0:00

Hey,

0:01

Curious Universe listeners. I'm

0:03

Jacob Penner, new producer here at the show. I

0:05

have a question for you. If you could

0:07

ask a NASA scientist or astronaut

0:10

anything, what would it be? Well,

0:13

here's your chance. This season, we

0:15

want to know what you're curious about. Send us your

0:17

question at nasa-curiousuniverse

0:20

at mail.nasa.gov

0:23

and we'll try to track down the answer. Thanks

0:26

and enjoy the show.

0:30

L-E, go for launch.

0:38

And

0:41

great news. All systems are go for

0:43

launch of Falcon 9 and ESA's Euclid

0:45

Space Telescope.

0:46

So I was very

0:49

lucky in that I got to go to

0:51

Florida to watch a Euclid launch

0:54

on July 1st, And

1:00

I know exactly how close I was because

1:02

like any good physicist, when the rocket

1:04

launched,

1:11

I could see the intensely

1:13

bright light and I started counting

1:16

seconds in my head.

1:17

Jason Rhodes is a scientist at

1:19

NASA's Jet Propulsion Laboratory. He's

1:22

an astrophysicist who studies what the

1:24

universe is made of and how it's structured.

1:27

Like any physicist will tell you, on Earth,

1:30

light travels faster than sound. So

1:33

Jason watched the rocket ignite silently.

1:36

Then he counted for about 20 seconds.

1:39

Until I got hit with the shockwave

1:41

and the sound and the rumbling. And

1:47

I'm a physicist, so I know the

1:49

speed of sound and air. So I could

1:52

figure out about how far I was away. It was

1:54

about four and a half miles. And that's

1:56

probably about as close as I would have wanted to be

1:58

because it was quite a rumbling.

1:59

and quite bright. This

2:02

rocket carried a telescope called Euclid

2:05

made by the European Space Agency with help

2:08

from NASA and other scientists around

2:10

the world. Euclid was headed

2:12

to a point in space almost a million

2:14

miles away from Earth. From there

2:17

it's designed to make a 3D map of the universe

2:20

including dark matter and dark energy,

2:22

mysterious elements of the universe that

2:25

we can detect but we don't know

2:27

much about them.

2:28

Euclid has its origins

2:31

in part in a paper I wrote

2:33

in 2004 with some colleagues.

2:36

So we described this telescope in this

2:38

paper and then we started to go to

2:40

space agencies and say, hey we

2:43

want the money to build this telescope.

2:45

Now this is a long process. I you

2:47

know pride myself on being a scientist and

2:49

thinking of things sort of dispassionately

2:53

and and logically and so I

2:55

thought I was going to watch this launch

2:57

with that sort of sentiment but

3:00

I became very emotional. It had

3:02

been the better part of 20 years of

3:04

my life and my career but

3:06

the other aspect of it for me was I felt

3:09

incredibly lucky to be part of this grand

3:12

adventure that is astronomy launching

3:14

a telescope into space. It's

3:16

one of in my opinion the

3:19

proudest and most important

3:21

human accomplishments is to be able to try

3:24

to understand the universe that

3:26

we live in.

3:30

This is NASA's Curious Universe.

3:33

Our universe is a wild and wonderful

3:36

place.

3:36

I'm your host Patti Boyd and in

3:39

this podcast NASA is your

3:41

tour guide.

3:42

Dark matter and dark energy

3:44

may sound like something Luke Skywalker

3:47

had to fight off in Star Wars. Unlike

3:50

the force they're real but

3:52

we do notice them in galaxies

3:53

far far away.

3:55

The stuff that we know here on Earth the

3:57

atoms and molecules

3:58

that make up our bodies are whole. The

4:01

moon and the stars and everything else we can see

4:03

is only about 5% of the universe. The

4:07

other 95% is dark matter

4:10

and dark energy. In this

4:12

episode, let's explore the

4:14

dark side of our universe.

4:15

We'll learn why cracking the secrets

4:17

of dark matter involves a battle between

4:20

machos and wimps. And we'll

4:22

hear how a couple of new space telescopes could

4:24

help us solve some of these mysteries or

4:27

give us new questions to investigate.

4:32

So let's start at the beginning with a question

4:34

that seems

4:34

pretty straightforward. What

4:37

is dark matter? Well,

4:38

that's a great question. I guess

4:41

if we knew the exact answer to that, we

4:43

wouldn't be sitting here today because yeah,

4:46

that problem would have been solved and maybe

4:48

I'd be studying something else.

4:50

This is Ami Choi.

4:51

She's an astrophysicist based at NASA's

4:54

Goddard Space Flight Center. I

4:56

study the universe on

4:58

the largest scales, really

5:00

just the biggest picture. I am

5:03

interested in what the universe is made out

5:05

of and then also the history of

5:07

it and how it evolved to

5:09

what we see today.

5:11

We may not totally understand dark

5:13

matter, but we do know there's a lot

5:16

of it.

5:19

It makes up about 25% of the universe,

5:22

but we can't

5:23

see dark matter and it barely

5:25

interacts with us here on Earth. We

5:27

notice it when we look on the scale of galaxies,

5:29

including our own, or clusters

5:32

made up of many galaxies. Dark

5:34

matter is a type of matter that

5:37

we indirectly observe through

5:40

its gravitational effects, but

5:42

that's the only way really that we know that it

5:44

exists because it doesn't emit

5:47

light and it doesn't interact

5:49

with light.

5:52

Far back as the late 1800s,

5:54

astronomers hypothesized some kind of

5:56

matter they couldn't see. In the 1930s, I

5:59

was a scientist. A Swiss astronomer

6:01

named Fritz Vicky was looking at

6:03

a distant cluster of galaxies.

6:05

He noticed the galaxies were moving a lot faster

6:08

than he expected. The only

6:10

ways Vicky could explain it was that the galaxies

6:12

had some kind of unseen mass. And

6:15

so that was a clear evidence

6:18

for Dark Matter, although at the time nobody believed

6:20

him. He was considered

6:22

an eccentric.

6:24

Decades later, in the 1960s

6:26

and 70s, an American astronomer

6:29

named Vera Rubin confirmed that

6:31

it existed. Since then, scientists

6:33

have found dark matter all over

6:35

the universe.

6:37

So we know that there's dark matter out there because

6:39

we can see how things move in relation

6:41

to each other, and we know that there's this mass that's

6:43

causing them to move in a certain way. Dark

6:46

matter is not dark in the sense that it absorbs

6:48

things and it appears black. It doesn't

6:50

absorb light. So clear matter

6:53

might have been a better name

6:55

for it because the light passes right

6:57

through. I don't think it has the same cachet

7:00

though or gives the same sense

7:02

of mystery.

7:04

By the time Jason started his career in

7:06

the 1990s, astrophysicists

7:08

thought they had a pretty good handle on the main

7:10

building blocks of the universe.

7:12

When I started graduate school in 1994,

7:16

we thought, the scientific community thought,

7:19

that the universe was made up of matter,

7:21

dark matter, and gravity. And

7:24

by the time I finished graduate school,

7:26

five years later, there had been a real

7:29

revolution in which the whole understanding

7:31

of cosmology was sort of upended.

7:35

The culprit was dark energy.

7:38

Now dark energy and dark matter are two totally

7:41

separate things. They're not called dark

7:43

because they're related. They're both

7:46

dark because we just don't know much about

7:48

them. So dark energy is

7:50

one of the biggest mysteries in all of science.

7:53

The roots of this mystery go back about

7:55

a hundred years.

7:57

Back in the 1920s, astronomers were just beginning to think that they

7:59

were dark. to realize that there

8:01

were other galaxies out there beyond the

8:03

Milky Way.

8:04

Well, I'm sitting here in Southern

8:06

California in Los

8:08

Angeles area. If I was outside,

8:10

I could look up at the mountains and I could see

8:13

Mount Wilson, which is the home

8:15

of a very famous observatory where

8:18

nearly a hundred years ago an astronomer named

8:20

Edwin Hubble was doing some observations.

8:24

Edwin Hubble was a groundbreaking

8:26

astronomer.

8:27

In fact, his work inspired the

8:29

Hubble space telescope,

8:30

which has been orbiting

8:32

our home planet and capturing pictures of the cosmos

8:34

for more than 30 years.

8:35

And Edwin Hubble, along

8:38

with some other astronomers at the time,

8:40

found that the universe was expanding.

8:42

It wasn't static or staying the same

8:45

size as people had previously thought.

8:48

Astronomers were pretty

8:49

sure that in a universe full of matter

8:51

and dark matter, eventually gravity

8:54

would throw on the brakes.

8:56

The universe may be expanding now, but

8:59

all of those particles would be attracted to each other

9:01

and the expansion would have to slow down. Maybe

9:04

it would even reverse and the universe would shrink.

9:07

And that's what scientists were looking for in the 1990s.

9:10

And so these two groups

9:12

were trying to understand how much the expansion

9:14

of the universe was slowing down. But

9:16

instead, they found a very surprising result.

9:19

And that result was that the expansion of the

9:21

universe is speeding up. That

9:23

is, there's something pushing the universe apart,

9:26

causing it to expand faster and faster

9:29

over time.

9:30

Astronomers call that something dark

9:33

energy.

9:34

Today we've calculated it makes up about 70% of

9:36

the universe.

9:38

But we can't say what it is or

9:40

where it comes from.

9:42

And I like to say that dark energy is

9:44

the name we give to our ignorance of what's

9:47

causing that accelerating expansion

9:49

of the universe. So it's sort of a catch-all

9:51

term for a number of possible explanations.

9:55

matter

10:00

and dark energy everywhere.

10:03

Ami says those effects are even imprinted

10:05

into the shape of the universe itself.

10:09

If you could zoom out and make

10:11

a map of the entire universe, you'd

10:13

see a cosmic web with tangles

10:16

of galaxies connected by thin strands

10:18

of matter. Dark matter, it has a gravitational

10:21

force and that's an attractive force that's pulling

10:23

things in. And then dark energy

10:25

is something that makes the

10:27

universe undergo an accelerated expansion, so it's

10:29

like a pulling things apart kind of

10:31

force. And it's really the interplay

10:34

between these two forces that shape

10:37

all of the universe that we can see,

10:40

including all of the matter

10:43

that does emit light.

10:45

Even though we can't directly see dark

10:47

matter and dark energy, astronomers

10:48

have come up with clever ways

10:50

to detect them and even measure them.

10:54

One technique

10:55

that Jason and Ami both use is

10:57

called gravitational lensing. And

10:59

gravitational lensing is the phenomenon

11:02

where light coming from very

11:04

distant galaxies on

11:07

their way to us as the observer,

11:10

their path can be distorted by

11:12

massive

11:13

objects between us

11:15

and where the light was emitted originally.

11:18

This comes from one of the wrinkles of Albert

11:20

Einstein's general theory of relativity. These

11:24

objects bend the fabric of space

11:26

itself. Huge objects

11:28

with lots of mass can warp space

11:30

so much that light doesn't travel

11:32

in a straight line. It gets bent

11:35

and distorted. When astronomers

11:37

look at far away galaxies, they can

11:39

see dark matter bending and distorting the

11:41

light headed toward

11:42

Earth. And I can use an analogy

11:44

here. Imagine you're standing on a very calm

11:47

day in front of a very crystal

11:49

clear pool and you throw a penny

11:51

to the bottom of the pool. Now

11:54

you can't really see the water because

11:57

it's crystal clear, but you can

11:59

see the penny at the bottom of the pool, and anyone

12:01

who's done this knows that you see a distorted

12:04

view of that penny. It doesn't appear

12:06

as it would just on the ground. And that's

12:08

because the light from the penny is traveling

12:11

through the water and the light is bent by

12:13

the water. So in this analogy,

12:15

that penny is like the distant galaxy

12:18

and the water is like the

12:21

dark matter. So we don't actually see the

12:23

dark matter. You don't actually see the water. But

12:25

you know it's there. You know the water

12:27

is there because you see a distorted view of

12:29

the penny. And we know that dark matter is there because

12:32

we see a distorted image of these background

12:34

galaxies.

12:35

In fact, astronomers can measure this

12:37

distortion throughout the universe by

12:40

looking at millions of galaxies.

12:42

With that information, they can see the effects

12:44

of dark matter and dark energy. And

12:47

that's just one technique.

12:49

The original discovery of dark energy came

12:51

from studying a particular type of supernova,

12:54

the huge explosions caused by dying

12:56

stars.

12:57

Each time one of these supernovae explodes,

13:00

it gives off a very well-known

13:03

amount of light over a very well-known

13:05

amount of time. So by measuring

13:08

that light, we can

13:10

figure out how far away that

13:13

supernova was.

13:16

So imagine you and a friend are walking

13:18

through the woods in the dark. It's

13:22

a still, quiet night. There's not

13:24

much of a moon, but you have flashlights

13:27

to show the way. For some reason, your friend keeps running off

13:29

on their own. But as long as you can see their flashlight,

13:33

you know where they are. Since you know how bright the flashlight

13:36

is, you can tell how

13:39

far away they

13:40

are.

13:41

And you can see if they're moving towards you or

13:43

moving away. Supernovae give

13:45

the same information to

13:47

astronomers. And by measuring those distances and seeing how

13:49

far away in time those distances are, because

13:51

it takes time, billions of years for the light to

13:53

reach us from

13:56

these distant galaxies, we can measure the light.

13:59

the expansion history of the

14:02

universe.

14:03

With these techniques, scientists have gathered

14:05

detailed information about our dark universe.

14:08

Not bad for something they can't see.

14:11

Now for dark matter in particular, Jason

14:13

says we actually understand it pretty well in

14:15

terms of how it behaves on large scales.

14:18

However, we don't understand dark matter

14:21

at what we call the particle level. We don't

14:23

know exactly what dark matter is made

14:25

up of.

14:27

To explain dark matter, you might have thought about

14:30

another mysterious object in the universe,

14:32

black holes. After

14:34

all, black holes have so much gravity

14:36

that even light can't escape them. So

14:38

they're definitely dark. Astronomers

14:41

have also wondered if black holes could explain

14:44

dark matter. In other words, if they

14:46

are the mass that is missing from the balance of

14:47

the universe.

14:49

Or maybe other objects, like a type of small

14:51

dim star called a brown dwarf.

14:53

There are these different types of astronomical

14:56

objects

14:57

which maybe are kind

14:59

of dark in some sense. It

15:01

makes it really hard for us to see

15:03

them. So these are all

15:06

examples of a type of object

15:08

which we call machos. So

15:11

machos are short for massive,

15:14

compact, halo object.

15:16

If machos explain dark matter, that

15:18

would mean it's made of the same protons and electrons

15:21

that make up everything around us. But

15:23

experiments to detect machos haven't

15:25

panned out. So many scientists

15:28

think that dark matter is made of something else.

15:29

Something a little more exotic. So

15:33

we think maybe the dark matter could be

15:35

a new type of elementary particle that hasn't

15:37

yet been detected.

15:39

But does have some of the properties

15:41

that we've found in other

15:44

ways from our astrophysical observations.

15:46

So they do have some gravitational force and

15:49

that they might be weakly

15:50

interacting.

15:52

And so the shorthand for this

15:54

class of

15:54

particles is WIMP. So

15:57

WIMP stands for weakly interacting.

15:59

massive particles. So,

16:02

you know, we have these wimps

16:04

as the leading candidates, so they seem to have

16:06

won out in this case over the machos,

16:09

which is kind of funny.

16:12

In many ways, our research into dark

16:14

matter and dark energy is just getting

16:16

started.

16:17

After all, we didn't even know dark energy

16:20

existed until 25 years ago.

16:22

NASA and other space agencies

16:24

have been building a new generation of space telescopes

16:27

designed specifically

16:28

to study the dark universe.

16:30

First up is Euclid, the European

16:32

Space Agency launch that Jason saw this

16:34

summer. And the

16:35

thing that's really exciting about Euclid

16:38

is it's got huge cameras,

16:41

lots and lots of pixels.

16:43

Over a six-year mission, Euclid

16:45

will show us billions of galaxies, looking

16:48

back 10 billion years into the

16:50

past.

16:51

To give you some idea of how powerful Euclid's

16:53

gonna be, it doesn't have

16:55

as big a mirror as the Hubble Space Telescope,

16:58

so it doesn't have quite the resolution

17:01

or the depth of a Hubble image. But

17:03

it's somewhat close. So, every

17:05

week it's gonna image as much of the sky as

17:08

Hubble has in its 30-year history.

17:11

All of that data will help Jason and other astronomers

17:13

learn more about the expansion history of the universe.

17:16

Then they'll be able to figure out the role

17:19

played by dark matter and dark energy.

17:22

Meanwhile, at the Goddard Space Flight Center

17:24

in Maryland, NASA's building a new

17:26

mission to the dark side with help from industry

17:29

and international partners. I mean,

17:31

this is a biased point of view, but I'm most

17:33

excited about the Nancy Grace

17:36

Roman Space Telescope since this is the

17:38

project that I'm working on here at NASA. The

17:41

Roman Space Telescope is still a few years

17:43

away. It's scheduled to launch by May 2027.

17:45

Like Euclid,

17:48

one of the mission's main goals is observing

17:50

dark matter and dark energy. They

17:52

will both make 3D maps

17:54

of the universe. But

17:56

the two telescopes have different strengths that

17:58

can work together to create a

17:59

powerful combination of observations.

18:01

Euclid will take

18:03

a wide survey of the universe in both

18:06

infrared and visible light. In

18:08

comparison, Roman's area

18:10

of study will be narrower but much

18:13

deeper. It has a lot of other

18:15

science goals besides the dark universe,

18:17

like finding exoplanets and studying objects

18:20

in the outskirts of our solar system. And

18:23

Roman's resolution is about the same as

18:25

Hubble's, but with a field of view 100

18:27

times wider. So we have

18:30

pictures from Hubble

18:32

of one of our neighbors, the Andromeda

18:35

galaxy. And Hubble,

18:37

it takes many, many individual

18:39

pointings. And then you mosaic those

18:41

pointings together to get the

18:44

overall picture of this nearby galaxy.

18:47

And Roman can do that very

18:49

efficiently because of how much area it can

18:51

capture in a single snapshot.

18:54

And so it can do that sort

18:57

of in two passes where

18:59

Hubble, it might take hundreds of

19:01

passes.

19:02

Once it launches, Roman will fly to the same

19:05

point in space as Euclid and the James

19:07

Webb Space

19:07

Telescope,

19:08

about one million miles away

19:10

from Earth.

19:11

This new fleet of telescopes has

19:13

a mix of capabilities that will allow

19:16

them to tag team with Hubble and other

19:18

observatories, each

19:19

of which has their own unique superpowers

19:22

that help us see the universe in different

19:24

ways. Hopefully they're all flying

19:26

together at the same time. And

19:28

you could think of things, for example,

19:30

like finding interesting objects in

19:33

the Roman field of view because

19:35

you're capturing so much area at one time,

19:37

you might then go try to look

19:39

at it with Hubble and JWST and

19:41

get a really even deeper view on

19:45

that particular

19:45

object.

19:47

So they're super complementary in that sense.

19:59

photos of huge clouds of gas

20:02

and dust were newborn stars form.

20:04

For astrophysicists, these space telescopes

20:07

provide something even more valuable, data

20:10

to feed into equations that describe

20:12

the universe.

20:13

And what we've found is those equations

20:16

predict new observations

20:18

that we haven't done before.

20:20

And sometimes those predictions pan out and

20:23

are true. And sometimes they aren't. And

20:25

then when they aren't, we have to revise our vision

20:27

of the universe.

20:29

In fact, there are already tensions

20:31

in how astronomers describe the cosmos.

20:34

It might be time to reevaluate those equations

20:37

and some fundamentals we think we know.

20:41

Based on what we know about dark matter and dark

20:43

energy, our models of the early universe

20:45

clash with what we understand about gravity. Something's

20:48

got to give. As we've taken

20:51

better measurements, the problem

20:53

has not gone away.

20:54

Maybe there's something that

20:58

is new that's not accounted for in

21:00

our current theories of general relativity

21:03

that means that the gravity

21:05

behaves in a particular

21:06

way that we haven't currently accounted

21:08

for. And in fact, if the problem

21:11

persists after taking

21:13

measurements with telescopes like Euclid

21:15

and Roman, it will tell us

21:18

that we either fundamentally don't

21:20

understand something about our measurements or

21:22

more interestingly, there's

21:24

new physics. Our understanding

21:27

of physics is incomplete.

21:32

This is why astrophysicists get out

21:34

of bed in the morning.

21:35

There's always an opportunity to shatter

21:37

the rules we think we know and

21:39

come up with something even more interesting. Jason

21:43

says it feels like that moment when he was a graduate

21:45

student a few decades ago. Once again,

21:47

astrophysics could get flipped on its head.

21:50

So we live in a time where there's these hints

21:52

of these tensions. And so for me

21:54

personally, I'm really excited

21:56

to see if these tensions play out.

21:59

And if they do... I want to know what's the

22:01

new physics that describes the universe.

22:05

Once Roman and Euclid are both in space,

22:07

it will take scientists years to analyze

22:10

their data. And it's hard

22:12

not to wonder.

22:13

What are we going to learn? What

22:16

secrets about dark matter and dark energy

22:18

are out there, just out of reach?

22:21

I definitely don't think that in my lifetime

22:23

we will have answered all of the interesting

22:25

questions. None of these

22:28

missions are just going to all of a sudden

22:31

give us the particular

22:33

definitive evidence for

22:36

understanding the universe completely. We'll

22:39

continue to learn a lot of new things and

22:42

things that I couldn't even say what

22:44

it is that we'll see, because they

22:46

are allowing us to explore the universe

22:48

in really new

22:49

ways.

22:52

With all of this new information, dark

22:55

matter and dark energy may not just

22:57

be mysteries waiting to be solved. They

23:00

could also be hints that we need to ask different

23:02

questions. Every

23:04

time we launch a telescope and we

23:06

start looking at the universe in a new way, we

23:09

learn about things we had no idea were

23:12

even

23:12

out there. I think

23:14

that's the most exciting part of where we are today. This

23:22

is NASA's Curious Universe.

23:25

This episode

23:28

was written and produced

23:29

by Jacob Pinter. Our executive

23:32

producer is Katie Conans.

23:34

The Curious Universe team includes Christian

23:36

Elliott, Maddie Olson and Michaela Sosby. Our

23:39

theme song was composed by Matt Russo

23:41

and Andrew Santaguida of System

23:44

Sounds.

23:45

Christopher Kim designed

23:46

our cover art.

23:48

Special thanks to Claire Andrioli, Barb

23:50

Mattson, Amber Strahn, Liz

23:52

Landau, Colin McNutt, the European

23:55

Space Agency and SpaceX.

23:57

If you liked this episode,

23:59

please let us know.

23:59

by leaving us a review and sharing NASA's

24:02

Curious Universe with a friend. And

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remember, you can

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follow NASA's Curious Universe in your favorite

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podcast app to get a notification each

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time we post a new episode.

24:15

I have a two-year-old daughter and she's starting to sing

24:17

Twinkle Twinkle Little Star and the astrophysicist

24:19

in me thinks, wow, it's not the star that's twinkling,

24:22

it's the atmosphere that's causing.

24:25

Hey Curious Universe listeners, are you interested

24:28

in more great stories from NASA? And

24:30

friends over at NASA TV have a big

24:33

announcement. NASA is launching an on-demand

24:35

streaming platform. It's called NASA

24:37

Plus. You can watch NASA's

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to podcasts all in one place. The

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best part? There's no subscription required

24:49

and it costs nothing. You

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can find NASA Plus on most major platforms

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through the NASA app on iOS

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and Android mobile and tablet devices, also

24:59

on streaming media players like Roku,

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Apple TV and Fire TV, and

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online on all kinds of desktop

25:05

and mobile devices. You can download

25:07

the NASA app now and be one

25:09

of the first to get NASA Plus when it

25:12

drops. Stay tuned and

25:14

stay curious.