Video Transcript; The Accelerating Universe

Up until the 1990s, there were really two main ideas of what might happen.  And those are illustrated in the first picture in the gallery.  The one idea is to say, well, there is a lot of stuff in our universe.  And so there may have been some initial expansion, we don't really know what caused that, but there's some initial expansion.  But there's a lot of gravity and that gravity is going to pull everything back together.  So it's going to slow down our expansion, eventually pull us back down, and maybe we'll have a big crunch.  So there was an initial expansion, and maybe it'll collapse back down.  

Now, some astronomers even went so far as to say maybe this is a cycle like maybe there's an expansion and then a crunch, and another expansion and a crunch, and just keeps going like this.  In some ways, it was kind of an effort to say, no, our universe, it's eternal, it's always been there and never had a beginning.  So this is one possibility.

Another possibility that was suggested is that our universe will just continue expanding forever, it will just expand about the same rate, it'll just kind of keep going.  And it'll get colder and colder.  Stars will live, stars will die; eventually, everything will just kind of die.

So those are the possibilities.  And you can see where we are in here at present; you know, the universe is expanding.  Now one way to try to answer this is to say, how is the speed of expansion changing?  We could say, if we're getting slower, if our expansion is getting a little bit slower, then maybe we're headed towards a big crunch.  We were initially expanding really quickly.  Now we're expanding slower.  

The other possibility is to say, well, if we're relatively constant, then we're just going to keep expanding forever.  So if we were going fast before, and we're still going the same speed, then there's not enough stuff in the universe, not enough gravity, to pull us back for a big crunch.  

So these observations were made.  They looked at the most distant objects they could.  They looked at distant galaxies, but they also looked at really bright supernovas.  Supernovas are great ways of measuring distance, remember, because they all have the same brightness.  And you can actually measure the distances, really accurately to really faraway galaxies.  Remember, really far away galaxies mean you're looking farther back in time.  So you can accurately measure, Hubble's law, speed versus distance for these faraway galaxies.  Particularly now in the 1990s, we can do this with the Hubble Space Telescope.  We can make better measurements that Hubble was ever able to make with this new technology: digital cameras, space telescopes.  

Well, this is what the actual data looks like.  And it's kind of confusing to make sense out of, but I want to just illustrate it here.  You'll see on, this is Hubble's law, and shown in a little different way.  Okay, so the vertical axis is essentially how far apart the galaxies are; how big the universe is.  It's a measure of how big the universe is.  And the horizontal axis is time.  So like, we trace this backwards.  Here we are today at time zero.  You go backwards, backwards, backwards, the universe must have been smaller and smaller and smaller.  So again, this is sort of direct evidence to say our universe is expanding, because we can see the galaxies were closer together, longer ago.

And there are several possibilities.  These are the models:  a re-collapsing universe, this is the big crunch, okay? Coasting in a critical model; that's expanding forever.  And here's the unexpected thing.  You see lots of data from distant galaxies that doesn't look very accurate as large error bars.  The supernova data is a really important because they’re really precise measurements.  And what they showed was that a third possibility that no one had considered is what the data seems to suggest.  And that third possibility is that the universe is not just expanding at a constant rate.  It's not slowing down.  It's not just at a constant rate, but the expansion seems to be accelerating, getting faster and faster and faster.  Now this was like, rock your world; like no one saw this coming.  Why is the universe expanding faster and faster?

Well, astronomers don't know.  We don't know.  We think gravity would slow things down.  It doesn't seem to.  If there's not enough stuff, maybe it would go at the same rate.  What can cause it to speed up?  Well, there must be some source of energy that's causing that to happen, but we don't see it.  We don't know what that energy is.  So in the same spirit of dark matter, whereas this matter that we see it's gravitationally there, but we can't see it, astronomers came up with a name dark energy, to say, okay, there is some sort of energy, we can measure its influence, because it's accelerating the expansion of the universe.  We know how much energy there is.  But we don't know what it is or what's causing it.  That's a shock.  Okay.

And that's kind of where things stand.  There are ideas, but no one really knows for sure.  And here's the real troubling thing.  You know, dark matter is not just a little blip on the radar.  Dark matter we said, with galaxies, represents 90% of the mass of the galaxy in dark matter.   It's significant.  Now, here's the other piece, dark energy.  You may have heard the equation before, it's credited to Einstein.  E=mc2 for that equation.  What it stands for is energy equals mass times the speed of light squared.  It's related to like nuclear reactions.  The idea is that mass and energy are essentially the same thing, like two forms of the same thing.  And if you can turn mass into energy, well, then, there you go.  That's an atomic bomb; mass being converted to energy.  And in some cases, energy can be turned into mass.  They're interchangeable.  So the quantity is sometimes called mass energy because depending on whether it's in the form of mass, or energy, it's the same stuff that can be transferred back and forth.  It's kind of crazy.  

But here's the point.  If you take all the mass in the whole universe, all that mass, and you include all the dark matter that's in the whole universe, you can say that there's some amount of energy associated with all of that mass.  Well, the amount of energy that is necessary to explain dark energy is even greater than all of that mass in the universe.  So if you were to create a little pie chart of the universe, and you were to say this is the mass energy of the universe, this is how it breaks down.  74% of the mass energy of our universe is dark energy.

We don't know what it is, but it's causing the acceleration of our universe.  22% of our universe is dark matter.  We don't know what it is, but it's interacting gravitationally with galaxies.  And with light.  It doesn't absorb light, but it interacts gravitationally with light.  Just 4% of the entire universe is the stuff we know and can interact with.  That's the periodic table.  Stars, galaxies, nebulas, planets, gas, hydrogen, helium, the stuff we know what it is.  96% of the universe, we know it’s there and we don't know what it is.  

And dark matter was discovered only in like the 60s and 70s, dark energy only in the 1990s.  These are very recent discoveries that are illustrating that there's an enormous, enormously high percentage of our universe, that we don't know what it is.  And this is what's propelling a lot of astronomers today to try to answer these questions.  What are these things? What are these things?  We know they're there, but we don't know what they are.  What a crazy situation to be in.

One of the articles that you're going to read is about the ongoing hunt for trying to understand dark energy and dark matter.  And it's going to talk about this particular telescope, a telescope located at the South Pole of the Earth.  And it's using, I think it's using microwave light and it's looking at clusters of galaxies, to try to make some sense out of this dark energy and kind of make a map of how all this stuff is working.  So you'll read a little bit more about it, but this is on the very cutting edge of what new research is being done.

Very cool.  I don't have much more to say about it because I don't know what the stuff is.  But it's certainly mind boggling and very intriguing.  Cool.  All right, well we'll see you for our very last video next.