that played Toto in The Wizard of Oz was credited

as Toto, but in reality the dog's name

was Terry. And when Terry died in 1945

her owner and trainer Carl Spitz buried her on his ranch

in Los Angeles. But in 1958

the Ventura Highway was constructed right

through Terry's grave. Her remains were

disturbed and have never been found. Fifty-three years later

a memorial was erected in Hollywood Forever Cemetery

in her honor but because she isn't burried

there, the memorial is not a grave. It's what's known

as a cenotaph, an empty

tomb. I was reminded of Toto's

cenotaph when I saw the cenotaph of Philopappos, atop the Hill of the Muses

in Athens. You see, I was recently in Greece

talking about YouTube with YouTube creators. The

all seen eye of Guy came along and we visited

the Acropolis, a Lion Gate - nearly a thousand years older than the Acropolis.

The earliest known analog computer. Plenty of beautiful

cats and I even took a selfie in

Delphi. I've seen all of these things and

how old they were, it made me wonder how will we

be remembered.

How will future archaeologists react to the ruins of today's

society they find thousands of years from now.

Will they do a good job piecing it

together? Will anything about you in particular

be remembered? And, for that matter,

how do we even know that the past really happened?

Not just the way we think it happened, but it all.

Seriously, can you prove that the universe wasn't created

last Thursday? That everything - every person, every memory you have,

every photo you've taken didn't just pop in into existence

last week or five minutes ago?

Last Thursdayism is the belief that the universe was created

last Thursday. It doesn't have actual

followers or rituals but proving it wrong

is impossible. Not because the universe

actually was created last Thursday but because Last

Thursdayism is not also falsifiable.

It cannot be shown to be false. In the evidence you bring up against it can be

explained away as part of the

everything that was created last Thursday.

Many people believe that in order for a theory

and explanation to be scientific it must be possible

to refute it, to prove it wrong, to test it.

So, instead, Last Thursdayism falls into the domain

of philosophy, where luckily

there are razors - little rules of

thumb that help shave off unlikely explanations.

The most famous is Occam's Razor. When faced with the choice between

explanations,

choose the one that requires diffused assumptions.

Occam's Razor can shave off

last Thursdayism because it requires

fewer assumptions to believe that, say, this beehive

tomb was constructed way back in the Bronze Age

and that I just visited it later than it does to believe that

the tomb, my memories of it and this footage of me

inside it just happen to coincidentally pop into existence at the same time

last Thursday. One of my favourite philosophical razors

cuts off so much stuff it's not even

called a razor. It's called Newton's

Flaming Laser Sword. It states

if something cannot be settled by experiment, then it is not worthy

of debate. So let's move on

to the past. What does Newton's

Flaming Laser Sword tell us about the past? I mean, it doesn't exist in the same

way

gravity or light or protons do. We can't do experiments on it,

build control groups, run trials. The past

just is what it was.

We will one day be the past and no matter how well we try to record

our stories ourselves, without

time machines future archaeologists are going to have to make a lot of guesses

about us.

But that's kinda cool.

Future humans will likely know way more than us today

about medicine, about exoplanets, about physics.

But one thing they almost surely

will not know more about than we do is

today. Will your great great great great grandkids

know your name? Will aliens, who visit Earth

millions of years after humans leave or go extinct,

understand that Animorphs was just

fiction, and not a history of our people?

You are destined to become whatever the future

thinks you were, if you're lucky.

Vandals, fire, natural disaster,

conquerors, thieves, all of these forces obscure facts

overtime, but no matter how well we tried to preserve

today for future history books, there's one type of

fog we are unlikely to avoid.

Apathy. Ira Glass put it well

when he asked his listeners a simple question: name

10 people from the 15th century.

We have records of more than 10 people but to most of us

they don't matter. In five hundred years

radio host will be making the same jokes but about us.

However, there is a legacy leave behind

that is irreversible. Immutable,

and in a way, unforgettable.

To conserve energy, turn off when not in use.

Or just keep them on. Energy will be conserved

no matter what you do. Even if you leave lights on all year,

there will be no less or more energy in the universe.

What's really being conserved when we turn off lights

are the resources we turn into energy

the lights can use. But if you counted up

all the energy in the system, before and after turning the lights on,

it would be the same. Energy also does something else.

Unless hindered from doing so, energy

will spread

out - it will disperse. That is,

in so few words, the Second Law of Thermodynamics.

It's how our universe works. It's why things that happen spontaneously

do. Energy spreads.

Even when a process locally concentrates energy,

like when a crystal forms or life grows,

the Second Law isn't violated because these processes

aren't independent from the larger world around them. They aren't

100 percent efficient. Hindrances can hold back the inevitable spread of energy for a

long time. The Second Law doesn't say

when energy will disperse - just that when it can,

oh it will. Balloons will deflate,

objects will fall, hot objects will cool down,

and perfume sprayed across the room will eventually migrate to your nose

even in really still air. How much

or how widely energy has spread out is measured

in entropy. Entropy is often called

"disorder", "chaos". But entropy is very different from macroscopic

messiness. This deck of cards is

themed after Greek philosophers. It's also arranged by

value and suit - the entire deck. But if I take the deck

and shuffle it, that is, disorder it, I haven't

actually increased the deck's

entropy,

because nothing about this deck of cards'

energy is different than it was before. However,

entropy in the greater world around us

has increased because in order to shuffle the cards

my body has to do work. It has to take energy concentrated in my cells

and change and disperse that energy into kinetic energy,

movement, and a little bit of heat from my body and from the cards,

friction, and a little bit of sound energy - that rustling noise.

So there's your real legacy.

Your contribution to the universe's growing

entropy. No process will be able to

undo the net increase in entropy

you accomplish in your life. History may forget you,

or misinterpret your accomplishments, or what stood for.

The ripples you leave behind may get redirected

but the universe will never be able to forget the

entropy you add. That's the law.

The Second Law of Thermodynamics.

Many scientists believe that this means that eventually

energy - heat - will be completely spread out

evenly throughout the universe. It will be the same temperature

everywhere, and at that point nothing will be able

to happen. Because in order for something to happen

entropy needs to increase, energy needs to spread, the move to change.

This may be the ultimate fate of the universe -

thermodynamic equilibrium. The

"Heat Death" of the universe. It's been estimated that at the rate things happen

this end the universe will occur in about

8 googol years, and you're contributing to it

by simply existing. A funny consequence of all this

is the fact that people who aren't very active, people who don't do much but lay

around

aren't just being lazy. In a way

they're being considerate. Sloth

maybe of vice, but to the universe

it's a fountain of youth. Choosing to do as little as possible

means consciously limiting your contribution

to the inevitable dispersal of energy and thus

in a teeny-tiny way postponing

the "Heat Death" of our universe.

Relaxing adds time

to the universe's life: in amount of time, to be fair, almost indistinguishable

from zero,

but still theoretically real. Being

lazy will make the universe last

longer. So thanks for

chilling out. Thanks for taking it easy. And, as always,

thanks for watching.