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People See the Double-slit Experiment for the First Time


People See the Double-slit Experiment for the First Time

I have made a follow-up video to clarify some flaws in this explainer

Quantum physics is weird. I hope this video makes you interested to read more about the experiment

Big thanks to my friends for being part of this video:

Caitie Browne:

Matt Beat:

Victor Osinga:
and second channel...

Jack Hendy (my brother):

Willie Rates:

Special mention to Kevin Li who's footage was lost to unfortunate circumstances...

The base footage is from Dr Quantum - Double-slit experiment, taken from
The clip is originally from What The Bleep Do We Know!?: Down The Rabbit Hole. A disclaimer is that this organisation contains some less-than-scientific ideas and supports some pseudoscience from what i've seen. That being said, I find this clip of Dr. Quantum to be an excellent educational tool for the double-slit experiment.

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The Quantum Experiment that Broke Reality | Space Time | PBS Digital Studios

The double slit experiment radically changed the way we understand reality. To check out any of the lectures available from The Great Courses Plus go to and get ready to learn about everything from cooking to calculus.

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The double slit experiment radically changed the way we understand reality. Find out what the ramifications of this experiment were and how we can use it to better comprehend our universe.

Written and hosted by Matt O’Dowd

Made by Kornhaber Brown (

Previous Episode

The Planck Length and the Origin of Quantum Mechanics

Veritasium and the Double Slit Experiment

Is Quantum Tunneling Faster than Light?

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Double Slit Experiment Explained Step-By-Step

In this video, we're gonna be talking about, what is in my opinion, the single most impressive experiment ever conceived: the Double Slit Experiment.

It's not just impressive for how it was first derived but also for all the variations that were done in later years that all give us a glimpse of how wonderfully weird the quantum world is.

But as weird as it is, the quantum world forms the building blocks of our reality so it's important to understand how things work.

We'll be covering:
› Double-Slit Experiment
› Which-Way Experiment (variation)
› Delayed Choice Experiment (variation)
› Diffraction
› Wave interference (peak / trough formation)
› Wave function collapse
› Misconceptions

Everything will be explained step-by-step so that anyone can follow.


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$10 Double-slit Experiment Vs. $2500 Double-slit Experiment

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Does Consciousness Create Reality? Double Slit Experiment may show the Answer.

The double slit experiment - Does consciousness create reality? Quantum mechanics shows us that particles are in superposition, meaning they can exist in different states and even multiple places at the same time. They are nothing more than waves of probabilities, until the moment that they are measured. One interpretation of this phenomenon is that the measurement being made requires a measurer, or a conscious observer. If this is correct, then it implies that consciousness has to be is an integral part of creating the world that we observe. Could this consciousness then be required for creating reality? Does this mean that there would be no reality without consciousness?

Experiments can show that what we think of as particles behave like waves. Waves of probabilities. This is the foundation of Quantum mechanics. The famous double slit experiment illustrates this. What is bizarre is that when you try to find out what’s going on at the slits by placing a detector at the two slits to try to figure out which slit the individual atoms are going through – the “WHICH WAY” information, they all of a sudden stop behaving like waves, and behave like particles.

Why do atoms and other particles behave this way? There are many interpretations of this phenomenon.

The most widely accepted interpretation, called the Copenhagen interpretation, was devised in 1925 by Neils Bohr and Werner Heisenberg at the University of Copenhagen. Their theory proposed that the atom when it is not measured, is not distinct. But the Copenhagen interpretation does not say anything about consciousness. But what is measurement after all?

Does measurement take place at the instrument that measures it? Does measurement necessarily require a consciousness? This is called the “measurement problem of quantum mechanics.” Physicists do not universally agree on a resolution. There are various interpretations.

One such interpretation is called the von Neumann–Wigner interpretation. This says that in the long chain of measurement, the collapse occurs at the moment that a consciousness interprets the measurement. The consciousness of the physicist is making the particle distinct. And without this consciousness, the atom would just be a wave of probabilities.

One fascinating interpretation is the many worlds interpretation. It was put forth by Hugh Everett in 1957. This theory postulates that there is NEVER any collapse, that we may be a measuring it in our reality, but there is no measurement happening in a different reality, and the wave function continues in that different branch of reality. But at some branch of reality, the particle collapse never actually happens. There is some new evidence that seems to support this idea of multiple realities. A paper published just this year in 2019 by Massimiliano Proietti at Heriot-Watt University in Edinburgh Seems to support the idea that at least two equally provable realities could exist at a quantum level at the same time.

So what is the correct answer? First let’s summarize what we know for sure – we know that measurement that records the which-way information of a particle indeed collapses a particle’s uncertainty wave. This particle collapse is consistent forward or backward in time as well, as shown by the delayed choice quantum eraser experiment.

As for many worlds, the equation allow it to be true, but since the other worlds appear to be inaccessible to us, there is no way to prove it. So just because it could be true, doesn’t mean it is true.

The Copenhagen interpretation is the most widely accepted, and in my view likely correct. It does not require a consciousness to interpret or even observe the results. I think the problem is with the word “observation” – which for many people seems to imply that someone has to look with their eyes. And eyes have a consciousness behind them.

But in quantum mechanics, this is not what the word observation means. So this unfortunate terminology of “observation” is what causes the confusion. In quantum mechanics an observation simply means the interaction of two quantum states that can collapse each other’s probability wave function. Does consciousness play a role. Probably not. And there is some new evidence that seems to show this.

A paper published by Shan Yu and Danko Nikolic in 2011 showed that a conscious observer was not necessary for the collapse. Their experiments measured the which-way information of a particle, but recorded it in the state of an atom. This information was not available to a conscious observer, but was preserved in the atom, in other words, it was available to the universe. Conclusion in video...

Two realities:
Delayed choice quantum eraser:
Yu and Nikolic:

#consciousness #doubleslit

Young's Double Slit demonstration

Lab demonstration of the interference pattern produced by Young's double slits using a red laser. I also show you the intensity plot that is commonly shown in textbooks.

Practise questions on Young's double slits here:

Here is another great video that shows different coloured lasers:

double slit experiment [NOVA]

The double slit experiment explained by NOVA
Episode: Quantum Leap (The Fabric of the Cosmos)

The Problem with Dr. Quantum's Double-slit Experiment

My original reaction video:

Quantum mechanics needs no consciousness:

PBS Space Time Quantum Eraser:

Which-way detector unlocks some mystery of the double-slit experiment:

Neil deGrasse Tyson explains Heisenberg's Uncertainty Principle from Joe Rogan Experience #919:

Can the results of a delayed choice quantum eraser be explained in laymen's terms that also shows that human consciousness is not a factor?:

Observer effect:

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The Double Slit Experiment FULLY EXPLAINED


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The Original Double Slit Experiment

Light is so common that we rarely think about what it really is. But just over two hundred years ago, a groundbreaking experiment answered the question that had occupied physicists for centuries. Is light made up of waves or particles?

The experiment was conducted by Thomas Young and is known as Young's Double Slit Experiment. This famous experiment is actually a simplification of a series of experiments on light conducted by Young. In a completely darkened room, Young allowed a thin beam of sunlight to pass through an aperture on his window and onto two narrow, closely spaced openings (the double slit). This sunlight then cast a shadow onto the wall behind the apparatus. Young found that the light diffracted as it passed through the slits, and then interfered with itself, created a series of light and dark spots. Since the sunlight consists of all colours of the rainbow, these colours were also visible in the projected spots. Young concluded that light consist of waves and not particles since only waves were known to diffract and interfere in exactly the manner that light did in his experiment.

The way I have always seen this experiment performed is with a laser and a manufactured double slit but since the experiment was conducted in 1801 I have always thought that it should be possible to recreate the experiment using sunlight and household materials. That is basically what I did here. I will show the interference pattern I observed with my homemade double slit on 2Veritasium but I chose to use a manufactured double slit here to ensure that the pattern was impressive for observers at the beach.

Special thanks to Henry, Brady, and Rupert for their cameos, Glen for filming and Josh for helping create the apparatus. Thanks also to the Royal Society for allowing us to view the original manuscript of Young's lecture and the University of Sydney for lending the double slits.

Music by Kevin Mcleod ( Danse Macabre, Scissors

Double Slit Experiment explained! by Jim Al-Khalili

If you can explain this using common sense and logic, do let me know, because there is a Nobel Prize for you..

Professor Jim Al-Khalili explains the experiment that reveals the central mystery of quantum mechanics - the double slit experiment.

Watch the full lecture here:

For more info on all things quantum, you can buy Jim's book Quantum: A Guide For The Perplexed now -

Sometimes called the two-slit or Young's experiment, it demonstrates that matter and energy can display the characteristics of both waves and particles, establishing the principle known as wave-particle duality. Furthermore, it questions the role of the observer in the outcome of events and demonstrates the fundamental limitation of an observer to predict experimental results.

For this reason, Richard Feynman called it a phenomenon which is impossible ... to explain in any classical way, and which has in it the heart of quantum mechanics. In reality, it contains the only mystery [of quantum mechanics], (see more at

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Dr Quantum - Double Slit Experiment

Dr Quantum - Double Slit Experiment

This clip is from: What The Bleep Do We Know!?: Down The Rabbit Hole and is used for educational purposes.

What Happens When You Put Antimatter in a Double Slit Experiment?

Interference patterns with particles have stumped scientists for years, but when they put antimatter through the test, they revealed an even bigger mystery.

This Is The Only Place Antimatter Can Survive In The Universe -

Read More:
First Observation Of Antimatter Wave Interference

“The periodic spatial distribution generated by the interferometer (Fig. 1) is revealed by a nuclear
emulsion detector. Nuclear emulsions14 offer submicron level position resolution in the detection of
ionizing particles9,15. They work as photographic films by exploiting the properties of silver-bromide
crystals embedded in a 50 μm thick gelatin matrix. For this experiment we developed a glass-supported emulsion detector and experimentally demonstrated its capability to resolve periodic patterns at the micrometric scale even with low signal contrast and on large areas”

This Classic Physics Experiment Could Finally Reveal The Long-Awaited 'Theory of Everything'

“That’s not so strange though - we know that matter (ping-pong balls) doesn’t behave in the same way as waves. But when physicists fired particles like electrons and photons at the double slit, expecting them to act like matter, they instead acted like waves, producing an interference pattern. And it gets even crazier than that. These electrons and photons aren’t acting like matter, but they aren’t acting like waves either, because they’re not messing with each other to produce an interference pattern.”

Antimatter mysteries 2: How do you make antimatter?

“Two CERN experiments, ATRAP and ALPHA, are grappling with that question. Their aim is to make antihydrogen – the simplest anti-atom possible, just an antiproton and a positron bound together – in sufficient quantity and for long enough to compare the spectrum of light it emits with that of regular hydrogen. Even the slightest difference between the two would shake up the standard model.”

Elements is more than just a science show. It’s your science-loving best friend, tasked with keeping you updated and interested on all the compelling, innovative and groundbreaking science happening all around us. Join our passionate hosts as they help break down and present fascinating science, from quarks to quantum theory and beyond.

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The Double Slit Experiment: interference patterns

Sean Carroll & Joe Rogan on the Double Slit Experiment, Quantum Mechanics

Sean Carrol and Joe Rogan on the double slit experiment

Sean Michael Carroll is a cosmologist and physics professor specializing in dark energy and general relativity. He is a research professor in the Department of Physics at the California Institute of Technology

Full Podcast:

Performing The Double Slit Experiment and Building an Interferometer

Saying that quantum mechanics is weird is massive understatement. As we explore smaller and smaller scales, the rules of nature become less intuitive. Originally scientists assumed that the smallest things were point like particles and built their models around this idea. But this all came crashing down thanks to the famous double slit experiment. Suddenly it was shown that light can behave like a wave. At first it was assumed that light is purely a wave but thanks to Louis de Broglie, we now know that almost all fundemental particles, and even collections of particles can exhibit wave like properties.

In this video we explore how the double slit experiment can be preformed using only candle soot and a laser pointer.

Since light has wave properties, we can exploit them using a device called an interferometer. These devices are the heart of some of the most advanced physics experiments on earth, including LIGO, the redefinition of the Kg and many others. Here we explore how a simple interferometer can be made at home.

More resoures on the topics covered:
Veritasium Double Slit Experiment -
Copenhaggen Interpertation -
Many Worlds Interpertation -
Pilot Wave Theory 1 -
Pilot Wave Theory 2 -
Measuring Plancks Constant -
FTIR Spectrophotometer -
Lego Optics Table -

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Hardy's Paradox | Quantum Double Double Slit Experiment

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This video is about Hardy's Paradox, wherein an electron and positron (or photons polarized horizontally and vertically) pass through Mach-Zehnder interferometers that overlap such that the particles have a chance of annihilating. If they do annihilate, then the interference pattern changes and there is a probability for both particles to be detected in the dark arms of the detector, that is, where previously there was no probability for detection for either particle. The paradox has implications for local realism, contextuality, lorentz elements of reality, and has been used as an experimental setup for weak measurements.

Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute!

Created by Henry Reich

Tom Campbell: A Step Further Than the Double Slit Experiment

How the double-slit experiment works, what the diffraction pattern means, why Tom Campbell's variations of this experiment will show this is a probabilistic reality, random atomic decay, beam splitters, and more, make for an interesting informal interview on an important topic-virtual reality!

My experiments will cause things to happen that have no material cause.

This is a concise version of a previous video by Tom Campbell focused entirely on a discussion of his variations of the classic double-slit experiment for physicists and those interested in the science behind Tom's theory of virtual reality.

For more a detailed explanation of his theory and experiments see: The Implications of Virtual Reality and the Physics Experiments, an excerpt from MBT LA.

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Double Slit Experiment (subtitulos en Español)

Experimento de Doble Rendija

Homemade Double Slit Experiment

Quantum laser pointers brings you the infamous double slit experiment right in the palm of your hand. In 1801 English physicist Thomas Young performed this experiment to determine if light was a particle or a wave. A laser shines a coherent beam of light through a film disc containing two parallel slits. Light striking the wall behind the slits producers a classic interference pattern. This surprising result means light passes through the parallel slits not as particles but as waves. When the peaks of two waves overlap it creates a band of light. When the peak of one wave meets the valley of another, light is cancelled out. Variations of this experiment spurred public debates between Albert Einstein and Neils Bohr on the true nature of reality. It’s been called the granddaddy of all quantum weirdness. This convenient and affordable double slit laser was designed for personal enjoyment and education.



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