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In this episode of Tiny Show and Tell Us, we talk about what dark energy and dark matter are made out of and how knowing more could upend our understanding of the Big Bang. Then we cover microchimeric cells � cells transferred between baby and mom � and how new research in mice shows that fetal cells that took residency in mom from a first pregnancy are replaced by new fetal cells of a second pregnancy.

Transcript of this Episode

Sam Jones: Welcome to Tiny Show and Tell Us, the bonus series where you write in with your favorite science news or factoid, we read your email aloud, and then dive deeper. I'm Sam Jones, and I'm here with my co-host Deboki Chakravarti.

Deboki Chakravarti: Hi, Sam. Last time we talked about Marfan syndrome and bacteria being the original genetic engineers, and I'm excited to talk about what we're going to talk about today.

Sam Jones: Same. Yeah. Before we get started, a huge thank you to Tien Nguyen for doing the research for this episode, and also a reminder that we are always looking for you all to write to us to be featured in these episodes. So email tinymatters@acs.org or fill out the form linked in the episode description.

Deboki Chakravarti: Okay. Sam, do you want to go first this time?

Sam Jones: I'd love to. And this one is... Well, you'll see. All right, so this Tiny Show and Tell Us is from listener Paul, who wrote in saying, "When scientists figure out what dark energy and dark matter are made out of, I think they'll have a better idea about the Big Bang." So we're talking about space.

Deboki Chakravarti: Great. Let's do it.

Sam Jones: I feel like honestly though, our listeners have I say forced in the nicest way, forced me to become more comfortable talking about these topics and actually diving into the research related to them. And so at the end of the day, this is very good for me, and I'm hoping people learn something because, yeah. Okay, so if there is one thing I know about Tiny Matters listeners, it's that they are fascinated by deadly diseases and by space.

And so dark energy and dark matter, I feel like they are just frequently coming up. They're frequently mentioned when it comes to that interest in space. So first, before we talk about dark matter or dark energy, let's talk about the Big Bang. What was it? The general consensus among physicists is that the universe was born 13.8 billion years ago in what has been termed the Big Bang.

So the energy making up everything in the universe today was squeezed into a tiny space. According to the Institute of Physics, they describe it as "far tinier than a grain of sand or even an atom."

Deboki Chakravarti: What?

Sam Jones: I know, and this tiny point of proposed infinite density and temperature really quickly ballooned in size, hence the name the Big Bang. Why did it balloon? We don't know. What existed before then? Was time even a thing? We also don't know. I had a moment where I was going through this yesterday and I started to legitimately feel dizzy thinking about it. It's really like, I'm sorry, wait, did time not exist?

Whew! I'm starting to have mortality anxiety or something. I don't know what it's. But anyhow, okay. There's a lot of very complicated science that helped researchers draw those conclusions. I cannot get into all of those because my brain doesn't have that capacity right now, but I am going to get into some more details.

So once the universe formed, in the first second of its existence, scientists have a pretty good sense of what happened based on theoretical models and experiments in particle accelerators like the Large Hadron Collider, which is where particles are smashed together at high speeds. And they're able to make predictions about how things may have happened in the past under similar conditions.

So within seconds of the Big Bang, things become less chaotic. They're super chaotic, they become less chaotic. And you have the formation of quarks, which are subatomic particles. In fact, the smallest particles known to science. From there, bigger particles like protons and neutrons began to form. And then within three minutes, the universe cooled to one billion degrees Celsius. So cooled is a relative term.

But with that cooling, the protons and neutrons could come together and form the nuclei that make up atoms. So atoms are made of protons and neutrons. After about 20 minutes, the universe has cooled off enough that things aren't fusing together anymore. So you needed that fusion in order to form those nuclei, right? So according to the Institute of Physics, "What was left was a hot, cloudy soup of electrons and hydrogen and helium nuclei."

And that hot soup lasted about 380,000 years. That's the end of the quote. I'm saying that hot soup lasted about 380,000 years. By then, the universe had cooled a lot more. And as it cooled, it continued to expand. And soon electrons linked up with nuclei to form the first atoms. It wasn't for hundreds of millions of years the first stars formed. That I didn't know. I didn't realize that it took... If we're talking billions, hundreds of millions is not actually that long.

But I was thinking that after the Big Bang, stars formed more quickly for some reason. So yeah, there was a lot of darkness in the early universe. Now, dark matter and dark energy, related, but different. I always mix them up. So they're dark, first off, because they don't emit light. But we know that they exist because they affect things that we can observe like galaxies.

So dark energy is a term that's used to describe whatever is making the universe not only expand, pushing galaxies further apart, but that expansion is speeding up. No one has ever directly seen dark energy or measured it, but there is something that's pushing the universe to expand faster than scientists would expect. It's like very Star Wars to me. There's this dark energy force. It's in the universe.

Some other basics about dark energy include that it seems to be uniformly distributed across the universe unlike dark matter, which get to in a second. Although I will note that there have been some really interesting recent studies that have been done. I just saw a Scientific American article come out today actually where there are scientists who are now saying that actually dark energy will vary some across time, and it's really thrown a wrench in some of the things that I'm going to say.

So again, I think it's really complicated, and maybe six months from now there will be people saying, "No, no, no, that's not true." But I think this is because so little is known, it's known to exist, but what it is is unclear. And so of course, there's going to be a lot of debate surrounding these topics. So just to keep that in mind. So we're going to get to dark matter.

We're still on dark energy. There's this theory that dark energy only started to make up the majority of the universe. So right now it's thought to make up around 70% of the universe, which is wild. But there's a theory that it only started to make up the majority of the universe around five billion years ago, which was significantly after the Big Bang, almost 10 billion years later.

But still, five billion years ago would have been before Earth is formed. And so once there was dark energy, it began to counteract the activity of dark matter. So unlike dark energy, dark matter holds galaxies and other cosmic structures together. So it's kind of like the inverse, and it's just as mysterious. So what is the potential connection between dark matter, dark energy, and the Big Bang?

Because remember, our listener Paul mentioned that knowing what dark matter or dark energy are made of could lead to a better understanding of the Big Bang. In an article from the University of Chicago, they talk about one of their researchers, an astrophysicist named Michael Turner, who is the one who actually coined the term dark energy in 1998. And he said, "I think dark energy is the most profound mystery in all of science. Until we understand it, we can't sensibly speculate about the destiny of the universe," which I thought was a great quote.

So a better understanding of dark energy could give us a better picture of how the universe began and has evolved, and also about how things will end. So we've talked about this a little bit in other episodes, but will the universe become so spread apart that it eventually freezes? Will it collapse on itself?

And then in terms of dark matter, recently, researchers have put forth the idea that there was actually a second Big Bang, a "dark" Big Bang, that sent dark matter across the universe at either the same time as the Big Bang or within a year of the Big Bang, which is also then our understanding of how the Big Bang happened and what happened right following it could then be impacted if we know that there was dark Big Bang right afterwards with dark matter. Yeah, it's so complicated.

Deboki Chakravarti: It's a lot to think about.

Sam Jones: It's a lot to think about. And then there was also a mathematical theory back in 2019 that dark matter was actually created before the Big Bang, which could, of course, completely upend our understanding of any sort of the event that led to our universe.

Deboki Chakravarti: Wow!

Sam Jones: So there's a lot there. I think that dark matter and dark energy are so fascinating because I think that there isn't really a debate at this point as to whether they exist. It's more a debate as to what they are exactly. And if they actually have this constant effect or if there's variability in how much they're either, in the case of dark energy, expanding our universe, or, in the case of dark matter, keeping galaxies together essentially. And so there's about a billion more questions than there are answers with this.

Deboki Chakravarti: Of course.

Sam Jones: But I do think that both are such a massive influence on our universe that you would have to then ask if we did know, oh, dark matter is made of X. How would that influence our understanding of how the universe began in the first place?

Deboki Chakravarti: Right.

Sam Jones: � i.e., the Big Bang. How would we then view the Big Bang?

Deboki Chakravarti: It's so weird how it's so... It's so theoretical, but not. I think that's the thing I struggle with with physics. It all feels so theoretical, but it's not.

Sam Jones: Right. I mean, it is. A lot of it is theoretical, but then there are these really cool experiments to back up those theories. And I think when I was talking about the beginning, within a second of the Big Bang, researchers know that this happened.

Again, you could find something new. You could understand dark matter or dark energy better, and maybe you say, "Actually, we're not so sure if that's what happened. But based on particle collision experiments, a lot of these theories hold up." It's just so interesting.

Deboki Chakravarti: Yeah. Wow. Well, thank you, Sam, for braving the world of dark energy and dark matter.

Sam Jones: Oh, you're welcome.

Deboki Chakravarti: I am coming to you today with a message from listener Ari, who says, "Hello. I have always been really fascinated by microchimeric cells, cells that are transferred to baby from mom, maternal cells, or from the baby to the mom, which are fetal cells. A cool paper was published recently that shows that in mice, fetal cells that took residency in the mom from a first pregnancy are replaced by new fetal cells of a second pregnancy. I guess this is a win for all of us second and last born children out there as a way to outdo our older siblings. Would love to hear a deeper dive into this niche topic.

Sam Jones: As an eldest sibling, I am offended that my sister would've done something like this.

Deboki Chakravarti: Yeah, I'm an only child, so whatever.

Sam Jones: Yeah.

Deboki Chakravarti: My cells are still circulating in my mom.

Sam Jones: Oh my gosh. Caroline, I'm going to give you a hard time for this the next time I see you.

Deboki Chakravarti: Yeah, I mean, this is really cool. So microchimerism refers to the small population of cells that come from an individual who isn't the host, and they are genetically distinct. So pregnancy is probably the most common source of microchimerism, but it can also happen from a few other things. So these are things like blood transfusions or organ transplants. You can end up with cells from somebody else.

Sam Jones: From somebody else or somebody else's fetus?

Deboki Chakravarti: No, no, no, sorry. The microchimerism is just like getting cells. Yeah, no, you won't get fetal cells from them. But apparently another way it could happen is if you are a fetus and you've got a roommate in the womb, I think if you've got a twin or something, I think apparently you can also get each other's cells.

Sam Jones: That makes sense. I'm sure it probably depends on if you're fraternal or identical, maybe.

Deboki Chakravarti: I mean, I guess that's important in terms of like if you're talking about them being genetically distinct. I wonder.

Sam Jones: I just wonder how having a separate placenta affects things.

Deboki Chakravarti: Yeah, I don't know.

Sam Jones: I don't know. I'm going too deep on this. Okay, sorry.

Deboki Chakravarti: I didn't look into that one much more deeply. I just thought that was really interesting. But we're going to talk about the pregnancy microchimerism. And so like Ari said, there are fetal microchimeric cells, which is when you get fetal cells in the maternal tissue. And then there are maternal microchimeric cells, which is when you get maternal cells in fetal tissues. And these were first identified in 1893, which is really cool.

Sam Jones: Shocking.

Deboki Chakravarti: Because there were fetal cells that were found in the lungs of women who I think had died unfortunately from eclampsia. In the work that Ari sent us, researchers and science claim that you can only have one set of microchimeric cells at a time. So if you are pregnant, you get the fetal microchimeric cells. Then you get pregnant again and those fetal microchimeric cells get replaced by a new microchimeric cells from the new fetus.

But Tien told us that when she looked deeper into it, she couldn't fully find proof that the fetal cells are fully replaced. And she also brought up some work from 2015 that says that microchimeric cells actually get accumulated over multiple pregnancies. So it wasn't clear to us if this paper was actually disproving a previous notion about whether or not fetal microchimeric cells get replaced or if it's maybe because it's mice, maybe it's different. I'm not really sure.

Sam Jones: Yeah, that is a good point too. And as Ari very nicely put in all caps, this is in mice.

Deboki Chakravarti: And then a few other interesting things. The number of these cells do go down after birth, but you can still have them long after having given birth.

Sam Jones: In the mom?

Deboki Chakravarti: Yeah.

Sam Jones: Okay.

Deboki Chakravarti: And then we don't actually know much about how they affect the body, partly because they're really hard to study. There aren't that many of these cells and they're hard to detect, but they could be potentially important for understanding maternal health. More cells coming from the fetus and found in maternal blood tends to correlate to preeclampsia and higher hypertension during pregnancy. So I just thought it was interesting that they might potentially have more health-related implications than we know. But it's also just really hard to study because they're hard to identify.

Sam Jones: Right. That is really interesting and complicated. And I feel like I want to look further into how this researcher in 1893 first identified fetal cells in the lungs of women with eclampsia.

Deboki Chakravarti: I was looking a little bit into this. So it was in 1893. Georg Schmorl, Schmorl, S-C-H-M-O-R-L, he was a pathologist at the University of Leipzig, and he was studying eclampsia. And it wasn't very well understood. And so he was actually doing autopsies on 17 women who had died from eclampsia, and he found some abnormalities.

And weirdly, I guess the thing that really set him off to what was going on was that when he looked at the lungs, he found large multinuclear cells that are similar to the cells that you find in placentas. And I guess that was kind of what led to the realization that these are fetal cells.

Sam Jones: Oh, that's really interesting because I was like, they didn't have so much of the technology where we could be like, well, let's do single cell analysis now and let's see, is this maternal or is this from the baby? He didn't have that. So it's really interesting that him just saying... I guess he could have said they were cells from the placenta, probably from the fetus, but it's not like he could genotype a baby and double check that.

Deboki Chakravarti: Right. Yeah. Yeah. He just knew that they looked like placenta cells.

Sam Jones: So fascinating. Also, didn't know that about cells and the placenta. So learning a lot. Cool. That's really interesting. I do hope that some of my cells are still circulating in my mom, because I think eldest sibling, very important. Love my baby sister, but I was first, so that's my domain.

Deboki Chakravarti: Yep. This is the joy of being an only child. I am the only.

Sam Jones: The petty competition is not necessary.

Deboki Chakravarti: Yup. Thanks to Ari and Paul for submitting to Tiny Show and Tell Us, a bonus episode from Tiny Matters, created by the American Chemical Öйú365betÖÐÎĹÙÍø and produced by Multitude. And a big thank you to science journalist Tien Nguyen, who did the research for this episode.

Sam Jones: You can send us an email to be featured in a future Tiny Show and Tell Us episode at tinymatters@acs.org, or you can fill out the form that's linked in the episode description.Ìý

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