Thanks to everyone pointing out my mistake in the comments! I incorrectly stated that Young did the double slit experiment with electrons.Young wasn’t the one to do the experiment with electrons - that was Davisson & Germer in 1927 right before the 5th Solvay conference. I think I’ve misread my notes somewhere when I was prepping this video because electrons weren’t even discovered until the end of the 19th century! I seemed to have smushed result in with Young’s experiment in 1801 when I was filming by accident. I don’t really write scripts just make some notes and chat around them, and sometimes this happens! Apologies that neither me or editing Becky spotted that one 🤦🏻‍♀️

So that's why they call themselves particle physicists, but are really wave physicists when no-ones looking?

My teacher once came up with the analogy of a cylinder: looking from the top it looks like a circle and from the right like a rectangle but actually it is none of both. It just depends on the way you encounter it, how it appears to you.

-Is light a wave or a particle? -Yes -Yes what? -Yes, ma'am

My favourite answer to the question "Is light a wave or a particle?" is "Yes.".

I always get a little 'giddy' when I see that famous picture from Fifth Solvay Conference.

I wish I had access to you and your kind of internet teaching(?) 55 years ago when I was 13. Stay safe. -Mike😷

Is Dr Becky a genius, or beautiful? Why not both!

French guy here: "de Broglie" is pronounced "de Breuille". And yes, it doesn’t make any sense, even for French people !

The way you can explain experiments and concepts in such a simple and understandable way and at the same time be sooo cientifically precise is amazing! I cannot imagine how hard you work for that, especially being part of Oxford and having the pressure of so many intelligent colleagues watching your videos. Youre an amazing person for making the videos you do! Cheers from Brazil!

You sing very well. Make a duo with Sabine Hossenfelder and compose a song "The waves are redshifting in the dus"

@12:41 I'm uncertain if that's a picture of Heisenberg, but @12:54 I am sure that Max Born is the grandfather of Olivia Newton John, who sang a lot about physics in her 1981 #1 hit "Let's get Physics all". Einstein visited Born's house for dinner often, but he died in 1955 and Olivia was born in 1957 so they never met, but Olivia literally followed in Albert's footsteps in Max's house.

I know that I'm months too late for this video but I have just discovered your channel a few days ago. I am enjoying your videos tremendously. When I was in 9th grade, I took an Astrophysics summer camp and one of the topics was particle/wave duality. One of the clearest memories of that time for me is the fascination that the lecture spawned within me and the love for science that grew from that.

Love the bloopers! Please don't stop including them! Thanks. X

Looking forward for the next video, this was so intresting... 👏

Amazing video as always, Dr. Becky! Can't wait to see more videos of this series! I would love a video regarding the CPT Symmetry and of course the work of the Dr. Chien-Shiung Wu and Emmy Noether. Thank you for making these phenomenal videos! 😀

I am so in love with the way she explain things ❤

2:45 I've seen this in physics textbooks a few times but I think this is the first time it's kind of _really_ cliked, wow thanks! (I actually doubt we never got shown this kind of experiment at school at some point but if we indeed did I guess it wouldn't have been memorable enough)

The picture at 19:34 - wow. Despite the great Erroneous Electron Experiment Scandal of 2020 this was a fine video. Please do more of these. I so agree, an understanding of the history of a scientific idea is critical in the overall comprehension of the idea itself. Historical perspective of application of the scientific method is vital, and is often makes for a cracking good story!

Solvay, wow talk about being in the room where it happened.

6:10 Growing up, my dad was a pilot and owned a small plane. I remember taking off and watching the shadow of the plane on the ground. As we climbed higher and higher the shadow would get smaller and more blurry. Finally, just before it vanished, it would turn into a bright spot. This was especially visible when flying above the clouds. I wondered about that for years and years. How could a shadow become a bright spot? Now I know.

So interesting. Enjoyed sharing this with my 7 year old granddaughter. She even has her own opinion of the nature of light. Thank you so much. From Bakersfield California USA.

Love the way that you explain "stuff" - thanks for your very informative and interesting content! The out-takes are fun. 🤣

Hey, I am loving your content. Your enthusiasm really helps people who don't come from scientific backgrounds to understand your explanations. I would love to see some content on Laniakea and the great attractor if you have not done so already.

This was well-presented and enlightening (no pun intended).

HAHA "The universe wept" I have a very difficult time to convince coworkers to pronounce Fresnel zone correctly in RF work. I gave up!

Thanks for posting this DrBecky!

Thanks for addressing these arguments. Awesome sauce!

Love your videos, Becky. Thank you. My suggestion: Is gravity a force or a curvature of space-time?

Ohh what is that book in the background, I think I'm gonna go buy it. Marketing successful! :D

I can't smash enough likes for this video. Great coverage of both the technical and human sides of this progression of ideas and evidence.

This channel always sets me in a great mood! (not to mention the superbe quality of the content itself)

Someone needs to do a compilation of all of Dr Becky's singing bits - that would be awesome!

The double slot experiment is the most mind bending thing I have ever seen and then they took it further with the delayed choice thing. If that doest blow your mind you havent got one. Should have explained what happens when you observe each photon though.

Great idea for a series. Can't wait for the next one.

I really appreciate they way you boil these videos down to a level that makes it easier for those of us who are not physicists to understand.

"Is light a wave or a particle?" Yes. Oh sure.... messes up Fresnel but nails Poisson...

I would love to learn more of the LHC, specifically, I cannot wrap my head around the way subatomic particles are detected. How do the quarks interact with normal matter?

I just discovered your channel lately and I love your way of describing things. As I studied experimental physics myself I am always a feeling a little uneasy when I listen to the WAY the dark whatever discussion is going one - I find it very useful to compare the way this is going with the Aether Theorie discussion. Would be great if you cover that? I already know Sabine Hossenfelders thoughts about it but would really appreciate your PoV too.

Lovely work Dr. Becky. Yes, both my students and I always find the intersection of light and matter the most interesting and puzzling. Thinking about what it would have been like to be at the 5th Solway conference always makes the back of my neck bristle.

You found a picture of Robert Hooke? Amazing. 😃

“There was a cat thrown amongst the pigeons” ... is the cat alive or dead or both ?

Words are hard, thank you for presenting all of this, I've been binge-watching it and this is a channel I've come to find quite interesting.

Always enjoy your posts. I really enjoyed your book as well. Please keep it up, it gives an old man something to think about!

Many years ago (actually decades) I was watching a live program about the crashing of a photo satellite on the moon's surface. I believe it originated in a conference room at Jet Propulsion Laboratory in Pasadena, California, USA. The satellite was sending back digital photos of the moon's surface in real time and the telemetry equipment was displaying the photos on a screen. One member of the panel of scientists was a major proponent of meteorites as the cause of the craters, another member was a major proponent of vulcanism as the source. With the last two or three photos (and one partial) the resolution became better than even the best of earth-based telescopes (marred by atmospheric turbulence). This was even in the face of the poor (by today's standards) resolution of the digital sensor on the satellite. It became clear to all on the panel that the origin of the craters had to be meteorites. --- The program continued with statements by the scientists and the proponent of the vulcan origin admitted he was wrong. His whole reputation had, within a couple of minutes, gone up in smoke. He was upset, disheartened, disappointed. But he retained a respectful level of civility. I was only in my late twenties and had not yet experienced such disappointments in my life/career. But I easily sensed his disappointment so late in his life and remembered the program, so I could relate it to you today.

I have an engineering degree, and even through all my physics classes, you explained the whole light particle/wave duality much better than anywhere else. It finally makes sense. Thank you!

What a great offer from you re asking you to cover a topic. Thank you so much!! Following on from your double slit vid, can you do one on Bell’s Theorem and explain how this shows that the uncertainty in Quantum Mechanics is not caused by our lack of knowledge about hidden variables but is fundamental part of the universe and maybe explain the concept of non-locality as well? I can hardly wait! Thank you. David

Dear Dr Becky. You are the #1 physics and cosmology "explainers" to people with limited physics backgrounds. Your enthusiasm is contagious. Thanks! Keep it up!

I like it, when you go into the history of a scientific debate. It shows in a nutshell the development of an idea and why it was controversial at a time. And about the Solvay conference: isn't it a shame, that Mrs. Curie was the only women there? As you pointed out in an earlier video, there have been many great female scientists throughout history of science!

SO... light is a particle, that is waving frantically at us.... :~) a "warticle" of sorts...

Interesting video - liked the style - and I was able to stay focused.

Top notch description! Thanks

Einstein: God does not play dice. Wolfgang Pauli: Einstein, stop telling god what to do.

"Imagine the reaction of the world if someone claims Einstein was wrong about something". Procedes to tell us how Einstein was wrong about something.

Nice summary of a great debate presented in a lively manner.

Very good video covering a lot of non-trivial concepts. Keep up the good work Dr Becky! BTW, my suggestion for the debate series would be how contemporary Bell's inequality experiments have tilted the scales towards instantaneous action at a distance. Your video got me delving into the Photoelectric effect. The Photoelectric effect, Hertz 1887, is that polished metal plates irradiated with light may emit photoelectrons. A threshold frequency "fo" was seen to exist at which only for f>fo will we see a current, this was not explained classically. Another result was that the magnitude of the current depends on the intensity of the light. The interesting result was that the energy of the emitted electron depended on the frequency of the irradiating light. E = hf - W was conjectured to explain the result, where h = Planck's constant, W = work function to expel the electron, and E is the energy of the electron (Einstein 1905). Millikan in 1915 empirically verified this expression that Einstein conjectured. He measured h, Planck's constant, to 1% accuracy apparently. Again, your videos are critical in explaining quite difficult concepts to your audience. Keep up the good work!

Is light a wave or a particle? That depends on how you look at it.

Light has dissociative identity disorder at its most fundamental level.

So each week I'm wandering along in life then BAM! Suddenly, I'm immersed in physics! And yet, Dr. Becky explains a really, really difficult subject better than most. I am always pleased to watch your videos, Doctor. May you live a thousand years and enjoy every day of it all.

Hi! Idk why but I'm binge watching all of your videos. And I just want to say Thank You!

Oh no! We are an old retired couple and the only way we know what day it is is when your video comes out...now we will always be off a day...sighhhhhh

My favourite fringe theory on this: 1. What we call light is actually a combination of a particle and a wave. 2. Both the wave and the particle have an independent existence. Particles don't become waves or vice versa. 3. A particle moves if and only if it encounters a wave. It's a guiding wave or "pilot wave" if you will. 4. Waves can travel along the direction of the particle's path (e.g. Both particle and wave go left to right), or exactly opposite to the particle's path (wave goes left, particle goes right). There's evidence for both.

Congratulations Becky, very intereting video about one of the most facinating physics dilema. I work designing and manufacturing light managament films and shade cloths for the greenhouse industry, and this physics dilema keeps me pushing to try to get a better undestanding of light.

Keep up the great work Dr. Becky. Love these videos. Best wishes.

Poisson must have been a bit of a wet fish at parties. Sorry, but I just had to - I'll see myself out. :-P

...guilty: as a german i love to see a native english speaker struggling with the right pronunciation and words!

I really enjoyed this video, I learned a lot. Thanks Dr. Becky :)

I have only just seen this video (I haven't been watching this channel all that long and am now getting through the vast catalogue of past videos). This is the first time an explanation of wave-particle duality has truly made sense to me and how light (and electrons etc) are waves until you try to measure them in some way and "force" them to act like a particle. I dunno, its a bit like the difference between a wave on a body of water and a molecule of water. Well anyway, its the first time I've been able to really visualise it, and I watch PBS Spacetime. Thank you Dr. Becky!

Physicist: Is light a wave or a particle? Programmer of The Matrix: Yes!

Can you imagine being there when they took that photo?! The who's who of the greatest minds the world has ever seen! Always enjoy your vids. :-)

That was a brilliantly easy to understand quantum sum up Becky, fascinating!

I really enjoyed this one Dr. Becky, faux pas and all! And, my book arrived this week, complete with your signature that I watched you write! i was hoping for one with the Galaxy but I'm happy anyway.

Loved this video. One of your finest.

I really liked this video! Well done!

just brilliantly clear articulation (as always) of a complex, confusing subject - love the out-takes :)

I completely understand why this stuff was the favourite part of you're physics degree - it's so fascinating. Consequently this is probably my favourite video of yours so far.

Fantastic video. The biggest physics project I had in high school back in the 1980’s was: Is light a particle or a wave? It was taught well and was 1/3 of our grade. But they didn’t say anything about the history of the conversation. A lot of students were annoyed because they didn’t give us the answer in the end. Knowing the history would have been very beneficial back then.

Sweet video! Very informative for a topic I've heard of but didn't know a lot about. I've Only ever really of light being seen as a wave or a particle but nothing more specific or helpful than that :D

Hi Dr. Becky, my name is Dr. William Walker. I am a physicist from ETH Zurich. Thank you for such a nice historical review of the nature of light. I have been studying the topic for 30 years and have more to add to the story. First of all I have theoretically and experimentally determined that nearfield light is instantaneous, and after one wavelength reduces to the speed of light. This has been determined by me and many other independent researchers over the past 20 years. This speed corresponds to not only the phase speed and group speed, but also the information speed. This observation is completely incompatible with Special Relativity, which limits everything to the speed of light. This was experimentally confirmed by me and others by measuring the time delay of radio waves between two dipole antennas, as the antennas were separated from the nearfield to the farfield. The observed results match perfectly with theoretical calculations using Maxwells equations. A re-derivation of Special Relativity shows that instantaneous nearfield light yields Galilean Relativity, and farfield light yields Special Relativity. But since space and time are real and can not depend on the frequency of light used, then Relativity must be an optical illusion, and space and time must be absolute as indicated by Galilean Relativity. Space and time of inertial moving objects can appear to change using farfield light, but the effects are not real, and can be proven using instantaneous nearfield light, which will show space and time are the same for all inertial reference frames. Because General Relativity is based on Special Relativity, then its affects on space and time must also be an optical illusion. So if General Relativity is wrong, what is a better theory of gravity? It is well known that General Relativity reduces to Gravitoelectromagnetism when Special Relativity does not apply, and for weak gravitational fields, which is all that we observe. Ref Wiki Gravitoelectromagnetism. This theory of gravity assumes gravity is a propagating field and follows a set of 4 Maxwell equations similar to those of electrodynamics, except for differing constants. It assumes gravity has electric and magnetic-like components. Because General Relativity reduces to Gravitoelectromagnetism for weak gravitational fields, then Gravitoelectromagnetism also predicts all the known gravitational experimental observations, including the instantaneous nearfield and the speed of light farfield. Also since Gravitoelectromagnetism assumes gravity is a propagating field, it can be quantized as a graviton, enabling the unification of gravity and Quantum Mechanics. With regards to quantum theory, Pilot Wave theory would become the preferred interpretation of quantum mechanics, due to its deterministic simplicity, if as I have shown, both instantaneous fields are a reality, and if the true form of Relativity is Galilean Relativity. For more information about my research, see the following short KZfaq presentation and the paper it is based on below: *KZfaq - New Interpretation of Relativity: kzfaq.info/get/bejne/qcuAl61o27m1poU.html *Based on the following paper: William D. Walker and Dag Stranneby, New Interpretation of Relativity, 2023: viXra.org/abs/2309.0145

really good explaining of this topic and I love the history side of it

Absolutely brilliant.. So perfectly done.. Bravo!!!

A great continuation for this great video would be De Broglie-Bohm's Pilot Wave and Bohmian Mechanics, why it is not well accepted and what it's non-locality means. Please Becky, please!!!

I remember thinking at the time that the idea of "duality" only meant it was neither, and we really didn't understand it at all. I'm reminded of Hilbert's assertion "Physics is too hard for physicists," implying that the mathematics of physics was poorly handled by most physicists. Einstein's statement “As far as the laws of mathematics refer to reality, they are not certain; and as far as they are certain, they do not refer to reality” is an example of that kind of bias. Throughout the 20th century, we've learned that the laws of mathematics do guide us in examining reality, and they provide a window through which we can understand reality without the bias of our limited physical senses.

Had to watch it twice to grasp it but I really enjoyed this video:D 10/10

Nicely explained!

Excellent - I have a mug with the 5th Solvay Conf. on it - the most important picture in history

Can you do the AMPS paradox debate, the whole ER = EPR situation, and aDS/cft correspondence? I'm very much a novice but, it's interesting! Also, these videos are great! Thank you for making them!

I didn't know about the disc and the shadow experiment. Thanks for allowing me to learn something today.

Thanks for this lecture Becky! This is my question; what about gravity? What is its carrier? Wave? Energy?

Dr.Becky I hope I state this correctly. I would like to see a great debate symmetry vs asymmetry when talking about the big bang and particle annihilation . BTW im an ignorant peasant when comes to physics but I find this topic very interesting and you make it so much fun. -Thanks Blake

Thank you so much for making this video. I have been looking for something that explained the photon side of things. The wave makes so much sense to me. This is perfect and makes sense given this history behind where we are today. Thank you again!

What a great video. Very clear discussion of a. Wry unclear topic. Brava!

The problem is Bohr only won the popularity contest, he didn't even take a coherent position. He assumed that electrons or photons or whatnot ever exist, when under the uncertainty principle they *never* have those properties with probability 1. Plus he never defined what it means to "observe" something.

hmm i think the problem is with human perception and how we conceptualize/analogize things with everyday objects around us we have to remember: 1) our perceptive and cognitive functions are evolved to allow us to survive, not to perceive things as they actually are 2) it may be only convenient for our cognitive processing to either perceive/conceptualize things around us as "objectives" or "Waves" or anything else - and thus it is only natural for us to imagine that the same "analogies" continue to apply if we keep subdividing an object into smaller bits etc (when in reality "objects" or "waves" only exists in our imaginative constructs) for example: if u perceived your table as it "Truly" is - you will realize it is actually mostly empty space (a more accurate representation of it would actually be some kind of force field in the shape of a table) 3) if we try to analogize from our imaginative constructs down to the nano level and things don't add up - it may simply mean it is our constructs that have broken down (we were never evolved to fully "visualize" elements of fundamental physics on a nano-level)

I vote that the next debate topic is on the interpretation of quantum mechanics, the whole “local hidden variable” topic and the beauty that is Bell’s inequality. Thanks for another fantastic video!

This video helped me get a couple of pronunciations and facts correct. Thanks!

I've always considered that light is a particle that leaves a _wave_ behind it, just like a boat leaves a wake in water, but the water here is "background" electromagnetic radiation. It may very well be that the measuring devices are only "seeing" the _wake_ of the photon, hence the interference pattern created by particles passing through the double slit.

Darling! You have taught me a lot more than 4 years of my bachelor's degree in engineering and science! Just in a few videos! And thanking to brilliant.org the base you set, it just made it concrete! And now I am hooked to your videos and keen to know more whats happening in astro field every day and month! Thanks a lot!!

That was amazing... great explanation.

Like the science - but especially love the outtakes at the end. :)