Our universe is a kaleidoscope of scientific mysteries.
And this month we're looking at the ideas and theories
that today may sound like science fiction
but could be tomorrow's science fact.
We'll meet multiple Chrises.
ALL: Yeah, right.
We'll be discussing Dark Matter,
and will we ever find it?
We have to find it in order to understand
its implications for our universe.
We've all heard of black holes, but what about white holes?
So as a black hole gulps matter in,
a white hole spews it back out somewhere else in space and time.
We'll discover whether interstellar travel is possible.
If we truly want to travel amongst the stars,
then we're going to have to break some rules.
And meet the scientists trying to design a language
that aliens would understand.
Will they tell us what they find beautiful?
And to help us on our strange journey,
renowned cosmologist Carlos Frenk takes an animated look
at some of the mysteries that fascinate him.
The more we learn, the more we realise
that there's a lot more that we do not know.
ALL: Welcome to The Sky at Night.
We're here at the Royal Society in London.
Established in 1660,
it has been at the heart of many exciting scientific discoveries.
Their members' roll reads like a veritable who's who
from the world of physics.
They include Isaac Newton,
William Herschel, who discovered Uranus,
and, more recently, Stephen Hawking.
The Royal Society also has a unique collection of works and memorabilia
spanning over the 350 years of its existence,
including two very special artefacts.
This book, A Discovery of a New World in the Moon,
was written by John Wilkins in 1638
and in it he discusses how to overcome
the great scientific challenges for a trip to the moon.
Now, what's amazing about it is that it was written
300 years before humans set foot on the Moon
and well before the invention of the combustion engine,
let alone the rocket.
This manuscript was written by John Michell in 1783.
At Cambridge, he studied gravity, its effect on stars,
and how they bound together to form galaxies.
One of his ideas, way ahead of its time,
was the hypothetical possibility of black holes.
This idea lay forgotten for over 100 years,
until Einstein was able to prove the case with his theories on gravity.
These ideas were considered fringe bizarre concepts founded in dreams,
but whose reality was established many years later.
So what are today's theories which are currently considered fanciful
but may be confirmed as reality in the future?
Come with us on a journey to the multiverse of mystery to find out.
And our first mystery is the theory
that there may indeed be multiple universes out there somewhere.
There is no reason to believe
that our universe is unique.
It is quite possible that just as our universe was created,
many universes were also created.
If that is the case, then we live not in a single universe
but in a vast collection of universes
that physicists refer to as the multiverse.
We can think of those as island universes, each with its own quirks,
maybe even each with its own laws of physics.
For example, there could be one of these other universes
where gravity is 100 times stronger than it is in our universe.
If we could somehow prove conclusively the existence
of multiple universes, of the multiverse,
that would be a genuine intellectual revolution -
a complete change in our cosmic thinking.
Over the last few decades, we've made great strides
in understanding the evolution of our grand and elegant cosmos.
But big questions remain to be answered.
In the beginning, we think there was a Big Bang,
but that doesn't explain why we have the universe that we do.
If gravity was weaker or stronger, if there was much more matter
or much less matter, if chemistry worked slightly differently,
then the universe would be very different
and probably a less happy place for life.
Now, maybe there's some fundamental theory,
one we don't have yet, that explains why the Big Bang just had to produce
the lovely, friendly universe that we find ourselves in.
But working out the details of that fundamental theory
is proving really rather difficult.
Ah, but there is a way out.
Where did you come from?
Oh, I'm you in another universe, but slightly different.
Are you...real?
Well, as the great philosopher Mercury once said,
"Is this the real life or is this just fantasy?"
Let's put that to one side for the moment.
Explaining why the universe is the way it is is easy.
No faffing about with the Big Bang required.
All you have to do is believe in the multiverse.
But I'm not sure I believe it.
Creating multiple universes is an extravagant way
just to get away with not understanding the Big Bang.
Well, I certainly believe it.
BOTH: Hello. Where've you come from?
Well, if there are multiple universes,
who's to say there's only one other universe in which a Chris exists?
And there's actually evidence to support that.
Some of our ideas about quantum mechanics,
the science of the very small, suggests that every time
an observation is made, the universe splits,
creating many worlds with many possibilities.
In this universe, I roll my dice...
..and I get a six, but that action has created five other universes,
one for each possibility, each with its own Chris
going on in his own universe.
Maybe your dice are loaded. Anyway, I don't think this helps explain
why we live in this universe - one so suitable for life.
Luck, I suppose.
Or maybe we just need to think bigger.
Seriously, this is too many Chrises.
Surely not.
In my theory, there are Chrises all over the place.
Every time any of us make a decision, every time I sip
or don't sip a Martini, look left or right, look up or down,
we create a new universe and a new Chris within it.
My brain is too small to contain infinitely multiplying
versions of myself.
Before we melt a Chris' brain, let's get back to trying to explain
why the universe is the way that it is,
and there's an approach to the multiverse that can help us here.
Just imagine that each universe can give birth
to another universe every so often.
It must be rare, so we might have to wait a long, long time
for it to happen.
But when it does, just imagine that this daughter universe
inherits some of the properties of its parent.
Now, if that's true... OTHERS: If!
Yes, "if", but if that's true,
then it explains why long-lived and stable universes are common.
It's certainly one explanation for why the universe
simply had to produce me. OTHERS: Yeah, right!
But... But, look, this is all a theoretical flight of fancy.
There's no evidence that any of you actually exist,
at least in my universe.
The Big Bang seemed crazy but all the evidence suggests
it really happened.
Multiverses are the same way.
And if I can roll enough sixes, I can prove it to you.
Getting six after six after six is mathematically so unlikely,
but in the quantum multiverse
it will always happen in at least one universe.
Bah, it's just evolution in action.
So how can I prove you lot right? What observation can I make?
What test can I do that will show that the multiverse is real?
Typical! When you ask the hard question, they disappear.
So it seems that in this universe we don't know yet but, who knows,
maybe in some other universe somebody woke up this morning
with just the breakthrough that we need.
Meanwhile, in this one, it remains a mystery.
I'm not sure about multiple Chrises.
Maybe one's enough, especially in this universe.
To investigate our next mystery,
we're travelling to another universe,
where instead of a restaurant that aims to put couples together
on their first date, this one invites scientists
to discuss the biggest mysteries in science.
First to arrive is cosmologist Hiranya Peiris.
Hello. How fantastic to see you again. Lovely to see you.
What I love about science is it's a way of finding out
about the world that we live in and it's full of mysteries.
Joining Hiranya tonight in scientific conversation
is physicist Emma Chapman.
I love talking to other scientists about science
because they'll always have thought of a different angle
of how to address a problem.
In 1933, Fritz Zwicky was studying photographs taken by Edwin Hubble
of the Coma Galaxy Cluster.
In them, he noticed that the galaxies were moving too fast
to be held together by gravity alone.
Zwicky had theorised Dark Matter but the problem didn't end there.
The dark side of the universe is a really big mystery.
The Dark Matter and the dark energy make up no less than 96%
of what the universe contains.
The stuff that you and I, the Sun, the Earth,
the stars, the galaxies are made of, that is just the icing on the cake.
It makes up only 4% of what our universe contains.
The most likely explanation for the Dark Matter
is that it's made up of some exotic, fundamental particle
that came into existence just a tiny fraction of a second
after our universe was formed in the Big Bang.
But it is a mystery.
So, back to our restaurant to discover what our scientists
think about the ongoing hunt for Dark Matter.
The crazy thing about Dark Matter is that we can point
to all this evidence and we can say it's definitely there
but we have no idea what it is. We just call it Dark Matter.
It doesn't interact with light in the way that normal atoms do,
like the atoms that you and I are made of.
But we really just don't know.
Yes, many people think that it could be
a new kind of elementary particle.
We know enough about the properties of such particles
in that we can say it's probably more massive
and slower moving than a neutrino.
We already have observational evidence about that.
But beyond that, we have not been able to narrow it down.
And it's proved very hard to find.
It's not through lack of searching, is it?
If you look at the average dark matter density in our solar system,
you can gather that all together, all of the Dark Matter
on Earth right now, put it all together,
it would come to about the mass of a squirrel,
and it could be anywhere on Earth, smeared out.
how on earth are we going to find something like that?
So, how are you getting on? Really well. Fantastic.
Could I interest you in talking more about the current experiments
which are happening around the world? Definitely.
That would be really fun. Brilliant.
Where do we start with something like that?
There's so many experiments.
I think the one that people had their eye on for quite a while
was the Large Hadron Collider at CERN, of course.
So that switched on in, what was it, 2008?
People thought maybe we'll make dark matter, but nothing has turned up.
So there's a little hope, but, honestly, most people think at most
it's just going to rule out a few of the more extreme candidates
as opposed to detect it directly.
We could also try to work out if there is Dark Matter
by signatures that you can see in the electromagnetic radiation.
For example, if Dark Matter annihilates with itself,
it could produce light.
And, in fact, the Fermi satellite has detected some very intriguing
gamma ray bursts, which I believe you know quite a lot about.
Yeah, there was a detection in 2018 where they thought
they might have seen a signature of Dark Matter interacting with gas
in the very early universe, bringing the temperature down
of what they were observing.
But more and more evidence is coming to make people doubt that a bit.
I personally believe that one of the best ways to look at Dark Matter
or look for Dark Matter is to go underground.
And so, for example, there's this huge experiment underground
which is using xenon, and they're waiting and waiting for years
to see if a Dark Matter particle will hit a xenon nucleus,
and they will run for about five years,
and in that time they maybe hope to see a handful of these interactions.
Real needle in a haystack stuff.
Would you like to meet and chat about Dark Matter together again?
Absolutely. Definitely. It was really fun.
I think the case for Dark Matter is very strong.
The biggest mystery is that we can't actually point to a particle
and say, "This is the Dark Matter."
So whatever it ends up being, we have to find it
in order to understand its implications for our universe.
When the problem of Dark Matter is finally resolved,
it will be a giant leap forward not just in physics
but in the very nature of our understanding of reality itself.
But there are still so many murky areas at the edge of our knowledge,
even for objects we can see with our telescopes.
In 2019, this image - the first of a black hole,
made headlines all around the world.
But some scientists think black holes may have an opposite sibling.
CARLOS FRENK: I think most people have heard about black holes.
Fewer may have heard about white holes.
White holes are, in a way, the opposite of a black hole.
Black holes eat everything.
White holes kind of vomit everything out.
Nothing can come out of a black hole.
Nothing can go into a white hole.
Whether white holes exist or not, it's a matter of heated debate.
Astrophysicist Becky Smethurst is an expert in black holes.
As we move into a black hole,
some scientists have considered whether the forces become so extreme
that a hole is pierced through the fabric of space and time,
exiting in another part of the universe,
or even a different universe entirely -
something known as a wormhole or an Einstein-Rosen Bridge.
A white hole that could spew out matter across time and space
is rather reminiscent of the beginning of our universe,
as described by the Big Bang Theory.
Now, this has led some scientists to ponder whether the universe
could have started inside a black hole
and that perhaps inside every black hole in the universe
is another universe.
Imagine you were to travel past the event horizon of a black hole.
No turning back now.
As you move further in,
the singularity becomes your entire universe.
Space stretches to infinity
as, according to Einstein's theory of general relativity,
the flow of time itself draws falling objects
into the centre of the black hole.
With infinite space, you technically have room for a whole new universe.
So could a white hole be the process of a black hole
internally spewing out all of its contents
to create a whole new universe?
Imagine a family tree of universes
with each new black hole creating entire universes of their own.
But there is another idea of what white holes could be.
When Stephen Hawking started considering black holes
from a quantum perspective,
which is what's happening on an unimaginably tiny scale,
he started to figure out that black holes are a little bit leaky.
And as they leak this aptly-named Hawking radiation,
they lose mass over time and get progressively lighter.
And there are scientists that are working on the cutting edge
of quantum gravity that think that in the unimaginably distant future,
when all the stars and galaxies in the universe have died out,
black holes might go bang,
effectively bouncing back all of the matter and light
and information that they have swallowed over time
and giving it back to the universe in one fell swoop.
This bounce back could be our white hole.
It's nice to think that here at the end of all things
there could be a little bit of light that comes back into the universe
and maybe starts things all over again.
Maybe this process has already happened time and time again.
While scientists ponder the existence of white holes
and if and how they can occur,
there's one thing that people do find easier to imagine
and that's the existence of extraterrestrial intelligence.
In 2021, a survey found that 50% of Britons
believe that aliens exist.
And there are certainly lots of films and television programmes
that imagine what first contact with an alien civilisation
would be like.
But how realistic are they and how would we really talk to aliens?
Astrobiologist Douglas Vakoch has been exploring these questions
in the hope one day he will speak to intelligent alien life.
Where there's life, there's language.
If you imagine that we listen to Earth from the skies,
we might hear one of about 7,000 languages.
We would be forgiven for thinking that only humans
had evolved language, but we'd be wrong.
Chimpanzees gesture instructions and emotions.
Whales sing to one another.
Prairie dogs have warning calls so complex
that experts think they describe the shape, the size,
even the colour of the creature that is a threat to the colony.
Life's capacity for language astounds me
and it also gives me hope.
Hope that life orbiting a distant star
may also have a capacity for language, for communication.
For me, the question isn't "Does alien life exist?"
It's "Could we communicate with them?"
Many years ago, in 1974, my friend, the late Frank Drake,
sent a message to a distant cluster of stars
using the most powerful radio telescope in the world.
It's now known as the Arecibo message -
our first message to aliens.
Using a binary code transmitted at two different frequencies,
he introduced counting, the DNA molecule
and a stick figure showing what humans look like, and much more.
Over the years, I worked on a new message
that would be even more understandable to extraterrestrials.
And so, in 2015, I created METI -
Messaging Extraterrestrial Intelligence.
Since Frank sent that first message, advanced studies of animal
communication have given us a cosmic Rosetta Stone.
Using these insights, METI have created a message
that teaches aliens about languages on Earth
and, I hope, how they can speak back to us.
Our message will be a treasure trove of science, art and human nature
with many different ways to unlock its secrets.
There's one more difference between METI's message and Frank's -
where they're sent to.
When Frank sent his message in 1974,
he targeted a globular cluster of stars called M13.
It's so far away that by the time our signal gets there
and we get a reply back, 50,000 years will go by.
METI is targeting stars much closer to Earth,
including one that's so close to home
we could receive reply in less than ten years if we're lucky.
So, if they do get our message, will they understand it?
And what will they send us back?
Will they use the language of binary numbers?
Will they show us what they look like?
Will they tell us what they find beautiful?
Will they say hello?
To me, this is the great mystery.
What will they pen back from their distant star?
I hope to have the answer in the not too distant future.
If we were able to prove that aliens exist and were able to communicate
with them, the next logical step would be to try and meet them.
The problem is that space is vast -
almost incomprehensible to the human brain.
One way to measure it is in light years.
That's the distance that light travels
over the course of an Earth year.
That's about 6 trillion miles.
To give you an idea how big that is,
our galaxy is 100,000 light years across,
so it takes light 100,000 years to get from one side to the other.
So with space being so vast, are we ever likely
to be able to explore it physically?
Humans have always been looking to travel faster and further.
And using ever more complicated technology, we've found ways
to travel to places our predecessors could have only imagined.
But one bit of travel has remained out of reach.
In the summer of 1950, the great Italian physicist Enrico Fermi
posed a question.
If the universe is so vast
and our galaxy contains hundreds of billions of stars,
why hasn't an alien civilisation come to visit us?
This simple but mysterious puzzle
has since been known as the Fermi Paradox.
But as a space scientist and engineer,
the question I want to ask is
what would it take for us to visit the aliens?
Light from Proxima Centauri, the next-door neighbour star to our sun,
takes over four years to reach us,
and that's travelling at the speed of light,
so we'd need some pretty impressive technology
if we want to explore the cosmos.
Interstellar technology.
So far, we've only managed to send humans...
..as far as the Moon, which feels pretty meagre on a galactic scale.
One of the major reasons for this is as space travellers we're slow.
Really slow.
The Apollo spacecraft reached speeds of 40,000km an hour,
which may sound fast, but even at top speed,
it would take 100,000 years to travel to Proxima Centauri.
If you want to visit other stars and the planets that surround them,
we need to find a way of travelling much, much faster.
When John Wilkins wrote about travelling to the Moon
in the 1600s, he imagined making the journey on a large sailing ship.
Well, that's not quite as crazy as it sounds
because one of our best current ideas
about travelling the long distances through space
is by using solar sails.
Instead of being propelled forward by wind,
they use radiation pressure from light.
In the future, powerful lasers could allow solar sails
to travel up to 10% of the speed of light.
At those speeds, we might be able to reach Proxima Centauri
in around 40 years.
So solar sails could make it possible
to travel to another star.
But it would take nearly half a lifetime
to reach even our closest stellar neighbour.
If we truly want to travel amongst the stars,
then we're going to have to break some rules
and travel faster than the speed of light.
Ah!
In 1994, a Mexican physicist called Miguel Alcubierre
outlined a warp drive for faster-than-light travel,
using a clever trick not to break the speed of light.
What if I want to move this ship at one end of the table
to the moon at the other end of the table?
The traditional way of doing it would be to move the ship.
That's how it's normally done.
But there is another way.
Rather than moving the ship or the moon,
what if I could gather up the tablecloth that lies between them?
Now the moon and the ship are much closer together.
What I've effectively done is I've scrunched up the space time
that lies between the two objects.
By contracting and expanding space time around the warp drive
in this way, we can move ourselves next to any star
as fast as we like without breaking the speed of light rule.
Of course, it's not that simple.
The Alcubierre warp drive is a theoretical possibility
but the actuality of warping space time is full of problems.
The amount of energy needed to power the drive might be a deal breaker.
It was calculated to be more than all the energy that existed
in the entire observable universe, which isn't ideal.
Whether interstellar travel is possible in the future
still remains a mystery.
But possibly with the right innovation,
we may get a little bit closer to travelling amongst the stars.
Let's hope one day we really do get to travel across our universe.
We could do a Sky at Night special
from the Andromeda Galaxy some 2.5 million light years away.
Well, it would certainly make my star guide look very different.
As ever, check out our website to find out what's going on
in the night sky.
And to see more of Carlos's mysteries.
Well, that's it from this universe.
And that's it for this year from The Sky at Night.
I can't wait to see what discoveries are made while we're off air.
So do join us for our return in 2023.
In the meanwhile, happy stargazing.
BOTH: Goodnight.