Introduction of guests Matt O'Dowd and Chuck Nice. First question from a listener about what's at the threshold of a quasar and if the big rip can rip into black holes.

Introduction and first question

Discussion of how gravitational lensing is used in observations. Questions about how the big rip would affect black holes and if material absorbed by black holes is lost forever.

Gravitational lensing and black holes

Discussion of quasars and their relationship to galaxies and the early universe. Questions about smaller black holes becoming quasars and the difference between quasars and active galactic nuclei.

Quasars, galaxies and the early universe

Discussion of using gravitational lensing to measure dark energy and the accelerating expansion of the universe. Questions about time dilation and Hawking radiation.

Dark energy, the expanding universe and Hawking radiation

Discussion of mini quasars formed by stellar mass black holes. Questions about what would happen if galaxies stopped rotating and how the big rip could destroy black holes.

Mini quasars, galaxy rotation and black hole destruction

- The episode of StarTalk will feature a Cosmic Queries segment with Matt O'Dowd, an expert in black holes, quasars, and gravitational lenses.
- The episode will explore topics such as the threshold of a quasar and the possibility of the big rip affecting black holes.
- Matt O'Dowd is a professor at Lehman College and an associate at the Department of Astrophysics at the American Museum of Natural History.
- He is also a host and writer for the PBS Space Time YouTube channel.
- Matt is working on a film called "Inventing Reality" which explores the connection between physics and neuroscience.
- The film is being produced by Andrew Kornhaber, a member of the Space Time team.
- Questions from Patreon members will be answered during the episode, focusing on topics such as energy density surrounding black holes and Hawking radiation.
- Hawking radiation causes black holes to lose mass and allows information to escape.
- The information that falls into a black hole can be retrieved from Hawking radiation, allowing for the possibility of reconstructing the original objects.

- The video discusses the concept of black holes and their relationship to the second law of thermodynamics.
- It explains that black holes have entropy, which is a measurement of the amount of disorder in a system.
- As a black hole grows and consumes matter, its entropy increases, indicating the amount of hidden information it contains.
- The video also mentions the holographic principle, which suggests that the information of the interior of a black hole can be encoded on its surface area.
- The concept of time dilation is briefly discussed, particularly in relation to observing distant galaxies and their timelines.

- The video discusses the concept of relativistic time dilation and its impact on studying phenomena in distant parts of the universe.
- The speaker mentions their co-authored paper on the measurement of time dilation in a supernova light curve.
- They explain that the expansion rate of the universe needs to be factored in when studying supernovae in the outer universe.
- The video then transitions to a discussion about a hole in the sun, which is dismissed as not being a cause for concern.
- The speaker explains the formation of accretion disks around black holes and how they can lead to the creation of quasars.
- They mention that smaller black holes can form mini quasars in special circumstances, such as falling into a binary orbit with another star.
- The video concludes with a discussion on the prevalence of quasars in the universe and their rarity in nearby galaxies.

- Quasars are not common in the universe, but we have seen many hundreds of thousands of them.
- The universe is big, so rare things can still be common.
- The Big Rip may affect black holes by causing them to evaporate more quickly.
- Gravitational lensing allows us to see distant objects, but adjustments may need to be made to the image due to the bending of light by gravitational fields.

- Gravitational lensing always produces an odd number of images due to a tiny image of the original object in between the main images.
- Gravitational lensing can be used to study the inner structure of quasars by reconstructing their appearance.
- The flickering of lensed quasar images can reveal the inner structure and size of the quasar.
- Measuring different path lengths in gravitational lensing can help understand the expansion history of the universe and the rate of acceleration.
- Planets larger than Jupiter are considered brown dwarfs or failed stars, depending on their formation.
- If galaxies stopped rotating, all stars would fall towards the center where a supermassive black hole is located.
- The solar gravitational lens mission is a plan to study exoplanets and find life using the gravitational lensing effect of the Sun. The timeline for this mission is uncertain.

- The idea of using the sun as a lens to see distant planets is still being explored
- A disc or coronagraph could be used to block the sun's light and reveal the planet
- The technique could allow for mapping the surface of distant planets
- The speaker has not personally revolutionized their understanding of astrophysics, but has been surprised by certain objects and findings in their research

- StarTalk episode featuring Matt O'Dowd discussing black holes, quasars, and gravitational lenses.
- Topics explored include the threshold of a quasar and the big rip affecting black holes.
- Matt O'Dowd is a professor and astrophysicist, known for his work on the PBS Space Time YouTube channel.
- Questions from Patreon members will be answered, focusing on energy density around black holes and Hawking radiation.
- The video discusses black holes' entropy, the holographic principle, and time dilation.
- Formation of accretion disks, mini quasars, and the rarity of quasars in nearby galaxies are also discussed.
- Gravitational lensing and its use in studying quasars, the expansion history of the universe, and exoplanets is explained.
- The solar gravitational lens mission, which aims to study exoplanets using the Sun's gravitational lensing effect, is mentioned.

Can we use gravitational lensing to view distant planets? Neil deGrasse Tyson and comedian Chuck Nice explore black holes, quasars, entropy, and more with astrophysicist and host of PBS Space Time, Matt O’Dowd.

On the next episode of StarTalk, it's a Cosmic Queries with my friend and colleague Matt O'Dowd, who's an expert in weird and wacky stuff in the universe, including black holes, quasars, gravitational lenses, and the like.

And more coming up on StarTalk Cosmic Queries.

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

Neil deGrasse Tyson here, your personal astrophysicist.

All right, we're doing cosmic queries today.

Yeah, and today we've got a friend and colleague, a friend of Startalk and a friend of mine, Matt Dowd.

And Matt, is that a fake Zoom background behind you?

Well, if the simulation hypothesis is correct, then yes.

I think we hear birds and things that's very beautiful your expertise is black holes quasars gravitational lensing really juicy tasty cosmic things all of which will kill you if you come in the vicinity of- Immediately.

You teach at Lehman College of the City University of New York.

You're also an associate here at the Department of Astrophysics at the American Museum of Natural History.

And you're a host and writer for the YouTube channel for PBS Space Time, which has nearly 3000000 subscribers.

So Matt, I see you're like into a film called Inventing Reality.

Yeah, this is a film that we recently got crowdfunded and we're in the process of writing.

It is about our quest for the fundamental.

It's about humanity's search for the underlying clockwork of nature, both from the point of view of physics, but also from the point of view of neuroscience, brain science, so it's connecting how our brains construct our models of the world and how that fact is connected to how science at a societal level constructs its models of the world.

So, working with my partner, Bahar Gholipour, who's a neuroscientist, we're writing it together.

being produced with and directed by Andrew Kornhaber who's part of the Space Time team.

So everyone should have like a neuroscientist at arm's reach.

Except I have to pay mine by the 45 minute.

We're solicited from our Patreon members.

The threshold of access to this feature is $5 a month.

By the way, Matt and I have overlapping expertise in the Venn diagram.

So what will happen is whatever is right in his bailiwick, he'll take it.

But if there's some spillage, I'll jump in too.

And if there's spillage from that, then Chuck can pick up the slack.

At that point, we're not looking at spillage.

We're looking more like at an environmental disaster.

That's kind of Exeval and Valdez territory.

And Chuck, what do you think about black holes?

My name is Blake and I'm from Mobile Alabama.

Can you elaborate on energy density surrounding a black hole and how Hawking radiation might work?

Is the material that falls into a black hole loss forever?

Wow, all right, so this is, to answer this question, I need to summarize a large fraction of 20th century physics in a minute.

Wait, wait, but we only have… I know, I'm gonna try.

You're gonna start your answer by saying, first let me summarize 20th century physics.

So here we go guys, the answer to your question is, I was born the son of a… Yeah, exactly.

I mean there's so much of the story of the development of 20th century physics is around black holes and this exact weird thing about black holes that what goes in seems to not come out and this is a paradox.

Let me get these questions 1 piece at a time.

So the energy density around the black hole, I mean, so first of all let's talk about a black hole.

It is a place where gravity has had its ultimate victory.

So it's usually the collapsed core of a star.

So you have this hyper dense region where it is the gravity so strong that light can't escape.

Okay, we don't know what's really inside a black hole, but there's this region around whatever that collapsed object is where you have what we call the event horizon.

And that's the distance from which light can't escape and is black.

Okay, you and so these things are invisible, You know, unless they're eating a star or a galaxy or something and then we see the mess they make.

But back in the 1960s, Stephen Hawking realized that black holes shouldn't actually be completely black, they should radiate.

And this was Hawking's most famous discovery called Hawking radiation.

And you – it's described in a couple of different ways.

1 way is that you have matter and antimatter particles spontaneously appearing near the event horizon.

Normally, they would vanish again, destroying each other.

But if 1 gets sucked into the event horizon, the other can escape.

Hawking's own description of it was talking about the positive and negative frequency modes of the quantum vacuum and how they get perturbed by the black hole leaving the vacuum itself generates particles which you see.

Okay, so Hawking radiation causes black holes to leak away their mass.

So there's the answer to the other part of the question.

When something falls into a black hole, we think now, so originally we thought that nothing could escape a black hole because nothing can travel faster than light, right?

But now I think most physicists believe that because you have this Hawking radiation, at least the energy that falls into a black hole can eventually leak away as that radiation.

And The really important thing about that is that not only can the energy get out, but the information can get out.

And this was the other perplexing thing about black holes.

It shouldn't be possible to destroy what we call quantum information, but via Hawking radiation many physicists now think that the details of what you threw into the black hole somehow get out by this Hawking radiation also.

So it's almost like whatever it is, although it's not a chair that went in.

All of the things, the blueprint information on that tiny, tiny level, when it comes out, that is still available.

Yeah, If you could go to the, you know, if you could collect all the Hawking radiation that evaporated out of a black hole over trillions of years, every little bit, and somehow piece it together, the worst jigsaw puzzle in the universe, you should be able to reconstruct the chair.

And that's what you guys say, mean when you say information, you're talking about all the stuff that we actually are on that.

The inventory on the quantum, all the way down to the particles.

Yeah, the information that you would need if you wanted to rewind the universe and find out what happened previously, if you had all the information, then in principle you could, you know, run the clock backwards and figure out what fell into the black hole in the first place.

And just to clarify a point you're making, you're saying it came out of the black hole, but in fact, it came out of the energy field in the vicinity of the black hole, which counts as coming out

So this is a, thank you for getting to the biggest hole in my argument here.

Hawking's arguments were based on sort of internal consistency arguments in that it had to exist for the universe to make sense, but the actual mechanism of its creation isn't clear.

We just know it has to sort of emerge from the vicinity of the black hole somehow.

But that counts for having come out of the black hole because it's using the gravitational energy density created by the black hole and it just happens to be outside of the event horizon.

Yeah, so 1 description of how this happens is that the thing that falls into the black hole, which is your antiparticle or your negative frequency mode or whatever, somehow gains negative mass or negative energy inside the black hole because the dimensions inside the black hole get all twisted around and so it's possible to have this relative negative mass go inside which causes the positive mass of the black hole to shrink a little bit.

How do we know black holes follow the second law of thermodynamics?

Because Matt, you know, we say the second law of thermodynamics in a way that's an observed phenomenon, right?

There's no deep principle deeper than it.

We just say, oh, looks like entropy increases everywhere, so let's make it a law, and Maybe the black hole violates this.

So the crazy thing about entropy is that it feels like it's something that just emerges from the way particles interact with each other, etc.

But it also seems like 1 of the most fundamental things in physics because no matter where you look entropy seems to increase.

With a black hole, there is a way to think about its entropy.

So we think of entropy as a measurement of the amount of disorder in a system.

So a system will always move towards states of more disorder.

Think about for example, the air in the room.

If you took all of the air and compacted it down into a ball this size, it would, first of all, you die of asphyxiation immediately, but the air would immediately burst out to fill the room.

This configuration where all the air particles are in this 1 spot, it would be considered a very special or very ordered configuration and so it would be considered low entropy.

So the only thing it can do from there is expand into a more disordered arrangement, fill the room, that would be high entropy.

In the case of a black hole, We can think of their entropy as in terms of information, just like we talked about.

So in the case of the air in the room, when the air fills the room, we know a lot less about the location of the particles of the air molecules, okay?

There's a lot more hidden information in the air in the room when it's filling the whole room compared to if we have this ball of air in our hands, then we have a much better idea of at least the location of all of the particles that are all in this ball of air, okay?

So entropy can be considered as a measurement of the amount of hidden information in a system.

And over time, we tend to lose more and more of the information of a system.

So for a black hole, as a black hole grows, it's swallowing things from the external universe and because we can't get information about what fell into a black hole out very easily.

As a black hole grows, its entropy increases, okay?

So the amount of hidden information increases.

And so, there's this very tight relationship between actually the surface area of a black hole and the amount of stuff that it's eaten which corresponds to the amount of information that that black hole is hiding.

And so I won't get into the next point but I got to mention it was this simple observation that the entropy of a black hole is proportional to its surface area that led us directly to the holographic principle.

The notion that the information of the interior of a volume can be completely encoded on the surface of that volume, and it led people like Leonard Susskind and others to realize that you could actually encode the interior of a universe on its surface area, and that's another story that led directly from this notion of black hole entropy.

Okay, so we're all two-dimensional holograms, that's the takeaway.

Chuck, I always knew you were just a two-dimensional person.

So, by the way, I don't know if I said that that was deepened us.

That was the the person You've been dogs deep in DOS

in DOS, okay okay, and This is Anthropocosmic Dylan Anthropocosmic I like it.

Comedy in space Documentaries like PBS space time They talk about future cosmic events in distant galaxies on Earth Timelines instead of saying the Sun will blow up in 5 billion years from the perspective of a galaxy far away How do you adjust for the time dilation so that the Information you're talking about is correct in the instant in terms of relatively it seems like galactic Simulation sort of step through a wormhole to film X solar systems All right, that should be exo solar because

What is the rate at which time ticks on things we're observing?

And if it's not ticking at the same rate that it was ticking here on Earth, who are we to put it on our timeline?

Which, by the way, thank you, Neil, for making me understand what the hell he was talking about.

So, why don't we pick that up when we return in segment 2 on StarTalk Cosmic Queries.

Weird, wacky stuff that our guest, Matt O'Dowd, is an expert in when StarTalk returns.

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Hi, I'm Chris Cohen from Haworth, New Jersey, and I support StarTalk on Patreon.

Please enjoy this episode of StarTalk Radio with your and my favorite personal astrophysicist, Neil deGrasse Tyson.

There's some deep stuff coming down here.

Matt O'Dowd, friend and colleague from Lehman College of the City University of New York.

We've got you in for like quasars and black holes and weird, wacky, fun things that will kill you post-haste in the universe.

So what we were talking about before the break was from Anthropocosmic Dylan who is actually Dylan from San Diego in the short what he was talking about It seems like galactic simulations kind of stepped through a wormhole to film exosolar systems Exosolar systems because you know, they're they're not really on our timeline, but we put them on our timeline, so what's the deal?

Yeah, how do we reckon the relativistic effects of time dilation in an expanding universe on a timeline that we're just trying to set up for the universe here on Earth.

I just asked you because I don't want to answer.

So the stuff that I study is far enough away that this matters.

Many of you have heard that the universe is expanding, which means that distant galaxies appear to be moving away from us, and you look far enough away, they're moving away from us at a big fraction of the speed of light.

And so Einstein showed us that the rate at which your clock ticks depends on your motion and the rates that you see a clock ticking depends on the motion of that clock relative to you.

Okay, so fast-moving objects you see that their clock appears to be ticking slower, right?

And so I, for example, study quasars in the very distant universe and We really have to take this into account.

Okay, so we might see these quasars fluctuating.

Okay, these are supermassive black holes that are eating a bunch of gas from the galaxy and they're pretty chaotic.

Super interesting to study that variability, but if you're looking at something that's half a universe away, then this thing called relativistic time dilation slows down their sputtering and spurting dramatically.

And so you have to remember that and put that fact into your calculation, otherwise you get it all wrong.

Yeah, fortunately, fortunately, it's simple algebra.

Yeah, I have my 1 paper that is co-authored with a Nobel laureate.

It's I think was the first measurement of time dilation in a supernova light curve.

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Cosmic Queries – Black Hole Paradox with Matt O’Dowd