So I'm Mike Lemonick.
And I'm Lee Billings.
And we're going to talk about dark matter.
Just a few weeks ago, Vera Rubin,
a very eminent astronomer, died.
And many people think she should have gotten the
Nobel prize for her early measurements
that suggested the existence of dark matter.
It's a grand picture that comes
together and every single piece of this
puzzle says 'Dark matter exists. It's real.
It's about eighty-five percent of the universe.'
Vera was looking at
the rotation rate of galaxies and she
was noticing that essentially this thing
was spinning around faster than it
really should be able to hold itself together
based on all the luminous stuff-
the stars and things we see in it.
So that suggests there's something hidden-
not luminous, dark-that is holding it together.
With gravity. With gravity, right.
When you look at clusters of galaxies
big collection of hundreds of galaxies
that are kind of a clump they're
orbiting around each other and it's sort
of the same thing they're orbiting too fast,
and if there's not some invisible
matter whose gravity holding it together
they should be flying out into the universe.
Right. So there's another thing
with clusters of galaxies.
Einstein showed that big collections of mass can
bend light from things beyond, like more
distant galaxies. And we can see that
lensing but the amount of lensing we see
comes from something much more massive
than the galaxies that are visible,
so there's some kind of matter there
whose mass is bending light.
Again that's consistent with dark matter.
And we can also look back to the cosmic microwave
background radiation and we can see kind of imprints.
It's subtle but an imprint within that
radiation that suggests 'Hey, there is
some kind of dark matter active even then.'
So then the question is: What is it?
And early on I think there were two ideas
MACHO's of course. That's a Massive
Compact Halo Objects which are supposed
to get these big dark things,
like planets for instance or even brown dwarfs,
that float on the outskirts of galaxies.
But the trouble is you already mentioned
Einstein's lensing and things.
You know, we have these objects can bend light.
We look for lensing and
shadows of those objects in the halo of the
Milky Way and other galaxies.
And we just don't see enough of them.
Right, so the search has really focused over the past
25 years or so on particles.
Astronomers called them Weakly Interacting Massive Particles
WIMPS
Very cute. So we've been looking,
and we've been looking, and so far nothing.
So far nothing! Some tantalizing
signals but they all go away.
So then the question comes up:
Is it time to throw out the whole idea of dark matter?
And people have suggested that
what's really wrong is not that there are
these particles out there we can't find.
It's that we don't understand gravity well enough.
There's a modification to Einstein's
gravity that would explain some of these things.
Yeah, and I think we have
to admit that's plausible
but is that the most plausible, the most parsimonious solution
I'm not sure if it is.
So if astronomers aren't yet ready to give up
on Einstein's theory of gravity,
why haven't we found these particles
if they're out there?
Well, it's it's tough to look for them.
We don't quite know exactly how
massive they are, exactly how they interact
with ordinary matter.
It's a needle in a haystack where
the haystack's the whole size of the universe essentially.
One analogy would be that we're trying
to build a net-the net being the
detectors that we can use to find these WIMPS-
and so how big do you make the
holes in your net to make sure that you're
doing a thorough search?
I think that you've got to make all
sorts of different nets of different sizes
and that takes awhile. Takes a long time.
Could take hundreds of years, in fact.
So if they don't find it next week,
the theory is still good.
Yeah, the theory is still good.
We should not throw out Einstein's
understanding the universe quite yet.
Okay. Dark matter, there ya go.
