Transcript

Transcript of YouTube Video: The Universe’s Second, Bigger Bang

Transcript of YouTube Video: The Universe’s Second, Bigger Bang

Welcome to our collection of transcripts of YouTube videos, where we provide detailed text versions of "The Universe’s Second, Bigger Bang" content.

00:00

Nearly 100 years ago, we started  telling ourselves a particular story

00:04

about the beginning of everything.

00:05

And it’s a story that starts with a  hot, unthinkably dense ball of matter,

00:10

and ends with right now.

00:12

You probably know it best as the Big Bang Theory.

00:15

And while different scientists may play  around with slightly different versions of it,

00:19

it does a pretty solid job of explaining  all the stuff we see in the universe today.

00:23

But there’s a lot of stuff we don’t see, too.

00:26

Like, after the Big Bang Theory first came about,

00:28

our picture of the universe expanded to  include a strange substance called dark matter,

00:33

whose presence we can detect,  but not the stuff itself.

00:36

And so far, this mysterious form of matter  has just been folded into the Big Bang.

00:40

Most theoretical astrophysicists  have carried on assuming

00:43

that everything popped into  existence during that one moment.

00:47

But what if this story we’ve told ourselves  for generations…about how stars and planets

00:51

and galaxies came to be…isn’t true  for their dark matter cousins?

00:56

Recently, some scientists have proposed  that the Big Bang was followed by a

01:00

“dark Big Bang,” which not only spawned  all the matter belonging to this

01:03

dark sector of reality, but spawned more  matter than was made in the original.

01:08

And if they’re right, studying  the Universe’s second,

01:11

bigger bang could help us solve the  mystery of what dark matter even is.

01:15

[♪ INTRO]

01:19

Now before we can talk about the Dark Big Bang,

01:21

we need to talk about the original Big Bang.

01:23

In 1931, a Belgian scientist/priest  named Georges Lemaître

01:28

made a simple conclusion.

01:30

Because humanity had recently discovered  that the universe was expanding,

01:34

as opposed to just always being there,  and all he needed to do was hit rewind.

01:38

The universe got smaller and smaller  until he hit the beginning of time.

01:42

So Lemaître proposed a “primeval atom.”

01:45

A super dense point that had the  whole universe packed inside it.

01:49

And some version of that has been  our universe origin story ever since.

01:53

In the early days, scientists hypothesized  that the universe’s energy started off

01:57

packed inside a singularity,  an infinitely dense, hot point.

02:01

And in this version of the story,  the Big Bang was the moment

02:04

when that singularity exploded  to create the universe.

02:08

That story explained the expanding  universe pretty well overall,

02:11

but it came with some thorny problems.

02:14

Like the fact that the very concept  of an infinitely dense point just…

02:18

doesn’t exist physically.

02:19

And if you take our best models of the universe

02:21

and try to rewind the clock all the way to zero,  the whole thing breaks before it gets there.

02:26

The laws of physics spit out nonsense.

02:29

So the modern concept of the  Big Bang is a little different.

02:33

It puts the Big Bang after a brief period in  the universe’s ancient history called inflation.

02:38

In this version of the story, there was a  sliver of a second at the beginning of time when

02:43

the universe expanded exponentially in size,  and it did so faster than the speed of light.

02:48

No one knows what triggered this  inflation or what came before it.

02:52

But within less than a billionth of a billionth  of a trillionth of a second, it was over.

02:57

And it was only then that all the  energy driving this breakneck expansion

03:02

turned into matter and light,  giving way to the Big Bang,

03:05

and giving rise to all the  stuff that is out there, today.

03:08

The thing is, the picture gets a  little fuzzy when we try to extend it

03:11

to the stuff we can’t see, which  makes up a big piece of the pie.

03:15

For example, for every gram of regular,  visible matter, cosmologists believe that

03:20

there are around five grams of so-called  dark matter…an invisible substance that,

03:25

at least as far as we know, only  interacts with objects through gravity.

03:29

We can watch it make stars  at the edges of galaxies

03:31

rotate faster than they would otherwise.

03:34

And we can see how it warps spacetime,  bending light that passes by it.

03:38

But we’ve never detected it directly.

03:40

So even though it’s been taunting  astronomers for nearly 100 years,

03:44

no one knows what dark matter is.

03:47

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04:50

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04:52

It’s part of what astronomers call the  dark sector, the part of the universe

04:56

that’s made up of mysterious substances  that we’ve never explored directly,

05:01

yet is most of reality as we know it.

05:03

The dark sector makes up  around 95% of the universe,

05:07

but all we know about it is how it pushes  and pulls on the rest of the universe…

05:11

the part that’s made up of regular  matter and energy and light.

05:14

So, the idea that everything in the dark sector

05:17

was born during the Big Bang  is as good a guess as any.

05:20

But it’s still just a guess.

05:22

There’s no actual reason  why it has to be that way.

05:24

We can’t observe the moments  immediately after the Big Bang,

05:27

because it was so hot and dense  that space was completely opaque.

05:31

Light couldn’t shine through the universe.

05:33

So we don’t even know for sure  what regular matter was doing,

05:36

let alone if dark matter was  there interacting with it.

05:39

And, considering that regular and dark matter  barely interact with each other anyway,

05:43

some scientists are considering whether dark  matter could have emerged at a later time,

05:47

in what they call the Dark Big Bang.

05:49

It’s all hypothetical at this point.

05:50

But as long as they’ve got this idea on the table,

05:53

their task is to figure out how a Dark Big  Bang might have gone down if it did happen.

05:58

It’s kind of like your lunch is missing, and  you’re trying to figure out if your dog ate it.

06:02

To solve the mystery, you might start by  imagining the potential clues to look for:

06:07

For example, you know your dog is a messy  eater, so if it really did eat your BLT,

06:12

it probably left some crumbs behind.

06:14

Plus, it’s not supposed to eat human  food, so it might get an upset stomach.

06:18

Or at the very least, it might not be  as hungry when dinnertime rolls around.

06:22

And astronomers are taking the  same general approach here.

06:25

They’re trying to paint a picture  of the hypothetical Dark Big Bang

06:29

so that observers can look for any  crumbs that suggest it really happened.

06:33

And one crucial detail is when it happened.

06:36

Hypothetically, anyway.

06:37

Cosmologists know that dark matter played a  big role in seeding the large-scale structure

06:42

of the universe today: It helped draw  regular matter into the massive web

06:46

of galaxy clusters that  stretches as far as we can see.

06:50

So it had to have been around  early enough to play that role

06:53

and fit into our models of  how that structure evolved.

06:56

And according to computer models,

06:57

a dark big bang most likely took place  a mere month after the regular one.

07:02

But a question that’s far more  important than the when is the what.

07:05

What, if anything, actually happened?

07:08

The team proposing this dark  hypothesis suggests that,

07:11

prior to this second “bang”,  there was a dark matter vacuum.

07:14

Now a vacuum is what we  think of as pure emptiness.

07:17

So in this dark matter vacuum there  would have been some regular matter,

07:20

but it would have been empty of dark matter.

07:22

But according to quantum  mechanics, nothing is truly empty.

07:26

Even so-called empty space is frothing  with particles that spontaneously…

07:30

and incredibly briefly…pop  in and out of existence.

07:34

So a vacuum still has at least  some amount of energy in it.

07:37

But that “at least” is important, because  a vacuum can have different energy states.

07:42

While it likes to be in the  lowest energy state possible,

07:45

better known as a true  vacuum, it doesn’t have to be.

07:48

And scientists refer to that  situation as a false vacuum.

07:51

You can think of a false vacuum like  a pothole on an inclined street.

07:55

If a ball gets stuck in the pothole,  whether it got kicked up the hill

07:58

or was rolling down the hill, it  can stay stuck for a long time.

08:02

But as soon as a car or a gust of wind  nudges the ball out of the pothole,

08:06

it will roll down the street and wind up  resting at wherever the bottom of the hill is.

08:10

Because the bottom of the hill is at  a lower energy state than the pothole.

08:14

Now, the energy state of a vacuum  is a little harder to picture,

08:18

but the basic concept is the same: A false  vacuum may be stable for a long time,

08:23

but it can suddenly drop to a lower energy state.

08:26

And this is called a phase transition.

08:28

On Earth, we’re familiar with certain types  of phase transitions that happen in chemistry,

08:33

like when liquid water vaporizes  into a gas or freezes into a solid.

08:37

And cosmological phase transitions  aren’t completely dissimilar.

08:40

They’re also sudden changes in  the form and properties of matter.

08:44

Some theorists hypothesize that  during the original Big Bang,

08:47

a phase transition transformed a false  vacuum into a smattering of particles,

08:52

not unlike how a gas condenses into a liquid.

08:55

And in this hypothetical Dark Big Bang,  something similar may have happened, too.

08:59

Just like a pot of water that’s beginning to boil,

09:01

a false vacuum on the verge of  a phase change begins to bubble.

09:05

And, yes, the cosmologists  actually refer to them as bubbles.

09:08

They’re little spots where the vacuum  starts dropping to a lower-energy state.

09:12

And as they expand at near-light  speed and bump into each other,

09:16

these bubbles collapse the  false vacuum into a true vacuum.

09:19

Now, in the case of the hypothetical  dark matter vacuum, the energy from these

09:23

expanding bubbles gets released as dark  matter and dark radiation…much like the matter

09:28

and light released in the collapse of  the vacuum that created the Big Bang.

09:32

But exactly what comes out of this dark  phase transition depends on how it plays out.

09:37

In one hypothetical scenario, bubbles  could slam together fast enough

09:41

that their energy can turn directly  into humongous dark matter particles

09:45

that are up to 10 trillion  times the mass of a proton.

09:48

The authors of this Dark Big Bang hypothesis

09:51

have affectionately dubbed them dark-zillas.

09:53

But if the phase transition plays out more slowly,

09:56

the colliding bubbles will first  create a hot plasma in the dark sector.

10:00

And while the plasma is hot,  small dark matter particles

10:04

will emerge from interactions within it.

10:06

It’s this kind of transition that could  create the most popular candidates

10:09

for dark matter particles out there, today.

10:11

They’re known as WIMPS, or weakly interacting  massive particles, and scientists are

10:16

actively searching for them with a bunch  of different experiments around the world.

10:20

Eventually, the plasma cools, slowing  down the interactions taking place

10:24

within the plasma, and ending  the creation of more dark matter.

10:28

But that’s just two scenarios of many.

10:30

And right now, theorists aren’t  sure which, if any, might be right.

10:33

But they hope they’ll find evidence  that points them in the right direction.

10:36

Because remember, even though this is all  hypothetical, and it all happened at a time we

10:40

can’t observe directly, it’s like the dog that  ate your sandwich when you weren’t looking.

10:44

The Dark Big Bang would have  left behind some crumbs.

10:48

And while those bubbles that  carry out the phase transition

10:50

between a false vacuum and  a real vacuum are invisible,

10:53

they would have generated  gravitational waves as they collided.

10:57

Gravitational waves are ripples that  warp spacetime as they pass through it,

11:01

subtly pinching and stretching  the distances between objects.

11:05

And thanks to advancements in technology,

11:06

scientists are getting better and better  at detecting tinier and tinier signals.

11:11

Like in 2023, a massive international  collaboration called NANOGrav

11:15

announced they had successfully detected

11:17

a sort of gravitational wave background  noise coming from all around us.

11:22

Buried within that signal would be  gravitational waves created during the Big Bang.

11:27

And eventually more detailed studies

11:28

will help scientists tease  apart exactly what made them.

11:31

And maybe one day, they’ll reveal  there really was a second Big Bang.

11:36

Or maybe they won’t.

11:37

Cosmologists don’t need a Dark Big Bang

11:39

to explain how we got a  universe full of dark matter.

11:42

And there are plenty of alternate proposals  that I don’t have time to dive into, here.

11:46

Like primordial black holes, or a kind of  ultradense matter called “quark nuggets”.

11:51

But I’m pulling for you Dark Big Bang,

11:53

if only to read all the fun sequel  names that people put in the comments.

11:58

[♪ OUTRO]