Is light a wave or a particle? | Great debates in physics

One of the most famous debates in all of Physics is one that spanned over four centuries and eventually led to Einstein and Bohr debating for most of the 20th century. It was all about the very nature of light - is light a particle (as Newton had insisted) or is light a wave (as people like Young and Maxwell insisted)? It was eventually a problem that quantum physics would solve...
Here's the video I mentioned on the history of light and trying to find the medium it propagates through: • Why can’t anything go ...
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The artwork in the background is a scientifically accurate map showing the orbits of more than 18000 asteroids in the Solar System, created by Eleanor Lutz. Find out more and buy one here: eleanorlutz.co...
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📹 Dr. Becky also presents videos on Sixty Symbols: / sixtysymbolsand Deep Sky Videos: / deepskyvideos
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👩🏽‍💻 Dr Becky Smethurst is an astrophysicist researching galaxies and supermassive black holes at Christ Church at the University of Oxford.
drbecky.uk.com
rebeccasmethur...

[@DrBecky]

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 🤦🏻‍♀️

[@pulkitmohta8964]

You are a human too, and it's natural to make mistakes. What's more important is to acknowledge the mistakes, which you did✌🏻

[@cleon_teunissen]

While it is the case that _when_ the electron double slit experiment was done is not essential to your narrative, this anachronism is a big error. I don't think you can count on viewers reading your pinned comment. I have to recommend that you re-record the video, and that you replace this version with a corrected video.

[@nigelm5777]

Cleon Teunissen Seriously?

[@leeeastwood6368]

Dr. Becky, the difference between you and a politician. you admit your mistakes, correct them, then move forward, rather than sulking and demanding that science changes!

[@cleon_teunissen]

@@nigelm5777 Well, yeah. For comparison, what if in a video by a physicist it is stated that Pluto was discovered by Urbain le Verrier, and that later Neptune was discovered.

[@johnthompson1928]

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

[@vladimirseven777]

And to find where you've been will be used cannon ball. Where spot left - there you were. In science this ball called "observer".

[@MountainFisher]

Not no-ones, but nobody's, sorry, lol. A Geneticist can say that we do not know what all of the functions of the so called "Junk DNA" are, but some theoretical physicists will say that their speculations are nearly real without any solid evidence. Many, and I do mean many theoretical physicists with more degrees than I, will call their speculations near to being fact, if not actually factual. The Universe from quantum fluctuations is a less than satisfying answer. Why will these "scientists" not say they have hit a Planck Wall? Their conjectures are tossed about in the Media because the are counting on their audience's ignorance. The people I am writing about sell books, lots of books, but not science. They became as E. O. Wilson's assessment of Dawkins was as a "journalist". Not a scientist, they gave that up to be celebrities. Do they have an emotional attachment to their theories? Yes of course. They defend themselves by disparaging philosophy all the while they use it. One said that "Philosophy is dead" a philosophical statement if ever there was one. It contradicts itself. It is a philosophic proclamation, but it cannot be true because it IS philosophy. There is no truth? Is that true? You get the picture? Beware of poor philosophers posing as scientists.

[@dankuchar6821]

I see what you did there! That's kind of funny.

[@MountainFisher]

@@dankuchar6821 It IS funny, but when science is being philosophical it is sad too. To listen to a physicist ask "what do you mean by truth? during a debate is disheartening. People hear these debates and gravitate to the more charismatic speaker rather than the more truthful speaker.

[@vladimirseven777]

@@MountainFisher It is part of human's logic. Who is authority. Science schools. Most of scientists doing nothing useful and waiting for 20+ people with brain will solve the problem. Acting as football fans.

[@JulesvanPhil]

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.

[@DrBecky]

I like that!

[@rayzorrayzor9000]

I think we might’ve had the same teacher , same analogy that I have never heard again (until I read yr comment) Lol 😂

[@perrydowd9285]

That is so well put. My lecturers in physics were always finding ways for us to visualise scientific models. They would have loved that as much as I do.👍

[@dcfromthev]

Perspective is a bitch

[@juzoli]

Jules Phil Exactly. I hate when someone describes it as “sometimes wave, other times particle”. No, it doesn’t change its property, it has both properties all the time. We could also say it is not particle, neither wave, but it is its own 3rd cathegory, with some similarities to both.

[@Payne2view]

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

[@elomnusk7656]

And no

[@protocol6]

de Broglie, Bohm, Bell and others might agree quite literally. It's a bit like asking if a black hole is both a singularity and massive warp in space-time.

[@elomnusk7656]

@@protocol6 well its actually the same thing. Massive warp of space time is a singularität by definition. Its more like as asking if space and time are the same thing

[@joshuahillerup4290]

Mine is "no"

[@joshuahillerup4290]

@@protocol6 no, Bell and Bohr disagree with each other on this

[@germancuervo945]

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

[@juanbernardez1295]

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

[@juriskrumgolds5810]

It's often referred as "A picture with highest IQ in history".

[@engineeredlifeform]

If I could go back in time, I'd be happy to push a tea urn around, hand out sandwiches, and just listen in.

[@jakemcmillian]

I would like to know how that group would respond to "the Universe is a simulation" theory

[@HassanPlayz]

@@engineeredlifeform i would but i honestly would not understand

[@Charis_Code]

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!

[@DrBecky]

Thank you! Very high praise

[@mpart_woodlathe-stuff]

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

[@juanvia8394]

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

[@TheNameOfJesus]

@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.

[@branscombeR]

This post led me to look up ON-J's Wikipedia entry, thinking maybe she was given her middle name after a certain well-known English mathematician of old ... sadly, not true but of course there is a lot of info about her grandfather, Max Born, who won the 1954 Nobel Prize in Physics for his "fundamental research in quantum mechanics, especially in the statistical interpretation of the wave function". There is also an interesting mention of her father, Brinley "Bryn" Newton-John, who worked at Bletchley Park on the Enigma project and so is quite likely to have known Alan Turing ... also, 'Newton-John's father was an MI5 officer ... who took Rudolf Hess into custody during World War II.' All very interesting stuff which was completely unknown to me. Coming from such a stellar scientific background, it was hardly surprising that her first pop music group, formed at the age of 14, should be called the 'Sol Four'. R (Australia)

[@francoism1926]

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

[@kitcat3263]

for me whole french spelling doesn't make any sense;) sry

[@theoneaboveall6768]

Evgeny Kobylyatskiy Je parle français and you are right 🤣😂🤦‍♂️🤦‍♂️

[@poptart2nd]

the french language was just a practical joke that got out of hand.

[@pjousma]

Dutch guy here: "Huygens" is pronounced "Huigens", where "ui" is done by pronouncing the sound as it appears in the English word 'man' followed by the Dutch long u.

[@DoSeOst]

As someone who learned both french and english at school as a foreign language, i have to say that the english spelling and pronounciation sometimes is much worse than the french (e.g. tough, though, thought). Let us not talk about grammar though. ;-) Btw the "gli" sound is italian as the name Broglie originates from Italy (Broglio or Broglia).

[@MaxG4880]

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.

[@robertholmes6348]

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

[@airmakay1961]

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!

[@vishal2352]

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

[@shubhamsingh3519]

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

[@shubhamsingh3519]

@Marko no one is talking to you Mr weirdo!

[@erictaylor5462]

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.

[@RowOfMushyTiT]

I doubt that is from the Fresnel interference, as sunlight is not monochromatic. What you are seeing is just the Umbra and Penumbra of the plane's shadow. The bright spot may occur when the Umbra disappears and the Penumbra from either side superimpose.

[@erictaylor5462]

@@RowOfMushyTiT Aren't they the same thing? The bright spot on the middle of the shadow is still there, it's just to small to see from altitude. Even when the dark shadow is gone, the bright spot is very small.

[@RowOfMushyTiT]

@@erictaylor5462 Fresnel diffraction is a very different physical phenomenon from the Umbra/Penumbra shadows of aircraft. In fact you need parallel illumination, a point light source, and monochromatic light (aka a laser) to avoid forming a Penumbra in order to do a Fresnel experiment properly. Only under these conditions will you see the bright spot in the center of the Umbra, which represents light waves that diffracted around the object. More likely in the plane shadow you are seeing some low angle reflections or refraction through the windows.

[@erictaylor5462]

@@RowOfMushyTiT I'm not disagreeing with you outright, but as you have provided only your word, I have no way of knowing if you are right or not. I don't know anything about you. However, judging from past You Tube comments, I'm taking what you say with a huge grain of salt. It is nothing against you. I'm sure you would do the same with me. Providing a link to further reading would be helpful here.

[@erictaylor5462]

@Boodysaspie I know I saw a video on this subject, and I finally found it. kzbin.info/www/bejne/r2rGaaKQaZ6jfMU Now you can stop arguing with me about something I never even disagreed with you on.

[@geraldfrost4710]

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

[@robkoppens9966]

Depends if you observe or not? I'd say why not both as wel, as well as funny at the very end. Very well explained matter and history. What a photo of those great minds. Coming to think of it....photo made possible by photons.

[@kyetexe954]

Genius-beautiful duality

[@Akswan]

She even ,if not for a breef showed her knie left it is now i'm a happier guy....

[@thetrickster9885]

Depends on how you look at it ;)

[@katherinekinnaird4408]

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.

[@TheGhostGuitars]

I'm curious, what IS her opinion on the nature of light? I've noticed that sometimes children may have an extraordinary insight into things without the contamination of preconceptions or expectations.

[@katherinekinnaird4408]

@@TheGhostGuitars well she says that if she shakes out a towel she can see tiny specks floating especially where light comes through a window. So she feels that light is particles. Probably not the answer you may expect but she sees the particles and believes they are part of light. Her response to the question " particles or waves" was spontaneously immediate. as her grandmother I enjoyed every bit of the discussion.

[@TheGhostGuitars]

@@katherinekinnaird4408 lol, not quite as expected BUT at same time, she's surprisingly close. IMO, I consider the specific points in spacetime on the light wave form is where light can manifest as particles and thus can take on properties of either as required. Thus her flapping of the towel is the wave form. The dust that's on the towel is the particles. Nurture that precious intuition, with that intuition she'll grow up to be someone influential in the sciences (or whatever she chooses to be in)!

[@katherinekinnaird4408]

@@TheGhostGuitars she will be thrilled when i read these to her tomorrow. Thanks so much for taking an interest in the up and coming minds of the future. Good health to you all. From Bakersfield California USA.

[@TheGhostGuitars]

@@katherinekinnaird4408 LOL, our future IS in our children! All we can do is try raise them best as we can and leave a decent world for them to live in. I only pray that they do a better job of taking care of this world than some of the people in charge has done! Lance from Honolulu, Hawaii.

[@Zestyclose-Big3127]

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)

[@voxelmaniam]

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

[@ybbcgfe]

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

[@nmarbletoe8210]

Great idea. i've seen a way of looking at Bells theorem with Venn diagrams...

[@iampracticingpiano]

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

[@Vodhin]

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.

[@Shads62]

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.

[@xiaoxiao-kg5np]

A. There are no such things as Photons. Nothing about Light is particle based. B. Experiment must be correctly interpreted, and to do that, we need ALL the CORRECT information. C. Half of the information about Light or sub atomic particles does not exist, so we ASSUME stuff. D. so trying to explain the double slit experiment given a half baked incomplete understanding of most of what were are actually doing, is going to only give nonsense results. Aka, Quantum Mechanics.

[@joshuahillerup4290]

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.

[@PixelatedPenfold]

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

[@TheGhostGuitars]

Hear hear! +1!

[@TheGhostGuitars]

@Bob Wilson I would if I had better PC and internet connection to download and edit those videos. Working on the PC hardware and software now as I plan to start a KZbin channel myself.

[@NZC_Meow]

@@TheGhostGuitars were you successful in making your channel?

[@TheGhostGuitars]

@@NZC_Meow Ah no there's a major shortages in some pc hardware right now, especially cpu and vid cards. I'm NOT gonna pay 4-figures for a vid card that debuted for 600-700$. The higher card are going for proportionally higher prices. This is utterly ridiculous!

[@HassanPlayz]

@@TheGhostGuitars hope you end out making it

[@kikitube79]

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

[@Matt-re8bt]

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

[@geoculus5606]

As I understand it, it's more accurate to think of gravity as a consequence or result of mass existing. Mass itself by existence curves space-time (somehow), and therefore the "force" of gravity exists, even though it's not a force since there's no work being done to make it.

[@cjphelp]

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.

[@Anacronian]

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

[@davidsharlot67]

I'm going to fly to America and buy one immediately. Just double masking and praying will probably save me from that disease, I heard was going around.

[@TwistedHot]

🔅

[@dcfromthev]

Wondering the same thing! A stack of books!

[@DjoumyDjoums]

Following what you said about wave-particle duality, it would be nice to see your take on the interpretations of it (copenhagen, many worlds, pilot wave etc). AFAIK it's still hotly debated nowadays.

[@abebuckingham8198]

It's only debated because the Copenhagen interpretation is silly and invites criticism.

[@nmarbletoe8210]

@@abebuckingham8198 If they are truly "interpretations" rather than different theories of physics, then the data can support any equally, it's more a matter of philosophy, so that would explain a lot of debate. . I like the Many Worlds but I am willing to accept that in some Worlds it might not be true lol

[@emilmckellar4932]

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

[@cam35mm]

Maybe you should work in the film industry. We have no problem in pronouncing Fresnel.

[@sleepy314]

@@cam35mm ...yeah, Fresnel lenses. I heard the name long before I saw it written. This was with lighthouses.

[@w00dchurch]

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!

[@iowafarmboy]

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!

[@euanthomas3423]

The whole point is that it makes no sense. Feynman whose Nobel prize was for QED called it screwy. You just learn the rules (like in a game of chess) and calculate with them.

[@williamwalker39]

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 KZbin presentation and the paper it is based on below: *KZbin - New Interpretation of Relativity: kzbin.info/www/bejne/qZazlX1tq7iErLM *Based on the following paper: William D. Walker and Dag Stranneby, New Interpretation of Relativity, 2023: viXra.org/abs/2309.0145

[@schmetterling4477]

Yes, that was total bullshit. ;-)

[@petercarlston8900]

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.

[@jppitman1]

That must have been the Ranger series of moon probes. I was glued to the TV when those pictures came in. And now--who`d a thunk it?--50 years later, I`ve seen craters on Pluto! I remain stunned as to what basic discoveries have been made in my lifetime, both scientifically and technologically, thanks to rational, smart people--the Dr. Becky`s of the world.

[@robertgoff6479]

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.

[@lamegoldfish6736]

You found a picture of Robert Hooke? Amazing. 😃

[@michaelsommers2356]

There are lots of pictures of him, just not many are contemporary.

[@NeverTalkToCops1]

Isaac Newton's quote: "If I have seen farther, that is because I have stood on the shoulders of giants." This was a deliberate insult to Robert Hooke, who was small in stature.

[@PuzzleQodec]

@@NeverTalkToCops1 I think Newton took a lot of credit for work he didn't do, and that he was fully aware of it.

[@Sebolains]

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!

[@inerlogic]

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

[@planexshifter]

All I know is they go down smooth-

[@nettyvoyager6336]

wave function

[@I_Don_t_want_a_handle]

There's something very fishy about his statistics ...

[@inerlogic]

@@I_Don_t_want_a_handle Poisson? Poisson? I LOOOVVEEEEE le Poisson!

[@andyreznick]

It's a Wavicle, obviously.

[@shexec32]

It wasn't Thomas Young who performed a double slit experiment on electrons (electrons had yet to be discovered). The electron double-slit experiment wasn't performed until 1961 (although the Davisson-Germer experiment of the 1920s demonstrated the wave nature of electrons through diffraction). PS. I also pronounce Fresnel as Frez-nel, and often say dualidy.

[@eddiebrown192]

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

[@paultheaudaciousbradford6772]

Depends how hungry the pigeons are.

[@KABNeenan]

Schrödinger: Yes.

[@ogi22]

@@KABNeenan Well... It was his cat after all...

[@Metal73Mike]

It simply is in superposition; it's both AND none :-). Ow, and if it's MY cat I can tell you the pigeon's wave-function WILL collapse and surely they'll be dead :P

[@zachyoung5598]

It depends on how far the cat was thrown from (and how many lives it has reamaining).

[@00bikeboy]

James Burke's Connections series made me fall in love with science history.

[@jppitman1]

Ohhh, yeahhh, I LOVED that series! Forgot all about it. Thanks for the reminder.

[@mikekottmeier855]

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?

[@5pecular]

Yes this is what gets me excited, would love to get my head around how we measured quarks muons tau electrons higgs boson etc

[@monster2slayer]

www.lhc-closer.es/taking_a_closer_look_at_lhc/1.detectors

[@IsaacRC]

I like most the Neils Bohr aproach (as a visual artist myself) the way it's observed can determine the result, like with the radio waves or the x-rays they are imperceptible except with only the right tools and thus explaining part of its nature.

[@MateusAntonioBittencourt]

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

[@markmd9]

Imagine the reaction of the world when someone proved that Einstein was wrong about something then someone else proved that he actually was right.

[@alleneverhart4141]

He's been found wrong on some minor points - coolworlds astronomer David Kipping stumbled onto a mathematical faux pas in an Einstein paper. Einstein was wrong about the dice thing. He was wrong about entanglement. He was wrong about lambda not once but twice! Stop treating him as infallible!

[@nmarbletoe8210]

@@alleneverhart4141 the key is to be right or wrong about the right things. he clearly had a knack for finding important problems to solve

[@Mythago314]

Imagine calling the cosmological constant your greatest mistake and then someone who's puzzled by dark energy digs up your mistake and decides it probably wasn't a mistake at all. Can't even make proper mistakes like regular people :(

[@mazilliusmashupgunz318]

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!

[@schmetterling4477]

The problem is that there simply is no wave-particle duality. That's just an old false dichotomy fallacy that won't go away. Quanta of energy can behave in many, many different ways. To quote Alan Adams of MIT (he has an excellent QM 101 course on KZbin): "Many electrons don't behave like waves. They behave like cheese.". The wave-particle duality fallacy is about as "scientific" as the four humors theory in medicine at this point. It's just a pity that even many physicists can't let go of it.

[@stoffls]

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!

[@mousquetaire86]

There was Lise Meitner

[@therearenoshortcuts9868]

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)

[@NeverTalkToCops1]

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

[@SvenRognelund]

Actually that was Niels Bohr that told Einstein that

[@ArthurCammers]

The universe plays god and the universe plays dice.

[@orsoncart1021]

This video and comment section are full of mistakes.

[@T4GTR43UM3R]

I see it like that: All fundamental particles are a wave and every interaction causes an exchange of energy. Therefore the frequency of the wave changes due to the interaction. And this is the reason why the wave function HAS TO collapse to a particle for a short time. The collapse to a particle is simply a rebuilding of the wave with its new energy level.

[@IIIRotor]

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

[@patrickfreeman9094]

Wavticle, pave, parvle...

[@msclrhd]

I like wavicle or partave.

[@patrickfreeman9094]

@@msclrhd I second "wavicle"

[@max10eb]

Since light is passing by its waves, ( hheeeeyy) , does that mean its a cross-dresser? :) lol

[@srinivastatachar4951]

So, it vacillates as well as oscillate? Is it that indecisive? ====================================================================

[@frankfowlkes7872]

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.

[@saarangsahasrabudhe8634]

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.

[@micaelramos9157]

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!!!

[@someoneelse3084]

Light has dissociative identity disorder at its most fundamental level.

[@suokkos]

Just like everything else ... me, you and they ...

[@Bassotronics]

It’s an electromagnetic Bose-Einstein condensate.

[@pleindespoir]

Am I doing it or ist it myself ?

[@geraldfrost4710]

It's manic, depressive, manic, depressive... It's electro, magnetic, electro, magnetic... How about "It's a particle waving at you!"

[@srinivastatachar4951]

Split personality? Schizophrenia? You think it is also paranoid? Maybe it listened to atoms and got rudely disillusioned when it found out that atoms make up everything! ====================================================================================================================================================

[@ecospider5]

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.

[@billp3547]

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

[@subhanusaxena7199]

My Oxford Professor Laszlo Solymar had the ultimate quote on this in his textbook Lectures on the Electromagnetic Properties of Materials when answering the question whether an electron is a particle or a wave: "That's how it is, said Pooh" (AA Milne).

[@nathanielhellerstein5871]

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

[@charlestaylor3195]

If you look at it?

[@profphilbell2075]

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.

[@neoanderson7]

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. :-)

[@eddiebrown192]

Meh .... they weren’t that smart ... it was easier for them because nobody knew nothing back them ...

[@paterfamiles]

Dr. Could gravity be a pilot wave that that carries waves and particles? So C would be speed of gravity and light cluld not exceed c ( gravity as the universal pilot wave ) And would a gravity pilot wave help explain inflation I love your KZbin broadcast! I feel enlightened , Edified, and amused. With every episode. Thank you

[@aussiebloke609]

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

[@PuzzleQodec]

Yes and Einstein must have looked like a rock.

[@jasondiasauthorpage615]

I was writing a novel a few years back and in the research encountered this astounding Feynman quote. It's him and Niels Bohr at the Nobel ceremony or something, and Feynman basically yells he figured out why there are as many electrons as positrons: it's because the positron is the electron traveling backward in time. Never heard it before or since. Obviously not a great debate in physics, but maybe you could shed some light on this one (whether the light is wave or not, just shed some). I'm quite enjoying these history-of-physics lectures in this debate frame.

[@schmetterling4477]

First of all, there aren't as many positrons as electrons at low energies, secondly, nothing travels backwards in time or it would necessarily carry information from the future to us. There is a so called CPT-symmetry that seems to be a fundamental consequence of Lorentz symmetry in local, hermitian quantum field theories. This is what Feynman was really talking about, but the general public would not understand it in that format.

[@st0ox]

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

[@bruceyboy7349]

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.

[@DrBecky]

Thanks!

[@bobcabot]

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

[@bobcabot]

@Peter Mortensen ja i did it kinda on purpose...

[@danuttall]

Wave-particle duality: What you see all depends on what you look for. If you look for a wave, you see wave properties. If you look for a particle, you see particle properties. The important thing to notice is that each refers to the same thing. An electron orbits the nucleus of an atom only where the orbital length is an integer multiple of the electron's wavelength in that situation, allowing it to set up a type of standing wave in its orbit. The orbital level is really a measure of the number of waves that the electron has during each trip around the nucleus. n=3 means that the electron's orbit has 3 wavelengths around the nucleus. Too bad this was not explained in high school chemistry when these numbers were introduced to me, but I figured out on my own just a few years ago; too bad I was not the first to figure it out, though.

[@plumfun6750]

What really boils my noodle....is finding out that electrons not only are both particles and waves...but they also pre-choose their form BEFORE you decide to even measure them. In other words...they 'go back in time to make sure they are what you expect'. ;) .. It would be interesting to hear you take on the 1999 "Delayed Choice Quantum Erasure" experiment, or the later one done in 2012 (?).

[@yogeshpatel2018]

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!!

[@sneakypress]

Dr. Rebecca, very, very good explanation of these principles pertaining to the physics and chemistry of light electro-magnetic radiation. It has helped put a lot of the ideas into perspective. ☺️

[@sneakypress]

And yes, it’s the history that we must learn from, in order to move forward, especially in science. 🤓

[@divyanshkaundal.369]

Dr. Becky if you are seeing this comment plz reply.I am watching this after 10 months.I make a hypothesis on this which I will be sharing here full .(first time because I have nothing to loose plz do not mind my English) So, I assume that light is a wave which is a disturbance in a electron (sound bogus but its not) . But here the medium is travelling with the wave ( don't understand ? ) let me explain :- Let a free electron who is moving with speed near to speed of light (that we observed i. e. Approx. 3×10^8 m/s) at this time the magnetic field experience by that electron counteract the inertia (I think a good word for explain this) but not completely but it is trying to counteract the electron which resulted in disturbance in the electron which result in the propagation of electromagnetic radiation which travel with the electron and because of the electron. This explain why light seem to have particle nature. Plz ask me question regarding this and I will tell you the possible answers to the questions. Like this Q. how electromagnetic radiation got the speed of light ( that we observed) ? This is because the electromagnetic force exerted on electron by its motion which gives ability to its wave to move faster but here is a misnomer it ablitise the wave means it ablitised the electron to move faster than its speed now this creates the disturbance i. E. Electromagnetic radiation. Its like a electron light equivalence hypothesis which suggests that the electron and light is not any more different from each other. I am waiting for you to post a reply or question. I know there are many questions regarding this.

[@rohscx]

Thanks for posting this DrBecky!

[@Lincoln_Bio]

As I understand it, the simplest way to look at it is that it's a wave until it interacts with something. It's this interaction that we usually refer to as observation. It's not even just light, *literally all particles* are also waves; the double slit experiment has been reproduced with entire molecules, (bloody enormous ones too, containing up to 114 atoms!) and near absolute zero - as a Bose-Einstein condensate - matter appears to give up on particle-like behaviour altogether. Everything in existence is the result of interacting/interfering waves; reality is the universe singing to itself :)

[@ArturdeSousaRocha]

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

[@Jayarbuck]

(Warning for photosensitive viewers this video contains some scenes with flashing/repetitive imagery, such as animations depicting rapid wave diffraction 02:47 and similar topics) Such a fascinating topic! Really goes to show that science is a group effort -- many different minds needed to delve deeper into the truth of the universe.

[@TomLeg]

Amazing that there were so many great physicists in 1900-1930. I suppose now everything is teamwork, so it's rarer for a single person to be associated with any discovery, other than Dr Higgs

[@skanavi53]

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

[@jøntantano]

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! 😀

[@autohmae]

F-ing best description of the double-slit experiment ever. Why don't people explain it as a wave of light first ?

[@RackBaLLZ]

I love that you talk about what nobody else is talking about. 👍

[@thequantumcat9880]

14:36 to 14:51 Even as a mathematician, I have to agree. Also, that part of the video made me realize it's probably time I change my desktop wallpaper since it's been that 5th Solvay conference colorized image for as long as I can remember

[@quantumradio]

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!

[@cbrtdgh4210]

18:31 is the answer xD My project recently involves using Fourier transforms (as does all modern tech via signal processing!), so I can't help but see everything in a wavy nature. Everything can be represented by a sum of sinusoids! Everything! Even this very video...

[@notsillyone]

C brtdgh can light be thought of in terms of a Fourier transform ? When it behaves like a particle is this because it like a Fourier transform with a narrow band of frequencies, and when it’s a wave it’s like a Fourier transform stretched out with a wide band of frequencies ?

[@mr51406]

14:00 The tall man with the mustache in the top left is physicist and explorer Auguste Piccard. He inspired two fictional characters: for his work and looks Professor Cuthbert Calculus in the Adventures of Tintin (Tournesol in French), and for his name and work Jean-Luc Picard of Star Trek. But that could be a fun time travel destination for Jean-Luc to make... I would and I definitely think you would too, Becky?

[@d5uncr]

Yeah, the cylinder analogy is very fitting. It's a 3-dimensional object that we see as either a circle or a rectangle if we're limited to only looking at it using 2 dimensions (x and y). And likewise - light could very well be a 4 (or more) dimensional object that we can only observe in 3.

[@matthewmartel9295]

2:43 I clearly heard "There was a cat thrown amongst the bitches".

[@DrBecky]

That’s works too 😂

[@terryhaines8351]

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.

[@TheD4VR0S]

I'd like to see a video on the debate about which interpretation of quantum mechanics is correct

[@steveegbert7429]

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.

[@sgcollins]

I want to see an hour long science documentary on the question: what is the real relationship between gravity, time and entropy? We know that gravitation affects time (spacetime that is), and that the second law of thermodynamics is somehow related to 'the arrow' of time. We know that spacetime is expanding, and we know that entropy is increasing. I would love to understand how those things tie together. The universe is going from a high mass concentration to a lower one; and from a lower entropy state to a higher one. Is this just coincidence? A physicist friend tells me that's way out there on the jagged edge of physics, and that we may not know the answer in our lifetimes. Why though? If I could, I would get Nic Stacey to direct, and Dr Becky to be the presenter. That is a show I would watch!

[@Zentauri77]

I remember a story Slavoj Žižek once told in one of his videos about Nils Bohr. (Don't know if it's true) Bohr has invited some other scientists into his cabin in the countryside. One of them recognizes a horseshoe nailed above the entrance door. "Why do you have such a superstitious item above your door? Do you believe in such things?" Bohr answered: "No, of course not. I am a scientist. But I've read that it works, no matter if you believe in it or not."

[@ferociousmullet9287]

Point of contention.......' Observe' is a slightly poor way to express the collapse of the wave function. It implies a conscious observer is required (which has caused confusion for many for a long time....). Which is not the case. Hence the 'measurement problem'.

[@daveseddon5227]

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

[@tablasolo]

Thanks for addressing these arguments. Awesome sauce!

[@Dyslexic-Artist-Theory-on-Time]

The simplest explanation is that light is a wave with particle characteristics as a probabilistic future unfolds photon by photon. This idea is supported by the fact that light photon ∆E=hf energy is continuously transforming potential energy into the kinetic Eₖ=½mv² energy of matter, in the form of electrons. Kinetic energy is the energy of what is actually ‘happening’. The dynamic geometry of this process forms an uncertain ∆×∆pᵪ≥h/4π probabilistic future continuously unfolding relative to the electron probability cloud of the atoms and the wavelength of the light.

[@schmetterling4477]

Nope. Try again. ;-)

[@Iamdebug]

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.

[@Incandescentiron]

I love the history you present within your topics. I would point science deniers toward your explanations as it points out how many scientists were involved in coming up with these theories, the experiments devised to test them out, and the amount of time it took to get there.