Sure. It came as somewhat surprising in the Arvin Ash video that he said 'light is a wave' as I thought that was settled and so initially I kind of dogmatically just rejected it. But on realising I really dont have a clue I watched it more closely. I think we are looking at 2 very different interpretations of phenomena, and it isn't guided by maths, it's ontology, if that is the correct word.

A field is a mathematical abstraction. I don't think the world is made of mathematical abstractions, even though some physicists have proposed this! The temperature field in Arvin's video is a mathematical model that consists of assigning to every point in a continuous 3D space the value of the average kinetic energy of nearby molecules.

Until we figure out what the universe is made of, we won't know what the fields in QFT are modeling. However, theorists hypothesized these fields, and they have proved useful in making calculations that agree with experiment.

Yes this is controversial. Gravitons are not part of the standard model. And yet, when the mathematics of a massless spin 2 field in QFT are worked out, with no other assumptions than that massless spin 2 quanta exist, you get general relativity out of it. So that is considered a big hint that this is a promising direction.

The fields act like particles because the field is quantized. You cannot create excitations in the field in an arbitrary way. You can only do so in packets of energy (quanta) proportional to the frequency (E=hf). In the EM field this quantum (the singular of quanta) of energy is called a photon. And you can only absorb energy from the field in the same way. So since you can only produce energy in discrete packets, and only detect them in discrete packets, they look like particles in our experiments.

QM does not require intelligent agency to create the universe. QM drops out of the QFT mathematics anyway - see this at about 40:20 in the Anthony Zee video I posted.



The Copenhagen interpretation is just wrong. Treat the observer (or any macroscopic device which measures a quantum effect) as a quantum system and it goes away. Easier said than done for macroscopic things consisting of on the order of ~10^23 molecules. I don't agree with Sean Carroll's favored interpretation either. There is just something deeper going on that we don't understand yet. Things like what is physically underlying quantum fields, and how does field collapse work.

https://www.quantum-field-theory.net...elds-collapse/

Sure. If immaterialism is false then materialism is true.

Tim, could you explain how QFT interprets the delayed choice experiments. Thanks.


PairTheBoard

I don't have the time for fairy tales

Found another good paper by Rodney Brooks.

https://arxiv.org/ftp/arxiv/papers/1710/1710.10291.pdf

Description of the experiment: https://arxiv.org/abs/quant-ph/0610241

Brooks:

Also even before looking into QFT, I never understood why the observer that collapses the wave function in the Copenhagen interpretation had to be a conscious human. Why couldn't Schrodinger's cat be the observer? Why couldn't the Geiger counter be the observer? To go in the other direction, why doesn't Schrodinger, upon opening the box, enter a superposition between having seen a dead cat and a live cat.

As it turns out, an atom in the Geiger counter either absorbs a radioactive decay product and collapses the field, or nothing happens and the cat lives. No mystical consciousness stuff going on here.

Anyway I don't like the idea of cruel thought experiments on cats, and I hope someday he gets his revenge:

Just thinking here. But it seems to me that this "collapse" from a non-local quantum field to the depository of its energy is only a relative localization of the quantum field energy. As an analogy, suppose you have a normal probability distribution with a very large sigma which "collapses" to (or absorbed into say) a normal probability distribution with a very small sigma. If the second sigma is small enough it might seem to us to be totally localized. But the localization is really only relative. Both the before and after still have infinite tails.

So if a photon of light's quantum field is absorbed by say the quantum field of an atom's electron it's not a total localization of the photon's energy. It only seems localized to us but is really only relatively localized. While peaking near the atom according to the new orbit it's still spread out. Seems like the math for the interaction of quantum fields should be able to handle this.


PairTheBoard

Sure someone could make the math work or invent new math if necessary, but not enough is known about what is happening during an interaction to even get started on that, AFAIK. For example, given a single photon entering a beam splitter leading to two detectors, we can't say which detector will register, even though the field reaches both of them. And it's not time based, since we can make one detector much further away than the other without changing the probabilities.

Haven't time to think all the new posts through but just want to put this one out there before I disappear for a bit.
Kim et al 1999 delayed choice quantum eraser, I don't think this is principally different from other QE experiments but this is the best for showing explicitly what is going on

https://en.m.wikipedia.org/wiki/Dela...quantum_eraser



Now its my turn to get incredulous with Dr Brooks, I hate having to overstep the mark with a guy who is clearly 1000 fold smarter and more educated than I am but he is just not right here.

"the photon is a field". No it isn't, by defintion of the terms photon and field and what we observe when we do this, or any experiment with single photons.

Photon = particle representing quantum of light
Field = a physical quantity, represented by a number or tensor, that has a value for each point in space-time.

Former is discrete, latter is continuous.
When we fire a single photon it registers as a particle/photon.

Secondly looking at the Kim et al set up, saying the photon always travels along both routes is not right. It is either the top or the bottom, red or blue. The genius here is to then scramble or retain the path information. We get a particle distribution for subsets D4 and D3 because the path info is known regardless of what happens with the quantum eraser part of the set up. Interference for D1 and D2, why? Because the knowledge of the path information has been obfuscated by the set up - information is causing the effect.

When Dr Brooks says QFT does not have a theory for field or wave function collapse, is he is saying he doesn't have a theory of causation? Yet by Copenhagen interpretation we do have the cause and effect relationship established. Therefore this is superior in my view.

Also I don't believe "consciousness" causing matter is a result of the experiment, it just naturally follows that to have information you need a transmitter and receiver.

So still weird huh?

Do they really model quantum fields as (complex?) values at "points". Wouldn't the more natural model be via Distribution Theory where distributions are evaluated at localities represented by test functions. Out of this model you get a nice application of Fourier theory and a nice Hilbert Space.

Also, if these "values" are complex values with magnitude and angle (phase?), what do the magnitude and angle (phase?) represent?


PairTheBoard

Fixed my post.

It's good there are different viewpoints. Who knows who is the most off? Say we are mainly discussing the 1% solid knowledge here. How do you compare that to Donald Hoffman's speculative maybe 10% of what there is in the world?

Here's the QFT story:

Under QFT the photon is a discrete excitation of the electromagnetic field. That defines it as a particle, because under QFT that's exactly what a particle is. Production and absorption of a photon are each only possible in a discrete way, which is why they emit and detect as we think of as particles intuitively. But as the photon propagates through space, it does so as a wave in a field.

By your definition of a particle, it has to take either one path or the other, but by the field definition, it can take both. Citing more and more complicated experiments does not change this.

See my post about Schrodinger's cat. Why does the observer have to be a conscious human? Why can't it be a conscious cat? Why can't it be a Geiger counter. That's a receiver of information, isn't it? Why is Schrodinger, after opening the box, not in a superposition of having seen a dead cat and a live cat, until a colleague opens the door to his lab and observes him?

https://en.wikipedia.org/wiki/Copenhagen_interpretation

I watched twenty minutes

That's longer than the average free porn vid! Here, I'll provide one more suited to your tastes:



I've never looked into who the interviewer is but he's apparently got enough credit to book many of the smart people.

Well I watched that short video and his TED talk also. This guy is fairly good at painting pretty pictures using bovine excrement, I'll give him that.

Probably the most concise and understandable explanation thus far so good job there. I appreciate this is mostly the same thing back and forth now but I think it is still worthwhile in clarifying what the positions are.

Here's a single particle build up for electrons -



In image (a) we see a record of individual electrons, particles, hitting the screen. Does QFT model claim that each of these electrons is a discrete excitation of the electron field? What evidence is there that each of the electrons propagated through space as a wave in a field, from the emitter, passed through both slits, yet was recorded as a particle?

In image (d) we see interference once enough electrons have been recorded.
In QFT is this a manifestation of the electron field or the wave function, or same thing?

Copenhagen interpretation - image (d) is the wave function manifest, the electrons don't know where to hit the screen because the information about which slit they went through is not known. When the path information is known, the electrons land as expected by particle trajectories -



Information is causative.

By the particle distribution observed, they only take one path. By the interference pattern they still took one path but are only able to manifest as the wave function determines, due to the absence of the which path information.

From the earlier anonymous post

The arrangement of the set up either allows or obfuscates the which path information, so a conscious human is not required. But the transmitter-receiver relationship exists, because information exists. And since knowledge or lack of knowledge of information is causative, we have to ask who knew this information and who is the information for? Why must this be a " who"? - because only intelligent agency can know.