Video Transcript: The Cosmic Microwave Background

But anytime you can gather more evidence to support an idea that that only reinforces your belief that the idea is in fact true. Well, the strong, enormously strong piece of evidence came along to support the idea of the big bang in the 1960s. Around that time, a Princeton Professor George Gamow had predicted kind of like what we discussed, you know, the universe must have been really, really dense, really, really hot. So light couldn't bounce around. And by the time it cooled down enough, that point where it cooled down so that light could actually move around, should have happened at a particular temperature, you know, when the universe reached 300,000 degrees or something like that. All right. That's the point where light should have been able to move freely, and that light from that initial Big Bang from that initial heat should still be flying around space. Because really, all of space had that heat and temperature and all that matter, which was shining giving off according to Wien's law would have been really bright. Really, really energetic light. Really blue, okay. And that light should be still those light waves should be flying around. As the universe gets colder and cooler. As it expands outward, it gets colder and colder, and that light should be red shifting, even more, all right, and getting cooler and cooler as well to the point where now, all right, it represents light that has red shifted all the way into the radio part of the spectrum. 

And there's a couple of ways of understanding this. One way to think about it is that okay, the universe has a temperature. There’s an average temperature for the universe. At the beginning there, it was really, really hot. Once the universe became transparent, you know, it was several 100,000 degrees. And now the universe is getting colder and colder and colder and it's glowing according to its temperature and as you get colder, you get fainter, and you get redder, right? That's one way to think about the glowing of the universe. So you and I, you know, our skin is about 70 degrees or glowing in the infrared and it's not super bright. So you need an infrared camera to see that my hands are glowing. The universe is what was predicted then to be quite cold now that the average temperature will be around three degrees Kelvin, three degrees above absolute zero. And that corresponds to glowing in radio light. Alright, that's really cool. As one way of thinking about it, it's probably the most useful way to think about it. 

Another way to think about it is to say well, if you're looking far far away, Doppler effect says it should be shifted more and more to the red and if your way at the farthest edge of the whole observable universe, it had to be shifted way to the red and you're going to be shifted all the way into the radio. Both of those are kind of equivalent ways of thinking about this, but in either that, the prediction was if this big bang really happened, then we should be seeing radio light everywhere in the sky. So this prediction was made, right? 

This is like, as like 50s 60s. and his team at Princeton decides Well, we're gonna build a radio telescope, just a small little one, put it on the roof of our building to look because this was a part of the radio spectrum where no one was looking at the sky, because it was such a long wavelength. So we're gonna look for it. And if we see it, well, that's gonna be a really strong, you know, confirmation, because we'll be seeing the light that's left over from this initial explosion. And there's really no other reason you would have that light there. Right. The idea came from a prediction that was made based on the Big Bang. And as we've seen before, when you have a theory that makes a prediction, and it's a weird prediction, and it turns out to be true, that's really strong evidence to support that theory. 

So here's the story. Around the same time, these two engineers who worked for Bell Labs communication like telephone communication, they were working with this radio dish. And around this time, this radio dish was used for communication purposes, right to send like television signals back and forth, like lots of signals. But there was this noise that was always in all their signals, kind of like a hiss that they were doing. So these two engineers that were young were tasked with kind of figuring out where is the source of this noise? You know, is it air traffic control, is it maybe its missile defenses, you know, from some faraway place in the United States? Where's this coming from? And as they tracked it down, someone suggested to them, right, they figured out exactly what wave length this was happening. And a mutual friend suggests them, you know, there's a scientist at Princeton, who's looking for some signals right around this part of the spectrum. And they were able to write a paper and say this emission, this light that we're seeing corresponds to exactly what was predicted for the light that first emerged after the Big Bang. 

So these guys discovered it entirely by accident, but ended up receiving the Nobel Prize for their discovery, because it was seen as a conclusive confirmation that the Big Bang model was a very accurate model and in fact, explains things that can't be explained otherwise. Not only the expansion of the universe, but also what's now called a cosmic microwave background. It's cosmic because we see it everywhere we look. It's in the microwave or radio part of the spectrum. And its background, it's just always there everywhere you look. 

Now the second picture in the gallery illustrates what this looks like. If you could see in this microwave part of the spectrum, what would the sky look like? Well, for those first observations, right, those first observations made by Wilson, Penzias back in the 60s, but they saw was that everywhere in the sky looks essentially exactly the same. It all had the exact same wavelength of light. Now keep in mind that the wavelength of light of light here is telling us something about the temperature. So when you see a map like this, like these maps, this is like a temperature map of the universe in these very cold temperatures. Temperature in that early universe also is telling us something about density, like how much stuff was there because when there's more stuff, it's a little warmer. 

So what this initial graph is showing us at the top of this chart is that really, that early universe was almost entirely uniform. A little yellow line there is really the plane of the Milky Way. So that's just that our galaxy is interfering with some of the light, but really everywhere we look in the sky, the universe and remember, we're what we're looking at is the first light we are looking back in time, as far as is possible. To the first light of the universe. We cannot see past this. Right? And what the universe look like then was basically completely uniform. A soup that was completely uniform of material. 

Over time, astronomers wanted to get better and more accurate maps. And so in 1992, a Radio Telescope was launched into space, a microwave telescope to be able to observe the cosmic background. And it found some small, small, tiny deviations. The goal here was to say okay, it's basically all the exact same temperature, but are there any minute differences, places where it was a little warmer or a little colder? Effectively, what we're doing here is mapping out what the sky looked like, in a sense, what the universe looked like at the very beginning of light, you know, at at roughly 300,000 years after the Big Bang, when the universe was just at its very beginning. 

And what it looked like is there weren't we there weren't like galaxies forming here and there because these were just huge clumps of material. And so areas that were a little hotter, were places where there was maybe a little more material a little cooler, a little less. We're trying to kind of get a sense, but really, it's essentially completely uniform. And in 2003, the Cobe satellite took the most accurate, accurate measurements yet, where it can measure these little tiny deviations and astronomers tried to use these deviations to basically understand how did we go from a uniform hot mass of material to all of these galaxies and groups of galaxies that we see today? What was that process? So they're using this data to try to figure that out? 

And one of the other things you can do with this data is you can very accurately measure the temperature of the universe. So let's think that to Wien’s Law, our favorite idea and all of astronomy Wien’s law, right, the hotter something is the brighter and bluer it gets. And one of the things you've noticed throughout this is that these curves have a very specific shape that are predicted by the equations of Wien’s Law. All right, and then as you get a little cooler, its shape actually changes but it has a very specific shape. Here's what's really cool. 

This Cobe satellite was able to map out, remember the graph here is brightness versus wavelength, right? So when we say the temperature, we're talking really about the peak brightness here corresponding to different temperatures, right or this this curve. But the point is, you map out all the different wavelengths say how bright does an object look at this color, how bright is it at this color in a spectrum, right? And then you can fit that to a model based on Wien’s Law and figure out its temperature very accurately. 

Now this is only true of black bodies, we call them right. And a black body is an object which is theoretical. It doesn't really exist. It's something which only emits thermal light. You know, a stars spectrum doesn't look perfectly like this, right? It has the whole rainbow or we see you know, the whole visible spectrum, but it has those little absorption lines in it. Right. So even stars they're nearly black bodies. They follow this really closely, but not perfectly. 

Well, the Cobe satellite took a spectrum of this microwave background. And the fourth picture in the gallery shows what that looks like. Okay, so you'll see this is a graph just like Wien’s Law. On the vertical axis we have brightness and on the horizontal axis, they call it frequency, but now this is just wavelength still, okay? This is color basically on the horizontal axis. What I want you to notice is that the green line is the predicted spectrum from Wien’s Law. That's what they would have expected it to look like for a specific temperature. The red dots are what was measured by the spacecraft. And you look at that graph up close, and I don't see a single place where there is any difference between them. 

So this idea in physics this Wien’s law that we've seen time and again, it can be confirmed in your own kitchen by turning the heat up on your stove and watching it glow bright red. When you look at this light from the very beginning of the universe, it matches this theoretical model this Wien’s Law perfectly. My understanding is this was shown in the conference in like the 1990s. I want to say let's see it was Oh in the 2000s like 2005. This was shown at a conference. My understanding is in the room, the audience stood up and applauded, a standing ovation for this graph. Isn't that crazy? 

But what I want you to take away from this is that this cosmic microwave background matches perfectly with what we would expect from the Big Bang model. And it matches not only, we have a match between this expansion data of galaxies, but we also have a match from this totally independent measure of the cosmic microwave background. Extremely strong evidence supporting this idea of a big bang. And this more than anything else that the initial discovery of the cosmic microwave background really sealed the deal for the astronomical community say okay, Big Bang model is it. That is how the universe began and in fact the universe had a beginning. And so that's what everyone agrees on, which is profound and that's what Christians have been saying since the very beginning. The universe has a beginning and God made it.

We've basically covered this last picture in the gallery as we've talked about it, but when we look at this light, this cosmic microwave background we are seeing the first light that can possibly be seen. And so the way to understand this drawing is on the left hand side, you have the beginning of time, right when when the Big Bang started.

And then you can see that our physics understanding actually is allows us to trace out what happens second by second after the Big Bang, how the first atoms formed, because it was too hot even for atoms to exist, and then the atoms formed, right. And then from the atoms formed, you could start to get formation of deuterium and helium. So some fusion took place, because it was so hot like the inside of a star. Right and then it says after about a month and had cooled to the point where the cosmic microwave background was fixed, and after about 380,000 years, it was the last time when this light was continuously being absorbed, and it finally was free to just move through the universe. 

And on the side, you can even see a temperature scale there. Now, our understanding of physics can bring us back. Now uh, well let's put it this way. We can observe in the sky all the way back to 300,000 years. 380,000 years after the Big Bang, we can look and see and try to understand. Behind that curtain we're left with our theoretical understanding of physics which we can test in the lab; we can confirm through experiments. Although we can't observe it directly. We can try to recreate some of those conditions where we annihilate atoms, bring them back together where we create huge temperatures and try to understand what's happening. 

And that model works really well, all the way to the first second after the Big Bang. No way. It works all the way to the first half a second after the Big Bang, you know, we can understand what happens all the way to the first millionth of a second after the Big Bang. No. Our understanding of physics allows us to accurately understand what happens all the way down to 10 to the minus 30. Actually 10 to the minus 40 seconds after the Big Bang. That means we understand what happens to 0.000 zeros at 40 zeros and then a one seconds like a millionth of a billionth of a billionth of a billionth of a second. Our laws of physics are so well understood that we can describe what's happening up until that moment. 

But scientists still aren't satisfied with that. They want to know what happens at time equals zero. Why did this whole thing begin? What started it? And we don't yet have an understanding of the physics that can cause something like that. How close can you get how close can I get my finger to this thing without touching it? Right? That's what physicists are doing. They want to get so close that they actually touch it and say, This is how it began. And we're not there with our understanding of physics. And it's a reasonable question to say can we ever get there because the temperatures involved the pressures involved are so enormous that the laws of physics don't apply. They don't make sense when you get to those kinds of extremes. 

We'll talk more about what limits there are to our understanding why those limits are there in a later video, but for now, I think you've seen some profound evidence that's really difficult to argue against in support of the Big Bang model.