F1 assigns equal probabilities to 0 and 1. This gives formulation #1 of the Hardy state.

4. If F2 does make a firm prediction for F1, she can further conclude that F1 has made a firm prediction for W2—namely, that W2 will measure + (0)—and hence can provisionally adopt that prediction as her own. Because of the sign conventions adopted in this circuit, F2’s prediction for F1 (in the 0/1 basis) is automatically a prediction for W2 (in the +/– basis).

5. F1 and F2 confer and check for two errors. First, whether, when F2 is able to make a firm prediction for F1 and W2, F1 either (i) could not make a firm prediction for W2, or (ii) made a different prediction. This tests the assumption of transitivity of knowledge. Note that F2 can adopt a prediction only if it is firm; if she tried to adopt probabilistic predictions, the next step would fail. A firm prediction can be made without using two-qubit gates. This selective reasoning is the main asymmetry in the experiment.

6. F1’s role is over, so her measurement can be undone, clearing the way for W1 to make his. F1’s prediction qubits can be put to other uses.

7. W1 measures particle in the +/– basis. If – (1), W1 is able to make a firm prediction—namely, that F2 measured 1. Otherwise W1 assigns weighted probabilities to 0 and 1. This gives formulation #2 of the Hardy state.

8. If W1 does make a firm prediction for F2, she can further conclude that F2 has made a firm prediction for F1 and thus for W2 and hence can provisionally adopt that prediction as her own. Because of the sign conventions in this circuit, we have to invert W1’s prediction for F2 in order to interpret it as a prediction for W2.

9. W1 and F2 confer and check whether, when W1 is able to make a firm prediction for F2 and W2, F2 either (i) F2 could not make a firm prediction for W2, or (ii) made a different prediction. As in step #5, W1 can adopt only a firm prediction or else the next step would fail.

10. F2’s role is over, so her measurement can be undone, clearing the way for W2 to make his.

11. W2 measures particle 2 in the +/– basis and obtains statistics for formulation #4 of the Hardy state, including -- (11) one run in 12.

12. W1 and W2 confer and check whether W1 erred, i.e. whether he predicted + (0) with certainty yet W2 obtained 1 (–). And he did err for one run in 12, half his predictions.

Just for fun, and just because I could, I ran this circuit on the IBM Q Experience online quantum computer. IBM's interface is sleek and easy to use, but I had to strip down the circuit to accommodate the hardware's limitations, not all of which are documented. I'm grateful to Paul Nation at IBM's Quantum Computing group for his help. The output is now a single error bit signaling a paradox: the second Wigner didn't observe – (1) as the other observers had predicted.

First I ran the circuit on IBM's own simulator and got such an error in 86 of 1024 trials, closely matching the theoretical prediction of one in 12. Then I ran it on an actual quantum computer located in Ourense, Spain. It was just as easy as running the simulator and took less than a minute. I got 461 errors in 1024 trials. This higher value suggest that the device is rather noisy. The other processors that IBM makes available gave similar results. I also checked some of the intermediate values and, not surprisingly, the early steps roughly match theory, while later ones deviate significantly.

To Each His Own

So, if the strange wiping of memory doesn't account for the paradox, what does? It comes down to the unpalatable choice between quantum physics and the objectivity of knowledge.

Quantum physics says the second friend does not—and could not—measure the second Wigner directly. If you can't measure something even in principle, most physicists would question whether that thing exists, in which case there isn't any such thing as a direct comparison of these two observers, and the observers commit a fallacy by pooling their knowledge to draw the comparison nonetheless. Yet pooling knowledge is what scientists do. They couldn't function otherwise.

If you accept quantum mechanics as hard fact, but then weaken the category of "hard fact," haven't you swallowed your own tail? Physicists created the theory and proved it experimentally by stringing together inferences. Every measurement they make is indirect—a long chain of "if this, then that" stretching from the state of a particle to a signal a human can perceive. Those who would give up objectivity to save quantum mechanics may lose both. (That said, maybe quantum mechanics has a theory of knowledge tucked inside it in the form of quantum Darwinism, see "The Evolution of Reality.")

Carlo Rovelli and others have argued for years that quantum mechanics is perspectival: there is no third-person view at all. They still accept some kind of postulate of consistency: observers' viewpoints may differ, but must mesh whenever they come into contact, so that no out-and-out contradiction arises. Yet they remove the most natural explanation for that consistency: a world independent of us. Frauchiger and Renner's experiment might nudge more people to adopt a perspectival view, but heightens the puzzle of how we ever come to any agreement.
attachments: Quirk_circuit.pdf
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