Did The Future Already Happen? – The Paradox of Time

00:00:02
Do your past, present and future all exist  right now? Are you watching this video,   being born and lying on your deathbed  at this very moment? Surprisingly,   the answer could be yes. But how can that be?  What does that even mean? How does time work? Imagine the universe like a child painting  pictures on paper. Each picture shows   everything that’s happening in the universe  in a single moment. With each new moment,   all kinds of things occur everywhere – people  are born and die, galactic civilizations expand,   you miss the bus – and our universe-kid makes  a new picture that replaces the old one. In this way you get something like a movie –  only the moment we’re in right now is real.   The past is what happened before, now  it’s gone. The future is still to come   and hasn’t been drawn yet. This is kind  of how time feels, right? Each moment   being replaced by the next one. The past  is far behind us, the future doesn’t exist. But what if time is something else? What if the universe-kid has already finished all  its drawings and stacks them on top of each other?   This way we get a block – a block of time that  contains the whole history of the universe. All   moments that have ever existed or will ever exist.  But in this block, in this stack of moments,   the past, the present and the future are  equally real and exist at the same time. This feels wrong – the only things  that we perceive as real are those   things happening now. How can the past  and future be real right now? The problem   is that according to the theory of  relativity, they kind of have to be.
00:01:51
Heavily simplified, relativity says  that time and space are not separated,   but one connected spacetime. When you move  through space, you are also moving through   the block. This means time passes differently  for different people, depending on how they   move through space relative to each other. And  this also means that what someone perceives as   “now” is a certain cut along the block – a cut  that will depend on how fast they are moving. So what you think is “now” is really only your  now – there are many different “nows” in the   universe and all of them are equally real. This  also means there is no universal past or future. Ok. This is a lot – how does this work? Imagine three alien spaceships a million light  years away. The first one just hovers in space,   not moving relative to you. You  both experience the same “now”,   the same present. If you had a magical  instantaneous internet connection,   you could do a video call right  now and chat about alien things.
00:02:55
The second spaceship is flying away from us at 30  km/s, about 3 times faster than a human rocket.   It is moving differently through the block of  time than you are, which means its “now” is   different from yours. With the magical internet,  the aliens can talk to your ancestors in 1924,   when humanity was discovering the  first galaxies outside the Milky Way. The third spaceship wants to visit Earth  and is flying towards you at 30 km/s,   moving at the opposite angle of the  second ship through the block of time.   It experiences yet another “now” – with the  magical internet, the aliens can talk to your   descendants in the year 2124, when humanity  has already built cities on Mars and Venus.
00:03:37
Ok, so we have three different “nows” – so  which one is correct? Well, that’s the problem.   Relativity is based on one powerful principle  – cosmic democracy: the fact that the point of   view of all observers in the universe is equally  valid. All those “nows” have to be equally real.   But if this is the case, your past, present and  your future all have to exist at the same time,   right now! Because for the different  aliens, they all happen in their present. This means that the distinction between  the past, the present and the future is   an illusion. The universe is not a bunch  of things evolving through time, like in a   movie – but a static block in which the past, the  present and the future all coexist and are real. How can that be? Well, think about a  galaxy outside the observable universe,   too far away to ever visit or see. But even  if you can’t get there and don’t see it,   it is still real. The future might be the same! But if the past is not far behind us and the  future actually exists, then… there is no   “movie”. Things don’t happen in the universe. The  universe just “is” – like a frozen block of dead,   cosmic ice, with everything that will  ever happen already written and decided. Is the Future Already Written? If all times coexist and are equally real,  then the future has to be already written. But that’s not how you experience things. It  feels like you can mold your future with your   decisions. It really feels like you’re free to  choose to stop watching YouTube to not miss the   bus. But if the future is set in stone, you  can’t “decide” anything. So are your choices   an illusion? Well… maybe. Maybe your free  will is a mirage. And maybe you missing the   bus was already predetermined at the Big  Bang, so feel free to continue watching. Except…quantum stuff is  ruining everything again.
00:05:42
Quantum processes can’t be predicted, not even in  principle. Not because we are silly and don’t know   how to do it – according to quantum physics,  quantum particles are intrinsically random. For example, if you have a radioactive  atom, it could decay at any moment,   in the next second or in the next  million years. We can calculate the   probability that it will decay tomorrow,  but no oracle in the universe will ever   be able to tell you with absolute  certainty if it will do so or not. But quantum particles can change the world.
00:06:14
Imagine a radioactive element randomly decays and  causes a genetic mutation in a nearby mammal. And   then many generations later that mutation  has led to a weird mix of duck and mammal   that makes no sense. Or the atom decays a day  later and the weird creature will never exist. If quantum stuff is really uncertain, the  future can’t be set in stone. But if the   future is an untold story, it can’t be  real in the same way as the past is. So what happens when uncertain  things, like the decay of our atom,   become real? Is that moment the present? Is  this “now”? But before we saw that cosmic   democracy makes it impossible to define  an absolute “now”. What’s going on here? It turns out that for every individual  object – you, an alien, an atom – the past,   the present and the future are always  well defined. Your death will always   happen after your birth – never before, and  never at the same time. Now you are clearly   between your birth and your death. So for  you at least, “now” makes perfect sense. If we don’t play tricks like going to the  other side of the universe and using aliens   in funny ways to find out what “now” means,  things again start to look ordered and nice,   and individual “nows” seem to exist.  Can we do something with them? Let’s return to our block universe. Maybe the  block does not contain the future – and maybe   we just imagined it wrong. Maybe the block is just  the past, and a thin layer on the surface is the   present. That surface is not smooth, but bumpy  and uneven. It’s been made by joining countless   individual “nows” – each experienced by  someone or something in the universe,   each equally real and valid. And all observers  do their bit, so cosmic democracy is still true. As new things happen and uncertain things  become certain –radioactive atoms decay,   new species of mammals arise, people  miss the bus– the border moves upward,   creating new time in the universe.  Instead of a frozen block of time with   a future that has already been written,  the block is growing and things happen.   You can again decide your future! Maybe  leave earlier so you won’t miss the bus! Let’s recap. We started with time as  a movie – one “now” after another,   where only the current “now” was real. Then  we found out that because of relativity there   are multiple “nows”, all of them real somehow –  which could mean that we are living in a frozen   block universe where things don’t happen and  you don’t really have free will. And we ended   up with a kind of growing block universe,  where time passes and the future is open.
00:09:03
So which is correct? What is real? The present?  The past? Are the dinosaurs as real as you are   right now? What do the aliens on the other  corner of the universe think about all this? To be honest, no one knows. What we’ve learned  are two possibilities to describe time, but   they’re not the only ones. Some scientists think  that the idea of “now” only makes sense near you,   but not in the universe as a whole. Others think  that time itself doesn’t even exist – that the   whole concept is an illusion of our human  mind. And others think that time does exist,   but that it’s not a fundamental  feature of the universe – rather,   time may be something that emerges from a deeper  level of reality, just like heat emerges from the   motion of individual molecules or life emerges  from the interactions of lifeless proteins.
00:09:56
We could go on, but… aren’t  you about to miss the bus? The concept of time is abstract and  elusive, possibly beyond complete   human comprehension. Fortunately, there’s a  vast world of things we do understand about   the universe that you can explore right now  — thanks to our friends at Brilliant.org.
00:10:19
Brilliant has thousands of bite-sized,  hands-on lessons in science, math,   technology, and beyond. Their latest  course, “Introduction to Probability,”   offers a practical guide to interpreting the  world. You’ll master the tools of chance,   risk and prediction while learning to model  real-world situations and running simulations   of everything from election results to who  will win the next World Cup. They even have   a lesson on “The Past and Future,” where  you’ll explore how past outcomes may not   reliably forecast future events in  the ever-evolving tapestry of time.
00:10:53
And since it’s always a good time to learn  we’ve created an entire series of lessons in   collaboration with Brilliant to take your  scientific knowledge to the next level.   These lessons let you further explore  the topics in our most popular videos,   from rabies and mammalian metabolism  to climate science and supernovae.   Think of each one as an interactive,  one-on-one version of a kurzgesagt video. To get hands-on with kurzgesagt lessons and  explore everything Brilliant has to offer,   you can start your free, 30-day trial by signing   up at Brilliant.org/nutshell.  And for kurzgesagt viewers:   the first 200 people to use our link get 20%  off an annual membership once their trial ends. Our shop has grown so much over the years,   thanks to all of you! Now it’s time to move  our precious products to a bigger warehouse! But should our tiny birbs really have to  carry all those boxes? No! Help us out   and grab a box in our biggest sale ever! But first, we’ll give you a little tour:  Here you can see how our posters are actually  created. And this is how our enamel pins are made.  But watch out – there are some pretty  creepy and dangerous things in here as well! And this is where the deals are crafted. They  will only be available for a short time and   as long as supplies last, so head over to the  shop now. The birds really appreciate your help!