Physics is Broken!!!

Last Thursday, an experiment reported that the magnetic properties of the muon, the electron’s middleweight cousin, are a tiny bit different from what particle physics equations say they should be. All around the world, the headlines screamed: PHYSICS IS BROKEN!!! And indeed, it’s been pretty shocking to physicists everywhere. For instance, my equations are working erratically; many of the calculations I tried this weekend came out upside-down or backwards. Even worse, my stove froze my coffee instead of heating it, I just barely prevented my car from floating out of my garage into the trees, and my desk clock broke and spilled time all over the floor. What a mess!

Broken, eh? When we say a coffee machine or a computer is broken, it means it doesn’t work. It’s unavailable until it’s fixed. When a glass is broken, it’s shattered into pieces. We need a new one. I know it’s cute to say that so-and-so’s video “broke the internet.” But aren’t we going a little too far now? Nothing’s broken about physics; it works just as well today as it did a month ago.

More reasonable headlines have suggested that “the laws of physics have been broken”. That’s better; I know what it means to break a law. (Though the metaphor is imperfect, since if I were to break a state law, I’d be punished, whereas if an object were to break a fundamental law of physics, that law would have to be revised!) But as is true in the legal system, not all physics laws, and not all violations of law, are equally significant.

What’s a physics law, anyway? Crudely, physics is a strategy for making predictions about the behavior of physical objects, based on a set of equations and a conceptual framework for using those equations. Sometimes we refer to the equations as laws; sometimes parts of the conceptual framework are referred to that way.

But that story has layers. Physics has an underlying conceptual foundation, which includes the pillar of quantum physics and its view of reality, and the pillar of Einstein’s relativity and its view of space and time. (There are other pillars too, such as those of statistical mechanics, but let me not complicate the story now.) That foundation supports many research areas of physics. Within particle physics itself, these two pillars are combined into a more detailed framework, with concepts and equations that go by the name of “quantum effective field theory” (“QEFT”). But QEFT is still very general; this framework can describe an enormous number of possible universes, most with completely different particles and forces from the ones we have in our own universe. We can start making predictions for real-world experiments only when we put the electron, the muon, the photon, and all the other familiar particles and forces into our equations, building up a specific example of a QEFT known as “The Standard Model of particle physics.”

All along the way there are equations and rules that you might call “laws.” They too come in layers. The Standard Model itself, as a specific QEFT, has few high-level laws: there are no principles telling us why quarks exist, why there is one type of photon rather than two, or why the weak nuclear force is so weak. The few laws it does have are mostly low-level, true of our universe but not essential to it.

I’m bringing attention to these layers because an experiment might cause a problem for one layer but not another. I think you could only fairly suggest that “physics is broken” if data were putting a foundational pillar of the entire field into question. And to say “the laws of physics have been violated”, emphasis on the word “the“, is a bit melodramatic if the only thing that’s been violated is a low-level, dispensable law.

Has physics, as a whole, ever broken? You could argue that Newton’s 17th century foundation, which underpinned the next two centuries of physics, broke at the turn of the 20th century. Just after 1900, Newton-style equations had to be replaced by equations of a substantially different type; the ways physicists used the equations changed, and the concepts, the language, and even the goals of physics changed. For instance, in Newtonian physics, you can predict the outcome of any experiment, at least in principle; in post-Newtonian quantum physics, you often can only predict the probability for one or another outcome, even in principle. And in Newtonian physics we all agree what time it is; in Einsteinian physics, different observers experience time differently and there is no universal clock that we all agree on. These were immense changes in the foundation of the field.

Conversely, you could also argue that physics didn’t break; it was just remodeled and expanded. No one who’d been studying steam engines or wind erosion or electrical circuit diagrams had to throw out their books and start again from scratch. In fact this “broken” Newtonian physics is still taught in physics classes, and many physicists and engineers never use anything else. If you’re studying the physics of weather, or building a bridge, Newtonian physics is just fine. The fact that Newton-style equations are an incomplete description of the world — that there are phenomena they can’t describe properly — doesn’t invalidate them when they’re applied within their wheelhouse.

No matter which argument you prefer, it’s hard to see how to justify the phrase “physics is broken” without a profound revolution that overthrows foundational concepts. It’s rare for a serious threat to foundations to arise suddenly, because few experiments can single-handedly put fundamental principles at risk. [The infamous case of the “faster-than-light neutrinos” provides an exception. Had that experiment been correct, it would have invalidated Einstein’s relativity principles. But few of us were surprised when a glaring error turned up.]

In the Standard Model, the electron, muon and tau particles (known as the “charged leptons”) are all identical except for their masses. (More fundamentally, they have different interactions with the Higgs field, from which their rest masses arise.) This almost-identity is sometimes stated as a “principle of lepton universality.” Oh, wow, a principle — a law! But here’s the thing. Some principles are enormously important; the principles of Einsteinian relativity determine how cause and effect work in our universe, and you can’t drop them without running into big paradoxes. Other principles are weak, and could easily be discarded without making a mess of any other part of physics. The principle of lepton universality is one of these. In fact, if you extend the Standard Model by adding new particles to its equations, it can be difficult to avoid ruining this fragile principle. [In a sense, the Higgs field has already violated the principle, but we don’t hold that against it.]

All the fuss is about a new experimental result which confirms an older one and slightly disagrees with the latest theoretical predictions, which are made using the Standard Model’s equations. What could be the cause of the discrepancy? One possibility is that it arises from a previously unknown difference between muons and electrons — from a violation of the principle of lepton universality. For those who live and breathe particle physics, breaking lepton universality would be a big deal; there’d be lots of adventure in trying to figure out which of the many possible extensions of the Standard Model could actually explain what broke this law. That’s why the scientists involved sound so excited.

But the failure of lepton universality wouldn’t come as a huge surprise. From certain points of view, the surprise is that the principle has survived this long! Since this low-level law is easily violated, its demise may not lead us to a profound new understanding of the world. It’s way too early for headlines that argue that what’s at stake is the existence of “forms of matter and energy vital to the nature and evolution of the cosmos.” No one can say how much is at stake; it might be a lot, or just a little.

In particular, there’s absolutely no evidence that physics is broken, or even that particle physics is broken. The pillars of physics and QEFT are not (yet) threatened. Even to say that “the Standard Model might be broken” seems a bit melodramatic to me. Does adding a new wing to a house require “breaking” the house? Typically you can still live in the place while it’s being extended. The Standard Model’s many successes suggest that it might survive largely intact as a recognizable part of a larger, more complete set of equations.

In any case, right now it’s still too early to say anything so loudly. The apparent discrepancy may not survive the heavy scrutiny it is coming under. There’s plenty of controversy about the theoretical prediction for muon magnetism; the required calculation is extraordinarily complex, elaborate and difficult.

So, from my perspective, the headlines of the past week are way over the top. The idea that a single measurement of the muon’s magnetism could “shake physics to its core“, as claimed in another headline I happened upon, is amusing at best. Physics, and its older subdisciplines, have over time become very difficult to break, or even shake. That’s the way it should be, when science is working properly. And that’s why we can safely base the modern global economy on scientific knowledge; it’s unlikely that a single surprise could instantly invalidate large chunks of its foundation.

Some readers may view the extreme, click-baiting headlines as harmless. Maybe I’m overly concerned about them. But don’t they implicitly suggest that one day we will suddenly find physics “upended”, and in need of a complete top-to-bottom overhaul? To imply physics can “break” so easily makes a mockery of science’s strengths, and obscures the process by which scientific knowledge is obtained. And how can it be good to claim “physics is broken” and “the laws of physics have been broken” over and over and over again, in stories that almost never merit that level of hype and eventually turn out to have been much ado about nada? The constant manufacturing of scientific crisis cannot possibly be lost on readers, who I suspect are becoming increasingly jaded. At some point readers may become as skeptical of science journalism, and the science it describes, as they are of advertising; it’s all lies, so caveat emptor. That’s not where we want our society to be. As we are seeing in spades during the current pandemic, there can be serious consequences when “TRUST IN SCIENCE IS BROKEN!!!

A final footnote: Ironically, the Standard Model itself poses one of the biggest threats to the framework of QEFT. The discovery of the Higgs boson and nothing else (so far) at the Large Hadron Collider poses a conceptual challenge — the “naturalness” problem. There’s no sharp paradox, which is why I can’t promise you that the framework of QEFT will someday break if it isn’t resolved. But the breakdown of lepton universality might someday help solve the naturalness problem, by requiring a more “natural” extension of the Standard Model, and thus might actually save QEFT instead of “breaking” it.

Has a New Force of Nature Been Discovered?

There have been dramatic articles in the news media suggesting that a Nobel Prize has essentially already been awarded for the amazing discovery of a “fifth force.” I thought I’d better throw some cold water on that fire; it’s fine for it to smoulder, but we shouldn’t let it overheat.

There could certainly be as-yet unknown forces waiting to be discovered — dozens of them, perhaps.   So far, there are four well-studied forces: gravity, electricity/magnetism, the strong nuclear force, and the weak nuclear force.  Moreover, scientists are already fully confident there is a fifth force, predicted but not yet measured, that is generated by the Higgs field. So the current story would really be about a sixth force.

Roughly speaking, any new force comes with at least one new particle.  That’s because

  • every force arises from a type of field (for instance, the electric force comes from the electromagnetic field, and the predicted Higgs force comes from the Higgs field)
  • and ripples in that type of field are a type of particle (for instance, a minimal ripple in the electromagnetic field is a photon — a particle of light — and a minimal ripple in the Higgs field is the particle known as the Higgs boson.)

The current excitement, such as it is, arises because someone claims to have evidence for a new particle, whose properties would imply a previously unknown force exists in nature.  The force itself has not been looked for, much less discovered.

The new particle, if it really exists, would have a rest mass about 34 times larger than that of an electron — about 1/50th of a proton’s rest mass. In technical terms that means its E=mc² energy is about 17 million electron volts (MeV), and that’s why physicists are referring to it as the X17.  But the question is whether the two experiments that find evidence for it are correct.

In the first experiment, whose results appeared in 2015, an experimental team mainly based in Debrecen, Hungary studied large numbers of nuclei of beryllium-8 atoms, which had been raised to an “excited state” (that is, with more energy than usual).  An excited nucleus inevitably disintegrates, and the experimenters studied the debris.  On rare occasions they observed electrons and positrons [a.k.a. anti-electrons], and these behaved in a surprising way, as though they were produced in the decay of a previously unknown particle.

In the newly reported experiment, whose results just appeared, the same team observed  the disintegration of excited nuclei of helium.  They again found evidence for what they hope is the X17, and therefore claim confirmation of their original experiments on beryllium.

When two qualitatively different experiments claim the same thing, they are less likely to be wrong, because it’s not likely that any mistakes in the two experiments would create fake evidence of the same type.  On the face of it, it does seem unlikely that both measurements, carried out on two different nuclei, could fake an X17 particle.

However, we should remain cautious, because both experiments were carried out by the same scientists. They, of course, are hoping for their Nobel Prize (which, if their experiments are correct, they will surely win) and it’s possible they could suffer from unconscious bias. It’s very common for individual scientists to see what they want to see; scientists are human, and hidden biases can lead even the best scientists astray.  Only collectively, through the process of checking, reproducing, and using each other’s work, do scientists create trustworthy knowledge.

So it is prudent to await efforts by other groups of experimenters to search for this proposed X17 particle.  If the X17 is observed by other experiments, then we’ll become confident that it’s real. But we probably won’t know until then.  I don’t currently know whether the wait will be months or a few years.

Why I am so skeptical? There are two distinct reasons.

First, there’s a conceptual, mathematical issue. It’s not easy to construct reasonable equations that allow the X17 to co-exist with all of the known types of elementary particles. That it has a smaller mass than a proton is not a problem per se.  But the X17 needs to have some unique and odd properties in order to (1)  be seen in these experiments, yet (2) not be seen in certain other previous experiments, some of which were explicitly looking for something similar.   To make equations that are consistent with these properties requires some complicated and not entirely plausible trickery.  Is it impossible? No.  But a number of the methods that scientists suggested were flawed, and the ones that remain are, to my eye, a bit contrived.

Of course, physics is an experimental science, and what theorists like me think doesn’t, in the end, matter.  If the experiments are confirmed, theorists will accept the facts and try to understand why something that seems so strange might be true.  But we’ve learned an enormous amount from mathematical thinking about nature in the last century — for instance, it was math that told us that the Higgs particle couldn’t be heavier than 1000 protons, and it was on the basis of that `advice’ that the Large Hadron Collider was built to look for it (and it found it, in 2012.) Similar math led to the discoveries of the W and Z particles roughly where they were expected. So when the math tells you the X17 story doesn’t look good, it’s not reason enough for giving up, but it is reason for some pessimism.

Second, there are many cautionary tales in experimental physics. For instance, back in 2003 there were claims of evidence of a particle called a pentaquark with a rest mass about 1.6 times a proton’s mass — an exotic particle, made from quarks and gluons, that’s both like and unlike a proton.  Its existence was confirmed by multiple experimental groups!  Others, however, didn’t see it. It took several years for the community to come to the conclusion that this pentaquark, which looked quite promising initially, did not in fact exist.

The point is that mistakes do get made in particle hunts, sometimes in multiple experiments, and it can take some time to track them down. It’s far too early to talk about Nobel Prizes.

[Note that the Higgs boson’s discovery was accepted more quickly than most.  It was discovered simultaneously by two distinct experiments using two methods each, and confirmed by additional methods and in larger data sets soon thereafter.  Furthermore,  there were already straightforward equations that happily accommodated it, so it was much more plausible than the X17.] 

And just for fun, here’s a third reason I’m skeptical. It has to do with the number 17. I mean, come on, guys, seriously — 17 million electron volts? This just isn’t auspicious.  Back when I was a student, in the late 1980s and early 90s, there was a set of experiments, by a well-regarded experimentalist, which showed considerable evidence for an additional neutrino with a E=mc² energy of 17 thousand electron volts. Other experiments tried to find it, but couldn’t. Yet no one could find a mistake in the experimenter’s apparatus or technique, and he had good arguments that the competing experiments had their own problems. Well, after several years, the original experimenter discovered that there was a piece of his equipment which unexpectedly could absorb about 17 keV of energy, faking a neutrino signal. It was a very subtle problem, and most people didn’t fault him since no one else had thought of it either. But that was the end of the 17 keV neutrino, and with it went hundreds of research papers by both experimental and theoretical physicists, along with one scientist’s dreams of a place in history.

In short, history is cruel to most scientists who claim important discoveries, and teaches us to be skeptical and patient. If there is a fifth sixth force, we’ll know within a few years. Don’t expect to be sure anytime soon. The knowledge cycle in science runs much, much slower than the twittery news cycle, and that’s no accident; if you want to avoid serious errors that could confuse you for a long time to come, don’t rush to judgment.

The New York Times Remembers A Great Physicist

The untimely and sudden deaths of Steve Gubser and Ann Nelson, two of the United States’ greatest talents in the theoretical physics of particles, fields and strings, has cast a pall over my summer and that of many of my colleagues.

I have not been finding it easy to write a proper memorial post for Ann, who was by turns my teacher, mentor, co-author, and faculty colleague.  I would hope to convey to those who never met her what an extraordinary scientist and person she was, but my spotty memory banks aren’t helping. Eventually I’ll get it done, I’m sure.

(Meanwhile I am afraid I cannot write something similar for Steve, as I really didn’t know him all that well. I hope someone who knew him better will write about his astonishing capabilities and his unique personality, and I’d be more than happy to link to it from here.)

In this context, I’m gratified to see that the New York Times has given Ann a substantive obituary, https://www.nytimes.com/2019/08/26/science/ann-nelson-dies.html, and appearing in the August 28th print edition, I’m told. It contains a striking (but, to those of us who knew her, not surprising) quotation from Howard Georgi.  Georgi is a professor at Harvard who is justifiably famous as the co-inventor, with Nobel-winner Sheldon Glashow, of Grand Unified Theories (in which the electromagnetic, weak nuclear, and strong nuclear force all emerge from a single force.) He describes Ann, his former student, as being able to best him at his own game.

  • “I have had many fabulous students who are better than I am at many things. Ann was the only student I ever had who was better than I am at what I do best, and I learned more from her than she learned from me.”

He’s being a little modest, perhaps. But not much. There’s no question that Ann was an all-star.

And for that reason, I do have to complain about one thing in the Times obituary. It says “Dr. Nelson stood out in the world of physics not only because she was a woman, but also because of her brilliance.”

Really, NYTimes, really?!?

Any scientist who knew Ann would have said this instead: that Professor Nelson stood out in the world of physics for exceptional brilliance — lightning-fast, sharp, creative and careful, in the same league as humanity’s finest thinkers — and for remarkable character — kind, thoughtful, even-keeled, rigorous, funny, quirky, dogged, supportive, generous. Like most of us, Professor Nelson had a gender, too, which was female. There are dozens of female theoretical physicists in the United States; they are a too-small minority, but they aren’t rare. By contrast, a physicist and person like Ann Nelson, of any gender? They are extremely few in number across the entire planet, and they certainly do stand out.

But with that off my chest, I have no other complaints. (Well, admittedly the physics in the obit is rather garbled, but we can get that straight another time.) Mainly I am grateful that the Times gave Ann fitting public recognition, something that she did not actively seek in life. Her death is an enormous loss for theoretical physics, for many theoretical physicists, and of course for many other people. I join all my colleagues in extending my condolences to her husband, our friend and colleague David B. Kaplan, and to the rest of her family.

A Catastrophic Weekend for Theoretical High Energy Physics

It is beyond belief that not only am I again writing a post about the premature death of a colleague whom I have known for decades, but that I am doing it about two of them.

Over the past weekend, two of the world’s most influential and brilliant theoretical high-energy physicists — Steve Gubser of Princeton University and Ann Nelson of the University of Washington — fell to their deaths in separate mountain accidents, one in the Alps and one in the Cascades.

Theoretical high energy physics is a small community, and within the United States itself the community is tiny.  Ann and Steve were both justifiably famous and highly respected as exceptionally bright lights in their areas of research. Even for those who had not met them personally, this is a stunning and irreplaceable loss of talent and of knowledge.

But most of us did know them personally.  For me, and for others with a personal connection to them, the news is devastating and tragic. I encountered Steve when he was a student and I was a postdoc in the Princeton area, and later helped bring him into a social group where he met his future wife (a great scientist in her own right, and a friend of mine going back decades).  As for Ann, she was one of my teachers at Stanford in graduate school, then my senior colleague on four long scientific papers, and then my colleague (along with her husband David B. Kaplan) for five years at the University of Washington, where she had the office next to mine. I cannot express what a privilege it always was to work with her, learn from her, and laugh with her.

I don’t have the heart or energy right now to write more about this, but I will try to do so at a later time. Right now I join their spouses and families, and my colleagues, in mourning.

A Ring of Controversy Around a Black Hole Photo

[Note Added: Thanks to some great comments I’ve received, I’m continuing to add clarifying remarks to this post.  You’ll find them in green.]

It’s been a couple of months since the `photo’ (a false-color image created to show the intensity of radio waves, not visible light) of the black hole at the center of the galaxy M87, taken by the Event Horizon Telescope (EHT) collaboration, was made public. Before it was shown, I wrote an introductory post explaining what the ‘photo’ is and isn’t. There I cautioned readers that I thought it might be difficult to interpret the image, and controversies about it might erupt.EHTDiscoveryM87

So far, the claim that the image shows the vicinity of M87’s black hole (which I’ll call `M87bh’ for short) has not been challenged, and I’m not expecting it to be. But what and where exactly is the material that is emitting the radio waves and thus creating the glow in the image? And what exactly determines the size of the dark region at the center of the image? These have been problematic issues from the beginning, but discussion is starting to heat up. And it’s important: it has implications for the measurement of the black hole’s mass (which EHT claims is that of 6.5 billion Suns, with an uncertainty of about 15%), and for any attempt to estimate its rotation rate. Continue reading

The Black Hole `Photo’: Seeing More Clearly

THIS POST CONTAINS ERRORS CONCERNING THE EXISTENCE AND VISIBILITY OF THE SO-CALLED PHOTON-SPHERE AND SHADOW; THESE ERRORS WERE COMMON TO ESSENTIALLY ALL REPORTING ON THE BLACK HOLE ‘PHOTO’.  IT HAS BEEN SUPERSEDED BY THIS POST, WHICH CORRECTS THESE ERRORS AND EXPLAINS THE SITUATION.

Ok, after yesterday’s post, in which I told you what I still didn’t understand about the Event Horizon Telescope (EHT) black hole image (see also the pre-photo blog post in which I explained pedagogically what the image was likely to show and why), today I can tell you that quite a few of the gaps in my understanding are filling in (thanks mainly to conversations with Harvard postdoc Alex Lupsasca and science journalist Davide Castelvecchi, and to direct answers from professor Heino Falcke, who leads the Event Horizon Telescope Science Council and co-wrote a founding paper in this subject).  And I can give you an update to yesterday’s very tentative figure.

First: a very important point, to which I will return in a future post, is that as I suspected, it’s not at all clear what the EHT image really shows.   More precisely, assuming Einstein’s theory of gravity is correct in this context:

  • The image itself clearly shows a black hole’s quasi-silhouette (called a `shadow’ in expert jargon) and its bright photon-sphere where photons [particles of light — of all electromagnetic waves, including radio waves] can be gathered and focused.
  • However, all the light (including the observed radio waves) coming from the photon-sphere was emitted from material well outside the photon-sphere; and the image itself does not tell you where that material is located.  (To quote Falcke: this is `a blessing and a curse’; insensitivity to the illumination source makes it easy to interpret the black hole’s role in the image but hard to learn much about the material near the black hole.) It’s a bit analogous to seeing a brightly shining metal ball while not being able to see what it’s being lit by… except that the photon-sphere isn’t an object.  It’s just a result of the play of the light [well, radio waves] directed by the bending effects of gravity.  More on that in a future post.
  • When you see a picture of an accretion disk and jets drawn to illustrate where the radio waves may come from, keep in mind that it involves additional assumptions — educated assumptions that combine many other measurements of M87’s black hole with simulations of matter, gravity and magnetic fields interacting near a black hole.  But we should be cautious: perhaps not all the assumptions are right.  The image shows no conflicts with those assumptions, but neither does it confirm them on its own.

Just to indicate the importance of these assumptions, let me highlight a remark made at the press conference that the black hole is rotating quickly, clockwise from our perspective.  But (as the EHT papers state) if one doesn’t make some of the above-mentioned assumptions, one cannot conclude from the image alone that the black hole is actually rotating.  The interplay of these assumptions is something I’m still trying to get straight.

Second, if you buy all the assumptions, then the picture I drew in yesterday’s post is mostly correct except (a) the jets are far too narrow, and shown overly disconnected from the disk, and (b) they are slightly mis-oriented relative to the orientation of the image.  Below is an improved version of this picture, probably still not the final one.  The new features: the jets (now pointing in the right directions relative to the photo) are fatter and not entirely disconnected from the accretion disk.  This is important because the dominant source of illumination of the photon-sphere might come from the region where the disk and jets meet.

My3rdGuessBHPhoto.png

Updated version of yesterday’s figure: main changes are the increased width and more accurate orientation of the jets.  Working backwards: the EHT image (lower right) is interpreted, using mainly Einstein’s theory of gravity, as (upper right) a thin photon-sphere of focused light surrounding a dark patch created by the gravity of the black hole, with a little bit of additional illumination from somewhere.  The dark patch is 2.5 – 5 times larger than the event horizon of the black hole, depending on how fast the black hole is rotating; but the image itself does not tell you how the photon-sphere is illuminated or whether the black hole is rotating.  Using further assumptions, based on previous measurements of various types and computer simulations of material, gravity and magnetic fields, a picture of the black hole’s vicinity (upper left) can be inferred by the experts. It consists of a fat but tenuous accretion disk of material, almost face-on, some of which is funneled into jets, one heading almost toward us, the other in the opposite direction.  The material surrounds but is somewhat separated from a rotating black hole’s event horizon.  At this radio frequency, the jets and disk are too dim in radio waves to see in the image; only at (and perhaps close to) the photon-sphere, where some of the radio waves are collected and focused, are they bright enough to be easily discerned by the Event Horizon Telescope.

 

The Black Hole `Photo’: What Are We Looking At?

The short answer: I’m really not sure yet.  [This post is now largely superseded by the next one, in which some of the questions raised below have now been answered.]  EVEN THAT POST WAS WRONG ABOUT THE PHOTON-SPHERE AND SHADOW.  SEE THIS POST FROM JUNE 2019 FOR SOME ESSENTIAL CORRECTIONS THAT WERE LEFT OUT OF ALL REPORTING ON THIS SUBJECT.

Neither are some of my colleagues who know more about the black hole geometry than I do. And at this point we still haven’t figured out what the Event Horizon Telescope experts do and don’t know about this question… or whether they agree amongst themselves.

[Note added: last week, a number of people pointed me to a very nice video by Veritasium illustrating some of the features of black holes, accretion disks and the warping of their appearance by the gravity of the black hole.  However, Veritasium’s video illustrates a non-rotating black hole with a thin accretion disk that is edge-on from our perspective; and this is definitely NOT what we are seeing!]

As I emphasized in my pre-photo blog post (in which I described carefully what we were likely to be shown, and the subtleties involved), this is not a simple photograph of what’s `actually there.’ We all agree that what we’re looking at is light from some glowing material around the solar-system-sized black hole at the heart of the galaxy M87.  But that light has been wildly bent on its path toward Earth, and so — just like a room seen through an old, warped window, and a dirty one at that — it’s not simple to interpret what we’re actually seeing. Where, exactly, is the material `in truth’, such that its light appears where it does in the image? Interpretation of the image is potentially ambiguous, and certainly not obvious. Continue reading

A Black Day (and a Happy One) In Scientific History

Wow.

Twenty years ago, astronomers Heino Falcke, Fulvio Melia and Eric Agol (a former colleague of mine at the University of Washington) pointed out that the black hole at the center of our galaxy, the Milky Way, was probably big enough to be observed — not with a usual camera using visible light, but using radio waves and clever techniques known as “interferometry”.  Soon it was pointed out that the black hole in M87, further but larger, could also be observed.  [How? I explained this yesterday in this post.]   

And today, an image of the latter, looking quite similar to what we expected, was presented to humanity.  Just as with the discovery of the Higgs boson, and with LIGO’s first discovery of gravitational waves, nature, captured by the hard work of an international group of many scientists, gives us something definitive, uncontroversial, and spectacularly in line with expectations.

EHTDiscoveryM87.png

An image of the dead center of the huge galaxy M87, showing a glowing ring of radio waves from a disk of rapidly rotating gas, and the dark quasi-silhouette of a solar-system-sized black hole.  Congratulations to the Event Horizon Telescope team

I’ll have more to say about this later [have to do non-physics work today 😦 ] and in particular about the frustration of not finding any helpful big surprises during this great decade of fundamental science — but for now, let’s just enjoy this incredible image for what it is, and congratulate those who proposed this effort and those who carried it out.