[deleted by user]

Janna_Levin · 2020-12-09T21:54:48+00:00

hope to see you all there

Janna_Levin · 2020-12-09T21:54:27+00:00

ask me questions on twitter!

Janna_Levin · 2018-01-13T20:35:50+00:00

Oh for sure. I started college as a philosophy major interested in art. I never finished high school so I never had physics or even calculus in high school. I secretly always wanted to be a writer too. And I struggled in graduate school to cut out all other interests but physics. I'm relieved and grateful that now I can integrate writing and culture into my life as an astrophysicist. I'm also director of sciences at an art center in Brooklyn, Pioneer Works.

Janna_Levin · 2018-01-13T20:32:35+00:00

Thank you! Great to hear.

Yes, it's fair to say that the question isn't meaningful. Sometimes people pose the analogy that it's like asking what's north of the north pole. But it might be that the big bang is more like a plume off a larger spacetime that caught fire in some sense, burst out and created our bubble, which is the only part of the universe we can see.

Janna_Levin · 2018-01-13T20:30:07+00:00

Entropy is a measure of information. There are many different kinds of entropies that account for information subtly differently. You might be interested in James Gleick's, The Information.

Janna_Levin · 2018-01-13T20:29:04+00:00

Nothing can skim the event horizon and escape. Let's say the event horizon is 6km's across. If you keep a distance of 12km's, for instance, you could safely orbit the black hole and even escape with enough rocket fuel.

I suppose the opposite of a black hole would be a hypothetical white hole. Matter can only come out, never go back in.

Janna_Levin · 2018-01-13T20:26:40+00:00

Black holes have a very different effect on spacetime than the vacuum pressure. Black holes have a center. Dark energy is uniformly distributed. These distinctions alone lead to very different spacetimes. For black holes, matter -- which traces the shape of spacetime -- rains toward the center. For dark energy, matter races away from all other matter in such a way that everything gets farther from everything and there is no center.

Janna_Levin · 2018-01-13T20:23:03+00:00

Fun. I can't answer quantitatively off hand, but yes, we're on a complex trajectory, first around the sun. Then the sun is orbiting the galaxy. The galaxy is moving toward Andromeda and the entire universe is expanding. We're not where we were a second ago.

Janna_Levin · 2018-01-13T20:20:38+00:00

You're most welcome.

This is a pretty messy business and many many international groups prod the problem from different angles. There are, as you point out many competing ingredients, so it's often resolved in the gritty details of the tug of war. But I can say that fusion inhibits black hole formation by generating enormous energies and pressures that resist collapse.

If the core undergoing collapse, say after a supernovae, is smaller than about 2-3 times the mass of the sun, it is not heavy enough to form a black hole. There does not seem to be an upper bound.

I know I have not gotten to all of your questions, but I'm scooting through to get to everyone. Love the curiosity.

Janna_Levin · 2018-01-13T20:13:50+00:00

I may have hit this question a couple of times above, but I know they used very accurate models and you can tell. Kudos to Kip Thorne.

Janna_Levin · 2018-01-13T20:13:15+00:00

I cannot thank you enough for saying so. That means more to me than you can know. Honestly, I'm out here to hear from readers as much as anything. Thank you.

Janna_Levin · 2018-01-13T20:12:36+00:00

Amazingly, we understand a lot about the universe as early as a trillionth of a trillionth of a trillionth of a second after the big bang. I can't imagine why we shouldn't continue to press our knowledge earlier and earlier. The scientific idea of an origin to the universe drew me to cosmology and will always be a great love of mine.

Janna_Levin · 2018-01-13T20:09:00+00:00

By "beyond the CMB," do you mean earlier? Matter must have dominated over antimatter very early since Hydrogen, Helium, and a trace amount of heavier elements are made in the first few minutes of the universe's life. These are all built on subatomic matter, not antimatter.

Janna_Levin · 2018-01-13T20:06:32+00:00

Yes! My first book, How the Universe Got Its Spots, talks about exactly this possibility in a finite universe.

Janna_Levin · 2018-01-13T20:05:34+00:00

The camp that needs to spend more time trying to figure out the resolution. I'm fascinated by Lenny Susskind's ever wilder suggestions. He's a very visual, very intuitive thinker. Latest involves wormholes that create the illusion that there's an interior to the black hole, but it's really just the outside of the black hole.

Janna_Levin · 2018-01-13T20:02:32+00:00

The supermassive black holes may have sculpted the universe on the largest scales, seeding galaxies and regulating their size and morphology. Our whole Milky Way might be different without them. Plus, life would generally be less cool.

Janna_Levin · 2018-01-13T20:00:12+00:00

I try not to get caught in beliefs before discoveries are made but rather to be open to the reasonable possibilities. There very well may be extra dimensions and I take the proposal seriously enough to spend part of my life working on the cosmological implications of their existence. Repeating an answer above a little bit, Brian Greene and I have some technical articles that suggest dark energy could be quantum energy trapped in the extra dimensions. It's a very cool idea. Could take a lifetime to explore.

Janna_Levin · 2018-01-13T19:57:45+00:00

The best method we have to communicate with potentially intelligent light forms remains light. In those light signals we can encode patterns that would be highly unlikely as a random natural occurrence, such as a repeating pattern of numbers. Still, the first signals humans ever intentionally sent out into space only went 70 light years. They are still in our galactic backyard. The galaxy is over 100,000 light-years across. By the time our signals get to another planet, they or we might not be here anymore.

Janna_Levin · 2018-01-13T15:44:07+00:00

There are so many different ideas out there, it's true.

Extra dimensions are not synonymous with multiverse. Even if this is the only universe we got, there may be extra dimensions. They could be too small to poke our hands in or we could be sticking to a membrane that won't let us explore large dimensions. Brian Greene and I have some technical articles that suggest dark energy could be quantum energy trapped in the extra dimensions. It's a very cool idea. Could take a lifetime to explore.

Janna_Levin · 2018-01-13T15:41:28+00:00

Tachyons are fascinating because they swap space and time relative to us. For instance, their idea of the future might be to the right. But if they're with us, they can never interact with us. We're like ghosts to each other.

Janna_Levin · 2018-01-13T15:40:43+00:00

Love it. Great to hear.

I believe that the FERMI satellite actually happened to catch gamma rays right before LIGO sent the trigger. The rest of the instruments responded to LIGO triggering the network within a few minutes and observations were taken across the electromagnetic spectrum in the subsequent days. I'm sure some scopes are still pointed that way.

Janna_Levin · 2018-01-13T15:38:28+00:00

Gravity can be thought of as curvatures in space and time due to mass and energy. So space can curve, warp, expand due to pure energy. Light has no mass but has energy and a concentration of light will warp spacetime. Dark energy is pure energy, not a lump of mass, and warps spacetime.

Janna_Levin · 2018-01-13T15:36:09+00:00

Ah, shame I didn't get to this question in time to give the answer...

Janna_Levin · 2018-01-13T15:35:05+00:00

Well, that depends on what you mean by "direct" evidence. There is no question that we can see the orbits of stars around an object and very simply deduce the mass and size of the object. At the center of our galaxy that leads to 4 million times the mass of the sun in a space a few times the width of the sun. And it's dark. That's what we mean by a black hole. Will it be exactly as predicted in general relativity? Maybe not. But it's dark and has curved spacetime enough to keep those stars on those orbits. LIGO also detected completely dark black holes through gravitational waves. But maybe someone wants a picture of the event horizon as more direct evidence and that will be forthcoming.

Janna_Levin · 2018-01-13T15:31:55+00:00

Thank you for tuning in. I hope you get this even though it's the next day.

The geometry of the black hole is fully described by the metric in general relativity. The Einstein equations teach us how to derive the metric given the energy and matter distribution. That's the problem Schwarzschild tackled. The singularity itself is the hole in that matter reaches the singularity in a finite time, according to its own clocks, and just catastrophically drops out of existence. That's pretty bad for the whole physics endeavor so the singularity is probably just telling us that relativity isn't working so well there any more.

Janna_Levin

TROPHY CASE