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.