0:00

Hello and welcome to this podcast

0:02

from the BBC World Service. Please

0:04

let us know what you think and tell

0:07

other people of Isis on social media. Podcasts

0:09

from the BBC World Service. are

0:12

supported by advertising. This

0:17

podcast is brought to you by eHarmony, the

0:19

dating app to find someone you can be

0:21

yourself with. Why doesn't eHarmony

0:23

allow copy and paste in first

0:25

messages? Because you are unique and

0:27

your conversations should reflect that. eHarmony

0:30

wants you to find someone who will get

0:32

you. How are you going to know who

0:34

gets you? If people see you the same

0:36

generic conversation starters, they message everyone else. Conversations

0:39

that actually help you get to know

0:41

each other. Imagine that. Get who

0:43

gets you on eHarmony. Sign up today. JD

1:02

Power ranks Sleep Number number one in

1:04

customer satisfaction with mattresses purchased in-store. And

1:07

now, the Queen Sleep Number C4 Smart

1:09

Bed is only $1,599. Save

1:12

$300 for a limited time. Only at

1:15

Sleep Number stores or sleepnumber.com.

1:16

and Hawaii. For JD Power

1:19

2023 award information, visit jdpower.com/awards.

1:21

Only at a Sleep Number

1:23

store or sleepnumber.com. Welcome

1:32

to CrowdScience from the BBC World

1:34

Service, where this week we're taking you

1:36

on a little journey. And

1:38

when I say little, I mean really,

1:41

really tiny. Imagine that you shrink yourself

1:43

by even a factor of 100. I'm

1:49

Anand Jagatiya, and this is cosmologist, Andrew

1:51

Pontson. Okay, so now you're around about

1:53

the size of an insect, say. And

1:56

you can imagine already, I mean the

1:58

world just seems so... different

2:00

if you shrink yourself just by a factor of 100.

2:03

Andrew is shrinking us down to miniscule

2:05

proportions so that we can zoom right

2:07

in to the smallest parts of our

2:09

world. But we are a very, very

2:11

long way away. So if we shrink

2:14

ourselves by another factor of 100. At

2:19

this point we are around about the

2:21

size of the width of a human hair. So

2:24

if you shrink yourself down you're now sort of lost

2:26

in this forest of human hairs

2:29

and the world would seem a

2:31

very, very frightening, very different place.

2:34

But we've still got a long way to go. We're going to shrink

2:36

down by another factor of 100. Now

2:42

you're one micrometer across. That's around

2:44

about the size of a bacteria.

2:48

So now all of the kind of living

2:50

world around you would be

2:52

constructed out of these bizarre creatures

2:54

that we can't see. But

2:57

once we're shrunk down to this size it's

2:59

suddenly in that realm and it would seem

3:01

incredibly alien. But we're

3:03

not here to look at bacteria. They're much too

3:05

big. There's another factor of 100. Now

3:11

you're about the size of the width

3:13

of a strand of DNA, the stuff,

3:16

the molecule that makes life. And

3:19

maybe about the size of a virus, say,

3:21

the sort of simplest thing that we associate

3:23

with life at all. And

3:26

you've still got that final factor of 100

3:28

to shrink down from there. And

3:32

now at last you are

3:34

a similar size to, well,

3:36

larger atoms. Atoms.

3:41

That is what we're here to see. The building

3:43

blocks of our universe. It

3:45

is basically impossible to conceptualise how small

3:47

atoms are, but one way of trying

3:49

to get your head around it is

3:51

to take the mental trip down through

3:53

levels of dimension that Andrew has just

3:55

guided us through. And we're here

3:58

because we want to understand what reality is.

4:00

he is actually like at the atomic scale,

4:02

which is what this week's question is all about. Back

4:07

in the human-sized world, here's crowd science

4:09

listener Alan. My name is

4:11

Alan and I live in Seton,

4:14

Gallivore, Northumberland in England. My

4:16

question to crowd science is,

4:19

is every atom unique? Everything

4:22

in nature is different and everything

4:24

manufactured is different once you look

4:26

at it in very fine detail.

4:29

All the snowflakes are different, every

4:31

living creature, every blade of

4:33

grass and every grain of sand is

4:35

unique. So I would assume

4:37

that every atom is unique and

4:40

everything is constantly changing. Thanks

4:45

Alan for your profound and poetic

4:47

question. The

4:50

natural world from plants to animals,

4:52

from rocks to crystals is full

4:54

of seemingly infinite variety. But

4:57

is that the case all the way down? As

5:00

we move to smaller and smaller scales,

5:02

are things still different from each other?

5:05

Are all the atoms of say

5:07

hydrogen in the universe fundamentally the

5:09

same? Or are they in

5:11

fact completely unique? It's

5:14

a really natural thought, I think your

5:16

listeners in very good company. This

5:18

is philosopher Eleanor Knox from King's

5:21

College London and as it

5:23

turns out, Alan's question has a

5:25

long history in philosophy and science.

5:27

Leibniz famously had the same

5:30

thought. He was a natural

5:32

philosopher, coincided with Newton, so kind of

5:34

there at the birth of what

5:37

we think of as modern science. One

5:39

of the inventors of calculus, so a very

5:42

good mathematician, he thought, look,

5:45

every time you see a leaf, it's ever so slightly different from

5:47

the leaf next to it. You could search all the leaves on

5:49

a tree and you wouldn't find too the same, likewise

5:52

for snowflakes. And it

5:54

looks like it's sort of a fact about our world that

5:57

everything when you look at it in enough

5:59

detail... is unique. Now

6:01

Leibniz had an explanation for that and it had

6:04

to do with God, like pretty much any philosopher

6:06

in that area of the world at the time.

6:08

He was a Christian and a believer, but he

6:10

in particular thought that God must have created the

6:13

best of all possible worlds. So there

6:15

couldn't be two identical objects because God would be

6:17

faced with a kind of impossible decision and he

6:19

couldn't create the best possible world. But

6:22

it's very understandable that your listener might look around the

6:24

world around them and think, oh yes, every single thing

6:26

is not an exact duplicate of any other. So

6:29

Alan isn't alone in wondering about

6:31

the nature of uniqueness. Great

6:33

thinkers have been pondering it for hundreds

6:35

of years and more recently philosophy has

6:38

also grappled with this question at the

6:40

atomic level. We'll come back to

6:42

Eleanor later in the show to hear about that. But

6:45

first let's get more of a handle on

6:47

what atoms actually are, what they're made of

6:49

and how they behave. Let's

6:51

shrink ourselves back down to Andrew

6:53

Ponson's atom's eye view of reality.

6:59

So how many factors of 100 have

7:02

we just traversed in over a few

7:04

seconds? Oh gosh, let's see. So there

7:06

was one to go down to insect,

7:08

two human hair, three bacteria, four DNA,

7:10

five to get down to the size of

7:12

an atom. And so that you know

7:14

so many factors of 100 in shrinking

7:17

down that I think we have to

7:19

prepare ourselves for the world on that

7:22

scale to be just fundamentally behaving in

7:24

a different way from what our everyday

7:26

experience would suggest. Yeah, I mean things

7:29

just get weird when you go down

7:31

that small, right? Yeah. So if

7:33

we go inside one of these

7:35

atoms then that we can see, is there

7:38

a way of describing what that looks like?

7:40

I mean, so maybe it's not physically possible,

7:42

but can you try and give us a

7:44

sense? Absolutely. So the picture we normally start

7:46

by painting is down to

7:48

a physicist called Niels Bohr. We're already

7:50

at the atomic scale, but if we

7:53

use our shrink rate a little bit

7:55

more we can go inside a hydrogen

7:57

atom and stand on its nucleus. Hydrogen

8:00

is the simplest atom in the sense

8:02

that its nucleus, we now know, is

8:04

made out of just one particle called

8:07

a proton. Under

8:10

us is a single proton, a

8:12

ball glowing with positive charge. So

8:14

that's got most of the mass

8:17

of the atom, which is actually just

8:19

locked into a tiny dot in the

8:21

centre. But if we look up, there's

8:23

something else moving around us. There

8:26

is the electron. A

8:29

single electron, negatively charged, in

8:31

the distance. Just whizzing around at immense

8:33

speeds. Going round and round. In a

8:36

way like, you know, planets go round

8:38

the sun. Yeah, so it's like a

8:40

tiny version or almost of like the

8:42

solar system. And that's basically the simplest

8:44

atom you can have. So

8:49

Andrew, if we went to a different atom,

8:51

let's say carbon, then how would those things

8:54

be different? There's just

8:56

more of them, really, extra protons

8:58

and also additional things that we

9:00

call neutrons. And they

9:02

also have to sort of balance

9:04

that out, extra electrons orbiting around

9:06

as well. Specifically for carbon, there

9:08

would be six protons and

9:11

six neutrons. Now

9:13

we're standing on a carbon nucleus made up of

9:15

not just one, but 12 particles

9:17

of two different kinds, all bunched

9:19

up. So now instead of just being a single

9:22

thing that you're standing on, it's somehow a collection

9:24

of 12 different particles

9:26

all clumped together very tightly.

9:29

And looking up, I can make out six

9:31

bright electrons. These

9:34

six electrons. Which are whizzing around

9:36

us at high speeds. So it's sort

9:38

of a bit like the difference between

9:41

a simple planetary system, if you like,

9:43

where there's one star and one planet

9:45

orbiting around it. And then something much

9:47

more complicated, where maybe you actually

9:49

have a few stars in the middle

9:51

and lots of planets orbiting far out.

10:01

So, if we think of atoms like

10:03

tiny planets, with a nucleus in the

10:05

middle and electrons orbiting around the outside,

10:07

what does that mean for Alan's question?

10:10

The atoms of different elements will, of course,

10:12

be different from each other. But

10:14

what about atoms of the same element? Are

10:17

they unique? Let's

10:21

say we have a billion carbon atoms. One

10:24

thing we can say is that they aren't all identical.

10:27

Every element has slightly different versions

10:29

of its atoms known as isotopes.

10:32

Isotopes. That's very slight variations

10:34

on an atom where it

10:36

has slightly more particles than

10:38

you were first expecting. So

10:41

in our billion carbon atoms, it's

10:43

possible to find isotopes that are

10:45

slightly heavier because added to our

10:47

12 particles in the nucleus is

10:49

another neutron. And we call

10:51

this isotope carbon-13. Those

10:54

are the exceptions that sort of proves the rule. By

10:56

and large, you'll just get the

10:58

same number of protons, neutrons and electrons

11:00

for each atom that you collect. Let's

11:05

stick with the normal version of carbon, carbon-12. Atoms

11:10

of carbon-12 can exist in slightly different

11:12

states, which is to do with the

11:14

energy of their electrons. Exactly

11:17

right, yeah. So they can change their state,

11:19

but the number of ways in which they

11:21

can do that is strictly limited. It's

11:24

possible for the electrons to be in different

11:26

energy states. Basically, they can

11:28

orbit at greater distances from the nucleus.

11:31

But there are only a certain number of

11:34

fixed energy levels that electrons can possess. And

11:38

as they orbit the nucleus, these electrons are

11:40

also spinning. A

11:43

bit like how the Earth also turns on its

11:45

axis while it moves around the Sun. Thinking

11:49

of it as spin is not a bad

11:51

start, but of course the reality of it

11:53

is rather more complicated. But it's a bit

11:55

like spin in the sense that it has

11:58

a sense of direction about it. All

12:02

of this is to say that atoms

12:04

of the same element aren't all exactly

12:07

the same, they can exist in different

12:09

configurations or states. But

12:11

from what Andrew has said, there's a finite number

12:13

of these states. And given

12:15

how many squillions of atoms there are in

12:17

the universe, that doesn't leave much room for

12:20

uniqueness. But

12:24

even if that is the case, listener Alan thinks

12:27

there is a way that atoms could be unique.

12:30

Well, if the electrons are moving,

12:32

that will all be unique to

12:34

each atom I feel because there's

12:36

such a vast amount of space

12:39

inside an atom, it feels

12:42

the amount of space and if

12:44

there's movement there, there's a vast

12:46

amount of opportunity for uniqueness. Are

12:49

you saying that there's just, you know,

12:51

there's essentially an infinite number of different configurations and

12:53

that means that then there must be, you know,

12:55

atoms must be unique in some sense? So there's

12:57

just so much space there for them to be

13:00

in, if the electrons are in a

13:02

different position in the

13:04

atom, then the two atoms are different.

13:07

I feel like what Alan is saying here makes

13:09

complete sense. So what's Andrew Ponson's

13:11

take? If you were to

13:13

compare two atoms of the same element,

13:16

wouldn't the position of their electrons as

13:18

they orbit the nucleus be ever so

13:20

slightly different? And wouldn't that

13:22

technically make them unique? Unfortunately

13:24

not. And the reason that that doesn't

13:26

work is because actually the picture we've

13:28

just been painting isn't our best picture

13:30

of how an atom really works. There's

13:33

something that we've neglected here, which is

13:35

quantum mechanics. This idea

13:37

of electrons being like little planets

13:40

whizzing around the central

13:42

nucleus just isn't right. We

13:45

sort of talk in these metaphorical terms, but they

13:47

quickly fall apart. We know

13:49

from experiments that the world down there

13:51

just doesn't work like that. Okay, so

13:53

whenever anyone says quantum, you know, stuff's

13:55

going to start getting a bit strange.

13:57

So could you sort of

13:59

try? best to explain what the quantum

14:01

model of the atom actually is. The

14:04

first thing to say is nobody really

14:06

understands what it means in the sense

14:08

that, you know, our

14:10

notions of understanding is so intertwined

14:12

with our experiences, right? So it's

14:15

often just expressed in terms of

14:17

maths. And that's not what we're

14:19

going to sit here and do, right? We're not going

14:21

to sit down and write down equations. We just have

14:23

to try and understand it in language as best we

14:25

can. Maybe a good place to start

14:27

is to understand why. Why does this

14:30

become necessary? What's wrong with the idea

14:33

of the electrons just being little chunks

14:35

of matter that whizz around like tiny

14:37

little planets? And actually,

14:39

it's already implicit in what we've been discussing.

14:41

If you imagine that you have this planet

14:44

whizzing around the nucleus and it wants to

14:46

lose as much energy as it possibly can,

14:48

the natural conclusion from that

14:50

would be, in that case, it's going

14:52

to spiral in, it's going to keep

14:54

spiraling in until it crashes into the

14:56

central nucleus. And you would

14:58

imagine actually atoms shouldn't be stable at

15:00

all. They ought to just

15:02

collapse in on themselves. And

15:05

the thing that came along to explain that was quantum

15:07

mechanics. So we might have

15:09

to change our picture of the hydrogen atom

15:11

as a tiny planetary system. Actually,

15:14

electrons are not quite like that. You can't

15:16

think of them as planets,

15:18

things with very well-defined

15:20

locations. Instead, you have to

15:23

imagine them as being composed out of

15:25

a wave. So it's more like a

15:27

smear or a ripple that

15:29

is going around the nucleus. Words

15:32

like smear or ripple are really just

15:34

metaphors here, but you can try to

15:36

imagine a circular wave that surrounds us.

15:38

And as soon as you do that,

15:41

then it doesn't have a single

15:43

well-defined location. So this

15:45

idea that you can distinguish things by

15:47

exactly where the electrons are sort

15:50

of falls apart once you get into this

15:52

quantum realm. Quantum

15:54

mechanics means that it's impossible for us

15:56

to pinpoint exactly where an electron is

15:58

at any given moment. even

16:00

if we were somehow able to look

16:03

at a single instant in time. Even

16:05

if you could imagine sort of the

16:07

best camera in the world that can

16:09

take a photograph instantly and so there

16:11

is no time window, even then there's

16:13

a tiny bit of smeariness left. And

16:16

because we're on such tiny, tiny

16:18

scales, that tiny bit of smeariness

16:20

that's left over is

16:22

enough to fundamentally change how we

16:24

should think about material itself. Coming

16:31

back to Alan's question about saying, like, well, we

16:34

can say that this electron is over here and

16:36

on this hydrogen atom and on this one it's

16:38

somewhere slightly different, you're basically saying

16:40

it's impossible for us to do that. We actually

16:43

can't pinpoint where electrons are. That's right. In a

16:45

standard atom, there's just no way to say, oh,

16:47

the electron is there as opposed to, you know,

16:49

halfway round on the other side. Which

16:52

means that listener Alan's argument for

16:54

the uniqueness of atoms based on

16:56

very slight differences in electron position

16:58

doesn't really work because it

17:00

doesn't make sense to even think of electrons

17:02

in this way. So

17:05

let's do a little thought experiment.

17:07

What if we were able to simply

17:09

swap out one atom for another? This

17:11

idea of atoms being interchangeable, if I

17:13

took a hydrogen atom that's inside you

17:16

and swapped it for another one, would

17:18

it be possible to ever know that I'd done that? No.

17:21

If you really just interchanged it and

17:24

it had, you know, similar amount of energy

17:26

in it, then no, you couldn't tell. OK.

17:29

And then if I

17:32

took that a step further and replaced every single

17:34

atom in you with another one, another version of

17:36

it, would you be able to tell that

17:39

I had done that? Would you be still you? I

17:42

believe I would still be me. I mean, this,

17:44

of course, is a big question in the Star

17:46

Trek universe, where, as far as I understand it,

17:49

when they transport from one place to another, essentially

17:51

the atoms are all sort of disassembled in one

17:53

place. And then a different set

17:55

of atoms are assembled in

17:58

another place. Who we are. is

18:00

about the way we're configured, you know, right

18:02

down to the configuration of the

18:05

neurons inside our brains. That

18:07

of course is, you know, also made out of atoms

18:09

and so on. So I think

18:12

you are quite at liberty to replace all the atoms

18:14

in my body if you wish to and you have

18:16

the right technology to do that. I'm not too worried

18:18

about that. Okay cool, we'll get you to sign a

18:21

disclaimer to that effect later. You're

18:24

listening to CrowdScience from the BBC World

18:27

Service. This

18:33

podcast is brought to you by eHarmony, the

18:36

dating app to find someone you can be

18:38

yourself with. Why doesn't eHarmony

18:40

allow copy and paste in first

18:42

messages? Because you are unique and

18:44

your conversations should reflect that. eHarmony

18:47

wants you to find someone who will get

18:49

you. How are you going to know who

18:51

gets you? If people see you the same

18:53

generic conversation starters, they message everyone else. Conversations

18:56

that actually help you get to know

18:58

each other. Imagine that. Get who

19:00

gets you on eHarmony. Sign up today. Helps

19:12

you sleep at a comfortable temperature? Sleep

19:15

Number SmartBeds lets you individualize

19:17

your comfort, so you sleep

19:19

better together. J.D. Power Rinks

19:21

Sleep Number Number 1 in

19:23

customer satisfaction with mattresses purchased

19:25

in-store. Shop the

19:28

sleep number smart bad starting at

19:30

nine hundred and ninety nine dollars

19:32

for a limited time. Prices higher

19:34

and Alaska and Hawaii for Jdpower

19:36

Twenty Twenty Three Award Information: Visit

19:38

jdpower.com/ Awards only it to number

19:40

store or sleep number.com. I'm

19:48

Anna Jagatia and today we're answering

19:50

listener Alan's question, are

19:52

all atoms unique? It's

19:56

a question that gets right to the heart of

19:58

the nature of reality. Great philosophical

20:00

minds have given a lot of

20:02

thought to uniqueness, but according to

20:04

our current understanding of atomic theory,

20:06

it turns out that atoms are

20:08

not unique. That

20:10

isn't to say that they're identical. They

20:13

can exist in different states to do

20:15

with energy and spin, but there aren't

20:17

an infinite number of these configurations of

20:19

atoms, just a handful. And

20:22

listener Alan's argument for the uniqueness

20:24

of atoms based on very slight

20:26

differences in electron position doesn't really

20:28

work either. In fact it doesn't

20:31

make sense to even think of electrons in this way.

20:34

And according to quantum mechanics, this is baked

20:36

in to the properties of the universe. But

20:42

quantum theory has even weirder implications

20:44

for Alan's question. Because

20:47

once you get to atoms with

20:49

multiple electrons, thinking about uniqueness becomes

20:51

very strange indeed. So

20:53

in the structure of the atom, as you get larger and

20:55

larger atoms, electrons, you know,

20:58

many many many electrons, but they come

21:00

in these sort of twos. That's philosopher

21:02

Elinor Knox, who we heard from earlier.

21:05

Those two electrons effectively share all

21:07

of their properties, exist in a

21:09

mathematical state such that they share

21:12

every single property that you

21:14

could possibly express about them. Okay,

21:16

I think that's quite sort of profound, isn't it? What

21:20

do you mean by they share every single property? Something

21:22

I can think of is it's the same between them

21:24

both. Yeah, I think that's

21:26

right. So I mean, actually, sometimes philosophers, modern

21:29

philosophers end up going back to Leibniz with

21:31

the puzzle, because of quantum

21:33

mechanics, because they worry that, look,

21:36

now that we're in quantum mechanics, what even makes

21:38

it the case that there are really,

21:40

you know, two particles there rather than one, given

21:43

that now we have a kind of state

21:45

forced upon them where you can't really say

21:47

anything about each particle individually. Okay, so you're

21:49

kind of moving into a realm where you

21:51

maybe, well, they're the same in a sense,

21:53

is that what you're saying? Yeah, I mean,

21:56

interestingly, quantum mechanics does have a thing called

21:58

So there's kind of a fact that there

22:00

are two of them and it makes a

22:02

difference that there are two of them. But

22:05

there's nothing you can say about electron number

22:07

one that's different from what

22:09

you can say about electron number two. They're

22:12

just the state that they

22:14

exist in, the quantum state they exist in

22:16

has exactly the same features. Can't

22:19

call one electron Alice and one electron Bob and

22:22

give you some kind of description of Alice and a description

22:24

of Bob that would pick them out separately. Which

22:26

of course you can do with all the

22:29

ordinary things that we meet. So I mean

22:31

that's kind of as non-unique as it's possible

22:33

to be, right? Yeah, yeah. For two different

22:36

things. Okay. And it's forced on

22:38

us by the laws of quantum mechanics. So it's not just something that

22:40

could be the case or happens to be the case. It's

22:42

something that quantum mechanics forces to be the

22:45

case with its laws. The way

22:47

that the rules of quantum mechanics work, particles

22:49

have to behave that way. I

22:53

think what Eleanor is saying here

22:55

is that these pairs of electrons

22:57

are so identical and so indistinguishable

22:59

that it challenges our conception of

23:01

what it actually means for something

23:03

to be unique. If

23:06

these two particles are the same in every single

23:08

way, even in terms of how

23:10

we describe their position in space, how

23:13

can they even be two particles?

23:17

Well, if your head is spinning like an

23:19

electron right now, mine is too. So don't

23:21

worry. And even physicists

23:23

don't really understand how quantum mechanics

23:26

actually works. Now

23:30

before we end this episode, there's one last

23:32

thing I wanted to explore, which

23:35

is really what we actually

23:37

mean by uniqueness. If

23:39

we go back to Listener Allen's question,

23:41

he pointed out that every blade of

23:43

grass, every snowflake, every grain of sand

23:45

is unique. But if the

23:48

atoms themselves that make all these things aren't

23:50

unique, when does uniqueness really

23:52

begin? I think we can say

23:54

there are things in the universe that could be unique,

23:57

might well be

23:59

unique. But I think that really becomes a

24:01

matter of complexity. So you notice

24:03

that uniqueness kind of disappeared as we drill down

24:05

to smaller and smaller and simpler and simpler particles.

24:09

Of course, when you combine loads of those

24:11

particles, the way in which we combine them

24:13

can be done in many billions, trillions, and

24:15

so on of ways. Once you have something

24:17

the size of a grain

24:20

of rice, let alone something the size of a human, there

24:22

are an awful lot of ways to combine particles

24:24

in different ways. So that's

24:26

why we see the kind of variety we

24:29

see in, say, snowflakes or leaves, or

24:31

indeed in humans. But

24:34

there's nothing in the physics that tells

24:37

you that it's not possible to have

24:39

a particle-for-particle replica of one

24:41

of these systems. So it seems

24:43

more a matter of just probability and playing

24:45

the odds now. So it sort of relates

24:48

to, I guess, the

24:50

number of atoms and the size of

24:52

the universe. So if the object that

24:54

we're thinking about has more atoms or

24:56

more constituent bits in it, then there

24:58

are bits in the universe, then it's

25:00

unlikely that you're probably going to get

25:02

that same combination of things again.

25:05

But it could happen just by chance. Yes,

25:08

I think that's right. I mean, one thing

25:10

to say is that the numbers get mind-boggling

25:12

very fast here. So the universe is really,

25:15

really, really extremely large. And

25:18

so even though the numbers of particles

25:20

in a grain of rice

25:22

are mind-bogglingly large, the size of the

25:24

universe is usually mind-bogglingly larger. So

25:29

certainly there will be some systems for

25:31

which it's extremely unlikely that

25:33

you would see a replica. There are some

25:35

systems for which it's extremely likely there's a

25:37

replica somewhere. But I think it's not

25:39

that there's anything stopping any

25:42

modulo Leibniz's theological worries,

25:44

which modern scientists probably

25:46

usually wouldn't have. There's

25:48

nothing actually preventing perfect replicas in

25:51

the universe. It's just that

25:53

in the same way that if you roll a dice,

25:56

2,000 times you get a particular sequence of numbers.

25:59

You're very, very, very... unlikely to roll that dice

26:01

2000 times and get that same

26:03

sequence of numbers again, you're very, very unlikely

26:05

to reproduce atom for atom replicas elsewhere

26:08

in any reasonable sized

26:10

bits of the universe. Notice

26:12

there the important caveat – reasonably sized

26:15

piece of the universe. But

26:17

what about the entire universe? There

26:20

is, of course, a sting in the

26:22

tail here, which is that our universe may

26:25

be infinite. We don't know. We don't know

26:27

how big the universe is. So if the

26:29

universe literally goes on forever, then

26:31

anything, no matter how complicated,

26:34

is repeated somewhere. And

26:36

that is a really bizarre thought. So

26:38

potentially if the universe is infinite, then

26:41

potentially nothing is unique? Yeah, if the

26:43

universe is infinite, then things must

26:45

get repeated because there's only a certain number

26:47

of ways. Even if it's very large, there's

26:50

still only a certain number of ways of,

26:52

say, bringing Lego bricks together. And in the

26:54

same way, there's only a certain number of

26:56

ways of bringing atoms together to form things

26:58

like you and me. Very

27:00

weird things happen with probabilities when we start

27:02

talking about infinity. It is mathematically true that

27:05

once you move to an infinite universe and

27:07

an infinite number of things, then you would

27:09

expect to see any

27:11

possibility crop up, in fact, an

27:13

infinite number of times. That

27:15

is a – that gets us deep into infinity.

27:19

Infinity is bigger than you think. Exactly. If

27:22

there's an infinite opportunity to do that, then

27:24

there is a copy of us somewhere out

27:26

there, far, far beyond

27:28

the reaches of our telescopes. Somewhere

27:31

out there, we're having this interview in

27:33

another studio on an alien planet. So

27:40

Alan, you wanted to know if all

27:43

atoms are unique? By

27:46

shrinking ourselves down to an atomic

27:48

scale, we've seen that in the

27:50

quantum realm, our ideas about reality

27:52

become pretty strange. Electrons

27:54

are not like tiny planets orbiting a nucleus.

27:56

They're more like smeared out waves, which are

27:58

more like a small wave. without definite

28:00

fixed positions. In

28:02

fact, pairs of electrons are so similar that

28:05

it's impossible to tell the difference between the

28:07

two, which is about as un-unique

28:09

as two things can get. But

28:12

then again, even things like snowflakes or human

28:14

beings, which common sense tells us have to

28:16

be unique, may not be as special as

28:18

we think. If our

28:21

universe is infinite, then there are

28:23

actually an infinite number of them. So

28:25

perhaps nothing is unique? This

28:29

is definitely not where I thought we would end

28:31

up, but here we are. Over

28:33

to you, Alan, for the credits. That's

28:38

it for this episode of Crowd Signs

28:40

from the BBC World Service. It

28:43

was presented by Anand Jagatia

28:45

and produced by Florian Ball. Today's

28:48

question came from me, Alan,

28:50

from Northumberland in the UK.

28:53

If you have a science question you'd like the

28:55

Crowd Signs team to look into, you

28:58

can do what I did

29:00

and email crowdsigns at bbc.co.uk.

29:06

Thank you very much for listening and

29:08

bye. Okay,

29:11

so before we go, we have a

29:13

bit of a podcast bonus for this

29:15

episode. So when we were researching this

29:17

topic, we were absolutely determined to prove

29:20

these pesky physicists wrong, like listener Alan

29:22

and find a loophole that would show

29:24

atoms can actually be unique if you

29:26

just think of them in a different

29:28

way. And I want to

29:30

introduce producer Florian who spent a lot of

29:33

time trying to do this. Hi, Florian. Thanks

29:36

for having me on, including me in

29:38

the podcast that I produce. You're

29:40

welcome, anytime. So tell us about

29:43

this rabbit hole that you went down.

29:45

Yeah, I spent a lot of time

29:47

going into this, spent a lot of time in the quantum

29:49

physics of it. And somebody thought, we got to go beyond

29:51

the quantum physics and maybe

29:53

there's something I can uncover

29:55

somewhere. And while I was

29:57

in South Africa recently, I couldn't help but

29:59

do an interview. somebody who's actually an astronomer.

30:02

Okay, so walk me through what you found

30:04

and how you kind of went on this

30:07

journey to try and find a unique atom

30:09

somewhere in the universe. Well,

30:11

in this episode, we spent a lot of time on hydrogen.

30:14

And a lot of it

30:16

is just floating around in space as

30:18

neutral hydrogen. So what I want you

30:20

to picture is a galaxy far, far

30:22

away, millions of light years, where there's

30:24

a single hydrogen atom in a sea

30:26

of hydrogen just floating in space. One

30:29

proton, one electron. And we

30:31

talked about spin in the episode. So suddenly

30:33

the spin of that electron can change. The

30:36

electron flips its spin so

30:39

that it's opposite to the spin of the

30:41

proton. This is astronomer Sarah Blythe, head of

30:43

the Department of Astronomy at the University of

30:45

Cape Town. If you were to watch one

30:47

hydrogen atom, you'd have to watch it for

30:49

about 15 million years to watch for that

30:51

one transition to happen. We're witnessing

30:54

something quite special here. 15 million years

30:56

is a long time in human timescales anyway.

30:58

Were you hoping that, you know, maybe you

31:01

could say at that moment in time that

31:03

specific hydrogen atom is unique? Oh,

31:05

absolutely. That was that was what I thought.

31:07

And and it is in some

31:09

way, I guess, different from sort of the

31:12

atoms that are directly around it. But

31:14

the problem is hydrogen is the most abundant chemical

31:16

in the universe. There's so much of it out

31:18

there that this happens a lot. So so one

31:21

hydrogen atom, the one, the singular one that we

31:23

talked about, releases a photon,

31:25

a photon of light, essentially a wave

31:27

of light. It's exactly 21

31:29

centimeters long. It just heads out into space. And

31:33

obviously some of these hydrogen atoms will emit

31:35

their photons in a direction that doesn't come

31:37

to Earth. But luckily, because there are just

31:39

so many hydrogen atoms in the universe at

31:42

any given time, some of them will

31:44

be emitting in the right direction and those

31:46

photons will make it to Earth. Now I

31:48

want you to picture another place. It's a

31:50

semi desert. It's called the Kuru. It's in

31:53

northern South Africa. And Sarah has

31:55

actually been there for research. It's quite

31:57

an amazing scene. So it's very beautiful

31:59

landscape. a few quiver trees dotted about,

32:02

and then you've got these big

32:05

dishes coming out of the ground. They

32:08

have a 13.5 meter diameter, so they're quite

32:10

big. 64 different

32:12

dishes that make up the Meerkat radio

32:14

telescope. Nice. I've always wanted to go

32:16

there. So you managed to take a

32:18

trip? I wish. The

32:21

reason it's in such a remote place is that

32:23

they need complete radio silence. If I show up

32:25

there with a phone or even recording equipment, they're

32:28

not going to let me do it. But that didn't allow me

32:30

to visit. But if a photon

32:32

hits one of those dishes, we can

32:34

detect that. We can detect that signal.

32:37

And it allows researchers to create images,

32:39

including parts of the galaxy which have never been

32:42

seen before like this. So welcome to

32:44

the lab. I'm Lucia Marchetti.

32:46

I'm the director of the Idea Visualization

32:48

Lab here at UCT. Would it be

32:50

possible for me to try it out? Absolutely. I mean,

32:53

you're here for that, right? Yeah.

32:55

So, so what do you

32:57

grab the headset? So

32:59

we have already loaded the... It seems

33:01

to be like some... Swimming in the data

33:03

now. Swimming in the data. But there seems

33:06

to be like this, this little blob. Yes. It's

33:08

yellow in the middle. And then a couple of

33:10

blobs around it. What am I looking at? You

33:12

are looking actually to a cube in which we, for

33:15

the first time, identified 49

33:17

new galaxies having a hydrogen

33:19

content. Oh, wow. And they

33:21

have been nicknamed the 49er.

33:25

And you can tell that is amazing

33:28

because we are not used to

33:30

find hydrogen so quickly. And because

33:32

it's a very hard science to

33:34

do and it's very faint to

33:36

detect in galaxies. And this

33:38

distance is very difficult as well. I

33:40

still find it crazy that just

33:43

hydrogen, this is the tiniest element that

33:45

we have on the periodic table that

33:48

somehow sends out the signal that we

33:50

can then look and observe these galaxies

33:52

that are incredibly far away. Yeah. Yeah.

33:55

But I mean, it's what I say to my

33:57

students all the time. I mean, in the end,

33:59

I. hydrogen is very, is this

34:01

building block. So in the end, the

34:03

stars, which are, and then galaxy, which

34:05

are very complex objects, still starting from

34:08

the very same building block of hydrogen.

34:10

Yeah. Yeah,

34:13

I mean, that really, that is amazing, how

34:15

these quantum processes to do with

34:17

spin, which is a weird concept to get

34:19

your head around, that that

34:21

can have these real world effects that

34:23

actually let us detect massive galaxies

34:25

that are hundreds of millions of light years

34:27

away from us. Yep,

34:30

and we wouldn't be able to do it

34:32

if it wasn't for this quantum world being

34:34

so strange and being very, very, very predictable,

34:38

which is interesting. We're sort of ending

34:40

the episode at the opposite of where

34:43

we started it. You know, it's so

34:45

not unique that we can literally say,

34:47

hey, we received this much signal from

34:50

hydrogen from that area of the universe.

34:52

That means it probably has around this

34:54

much hydrogen because we know

34:56

exactly how many atoms do it. Well,

35:00

I definitely applaud your

35:02

trying, Florian, and

35:04

it was definitely an interesting rabbit hole to

35:06

go down, so thank you. No

35:09

worries, thank you for having me. Welcome

35:19

to The Bright Side, a new

35:21

kind of daily podcast from Hello

35:23

Sunshine, hosted by me, Danielle Robé.

35:25

And me, Simone Boyce. Every

35:28

weekday, we're bringing you conversations about

35:30

culture, the latest trends, inspiration, and

35:33

so much more. We'll hear from

35:35

celebrities, authors, experts, and listeners like

35:37

you. Bring a little optimism into

35:40

your life with The Bright Side.

35:43

Listen to The Bright Side from Hello Sunshine

35:45

on the iHeartRadio app or wherever you get

35:47

your podcasts.