Hi
Hello.
To celebrate world space week we're asking
how fast is the universe expanding?
and the answer is 0.007 per cent per million
years
in the late 90's two teams of astronomers
measured the rate of expansion by looking
at the light of exploding stars in distant
galaxies.
The teams realised that not only was everything
flying apart but accelerated apart and they
won a Nobel Prize for their efforts.
but of course theoretical physicists had already
anticipated the acceleration and to get to
the bottom of why we first need to look at
what the acceleration really means.
We think the universe began with a monumental
explosion.
In the beginning all the matter in the universe
was violently thrown apart in the appropriately
named Big Bang.
but even when stuff if flying apart it can
even be stopped.
Imagine Tom and I are in deep space flying
apart from each other our gravitational attraction,
even though it's quite small, might be enough
to slow us down and pull us back together.
likewise cosmologists imagine that like gravity,
it would win out.
All the matter in the universe would come
back in a catastrophic big crunch.
That's why the world of science was shaken
to it's very foundations by the revelation
that the expansion of the universe was actually
accelerating apart.
The stage was now set for an ever lasting
expansion turning the cosmos into a cold lifeless
vacuum.
The heat death of the human race.
All from a simple observational measurement.
hmmm, but actually, as I said long before
these observations, theorists realised that
the universe could be accelerating.
Even Einstein knew that it might be possible,
by the mid 1980s we had a good account of
how much stuff and energy that was in the
universe even including things like dark matter.
hold on, didn't martin archer do a video on
that?
he did.
But even taking that in to account there still
wasn't enough stuff compared to theorists
favourite theory predicted.
That's when they realised there could be extra
stuff completing the picture in the form of
something called vacuum energy which has negative
pressure which makes the universe expansion
accelerate just as was eventually observed.
vacuum energy is a concept borrowed from the
bizarre world of quantum particles.
Even if you have no matter at all you can
still have residual energy left over.
The problem is because we don't have a complete
understanding of quantum gravity.
We don't know how much energy there should
be and indeed how it should behave.
So you can't actually predict the rate of
acceleration.
and that was the genius of the 1980s theoretical
cosmologists, working out how much accelerating
dark energy had to be there just be looking
at how much stuff in total they expected.
yeah, by employing the sophisticated mathematical
technique of subtraction they were able to
infer that there wasn't enough stuff there
and jumped to the conclusion that it must
be vacuum energy.
And a new generation of theorists continued
to astound us by providing bold insights into
what this vacuum energy is.
Andrew.
Yeah, there are lots of and we're building
some new telescopes
oh right, new and improved observations
I don't know why you're being so high and
mighty, what have you brought to the table?
What you're gonna say you discovered the Higgs
Boson, scalar fields, possibly something about
that?
No, no, not necessarily.
You see I've been doing a bit of reading around
and actually it turns out that the acceleration,
the expansion of the universe, is all down
to dark energy.
good.
