Why does light slow down in water?
Why does light slow down in water

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There are many mysteries of physics for which you can find explanations online and some of those explanations are wrong. In this video, Fermilab’s Dr. Don Lincoln takes on the mystery of why light travels slower in water and glass. He lists a few wrong explanations and then shows you the real reason this happens.


Sunny shah : But why does it bend at an angle after hitting the glass?

Eric Marsh : I just passed this link on to answer a Quora question

Steve Jones : A slight irony that in a video explaining the real reason why light travels slower through a transparent reasons has little animations of atoms as mini solar systems with electrons orbiting the nucleus rather than inhabiting orbitals. I guess we are never going to get away from that imagery...

Hussein Tofaili : But why waves from oscillating electrons move slower?

electroarv : Interesting matter! I wonder how we fit evanescent fields in this explanation though..

TacticusPrime : So it's kinda like dropping a magnet down a pipe.

Batrax : Sorry but for me this video raised more questions than it answered. First of all, why doesn't the "original" wave come out of the glass weaker? With no other information, I would expect all light entering glass to exit at two different times: the first, travelling at exactly the speed of light in a vacuum, made up of respectively the original light emitted by the laser and the independent light emitted by the photons (dimmer because it lost some of its energy to the electrons). And the second, the sum of both waves, arriving later because it was travelling slower. Also, why does the light change path as a result of it slowing down? Going with your explanation, shouldn't the sum-wave move in the same direction, if slower? I knew I didn't have a grip on it before, now I feel like I'm gripping it by the blade...

ViperDaniel : But why does the wave generated by the electrons move at a different speed?

divyam goel : When a charge oscillates, it produces an electromagnetic wave. Why is this EM wave slower than the light (which is also an EM wave) entering the medium resulting in a net decrease in the speed of light?

TheAbc45678 : Wow. But at the same time, I'm now perplexed by more fundamental questions related to fields.

OHM-968692 : Ok this makes absolutely no sense, but I'm glad my wrong idea was debunked.... For like the 4th time... why can't y'all agree on an explanation?

ARCSTREAMS : he says "the atom is absorbed by the photon" he makes mistakes talking that way

Haim Ben Avraham : it's a well-known fact I learned in Ireland ... light slows down in water because it's thirsty.

Artemio Fava : Dear Dr, What happens with the color of the ligt inside the glass? If the speed slowes down the wavelenght enshorten, so does the colour becomes more bluish?. Best regrads

philip formby : I will listen to any scientist who wears a pink Floyd t shirt

kd1s : Ah very nice introduction to Fourier transforms. Excellent.

BLH BSIT : That answer is very logical. Thx

Doxie Lain : Wow, very interesting. Thank you, this explanation was clearly presented and makes a lot of sense the way the discourse developed.

Dave Dewhurst : Excellently explained. All your explanations are clear and succint. Thank you.

gearsplayer0612 : This is so informative and easy to digest. You and your editor(s) are artists.

David Smookler : I love finding underlying correct answers. : )

Jeb Julian : glossed over constructive interference with electrons :p still can't work out the speed limit. Thank you for the video!

Liudas Survila : very well explained, subscribed, thank you!

Shmalentine : Extra points for the Pink Floyd attire. :)

James Ryan : Pink Floyd opened my eyes. Without drugs, btw. .

laurencefisher1 : keep your hands STILL please

Raymond K Petry : *_...but why are colored photons at different speeds through glass prisms...why do x-rays scatter with multiple angles off individual atoms...how is deBroglie's theorem adding frequencies where photons are superpositioned...none of Don's physics makes 5th grade sense—it's like Ptolemy's Almagest of quantum epicircles 1900 years behind times; 'Are we homeworking yet'..._*

Kickin Rocks : Is your coat made of vantablack?? So hi tech.

j p : Great video thanks! I hope Uli enjoyed his cake.

Umer Mukthar : All em wave travel in same speed

john noe : Something about this guy rubs me wrong. In another video I was watching he stated some things that were incorrect according to what I've been able to learn from other experts. And the fact that he's trying to impress us with a blackboard full of math formula's/equations etc. is telling me he an insecure person and believes he needs that blackboard to help build him up in our eyes.

Bemused Indian : I was so sure of the scatter theory, even convinced a few people. Going to tell them ASAP. Thanks.

Andre Williams : You really put a lot of information in a short video on I'm really impressed and combining all the intrical interactions and easily understandable manner

Alexander K. : Professor Fermilab --- I love you ( and I am 56 years old)! Please continue!

Brandon : I'm guessing the pink floyd shirt was on purpose.

Maurizio Pavel : THANK YOU! I had this question for a lot of time and I'm glad I found this explanation now, because I couldn't have understood back then! Very well organised and very interesting!

Dieter Bletten : nice T-Shirt!

Anubhav Mahapatra : Very well presented through basics

Life's a card game : Wow, just wow. I've been wrong for many years. I believed the second of the wrong theories. Thank you so much for correcting me.

A.K.M. Mahfuzul Islam : Yes, correct explanation. Your explanation was easy to understand. Thank you.

Pascal S. : Super easy explanation. That is the last reason I would ever have assumed why light is slowing down. So crazy 🤪 I'm amazed by that

John Smith : Another excellent and informative vid - Great as all your vids are - but the central question remains - did you remember Uli's cake?

amaraojiji : You have a peculiar phenomena around the rainbow on you shirt. The green part of the spectrum is been absorbed by your video editor and remitted as blackboard drawing.

nischaya tomar : U got a new subscriber sir...explaining with the help of graphics is really really really helpful.

Dumble Door : Interesting, then it kind of work similarly as a magnet moving through a copper tube, generating electricity in the copper tube, resulting in a magnetic field that slows the magnets passage through the tube. 🤔 I wonder if there is a connection here somehow?

Onkel Tschimi : Ive been looking for the answer to this question for years. Absolutely amazing. Thank you

buzzcrushtrendkill : Thanks for the great explanations Mr. Dancing Hands

Quahntasy - Animating Universe : Did not explain the change in direction. But very well presented. Thanks!

28mmForge : Hey its Dr Lincoln.. I watched his course on the great courses