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The Nobel Prize in Physics 2020

nobelprize.org

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Re: The Nobel Prize in Physics 2020

#31

Post by Sharlin »

uHuge wrote: post #14
frereubu wrote: post #9

Earlier quoted context omitted.

An illustration in the press release contains this phrase: "When a massive star collapses under its own gravity, it forms a black hole that is so heavy that it captures everything that passes its event horizon. Not even light can escape. At the event horizon, time replaces space and points only forward. The flow of time carries everything towards a singularity furthest inside the black hole, where density is infinite…

That is a misunderstanding and a simplistic depiction of the inner structure inside the event horizon sphere. True is we have no observations of the internals but time ending is in contradiction to the cones of particles ejected from the "hole", observed by astronomers.

Black hole jets do not originate from beyond the event horizon. They are made of matter in the accretion disk surrounding the black hole that spirals inward but is deflected and ejected by the black hole's magnetic field.

Re: The Nobel Prize in Physics 2020

#32

Post by psychoslave »

sharpneli wrote: post #13
frereubu wrote: post #9

Earlier quoted context omitted.

An illustration in the press release contains this phrase: "When a massive star collapses under its own gravity, it forms a black hole that is so heavy that it captures everything that passes its event horizon. Not even light can escape. At the event horizon, time replaces space and points only forward. The flow of time carries everything towards a singularity furthest inside the black hole, where density is infinite…

Non poetic but hopefully bit more understandable explanation of what it tries to say: After crossing the event horizon the radial direction becomes like time. And what used to be time becomes like space. What this means that you will inevitably travel to the center, just in the same way as you travel into the future in normal life. Inside the event horizon the center is not at any place that you can see, instead it i…

To be fair, the universe will never confront you to such a puzzling situation, as it will kindly squash you under heavy gravity before you come close to any object so massive.

Re: The Nobel Prize in Physics 2020

#33

Post by satori99 »

fsnowdin wrote: post #16

I thought we already knew there was a supermassive black hole in the center of the Milky Way for a while now? What specifically did Genzel and Ghez do to expand on that knowledge? I'm curious to know.

Made this cool video?

https://www.youtube.com/watch?v=u_gggKHvfGw

Re: The Nobel Prize in Physics 2020

#34

Post by SiempreViernes »

Sharlin wrote: post #24
SiempreViernes wrote: post #10

Earlier quoted context omitted.

Honestly, "time replaces space" is probably intentionally dramatic: I don't think anyone really means more than that the light-cone is so tilted it lies completely outside of where it started. In practice it just means that wherever you try to go you'll end up in the same place, basically you're going down a funnel and the exceptional thing is that the funnel is made out of spacetime itself.

Well, time does very concretely swap roles with one of the spatial dimensions, namely the radial one. They change signs in the metric, making the radial dimension timelike and the old temporal dimension spacelike.

I think there is more to the special status of time than just the sign convention used, so I find this mathematical detail about as interesting as the singularity on the event horizon.

Re: The Nobel Prize in Physics 2020

#36

Post by fsnowdin »

xioxox wrote: post #28
fsnowdin wrote: post #16

I thought we already knew there was a supermassive black hole in the center of the Milky Way for a while now? What specifically did Genzel and Ghez do to expand on that knowledge? I'm curious to know.

Have a look at the linked documents giving the popular science background. They led the teams that gave the decisive proof that there is black hole at the galactic centre. The teams developed techniques to precisely measure the orbits of the stars which orbit the central black hole. Looking at the speed of the stars, particularly as they pass close to the object, you can measure its mass and put a constraint on its s…

Now that's an answer. Thanks for the detailed reply!

Re: The Nobel Prize in Physics 2020

#37

Post by abdullahkhalids »

konschubert wrote: post #12
frereubu wrote: post #9

Earlier quoted context omitted.

An illustration in the press release contains this phrase: "When a massive star collapses under its own gravity, it forms a black hole that is so heavy that it captures everything that passes its event horizon. Not even light can escape. At the event horizon, time replaces space and points only forward. The flow of time carries everything towards a singularity furthest inside the black hole, where density is infinite…

I’m a Physicist (Not Astrophysicist, but still. ) I can assure you that this is also gibberish to me. These kind of popular science translations are like one-way hash functions. If you really understand the science, you can probably recognize where they are coming from. But by themselves they contain 0 information.

As someone who understands hash functions, I understand where you are coming from and got non-zero information from your comment.

Re: The Nobel Prize in Physics 2020

#38

Post by fsnowdin »

nabla9 wrote: post #29
fsnowdin wrote: post #16

I thought we already knew there was a supermassive black hole in the center of the Milky Way for a while now? What specifically did Genzel and Ghez do to expand on that knowledge? I'm curious to know.

We already know it because Genzel and Ghez discovered it. Their work goes back 30 years.

When I heard about this, I seriously thought we just only discovered Sagittarius A* this year and that I must have fucked up my memories. Thanks for the clarification!

Re: The Nobel Prize in Physics 2020

#39

Post by tegeek »

What is more poetic than a mathematical model of a black hole? Look at this

A "finished" black hole (The end state of the gravitational collapse) doesn't have a volume or any density.

This is the mathematical solution first obtained by Schwarzschild in 1916. So standard mathematical solutions of the black holes are vacuum solutions.

There is "nothingness" inside the event horizon.

The outside observer would see a collapsing sphere of dust, but over time, as the radius of the sphere approaches the (yet to form) event horizon, gravitational time dilation makes everything appear increasingly in slow motion. The actual moment of horizon formation is never seen, it remains forever in the future for the outside observer.

For the in falling observer, the situation is different. The moment once the horizon is crossed, there is no escape. The observer will find himself inside an ever shrinking “universe” of dust everywhere. The singularity is an unavoidable future moment in time, when the density of this “universe” becomes divergent and time itself comes to an end.

So there you've a vacuum. A "universe" of vacuum everywhere where there is no time exists.

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