Computing Limit - Computerphile 

From Wikipedia: "The Fredkin gate is a circuit or device with three inputs and three outputs that transmits the first bit unchanged and swaps the last two bits if, and only if, the first bit is 1." "It is universal, which means that any logical or arithmetic operation can be constructed entirely of Fredkin gates." It even shows how you can make AND, OR, and NOT from Fredkin gates. So it truly can replace everything. Also, oddly enough, you can implement them using AND, OR, NOT, and XOR. It's so weird. We NEED a video on these things, Sean!

Informæætion

It's important to note that reversible computing is not a free lunch. The crucial bit he omitted is that a reversible computation with no energy input is a random walk, it diffuses forwards and backwards through the computation and may take infinite time to reach the output state you desire. However, you may add energy system to drive the computation forwards. So there is a fundamental tradeoff between energy cost and computation speed.

Your mantra at 0:50 is pretty much how I went through university. Also another good one that I follow is: "A complex thing is just lots of simple things put together" (which means that if it is too hard you haven't broken it down enough yet)

This guy looks like Vsauce's dad.

9:34 The whistle was roughly 1180 Hz

'I have a theoretical degree in physics'

I could do with an electrical engineering phile

5:10 : "Is that not just because we have two inputs and only one output?" LoL Phil has a very appropriate reaction here. That question was indeed a very neat insight about the whole thing.

He explains things like opening wikipedia tabs all over the place and closing them one after the other.. takes some focus to keep up with his goal but like it

This guy's infinite enthusiasm and unbounded love for his subject matter is self-evidently just way off the charts. See what I did there? Infinite and unbounded? Off the charts? Those things are just as true in terms of what he's talking about as they are of how passionately he tries to get things accross It's just that he does it all so much more spontaeously and infectiously than I ever could. Simply awesome.

What an excellent presenter. Had me engaged from start to finish.

One of the best episodes, IMO. It tied several interesting concepts together very nicely. Great job!

"Uncertainty principle" Is great name for progressive technical death metal.

I think this is the best video I have seen on here. My favourite professor/presenter over from minutephysics talking about fundamentals of computer science. Just amazing. Thank you so much for this!

Mathematically speaking, this reminds me of inverse functions. The system is reversible if every final position can be paired with at most one initial condition. Which in math terms is like saying the mapping from the initial condition set to the final condition set must be injective (i.e. must be a monomorphism).

Dear Computerphie team. I have added accurate English captions as well as Russian captions about a year ago. Could you please review and perhaps publish them, should you be satisfied. Thank you!

I'm only a recreational physicist. Is this why I can't find the link?

Teacher: “You there. Explain what Quantum Physics is” Me: “Hold my acoustic guitar”

This is one of the most interesting Computerphile videos I've seen in a long time. It's one of those topics that you don't ever hear about in when doing a bachelor's degree or working in software, but is still incredibly fascinating.

so when do we get consumer level machines with 10^50 flop processors? and can it run crysis?

When sending Morse code (or any digital transminnion) you often run into the frequency vs bandwidth problem. You can use a verry narrow audio filter with slow speeds but that same filter is useless at high speeds. The filter resonates or "rings" and you hear a nearly steady tone and all information is lost.

That was MIND BLOWING. Totally understood exactly why he took so long to explain it, he had to set up prior knowledge at each point so you could follow along. Amazing that we have actually figured this out.

Wow, I got goosebumps at the end of the video when you explain how far away we actually are from the computational limit.

Prof Moriarty has always been one of my favourites, but I think this might be his best video yet.

"Narrow in time, wide in frequency. Wide in time, narrow in frequency." Best.Quote.Ever.

Thank you, that's the best short explanation of the Uncertainty Principle I've seen. I also took a while to come to that realisation, and any time anyone asks me to explain it I've gone for a very similar explanation to the one you gave there. Far too many "explanations" confuse it with measurement issues.

I did a search for "computational limits" and this is one of the few relevant videos. Great video. Thank you. I first read about the limits of computation in "The Singularity is Near" and I realized the connection to reversibility in the YT video "Quantum Computing for Computer Scientists". I would love to see more on this topic.

coding as a way of explaining maths… now that would make an interesting series :-)

I was listening to Prof. Moriarty while working away on my own stuff and I look over and suddenly there's a guitar.

These videos are just amazing. Congratulations to the professors and to whoever had the idea of making them (the videos, not the professors. Though they deserve some credit too (the professor makers, I mean)). They surely make me wish I had studied at Nottingham.

This video captures so many aspects of what makes science/math popularization work: - Both Phil and Sean are clearly excited about the topic. The synergy between them creates a dynamic tension surrounding the core principles being discussed. - The topic itself doesn't just cross the boundaries between math, computing and physics, it unifies and annihilates them. - The topic also neatly covers so many orders of magnitude, lending a perceptible scale to the entire topic. - The most advanced math used was the AND gate. The demos were a dead tennis ball and a guitar. So much from so little! - Fundamentals! "Long time, narrow frequency band. Short time, wide frequency band." Awesome. Well done!

Could we actually get an electric engineering phile channel?

10**50 operations per second in what frame? Per watt, compute thread, cubic meter of cpu?

I have a take-home exam right now. Damn you Computerphile! That was his best video to date. There were sooo many interesting aspects of physics and information that was so well explained.

Watching this (and Numberphile..) makes me feel so nerd and happy... I really enjoyed this video, thanks!

Why are there pink fluffy ears on the desk

But can it run crysis? Sorry I had to. Imagine gaming in a dual blackhole Intel cpu.

Well, I wish youtube and this channel existed back in the days when I was an undergrad. Love you, guys

Fantastic video! I really appreciate the link between the tennis ball system and the logic gate. Thanks!

Yay, I have the exact same mantra as a student. I always try to code stuff to truly "get it". If I can explain a concept to a dumb machine, I must know it.

Yes to electrical engineering-phile!

Thank you so much for this video. Been interested in that topic for years, but never found any information on it.

I have been eating up videos from this channel. Not a clue for most of it but I love it, cheers :)

How is the spelling of the "fredgen gates" that he mentions at 5:54? I would like to read more about them but Googles autocorrection doesn't point me into the right direction.

They asked me how well I understood theoretical physics. I said I have a theoretical degree in physics. They said welcome aboard!

Have a total geekcrush on dr. Moriarty! :) This video touches some very interesting and far out points in a very nice and understandable way. Am a computer engineer, love the phisics in this video. Thank you for a great work you do at Computerphile and the Nottingham University.

Amazing, the ending blew my mind completely. Also, as a guitarist in a metal band I really enjoyed the explanation haha

Buy some new strings

I think this is Phil's best video yet.

I remember reading before about a limit for computing speed called bremermans limit something like 2 x 10^47 bit per gram per second, what relation does this.have to.that ?

Awesome video! Really enjoyed the connection between physics and information.

Link to the paper: arxiv.org/pdf/quant-ph/9908043.pdf

The whistle was 1150 Hz

This man has a truly awesome gift for information transfer! I envy his students.

SUCH a great channel!!!! What an immense level of value!❤️❤️❤️❤️

That was some quick thinking for the explanation of the fluffy ears. Nice

But can it run Crysis ?

Thanks to Professor Moriarty and the Computerphile team, it was a very interesting topic.

Does Phil teach? From start to finish he was throurough and his analogies were perfect. I feel like I could actually make it through a university level physics class if he was teaching. Thank you for the content everyone.

Where’s the physicists’ video?

This episode felt all over the place.

This is so interesting! I love these topics, even thou i dont understand everything, (language but also information wise) i really enjoy information on these Computing limits

"is that not just because we've got 2 inputs and only 1 output"... quite possibly the best question i've heard on any related channel... fantastic

Man I love Prof. Moriarty. He's one of my favorite things about Sixty Symbols and his very rare appearances here are great.

I really love Prof Moriarty, thanks for putting up with what you had to put up with...I really appreciate it.

50-hours video on the Observer's Paradox, I'd GLADLY watch it!

Holy crap. That ending comparing height to the observable universe really set things into perspective.

That accent...

Phil is such a great presenter. I don't care if he has different political opinions; when it comes to science, he's fantastic.

The way Uncertainty Principle works, remind me of the Euler's number (e), and its Compound interest interpretation.

Already my favourite in the series xD 3brown1blue has a nice visual representation of the uncertainty principle through Fourier analysis that relates really well with the guitar string analogy here.

I thumb up every video that sends me to Wikipedia.

Approximately D above middle C, around 277Hz

I loved this presentation and the editing was fun too.

I don't know if anyone had already pointed this out, but 1 FLOP (floating point operation per second) isn't equivalent to 1 bit of operation per seconds used by the MIT paper. Floating point math are complex operation, and there are multiple types of floating point function. 1FLOPS on average roughly translate to 20,000 bits of operation per second according to some paper. So we are five orders of magnitude closer to the fundamental limit than this video suggested at the end. There is also another issue to compare FLOPS with figure given by this paper. Notice FLOPS is per second, While the 10^50 figure isn't divided by time. They simply convert a kilogram of mass into pure energy and calculate how much calculation this much energy can perform. When we talk about Laptop level we usually associated this with its power envelop. Based on some rough calculation from their numbers for a 100W laptop the fundamental limit would be around 3x10^31 FLOPS.

I'm a simple man. I see a video with Prof. Moriarty, I press like.

I'm a physicist and there's no card neither a link in the description. Guess I'm too early.

Love videos with Prof. Moriarty, always super engaging

Got that Paul Davies book when it came out during my physics a-level. Blew my mind.

Assembly language. The only fun way to go.

This probably needs the word RANT in the title...

I don't know if he is correct, but that was an absolutely brilliant way to communicate how far we have to go to reach our computing limit.

"Here’s the fascinating thing: What costs the energy is not the computation itself, it’s erasing information." Phil once again blows my goddamn mind with something that ought to be obvious. I love you, man.

Aww he put 0-0, 1-0, 0-1, 1-1, so not ascending ^^ just kidding, it doesn't change anything for the explanation

The limit is Crysis.

My computer science professor told me that another aspect would limit the speed of computers: The speed of light. If we increase the speed of CPUs more and more, the electrons have to cross the CPU chip in a shorter and even shorter time. At some point, they will reach a physical speed limit (practically not even close to the speed of light), so they won't be able to travel the 2-5 centimetres of one edge of the CPU to the other during that single flop. According to the professor, if we reach that limit, our only chance to further increase computing speed would be parallelization of multiple of those close-to-the-limit chips.

Excellent. Thanks for the clear sense of scale at the end there, even though I know the size of the observable universe doesn't actually fit in my brain except as a symbol.

I don't agree with phils political views either but would you leave the hate out of a video where he's not spouting his political views - its educational there's nothing to dislike about it

I have had my share of problems with Prof. Moriarty's opinions, but this is one case where deleting comments is something I really understand. Drop it, guys, I think we all get it. Move on and watch something else if you can't. He's still a really smart, charismatic guy from whom we can all learn a lot.

This was fantastic, this guy is great at explaining things.

Love this topic so much, it's my life - trying to understand what kind of place I am living in within.

Not exactly the most organized presenter on this channel.

Love seeing you back, as assbackwards as you behaved i still love you and what you do, you made a Christmas tree out of atoms for feck's sake!

Best Computerphile show yet IMHO.

This video was a roller coaster from start to finish

what's with all the negativity towards prof Moriarty?

I like Phil

Perhaps a next video from Phil on Erik Verlinde's theory about gravity being an emergent property of viewing information associated with the location of material bodies in a specific way?

Love this man. Great teacher. Wish I could attend.