Revised Schrödinger's cat experiment challenges reality
A classic experiment gets an update that contradicts key assumptions of quantum mechanics.
- Physicists revise the Schrödinger's cat thought experiment.
- The new version leads to contradictions in quantum theory.
- Scientists are stumped by the implications.
Quantum mechanics has produced its share of weird ideas, not least of which is what's probably the world's most famous thought experiment devised by physicist Erwin Schrödinger in 1935. It described the uncertain fate of a cat trapped in a box with a deadly substance. Now the experiment got an update from two physicists, leading to conclusions that threaten to undermine the foundations of the whole field.
By replacing the cat in the box with multiple physicists doing experiments, the duo of Daniela Frauchiger and Renato Renner of the Swiss Federal Institute of Technology (ETH) in Zurich has caused heated debates among physicists for the past two years.
Schrödinger's original idea proposed that if you put a cat in a box, along with a possibly decaying radioactive substance which would release a killer acid, the cat could be both alive and dead until that box was opened, fixating its state. Schrödinger devised this scenario to point to inconsistencies in the so-called Copenhagen interpretation of quantum mechanics, created by Niels Bohr and Werner Heisenberg in the 1920s.
The interpretation states that a quantum particle can exist in all possible states until an observer forces what's called "the wave function collapse", making the particle choose one probable state. Unfortunately, as Schrödinger showed, this theory may work on the quantum level but when applied to larger objects like cats, it becomes somewhat ridiculous and impossible—the cat cannot be both alive and dead.
Still, the Copenhagen interpretation has persisted, in part due to saying that while quantum objects may exist in uncertain states, experimental observation can give certain results. It is that certainty which the new thought experiment has attacked.
Diagram for the Schrödinger's cat thought experiment, showing the radioactive substance and the hammer that will potentially be dropped to spill the acid, thereby killing the cat.
The conceptual experiment by the scientists from Zurich involves putting two physicist cats into boxes. One cat would toss a coin and using its knowledge of quantum physics send a message to the other cat. That second cat, in its turn, would also employ quantum theory but to detect the message from the other cat and guess the coin toss. If two outside observers were to open these boxes, they would some times be able to guess with certainty how the coin landed but on occasion their conclusions would not agree.
"One says, 'I'm sure it's tails,' and the other one says, 'I'm sure it's heads,'" described that eventuality Renato Renner.
That's like implying reality can split in two on occasion.
This paradox has stumped other scientists as well. "I think this is a whole new level of weirdness," said Matthew Leifer, a theoretical physicist at Chapman University in Orange, California to Nature magazine.
There is a potential way this experiment can actually be carried out, but it would involve quantum computers that are not in existence yet.
The scientists originally published their argument online in 2016. Check out their final paper "Quantum theory cannot consistently describe the use of itself" from September 2018 in Nature magazine.
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The idea of 'absolute time' is an illusion. Physics and subjective experience reveal why.
- Since Einstein posited his theory of general relativity, we've understood that gravity has the power to warp space and time.
- This "time dilation" effect occurs even at small levels.
- Outside of physics, we experience distortions in how we perceive time — sometimes to a startling extent.
Physics without time<p>In his book "The Order of Time," Italian theoretical physicist Carlo Rovelli suggests that our perception of time — our sense that time is forever flowing forward — could be a highly subjective projection. After all, when you look at reality on the smallest scale (using equations of quantum gravity, at least), time vanishes.</p><p style="margin-left: 20px;">"If I observe the microscopic state of things," writes Rovelli, "then the difference between past and future vanishes … in the elementary grammar of things, there is no distinction between 'cause' and 'effect.'"</p><p>So, why do we perceive time as flowing <em>forward</em>? Rovelli notes that, although time disappears on extremely small scales, we still obviously perceive events occur sequentially in reality. In other words, we observe entropy: Order changing into disorder; an egg cracking and getting scrambled.</p><p>Rovelli says key aspects of time are described by the second law of thermodynamics, which states that heat always passes from hot to cold. This is a one-way street. For example, an ice cube melts into a hot cup of tea, never the reverse. Rovelli suggests a similar phenomenon might explain why we're only able to perceive the past and not the future.</p><p style="margin-left: 20px;">"Any time the future is definitely distinguishable from the past, there is something like heat involved," Rovelli wrote for the <a href="https://www.ft.com/content/ce6ef7b8-429a-11e8-93cf-67ac3a6482fd" target="_blank"><em>Financial Times</em></a>. "Thermodynamics traces the direction of time to something called the 'low entropy of the past', a still mysterious phenomenon on which discussions rage."</p>
The strange subjectivity of time<p>Time moves differently atop a mountain than it does on a beach. But you don't need to travel any distance at all to experience strange distortions in your perception of time. In moments of life-or-death fear, for example, your brain would release large amounts of adrenaline, which would speed up your internal clock, causing you to perceive the outside world as moving slowly.<br></p><p>Another common distortion occurs when we focus our attention in particular ways.</p><p style="margin-left: 20px;">"If you're thinking about how time is <em>currently</em> passing by, the biggest factor influencing your time perception is attention," Aaron Sackett, associate professor of marketing at the University of St. Thomas, told <em><a href="https://gizmodo.com/why-does-time-slow-down-and-speed-up-1840133782" target="_blank">Gizmodo</a></em>.<em> "</em>The more attention you give to the passage of time, the slower it tends to go. As you become distracted from time's passing—perhaps by something interesting happening nearby, or a good daydreaming session—you're more likely to lose track of time, giving you the feeling that it's slipping by more quickly than before. "Time flies when you're having fun," they say, but really, it's more like "time flies when you're thinking about other things." That's why time will also often fly by when you're definitely <em>not</em> having fun—like when you're having a heated argument or are terrified about an upcoming presentation."</p><p>One of the most mysterious ways people experience time-perception distortions is through psychedelic drugs. In an interview with <a href="https://www.theguardian.com/books/2018/apr/14/carlo-rovelli-exploding-commonsense-notions-order-of-time-interview" target="_blank"><em>The Guardian</em></a>, Rovelli described a time he experimented with LSD.</p><p style="margin-left: 20px;">"It was an extraordinarily strong experience that touched me also intellectually," he said. "Among the strange phenomena was the sense of time stopping. Things were happening in my mind but the clock was not going ahead; the flow of time was not passing any more. It was a total subversion of the structure of reality."<br></p><p>It seems few scientists or philosophers believe time is completely an illusion.</p><p style="margin-left: 20px;">"What we call <em>time</em> is a rich, stratified concept; it has many layers," Rovelli told <em><a href="https://physicstoday.scitation.org/do/10.1063/PT.6.4.20190219a/full/" target="_blank">Physics Today</a>.</em> "Some of time's layers apply only at limited scales within limited domains. This does not make them illusions."</p>What <em>is</em> an illusion is the idea that time flows at an absolute rate. The river of time might be flowing forever forward, but it moves at different speeds, between people, and even within your own mind.
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