If a tree falls in a forest and no one is there to hear it, does it make a sound? Perhaps not, some say.And if someone is there to hear it? If you think that means it obviously did make a sound, you might need to revise that opinion.We have found a new paradox in quantum mechanics one of our two most fundamental scientific theories, together with Einstein's theory of relativity that throws doubt on some common-sense ideas about physical reality.
Take a look at these three statements:
These are all intuitive ideas, and widely believed even by physicists. But our research, published in Nature Physics, shows they cannot all be true or quantum mechanics itself must break down at some level.
This is the strongest result yet in a long series of discoveries in quantum mechanics that have upended our ideas about reality. To understand why it's so important, let's look at this history.
Quantum mechanics works extremely well to describe the behavior of tiny objects, such as atoms or particles of light (photons). But that behavior is very odd.
In many cases, quantum theory doesn't give definite answers to questions such as "where is this particle right now?" Instead, it only provides probabilities for where the particle might be found when it is observed.
For Niels Bohr, one of the founders of the theory a century ago, that's not because we lack information, but because physical properties like "position" don't actually exist until they are measured.
And what's more, because some properties of a particle can't be perfectly observed simultaneously such as position and velocity they can't be real simultaneously.
No less a figure than Albert Einstein found this idea untenable. In a 1935 article with fellow theorists Boris Podolsky and Nathan Rosen, he argued there must be more to reality than what quantum mechanics could describe.
Read more: Einstein vs quantum mechanics ... and why he'd be a convert today
The article considered a pair of distant particles in a special state now known as an "entangled" state. When the same property (say, position or velocity) is measured on both entangled particles, the result will be random but there will be a correlation between the results from each particle.
For example, an observer measuring the position of the first particle could perfectly predict the result of measuring the position of the distant one, without even touching it. Or the observer could choose to predict the velocity instead. This had a natural explanation, they argued, if both properties existed before being measured, contrary to Bohr's interpretation.
However, in 1964 Northern Irish physicist John Bell found Einstein's argument broke down if you carried out a more complicated combination of different measurements on the two particles.
Bell showed that if the two observers randomly and independently choose between measuring one or another property of their particles, like position or velocity, the average results cannot be explained in any theory where both position and velocity were pre-existing local properties.
That sounds incredible, but experiments have now conclusively demonstrated Bell's correlations do occur. For many physicists, this is evidence that Bohr was right: physical properties don't exist until they are measured.
But that raises the crucial question: what is so special about a "measurement"?
In 1961, the Hungarian-American theoretical physicist Eugene Wigner devised a thought experiment to show what's so tricky about the idea of measurement.
He considered a situation in which his friend goes into a tightly sealed lab and performs a measurement on a quantum particle its position, say.
However, Wigner noticed that if he applied the equations of quantum mechanics to describe this situation from the outside, the result was quite different. Instead of the friend's measurement making the particle's position real, from Wigner's perspective the friend becomes entangled with the particle and infected with the uncertainty that surrounds it.
This is similar to Schrdinger's famous cat, a thought experiment in which the fate of a cat in a box becomes entangled with a random quantum event.
Read more: Schrdinger's cat gets a reality check
For Wigner, this was an absurd conclusion. Instead, he believed that once the consciousness of an observer becomes involved, the entanglement would "collapse" to make the friend's observation definite.
But what if Wigner was wrong?
In our research, we built on an extended version of the Wigner's friend paradox, first proposed by aslav Brukner of the University of Vienna. In this scenario, there are two physicists call them Alice and Bob each with their own friends (Charlie and Debbie) in two distant labs.
There's another twist: Charlie and Debbie are now measuring a pair of entangled particles, like in the Bell experiments.
As in Wigner's argument, the equations of quantum mechanics tell us Charlie and Debbie should become entangled with their observed particles. But because those particles were already entangled with each other, Charlie and Debbie themselves should become entangled in theory.
But what does that imply experimentally?
Read more: Quantum physics: our study suggests objective reality doesn't exist
Our experiment goes like this: the friends enter their labs and measure their particles. Some time later, Alice and Bob each flip a coin. If it's heads, they open the door and ask their friend what they saw. If it's tails, they perform a different measurement.
This different measurement always gives a positive outcome for Alice if Charlie is entangled with his observed particle in the way calculated by Wigner. Likewise for Bob and Debbie.
In any realisation of this measurement, however, any record of their friend's observation inside the lab is blocked from reaching the external world. Charlie or Debbie will not remember having seen anything inside the lab, as if waking up from total anaesthesia.
But did it really happen, even if they don't remember it?
If the three intuitive ideas at the beginning of this article are correct, each friend saw a real and unique outcome for their measurement inside the lab, independent of whether or not Alice or Bob later decided to open their door. Also, what Alice and Charlie see should not depend on how Bob's distant coin lands, and vice versa.
We showed that if this were the case, there would be limits to the correlations Alice and Bob could expect to see between their results. We also showed that quantum mechanics predicts Alice and Bob will see correlations that go beyond those limits.
Next, we did an experiment to confirm the quantum mechanical predictions using pairs of entangled photons. The role of each friend's measurement was played by one of two paths each photon may take in the setup, depending on a property of the photon called "polarisation". That is, the path "measures" the polarisation.
Our experiment is only really a proof of principle, since the "friends" are very small and simple. But it opens the question whether the same results would hold with more complex observers.
We may never be able to do this experiment with real humans. But we argue that it may one day be possible to create a conclusive demonstration if the "friend" is a human-level artificial intelligence running in a massive quantum computer.
Although a conclusive test may be decades away, if the quantum mechanical predictions continue to hold, this has strong implications for our understanding of reality even more so than the Bell correlations. For one, the correlations we discovered cannot be explained just by saying that physical properties don't exist until they are measured.
Now the absolute reality of measurement outcomes themselves is called into question.
Our results force physicists to deal with the measurement problem head on: either our experiment doesn't scale up, and quantum mechanics gives way to a so-called "objective collapse theory", or one of our three common-sense assumptions must be rejected.
Read more: The universe really is weird: a landmark quantum experiment has finally proved it so
There are theories, like de Broglie-Bohm, that postulate "action at a distance", in which actions can have instantaneous effects elsewhere in the universe. However, this is in direct conflict with Einstein's theory of relativity.
Some search for a theory that rejects freedom of choice, but they either require backwards causality, or a seemingly conspiratorial form of fatalism called "superdeterminism".
Another way to resolve the conflict could be to make Einstein's theory even more relative. For Einstein, different observers could disagree about when or where something happens but what happens was an absolute fact.
However, in some interpretations, such as relational quantum mechanics, QBism, or the many-worlds interpretation, events themselves may occur only relative to one or more observers. A fallen tree observed by one may not be a fact for everyone else.
All of this does not imply that you can choose your own reality. Firstly, you can choose what questions you ask, but the answers are given by the world. And even in a relational world, when two observers communicate, their realities are entangled. In this way a shared reality can emerge.
Which means that if we both witness the same tree falling and you say you can't hear it, you might just need a hearing aid.
This article was originally published atThe Conversation.The publication contributed the article to Live Science'sExpert Voices: Op-Ed & Insights.
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- Improving LIDAR and GPS: Breaking Through the Resolution Barrier With Quantum-Limited Precision - SciTechDaily - January 18th, 2021
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- New quantum technology projects to solve mysteries of the universe - Open Access Government - January 14th, 2021
- Exploring the unanswered questions of our universe with quantum technologies - University of Birmingham - January 14th, 2021
- Wormholes may be lurking in the universe and new studies are proposing ways of finding them - The Conversation UK - January 14th, 2021
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- Quantum Superposition Evidenced by Measuring Interaction of Light with Vibration - AZoQuantum - December 24th, 2020
- Superpositions The Cosmic Weirdness of Quantum Mechanics - The Daily Galaxy --Great Discoveries Channel - December 24th, 2020
- Here's Why Quantum Computing Will Not Break Cryptocurrencies - Forbes - December 24th, 2020
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- Scaling the heights of quantum computing to deliver real results - Chinadaily.com.cn - China Daily - December 24th, 2020
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- Meet the kaon - Symmetry magazine - November 10th, 2020
- There Are Places in the World Where Rules Are Less Important Than Kindness by Carlo Rovelli review - The Guardian - November 10th, 2020
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- Quantum Technology: Harnessing the Power of Quantum Mechanics - Analytics Insight - November 8th, 2020
- Will the Universe Remember Us after We're Gone? - Scientific American - November 8th, 2020
- Threat of Quantum Computing to Bitcoin Should be Taken Seriously, But theres Enough Time to Upgrade Current Security Systems, Experts Claim -... - November 8th, 2020
- Pablo Jarillo-Herrero receives the Lise Meitner Distinguished Lecture and Medal - MIT News - November 8th, 2020
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- Reimagining the laser: new ideas from quantum theory could herald a revolution - The Conversation AU - October 29th, 2020
- Deep Reality: Art, Physics, the Unseeable and Space-Time - UNM Newsroom - October 29th, 2020
- Physicist breaks down the science of 11 iconic DC movie scenes - Insider - INSIDER - October 29th, 2020
- Q&A: Stanford MacArthur fellows talk creativity and 'publish or perish' - The Stanford Daily - October 29th, 2020
- Prime Minister's Prize for Science awarded to gravitational wave scientists - ABC News - October 29th, 2020
- Is math really the language of nature? This physicist is on a quest to find out. - News@Northeastern - October 29th, 2020
- Life and Work: Teaching in the Time of COVID: A Tale of Three Universities - All Together - Society of Women Engineers - October 29th, 2020
- COMMENTARY Covid seen to worsen poverty - The BVI Beacon - BVI Beacon - October 29th, 2020
- Quantum Time Twist Offers a Way to Create Schrdinger's Clock - Scientific American - October 24th, 2020
- Quantum Tunnels Show How Particles Can Break the Speed of Light - Quanta Magazine - October 24th, 2020
- A New Timekeeping Theory Reconciles Einstein's Relativity and Quantum Clocks - Science Times - October 24th, 2020
- Could Schrdingers cat exist in real life? We propose an experiment to find out - Scroll.in - October 24th, 2020
- Post-doctoral Fellow, Department of Physics job with THE UNIVERSITY OF HONG KONG | 230760 - Times Higher Education (THE) - October 24th, 2020
- Province gives $11.8M to U of C for quantum research, other projects - Calgary Herald - October 24th, 2020
- Physicists clock the fastest possible speed of sound - Live Science - October 24th, 2020
- Column: A new era of electric vehicles could be on the way - Gainesville Times - October 24th, 2020
- Beyond Homo Sapiens A Slightly Different Roll of the Darwinian Dice (Weekend Feature) - The Daily Galaxy --Great Discoveries Channel - October 24th, 2020
- Diamonds Are a Quantum Scientist's Best Friend: Discovery May Revolutionize the High-Tech Industry - SciTechDaily - October 24th, 2020
- The many paths of muon math | symmetry magazine - Symmetry magazine - October 24th, 2020
- Sumit Das to Deliver 2019-20 A&S Distinguished Professor Lecture on 'Deconstructing Space-Time' - UKNow - October 24th, 2020
- Of Science, Philosophy and Revelation - Greater Kashmir - October 24th, 2020
- In Waterloo they're looking for nature's deepest and weirdest secrets - National Observer - October 24th, 2020
- Max Planck and the Birth of Quantum Mechanics - SciTechDaily - October 15th, 2020
- Reality Does Not Depend on the Measurer According to New Interpretation of Quantum Mechanics - SciTechDaily - October 15th, 2020
- Bringing the promise of quantum computing to nuclear physics - MSUToday - October 15th, 2020
- Could Schrdinger's cat exist in real life? Our research may soon provide the answer - The Conversation AU - October 15th, 2020
- A Force From Nothing Used to Control and Manipulate Objects - SciTechDaily - October 15th, 2020