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The Nobel Prize in Physics 2020

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Re: The Nobel Prize in Physics 2020

#131

Post by entropicdrifter »

pbhjpbhj wrote: post #96
pa7x1 wrote: post #46

Earlier quoted context omitted.

The radial direction of the inside of the Schwarzschild Black Hole is timelike. This means that; inside the event horizon, the inevitable passage of time becomes the inevitable move towards the singularity at the center of the Black Hole. To answer your question in clear terms: No, you cannot move freely in the radial direction. Only towards the center, in the same way you cannot move freely forward or backwards in t…

Considering a point particle, what constrains it from orbiting [which is what I'm assuming we're meaning here as all matter has to move radially to cross the event horizon]? If it had a tangential component to its momentum prior to meeting the event horizon (EH) wouldn't it continue to orbit past the EH?

I think by definition the event horizon can only be crossed in one direction (towards the center). By this I mean nothing escapes once it is past that point. It's defined by being the point of no return

It is the point at which nothing, no matter how fast or massive, can possibly return from the gravitational pull. For instance: light, traveling at the speed of light in a vacuum, cannot escape once it has crossed the event horizon; it's pulled inevitably inward.

Re: The Nobel Prize in Physics 2020

#132

Post by codebolt »

mongol wrote: post #105
melling wrote: post #74

Earlier quoted context omitted.

He has also written a few books. https://www.amazon.com/Roger-Penrose/e/B000AQ045A%3Fref=dbs_...

Has anyone read his writings on consciousness? When I was young and still believed in free will I imagined that consciousness used quantum mechanics as a way to generate free will. I later learned that Penrose had theories that sounded similar. But have not read about it.

I've read both. The first was the most impactful to me personally. The way he uses Gödels theorems to argue against the computability of consciousness is actually quite ingenious and it's presented in such a straightforward way that I could easily grasp it from first principles. I also find the criticisms I've seen against it to be knee-jerkish and flimsy.

Orch OR seems like a shot in the dark, and while certainly an interesting thought experiment I'd like to see more evidence before I buy in to it.

Re: The Nobel Prize in Physics 2020

#133

Post by srtjstjsj »

pa7x1 wrote: post #46
stallmanite wrote: post #44

Earlier quoted context omitted.

Ok that explains how space becomes timelike. But I never hear anyone address how time becomes spacelike. In what sense does it become spacelike? Can one move back and forth in time inside the event horizon?

The radial direction of the inside of the Schwarzschild Black Hole is timelike. This means that; inside the event horizon, the inevitable passage of time becomes the inevitable move towards the singularity at the center of the Black Hole. To answer your question in clear terms: No, you cannot move freely in the radial direction. Only towards the center, in the same way you cannot move freely forward or backwards in t…

You paraphrased the GP post about space becoming time, but didn't answer the Parent question about time becoming space:

> In what sense does [time] become spacelike? Can one move back and forth in time inside the event horizon?

Re: The Nobel Prize in Physics 2020

#134

Post by srtjstjsj »

sharpneli wrote: post #47
stallmanite wrote: post #44

Earlier quoted context omitted.

Ok that explains how space becomes timelike. But I never hear anyone address how time becomes spacelike. In what sense does it become spacelike? Can one move back and forth in time inside the event horizon?

It just becomes like space. You can freely move around it without any issues. It’s no longer time, just as the radial direction is no longer space. How it happens? Normal spacial direction has positive sign. Time has negative. When crossing the horizon the equations become such that t gets a positive sign and the radial direction a negative one. After that they behave as expected.

Is that because you could move away from the center (a bit) to delay your progress toward the center singular?

Re: The Nobel Prize in Physics 2020

#135

Post by mannykannot »

codebolt wrote: post #132
mongol wrote: post #105

Earlier quoted context omitted.

Has anyone read his writings on consciousness? When I was young and still believed in free will I imagined that consciousness used quantum mechanics as a way to generate free will. I later learned that Penrose had theories that sounded similar. But have not read about it.

I've read both. The first was the most impactful to me personally. The way he uses Gödels theorems to argue against the computability of consciousness is actually quite ingenious and it's presented in such a straightforward way that I could easily grasp it from first principles. I also find the criticisms I've seen against it to be knee-jerkish and flimsy. Orch OR seems like a shot in the dark, and while certainly an…

There have been many responses to the Gödelean argument that miss the point, but I have been persuaded that it is vulnerable on the basis of its assumption that a logical system must be sound if it is to be a candidate for capturing a human's reasoning powers. Minsky, among others, pointed out that our ability to believe falsehoods, and to hold contradictory beliefs, opens the possibility, if not the expectation, that human reasoning is not sound.

Re: The Nobel Prize in Physics 2020

#136

Post by KingFelix »

JackFr wrote: post #70

It's funny when you know of a scientist and their work, but years later you find out what you knew them for isn't what they did best or what they're famous for... I only knew Penrose from Penrose tilings and as the author of The Emporer's New Mind. Black holes? Who knew.

He was Stephen Hawkings Teacher!

Re: The Nobel Prize in Physics 2020

#137

Post by sharpneli »

srtjstjsj wrote: post #134
sharpneli wrote: post #47

Earlier quoted context omitted.

It just becomes like space. You can freely move around it without any issues. It’s no longer time, just as the radial direction is no longer space. How it happens? Normal spacial direction has positive sign. Time has negative. When crossing the horizon the equations become such that t gets a positive sign and the radial direction a negative one. After that they behave as expected.

Is that because you could move away from the center (a bit) to delay your progress toward the center singular?

You can’t move away from the center. You can move in direction around it (while still moving towards it at the same time). And you can move in the previously time now just space.

Delaying your fall is precisely the same as trying to avoid tomorrow by moving around. Moving away from the center is like moving back in time. No matter how you move in the spatial dimensions you can’t do it.

With the exception of faster than light travel. That allows you to move away from the center, and it also allows you to avoid tomorrow. It’s pretty much the same as time traveling in general relativity.

Re: The Nobel Prize in Physics 2020

#138

Post by cb321 »

codethief wrote: post #127
kdavis wrote: post #18

Earlier quoted context omitted.

Yes. Penrose’s prize is largely for the Penrose-Hawking Theorems[1]. [1] https://en.wikipedia.org/wiki/Penrose–Hawking_singularity_th...

What I don't understand is this: The Singularity Theorems already assume the existence of a trapped surface (and by implication, of a marginally outer trapped surface, i.e. an apparent horizon, i.e. a black hole) and then conclude that there must be a singularity inside. Experimentally, though, we know absolutely nothing about this and the recent black hole-related discoveries (gravitational waves, Event Horizon Tele…

I believe your point is valid. If the universe ends in big crunch there may also be insufficient proper time to form a singularity. People often confuse event horizons for singularities, partly because of Penrose's work. :) I think Penrose has made many contributions worthy of recognition, though I am not sure Nobel committee press releases are the best place to look for them.

Re: The Nobel Prize in Physics 2020

#139

Post by pa7x1 »

srtjstjsj wrote: post #133
pa7x1 wrote: post #46

Earlier quoted context omitted.

The radial direction of the inside of the Schwarzschild Black Hole is timelike. This means that; inside the event horizon, the inevitable passage of time becomes the inevitable move towards the singularity at the center of the Black Hole. To answer your question in clear terms: No, you cannot move freely in the radial direction. Only towards the center, in the same way you cannot move freely forward or backwards in t…

You paraphrased the GP post about space becoming time, but didn't answer the Parent question about time becoming space: > In what sense does [time] become spacelike ? Can one move back and forth in time inside the event horizon?

Sorry, I missed that. The time direction does indeed become spacelike inside the black hole. The most remarkable consequence of this is that the singularity is at the future of every test particle that crosses the horizon.

This can be seen best in a conformal diagram or Penrose diagram (now that he has a Nobel prize might as well use the name of his creator).

Here is the Penrose diagram of a star collapsing gravitationally into a Black Hole and its evaporation via Hawking radiation: https://fias.uni-frankfurt.de/~hossi/Bilder/BR/bhevap_l.jpg

You should track the r=0 line, initially it points upwards (it's timelike) as it chugs along at the center of the star as it collapses gravitationally. When the BH forms, it becomes horizontal (spacelike) and lies at the future of every test particle that enters into the BH. The singularity is inevitable for anything that crosses the horizon.

The Black Hole will at some point have radiated all its energy in Hawking radiation at which point it disappears and r=0 becomes timelike again.

Unfortunately it's hard to make it easier to understand without indulging in some math.

Re: The Nobel Prize in Physics 2020

#140

Post by pbhjpbhj »

pas wrote: post #76
melling wrote: post #71

Earlier quoted context omitted.

i thought that a black hole could eventually disappear through Hawking radiation. Eventually being a really long time.

Yes, it could, and yes, it theoretically [in some models] contains/radiates information. But the "radiation" happens right at the event horizon, the particles that get emerge have been "created" on the outer side. https://www.youtube.com/watch?v=XT_iZ7QEit8

This seems as good a place as any to ask: when the particle-antiparticle pairs are made at the event horizon, one falls in, the other is emitted as radiation. Why don't the p & ap produced then pair up with and annihilate with other ap and p created in the vicinity such that it wouldn't really be detectable over ordinary vacuum activity. This could happen both inside and outside the horizon. It seems like Hawking radiation (if I've understood correctly) could be produced but would be almost impossible to detect as it would all annihilate immediately?

What have I missed?

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