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Tai Asks Why

Season 2 – Why is space so dark if it’s full of stars?

VOICE: This is a CBC podcast.

TAI: Whenever I get out of the city, I always love looking up at the stars. Not only do they look cool, but seeing the vast expanse of space, always brings up a really big question for me. Why does the night sky so dark? Because if NASA is right, there are trillions of stars in the sky. Then shouldn't the sky just constantly just be bombarded with the starlight? I know that light can travel pretty far in space. Like guys the sun is around 150 million kilometers away. And not only does the light still get here, the light is still strong enough to just burn us too. So what is in between all these stars? It can't just be black holes just constantly just like sucking up all the light. Why can't I see the light of trillions of stars when I look up at the night sky? Why is space so dark?

[Tai Theme Song]

TAI: I'm Tai and this is my podcast Tai Asks Why. There are just so many good questions out there that are just lingering, waiting to be answered. How does a song get stuck in your head? What is déjà vu? When the dinosaurs died, how did other animals survive? What are animals saying to each other? What is the science of bullying? And why is space so dark if it's filled with so many stars.

NEIL DEGRASSE TYSON: So you have questions.

TAI: So I don't want to brag, but I recently won an award and I got to go to this big ceremony in New York. And the thing is, while I was there, I got to meet my personal hero.

NEIL DEGRASSE TYSON: My name is Neil DeGrasse Tyson and I'm your personal astrophysicist.

TAI: So if you don't know, Neil DeGrasse Tyson is an amazing astrophysicist and just a generally really smart dude. He's the reason I got really into space and the inspiration that gave me this question you guys. I kinda kind need to ask him it you know? So Neil DeGrasse Tyson

NEIL DEGRASSE TYSON: Yes

TAI: Why is space so dark?

NEIL DEGRASSE TYSON: That's a deep question. Space is dark because the universe is expanding. That's why space is dark. It's expanding and it's finite. Because if the sightlines through space ends on a star, then that intensity of that star light would be the brightness of that spot. But most places you look do not land on a star. So the expansion dilutes starlight. And not only that, we don't live in an infinite universe. Because if there were infinite, eventually your sightline would land on a star. And if it did that, the whole night sky would be ablaze with starlight. But it's not.

TAI: Hey guys I'm tryna play it cool, but, you know, I just talked to Neil DeGrasse Tyson so it's a pretty big deal.

[Music]

TAI: The reason we see darkness instead of all starlight everywhere is because the universe is expanding so the starlight is moving away from us. And also because the universe is finite. If we look in a certain direction, there might not just be a star there, but that's some big confusing really works your mind answer so I have a lot of follow up questions. I have to get some more answers. But Neil was busy doing amazing astrophysics stuff, so I went to visit my other personal astrophysicist. Heidi White at the University of Toronto to help me see what's going on with all this light in the Cosmo's.

HEIDI WHITE: Here we go. All right. Now let's turn this on.

TAI: We're on the roof of the astronomy building in downtown Toronto in a warm, pretty clear, really windy night. Well it looked it looks like you're about to like fire a laser. We're just firing up the telescope to check out some bright space objects that are close to us.

HEIDI WHITE: Look, Tai, do you see that? Wait let's move it a little bit. You see this?

TAI: Oh hello

HEIDI WHITE: Let me move it up so you can.

TAI: Hello friend.

HEIDI WHITE: You see that?

TAI: Yeah

HEIDI WHITE: That's Jupiter and do you see these things.

TAI: Yeah.

HEIDI AND TAI: Those are moons.

TAI: We've found moons lets go. Heidi tells me I'm not alone in wondering why everything around my new pal Jupiter is so dark. Three hundred years ago apparently, there was this dude named Wilhelm Olbor who asked the same question.

HEIDI WHITE: You know the observing that we're doing right now is very similar to the night sky observing that Olbor did. Olbor was a doctor during the day and at night he turned like the roof of his house into an observatory. And he would go out at night, just like we are, and study what he could see in the solar system.

TAI: So because Olbor wondered why the sky was so dark. Apparently they named the question after calling it Olbor's paradox. Basically the paradox is that if the universe is infinitely big, infinitely old, which is infinite general as they believed seventeen hundred, then the whole sky should appear to be super bright all the time. But it isn't. And we know now as my boy Neal said, the universe isn't infinitely big neither is it infinitely old. So why does that change the brightness of the sky?

HEIDI WHITE: What do you know about our universe and how long its been around?

TAI: Thirteen point five billion years. Like thirteen point six now?

HEIDI WHITE: Yeah, it's close. About thirteen point eight. Yeah. So we know that our universe had a beginning. And you know what that beginning was?

TAI: A big bang was. It's not a bang really it's more just a very wet inflation. It just went really big there was no big explosion or anything. It just kind of inflated like a balloon very quickly.

[Balloon inflating]

HEIDI WHITE: Yeah, that's a really good analogy actually to to visualize the expansion of space time one really good thing you can do is take a balloon and put a bunch of dots on it and then blow up the balloon and you start to see as you put more air into it. That's sort of what's happening in space time. Things are moving further and further away from one another. But this is important in the context of understanding that the answer to Olbor's paradox because what this means is that things haven't always been the way they look right now. The speed of light is fixed and what that means is that if we look far enough away, what we're effectively doing is looking back in time. In that way, telescopes can actually be time machines because the most distant star's light in the universe hasn't had time to actually travel through space because it's been expanding to actually reach us.

TAI: The speed of light is three hundred thousand kilometers a second, so the light from Jupiter takes 30 minutes to reach us here on Earth. So when we see it, we're seeing Jupiter as of 30 minutes ago. And then there's light in the universe that is thirteen point eight billion light years away. This is the stuff made in the Big Bang guys, so we can't see it yet because you know we're not that old yet. Maybe by the time I'm in high school I'll be seeing light from a random star that I can't see today cause it'll finally be getting to my eyes. But also maybe not cause well, as the space time continue balloon just inflates and inflates further, it'll just take even longer for that light to reach our eyes.

HEIDI WHITE: Every part of the universe is expanding, it's expanding at a very high rate and it appears to be accelerating in its expansion. And so if the universe is expanding, that's producing an effect that we call redshift. Redshift is this effect by which objects moving away from us. The wavelength of the light that they admit it becomes stretched out. And what happens is that as this wavelength becomes stretched out, the frequency decreases and it shifts that light to redder and redder wavelengths. At some point, objects are going to be far away from us enough that they're moving away from us fast enough that that redshift is going to shift them right out of the part of the electromagnetic spectrum that our eyes can see.

TAI: This is some deep, confusing stuff so just try to bear with me here. Basically, we see a light as a wavelength, and when that light is moving away from us, it gets stretched. And the more stretched out a wavelength is, the more red it looks. So our eyes would see this more and more red. But at some point it'll just get so stretched out that we actually can't see it. It's called infrared. And it just goes into a part of the spectrum we can't see. So there could be stuff in the darkness between the stars and we just can't see it because it's moving away from us so quickly. Maybe if I get closer to these stars I'd be able to get a clearer picture what's going on here? But how would I do that?

HEIDI WHITE: Hen times in the basement. So we have an inflatable planetarium, and so what you're hearing is actually the fans that pump air into the planetarium to keep it inflated.

TAI: It looks like the Swedish berries from Maynards, but it's like all black and massive kind of.

HEIDI WHITE: I'd say it looks like a kind of like an igloo.

TAI: It has the

HEIDI WHITE: A bouncy castle.

TAI: It does look like a bouncy castle.

HEIDI WHITE: All right. So maybe what we could n do is lift off from Earth.

TAI: Zoo. Woah woah, it's awesome. It's just very weird cause like you zoom out a little bit and then you just, pow, orbits in the face.

HEIDI WHITE: We're now looking at Earth at this moment. I'm going to hand you the controller. OK. We're gonna have you zoom out as far as we can go in the universe. So we're zooming past our solar system.

TAI: Like you can definitely see light during the belt or the Milky Way, but other than that it still seems kind of dark.

HEIDI WHITE: So keep going.

TAI: Oh, why is it so bright? Oh, the things are moving. Wha What. So what Heidi is showing me is that the constellations that look like a six year old's poorly connected, connect the dots here on Earth look totally different when you zoom out beyond our solar system and see them in the third dimension. From Earth they all look so close together and you know, you connect 1 and 2, 3 and 4 and boom, you get yourself a horse. But when you get into their neighborhood, they're super far away from each other.

HEIDI WHITE: So those constellations that we see in the night sky are 2D projections of stars in 3D space. And so as you zoom out a little bit more, you can start to see the actual connections that we've made from our perspective on Earth. You going little more?

TAI: That's the Milky Way.

HEIDI WHITE: This our galaxy. This is the galaxy that hosts our solar system, our our home on Earth. You see that the earth and our solar system is sort of situated. If you imagine the center of our galaxy to be the big city., we're kind of out in the suburbs. Right. You can see that we're further out in the Milky Way.

TAI: It's like a fried egg, but it got like horribly burnt. But then the big question is, it's very bright. Like the especially the center. It's very bright, so then how come we only see a very small portion of the of like the things we see in our light night sky with all the constellations and such?

HEIDI WHITE: That's actually a great question. So why does it look like a streak on the night sky and it looks like like a like a disc here, like a big circle. Right. So when we are looking through on our night sky when we see the Milky Way, this is what we're seeing. We're seeing the projection of it through the disc of the Milky Way because we're inside the disc of the Milky Way.

TAI: It's being a jerk and it's just blocking everything.

{Music]

TAI: Picture this. If our solar system is the size of a quarter, pretty small. then the Milky Way is the size of the United States of America. So the Milky Way shaped like an America sized fried egg. And we're just literally just a tiny coin in the suburbs of the egg white. And that's also why when you look away from the city's bright lights, the Milky Way in the sky looks kind of like a bed. And that's us just looking across the egg white. At more egg white. Back at the planetarium, I am now fully zoomed out as far as we can go to get a picture of our universe, the Milky Way, our fried egg is now just a tiny dot. Like pinhead dot. There's a whole bunch of other pinhead dots filling up the screen. Ballpark, how many dots are we looking at right now?

HEIDI WHITE: Trillions. In the observable universe, there's trillions of galaxies.

TAI: So the lesson I want you to take away from this kids is that we're small and nothing we ever do matters.

HEIDI WHITE: I think personally for me I find that relaxing.

TAI: It's a good thing, I failed the test. Well, now it doesn't matter, woo. So to recap all this, there is a whole bunch of stuff out there in the universe emitting its light pwaowa. Some of it's being sucked away from us so fast and the expansion of space thatt the light is now invisible to us. Some it's being blocked by us being inside the egg white of the Milky Way. And some of it just hasn't had enough time to reach us yet because it's billions on billions on billions of light years away. That explains why it's so hard to see all the stars and the planets and all that stuff so far away from Earth. Hard, I said, but not impossible.

JESSE DOTSON: I think it's really cool to stand there and think about the fact that there are so many planets going around those other stars and just try to imagine what might they be like.

TAI: This is Dr. Jesse Dotson.

JESSE DOTSON: Hi.

TAI: Hi. She's thinking about planets around the stars because that's her job. She's a project scientist at NASA's Ames Research Center. She's one of the many people who look out into the darkness of space, the world beyond our solar system to try to figure out what's actually out there using a space telescope called Kepler.

JESSE DOTSON: So Kepler is a spacecraft that we launched just a little over 10 years ago and the purpose of Kepler was to look for planets around other stars. We did that for about nine and a half years, and last fall, the spacecraft's fuel ran out. And now we are continuing to dig through the data to find all the planets that we can and learn all we can about the stars we observed.

TAI: What exactly does Kepler look at?

JESSE DOTSON: So the way we find planets with Kepler is we stare at stars in the original for years, we stared at 150,000 stars at a time and we looked at them almost continuously for four years. And what we are looking for were little dips in the light coming from those stars,.

TAI: Oh, because that means a planet just passed in between Kepler and the star.

JESSE DOTSON: Exactly. When you see one dip and you start to get interesting. You see a second dip and you get really interesting. And when you see a third dip and they're happening kinda like get a steady beat at a steady period. Then we get really interesting. We do some other checks before we then declare it. Yay! This is a confirmed planet.

TAI: This is like a been like a dream of mine to talk to somebody about this for like seven years so just I might be a little bit taken aback. But how many, you said that you've seen a whole bunch of stars, but how many planets of all these stars have you confirmed?

JESSE DOTSON: OK. So I checked the number for you this morning. And from the Kepler spacecraft, we have confirmed two thousand seven hundred and two planets around other stars.

TAI: Cool.

JESSE DOTSON: I think it's really cool and exciting.

TAI: OK, good cause I oh my God I think that's awesome, too.

JESSE DOTSON: You know, we have found planets that are unlike anything in our solar system. We have found planets that orbits two stars at the same time. We have found planets that are so close to their host star that they're just, you know, thousands of thousands of degrees. Their years last, you know, two days. It's just the the diversity of what we've seen, it almost is beyond what you can imagine if all you knew was our own solar system. And I think that's just so cool to realize how different and exciting planets can be.

TAI: But those are the planets. What about our stars?

JESSE DOTSON: There's a couple things. One, we can learn a lot about the stars, whether or not they have a planet in front of them by just looking at how the stars light varies and particularly with big red giant stars, we can see the variations that are kind like the the star stuff waffling or like sloshing around and it sloshes around and particular frequencies that actually tell us things about what's going on inside of that star. But something else is we've looked at a bunch of galaxies outside of our own. And looking at those galaxies we have seen supernova go off. And so supernova are stars that have essentially reached the end of their life and they explode.

TAI: Bang stars.

JESSE DOTSON: Yeah. And with Kepler, we got to see how that explosion started. And you can learn a lot about an explosion if you can see the start.

TAI: It really sounds like it could be even cooler than the explosion itself just seeing how the sun itself just kind of just dies and just emits this final burst of the explosion juice.

JESSE DOTSON: Now, of course with Kepler, what we see is we see this little teeny tiny point of light get brighter, a brighter, brighter, brighter and then fainter, fainter, fainter.

[Music]

TAI: Hold up. One thing I do know about these bang stars in space that sometimes they can make these black holes does mean this dark space between the stars could just be a whole bunch of black holes.

JESSE DOTSON: So black holes suck everything in that gets to them. But the thing is, they're pulling stars and dust and gas in, and as all this stuff gets pulled in by the black hole, you get stars and gas and dust that are much closer together than in most other places in the universe. And then they start to bump into each other and heat each other up, and so all this energy that you're seeing is the energy that doesn't get sucked in the black hole but is created because the black hole is pulling all these things in close to it. Once anything goes into the black hole, whether it be a star or a dust particle or a light photon. It never comes back out again.

TAI: Whoa. Have you ever seen one of these black holes using Kepler?

JESSE DOTSON: We have seen what people call active galactic nuclei or AG ends. And what that is, that is there's a black hole in the center and stuff is being pulled into the black hole. But some of the stuff goes into the black hole some of the stuff bounces around and it creates really bright flashes of light. And so we have observed those bright flashes of light.

TAI: So light even helps us understand darkness. That's so weird because, you know, you're using the opposite of something to understand the opposite of the thing. So how important is light then to your to studying outer space?

JESSE DOTSON: So light is absolutely critical to studying outer space. Almost everything we know about outer space, we've learned by looking at light, at different wavelengths in different energies and trying to figure out what that light is telling us.

TAI: Well, OK. You know, like I didn't really know what else I was expecting. But, you know, light's light's pretty cool. Thank you so much.

JESSE DOTSON: Well, it's been a lot of fun Tai.

TAI: I think that we should, like, keep in touch, though pen pals, please.

JESSE DOTSON: You bet Tai.

[Music]

TAI: Pen pals from NASA. It's pretty great, guys. It's pretty great. Now when I look up at the dark sky, I can really appreciate all the different things that make it so I'm just not blinded by a bombardment of light. You know, it's also a little uneasy that there could be death lasers coming towards us it would just go under our radar. Our poor eye radar. And, you know, I have this whole appreciation for these stars and the planets, the dark stuff between them. It's just kind of cool cause, you know, since space is so dark, it makes the star stand out that much more. Space is cool.

[Music continues]

VOICE: Light beams travelling for. Light beams traveling headed for who knows

TAI: Thank you guys so much for listening. I'm Tai Poole. The show is produced by Veronica Simmonds and Amanda Buckiewicz. Our digital producer is Judy Gu. Today, my guests were Heidi White, Dr. Jesse Dotson and special thanks to Tina Verma and course, Neil DeGrasse Tyson guys woo, still kinda can't believe I did that. Theme music is by Johnny Spence, and another big thanks to Johnny for helping me write and record the Dark Space song.

KIEN: Next time on Tai Asks Why: Catchy Songs.

VOICE: When you think about it, how could we ever have remembered the alphabet if it wasn't for the song?

TAI: Till next time I'm Tai, keep looking up.

VOICE: For more CBC podcasts, go to CBC.ca/podcasts

TRANSCRIPT: Tai Asks Why - Season 2: Why is space so dark if it's full of stars?

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