Dark matter and dark energy are locked in an epic battle for control of the cosmos, and the winner will determine the fate of the universe; new discoveries might reveal which force will emerge victorious.
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LearningTranscript
00:00Across the universe, an endless war rages.
00:11A bitter struggle between invisible forces.
00:15We've seen this cosmic battle go on for the past 14 billion years.
00:20Like two navies fighting it out in the ocean of space-time.
00:25Dark matter and dark energy.
00:28Battling for control of the universe.
00:32They've shaped the entire history of the universe.
00:35They're not about to stop now.
00:38Shadowy forces dictating our past, our present, and our future.
00:44The dark universe is kind of a puppet master behind the scenes, guiding the universe that we can see.
00:50It's taken over the universe, and eventually it may well destroy the universe.
00:58As we look out across the universe, we see nebulas.
01:21The dark universe is a very common phrase to describe our universe,
01:51and it turns out most of our cosmos is dark.
01:56Dark not as in night.
01:58Dark as in doesn't interact with light.
02:01And dark as in we don't really understand it.
02:04All the objects in our daily experience, our bodies, the air, the chair that you're sitting in, the planets and stars,
02:13all of that only adds up to 5% of the universe.
02:19It's the other 95% that is the dark stuff, the dark universe.
02:23The dark universe is made of two forces.
02:31Dark matter and dark energy.
02:36In a way, the dark matter and dark energy sort of oppose each other.
02:43Dark matter has positive gravity that pulls things together.
02:47And dark energy has repulsive gravity that pushes things apart.
02:52To encapsulate that in one sentence, dark matter is attractive, dark energy is repulsive.
02:59Since the dawn of time, two forces slugging it out for control of the universe.
03:05Dark matter and dark energy are locked in this epic struggle.
03:08The dark matter is trying to bring things together.
03:11The dark energy is trying to drive everything apart.
03:13So it's basically a battle.
03:16Who's going to win?
03:21It's a struggle that started 13.8 billion years ago.
03:26In the cosmic furnace of the Big Bang.
03:31The infant universe was a super hot ball of intense radiation.
03:36But suddenly, it started to transform.
03:41It cooled and expanded.
03:43Triggering the birth of the regular universe.
03:47And the dark universe.
03:50Scientists believe that both dark matter and dark energy formed in the first moments of the Big Bang.
03:58It would have formed probably just fractions of a second after the Big Bang.
04:03Around the time that normal matter formed.
04:06And the processes that created the normal matter we know all about.
04:09Similar processes probably created the dark matter.
04:13During these first microseconds, the universe was a hot, dense ball of matter and energy.
04:21They're two sides of the same coin.
04:25Matter can convert into energy.
04:27And energy can convert directly into matter.
04:32Visible particles of regular matter forming atoms, planets, stars, and us.
04:39And other particles.
04:42They are invisible.
04:44They are dark matter.
04:46One of the big mysteries that we as astronomers have to solve is what this dark matter is.
04:52We just don't know.
04:55The idea of a type of matter that you can't see and that acts differently than normal matter is sort of out there.
05:01It's sort of weird.
05:02But the dark universe does leave clues.
05:08It's like a crime scene.
05:09You know that a crime has been committed even though you don't know the perpetrator yet.
05:15We see the hints.
05:17We see the signs.
05:18We see the signals that something funny is happening in our universe even though we don't know exactly what's causing it.
05:26There are several contenders for what dark matter could be.
05:30It could be normal matter that we just don't see.
05:34Or it could be some sort of exotic matter, a particle of some sort that we haven't detected yet.
05:39It could be a species of particle like an electron, like a proton, like a quark, but a special kind that doesn't interact with light.
05:52One of the favorite possible models of dark matter are WIMPs, weakly interacting massive particles.
05:57WIMPs may not interact strongly with other matter or light, but they do exert a gravitational pull.
06:08So they're the best candidates for the particles of dark matter that formed in the Big Bang.
06:13The early universe was intensely hot and dense, full of new particles of both visible matter and invisible dark matter.
06:26Dark energy has existed since the time of the Big Bang.
06:37Dark energy was always there.
06:39We don't know how much of it there was, but it's possible that the same amount of dark energy was always there.
06:45Our understanding of what that dark energy is, is very limited.
06:53If you were to ask a room full of ten theoretical physicists on the nature of dark energy, you'd get about twelve different answers.
07:01We're not sure what dark energy is.
07:05Dark energy is just a fancy name for our ignorance.
07:08Dark energy is nothing more than a placeholder name for this enormous gap in our understanding of how the cosmos works.
07:16But we don't understand it at all.
07:19That's true.
07:23One potential answer to what dark energy actually is may be found in so-called empty space.
07:31Could this be the source of dark energy?
07:34We used to think of space as just boring emptiness, but now I think it's healthier to think of space as a kind of substance.
07:44A substance that carries a strange type of energy.
07:48Every small region of space has a little bit of energy in it, just associated with the vacuum itself.
07:55Vacuum energy is the idea that vacuum isn't empty, that there's something there, there's an energy in it.
08:01It's a kind of anti-gravity.
08:06Perhaps this vacuum energy that pushes against gravity is the mysterious dark energy?
08:15We simply don't know.
08:19We're not sure that the dark energy is the vacuum energy.
08:23It could be a new type of energy that permeates all of space.
08:27This is what we're trying to measure now.
08:29Dark energy and dark matter forged in the intense heat of the Big Bang.
08:37Opposing forces, one attractive, one repulsive.
08:42But together, over 13.8 billion years, they will shape the history of the universe.
08:59The story of the universe is dominated by two powerful opposing forces.
09:15Dark matter and dark energy.
09:18For 13.8 billion years, they've battled it out for control of the cosmos.
09:24Dark matter and dark energy are out there, and they've shaped the entire history of the universe.
09:30Our universe is actually the balance between dark forces.
09:33Dark matter is trying to draw everything together, and dark energy is trying to rip everything apart.
09:39After the Big Bang, the infant universe was small.
09:44Intensely hot.
09:45Dark matter, the force bent on bringing things together, thrived.
09:55But in this compressed space, dark energy, the force trying to drive things apart, had no room to act.
10:02When things were closer together, the density of matter and radiation was bigger, so big that the dark energy didn't matter.
10:12The environment was also tough for normal matter.
10:17It was so hot, intense radiation prevented visible matter from bunching together to form atoms.
10:24If any normal matter tried to clump together through gravity or some other force, this energy would just basically blast it apart.
10:32In the very early universe, when our universe was a lot smaller and a lot hotter and a lot denser, matter, normal matter, tried to collect together.
10:41Wanted to join the party.
10:43But it was prevented from doing so because there was also radiation that would throw it out.
10:48Unable to stick together, normal, visible matter sped out across the infant cosmos in a blizzard of particles.
11:00But then, dark matter, the force that brings things together, intervened.
11:07Dark matter doesn't talk to radiation, doesn't talk to light, can do whatever it wants.
11:13It starts clumping together.
11:14Radiation pushes normal matter apart, stopping it from forming dense regions.
11:22But photons simply pass straight through the dark matter, allowing it to clump and fall into dense pockets or wells.
11:32The dark matter begins to clump together gravitationally.
11:37And this means that the matter is going to fall into those dark matter wells.
11:41Over time, more and more regular matter is pulled into the dark matter wells.
11:48The regions that have a little bit more stuff, gravity makes them bigger.
11:52And the regions that have less stuff, those expand more.
11:55So you have little pockets of slight extra matter, have more and more and more matter over time.
12:01Gravity-rich pockets of dark matter pull particles of regular matter together.
12:10Gradually, they form giant clouds of hydrogen and helium gas.
12:16Dark matter has laid the foundation stones of the cosmos.
12:20This force may be dark, but it's highly creative.
12:28And now, 180 million years after the Big Bang, everything is in place for the next dark matter construction milestone.
12:38The creation of stars.
12:41We know stars in the very early universe at the edge of time had to form from the collapse of gas clouds under their own gravity.
12:53But there's a problem.
12:55The clouds of hydrogen in the infant universe can't collapse.
13:00And no collapse means no stars.
13:03The gas in the early universe has a lot of pressure.
13:07And this pressure keeps it from collapsing.
13:09The dark matter doesn't experience that kind of pressure.
13:12So the dark matter can clump up and make sites for structure formation.
13:17So dark matter comes to the rescue, creating regions of higher gravity.
13:23Dragging in hydrogen gas, forcing the clouds to get denser and denser.
13:28Creating the conditions for collapse, and then creation.
13:40So it's only when the gravity of the dark matter overwhelms the pressure of gases, that the gases can collapse and turn into stars.
13:50As soon as the gas cools down, it can fall into those potential wells that the dark matter created.
13:55Almost like little nurseries for stars, and they start forming in earnest.
14:02Dark matter provides a boost of gravity to kick-start hydrogen into constructing the first stars.
14:10Stars that are the seeds of the first galaxies.
14:14So it's dark matter that would have coalesced in the early universe and grown from there.
14:20And then the luminous component of the universe, the things that we think of as being the universe itself, like stars and galaxies, would have just been along for the ride.
14:29Without the presence of dark matter to seed structures, there wasn't enough time in the early universe to form galaxies.
14:39Which means you and me have to thank dark matter for our existence.
14:45And dark matter now begins a much more ambitious architectural project.
14:52To shape the entire universe itself.
14:56To build the biggest structure ever constructed.
15:00The Cosmic Web.
15:01The Cosmic Web.
15:09The Cosmic Web.
15:11The Cosmic Web.
15:20The Civilian War between dark matter and dark energy has been raging since the birth of time.
15:29But in the early years,
15:31it's a one-sided contest.
15:33in the early universe the only thing that really mattered was the dark matter and the normal matter
15:39dark matter the force that brings things together is in the driver's seat
15:51dark energy the force that pulls things apart is the underdog we've seen this cosmic battle go on
15:59for the past 14 billion years fortunately for us the dark energy got off to slow start
16:06meanwhile dark matter is busy at work building the universe not only does it trigger the birth
16:14of the first stars it embarks on an even more formidable construction project the cosmic web
16:24there's this large scale structure of filaments that galaxies seem to form on and that's what we
16:33call the cosmic web and we can trace the formation of this cosmic web all the way back to the early
16:40universe now this is such a huge structure we don't think there's time in the universe for
16:45matter's gravity alone to do this there must have been an underlying scaffold of dark matter
16:51the dark matter started forming into these filaments and when the universe cooled enough
16:55normal matter could start to stream into this gravitational attraction of the dark matter
17:00that became the scaffolding on which this large-scale structure was built the filaments of dark matter
17:07joined together drawing in more and more hydrogen gas dense clouds of gas build up at the junctions of
17:15the filaments the point where gravity is at its strongest
17:23slowly and surely a familiar looking structure starts to take shape if you've ever gone outside
17:30and you can see a spider web covered in dew that's kind of like what happened with the universe in this
17:37case the spider web is the structure of the dark matter it's all of these filaments and the moisture in
17:43the air is what condenses around them just like the normal matter fell into the dark matter web to
17:49form these gigantic structures in the universe dark matter the universe's master builder succeeds in
17:56stitching together a cosmic web this will be the framework for the entire universe and so it is dark
18:05matter that would choreograph and sculpt the shape of the universe itself one of the amazing things about
18:11dark matter is without it we wouldn't be here it's hard to imagine how you could have structure in
18:17the universe without dark matter galaxies and then galactic clusters form at the junctions of the filaments
18:25slowly but surely the universe begins to take shape when we look at this structure over a cosmic scale
18:33we see that it looks kind of like a sponge you see voids with galaxies all over the edges of them
18:39that is the structure that was formed by the dark matter in the early universe dark matter is the
18:46thing that enabled that that provided enough gravity for the initial seeds of structure formation to
18:52coalesce for galaxies themselves to form and of course without galaxies there are no stars and there's no
19:00planets and there's no us for nine billion years dark matter orchestrates the construction of the universe
19:10in these the first battles of the cosmos this constructive force is the clear victor
19:17for the time being the dark matter has won galaxies continue to form clusters of galaxies are getting
19:23bigger over time but dark matter's success in building up the universe sets in motion its potential downfall
19:37as the cosmic web evolves into a more complex structure
19:44gaps form between the filaments the cosmic voids
19:48the cosmic voids formed because other more dense regions of the universe gravitationally stole material
19:59away from them so the dense parts of the universe accumulated more matter at the expense of the less dense
20:06parts which then became voids and lurking in these voids dark energy since the dawn of time it's been waiting
20:17for its opportunity now it's preparing an offensive that may help it conquer the universe in the very
20:26earliest times the dark matter dominated everything it was the big brother pushing the little brother
20:32around but in the long run the dark energy is going to overpower dark matter and so the relationship
20:38is entirely flipped we used to think the fate of the cosmos itself depended on dark matter and it turns out
20:46that's not the case at all the fate of the universe depends entirely on dark energy
20:52the long reign of dark matter may be coming to an end dark energy the great destroyer is hoping to
20:59take control this destructive force has one overriding aim to tear the universe apart
21:16our universe is at war a relentless conflict between dark forces for the first nine billion years
21:35dark energy is subjugated dark matter has the upper hand
21:40the universe emerged from the big bang the dark energy played no role it was insignificant
21:50but at some stage in the 14 billion years since the big bang these roles became reversed dark energy came
22:00to be the more powerful force the question was when the answer came at the end of the 20th century
22:09so it was a an amazing breakthrough really important in 1999 scientists measure the expansion of the universe
22:18what they find shocks them they expect the speed of expansion to be decreasing
22:28in fact it's actually increasing and getting faster all the time
22:34the data indicate that for about the first nine billion years it was slowing down but then
22:40in the past five billion years it started accelerating faster and faster alex filipinko was part of the
22:48team that made this explosive discovery it befuddled us this isn't how nature was supposed to be behaving
22:57and in fact initially we thought that there was something wrong with either the observations or the measurements
23:03i didn't believe it for the longest time when the first data came out i'm like i don't believe this no way
23:09but it's it's in the data it's there you can't escape it this is as shocking as if you held up a rock
23:16let go of it and it went up into the air
23:21five billion years ago galaxies started moving apart faster than before the question is why
23:28what could be causing that well one thing is clear it must be getting some extra energy from somewhere
23:36there is one main contender for what may be supplying this extra energy a force with repulsive
23:43gravity a force that pushes things apart this is what astronomers call dark energy it's this mysterious
23:51repulsive force that we know exists in the universe and we have no idea what it is
23:58physicists may not agree on what dark energy is but there is a consensus on where this repulsive force
24:05has the most influence in the regions between galaxies and galaxy clusters the cosmic voids
24:15they're actually filled to the brim with dark energy the first time dark energy is really going
24:21to make its mark in the universe is going to be the time when the first cosmic voids begin to appear
24:28we see dark energy's effects throughout the universe but when we look into the cosmic voids which are the
24:37most empty regions of our universe this is where dark energy is strongest
24:42dark energy is the repulsive force pushing things apart it prefers the voids where gravity is weak
24:54these are areas where there's a lot less dark matter and because the overall density is low
24:59that's where the dark energy starts to peak out and can really drive those voids to expand so the
25:05expansion and acceleration of the universe are driven by the dark energy in those regions
25:11dark energy pushes things apart things that get in its way things like the cosmic web
25:21dark matter and normal matter are also in its path
25:25and are bulldozed out across the cosmos slowly but surely the balance between dark energy dark matter
25:36is changing
25:39imagine you have a giant swimming pool and at the very bottom there's a puddle of water
25:44with a splash of whiskey so you have sort of a strong whiskey drink down at the bottom of your pool
25:49but now you start dumping water into your pool no more whiskey and it begins to get diluted and
25:54diluted and eventually you just have a swimming pool full of water with one shot of whiskey mixed in
25:59that's not a very strong drink it's basically a water swimming pool that's pretty much happening with
26:04the dark energy at first it's a one-to-one mixture of dark matter and dark energy but in the long run
26:10it's all dark energy and pretty much no dark matter left over
26:13the forces of dark energy are on an unstoppable march picking up more and more power from the vast
26:23scale of the cosmic voids dark energy is intrinsically very weak there's very little dark energy and this
26:31repulsive effect in every cubic centimeter but the universe is vast space is big
26:37so cumulatively all this small amount of stuff adds up to a very large amount and over a scale
26:47encompassing the entire universe the dark energy dominates
26:50but it's been a very long process after the big bang dark matter dominates for the first nine
27:00billion years
27:03then five billion years ago dark energy starts to get the upper hand it causes the expansion of the
27:10universe to accelerate and the space and the voids to grow more rapidly as this space expands there's
27:19more and more dark energy because you have a bigger space it sort of creates itself with the expansion of space
27:26dark energy has a sneaky way of taking over because it causes the space to stretch out and get twice
27:32as big so now there's twice as much dark energy dark energy just can't stop pushing causing the empty space
27:41of the voids to continuously expand as the universe expands because of dark energy more and more dark
27:51energy is being created dark energy is definitely gaining the upper hand on dark matter it was always
27:57there but it took over compared to other stuff eventually creating enough energy to supercharge the
28:06expansion of the universe
28:11this acceleration continues the universe is getting bigger and bigger and it's all powered by the
28:17forces of repulsion dark energy and for the universe that could be very bad news if that's the case dark
28:27energy may destroy the universe it will get stronger and stronger until it literally rips apart the fabric of
28:34space-time
28:50dark matter and dark energy have been battling each other for 13.8 billion years for the first 9 billion years
28:58dark matter dominates dark matter exerts positive gravity but pulling everything together leads to one
29:08inevitable outcome if the universe was totally dominated by matter eventually our expansion would
29:15slow down glide to a stop and then turn around and collapse into a small dense state from where it came from
29:25an event we call the big crunch during the big crunch gravity would play havoc with the cosmos
29:34galaxies would be dragged together stars and planets would smash into each other the universe would collapse
29:44in a blazing inferno of super dense matter and energy
29:53fortunately none of this will probably happen
29:59scientists have now dismissed the possibility of a big crunch
30:06we don't face that because we have a universe filled with dark energy
30:10dark energy is causing the universe to do something else something it would prefer not to do it is
30:17accelerating the expansion of the universe as dark energy gets stronger it supercharges this expansion
30:26the presence of dark energy is like a high octane additive into a gas tank where a car isn't just coasting
30:37along it's boosting along it's boosting along and that's what's happening with our universe
30:43if that's correct this supercharged expansion will continue for the next few billion years
30:50the repulsive force of dark energy will become invincible and such unbridled power will come with a high cost
30:58the universe is the universe is the universe is the universe is the universe is the universe is the
31:08infinity stones in the hands of sir thanos but those two are make-believe the real one is dark energy
31:15it's the real ultimate universe destroyer
31:20the universe may pay the ultimate price for this ever-increasing expansion driven by dark energy
31:27and if that continues forever the future of the universe is very very simple it continues to expand
31:34to accelerate everything moves apart from everything else and the universe becomes empty
31:41there'll be nothing left but cold desolate empty space forever
31:47dark energy will finally win the long war with dark matter
31:52but the result won't be pretty this future universe will be cold dark and empty eventually it's going
32:01to get so cold that really nothing can happen in it it's the big chill it gets colder and colder and
32:08darker and darker everything will fade out and though it began with a bang it's going to die in a whimper
32:15the universe flat lines because of dark energy the universe dies in a big chill galaxies are so far apart
32:25they're distant islands in a sea of darkness gradually the galaxies die too star birth stops and the universe fades away
32:36or maybe not there's another far more violent scenario here dark energy just goes from strength to strength
32:49it could be that dark energy is so strong that will multiply upon itself as the universe gets bigger
33:00this is a process that we call phantom dark energy phantom energy is dark energy on steroids
33:09it multiplies uncontrollably in the voids tearing at the fabric of the universe and a process called the big rip
33:18dark energy dark energy dark energy dark energy is weird enough but imagine the possibility that
33:25there is more and more of it as time goes on and it's called phantom energy and in that case it would rip
33:33everything apart even black holes it will start to rip apart galaxies themselves rip apart solar systems
33:51rip apart people rip apart atoms rip apart nuclei
33:58the universe as we know it will be destroyed but the big rip may not be the end of everything
34:16there will be no normal matter and no dark matter
34:21and with nothing left to conquer phantom energy may use its powers to become a creator
34:27triggering a rebirth eventually when you get to this ultimate stage of emptiness because of the
34:36phantom energy we're actually able to turn the universe around and get it to collapse again
34:41and then go through a series of bounces so we call it the phantom bounce
34:47with this phantom bounce all energy left in this dead universe starts to collapse
34:53and eventually it becomes hotter and hotter and denser and denser and then the fiery inferno
34:59eventually pushes you back out into another big bang and this just keeps going on indefinitely
35:07so the destructive and repulsive dark energy spawns a force that becomes the ultimate universe recycler
35:14the end state of our universe would lead you back into another cycle a whole new big bang from the beginning
35:22in the end dark energy may kill the cosmos or it may create a new one
35:34dark energy is mysterious dark energy is unknown dark energy is going to do whatever it feels like
35:41maybe dark energy will go away maybe dark energy will decay and become a flood
35:47of new matter and radiation maybe dark matter will get stronger we don't know
35:56for now we think dark energy will determine the fate of the universe
36:02but all of our evidence is speculative what if we have it all wrong what if there is no dark universe
36:10a large part of our understanding of the universe's past present and future is based on educated guesswork
36:37about two invisible forces dark matter and dark energy but it's pure speculation
36:49perhaps dark matter and dark energy don't exist there's not new stuff in the universe anything is
36:57possible dark energy in particular might not be real so maybe there's something else that could be
37:02pushing the universe apart so we could absolutely be wrong about dark energy and dark matter maybe they
37:07don't exist maybe tomorrow we'll discover that our understanding it was wrong all along
37:14that's an awful lot of maybes let's add one more when it comes to finding answers
37:21maybe we're looking in the wrong place
37:23one possibility is that there are other universes out there pulling outward so to speak on our universe
37:34that might be the answer but most theoretical physicists and astrophysicists these days
37:39think that dark energy is real because that seems to be the simplest explanation for a wide variety of observations
37:47no one really knows what dark energy is made of maybe the answer lies in the past
37:56the best theory for dark energy we have right now is the simplest one and the oldest one
38:00and that's the idea that it's a cosmological constant
38:05albert einstein came up with the idea of a cosmological constant in 1917
38:10he suggested that space has its own energy energy that can affect the way the universe expands
38:22when edwin hubble proved the universe is expanding einstein thought the cosmological constant
38:28was his biggest blunder but observations that the expansion of the universe is accelerating
38:35reveal einstein was right all along well here we are
38:40we've reintroduced the idea so einstein's biggest blunder
38:46may have actually conceptually been his greatest triumph
38:52but to understand the true nature of the dark universe we may need to reevaluate what we think we know
38:59about gravity when we're trying to understand dark energy and dark matter there's a chance that just our
39:07fundamental theories of gravity are wrong that general relativity isn't quite right
39:14einstein's theory of general relativity explains how gravity works how stars orbit in galaxies and
39:21planets orbit stars
39:25some scientists wonder if altering this theory will help us understand the dark universe
39:31so you need not absolutely believe that there is something actually called dark matter you need
39:38only understand that there is something in the universe which behaves like dark matter for example you could
39:44effectively mimic the behavior of dark matter by modifying our current theory of gravity
39:49but successfully modifying einstein's theories on gravity is a big challenge
39:56einstein's equations are very robust you don't faff around with einstein with impurity
40:02for decades theoretical physicists have toyed with einstein's equations
40:10looking for ways to explain dark matter and dark energy or make them go away as yet no one
40:18is managed the dark universe persists i think that the best description of the observations we have today
40:27is that dark matter exists it's out there as well as dark energy i think dark energy exists i think dark
40:34energy is real but i must admit that sometimes at three o'clock in the morning i wake up screaming
40:40worried that in fact we've settled on the wrong answer and that in a couple of hundred years they're going
40:47to be laughing at us until then our observations tell us the battle between dark matter and dark energy
40:57has shaped the universe dark matter dictated the past built the galaxies the stars and the planets
41:09dark energy will determine its future potentially tearing the universe apart just because we can't
41:19see dark matter and dark energy directly doesn't mean they have not had a profound effect on the
41:24evolution of the entire universe the dark universe was there at the beginning of the universe shaping it
41:31and actually creating the conditions for us to be here and it's taken over the universe and eventually
41:37it may well destroy the universe our universe may be dominated by the long struggle between dark
41:45matter and dark energy but all of this conflict has led to a creative outcome an outcome for which we
41:53should all be grateful the name dark matter suggests that it's something nefarious and somehow bad for us
42:01but actually it's turned out that dark matter is very much our friend because if it weren't for the dark
42:06matter we wouldn't be here there's a wonderful irony to calling it the dark universe because now we're
42:13actually beginning to shed light on how the universe began how the largest structures in the universe
42:18evolved we wouldn't be here without this dark universe it's not dark at all it's shedding light on our own
42:23reality