The Weird Experiment that Changes When Observed

The double-slit experiment  defies our understanding. It involves a laser shooting beams  of light particles, called photons, at a screen with two parallel slits. If we mark all the spots where  the photons hit the second wall, we should expect to see two strips  to correspond with the two slits.

But that’s not what we see. Instead, we see an alternating  pattern of light and dark bands. This is characteristic of the behavior of waves  that pass through both slits simultaneously, interfering with each other to create  the pattern on the second screen.

The bright lines are where the top of waves  meet, resulting in a more intense or brighter area on the screen. The darker bands are where  the top of one wave meets the bottom of another, so they cancel each other out, resulting in  a less intense or darker area on the screen. Here is a photo of a real interference pattern.

The original double-slit experiment was conducted  in 1801 by British polymath Thomas Young. Since then, it’s been performed  with various types of particles, including electrons, and they were  found to behave in the same way. This phenomenon occurs even if the  photons are fired one at a time, which suggests that the photon is interfering with  itself as if it passes through both slits at once.

Physicists were so stumped that they decided to  observe which slit the particle went through. And that’s when things get really weird. When scientists used a measuring device to  observe the slit that each photon passed through, the interference pattern disappeared, and  the photons started behaving like particles.

Instead of the spectrum of light and  dark bands, we see two bright bands, indicating that the photons  chose one slit or the other. So light can display characteristics of both particles and waves, known  as wave-particle duality. It appears that light decides  to behave as a wave when it’s not being watched and acts like a  particle when it is being measured.

The mere act of observing which slit it went  through changed the behavior of the photons! Almost as if they were aware  they were being watched! It’s kind of like how in a video game, the environment and objects only load when  the player focuses on or interacts with them.

The entire world isn't rendered all at once, allowing the game to save processing  power and optimize resources. Likewise, light seems to behave  like waves, but when we observe it, it's as if we're "loading" its properties,  causing it to change and act like particles. Physicist Richard Feynman famously said, "the double-slit experiment is absolutely  impossible to explain in any classical way and has in it the heart of quantum mechanics. 

In reality, it contains the only mystery. " The most widely accepted theory to explain this  phenomenon comes from physicist Niels Bohr, who proposed that particles like photons don’t  have definite properties until they’re observed. So in the case of light, photons exist  in a wave-like form representing a range of possible positions until they are observed.

When we measure or observe the particle, we force it to “choose” a definite  state, behaving like particles. This is called the Copenhagen interpretation,  named in honor of Bohr’s home city. However, to this day, no one knows why observing  a particle causes its behavior to change.

Not everyone was a fan of Bohr’s theory. Einstein disagreed that particles could be  in multiple states at once until observed. He was uncomfortable with the  inherent randomness of such an interpretation and famously said, “God  does not play dice with the universe.

” Einstein believed that the universe  followed a consistent set of rules, like how his general relativity theory  predicted the motion of planets around the sun. He spent his later years trying to develop a unified theory that explained everything  in the universe, but he didn’t succeed. Physicists recently conducted a  variation on the double-slit experiment.

In April 2023, researchers at Imperial  College London swapped out the screen with two slits for a transparent material  used in smartphone screens called ITO. They first fired a laser beam at the material. When a second laser was directed at  the material and pulsed super quickly, in quadrillionths of a second, it caused the  material to become temporarily reflective.

The interaction of Laser 2 with the  material changed the frequency - and therefore the color - of the light from  Laser 1 that was reflected off the material. This experiment shows that by manipulating time  rather than space, they were able to create interference patterns similar to the interference  observed in the original double-slit experiment. There are certain things in  life we take for granted.

If you don’t get enough sleep,  you’ll feel tired and groggy. If you drive recklessly, you are more  likely to get into a car accident. But sometimes, there are principles that  govern our lives that we just can’t explain.

The perplexing result of the double-slit  experiment is up for interpretation, with some suggestions that this is  evidence our world could be “programmed”. So far, not even the best scientific minds can explain the bizarre behavior  of particles…at least, not yet. There are many puzzles that are perplexing.

For example, can you tell what’s  wrong with the gears Leonardo da Vinci wanted to use in his military  tank design from the 15th century? This is one of the thousands of  problems you’ll find on Brilliant, a website and app where you  can learn STEM interactively. My viewers especially love Brilliant’s lessons  in computer science, data science, and math.

causing the front and back wheels  to rotate in opposite directions. So the tank will never be able to move  at all. This was possibly an oversight or an intentional mistake to protect his  design from being built without his support.

For more puzzling questions like these, you can  try out Brilliant for free for 30 days by heading to the custom link in my description:  brilliant. org/newsthink. And the first 200 people who sign up with my link will  get 20% off their Premium subscription, which gives you access to all the offerings.

Thanks for watching. I’m Cindy Pom.