Dinosaurs: Dark Matter Kills Animals and Defends Physics – 02/04/2022 – Science

The search for evidence of the mysterious dark matter has continued for nearly half a century, prompting researchers to think outside the box.

But it’s hard to be more creative than Lisa Randall, the Harvard particle physicist, who hypothesized that dark matter killed dinosaurs.

Hey, wasn’t that lightning bolt crashing into Earth 66 million years ago? Calm down, yes it was. This part is not up for debate. But Randall points out that this only happened due to the episodic and periodic transit of the Solar System through the disk of the Milky Way.

Crossing the galactic plane, the gravitational interactions of the dark matter in it with some distant objects orbiting the Sun may lead many of them toward the inner part of the planetary system, causing violent collisions, including those that have killed. dinosaurs.

There are a lot of “ifs” associated with this premise.

It works if, in fact, there is a periodic increase in large impacts every 32 million years (which not everyone agrees with).

If only some of the dark matter behaves differently than usual models, by focusing in the galactic disk, rather than just forming a somewhat homogeneous globular halo around it.

And if there’s enough of it in the disk to cause gravitational effects on things in the so-called Oort cloud, the farthest repository of remnants of the solar system’s formation. This is just to name the three biggest “ifs”.

The conversation is of course complex, and American particle physics has written an entire book to break it down. “O Universo Invisível”, originally published in the US in 2015, is now released in Brazil by Companhia das Letras. Read the best excerpts from the interview with the author below.

One of the great ideas of the book is the idea that everything, even if it seems far from everyday reality, forms a picture that explains what we are doing here. A comparison can be made with what Carl Sagan used to name cosmic consciousness. Is it around?Let me say that there are very different ways of thinking that everything is connected. There’s kind of this, I don’t know, like “the secret” or something, and I want to make it clear that I’m not talking about it. I am not talking about the mystical ways in which things can be connected.

I don’t think of it as consciousness, but as the fact that if you seek to understand what you are at the most basic level, what you are made of, then you see that without these specific components, without these specific laws of physics, you cannot have the world that you see today. , It is amazing.

I mean, to think that some seemingly unrelated stuff actually contributed to our existence. These links are not always entirely straightforward, or even close to obvious. Sometimes the answers are right under your nose, but other times, to get a really deep understanding, you need to go back to the basics.

In the “Invisible Universe”, he introduces the idea of ​​the interaction of dark matter and the possibility of making a second disk of it in the Milky Way, and commented that data from the Gaia satellite will help put some limitations on this hypothesis. The book was written in 2015, and now there is data from Gaia. How has the hypothesis been implemented since then?There have been many scholarly articles where they are looking for the disc. Two of the claims are to exclude certain parameters, and the other sees evidence of a disk with a slightly lower density than we want.

I would not definitively conclude that it has been eliminated, nor that it exists either.

The evidence is not conclusive, but there are some suggestions for a disk slightly less dense than might be shown to cause such a disturbance in the Oort Cloud, in the outer parts of the Solar System. So I wouldn’t call it wow, but I wouldn’t rule it out either.

By grouping dark matter and dinosaurs together, you can bring up the idea that there was a frequency of mass extinctions…Let me just say, periodicity in large comet impacts. Not all of them led to a mass extinction, the latter resulted from an object like this… I just want to distinguish the real physics, which is an object that hit the Earth, from a mass extinction, which is one more step.

In the book, you present this as a not very assertive idea. Some people think this patrol is there, others don’t think it would be a patrol-like noise. I wonder if, since the book was published, you’ve been following this field too, if there are any new developments.No, I don’t, but you should keep in mind that what we’re looking at as evidence are pits from potential comet impacts. And they are there. Unless they find out more about it, the stats are what they are.

We are looking for craters from the last 500 million years. I mean, it’s really cool to have this evidence, these big craters that came from big bodies, bigger than a kilometer. And the fact that there are only 20 or 25 of them that we know about, the stats are poor, favors better stats.

We show that the hypothesis is statistically favorable, but not by an enormous amount that necessarily convinces everyone. including ourselves.

We still want to know if this is true or not. But what we loved about this project was the promotion of that discussion.

And of course, the big elephant in the room is the dark matter. It’s been seven years since I wrote the book and it seems like we’re still on the same point. There are experiments, some interesting results, but no definitive conclusions. What has changed since then?On the frontiers of science, you always do things that are hard to study. I mean, if they were easy, someone would have done it in the last century and you’d be out of work. So you study the hard stuff.

In the case of dark matter, just remember, it’s something we know through gravitational effects, but we don’t know on a fundamental level.

Is it gross? What is your mass? What are their interactions, if any? What we do know is that it interacts very weakly with our material.

Other than gravity, we don’t know of any other interactions, so what that tells us is that they’re not the things we’re familiar with. It’s something new and exciting.

And people have searched for it under what I would say is an optimistic assumption that it is somehow related to extensions of the Standard Model of particle physics. And they didn’t find it.

So I think the biggest change, although it may be behind the scenes and you may not see it there, is people realizing that there are other possibilities for what dark matter could be and thinking creatively about new ways to look for it. Of course, we still don’t know what it is, but I wanted to say it’s not entirely shocking that we don’t know what it is.

By definition, it’s something that doesn’t interact much with matter, which means it’s really hard to see. So the fact that we didn’t actually see something that’s so hard to see isn’t incredibly surprising.

In the book, you defend the idea that astrophysics at this point contributes more to understanding dark matter than particle experiments. Is that still your opinion?It depends on what you call particle experiments and it depends on what dark matter is. I think we should not underestimate any of them.

We don’t know what it is and we don’t know how we will find it, so we want to think of all possible ways…

I think we’d be very lucky if we found them in particle physics experiments, because that means they have interactions or connections with the Standard Model in ways we don’t know are true.

So I would say that astrophysics methods are somewhat more general in some cases. But that doesn’t mean we should do one or the other. We must do both.