The Nobel Prize in Physics 2020 | Hacker News Reader

The Nobel Prize in Physics 2020

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Such a joy to see Sir Roger Penrose awarded with this honor. One of my favorite contemporary intellectuals.

If anyone hasn't seen it, I recommend his recent appearance on the Lex Fridman podcast: https://www.youtube.com/watch?v=orMtwOz6Db0

I somehow always had the impression that Roger Penrose was a numerical computation guy (Moore-Penrose pseudoinverse).

I did not realize he had this vast of scope of a contributions in physics. Certainly quite impressive.

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.

Here is an interesting discussion of this work by physicists: https://www.scottaaronson.com/blog/?p=2756

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.

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.

IIRC be wrote about that in The Emperor's New Mind a formative book for me (even though I was still at highschool when I read it) but one I haven't really returned to now I've a more academic understanding of the subject matter. To-do!

Another list: https://www.worldcat.org/identities/lccn-n82139094/

penrose tilings is a contributions to pure mathematics, too

Veritasium YouTube channel has a good video on Penrose tiles that my kids just watched, https://youtu.be/48sCx-wBs34 .

Yes so exciting to see this. His book the Road to Reality is revolutionary to me and I have not even finished it (still digesting). Every time I hear him speak it seems I learn some new perspective on the universe that fundamentally changes my thinking, really inspiring person.

Now we’ve got to listen to his Orch OR theory about how microtubules are quantum computers of consciousness! as a biologist I’m so excited for this theory to catch on and refine our notions of neuronal information processing beyond synaptic theory.

I'm elated that Andrea Ghez won!! She came to talk at my high school in 2007, and sparked a lot of my interest in astrophysics. Highly deserved. Here's something closely related to her research that always blows my mind: A video of stars orbiting Sag A*: https://www.youtube.com/watch?v=B0QRpid5_QU

Amazing that this video is not more widely known! Thanks

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.

You shouldn't forget that, since the mathematical equations have a singularity at the center of a black hole, we can be reasonably sure that they are in fact incomplete and can't accurately describe the internal structure of a black hole.

So, take any such description with a grain of salt. It's much more correct to say that our current models can't accurately predict what is happening past the event horizon of a black hole.

First there is nothing called center of a blackhole. What mathematics tells us is exactly what is a black hole. After crossing the event horizon, there is no time so there is no "information" exists. Its the end of "everything" which I wrote "nothingness". Thats what is in the black hole. Thats the structure.

There is very much time after crossing the event. It happens to not correspond to the "t" coordinate that a distant observer would call time, but it still exists.

The mathematics describes 2 singularities with black holes. 1 singularity occurs when describing the black hole using the coordinate system of an observer at constant distance. This is a coordinate singularity and goes away under an appropriate change of coordinates.

Another singularity occurs at what the constant distance observer would describe as the "center" of the black hole. This is not a coordinate singularity. The curvature there goes infinite regardless of your coordinate system.

Whether or not you want to call this singularity the "center" is a matter of opinion. An observer within the event horizon would describe the singularity as a time, not a location, so "center" certainly has some connotations that you may want to avoid. On the other hand. In the coordinate system that I normally see used to describe the interior of black holes, the singularity occurs at the surface r=0; which sounds kind of center-ish.

> 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.

Makes me wonder. We used to believe that it's possible for our universe to eventually collapse, reversing the Big Bang in a Big Crunch. From what I recall, current evidence points against it, but if we were to live in such a universe doomed to a collapse - wouldn't that mean we'd be living in a universe-sized black hole?

(A black metahole if you like.)

The press release has a popular science background - https://www.nobelprize.org/uploads/2020/10/popular-physicspr...

Highly recommend the illustrations on the press release for a quick overview

Cross section of a black hole (pdf) - https://www.nobelprize.org/uploads/2020/10/fig2-phy-en-cross...

The Milky Way - https://www.nobelprize.org/uploads/2020/10/fig3-phy-en-milky...

Stars closest to the centre of the Milky Way - https://www.nobelprize.org/uploads/2020/10/fig4-phy-en-stars...

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 and time ends."

I enjoy reading passages like that because there's a point where I lose comprehension completely - after "Not even light can escape" - and the rest of it is enjoyably poetic gibberish to a non-physicist like me. It reminds me of the beginning of The Four Quartets by TS Eliot:

  Time present and time past
  Are both perhaps present in time future,
  And time future contained in time past.
  If all time is eternally present
  All time is unredeemable.
  What might have been is an abstraction
  Remaining a perpetual possibility
  Only in a world of speculation.
  What might have been and what has been
  Point to one end, which is always present.

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.

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.

Not only that, but in this case, given that we don't have a theory of Quantum Gravity yet, the notion of "what happens" at the singularity is inevitably mystical.

The press release is glibly going from "science mode" to "mystical mode" and acting like it's all known by physics, which it's not. (I'm not really complaining ... it's a press release, after all.)

That's because the black hole sucked all the information out of it. Haha.

Look, if it gets us phrases like “… where density is infinite and time ends.” then I’m here for them.

I cannot wrap my mind around what it means, but it’s a savage description.

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 is in your future.

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.

Not necessarily, a supermassive black hole can have quite bearable gravity at the event horizon (as the event horizon radius depends linearly on the mass and the gravity declines quadratically with distance). You still wouldn't be able to communicate your experiences though.

Doesn't an event horizon imply a gravitational pull so strong not even light can escape? Isn't the effect of gravity the same at the event horizon for all sizes of a black hole?

I thought the size only affected the "acceleration" of the gravitational pull based on the distance from the singularity? A supermassive black hole means you will take longer to be spaghettified, but it will still happen and it will happen before you cross the horizon, won't it?

A uniform force doesn't do anything harmful to you. You get stretched into spaghetti by the difference in force between the ends of your body. In large black holes that difference can be small even as you pass through the horizon (where the total force is large).

In some sense, there is no such thing as a gravitational pull. What there is is a curvature of space-time that causes an apparent force in some coordinate systems [0]. For a sufficiently large black hole, gravity is effectively constant in the vicinity of the event horizon; which means there exists a coordinate system where the space around (a small region of) the event horizon is essentially flat space. From the perspective of an outside observer, you would appear to flatten as you approach the event horizon, but this is a consequence of the coordinate system. You don't feel any effect at that point.

The reason light cannot escape from past the event horizon is that that is the point where space-time is so warped that what you consider a perfectly normal time axis is, from the perspective of an outside observer, now pointing in a spatial dimension directly towards the center of the black hole.

In contrast, regardless of how small you are, there is some point where you do experience tidal forces and feel yourself getting spaghetti. For a small black hole, this is before you pass the horizon, for a large black hole, it is after.

[0] The distinguishing feature between a real force like gravity, and a truly fictitious force like the centrifugal force, is that for the later, you can construct a coordinate system where the force disappears at all locations. For a real force, you can construct a coordinate system where the force goes away at any given point; but there will always be some point with an apparent force.

What is supposed to happen with different types of chemical bonds? If half of a molecule is inside a black hole and half is outside, the half inside is necessarily constrained to the black hole, while a molecule outside does not have such constraint. The chemical bonds should be also necessarily broken at least for a moment, since an atom inside black hole can not exert electromagnetic effects on an atom outside black hole. Wouldn't it create a bias across your whole body with some really weird atomic / chemical consequences?

In General Relativity, locally all reference frames are flat. This does not change at the event horizon, chemistry continues to work normally. It is just that in the time it takes for half the molecule to affect the other half, the other half will have slipped across the event horizon.

There is a classic analogy of light traveling through space-time being like ants crawling on a balloon. A black hole is a spot where the balloon is being sucked in. Faster and faster as you get closer. The event horizon is where the speed at which the balloon moves matches the speed of the ant. There is nothing special from the ant's immediate perception about this line, but if the ant crosses, it is doomed.

Nothing happens (locally) at the event horizon, everything works as normal. The analogy that is often used is fish upstream from a waterfall. At some point the current of the stream becomes so strong that the fish can no longer escape from the waterfall, but actually at that point nothing happens from the point of view of the fish, since it is carried by the current, you need a global view to notice that the fish is doomed past that point.

And similar in case of a black hole, you are falling through the event horizon and nothing happens, it is just that calculating what you need to do to escape, you note that it is too late.

To expand a bit on the molecule situation, when one of the atoms is inside the black hole, then parts of its electric field are still outside and influence the other atom. To have the other atom escape to infinity, you would need to break the part of the bond "still outside" and the gravity of the black hole.

> If half of a molecule is inside a black hole and half is outside,

You know how the universe is expanding, such that the milky way is moving away from (sufficiently) distant galaxies faster than the speed of light? But chemistry still works fine here? When you fall into a black hole, you accelerate until you're moving away from the rest of the universe faster than light, but all your atoms are still (relatively, assuming the black hole is large enough to have negligible tidal forces) stationary relative to each other. The event horizon is just the point where your speed relative to the effectively-distant[0] outside universe exceeds the speed of light. Any signal you emit can't be moving facter than c relative to you, so it will always be moving away from the outside universe (v<-c implies v+v'<0).

0: "Nothing can move facter than c" refers to relative motion of objects near each other, which is why the Hubble expansion of the universe doesn't contradict that either.

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 time.

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?

Nothing forbids a slight tangential component but the movement of the test particle is inevitably decreasing in r.

Closed orbits are impossible though, all test particles finish at the singularity in a finite amount of proper time.

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.

> what constrains it from orbiting

Not quite what you seem to be asking, but the event horizon is the point where[0] the escape velocity is equal to the speed of light; the orbital velocity at that distance is greater (by a factor of ln 2 IIRC, so v_orbital ≈ 1.44c). There's a more distant distance, called the innermost stable orbit or the photon sphere, where the orbital velocity is equal to c (so photons will orbit if you emit them tangentially at this height), but the escape velocity is only ~0.69c.

0: It's not quite right to say that that's because the escape velocity is equal to c, though.

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.

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.

This reminds me of the games you can play flipping signs in relativistic equations when you make v > c. You can interpret those in a lot of fun ways too.

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.

I have heard of space becoming timelike, but have never heard of time becoming spacelike in a black hole. Do you have more information on that?

PBS Space Time is pretty decent and understandable source if one doesn’t want to wade trough the maths. I heavily recommend the whole black holes playlist. https://www.youtube.com/playlist?list=PLsPUh22kYmNBl4h0i4mI5...

I do want to wade through the maths, and I have to some degree, and I've never come across time becoming spacelike (which would imply rotation past the null vector, which afaik is not something that happens in a black hole).

Thanks, that's much more helpful, although still pretty mind-bending.

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.

Worth noting that the "BH so massive even light can't escape" meme, a staple of popular science, wouldn't make sense since photons don't have mass. What's happening is that space is skewed (according to Schwarzschild if I got it right). It can be better groked with a modern depiction of a BH such as in eg "Interstellar" where the far end of the accretion disk is observed as a second disk.

Light has mass-energy, and mass-energy both affects and is affected by the gravitational field. Indeed it is theoretically possible to make a black hole out of nothing but photons [1].

[1] https://en.wikipedia.org/wiki/Kugelblitz_(astrophysics)

> Worth noting that the "BH so massive even light can't escape" meme, a staple of popular science, wouldn't make sense since photons don't have mass.

Even worse, it is frequently explained with an analogy to escape velocity. You have a certain escape velocity at the surface of the Moon, the analogy starts, and your rocket needs to exceed that to get out. Gravity is stronger at the surface of Earth, so escape velocity there is higher, and rockets need to go even faster.

At the event horizon, gravity is strong enough that escape velocity is the speed of light, and so nothing can get out because you can't go faster than light.

Great--except the escape velocity thing only applies to trying to get out ballistically. (Current rockets are essentially ballistic because they expend most of their fuel while still deep in Earth's gravity well).

Escape velocity explains why someone inside the event horizon can't throw things out of the black hole using a catapult, or using a rocket that expends all its fuel before reaching the event horizon.

It doesn't explain why something with continuous thrust could not get out. It doesn't explain why someone inside couldn't build a ladder that extends past the event horizon and simply climb out. It doesn't explain why someone outside could not lower a tether in and pull someone out.

I wonder what happens if you inject parts of that into GPT-3... maybe we solve some mysteries with that

https://www.youtube.com/watch?v=mht-1c4wc0Q

I hope it helps. I think this is the cleanest explanation with actual visual representation.

Edit: Sorry this one is even better.

How Time Becomes Space Inside a Black Hole | Space Time

https://www.youtube.com/watch?v=KePNhUJ2reI

Here's a simple explanation, with pictures:

http://visualrelativity.com/LIGHTCONE/schwarzschild.html

And here's a more technical one:

https://en.wikipedia.org/wiki/Penrose_diagram#Black_holes

In some sense, nothing particuarly interesting happens at the event horizon of a black hole. For a sufficiently large black hole, the space at the event horizon is essentially flat [0]. The time and space swapping weirdness is entirely an artifact of the coordinate system being used.

If you think of spacetime as a 4 dimensional geometry, there is no particularly reason to pick out any specific shape of the "time" coordinate. For a given interval in space-time, there is notion of "proper time" that is invariant to coordinate system transformations, so a given observer does have an "ideal" coordinate to use for time. The "proper time" of a given observer could be the space axis of another coordinate system.

Assuming you have enough background in math, what I think is a reasonably understandable explanation is here:

https://www.youtube.com/watch?v=yv2-KPagCQs&feature=youtu.be...

Once he gets through explaining the hyperbolic coordinate sytstem, you can skip ahead to

https://www.youtube.com/watch?v=yv2-KPagCQs&feature=youtu.be...

Space is time line:

https://www.youtube.com/watch?v=yv2-KPagCQs&feature=youtu.be...

A somewhat clarifying picture of it taking "infinite" time to cross the event horizon, without anything interesting happening near the event horizon:

https://www.youtube.com/watch?v=yv2-KPagCQs&feature=youtu.be...

[0] As with any gravitational object, there are tidal forces. However, due to the increasing radius of the event horizon, the strength of the tidal forces at the event horizon decrease as the mass of the blackhole increases.

I cannot but disagree with you on Eliot. It is a christian image and he is talking about God’s view of History.

The waste land is at times gibberish, though, in his own words.

The PR seems like a double dig on Hawking. "Nothing, not even light, can escape." except Hawking radiation?

Hawking radiation is emitted from the outside, if you start beyond the barrier it's usually not counted as an escape.

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?

The particle []or[] antiparticle (only one avoids falling in) produced usually does pair up and annihilate with another (anti)particle, but that happens above the event horizon, so the photon resulting from that annihilation sometimes is pointed away from black hole and escapes. It's only very small black holes where the pair-production particles themselves have sufficient height and speed to escape.

Good question, but I have no idea, and ... it's ... complicated. Basically don't think about it in that way, because the math uses QM and frequencies.

https://math.ucr.edu/home/baez/physics/Relativity/BlackHoles...

http://www.scholarpedia.org/article/Hawking_radiation#The_or...

Congrats! Am so happy that Penrose lived long enough to be able to see an actual movie of a black hole ;)

Monitoring the Morphology of M87* in 2009-2017 with the Event Horizon Telescope

https://arxiv.org/abs/2009.11842

And when all is said and done I believe his insights into the Quantum Correlates of Human Consciousness may end up being the most fruitful

Consciousness in the Universe: Neuroscience, Quantum Space-Time Geometry and Orch OR Theory

https://web.archive.org/web/20120616045402/http://www.quantu...

Or lived long enough to receive the prize at all - 1965 was 55 years ago!

55 years is half-way back to the time when galaxies-as-more-than-nebula-inside-our-galaxy was finally settled.

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!

Penrose has written the best science book I've ever read. "The Road to Reality". I read it some ten years ago, and it renewed my interest in physics. I must have read at least three dozen of the books in its bibliography since.

Wow, I didn't realize Penrose hadn't won one already. He clearly deserves it!

better late than never

It's too bad that Wheeler didn't live long enough to share it.

Theoretical physicists are less and less likely to receive Nobel prizes during their lifetime. It took 50 years for Higgs to get his.

Nobel prizes reward experimentally verified discoveries and I suspect the direct observation of a black hole is what finally got Penrose his Nobel. But discoveries like Hawking radiation didn't result in a Nobel prize because even though it is a well accepted idea among physicists, it hasn't been observed yet.

As theories predict things that require more and more extreme conditions and precise instruments, the time between theory and experimental validation gets longer and longer.

It's too bad that Stephen Hawking is dead. He also deserved to be on this list.

It looks like Hawking missed the Nobel prize by two years then. This is almost the same like with Fischer Black.

Ron Drever also missed out on the Nobel prize for the discovery of gravitational waves by about 6 months [1].

[1] https://www.bbc.com/news/science-environment-39212305

Hawking could joke about it. From one of his guest appearances on "The Big Bang Theory", where Sheldon is having some issues when a rival has outclassed him, and Leonard brings in Hawking to have a talk with Sheldon:

Stephen Hawking : I understand you're struggling with professional jealousy.

Sheldon Cooper : Thanks, Leonard, now he's not going to think I'm cool.

Stephen Hawking : Don't worry. I know how you feel. I have never won a Nobel prize.

Penny : Oh, wow, that doesn't seem fair.

Stephen Hawking : It's fine. I've been on The Simpsons.

Sheldon Cooper : How do you deal with the success of your colleagues?

Stephen Hawking : I remind myself every scientific advancement is a victory. Also, I was on Star Trek.

The first meeting between Hawking and Cooper was pretty funny. Hawking couldn't make very much in the way of facial expressions, but you could tell he was having a good time [1].

[1] https://www.youtube.com/watch?v=wlrOKpQ6UBI

Impossible not to read this in "his" voice, in which he was so good at expressing this sort of wit.

Roger Penrose! If there’s anyone I could think of who deserves the prize, it would be him

I'm not a physicist but have been reading up on this topic (gravity, general relativity etc.,).

Could someone please ELI5 to me why hasn't Schwarzschild been awarded Nobel prize? I read that his work played a big role in discovery of Black Hole and the concept in general. Heck, his name even appears no less than 19 times in the Nobel Committee's article [1]!!

[1] https://www.nobelprize.org/uploads/2020/10/advanced-physicsp...

Nobels are not awarded posthumously, and he died in WWI.

On that subject, “Einstein’s War” is an interesting read on the interplay between WWI and the development of general relativity.

What a supreme loss to physics.

One could say, "his absence left a black hole?"

I'll see myself out.

At the time of Schwarzschild, black holes were only a purely theoretical concept. We only started to get evidence that they exist in the 80s and later.

Speaking of Karl Schwarzschild, here's an interesting tidbit that, in my experience, few non-German speakers know:

The literal translation of "Schwarzschild" (or "schwarzer Schild") to English would be "black shield". So him discovering the first black hole spacetime was certainly very appropriate! :)

(Similarly, I was very happy when I first heard about the Poynting vector [0] which, roughly speaking, indicates the direction in which an electromagnetic wave travels.)

[0] https://en.wikipedia.org/wiki/Poynting_vector

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.

Back in the day they each led research to detect irrefutable evidence of it. This isn't anything new and groundbreaking.

I think that's rather unfair. The measurements are still ongoing with ever-increasing accuracy. In 2018 they managed to record the closest approach of the star S2, measuring a velocity of 7000 km/s at its maximum. This was after mapping the full 16 year orbit. I know that Genzel is still actively researching this topic with his group, see e.g. https://www.mpe.mpg.de/7433286/news20200416

Ghez is very active. Both her group and Genzel's group are at the very leading edge.

I haven't found an updated GIF, but even when I first saw images like this around 2002, it was clear she was chasing something awesome.

https://www.physicscentral.com/explore/people/images/2008orb...

That is true, but the prize was awarded to Genzel for “for the __discovery__ of a supermassive compact object at the centre of our galaxy” (emphasis mine), not for the (impressive no doubt) follow-up work, so my comment was done in that context. That being said, I should have been a bit more enthusiastic about the infrared group's work to not appear dismissive on their ongoing contribution.

Fun fact: looks like we're both in MPE (although I left two years ago).

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 size. The only thing which is small enough and heavy enough is a black hole. Doing this required lots of advances in data analysis and adaptive optics to be able to measure the stars orbits to enough precision.

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

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!

The Penrose-Hawking singularity theorems go back 55 years to work starting in 1965. No joke. This has be to near a record in time lag between the work the Nobel committee recognized and when that work was first published. Better late than never I guess (but too late for Hawking, as has been mentioned elsewhere..) EDIT - a detailed analysis: https://physicstoday.scitation.org/do/10.1063/PT.5.2012/full...

I've always thought Nobel prizes are awarded based on the winners' works in that particular year so this came as huge surprise.

Too late for Hawking indeed, he could've very well been one of the winners today.

There's a huge backlog of people who deserve Nobel prizes. The committee is also conservative, and doesn't want to give out a prize for something that turns out to be wrong. Both factors mean that it takes years from discovery to the awarding of a Nobel prize.

It's one thing to allow enough time to pass before a given theory/experiment can be considered as "accepted" by science, and therefore eligible to the award.

However, the Nobel committee's rules can be considered archaic to a fault: 3 winners at most, all winners must be living at the time of the award.

If you want an egregious example of exclusion, look at the 2013 Nobel prize for the discovery of the Higgs boson. The prize was given to Higgs and Englert [0], but by any measure it should have been awarded to the five living scientists who made the discovery [1].

Was there really any reason to exclude Guralnik, Hagen and Kibble, who were all alive at the time of the award, other than a strict adherence to the "rule of three"?

[0]: https://web.archive.org/web/20131008193310/http://www.nobelp...

[1]: https://en.wikipedia.org/wiki/1964_PRL_symmetry_breaking_pap...

Even increasing it to 5 people wouldn't solve the problem. The Nobel prize could be awarded at the institution level rather than invidually but I'm sure there'll be objections to that as well.

The opposite, really. Nobel prizes are given out for major works which are now well-accepted. This can take decades, so typically the Nobel is given to now-old scientists as recognition for work done when they were young.

Made this cool video?

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

Penrose's contribution is reviewed in https://arxiv.org/abs/1410.5226

Why do they specify that two of them split only half of the prize, versus just that all three share it? Does anyone care _how much_ of a Nobel prize you have?

They are saying that RP's theoretical contributions are equal to the experimental contributions of the other two.

A Nobel Prize is about a million dollars cash.

Ah, they split the cash along those lines? I see.

Think of it as the price is shared between two discoveries, and for each discovery a certain number of people share that part.

Very much deserved, but why does it take so long to award this prize? Clearly they could have valued this research 20 years ago?

The black hole "observation" only happened a year or two ago, no?

The Nobel is awarded for actual experimental discoveries and validation of theories, not just unproven theoretical speculation.

Weinberg, Glashow, Salaam (1979) were theoreticians, but their theories for electroweak unification had been validated in many experiments during the 1970's, especially weak neutral currents at CERN in 1973.

Higgs & Englert (2013) had to wait for 50 years for their theory to be validated. The ATLAS & CMS experimentalists who discovered the Higgs particle were passed over, but they outnumbered them ~1,000:1, and only up to 3 people are allowed to get the prize in one year.

https://physicsworld.com/a/overlooked-for-a-nobel-the-cern-p...

https://www.theguardian.com/science/life-and-physics/2013/oc...

However, Rubbia & van der Meer (1984) got the prize for discovering the W and Z (ultimate proof of electroweak unification) on behalf of the large CERN SPS collaboration.

I read his book "the emperors new mind" in 1990, which is a fantastic book. It has a great section on computability.

Would Hawking have got it with them?

Not sure, he's most famous for work on black hole thermodynamics, not really about formation.

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 Telescope) can certainly not be seen as a proof of the existence of singularities, either.

Now the Nobel Prize committee says that the discovery is actually

> “for the discovery that black hole formation is a robust prediction of the general theory of relativity.”

But this has virtually nothing to do with the most famous piece of work by Penrose, i.e. the Singularity Theorems.

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.

At most three people can win, so they would have had to bump one of the three who did win.

Animation of the Stellar Orbits around the Sagittarius A* black hole (based on real data) https://www.youtube.com/watch?v=AZhUQl-wmq0

> Roger Penrose used ingenious mathematical methods in his proof that black holes are a direct consequence of Albert Einstein’s general theory of relativity.

Where can I learn more about these ingenious math models in a way that an adult can understand, but one that's been out of math for a while? Is there a good YouTube video?

I'm searching but it's coming up with many hour-long lectures by Roger Penrose that seem unrelated to the specifics of thise prize

You're looking for lectures on the Hawking-Penrose singularity theorems. I don't know if there are any videos about them, but at least knowing the name should help you search.

> an adult can understand, but one that's been out of math for a while?

That might not be possible. I remember struggling with the proofs of the singularity theorems, in the last year of my physics degree, after two semesters of differential geometry. Some of the things that people win the Nobel Prize for are genuinely hard.

The Large Scale Structure of Space-Time is the classic. However, it's the book that Hawking was referring to in his joke about every equation halving the sales.

Reminds me on Einstein getting the nobel for only a minor achievement, whilst his big one, the https://en.wikipedia.org/wiki/Penrose_interpretation is still waiting to be verified. A proper GUT finally.

https://www.nature.com/articles/s41567-020-1008-4

https://www.sciencemag.org/news/2020/09/one-quantum-physics-...

https://news.ycombinator.com/item?id=24401462

Can someone please provide the link to Roger Penrose’s ground breaking article about black hole.

https://arxiv.org/abs/1410.5226 is a good review.

Thank you, much!

Genuine question: Do they ever not give a nobel prize? Have there been years where no significant progress was made?

Since the start, in 1901, there are some years when the Nobel Prizes have not been awarded. The total number of times are 49. Most of them during World War I (1914-1918) and II (1939-1945). In the statutes of the Nobel Foundation it says: “If none of the works under consideration is found to be of the importance indicated in the first paragraph, the prize money shall be reserved until the following year. If, even then, the prize cannot be awarded, the amount shall be added to the Foundation’s restricted funds.”.

Physics: 1916, 1931, 1934, 1940, 1941, 1942

Chemistry: 1916, 1917, 1919, 1924, 1933, 1940, 1941, 1942

Medicine: 1915, 1916, 1917, 1918, 1921, 1925, 1940, 1941, 1942

Literature: 1914, 1918, 1935, 1940, 1941, 1942, 1943

Peace: 1914, 1915, 1916, 1918, 1923, 1924, 1928, 1932, 1939, 1940, 1941, 1942, 1943, 1948, 1955, 1956, 1966, 1967, 1972

https://www.nobelprize.org/prizes/facts/nobel-prize-facts/#:....

The science prizes are typically for work done decades previously that have stood the test of time.

How do we know our entire visible universe isn’t at the event horizon of a larger black hole?

> Einstein did not himself believe that black holes really exist

Wow.

Einstein did not believe in gravitational waves either.

He also famously added the cosmological constant because he didn't like the idea of an expanding universe.

Do you have a source for this? I thought they were a direct prediction of GR and this link says the same: https://www.ligo.caltech.edu/page/what-are-gw

You can read about it in Abraham Pais' scientific biography of Einstein, _Subtle is the Lord_.

I don't have a copy of that book, but the abstract of this paper from 1937, co-authored by Einstein, claims that gravitational waves are a prediction of GR: https://www.sciencedirect.com/science/article/abs/pii/S00160...

https://en.wikipedia.org/wiki/Sticky_bead_argument

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