Single Photon Interference

What happens when single photons of light pass through a double slit and are detected by a photomultiplier tube? In 1801 Thomas Young seemed to settle a long-running debate about the nature of light with his double slit experiment. He demonstrated that light passing through two slits creates patterns like water waves, with the implication that it must be a wave phenomenon.

However, experimental results in the early 1900s found that light energy is not smoothly distributed as in a classical wave, rather it comes in discrete packets, called quanta and later photons. These are indivisible particles of light. So what would happen if individual photons passed through a double slit? Would they make a pattern like waves or like particles?

[joshuanicholls]

Now, try to detect which slit the photon goes through. This is when the experiment becomes truly mind blowing.

[houdiinii]

When i was in 9th or 10th grade our teacher showed us the double slit experiment with a laser and we could see the interference pattern in the dark classroom. Now i feel really thankful that i had the opportunity to witness this live and become fascinated by science. Sadly i wasn't so aware of that when i was at school, but i think deep inside it helped to build up a fascination for physics and science in general.

[ivayloi]

I think you must first prove that there is such thing as "single photon" and you are actually tracking it. As far as I'm concerned, you made the same experiment, with lower intensity light, and the pattern is just less visible... Actually I would be shocked if you got anything different, that would break the most fundamental idea of the field as something continuous in space. What you did is just lowering of the field to the point where your measurement system struggle, nothing fundamentally different... My vision is that what we call "photon" is just property of the field, and the only way to be shocked is to assume something wrong in the first place - that it's a "particle" and you can "track" it.

[ChaosUnit]

As much as I like the idea, I'm not sure "wavicle" is going to catch on.

[Jamesey]

We spent close to two hours covering this topic in Physics today, this video contains everything that the teacher taught to us in two hours but in 6 minutes.

[jerryharvey]

Is there any videos which show the effects of the double-slit experiment observed, and also unobserved?
I've looked for videos that demonstrate both the interference pattern and the wave-function collapse, yet without luck!
If the double-slit experiment were filmed, wouldn't that register as a form of observation, which would cause the WFC?
Where exactly within or around the experiment, can't we secretly look? That if we observe, the wave-function collapses?
If the WFC occurs when being observed, how is interference pattern also visible, as I think it was with this video?
Anyway, just a few questions. Thanks!

[flawq]

4:20 🎶WHAT IS LIGHT, BOSONS DON'T HURT ME, DON'T HURT ME, NO MORE🎶

[josephbeno]

Ok. How can you possibly prove only one "point particle" AKA photon is shot at one time? Even if you shot one wave 1(sin), they could have a shadowing effect next to the blockage of the slit. That combined with multitudes of single waves they average out. Easy way of understanding... Why can I hear Chicago radio station WLS (50, 000 watts) in Colorado. The curvature of the earth does not allow for "line of sight" despite the mile high city. I have coined the phrase. "SHADOW DIFFRACTION". Its when the waves continue around the obstruction. It is like hearing sound from behind a building. Let this be my publication of my theory. Thanks.

[TheCls]

Now there is a theory that photon IS a particle but space is the wave behavior, so even if you shoot one single photon throught the slits, the photon will follow the space wave. Like a boat on water it will go straight but follows the wave of the ocean. Maybe you need to go at the speed of light to behave like a wave. If you could shoot me at the speed of light like a particle throught a giant slit, I, the particle, would follow the wave of space making me look both like a particle and a wave.

[tobuslieven]

3:49 Could you say that it travels as a wave, but interacts at a point? I feel like this is a pretty intuitive explanation, but I've never heard it said this way. The explanation that makes it seem mysterious seems to always be preferred. It travels as a wave, and collapses to a point when it interacts.

[SACHINSTRUCTURE]

I had many thoughts and questions after seeing this video:
1. what is the size of each slit? how far apart the slits are individually? what is the size of photon or wave? at what distance the light generator is from slits? and how far is the sensor/receiver?

2. What if the each slit is closed alternatively?

3.what if there are more than two slits?

4. what if we place two photon guns at an angle to each other to fire photons through single slit and try different options?

5.what if we place two photon guns at an angle to each other to fire photons through double or more slit and try different options?

[robertfennis]

I have a great word. Golfbal. In Dutch 'golf' besides the sport is also the proper translation of the term wave. We also don't use spaces when we use word combinations so golfbal would be a 'golf ball' or literally translated 'wave ball'. I always joke around with this at my university since its quite funny if you are Dutch.

[cirdiam]

Derek, This is a very interesting topic. I hope you do more videos on it. I summarize what's going on this way: "things travel as waves, they appear as particles". It's true for all things - just not very noticeable for big things which are collections of a bunch of small things travelling as waves and appearing as particles. You'll notice that with mirrors and beam splitters and slits and screens you can get the wave to bend, split, or pop. When it pops - that's the wave manifesting as a particle. I think you can get deeper insight into this by asking yourself - "why is it that fiddling with the wave sometimes makes it pop, and sometimes not?" What is the boundary of fiddling that just under it the wave continues - although perhaps bent - and just above that amount of fiddling and it pops. What are the factors that determine how much fiddling can happen before popping occurs. Also when I see a wave pop - and you watch the same thing - do you see it pop to the same place? I've never seen or read about experiments along this line. If you can - can you do some experiments along those lines. I don't have access to equipment to do it myself.

[obiwan]

I totally love what you're doing here. You're like the perfect mix of my physics and chemistry professor from High School. I've been wanting to re-visit this, and some of the other items you've touched on, just to refresh my memory, it has been 30 years since my last formal class. Thanks!

[plaguedoctr]

Wait a sec...
"I can't possibly block all of the light"
and
"It's counting a single photon at a time"
Huh???

[jasonjackson]

"We now know that they are just waves. They only appear as particles" - Sean Carroll

[potawatomi]

Your videos are outstanding: informative, engaging, educational and interesting. Thank you Derek!

[AppleYou]

I prefer a “partywave”, especially when we’re dealing with colored lights (and music)

[vyvianalcott]

I've always thought that light was particles that move as a wave. Much like with sound, there are points of high and low density in the concentration of particles. The particles themselves are also moving forward in the same direction as the wave, and it is the incredible speed of the particles that make it difficult to differentiate between the types of movement. Since photons move at slightly less than C, there is still enough of a difference between the two types of movement (linear and wave) that this doesn't seem impossible. The information represented by the wave can translate at exactly C, while the photons themselves are slightly limited by the energy representing an infinitesimally small mass.

I'm not sure I've explained this very well, but am I entirely wrong in the way I understand this? It sounds like you're saying they couldn't possibly exist in both states at the same time, but it still doesn't seem unlikely. A wave is just a method of travel, a contracting and separating of particles. It's hard to visualize something that both moves forward and has an elasticity of speed that would allow for wave propogation, but I'm nowhere near adept enough with mathematics to validate or disprove the possibility.

I hope I haven't taken too much of your time with an inane question. If you have read this, I appreciate as much as that. Keep making awesome videos, Derek; As much as I enjoy other science related channels I never learn as much with Destin or Michael as I do from you.

[Leiaissocute]

I would love to see a video that discounts all the other possible explanations for the same result being obtained whether particles are fire one at a time or sumultaneously. It seems a pretty big leap (a quantum one in fact) to arrive at a quantum explanation, without first discussing the many possibilities that mechanical physics offers.