Quantum Field Theory and the Limits of Knowledge - Sean Carroll - 12/7/22

©2022 California Institute of Technology

[nardewww]

God, this is a masterpiece. This should be part of some super popular show to give it more outreach.

[elwood.downey]

Thank you Dr Carrol for speaking so carefully, your logic is refreshing.

[aaronmbowden]

They should make this video at the start of every discussion of consciousness and religion

[bryandraughn]

Excellent!
I don't know how many times I've had to explain to someone that there is no way to gauge "how much there is to know." or how close we might be to reaching that point.
We could be close, or very far away, but it's impossible to say unless you already know everything and therefore can measure our current position in comparison.
I grow tired of hearing "We don't know anything." from certain individuals who hate science.😊

[DanishIV]

If it is true, that the dire thought can change the electromagnetic field (pattern), then I think it proves that it can not be emergent relative to the quantum (electromagnetic) field(s)
With emergent phenomena, I can not change the fundamentals
I can not split a proton with a chisel

[bentationfunkiloglio]

Logic and well reasoned discourse are total buzz kills.

Professor Carroll did a great job scoping his presentation. Other comments notwithstanding, he wasn’t opining on the fundamental nature of reality or discounting spirituality.

He simply stated that we (humans) have created a very accurate model that describes/predicts the physical world we (humans) interact with during our everyday lives.

Not a controversial assertion given he also described the limits of that model.

[nneisler]

For everyday life, Archimedes is fine for me.

[schmetterling]

The curious thing about "the limits of knowledge" phrase is that logically it does not apply to quantum field theory. QFT simply tells us what knowledge is available in this universe. That we were hallucinating in the past that there should be "more" than there actually is is not a loss of knowledge. It's a loss of collective foolishness. We are getting smarter by understanding these things, not somehow less capable of learning.

[mikebellamy]

The approximate 65% ~ 35% divide in the two pole questions tells me that everyone starts with a bias which is based on an underlying world view which is so deeply held there is almost zero chance of anyone changing it regardless of the case against it being put even competently and clearly. This is very dangerous for those who happen to be wrong and I think the test for that is to ask yourself honestly "could you be wrong" then look for that assuming your bias is wrong.

[PetraKann]

A fantastic explanation of the spherical cows that underpin Physics.

[cademosley]

Great lecture! My first reaction is that Sean would really benefit with a primer on functionalism in philosophy of mind. Functionalism is usually associated with emergentism, so I think it may even be close to his actual position after he read up on it, if he has a chance, but I don't know. But in any event I think he could make great contributions to the functionalism debate because of how it intersects with this lecture.

An important thing to mention at the start is that philosophers of mind distinguish "physicalism" from "functionalism". Functionalism is still a physical theory, but the actual physical arrangement isn't relevant. A silicon based computer (at least perhaps one still far in the future) could have the same conscious experience as a carbon-based human, but of course both still operate based on the vanilla physics and chemistry of neurons and CPUs. So both are still "physical", but it's not "philosophical physicalism".

I think that functionalism is even the majority position in philosophy of mind, if you took a poll, and I'm even more confident that most would "✓" the box saying "they are not physicalists". But what they mean by the term "physicalism" is different than the way Sean used it in this lecture, as he was talking about a much more general claim that "there is a physical basis". I think most philosophers of mind would agree with that, sans the few Sean was targeting in this lecture (strict or property dualists and mental monists). But that position, "it's all physical", includes both "philosophical physicalism" (which itself has to brands: 1. "token physicalism", only this exact arrangement of neurons can be conscious; and 2. "type physicalism": only arrangements of neurons of this general type can be conscious) and "functionalism" (any physical system with this general functional arrangement, to the extent it can physically manifest it, can be conscious, and consciousness is an emergent property of that arrangement, the functional state, manifestable through many different physical states, and not the specific underlying physical state itself per se). Functionalism vs. philosophical physicalism is just the next layer in the debate, both "physical", where a lot of the real action is happening these days, I think.

Okay, that's my little contribution to the discussion here. Thanks for the great talk and food for thought!

[SpotterVideo]

Both Matter and Energy described as "Quanta" of Spatial Curvature. (A string is revealed to be a twisted cord when viewed up close.)

Is there an alternative interpretation of "Asymptotic Freedom"? What if Quarks are actually made up of twisted tubes which become physically entangled with two other twisted tubes to produce a proton? Instead of the Strong Force being mediated by the constant exchange of gluons, it would be mediated by the physical entanglement of these twisted tubes. When only two twisted tubules are entangled, a meson is produced which is unstable and rapidly unwinds (decays) into something else. A proton would be analogous to three twisted rubber bands becoming entangled and the "Quarks" would be the places where the tubes are tangled together. The behavior would be the same as rubber balls (representing the Quarks) connected with twisted rubber bands being separated from each other or placed closer together producing the exact same phenomenon as "Asymptotic Freedom" in protons and neutrons. The force would become greater as the balls are separated, but the force would become less if the balls were placed closer together. Therefore, the gluon is a synthetic particle (zero mass, zero charge) invented to explain the Strong Force. An artificial Christmas tree can hold the ornaments in place, but it is not a real tree.

String Theory was not a waste of time, because Geometry is the key to Math and Physics. However, can we describe Standard Model interactions using only one extra spatial dimension? What did some of the old clockmakers use to store the energy to power the clock? Was it a string or was it a spring?

What if we describe subatomic particles as spatial curvature, instead of trying to describe General Relativity as being mediated by particles? Fixing the Standard Model with more particles is like trying to mend a torn fishing net with small rubber balls, instead of a piece of twisted twine.

Quantum Entangled Twisted Tubules:
“We are all agreed that your theory is crazy. The question which divides us is whether it is crazy enough to have a chance of being correct.” Neils Bohr
(lecture on a theory of elementary particles given by Wolfgang Pauli in New York, c. 1957–8, in Scientific American vol. 199, no. 3, 1958)

The following is meant to be a generalized framework for an extension of Kaluza-Klein Theory. Does it agree with some aspects of the “Twistor Theory” of Roger Penrose, and the work of Eric Weinstein on “Geometric Unity”, and the work of Dr. Lisa Randall on the possibility of one extra spatial dimension? During the early history of mankind, the twisting of fibers was used to produce thread, and this thread was used to produce fabrics. The twist of the thread is locked up within these fabrics. Is matter made up of twisted 3D-4D structures which store spatial curvature that we describe as “particles"? Are the twist cycles the "quanta" of Quantum Mechanics?

When we draw a sine wave on a blackboard, we are representing spatial curvature. Does a photon transfer spatial curvature from one location to another? Wrap a piece of wire around a pencil and it can produce a 3D coil of wire, much like a spring. When viewed from the side it can look like a two-dimensional sine wave. You could coil the wire with either a right-hand twist, or with a left-hand twist. Could Planck's Constant be proportional to the twist cycles. A photon with a higher frequency has more energy. ( E=hf, More spatial curvature as the frequency increases = more Energy ). What if Quark/Gluons are actually made up of these twisted tubes which become entangled with other tubes to produce quarks where the tubes are entangled? (In the same way twisted electrical extension cords can become entangled.) Therefore, the gluons are a part of the quarks. Quarks cannot exist without gluons, and vice-versa. Mesons are made up of two entangled tubes (Quarks/Gluons), while protons and neutrons would be made up of three entangled tubes. (Quarks/Gluons) The "Color Charge" would be related to the XYZ coordinates (orientation) of entanglement. "Asymptotic Freedom", and "flux tubes" are logically based on this concept. The Dirac “belt trick” also reveals the concept of twist in the ½ spin of subatomic particles. If each twist cycle is proportional to h, we have identified the source of Quantum Mechanics as a consequence twist cycle geometry.

Modern physicists say the Strong Force is mediated by a constant exchange of Gluons. The diagrams produced by some modern physicists actually represent the Strong Force like a spring connecting the two quarks. Asymptotic Freedom acts like real springs. Their drawing is actually more correct than their theory and matches perfectly to what I am saying in this model. You cannot separate the Gluons from the Quarks because they are a part of the same thing. The Quarks are the places where the Gluons are entangled with each other.

Neutrinos would be made up of a twisted torus (like a twisted donut) within this model. The twist in the torus can either be Right-Hand or Left-Hand. Some twisted donuts can be larger than others, which can produce three different types of neutrinos. If a twisted tube winds up on one end and unwinds on the other end as it moves through space, this would help explain the “spin” of normal particles, and perhaps also the “Higgs Field”. However, if the end of the twisted tube joins to the other end of the twisted tube forming a twisted torus (neutrino), would this help explain “Parity Symmetry” violation in Beta Decay? Could the conversion of twist cycles to writhe cycles through the process of supercoiling help explain “neutrino oscillations”? Spatial curvature (mass) would be conserved, but the structure could change.

Gravity is a result of a very small curvature imbalance within atoms. (This is why the force of gravity is so small.) Instead of attempting to explain matter as "particles", this concept attempts to explain matter more in the manner of our current understanding of the space-time curvature of gravity. If an electron has qualities of both a particle and a wave, it cannot be either one. It must be something else. Therefore, a "particle" is actually a structure which stores spatial curvature. Can an electron-positron pair (which are made up of opposite directions of twist) annihilate each other by unwinding into each other producing Gamma Ray photons?

Does an electron travel through space like a threaded nut traveling down a threaded rod, with each twist cycle proportional to Planck’s Constant? Does it wind up on one end, while unwinding on the other end? Is this related to the Higgs field? Does this help explain the strange ½ spin of many subatomic particles? Does the 720 degree rotation of a 1/2 spin particle require at least one extra dimension?

Alpha decay occurs when the two protons and two neutrons (which are bound together by entangled tubes), become un-entangled from the rest of the nucleons

. Beta decay occurs when the tube of a down quark/gluon in a neutron becomes overtwisted and breaks producing a twisted torus (neutrino) and an up quark, and the ejected electron. The production of the torus may help explain the “Symmetry Violation” in Beta Decay, because one end of the broken tube section is connected to the other end of the tube produced, like a snake eating its tail. The phenomenon of Supercoiling involving twist and writhe cycles may reveal how overtwisted quarks can produce these new particles. The conversion of twists into writhes, and vice-versa, is an interesting process, which is also found in DNA molecules. Could the production of multiple writhe cycles help explain the three generations of quarks and neutrinos? If the twist cycles increase, the writhe cycles would also have a tendency to increase.

Gamma photons are produced when a tube unwinds producing electromagnetic waves. ( Mass=1/Length )

The “Electric Charge” of electrons or positrons would be the result of one twist cycle being displayed at the 3D-4D surface interface of the particle. The physical entanglement of twisted tubes in quarks within protons and neutrons and mesons displays an overall external surface charge of an integer number. Because the neutrinos do not have open tube ends, (They are a twisted torus.) they have no overall electric charge.

Within this model a black hole could represent a quantum of gravity, because it is one cycle of spatial gravitational curvature. Therefore, instead of a graviton being a subatomic particle it could be considered to be a black hole. The overall gravitational attraction would be caused by a very tiny curvature imbalance within atoms.

In this model Alpha equals the compactification ratio within the twistor cone, which is approximately 1/137.

1= Hypertubule diameter at 4D interface

137= Cone’s larger end diameter at 3D interface where the photons are absorbed or emitted.

The 4D twisted Hypertubule gets longer or shorter as twisting or untwisting occurs. (720 degrees per twist cycle.)

How many neutrinos are left over from the Big Bang? They have a small mass, but they could be very large in number. Could this help explain Dark Matter?

Why did Paul Dirac use the twist in a belt to help explain particle spin? Is Dirac’s belt trick related to this model? Is the “Quantum” unit based on twist cycles?

I started out imagining a subatomic Einstein-Rosen Bridge whose internal surface is twisted with either a Right-Hand twist, or a Left-Hand twist producing a twisted 3D/4D membrane. This topological Soliton model grew out of that simple idea. I was also trying to imagine a way to stuff the curvature of a 3 D sine wave into subatomic particles.
.

[vanikaghajanyan]

35:28 To quantum expression for the gravitational potential: "Containing all information about the gravitational field." (Einstein), you can come according to the classics (G), SR ©, and De Broglie's hypothesis (h), - without GR and QM:
a. Kepler's third law: Gm=(r^3)w^2.
b. The researcher will notice that electrodynamics has achieved great success, compared with mechanics, thanks to the introduction of the concept of current, and will write down Kepler's law as follows: I(G)= mw=v^3/G, where I(G) is the gravitational current. By the way, Maxwell's realization of the displacement current effect is the culmination of all (mechanics+electrodynamics) classical physics.
c. The researcher will get acquainted with the semi-classical Bohr theory, where the quantization rule of the angular momentum: the moment modulus in a stationary orbit is determined by the formula mvr=nħ (n=1, 2, 3, ..). As well as with the de Broglie hypothesis: a free particle should be compared with a plane monochromatic wave, and the wave parameters are frequency and length waves are associated with mechanical characteristics - momentum and energy: k=p/ħ=w/c. And, based on Kepler's law, will write down Newton's law as follows: F=mg=m|a|= v^4/G=(ħ/c)w^2.
d. The researcher will remember Einstein's time dilation and the equivalence principle [see Pauli, RT, "Simple consequences of the equivalence principle", where v^2=(rw)^2=-2Ф(centrifugal)~-2Ф(G)], and finally writes the quantum expression for the Newtonian gravitational potential as follows: Ф(G)=(-1/2)[Għ/c]^½(w) = (can be tested experimentally in the laboratory at the moment).
One of the important regularities that the formula reveals is the quantization of not only the orbit, but also the wave itself (obviously, the problem of particle/wave dualism disappears at the same time): πr=nλ=(n+n')2r(pl), that is, λ=(1+n'/n)λ(pl), where n' (=0, 1, 2, 3…) is the orbit number, n (=0, 1, 2, 3…) is the number of particles (quanta).
In other words, mc^2=ħw; where m (=M/n'=2∆m/n) is the quantum of the complete and mass defect of the system: moreover, the parameter mλ covers the entire spectrum of particles.

[gene]

Knowledge is only valuable, when it produces a product of value.

[wafikiri_]

I do understand cognition and consciousness, in various mutually-related mathematical, physiology-grounded ways.

[sanjibkarjee]

Consiousness can't be explained and it has infinite degree of freedoms. That is connected to the hard problem of Consiousness which will remain forever.. we can reach to abstract. But not to Consiousness.

[MisakaMikotoDesu]

Glad to see him not only mention the idea of consciousness being fundamental, but doesn't discredit it either. He is correct however that it's an irrelevant argument in the domain of physics without making testable predictions.

[davidwilkie]

A fine example of Socratic Method response to assertion and debate via Disproof Methodology, Metaphysical Philosophy in constructive discussion. (Students should retaliate in kind and mutual respect)

[notanemoprog]

There is a one minute and thirty seconds long attempt at total dismantling of the very foundations of the entirety of Sabine Hossenfelder's life project AKA "superdeterminism" @48:25 and it would be interesting to hear her response

[pdelong]

Hi @seancarroll, could you please write a book on QFT? (I'm half-joking... but I'm also half-serious.)

Kidding aside, if you did write one, I'd be among the first in line to purchase a copy.

It's difficult to find a QFT textbook which stays grounded [1], and properly motivates the material. Even the texts which are intended for an audience of students approaching the subject via self-study [2], tend to be a bit opaque to a relative outsider to the field.

Your explanation of renormalization and ultraviolet cutoff finally make that aspect clear to me, in spite of the fact that you haven't even shown much math yet.

So, that's a long-winded way of saying, great lecture (even though I'm only halfway through, so-far). I'll probably be picking-up your GR textbook.

- Paul

Footnote 1:

...well, as much as is possible anyway, given the subject matter.

Footnote 2:

...who (for example) got their EE BS years ago, and stayed current in his (or her) physics knowledge (just to pick a random example). ;-)