E=mc^2, the most famous equation in the world,

describes the fact that anything with mass possesses a huge amount of energy, in principle

– like, a 5kg cat has enough energy in its mass to power the entire country of Norway

for a year – if only the energy could somehow be fully extracted from the cat. But it turns out that efficiently extracting

energy from mass is a very hard thing to do. Anti-matter is, of course, the most efficient

way of extracting energy from mass since, if you collide a cat with a cat made of anti-matter,

100% of the mass of the cat and anti-cat will be converted into energy (powering Norway

for 2 years). But the universe has almost no naturally-occurring

anti-matter, so it’s not a practical choice for generating energy, since you’d first

have to use a lot of energy to make a large mass of antimatter. Since we can’t use antimatter, there are basically

three options left to us: chemical reactions, nuclear reactions, and gravitational reactions

– aka stuff getting pulled together by gravity, like matter falling into black holes. Chemical reactions, for example, are so bad

at extracting energy from mass that we don’t even think about what they’re doing as converting

mass to energy (even though it is). As an illustration, reacting a balloon of

hydrogen and oxygen gases creates a nice big explosion, but the end-products of the reaction

only weigh half a nanogram less than the initial reactants , which amounts to a measly 0.00000001%

efficiency of converting mass into energy. At that rate, you’d need ten billion cats

to power Norway for a year. Nuclear reactions are a lot more efficient,

but still pretty bad on an absolute scale: splitting uranium-235 into krypton and barium

converts only about 0.08% of the uranium’s mass into energy, and fusing hydrogen into

helium like in the sun converts about 0.7% of the hydrogen’s mass into energy. At that rate you’d need 150 cats to power

Norway for a year. This where black holes come in – they’re

about as good as it gets in our universe for extracting energy from mass. Which may sound weird, because, as you’ve

probably heard, nothing can escape black holes – once inside. But the efficiency of black holes comes from

what stuff does while falling towards them, before passing the no-turning-back point of

the event horizon. Anything that falls in a gravitational field

speeds up, gaining kinetic energy, and if it then crashes into something it can convert

that kinetic energy into heat. That heat can then radiate away as infrared

radiation, slightly decreasing the mass of the object. For planets and stars, this conversion of

mass into energy is pretty pathetic: an object falling to the surface of the earth releases

only about one billionth of its mass as energy. That’s basically as bad as a chemical reaction! But black holes have something special going

for them: they are stupendouslysmall. A black hole with the mass of the earth would

be about 2 cm across, providing way farther for an object to fall – and since gravity

gets stronger and stronger the closer you are to an object, objects falling into black

holes get accelerated to ridiculous speeds. Specifically, an object falling all the way

to the event horizon of a black hole will have kinetic energy equivalent to converting

roughly half of its half of its E=mc2 mass energy mass. However, if the object continues to fall into

the black hole, all of that energy will be stuck inside the black hole. The way to actually convert mass into energy

that goes out into the universe is to have the object slowly spiral into the black hole,

crashing into other stuff, heating up, radiating that energy away thereby losing mass and speed,

slowing down more, spiraling to a yet lower orbit, and so on, all the way down to the

innermost possible orbit. And this is exactly what accretion disks around

black holes do! So how good are they at converting mass to

energy? Well, for a non-rotating black hole, the innermost

possible circular orbit is actually 3 times farther out than the event horizon, and in

order to spiral in to that point an object has to convert around 6% of its mass into

energy radiated away to the outside universe. After that point if it loses any more energy

it’ll plunge down into the black hole, after which no more energy can be extracted. But at this 6% rate, you’d only need to

throw 17 cats into a black hole to power Norway for a year. Compared to the 0.00000001% efficiency of

chemical reactions and the 0.7% efficiency of nuclear reactions, 6% for a non-rotating

black hole may seem pretty good. But rotating black holes are even better,

because of how they bend spacetime. They literally “drag” things orbiting

them in the direction of their rotation, which means the innermost possible orbit can be

much closer to the black hole (as long as you’re rotating along with the black hole). The details depend on how fast the black hole

is rotating, but for a very quickly rotating black hole the innermost possible orbit coincides

with the event horizon! And the event horizon itself is half as big

as for a non-rotating black hole. Combined together, this means that matter

falling into rotating black holes can convert as much as 42% of its mass into energy. Or equivalently, you’d only need 2 and a

half inspiralling cats to power Norway for a year. So, if you really want to convert the mass

of an object into energy, don’t bother with chemical reactions, or nuclear fission, or

nuclear fusion: throw it into a rapidly rotating black hole. If you’re wondering how I calculated the

efficiencies of converting mass to energy, you can just divide the energy any reaction

releases by the mass energy of the things involved – for example, when radium radioactively

decays into radon and helium it releases 6.6 MeV of energy, and the mass energy of a single

neutron or proton is about 940MeV, so I’ll leave it to you to figure out how efficient

alpha decay is at converting mass to energy! Or you can learn more about nuclear fission

and fusion by finishing this quiz on Brilliant.org, which is this video’s sponsor and is full

of interactive quizzes and mini courses on physics and math. If you really want to understand physics deeply,

you have to work through calculations and solve problems yourself, and Brilliant offers

an interactive online way to do just that. You can check out their course on black holes

for free using the link in the description, and if you decide to sign up for premium access

to all of their courses, you can get 20% off by going to Brilliant.org/minutephysics. Again, that’s Brilliant.org/minutephysics

which lets Brilliant know you came from here.

## Comments

Author

2:13 Cooper was right! INTERSTELLAR was'nt So dumb!

Author

What if you tripped when you throwing the cat? Have you thought of that? The cat will die of suffocation, and you are converting yourself into pure energy

Author

Guys in Norway stop watching this vid now!! You are killing those lovely cats by consuming electricity!!😢

Author

I need a cat

Author

Whats it with science and cats..

Author

Excellent. Extinction Rebellion -> Feline Extinction "Revolution". Just submit this to Greta Thunberg for approval (you may have convert Norways to Swedens, however).

Author

Then you lose all your energy in the process of capting it and sending it to Earth

Author

It is all very good and well, but how would you collect all that energy from that black hole and convert it into some usable form?

Author

Does that mean that every conversion of energy from one form to another causes the related matter to lose mass? So when I walk up stairs, I'm gaining a tiny bit of mass, and when I inevitably jump out the 50th story window, my shattered corpse on the pavement below will have less mass than when I exited the stairwell on the 50th floor?

Author

Just….

throw it into a black holeAuthor

now do the same thing , but replace cats for humans .

Author

Dude, everything outside IS boring…

Author

I don't think you can see/tell but, I'm rolling my eyes right now…

Author

And I DO NOT CARE…

Author

Go to 4:58

Author

This guy: antimatter is an impractical way to convert mass to energy

Also this guy: just throw cats into a rotating black hole

Author

stop cat abuse

Author

So you're saying we should built a power plant that captures the energy radiated by objects falling into black holes?

Sounds reasonable.

Author

Hawking radiation?

Author

I'll take one black whole … and some cats please.

Ostensibly, the rotation rate of the black hole would also have some effect (beyond merely being rotating or not) – get a faster one.

Author

how if hadron collider is powered by their own produced antimatter?

STONKS

Author

2 minutes silence for all cats that died during these events. May their souls rest in peace🙏🙇♂️🐱🐈🐱🐈🐱🐈

Author

What about pokeballs

Author

Also they did the black hole thing in SOLO: A STARWARS STORY

Author

When your friend says they have problems: 5:16

Author

Is this cat dead or alive or both at same time.

Author

Cats Cats Cats… Everywhere….

Author

So, we’ve heard about cats. What about other animals?

Author

Whoa, whoa, whoa, Henry…

How the hell am I supposed to find half a cat?

Author

Cat Abuse.

10 million cats every 2 years…

60 years later-

all the cats are extinct.

Author

You're so much obsessed with cats!

Author

How can a black hole with the mass of the earth be 2cm big? I mean, how could we possibly know? I thought we only just proved their existence, and the science behind them is still unknown? We don’t actually know what it is, just theories? I am just curious, would love an answer from someone, thanks

Author

The world : We need more power

minutephysics : Cats

Author

Animal cruelty!!!

Why are you using cats?!?

Use flies instead!!

Author

Black holes convert 100% of their mass into energy over time (Hawking radiation), you just gotta wait until Sun goes boom, then wait that amount of time a couple bajillion times

Author

Why Norway

Author

But how do we harness this energy?

Author

WAIT A MINUTE

THAT’S THE FUCKING ANSWER TO THE ULTIMATE QUESTION TO LIFE, THE UNIVERSE AND EVERYTHING

Author

This video is awesome!

Author

There is one frame in there that says : 42 , coincidence, I think not

Author

why cat？what did he do！

Author

¡Superb! Thank you so much 💛

Author

but how do we harness this cat energy?

(Of course, this would be more clear considering we would be a civ capable of going close to spinning black holes and throwing cats to them.)

Author

I knew it. the answer to energy crisis had to be the number 42.

Author

What about colliding matter with strange matter

Author

Why is this so satisfying? Is it the cats?

Author

3:06 – relative to what would the infalling particle at the horizon have a kinetic energy of mc²/2? the local velocity relative to a stationary observer would be c so the kinetic energy relative to a local observer should go to infinity as the limit of r approaches the horizon. the redshifted kinetic energy at infinity would be the local kinetic energy divided by the lapse function, which gives 1mc² in the limit of r=rs, so how do you arrive at mc²/2?

Author

I can't help but wonder but is there even a theoretical way to capture this converted energy ?

Author

explain…-_- there is a sudden flash

4:58

Author

Black holes give 100% of the mc2.

It's called hawking radiation.

Author

The Answer just started to make actual sence right now:)

Author

This man belong to Norway and Hate cats

If you want to power , then power China and India (population )

Author

I hate cats, 7 billion to power a small country for a year? Now thats a power solution i can get behind!

Author

3:30 When matter spirals down into a BH, it actually accelerates. What it looses is angular momentum. Counter-intuititive…. but that's what happens.

Author

So what you're saying is that we need to burn 10 billion cats to power Norway….. got it.

Author

Dude, why did you have to use cats? That's a bit grim

Author

Hmmmmm wait…. Not all energy matter releases is from its mass, that's the case only in nuclear reactions and the like…. Usually the released energy is converted from OTHER FORMS OF ENERGY; e.g. kinetic (e.g. thermal), electrostatic (e.g. chemical bonds), potential energy (related to gravity)! What the hell are you talking about, man? Was I taught physics wrong in school?

I wish I could dislike this misleading, very wrong video more than once!

Author

But when he says the mass is converted to energy and radiated during the black hole spiral what does that mean? What kind of energy? How does the mass reduce?

Author

antimatter discovered and can be harnessed in the future..

cats: sweating

Author

4:58 42 coincidence I think not

Author

This is so fucking matrix

Author

2028: rise of the planet of the cats.

Author

* ludicrous speeds… 😀

Author

But what about the efficency of capturing the released energy, which for the black hole would entail a complete dyson sphere to capture the energy and send it to Norway….

Author

Greetings from Norway!

Author

I’m….. fusion Energy though?

Author

I am from 3542, and I can indeed confirm that we sacrifice 2.5 cats a year to feed Norway.

Author

Instructions unclear, cat became national animal of Norway.

Author

Fuck Norway!!!

I'm not giving my cat to power them for 1 year.

Author

But how do you utilize the energy from throwing stuff into black holes as tangible power for lights/computers/etc

Author

So… that's why 42 is the answer to ultimate question of life, universe and everything 😨

Author

But would collecting the energy ever be even remotely viable? Even in a sci fi sort of future?

Author

Lets burn ten billion cats to power norway

Author

Now where is my cat?

Author

So how about the dyson sphere?

Author

No one:

..

Me: Antimatter

..

..

minutephysics: Enty-matter!!

Author

4:58 If you blinked

You missed the 42% written big on the screen!

If your eyes are sharp

Then you can see

It is written there

"42

Coincidence? I think not"

Author

42

The answer to life, universe and everything

Author

Even after 2 years he can't even get 75k likes but ssundee can do it 200k in 7 hours

Author

As a Norwegian, I can confirm: Norway is powered by cats

Author

Nuclear reactions can have 1 cat power Norway for 2 days, 10 hours and 20 minutes. I did the math.

Author

Did anyone noticed a big 42 at 4:58 if u are not able to see watch it 0.25x

Author

One thing to consider though is how long it takes to make that conversion. Time dilation would be an issue to consider.

Author

Norwegian minister of energy sees his video:

"That's it guys, divert all of our funds into researching svarte hul & katter."

Energy crisis solved.

Author

don't panic

Author

But what does it taste like?

Author

H

E

L

L

O

Author

chuck norris will make black hole into cat

Author

well how do you gather energy from that falling object? surely whatever that process is would be extremely lossy as well if not more so than the other methods?

Author

PETA wants to know your location

Author

I made a catapult and threw 10 cats (I had 12) upwards, hopefully at least one of them will hit a black hole and then I won't have to pay no more energy bills for the rest of my life!!!! Why didn't no one thought about this before?

Author

Top measurements units:

Meters

Yards

Football fields

Texas

CatsAuthor

DON'T burn your cat

throw it into a nuclear reactor

throw it into the sun

BUT do throw it into a black hole

Author

Okay, but how do we harvest the power being released so close to a black hole? The energy might be there, but being able to use it is another thing entirely.

Author

what about micro kugelblitz black holes? due to hawking radiation working exponentially faster at smaller black hole masses, couldn't you just feed a tiny black hole a constant stream of matter and have it basically convert the mass directly into gamma rays? AND get some energy out of the falling as well, seems ideal

Author

Lotta talk about black holes and cats, a lot wrong with that if u ask me

Author

Why are the Norwegians using cats to power their country?

Author

Anyone else pick up on the really quick "42" at 4:58

or was it just me?

Author

What would be the energy requirements for containing the black hole?

Author

2:27 so if light is affected by gravity, it would than mean that light would accelerate faster than light ?