What is the maximum Bandwidth? - Sixty Symbols

Just how much data can we transfer using fibre optic cables?
Featuring Professor Mike Merrifield from the University of Nottingham... / profmike_m
Check our Computerphile: / computerphile
Visit our website at www.sixtysymbols.com/
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And Twitter at #!/periodicvideos
This project features scientists from The University of Nottingham
www.nottingham.ac.uk/physics/i...
Sixty Symbols videos by Brady Haran
A run-down of Brady's channels:
periodicvideos.blogspot.co.uk/...

[@GravisTKD]

Ironically, the video stopped to buffer as soon as he mentioned "bandwidth" for the first time. I chuckled.

[@NOMAD-qp3dd]

hehehe

[@oskarjankowski5709]

no it didn't

[@stabgan]

I fapped

[@kindlin]

Oskar, Do you not know what buffering is?

[@TruthNerds]

I conclude that the bandwidth of your line is less than 800 terabits per second. ;-)

[@omegasrevenge]

"A terrabyte of data.... in a few hundredths of a second." *Salivate*

[@jimdecamp7204]

Run lots of cables in parallel. Problem solved.

[@Austin101123]

And that's on a single wire. I imagine you could have 1000s of wires on a single cable, yes? Maybe you run into more physical limitations or errors at too small of a size too, though

[@fudgelame]

Run lots of cables in parallel yes but also with slightly different properties allowing them to be a control for overall transmission (plus 'overhead') for further range of frequencies (handling things as a bundle). Ie the different cables extend in part the range of frequencies available resulting in more relative bandwidth per cable.

[@jimdecamp7204]

There is an energy density problem, and mutual coupling between wires. Shannon's theorem says that data rate is given by bandwidth times signal to noise ratio. (For our purposes, dynamic range is a limit on signal to noise ratio.) A one Hertz bandwidth on a single cable can transmit a terabyte per second with a mere 44 teradB of dynamic range, or equivalently 8 x 10^12 bits of resolution.

[@MrRyanroberson1]

all we need is to start encoding data in sperms and transmit them through pipes. they carry terabytes of data per teaspoon, so if we want to copy entire massive databases just have a sperm truck go to the new location, then do a memory check to see if everything transmitted and use the internet to make up the tiny difference.

[@YassineAvernakis]

I like the part were the Professor says he doesn't know how much long is the shortest pulse, but says "I can look it up if you want". Such great minds have no problem with not knowing something, while this planet is so full of know-it-all s.

[@nozz71]

Humility will get you a long way in this field! 10:18

[@thedude951]

*cough*Neil Dygrasse Tyson*cough*

[@giorgosd3624]

Its just a number, i dont think anyone is proud of remembering numbers

[@JorgetePanete]

@@thedude951 Degrasse

[@JorgetePanete]

@@giorgosd3624 It's* don't*

[@AliMoeeny]

Wow, that was the best explanation of fourier transform I've ever seen.

[@StefanoBorini]

Ali Moeeny I am not sure. He introduced some math, but he steered clear of even naming FT. I think that if he directly went for the concept, explained it, and made it part of the vocabulary, the whole explanation would have sound less sketchy.

[@wiadroman]

+Ali Moeeny What are you talking about, he didn't explain FT at all.

[@ryanmcgowan3061]

+Ali Moeeny I was kind of surprised that I got to the end of the video and Fourier Transform was never brought up.

[@DigGil3]

The word of the day is "fourier series".

[@mattsmith2115]

*Pee Wee and the audience go apeshit*

[@stevenswift310]

That is two words.

[@malou5290]

harmonics :)

[@ElasticReality]

I think our science has gotten to the point where a little Fourier De-synthesis might be just what the doctor ordered.

[@MrJdcirbo]

That's not one word. It's an infinite number of words with varying phases and amplitudes added together. 😉

[@samueletorregrossa1923]

I'm not a physicist, but once you get used to this type of video you start to understand them better and better, it just takes time,

[@TURBOMIKEIFY]

This explains why musical instruments make that "wobbly" sound when they're out of tune on the same note. AMAZING!

[@niks660097]

yeah, especially in guitars you can hear beats and harmony off diff. instruments creating non-periodic reverbs, musicians are pretty close to science compared to other non-scientific fields..

[@theCodyReeder]

What is the ultimate limit for sending through the vacuum of space?

[@justuseodysee7348]

That would be whole spectrum from kilometers long radio waves to planck length sized photons. It would be some absurdly large number

[@vaibhav1618]

I think the lower bound is definitely the size of intergalactic dust (so perhaps IR?) I don't think there is an upper bound tbh, since space can have almost no mattet (a few atoms per m^3).

[@voxelsofsorrow]

@@vaibhav1618 what about the bandwidth of a signal sent between two Casimir plates at vacuum? that'd be interesting to graph out.

[@vaibhav1618]

@@voxelsofsorrow interesting, but what are we charting? Bandwidth vs plate separation?

[@voxelsofsorrow]

@@vaibhav1618 exactly! it's kinda interesting because the plates will cut off lower frequencies while allowing higher frequencies as they get closer

[@alfpumper]

Please make more videos about "engineering" I love physics, but the fact that I am an engineer, makes me want more videos like this. I have watch this channel for a year or so, please keep it up!

[@KevinVanOrd]

Michael Merrifield , I just wanted to thank you for making me passionate about topics I never knew I had passion for until I saw your videos here and on Deep Sky Videos. You have pushed me to learn and understand some of the involved math, encouraged me to purchase a telescope for skygazing purposes, and opened up new areas for me to explore. I am more grateful to you, Ed Copeland, Meghan Gray, Phil Moriarty, and Roger Bowley than I could ever express.

[@alexdrudigmail]

The reason why you don’t switch on and off and use a sum of sine waves to make 1s & 0s instead (Brady’s unanswered question) is that by modulating multiple sine waves you can actually encode a crapload more information per second into the optical fiber. The resulting non-sine signal contains many more contemporaneous 1s encoded. Professor Merrifield explained instead that you can simulate the “ON/OFF” physical phenomenon with a finite sum of many sine waves. The more numerous they are, the more squared is the resulting wave, and the easier it is to tell a 1 from a zero, hence a wider bandwidth.

[@jessstuart7495]

A sine wave can convey three pieces of information. Amplitude, Phase, and Frequency. The 19kHz FM pilot tone used to decode stereo information (United States) is an example. You can think of turning a sine-wave on/off as multiplying the sine-wave by a windowing function that is 1 when the sine-wave is on, and 0 when the sine-wave is off. The windowing function has a frequency spectrum of its own, and this gets convolved with the sine-wave's spectrum in the frequency domain. A pure sine-wave's spectrum looks like two impulses (sharp spikes) at +f and -f. A rectangular (perfectly "square" pulse) window function's spectrum is a sinc (sin(x)/x) function. When the sinc spectrum gets convolved with the sine-wave's impulse spectrum, it copies, shifts, and divides by 2 the sinc spectrum around +f and -f. Negative frequencies arise from converting Real valued time-domain signals into their complex-frequency domain representation. Check out the Shannon-Hartley Theorem that relates maximum channel capacity to Channel Bandwidth and Signal-to-Noise ratio.

[@rehoboth_farm]

I think you missed the point he was trying to convey.

[@davecrupel2817]

That's not the *type* of information he is referring to. That is nothing more than the nature of the transmission. You need an oscilloscope to translate that. Hes talking about using that like morse code.

[@InsaneMetalSoldier]

That moment when I realize this is not Computerphile o.0

[@lazeran4900]

+Juan Bonnett the moment when someone realise or deeply interiorise that the basic sciences are actually the thing that the modern technology comes from.

[@NebulusVoid]

+Lazeran that moment when you realise that this is topic is grey and could be found on either one

[@kindlin]

Bandwidth isn't computerphile? With current technology there is a known maximum bandwidth that we could Mor's Law predict ourselves into a problem with, in a relatively short time frame. At that point laying more wire to fill an exponentially increasing demand isn't plausible, you need better technology with a higher bandwidth or better compression to send less data. This all seems pretty computer related, to me.

[@unguidedone]

i know.... i was like :0

[@overlordalfredo]

All he talks about is in fact rudimental Computer stuff. *You learn what bandwidth is and how it is “produced“ when you are learning any computer related job!*

[@thisguy1ify]

I really love the style of these short lectures. The "student" asks a very well scripted question (or at least it seems scripted) which allows for reflection from the viewer to then connect the dots. I personally feel this KZbin channel is the best at communicating often very complex scientific concepts to a very wide range of audience. Cheers!

[@onthelongestroad]

Fascinating - it actually makes sense to me the way you explained it. Thanks, Professor (and Brady of course)!

[@bobee123456]

Found this video really helpful, appreciate you guys taking the time to film and upload it

[@earthworm768]

I have to admit, I have never heard of the range on frequencies that are able to travel down the optical fiber to be the limiting factor. I was taught that it was the Group Velocity Dispersion that limited the data rate, as due to this effect the pulses spread out temporally (That is, the pulses duration continues to increases as the pulse travels down the fibre). This increase of pulse duration makes it so that if pulses are fired too quickly after each other, sometime down the fiber the pulses would spread into each other and you will lose your nice wave packets and hence your data.

[@skardykats]

That is true. However he's talking about different types of limit. It is also strange that he talked about visible spectrum when fibre optics use only IR.

[@ronaldderooij1774]

Well I too mostly understand what is explained, but not quite this time. He lost me at the point that he explained that if you switch a laser on and off, it is a superposition of waves and if you keep it on continuously, it isn't. I understand the Heisenberg uncertaintly principle, and I understand superposition, but I cannot understand what that has to do with it. I also understand the (unmentioned) Fourier analysis, but I cannot make one single image in my mind on what the difference is between switching a laser on/off and leaving it on continuously.

[@skardykats]

Ronald de Rooij The thing that he said about continuous wave (CW) is true. It is almost never really exists in real world. I do a lot of EM simulation, and it is a real problem to simulate a CW. We use different kinds of tricks to suppress high frequency signals that permeates from starting the so called 'CW'. These high frequency signals are real problems in our frequency domain analysis.

[@KaitharVideo]

While I understand the argument being made in the video, it feels like he's contradicted himself. I was under the impression that individual photons represented a packet of energy of a single frequency... What he's saying suggests that a photon itself is a superposition of multiple frequencies?

[@maggsgorilla]

earthworm768 - actually group velocity dispersion (group delay in the radio world) means that different wavelengths travel through the fibre at different speeds and the frequency components arrive at different times which blurs the pulse edges. it can be partially corrected. it is still a function of bandwidth

[@LynkedVideos]

Why wasn't the term heterodyning used in this video? Bandwidth requirements become much more understandable, when the concept is explained. Two frequencies will combine to create both constructive and destructive frequencies. Heterodyning was demonstrated with the iPhone-based tone generators, but not clearly explained. If a 1000Hz tone is pulsed at 1Hz, the transmitter will occupy 2Hz from 999-1001Hz. Today's data networks use something called Dense Wave-division Multiplexing. We combine multiple frequencies often near 190THz with spacings of a mere 0.8nm, each channel representing 10Gbps. Prisms are readily available to combine up to 80 channels on a single pair of fibers, which translates to 800Gbps, or a Terabyte of raw data in 10 seconds.

[@agerven]

@Michael Hall: What you're talking about is the actual binary information that is transmitted. The video is concerned about the physical limits in transmitting information accross a fiber-optic cable. And mind you, as the professor clearly states, a mathematically true pulse requires an infinite amount of frequencies or otherwise an infinite amount of preparation and decay times to form. Fortunately quantummechanics comes to the rescue there giving us a bounded physical world i.s.o. a purely mathematical one. I really love that part.

[@Aemilindore]

You sir explained a whole lot of wireless communication to me in minutes! Thanks prof. Your students are so lucky to be taught by you! Please consider doing more videos on wireless communication. Yours will make a great channel.

[@montlejohnbojangles8937]

This just cleared up a huge hole in my understanding of waves and bandwidth. I heart you guys lots.

[@EngineeringNS]

Can't wait for 10TB/s speeds...

[@NebulusVoid]

+Engineering Nonsense I know right.

[@madmatthew1]

+Engineering Nonsense But that will need to be split through the whole population since we share fibre cables

[@EngineeringNS]

Matthew Lowe its not just one cable, under water, but networks. Right?

[@madmatthew1]

Yeah, I was going to say there will be thousands bundled up, but I doubt there will be enough to provide each household within a city with 10TB/s

[@EngineeringNS]

Matthew Lowe True

[@gl1500ctv]

This reminds me of how they said CAT7 cable was going to be needed to handle the bandwidth of gigabit Ethernet and within a few years the engineers figured out how to do it over CAT5 cable with the right processing power and better noise reduction algorithms. Then wireless added new modulation schemes and multiplexing and jumped from 802.11b to 802.11n to 802.11ac. The lesson: don't tell an engineer there is a limit as they will find ways to exceed your limits.

[@911gpd]

Stephen Furr I absolutely didn't get a clue of what you're talking about except the last sentence that I like very much and do agree with :)

[@911gpd]

allen mathew Thanks :)

[@colemarc]

+Stephen Furr Advancements in technology only push the speed near and near to the fundamental limits of the media. If the media is for example a CAT5 cable with a given noise floor you can only push so much information down the line (see Shannon theorem).

[@AlexanderBollbach]

here here

[@deplorableamerican9451]

Stephen Furr there's a limit ;)

[@memeswillneverdie]

You know I revisit this video as an audio engineer and it explains the basics of impulses, intermodulation distortion (kinda), it hints at the nyquist Shannon sampling theorem (in the sense that you need to decide the bandwidth you need which will define the sampling rate), the Fourier transform (all sounds are just a combination of different frequencies), digital clocking, pulse code modulation (in a very roundabout way in terms of thats the pulses hes on about). All of these things took me quite a while to fully grasp and he explained/eluded to them in the span of 10 ish mins, bravo.

[@BonjourHalloHello]

A brilliant explanation, and really helpful for my A-Level Physics! Thanks.

[@foreverofthestars4718]

I want to be in his class

[@calmvolatility2787]

you say that b/c you saw the bottle of scotch on the desk behind him LOL, that would be a fun class

[@redshift1976]

No one is in his class.

[@dromeiro]

The number of "beatings" per second its equal to the difference between the two frequencies in hertz. So, 1000Hz and 1001Hz: 1Hz difference, or one beating per second. 1000Hz and 1002Hz: 2Hz difference, or two beatings per second.

[@asifinamdar7913]

When he played two tones of different frequencies, superposition of two signals took place. It will result into wave/signal of different frequency. Therefore, that resulting frequency will be LCM of the two original frequencies.

[@ricma9710]

That frequency pulse was incredible, thank you professor Mike, it was very cool.

[@TheBandScanner]

One of the best videos I've seen from this channel.

[@tjpld]

So that would be around 80 Tbps or 80.000 Gbps. Should be enough for future applications. Looks like some people even managed to almost reach the maximum. www.techspot.com/news/52066-hollow-fiber-optic-cable-tops-73tbps-promises-near-light-speeds.html We really need fiber optical cables everywhere and into every building. You'd only have to upgrade the terminals and recievers to get higher bandwidths in the future.

[@Crazy_Diamond_75]

1TB in a few hundredths of a second?!?! JFC

[@then33k4]

JFC is a Mexican fast food chain.. right.. right ?

[@JM-cv7nv]

AMGwtfBBQsauce In the future, that might seem like a small amount. In the 1900's, one MB used to be incomprehensibly big.

[@Crazy_Diamond_75]

Jojo Mcguire Which decade are we talking about? Computers didn't even exist in 1900, but multi-gig hard drives were pretty standard by 2000.

[@classicsignofgivinguponaus3685]

AMGwtfBBQsauce I think it's a typo and he meant 1990, however, even then 1 MB wasn't too big. The 80's now, that's a different story.

[@Crazy_Diamond_75]

Ashley Wyatt "Why would we need any more than 50KB of storage?"

[@coreytk]

Excellent video, learned a lot! The way the delta f delta t formula presented in the beginning was tied in at the end to drive the point home really made everything make even more sense, thanks for the great video!

[@kyler133]

Great video. I watched it three times in a row to make sure I absorbed every bit of precious information. This video gives you an idea of what our future technologies could be capable of and when we may begin seeing the limitations of fiber and looking to bring about a new way of transmitting data.

[@malango255]

Man I don't miss my 56k dial up days haha.

[@egv2271]

I'm pretty happy with 100TB a sec...

[@volodyanarchist]

10 years ago you would be very happy with 56 Kib per second. And in 10 years, once high definition holographic VR movies will start including DNA and psychological information of each character allowing you to create alternative plots as you go and you will try to download something like this, 100 TiB per second might look like a slow connection.

[@darrenpope755]

VolodyA! V Anarhist Time for you to write a book. I bet that came off the top of your head, didn't it? Run with it! I also noticed your use of the tebibyte symbol... while I applaud your effort, I don't think it will catch on.

[@volodyanarchist]

))) About TiB... i don't do that to "catch on", but because otherwise it's ambigous.

[@darrenpope755]

VolodyA! V Anarhist As you already know TiB = 1024^4 and TB= 1000^4 bytes... I think the public has spoken with the use of kilo, mega, giga and tera. The only ambiguity would be the public's clear ignorance of the difference and why it's important. That's why I was saying it won't catch on... the general public won't start saying the right thing. But, I applaud your effort to be exact!

[@GraveUypo]

VolodyA! V Anarhist you probably meant 20 years ago. 10 years ago was 2005! some of us already had megabyte connections back then (i think i was at 800kbps)

[@p.s.design4338]

this Prof's explanation is really enjoyable.

[@papa515]

Brilliant - Of all the explanations, I've seen, this is the best explanation of bandwidth.

[@dddmemaybe]

We've come so far that I can stream videos in quality higher than my eyes can percept, and loaded faster than I could watch them. :D Computers might as well be magic from my understanding of them.

[@GamePhysics]

Terabytes in milliseconds you say? That's amazing.

[@GamePhysics]

KaneLongTroy If we assume 1tb in a millisecond, that will still be done in 0,002 seconds. That's pretty fast.

[@SkyLake101]

+GamePhysics Regular computers won't be able to process that much of speed

[@Romenadan]

Absolutely fantastic video! This is something I had wondered about for a long time! I didn't realize the uncertainty principle included the pair of energy and timing of a photon, which really is key to understanding why the range of frequencies needed to turn the sine to a square increases as pulsewidth decreases.

[@ruelj2]

This is my favorite video of all sixty symbols!! Please make a video about Fournier's equations!!

[@chillsahoy2640]

Talking about photons got me thinking. What is the smallest wavelength difference that two different photons could have? I understand that each photon has a particular energy, determined by its wavelength, so that a photon can have wavelength x, and the next highest energy photon will have wavelength x-n. But what is the value for n? Is it the Plank length?

[@CalculatedRiskAK]

+E “Anonymous Nerdfighter” Hernandez The smallest wavelength difference, I would assume, would be one Planck Length. The reason is because the Planck Length is the smallest discrete distance that can be traveled and measured in the universe, so it would be impossible for two wavelengths of light to differ by any less than that.

[@AllTreble]

I calculated his answer a bit more so its easier to understand. In terms of data transfer the ultimate limit you can send is about 50,000,000 Mbyte/sec or 400,000,000 Mbit/sec in a fiber lika that (from blue light to red light)

[@louistournas120]

Let's see the math.

[@jimdecamp7204]

Google Shannon's Theorem.

[@onecanina]

Brady, don't forget the sixty symbols channel. I love them all but this is my favorite and you don't t upload enough here!

[@radoslawbiernacki]

Sir, this is the most beautiful and concrete explanation of Quantum physic, Fourier Transformation and Information theory lectures in the whole universe!!! I'm a engineer and finally after all those years someone showed me how to explain connections in all of those laws using one simple example!. This really worked for me!!! Thank you!!

[@abhiaerospace]

sir what was that app for different frequency generation ? i need it.

[@MrMamanDon]

Search for frequency genrator apps on play store or app store. To replicate that pulsing effect, choose a stable frequency let's say 1khz and then play 1.01 khz in other phone.

[@mhdadk]

What's the app called?

[@guymartin1949]

I learned something new! What a fantastic explanation. I had no idea that optical communications relied on the wave component of light to transmit information. Thank you so much Professor Merrifield. I absolutely love watching your videos. Don't be discouraged by negative comments. You can't please everyone and the people you do reach are very grateful for sharing your knowledge with us.

[@billpiper795]

Fascinating. I love the quantum mechanics tie-in to the bandwidth discussion.

[@sheet-son]

More cables. Problem solved. Pay me billions.

[@KatzRool]

good jorb. *clap*..*clap*..*clap*...

[@Vesperidone]

But you'd need the receivers to process the additional cables and compile it all together, which may not actually save time.

[@BlackMasterRoshi]

Stuart Hull Gamma rays are ionizing radiation so they just smash into atoms and knock electrons off them, often changing the properties of the atoms in the process. It would not be easy to find anything like an optic cable to shove them down. Radio waves have much longer wavelengths and they just pass through many substances or get absorbed. The range we have to work with for fiber optics is pretty much infra red through lower ultra violet.

[@ShamelessHorse]

Mexicano President Many Jobs!

[@itsiwhatitsi]

Give Billions to the Bat-Cat!!

[@RealBenAnderson]

As a big fan of your videos and someone who normally has no problem understanding them, I have to admit none of this made any sense to me. I would greatly appreciate it if you could make another video explaining this better. I know you have lots of videos to make but this seemed interesting but was really not explained well in my opinion, so if you get a chance I would love an opportunity to actually understand what he is talking about here.

[@theInternet633]

Yeah normally i understand everything pretty well too but this time i really struggled to understand anything of substance the first time watching. By now i only understand the first part of the video, where the delta f * delta t = 1 formula comes from.

[@panzach]

(1) The speed of your fiber connection is how much information can travel through (2) Information is 1s and 0s (3) "1" and "0" are basically "pulse" and "no pulse") (4) The shorter in duration the pulses the more pulses can travel through your fiber within a given period of time (5) A short (duration) pulse can only be created by combining loooots of waves of different frequencies (6) There is a limitation on what range of frequencies (bandwidth) your fiber can support (7) Since the range of frequencies is limited, the duration of the supported pulses is also limited, because of (5)

[@nickmagrick7702]

2:04 a resonance. A pattern of the waves complimenting each other and getting stronger, or canceling out and making the noise more fuzzy. Like pushing your legs on a swing set

[@ruadeil_zabelin]

Don't let it get to your head. I love watching your (and Brady's) video's. Even if it's about a field I already have knowledge about (like in this case), it's still interesting to watch. Keep it up :) Love it.

[@user-zi8jn1go8k]

So if we have let's say a green laser and switch it on and off quickly it shuoldn't be a single wavelength anymore, right? Does it mean that if we put a filter in front of laser, that will allow only a green light to pass we will se the laser only when it is switched on constantly? And if we start to switch it on/off what would we see? No light at all? Or constant light? This idea seems weird to me :\

[@rossinator98]

+Роман Плетнев I like your thinking. I imagine the time we would see the laser as "on" would decrease as we decreased the number of frequencies allowed through the filter. As we decrease the frequencies allowed through it essentially becomes opaque which makes sense as then the time we perceive the laser as on would be zero. So the delta t (time of perceived pulse) through the filter is proportional to delta f of the filter (i.e range of frequencies allowed through)? No idea, just speculating...

[@Maric18]

+Роман Плетнев since the filter can physically not be that precise, you would only cut the end and the beginning of each pulse. if you switch fast enough, the time until it is close enough to your target frequency would be longer than the length of the pulse, if you know what i mean. If the totally unrelated mental image helps, think of the sound an organ makes if it turns on while you are pressing the keys (it is one of my favourite sounds :D)

[@lcbp2009]

+Роман Плетнев +Ross Sullivan +Maric I understand your confusion, it's because the vid explain it poorly. The vid is only 11 min it cannot cover everything of a 2 h class on the subject. Here the explanation: every signal that is not pure can be written as a sum of a pure signal, when I say pure I mean it contains only 1 frequency, and it means the signal can be drawn as a perfect sinusoide. Now when you switch on a off periodically the green laser, if you look at the signal as a whole you will see (if for example the period is 1s) 1s there is a pure sinusoide then 1s there is nothing, and so on until you decide to stop it. It is then impossible to mathematically describe the whole signal with one and only one frequency (the frequency of the green laser). Only by using the sum of many frequency you can mathematically reconstruct the whole signal. In other word, by using a lot of different frequency, and add them together you can achieve the same result as if you were turning on and off the laser. Hence the "it contains a lot of different frequency". As for how can adding different frequency can result in total darkness (equivalent to when you turn off the laser) you can look into interference. So to answer your question if the signal was obtained by turning on and off then you will see nothin, but if the signal was obtained by the addition of many frequency, you will filter the green light and obtain all the other. For more info look into Fourier series.

[@LouSaydus]

Роман Плетнев same light but with just less energy because you filtered some of it off

[@janetjack9472]

And what in case we are capable of sending a single photon. We put a filter. And what does even very long lasting sine wave of light freq mean? That photons come in an extremely ordered fashion one after another without any differences in space gaps between them in a straight path?

[@XxXKi11erXxX]

you forgot about modulation, if you use QAM 65536 you would have 16 times the Data conveyed, so you would end up at about 1600TB/s which is more than enough

[@JurisKankalis]

Great and thorough explanation. Kuddos!

[@onqproductions]

That was awesome. Great job.

[@arnabbiswasalsodeep]

What's the name of the app

[@Amethyst_Friend]

'application'

[@Bassotronics]

11:22 = O_o I need that internet speed!

[@axiezimmah]

your computer won't be able to handle it.

[@nmarbletoe8210]

i wonder if it would melt the fiber

[@PongoXBongo]

Those crazy levels of speed are more commonly found in trans-oceanic cables, where billions of people's bits are going over a single bunch of fibers (like a shared cable internet connection on steroids).

[@PongoXBongo]

G4mm4G0bl1n I never said it was a single fiber. I said "cable" and "bunch of fibers". Those cables are massive bunches of fibers. My point was that the only real need for anywhere near theoretical single fiber bandwidth is in those transoceanic fibers. No home or business network, metro net, ISP, etc. needs that at this point.

[@PongoXBongo]

G4mm4G0bl1n Not at all. I specifically said "at this point" not "never". As long as LANs are capped at 1 maybe 10 Gbps, WANs need not be faster. Will the need be there soon enough, of course. But not today.

[@DavidHager1]

Awesome explanation and really interesting.

[@darkercheese]

Thanks! These technicalities are why I love science.

[@grrr1351]

Anybody else love those pulses instead of get annoyed?

[@EvanBoyar]

You actually could encode information in an unchanging sine wave; you could encode it in the exact frequency. Let's say I wanted to encode the word "it". If you break "it" down into ASCII, that's 0x69, 0x74 (in hex), or 0110100101110100 (squished together in binary), depending on how you decide to do it. Anyway that translates to the number 26996 in decimal. So, if you wanted, you could send out a tone at 26996 Hz. If another person listened to the signal and figured out what frequency it was (easy with computers!), they could decode that number into "it"! But yeah, this is obviously a silly idea. Just having some fun!

[@JavierRuizGonzalez]

Well, there is a problem with the "easy with computers" part. So far with the word "it" we are outside the frequency range of digital audio, so you will need special hardware to digitize the incoming 26996 Hz signal. And "it" is a very short word. I'll let you calculate the frequency of the word "information" with your system, but I guess we would in the 10^27 Hz range... By the way, an unchanging sine wave has to be infinite in time, to be unchanging. Otherwise it'll contain other frequencies. As you said, having some fun.

[@saltyman7888]

There is also the problem of having the different peaks and valleys of different frequencies smearing together and also losing the information.

[@ericsbuds]

awesome video. loved the topic.

[@agerven]

Wow, certainly entertaining and covering some essentials of physics. As expected, in the end, the numbers prof. Merrifield comes up with are related to the actual transmissive boundary conditions of the fiber. In this case conditions that allow light in the optical spectrum to pass without significant damping through the cable. I love it when he gets so enthousiastic that he applies the theoretical fourier analysis and even quantummechanics to the question. Of course he's right there, very capable man, but then you're talking about the absolute theoretical limits in general. And whether one or the other is true and what 'true' actually means is subject to an endless discussion that I sometimes happily dive into but in general constraint myself from. So yes, great stuff this video and sure to rewatch it a number of times!

[@thrael3]

frequency limit =/= information limit because you can modulate amplitude. i.e. each spike may have different height and contribute to several bits without pushing frequency limit.

[@aigarius]

Information limit is reached when spikes as just barely high enought to be detectable as something different from zero. Any higher than that and you are wasting time that the spike needs to climb and then fall again.

[@davecrupel2817]

7:22 GIF

[@lunarmodule6419]

LOL

[@KieronMiddleton]

That's my next physics lesson plan sorted..thanks SixtySymbols!

[@Logarithm906]

It's brilliantly explained. He starts with the beats that happen when two waves of different frequency superposition against each other (with a handy graph showing it beating in real time). He then draws an "infinite" sine wave and a pulse. You can clearly see that the pulse has tails, these tails that go to zero which is clear evidence that something other than the sine wave (like another frequency) is affecting the wave. A pure sine wave would just stop with no tails.

[@Majinant]

Thanks for freaking out my kitten.

[@jaydunsmore050897]

and im stick with 5 down and 0.85 up :(

[@johnclavis]

I understood just about all of that! Thanks very much for a really interesting video!

[@slinkytreekreeper]

That was fascinating stuff, thankyou!

[@luckyyuri]

10:22 that's exactly how i proceed when someone asks me what's the capital of france or something...

[@Schwuuuuup]

this must be the most confusing explanation on that topic. He must be related to my old Math teacher who could explain things only to those who already knew it all... :-/

[@ludbrooks]

As a non-physicist I was doing great for the first 4.5 mins and then it all went! However I still love watching these videos of Brady's in the hope that I will start understanding eventually. Still envious of how Brady seems to understand so much as shown by his responses. I am beginning to think he no longer represents the "ordinary" person and so would like to volunteer my services for future videos!

[@plantera07]

Professor Merrifield is the best. I could listen to him all day.

[@lumpyfishgravy]

There is no such thing as DC.

[@jessstuart7495]

If we only had infinite time.

[@lumpyfishgravy]

Correct!

[@Ritefita]

very interesting. Can you tell more about it? Do you mean a light-speed electrons movement? a simple wire faster than optical? then why? whaaaaaa ????

[@lumpyfishgravy]

DC is zero frequency. A signal that is DC never changes. But the universe has only finite time, therefore the signal can only be DC if we make assumptions about its border conditions at the beginning and end of time.

[@Ritefita]

Mike Page no, i didnt) DC is undestandable. never changing dc is not information. the universe and time is not understandable. if you want infinite, never changing, dc then you just need an infinite energy for this useless circuit. wtf

[@KnDoy]

I get 5 mbps -__-

[@gnagarn87]

Are you sure that you don't have a DSL connection? Considering the fact that the slowest speed i can get with fiber optic connection is 10 down and 5 up makes me wonder.. I can get, depending on the speed/plan you pick, anything from 10Mbit/s and all the way up to 1Gbit/s both up and down, for a fairly low cost. I currently have 100Mbit/s and pay about $45/month (USD).

[@Mrfailstandstil]

Gnagarn 100 mbit/s in USA or the world, dl and ul???

[@zinqtable1092]

750Kb/s keep whining

[@youngpatriot]

Of course that is my understanding, based on high school science some thirty plus years ago. Now everyone who really understands his question can attempt to reply correctly if I am not doing so, in terms such as I have used. Thanks.

[@GetOutsideYourself]

Very cool explanation. I love everyday applications of quantum principles. The whole video I was wondering if he was going to get to the absolute limit of fiber. Glad you pinned him down in the end.

[@megadeathx]

This is the worst explanation I've ever heard on this channel.

[@HughPryor]

I think the full explanation would take many times longer... I did watch another video explaining the same concept only marginally better - probably minutephysics...

[@problem5279]

Really an eye opener, to understand what Shannon's bandwidth really meant. Thank you

[@Archiekunst]

Mike Merrifield! Best teacher!

[@peterreid3077]

Thank you Professor - never really understood how Bandwidth limits were arrived at - until now that is!

[@bigboam]

Learned something new today. Good video.

[@Pants4096]

It can be instructive to show what happens to a sharp pulse when it has passed through a bandwidth limitation, what it looks like when it's received. Because some of the frequencies are gone, the edges get "fuzzy". That relates to how short the pulse can be, or how short a delay between two pulses, before it's too fuzzy to find the edges and tell one pulse from another. If you ever tackle radio transmission in your videos, Single SideBand radio deals with exactly this kind of thing.

[@RaminHonary]

I wish he had mentioned Fourier transforms, or shown how a time-domain graph can be converted to a frequency-domain graph because that is the equation you use to figure out which freqncys are produced when you create a wave that isn't sinusoidal. When you look at the freqncy domain you can see the stripe or "band" of freqncys needed to recreate the time-domain graph and you can then impose the band of freqncys that fibre-optics are physically able to carry to see the actual "width of the band."

[@shirinbas]

What a masterful description of the uncertainty principle

[@Jahooba]

Fascinating!

[@ChrisWalshZX]

A great insight into quantum uncertainty from particle-wave duality.

[@arturzathas499]

along with numberphile this is possibly the best channel in the entire net

[@Kd8OUR]

I do radio as a hobby and this is a great video.

[@achimhanischdorfer3403]

Nice explanation. I think that this will help many people understand better how stuff works at quantum level.

[@JakeDavidHarrison]

That's what the video is about, the shortest period you can send the light for has a limit; the shorter the period, the more frequencies of light that are required and fibre optic cable only has a limited amount of light frequencies it can transmit - which we generally call 'visible light'.

[@AstroMikeMerri]

Very good point: the part presented in this video is, technically, the element related to Nyquist sampling, or the B in your equation. With good engineering and high S/N, you can do better as set out in the Shannon-Hartley theorem, but note that you only gain logarithmically: massively increase your S/N from 10 to 10000, and you only increase your channel capacity by a factor of 4 . The dominant physical limitation remains the bandwidth of the fiber, for the reasons described in the video.

[@hoerbschmidt618]

That was a great explanation. Thank you very much! Best regards from Germany :-)

[@ZeZapatiste]

Extremely interesting. Thanks.

[@wknight8111]

I kept expecting them to talk about Fourier series and showing how waves of different frequencies can be added together to form square waves and whatever, so it was fun to see him take a different approach. For modern fiber optics or other transmissions with huge bandwidth needs, it's more likely that they would multiplex multiple slower streams together than to try to smoosh everything into a single stream with femto-second square wave pulses.

[@tedarcher9120]

They don't use square pulses, they shift sine phase one or the other way and use different pieces of sine wave to code 1 and 0. Square pulses will just stretch on the way because they have so many different frequencies

[@maggsgorilla]

this can be displayed in spectrum analysis of pulse modulation where the prf increases. at prf of 1Hz the spectrum is effectively a flashing carrier, but with increase in prf more bandwidth is required and nice patterns form

[@Souraneel]

Thank you Prof Merrifield and Sixty Symbols. This is a very complicated topic I couldn't get my head around as I find it hard to understand the structure of a wave.