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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.
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.
@@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.
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.
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😪
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 🤫🙃]
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🤞.
A bunch of thieves. The inventor of interstellar Propulsion Process and spacecraft Photon 137 alpha , commonly known as the Aurora Borealis Launch Vehicle.
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.
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 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 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.
@@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.
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.
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.
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.
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
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.
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.
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.
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
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.♥️
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...
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.
and yet you use a 12 hour clock and 90 degree angles etc... lol meter was introduced not because it is better but because the rest of the world wanted to take control. As you can see doing that to time and angles and other areas of measurement is truly nonsensical. You know they actually tried to convert bytes to base 10 and all programmers laughed at them. BASE 16 is much better. BTW he was not kidding when he said 10 hour day they tried to do that and that was epic fail.
@@macheadg5er Those aren't nonsensical. Dividing a circle into 360 parts is rather so convenient that it's one of the oldest convention, first used by Babylonians 4000 yrs ago, and still being used to this day.
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.
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 :)
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
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.”
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.
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
_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.
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.
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
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.
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)!
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.
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.
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.
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.
"A rose by any other name is still a rose, and smells as sweet"! Same with 'c' ! I think the poets understood this much before the scientists! Thank you Mahesh for this thought-provoking video.
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
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.
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.
@@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).
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.
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.
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...
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
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.
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
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.
I am an American, and I have done a fair bit of construction, along with fine woodworking and metal fabrication. I can say from my experience, that the metric system is far superior when doing small measurements. For example, drilling and tapping holes is extremely easy. An m6 bolt is 6mm, and the drill size is 5.5mm. Easy peasy. Precision measuring in fine woodworking is way easier too. .5mm is much easier to see on a ruler than 1/16. However, for construction, the cm is an awkward size for cutting boards to. .1mm is too precise, and .5cm is not precise enough. 1/8" is just right. It's just easier using inches. I've tried both. Plus, at this point, all of house construction is based off sheet goods being 4' x 8'. We couldn't switch to metric now if we wanted to. Sheets have to be 4x8 to match the framing. Swapping now would be chaos the likes of which we never seen.
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?
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.
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.
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.
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
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)...
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.
@@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.
The decimal division of angles was actually used in France for official topography until 1993. It can be found on some (older?) pocket calculators as an option, as well as degrees and radians. The name of the unit is "grade", subunits being milligrades and so on…
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
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?
There's another twist to this story. The actual circumference of this quarter globe measured from the pole, we now know to be 10,002 km. Which means we now need to change the size of our meter. And redefine the speed of light
Meter is already redefined: length of the path travelled by light in vacuum during a time interval of 1/299792458 of a second I.e. the reason the quarter globe is 10002 meters is due to the meter being refined
@@A_G8_M The change to the meter based on the speed of light wasn't that large. Indeed, when the metric system was defined, they measured the meridian precisely for that purpose, and simply made a measurement error.
@@A_G8_M And which 60 sec rule did you use. The 60 sec rule that aligns with the 60 minutes to make an hour? What if there were no 24 hours. Oh wait that is not a what if, that is actual fact. There are not 24 hours in a day. Which concludes there are not 60 minutes to the hour. Which concludes there are not 60 secs to the minute. I have to now ask. What needs to be refined. The Calendar or Time?
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.
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
Great video. I am always amazed to see just how human-centric our science is. It makes sense, I mean our reference point is a human reference point. Thanks for another entertaining video!
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.
@@fuseteam who wants simple? Why, it'd be even more entertaining to use everything based off of constants, such as Planck units. Now, the punchline being, think about ordering lunch meats and produce in Planck mass units... Some years ago, a physicist was charged with a minor traffic violation, running a red light. He tried a blue shift defense, alas, the jurist wasn't as conversant in physics as he could have been, otherwise the national debt would've been eliminated by one physicist's defense that he was speeding, so that red appeared green...
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.
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
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
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
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.
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!
Another issue we have is the definition of the meter doesn’t identify that the speed of light can only be measured as an average speed in 2 directions with an end point same as the start point and dividing that by 2
The one-way propagation velocity of light (in a vacuum, in an inertial reference frame) has been measured to be isotropic in all directions to within one part in 10⁻¹⁴ (Kennedy-Thorndike and Mössbauer rotor style experiments, for example, but especially the Compton Edge experiment in 2010 by Bocquet et al.) (Not to mention the electric permittivity and magnetic permeability of free space have also been measured to be constant.)
@ESponge2000 Yes. It's impossible to test the one-way speed of light with two "synchronized" clocks, but it is possible to test the isotropy of the speed of light in all directions... which has been done several times. The experimental lower bound for anisotropy in the speed of light is less than one part in 10⁻¹⁴
That's a good thing. We don't know if the speed of light is the same in every direction. Imagine the length of a meter where dependent on the direction.
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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.
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?
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.
that's why they say that physics is just a Model to understand the universe and not just "the way things are"
.......
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
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
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.
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
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!
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.
At this point it is a necessity that you do a Q&A episode
Love your explanation.
Always exciting to listen.
Thank you.
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.
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.
I was wondering this seconds before you uploaded it
Great, now I need a Helium Neon laser and some Cesium-133 to brag about the fish I caught yesterday
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.♥️
You explain things so well and make it so interesting. Great video!
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
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.
Thank you for not using miles, feet , inches amd other nonsesical units
and yet you use a 12 hour clock and 90 degree angles etc... lol meter was introduced not because it is better but because the rest of the world wanted to take control. As you can see doing that to time and angles and other areas of measurement is truly nonsensical. You know they actually tried to convert bytes to base 10 and all programmers laughed at them. BASE 16 is much better.
BTW he was not kidding when he said 10 hour day they tried to do that and that was epic fail.
@@macheadg5er Those aren't nonsensical. Dividing a circle into 360 parts is rather so convenient that it's one of the oldest convention, first used by Babylonians 4000 yrs ago, and still being used to this day.
@@macheadg5er why would they change bytes to base 10
@@macheadg5er360 (so 90) degrees is handy, has a lot of factors
@@macheadg5er did you know that feet, mile, inch etc that US love so much is defined by metric/SI units since 1959
Quickly becoming my fav physics YT personality
very well explained. thanks!
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.
Learned something new. Thanks.
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.
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
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.”
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.
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
_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.
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.
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
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.
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)!
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.
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.
Great video Mahesh
Thanks ^_^
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
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.
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.
"A rose by any other name is still a rose, and smells as sweet"! Same with 'c' !
I think the poets understood this much before the scientists!
Thank you Mahesh for this thought-provoking video.
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
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.
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.
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.
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.
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
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...
I love this guy ❤
I wish my professors were like this
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"
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
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.
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.
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.
I am an American, and I have done a fair bit of construction, along with fine woodworking and metal fabrication. I can say from my experience, that the metric system is far superior when doing small measurements. For example, drilling and tapping holes is extremely easy. An m6 bolt is 6mm, and the drill size is 5.5mm. Easy peasy. Precision measuring in fine woodworking is way easier too. .5mm is much easier to see on a ruler than 1/16. However, for construction, the cm is an awkward size for cutting boards to. .1mm is too precise, and .5cm is not precise enough. 1/8" is just right. It's just easier using inches. I've tried both.
Plus, at this point, all of house construction is based off sheet goods being 4' x 8'. We couldn't switch to metric now if we wanted to. Sheets have to be 4x8 to match the framing. Swapping now would be chaos the likes of which we never seen.
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?
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.
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.
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.
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
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
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.
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.
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.
Big fan of your videos ❤❤
The decimal division of angles was actually used in France for official topography until 1993. It can be found on some (older?) pocket calculators as an option, as well as degrees and radians. The name of the unit is "grade", subunits being milligrades and so on…
It's still used :) and still available on calculators
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
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?
"just saying" no such thing as objective vacum. love you way of phrasing and approach of thinking anyway
There's another twist to this story. The actual circumference of this quarter globe measured from the pole, we now know to be 10,002 km. Which means we now need to change the size of our meter. And redefine the speed of light
Meter is already redefined: length of the path travelled by light in vacuum during a time interval of 1/299792458 of a second
I.e. the reason the quarter globe is 10002 meters is due to the meter being refined
The speed of light remains the same regardless of how long a meter is: c is a constant that humans have measured with extreme precision.
@@A_G8_M whoosh
@@A_G8_M The change to the meter based on the speed of light wasn't that large. Indeed, when the metric system was defined, they measured the meridian precisely for that purpose, and simply made a measurement error.
@@A_G8_M And which 60 sec rule did you use. The 60 sec rule that aligns with the 60 minutes to make an hour? What if there were no 24 hours. Oh wait that is not a what if, that is actual fact. There are not 24 hours in a day. Which concludes there are not 60 minutes to the hour. Which concludes there are not 60 secs to the minute. I have to now ask. What needs to be refined. The Calendar or Time?
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.
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
1m = 1/299792458 seconds
Great video. I am always amazed to see just how human-centric our science is. It makes sense, I mean our reference point is a human reference point. Thanks for another entertaining video!
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 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?
perhaps this is the reason why scientists using c = 1 or c = 100% rather than that specific number
Nah that just cause that simplifies calculations
@@fuseteam who wants simple? Why, it'd be even more entertaining to use everything based off of constants, such as Planck units. Now, the punchline being, think about ordering lunch meats and produce in Planck mass units...
Some years ago, a physicist was charged with a minor traffic violation, running a red light. He tried a blue shift defense, alas, the jurist wasn't as conversant in physics as he could have been, otherwise the national debt would've been eliminated by one physicist's defense that he was speeding, so that red appeared green...
@@spvillano the planck units are exactly wat c=1 is, which greatly simplified physics calculations ;)
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.
7:16 WHYYYYY!!! WHYYYYYY YOUR MIC IS CHANGING COLOURRR
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
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
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
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.
Why is your mic magically colour changing?
Because it's a magic mic
FYI: There were a few times near the end of the video where you said 10 million instead of 10 thousand.
“I know you probably think this sounds preposterous”
Yes …. My thoughts exactly
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!
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.
Another issue we have is the definition of the meter doesn’t identify that the speed of light can only be measured as an average speed in 2 directions with an end point same as the start point and dividing that by 2
The one-way propagation velocity of light (in a vacuum, in an inertial reference frame) has been measured to be isotropic in all directions to within one part in 10⁻¹⁴
(Kennedy-Thorndike and Mössbauer rotor style experiments, for example, but especially the Compton Edge experiment in 2010 by Bocquet et al.)
(Not to mention the electric permittivity and magnetic permeability of free space have also been measured to be constant.)
@@juliavixen176 using 2 location clocks/photon clocks (wave pattern) , the problem is we can’t sync them
@ESponge2000 Yes. It's impossible to test the one-way speed of light with two "synchronized" clocks, but it is possible to test the isotropy of the speed of light in all directions... which has been done several times. The experimental lower bound for anisotropy in the speed of light is less than one part in 10⁻¹⁴
That's a good thing. We don't know if the speed of light is the same in every direction. Imagine the length of a meter where dependent on the direction.
@goswinvonbrederlow6602 We *DO* know that the speed of light can not differ by 0.0000000000001% in any direction. This _has been measured_
Can you make a video about how the kilogram was redefined in 2019 and why was it defined in a such way?