J. Bradford DeLong's Blog, page 295

I think I have got it: Re: Scott Aaronson: It���s hard to...

I think I have got it: Re: Scott Aaronson: It���s hard to think when someone Hadamards your brain: Frauchiger and Renner say: State |��>:

$ |\psi> = \frac{|00> + |01> + |10>}{\sqrt{3}} $

and Alice and Bob will measure the first and second qubits of this state in the basis {+,-}. There are three components to the state |��>, and in them:

|00>: If Alice were to measure in {0,1}, then Alice would know that if Bob were then to measure in {+,-}, Bob would measure |+>. If Bob were to measure in {0,1}, then Bob would know that if Alice were then to measure in {+,-}, Alice would measure |+>.
|01>: If Alice were to measure in {0,1}, then Alice would know that if Bob were then to measure in {+,-}, Bob would measure |+>.
|10>: If Bob were to measure in {0,1}, then Bob would know that if Alice were then to measure in {+,-}, Alice would measure |+>.

Frauchiger and Renner then say: Turn these counterfactual subjunctive "were to measure in {0,1}"s into actual measurements by having Charlie and Dianne do their own measurements in the {0,1} basis on the first and second qubits, branching the universe into (1), (2), and (3).

In this branch Charlie knows that Bob will measure |+> were he to get around to measuring before decoherence of the second qubit takes place, and Dianne knows that Alice will measure |+> were she to get around to measuring before decoherence of the first qubit takes place.
In this branch Charlie knows that Bob will measure |+> were he to get around to measuring before decoherence of the second qubit takes place.
In this branch Dianne knows that Alice will measure |+> were she to get around to measuring before decoherence of the first qubit takes place.

Frauchiger and Renner then say: In each branch, Charlie and Dianne write down, respectively, "I have measured qubit 1 in the {0,1} basis, and I may know that Bob will measure |+>" and "I have measured qubit 2 in the {0,1} basis, and I may know that Alice will measure |+>". They then apply the fact that Charlie and Dianne have measured and the principle of the excluded middle to conclude that it is logically impossible���no matter how the branching has taken place���for both Alice and Bob to simultaneously measure |-->.

Frauchiger and Renner then say: If we then opened the boxes and decohered Charlie and Dianne, we would be done. But...

Frauchiger and Renner then say: Frauchiger and Renner then apply quantum erasers to Charlie and Dianne. The quantum eraser leaves their "I have measured..." messages intact and visible. But the quantum erasers recombines the branches and the restored coherent state is still (or again?) |��>. And then when Alice and Bob do their measurements in the {+,-} basis, 1/12 of the time we find |-->. And so either the principle of the excluded middle or the standard use of the subjunctive must fail for QM to be true.

But actually: State |��>, and Alice and Bob will measure the first and second qubits of this state in the basis {+,-}���

There are three components to the state |��>, and in them:

|00>: If Alice were to measure in {0,1}, then Alice would know that if Bob were then to measure in {+,-}, Bob would measure |+>. If Bob were to measure in {0,1}, then Bob would know that if Alice were then to measure in {+,-}, Alice would measure |+>.

|01>: If Alice were to measure in {0,1}, then Alice would know that if Bob were then to measure in {+,-}, Bob would measure |+>.

|10>: If Bob were to measure in {0,1}, then Bob would know that if Alice were then to measure in {+,-}, Alice would measure |+>.

Frauchiger and Renner then turn these counterfactual subjunctive ���were to measure in {0,1}���s into actual measurements by having Charlie and Dianne do their own measurements in the {0,1} basis on the first and second qubits, branching the universe into (1), (2), and (3).

But, contrary to Frauchiger and Renner's reasoning above, actually:

In this branch Charlie knows that if the wave function has collapsed���if the universe has branched���Bob would measure |+> were he to get around to measuring before decoherence of the second qubit takes place. In this branch Dianne knows that if the wave function has collapsed���if the universe has branched���Alice would measure |+> were she to get around to measuring before decoherence of the first qubit takes place.

 

But Charle and Dianne know that even though they have done their measurements they are in their boxes, and hence the wave function has not yet collapsed���the universe has not yet branched.

 

Thus Charlie and Dianne know that when it comes time for Bob and Alice to do their measurements in {+,1}, there will be contributions not just from the $ \frac{|00>}{\sqrt{3}} $ component of $|\psi>$, but from the $ \frac{|01>}{\sqrt{3}} $ and the $ \frac{|10>}{\sqrt{3}} $ components of $|\psi>$ as well.

 

And so they do not know that if Bob were to measure in {+,-} Bob would measure |+> and that if Alice were to measure in {+,-} Alice would measure |+>.

 

Instead, they know that they are uncertain about what Bob and Alice will measure. They know that the facts that Charlie and Dianne know that they have obtained definite results in the {0,1} basis have (or will have had) no consequences for the true wave function, which remains the original $|\psi>$, and will remain $|\psi>$ until Alice and Bob do their measurements.

Similar...

Similar...

?

And is the lesson that:

(A) Many-worlds does not have a problem if agents properly understand what the branching structure of the universe will be when decoherence occurs.

(B) Other approaches have a big problem, because not even conscious and certain measurement by Turing-Class intelligences justifies a movement from the quantum-superposition to the classical-probabilities level of analysis.

?

I think I have got it!
Apropos of "Wigner Has Many Friends"...
Wigner has many friends, and they can disagree...
Renato Renner and Scott Aaronson: It���s hard to think when someone Hadamards your brain
Daniela Frauchiger and Renato Renner: Quantum theory cannot consistently describe the use of itself
http://nbviewer.jupyter.org/github/braddelong/weblog-support/blob/master/2018-09-27%20Aaronson%2C%20del%20Rio%2C%20Frauchiger%2C%20Renner-%20Quantum%20Theory%20Cannot%20Consistently%20Describe%20the%20Use%20of%20Itself.ipynb

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Kevin Drum: Technology Is the Key to Success, But Probabl...

Kevin Drum: Technology Is the Key to Success, But Probably Not the Technology You Enjoy: "I���d put it more bluntly: unless they���re forced to at the point of a metaphorical gun... service-sector managers are lazy... in a very specific way: they don���t really understand technology...

...hey don���t want to understand technology; and they refuse to bother making their underlings understand technology. They much prefer to do all they stuff they enjoy doing instead: schmoozing customers, holding meetings, reading and writing reports, and so on. As near as I can tell, this hasn���t changed much in the past 20 years, and it���s surprisingly true even in tech companies themselves.... They still don���t care much about the technology behind logistics and marketing and operations. It���s just too boring. And so they leave money on the table. But so does everyone else, so hardly anyone notices since plenty of cash is rolling in anyway. This needs to change. In the same way that successful companies in the 50s benefited from rigorous old-school management techniques that needed to be daily routines, successful companies today need to really, truly, and rigorously insist that everyone from the vice presidents down understands and uses the best possible technology. Stop complaining that it���s boring. Stop complaining that it���s hard to use. Stop complaining that typing is hard because of your arthritis or whatever your excuse of the week is.

If you���re not spending ten hours out of every week deeply engaged with other managers and lower-level workers about the technology that runs your company and how to make it better, then you���re probably wasting your time. Most of you probably spend more time understanding your latest favorite videogame or internet chatroom than you do on the technology that your entire company sits on top of. Good technology, diligently and rigorously applied, is what differentiates companies today. Use it. Hire only people who are willing to use it. And fire anyone who won���t...

#shouldread

Hamilton Project: Place-Based Policies for Shared Economi...

Hamilton Project: Place-Based Policies for Shared Economic Growth: "Depending on where they live, people across the United States experience drastically different economic outcomes...

...It is necessary to understand why some communities have thrived and others have not. Mindful of the ways in which many existing place-based policies have failed, it remains imperative to explore new, evidence-based policy options that can ultimately yield more broadly shared economic growth, including: employment subsidies, educational interventions, and more appropriately targeted federal grants. On September 28, The Hamilton Project at the Brookings Institution will host a forum to explore the most effective policy options to foster place-based policies for shared economic growth. The forum will feature introductory remarks by former U.S. Treasury Secretary Robert E. Rubin and a fireside chat between Deval Patrick, former Governor of the Commonwealth of Massachusetts, and David Leonhardt, associate editorial page editor and op-ed columnist for The New York Times. The forum will also include three roundtable discussions featuring: Rebecca Blank, chancellor, University of Wisconsin-Madison; Shaun Donovan, senior strategist and adviser to the president on Allston and campus development, Harvard University; Maurice Jones, president and CEO, LISC; Frederick Wherry, professor, sociology, department representative, sociology, Princeton University; Louise Fox, chief economist, USAID; Tracy Jan, race and economics reporter, The Washington Post, among other distinguished scholars and experts....

#shouldread

Back in the 1990s we in the Clinton administration put Br...

Back in the 1990s we in the Clinton administration put Breyer on the Supreme Court in the belief that the Court needed somebody who genuinely understood antitrust. But the Republican justices have given him zero deference, even though he knows the issues and they do not. And this is an increasing problem: Fiona Scott Morton: [There is a lot to fix in U.S. antitrust enforcement today(https://equitablegrowth.org/there-is-...): "Last month���s court decision allowing AT&T Inc. to acquire Time Warner Inc. is an example of the inability of our current system of courts and enforcement.... Judge Richard Leon demonstrated a lack of understanding of the markets, the concept of vertical integration, corporate incentives, and the intellectual exercise of forecasting what the unified firm would do... a poor decision...

...The Supreme Court decision in Ohio v. American Express Company further weakens antitrust enforcement by complicating the analysis and raising the standard of proof for platform business cases. There are many other settings where consumers deserve similar efforts to protect competition and where the two federal antitrust agencies have yet to take enforcement steps.... [There] are low-risk and high-return cases for U.S. antitrust agencies to bring... [that] will require the agencies to look beyond old markets with lots of precedent, and instead analyze the products that consumers are now buying such as online hotel bookings, credit cards, technology standards, and mutual funds, or markets where consumers are selling such as labor markets. These are markets that do not have established jurisprudence or a recent history of enforcement.... More novel cases are harder to bring because an existing draft complaint is not already sitting in the files of the enforcement agencies...

#shouldread
#antitrust
#monopoly
#monopsony

Jan Bakker, Stephan Maurer, J��rn-Steffen Pischke, and Fe...

Jan Bakker, Stephan Maurer, J��rn-Steffen Pischke, and Ferdinand Rauch: Trade and growth in the Iron Age: "The first millennium BC... the growth effects of one of the first major trade expansions... the systematic crossing of the open sea in the Mediterranean by the Phoenicians. A strong positive relationship between connectedness and archaeological sites suggests a large role for geography and trade in development even at such an early juncture in history...

...Seafaring in the in the Mediterranean started with hunter-gatherer societies around 10,000 BC; we know that humans began to settle islands at that time (Broodbank 2006).����They also moved obsidian, a volcanic rock, over considerable distances.��With the advent of the sail around 3,000 BC, ships had a considerable cost advantage over land transportation. Regional trade networks grew in importance in the Mediterranean during the next two millennia.����However, most of this sailing was coastal.����While sailors made open sea crossings where they were difficult to avoid, for example to reach Cyprus, Crete, or to cross from Albania to the heel of the Italian boot, coast hugging prevailed elsewhere.����Only from around 900 BC did Phoenician and other sailors begin to systematically and routinely cross the open Mediterranean. A dense trading network began to emerge, and on the eve of classical antiquity, the Mediterranean was constantly criss-crossed by Phoenician, Greek, and other sailors.��This was an expansion in scale and scope far beyond the trading activities which went on before....

We exploit the fact that open sea sailing creates different levels of connectedness for different points on the coast.����The shape of the coast and the location of islands determines how easy it is to reach other points, which might be potential trading partners, within a certain distance. We create such a measure of connectedness for travel via sea. Figure 1 shows the values of this measure on a map and demonstrates how some regions, for example the Aegean but also southern Italy and Sicily, are much better connected than others.��

Measuring growth for an early period of human history is more difficult as we have no standard measure of income, GDP, or even population.����We quantify growth by the presence of archaeologic sites for settlements or urbanisations. While this is clearly not a perfect measure, more sites should imply more human presence and activity. We then relate the number of active archaeological sites in a particular period to our measure of connectedness. We find a large positive relationship between connectedness and archaeological sites.����The effect of connections on growth in the Iron Age Mediterranean are up to twice as large as the effects Donaldson and Hornbeck (2016) found for US railroads. Although these results are unlikely to be directly comparable, the magnitudes suggest a large role for geography and trade in development even at such an early juncture in history...

#shouldread
#economichistory
#globalization

Kate Bahn: @lipstickecon: "This FRB report concludes that...

Kate Bahn: @lipstickecon: "This FRB report concludes that declining prime-age LFP is due to the decline in "traditional blue-collar jobs" without deconstructing what made these 'traditional' jobs good-unions...

...Growing care work jobs could be good "blue-collar jobs" too if we increased the cost of care by internalizing the public benefits of social reproduction. Unions and public support/subsidies can play a critical role in this...

#shouldread

Apropos of Wigner has many friends...: Renato Renner: It�...

Apropos of Wigner has many friends...: Renato Renner: It���s hard to think when someone Hadamards your brain: "Hi Scott: There are currently many who are blogging about our result, so I started to use my little quantum random number generator on my desk: outcome 0 means I don���t react to it, outcome 1 means I write a reply. For your blog the outcome was 1! Now, we are already in a situation that involves superposed agents...

...namely me who wrote this reply and you who are reading it. (I am assuming that you do not believe in objective wavefunction collapses and hence accept assumption Q of our paper.) You would now probably say that this does not prevent us from reasoning as usual, but that we would be getting in trouble if our brains were subject to measurements in the Hadamard basis. So far I would definitively agree. And I would certainly subscribe the claim: ���It is hard (if not impossible) to think after someone has Hadamarded your brain.��� But this brings me to the core of my reply. Note the small difference between my claim and your title. While I agree that it is hard to think after someone has Hadamarded your brain, I do not see any reason to deny that we can think before the Hadamarding.

Talking more technically, the reason why, as you noted, I do not endorse your scenario (the ���Wigner���s friendification of Hardy���s paradox��� or maybe the ���Hardyfication of Wigner���s paradox���) is that it neglects a key element: Your simplified argument completely ignores the timing. But, clearly, it makes a difference whether I think before or after my brain is Hadamarded. In our argument, we were therefore careful to ensure that, whenever one agent talks about the conclusions drawn by another agent, he does so before any Hadamarding. This should be apparent from Table 3 of our paper, which essentially summarises our entire argument. Take, for example, the reasoning by agent $\bar{W}$. He reasons around time 0:23 about the conclusions drawn at time 0:14 by agent F. The key fact to notice here is that both relevant agents, i.e., F and $\bar{W}$, are in a similar situation as we are (hopefully) now when reading this text. While, from an outside viewpoint, they may be in a superposition state, no Hadamard has been applied to them.

The only way I can hence make sense of your claim that we are using an additional implicit assumption in our argument (the chaining of statements) is that you are questioning the step that, in Table 3, corresponds to going from the third column to the fourth (the ���further implied statement���). Did I get this right? (All the other steps are explicitly covered by our three assumptions, Q, C, and S.)

Before concluding, and since you mentioned this several times in your blog, let me stress that ���consciousness��� does not play any role in our argument. The agents may as well be computers, which are programmed with rules corresponding to our assumptions Q, C, and S, and which they use for their reasoning (summarised in Table 3). So, when we talk about ���agents���, we just mean ���users��� of quantum theory. After all, the question we are asking is: ���Can quantum theory be used to consistently describe users of the same theory?��� This question has little to do with consciousness (which is why we tried to avoid this term)...

Scott Aaronson: It���s hard to think when someone Hadamards your brain: "Thanks; I���m glad that my blog post was one of the lucky ones to earn a reply from you! I acknowledge how much care and attention you devote in your paper to the issue of timing...

.... But I contend that, no matter how we formalize the statements in question, and what it means for the agents to ���know��� the statements, there will some place where we illegitimately cross the temporal Rubicon between before and after Charlie���s brain gets scrambled by a measurement in the Hadamard basis. Somewhat flippantly, I might say: we know this must be the case, because the end result contradicts the predictions of QM! More seriously: at two nearby stages of (my version of) your argument, we conclude that Diane���s brain is in the state |1���, and then that Diane���s brain is in the state |+���. So, I can isolate where I get off your train to somewhere between the former statement and the latter one���

Incidentally, point taken about the word ���consciousness.��� But that leads to an interesting question: you say it���s not important if Charlie and Diane are ���conscious���; all that matters is whether they���re ���agents using quantum mechanics.��� But if so, then couldn���t we treat even a single qubit as a ���QM-using agent,��� in the same sense that one qubit could be said to ���measure��� another qubit when they���re entangled? In that case, would you agree that the experimental tests of Hardy���s Paradox have already tested your paradox as well?...

Renato Renner: It���s hard to think when someone Hadamards your brain: "I also felt lucky when I saw that my quantum random number generator chose your blog. But now, after rethinking the consequences that future Hadamards can have, at least according to your interpretation, I am afraid that the result of my random number generator may not even exist...

...More seriously: I would expect that anyone who claims that our argument is flawed should be able to localise the flaw. So, here is the challenge: Read Table 3 (in the order of increasing superscripts, which specify at what time they are made) and identify the first entry you disagree with. This should be a rather easy task: each entry corresponds to a well-defined statement that you (if you were an agent taking part in the experiment and had observed the outcome indicated in the second column, labelled ���assumed observation���) should either be willing to make or not.

Having said this, I would of course never try to impose homework on you, Scott. Therefore, starting from your analysis of your simplified ���Alice-Bob-Charlie-Diane��� argument, I tried myself to reverse-engineer what you would say about our original thought experiment. This reverse-engineering is certainly not unique (partially because you dropped all timing information). However, I found that the only statement to which your concern that we ���illegitimately cross the temporal Rubicon��� may apply, at least remotely, is the very first of the table, i.e., $\bar{F}^{n:02}$, for it relates an observation at time n:01 to an observation at time n:31. But my conclusion would then be that you just disagree with Assumption Q (which would of course be fine).

Unrelated to this: Your question about experimental tests is indeed an interesting one. I���ll comment on it later (to avoid making this comment even longer)...

Diane Coyle: The Long Arc of UK Productivity: "Nick Craft...

Diane Coyle: The Long Arc of UK Productivity: "Nick Crafts has a compact book... about the trajectory of the British economy... Forging Aahead, Falling Behind and Fighting Back.... Nick���s somewhat idiosyncratic���but highly plausible���view that the seeds of the country���s post-world war 2 relative decline were sown in the institutions that enabled it to perform so well during the 19th century...

...The argument is that being caught up by other countries was no shame, but being overtaken in absolute income per capita levels by all other comparator countries in the second half of the 20th century reflected significant policy failures. The policy failures, in Nick���s view, date to the emergence of liberal market economy institutions in the early phases of the Industrial Revolution.�� Although understandable at the time���notably the development of equity financing with dispersed shareholdings, rather than bank financing, and decentralized strong craft unions due to the importance of skilled labour for the young technologies���their persistence into the 20th century meant Britain lacked the ���social capability��� that would have enabled it to take productive advantage of 2nd and 3rd Industrial Revolution technologies. The continental co-ordinated market economies fared better. The other key policy failure underlined in the book is the weakness of competition policy in the domestic market, combined with the slow removal of barriers to competition from imports due to delayed entry into the European Economic Community.... It���s a persuasive account...

#shouldread

Judea Pearl: "Confounders, Colliders, and Mediators: As y...

Judea Pearl: "Confounders, Colliders, and Mediators: As you surely know by now, mistaking a mediator for a confounder is one of the deadliest sins in causal inference and may lead to the most outrageous errors. The latter invites adjustment; the former forbids it..."

Antitrust law and policy is probably the most "relatively...

Antitrust law and policy is probably the most "relatively autonomous" piece of our whole legal system. The laws as enacted by Congress and signed by the President change rarely and slowly. How those laws are enforced���and how business is then conducted in the shadow of the possibility of resort to the courts for antitrust cases���changes much more radically and substantially. It is a dance of intellectual fashion, some serious benefit-cost analysis, and a great deal of lobbying and lobbying-funded motivated reasoning. My view is that the answers to the three questions Michael Kades suggests the FTC examine are: yes, no, and no, respectively. But it is very good that the FTC is thinking about this: Michael Kades: In re: Competition and Consumer Protection in the 21st Century: "Equitable Growth suggests that the hearings include the following three topics: 1. Is monopoly power prevalent in the U.S. economy?...

>...2. Do the antitrust laws as applied by the courts correctly balance the benefits and costs of deterring anticompetitive conduct and permitting procompetitive conduct?... 3. Does the Federal Trade Commission have the resources it needs to fulfill its competition mission?...

#shouldread