We're All Swimming In Big Bang Juice

This episode delves into the cosmic microwave background and its significance in understanding the early universe.

1. The cosmic microwave background (CMB) was discovered accidentally and has since been crucial in studying the early universe.
2. The CMB provides evidence of the universe's hot, dense state shortly after the Big Bang.
3. Temperature variations in the CMB help scientists infer the early universe's density fluctuations, crucial for galaxy formation.
4. Technological advancements in observational equipment are vital for deeper understanding and validation of cosmological theories.
5. The episode underscores the importance of continuous discovery and foundational research in advancing scientific knowledge.

1: Discovery of the Cosmic Microwave Background

Exploring the accidental discovery of the CMB by Penzias and Wilson, highlighting its significance in cosmology. Regina Barber: "They put out a paper with their findings, basically saying, we found this background noise and we don't know what it is."

2: Understanding Early Universe Conditions

Discusses how CMB studies contribute to understanding the early universe's conditions, emphasizing temperature and density. Renee Hlajek: "It's this light from about 400,000 years after the beginning of the Big Bang era."

3: Technological and Theoretical Advances

Focuses on the impact of technological advancements on cosmological theories and the interpretation of CMB data. Chanda Prescott Weinstein: "This is a hard problem, because part of the work is making sure that what we call the data analysis pipeline is well understood."

1. Stay curious about the origins of the universe and support scientific research.
2. Educate others about the significance of foundational scientific discoveries like the CMB.
3. Encourage interest in STEM fields to ensure continued advancements in technology and theory.
4. Advocate for funding and resources for scientific research to further our understanding of the universe.
5. Engage with scientific content and discussions to appreciate the ongoing journey of discovery in cosmology.

The Big Bang: The moment when our universe — everything in existence — began....Right?

Turns out, it's not quite that simple.

Today, when scientists talk about the Big Bang, they mean a period of time – closer to an era than to a specific moment. Host Regina Barber talks with two cosmologists about the cosmic microwave background, its implications for the universe's origins and the discovery that started it all.

People

Regina Barber, Chanda Prescott Weinstein, Renee Hlajek

Guest Name(s):

Chanda Prescott Weinstein, Renee Hlajek

Content Warnings:

None

Regina Barber
You're listening to short wave from NPR. Hey, short wavers, it's Regina Barber. Can I admit something to you? I learned about the beginning of the universe the way I learn about a lot of things on tv.

For thousands of years, people have wondered about the universe, that it all started with a singularity, a brief moment in time called the Big Bang. One view of the universe prevailed. But here's the thing. Even though that definition is fairly common, it's not how many scientists talk about the big bang.

Chanda Prescott Weinstein
Now, today, when you hear people use the phrase big bang, they often mean the time period that we might otherwise call the early universe. So they're often talking about, I don't know, roughly like the first few hundred thousand years of spacetime's existence, the Big Bang era, instead of just the big Bang.

Regina Barber
Thats Chanda Prescott Weinstein, a theoretical physicist and an expert in cosmology, which is the study of how the universe began. But how do we observe that beginning, that big bang era? And why do we talk about it differently now? To understand that, we have to go back 60 years to a lab with a giant horn shaped antenna in New Jersey and to two radio astronomers, Arno Penzias and Robert Wilson, to see photos of them.

Renee Hlajek
They're standing next to this giant antenna, arms wide open, looking at the sky. And one of the things that they noticed is it didn't matter where they pointed this detector in the sky, they had a residual noise, kind of a background.

Regina Barber
Renee Hlajek is an observational cosmologist. She's also a spokesperson for the dark Energy Science collaboration, which studies the acceleration of the cosmos.

Renee Hlajek
They spent a lot of time trying to figure out what it could be, including the bird poop that had been collected in their detector, they try to calibrate all their instruments.

Regina Barber
They thought it was New York, maybe.

Renee Hlajek
Yeah, they were just like, where is this coming from? But it wasn't directionally dependent, and that's super important. So if you look anywhere in the sky, you'd see this.

Regina Barber
So they put out a paper with their findings, basically saying, we found this background noise and we don't know what it is.

Renee Hlajek
And at the same time, people were saying, oh, if we understand how the nuclei formed in the early universe, we understand that the universe must have been hot and there must be a background. So in a sense, they were looking, trying to design experiments to look for this. But Penzance and Wilson serendipitously discovered it first. And so as soon as they put out their paper saying, oh, we see this background the theorists who are working on this were like, oh, shoot. This is exactly what we. What we thought we should get. So it was that discovery of the cosmic microwave background, which we call it now, that, to me, catapulted this era into the modern age.

Regina Barber
So today on the show, the background noise of the universe, we get into what the big bang is, why scientists talk about it differently than they used to, and how the cosmic microwave background and its fluctuations help us understand the early universe. I'm Regina Barber, and you're listening to short wave, the science podcast from NPR.

So we talked about how the cosmic microwave background was found with this, like, serendipitous accident, basically. And the scientists found out we could detect radiation from the beginning of the universe. And so, Renee, based on this background, this CMB, what do we know about the early universe?

Renee Hlajek
Okay, so the universe is hot at this early time, and it's so hot that it sort of. We think of the three phases of matter as, you know, solid, liquid, gas. But really, there's a much more important phase of matter to my heart, which is plasma.

It's so hot that you don't have atoms. You just have electrons and nuclei, atoms. And because the electrons are free, they can interact with photons. So they basically bounce around as if you're trying to walk through a big crowd or you're at a nightclub. The photons and the electrons are interacting with each other. Right. They're bouncing around.

It's the same reason why the sun is opaque, and it's opaque because of this bouncing around, we basically say that the photon can't travel very far without interacting with another electron.

And so what happens is, as everything gets older, everything gets cooler. Of course, the same is true of the universe.

Regina Barber
I slowly got that.

Renee Hlajek
Okay, so, as the universe is cooling, eventually it gets cool enough that, in fact, the electrons and protons can now combine, and they can become neutral atoms. And what happens is, at that moment, which we call the last scattering surface, so the last scattering between photons and electrons, it's kind of like the photons are now free to stream away. And so that is the moment when, essentially, we can see the photons because they're now streaming towards us from the distant past.

And that radiation is what we call the cosmic microwave background.

So it's this light from about 400,000 years after the beginning of the big bang, in this big bang era. And we can see it on the.

Regina Barber
Sky, and it's not, like only in the sky, it's all around us, right?

Renee Hlajek
Yeah, absolutely. We're actually just swimming in the light of the big bang. A nice thought that I like to say to people is if you get on the subway in a city and you sit down and you feel that the seat is warm, you know that someone was there before you, right? Because you have the heat, residual heat under the chair, and that's sort of the same thing. We look out everywhere in the sky, and we see this microwave light just everywhere. It's that, you know, hot subway seat, but all over the sky.

Regina Barber
I have sat in many of those subway seats. I love that analogy. Okay, Chanda, but this light in the cosmic microwave background generally has, like, this very specific temperature of about, like, 2.726 kelvin, or roughly negative 455 degrees fahrenheit. I'm just reading these numbers. I don't have them in my brain. Like, shout out to our producer, Hannah Chen, for that research. Thank you so much. And that's, like, super cold. Like, how is temperature associated with this light?

Chanda Prescott Weinstein
Right? So, if we think back to the earlier moments in the cosmos, so, kind of that hot big bang era, we have this time period where the universe is very hot, as Renee was talking about. There is this plasma. Photons are bouncing around. They're hitting electrons. And then at some point, the universe is just cool enough that those photons start flying freely. They're not running into things. They can kind of travel for long distances without hitting something.

This is like the Doppler effect, like an ambulance coming towards you and then away from you. First, the sound waves compressed, and then the sound waves stretch out.

And so the same thing can happen with light. And this is happening as spacetime is expanding.

And so this effect is also happening with the light that makes up the cosmic microwave background radiation. And that means that the light, as we see it today, has a different energy and wavelength associated with it than the energy and the wavelength that it started out with, simply because spacetime has had over 13 billion years to expand since that time happened. And so that means, yes, that in the future, like, very distant future, like, in about 4.5 billion years, when the sun goes nova, that that temperature is actually going to be different than the one that we measure today. So this is that that temperature that we're measuring today is a snapshot of the CMB, the cosmic microwave background radiation.

Regina Barber
Now, okay, so when we're looking at this, like, cosmic microwave background temperature, what does that tell us about the early universe?

Renee Hlajek
So, the key thing is that we're not only interested in that overall temperature, but we're interested in does the temperature differ slightly from position to position on the sky because any temperature differences actually start to give us insights into the theory of how this cosmic microwave background happened and what the physics was like. And what we found is that from place to place on the sky, the cosmic microwave background is different by only one pot in 100,000. Now, that's, like, phenomenally uniform across the sky. It's kind of like saying a drop of water in a gallon if you put, like, a tiny drop of food coloring or whatever.

But those fluctuations in the temperature from place to place tell us something about what the physics was like at that early time.

Regina Barber
Right. I mean, they tell us about the variations in density during that, like, early time, which in turn tell us something about the origin of galaxies. Right. So what do you use to make these, like, heat maps of the cosmic microwave backgrounds? Like, how do scientists measure these, like, tiny fluctuations?

Renee Hlajek
So the devices are called transition edge sensors. So we don't think of the telescope as a mirror in the same way you do for an optical telescope. We have these huge detectors with all these tiny little individual detectors, thousands and thousands of them, into a big array. And then we scan the sky. Typically, we'll scan the sky from different places. So there are a bunch of different experiments. So we have a big telescope that allows us to collect this microwave light. And then, you know, at the back of the. Of the telescope, there are these detector arrays, typically, and those are either put in telescopes in Chile or telescopes at the south pole or sometimes in space.

Regina Barber
Got it. Got it. What I think I would like to kind of talk about next is, like, how do we use that data for theory? So, Chanda, when we have all of this data, that's, like, building up, you know, over the decades, and now we're going to probably get even more sophisticated devices in the future.

What is that tell theory? What does that tell us about the beginning of our universe?

Renee Hlajek
Yes.

Chanda Prescott Weinstein
I will actually just say that this is a hard problem, because part of the work is making sure that what we call the data analysis pipeline is well understood, that the instruments are very well calibrated, and that we know how those things work. Then, assuming all of those things are true, there are a series of assumptions that have to be made about what the correct model of cosmology is in order to actually process the data. And so, in fact, this is not something that's widely known. The cosmic microwave background radiation is actually our strongest piece of evidence for the existence of dark matter, because you get that match between the theory and the experiment so beautifully. If you put dark matter into it, you take dark matter out of it, and the line, they don't match anymore.

Regina Barber
Dark matter being this, like, invisible, mysterious matter in the universe scientists are trying to understand.

Chanda Prescott Weinstein
But it is, in many ways, a little bit like putting a puzzle together where you're like, if I put the wrong piece here, then none of the other pieces around it are going to fit.

Regina Barber
Which brings me to my last question. Earlier, we talked about the early cosmic microwave background as opaque. We can see the immediate aftermath of the Big Bang era, but we don't know what caused it. Is there any way for us to figure out what caused the big Bang by looking at all these parameters and trying to fit these models? Does it tell us anything about what happened before the very first milliseconds of time? Or is it.

Is that impossible?

Chanda Prescott Weinstein
Yeah. So I think, as with most things in science, we have to get kind of specific about what we're looking for. And on some level, this question is also about what is the boundaries of what science can do and what we think science actually is. I think the bigger point that I would want people to walk away with is that there are times when we come up with ideas that we think we. We can't test or that we don't know how to test, and that later it becomes clear that we actually can test them and that it is a matter of time and human ingenuity.

Regina Barber
Yeah, I mean, that's part of Penzias and Wilson's story, right? Like, they make this discovery by accident, and it turned out to be, like, foundational. That's. That's one of my favorite things about, like, science and being a scientist and, you know, this chandra and renee, like, it's all about this constant discovery, discovery of, like, new things, right?

Chanda Prescott Weinstein
I spend my life on dark matter. It could be that the first real, definitive evidence for direct detection of dark matter in the laboratory is going to happen the day after I die. I work every day knowing that that is just how the cookie crumbles. I think my hope as a scientist is not that I will be the one to make the great discovery or idea. And I think that's a very outdated way of thinking about what science is about.

My hope is that the work that I do now helps to continuously lay the foundation for us to push the boundaries of our understanding forward, whether it's this generation or a generation, like, seven generations from now that works out some of the problems that I've committed my life to. Science is a multigenerational enterprise, and so I think that that's really the way to think about these questions is maybe right now we're not sure that we can test or answer that question. But as scientists, it's not our job to say never. It's our job to figure out, could this be possible later?

Regina Barber
I love that. Thank you so much, Chanda and Renee, for coming to talk with us today.

Chanda Prescott Weinstein
Thank you for having me.

Renee Hlajek
It's super fun.

Regina Barber
Before we head out, a reminder that we'll be back tomorrow with our regular shortwave and back Tuesday with our final installment of the space Camp series. And I have this sneak preview from one of our experts.

Katie Mack
Hey, short wavers. It's Katie Mack, cosmologist and connoisseur of cosmic catastrophes. Now that you're experts on the universe as we know it, now join me as we theorize about how it could be in billions or maybe trillions of years, there's still a lot to learn about our ultimate cosmic future.

Regina Barber
This episode was produced and fact checked by Hannah Chin. It was edited by our showrunner Rebecca Ramirez. It was engineered by Maggie Luthar. Julia Carney is our space camp project manager, Beth Donovan is our senior director, and Colin Campbell is our senior vice president of podcasting strategy. Special thanks to our friends at the US Space and Rocket center, home of Space camp. I'm Regina Barber, and you're listening to shortwave, the science podcast from NPRdeM.