Don’t let yourself get entangled with these four misconceptions of quantum mechanics: ScienceAlert

Quantum mechanics, the theory that governs the world of atoms and tiny particles, certainly has the X factor.

Unlike many other areas of physics, it is strange and counter-intuitive, which makes it both fascinating and intriguing.

When was the Nobel Prize in Physics in 2022 Awarded to Alan Aspect, John Clauser and Anton Zeilinger To research shedding light on quantum mechanics, Aroused excitement and discussion.

But discussions of quantum mechanics—whether in chat forums, in the media, or in science fiction—are often clouded by a number of persistent myths and misconceptions. Here are four.

1. A cat can be alive or dead

Perhaps Erwin Schrödinger could not have foreseen this thought experimentSchrödinger’s cat, it will reach Internet meme status in the 21st century.

It suggests that an unlucky cat stuck in a box with a kill switch triggered by a random quantum event – radioactive decay, for example – can be both alive and dead at the same time, as long as we don’t open the box to check.

We’ve known for a long time that quantum particles can be in two states – say in two locations – at the same time. We call this an overlay.

Scientists were able to show this in the famous double slit experiment, where a single quantum particle, such as a photon or electron, can pass through two different slits in a wall simultaneously. How do we know that?

In quantum physics, every state of a particle is also a wave. But when we send a stream of photons – one by one – through the slits, it creates a pattern of two waves that interfere with each other on a screen behind the slit.

Since each photon did not have any other photons to interfere with when it passed through the slits, this means that it must have passed through both slits at the same time – and interfered with itself (photo below).

Illustration of the double slit experiment, in which a flashlight shines through two slits, light waves travel from one wave to multiple waves through the slit.
(Dorling Kindersley/Dorling Kindersley RV/Getty Images)

For this to work, the states (waves) must be in the superposition of the particle that passes through both slits”coherent– Having a well-defined relationship with each other.

These superposition experiments can be performed with objects that are constantly increasing in size and complexity.

One famous experience by Anton Zeilinger in 1999 demonstrated a quantum superposition with large particles of carbon 60 Known as “buckyballs”.

So what does this mean for our poor cat? Is he really alive and dead as long as we don’t open the box?

It is clear that a cat is not like a single photon in a controlled laboratory environment, it is much larger and more complex.

Any cohesion that may be between the trillions and trillions of atoms that make up the cat with each other is very short-lived.

This is not to say that quantum coherence is impossible in biological systems, just that it does not generally apply to large creatures such as cats or humans.

2. Simple comparisons can explain entanglement

tangle It 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 – regardless of the distance between them.

Common explanations for it Usually includes everyday things From our classic macroscopic world, like dice, cards, or even pairs of odd-colored socks.

For example, imagine that you tell your friend that you put a blue card in one envelope and an orange card in another envelope. If your friend takes one of the envelopes, opens one of the envelopes, and finds the blue card, he will know you have the orange one.

But to understand quantum mechanics, you have to imagine the two cards inside the envelopes in a common superposition, which means they are both orange and blue at the same time (specifically orange/blue and blue/orange).

Opening one envelope reveals one randomly selected color. But opening the second still always reveals the opposite color because it is ‘frighteningly’ linked to the first card.

One can force the cards to appear in a different set of colours, similar to doing another kind of measurement. We can open an envelope asking: “Are you a green or a red card?”.

The answer will be random again: green or red. But crucially, if the cards are intertwined, the other card will always yield the opposite result when asked the same question.

Albert Einstein attempted to explain this with classical intuition, noting that cards could have been supplied with Hidden set of internal instructions Which told them what color they appear when asked a particular question.

He also rejected the apparent “scary” act between the cards that seemed to allow them to affect each other instantly, meaning communication faster than the speed of light, something that Einstein’s theories forbid.

However, Einstein’s explanation was later ruled out by Bell’s theory (a theoretical test devised by physicist John Stuart Bell) and experiments by Nobel laureates in 2022. The idea that measuring one entangled card changes the state of the other is not true.

Quantum particles are mysteriously connected in ways that we cannot describe with everyday logic or language – they do not communicate while also containing a hidden code, as Einstein believed.

So forget about the everyday stuff when you think about tangles.

3. Nature is unreal and “unlocal”

It is often said that Bell’s theory proves that nature is not “local”, and that a thing is not only directly affected by its immediate surroundings. Another popular explanation is that it indicates that properties of quantum objects are not “real”, and that they did not exist prior to the measurement.

But Bell’s theory We are only allowed to say Quantum physics means that nature is not real and local if we assume some other things at the same time.

These assumptions include the idea that measurements have only one consequence (and not 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 history.

Despite Bell’s theory, nature may be both real and local, If you let me break some other things We consider common sense, like time to move on. Hopefully, further research will narrow down the large number of possible explanations for 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 abandoning the concept of local reality.

4. Nobody understands quantum mechanics

a classic quote (attributed to the physicist Richard Feynmanbut also in this form a paraphrase Niels Borg) speculates: “If you think you understand quantum mechanics, you don’t.”

This opinion is widely disseminated in public. It is supposed to be impossible to understand quantum physics, including by physicists. But from a twenty-first century perspective, quantum physics is neither particularly mathematically nor conceptually challenging for scientists.

We understand them so well, that we can predict quantum phenomena with high accuracy, simulate highly complex quantum systems, and even begin to Building quantum computers.

Superposition and entanglement, when explained in the language of quantum information, require nothing more than high school mathematics. Bell’s theory requires no quantum physics at all. It can be derived in a few lines using probability theory and linear algebra.

Perhaps the real difficulty lies in how to reconcile quantum physics with our self-evident reality. Not getting all the answers will not prevent us from making further advances in quantum technology. We can just simply shut up and count.

Fortunately for humanity, the Nobel laureates Aspect, Clauser and Tesselinger refused to be silent and kept wondering why. Others like them may one day help reconcile quantum weirdness with our experience of reality.Conversation

Alessandro Federizziphysics professor, Heriot-Watt University And the awsome ownerphysics professor, Heriot-Watt University

This article has been republished from Conversation Under a Creative Commons License. Read the original article.

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