How did we measure the fastest speed there is? | The History of the Speed of Light Part I

[@DrBecky]

Sounds like I had a brain typo at the beginning of this video and mixed up the digits when I quoted the speed of light! It should be 299,792,458m/s Also, we didn’t define the speed of light as 300,000,000 m/S because then the dimensions of everything around the world would have changed!

[@mr51406]

Thanks for solving my “What if”! ☮️❤️⭐️

[@macgyveratlarge2133]

I was taught that is was 186,000 mi/sec in a vacuum. I simply went from there, since it still uses a common standard. Conversions from that are fairly easy.

[@Mister_Pedantic]

@@Paygelove Standing on the shoreline of Lake Ontario here in Toronto, I can see the curvature.

[@LeonardLeon]

​@@Paygelove Actually the coriolis effect can be measured. There is actually a formula to calculate the coriolis force strength. Sailplane pilots and meteorologists can show it to you. They can also explain how the atmosphere moves even with the coriolis force. But this is a half hour discussion with somebody smart. You will need at least 5 hours.

[@omanshsharma292]

mam u made my day

[@aidanjt]

I love these astrophysics history episodes, they're fantastic.

[@valeriobertoncello1809]

They are

[@rachel_v_k]

I agree.

[@RezaRob3]

I loved watching that. Thank you Dr Becky Smethurst.

[@michael.forkert]

aidanjt One of the meanings of FANTASTIC is: BASED on FANTASY. Another meaning for FANTASTIC is UNREAL.

[@rachel_v_k]

@@michael.forkert So, therefore... What? Were you going to say something?

[@neuvocastezero1838]

That parallax star field animation is super cool. Also, "The meter is something we humans have invented as just sort of like... a yardstick." Classic.

[@allangibson8494]

And the meter exists because the French couldn’t agree on how long a “yard” was. Every town in France had a different length yard, inch and foot (with different numbers of inches in a foot as well)).

[@pimwillemsma9547]

The fact that Rømer actually drew a face on the sun in his diagram, brings a smile to my face everytime I see it.

[@barthvapour]

Good ole Romer!

[@shadowprince4482]

I'm a total science nerd and somehow I never heard about the Jupiter/Io experiment. At first I thought it was completely stupid to put it lightly then I was massively humbled when I saw how it was done. It was possibly the most brilliant thing I have ever seen!

[@josephvelez7680]

I thought the same!

[@antoniobragancamartins3165]

Dr Becky, I'm Brazilian man, I'm not a physic and I'm not an astronomer, I'm a telecommunications specialist, but I'm an enthusiast with space, and i want to say you explain in an way that we understand perfectly. Thanks!

[@Bollibompa]

P H Y S I C

[@pythondrink]

Even if you didn't mention you were Brazilian, I would have still figured out that English wasn't your native language bcoz your English was quite formal. Btw, you clearly meant _physicist_ .

[@carlosv6813]

@@pythondrink bcoz is not English either, pal.

[@pythondrink]

@@carlosv6813 idu. Maybe you made a typo.

[@theCodyReeder]

I’m going to make my own measurement system in which distance units are defined by how far light travels in one hyperfine transition of a ceasium atom.

[@DrBecky]

You can name the unit the Cody 👍

[@EnglishMike]

I prefer marshmallows...

[@Gene_the_OG_Raver]

Cody, you are TOO funny... in still trying to find out where the light travels the slowest in our universe. I'm sure there are places where it drops down to just a few kilometers per hour, or even slower.

[@JustFamilyPlaytime]

@Michael Bishop I like it - no more c^2, so now E=m!

[@JustFamilyPlaytime]

Well Dr. Becky says that light takes 11ms to travel 1600m, so she thinks light travels at roughly 145km/sec. Maybe you can help her out?

[@PatricRogers]

My 11yo daughter and I have long shared a love of astronomy, and we enjoy your channel together. She recently started sitting in the front seat of the car with me, and she *asks* me to put on your channel while we drive, instead of playing music on the radio, or music videos. Thank you for being awesome and making such incredible science and the amazing beauty of the complicated real life universe fun and kid-friendly.

[@Jackie-wn5hx]

That's wonderful to hear. Parent and child both interested in astronomy is great. My dad and I both loved the Star Trek franchise, but that doesn't count as science.

[@samrodian919]

You have just delivered the most entertaining physics lesson I have ever heard! Thank you Dr. Becky.

[@zachzorn9930]

Looking at a smart and pretty woman makes it much more entertaining

[@Insightful_Truth]

@@zachzorn9930 Who is smart and pretty ?

[@zachzorn9930]

@@Insightful_Truth dr becky.

[@BotanyDegreePilkerton]

she lied right TO YOU FACE lol moron

[@kayinoue2497]

Your excitement for science and sharing it with others is incredibly endearing and such a joy to see. Thank you for what you do.

[@DrBecky]

Thank you Kay for your kind words!

[@garytyme9384]

Pity that she is incorrect.

[@sethtenrec]

@@garytyme9384 troll any?

[@garytyme9384]

@@sethtenrec Hardly, just facts that this "Dr" will not engage with.

[@MrImmers]

Your enthusiasm is very captivating 🤩🤩🤩🤩

[@issamedoot2864]

Thank you for having this video and this channel. You appeared in my recommendations list and your videos are just amazing. I have learned so much in such a short amount of time! I am currently in university and I became excited when I saw how the equations and math I am learning are being applied in this video. I look forward to seeing more of your videos!

[@DrBecky]

Thanks Eric 🤗👍 good luck with all your studies

[@AWildBard]

This is the kind of question I've always asked. How do we know what we know? Love this video Can't say I understand it completely, but I guessed there was a process, and this is a great history / science lesson.

[@DarkMatterBurrito]

I'm probably crazy, but it seems like using a meter to define the speed of light but then using the speed of light to define the meter is circular reasoning in a way.

[@sydhenderson6753]

Once you have decided the definition of a second, then it's actually pretty natural. I'm amazed, though, that they defined it as an integer fraction. Now if we refine the speed of light to more accuracy, the length of a meter changes. It must have been tempting to say a meter is the distance light moves in 1/300000000 of a second (in a vacuum), but that would have required changing a couple of centuries of scientific papers. We could always redefine a foot to be the time that light moves in 1/1000000000 seconds. Maybe everyone would convert to the English system.

[@Gam3B0y23r0]

Finally! youtube recommended an excellent channel! I even clicked the bell

[@theoysterman1]

Please take a look at PBS spacetime. kzbin.info/www/bejne/o6S5pnZ7qJ2MmtE

[@alwaysdisputin9930]

@@theoysterman1 oh god PBS Spacetime is often confusing with their explanations. DrPhysicsA is the best IMO. I like Dr Becky. I like ScienceClic. Everyone makes mistakes however. We must replace them all with robots ASAP. +++ REPLACE ++++

[@StasiSLG]

Hi Dr. Becky, happy to see another video from you. After I saw the previous one about a day of yours, I'm even more impressed you find the time to make these videos for us. So on behalf of everyone 'I hope': Thank you for your time and dedication, we greatly appreciate you.

[@IVANHOECHAPUT]

I was riveted to my computer screen! Great presentation, but what impressed me most were the outtakes at the end. You are very intelligent, human and adorable!

[@tadbeer3090]

Wish I had you as my Physics Professor, my major would be completely different now! Your videos are motivating & informative. Keep it up!

[@manifold1476]

Wanker

[@ccchhhrrriiisss100]

This is an amazing video! Thank you for doing such a wonderful job explaining science at an easily understood level. I've been sharing these videos with family members (including my nephews and nieces).

[@butthurtz5025]

I love this and could listen to this lady all day long.

[@Yora21]

That parallax animation is amazing. I didn't expect the effect to be that big.

[@manipunation]

Yes it was amazing! And unbelievable, as that means that when you see a star chart, you aren't even seeing an accurate representation of the positions of stars in the sky. You are only seeing an approximation. Either that or you are seeing an accurate representation of the stars in the sky, but for only one particular day of the year.

[@leapdrive]

Parallax angles are also used to measure the distance of stars in parsecs. A parallax second or parsec is equal to 3.26 lightyears if measured from the two edges of the earth orbit.

[@thesinistermobs1564]

Greatly exaggerated

[@jpdemer5]

@@thesinistermobs1564 Greatly indeed - it takes close examination of photos to see the parallax at all.

[@4legdfishman]

WOW, I never knew until today, what humans went through to figure out the speed of light! Thanks for that. New subscriber!

[@LancePhillip212]

Yes, for all our self-made problems, we have some things to be proud of as a species too.

[@lorrinrodrigueshs-bcp192]

Yes, it was much easier for the non-humans to calculate the speed of those rascally little photons & neutrinos etc.

[@andrewmullen4003]

Thanks Dr Becky, for the quote of the century, "the meter is like a yardstick" love it, works on many levels!

[@ddsoco1]

I recently discovered your channel and just want to say how much I enjoy it, especially these historical overview episodes. They really are fantastic, even to a piano teacher with arithmophobia like me. Congratulations. I also like how you avoid using a soundtrack. Makes it easier to focus on the content. Cheers.

[@robertlozyniak3661]

Piano teacher? Arithmophobia? I thought music was just math in disguise.

[@ddsoco1]

Robert Lozyniak Yes it is, but it sounds *way* better.

[@jppitman1]

@@ddsoco1 Even the early talkie film makers began to use music to fill up the empty spaces. But, Dr. Becky is so animated and engaging that any underlying music would be distracting to her videos because she leaves no empty spaces whatsoever in her dialogue. Her abundant enthusiasm for her subjects is her "music".

[@captphobos7764]

Great video... you packed it all in so well that my head hurts in a good way, looking forward to part 2, thanks editing Becky :^)

[@bengreatorex502]

This is a brilliant channel on YT. Rebecca explains these concepts as clearly as anyone could, in my opinion.

[@AndrewMerts]

At 2:07 there's a note that there should have been 11ms of delay between observations. That figure is off by a factor of ~2000. 11 light-milliseconds is equal to 2049.1 miles. The actual delay should have been only 5.37 microseconds.

[@bottlekruiser]

I think it's a rounded round-trip delay. So it's off by exactly one SI prefix

[@AndrewMerts]

@@bottlekruiser Yeah, they made two mistakes. They used the round trip time, which is wrong as it should only be the one way delay, and they also swapped microseconds for milliseconds.

[@Geosearchef]

I scrolled way to long to find this :) .

[@OrcinusDrake]

Thanks I just calculated myself cause that number looked very wrong lol.

[@Locut0s]

I’m amazed that Rømer was able to measure the speed of light as accurately as he was able to given the state of knowledge of the universe in the 17th century. To say nothing of the tools available at the time.

[@ericsonnen5248]

Locut0s truly amazing

[@kdog3908]

Yes! Much like Eratosthenes and Al-Biruni and their measurements of earth circmuference and radius. Very accurate given the tools at their disposal.

[@XrisD147]

These people have very logical minds.

[@wormfighter1]

I love how excited you are about your topic.

[@CybranM]

Oh, I never realized you have a youtube channel, you're one of the best guests on DeepSkyVideos! Thanks for making great content

[@uprightape100]

Thank you so much, Becky. That was lovely.....had to watch it twice.

[@harshininarayanan5277]

Amazing and such a great reference video as we are studying a small part in the measurement of speed of light in optics. Our syllabus only covers Fizeau's method(which I couldn't comprehend at first but this helped me plenty😀)..and it was mindblowing to know that they've made so many observations and conducted so many experiments to reach this defined value. Great video as always, Dr.Becky! 😁

[@followthetrawler]

"We as humans defined a metre as a 'yard' stick" - Dr Becky, made me laugh - hope it was intentional.

[@mrmarmellow555]

LOL Yea but yea BUT Were That yard Measured wit 'an YardFoot or an YARD-ARM LAD?? AYE;🙄 ... 😆😇🤓😎🇳🇿

[@fivish]

A Meter is approximately a Yard. The Kilometer is short of a Mile by 666 Yards!

[@georgeemil3618]

"Yard-stick" is used as a common phrase or figure of speech. If someone asked what the car's mileage was and the answer was 10km/l, it'd be awkward but still understandable.

[@chrisspere4836]

@@fivish hi, a yard is approximately 3inches longer than a metre

[@allangibson8494]

Particularly as a yard has been defined by the meter since 1959 (when the length of an inch was redefined to exactly 25.4mm).

[@ImAllInNow]

I was today years old when I realized that Diagon Alley was a pun on diagonally. 9:03

[@glom66]

I was today years old when I realized they were saying diagon alley instead of diagonally

[@ProfRonconi]

@@glom66 As a non-native speaker, the difference between dʌɪˈaɡ(ə)nəli and dʌɪˈaɡnˈalʌɪ' was enough to make miss the joke for a few seconds. And in any case the joke was rather lame. When I explained it to my daughter she she just said a perfunctory "OK". Think of he potential of "magically" "incorporeally", "optionally", etc.

[@itsklein73]

my life is a lie

[@Timberwolf69]

@@ProfRonconi It's probably because we as non-native speakers don't have the same amount of slop in our english as a native speaker. If you speak Diagon Alley fast enough, it gets quite similar to diagonally, as the pronounciation tends to get less pronounced with increased speed.

[@blameitondanny]

I'm a non-native speaker and I quickly noticed the pun. Especially after seeing Knockturn Alley sounds a lot like Nocturnal.

[@isellburritos123]

Great explanation! Clear and concise. Funny edit error at 13:10, great to see your performance is solid in the outtakes ;) Love your channel!

[@attiajos]

I watched another video about the same subject, narrated by a man, and it was almost the same, word for word, including the rain analogy. Not sure who gets the credit here.

[@pythondrink]

​@@attiajosjust check who's video is older

[@Lusa_Iceheart]

Me: Makes an unclean-able mess in the microwave My excuse: A Physicist told me it was science.

[@lyrimetacurl0]

Did you do the plasma thing?

[@macgyveratlarge2133]

I've microwaved a considerable number of potatoes in microwaves, and never once poked a hole. Never had one explode, either.

[@Dlopergizer]

Lusaceheart, I literally laughed out loud reading your post!

[@thatboyken]

I don't really understand the phsyics thing and I am probably too old to learn it but I love listening to your videos , keep it up because I am quite sure that you are giving some of the younger generation a reason to get involved .

[@michaelbauers8800]

Never to old to learn. I have been teaching my mom, who is over 80, how to play kenken. How to factor numbers. How to eliminate possibilities. She had the benefit of knowing Sudoku, but she's learning new ideas

[@AC-bi3bz]

A very informative, entertaining video … your bubbly, enthusiastic presentation make it fun to watch! I am continually humbled by what some very bright people have discovered / researched / deducted in the past … before computers, internet & co. … standing on the shoulders of giants …

[@Magickaplays]

The Focus seems to like the PHD Certificate

[@theCodyReeder]

It’s a lot easier for the camera to pick out something with high contrast (text) to auto focus on. I use a page of text when focusing my high speed camera.

[@PieterPatrick]

@@theCodyReeder CODY!!! ...Great seeing you here. :-)

[@PieterPatrick]

I first thought it was in low resolution. :-) But than I saw the certificate.

[@sundhaug92]

She's slightly too far forward, so something behind her is appearing focused

[@tucatnev123]

Wow, Cody's is actually suggesting to have Kiss Band like make up for Becky and zebra onesie? Wow, just wow. So... ...let's see that, only for the observation of the autofocus , OC

[@jackjones3657]

This makes you realize how successive generations stand on the ground laid by those who have gone before.

[@Hal2718]

"If I have seen further it is by standing on ye sholders of Giants" - Isaac Newton

[@megaxenu753]

That's not necessarily true. The astrophysical methods of measuring light are very different to the electromagnetic ones. If you ask me zipping a laser around in a lab is typical lazy microwave meal 20th and 21st century cop outs.

[@megaxenu753]

@nuff sed the fact is they are measuring the speed of a laser and not the speed of photons emitted by the sun or any other star for that matter.

[@megaxenu753]

​@nuff sed you don't know that. you can't know that. one day people will look back at your belief and deem it as crazy as light being generated by your eyes.

[@megaxenu753]

@nuff sed as far as i understand relativity doesn't work well with quantum theory. there are lots of problems around subatomic particles that can't be explain because people can't accept that some rules we have created for ourselves might not apply. in the next few decades people will have to let go of those kinds of assumptions.

[@jimsandoval7633]

So much history in this video, I had to seat, watch and enjoy every Usec of it. It is amazing how resourceful those guys from way back them were. Thank your for putting all this information together for us. Your video makes astrophysics so amazing and interesting. We just witness over 300 years of history all the way to TODAY!

[@AstroQuest1]

Thanks for explaining Romer's method in more detail. Your explanation is the first one I have seen that made sense to me. Cheers Kurt

[@jamesanderton8817]

13:11 Oooo Editing Becky is going to be mad.

[@Legen_Terry]

For a minute there I thought that I was in the matrix and just experienced some déjà vu.

[@wlan246]

@@Legen_Terry For a minute there I thought that I was in the matrix and just experienced some red déjà vu.

[@GREGGRCO]

Becky ! OMG, WE GET TO SEE HIS HAND WRITING ! AND WHEN TROUBLESHOOTING I HAVE TO TAKE NOTES LIKE THIS ! HIS NOTES LOOK LIKE THEY COULD HAVE BEEN WRITTEN TODAY !! THIS WAS SO COOL DR. SMETHURST ! THAT WAS REALLY STUNNING FOR ME. THANK YOU ! AND HIS SOLUTION ! PRETTY GOOD THINKING ! MATH IS TIMELESS. OR ALL ENCOMPASSING, ONE; OR BOTH.

[@JobBouwman]

It is so nice that Sophie Ellis-Bextor is now into Astronomy.

[@spyrilleedinlarge5319]

She had to. There was blood on the dance floor

[@I_Don_t_want_a_handle]

nah, can't be SEB as this lass can sing.

[@EtzEchad]

I love things like this. The history of science is often as interesting as the science itself.

[@tonyr.5111]

Thank you for the clear, concise explanation... Very ENLIGHTENING!!! 👍👏👏👍

[@davidmitchell9003]

I find it a little sad that guys hundreds of years ago were/are light years ahead of me in physics

[@wirenutt57]

Apparently so - a light year is a measure of distance, an incredibly huge distance, while you seem to be referring to units of time.

[@firstlast-fr1le]

@@wirenutt57 He is not wrong though, other than the accuracy of the statement. These guys were wicked smart. Way ahead of me or any of my friends / co workers. I try to have simple conversations with some folk and they can't even grasp the most basic concepts. I myself am not advance in mathematics by any means but i understand the basics - many folk even today just don't get it at all. With everything we know to be true most people are still science illiterate and all the info is there if ya just even bother to look.

[@KennethSorling]

Check out old Archimedes! He was the monster mind of the ancient Greek world-

[@whiteshadow1771]

ain't it the truth

[@christianheichel]

Those were the Einsteins and Coca-Cola's of the day we're just the off-brand dollar stores/John and Jane Doe's. lol.

[@philipmartin2622]

Back in the 1960s I remember using a new ruby red laser, a spinning mirror, a tuning fork and a meter stick to measure the speed of light. We used the tuning fork to match with the frequency of the motor spinning the mirror and we used the meter stick to measure how far the reflected light shifted as the mirror was brought up to the tuning fork frequency speed in cycles/second. Some simple math gave us the speed of light which was remarkably close to the accepted value at the time. We then took a six inch machinist's ruler and the meter stick to calculate the wavelength of the ruby red laser. The machinist's ruler acted as a diffraction grating and we measured the first, second and third order diffraction lines on the laboratory wall. Crude experiments that gave very accurate results. I'm sure every physics major over the years has done some version of these experiments.

[@billszentagotay8819]

This lady knows her stuff, and is very bright as a good teacher. Keep it up!!!

[@Ray_Sellner]

I have no idea how this ended up in my feed. I went from a physics lesson to melting marshmallows. I'm good.

[@dcterr1]

I recall measuring the speed of light with a laser and a rotating mirror in my physics lab in college. We obtained what I thought at the time was a very accurate measurement of 2.998 * 10^8 m/s. Pretty cool to know you can do as well with a microwave oven!

[@mechmania8450]

Very good I like to know how they struggled in the old days to come up with things we now take for granted, great explanation.

[@clayz1]

In my city, 25 miles per hour is the defined universal speed limit.

[@Ojisan642]

Pro tip - turn off autofocus. You’re not changing your distance relative to the camera during the video, so you don’t need autofocus.

[@h00b00]

It's deliberate. Soft focus is a simple trick to look more youthful.

[@oldkid8811]

excellent video Dr. Becky. one of your best IMO

[@PolioVitruvius]

Thanks! What I find most interesting about light is that it is invisible unless it enters your eye. A room could be filled with light as bright as the sun and you wouldn’t see any of it by looking through the room. The idea of light being invisible to the eye is fascinating.

[@hurri7720]

We can only see the visible part of light, sort of obvious, but there is also for us an invisible part of light.

[@PolioVitruvius]

@@hurri7720 How can you SEE ‘visible spectrum light’ that passes from point A to point B in front of your eyes? You can’t. That is the irony. You only see the light that reflects off something and then enters your eye.

[@hurri7720]

@@PolioVitruvius , tried to look at the sun, seen nothing.

[@PolioVitruvius]

@@hurri7720 Well you will only see the light that goes from the sun to your eyes. You cannot see all the other light that goes past you until it bounces off something and then enters you eyes.

[@hurri7720]

@@PolioVitruvius , yes, that is true, like when you look at the moon at night.

[@Alex-Lay]

The idea of the meter being a yard stick is surprisingly amusing.

[@hannanpakthini7221]

Why???

[@TheMarrethiel]

@@hannanpakthini7221 a yard is three feet? I am guessing it is the play on words

[@lesliefranklin1870]

@@TheMarrethiel In that case, the phrase "being a yard stick" refers to a generic measuring device. In other words, it is being used as a metaphor. However, a meter and a yard have so much in common that the phrase can also literally be used as a very rough estimate. The humor derives from the double wordplay.

[@macgyveratlarge2133]

Three inches of difference is noticeable enough to affect the speed greatly. Yardsticks were an arbitrary measurement by the will of a king, meters are based on the measument of the planet itself. Anyone care to wager on the reliability of a king compared to a planet?

[@HAL-nt6vy]

@@macgyveratlarge2133 Which king are you sloppily nattering about? A yard is three feet. Our foot is identical to the foot used at the beginning of western civilization in Ancient Greece. The length of the foot was established for the first Olympic games in 776 B.C.

[@nimbusnation9584]

I really really love your sense of humor... And your video they are so straight forward

[@TomLeg]

Brighter light, higher number f-stop, wider depth of field ... Dr Becky in focus wherever she sits. It's a concept to explore.

[@geoffgwyther7269]

Not ``wider``. .... ``deeper.

[@TomLeg]

@@geoffgwyther7269 is right, strictly speaking. Since the in-focus plane is a constant from the camera, I imagined myself with the camera on one side and the subject on the other, so the D.O.F. would be a width.

[@johnneuman9470]

YAAAAAAAAAAAAAAAAAY! It’s science time with my favorite astrophysicist Dr. B!!!!!!!! 😀❤️

[@DrBecky]

👋👋👋👋

[@rhoddryice5412]

Congratulations to beeing first at 9/10 LS

[@erictaylor5462]

Actually, it's Doctor S. But if I ever meet her, it might be Dr. T.

[@johnneuman9470]

Rhoddry Ice you could see the red and blue shifts of my fingers upon the keyboard 😬

[@robertlawrence9000]

@@erictaylor5462 competition? 😂

[@meow75714]

Great video Becky! Thanks for sharing the knowledge.

[@tubastud06]

25 minutes of me not being productive at work. Thank you for the break :D

[@calyodelphi124]

Your next door neighbor was playing "L'amour est un oiseau rebelle", the infamous "Habanera" song from Carmen! :D

[@reymundoguiquing6054]

You are very brilliant Dr. Becky

[@leplum2001]

You could have said, "As an experiment I am shooting this video in soft focus mode." :-)

[@AusRED5]

i thought maybe I had one too many to drink for a sec! lol

[@stanervin6108]

I think that it is very sensuous.

[@leplum2001]

@@stanervin6108 **raises an eyebrow**

[@FabianoCores]

Hey... use lots of quality light, and put a higher F number (smaller apperture)... you'll have less problems with focus! The video is awesome by the way!

[@mardanananak]

Maybe somebody heard that f5. 6 was a sweet spot.

[@stevegladden1364]

Microwaves (ovens) use a free running oscillator (magnetron) which varies in frequency quite a bit. Also the measuring stick that you grab out of the tool box to measure the ... Yes you get the idea and we certainly enjoyed the humor in this part of the video! Also enjoyed the smores very much so.

[@stevegladden1364]

I think I'm craving a toroidal snack.

[@Morbacounet]

Editing Becky : what have you done, filming Becky ? Everything is blurry ! Filming Becky : well, you forgot to remove one of the two "red flags" at 13:10.

[@mahmoudabuzamel7038]

Interesting Dr. Rebecca! That raises a one good question: "What are really the units of measurements of the universe instead of meters, seconds, etc.?"

[@michaeltabony3911]

IMHO, the units of measurements of the universe are probably some multiple of Planck's units. His units seem to have relevance to the "real" world rather than just being a human yardstick construction. Some, however, such as length and time are so tiny they would be rather useless in our day-to-day world. Their use would therefore open the eyes of the public to some of our challenges to understanding the universe.

[@Ukraine-is-Corrupt]

I applaud you for stating clearly & upfront that the Speed of Light is nowadays, a definition & not a measurement any more; most other people on KZbin seem to miss that point - & it's a very important point

[@fanq_]

that moment when using the word YARDstick to explain how arbitrary a METER was

[@novalightXY]

Compared to the imperial system, metric system is super nice. I'd also disagree on arbitrary, that would be, if 1m was measured as the length of my cats's stride in winter at 12 pm, or something to that effect :P

[@JoeDeglman]

Right we define the Second and the Meter off of the speed of light so as to prop up Einstein and he will not be wrong, because when the speed of light does change we just change the meter and second along with it. As she discussed with permittivity and permeability, the flux density changes with each energy system, such as the Earth compared to other planets, they have a different magnetic field density, and therefore different speed of light. So the speed of light cannot be a universal constant, so we just change the meter and second to make the speed of light a constant to prop up Einstein, yet again. I am glad to see she is finally, although inadvertently, noticing that Einstein cannot be right, yet it seems she has not pieced it all together.

[@sphaera2520]

Joe Deglman I’m a little confused here, what exactly do you mean when you suggest c changes based on the energy density of the system? I know this isn’t what you mean but it seems like you’re saying light move slower in water than it does air therefore... We’ve always known this, which is why the definition presumes is light in a “perfect” vacuum. In this context, the energy density should be at its base value. The fact that this property changes when you’re near earth vs near jupiter, would be the equivalent of that quantity being different in air vs water. Or maybe I’m way out of my depth but do elucidate.

[@JoeDeglman]

@@sphaera2520 I am telling you that mainstream is lying about the ether medium being nonexistent. The magnetic field that flows around all moving charges that is in fact the ether medium, it permeates the universe, and is stored inside a vortex ring, or z-pinch around an atom, a planet, a galaxy and anything else with a plane of inertia that has charged particles rotating around it in orbit., like spirals and ecliptic planes, and around an inductor coil or any other energy system. That increased density of stored medium density is responsible for the slow down of light in all matter, such as a prism. The so called flux density is in fact particles of that medium being drawn into an energy storage system or plasmoid, that is responsible for the speed of light. The redshift that mainstream attributes to the doppler shift has been shown not to work.. There are several models for doppler redshift, and universe expansion, and none of them agree. What does agree with redshift is flux density or the amount of energy stored in an energy system. It is in fact the only thing in common with back EMF, I.E. what slows electrons down, the magnetic flux density, in an inductor coil for example. So the same reason that an inductor coil or z-pinch can crush a pop can, I.E. flux density, also slows light down. Water and glass slow down light because of that increased flux density within the space between the atom. In a vacuum, it is only possible to remove that matter from it, but the magnetic field cannot be removed from a vacuum, it flow right through the walls of the vacuum, but that flux will be less dense than in water and glass, but will be of a different density in a vacuum on another planet. It is that change in density of that medium that permeates the glass and water vs a vacuum, that is responsible for the decreased speed of propagation of light in the glass and water.. So the flux density or stored particle density here on earth will be different here than in the vicinity of another planet, due to the induced magnetic field density there. And the redshift of light from there will be different for that reason and has very little to do with doppler. That is why the doppler models of redshift do not work, because they attribute that redshift solely to doppler, and that is also why we get an erroneous model of the Universe expansion.

[@carly09et]

@@sphaera2520 this is the metrology problem - circular definition - it locks the dogma of relatively. Parallax is the only freedom in such systems :(.

[@Smonserratm]

Why didn't we do ourselves a favor by defining it as 300000 km/s and have a slightly shorter metre?

[@Scoobydcs]

Because the whole metric system was based around water. 1m cubed is 1 metric ton of water

[@condorboss3339]

It would have been great if the SI measurements had been created from that in the beginning, but now so many other measurements derive from the original standard that we would have to reconstruct our entire system. (It isn't possible to 'fudge in' the old derivations because the tolerances were already finer than the ratio of 299,792,458/300,000,000.)

[@theCodyReeder]

Sergi Monserrat Mascaró because then property boundaries would have weird values. A square kilometer would now be slightly less. That would upset a lot of people.

[@denmaroca2584]

Because it would cost an absolute fortune and cause years of chaos as we recalibrated everything to fit the new meter, especially when it came to precision engineering.

[@tncorgi92]

@Gordon Bird and don't forget Smoots.

[@sergiowybo3662]

Lovely, fantastic, well explained, deeply grateful !

[@ahooper99]

Citations on a science video, YAY! and to papers from the 17th century!

[@DavidMaurand]

on galactic scales, the speed of light is ponderously slow.

[@tomklein3718]

The videos are fantastic. Keep them coming. I've often said if I win the lottery, I would return to college and get a degree in Physics. It is fascinating but the chance of making a living at it seems pretty small. I chose software. Back in 1980 there were few women in my Physics 101 classes. Glad to see you've made it your passion. Doubt you were alive in 1980, LOL. If you make it to the USA, Washington University in St. Louis is great place to lecture. I'll be the old guy slipping into the back of the hall to listen. It is rare that someone of your intellect can take the difficult concepts easy to understand. Thanks again.

[@Skukkix23]

Wow cant believe that a very smart philosopher back in the day really thought light is coming from the eyes but couldnt figure out why we cant see in the dark or why fires illluminate things

[@colinp2238]

He never attended night classes.

[@Drummerx04]

Frankly this is just seems to be what philosophers do. They hyper obsess over simple concepts that even 12 year old children are worldly enough to understand, then they regurgitate those ideas with somewhat elegant language and the world laps it up like they haven't had the same thought before. When it comes to discovering valid scientific concepts, their track record is abysmal.

[@El-clartitan]

@@Drummerx04 That's a very ignorant description of philosophy. Also, 'discovering valid scientific concepts' is not something philosophers seek to do.

[@Drummerx04]

@@El-clartitan It's an opinion I have formed after discussing topics with philosophy enthusiasts/students over many years. A significant majority act as though their ability to think is somehow superior, as a college educated elite would stereotypically view a cashier at McDonald's. Any conclusion they reach is either plainly deduced with logical reasoning, is purely subjective, or has no bearing or effect on reality. I mentioned 'discovering valid scientific concepts' as a stand in for 'coming up with something useful'.

[@fanq_]

@Skukkix23 I believe the full story is "our eyes emit things, and if the object is lit (i.e. the object is bathed in what we understand as "light") then the rays will return to our eyes and we will see them" or something along those lines, it's been a while since I've heard that told in full

[@cyphern]

18:25 "a meter [is] something [we] have invented as sort of like a yard stick". Where "sort of like a" means 1.0936 yardsticks :)

[@zidaryn]

Lol

[@DrHealth4Life]

The music you were hearing in the background is from the Opera Carmen. You did a wonderful job singing and it it was highly recognizable.

[@anthonydavidson6139]

How do we know the law of physics are the same in every part of our universe as it is for us locally?

[@kilroy1964]

We don't. But it fits in well with observations, and our working theories have utility. That's the essence of science, not Truth.

[@paulebberson4884]

They are not - Scientists are unable to say what the laws of physics are inside a black hole. Also looking back in time the Big bang theory breaks many current laws of Physics.

[@mitseraffej5812]

This is the argument Christian Creationists use to explain how celestial objects can be measured as being millions or billions of light years away yet the universe is only 6 thousand years old. That is the speed of light was a lot greater in the past.

[@douglasstrother6584]

"Dammit, Jim! I'm an Astrophysicist, not a Videographer!"

[@psyclobe]

You are so full of life and curiosity, its contagious

[@rosman2635]

Hard to believe light from a candle travels at same speed of light from the sun.

[@rosman2635]

@William White Thanks William but a candle may just need air to burn as air is roughly 80/20 so not much oxygen for light to travel through more nitrogen if anything so we are told. Ah so the speed of light varies. Is a photon invisible?

[@rosman2635]

@William White I am confused, I read a paper published by Fleming discussing the corpuscular theory of light and he states that depending on the surface on which the light falls the candle will certainly emit photoelectrons in vacuo up to ten feet. Then there is a the situation of light from a star receding from us travelling at same speed as a star approaching us. Then how does a photon escape from the sun when it is only observed when it interacts with matter and finally sorry would light slow down as it approaches a mass and its gravitation. 1 more light slows through a medium but then resumes its speed again I know there are complex theories but really is light that complex - cheers

[@manpreet9766]

William White actually eyes can detect a single photon under certain conditions. The faintest stars which we can see have only few photons striking our receptors.

[@leeadickes7235]

Nothing emits light. It's all perturbations of the ether.

[@rosman2635]

@@manpreet9766 VLS is touted as the alternative to big bang which has too many problems to fix.

[@scottmuck]

AH, I get it, a meter is defined as a sort of yard stick. So it’s the yard that is fundamental. I knew it.

[@loganpe427]

Dr Becky you must be the most humble really smart person I've ever seen & heard. Very cool! 😁👋🏻.

[@Lokithefeline]

for so many reasons, this lady is the most beautiful person in the world.

[@porkpie2884]

11ms to travel a mile( should be 5.4us )

[@Shadow81989]

apart from ms/us I think it was one mile to the mirror, so light has to travel back and forth -> 2 miles, right?

[@TheEulerID]

@@Shadow81989 yes, in which case it was 11 micro-seconds (so wrong by three orders of magnitude).

[@tanman999]

Technically should be 8 micro seconds since the speed of light is slower through air (124,000 miles/second).

[@TheEulerID]

@@tanman999 That's wrong on two counts. The speed of light in air is about 99.97% of that in vacuum as the refractive index is only 1.003. So the speed of light in air is only about 60 miles per second slower in air than in a vacuum. The figure you've quoted is more typical of the speed of light in glass with refractive indexes of the order of 1.5. The speed you quote is typical of what you might expect in an optical fibre link (and I've had a lot of experience of those). However, the physicist in me squirms using miles in a scientific context. Secondly, if the speed of light was slower then it could not possibly decrease the delay observed. Rather than going from 11 to 8 it would go up to 16.5 micro-seconds (as it's a 2 mile round-trip).

[@davevann9795]

Becky did not mention a mirror, and in accounts of Galileo's experiment, I found no mention of a mirror. According to the Las Cumbres Observatory website, if Galileo and his assistant were one mile apart, and even including the slower speed of light in sea level atmosphere, the time difference would be 0.0000054sec or 5.4us. Meanwhile, Galileo was trying to use his own pulse to measure the difference in light travel time.

[@frunsebischkek1050]

Vielen Dank. Sehr unterhaltsam und interessant. Habe den Kanal auch aboniert, weil Dein Englisch so perfekt und verständlich ist.

[@profcrabbe]

How did you skip Michelson? He won the Nobel prize for this

[@TomLeg]

So the microwave experiment uses a ruler to determine the length of a ruler

[@mutototokatanga]

Thank you Dr Becky, enlightenment much appreciated going beyond gravitational forces!

[@333rpd]

Ptolemy , it's a silent "P", like in swimming. :)

[@HAL-nt6vy]

Finally, a comment worth my time! Thanks, KZbin.

[@williamanderson5437]

Ptolomy - The Pee is 'silent' - like in swimming.............

[@gazzyal9371]

I really enjoy watching your video's.. and your easy on the eyes too keep up the good work Dr.

[@deluxeassortment]

Why do we still call it the speed of light? Shouldn't we be calling it the speed of causality?

[@deluxeassortment]

@William White There is no practical advantage, it's an advantage of understanding. The speed of light is also the speed of gluons and the speed of gravity, which have nothing to do with light. The speed of causality goes deeper than just light, it's an inherent maximum speed for all massless particles and purturbations in any field. It is _currently accepted_ that the speed of light and the speed of causality are the same, but if you'll consider an unrelated an non-analogous example, the discrepancy discovered between the speed of sound and the "sound barrier". Not that I forsee anyone discovering such a discrepancy between light and causality.

[@deluxeassortment]

@William White "changes the value of the gravitational field at a distance from that point after a finite time" Distance/time=velocity, does it not? I said "perturbation in any fields". There are some that would disagree with you about gravity not being a thing, although there is not yet evidence of a graviton as there is a photon. But the effect is the same, a finite velocity for the propagation of gravitational effects. Perhaps I should have said "speed of gravitational waves"? journals.aps.org/prl/abstract/10.1103/PhysRevLett.119.161102

[@deluxeassortment]

@William White You'll have to forgive me, I'm only a layman. I am trying to understand, which is why I am "hung up on precise definitions". If I'm not mistaken, the Lorentz transformation is only applicable to comparing different reference frames? The simple velocity formula still applies, just with different values in different reference frames. Gravitational waves still arrive at the observer at the same moment as the light from the source, do they not? If a gravitational wave propogates at c, and light propagates at c, why is this an issue? Please help me understand, rather than being shocked at my ignorance :)

[@deluxeassortment]

@William White Most of the scientists I have spoken with have just called it _c._ I only really hear the term "speed of light" in science communications anyway. So, all of that said, it's the science communications I was referring to, such as this video. I knew when I made the statement it would be a radical change, so I guess I didn't think it all the way through. You're right, it would elicit odd looks from colleagues.

[@AZOffRoadster]

I would prefer it, since we know we can slow down photons and is thus not a constant. Show me a 'perfect vacuum'.

[@xDubstepify]

Christian Huygens, one of the least known most brilliant men on the planet

[@michaeljohnangel6359]

Indeed he is. Also, his dad was Rembrandt's first patron and helper (business-wise).

[@blessedheavyelements8544]

Thank you Doctor for the video/information and hard work! Best Regards and Best Wishes!

[@Lloyd33]

@1:20 Actually, our eyes do produce light. Our entire body does. Ever used a FLIR camera? Humans glow many lovely shades of infrared. =P

[@AbdullahKhan-sl3mg]

*Our eyes do not produce visible light 😉

[@Lloyd33]

@@AbdullahKhan-sl3mg Well, no.. not light within the human visual spectrum range of around 380 nanometers to 740 nanometers, but I guarantee you frogs and snakes can see our eyes giving off light somewhere in the 700 nanometer to 1 millimeter wavelength range.

[@bitrage.]

@@Lloyd33 tru but our sonar cant TOUCH whale or dolphin

[@captainboggles]

@@AbdullahKhan-sl3mg what is visible light?

[@tbrazier1]

N)

[@HotFootPhoto]

Either the camera is out of focus or my eyes went crossed trying to understand what she was saying.

[@JareddarArt]

That's ok, my understanding of the basics of light completely differ from this stunning woman with more knowledge than I have. The odd thing being in order for something to be defined it MUST be measured. Hey ho, I guess us mere mortals must merely ask stupid questions and hope.

[@Buddythunder1]

What a delightful history! One of your best.