Why is the speed of light 299,792,458 m/s? (and not 300,000 km/s)
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Let's explore how the speed of light in vacuum is connected to the size of the earth!
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Why is it round up to 3/ms. I would like everyone to know photons can not be measured from the side. Just observe a beam of light. Simple. The very worst part of this video is that the Light from space was thrust forward by unknown force. Splitting of an atom. Or burst of Gas. Either way the universe has frequency and other photons. The universe also has Nebulae. Gas clouds Photons pass through. Light speed is false. I will say it until I die. To calculate the speed of light you need a true particle. Alone in space there is more than one single particle. In space the particle could bounce off of reflective surfaces. Such as the moon. That also questions a laser hitting a target on the moon. If it misses the target it would still bounce back after the surface of the moon absorbed the velocity a bit to reduce the bounce back. There are so many values that can disprove light speed. Fix your thinking. Make it correct. Don't make it valuable to profits.
Also why is your mic magically colour changing?
There is a book called Lightspeed by John Spence (ASU professor who has since passed) that recounts the history of how we came to measure the speed of light. It's a quick and interesting read that I highly recommend.
1 metric angular minute would be 1 kilometer. Coincidentally, 1 angular minute (1/(90*60)) is 1 nautical mile.
@@Alexagrigorieff Except there are not 60 secs in a minute or 60 minutes in an hour because there are not 24 hours in a day. I have measured it to 23.72 hours in a day. And three days of the year do not see a full day night cycle. Which is why we add an extra day to the calendar every four years.
In case you are wondering, the second is define using a caesium atom
And the second is also related to the earth’s rotation, which is decreasing. 😅
Both are sources for the measurement of the second, the caesium resonance being a finer standard of precision this week - until something more precise is discovered and rendered reliable. Indeed, I recall proposals to utilize pulsars for time standards, despite their rates also slowing - ever so slowly.
But, it does outline one of the arbitrary units selected by humanity - the second. As opposed to coming up with a time standard based upon universal constants, which will never vary as long as we're inside of this universe. At least, they'd better not vary, variable constants would put physics into a cocked hat and take chemistry with it.
in case anyone is wondering.. i think a kilo is still a shiny ball in a safe in bern or something
The US would still use 60 seconds/minutes. Just to piss off the rest of the world
@@gregoryallen0001 the kilogram is defined by Planck's constant since 2019. The old kilogram standard is in Sèvres, near Paris (France, not Texas ;) )
Mahesh is a prime example of a person who does not take knowledge for granted.
Learning the value of c is knowledge. But mahesh really wants to know "why" it is. Thanks to these kind of people we take knowledge to the next level.
And that's exactly what is wrong in our schools. I always tried to rediscover what we learnt while the rest of the class just learned by heart.
A friend showed me that while we learnt for the A-level and I did not understand a particular math problem all I had to do was replicating the answer with slightly different numbers. And it worked! To this date I have no idea what exactly I calculated.
Also I did do slightly better in math it deeply disappointed me that you can get good grades without knowing the context😪
Wh-that’s my credit card number!
Then expiry date and CVV of your card 😂
😂😂
Tell us the four digits in the back of the card. Just wanna know
@@sgiri2012 Yes it is important for science! :D
@@Jussimasa-bs9mc 😂 I think so
Yesterday I was talking with Feynman. He said that Mahesh is not interested in Heisenberg Uncertainty Principle, I said to him that no, he loves quantum physics. But he is not ready to believe it. I hope you will make video about explaining Heisenberg Uncertainty Principle and its relationship with enstiens relatively or only explaining it. [Oh, you wonder that how I talked to Feynman? That's because I stole your secret - Magic Mushrooms 🤫🙃]
Mom bro is again talking to himself 😂.. but ya he should definitely make a video on The Uncertainty Principle
Hey there! It's me, Feynman. I remember our chat, and I'm still convinced you're dodging the Uncertainty Principle like a quantum ninja! Even Einstein agrees with me. Prove us wrong, Mahesh! Drop some quantum knowledge on us. Until then, I'm in quantum superposition, waiting for you to embrace the uncertainty!
Cheers,
Feynman (and a very amused Einstein)
@@well-thy Yeah, even I am in superposition. I am happy and thankful for his great knowledgeable videos but I am also a bit sad because his quantum mechanics videos are getting too late. Quantum Physics was a bit confusing for me. I always got confused on basic quantum assumptions and theories like "Electron spin". I always wondered how an electron can spin, untill I found his video mentioning about it. His video on Quantum Mechanics (video on electron spin) made me to subscribe and follow his channel. I Hope he post that video soon🤞.
😂😂😂 you stole Mahesh's secret shrooms stash?
I use an ouija board…🤷🏾♂️
But you know what would not be changed by our arbitrary units decisions? The fine-structure constant!
That's fine
A bunch of thieves. The inventor of interstellar Propulsion Process and spacecraft Photon 137 alpha , commonly known as the Aurora Borealis Launch Vehicle.
All constants without a unit are independent of our choice of units. The same goes for the fine structure constant.
But one would still be able to change it's value if one were to go to different number system, e.g. if we were in octal number system we'll be writing the number differently.
@@VARUNRAJS-IMS We'd be writing the number differently but it does not change its value.
The definition of the second also impacts this value.
yes, exactly. I was going to say the same thing, but thought someone else must have made that comment already
True. But the definition of meter was directly co-related with the planet's size. The definition of the second directly with the planets rotation rate.
So maybe a more wholesome video could have been how the planets size and it's rotation rate controlled the value of speed of light! :)
@@Mahesh_Shenoy it's fortunate that the planetary size is unalterable and perpetually static. Perish the thought if the planet were shrinking!
Oh, crapmuffins! Oh well, go with a fraction that's approximately correct enough to fudge in, use SI for everything else, pretend it still isn't an arbitrary unit of measure...
Largely because, it's a pain in the ass to keep changing standards of measurements and when the metric system was invented, we had absolutely no clue what many constants were, such as oh, ℏ or G and heaven help us, we're talking about C, just to muddle even Planck units that are constant based, rendering constants variable until we finally make up our minds.
But then, I'd really be growing to hate life if I had to buy lunch meat in Planck mass units...
The duration of a second is not just correlated to the length of a day, but also the heart beat frequency of humans
The length of a meter is then dependant of the definition of a second.
A meter is defined as 1/299,792,458 of the distance travelled by light in a second, yet a second is not defined as the time required by light to travel 299,792,458 meters.
A second is defined as the time required for 9192631770 cycles of radiation produced by caesium 133 atom under certain conditions. Yet a meter is not defined as the distance travelled by light during 30.6633187884 cycles of caesium 133 atom
At the end of the day, both meters and seconds are man-made units for the purpose of putting numbers to lengths. Lengths that are closely related to our situation ==> the size of Earth and it's rotation speed.
Had we lived on Mars, a meter would be shorter in length and a second would be slightly longer in time. Our measuring units would be different but the universe would function the same way.
I sometime wonder, if we changed the scales of our measuring tools (such as redefining values of space, time, mass, energy...) if we could better visualize relativity between cause and effects on which we based our laws of physics.
that's why they say that physics is just a Model to understand the universe and not just "the way things are"
.......
That's why the speed of light has this value in this particular units. Now, why is the speed of light what is is, regardless of the units. Well, it had to be some value, sure. But the speed of light was PREDICTED theoretically, independently of any measurement of the speed of light. The Maxwell equations for electromagnetism has a solution in the vacuum, that is, they give the evolution of the electric and magnetic field with time in a case where there is no charge or magnetic dipole around. That's an electromagnetic wave. The speed of that electromagnetic wave comes that equation, in function of 2 2 other universal constant, seemingly unrelated to light: ϵo and μo, (the permeability and permittivity of vacuum), who describes how good of an insulator and how much magnetic resistance the vacuum has. These values were measured with physical experiments like measuring electric fields around a charged object and magnetic fields around a wire with a current. Seemingly nothing to do with the speed of light. In fact, the fact that the theoretical speed of the electromagnetic wave happened to be exactly what we had already measured to be the speed of light was a strong hint that the light is an electromagnetic wave, something that was not known back then.
That's more the question I was hoping to be answered! But still a fascinating video. Thanks for the info!
@@tillyjamesYeah. I actually expected the video to be about this.
But as you said those two constants were measured sooo :D
@@blackhogarth4049 ... Of course. As I said, the speed of light had to be something. What I found very interesting is that the theoretical prediction of the speed of an electromagnetic wave in the vacuum, in function of these 2 constants that involved no measurement of the speed of light, matched perfectly with the measured value of the speed of light, that nobody knew was an electromagnetic wave. It must have been an amazing "aha!" moment.
But, the speed of light expressed in our Earthly measuring units doesn't change according or due to units used, right?
I'm somewhat frustrated by this video because it talks only about measuring units, instead of the speed itself.
I thought the author would say that here on Earth, the speed is different from the speed in the Universe. That is so far according to our knowledge false, but still, intriguing! If the gravitation forces differ from one body or system to another, I expect that time will differ as well and surprise us one day! And if time runs faster in other parts of the Universe (time is such a fickly thing anyway!), will the light flow through such regions slower or faster?
I don't believe anyone can explain this satisfactorily to me.
If the speed of light ended up being exactly 300,000,000 m/s for the original meter, it would be exhibit A for so many conspiracy theories.
Just like in lottery, the combination 1-2-3-4-5-6 has the exact same chances as any other 6 digits combination of being drawn. But if it happened people would lose their mind.
As a child, I thought it rather curious that the earth’s circumference was conveniently a round 40,000 km.
but now you know better, the circumference is exactly a 1000 marathons
Love the story telling
I request you to make a video on
" HOW LONG IS 1 SECOND"
It would be a great Idea
do consider it
I think that its approximately 1 second long
photon clock example
I second that.
@@shardulkamble5780I just did the math, and your answer seems to be very close. How did you know that?
Great video. The speed of light is also dependent on our definition of the SECOND. You touched on this in the video, that the French considered changing the duration of the measurment of 1 SECOND. The original SECOND, which is what we use today, is based in Babylonian times, when they used a base-60 numbering system rather than our base-10. They subdivided 1 solar-day into 24 hours made up of 60minutes/hour and 60seconds/minute. So if the Earth rotates around the Earth slower or faster, or the revolution of the Earth around the Sun is faster/slower (see difference between solar-day and sidereal-day) the SECOND would be a different duration and our numerical definition of the speed of light would be different. Continuning with this idea, if we used base-60, or base-20, or base-X, rather than a base-10 number system, our numerical value of the speed of light would change. I like to think of the speed of light as 1 planck length/planck time (which is a bit circular in logic, but that's kind of the point of the constant c)
The Babylonians didn't use seconds for measuring time. *Nobody* used seconds for time until after the invention of mechanical clocks in the 1500's. And even in the 1600's people only used half or third minute divisions of time. The idea of dividing the (mean solar) hour into "minutes", "seconds", "thirds", and "fourths" was created by Abu Rayhan Muhammad ibn Ahmad al-Biruni in around 1000CE (with regards to the lunar cycle).
It was Gauss in the 1800's who proposed using the "Second" as the basis for defining all the other units for measuring time.
Babylonians probably used first and second 60 divisions of an angle degree, which itself is 60 division of a quarter of circle
I'm about 10 seconds in and I hope to God everybody realized that you're talking about.It's based on our measurement system!
Love your explanation.
Always exciting to listen.
Thank you.
There are really two questions here. 1) how do we calculate the speed of light 2) what units are used in this calculation. The formula for speed of light in any medium is c=sqrt(1/permeability*permittivity). This is from the wave equation derived from maxwells equations. The value taken will be dependent on the units you use. mph,mps,kps,kph ..,. Of course we came up with the concept of electric and magnetic flux. So the speed is constant because we use flux instead of field.
when calculating location at sea, one minute of arc is one NAUTICAL MILE. but that's probably approximate. your videos are startlingly educational. i really thought i was too old to learn anything else! thank you.
Make sure it's minute arc of latitude, not longitude.
But if you just said shrew the old number and fixed it at 3*10^8 m/s the old meters would only be off by 1- 299792458/300000000 = 0.00069180666 or about 0.7 mm. I am sure some scientists would be mad at that but if we just clarify what meter were using for a few years while everyone adjusted then we could have such a nice number to represent length until science dies or whatever. And if we did it for the other units like the second, then all of the units and their definitions could be so simple to remember a little kid could remember it. It may even make science just that much more easier for beginners. Personally I am on the team that if it would make 100 scientist mad for every one kid with dyslexia it helped, its worth it.
lol
We could just use "Natural Units" where the speed of light is defined to be exactly "1" ...which is exactly what Physicists do.
Unfortunately that will never happen because everything that is produced using a meter would now need to account for that change and that would generate a huge chaos in manufacturing and even if we decide to do that there are like thousands of different constants in physics that still wouldn't be round and would need to be recalculated afterwards
I know this is an older post, but just wanted to thank you for doing the math for the exact answer I was looking for.
Before watching the video; surely the reason why the speed of light is 299,792,458 m/s (and not 300,000 km/s) is down to the choice of units humans have made for distance & time. Select them carefully and you can make it any number you desire. 1 lightsecond per second if you like.
At this point it is a necessity that you do a Q&A episode
Same reason it takes more digits than practical for me to memorize, to define the ratio between pounds and kilograms. They had to maintain consistency with the legacy definitions of the units, when defining the new standard.
Luckily we at least ended up with an inch of exactly 25.4 millimeters, and Fahrenheit degrees that are a not nice but workable 9/5 ratio to Celsius degrees (plus the offset of 32). It could have been worse.
Hey Mahesh, I just wanted to thank you for your dedication in teaching physics. I relied on most of your lectures in khan academy for class 12. You have explained abstract physics concepts so beautifully.I survived 11th and 12th because of you. Lots of love.♥️
As I understood from other sources, the meridian-based definition was set to be that particular number in order to be close to ever older definition of meter. It was the length of a simple pendulum with a semi-period of one second. That's why g ≈ π² m/s² by the way. But gravity varies across the Earth, so that definition had been unstable.
Thank you for explaining also the reason why the circumference of the earth is pretty close to 40000km (actually 40075.017 km at the equator, and 40007.863 km through the poles)
That's pretty cool I'm assuming the "minor" difference in thickness is due to the centrifugal force as the Earth spins which is kind of crazy to visualize
it's really ridiculous why they haven't rounded to 300K cause neither the pole-equator wasn't measure exactly at the time (using just primitive triangular method) nor the speed of light on that piece of iron :)
We could just use "Natural Units" where the speed of light is defined to be exactly "1" ...which is exactly what Physicists do.
Another very interesting question here would be: Where does the second come from?
It came from the 60th division of the minute, which is known to be used since the ancient times. That's why it's called "seconds", because is the second 60 divisions of the hour. When second was officially adopted as a IS unit, the define the second based on the period of revolution of Earth around its axis, A.K.A., the Earth's day. However, that's very imprecise, since the speed the Earth rotates around its axis varies due to tides, moon, sun and all these stuff. So they define the second as a certain division of the time Earth took to orbit around the sun at the year of 1900. Finally, to make the second a more "natural" unit, like they wanted to do with the IS units in the first place, they define the second based on the inverse of the frequency of a particular electron from cesium-133 takes to jump from one energy state to another. Trust me, this frequency is very wierdly constant, and that's why that's not only the current definition of the second but also the most precise we have came out with
😂no way you mean that for real: you can just calculate a second from any time period: year, month, hour, millisecond…
@@legat-i7b dont say that. That's actually a great question
It’s the time taken for a Caesium atom to complete 9,192,631,770 oscillations.
@@MarcusViniciusSilvaDaRosa how that
very well explained. thanks!
Never thought about the fact that 1m = 1 decimal arc second of latitude.
I always assumed they took the paris distance and just chose a power of 10 that had a useful length.
Millimetres (1/1000)m are useful for measuring small things.
Metres are useful for measuring things at an intermediate size.
Kilometres (1000m) are useful for measuring travel etc.
8:02 You're right, based on the uncertainty you provided (299,792,456.2 ± 1.1 m/s), rounding to 299,792,458 m/s wouldn't be the most appropriate way to represent the measurement.
Here's why they likely chose 299,792,458 m/s:
Uncertainty: The uncertainty in your example is 1.1 m/s. This means the true value could be anywhere between 299,792,455.1 m/s and 299,792,457.3 m/s. Rounding to 299,792,458 m/s would lose some information about the uncertainty.
Significant figures: Scientists use significant figures to indicate the certainty of a measurement. In your case, considering the uncertainty, the speed of light would likely be reported as 299,792,456 m/s (keeping only the first digit after the decimal point that falls within the uncertainty range).
Historical context: It's possible the actual measurement they were referencing had a different uncertainty value. Back in 1983, when the meter was redefined based on the speed of light, the uncertainty in the measurement was likely much smaller than 1.1 m/s. This could explain the specific value of 299,792,458 m/s being chosen for the definition.
Overall, if you're referring to a specific measurement with an uncertainty of 1.1 m/s, then reporting 299,792,458 m/s wouldn't be the most accurate way to represent the data. Reporting 299,792,456 m/s (or following proper significant figure guidelines) would be more appropriate
Maybe rounding it up is to ensure that, despite the uncertainty, nothing gets faster than c.
Great, now I need a Helium Neon laser and some Cesium-133 to brag about the fish I caught yesterday
if the meter was bigger or smaller, the speed of light could have remained the same number. since the definition of a second could have been different
Lol
_You are truly awesome._
*My request for you:*
Geomagnetic solar storms on Earth in the context of religious teachings across the globe, please. There is an unmistakable link between "divine wisdom" and solar storms when you look at the dates of the events throughout history.
Nice video. I guess you intend to follow up with another video about the derivation of the speed of light in a vacuum based on how James Clerk Maxwell did it. It is worth it.
The second could've been different if we had that 10hr time system as well.
The second would've been 13.6% shorter.
This would've resulted in light being measured as travelling 259,020,689.9m/s instead of 299,792,456.2m/s.
The meter would've ended up being roughly the same physical length since it's based on the size of the Earth, but we would have different digits for the speed of light.
For why the meter was originally set to be 1/10'000'000 of the distance from the equator to the north pole, that was probably to have the meter be at least in the same order of magnitude as a commonly used existing unit of length. Same reason a liter was defined as a volume of liquid that fills a cubic decimeter rather than a cubic meter, because a liter is a reasonable liquid volume and 1m^3 is much less so.
You explain things so well and make it so interesting. Great video!
Don't know yet if you touch down on this as I am only a third through, but the Longitude/Latitude of the Giza Pyramids is the speed of light withing a 20 degree margin of error
The reason they rounded it up to 299792459 and not 299792457 was to reconcile the relationship of the inch to the centimeter to a wholesome 2.54!!! I figured it out! So that is why they did that number it’s closest to the original meter length that rounds not just the c definition but also metric to imperial units 😊 current inches per second is an integer. However , since 12 inches to a foot and 5,280 feet to a mile is not divisible into that integer the miles per second of c is not an integer but that’s ok neither is the km/s an integer either
Edit: ooops false alarm my calculator was rounding it sorry
I have a question, if we are moving fast shouldn't we arrive at a destination earlier but then why, if we move at the speed of light the time of our destination time moves faster than our personal time.
Imagine we are revolving around the earth at the speed of light so our personal time should move slower than the time on earth but the earth itself revolves around the sun which is also moving through space. Even if the space is contracted. What would happen to our position relative to the earth even if we are moving along with the earth and revolving at the speed of light simultaneously
I liked it, but it's not only the distance on which the speed of light depends but also the time because it's meters per second.
Calculation of one second is also an interesting bit of history. I think that will be another topic for you to discuss about here in this channel.
Nice video, Mahesh. There is another interesting tie in with the earth and the meter that I don’t think you’ve fully mentioned and that was the original definition of the meter is based on the circumference of the earth. Here’s the meta-AI response to my question about this. “Yes, you are correct! The French originally defined the meter in 1791 as one ten-millionth of the distance from the equator to the North Pole along a meridian passing through Paris. This was based on the work of French astronomers Jean-Baptiste Joseph Delambre and Pierre Méchain, who measured the length of a meridian arc between Dunkirk and Barcelona. The idea was to create a universal standard of measurement based on the Earth's dimensions. However, due to slight inaccuracies in their measurements, the meter was later redefined in 1889 as the distance between two marks on a platinum-iridium bar stored in Sevres, France, and again in 1960 as a multiple of the wavelength of a specific light emission. Today, the meter is defined as the distance traveled by light in a vacuum during a time interval of 1/299,792,458 of a second.”
One would think that the circumference of the earth is then exactly 40,000km, but turns out, with all the approximations that happened over the centuries, 75 extra kilometers just magically showed up.
The decision to define the distance from pole to equator as ten million meters was probably also partly for convenience, as this set the length of a meter to around the same length as a yard (which is about 0.914 meters) and roughly the same order of magnitude as a foot. Also it meant that the height of people would generally land somewhere between 1 and 2 meters and that you could reasonably approximate meters with taking steps (if somewhat longer than you normally would). So, it was all around a pretty convenient length to choose.
Alternatively, we could look at the speed of light's definition in terms of seconds. Humanity had a sort-of metric system prior to the french revolution, which was units/subunits be maximimally divisible by integers, into integers for easy math. This led to a lot of things divisible by 12, 24, 60, 360. The second was defined as the **second** subdivision (1/60) of an hour, which itself was defined as 1/24 of a rotation of the earth, relative to the sun (not a sidereal day). So if earth rotated just a bit faster, we'd have c==3E8 m/s exactly. Or if we based hours on sidereal day length, and it was just a little longer...
Ok at 1:20 , before seeing the rest of the video, I will take a guess.
It's the units
The size of the Earth defined the meter, and the length of a day defined the second, so any particular velocity in m/s is set (indirectly) by the size of Earth.
And yes the modern definition of the second is set by Cesium vibration, and the modern definition of the meter is set by _c_ , but those were applied long after the speed of light was measured.
EIDT: And after the video that was it. Really only covered meters and not seconds (except for the "metric time" bit), but still.
It's also a good entry point into the Planck units, as they were developed to be independent of any human origin.
Also also, as noted above, we've been redefining the SI units to get away from needing the master objects in Paris, and we've done all except the kilogram. 1 kg is still by definition the mass of the metal block in Paris.
Thanks. The kg has been redefined by fixing the Planck's constant in 2019
@@Mahesh_Shenoy Ooh, neat!
2019 so only recently. But now we should have a full system of measurement that doesn't rely on any particular physical object. So any hypothetical alien contact, or off-world colony or whatever can use standard measurements without needing to calibrate with an object.
I've always found it fascinating that there was a building in Paris that had a bunch of objects that were the definition of SI units.
Societies around the world came up with 7 days per week. People like using units they’re naturally comfortable with. It’s probably why no one minded when the definition of the “foot” had to change on every king change, because the actual length wouldn’t change too much. The fraction the French earth-measurers chose was highly likely to make the new meter in the same length class as the yard.
Learned something new. Thanks.
Without seeing the video This one is easy - it's because we are the ones who define the terms. A second is what it is because we say so. The same with all units of measure. Sure we now base them off unchanging universal constants but ultimately it's still just arbitrary.
.
So short answer - it's because we decided what a second and a meter was before measuring the speed of causality.
I have a followup question... If the speed of light determines the length of a meter (distance), then what determines the unit of time? My understanding is that it is based off vibrations of a Cesium atom. Well, a vibration is simply a motion back and forth, right? The frequency is determined by the distance back and forth, right? Well...If the distance is determined by the speed of light and the second is also determined by the speed of light, aren't we using the speed of light to define itself? Can you please help explain this?
No. We are not using the speed of light to define the second. We are using the amount of times an electron of the cesium 133 attom takes to jump from a certain energy state to another. When this electron jumps exactly 9,192,631, 770 times, that's how we define that exactly one second has passed. In no moment we need the speed of light to know this value
@@MarcusViniciusSilvaDaRosaElectron jumps? No, I don't think you have quite the right perception. It is vibrations. Electrons only jump once to a lower orbit and won't do that again unless additional energy is applied to the system. That is something different.
@@ronrothrock7116 jumping, vibration, the logic will lead to the exact sane conclusion. Vibrations are basically frequency of something. Frequency are measured in Hz or (1/s). They do not use meters on their definition. So we don't have to know the distance between the two energy states that the electron is vibrating, only the ammount of time it does it and set that as exactly equal to the frequency in Hz, which leads to the definition of the second
@@MarcusViniciusSilvaDaRosa You are making my point, but not seeing it. A frequency is recurrent "bouncing" back and forth (or a non-circular orbit). That is a distance. The string on a guitar vibrates back and forth over a distance and the frequency is how often, but it doesn't change the fact that there is a distance portion to this system we are describing. The electron is traveling a different distance in order to get a vibration frequency. If we assume the electron is jumping orbits like you said, the jump is the distance. Electrons have a total distance they travel over that number of vibrations in 1 second. If the distance were greater the frequency would be lower because it would take longer to travel. So distance is what determines the frequency.
@@ronrothrock7116 aaaahhh no? This distance you are talking on the guitar string only defines the amplitude of the vibration, not the frequency itself. Your analogy does not stand. Amplitude is measured in m, a distance. Frequency is 1/s. The same guitar string could make the same frequency with different amplitudes, so it does not depend on the distance it bounces. The same logic could apply to the electron, specially knowing that electron suddently jumps from state to another without passing from the middle points between these states
Am I the only one that wishes we adapted that full metric system? All those beautiful round numbers! Did rounding the speed of light change the meter enough to make the earth’s circumference 40,008km, because I don’t like that. Can we start over again?
to sum it up for people who still dont understand: scholars hated adapting to every measurement known before since they were not at all precise, so they created one arbitrarily, from scratch, to be the most precise one. thats it.
Actually GR requires a variable speed of light depending on the amount of gravity there is. The parameters to measure light’s speed change so light’s speed itself changes. It’s not complicated. The combined effect of time speeding up away from the center of a galaxy according to GR while the measure of distance increasing away from the center of the galaxy according to GR makes causation much faster. This is the reason for faster than expected motion of the outer spiral arms of galaxies and superluminal motion appearing to be faster than the speed of light while maintaining the speed of light because causation itself is faster. It’s also the reason we can see distant starlight in 6,000 years because light travels faster between galaxies where there is very little gravity to slow it down.
Fascinating to consider the relationship between meters (or cm) and milliliter and grams - at least I once learned that a cubic cm of water = 1 millileter, which is same as 1 gram of mass. Which leads down the rabbit hole of mass vs weight
actually, the first value of the meter was considered to be 1/40,000,000 of the Paris meridian. Now the Paris Meridian is a 'Meridian Line' passing through the 'Paris Observatory' in Paris, France - 2°20′14.02500″ East Longitude. It was a long-standing rival to the Greenwich Meridian as the world's 'prime meridian'. "Paris meridian arc" or "French meridian arc" (French: la Méridienne de France) is the name of the meridian arc measured along the Paris meridian. where it was calculated by the 'arc measurement method'.
When I was in elementary school in Paris, in the late 1950's, we recited "Le mètre est la dix-millionième partie du quart du méridien terrestre" (The meter is the ten millionth part of one quart of the Earth's meridian)...
@@ahoj7720 that's great
Time & Space, existed at the point, we can't measure Time if can't measure space and vice versa, so ultimately we have to lock one entity either Time or Space, that's why we have first marked 1s then measured space that light travels in 1s. If our time measurements is not accurate then speed of light would also be incorrect or different
Maybe it's that ...456 has a 2³ in its factorisation, ...457 had a 3², but ...458 only has primes to the power of 1. If that's important to physicists...
That was my thinking as well. I think they probably liked the specific mathematics of it
According to WolframAlpha, the prime factorization of 299792458 is
2 × 7 × 73 × 293339
For the speed of light, they should have used a number whose reciprocal has a relatively small number of nonzero digits.
The people who came up with the metric system were as loony as the people who defined an inch as the length of three barely corns.
Their first attempt: 1/10-millionth of a distance 1) no one had ever measured directly and 2) was inaccessible to anyone who lacked the resources complete a multi-year surveying effort.
Their second attempt: the length between two scratches on a bar they squirreled away and made inaccessible.
The "experts" who defined the meter were not practical people. A number that factors to 2 × 7 × 73 × 293339 was not a practical choice.
@@artsmith1347 Probably because someone was obsessed with the number 73 like Sheldon Cooper.
If we would shrink the meter by a bit less than 0.7 millimeters (current value), Mount Everest would grow by 8 cm, the circumference of the earth would be about 28 km longer, and the speed of light would be exactly 300,000,000 m/s. Higher mountains, more space and a sensible speed of light!
That's easy! Just move Paris 0.8 mm.
Or wait a bit, the earth is shrinking anyway.
And switch to something not arbitrary like city to equator, size of a shrinking planet or the length of a lobster's penis or something and go with standards based off of universal constants.
Who am I kidding, by the time we'd do that, we'd be in a different universe with variable constants or something.
Speed of light * 4 / (30 * polar circumference of earth) = .9991 Hz, for reference. This is how close we got to the clean number in reality.
Wow I knew about the old definition of the meter, but I had no idea how they actually defined it in the first place. The idea that it was to be based on the size of the earth is fascinating, and extremely ambitious.
The base metric units have just been redefined based on the physical constants.
Well, the speed of light in a vacuum is constant, irrespective of the units you choose to use. And the meter was originally based on the circumference of the Earth.
This video has confused a lot of people. A measurement unit can be anything, any length. It does not affect the speed of light. The speed of light can be any number depending of your measuring unit and its length.
"just saying" no such thing as objective vacum. love you way of phrasing and approach of thinking anyway
the meter is defined according to the size of earth AND the second is defined by the rotation of the earth around the sun. Both meters and seconds are defined by humanity.
Also:
the meter is older than 140 years; is more than 200 years old.
Was measured the distance between Burkerke and Barcelona (Catalonia), as an arc from the earth's circunference. And the meter is a metric piece of that arc corresponding to a 0,0000001 of a quarter of the earth's perimeter.
en.wikipedia.org/wiki/Arc_measurement_of_Delambre_and_M%C3%A9chain
A 1/10 of a meter is a decimeter, dm.
A cube with 1 dm sides is 1 litre.
The weight of 1 litre of water is 1 kg
Water freezes at 0 degrees Celsius and boils at 100 degrees Celsius.
Let's go metric inch by inch!
Now the question rise in my mind, how did the scientists measured the length to the pole. which instruments did they used for it?
And what about the speed of light. which technology is been used for its measurement?
Quickly becoming my fav physics YT personality
Before the video begins it’s because the number is less important than the unit. The speed of light in relation to the meter is what it is , but if the meter was bigger the. Umber would be smaller , and vice versa
They should have just remeasured the meter based on 300,000,000 meters per second. This would help in calculations, it looks better, and the difference in length between that meter and our current meter would be nearly impossible to detect.
The number changes because the length of a meter is based on the size of the earth. The speed of light does not change, the ruler being used does.
Another fun fact is that the French National Assembly actually had a numerical error when going through France and calculating Earth's circumference. Which is why Earth's circumference is 40,075km instead of 40,000km
I randomly recalled today that the definition of a metre is related to the speed of light and now I am watching this video(not because I thought of the definition of a metre but just because it keeps showing up in my feed)!
8:11 can't they redifine it to 3*10^8m/s instead? Because that is also very close to that, so it wouldn't make much diffrence
I think they did it because, we already had many calculations and other things done with the previous value of the meter. Using the value 3*10^8 will change the defined meter length with a larger value. So we had to redo all those calculations. So they used the value 299792458.
@@anurupsil8216 but the diffrence is very small. It is only 0.07% which is very tiny difference, so it shouldn't be a huge problem.
@@3141minecraft Another reason could be because the factorization of ...456 has a 2³, ...457 had a 3², but ...458 only has primes of powers of 1. If it mattered to the physicists... now they considered both of these reasons and considered the optimal value.
@@3141minecraft actually those 0.07% make a lot of difference, because the margin of error would be on the meter scale, and we are using it to define the meter itself! That would throw most equipements to dumpster because most of them measure on the scale of centimeters or less. If the meter would be severly affected, imagine the smaller derivatated ones
@@MarcusViniciusSilvaDaRosa Nptice: re-defining the speed of light as 3*10^8 m/s changes the meter by a factor of 3*10^8/299792458
So, if we multiply the things that we mesured by that factor should fix that issue.
It seems you can define the speed to be anything you want.
Speed is based on an interval of distance and an interval of time.
Change either of those intervals and you get a new speed.
It also seems that the speed of light doesn’t have to be the same for all observers, if you define the meter to be 1 wavelength of light or the second to be based off the frequency of light.
You can't really define a meter with those variables. The wavelength and frequency of light exist in a range of possibly infinite values, the definition of a unit of measurement must be a constant value.
Changing the definition just changes the symbol we use for the thing and not the thing itself, I can define an year to be 5 revolutions around the sun and suddenly I'm a 5 year old now, but it still means the same thing.
@@Haris-bg4jy I would agree that there are issues created by using a unit defined as such.
However I imagine it to be something like asking how many steps does it take you to walk from your house to school or work? A step can be a unit of measurement. It is not consistent. It could take someone else a different amount of steps to complete the same interval. But it can be a measurement.
And I agree it is just a different language used to describe the same observations from a different perspective.
It just seems that we have defined the speed of light to be the same by convention. However as a result light must now have variable wavelengths and variable frequencies. But instead of keeping the speed of light the same what happens if we make the frequency of light constant or the wavelength of light to be constant? For wavelength to be constant and frequency to be variable would require variable speeds of light. For frequency to be constant and wavelength to be variable would also require the speed of light to become variable.
And we could define light to function like either of those representations, however I do not think those representations would be the most natural with how our sensory perception has developed. But mathematically the system could be described using those conventions or definitions.
@@rossholst5315 That's actually a very interesting concept, I'll have to look a lot more into it but thanks for giving me something to think up on!
@@Haris-bg4jy you are welcome.
I had been thinking about this a bit more.
Why is it when the frequency of light changes do we not say light has changed speeds? How is frequency different than a speed? If you increase the frequency at which you do something are you not speeding up?
Obviously when the frequency changes so does the wavelength.
But if light is a wave, and we are measuring the speed of light why are we not measuring the speed in waves per second? If you look at the speed of light not in meters per second, but waves per second, light comes in all different speeds.
If you were sending a message via light such that the message was encoded into 1 wavelength. And we use a typical Doppler effect image, the rate at which the message can be read will depend on the frequency of the light that the observer receives. So it will take someone reading redshifted light longer to process the same message vs the person processing a message sent via blue shifted light. They both will start processing the message at the same time as the wave front will travel at the same speed for all observers. But the wave tail is not traveling at the same speed because the location of the source has changed. So the time to process information will be different even though the speed of light in meters per second is equal for both observers.
It would seem that this is why higher frequency light is more energetic light as it is essentially light that is moving faster in a sense, even though in meters per second it is all moving the same velocity.
But it also makes sense to think that as the frequency of light increases the wavelength of light shrinks. This means the radius or amplitude of the wave would need to shrink.
If light is the media that information about electric and magnetic fields are shared, then light of a shorter wavelength and amplitude would also carry information about a charge rotating in a tighter circle. And since electric field strength is proportional to the distance squared, a charge rotating in a tighter circle would have greater energy even though the length of the wave times the frequency is the same for all light.
This to me explains the why of the photoelectric effect and why frequency of a photon is related to the energy of light. Now you can increase amplitude by sending more of the same waves which does increase the total energy, but it does not increase the energy per photon.
However, I’m do not have a degree in physics. I am passionate about physics, and my thoughts could be wrong. But it seems to explain many of the observed effects.
But mostly I would say just say to think critically, and from multiple perspectives.
Again I don’t believe any of this information is new. It’s just looking at the same information differently. But like you said the information is the same. The information hasn’t changed just how we can interpret the information.
And I appreciate the comment so that I had the opportunity to think about this more. Again I don’t know whether I am right or wrong. These are just my ideas and I appreciate challenges and other perspectives. I find being wrong is often a better teacher than being right. It’s rare I remember the times I was right but when I am wrong I tend to remember it.
If you have any thoughts or comments I would love to hear them. Thanks again!
Interesting video, Mahesh, but I think it sidesteps the question the student was actually asking, doesn't it? :)
This explains why the meter (and by extension, the kilometer) is the size it is, but it leaves open the question of why the speed of light is exactly the value it is. It might be possible to live in a universe where the meter is exactly the same size, but light goes at a different speed. That would, in turn, of course, make the meter a different size once we moved to that way of measuring a meter. The size of the Earth would affect the size of the meter, but it wouldn't affect the actual speed of light.
I was wondering this seconds before you uploaded it
You have to be careful and distinguish clearly between two different things: On the one hand, the speed of light, which is a fundamental constant of our universe and has nothing to do with the planet Earth, and which we cannot explain other than "Well, it has to be *something,* right?". On the other hand, the numerical value of said constant, when expressed in our human units, which will obviously have an Earth-centric history to it, including the size of the Earth, because that's where our meter comes from, and the rotational period of the Earth, which is where our second comes from.
1m = 1/299792458 seconds
The USA does use the metric system.
Many of us use metric at work all the time. We use imperial in our day to day lives though.
The Speed of Light isn't much about light actually, it is about the Speed of Causality. That is why C is used for Speed of Light, because its the same speed. But why?
The thing is, Speed of Causality is the speed at how fast information can travel in space. Light on the other hand has an infinite speed, that is just slowed down by the Speed of Causality, because it cannot travel faster through space. Traveling through space is exchanging information to its neighbor (your clock example). And because Light cannot be faster than Causality, its max speed is the exact same, as nothing else is faster anyway.
8:36 Why did we decide to add two metres to the new definition of the metre 40 years ago? Even with the uncertainty added to the old definition of light, we still would have gotten (at most) 299,792,457.3, which should have just been rounded down
I presume they chose ...458 instead of ...457 as 7 is harder to divide and doesn't yield integer or fixed decimal parts, whereas 8 does -- e.g. 458/8 = 57.
Question from the video (Why does E= mc²):The energy of Mass (m)is 10J and it loses photons of 2 and .02 J energy. Then why it's mass is not decreased it remains still same in (1/2)mv² but in case 1 the mass decreases . Please sir answer
My supposition on the slight, 2 unit, increase in the ratio between the meter and the speed of causality: the “second” unit, for time, has gone through similar standard updates. The number we have is probably an adjustment due to the second slightly changing.
Actually, the speeed of light not only contains the meter, but also the second. Which means that the speed of light not only depend on the size of the planet, but also on its movement (which decides the average length of a day) and the fact that the Babylonians happened to use a base 60 system (that's the reason why an hour has 60 minutes and minute has 60 seconds), as well as whatever history is behind the day having 24 hours.
Grammatical error in the title for later reference, "Why is the speed the of light 299,792,458 m/s? (and not 300,000 km/s)"
For those still not spotting it - "Why Is the Speed *the* of Light"
I have a lot of question to that Standard meter bar... E. g. The accuracy was allegedly in 3-digit nanometer range. But how the heck could somebody derive that length from this bar? I mean, the grooved marking lines alone would be several ten micrometer wide. I have the feeling, nobody never ever _used_ these old bars actually.
You just set the definition to include or exclude the grooves (I believe they excluded it).
@@JoeAuerbach and even then you get too much deviation. Due to the grainy structure of metals, even super fine hand made grooves look like inversed rocky mountains at the corresponding maginfication (as a materials scientist, I look at such images every day). It's so hard to define a "line" this way at this level of accuracy... Don't know how they would have handled that. Further, back in the days, the only had light microscopes which can't do more than 1000x. It's barely enough to make out features in the micrometer range. Forget about nanometers...
In fact, the first value of the meter was considered to be 1/40,000,000 of the Paris meridian. Now the Paris Meridian is a 'Meridian Line' passing through the 'Paris Observatory' in Paris, France - 2°20′14.02500″ East Longitude. It was a long-standing rival to the Greenwich Meridian as the world's 'prime meridian'. "Paris meridian arc" or "French meridian arc" (French: la Méridienne de France) is the name of the meridian arc measured along the Paris meridian. where it was calculated by the 'arc measurement method', which is a standard trigonometric process. It is a precise process.
@@JoeAuerbach for reference, you can find an image here (I can't link directly, so copy the string):
chemie-master[dot]de/pse/lr_urmeter.jpg
There was always a group of lines, so bold that you can see them with bare eyes. No matter if you include or exclude them, it seems impossible to me to derive a length measurement in +/- 0.1 microns from that (this was their alledged accuracy).
@@b.s.7693they were not handmade, precise tools created the marks.
Great video Mahesh
Thanks ^_^
I think that the speed of light can be calculated using Maxwell's equations that describe electromagnetism. The equations say that the speed of all electromagnetic waves, including light, equals the ratio of two empirical constants. One constant has to do with the permeability of empty space to electric fields, the other to the permeability to magnetic fields. Of course, one can always ask why these constants take the values they do. Now we have two questions needing answers, whereas there was only one such question about the spssd of light!
I am presenting you my intuition about what photon exactly is and tried to combine wave and particle nature in one thread.
When we think about particle nature of light, then we assume light as a particle because in some experiments like photoelectric effect, quantisation of light was seen that was not possible if light shows wave nature here. (According to current understanding).
In wave nature intensity means greater amplitude while in particle nature , intensity means number of photons. But how this can be possible that a same quantity is defining two completely different things!!
Here is my intuition.. let suppose we have a wave with intensity A and frequency F.
During phenomena like photoelectric effect, the light wave gets split into numbers of low intensity wave(n) but with same frequency. Each wave have intensity(a) equal to intensity of actual wave divided by total number of new waves formed
a= A/n
But they also have same frequency.
In short the energy of larger wave get equally distributed among smaller waves.
Match this process with particle nature. If we increase intensity, number of photons will increase. Same is also happening here, as intensity will increase total numbers of waves will also increase.
And how much amplitude would be at each wave will decided by its frequency that is constant for all of them.
Conclusion:- The Photon are not very different from waves. They are just the quantised form of light when light get split. (Photon is wave with quantised energy).
This unite dual nature of light and also explain why energy of photon(smaller wave) do not depend on intensity rather on frequency.
E=hf
( Because frequency of wave determine how much energy to come in smaller waves from larger one)
Please reply sir ❤
What about the density of water?
I thought the meter was measured to make 1 liter of water (about 1 dicemiter cubed or 10 to -3 power of the meter cube) weight 1 kg
Isn't that true ?
I love this guy ❤
I wish my professors were like this
The reason why the last digit of speed of light is 8 and not 6 is because they added the correction value 1.1 to 6.2 = 7.3 and to make it exact ceil it to 8.
why ceil and not floor? Floor is after all literally closer
@@SaltHuman because they wanted to cover the error range, if you floor it you loose the error range.
@@dlogic1 Okay. But where did the 1.1 come from?
@@SaltHuman It's the error of measuring the speed of light.
@@dlogic1 hm. thanks
If the meter changed, then 1dm³ of water will have difference size, and the kilogram is also changed.
The kilogram hasn't been defined that way for more than 200 years.
the question still remains why speed of light is what it is !
Given time dilation, how did we define what a second is?
And if second itself is a relatively calculated value then what exactly does it mean that light has a speed of some meters per second?
we get to proper time if there is no relative motion, so we can define a very objective standard of time by a vibration period of atoms in a stationary solid crystal in standard conditions. The time dilation in individual atoms due to their motion won't matter; what matters is the constancy
12:30 you need the distance from the angle point,to measure arc lenght
This explains the units used, but avoids the much more interesting question of WHY is the fundamental constant c the universal actual value it is, regardless of units used.
French Revolution >> Every other revolution
How tf is that in anyway relevant to the video? There's a reason why people don't take your videos seriously
I know this is an older video, but I'm curious, what percentage smaller would the earth have to be to get an even 300,000,000 m/s speed for light?