Friday, October 28, 2016

Economist shouldn't be used as source for what is "scientific"

Update 30 October 2016: George H. Blackford responds in comments below (and here). I agree with his point that the lack of consensus on dark energy in physics is trivial (i.e. it has no effect on humans) compared with the real world consequences of a lack of consensus on economic policy. Additionally, a distinction should be drawn between Milton Friedman's "as if" methodology itself and how it is perceived in economics (e.g. Noah Smith seems to exhibit the perception, disagreeing with it [I responded to this here]). I will follow up with more after taking some time to digest George's comments.
Update 1 November 2016: We have blogging sign! The response has posted.


Here we go again (here, here). The author of this terrible article is George Blackford, who has a Phd in economics. Since economics is oh so scientific in its approach, we should of course consult an economist on how to be scientific. Blackford takes a dim view of Friedman's "as if" approach:
Economists Should Stop Defending Milton Friedman’s Pseudo-science 
On the pseudo-scientific nature of Friedman’s “as if” methodology
... Friedman poses [the billiard player] analogy in the midst of a convoluted argument by which he attempts to show that a scientific theory (hypothesis or formula) cannot be tested by testing the realism of its assumptions. All that matters is the accuracy of a theory’s predictions, not whether or not its assumptions are true. 

Let me borrow from Wikipedia:
Effective theory 
In science, an effective theory is a scientific theory which proposes to describe a certain set of observations, but explicitly without the claim or implication that the mechanism employed in the theory has a direct counterpart in the actual causes of the observed phenomena to which the theory is fitted. I.e. the theory proposes to model a certain effect, without proposing to adequately model any of the causes which contribute to the effect. ...
In a certain sense, quantum field theory, and any other currently known physical theory, could be described as "effective", as in being the "low energy limit" of an as-yet unknown "Theory of Everything".
The extra underlining is mine. The way physicists understand all of physics today is as an effective theory. Planets move according to Einstein's general relativity as if spacetime was a kind of 4-dimensional rubber sheet bent by energy. In fact, gravity might well be a fictitious entropic force based on information at the horizon. Or it could be strings. But for most purposes, it behaves as if it is a rubber sheet.

So what Blackford considers to be pseudo-science is in fact precisely science. That's a pretty bad starting point, but it keeps getting funnier every time I read it ...
Now it seemed quite clear to me back in 1967, and it still seems quite clear to me today, that it is the purview of engineering, not science, to catalog the circumstances under which a theory works and does not work and to estimates the errors in the predictions of theories along with the cost involved in using one approach or another.
I busted out laughing when I read this. Funny story. One of the people on my committee at my thesis defense asked me exactly this question about the chiral quark soliton model -- where does it work, and where does it fail. Little did I know that Blackford had figured out back in 1967 that this kind of question should have been reserved for an engineering graduate student, not a theoretical physicist. I've been using Noah Smith's words for this: defining "scope conditions".

I also work as an engineer, and this is not what engineers do either. Engineers design and build systems using existing science. Sometimes they find limits or new things when they do.

Blackford continues to demonstrate his naivete about science:
The fundamental paradigm of economics that emerged from this methodology not only failed to [anticipate] the Crash of 2008 and its devastating effects, it has proved incapable of producing a consensus within the discipline as to the nature and cause of the economic stagnation we find ourselves in the midst of today.
In order to tell whether or not the global financial crisis could be anticipated by the correct economic theory, you would in fact have to have that correct economic theory in hand. As it goes, modern economics generally says the timing of recessions, like say, the timing of earthquakes, is random. Therefore the failure to anticipate the crisis is not evidence against the theory. In fact, it is actually the ability to anticipate the crisis that would be evidence against it! [However, this does not however confirm the theory. Just because you can't predict crises, doesn't mean no one can predict crises.]

Currently physicists are incapable of producing a consensus within the discipline as to the nature of dark energy. Does this mean the fundamental paradigm of physics is flawed? No, it just means you don't understand everything yet.

I called this naive view of science "wikipedia science". Everything is supposed to have a consensus answer already. This is how science that is taught in grade school works, but not how science as practiced by scientists works.

Some other funny bits ...
Newton’s second law assumes that force is equal to mass times acceleration.
It does not. It defines force as the rate of change of momentum.
If it could have been shown that any of the assumptions on which the derivation of the Newtonian understanding of this law depend were demonstrably false, the Newtonian understanding of this law would most certainly not have been accepted, at least not by physicists.
I like the idea of physicists existing at the time of Newton. Reading his journal articles and writing comments in response. But they were called natural philosophers (physic had more to do with medicine at the time), and there really wasn't a codified scientific method at the time. People had accepted hundreds of things that were demonstrably false at the time -- and "physicists" understood Galileo's bodies falling at the same rate without air resistance despite no experiment being done until hundreds of years later.

I also assume c = ∞ (or more technically v/c << 1) all the time. It is demonstrably false (for hundreds of years). Basically, I take Galilean invariance to be an effective description of Lorentz invariance. The most accurate theory in the universe (quantum field theory) assumes spacetime isn't curved (even though it is).
 ... all of the major advances in the physical sciences that have come about since the time of Galileo were accomplished as a result of 1) Galileo rejecting the unrealistic assumptions of Aristotle, 2) Newton rejecting the unrealistic assumptions of Galileo, and 3) Einstein rejecting the unrealistic assumptions of Newton
The assumptions weren't rejected because they were unrealistic. They were rejected because the theory was wrong and a new theory was put forward that was more empirically accurate.

I also know some biologists and chemists that would probably object to saying this about "all of the major advances in the physical sciences". 
... mainstream economists justified on the basis of an economic theory that assumes speculative bubbles cannot exist ...
This is not an assumption, but a consequence of the assumptions (that agents are rational), and in fact a consequence of one particular economic theory. There is lots of research in this area. For example, here is my copy of mainstream economists Carmen Reinhart and Kenneth Rogoff's book [pdf]:

This is also pretty funny:
Friedman is quite wrong in his assertion that there is a “thin line . . . which distinguishes the ‘crackpot’ from the scientist.” That line is not thin. It is the clear, bright line that exists between those who accept arguments based on circular reasoning and false assumptions as meaningful and those who do not.
There may be a bright line, but given the things he's said, I'm not sure Blackford knows where it is. He should definitely not be the one guiding us.


To be continued ...

... And here we go:
Friedman argues that the relevance of a theory cannot be judged by the realism of its assumptions so long as it is also argued that it is as if its assumptions were true. Aside from the fact that this argument makes absolutely no sense at all as a foundation for scientific inquiry, it begs the question: Why should mainstream economists be taken seriously if their theories and, hence, their arguments are based on false assumptions?
Now it is true that saying a theory is an effective theory are not a defense against investigating the assumptions. "False" (according to understanding at the time) assumptions leading to a correct understanding or empirical success are a really good source of new discoveries. For example, according to all known science at the time, discrete, quantized photons were in contradiction to the enormously successful Maxwell's theory of continuous electromagnetic fields. However Planck used this "false" hypothesis (at the time) and was able to describe blackbody radiation. The logical reconciliation of Maxwell and Planck's hypothesis did not come until fifty years later with quantum electrodynamics.

Basically, there is no way to tell whether "false" assumptions we have today are really "false" in the eventual theory. Rational agents are "false" empirically based on experiments with real humans. Homo economicus is very different from Homo sapiens. However, it may well be that Homo economicus is emergent. So saying the assumption of rational agents is false might be correct for the micro theory, but is wrong for the meso- theory and macro- theory.

Also, I can't stand this new understanding of the phrase "begs the question". That's just my opinion.
Is it any wonder that this [economic] paradigm ignores the relevance of the essential role of cooperative action through democratic government
I'm pretty sure that government spending is discussed as part of mainstream economics. Let me check. Yep [pdf]. Is this supposed to be some kind of other role? Has Blackford come up with an economic theory that is more empirically accurate than mainstream economics that fits his assumption of the primacy of government (that differs from mainstream theories where government actions matter)? If he hasn't (and he hasn't) then Blackford is being seriously hypocritical. He is committing the exact same crime (assuming an unrealistic role of government for which there is no empirical evidence) he accuses Friedman of (assuming an unrealistic role of rational agents for which there is no empirical evidence).
To the casual observer it would appear that as a result of the policies supported by mainstream economists over the past fifty years ... eventually led to the Crash of 2008
Point of fact: there have been fewer recessions in the US in the past 50 years (7) than in the prior 50 years (11). The past 50 years included the so-called "Great Moderation", and the recessions of 1966-2016 were also milder than those of 1916-1966 (which included the Great Depression). Is Blackford going to use a single data point as evidence for the failure of mainstream economics? Apparently, yes. And here he is trying to lecture people about what is "scientific"!
... the fundamental paradigm of economics that has emerged from these accomplishments is incapable of providing a consensus within the discipline of economics as to the nature and cause of the economic stagnation we find ourselves in the midst of today. To make matters worse, the kind of explanation of this stagnation given above cannot even be examined within the context of this fundamental paradigm let alone understood within this context since the effects of accumulating debt or of changes in the distribution of income are assumed to be irrelevant within this paradigm.
Just because it hasn't done so yet doesn't mean it is incapable. Again, physicists have no consensus about what dark energy is. This doesn't mean physics is incapable of coming up with one.

And you can look at economic stagnation in terms of the mainstream paradigm (and even with a neoclassical slant that Blackford continues to conflate with mainstream economics). And there have been studies of accumulating debt and income distribution. It's just hard to see any real effect in the data. And again we have an example of assumptions made because Blackford thinks they should be included, but doesn't provide us with a more empirically accurate theory based on their inclusion.

There is a big difference between mainstream economics refusing to acknowledge things that are important and mainstream economics ignoring you because those so-called important things don't seem to have a measurable effect or lead to a more accurate theory.

* * *

I'd like to take a moment and say that while unrealistic assumptions are may definitely be a soft spot in a theory, so is including things in the theory because you think they are important rather than because they have been demonstrated to improve the theory.

In the 1800s, it was considered realistic to include aether -- because waves obviously have to propagate in some medium, right? The thing is, sometimes it's hard to tell which of your assumptions are aether and which are the invariance of the speed of light ahead of time. Without comparing to the empirical data, you really don't know what's realistic and what's not.

What if both H. sapiens and H. economicus in economic theories led to the same theoretical outcome? Unrealistic assumptions about photons lead to the Einstein solid which is quite close to the better Debye model (nice discussion at the link). The existence of such results renders the unrealistic assumptions charge useless on its own. We really only know if certain assumptions lead to empirically valid outcomes. If more realistic assumptions lead to better comparisons with data, then unrealistic assumptions are a problem. However, at that point you already have a better theory! The real argument shouldn't be about the assumptions of the old theory -- just show that the new theory is better.

And that is one of the major problems I see with alternative approaches to economics.

New approaches tend to criticize the old approach in some way (not exhaustive, not orthogonal):

However, each of these, except for the last one, has failed to lead to a more empirically accurate theory. Or even one that is equally accurate! There are complaints about being ignored -- and really it makes some sense when the mainstream theories aren't very empirically accurate either. However, alternative approaches to economics will continue to be ignored until they show that they are better than mainstream theory in some quantifiable way. Usually, that is through more accurate theories. Einstein was allowed to dislodge Newton because Einstein's theory made predictions that were more accurate than Newtonian physics. It wasn't because Einstein criticized how "mainstream physicists" approached mechanics with "unrealistic assumptions". Einstein's assumptions (constant speed of light, no preferred reference frame) were considered unrealistic! The results (length contraction, time dilation, energy-mass equivalence) were considered even more unrealistic!

Blackford wants us to be scientific. Let me give a positive example. I think information transfer economics is a good example of being scientific. I probably fail sometimes, but I strive to apply my training as a theoretical physicist.\

  1. Clearly state your assumptions
  2. Show how your theory connects to mainstream economic theory
  3. Compare your theory to the empirical data and make predictions
  4. Show how your theory is better than mainstream

It's not very complicated!

And there we have the second major problem I see with alternative approaches. I feel that in the same way some progressives can't bring themselves to vote for Hillary Clinton because it might taint the purity of their progressivism, heterodox economist can't seem to say how their theories connect to mainstream economics. Don't be afraid of this! It's a great way to show your theory is consistent with lots of the empirical tests in the literature.

1. Acquire basic competency in whatever field of science your discovery belongs to.

2. Understand, and make a good-faith effort to confront, the fundamental objections to your claims within established science.
3. Present your discovery in a way that is completetransparent, and unambiguous.
Understanding the connections to existing theory is critical to #1 and #2.

And if your theory doesn't have outputs that can be compared to data -- guess what, it's philosophy, and it can safely be ignored.


  1. "The most accurate theory in the universe (quantum field theory) assumes spacetime isn't curved (even though it is)."

    Is this an example of scope at play?

    1. Yes, QFT is applicable when the energy scale E is smaller than the energy scale set by the curvature of space time 1/R. When these are comparable, you'll need a quantum theory of gravity.

  2. "They were rejected because the theory was wrong and a new theory was put forward that was more empirically accurate."

    Why were the theories respectively wrong?

    1. Close to the surface of the Earth, gravitational acceleration is roughly constant g (Galileo), but Newton's theory says that e.g. it should change with altitude

      g(r) = G Me/(Re + r)^2

      Einstein adds the ability to have tiny fluctuations (gravity waves, recently directly observed) as well as making it consistent with Lorentz invariance (Newton's gravity acts instantly millions of miles away, while in general relativity it has a speed limit of c).

    2. Could it have been that their beginning propositions/premises/assumptions were wrong?

      I guess you're going to say no.

    3. You could say yes: Galileo assumed 32 ft/sec/sec had infinite scope, which is wrong.

      Or you could say no: Galileo's assumption of a constant value of g near the surface of the earth is as good today as it was in the 1600s (and is still used today in Mechanics 101).

      There really isn't a binary here. It's similar to problem with Popperian falsification. Popper says Newton was falsified by Einstein, but no physicist would consider Newton's laws "false". They're true in certain limits and wrong outside them.

      Popperian falsification assumes infinite scope for theories, which none have. Einstein is already "falsified" even though no experiment has ever measured an error. It's because it's inconsistent with quantum mechanics.

      And in that sense, every theory is false if you assume infinite scope. Which is why physicists don't -- they take every theory to be an effective theory and say things like theory X is empirically accurate within some scope.

    4. Scope doesn't explain why a theory is wrong. Scope merely circumscribes the data to which a theory applies. It does not of itself explain why a theory does not apply to other/all data.

    5. "You could say yes.."

      You don't really want to say "yes", because that would completely undermine the diatribe above made in support of Friedman's analogy, that you hope passes as reasoned argument.

    6. "Scope doesn't explain why a theory is wrong. Scope merely circumscribes the data to which a theory applies. It does not of itself explain why a theory does not apply to other/all data."

      Um, ok. Nothing explains why a theory is wrong except for the correct theory (from which you can usually derive the scope conditions for the wrong theory, e.g. Newton is ok for v << c because Newton is the leading terms of expanding the Lorentz factors in special relativity in v/c).

      "You don't really want to say "yes", because that would completely undermine the diatribe above made in support of Friedman's analogy, that you hope passes as reasoned argument."

      Say what you will, but Friedman's "as if" methodology is precisely what physicists call "effective theory".

      You don't need to take my word for it. Here is Steven Weinberg [pdf]. Weinberg uses the term "phenomenological Lagrangians", but that was the terminology before physicists started calling it "effective field theory".

    7. "Nothing explains why a theory is wrong except for the correct theory....."

      It's not that simple. Within the "wronged" theory itself is an explanation.

      Scope is a description. It is not an explanation. It does not explain anything.

      You don’t want to deal with explanation because if you did you would have nothing to stand on.

      Your use of scope as an argument against the usefulness/validity of economic theory is facile and completely self serving.

      Saying Newtonian theory is wrong because of scope is facile.

      Your ridicule of a fine economist like George Blackford is abhorrent and typical of the hubris and arrogance you routinely display in your blog. He is a thousand times the economist you will ever be.

      It is you, manacled by a self serving prejudice, who does not, will not and cannot understand anything beyond the mindless buzzing of whatever it is that constitutes matter in its finest forms.

      Lucky for you I off for a few days, leaving you to rant and rave at will.


    8. "It's not that simple. Within the "wronged" theory itself is an explanation."

      That one gave me a good belly laugh. You are saying that within Newtonian mechanics is special relativity?

      "Saying Newtonian theory is wrong because of scope is facile."

      I assume you said this? Because I did not. I said Newtonian theory is right if you consider scope.

      "[Blackford] is a thousand times the economist you will ever be."

      But Blackford is obviously not a very good scientist, which was the point of my post. In fact the title of my post is Economist shouldn't be used as source for what is "scientific". My abilities as an economist are not germane to this scientist's criticism of Blackford's ineptitude at science.


      I'm pretty sure you don't understand what I am saying because you consistently get it wrong. Your criticisms are not much more than ad hominem attacks. ("You don't want to deal with explanation ... ", "Your use of scope ... is facile and self serving", Blackford "is a thousand times the economist you will ever be", "manacled by a self-serving prejudice ... "cannot understand anything beyond the mindless buzzing of ... matter"). This only gives the impression that you don't have any logical points to make and just want to insult me.

      Which is fine. I largely don't care if you call me names because I wouldn't want to be the kind of person you would find meritorious.

    9. "I largely don't care if you call me names because I wouldn't want to be the kind of person you would find meritorious."

      That's precisely the retort my parents taught me to respond with to elementary school yard taunts! 😂

    10. "That one gave me a good belly laugh. You are saying that within Newtonian mechanics is special relativity?

      You repeatedly ascribe to me opinions/statements/whatever, that you say I have given/made.

      The way you repeatedly refute arguments is to construct straw men - you do this when you are under the pump - you have no other valid means of making argument so you resort to intellectual skulduggery.

      "I said Newtonian theory is right if you consider scope."

      Exactly the same thing as I said.

      You have shown no inclination to explain why Newtonian theory is out of scope. The reason is that if you did so, it would completely undermine your line of argument regarding Friedman's billiard player analogy. And if you undermine that, then your line of argument dealing with scope is emasculated.

      There is one clear way in which scope applies to economics and that is in the difference between macroeconomics and microeconomics (throw in mesoecconomics if you like). The distinctions you are drawing are nonsense and self serving.

      If science relies on the notion of "effective theory" then I can understand why theory after theory is, thru time, subsequently abandoned and supplanted by another theory. New data appears (as instruments become more sensitive for instance), the old theory is no longer tenable so it's dumped. This is a gross form of curve fitting (which you personally practice as a high art and call the scientific method). It explains nothing. Your version of prediction is a sham. If the alternative approach of examining starting premises was more rigorously adopted, then theoretical weaknesses might be more easily identified. It's a wonder science has progressed at all and perhaps explains why string theory and the like has more or less slumbered in a cul de sac for 50 years. It's waiting for the right data to come along and either refute it or validate it. Seems a unsound way of doing business, devoid of all logical integrity. (I actually know nothing about string theory - so I guess you'll have a field day with what I have said - I see a battalion of straw men marching over the hill. LOL!)

      I suggest you go and learn some economics - you seem to be clever enough - you might even make a valuable contribution.

    11. " This only gives the impression that you don't have any logical points to make and just want to insult me."

      This is a little rich given the way you have conducted yourself in your blog above.

  3. Interesting read Jason. Since I'm not a scientist I really enjoy these posts giving a little insight into how science works and what is and what is not science from a scientist's perspective, and of course tying that into economics.

    Since most economists are reluctant to attempt to understand what you've put together here I sometimes wish a fellow physicist (or other scientist) with an interest in economics would come take a look, just to kick the tires a bit and give their perspective. I've suggested this to a few via online comments, but I don't think any have yet (AFAIK). Of course F&B have reviewed your paper and then the guy (name escapes me) whom you co-authored something with in a different field (brain waves?).

    I haven't been paying as much attention to all your posts recently. Did I miss someone that had an interesting perspective, say from a scientific background?

    1. Todd Zorick: the name that escaped me.

    2. I've discussed things on occasion with some of my colleagues (one of whom is a mathematician who used to teach economics), and the reviewer of the EEG paper gave Todd and myself an interesting perspective.

      The idea was originally supposed to be used to understand prediction markets, and I talked with some people with regard to that some time ago.

      Cameron Murray (Austrialian economist) and Brennan Peterson (physicist) are reviewing the book. And I've started a conversation with Gregor Semieniuk (UK economist).

      Things are progressing.

    3. Great to hear that things are progressing. Also, thanks for the details, names and links.

    4. BTW, you've probably already seen this, but I just read it today and really enjoyed it:
      I was shocked to see he had over 400 comments. I think there's a "scope condition" tie-in with your post here.

  4. This comment has been removed by the author.

  5. Oh my. You seem to be so flabbergasted by my paper criticizing the failure of economists to abide by the principles of science that it has led you to declare: “Since economics is oh so scientific in its approach, we should of course consult an economist on how to be scientific.” Judging from the tenor of the rest of your criticism, this sarcastic remark seems to say that “economics is so unscientific an economist can’t possibly understand how truly scientific economics realy is.” Which side of this argument are you on? If you wish to argue both sides it’s ok with me. At least that way we may be able to agree at least half the time ;-)

    You explain ‘effective theory’ in terms of Friedman’s as if methodology and point out that “all of physics today is an effective theory” as if this has something to do with my paper. My paper is about how Friedman’s as if methodology is used in economics. It’s not about how it is used in physics. I don’t know that much about physics, but I believe there is a fundamental difference between the two disciplines in this regard.

    As far as I can tell, the basic paradigms of physics are not, for the most part at least, based on demonstrably false assumptions and these paradigms can be used to explain a tremendous amount of data in the real world. I see much of economics to be fundamentally different. The basic paradigm of economics (specifically, the perfectly-competitive general equilibrium model) is a) based on demonstrably false assumptions, b) has virtually no correspondence to anything that exists in the real world, and c) can be used to explain virtually nothing.

    Now the fact is that I don’t really have any objection to this paradigm in that I don’t see it as completely worthless, but I do object when economists make arguments based on the false assumptions of this paradigm that, in my view, make no sense at all other than as a pseudo-intellectual justification for policy recommendations derived from ideological beliefs. I could be wrong, but it seems to me that this sort of problem was more or less purged from physics sometime in the seventeenth or eighteenth century as the university system rose and the power of the church declined. As a result, I don’t see the lack of consensus in physics to be in any way comparable to that in economics due to the ideological blindness I see as the fundamental cause of the lack of consensus in economics.

    (Continued here: )

    1. It is exceedingly difficult for me to understand why you insist on defending the use of Friedman's methodology in physics in criticizing my paper. My paper is about the misuse of Friedman’s methodology in economics, not in physics.

      Over the past fifty years mainstream economists have developed highly sophisticated mathematical models based on absurd assumptions that were justified in the name of Friedman's as if methodology. Those models were used as an intellectual justification for deregulating the financial system in a way that blew up the world's economy. This occurred in spite of the fact that hundreds, if not thousands of years of historical data have shown that unregulated or poorly regulated financial institutions inevitably lead to financial crises that, in turn, cause economic, political, and social catastrophes.

      When I tried to discover why this happened I found that in spite of the overwhelming historical evidence that warned of the catastrophe that would result, virtually no mainstream economists spoke out against this deregulation as it took place, and those who tried were ridiculed and marginalized within the discipline of economics in much the same way you marginalize Minsky, Keynes, and what I have tried to do in Where Did All The Money Go?. I also discovered that the reason virtually no mainstream economists spoke out against this deregulation is that over the past fifty years free-market ideological beliefs have come to permeate the discipline of economics, facilitated by an egregious misuse of Friedman's as if methodology.

      When I write a paper attempting to explain this misuse within the discipline of economics you ridicule my attempt mercilessly in defense of its use in physics. At the same time, in one of the posts you link to you claim:

      "I am not defending the implications Friedman makes from this analogy about economics . . . . The problem is that this analogy doesn't defend against theories that fail to match the data which is a more serious issue in economics than a particular mathematical approach."

      You will just have to forgive me for finding this a bit confusing.

      When I present a reasoned analysis of the historical data and a detailed explanation as to why the inevitable result of deregulating or poorly regulating the financial system leads to a catastrophe, you insist on ignoring these historical data and my reasoned argument and explanation in the absence of a mathematical model that more accurately predicts the economic data that you want to predict—data that doesn't even include the variables that I see as being crucially important to an understanding of the historical data that I try to understand and explain. You boldly take this position in spite of the fact that this is the same kind of reasoning and argument used to ridicule and marginalize those economists who tried to oppose the economic policies that were responsible for blowing up the world’s economy in the first place.

      This seemed rather confusing to me at first, but I now suspect the key to this mystery may be hidden in your response to my statement: "If you had bothered to look at these references ... it would have become apparent to you that I have spent an excruciating amount of time and effort in examining data and attempting to develop a theory that explains that data."

      (Continued here: )

  6. Jason,

    You wrote

    The most accurate theory in the universe (quantum field theory) assumes spacetime isn't curved (even though it is).

    We may have to take your word for that, as I doubt many of your readers (me included) are physicists.

    However, a clarification is in order. What do you mean by that, exactly?

    One thing is to say that quantum field theory (QFT) does not require spacetime to be curved. In other words, spacetime curvature is irrelevant to QFT.

    Another quite different thing is to say that QFT specifically requires spacetime to have no curvature.

    From what you wrote, it's hard for me to tell which of these alternative meanings you have in mind.

    B.L. Zebub

    1. The electron magnetic moment is the most accurately computed theoretical quantity currently known, precisely computed to 10 decimal places. It is a QFT result.

      QFT does explicitly require space time not be curved because it is mathematically inconsistent with general relativity (the theory of space time curvature).

      It is true that space time is usually approximately flat over the region you would usually compute things with QFT, but that's just effective field theory. Basically QFT is good for energies less than the Planck scale. You could also add it as an external classical effective field (but then you can introduce renormalizability issues that you end up sweeping under the rug that are, if memory serves, actually worse than the original problem of neglecting curvature).

      But that is my general point, either of your interpretations are valid by way of effective theory.

      At the bottom of the issue is that gravity and quantum mechanics are theoretically incompatible. You have to treat them inconsistently if you want to put them together. How you go about that inconsistency is a modelling choice, and ends up being effective theory.

    2. Thanks

      At the bottom of the issue is that gravity and quantum mechanics are theoretically incompatible. You have to treat them inconsistently if you want to put them together. How you go about that inconsistency is a modelling choice, and ends up being effective theory.

      A bit disturbing, but I'll have to think about it.

      B.L. Zebub