Can someone explain dual slit experiment why is it a big thing ?
In: Physics
Photons go through a special board with two openings (like little doors!) and in this special circumstance, photons will act like a wave!! Waves are able to combine and overlap with eachother to cancel or amplify their impact, but particles cannot. This means that photons are a combination of both waves and particles! Crazy huh?!
If you shoot marbles at a double slit and measure where they landed, they only land in two bands, like you would expect. But if you do the same thing with electrons, you don’t see just two bands. You see an [interference pattern](https://cdn.britannica.com/84/284-050-246DA1E0/interference.jpg). This can’t be explained by the electrons interfering with eachother, as the pattern appears even if you shoot the electrons one at a time. The only explanation is that electrons behave like waves.
However, if you put a detector at one of the slits to see exactly which one the electron goes through, you don’t get the interference pattern anymore, but rather the familiar two bands. The only explanation for *this* is that electrons behave like particles.
Combine the two above statements and you reach the conclusion that electrons *must* behave as both particles and waves.
Others have explained what the experiment is so I won’t repeat their answers.
It’s a big thing because it means that things aren’t as simple as balls bouncing off each other. So we had to change our ideas from the classical version of matter, and that led to new ideas and methods.
This was controversial not too long ago, scientists who came up with other amazing and correct ideas about how the universe works couldn’t accept it at first, so it was kind of an argument where the smart people took sides.
There really isn’t any argument anymore though, you can do the experiment yourself at home with a laser pointer and smoke.
You flip a coin and it comes up heads, you’re not surprised. You flip a coin and it comes up tails, you’re not surprised. You flip a coin and it comes up both heads and tails simultaneously and you suddenly realize that the coin isn’t what you thought it was. In this analogy heads is “photons are waves” and tails is “photons are particles.”
The actual experiment involves taking two narrow slits near together and firing photons through them. If they make two distinct patches on your measuring screen, then they’re particles; if they make an interference pattern then they’re waves. They make an interference pattern. Neat, photons are waves! Easy enough. Then you find a way to fire photons one at a time through the slit so they can’t possibly interfere with each other… and somehow they still make an interference pattern. This makes no sense if photons are waves *or* particles, but it also doesn’t make any sense (according to your current model) for them to be *both*. So the only thing you can conclude is that they’re something else entirely, something that isn’t a particle or a wave but can act like both of those things. And you have no idea what that might be.
We’ve been studying them for a long time after that so now we have *some* idea but it’s still a little bit shaky. There have also been a number of follow-up experiments that revealed further brain-breaking weirdness.
The double slit experiment shows that we fundamentally do not understand what light (and for that matter, everything else) actually is. Depending on how we set up the experiment, we can get particles of all kinds (photons, electrons, etc.) to behave like either little balls or like waves of energy. We can do this with every minuscule particle – all the things that make up everything we can feel and see and react to (including all the things that make up each of us). So are these things that make up everything like tiny little balls or are they like waves of energy? The answer is yes – they are BOTH of these things simultaneously. From our everyday perspective of the world around us, this seems impossible. Yet we can experimentally verify that it’s true. Even more than that, the experiment seems to suggest we can change whether these things act like balls or waves based on just “looking” at them? We don’t really look at them, but we can use detectors that are effectively our eyes in these experiments. So now we know that everything is simultaneously both tiny little balls and waves of energy, and we also know that we can change how they interact with us and the entire world by whether we “look” at them. It makes no sense based on our everyday experience, but we know it’s true based on experiments.
The double slit experiment is set up by shooting particles (photons, electrons, etc.) at a small board with two slits cut into it. Initially, a stream of particles was shot at the board, and an interference pattern emerged on receivers on the other side. Waves make interference patterns, so we can conclude these particles are waves, or at least that a collection of particles is a wave (or acts as a wave). So the next step was to shoot the particles at the slit one at a time. If you shoot paintballs one at a time at a wall with two slits, you’ll get splatters on the other side in two lines (basically, whatever is directly behind the slits). So the experimenters expected to see the same thing when shooting particles one at a time through the slits. But that’s not what happened. Instead, the same interference pattern happened, which means that each particle INTERFERES WITH ITSELF, meaning each particle is actually a wave!
Weird, but we’re not done. The experimenters then set up detectors in front of the board to look at each particle as it went through one slit or another. So now they know which slit each one went through. And that knowledge changed the outcome! Instead of an interference pattern, two stipes emerged on the detectors. This means we can change what happens (and whether these things act like little balls or like waves) based on what we know.
And then there’s a version of the experiment called the “quantum eraser” which gets even more bizarre – it seems to change the behavior of the particles in the past. Too much to explain here, but it shows we really don’t understand what all these things are at a fundamental level. We have really good tools for understanding what they do, but we can’t really say what they are.
Just watch this video, it explains and demonstrates it very simply. https://youtu.be/NvzSLByrw4Q?si=NvuL8xgPoUv8S5uv
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