This is incorrect and bad faith representation of Carrol's position.

While Carrol is proponent of MWI, he is calling more research on foundations of quantum theory in general. If you follow his podcast it's clear what his position is. Some of these so called interpretations are "legitimately distinct physical theories, with potentially new experimental consequences". In this article he specially mentions Ghirardi–Rimini–Weber theory. https://en.wikipedia.org/wiki/Ghirardi%E2%80%93Rimini%E2%80%...

If Hawking Radiation can never be observed till the heat death of the universe, is that pseudoscience, or just really hard to test?

At this regime, all of physics is very hard to design an experiment for on ranges we have access to.

The characterization is a little bit harsh, but yes. The Copenhagen interpretation is non-falsifiable, (relative to MWI) so while I don't know what it is, I know it isn't science.

There's a reason most reputable scientific journals don't accept papers dealing with interpretations of quantum mechanics. There's no "there" there.

Hawking radiation is interesting because a proof of lack of Hawking radiation is a proof of the falsehood of quantum mechanics. Which is really interesting; any time you can falsify something like quantum mechanics every physicist should be paying attention. Also, if certain models of string theory are correct, particle accelerators like the LHC should be able to produce micro black holes, which will then evaporate in detectable ways. So Hawking radiation is of observational interest as of 2010 as a possible way to provide evidence to support string theory. (spoiler alert: we didn't find any)

Or why is mwi impossible to verify.

[1] There is this one theory whose name I cannot remember, where each particle in the universe gets their wavefunction multiplied by a delta function or very thin gaussian at random intervals, and whose sudden localization also causes a sort of chain reaction and localizes all particles it is entangled with. This theory is interesting because it helps set a (statistical) limit between microscopic and macroscopic interactions; basically, when you go past a certain number of entangled particles, everything will be well-localized virtually all of the time, but for small numbers of particles we'll see quantum phenomena. Unfortunately I recall this theory having too many holes, and perhaps it has already been falsified, but the point is that at least it made an effort to address inherent problems in QM (namely, wavefunction collapse) in a way that physicists actually should; by making testable claims.

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

That's a pretty big "if". As I suspect you know, how much Hawking radiation a black hole generates is inversely proportional to its size (it's probably an inverse square function to be precise, I forget).

A consequence of that is that supermassive black holes, the kind at the center of galaxies that we are most likely be able to indirectly (or even directly) observe, will generate almost none and whatever is generated will likely be outshone many orders of magnitude by the accretion disk anyway.

But... small black holes should shine extremely brightly, albeit briefly. A black hole resulting from a supernova will take a stupendous amount of time to lose enough mass (from Hawking radiation) to get this small and the window of time is so small we're unlikely to ever directly observe this.

But if we can ever figure out a way to lase gamma rays we can construct so-called Kugelblitz black holes (that some call the ultimate battery or even the ultimate computer).

Granted there's no theorized let alone practical way of lasing gamma rays, which is a problem.

But nevertheless, the theory of Hawking radiation makes testable predictions so yes, it's unlike Many Worlds (or even, honestly, string theory).

We might decide a theory isn't testable even on principle, or discover that a theory we thought that wasn't testable actually is testable, but we'll never know until we do the work.

Our understanding of quantum measurements is much better now than it was at the advent of quantum mechanics, and it's understood that there's no such thing as an "abrupt" collapse of a wave function during measurement, it's instead a continous process involving entanglement and decoherence between two quantum systems (the system being measured and the measurement system). This understanding allows us to explain any measurement process using only "plain" quantum mechanics, i.e. unitary evolution of two coupled systems described by a Hamiltonian. If we just look at the Hamiltonian of the measured system it will seem that it shows wave function collapse because its evolution is non-unitary, but the evolution of the entire system is still unitary. From this angle I personally find any further invokation of a wave-function collapse mechanism unnecessary, and I think it overcomplicates quantum mechanics without giving us any benefits, so we might as well do away with it. Unfortunately, most courses on quantum mechanics still introduce the students to wave-function collapse when explaining measurement outcomes, which might be the reason that so many physicists have a bad understanding of the measurement process. Of course wave-function collapse is still a good shortctut for describing strong quantum measurements, I think it should be introduced as an approximation of a continuous measurement though.

Carroll does not mention his preference for many-worlds in the article because that's not what it's about. The fact that he has a preferred interpretation is not relevant to the point that physicists should pay closer attention to the lack of consensus on the interpretation of qm.

I don't see that in this particular article (which is not to say it isn't there in other articles Carroll has written). In this article, he is simply pointing out that QM is the only physical theory we have ever had that does not have a single generally accepted interpretation. Not believing the MWI is fine (I'm not a fan of it myself), but that just means you have to find some other interpretation that works, and nobody has done that; every interpretation of QM has issues that nobody has figured out how to resolve.

The universe is constantly splitting. Not just when there is decoherence.

Or more accurately. Every possible state of the universe has a probability amplitude right now. And those probability amplitudes are constantly evolving, diffusing into each other, interfereing with each other.

Every such state with a probability amplitude is a world of the many worlds.

Then please write about these probes, and not just the rant that "nobody understands."

The public doesn't have to worry (and we don't have to read) about the "interpretations" until there is a specific proposition of how to do such probe an the experiment can be constructed and performed.

He writes "students who demonstrate an interest in the topic are gently but firmly — maybe not so gently — steered away, sometimes with an admonishment to “Shut up and calculate!”."

My answer to this article would be, to theoretical physicists: "shut up and construct an experiment that can be performed." As long as there's no practical difference (in the sense that any experiment that can be imagined can demonstrate it) there's just no physics there.

So yes... "shut up and calculate."

[1] https://thoughtexperiments.net/quantum-suicide/

If someone does it and doesn't die would you think that did prove anything?

If one thousand people do it and one of them is still alive after 10 coin flips does that prove anything?

What is the detectable physical difference? How do you carry on an experiment to detect that physical difference? What is the protocol to determine that the physical difference has been detected?

Please let me know how should we do to not totally ignore this.

So if you are still alive in 1M years that’s evidence of QI. Basic Bayesian reasoning.

You can always just be lucky; maybe gravity causes the Earth to move randomly and we've just been lucky to see if orbiting the sun for the past few years.

Or, the universe was split before and that quantum uncertainty is really us perceiving those already-existing other universes. The collapsed wave is really just us measuring the only particle, the one in our universe, capable of stronger interactions. Under that interpretation the rest of the electron shell is a cloud of other electrons existing across universes but unable to interact strongly in ours, literal ghost particles.

This is testable, if not practical atm. If something like an electron exists in ghost forms across multiple universes then they may be linked in those other universes more strongly than ours, a concept that may offer explanations for a variety of quantum behaviors. Proof of this would be the observation of a reliable link between particles not linked in our universe.

---

Consider the famous Schroedinger's Cat.

The decayed particle has two states: decayed and not decayed.

The cat has two states: dead and alive.

The researcher that opens the box has two states: sad and happy.

The waveform does not collaprse. The particle, the cat, and the researcher each have a uncollapsed waveform; i.e. are in both states.

However, these waveforms are not independent; they are entangled. The decayed particle is coincident with the dead cat and the unhappy researcher. And the undecayed particle with the alive cat and the happy researcher.

All states "exist" simultaneously, but not independently. This bifurcation in the wave function magnitudes is a "split" in the universe: every future waveform interaction will be in the context of decayed particle/dead cat/unhappy researcher and undecayed particle/alive cat/happy researcher.

"Many worlds" sounds nonsensical, but it is really just a colloquial expression for waveform entanglement.

---

Now this does present a philosophical question on how consciousness functions in light of the split waveforms.

I maintain that science -- quantum mechanics or otherwise -- has no explanation or even language to express "consciousness". It's like asking science an ethics question. And this inability applies to all science, not just quantum mechanics.

MWI distinguishes itself by omitting (as you say) any notion of "collapse" from its axioms. This is appealing for simplicity but the problem is how it connects to experimental results:

1. How does the Born rule arise? If the universe split into two but the measure of cat-dead is 1/pi, why do I find myself in the cat-alive universe more often?

2. More generally, how does randomness arise? MWI contains only deterministic axioms, so how can it explain the experimental observation that measurements of similarly prepared states result in different values?

Imagine instead of a single experimenter observing a billion possible outcomes, a billion experimenters observing a single possible outcome.

The hope of MWI is to produce a simpler theory by eliminating an axiom. If this forces us to axiomatize "conscious observers" then it has already failed. Though I admit it may be fun to think about.

My guess would be that they are all consciously experienced, some more and some less. The alternative seems to be to say that they are so called "p-zombies". Very similiar to us, evolving according to the same laws, but not concious. But it's really up in the air.

> 1. How does the Born rule arise?

> 2. More generally, how does randomness arise?

As you said, with Many Worlds there is no randomness. The multiverse is entirely deterministic. Randomness is a Copenhagen-like concept.

There is a "universe" with an alive cat and a "universe" with a dead cat. These universes have a certain waveform distribution.

Neither of these universe are any more real or extant than the other (they have the same magnitude).*

* Though consciousness and its observations seems to follow only one path. This is a peculiarity outside the realm of physics.

Of course physics can answer this: the human minds on the different branches can't physically interact. They can't share memories. Each one is going to remember experiencing only its own branch.

Whether this is a problem or not depends on what your conception of consciousness/identity is. I see a conflict or unanswered problem there; you may not.

Wondering why you're a specific one of them and not the other seems equivalent to me to wondering why you're you and not some another person in our own world. I think it's an interesting question, but I'm not sure what an answer to it could possibly look like (since any answer that says why you're you somehow needs to work out differently for other people to explain why they're themselves too) which implies the question is malformed somehow. (If your consciousness were ... someone else, or even switched people it was tracking somehow, it's not like anyone would notice.)

Indeed.

MWI's solution to this is to say the experiments are wrong, and the results are actually the same. It rejects empiricism to simplify the theory. But that's not good science.

> Neither of these universe are any more real or extant than the other (they have the same magnitude)

What is meant by "magnitude?" It can't be the measure of the wavefunction because those can easily be different, e.g. if the particle's decay probability is not 50%. This is the Born rule problem again.

It’s as if non-determinists aren’t sure that 2 doesn’t act like a 3 sometimes because of decoherence and so 2 + 3 = 6 as a result.

Where am I going wrong in this line of thinking? How could randomness be injected into a system without superpositioning of quarks? Is that literally the only way?

Is Hawking radiation the smoking gun we think it is?

Edit: I admit I am tired when posting but this topic is perhaps one of the most fascinating of all. I can’t stay away.

It's like matrix multiplication: yes you can wind up with more elements after the operation, but the result as a whole is entirely deterministic.

If you defined matrix multiple multiplication where you collapsed the result down to a single unspecified vector, then you would have "randomness" (according to the selection).

Many worlds says "don't choose"; keep the entire matrix, and the results will get larger and larger.

The universe is not fundamentally rolling dice, though it appears that way from your perspective since you can only see a single slice of the matrix.

So the “realm of physics” is now disconnected from empirical reality? Great.

Unfortunately, yes. Empirical reality is limited by the empiricist.

David Deutsch (in many ways, the father of quantum computing) initially imagined quantum computing as a way to test MWI: if a problem could be solved that required more gates than there are particles in the universe, then it would (so the argument goes) prove that the problem was being solved in the multiverse.

This is quite a popular claim among the Physics community. It goes even further saying: those who understand it don't understand it. ;-) Emphasizing how counter-intuitive the concepts are and also the fact the even Standard QM (with 1 or 2 particles) is still a research topic. Even Einstein didn't believe in QM as it stands now.

Where does the energy come from to create the other universes?

> A lot of physicists also don't see any value in MW's interpretation since it offers no predictive value

is not entirely correct either.

This is the probably best "explain like I am an undergraduate not in Physics" article on Everett's proposal.

https://plato.stanford.edu/entries/qm-everett/

To further summarize the value of Everett's proposal:

In the standard von Neumann-Dirac collapse formulation of QM, a collapse happens when we measure it. But what a measurement event looks like and conditions when it occurs are not described by the theory at all. This is one reason why QM cannot completely describe the universe, or approximate it. Note that even if we can describe what a collapse is, this+QM still fails to model parts of the world, only approximating it.

But one can try to propose a formulation of QM that agrees with the collapse formulation, that does not have that collapse, so that it is closed in the sense that for each system of observers observing a quantum system collapsing, that system can be modeled as quantum system itself. That is Everett's proposal. From the linked article,

> Everett’s solution to the problem was to drop the collapse postulate from the standard formulation of quantum mechanics then deduce the empirical predictions of the standard collapse theory as the subjective experiences of observers who were themselves modeled as physical systems in the theory. The result was his relative-state interpretation of pure wave mechanics.

In MWI there is no collapse event, because there are no observers in the traditional sense that may collapse the system. In MWI we resign and just say that observers are subject to QM, and when a "measurement" is made, what happens is that observers and the observed system get entangled so that certain combinations of properties of the observer-observed system are not possible. This entanglement of two projections of a composite system can be described in the language of QM.

> what is predicted by standard QM, because the MWI is supposed to recover the same predictions.

MWI recovers the same predictions. Where in standard QM if one says an observer observes that a system may collapse 40% in state a and 60% in state b, MWI says that in systems (of the observer and the observed) where the observer makes the observation in the same exact manner, the observer will record state a with the system in state a 40% and the observer will record state b with the system in state b 60%, and there are no states where the observer observes something and the subsystem is in the other state.

Of course, you can simply model the entire system of observer and observed in standard QM and recover the same relative predictions without invoking the absolute observation of an observer. In MWI we do away with the conceit that there is an absolute observation of an absolute, but ill-defined observer.

If standard QM has no problem to make predictions then I agree than in principle the MWI could make the same predictions (but it seems to me that in practice it can only make predictions by using standard QM and saying that those are the same predictions that could in principle be derived).

Edit: it's too late to alter my original ancestor comment, but I think the way I wrote it may have yielded a misunderstanding. I didn't mean to suggest that MWI has value because it can predict phenomena. I meant to say that it has value because it is a metaphysically cleaner model of reality than the collapse interpretations.