Single Photon Interference

Veritasium
Veritasium
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Published 2013-03-13
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?
All Comments (21)
  • @joshuanicholls2692
    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.
  • @jatinrawat777
    This is amazing knowing that one of the chapters we are taught in last year of high School (or a lesson) is so close to the Quantum Mechanics. I am 18 and I am happy that I could find out that my high Physics whether it was newtonian physics or any other branch... Believe me when I say "it was was astonishing!"
  • @potawatomi100
    Your videos are outstanding: informative, engaging, educational and interesting. Thank you Derek!
  • @45obiwan
    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!
  • @jeevanshudhawan
    The best visual explanation of double slit experiment I have seen till date. Thanks Veritasium.
  • @ChaosUnit178
    As much as I like the idea, I'm not sure "wavicle" is going to catch on.
  • @robelicit
    Well done 🎯 This visualization helped to clear up the basics of the timing & phase better than any other video/explanation. 🚀👊🍸
  • @Jamesey162
    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.
  • @braeburnhilliard8340
    I like how you explained the waves interference. It was Very helpful and helped me understanding that a little better.
  • @ti2218
    I found you from my Astonomy class, now I just watch you for fun and education. Great videos, very fascinating!
  • @SACHINSTRUCTURE123
    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?
  • @cirdiam1800
    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.
  • @dabyseka
    Thank you for your amazing content! You're helping me so much!!!
  • @flawq3217
    4:20 🎶WHAT IS LIGHT, BOSONS DON'T HURT ME, DON'T HURT ME, NO MORE
  • @robertfennis6088
    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.
  • @jerryharvey3304
    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!