Dark Universe Decoded with Katherine Freese

What are the main candidates for dark matter? Neil deGrasse Tyson and comic co-host Chuck Nice sit down with theoretical physicist Katherine Freese to tackle fan questions about dark matter, dark energy, and the dark universe at large.

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Neil deGrasse Tyson?

  We are growing our stable of cosmologists.

• 0:02Chuck Nice?

  Yes.

• 0:02Neil deGrasse Tyson?

  Katie Freeze coming in.

• 0:04Chuck Nice?

  That's right.

• 0:04Neil deGrasse Tyson?

  About dark matter, dark energy, big bang, rocking.

• 0:07Chuck Nice?

  Yep, the only cosmologist who sounds like a Batman villain, Katie Freeze.

• 0:13Neil deGrasse Tyson?

  Coming up on StarTalk.

• 0:17Neil deGrasse Tyson?

  Welcome to StarTalk, your place in the universe where science and pop culture collide.

• 0:26Neil deGrasse Tyson?

  StarTalk begins right now.

• 0:30Neil deGrasse Tyson?

  This is StarTalk. Neil deGrasse Tyson, your personal astrophysicist. This is gonna be a Cosmic Queries edition on cosmology. There's no end of Cosmic Queries we can do on cosmology.

• 0:45Chuck Nice?

  I suppose there is not.

• 0:47Neil deGrasse Tyson?

  This is Chuck Nice, right here.

• 0:48Chuck Nice?

  That's right.

• 0:49Neil deGrasse Tyson?

  Professional comedian, stand-up comedian.

• 0:50Chuck Nice?

  There is an end to me.

• 0:54Neil deGrasse Tyson?

  So cosmology.

• 0:55Chuck Nice?

  Yes.

• 0:55Neil deGrasse Tyson?

  So we're broadening our stable of cosmologists to whom we can reach out.

• 0:59Chuck Nice?

  Yes.

• 1:00Neil deGrasse Tyson?

  For our queries.

• 1:01Chuck Nice?

  Right.

• 1:01Neil deGrasse Tyson?

  And today, we have a second timer.

• 1:04Chuck Nice?

  That's right.

• 1:04Neil deGrasse Tyson?

  The one and only Katie Freeze. Katie, welcome back.

• 1:09Neil deGrasse Tyson?

  Welcome back to StarTalk.

• 1:10Speaker 02

  Thank you, thank you.

• 1:11Neil deGrasse Tyson?

  Last time you were here, I think we talked about the search for dark matter and. We did.

• 1:18Speaker 02

  We did.

• 1:19Neil deGrasse Tyson?

  Cause that's cosmology writ large and we just, we poked your brain about all manner of things. And this is gonna be a Cosmic Queries where we have told our Patreon supporters that you're gonna be on. And they, they're fans of yours and they've written in, or they became fans of yours when they saw your expertise.

• 1:38Chuck Nice?

  That's right.

• 1:39Neil deGrasse Tyson?

  And they wrote in and the questions are here.

• 1:41Speaker 02

  Well, thanks a lot. I haven't seen these queries.

• 1:44Neil deGrasse Tyson?

  Well, neither have I. He's the only one who's seen them.

• 1:46Chuck Nice?

  Yes.

• 1:47Speaker 02

  Okay.

• 1:47Neil deGrasse Tyson?

  So.

• 1:47Chuck Nice?

  And I'm the only one who can't answer them.

• 1:54Speaker 02

  That may be true.

• 1:55Neil deGrasse Tyson?

  That is kinda funny. The only people can't answer them haven't seen it. And the one who can't answer it has.

• 2:01Chuck Nice?

  They have it.

• 2:02Neil deGrasse Tyson?

  So... A couple of times, people have asked questions that no one has been able to answer. Like with the quark one going into a black hole.

• 2:11Chuck Nice?

  Yeah, exactly. Quark into a black hole.

• 2:12Neil deGrasse Tyson?

  That we still...

• 2:13Chuck Nice?

  We still don't know the deal.

• 2:13Neil deGrasse Tyson?

  We still don't know that one.

• 2:14Chuck Nice?

  Everybody says that's...

• 2:15Neil deGrasse Tyson?

  Maybe Katie knows. We can find out.

• 2:17Chuck Nice?

  Well, we should find out, yeah.

• 2:18Neil deGrasse Tyson?

  Well, let me get your bio here. Director of the Weinberg Institute for Theoretical Physics, UT Austin. That's Stevie Wonder, Steven Weinberg.

• 2:27Speaker 02

  Yeah.

• 2:28Neil deGrasse Tyson?

  Right?

• 2:28Speaker 02

  So Steve Weinberg, my hero, one of the founders of the standard model of particle physics.

• 2:33Neil deGrasse Tyson?

  Yes.

• 2:34Speaker 02

  He was the greatest physicist of our time, in the opinion of many, including me. His office was three doors down from me. He recruited me to UT Austin. Maybe that's why I think he's the greatest physicist.

• 2:47Neil deGrasse Tyson?

  That helps. Who gave you the good job, right?

• 2:50Speaker 02

  Yeah, yeah.

• 2:50Neil deGrasse Tyson?

  But he was only named...

• 2:51Speaker 02

  No, seriously.

• 2:52Neil deGrasse Tyson?

  He was only named in his death, obviously.

• 2:53Speaker 02

  Yeah, he died about three years ago.

• 2:55Neil deGrasse Tyson?

  Yeah, okay.

• 2:56Speaker 02

  And we started the institute in his honor.

• 2:59Neil deGrasse Tyson?

  And now, he's more a hero for me than he is for you.

• 3:03Speaker 02

  Why is that?

• 3:04Neil deGrasse Tyson?

  Cause he went to my high school.

• 3:05Speaker 02

  Oh.

• 3:06Neil deGrasse Tyson?

  Ba-bang!

• 3:07Speaker 02

  Oh, Bronx Science.

• 3:07Neil deGrasse Tyson?

  The Bronx High School of Science.

• 3:09Speaker 02

  Oh, yeah, yeah, yeah.

• 3:09Neil deGrasse Tyson?

  Both he and Shelley Glacho.

• 3:11Speaker 02

  Yeah.

• 3:11Neil deGrasse Tyson?

  Went through, were in the same class. They were classmates and both shared the Nobel Prize.

• 3:16Speaker 02

  Okay, so the moral of the story is, when are you getting your Nobel Prize?

• 3:20Neil deGrasse Tyson?

  I didn't mean to set it up that way. That was not... So what else do I have here? And you spent some time at Stockholm University? And that's ending, coming up very shortly?

• 3:29Speaker 02

  Ten years. They gave me a really... The Swedish government gave me a $15 million grant over 10 years to do cosmoparticle theory. And that was so much fun.

• 3:39Neil deGrasse Tyson?

  Wow.

• 3:40Speaker 02

  Oh, wow.

• 3:40Neil deGrasse Tyson?

  Did you have students too and everything?

• 3:42Speaker 02

  Oh, I did.

• 3:43Neil deGrasse Tyson?

  With a budget to go back?

• 3:44Speaker 02

  I did, yeah. So I had students and I had postgraduate fellows and everybody running up and down the halls, having great ideas and having fun. It was awesome.

• 3:54Neil deGrasse Tyson?

  Wow.

• 3:55Speaker 02

  Yeah.

• 3:55Neil deGrasse Tyson?

  Okay. Cause I think when we last interviewed you, you were like fully up and running with them. And what else? Oh, and I'd love this back now 10 years ago. The Cosmic Cocktail. Ooh. Can you get a better title than that? Shake it, not dirt. I don't think so. Three Parts Dark Matter.

• 4:16Speaker 02

  Yeah.

• 4:17Neil deGrasse Tyson?

  That's about right. That's pretty cool, man.

• 4:19Speaker 02

  You know, the amazing thing about that book is that I still give public lectures about it. And people are still buying lots of them. In fact, Amazon ran out again.

• 4:28Neil deGrasse Tyson?

  Whoa.

• 4:28Speaker 02

  And that was a book I wrote 10 years ago, so.

• 4:30Neil deGrasse Tyson?

  Good for you.

• 4:31Speaker 02

  I guess it was a good one.

• 4:32Neil deGrasse Tyson?

  Whoa.

• 4:33Speaker 02

  And you wrote a blurb for it. You said, what did you say? I don't know, three parts dark matter, seven parts memoir or something like that?

• 4:40Neil deGrasse Tyson?

  Right, because it was folded into your life.

• 4:42Speaker 02

  It was.

• 4:43Neil deGrasse Tyson?

  Yes, very important feature of that. Thanks for reminding me. It just made it a much more interesting account.

• 4:48Speaker 02

  Yeah.

• 4:49Neil deGrasse Tyson?

  Right, right, cool. Here's another plug for it.

• 4:52Speaker 02

  Thank you.

• 4:53Neil deGrasse Tyson?

  Amazon ran out again.

• 4:56Neil deGrasse Tyson?

  So, we're gonna chat for a bit before we go to Q and A.

• 4:59Speaker 02

  Okay.

• 4:59Neil deGrasse Tyson?

  Catch us up on a couple of things. The James Webb, there's been a lot of talk about these early galaxies that it has discovered in a zone of the early universe where you're not supposed to.

• 5:10Speaker 02

  So wait, you're talking about the James Webb Space Telescope?

• 5:11Neil deGrasse Tyson?

  Yeah, yeah, not the administrator of NASA during the 1960s.

• 5:15Speaker 02

  Yes.

• 5:15Neil deGrasse Tyson?

  After whom the telescope was named.

• 5:17Speaker 02

  Yes.

• 5:18Neil deGrasse Tyson?

  You know, he was an accountant. James Webb? Yeah. I did. One of the rare non-scientists after whom a telescope is named. An accountant? I think that was his main training. That's pretty wild. I gotta say.

• 5:30Speaker 02

  I guess he was, what was he important for in NASA?

• 5:33Neil deGrasse Tyson?

  He was head of NASA. Was the head of HR taken?

• 5:37Neil deGrasse Tyson?

  While we went to the moon, he was head of NASA.

• 5:39Speaker 02

  Ah.

• 5:40Neil deGrasse Tyson?

  So it was, it was, give a little back to that. Look at that. Fact, because you need, you need good administrators, not just good scientists to make stuff happen. Well. When you're in bureaucracy. You're a damn good administrator when they start naming stuff after you.

• 5:54Neil deGrasse Tyson?

  So, what's this we hear about paleo detectors? What is that? Is that a thing?

• 5:59Speaker 02

  Yeah.

• 5:59Neil deGrasse Tyson?

  What is that?

• 6:00Speaker 02

  Well, the paleo part means that they've been around for a billion years. And so, let me back up. We're trying to figure out what dark matter is made of.

• 6:09Neil deGrasse Tyson?

  Yes.

• 6:10Speaker 02

  And we think it's some kind of particle we haven't identified yet.

• 6:13Neil deGrasse Tyson?

  Yes.

• 6:13Speaker 02

  And, most of the experiments now involve these giant, tons and tons of liquid xenon. And so, the idea is, okay, instead of having-

• 6:22Neil deGrasse Tyson?

  That's because xenon has some probability of interacting with a dark matter particle.

• 6:27Speaker 02

  Yeah, yeah, dark matter particles flying around in the galaxy. And by the way, there would be billions going through your body every second. Yeah, yeah, but it's okay, only one a month hits you.

• 6:36Chuck Nice?

  I thought I felt tired for a reason.

• 6:38Speaker 02

  And so-

• 6:39Neil deGrasse Tyson?

  Wait, wait, wait. You know, there's a lot of elements on the periodic table. Why do you know that xenon might work when we otherwise know nothing about dark matter?

• 6:48Speaker 02

  The way these detectors work is the dark matter comes along, hits one of these xenon atoms, deflects off of it, and the xenon gets some energy deposited in it, and they're able to detect that. So, you have to have a detector design that works, and with xenon, we know how to do it.

• 7:05Neil deGrasse Tyson?

  Okay, so it could be any particle that that would happen to, but xenon has some other convenient properties?

• 7:12Speaker 02

  So, the kind of interactions we're looking for is from the weak force, very, very weakly interacting particles.

• 7:19Neil deGrasse Tyson?

  Hence the name.

• 7:20Speaker 02

  Hence the name, weakly interacting massive particles. And, there's, people need to build detectors that are, that they know, you need to know how to build the damn detector. I don't know how to answer this one, Neil.

• 7:33Neil deGrasse Tyson?

  No, no, so let's say differently. A neutrino detector, for example, that uses vats of liquid-

• 7:40Speaker 02

  Yeah.

• 7:40Neil deGrasse Tyson?

  ...uses like, some kind of chlorine molecule, but not xenon. So, where are these xenon detectors?

• 7:49Speaker 02

  They're deep underground.

• 7:50Neil deGrasse Tyson?

  Okay.

• 7:51Speaker 02

  One of them is underneath the Apennine Mountains outside of Rome, okay?

• 7:55Neil deGrasse Tyson?

  Ooh, you know, the Apennine Mountains on the moon. Named after those.

• 7:59Chuck Nice?

  I was gonna say that you've actually said that.

• 8:03Neil deGrasse Tyson?

  Yeah, Italy came first.

• 8:04Chuck Nice?

  The mountains here.

• 8:05Neil deGrasse Tyson?

  The reason why I know them and the reason why they are important is the phase of the moon that's best for telescopic views is half moon.

• 8:14Chuck Nice?

  Okay.

• 8:14Neil deGrasse Tyson?

  Because shadows are the longest and the Apennine Mountains crosses the half moon divider, the terminator, and so Apennines just pop on a first sighting of the moon.

• 8:25Speaker 02

  Oh, cool.

• 8:26Neil deGrasse Tyson?

  So to me, the Apennine Mountains are on the moon, not in Italy.

• 8:29Speaker 02

  All right, all right. Well, if you could build something on the moon, that would be even better because the reason you have to go underground is to get away from cosmic rays.

• 8:36Neil deGrasse Tyson?

  Okay.

• 8:37Chuck Nice?

  Right.

• 8:37Speaker 02

  And there's a million cosmic rays for every one of these dark matter particles if you're on the surface of the earth, so we go deep underground because the cosmic rays don't make it down there.

• 8:46Neil deGrasse Tyson?

  But the dark matter particle would.

• 8:48Speaker 02

  But the dark matter particles would.

• 8:49Neil deGrasse Tyson?

  Okay, based on what we think dark matter particles would be like.

• 8:54Speaker 02

  Well, because they're only weakly interacting.

• 8:55Neil deGrasse Tyson?

  Okay.

• 8:57Speaker 02

  And normal, normal particles.

• 8:59Neil deGrasse Tyson?

  Would interact electromagnetically.

• 9:01Speaker 02

  If you and I collide, we're not getting very far.

• 9:03Neil deGrasse Tyson?

  No, that's right.

• 9:04Speaker 02

  Because we have a lot.

• 9:05Neil deGrasse Tyson?

  We don't pass through each other.

• 9:06Speaker 02

  We don't pass through each other.

• 9:07Neil deGrasse Tyson?

  Right.

• 9:08Chuck Nice?

  I'll tell you something about xenon, makes a hell of a headlight.

• 9:16Chuck Nice?

  Just wanted to contribute something, I don't know.

• 9:19Speaker 02

  I'll tell you, want to hear another something about xenon? There's another thing about xenon, it's become very expensive because the xenon experiments have bought the entire world supply.

• 9:29Chuck Nice?

  Get out.

• 9:30Speaker 02

  No, I'm serious.

• 9:31Chuck Nice?

  Wow.

• 9:32Speaker 02

  I'm serious.

• 9:33Chuck Nice?

  Now you tell us.

• 9:34Neil deGrasse Tyson?

  Yeah, you should have told us.

• 9:35Chuck Nice?

  You should have told us before these experiments started.

• 9:37Speaker 02

  Which is why.

• 9:38Chuck Nice?

  We could have got in on the cornering of the xenon market.

• 9:40Speaker 02

  Oh, my God, that's true.

• 9:41Chuck Nice?

  Yeah.

• 9:43Speaker 02

  Which is why we want to propose an alternative. So instead of these, instead of giant detectors, we're gonna dig up little rocks from deep underground and they've been collecting dark matter tracks for a billion years, so we're replacing volume with time.

• 9:59Chuck Nice?

  Wow.

• 9:59Speaker 02

  Isn't that cool? Hence paleo.

• 10:01Neil deGrasse Tyson?

  Oh.

• 10:01Chuck Nice?

  Okay, now that is, first of all, that's very smart, but yeah.

• 10:05Neil deGrasse Tyson?

  Wait, wait, so how do you know which rock to get? Or any rock.

• 10:08Speaker 02

  Oh, well, we had to, we had to talk to a lot of geologists. And, you know, this was the first a paper with a few theorists, we're in 2018. And next thing you know.

• 10:18Neil deGrasse Tyson?

  This was, so 2018, that was only a proposal?

• 10:20Speaker 02

  It was, yeah, we wrote a bunch of theory papers. Not every day does this stuff turn into reality. I've done it twice now, you know, the underground detectors. I wrote papers that got that going. And now with paleo detectors, that's actually becoming a major experimental effort. Isn't that cool?

• 10:34Neil deGrasse Tyson?

  And it's a cool type name for a detector, too.

• 10:36Speaker 02

  Yeah.

• 10:37Neil deGrasse Tyson?

  Yeah, so they tell you which rocks would best respond to this.

• 10:39Speaker 02

  Yes, and the answer is olivine.

• 10:41Neil deGrasse Tyson?

  Ooh! Olivine.

• 10:43Speaker 02

  Olivine.

• 10:43Neil deGrasse Tyson?

  I know olivine.

• 10:44Speaker 02

  You do?

• 10:45Neil deGrasse Tyson?

  Yes.

• 10:45Speaker 02

  Oh, okay.

• 10:46Neil deGrasse Tyson?

  There's a class of meteorite called palisites. Where, oh my gosh. You, so where do you get a meteorite from? It's a smashed, whatever it used to be. Right. Right, okay, so if it's a protoplanet, and it partially, as the geologists would say, differentiated, because at some point in its formation, the heavy stuff would fall to the middle, the lighter stuff would float to the top. Right. Okay? If, however, it cools before it fully segregates, then the metallic innards can trap olivine crystals.

• 11:21Speaker 02

  Oh, wow.

• 11:21Neil deGrasse Tyson?

  Within it, as they were slowly bubbling their way up to the top. Mm-hmm. And so, a slice of these meteorites, rear lit, if it's thin enough, the thickness of an olivine crystal, you see the metallic meteorite and these green crystals glowing through. And we have a sample of one in our hole of the universe.

• 11:39Speaker 02

  Oh, very cool!

• 11:41Neil deGrasse Tyson?

  It's called a palisite.

• 11:41Speaker 02

  Oh, I gotta see this.

• 11:43Neil deGrasse Tyson?

  I'll take you down, right after this. Very cool, very cool. So, so, in other words, it's rare because the boundary layer between the dense middle of a protoplanet and the lighter things that float up is very thin. Mm-hmm. And so, when you smash the whole thing, you have a lot of rocky stuff, less metallic stuff, and even less at the boundary layer.

• 12:05Speaker 02

  Ah.

• 12:05Neil deGrasse Tyson?

  So.

• 12:06Speaker 02

  Well, can we borrow your olivine to look for dark matter tracks, please?

• 12:09Neil deGrasse Tyson?

  I, I, you gotta know somebody.

• 12:12Speaker 02

  Okay.

• 12:12Neil deGrasse Tyson?

  You gotta know somebody who works here.

• 12:16Speaker 02

  Thought I did.

• 12:19Neil deGrasse Tyson?

  Yeah, no, we can totally, we can totally explore them. That could be the key. Sitting under our noses. It's been here for 25 years.

• 12:24Speaker 02

  Uh, well, then it's been collecting cosmic ray tracks.

• 12:27Neil deGrasse Tyson?

  Oh, yeah, no, it's, we didn't have it.

• 12:29Speaker 02

  Sad.

• 12:30Chuck Nice?

  Yeah. Do you guys have any, like, deep under the earth here? Like, is there a?

• 12:34Neil deGrasse Tyson?

  But it still has to get through the building.

• 12:36Speaker 02

  Yeah, we want to know about the sub-basements in this building.

• 12:39Neil deGrasse Tyson?

  It still has to get through the building, though. The cosmic rays have to get through the building.

• 12:43Speaker 02

  Yeah, well.

• 12:43Neil deGrasse Tyson?

  That'll block some of them, right?

• 12:45Speaker 02

  Nah.

• 12:48Neil deGrasse Tyson?

  Alright, so, congratulations on this.

• 12:50Speaker 02

  Thank you.

• 12:51Neil deGrasse Tyson?

  This is now a burgeoning, next, next step in this. So why a billion years and not 100 million or 50 million? Does it matter?

• 12:59Speaker 02

  Well, we have to go deep enough to get away from cosmic rays, and that's actually like 5 kilometers.

• 13:05Neil deGrasse Tyson?

  Oh, that's deep.

• 13:06Speaker 02

  It's deep. And then the other idea is if we get rocks from different ages, we are also can study neutrinos, because neutrinos will also leave tracks. The tracks will be different, okay, so you can tell the difference. But then you can figure out how many supernova went off in the galaxy, if you look in the past, a different amount of time. Isn't that cool?

• 13:27Chuck Nice?

  Wow. And that is because the supernova, that's where the neutrinos come from.

• 13:31Neil deGrasse Tyson?

  Copious.

• 13:32Speaker 02

  Oh, I forgot to say that. Yeah, neutrinos give off a lot of supernova. No.

• 13:38Speaker 02

  No, no, no, supernova give off a lot of neutrinos, and so you, which supernova, which are dying, exploding stars. And you can look for the neutrinos from the supernova.

• 13:47Chuck Nice?

  Right. Cool, man.

• 13:49Neil deGrasse Tyson?

  And neutrinos are, once again, your weekly interacting.

• 13:52Speaker 02

  Yeah, they are also weekly interacting particles, yeah.

• 13:54Chuck Nice?

  Yeah, most unfortunate.

• 13:56Speaker 02

  Now, the other thing you can do with.

• 13:58Neil deGrasse Tyson?

  Weekly interacting particles, yeah.

• 14:00Speaker 02

  Uh, well, we know who named them that.

• 14:02Neil deGrasse Tyson?

  Who named them? I forgot.

• 14:04Speaker 02

  Uh, Mike Turner?

• 14:05Neil deGrasse Tyson?

  Is that right? Mike Turner.

• 14:07Chuck Nice?

  That would have made sense if you said Ike Turner.

• 14:11Speaker 02

  Whoa. The word eponymous comes to mind.

• 14:28Speaker 03

  I'm Nicholas Costella and I'm a proud supporter of StarTalk on Patreon. This is StarTalk with Neil deGrasse Tyson.

• 14:43Neil deGrasse Tyson?

  So I've got one more question before we go to Q and A. Some of the results of the James Webb Space Telescope and other sources suggest that we cannot reconcile the age we have derived for the universe by these different methods. One of them is from the CMB, Cosmic Microwave Background, others is from galaxies at other times. And it has been suggested that you can reconcile them if dark energy changes over time.

• 15:15Speaker 02

  The biggest evidence for dark energy changing over time comes from a different experiment, the DESI experiment.

• 15:23Neil deGrasse Tyson?

  Okay.

• 15:24Speaker 02

  What they're looking at...

• 15:25Neil deGrasse Tyson?

  Lucy and DESI? No.

• 15:28Chuck Nice?

  Dark matter, you got some explaining to do!

• 15:31Speaker 02

  Oh, that's good, that's good.

• 15:33Neil deGrasse Tyson?

  But DESI, so, other than Lucy and DESI, what does DESI stand for astrophysically?

• 15:38Speaker 02

  The Dark Energy Spectroscopic Instrument.

• 15:41Neil deGrasse Tyson?

  Okay, alright, that's clean and simple. And what does that tell us?

• 15:47Speaker 02

  What they're looking at is, based on some physics from the early universe, and there were waves which froze out at the same time the Cosmic Microwave Background was produced, that's 400,000 years after the Big Bang, which is like, I don't know, a thousandth of a percent of the age of the universe today. And what those waves did was leave an imprint that throughout the rest of time, galaxies form in these spheres left over from those waves. And so as time goes on, you look at how big are those spheres, and that tells you about the expansion of the universe.

• 16:23Neil deGrasse Tyson?

  Yes.

• 16:24Speaker 02

  And what they're saying is...

• 16:25Neil deGrasse Tyson?

  Because the spheres would grow with the universe.

• 16:27Speaker 02

  Yeah.

• 16:27Neil deGrasse Tyson?

  Yes.

• 16:27Speaker 02

  Yeah, and so by studying that, you can figure out what the expansion is doing, is it accelerating, what is it doing? And what they claim is that the dark energy, which everybody, the vanilla model, is that it doesn't change in time, but it definitely affects the overall expansion of the universe no matter what, it's causing the acceleration, so we think. And what they're claiming is that the acceleration is slowing down.

• 16:53Neil deGrasse Tyson?

  Oh.

• 16:53Speaker 02

  So it's a decrease in the dark energy contribution to the universe. So now can I put it in a plug for my own work?

• 17:01Neil deGrasse Tyson?

  Please.

• 17:02Speaker 02

  We look, so my collaborator Yunhong and I, so we looked at the same data and we looked at it differently with a simpler way of interpreting the data and we do not find that Evans to be very strong, actually. So I don't think it's happening. But big picture, there's a big debate. Is it real? Is the dark energy changing with time or not? Is it time varying or not? And different people have different opinions.

• 17:24Neil deGrasse Tyson?

  If you found a simpler way to look at it.

• 17:26Speaker 02

  Yeah.

• 17:27Neil deGrasse Tyson?

  Where the effect goes away.

• 17:28Speaker 02

  Yep.

• 17:29Neil deGrasse Tyson?

  And we were betting on the likelihood of one truth or another, I'm betting with a simpler explanation.

• 17:35Speaker 02

  Thank you.

• 17:35Chuck Nice?

  Mm-hmm.

• 17:36Speaker 02

  Well, me too, obviously.

• 17:37Neil deGrasse Tyson?

  That taps Occam's razor.

• 17:40Speaker 02

  Well, from the data, we're directly extracting the dark energy density, the amount of dark energy, instead of going through a...

• 17:49Neil deGrasse Tyson?

  A secondary.

• 17:50Speaker 02

  A secondary thing which is called the dark energy equation of state. So we're doing it more directly, so that's why I like what we're doing better.

• 17:57Neil deGrasse Tyson?

  So you know about Occam's razor?

• 17:59Chuck Nice?

  Uh, if, let me just think. Removing all other considerations, the simplest answer is the most likely.

• 18:06Neil deGrasse Tyson?

  That's a modern interpretation. What he actually said was...

• 18:09Chuck Nice?

  Go ahead.

• 18:10Neil deGrasse Tyson?

  Multiplicity ought not be posited without necessity.

• 18:14Chuck Nice?

  Oh, wow!

• 18:15Speaker 02

  Wow!

• 18:15Chuck Nice?

  Damn!

• 18:18Neil deGrasse Tyson?

  So Occam, named for William of Occam, he goes way back.

• 18:21Chuck Nice?

  Okay.

• 18:22Neil deGrasse Tyson?

  Yeah, like 700 years.

• 18:24Chuck Nice?

  Wow.

• 18:25Neil deGrasse Tyson?

  So he had some insights into nature that persist to this day. William of Occam.

• 18:30Chuck Nice?

  Sure enough. He knows how to turn a phrase, that's for sure.

• 18:34Neil deGrasse Tyson?

  So I'm betting on Katie on this one, definitely.

• 18:37Chuck Nice?

  Very cool.

• 18:38Neil deGrasse Tyson?

  So, but let me exit this before we get to the questions with a related question.

• 18:43Speaker 02

  Okay.

• 18:44Neil deGrasse Tyson?

  You said the vanilla version of dark energy is that it does not change over time.

• 18:47Speaker 02

  Yeah.

• 18:48Neil deGrasse Tyson?

  That's how it appears in Einstein's general relativity.

• 18:51Speaker 02

  Yeah.

• 18:51Neil deGrasse Tyson?

  It is a constant.

• 18:53Speaker 02

  Yeah. A cosmological constant.

• 18:55Neil deGrasse Tyson?

  Right. If you want to start making that not constant, then it's no longer Einstein's general theory of relativity. It's some modification to it.

• 19:04Speaker 02

  No, it doesn't...

• 19:07Neil deGrasse Tyson?

  How does he accommodate, how can his formulation of general relativity accommodate...

• 19:15Neil deGrasse Tyson?

  A cosmological constant that's not constant.

• 19:17Speaker 02

  I just want to say about dark energy, it is a complete mystery to all of us. We have no idea what's going on, to be honest, okay? We could call it gobbledegook.

• 19:27Neil deGrasse Tyson?

  I've already named it. Dark matter, dark energy, or Fred and Wilma.

• 19:30Speaker 02

  Okay.

• 19:31Neil deGrasse Tyson?

  Because it doesn't have any bias at all. They're just two words.

• 19:35Speaker 02

  Well, I don't know, because we know dark matter exists. I'm not so sure about dark energy. I want Wilma to exist, but anyway.

• 19:43Speaker 02

  But, so dark energy, there's two, there's two possibilities. One is, as you said, you have to modify Einstein's equations.

• 19:50Neil deGrasse Tyson?

  And that feels wrong to me.

• 19:51Speaker 02

  Well, you know, I actually had an idea for how to do that in 2002, but let's not go there. I want to talk about the other way, which is, we stick with Einstein's equations.

• 20:00Neil deGrasse Tyson?

  Wait, in 2002, you had a way to modify Einstein's general theory of relativity?

• 20:04Speaker 02

  Well, more specifically, the evolution equation for the universe.

• 20:08Neil deGrasse Tyson?

  Yeah.

• 20:09Speaker 02

  The Friedman equation for the universe. What I, what I, we had been working in extra dimensions. If you have string theory.

• 20:16Neil deGrasse Tyson?

  As one would do.

• 20:18Speaker 02

  Yeah, as one would do, because.

• 20:20Neil deGrasse Tyson?

  As one does.

• 20:21Speaker 02

  Yeah, as one does. So in string theory, you have to have 10 spatial dimensions, instead of the XYZ.

• 20:29Neil deGrasse Tyson?

  T, yeah.

• 20:29Speaker 02

  The normal ones that we, that we usually work with. And if you do that, it's possible that, well, our universe is a three-dimensional surface in there. And there could be another one. And the stuff in between, which we call the bulk, is pulling on our surface and causing the equations to change.

• 20:46Neil deGrasse Tyson?

  Oh. Interesting.

• 20:48Speaker 02

  So we posited.

• 20:49Neil deGrasse Tyson?

  Okay, so, so the equations would be sound within the universe, left to its own devices, but influenced outside of it, you gotta get, you gotta give it some slack.

• 20:59Speaker 02

  Yeah, you do. You gotta add these other terms into the equations, which describe the evolution of our three-dimensional universe.

• 21:06Neil deGrasse Tyson?

  She just called our universe a slice.

• 21:08Speaker 02

  I did, yeah.

• 21:10Chuck Nice?

  I believe that.

• 21:10Speaker 02

  It's kind of an interesting slice. I like it.

• 21:12Chuck Nice?

  Yeah.

• 21:13Neil deGrasse Tyson?

  It's a dimensional slice.

• 21:15Speaker 02

  Yeah.

• 21:16Neil deGrasse Tyson?

  That's a dig if I ever heard one.

• 21:17Chuck Nice?

  I don't know. Like during my ayahuasca trip, I met some beings that told me that there were dimensions alongside of our dimension, like more than we could ever know. Dimension, dimension, dimension, and that there were dimensions above and dimensions below. I don't want, anyway, I don't even know why I said this. Let's, but yeah.

• 21:38Speaker 02

  But you know what they're called in, in physics? They're called brains. B R A N E.

• 21:43Chuck Nice?

  Okay.

• 21:44Neil deGrasse Tyson?

  Which is short for membrane.

• 21:45Chuck Nice?

  Membrane, yeah.

• 21:46Speaker 02

  It's short for membrane.

• 21:47Chuck Nice?

  Yeah, just like, yeah.

• 21:47Speaker 02

  Yeah, yeah.

• 21:49Chuck Nice?

  Uh, like thin little dividers.

• 21:51Speaker 02

  So the question you're asking, do some other of these brains contain B R A I Ns?

• 21:56Chuck Nice?

  Mm-hmm.

• 21:57Neil deGrasse Tyson?

  Ooh.

• 21:58Speaker 02

  And we don't know.

• 21:59Neil deGrasse Tyson?

  Because we know ours does.

• 22:00Chuck Nice?

  Right. I mean.

• 22:01Speaker 02

  I think so.

• 22:03Chuck Nice?

  I was gonna say, if you wanna call it that. We use the term loosely in arguments.

• 22:10Speaker 02

  So on the, can I tell you what I called this theory?

• 22:13Neil deGrasse Tyson?

  What?

• 22:14Speaker 02

  I called it Cardassian cosmology. And the reason is that Lisa Randall was going on about the warp factor, which I thought.

• 22:22Neil deGrasse Tyson?

  It's another physicist up at Harvard.

• 22:24Speaker 02

  Oh yeah, she's great. And so she was talking about the warp factor in her theory and I thought they came from Star Trek, but actually it's just a relativity term that I had heard called something else. And so I thought, well, I'm gonna go to Star Trek, so I went for the Cardassians. So I called it Cardassian expansion because everything would be made of ordinary matter, ordinary radiation, ordinary stuff. No weird dark energy, but the equations would be different. And so like the Cardassians, they are, they're weird looking, but they're made of the same. But they're, but they're two bipeds like we are and their goal is accelerated expansion of their evil empire.

• 23:00Chuck Nice?

  Correct. That's right. They're quite draconian and their whole purpose is to take over everything. Yeah.

• 23:06Speaker 02

  Well, Cardassian.

• 23:07Chuck Nice?

  Yeah, they're the Cardassians. Yeah.

• 23:11Chuck Nice?

  Yeah.

• 23:11Neil deGrasse Tyson?

  Well, all right, so you got questions?

• 23:12Chuck Nice?

  We got, we got, let's get to it. Let's jump right in. These are directly for, uh...

• 23:16Neil deGrasse Tyson?

  And you haven't seen these questions?

• 23:18Speaker 02

  Uh, no, that's not fair.

• 23:19Neil deGrasse Tyson?

  Why? What do you know?

• 23:21Speaker 02

  Well, I don't know.

• 23:21Neil deGrasse Tyson?

  That's the whole thing here.

• 23:22Speaker 02

  All right, all right.

• 23:23Chuck Nice?

  Well, this first question is from Anthropoc cosmic Dylan, who basically says, hey, yeah. He says, "How do dark stars work? What would they be like to visit? And how do they impact extrasolar systems and potentially astrobiology?" So he's just, he wants you to just answer everything. Answer it all, Captain.

• 23:42Neil deGrasse Tyson?

  Let me pre-pen that.

• 23:43Chuck Nice?

  Go ahead.

• 23:44Neil deGrasse Tyson?

  In, was it the 1800s or late 1700s? There was a calculation done by a physicist who said to himself, "The gravity on a star is whatever it is, but if the star shrinks, the surface gravity goes up. There'll be a point where the surface gravity prevents life from escaping, and the star will disappear from the universe."

• 24:05Speaker 02

  In other words, what we call now a black hole.

• 24:07Neil deGrasse Tyson?

  Exactly. So it was like the first attempt at thinking about what we now would call a black hole. But so, that technically would be a dark star.

• 24:15Chuck Nice?

  Like a dark star.

• 24:16Neil deGrasse Tyson?

  I don't think that's what this question is about. I think they're asking, if matter can make planets, can dark matter make planets?

• 24:23Speaker 02

  No, I mean, I think he's asking about my work on dark stars.

• 24:27Neil deGrasse Tyson?

  Oh!

• 24:27Speaker 02

  And dark stars are not made of dark matter. They're, the first stars that form, and they would be made of ordinary stuff. Ordinary hydrogen, ordinary helium, almost entirely. But they're powered by the, by the dark matter that's inside them. But doesn't, so it's ordinary matter powered by dark matter.

• 24:44Neil deGrasse Tyson?

  This is one of your early papers.

• 24:45Speaker 02

  It's, instead of by, there's no fusion. It's dark matter power.

• 24:49Chuck Nice?

  Wow!

• 24:49Speaker 02

  Yeah.

• 24:50Neil deGrasse Tyson?

  That's some crazy innovative stuff.

• 24:52Speaker 02

  And these things, if, if they exist, these things, I'm so excited because we have candidates for them in the James Webb Space Telescope. I'm so excited. They would start out at about the same mass as the sun, but then they would grow, grow, grow, until they become a million times as massive as the sun and a billion times as bright.

• 25:09Neil deGrasse Tyson?

  They grow because they're absorbing dark matter.

• 25:11Speaker 02

  No, because they're absorbing ordinary matter. Normal stars can't keep growing because their surfaces are hot. You know, they have fusion. Fusion's hot.

• 25:19Neil deGrasse Tyson?

  Right.

• 25:19Speaker 02

  And then so they blow stuff off. But dark stars are cool. Oh, in radius, they're 10 times the distance between the Earth and the Sun.

• 25:27Neil deGrasse Tyson?

  So they're huge?

• 25:28Speaker 02

  They're huge and they're cool, which means they can keep accreting matter. Grow, grow, grow, and they get really, really big.

• 25:33Neil deGrasse Tyson?

  So there's no pressure on the outer surface to prevent new matter from accreting to it?

• 25:37Speaker 02

  Yeah, exactly. Exactly right. Yeah, yeah, yeah. So they can get really big. And we have candidates in the James Webb Space Telescope for some of those really early objects that are super bright and they don't know how to explain them. Well, we'll take them.

• 25:48Neil deGrasse Tyson?

  You'll take them?

• 25:49Speaker 02

  We'll take them.

• 25:49Chuck Nice?

  Whoa.

• 25:51Speaker 02

  Yeah, I'm excited.

• 25:52Neil deGrasse Tyson?

  When you win your Nobel Prize, will you come back on the show?

• 25:56Chuck Nice?

  Was that a kiss-off?

• 25:58Speaker 02

  No!

• 25:59Chuck Nice?

  Oh, okay.

• 26:00Neil deGrasse Tyson?

  Did you read the body language? That was a very, very...

• 26:03Speaker 02

  Oh, no, I'm sorry.

• 26:05Neil deGrasse Tyson?

  No, he's still learning social cues.

• 26:07Speaker 02

  Oh, I meant the opposite.

• 26:09Chuck Nice?

  Oh, okay, cool, yeah. I'll tell you this much. Once you... He's right. That is Nobel stuff right there, man. That's fantastic.

• 26:17Neil deGrasse Tyson?

  So the...

• 26:18Speaker 02

  You know, the thing about Astro... About my field is that you can have a great idea. And, you know, let me back up. Usually, when you have a great idea, you kill it in 10 minutes because it violates some observation. Occasionally, it not only survives those first 10 minutes, but then people start telling you, "Did you know you solved this problem? Did you know you solved that problem?" And that's what's going on here.

• 26:39Neil deGrasse Tyson?

  Yeah, that's...

• 26:39Speaker 02

  We keep solving problems. So dark stars could explain a lot of things. They could explain, once they die, the supermassive black holes that you see in the early universe. They could explain the blue monsters, and they could explain the little red dots. And I figured you'd like those terms.

• 26:53Neil deGrasse Tyson?

  Wow.

• 26:54Speaker 02

  Yeah.

• 26:55Neil deGrasse Tyson?

  These are all... They're very bluntly descriptive of stuff we see in the early universe. Because there's nothing nearby that we have a counterpart to. There's a red dot. It's a red dot.

• 27:05Chuck Nice?

  Okay, so we call it a red dot. Now, what about the blue monster? Where'd you get that reference?

• 27:10Speaker 02

  Blue monsters are really, really, really bright objects way early in the history of the universe.

• 27:16Neil deGrasse Tyson?

  Yeah, it should be like the formation of galaxies. I mean, we know they're blue. They don't look blue. They look very infrared, because that blue has been red-shifted to the sweet spot of the James Webb Telescope. Yeah, yeah.

• 27:26Chuck Nice?

  But, yeah, that's very cool. All right. Okay, well, hey, what a great question, anthropoc...

• 27:32Neil deGrasse Tyson?

  So she said she's coming back after her Nobel Prize?

• 27:34Chuck Nice?

  Absolutely. Now, here's the next question. Can I wear your Nobel Prize when you come back?

• 27:40Neil deGrasse Tyson?

  So here's the best line related to that. It was from Hoop Dreams. Do you know the line?

• 27:44Chuck Nice?

  I don't know. I don't know.

• 27:45Neil deGrasse Tyson?

  You know this line? You know the movie?

• 27:46Chuck Nice?

  I don't think I know Hoop Dreams.

• 27:48Neil deGrasse Tyson?

  Hoop Dreams. Dude, it's a documentary.

• 27:51Speaker 02

  Oh, you don't know Hoop Dreams?

• 27:52Chuck Nice?

  I do not know Hoop Dreams, but go ahead.

• 27:54Neil deGrasse Tyson?

  Yeah, it's a documentary of following high school students, some who have ambitions to play in the NBA.

• 28:00Speaker 02

  Oh, okay.

• 28:01Neil deGrasse Tyson?

  Okay, and the social dynamic that surrounds it. It's a documentary. But here's the line. "When you're rich and famous, will you remember us?"

• 28:11Speaker 02

  Mm-hmm.

• 28:12Neil deGrasse Tyson?

  As one of them goes off. And he says, "If I'm not rich and famous, will you remember me?"

• 28:19Speaker 02

  Oh, that's good.

• 28:21Neil deGrasse Tyson?

  That's good.

• 28:22Speaker 02

  That's really good.

• 28:22Chuck Nice?

  I'm gonna tell you the answer to both those questions is...

• 28:25Speaker 02

  Ouch!

• 28:25Chuck Nice?

  No. The answer?

• 28:28Speaker 02

  Yeah.

• 28:29Chuck Nice?

  No. And to both. Alright, let's move on.

• 28:32Neil deGrasse Tyson?

  Let's hit take.

• 28:32Chuck Nice?

  This is Nate. And Nate says, "Hello, Dr. Tyson, Dr. Freeze, and Lord Nice. Uh, this is Nate from southern Idaho. If dark energy has gravitational effects on everything just like regular matter does, why does it not coalesce and push away from itself? This seems counterintuitive considering the fundamental nature of gravity is to pull things together by bending spacetime. Does dark energy abide by its own rules? Where it can cause gravity, but it isn't affected by it? This would imply that it is not influenced by the curvature of spacetime in which it causes." Ooh. This guy did some thinking here. Freaking Nate, bro!

• 29:13Neil deGrasse Tyson?

  Whoa!

• 29:14Chuck Nice?

  Dude!

• 29:14Neil deGrasse Tyson?

  Whoa. So let's start from scratch.

• 29:17Chuck Nice?

  Yeah.

• 29:17Neil deGrasse Tyson?

  We're calling it dark energy because it's a placeholder term. We don't know what the hell it is.

• 29:22Speaker 02

  Right.

• 29:23Neil deGrasse Tyson?

  But if it's energy at all, then it has a mass equivalent and it should have gravity. So, does dark energy have gravity?

• 29:31Speaker 02

  The definition of matter is that it feels gravitational attraction.

• 29:35Chuck Nice?

  Mm-hmm.

• 29:35Speaker 02

  So that's true for ordinary matter. That would be you. And me, and you.

• 29:40Chuck Nice?

  I was gonna say, thanks.

• 29:41Neil deGrasse Tyson?

  He's not ordinary matter.

• 29:42Speaker 02

  He's not ordinary matter, and it would be dark matter, so all of that stuff clumps together. It's attracted together.

• 29:48Neil deGrasse Tyson?

  And energy contains a matter equivalent.

• 29:51Speaker 02

  No, you know, for ordinary matter and energy, that is true, but for dark energy, it is completely different from matter. It is something that's causing a repulsive behavior. It's pushing things apart from one another.

• 30:02Neil deGrasse Tyson?

  That's why we should call it just Wilma, something that doesn't have the word "energy" in it.

• 30:06Speaker 02

  Yeah, yeah, so it's confusing, because matter and energy in the ordinary world are related, but dark matter and dark energy are probably not.

• 30:14Neil deGrasse Tyson?

  Okay, so the foundation of this question is not valid, because it's assuming that it's participating in the curvature of spacetime, and if it's helping to make it, why isn't it responding to it? Why is it spreading things out rather than pulling things in?

• 30:28Speaker 02

  Well, I mean, it does fit into Einstein's theory of general relativity. It's just that if you have this vacuum energy, it causes repulsion rather than attraction. It causes acceleration. So it's a completely different type of behavior.

• 30:43Neil deGrasse Tyson?

  We calculated with that, and you're off by like...

• 30:47Speaker 02

  Oh, 10 to the 120?

• 30:48Neil deGrasse Tyson?

  Power.

• 30:49Speaker 02

  Yeah, in the exponent, yeah, that's true. Well, I'm not saying we understand it. I'm not saying we can calculate it.

• 30:55Chuck Nice?

  That's funny.

• 30:56Neil deGrasse Tyson?

  Isn't that the biggest mismatch between a theory and a calculation ever?

• 31:00Speaker 02

  Yeah, it's really, it's just unbelievable. Vacuum energy, what does that mean? Well, what it means, by the way, there's vacuum energy in this room that you could measure. There are particle, and it doesn't mean there's nothing. It means particle-antiparticle pairs that pop into existence. They last infinitesimal amount of time, and then they disappear again. But that serves as an energy, and it has been measured. There's been two plates that are attracted.

• 31:25Neil deGrasse Tyson?

  This is not the Casimir effect.

• 31:27Speaker 02

  Yes, the Casimir effect.

• 31:28Chuck Nice?

  It is!

• 31:28Speaker 02

  It's the Casimir effect, absolutely.

• 31:30Neil deGrasse Tyson?

  This is where two, in a vacuum, two parallel plates, you bring them very, very close together, and there's a point where there's...

• 31:37Chuck Nice?

  They just attract, right?

• 31:38Speaker 02

  Yep, yep, yep. It's the same vacuum, the same, exactly the same thing.

• 31:43Chuck Nice?

  That's pretty wild.

• 31:44Speaker 02

  But if you do the mathematical calculation, your answer is too big by 10 to the 120 in the exponent. So if you add up all the contributions from all those particles, it gets the wrong answer, and that's considered one of the biggest...

• 32:00Neil deGrasse Tyson?

  It's the very wrong answer.

• 32:02Speaker 02

  One of the deepest unsolved problems in all of physics.

• 32:04Neil deGrasse Tyson?

  All right.

• 32:05Speaker 02

  And it gets worse. People thought, well, it gets worse. People thought, yeah, look, somehow, somebody will figure out how to bring that number down to zero and we'll be, we'll be good. No. All of a sudden, it looks like there's a small amount left over. Well, it's, it's, it's not that small for, for our universe. But compared to 10 to the 120, there's dark energy, which means there is some vacuum left over that's driving acceleration. It's neither, the big answer nor is it zero. It's somewhere in between. What the heck?

• 32:35Neil deGrasse Tyson?

  All right.

• 32:36Speaker 02

  I feel like I'm talking too much.

• 32:37Neil deGrasse Tyson?

  No!

• 32:38Chuck Nice?

  We love it.

• 32:38Neil deGrasse Tyson?

  That's the whole point of why you're on here.

• 32:40Chuck Nice?

  Exactly, yeah. Ooh, wow.

• 32:42Neil deGrasse Tyson?

  If you're talking a lot, it means I have less to add.

• 32:46Speaker 02

  Oh.

• 32:46Neil deGrasse Tyson?

  So it is, your words and ideas and brilliance are gracing the stage.

• 32:51Chuck Nice?

  You're a real expert.

• 32:56Speaker 02

  On some, on something.

• 33:18Chuck Nice?

  All right, let's go to Sumit Sharma, who says, hello, Dr. Tyson, Dr. Freeze, Lord Nice. This is Sumit from Delhi. I am a new member here.

• 33:27Neil deGrasse Tyson?

  Nice, okay.

• 33:27Chuck Nice?

  Patreon member.

• 33:28Neil deGrasse Tyson?

  Welcome.

• 33:29Chuck Nice?

  Well, go ahead, you do it.

• 33:30Neil deGrasse Tyson?

  Welcome to the universe.

• 33:32Chuck Nice?

  There you go. You got an official welcome there, Sumit.

• 33:34Neil deGrasse Tyson?

  In my cosmos voice.

• 33:35Chuck Nice?

  That's right. I want to know where does the scientific consensus stand on WIMP as an alternative hypothesis to dark matter today? I don't understand that. But anyway, I don't understand.

• 33:46Neil deGrasse Tyson?

  WIMP is the abbreviation.

• 33:47Chuck Nice?

  I know, weakly interacting mass and particles.

• 33:50Speaker 02

  It's a candidate for the dark matter.

• 33:52Chuck Nice?

  Oh, okay, but it can't be a substitute, but, but anyway.

• 33:55Speaker 02

  No, it is, it is a type of dark matter.

• 33:57Chuck Nice?

  It's a type.

• 33:57Neil deGrasse Tyson?

  That's the answer.

• 33:58Chuck Nice?

  That's what that's the answer.

• 33:59Speaker 02

  It's a type of dark matter, yeah.

• 34:00Chuck Nice?

  Also, since dark matter is invisible and hard to detect directly, what indirectly, what indirect properties or effects of dark matter are scientists currently studying? And by what methods? I love that. Like, yeah, so what's the deal? It doesn't interact with anything. How are you guys measuring it? How are you figuring out anything about it?

• 34:17Speaker 02

  You know, the thing about dark matter is we've got about 20 different candidate particles that it could be.

• 34:23Chuck Nice?

  Okay.

• 34:24Speaker 02

  Some of them are well motivated and some are, hmm, not as much. So my favorite three would be wimps, axions, and primordial black holes.

• 34:34Chuck Nice?

  Okay.

• 34:35Speaker 02

  So wimps, the weakly interacting massive particles, they do have an interaction, which is the weak interaction, the weak force.

• 34:42Chuck Nice?

  Okay.

• 34:43Speaker 02

  And axions, what they do is that they can actually, in the presence of a magnetic field, they turn into photons, into light. So they can switch axion photon, axion photon, and then you can detect that light. Now, primordial black holes, they would be black holes that formed very early in the history of the universe.

• 35:02Chuck Nice?

  They don't evaporate right away?

• 35:03Speaker 02

  Some of them do, so they have to be bigger than, the smallest ones do. But there would be some left over, and they form wherever there's some region of the universe that has more, an excess of stuff in it, an over-density, that collapses into a black hole. And that, for example, could be at some phase transition in the early universe, this is like when water boils, it switches from liquid to gas, and that's where you get these fluctuations, and boom, you might make primordial black holes. And the reason people care nowadays is because gravitational wave detectors are seeing merging black holes, and some of those could be primordial black holes. So people got all excited about primordial black holes again.

• 35:48Chuck Nice?

  Okay.

• 35:49Speaker 02

  As far as wimps go, there's, oh, you can either, to find them, you can make it, shake it, or break it.

• 35:55Chuck Nice?

  Right on. Go ahead, do your thing. Shake what your mama gave you.

• 36:03Speaker 02

  Well, we're not doing the, let's talk about the make first.

• 36:05Chuck Nice?

  Make it, shake it, or break it.

• 36:06Speaker 02

  Make it, shake it, or break it. So the make it is, in particle accelerators, such as the Large Hadon Collider at CERN, you shoot really rapidly moving protons into each other. Moving nearly at the speed of light and out come potentially dark matter particles like wimps and you look for them that way. No discovery yet, okay?

• 36:27Neil deGrasse Tyson?

  So it would have a signature that you couldn't otherwise identify and you would describe it to dark matter.

• 36:32Speaker 02

  Yeah.

• 36:32Neil deGrasse Tyson?

  Because you otherwise know what you're supposed to get out of it, right?

• 36:36Speaker 02

  Yeah, if it's ordinary stuff, then you know what to expect.

• 36:38Neil deGrasse Tyson?

  Right.

• 36:39Speaker 02

  But if you're making some kind of new particles, then they might escape from the detector without, and you'd see that as missing energy.

• 36:48Chuck Nice?

  Okay.

• 36:49Speaker 02

  You'd add up all the energy of all the particles coming out and get there to be some missing energy.

• 36:53Chuck Nice?

  Right, right on. Okay, there you go.

• 36:55Speaker 02

  And you want to hear about the shake it?

• 36:57Chuck Nice?

  Yes.

• 36:57Neil deGrasse Tyson?

  Yeah, yeah, yeah.

• 36:58Chuck Nice?

  And break, I mean, yeah.

• 37:00Neil deGrasse Tyson?

  Now, we've got to make it. You can't, you can't leave without shaking it and breaking it.

• 37:04Speaker 02

  Okay, so the shake it is you've got your detector deep underground and a particle comes along, hits your detector, gives it a little bit of energy and you look for that energy deposit. So it's shaking that nucleus.

• 37:22Chuck Nice?

  Like a little vibration.

• 37:24Speaker 02

  Exactly, in some cases. That's exactly what they're looking for in some cases.

• 37:29Chuck Nice?

  Yeah, got you, got you.

• 37:30Speaker 02

  Or some, some light that comes off or whatever. So that's what they're doing.

• 37:33Chuck Nice?

  Okay.

• 37:34Speaker 02

  And then the break it, that's called indirect detection and that's when, well, dark matter particles, these wimps, can be their own antimatter and that means when they hit each other, they annihilate and turn into something else. And what you got to do is measure that something else. So people are looking for neutrinos. You know where they look, where those detectors are? Underneath the ice at the South Pole.

• 37:55Neil deGrasse Tyson?

  That's Ice Cube.

• 37:57Speaker 02

  That's Ice Cube.

• 37:57Neil deGrasse Tyson?

  Ice Cube.

• 37:58Speaker 02

  Yep, two miles down.

• 37:59Chuck Nice?

  Straight Outta Compton. I mean, Straight Outta South Pole.

• 38:02Speaker 02

  Oh, that's good, that's good, that's good, yeah.

• 38:07Neil deGrasse Tyson?

  Because Ice Cube wasn't in Straight Outta Compton.

• 38:08Chuck Nice?

  Yes, he was.

• 38:09Neil deGrasse Tyson?

  The actor, yeah.

• 38:10Speaker 02

  Yeah, yeah, that's good.

• 38:11Neil deGrasse Tyson?

  The rapper.

• 38:11Speaker 02

  We like that, yeah.

• 38:12Chuck Nice?

  All right. Yeah, that was great. What a great question Sue made for your first time asking anything here on StarTalk.

• 38:20Neil deGrasse Tyson?

  From Old Delhi.

• 38:21Chuck Nice?

  From Old Delhi. Make it, shake it, or break it. Just remember that. All right. All right, this is Chris Hampton. He says, uh, dear Lord nice or barren.

• 38:29Speaker 02

  Wait a minute, Christopher Hampton, that was a playwright. It's a playwright.

• 38:33Neil deGrasse Tyson?

  Really?

• 38:34Chuck Nice?

  Yes. I'm not familiar with him.

• 38:36Speaker 02

  Yes.

• 38:36Chuck Nice?

  Oh, very cool.

• 38:37Neil deGrasse Tyson?

  Is it a living playwright?

• 38:38Speaker 02

  I think so.

• 38:39Neil deGrasse Tyson?

  Okay, so it could be him.

• 38:40Chuck Nice?

  Mm-hmm.

• 38:41Neil deGrasse Tyson?

  Okay, treating nice.

• 38:42Chuck Nice?

  There you go. He says, "Dear Lord Nice or Baron." No, actually, you dubbed Paul Mercurio Baron. So, it's just, which by the way, I found out they're kind of the same, the titles. Which, you know, we're gonna have to demote Paul.

• 38:58Chuck Nice?

  I'm joking, I love him. "Could dark energy be caused by a constant inflow of spacetime itself, perhaps through black holes from a parent universe? In other words, we're bringing more in than there is flowing out, like a Brita flatiron system." Okay.

• 39:17Speaker 02

  Oh, wow.

• 39:18Chuck Nice?

  Yeah.

• 39:19Speaker 02

  I'm not sure how to answer that one.

• 39:20Neil deGrasse Tyson?

  Brita flatiron system?

• 39:21Speaker 02

  Yeah, what the heck is that?

• 39:22Chuck Nice?

  I don't know what a Brita flatiron system is. I have a Brita at home, I put water in it. And, uh, yeah, it flows through and then I drink it. But, um...

• 39:30Speaker 02

  I mean, you know what Einstein had to do to get a static universe? He had to have material somehow bubbling into our universe and appearing out of nowhere on a regular basis. So that is not an insane idea, and people have thought about that.

• 39:42Neil deGrasse Tyson?

  He knew, you know what Isaac Newton's solution to that was?

• 39:46Chuck Nice?

  Go ahead.

• 39:46Neil deGrasse Tyson?

  It was, if the universe were just finite, then all the galaxies would collapse to each other.

• 39:53Chuck Nice?

  Okay.

• 39:54Neil deGrasse Tyson?

  Okay? He didn't think of the universe as expanding.

• 39:56Chuck Nice?

  Right.

• 39:57Neil deGrasse Tyson?

  But, he said, "The only way out of this is if the universe is infinite."

• 40:00Chuck Nice?

  Infinite, right.

• 40:01Neil deGrasse Tyson?

  Then you can't favor one point or another.

• 40:04Speaker 02

  Oh, really? Newton said that?

• 40:05Neil deGrasse Tyson?

  Yes.

• 40:05Speaker 02

  Wow.

• 40:06Neil deGrasse Tyson?

  Yes.

• 40:06Speaker 02

  Smart guy. Damn!

• 40:08Neil deGrasse Tyson?

  That's why he's sitting right over there on my desk.

• 40:11Chuck Nice?

  Did he know the universe... Oh, but that's because he didn't know the universe was expanding, right?

• 40:14Neil deGrasse Tyson?

  No, no, no, no.

• 40:15Speaker 02

  No, no, that was 1929 that they figured that out.

• 40:17Chuck Nice?

  Ah, okay.

• 40:18Speaker 02

  Einstein did not like it.

• 40:20Neil deGrasse Tyson?

  Yeah, the expanding universe was too weird for everybody.

• 40:22Chuck Nice?

  For everybody, yeah. What did Einstein say, something about God or playing...

• 40:27Neil deGrasse Tyson?

  He's always talking about God.

• 40:28Speaker 02

  That was quantum mechanics.

• 40:28Chuck Nice?

  That was quantum God playing dice, like the expanding universe, yeah.

• 40:32Speaker 02

  He didn't like the quantum mechanics? He didn't like the expanding universe? Isn't that interesting?

• 40:36Chuck Nice?

  That's wild.

• 40:37Speaker 02

  Which a lot of this is, these are fields of physics that he started.

• 40:41Chuck Nice?

  That he created.

• 40:42Neil deGrasse Tyson?

  Crumbs that fell off his plate.

• 40:44Chuck Nice?

  From the stuff that he was just like...

• 40:46Neil deGrasse Tyson?

  The Nobel Prize is given to crumbs that fell off his plate.

• 40:49Chuck Nice?

  Well, I don't know what the hell this is, but whatever, let's move on, and that's him. Wow, that's amazing.

• 40:54Speaker 02

  I just...

• 40:54Chuck Nice?

  That's, that's pretty wild. All right, but when he says "a constant inflow of spacetime itself..."

• 41:00Speaker 02

  No.

• 41:00Chuck Nice?

  No.

• 41:01Speaker 02

  I don't, that doesn't make any sense to me, so I'm gonna just say no.

• 41:03Neil deGrasse Tyson?

  So, so spacetime can't come from another brain?

• 41:07Chuck Nice?

  Right.

• 41:08Speaker 02

  Spacetime would, to me, would include all of that stuff?

• 41:12Chuck Nice?

  Got you.

• 41:13Speaker 02

  We're all living in, within spacetime.

• 41:15Neil deGrasse Tyson?

  Okay, okay.

• 41:16Speaker 02

  I'm a little uncomfortable with that notion.

• 41:19Chuck Nice?

  Okay. Listen, I'll accept that because we are all living in spacetime. So, you know, that's pretty simple to accept. Greetings, STEM nerds.

• 41:28Neil deGrasse Tyson?

  Yeah!

• 41:29Chuck Nice?

  Mike from Colorado. Yeah, there you go, buddy. Uh, Mike from Colorado here. Since the time of Edwin Hubble, we look at distant galaxies and calculate their speed based on the redshift we measure, which we attribute to the Doppler effect. However, we also know that photons lose energy when traveling out of the gravitational field, which also exhibits as a redshift. Given that dark matter accounts for some 80% of the gravitation in the universe, how do we know how much redshift is due to the Doppler effect? And how much is due to gravitation? Is it possible that the speeds we calculate for distant galaxies are just an upper bound on their actual speeds?

• 42:09Speaker 02

  Well, there are, on the average, galaxies are moving apart from one another. That's the Hubble expansion. That causes light between some distant past and us now to stretch, the wavelength of light stretches.

• 42:27Chuck Nice?

  Right.

• 42:27Speaker 02

  However, there's no question when you go, for example, some of that light, if it goes through a galaxy on the way here, or goes through a cluster of galaxies, that also changes its wavelength. And, in fact, we use that to figure out where a cluster is, or what a cluster is doing. So, it's useful information. And we're very aware that you have both effects going on at the same time. So, if you're inside our galaxy, like in this room, we're not feeling the expansion. We're not feeling it.

• 42:55Neil deGrasse Tyson?

  I'm feeling it.

• 42:57Speaker 02

  Yeah, you're feeling it?

• 43:02Neil deGrasse Tyson?

  So, this reminds me of what they used to call the tired light model.

• 43:05Chuck Nice?

  Okay.

• 43:05Neil deGrasse Tyson?

  The light's just too tired.

• 43:06Chuck Nice?

  Right.

• 43:07Neil deGrasse Tyson?

  Come through.

• 43:07Chuck Nice?

  I've been through a lot, y'all.

• 43:11Chuck Nice?

  I'm telling you, traveling, traveling between these galaxies, y'all don't know, this is oh lord, it's killing me, man, killing me.

• 43:20Neil deGrasse Tyson?

  Tired light, because it would, you know.

• 43:22Chuck Nice?

  I don't even have masks, I feel so damn heavy.

• 43:26Chuck Nice?

  Oh, y'all don't know, y'all don't know.

• 43:29Neil deGrasse Tyson?

  So.

• 43:30Chuck Nice?

  Okay.

• 43:33Neil deGrasse Tyson?

  So tired light would be reddened.

• 43:35Chuck Nice?

  Right.

• 43:36Neil deGrasse Tyson?

  Okay, it would be reddened, however, there's also spectral features of elements within the spectrum. So you could take regular light and it would reden, but if it's the expanding universe,

• 43:51Neil deGrasse Tyson?

  and it's Doppler shifted, the lines would shift.

• 43:54Speaker 02

  Yeah, yeah.

• 43:56Neil deGrasse Tyson?

  They would shift and had nothing to do with red or anything, they would just shift.

• 44:00Chuck Nice?

  Gotcha.

• 44:00Neil deGrasse Tyson?

  And they shift.

• 44:01Speaker 02

  Yeah, they sure do.

• 44:02Neil deGrasse Tyson?

  They sure do.

• 44:03Chuck Nice?

  Gotcha.

• 44:03Neil deGrasse Tyson?

  And so, you can still have tired light, but you can't blame that redness on the expanding universe.

• 44:11Chuck Nice?

  Very cool, that's a good answer.

• 44:13Neil deGrasse Tyson?

  And if we animate StarTalk, you will be the voice of the photon.

• 44:20Chuck Nice?

  I done had a hug, did I?

• 44:22Speaker 02

  Wait, now who's gonna be the wimp?

• 44:28Speaker 02

  Oh, and then of course, before that, there were the machos.

• 44:30Neil deGrasse Tyson?

  The machos.

• 44:30Chuck Nice?

  Oh, that's right.

• 44:31Neil deGrasse Tyson?

  Massive, compact halo objects.

• 44:34Chuck Nice?

  Right.

• 44:34Neil deGrasse Tyson?

  So for a while, we had machos and wimps.

• 44:35Chuck Nice?

  Macho and wimp.

• 44:36Speaker 02

  Yeah, we did.

• 44:37Neil deGrasse Tyson?

  Just so you know, men were naming things.

• 44:39Chuck Nice?

  Yeah, right, yeah.

• 44:40Speaker 02

  And the experiments looking for machos, ogal.

• 44:44Neil deGrasse Tyson?

  Ogal, yeah.

• 44:45Speaker 02

  Eros, ogal, eros, and macho.

• 44:49Neil deGrasse Tyson?

  Yeah.

• 44:50Chuck Nice?

  Okay.

• 44:50Neil deGrasse Tyson?

  Ogal, optical gravitational lens experiment.

• 44:55Chuck Nice?

  Okay.

• 44:56Neil deGrasse Tyson?

  And.

• 44:57Speaker 02

  Eros, E-R-O-S.

• 44:58Neil deGrasse Tyson?

  What did that stand for?

• 44:59Speaker 02

  I don't know, the god, the god of love, like Cupid.

• 45:02Neil deGrasse Tyson?

  Yeah, yeah, yeah, yeah, yeah.

• 45:03Chuck Nice?

  It's the only one I like.

• 45:06Speaker 02

  What's wrong with Venus?

• 45:07Chuck Nice?

  Well, first you ogle, and that causes arrows.

• 45:13Neil deGrasse Tyson?

  We got time for one last question, if you can answer it fast. Okay, go.

• 45:16Speaker 02

  Okay.

• 45:17Chuck Nice?

  Okay, here we go. Uh, this is Brian Whelan.

• 45:19Neil deGrasse Tyson?

  It's a test of you.

• 45:19Chuck Nice?

  Brian Whelan says, "Hello, Dr. Tyson, Freeze, and Lord Nice. Captain Ben from Sag Harbor here, reaching out thirty thousand, thirty-five thousand feet en route home." Oh, he's, he's, he's actually in the cockpit, sending us this, this message.

• 45:35Neil deGrasse Tyson?

  Oh, 'cause he's captain?

• 45:35Chuck Nice?

  He's captain.

• 45:36Speaker 02

  Wow.

• 45:37Neil deGrasse Tyson?

  Wait, shouldn't you be flying the plane?

• 45:38Chuck Nice?

  Well, no, at thirty-five thousand feet, the plane flies itself.

• 45:40Neil deGrasse Tyson?

  Okay, I guess so.

• 45:42Chuck Nice?

  Uh, he goes...

• 45:43Neil deGrasse Tyson?

  Still?

• 45:44Chuck Nice?

  Yeah, still. Yeah, this doesn't inspire competence, okay? That's all we're saying.

• 45:49Neil deGrasse Tyson?

  Okay, okay.

• 45:50Chuck Nice?

  I'd rather you be drinking. All right?

• 45:54Neil deGrasse Tyson?

  Drinking, we're still paying attention.

• 45:56Chuck Nice?

  Exactly. He says, "Listen, I've been wondering, does dark matter coalesce and condense similarly to regular matter? And if not, why not? It doesn't interact electromagnetically, but would gravity do something similar? Sending this message also on my birthday." Happy birthday, Captain Whelan."

• 46:13Neil deGrasse Tyson?

  Captain Whelan.

• 46:13Speaker 02

  Yes.

• 46:14Neil deGrasse Tyson?

  So that has some overlap with the previous question, but let me tune that a little better. All right? If it interacts weakly, that's still an interaction.

• 46:23Speaker 02

  Mm-hmm.

• 46:23Neil deGrasse Tyson?

  So why doesn't it just make weak planets, instead of regular planets?

• 46:28Speaker 02

  Well, I'm gonna answer, I'm gonna say something else first, which is that without dark matter, we wouldn't exist. It had to collapse and clump, and make protogalaxies, before ordinary matter could do it. And then ordinary matter falls into those things.

• 46:42Neil deGrasse Tyson?

  You're telling me that there are protogalactic dark matter galaxies out there?

• 46:46Speaker 02

  There were, in the early universe, and then ordinary matter fell in there. But is it possible there are some purely dark galaxies that don't have any stars in them? Yes, and people are looking for that, for sure. Isn't that cool?

• 47:00Neil deGrasse Tyson?

  Wait, wait, wait. Okay, yes.

• 47:02Speaker 02

  Very cool.

• 47:03Neil deGrasse Tyson?

  Very cool. So it wouldn't so much be dark, because that would imply it absorbed light. But they don't interact with light. They would just be invisible.

• 47:11Speaker 02

  Well, made of dark matter, right. So there's nothing to see.

• 47:14Neil deGrasse Tyson?

  There's nothing to see.

• 47:15Speaker 02

  Well, except...

• 47:16Neil deGrasse Tyson?

  No, no, no. If it doesn't interact with light...

• 47:20Speaker 02

  Right.

• 47:20Neil deGrasse Tyson?

  Then, then light just passes through, rendering them transparent.

• 47:24Speaker 02

  No, because of Einstein's lensing, gravitational lensing.

• 47:27Neil deGrasse Tyson?

  Oh, you see the lensing effects.

• 47:29Speaker 02

  You see distant galaxies, the light from behind the dark galaxies will get bent.

• 47:34Neil deGrasse Tyson?

  Okay, so it gets bent.

• 47:35Speaker 02

  So you see that.

• 47:36Neil deGrasse Tyson?

  But the galaxy itself, or the dark matter thing itself, would be invisible to you, right? You could just walk through it and you wouldn't even know.

• 47:45Speaker 02

  Yes.

• 47:46Neil deGrasse Tyson?

  Ooh.

• 47:47Chuck Nice?

  That's cool.

• 47:47Neil deGrasse Tyson?

  There's some serious science fiction material there.

• 47:50Chuck Nice?

  There is.

• 47:51Speaker 02

  Yes.

• 47:52Chuck Nice?

  Interesting. I love it.

• 47:53Neil deGrasse Tyson?

  Chuck, have you met my dark matter friend?

• 47:57Chuck Nice?

  Oh, well, he looks like a black rabbit.

• 47:59Neil deGrasse Tyson?

  What's a black rabbit?

• 48:00Speaker 02

  Harvey the rabbit?

• 48:01Chuck Nice?

  There you go. Harvey was a white rabbit. He's dark matter. He's a black rabbit.

• 48:05Neil deGrasse Tyson?

  Oh, sorry, okay.

• 48:06Chuck Nice?

  I just went too far too fast. I went too far too fast. This is what happens.

• 48:10Neil deGrasse Tyson?

  Well, Katie, thanks for joining us again.

• 48:12Speaker 02

  Thank you. That was fun. It was really fun.

• 48:14Chuck Nice?

  Another great show.

• 48:15Neil deGrasse Tyson?

  Now, if I remember correctly, you have kin in the city, so you...

• 48:18Speaker 02

  My boy, my son.

• 48:20Neil deGrasse Tyson?

  Your son, so you get through town every now and then.

• 48:22Speaker 02

  I do, all the time.

• 48:23Neil deGrasse Tyson?

  We will nab you 100% of the time.

• 48:25Speaker 02

  I have a rent-stabilized apartment. I just signed it to your lease, so I'll be here.

• 48:30Neil deGrasse Tyson?

  Whoa.

• 48:31Chuck Nice?

  All right.

• 48:32Neil deGrasse Tyson?

  Whoa.

• 48:32Speaker 02

  Yeah.

• 48:32Neil deGrasse Tyson?

  Okay, we will, every time you come back here, you're coming right here, you're gonna sit right there.

• 48:37Speaker 02

  And actually, those queries were fun.

• 48:39Neil deGrasse Tyson?

  See, even though you hadn't heard or seen them before.

• 48:41Speaker 02

  That's right.

• 48:41Neil deGrasse Tyson?

  Yeah, okay.

• 48:42Speaker 02

  They were good.

• 48:42Neil deGrasse Tyson?

  All right, good.

• 48:43Chuck Nice?

  Well, the audience knows you now, so believe me, they got a lot more questions for you.

• 48:46Neil deGrasse Tyson?

  You got it.

• 48:47Speaker 02

  Sounds great. And you guys are so much fun.

• 48:50Neil deGrasse Tyson?

  Oh, well, thank you.

• 48:51Chuck Nice?

  Yeah.

• 48:58Neil deGrasse Tyson?

  Well, there, give me a fist bump on that. All right, all right. Yeah, we'll take it.

• 49:03Neil deGrasse Tyson?

  This has been another StarTalk Cosmic Queries, a cosmology edition. I'm loving these. Nice. And how many cosmologists we got? We got Jana, we got Brian Green.

• 49:13Speaker 02

  Oh, Jana Levin, just so you know, was my first graduate student.

• 49:16Neil deGrasse Tyson?

  Whoa!

• 49:18Speaker 02

  Yeah.

• 49:18Neil deGrasse Tyson?

  Very cool. Whoa! Okay, we have the two Bryans. Yep. We have Brian Cox and Brian Green. That's... what more do you need? Yeah. We got... We got Chuck Lutu. Oh, Chuck Lutu, but he's not a deep cosmologist. He's an extragalactic guy. Extragalactic guy. Yeah, yeah, yeah. Yeah. All right. We got enough. Yes, enough, definitely. Anybody else out there, come on.

• 49:40Neil deGrasse Tyson?

  All right, we gotta call it quits there. Chuck, always good to have you. Always a pleasure. Katie, you're gonna be a regular from now on.

• 49:45Speaker 02

  That sounds great.

• 49:46Neil deGrasse Tyson?

  All right.

• 49:46Speaker 02

  Love it.

• 49:47Neil deGrasse Tyson?

  You got it. Neil deGrasse Tyson, you're a personal astrophysicist. As always, bidding you to keep looking up.