---
# System prepended metadata

title: Quantum myths

---

# Quantum myths

There are a few common myths about quantum mechanics that I'd like to address. A full understanding of the issues requires math, which most people don't have the time for. So here I will try to explain them as simply as possible.

---

### The measurement problem

> *I suspect that a substantial majority of physicists who use quantum mechanics in their everyday work are uninterested in or downright hostile to attempts to understand the quantum measurement problem.* 
> 
> --- Caltech physicist Sean Carroll

The biggest mystery still surrounding QM is the nature of measurement. *Why* do superpositions seemingly "collapse" into one result or the other? And when, exactly does this happen? Here are two common (but unhelpful) answers.

1. *Every* physical interaction constitutes a measurement!

Here's the idea: if *any* physical system interacts with your superposition in a way that depends on its "branches" (e.g., "if the particle is spin-up, I'll do *this*; otherwise I'll do *that*"), we can describe that system as a kind of "measurement device."

From *your* perspective, all that has happened is that the device *joined* the superposition. The two are now said to be *entangled.*

We can also talk about what it looks like from the *device's* perspective, but that would be anthropomorphizing it, and would confuse the issue. On the other hand, *other people* can be considered such devices from your perspective.

That's the main takeaway from this answer: QM gives no reason to treat *other people* (or their consciousness) as different from other physical devices. It should *not* be misunderstood as saying that we have solved the measurement problem --- but it often is.

There's another myth that this should demolish:

> *The electron decided to act differently, as though it was **aware** that it was being watched!!* 
>
> -- New Age movie [What The Bleep](https://youtu.be/5WV1SMoVYDM?t=266)

In the two-slit experiment, when the particle interacts with the detector, it *entangles* with it. One implication is that its behavior changes. This can be understood purely mechanically, and has nothing to do with "awareness" or "decisions." This relates to the second supposed answer.

2. Decoherence solves the measurement problem!


> *If you simply stick a cat in a box and link its fate to the outcome of some quantum event, you’re not likely to put it in a superposition of alive and dead, because decoherence will almost instantly force it into one state or the other.* --- A physics Ph.D. writing for [Quanta Magazine](https://www.quantamagazine.org/real-life-schrodingers-cats-probe-the-boundary-of-the-quantum-world-20180625/)

This one is deeply frustrating, because it's frequently repeated even by physicists who know (or *should* know) better.

Decoherence is an advanced topic in QM, but the basics are easy to understand. Here's what it says:

Any time you have a superposition, you can theoretically *prove* that it's a superposition by doing something called an *interference experiment.* But there's a catch: to do this, you need precise control over *all the particles* involved in the superposition.

When these particles are carefully isolated in a lab, this is technologically feasible. We've even demonstrated it with *billions* of particles --- and there's no evidence of any theoretical upper bound. On the other hand, if so much as a single photon entangles with your system, you're in trouble: it will zip off at the speed of light, and you no longer have precise control over all the particles. Air molecules are problematic for the same reason.

Therefore, in any realistic "Schrodinger's Cat" setup, any hope of proving the superposition evaporates almost immediately. That much is true. But to say that it is therefore "force[d] into one state or the other" is false. Decoherence indeed explains why it's technologically infeasible to *prove* the superposition, but everything we know about QM says that there *still is one.*

[From the Stanford Encyclopedia of Philosophy](https://plato.stanford.edu/entries/qm-decoherence/#SolMeaPro):

> Unfortunately, naive claims of the kind that decoherence gives a complete answer to the measurement problem are still somewhat part of the ‘folklore’ of decoherence, and deservedly attract the wrath of physicists (e.g. Pearle 1997) and philosophers (e.g. Bub 1997, Chap. 8) alike.

[Physics StackExchange](https://physics.stackexchange.com/questions/373905/):

> So decoherence explains why you can, in many worlds, separate the worlds and say they do not come in contact again. ... But the collapse itself is not explained, there is still the sum [*N.B.: superposition*] in the above formula, still an "and" ...

---

### Consciousness?

Okay, so what's the upshot? It's this: QM only tells us the following.

1. Until you entangle with the system, you may (or in principle, *must*) treat it as a superposition.
2. Afterward, you are free (indeed, *compelled*) to treat it as "collapsed." It is not merely technologically infeasible for you to demonstrate the superposition, but as far as we know, impossible in principle.

In other words, there is indeed a meaningful sense in which the Cat attains a fate precisely when its information reaches *you, personally.* Sure, that is only true in "this world," but "this world" is the only one you can ever experience. Everone and everything you will ever know lives in that world. Or if you prefer, every *version* of people that you can ever interact with lives here, where *you* are the branching point for all quantum events.

If you try to pin down what "you" means here, you will quickly find yourself narrowing down on "your consciousness." Not for any mystical reason, but because you'll notice that any physical component of yourself (such as your toe) can be treated as an external measurement device from "your" perspective.

Of course, science hasn't provided a clear explanation (or even *definition*) of "consciousness," so very few physicists choose to draw any connection here. Moreover, there are many ways that information from quantum events can reach (and influence) you in ways that wouldn't normally qualify as "conscious," but which presumably entangle you nevertheless. So it would be hasty to draw any concrete conclusions here.

Nonetheless:

> *I think consciousness will remain a mystery. Yes, that's what I tend to believe. I tend to think that the workings of the conscious brain will be elucidated to a large extent. Biologists and perhaps physicists will understand much better how the brain works. But why something that we call consciousness goes with those workings, I think that will remain mysterious. I have a much easier time imagining how we understand the Big Bang than I have imagining how we can understand consciousness.* 
> ...
> *I’m not going to attempt to define consciousness, in a way that’s connected with the fact that I don’t believe it will become part of physics. And that has to do, I think, with the mysteries that bother a lot of people about quantum mechanics and its applications to the universe.* 
> ...
>  *Quantum mechanics kind of has an all-embracing property, that to completely make sense it has to be applied to everything in sight, including ultimately, the observer. But trying to apply quantum mechanics to ourselves makes us extremely uncomfortable. Especially because of our consciousness, which seems to clash with that idea. So we’re left with a disquiet concerning quantum mechanics, and its applications to the universe. And I do not believe that disquiet will go away. If anything, I suspect that it will acquire new dimensions.* 
> 
> -- Edward Witten, a physicist so overpoweringly brilliant that his fellow string theorists casually throw around terms like ["smarter than anyone else"](http://www.nytimes.com/1987/10/18/magazine/a-theory-of-everything.html?pagewanted=all) and "head and shoulders above the rest."

---

### The "law of attraction?"

Quantum mechanics does *not* say that you can choose (or even influence) the outcome of a quantum event --- or in many-worlds speak, *which* world you end up in. On the other hand, it also doesn't say that you *can't.* Instead, it says that such a question isn't even physically meaningful.

From the many-worlds perspective, "you" end up in *both* branches, so the question of "which branch" evaporates. Even in single-world interpretations, the outcome is *provably* not determined by any physical facts. Therefore, whatever might be supposedly influencing outcomes would be by definition outside the domain of physics.

---

### Bonus myth: QM is only relevant in very fringe cases

Most quantum mechanical events have no macroscopic implications. For example, a photon may go *this way* or *that,* but even if *many* do that, they tend to average out to produce noise that has no cosmic implications.

On the other hand, the *Schrodinger's Cat* setup is carefully designed to amplify a microscopic quantum event to the macroscopic level. You could imagine that it's a dictator's cat in there, and if it dies, he declares nuclear war. Macroscopic implications, indeed!

But such a device is extremely contrived. No such "amplification" devices exist in nature --- or *do* they?

Recent research in quantum biology suggests that the answer is such devices *do* exist. For example, we now know that humans can consciously detect light at (or close to) the level of *single photons.* This means that our brains are indeed capable of amplifying individual particles to the *behavioral* level. 

Of course, you are unlikely to make any big decisions based on whether you saw a single photon or not, but it is conceivable that if you are on the edge of a decision, you can be nudged one way or another due to small variations in your neurotransmitters.

Therefore, when you go to sleep and wake up 8 hours later, billions of people potentially have brains that are in indeterminate states, which they will them further amplify out into the world --- meaning that the set of possible worlds you wake up to every morning is probably more vast than we normally imagine.

Just some food for thought.

