Don’t let these 4 quantum mechanics fallacies fool you : ScienceAlert
Quantum mechanics, the theory that governs the microworld of atoms and particles, certainly has an X factor.
Unlike many other areas of physics, it is bizarre and counterintuitive, which makes it dazzling and intriguing.
When was the 2022 Nobel Prize in Physics? awarded to Alain Aspect, John Clauser and Anton Zeilinger for research that sheds light on quantum mechanics, it generated excitement and discussion.
But debates about quantum mechanics—whether on chat forums, in the media, or in science fiction—can often be muddled thanks to a number of persistent myths and misconceptions. Here are four.
1. A cat can be alive or dead
This suggests that an unfortunate cat stuck in a box with a kill switch triggered by a random quantum event—radioactive decay, for example—could be alive and dead at the same time, until we open the box to check.
We have long known that quantum particles can be in two states – for example in two locations – at the same time. We call this superposition.
Scientists were able to demonstrate this in the famous double-slit experiment, where a single quantum particle, such as a photon or an electron, can simultaneously pass through two different slits in the wall. How do we know that?
In quantum physics, the state of each particle is also a wave. But when we send a stream of photons—one at a time—through the slits, it creates a pattern of two waves that interfere with each other on the screen behind the slits.
As each photon had no other photons to interfere with when it passed through the slits, this means that it had to pass through both slits at the same time – interfering with itself (image below).
However, for this to work, the states (waves) in the superposition of a particle passing through both slits must be “coherent” – have a well-defined relationship with each other.
These superposition experiments can be performed with objects of increasing size and complexity.
So what does this mean for our poor cat? Is it really both alive and dead until we open the box?
Obviously, a cat is nothing like a single photon in a controlled lab environment, it’s much bigger and more complex.
Any coherence that the trillions and trillions of atoms that make up a cat might have with one another is extremely short-lived.
This doesn’t mean that quantum coherence is impossible in biological systems, just that it generally won’t apply to large creatures like cats or humans.
2. Simple analogies can explain the entanglement
Entanglement is a quantum property that connects two different particles so that if you measure one, you automatically and instantly know the state of the other – no matter how far apart they are.
The usual explanations for it they usually involve everyday objects from our classical macroscopic world, such as dice, cards or even pairs of oddly colored socks.
For example, imagine telling your friend that you put a blue card in one envelope and an orange card in another. If your friend takes and opens one of the envelopes and finds a blue card, they will know you have an orange card.
But to understand quantum mechanics, you have to imagine that the two cards inside the envelope are in mutual superposition, meaning they are both orange and blue at the same time (specifically orange/blue and blue/orange).
Opening one envelope reveals one randomly determined color. But opening the second one still always reveals the opposite suit because it is “spookily” connected to the first card.
One could make the cards appear in a different set of colors, similar to doing other types of measurements. We could open the envelope with the question: “Are you a green card or a red card?”.
The answer would again be random: green or red. But the key is that if the cards are tangled, the other card would still always give the opposite outcome when asked the same question.
Albert Einstein tried to explain this with classical intuition, suggesting that the cards could be rigged a hidden, internal instruction set which told them what color to appear in given a certain question.
He also rejected the apparent “spooky” action between the cards that seemingly allows them to instantaneously affect each other, which would mean faster-than-light communication, something forbidden by Einstein’s theories.
However, he later rejected Einstein’s explanation Bell’s theorem (a theoretical test made by physicist John Stewart Bell) and the 2022 Nobel Prize experiments. The idea that measuring one twisted card changes the state of another is incorrect.
Quantum particles are just mysteriously connected in ways we can’t describe with everyday logic or language – they don’t communicate, and they contain a hidden code, as Einstein thought.
So forget about everyday objects when thinking about entanglement.
3. Nature is unreal and ‘non-local’
It is often said that Bell’s theorem proves that nature is not “local”, that an object is not only directly influenced by its immediate environment. Another common interpretation is that it implies that the properties of quantum objects are not “real”, that they do not exist before measurement.
But Bell’s theorem it just lets us say that quantum physics means that nature is not both real and local if we assume several other things at the same time.
These assumptions include the idea that measurements have only one outcome (rather than multiple, perhaps in parallel worlds), that cause and effect flow forward in time, and that we do not live in a “clock universe” where everything is predetermined. since the dawn of time.
Despite Bell’s theorem, nature can be real and local, if you allowed to break some other things we consider common sense, such as time moving forward. And we hope that further research will narrow down the large number of potential interpretations of quantum mechanics.
However, most of the options on the table—for example, time flowing backwards or the absence of free will—are at least as absurd as giving up on the concept of local reality.
4. Nobody understands quantum mechanics
This attitude is widely held by the public. Quantum physics is supposedly impossible to understand, including by physicists. But from a 21st century perspective, quantum physics is neither mathematically nor conceptually particularly difficult for scientists.
We understand it extremely well, to the point where we can predict quantum phenomena with great precision, simulate very complex quantum systems, and even begin to they make quantum computers.
Superposition and entanglement, when explained in the language of quantum information, require nothing more than high school math. Bell’s theorem does not require any quantum physics at all. It can be derived in a few lines using probability theory and linear algebra.
The real difficulty may lie in how to reconcile quantum physics with our intuitive reality. Not having all the answers will not stop us from making further progress with quantum technology. We can simply shut up and do the math.
Fortunately for humanity, the Nobel laureates Aspekt, Klauser and Zeilinger refused to be silenced and kept asking why. Others like them may one day help reconcile quantum weirdness with our experience of reality.
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