*Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime*

That is the new, interesting, and engaging book by Sean Carroll.  Some of it is exposition, the rest argues for a version of Many Worlds Theory, but with a finite number of universes.  Here is one excerpt:

String theory, loop quantum gravity, and other ideas share a common pattern: they start with a set of classical variables, then quantize.  From the perspective we’ve been following in this book, that’s a little backward.  Nature is quantum from the start, described by a wave function evolving according to an appropriate version of the Schroedinger equation.  Things like “space” and “fields” and “particles” are useful ways of talking about that wave function in a appropriate classical limit.  We don’t want to start with space and fields and quantize them; we want to extract them from an intrinsically quantum wave function.

I very much liked the discussion on pp.300-301 on how a finite number of quantum degrees of freedom implies a finite-dimensional Hilbert space for the system as a whole, that in turn constraining the number of worlds in an Everett-like model.  If only I understood it properly…

You can buy the book here.


Let me know when this stuff becomes even a little bit falsifiable.

This is an economics blog. Nothing here is falsifiable.

Engineering isn't science, so maybe this does not meet your exacting standards (though obviously engineering does operate with empirical falsifiable devices)? 'Many modern electronic devices are designed using quantum mechanics. Examples include the laser, the transistor (and thus the microchip), the electron microscope, and magnetic resonance imaging (MRI). The study of semiconductors led to the invention of the diode and the transistor, which are indispensable parts of modern electronics systems, computer and telecommunication devices. Another application is for making laser diode and light emitting diode which are a high-efficiency source of light.

Many electronic devices operate under effect of quantum tunneling. It even exists in the simple light switch. The switch would not work if electrons could not quantum tunnel through the layer of oxidation on the metal contact surfaces. Flash memory chips found in USB drives use quantum tunneling to erase their memory cells. Some negative differential resistance devices also utilize quantum tunneling effect, such as resonant tunneling diode. Unlike classical diodes, its current is carried by resonant tunneling through two or more potential barriers. Its negative resistance behavior can only be understood with quantum mechanics: As the confined state moves close to Fermi level, tunnel current increases. As it moves away, current decreases. Quantum mechanics is necessary to understanding and designing such electronic devices.' https://en.wikipedia.org/wiki/Quantum_mechanics#Electronics

You might be on to something.
Bill Gates: "Economists don't actually understand macroeconomics."


Keynes did. But Keynes was tanstaafl.

Milton Friedman wanted free lunches. He cleverly created a framework to argue for free lunches.

The result has been exploding debt to pay for the free lunches.

You can not pay consumers $100 a week and then sell them what they produced for $200 a week.

Oddly the sellers pocketing the $100 in profit do not want to loan the $100 to consumers because they know that's a gift. Instead they loan it to government to give it to consumers so they can collect it as profit, doubling their profits each cycle.

Irrelevant, the subject isn't quantum mechanics but string theory. The former has been extensively tested and verified, the latter has not in 40 years produced a falsifiable hypothesis.

String Theory isn't science, it's mysticism.

Specifically, the book is (or at least contains) an argument for the many-worlds interpretation of quantum mechanics. You know, the multiverse and all that.

It's a lot more esoteric than plain vanilla quantum mechanics.

My thought exactly. This is closer to theology than science. The gross structure of the observable universe is based on observation; multiverses, inflation, etc. will probably be overturned because they are based on computer simulations.

It's why I gave up science for a life on Wall Street. STEM is lousy for careers while working for a bank or a hedge fund will do wonders for your bank account. Our industry is so important that the government will bail us out while STEM gets another cut in science funding even in good years.

Quantum Mechanics Is Just Two Other Words For Socialism.

Quantum Mechanics Is Just Two Other Words For Science.

Science makes falsifiable predictions.

And engineering makes operating devices.

Quantum mechanics makes falsifiable predictions such as the intensity and wavelength of spectral lines from various species. Atomic, nuclear, condensed matter, and particle physics are more or less applied quantum mechanics. Quantum Electrodynamics is the most successful scientific theory every produced by humanity as it has predicted the measurement of the fine structure constant to one part in a 100 million.

Of course, that doesn't mean that Sean Carroll's work isn't nonsense. If you want to read an accessible (though perhaps somewhat over the top) criticism of Carroll's work and other various non-traditional interpretations of quantum mechanics, you could do worse than check out Lubos Motls's blog:


Some actual science on quantum mechanics would be a refreshing change.

Clicked the wrong reply, but some actual engineering using quantum mechanics seems to be some information that might have passed you by.

People telling that quantum theory can be falsifiable are both correct and incorrect.
1) Some basic things about quantum theory has been proven and are used nowadays for many electronic applications.
2) HOWEVER! Physics does not know yet why quantum behaviour is the way it is and how it can be united with theory or relativity (which is also proven to work in certain cases). Both of those work relatively well and are used in current technology. However, some specific edge cases (very small and very dense gravitational fields are one example) cannot be explained, since both of those theories contradict each other. Therefore, physics is trying to find some overarching theory that could explain both theories at the same time and give answers to those edge cases. There are some possible ones, but none has been proven as of yet (and might not be neither provable nor falsifiable with our current technology and energies).

I don't think we're all living in a computer simulation, but if we are, those edge cases and the breakdown of meaning at the extremely small and extremely large scales would be evidence of that. The programmers didn't think they had to get that granular.

Carroll is an atheist, or "poetic naturalist" as he describes himself. Only someone who is extremely self-confident can identify as an atheist - one may have doubts about the existence of a divine being, but how would one know? Agnostic maybe, but atheist? Carroll's Many Worlds Theory must be viewed from that perspective. How does one know that there are many worlds, many of you and me and Tyler Cowen and Sean Carroll? And many Donald Trumps! God help us.

The theory that makes the most sense to me is that it's all turtles. All the many worlds are full of turtles.

I refuse to believe in theory that doesn't include a layer of elephants!


If you're going to write about QM there's a case for spelling "Schoedinger " correctly.

"That's how we spell it in this world" neatly illustrates the metaphysical extravagance of Many Worlds.

I usually completely ignore your posts, but today I must say: bravo. Even I smiled because of this horrendous joke. Thank you.

Sure, but is that number uniquely determinable...

What is Trump's view on the quantum world? Certainly a self described genius with his intellectual caliber and formidable command of science must have something intelligent to say.

What is Justin Trudeau's? Or Nina Totenberg's? That's a silly comment. Quantum physics is an arcane, largely theoretical field understood by a handful of cloistered academics.


Monsieur PM

We make a sequence of orders from Walmart, orders made at semi random moments as we need them. But they must pass through the delivery system, a constrained channel. So Walmart is free to take my stream and requantize them, two packages that aggregate together may be repackaged as one. The trick is to set the congestion level at the fullfilment center, catch as may redundant packages without making the queue unstable. Our abstract tree again. I am suggesting we ski[p probability and replace it with hologram, instead of probability of event we use accuracy of hologram measurements. Our fields,tie and space are induced by the hologram.

If you extend my analogy to UPS delivering packages we find they can very accurately define packages per hour over my hometown of half a million. That is Newton's calculus, working, in the range of a day's activities.

Who made Newton's calculus work? The postal aggregation centers. Those folks deliberately congest the packages so they optimally fill a eep of panel truck that can prowl the street in off commute time. They deliberately 'requatize' goods in flow to make time and space work, they make a city map useful.

The sticking point in physics is that there is a fastest thing, and we can set that as a constant. That implies, in sample data version, that there is a finite bandwidth implies there is a smallest thing, that means no such thing as empty spots on your formulations, and that implies you combinatorials are limited when maximizing entropy (minmizing redundancy), at the smallest level. A pure vacuum has infinite bandwidth, we ruled that out, all no empty space for implied subdivisions. This all boils down to Avogadro's number, in the end. Every universe has one, and they are quantized by the dimensionality of the universe. Every universe reaches a point where packing one more smallest thing yields an impossible vacuum somewhere else.

Go back to the postal model, the manager has to deliver the days mail. His objective is o sit near the city, and congest the incoming mail piles enough to send panel trucks, and jeeps out, on a generally decreasing density basis.

What is she doing each day? Direcing her trucks and jeeps to be optimally separated on a nearly straight radius. She is having the trucks literally compute pi, the same way your teach proved it to you in class, the subdividing pie. Nature has to compute those transcendentals, they are not energy free.

Our realm of baryonic matter constituting only c. 5% of the matter, mass, and energy in our universe that we can detect and measure directly using instruments of baryonic construction, someone might argue that a lot more remains "hidden" than the quantum states native to our baryonic realm.

A science satirist, I do wonder how the rubes will ever be able to explain to anyone's satisfaction exactly how we can insist that our baryonic realm is "The Main Event": we have no clue what transpires on daily and hourly bases in the realms of dark matter and dark energy that either permeate or help shape our pitiful realm, baryonic matter now giving the impression of being only a vestigial appendage--a sideshow--to wherever "the important stuff" is going on.

BTW: for anyone interested the producers of "Timelapse of the Future" (available on YouTube) illustrate the elapse of 20 thousand trillion trillion trillion trillion trillion trillion trillion trillion years in a 20-minute video, although some of their assumptions necessarily remain conjectural (proton decay chief among them).

I'm not much more than a layman here, but leaving aside dark energy as unfathomable to me, if dark matter did something really interesting it would seem to have to clump.

Since it observably does not (whatever the heck it is, particles, modified gravity, whatever) it seems to be spread really thin. The speed of light being what it is, that would seem to preclude things like dark matter chemistry or life or machines or what have you.

If, dear commentator, you are a particle physicist who disagrees with me, please take it easy 'cause I'm not asserting any great authority here.

My understanding is that there is evidence dark matter doesn't clump because (1) we don't observe lensing from big clumps, and (2) it can't self interact much or we'd notice that effect in other ways.

Certainly, I am nothing more than a layman (something less, depending on who tells the tale), with a layman's enthusiasm for space science in this Golden Age of astronomy.

Our friends at Wikipedia tell us that Lord Kelvin initiated the "dark matter hypothesis", his surmise joined by Poincare shortly thereafter, before being endorsed by many more: so the "history" of dark matter is barely one century old.

Barely one century old: this at the end of humanity's six millennium experiment with "civilization". Though our physicists and astrophysicists seem aware of this invisible and directly undetectable non-baryonic matter (?), it continues to elude.

From this I can only begin to conclude that we may with utterly equal validity hypothesize that "invisible realms" stand squarely behind whatever invisible "dark matter" envelope holds the fragile contents of our miniscule baryonic universe. (No need to hypothesize an infinite regression or remove: but if one invisible realm poses a valid hypothesis, so does any other invisible, non-baryonic realm--to my provincial way of thinking.)

It doesn't matter. Climate change will end all branches of the multiverse.

Superb book. I’m just about finished. I’m also a big fan of David Deutsch’s books. All are accessible to general readers.

Deutsch's books are great, although I won't really understand his time travel chapter in "The Fabric of Reality" until my brain is uploaded into the cloud.

Naturally-occurring ice may soon become deeply hidden from us (perhaps permanently, for purposes of ephemeral states and civilizations):


(Much or most of the Greenland, Iceland, and Antarctic glacial melting seems to result from rising ocean temperatures, not from rising air temperatures.)

These data don't look at all optimistic for enthusiasts eager for the advent of a new Ice Age:


Greenland, meh. It melted during the Medieval Warm Period. If it hadn't it would have been called Whiteland.

Those Norse were great marketers.

Our household avidly reads MR and enjoys the breadth of topics discussed that are outside our field (he's a programmer, she's a scientist). Tyler's musing that "if only I understood it properly" -- while probably undue modesty -- reminded me of a question we wondered once: is there a scientific "Tyler Cowen" out there? That is, another intellectual of equal curiosity and academic reach, but based in something like a STEM field. Would love to follow the blog of that person(s) too.

Great comment and question. I would like to know this as well.

Essentially a STEM-specialized "Generalist" versus Tyler Cowen's economics-specialized "Generalist"...

Applied Science (YouTube) is fun, but one subject at a time, and hands on, rather than a maven:


An ode to YouTube and "mass-scale tacit knowledge transmission" is here:


Oh, if you want an opinionated blog:


And the venerable slashdot


Not really generalist, or as prolific in terms of blogging, but maybe Scott Aaronson (https://www.scottaaronson.com/blog/) or John Baez (https://johncarlosbaez.wordpress.com/)

Thanks, both of those look good!

Is there a "scientific" MR out there? Great question. My answer:"Yeah, no; that'd be an oxymoron."

I see your “opinionated” and raise, with Lubos Motl, who, I think, gets it right:


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