Malcolm? Oh no, that's alright.
Does he let people drink in the observatory?
Right, we're breaking the rules.
I'm Marnie Chesterton, host of CrowdScience, and for a previous episode on
the BBC World Service I climbed up to a little-known observatory in central
London, partly to drink hot cocoa but mainly to uncover the secrets of the Universe.
If you look up, you can see it's sort of hazy. There are stars, you can see
the stars but it's sort of hazy. That's just pollution in London and it
means that you can see bright things. But it's quite difficult spotting galaxies.
Step on the planks.
The reason the CrowdScience team tackled
ice-covered planks at nighttime was that listener Koon-Hou from Singapore
sent us a question and we exist to answer your science queries. Here's a quick recap.
My question is regarding dark matter and if there's any way that we
can understand it more and maybe find it useful for daily living.
Our quest to find Koon-Hou answers took us down the deepest mine in the UK.
How deep is it?
It's 1.1 kilometres.
So how long do we have to spend in the lift?
Seven, eight minutes.
That's a long time to spend in the lift.
And we met professor Katherine Freese from the University of Michigan.
And I'm also a guest professor at Stockholm University.
And how long have you been working on finding dark matter?
I have been working on it since I was a
graduate student so I'm gonna say that was 25 or 30 years ago. Oh more than that.
OK, so don't tell people.
We asked Katherine what real-world applications
might come from this search for dark matter.
You know at this point I don't
know what those are gonna be but the past history shows that there will be
something really major that comes out of it.
So I can give you some examples from the past.
One of the big ones that came out
of nuclear physics is MRI. So nowadays MRI is used in hospitals everywhere
where - my shoulder hurts, what's exactly going on? -
so they did an MRI of that.
But that again was a surprising off-shoot. It was based on detectors for
nuclear physics. Then they turned out to really change our lives for the point of
view of health.
You can hear more on this if you go back and listen to that show.
Just search for 'why does dark matter matter?' in your podcast app.
So that was then.
Now CrowdScience often turns into a kind of conversation with our
listeners because episodes spawn more questions and it turns out that you lot
love a physics mystery. We received loads more emails with questions relating to
dark matter. Questions that we're going to tackle today.
To help me I'm joined in the studio by two astrophysicists. Down-the-line from
the University of Arizona is Burçin Mutlu-Pakdil and sitting next to me is old
friend of the show Matt Middleton from the University of Southampton.
Welcome to you both.
Thank you.
Old?
Old as in been on the show before.
Grizzled.
Yes.
First I think we need a
recap on what dark matter is. Burçin, you first.
So, most of the things that we
see and we are familiar with is normal matter and it is only 5% of the Universe.
So 25% of the Universe is dark matter. That's the mysterious object. We don't
know much about the nature. We cannot touch it, we cannot smell it, we cannot hear it.
But it is there because we can see its gravity there and the rest of
the Universe, the giant portion, is dark energy which is much more mysterious
than dark matter. We just know it is energy that makes the Universe expand.
OK so this stuff, dark energy and dark matter, it's most of the make-up of the Universe
and dark matter is five times as much as all the stuff that we can see -
the stars and you and me and everything.
Everything that I'd consider to be stuff.
How do we see normal matter like the
microphone in front of me and you?
We see objects because of light, which is
electromagnetic radiation and we see objects because the light bounces off to
our eye and from that we can see the objects. But the dark matter doesn't have
that effect. It is just transparent. It just goes through it. So because of that
we cannot see them.
So if you shone a light on dark matter, what would happen?
It'd go through.
What we call the interaction, the ability for this dark
matter to interact with anything is incredibly small except we think via gravity.
So let's talk about gravity.
Gravity is the attraction between two things that have mass. The reason we know that
there's dark matter out there is because matter has mass. The bigger the mass, the
stronger the gravitational pull. Our planet orbits the Sun because the Sun's
massive mass pulls it into orbit. So we can't see dark matter. But can we see gravity?
Yes and a Swiss astronomer first noticed this whilst watching how
galaxies move. His name was Fritz Zwicky
This is a very famous scientist called Fritz Zwicky and he looked at galaxy clusters. Now galaxy
clusters contain thousands and thousands of galaxies and we think that these
things should be essentially not flying apart. So if you look at how fast they're
going you can work out how much mass there should be there and Fritz Zwicky
discovered that in order to keep them shuffling around all over the place and
not flying apart yet to have much more mass there than you could see in the stars.
I wanted to see this for myself and so paid a visit to professor Malcolm Fairbairn.
He's the one with a telescope dome on the roof of his university,
King's College London.
If you look up there you'll see a cloud in the middle of the eyepiece and it
really doesn't look like very much. In fact you might find it quite difficult to see it.
No, I can see it. Yeah there's a fuzzy bit.
Mm-hmm. Yeah so that's the very centre of the Andromeda galaxy.
Is Andromeda our closest?
Andromeda's is the closest big galaxy.
There's a few little ones that are closer. Well there's lots of little,
very little ones, that are closer but Andromeda's about the same size of the
Milky Way and Andromeda is moving towards us. I think it's about 150
kilometers per second and we can use that observation to weigh the entire
system and the answer is that the whole thing weighs something like five million
million times the mass of the Sun and we can't see anywhere near that number of
stars so there has to be something else there and we think that most of it is dark matter.
So there's a whole load of stuff out there that's stuff that we can't see
but we think is there?
Yeah and there's lots and lots of other observations
which suggests the same thing. From the smallest galaxies right up to the
largest clusters, we see that on every scale we need something to explain how
quickly things are moving around that we can't see.
Physicists like Malcolm have
calculated the amount of mass in things like the Andromeda galaxy and there's lots
supposedly there that we can't see, hence dark matter.
Burçin, can we talk about what dark matter might be?
There's a huge discussion about that,
we really cannot say anything about its nature yet so we right now we
have a promising hypothesis that suggests that it is called matter which
doesn't refer to the temperature but it is referring to the speed of that
particle which means it is moving very slowly and based on these cold dark
matter idea right now we could actually explain most of the observations that we have today.
Cold meaning slow moving. Dark meaning can't see it.
Matter meaning stuff with mass. The cold dark
matter hypothesis fits what we can see but physically I mean what is it?
This is where theoretical physicists come up with ideas that explain what we can observe.
There are several competing theories with great sounding names like WIMP.
Well it turns out they're WIMPS. Which I don't mean that they've got no
sort of spine or you know any fortitude. What I mean is they're weakly-interacting
massive particles - WIMPS - and our best guess of the minute is that
they formed in the very, very early Universe. Now our Universe went through
something called the Big Bang. OK now the Big Bang was an explosion in space
and time, of space and time, and it was really, really hot. The great thing about
things that are really, really hot and you've got really high-energy radiation is that
you can spontaneously create matter out of radiation. The remnants of those
particles are what we think is dark matter.
While Matt is busy thinking about what dark matter is, listener Gautam is
thinking about what this mysterious stuff might contain.
Hello, I'm Gautam from New Delhi in India. My question for CrowdScience is this.
If there is dark matter and dark energy does it mean that there could be dark life too?
So since I was you know going through scientific stuff and I realised that what you need
for life is energy and matter. So now if there is dark energy and dark matter it
was one of those thought experiments so since I couldn't find an answer who
better than to ask outside?
Who better indeed and it kind of makes sense
because the stuff that we're made up of is only 4% of the Universe and if the
rest of the Universe is dark, what's to say that there isn't something or
someone somehow lurking out there?
Exactly, so if there is such a huge chunk
that is absolutely unknown, why discount anything?
Do you imagine it as something
that is around us or is it in a galaxy far, far away?
It has to be around us like
what we are given to explain is dark matter is everywhere, it's in this room,
it's outside the rooms, it's everywhere. So if we are surrounded by it, we are living in it.
Just listening to what you guys are talking about I was imagining something
like a massive jungle all around us with, like, I don't know, dark lizards.
Exactly, yeah.
I don't know what else... flying all around us and yet we're totally unaware.
Totally, yeah, exactly.
It's kind of nuts isn't it?
That was producer Graihagh and Gautam and me going through his thought experiment,
which sounds very science fiction. But how much of it is science and how much
of it is fiction? I've got two astrophysicists who may be able to help me.
Matt, I'm gonna come to you first because you are shaking your head and
you have been all the way through our talk of feelings and lizard worlds.
Don't worry, I love feelings and lizard worlds.
So what do you reckon? Like, if there is that much that we can't see
maybe there's all sorts of exciting things going on in it that we just can't see?
The answer is probably no, unfortunately. The reason for that is
that life as we know it, complex organic creatures, require quite complicated
molecules and things like that, so amino acids which are built of molecules,
which are built of atoms, which are built of particles that have been glued together.
Now the leading contender for dark matter are particles which only clump together
because they have mass. They don't interact in any other sort of way.
So actually creating complex structures of the sort that produces life doesn't seem possible.
Now dark matter does form structures in the Universe but those
structures are not sentient.
Burçin, if I can bring you in at this point.
I mean, we're assuming that this life
would be like us but if dark matter is fundamentally different from normal
matter is there any reason to think it wouldn't be able to glue complex
molecules together using another force?
For me I feel like yeah it can be but
for us as a scientist we need proof maybe, maybe a signal, that there should
be an event that we cannot explain with our own knowledge. Then we could come up
with hypotheses such as dark life. Then we will say that OK only dark life
would explain this thing but right now we don't have that.
OK so it might be possible but there isn't any evidence or any theory by which it might
be working or having any influence so it's going to stay in the realm of
science fiction for now?
Yeah, it is not a scientific idea but it's totally a great idea.
Matt, anything to add?
I mean, you should never close your mind to ideas. My view is no. From a scientific point of
view what we know about dark matter means that you could not form life from it.
We rang Gautam and played him the interview.
Hello. It's Graihagh and Marnie.
He has some poignant points that we want to share.
Well all I can say is that if dark matter wasn't there the
galaxies as we know them they wouldn't be able to form. If dark matter wasn't
there the galaxies have the momentum that they would spin out of control.
Now if they would spin out of control obviously we would not have galaxies, we would not
have stars, stars would not have planetary systems and by extension life
as we know it would not exist without dark matter.
So that's an interesting point
about life as we know it existing because of dark matter but how do you
feel about dark life? Life as we don't know it not existing according to the astrophysicists?
I think to give an absolute categorical refusal that dark
life cannot exist is very unscientific. Since we know nothing about dark energy
or dark matter we may know a little bit about dark matter but dark energy is
absolutely dark so to give such a categorical refusal that dark life is
not possible, well it seems very, very unscientific.
Well I think everyone would be in agreement that more research is required.
Yes.
Gautam thank you so much. I really appreciate your question.
Thank you so much. It was a pleasure talking to you.
You're listening to CrowdScience from the BBC World Service.
This week Marnie Chesterton is finding out the answers to our questions about dark matter and dark energy.
If you have a question you'd like us to answer you can send yours to
crowdscience@bbc.co.uk. That's exactly what Yoseph did.
My name's Yoseph and I'm from Utah in the United States of America. My question
for CrowdScience is could black holes make up some of the dark matter in our Universe?
So... yeah.
Are you particularly physics-minded?
Yeah I work in aviation so I think about physics a little bit here and there.
I don't feel like I'm
qualified to be asking these questions on behalf of you guys.
Neither do I.
But it's fine.
We're gonna have two physicists in the studio and I'm gonna put your questions to them.
Awesome.
Matt.
So there's a competing theory to WIMPS which
beautifully is called MACHOs.
Match oh! No, we're not doing it. Oh you guys suck.
I mean, I just thought I'd let you sing a solo there.
Right so MACHOs are massive compact halo objects. So around
our galaxy we think there is a dark matter halo and we don't really know
what it's made of. What we do know is that when stars die
they form objects which typically are either really, really faint so that we
could never actually detect them if we looked for them and black holes don't
emit light either so they're difficult to find. So for quite a long time there's
been this idea that maybe some parts of dark matter could be these very faint or
completely black objects.
So Yoseph is right that black holes are contributing
to the amount of dark matter but do we have a figure? Do we know how much?
It's just incredibly small. I'm afraid I don't know an exact figure but it isn't very, very much.
Is it like 1%?
I suspect it's lower than that.
OK back to Yoseph.
I feel surprised actually. I just thought of it and I had no idea I
was gonna be totally wrong so I feel pretty surprised actually.
Where would you like your Nobel Prize to be sent?
Well I guess I'd like to pick it up in person.
Oh yeah good point.
So as we've heard, dark matter makes up about 26% of the Universe. The normal
matter, the stuff we can see around us, that's four percent of the Universe so
by my maths that's a total of 30%, leaving 70% unaccounted for.
Scientists call this segment dark energy. Do we know what it is and if not will we ever know?
That's what listener Zuzelle got in touch to ask and I'm here at the University of
Cape Town in South Africa to try and find an answer.
Yeah I'm Renato Costa. I'm from Brazil
and I'm doing my post-doc here at the University of Cape Town.
So Renato, what is dark energy?
Yeah if you think about the Big Bang and
gravity the way it is, gravity is attractive and if it started as an
explosion all the matter is going further and further away but it's
attracting each other so it should be decelerating, stopped at some time.
What we observe is the opposite. It's going further away and accelerating so that's
what we call dark energy. So I have here a very simple experiment to show that
which is a balloon with some dots on that and like the dots are the galaxies
we are observing and the balloon itself is our Universe. So if I blow this balloon.
[Inflating noise.]
So Renato has drawn some black crosses on an orange balloon and you've
blown it up a little bit and there's a distance between I'd say sort of a
couple of centimetres between each.
Exactly I have a tape measure here you
can measure that in centimetres.
OK... four centimetres.
OK so imagine that that's our observation now and later in the day or
in the years I observe again and then it's basically what's happening is the
Universe is inflating
[Inflating noise.]
Now the distance between our galaxies is seven centimetres.
Exactly. So that's the concept of dark energy.
The thing is that we usually want to know more than just
observation itself. We want to explain that and mathematics usually
gives you the language to describe that deeper and then you kind of lose track.
It's exactly like if I start talking to you in German here. Maybe you know German
but anyway Portuguese because I'm from Brazil. So if I start start talking
Portuguese you're not going to understand it, which is completely,
completely normal. I love it though, we're getting into the realm of philosophy.
We did a programme on magnets and I was desperately trying to understand
electromagnetism and I found it a huge comfort that Richard Feynman said I can't
explain magnets in any way that would make any sense to you and I think he was
just talking about... he could explain them but it's in a language of maths which
works best written down and it's not really a language of conversation.
Yeah.
We're in a room with blackboards with all sorts of mathematical equations written down.
Exactly.
Not a great language for radio.
I agree.
Disappointing.
But we thought we'd give it a go all the same.
Renato tells me that we don't know what's causing the Universe to expand but
scientists have some ideas and one popular one is that we need to modify
Einstein's theory of gravity. Tweak our equations so to speak. That sounds easy, but it's not.
But also not only that you have to recover all the successes from
general relativity.
Because some people propose modified gravity theories that
explain dark energy but masses with all the other successes of general relativity.
So Newton's theory
of gravity explains most of the stuff that I can see. Einstein's explains even more.
People when they're trying to modify that to explain dark energy
haven't come up with anything that doesn't mess with the building
blocks that we've already explained.
It usually is easy to
explain dark energy but you mess with everything else at the same time.
To modify that is not a easy task.
At this point I'd like to introduce CrowdScience
listener Lawrence. He's come up with a different theory to explain dark energy.
My name is Lawrence. I'm from the Canary Islands. I was actually born in
New Zealand but I've lived in Europe most of my life and I'm now a Spanish citizen.
Great and what is your question for CrowdScience?
My question is could
the effect that we perceive as being caused by dark energy have an origin
outside our Universe? Is it possible that our Universe although vast is merely a
bubble in something much more extensive that surrounds it and beyond the limits
of our perception and that as the matter in our Universe expands within its
bubble and gets nearer the limit, the mass outside exerts a greater
gravitational pull on it and causes the rate of expansion to increase.
So when people talk about the Big Bang it makes you think of our Universe as an
explosion, expanding out into the void. What Lawrence
who's a maths teacher is suggesting is more like our Universe is an air bubble
in a massive block of Swiss cheese. So that means that there's a huge amount of
matter surrounding our bubble and as we've established, more mass means more
gravitational pull. So the huge amount of mass outside our air bubble Universe
could be pulling the Universe apart. I put the Swiss cheese theory to Renato,
who drew me a diagram to help explain that the idea of forces pulling the
Universe apart doesn't add up.
We draw these over density everywhere or
the circle of extra matter outside the horizon and what I'm saying is that it's
not possible because gravity will pull in all directions actually exactly equal.
So this statue is not gonna move.
So it's the material from one side's
gonna pull us but the material from the other side is gonna pull us and in
conclusion we won't go anywhere.
Exactly. Nothing will move.
We'll be exactly compensated from the other side.
So the only real way of
explaining the acceleration of the Universe as far as you guys worked out
is that something between the galaxies that is pushing everything.
Yeah something from inside. It's not something from outside.
That's a shame
because I really like Lawrence's theory I was like, oh yeah of course, why are we looking at all
of this stuff that's being made inside space? Actually maybe there's just
something outside that we can't see that's pulling everything? I thought
about that as well and I was like, and that's a good thing to do, why not? Then I
got the answer. So, cool. But it's not that simple so it's a very good question.
In summary, dark energy could be a modified theory of gravity
but it needs to work with Einstein's and Newton's explanations and if this is the
answer no-one's come up with it yet. Sadly for Lawrence, Swiss cheese theory is wrong.
Our Universe is expanding and pushing apart, not being pulled.
But this isn't the only idea. There are loads of theories on this because dark energy is
even more of a mystery than dark matter. Maybe dark energy is a fifth force to
add to the four fundamental ones we have in the Universe? But back to Zuzelle and
other listeners who want answers. Will we ever know what it is?
But South Africa itself has the SKA, which is the Square Kilometre Array, which would be
the largest radio telescope on Earth.
And that's gonna test dark energy theories?
Yeah that would be great for testing dark energy theories and the dark energy itself.
Do you think you're gonna get an answer in your lifetime?
I would say that for the new generation that wants to study physics and cosmology or
astrophysics the two biggest problems is dark matter and dark energy so that any
person that is willing to study these things should attack these problems.
Thanks to Renato Costa in Cape Town and his balloon-blowing Universe.
[Inflating noise.]
Also thanks to our studio physicists Matt and Burçin. I had one final question
for them, which is why is finding dark matter and dark energy important?
Because the Universe is full of them!
We really understand, we really want to know what is going on in the Universe and how the
Universe works. So to really understand what's going on in everything in
the Universe, in galaxies, we really need to understand the nature of the dark matter.
With the current models we have a nice picture that explains most of the stuff
that we see but still it's not enough without the nature of dark matter.
We are facing lots of problems in our observations.
So I completely agree that
understanding dark matter is really important. It's important for particle
physicists and it's important for astrophysicists and it's kind of
important for us as well because the stuff that's in the Universe - so normal
matter, radiation, dark matter, dark energy - if you add all that up that tells us
what's actually going to happen to the Universe. If there's too much stuff the
Universe will end up contracting back onto itself when it was something called
a Big Crunch and so everyone gets really really close together they're really hot
and everyone dies. Or maybe there's not enough stuff in which case things start
flying apart and it's a bit sad, everyone gets a bit cold and the Universe dies
that way. So understanding and weighing that stuff is really, really important
for the fate of our Universe. Is the fate of our Universe a big enough reason?
Yeah that's a pretty big and depressing reason. It ends in death doesn't it?
Well, doesn't everything?
Just to reassure people, this isn't happening in the next four to six years, is it?
I promise nothing.
I want people to be phoning in and saying that the Universe is going to end.
No, not for a very, very, very long time.
We're talking millions, billions.
Numbers that are so big it shouldn't worry you.
OK, phew.
On that optimistic note that's it for CrowdScience this week. So what have we
discovered from testing listeners' theories? I mean I'd like to bring
producer Graihagh in at this point. Graihagh, what have you learnt?
That we really don't know much about the vast majority of our Universe. That's my take-home for today.
I'd like to say something concrete so I'm gonna go with that dark matter is
probably a particle and that there are many hypothetical candidates but WIMPS
are the ones that most scientists are betting on but anything is of course
possible until scientists can confirm one. Dark life on the other hand...
Oh, I was so sad when Matt was just categorically like no this is not
possible. I really wanted there to be something out there all around us with
the dark lizards and the dark jungle all flying around us.
But of course for a lizard maybe you need a multicellular organism and so you need atoms to stick
together and that's exactly what Matt's saying is not going to happen and then
of course there's dark energy too.
I just think there's so much more about our
Universe that we need to understand and it's fascinating. It's a great time to be
a physicist. Also it's a great time to be a listener to CrowdScience because
we've dealt with quite a few listeners' theories this week and I have to say
they have been really good and do keep them coming.
If you have any thoughts or
comments, theories, suggestions, send them to crowdscience@bbc.co.uk.
That's it from us. I'll leave it to our listeners to read the credits.
You've been listening to CrowdScience from the BBC World Service. One of the questions sent in this week
from me, Gautam in India.
And me, Lawrence from the Canary Islands.
And me, Yoseph from America, among others.
If you have a question you'd like the team to tackle,
email it to crowdscience@bbc.co.uk
This programme was produced by Graihagh Jackson and presented by Marnie Chesteron.
Thanks for listening and goodbye.
you