Inferring invisible things through gravity

17:19parts in a way that we might not be able to in other lines of inquiry in this area. >> Yeah, that's right. So, what we want to do is essentially count how many of these clumps there are and measure how dense they are. Those are sort of the two uh you know, two of the most interesting types of measurements you can make. But, it's hard, right? Because they don't interact with light. >> Mhm. >> We can't like detect them directly. We have to rely only on gravity. But, it's not impossible. So, so let me give you a you know, think about this situation for a second. >> Okay. Okay. >> Suppose that we couldn't see the moon for whatever reason. Maybe it was We're

17:59on a planet where it's always cloudy, but there's a moon and there's an ocean. >> Okay. >> So, you would be able to infer that something like the moon exists based on the tides. Because the the moon's gravity is partially responsible for the tides. >> It's the the idea, you know, it's the graphics you see where Earth is here and the moon as it goes around, you see the water on the surface of the Earth track with the the orbiting of the moon, which is what actually generates the tides itself. >> That's right, yeah. So, even even if you were in a situation where you couldn't see the moon >> Ah, yeah, yeah, yeah, yeah. >> be able to infer that it exists, which I guess in this analogy is like the rotation curve argument, right? So, we're pretty sure

18:40that there's stuff there, but we could take it one step further, right? And you could you could also estimate properties of the moon based on the tides, right? >> This this is the point is through indirect obser- even though we can't directly observe dark matter, in your analogy, if we couldn't if the moon was dark matter and we couldn't directly observe it because we were in a cloud of whatever nuclear dust everywhere, um we would still be able to infer that it's there because it has direct impacts on some derivative observation, which in this case is the tides. >> That's right. Yeah, and so it turns out that you know, we don't use tides in astrophysics. What we can actually use

19:21is light because it turns out that light is actually bent by gravity. So, a gravitational field will deflect the path of light. We can see light. And so we can use the fact that that images of astronomical objects will be slightly distorted by the gravity from dark matter to study the dark matter even though we can't detect the dark matter directly. >> It's okay, very interesting. So, in this case in the just keeping with this analogy, if dark matter is the moon, um and then the water of the ocean that causes the tides is light. The water gets disturbed by the moon, which creates high low tide and you

20:02know, all that flow. Similarly, dark matter impacts light as it's traveling into our instruments. And it's going to distort it a little bit in the same way the moon would distort the tide, and we can measure that distortion to then derive some understanding of the size and what was this the two measurements was size and >> And the internal structure of these clumps. >> clumps. Am I am I getting that right? >> That's exactly right. >> Very interesting. Okay, okay. And so this is where where your area of research focuses. >> Right. So, that was the longest intro of all time, right? That's the problem. >> But that's that's the that's the best

20:42part is really understanding deeply what are we trying to what are we looking for trying to measure? >> Yeah, that's right. So, we are trying to measure the properties of these small I say small, keep in mind that they're enormous, right? But from a cosmological standpoint, they're very small. >> Yeah. >> These small clumps of dark matter using light and the deflection of light by the gravity of those clumps. Imagine if I asked you to describe the room that we're in now using gravity. Okay? This maybe that's gives you another way of thinking about this, right? It's It's a very challenging thing to do is to understand the structure of some uh material using only gravity. >> I I I I literally was like I don't even

21:24I literally was like I don't even know where to start. But this is this is fascinating. And I I I So now that sets the table really nicely because I think I understand the problem set. Um and and there's so many implications to being able to better understand this area because it'll totally impact our ability to map the early models of the universe and you know, different types of existing um um space-based telescope and ground-based telescope missions. But when when we now talk about you as a researcher having clearly defined the problem now that we're trying to look at

22:05you know what is Now what is your day-to-day kind of look like in trying to solve for that now well-defined problem?