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Uploaded 25-04-18

It’s been conjectured that the center of the Milky Way is swarming with tens of thousands of black holes. And now we’ve actually seen them.

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Previous Episode:
Using Stars to See Gravitational Waves
https://www.youtube.com/watch?v=xnwXyPU_ps0

This episode of Space Time Journal Club looks at the paper:

A density cusp of quiescent X-ray binaries in the central parsec of the Galaxy
by Hailey, Mori, Bauer, Berkowitz, Hong and Hord (2018)
https://www.nature.com/articles/nature25029

The core of our galaxy is a wild place. The stars are so densely packed that the night sky would be 500 times brighter. A supermassive black hole, 4 million times the mass of our Sun lurks in the center. It flings nearby stars into extreme slingshot orbits. It consumes anything that gets too close is consumed, burping a blast of X-rays. We know these things because we see them from our comfortable vantage point 28,000 light years out in the galactic disk. But there’s one particularly terrible feature of the core of our galaxy that, until now, has only been has only be hypothesized: The central few light years of the Milky Way is thought to contain a vast swarm of smaller black holes that have rained in from the surrounding galaxy.

Hosted by Matt O'Dowd
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Uploaded 04-11-19

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Why does it appear, that humanity is the lone intelligence in the universe? The answer might be that planet Earth is more unique than we've previously assumed. The rare earth hypothesis posits exactly this - that a range of factors made Earth exceptionally unusual and uniquely able to produce intelligent life.

In upcoming episodes we’ll be exploring the anthropic principle and its two main versions - the strong and the weak anthropic principles. The strong anthropic principle tells us that the observed universe must be able to produce observers - including the contentious idea that this predicts the existence of universes beyond our own. But in today's episode we’re going to focus on the weak anthropic principle. It says that we must find ourselves in a part of the universe capable of supporting us. For example, in a planetary biosphere rather than floating in the void between the galaxies. This may seems tautological, but accounting for this observer selection bias is important to understanding why the universe looks the way it does from our perspective. And the weak anthropic principle is much more useful than that. When combined with the apparent absence of alien civilizations, it may tell us why intelligent life is incredibly rare in our universe.

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Uploaded 01-07-19

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Energy too cheap to meter - that was the promise of nuclear power in the 1950s, at least according to Lewis Strauss chairman of the Atomic Energy Commission. That promise has not come to pass - but with some incredible new technologies, perhaps it still could. The question is - should it?

Hosted by Matt O'Dowd
Written by Matt O'Dowd
Graphics by Leonardo Scholzer
Directed by Andrew Kornhaber
Produced By: Kornhaber Brown

If we want to convert mass into energy, fission gives the most bang for our buck. Unfortunately that “bang” can be literal. Use of nuclear energy may risk the proliferation of nuclear weaponry, and there’s also the problem of nuclear waste, and the specter of horrible accidents. This last one was painted in terrifying detail in the recent dramatization of the Chernobyl disaster. Nuclear reactors sound scary because the disasters are pretty epic. However the reality is that far, far more people die from straight up air pollution due to coal-fired power plants than ever died in a nuclear reactor accident. In fact the radioactivity around coal-fired plants is also higher due to the trace but completely uncontained radioactive products of coal burning.

But the most compelling attraction is that nuclear power doesn’t directly produce carbon emissions. In fact nuclear power may be our most sure path to reducing carbon emissions and halting climate change. But can we do nuclear power safely enough? There are modern ideas – including the much-hyped thorium reactor – that suggest maybe we can. Before we can understand those we’ll need to review how nuclear reactors work.


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سلطان الخليفي

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Uploaded 23-03-21

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“A moving arrow is at rest.” This is obviously a nonsensical contradiction. But Zeno, a Greek philosopher famous for his metaphysical trolling, devised a paradox whose conclusion is just this. Here’s how it goes: if you look at an arrow flying through the air at any instantaneous snapshot in time, the arrow doesn’t travel any distance. If time is composed of an infinite number of these snapshots, and the arrow doesn’t move in any of them, then the arrow is at rest during the entirety of its flight. The moving arrow is at rest.

In fact, if we’re talking about a quantum arrow, there may be a way to freeze its motion simply by looking at it, through the aptly named quantum Zeno effect. The quantum Zeno effect predicts that certain quantum events - like the electrons moving between atomic energy levels, or the decay of atomic nuclei, can be frozen through the simple act of observation. I’m going to tell you about some very real experiments that claim to have demonstrated this phenomenon. But first, let’s see if the quantum Zeno effect can save us from being shot by a quantum arrow.

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Hosted by Matt O'Dowd
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Uploaded 27-01-22

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Fact: in a black hole, all of the mass is concentrated at the singularity at the very center. Fact: every black hole singularity is surrounded by an event horizon. Nothing can escape from within the event horizon unless it can travel faster than light. Fact: gravity travels at the speed of light. So how does a black hole manage to communicate its gravitational force to the outside universe? How does gravity escape a black hole?

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Hosted by Matt O'Dowd
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Spacetime is produced by Kornhaber Brown for PBS Digital Studios.
This program is produced by Kornhaber Brown, which is solely responsible for its content.
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Uploaded 10-01-18

We can now map the interiors of stars by “listening” to their harmonies as they vibrate with seismic waves. Learn through active problem-solving at Brilliant: https://brilliant.org/SpaceTime/



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Previous Episode:
Extinction by Gamma Ray Bursts
https://www.youtube.com/watch?v=8HvwNOSnveE

These equations of hydrostatic equilibrium allow us to calculate things like the density and temperature of the core, the way energy flows to the surface, and even the lifespan of stars. These models are largely built around what little we can learn from the light we receive directly from the surface of stars. But how do we test these models if we can never see beneath those surfaces? We may not see light from beneath the stellar surface, but another type of wave travels freely throughout stars. I’m talking about seismic waves.

Hosted by Matt O'Dowd
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Sounds of stars by Manuel Perez de Lema Lopez
https://youtu.be/0ogyKgV4KN4

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