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  • Hey, Vsauce. Michael here. The dog

  • 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