0:12
Well, first of all, we've seen that space is far from empty.
Even though mass is tenuously distributed through
space, there's a lot of matter in space.
For example, there is, within the galaxy, there's what
we call the interstellar medium made of different kinds
of gas clouds of different densities.
And those gas cloud, the gas that's distributed through
space is, there's enough of it for sound to propagate.
So, in space actually, someone could hear your scream if you could scream.
and, of course, they had a receiver to get the right kind of the frequencies.
So not only soundwave but also shockwave
can propagate through these interstellar gaseous medium.
0:48
On larger scales, on the scale of galaxies,
we have seen that there's different types of galaxies.
There's spirals and there's elliptical, and then each of
these has a super massive black hole at the center.
So, super massive black holes, 10 to the 6th, 10 to the 7th, 10 to the 8th, 10
to the 9th times the mass of the sun are all out there at the center of galaxies.
And so galaxies and super massive black holes go together.
Something about their formation early on has linked these two
kinds of objects together.
1:18
In some cases though, super massive black holes are ejecting
enormous amounts of matter, if enough matter is spiraling inward.
Of course the black hole, anything that falls into the black hole can't get out.
But material around the black hole, that's spiraling inward.
Some of that material can still escape and form
these amazing jets of material that shoot out into space.
1:37
Galaxies are not, they don't occur singly, but you actually see galaxies in
groups or in clusters.
And in clusters in particular, the clus, clusters are
large collections of galaxies hundreds or thousands of galaxies.
And there's space, actually there's the intercluster medium as
well, a hot gas that fills the clusters themselves.
1:56
You can get the groups themselves, and the clusters themselves, will combine to
form what are called superclusters, and these
are the largest scales of structure in
the universe. They have sort of filaments.
They form themselves into filaments with enormous voids in between them.
So, if we pull back all the way out, what we finally see
is that the universe is a homogeneous, a collection of filaments and foam.
Sort of what we like to think of as the cosmic sponge.
So there's structures all the way up to the supercluster scale
and then beyond that, you finally see a statist, a statistical
homogeneity of mass and its distribution in space.
2:36
So, the universe is made up, the matter in
the universe, is made up primarily of dark matter.
80 per 7, 87% of the universe is dark matter, 13%
is normal matter, the kind of stuff we're made out of.
And what that tells you is, we really, it's pretty amazing for all
of our accomplishments, we still don't know what the universe is made out of.
This stuff we call dark matter, we have no
idea what it actually is, we only know, we can only infer its presence
based on things like the motion of the luminous matter that we can see.
The the gravitational lensing, the effect on space
time that we see around superclusters, or clusters, etcetera.
So it's really a remarkable fact that as, as much progress as
astronomy has made, we're still literally in the dark, about the largest constituent
structure, or largest constituent constituents of the universe.
So and finally, if we, you know, look at
all the matter that makes up the observable universe,
what we see is that it covers a space
that is roughly 91 billion light years in diameter.
So there you have it, space is pretty big and it is full of stuff.
And of course, what we're talking about here is the observable universe.
The part of the universe that we
can see that where light has had enough time
since the beginning of the universe to actually reach us.
There is, from what we understand right now,
this is the subject of our next lectures.
cosmologically, we believe that the universe is infinite.
So there's an infinite amount of stuff out there.
And infinite amount, infinite parts of the universe that
we cannot see and we don't know anything about.
Which is a mind boggling idea So okay.
That's it for lecture for our third week.
Now we go on to ask truly cosmological questions.
And that will be where we start next time.
Thank you.
Adam FrankProfessor
