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00:00 Time is one of the greatest mysteries of the universe.
00:03 Events move in a sequential string, flowing from the past into the present and gliding
00:08 into the future.
00:09 For millennia, we have built our lives around the transitions between day and night and
00:13 from season to season.
00:15 Human beings first started to measure time in around 1500 BCE, using sundials in ancient
00:20 Babylon and Egypt.
00:22 But we only measure time.
00:23 We didn't invent it.
00:25 This is Unveiled, and today we're answering the extraordinary question; when did time
00:29 start and how will it end?
00:33 Do you need the big questions answered?
00:35 Are you constantly curious?
00:37 Then why not subscribe to Unveiled for more clips like this one?
00:40 And ring the bell for more thought-provoking content!
00:44 From our perspective, time is an arrow that flies in one direction.
00:48 Cause and effect exist in a seemingly irreversible sequence from past to future.
00:53 We can remember the past, but with the exception of alleged seers and soothsayers, cannot remember
00:58 times yet to come.
01:00 Ancient Greek philosophers endlessly debated the origins of time.
01:04 Aristotle defined it as movement and change.
01:07 He argued that it could not have had a beginning because for something to begin, there would
01:11 have to have been a time beforehand when it didn't exist, which is self-contradictory.
01:15 Later, Christian theologians tackled the issue and came to the opposite conclusion.
01:20 St. Augustine believed in a god that superseded space and time.
01:24 A truly infinite creator like the Christian god could create existence and time out of
01:29 the void.
01:31 When considering what God did before the first day, Augustine replied that since God created
01:36 time, there simply was no before.
01:40 Hundreds of years later, Albert Einstein pushed the debate forward with his theory of special
01:44 relativity.
01:45 He discovered that time is relative to the observer.
01:48 For example, if two observers are moving relative to one another, the one who's moving at a
01:52 higher velocity will experience time as passing more slowly.
01:56 So, if you launched off in a spaceship at high speeds and returned to Earth, less time
02:01 will have passed for you than for everyone else back home.
02:04 The more one accelerates towards the speed of light, the more pronounced this time dilation
02:08 gets.
02:09 Using decades of space observations, physicists then built on Einstein's work, tracking the
02:15 origins of the universe back to an infinitely dense point known as the singularity.
02:20 The universe as we know it expanded in an event colloquially called the Big Bang, a
02:25 period of rapid cosmic inflation.
02:28 And so, according to this theory, time began at the same time as our universe did, between
02:33 13.7 and 13.8 billion years ago.
02:37 As such, the Big Bang has generally been considered to be the likely source of both the universe
02:41 and time for almost a century.
02:43 And asking "what came before the Big Bang?" is like asking "what's south of the South
02:48 Pole?"
02:49 You lack an adequate frame of reference to answer the question.
02:52 Even the famed physicist Stephen Hawking dismissed the question's relevance in his book, A Brief
02:56 History of Time.
02:58 He contended that even if time existed before the Big Bang, there's literally no information
03:03 from that time frame to observe.
03:05 It would have no effect on the universe as it exists now, and therefore the problem is
03:09 effectively meaningless.
03:11 But that may no longer be an entirely accurate assessment.
03:14 As technology advances, astronomers and cosmologists are able to take ever more detailed measurements
03:20 of the cosmos.
03:21 Today, we've learned that extrapolating backwards to a singularity may be the wrong approach.
03:27 Since the 1980s, scientists have been able to take incredibly accurate readings of the
03:31 cosmic microwave background radiation, the CMB, the afterglow of the Big Bang itself.
03:37 The patterns and magnitudes of fluctuations in the CMB can act as both cartographer and
03:42 historian of the universe.
03:44 One of the many things we can extrapolate from cosmic radiation was whether or not there
03:48 was a maximum temperature in the early stages of the universe.
03:52 According to data accrued by NASA's Wilkinson Microwave Anisotropy Probe and ESA's Planck
03:57 Space Observatory, there was a temperature cap.
04:00 Their observations indicate that the universe never reached a temperature higher than 10
04:05 to the 29th power Kelvin.
04:07 Why does that matter?
04:08 What does that have to do with time?
04:10 While 10 to the 29th power Kelvin is very hot, it's more than 1,000 degrees cooler
04:15 than the temperature equated with a singularity.
04:18 And that casts into doubt whether we can extrapolate from the Big Bang to a singularity.
04:22 Moreover, it tells us that there actually may have been a before the Big Bang, after
04:27 all.
04:28 So, what could have caused the rapid expansion of space that created our universe, instead?
04:32 And wouldn't the gravity of ordinary matter have slowed that expansion?
04:36 Well, some physicists believe that this spurt of inflation was due to a quantum field containing
04:40 a massive amount of potential energy.
04:43 Potential energy, when compared to kinetic energy or rest mass, causes gravitational
04:48 repulsion.
04:49 This quantum field hit the gas on inflation and helped cause the Big Bang.
04:53 There are two theories that account for this.
04:56 One is called loop quantum gravity, which is linked to a cosmology in which the universe
05:00 bounces between contraction and expansion.
05:03 The other, which is more familiar to most people, is string theory.
05:07 String theory is an incredibly complicated notion.
05:10 In short, it suggests that instead of point-like particles, the universe may actually be composed
05:16 of one-dimensional strings.
05:18 What we see as a particle is actually just a string vibrating with a unique frequency.
05:23 And though string theory began as an explanation for the interactions of particles like protons,
05:28 it has now evolved into a potential theory of everything - a unified theory of physics.
05:34 Once particle theory makes way for vibrating strings, new properties appear and reveal
05:39 interesting possibilities.
05:41 And with regards to time, specifically, string theory proposes that the Big Bang was not
05:46 the origin of our universe.
05:47 Instead, it did come about as a result of what existed before.
05:52 As the father of string theory, Gabriele Veneziano, put it in Scientific American, quote, "String
05:58 theorists expect that when one plays the history of the universe backward in time, the curvature
06:03 of spacetime starts to increase.
06:05 But instead of going all the way to infinity at the traditional Big Bang singularity, it
06:11 eventually hits a maximum and shrinks once more."
06:15 End quote.
06:16 In this scenario, it may be the case that the Big Bang wasn't the beginning of time.
06:20 Instead, it may just represent an immeasurably energetic transition from acceleration to
06:25 deceleration.
06:27 In Veneziano's pre-Big Bang scenario, the pre-Big Bang universe was almost a perfect
06:32 mirror image of the post-Big Bang one.
06:35 This means that if our future spills out into infinity, so does our past - which then means
06:41 that there is no beginning of time, and no end.
06:44 But this is entering territory where physics as it currently stands fails us.
06:49 The nature of inflation wipes out what happened during its earliest stages, leaving us without
06:54 any data to go by.
06:55 As of now, we are only able to make educated guesses at the origins of time.
07:00 Is there such a thing as time's end, however?
07:03 In some ways, the continuation or cessation of time is relative to your place in the universe.
07:09 For example, time needn't perish everywhere all at once.
07:12 There may therefore already be places in our universe where time has ceased.
07:17 According to relativity, for example, the time dilation of a hypermassive black hole
07:22 could get so extreme at its core that time may well expire altogether, all the while
07:27 it marches on and on outside of it.
07:30 So, finally, when it comes to the question of "will time end everywhere?" we similarly
07:35 enter the realm of speculation depending on the possible ultimate fate of the universe.
07:40 Some researchers in the field of quantum gravity believe that time stretches on infinitely
07:45 with neither beginning nor end.
07:47 The universe, they say, always was and always will be, with events like the Big Bang just
07:52 marking massive transitions.
07:54 Others point to possible endings of the universe as marking the end of time, as well.
07:59 Based on the universe's rate of expansion and mass, many scientists believe that it
08:04 will continue to expand forever, leading to heat death or a "Big Freeze".
08:10 In this scenario, we could see time slowly lose its properties.
08:14 The Oxford physicist Roger Penrose, in his book Cycles of Time - An Extraordinary New
08:19 View of the Universe, paints a picture reminiscent of Salvador Dali's Persistence of Memory.
08:25 Though you could tell the chronology or order of events, duration would lose meaning.
08:30 Time, like matter, would expand infinitely until it essentially vanished altogether.
08:36 Then again, while it isn't the favoured theory, if there is enough mass in the universe
08:41 to eventually slow and stop its expansion, it could end in a "Big Crunch", collapsing
08:46 into a new, hot, dense state.
08:49 If so, a "Big Bounce" could be what follows next, resulting in time ceasing and restarting
08:54 - much as it may have with the Big Bang all those years ago.
08:59 Theologians and philosophers have debated the origins and nature of time for thousands
09:03 of years.
09:05 Science and cosmology eventually came along to support or debunk those notions.
09:10 Is time an arrow that flies in one direction?
09:13 If so, does it eventually hit a target, or does it fly forever?
09:17 Or is time a cycle that starts and stops with the birth and death of a universe?
09:22 We don't have a definitive answer, and may never find one.
09:25 But theoretical physics has come a long way over just the last century.
09:30 Many hope that we may develop the answers… in time.
09:34 What do you think?
09:35 Is there anything we missed?
09:37 Let us know in the comments, check out these other clips from Unveiled, and make sure you
09:41 subscribe and ring the bell for our latest content.