Computing Limit - Computerphile

Just how far can we go with processing speed? Physicist Professor Phil Moriarty talks about the hard limits of computing.

This video was filmed and edited by Sean Riley.

[ZipplyZane]

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!

[BergerKing]

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.

[RobinHilton]

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)

[gingerman]

'I have a theoretical degree in physics'

[peterfriedman]

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.

[apacheglider]

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

[luciengrondin]

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.

[fasulia]

I could do with an electrical engineering phile

[chrisjonesowns]

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

[morbid.]

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

[erikwiberg]

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

[flymypg]

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!

[ElagabalusRex]

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.

[enkoid]

"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.

[seanspartan]

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).

[SpikeTheSpiker]

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.

[JustOneAsbesto]

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

[LukeVilent]

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!

[soraaoixxthebluesky]

Teacher: “You there. Explain what Quantum Physics is”

Me: “Hold my acoustic guitar”

[thejumperkin]

"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