What we still don't
know
Astronomer Royal Sir Martin Rees investigates ...
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Why are we here?
Programme Contents:
1. Seeking answers
2. Universe’s ingredients
3. Cosmological factories
4. Something missing
5. Cosmic enemy
1. Seeking answers
Philosophers and theologians have long debated our purpose in the universe. We
have always assumed that there is some higher purpose for humanity, but the universe
it seems may have other ideas.
In Why Are We Here? Martin Rees explains how scientists have had to revise
long-held beliefs about the very nature of the universe, and in the process re-evaluate
our place here. To do this, Rees presents some of the most fundamental questions
about the universe and our own origins: What was the beginning? What is the nature
of life? What is the future of the cosmos and the nature of reality?
The answers may not be what you expect. Empty space is not so empty after all.
Most of the universe is made up not of atoms, as previously thought, but of a
mysterious and elusive substance called ‘dark matter’. Without it
the universe simply would not exist.
But working against dark matter is an even more mysterious force that threatens
to tear the universe apart – ‘dark energy’.
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2. Universe’s ingredients
Arguments about the very nature and fabric of the universe stretch back to the
pre-Socratic philosophers. But the atomist theories of Ancient Greece are a far
cry from what we now know. ‘The bedrock of 20th-century science was to understand
that we and everything else are made up of atoms,’ says Martin Rees.
There are 92 types of naturally occurring atoms, allowing
for billions of different combinations, forming the chemical components that
underlie everything from the simplest crystals to the most complex objects that
we know of – human beings.
Humans contain 10,000 trillion trillion atoms, linked together
in a very complicated way. Building something as complex as a human being involves
more than just massing together atoms. Says Max Tegmark of the Massachusetts
Institute of Technology: ‘The big difference between a dead thing like
a crystal and a living thing is not what they are made of. They’re both
made of the same building blocks. It’s rather the complexity of how they’re
put together.’ You have to keep arranging these atoms in new and different
ways without repeating yourself. ‘That’s how you get this fantastic
complexity which to me really is the hallmark of life,’ says Tegmark
It has taken nature about 4 billion years to get from the simplest life forms
on primordial Earth to the complex life forms of today. We just don't know how
that happened, but we do know that the staggering variety of different substances
would never have been possible if the universe hadn’t created the 92 different
types of atoms that underlie everything that we know about.
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3. Cosmological factories
To truly figure out our origins in the universe and understand how and why nature
created us, we have to understand where atoms come from. And to do that we have
to look not at Earth but to the stars.
The Big Bang is the cosmologist’s story about how everything in the universe
was created in a giant fiery explosion nearly 14 billion years ago. But the story
of creation doesn’t end with the Big Bang. The early universe was nothing
like it is today; the building blocks necessary to create complex living things
simply did not exist. The rich variety of atoms that exists now hadn’t been
created. The universe was nothing more than a diffuse, uniform gas consisting
of just two of the most basic types of atoms – hydrogen and helium.
But nature somehow turned these fundamental atoms into the 92 atoms we have today.
‘The main force that changed the universe from being simple and boring to
being rich and complex was gravity,’ says Max Tegmark. Because it attracts
everything, gravity was able to draw great loads of these hydrogen and helium
atoms together to form objects that we now see all across the sky – stars.
All the atoms we see around us are found in stars,
but to begin with stars were made of just hydrogen and helium. Stars are the
atomic factories of the universe, creating new atoms in a fusion reaction. As
the temperature at their cores rose higher and higher, one by one smaller atoms
fused and transformed into bigger atoms building up all the 92 atoms. Then when
the star runs out of nuclear fuel, its core collapses which causes it to spectacularly
explode in what is called a supernova. In the process, these explosions spew
out all these manufactured atoms, the raw ingredients of everything.
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4. Something missing
Cosmologists had figured out how the most complex things were created, but unknown
to them their story of how we came to be lacked a crucial ingredient – a
substance that had filled the universe since the very beginning and had completely
evaded their detection.
Back in the 1930s, a few number-crunching astronomers recognised that galaxies
should have been thrown apart by their own masses, had they not been held together
by something more than the gravitational pull of all visible matter. For decades
they were reluctant to take the idea on board: that the gravitational forces in
galaxies couldn’t have been sufficient to hold them together. There must
have been something else; some kind of ‘cosmic glue’.
Astronomers eventually called this cosmic glue ‘dark
matter’. They deduced that the majority of the universe is not atomic
at all, in fact nearly 85% of it is made from this mysterious dark matter. What
they couldn’t work out is how it was involved in the story of our creation.
Unlike atoms, we know relatively little about dark matter. It passes straight
through atomic matter and emits no light or radiation, making it very difficult
to detect or measure.
So far we only know it exists from its gravitational pull. But it was this extra
gravity that had been lacking from the cosmologists’ creation story all
along. Max Tegmark says it’s now clear that we need dark matter and its
gravitational pull to form things like galaxies. If it weren’t for this
extra pull we
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5. Cosmic enemy
It took several hundred years for explorers and navigators to map out Earth. In
the last couple of decades we have done something analogous for the vast universe
we are able to measure – a universe extending ten billion light years from
us. But having figured out the story of how we came to be, of how everything in
the entire universe, including dark matter, played a role in our creation, cosmologists
set out to discover for how long this unique complexity will continue.
To understand what fate the universe has in store for us, they looked to the past
to see how the universe has evolved so far. Since the Big Bang, the universe has
been expanding outwards, but it was assumed that this expansion has been slowing
down as the gravitational pull of all matter attempted to draw everything back
together.
By studying supernovas, stars that had exploded some 10 billion years ago, it
was possible for scientists to gauge this expansion through time. But what they
found alarmed them. Instead of slowing down, the universe appeared to be expanding
faster. Nothing that we knew about the universe could explain this. Eventually
they had to face facts: a force existed that could counteract and overcome all
the gravity in the entire cosmos and drive it to expand faster and faster –
they called this ‘dark energy’.
While we understand very little about dark energy, physicists have concluded that
its role appears to be to destroy everything that dark matter has helped to create.
By making everything expand faster and faster, dark energy will eventually tear
everything apart. It will annihilate complex objects and the atoms that compose
them. If they’ve got this right, the grim truth is that the future for us,
for complexity, for anything made of atoms is total destruction.
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Are we alone? |
Why are we here? | Are we real?
Find out more | Home
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