Wednesday, March 28, 2018

Why Black Stars Aren’t A Thing.

Not a black star,
but about equally real.
I came to physics by accident. I had studied mathematics, but the math department was broke. When I asked the mathematicians for a job, they sent me to the other side of the building. “Ask the physicists,” they said.

The physicists didn’t only give me a job. They also gave me a desk, a computer, and before I knew I had a topic for a diploma thesis. I was supposed to show that black holes don’t exist.

I didn’t know at that time, but it was my supervisor’s shtik, the black-holes-don’t-exist-speech. Prof Dr Dr hc mult Walter Greiner, who passed away two years ago, was the department head when I arrived. His argument against black holes was that “God wouldn’t separate himself from part of the universe.” Yo. He mostly worked on heavy ion physics.

I had made pretty clear to him that I wasn’t interested in heavy ion physics. Really I wasn’t sure I wanted to graduate in physics at all; it wasn’t even my major. But I was the math person, so certainly I could prove that black hole’s weren’t, no?

It was either that or computer simulations of big nuclei or back to the broke mathematicians. I picked the black holes.

That was 1997. Back then, measurements of the motion of stars around Sag A* were running, but they would not be published until 1998. And even after Sag A* proved to be dark, small, and heavy enough so that it should be a black hole, it took ten more years to demonstrate that indeed it doesn’t have hard surface, thus providing evidence for a black hole horizon.

We now know that Sag A* is a supermassive black hole, and that such black holes are commonly found in galactic centers. But when I was a student the case was not settled.

Greiner had explained to me why he thought black holes cannot form in stellar collapse. Because we know that black holes emit radiation, the famous “Hawking radiation.” So, when a star collapses it begins emitting all this radiation and it loses mass and the horizon never forms. That was his great idea. Ingenious! Why had no one thought of this before?

After some months digging in the literature, it became clear to me that it had been tried before. Not once, but several times, and equally many times it had been shown not to work. This was laid out in various publications, notably in Birrell and Davies’ textbook, but Greiner’s interest in the topic didn’t go far enough to look at this. Indeed, I soon found out that I wasn’t the first he had put on the topic, I was the third. The first delivered a wrong proof (and passed), the second left. Neither option seemed charming.

Black hole with accretion disk
and jet. Artist's impression.
[Image Source]
The argument for why Greiner’s idea doesn’t work is a shitload of math, but it comes down to a very physical reason: You can’t use Hawking radiation to prevent black holes from forming because that’s in conflict with the equivalence principle.

The equivalence principle is the main tenet of general relativity. It says that a freely falling observer should not be able to tell the presence of a gravitational field using only data from their vicinity, or “locally” as the terminology has it.

Hawking radiation obeys the equivalence principle – as it should. This means most importantly that an observer falling through the black hole horizon does not notice any radiation (or anything else that would indicate the presence of the horizon). The radiation is there, but its wavelengths are so long – of the size of the horizon itself – that the observer cannot measure the radiation locally.

If you want to know how Hawking-radiation affects the black hole you must calculate the total energy and pressure which the quantum effects creates. These are collected in what’s called the (renormalized) stress-energy-tensor. Turns out it’s tiny at the black hole horizon, and the larger the black hole, the smaller it is.

All of this is perfectly compatible with the equivalence principle. And that’s really all you need to know to conclude you can’t prevent the formation of black holes by Hawking-radiation: The contribution to the energy-density from the quantum effects is far too small, and it must be small because else an infalling observer would notice it, screwing over the equivalence principle.

What normally goes wrong when people argue that Hawking-radiation can prevent the formation of black hole horizons is that they use the result for the Hawking radiation which a distant observer would measure. Then they trace back this radiation’s energy to the black hole horizon. The result is infinitely large. That’s because if you want to emit anything at the horizon that can escape at all, you must give it an infinite amount of energy to start with. This is nonsense because Hawking radiation is not created at the black hole horizon. But it’s this infinity that has led many people to conclude that a collapsing star may be able to shed all of its energy in Hawking radiation.

But whenever you do physics and the math gives you an infinity, you should look for a mistake. Nothing physically real can be infinite. And indeed, the infinity which you get here cannot be observed. It is is cancelled by another contribution to the stress-energy which comes from the vacuum polarization. Collect all terms and you conclude, again, that the effects at the horizon are tiny. Done correctly, they do, of course, obey the equivalence principle.

In summary: Yes, black holes evaporate. But no, the energy-loss cannot prevent the formation of black hole horizons.

That was the status already in the late 1970s. Walter Greiner wasn’t the first but also not the last to try using quantum effects to get rid of the black hole horizon. I come across one or the other variation of it several times a year. Most recently it was via a piece on Science Daily, which also appeared PhysOrg, Science Alert, Gizmodo, BigThink, and eventually also Scientific American, where we read:
Black Hole Pretenders Could Really Be Bizarre Quantum Stars

New research reveals a possible mechanism allowing “black stars” and “gravastars” to exist

These articles go back to a press release from SISSA about a paper by Raúl Carballo-Rubio which was recently published in PRL (arXiv version here).

Carballo-Rubio doesn’t actually claim that black holes don’t form; instead he claims – more modestly – that “there exist new stellar configurations, and that these can be described in a surprisingly simple manner.”

These new stellar configurations, so his idea, are stabilized by strong quantum effects in a regime where general relativity alone predicts there should be nothing to prevent the collapse of matter. These “black stars” do not actually have a horizon, so the quantum effects never actually become infinitely large. But since the pressure from the quantum effects would get infinitely large if the mass were compressed into the horizon, the radius at which it stabilizes must be outside the horizon.

In other words, what stabilizes these black stars is the same effect that Greiner thought prevents black holes from forming. You can tell immediately it’s in conflict with the equivalence principle for there is nothing locally there, at the horizon or close by it, from which the matter would know when to stop collapsing. At horizon formation, the density of matter can be arbitrarily low, and the matter doesn’t know – cannot know! – anything about redshift from there to infinity. The only way this matter can know that something is supposed to happen is by using global information, ie by violating the equivalence principle.

Indeed that’s what Carballo-Rubio does, though the paper doesn’t really spell out where this assumption comes in, so let me tell you: Carballo-Rubio assumes from the onset that the system is static. This means the “quantum star” has no time-dependence whatsoever.

This absence of time-dependence is an absolutely crucial point that you are likely to miss if you don’t know what to look for, so let me emphasize: No stellar object can be truly static because this means it must have existed forever and will continue to exist for all eternity. A realistic stellar object must have formed somewhen. Static solutions do not exist other than as math.

The assumption that the system be static is hence a global assumption. It is not something that you can reach approximately, say, at the end of a collapse. Concretely the way this enters the calculation is by choice of the vacuum state.

Yes, that’s right. There isn’t only one vacuum state. There are infinitely many. And you can pick one. So which one do you pick?

Before we get there, allow me a digression. I promise it will make sense in a minute. Do you recall when Walter Wagner sued CERN because turning on the LHC might create tiny black holes that eat up earth?

It is rare for black hole physics to become a matter of lawsuits. Scientists whose research rarely attracts any attention were suddenly in the position of having to explain why these black holes, once created, would be harmless.

On the face of it, it’s not a difficult argument. These things would have interaction-probabilities far smaller than even neutrinos. They would readily pass through matter, leaving no trace. And being created in highly-energetic collisions, they’d be speedy, fly off to outer space and be gone.

But then, these tiny black holes would have a small but nonzero probability to become trapped in Earth’s gravitational field. They would then keep oscillating around the center of the planet. And if they stuck around for sufficiently long, and there were sufficiently many of them, they could grow and eventually eat up Earth inside-out. Not good.

That, however, the scientists argued, could not happen because these tiny black holes evaporate in a fraction of a second. If you believe they evaporate. And suddenly theoretical physicists had to very publicly explain why they are so sure black holes evaporate because otherwise the LHC might not be turned on and their experimentalist friends would never forgive them.

Rather unsurprisingly, there had been one-two people who had written papers about why black holes don’t evaporate. Luckily, these claims were easy to debunk. The court dismissed the lawsuit. The LHC turned on, no black holes were created, and everyone lived happily ever after.

For me the most remarkable part of this story isn’t that someone would go try to sue CERN over maybe destroying the world. Actually I have some understanding for that. Much more remarkable is that I am pretty sure everyone in the field knows it’s easy enough to find a theoretical reason for why black holes wouldn’t evaporate. All you have to do is postulate they don’t. This postulate is physical nonsense, as I will explain in a moment, so it would merely have complicated the case without altering the conclusion. Still I think it’s interesting no one even brought it up. Humm-humm.

So what’s that nonsense postulate that can keep black holes from evaporating? You choose a vacuum state in which they don’t. Yes, you can do that. Perfectly possible. It’s called the “Boulware state.” The price you pay for this, however, is that the energy created by quantum effects at the black hole horizon goes to infinity. So it’s an unphysical choice and no one ever makes it.

Ah! I hear you say. But not very loudly, so let me summarize this in plain terms.

You can assume a black hole doesn’t evaporate on the expense of getting an infinite amount of stress-energy in the horizon region. That’s an unphysical assumption. And it’s the same assumption as postulating the system does not change in time: Nothing in, nothing out.

And that – to tie together the loose ends – is exactly what Carballo-Rubio did. He doesn’t actually have a horizon, but he uses the same unphysical vacuum-state, the Boulware state. That’s the reason he gets such a large quantum pressure, hence violating the equivalence principle. It comes from the assumption that the system is static, has always been static, and will always remain static.

Let me be clear that Carballo-Rubio’s paper is (for all I can tell) mathematically sound. And the press-release is very carefully phrased and accurate. But I think he should have been clearer in pointing out that the assumption about time-independence is global and therefore he is describing a physically impossible situation that is not even approximately realistic.

If you followed my above elaborations, it should be clear that the details don’t matter all that much. The only way you can prevent a horizon from forming is to violate the equivalence principle. And worse, this violation must be possible when space-time curvature is arbitrarily small, as small or even smaller than what we have here on Earth.

Of course you can postulate whatever you want and calculate something. But please let us be clear that all these black stars and gravastars and quantum stars  and what have you require throwing out general relativity in regions where there is no local measure whatsoever that would call for such a breakdown. Doesn’t matter how much math you pour over it, it’s still in conflict with what we know about gravity.

The realistic situation is one in which matter collapses under its gravitational pull. In this case you have a different vacuum state (the Unruh state), which allows for evaporation. And that brings you full circle to the above argument for why the stress-energy is too small to prevent horizon formation. There’s no way to avoid the formation of a black hole. Nope, there isn’t. Black holes really exist.

As to my diploma. I simply wrote my thesis about something else but didn’t mention that until after the fact. I think Greiner never forgave me. A few years later he fired me, alas, unsuccessfully. But that’s a different story and shall be told another time.

That was a long post, I know. But I hope it explains why I think black stars and gravastars and qantum stars and so on are nonsense. And why I happen to know more about the topic than I ever wanted to know.

Monday, March 26, 2018

Modified Gravity and the Radial Acceleration Relation, Again

Have I recently mentioned that I am now proud owner of my personal modified gravity theory? I have called it “Covariant Emergent Gravity.” Though frankly I’m not sure what’s emergent about it; the word came down the family tree of theories from Erik Verlinde’s paper. Maybe I had better named it Gravity McGravace, which is about equally descriptive.

It was an accident I even wrote a paper about this. I was supposed to be working on something entirely different – an FQXi project on space-time defects – and thought that maybe Verlinde’s long-range entanglement might make for non-local links. It didn’t. But papers must be written, so I typed up my notes on how to blend Verlinde’s idea together with good, old, general relativity.

Then I tried to forget about the whole thing. Because really there are enough models of modified gravity already. Also, I’m too fucking original to clean up somebody else’s math. Besides, every time I hear the name “Verlinde” it reminds me that I once confused Erik Verlinde with his brother Herman, even though I perfectly know they’re identical twins. It’s a memory I’d rather leave buried in the depths of my prefrontal cortex.

But next thing I know I have a student who wants to work on modified gravity. He’s a smart young man. Indeed, I now think he is a genius. See, while I kept blathering about the awesomeness of McGaugh et al’s recent data on the radial acceleration relation, he had the brilliant idea of plotting the prediction from my model over the data.
Figure 1 from arXiv:1803.08683

Eh, I thought, look at this. (Deep thoughts are overrated.)

The blue squares in this figure are the data points from the McGaugh et al paper. The data come from galactic rotation curves of 156 galaxies, spanning several orders of magnitude. The horizontal axis (gB) shows the acceleration that you would expect from the “normal” (baryonic) mass. The vertical axis (gtot) shows the actually observed (total) acceleration. The black dotted line is normal gravity without dark matter. The red curve is the prediction from my model; 1σ-error in pink. For details, see paper.

As the data show, the observed acceleration is higher than what the normal (Newtonian limit of ) general relativity predicts, especially at low accelerations. Physicists usually chalk this mismatch up to dark matter. But we have known for some decades that Milgrom’s Modified Newtonian Dynamics (MOND) does a better job explaining the regularity of this relation, in the sense that MOND requires less fumbling to fit the data.

However, while MOND does a good job explaining the observations, it has the unappealing property of requiring an “interpolation function”. This function is necessary to get a smooth transition from the regime in which gravity is modified (at low acceleration) to the normal gravity regime, which must be reproduced at high acceleration to fit observations in the solar system. In the literature one can find various choices for this interpolation function.

Besides the function, MOND also has a free constant that is the acceleration scale at which the transition happens. At accelerations below this scale, MOND effects become relevant. Turns out this constant is to good approximation the square root of the cosmological constant. No one really knows why that is so, but a few people have put forward ideas where this relation might come from. One of them is Erik Verlinde.

Verlinde extracts the value of this constant from the size of the cosmological horizon. Something about an insertion of mass into de-Sitter space changing the volume entropy and giving rise to a displacement vector that has something to do with the Newtonian potential. Among us, I think this is nonsense. But then, what do I know. Maybe Verlinde is the next Einstein and I’m just too dumb to understand his great revelations. And in any case, his argument fixes the free constant.

Then my student convinced me that if you buy what I wrote in my last year’s paper, Covariant Emergent Gravity doesn’t need an interpolation function. Instead, it gives rise to a particular interpolation function. So then, we were left with a particular function without free parameters.

If you have never worked in theory-development, you have no idea how hair-raisingly terrible a no-parameter model is. It either fits or it doesn’t. There’s no space for fudging here. It’s all or nothing, win or lose.

We plotted, we won. Or rather, Verlinde won. It’s our function with his parameter that you see plotted in the above figure. Fits straight onto the data.

I’m not sure what to make out of this. The derivation is so ridiculously simple that Kindergarten math will do it. I’m almost annoyed I didn’t have to spend some weeks cracking non-linear partial differential equations because then at least I’d feel like I did something. Now I feel like the proverbial blind chick that found a grain.

But well, as scientists like to say, more work is needed. We’re still scratching our heads over the gravitational lensing. Also the relation to Khoury et al’s superfluid approach has remained murky.

So stay tuned, more is to come.

Tuesday, March 20, 2018

Hawking’s “Final Theory” is not groundbreaking

Yesterday, the media buzzed with the revelation that Stephen Hawking had completed a paper two weeks before his death. This paper supposedly contains some breathtaking insight.

The headlines refer to a paper titled “A Smooth Exit from Eternal Inflation” in collaboration with Thomas Hertog. The paper was originally uploaded to the arXiv in July last year, but it was updated two weeks ago. It is under review with “a leading journal” which I suspect but do not know is Physical Review D. Thomas Hertog gave a talk about this at the conference which I attended last summerYou can watch the video of Hertog’s talk here.

According to The Independent the paper contains “a theory explaining how we might detect parallel universes and a prediction for the end of the world.” Furthermore, we learn, “Hawking also theorised in his final work that scientists could find alternate universes using probes on space ships, allowing humans to form an even better understanding of our own universe, what else is out there and our place in the cosmos.”

In the Sunday Times you can read that the paper “shows how we might find other universes”  and in The Telegraph you find a quote by Carlos Frenk, professor of cosmology at Durham University who said: “The intriguing idea in Hawking’s paper is that [the multiverse] left its imprint on the background radiation permeating our universe and we could measure it with a detector on a spaceship.”

Since the paper doesn’t say anything about detecting parallel universes, I was originally confused whether the headlines were referring to another paper. But no, Thomas Hertog confirmed to me that the paper in question is indeed the paper that is on the arXiv. There is no other paper.

So what does the paper say?

The paper is based on an old idea by Stephen Hawking and Jim Hartle called the “no-boundary” proposal. In the paper, the authors employ a new method to do calculations that were not previously possible. Specifically, they calculate which type of universes a multiverse would contain if this theory was correct. The main conclusion seems to be that our universe is compatible with the idea, and also that this particular multiverse which they deal with is not as large as the usual multiverse one gets from eternal inflation.

It’s not entirely uninteresting if you are into multiverse ideas, because then you need this information to calculate the probability of our universe. But it is also a very theoretical paper that does not say anything about observational consequences.

The only thing that the paper does say is that inflation took place. And inflation predicts that gravitational waves produced in the early universe should leave an imprint in the cosmic microwave background (CMB). This is the CMB polarization signal that BICEP was looking for but didn’t find. There are, however, some satellite missions in the planning that will look for it with better precision.

So how do we detect parallel universes? By detecting the CMB polarization. I do not kid you.

Here’s what Hertog said about this:
“This model predicts that our universe came into existence with a burst of rapid expansion called cosmic inflation. A big bang of this kind amplifies gravitational waves which in turn show up in satellite images of [the pattern of temperature fluctuations in] the cosmic microwave background. Future satellite missions should see this, if the theory is correct.

Observational evidence for the no-boundary model [in the form of gravitational waves from the big bang] would yield strong evidence for a multiverse. This paper provides a step towards a mathematically sound and testable model of the multiverse. That constitutes a significant extension of our notion of physical reality.

Some cosmologists have argued against the multiverse on the basis it can’t be tested. However our model shows that observations in our own universe can provide strong evidence for the existence of other universes. ”
Allow me put this into perspective.

Theoretical physicist have proposed some thousand ideas for what might have happened in the early universe. There are big bangs and big bounces and brane collisions and string cosmologies and loop cosmologies and all kinds of weird fields that might or might not have done this or that. All of this is pure speculation, none of it is supported by evidence. The Hartle-Hawking proposal is one of these speculations.

The vast majority of these ideas contain a phase of inflation and they all predict CMB polarization. In some scenarios the signal is larger than in others. But there isn’t even a specific prediction for the amount of CMB polarization in the Hawking paper. In fact, the paper doesn’t so much as even contain the word “polarization” or “tensor modes.”

The claim that the detection of CMB polarization would mean the multiverse exists makes as much sense as claiming that if I find a coin on the street then Bill Gates must have walked by. And a swarm of invisible angels floated around him playing harp and singing “Ode To Joy.”

In case that was too metaphorical, let me say it once again but plainly. Hawking has not found a new way to measure the existence of other universes.

Stephen Hawking was beloved by everyone I know, both inside and outside the scientific community. He was a great man without doubt, but this paper is utterly unremarkable.

Note added May 2nd 2018: The paper was now published in JHEP.

Wednesday, March 14, 2018

Stephen Hawking dies at 76. What was he famous for?

I woke up this morning to the sad news that Stephen Hawking has died. His 1988 book “A Brief History of Time” got me originally interested in physics, and I ended up writing both my diploma thesis and my PhD thesis about black holes. It is fair to say that without Hawking my life would have been an entirely different one.

While Hawking became “officially famous” with “A Brief History of Time,” among physicists he was more renowned for the singularity theorems. In his 1960s work together with Roger Penrose, Hawking proved that singularities form under quite general conditions in General Relativity, and they developed a mathematical framework to determine when these conditions are met.

Before Hawking and Penrose’s work, physicists had hoped that the singularities which appeared in certain solutions to General Relativity were mathematical curiosities of little relevance for physical reality. But the two showed that this was not so, that, to the very contrary, it’s hard to avoid singularities in General Relativity.

Thanks to this seminal work, physicists understood that the singularities in General Relativity signal the theory's breakdown in regions of high energy-densities. In 1973, together with George Ellis, Hawking published the book “The Large Scale Structure of Space-Time” in which they laid out the mathematical treatment in detail. Still today it’s one of the most relevant references in the field.

A somewhat lesser known step in Hawking's career is that  already in 1971 he wrote one of the first papers on the analysis of gravitational wave signals. In this paper together with Gary Gibbons, the authors proposed a simple yet path-leading way to extract signals from the background noise.

Also Hawking’s – now famous – area theorem for black holes stemmed from this interest in gravitational waves, which is why the paper is titled “Gravitational Radiation from Colliding Black Holes.” This theorem shows that when two black hole horizons merge their total surface area can only increase. In that, the area of black hole horizons resembles the entropy of physical systems.

Only a few years later, in 1974, Hawking published a seminal paper in which he demonstrates that black holes give off thermal radiation, now referred to as “Hawking radiation.” This evaporation of black holes results in the black hole information loss paradox which is still unsolved today. Hawking’s work demonstrated clearly that the combination of General Relativity with the quantum field theories of the standard model spells trouble. Like the singularity theorems, it’s a result that doesn’t merely indicate, but prove that we need a theory of quantum gravity in order to consistently describe nature.

While the 1974 paper was predated by Bekenstein’s finding that black holes resemble thermodynamical systems, Hawking’s derivation was the starting point for countless later revelations. Thanks to it, physicists understand today that black holes are a melting pot for many different fields of physics – besides general relativity and quantum field theory, there is thermodynamics and statistical mechanics, and quantum information and quantum gravity. Let’s not forget astrophysics, and also mix in a good dose of philosophy. In 2017, “black hole physics” could be a subdiscipline in its own right – and maybe it should be. We owe much of this to Stephen Hawking.

In the 1980s, Hawking worked with Jim Hartle on the no-boundary proposal according to which our universe started in a time-less state. It’s an appealing idea whose time hasn’t yet come, but I believe this might change within the next decade or so.

After this, Hawking tried several times to solve the riddle of black hole information loss that he posed himself, alas, unsuccessfully. It seems that the paradox he helped create finally outlived him.

Besides his scientific work, Hawking has been a master of science communication. In 1988, “A Brief History of Time” was a daring book about abstract ideas in a fringe area of theoretical physics. Hawking, to everybody’s surprise, proved that the public has an interest in esoteric problems like what happens if you fall into a black hole, what happed at the Big Bang, or whether god had any choice when he created the laws of nature.

Since 1988, the popular science landscape has changed dramatically. There are more books about theoretical physics than ever before and they are more widely read than ever before. I believe that Stephen Hawking played a big role in encouraging other scientists to write about their own research for the public. It certainly was an inspiration for me.

Good bye, Stephen, and thank you.

Tuesday, March 13, 2018

The Multiworse Is Coming

You haven’t seen headlines recently about the Large Hadron Collider, have you? That’s because even the most skilled science writers can’t find much to write about.

There are loads of data for sure, and nuclear physicists are giddy with joy because the LHC has delivered a wealth of new information about the structure of protons and heavy ions. But the good old proton has never been the media’s darling. And the fancy new things that many particle physicists expected – the supersymmetric particles, dark matter, extra dimensions, black holes, and so on – have shunned CERN.

It’s a PR disaster that particle physics won’t be able to shake off easily. Before the LHC’s launch in 2008, many theorists expressed themselves confident the collider would produce new particles besides the Higgs boson. That hasn’t happened. And the public isn’t remotely as dumb as many academics wish. They’ll remember next time we come ask for money.

The big proclamations came almost exclusively from theoretical physicists; CERN didn’t promise anything they didn’t deliver. That is an important distinction, but I am afraid in the public perception the subtler differences won’t matter. It’s “physicists said.” And what physicists said was wrong. Like hair, trust is hard to split. And like hair, trust is easier to lose than to grow.

What the particle physicists got wrong was an argument based on a mathematical criterion called “naturalness”. If the laws of nature were “natural” according to this definition, then the LHC should have seen something besides the Higgs. The data analysis isn’t yet completed, but at this point it seems unlikely something more than statistical anomalies will show up.

I must have sat through hundreds of seminars in which naturalness arguments were repeated. Let me just flash you a representative slide from a 2007 talk by Michelangelo L. Mangano (full pdf here), so you get the idea. The punchline is at the very top: “new particles must appear” in an energy range of about a TeV (ie accessible at the LHC) “to avoid finetuning.”

I don’t mean to pick on Mangano in particular; his slides are just the first example that Google brought up. This was the argument why the LHC should see something new: To avoid finetuning and to preserve naturalness.

I explained many times previously why the conclusions based on naturalness were not predictions, but merely pleas for the laws of nature to be pretty. Luckily I no longer have to repeat these warnings, because the data agree that naturalness isn’t a good argument.

The LHC hasn’t seen anything new besides the Higgs. This means the laws of nature aren’t “natural” in the way that particle physicists would have wanted them to be. The consequence is not only that there are no new particles at the LHC. The consequence is also that we have no reason to think there will be new particles at the next higher energies – not until you go up a full 15 orders of magnitude, far beyond what even futuristic technologies may reach.

So what now? What if there are no more new particles? What if we’ve caught them all and that’s it, game over? What will happen to particle physics or, more to the point, to particle physicists?

In an essay some months ago, Adam Falkowski expressed it this way:
“[P]article physics is currently experiencing the most serious crisis in its storied history. The feeling in the field is at best one of confusion and at worst depression”
At present, the best reason to build another particle collider, one with energies above the LHC’s, is to measure the properties of the Higgs-boson, specifically its self-interaction. But it’s difficult to spin a sexy story around such a technical detail. My guess is that particle physicists will try to make it sound important by arguing the measurement would probe whether our vacuum is stable. Because, depending on the exact value of a constant, the vacuum may or may not eventually decay in a catastrophic event that rips apart everything in the universe.*

Such a vacuum decay, however, wouldn’t take place until long after all stars have burned out and the universe has become inhospitable to life anyway. And seeing that most people don’t care what might happen to our planet in a hundred years, they probably won’t care much what might happen to our universe in 10100 billion years.

Personally I don’t think we need a specific reason to build a larger particle collider. A particle collider is essentially a large microscope. It doesn’t use light, it uses fast particles, and it doesn’t probe a target plate, it probes other particles, but the idea is the same: It lets us look at matter very closely. A larger collider would let us look closer than we have so far, and that’s the most obvious way to learn more about the structure of matter.

Compared to astrophysical processes which might reach similar energies, particle colliders have the advantage that they operate in a reasonably clean and well-controlled environment. Not to mention nearby, as opposed to some billion light-years away.

That we have no particular reason to expect the next larger collider will produce so-far unknown particles is in my opinion entirely tangential. If we stop here, the history of particle physics will be that of a protagonist who left town and, after the last street sign, sat down and died, the end. Some protagonist.

But I have been told by several people who speak to politicians more frequently than I that the “just do it” argument doesn’t fly. To justify substantial investments, I am told, an experiment needs a clear goal and at least a promise of breakthrough discoveries.

Knowing this, it’s not hard to extrapolate what particle physicists will do next. We merely have to look at what they’ve done in the past.

The first step is to backpedal from their earlier claims. This has already happened. Originally we were told that if supersymmetric particles are there, we would see them right away.
“Discovering gluinos and squarks in the expected mass range […] seems straightforward, since the rates are large and the signals are easy to separate from Standard Model backgrounds.” Frank Paige (1998).

“The Large Hadron Collider will either make a spectacular discovery or rule out supersymmetry entirely.” Michael Dine (2007)
Now they claim no one ever said it would be easy. By 2012, it was Natural SUSY is difficult to see at LHC and “"Natural supersymmetry" may be hard to find.” 

Step two is arguing that the presently largest collider will just barely fail to see the new particles but that the next larger collider will be up to the task.

One of the presently most popular proposals for the next collider is the International Linear Collider (ILC), which would be a lepton collider. Lepton colliders have the benefit of doing away with structure functions and fragmentation functions that you need when you collide composite particles like the proton.

In a 2016 essay for Scientific American Howard Baer, Vernon D. Barger, and Jenny List kicked off the lobbying campaign:
“Recent theoretical research suggests that Higgsinos might actually be showing up at the LHC—scientists just cannot find them in the mess of particles generated by the LHC's proton-antiproton collisions […] Theory predicts that the ILC should create abundant Higgsinos, sleptons (partners of leptons) and other superpartners. If it does, the ILC would confirm supersymmetry.”
The “recent theoretical research” they are referring to happens to be that of the authors themselves, vividly demonstrating that the quality standard of this field is currently so miserable that particle physicists can come up with predictions for anything they want. The phrase “theory predicts” has become entirely meaningless.

The website of the ILC itself is also charming. There we can read:
“A linear collider would be best suited for producing the lighter superpartners… Designed with great accuracy and precision, the ILC becomes the perfect machine to conduct the search for dark matter particles with unprecedented precision; we have good reasons to anticipate other exciting discoveries along the way.”
They don’t tell you what those “good reasons” are because there are none. At least not so far. This brings us to step three.

Step three is the fabrication of reasons why the next larger collider should see something. The leading proposal is presently that of Michael Douglas, who is advocating a different version of naturalness, that is naturalness in theory space. And the theory space he is referring to is, drums please, the string theory landscape.

Naturalness, of course, has always been a criterion in theory-space, which is exactly why I keep saying it’s nonsense: You need a probability distribution to define it and since we only ever observe one point in this theory space, we have no way to ever get empirical evidence about this distribution. So far, however, the theory space was that of quantum field theory.

When it comes to the landscape at least the problem of finding a probability distribution is known (called “the measure problem”), but it’s still unsolvable because we never observe laws of nature other than our own. “Solving” the problem comes down to guessing a probability distribution and then drowning your guess in lots of math. Let us see what predictions Douglas arrives at:

Slide from Michael Douglas. PDF here. Emphasis mine.

Supersymmetry might be just barely out of reach of the LHC, but a somewhat larger collider would find it. Who’d have thought.

You see what is happening here. Conjecturing a multiverse of any type (string landscape or eternal inflation or what have you) is useless. It doesn’t explain anything and you can’t calculate anything with it. But once you add a probability distribution on that multiverse, you can make calculations. Those calculations are math you can publish. And those publications you can later refer to in proposals read by people who can’t decipher the math. Mission accomplished.

The reason this cycle of empty predictions continues is that everyone involved only stands to benefit. From the particle physicists who write the papers to those who review the papers to those who cite the papers, everyone wants more funding for particle physics, so everyone plays along.

I too would like to see a next larger particle collider, but not if it takes lies to trick taxpayers into giving us money. More is at stake here than the employment of some thousand particle physicists. If we tolerate fabricated arguments in the scientific literature just because the conclusions suit us, we demonstrate how easy it is for scientists to cheat.

Fact is, we presently have no evidence –  neither experimental nor theoretical evidence –  that a next larger collider would find new particles. The absolutely last thing particle physicists need right now is to weaken their standards even more and appeal to multiversal math magic that can explain everything and anything. But that seems to be exactly where we are headed.

* I know that’s not correct. I merely said that’s likely how the story will be spun.

Like what you read? My upcoming book “Lost in Math” is now available for preorder. Follow me on twitter for updates.

Saturday, March 10, 2018

Book Update: German Cover Image

My US publisher has transferred the final manuscript to my German publisher and the translation is in the making. The Germans settled on the title “Das Hässliche Universum” (The Ugly Universe). They have come up with a cover image that leaves me uncertain whether it’s ugly or not which I think is brilliant.

New Scientist, not entirely coincidentally, had a feature last week titled “Welcome To The Uglyverse.” The article comes with an illustration showing the Grand Canyon clogged by an irregular polyhedron in deepest ultramarine. It looks like a glitch in the matrix, a mathematical tumor on nature’s cheek. Or maybe a resurrected povray dump file. Either way, it captures amazingly well how artificial the theoretical ideals of beauty are. It is also interesting that both the designer of the German cover and the designer of the New Scientist illustration chose lack of symmetry to represent ugliness.

The New Scientist feature was written by Daniel Cossins, who did an awesome job explaining what the absence of supersymmetric particles has to do with the mass of the Higgs and why that’s such a big deal now. It’s one of the topics that I explore in depth in my book. If you’re still trying to decide whether the book is for you, check out the New Scientist piece for context.

Speaking of images, the photographer came and photographed, so here is me gazing authorly into the distance. He asked me whether the universe is random. I said I don’t know

Tuesday, March 06, 2018

Book Review: “Richie Doodles,” a picture book about Richard Feynman by M. J. Mouton and J. S. Cuevas

Richie Doodles: The Brilliance of a Young Richard Feynman
Rare Bird Books (February 20, 2018)

I’m weak. I have a hard time saying “no” when offered a free book. And as the pile grows, so does my guilt for not reading them. So when I was offered a free copy of a picture book about Richard Feynman, of course I said “yes.” I’d write some nice words, work off some guilt, and everyone would be happy. How hard could it be?

So the book arrived and I handed it to the twins, that being my great plan reviewing a children’s book. I don’t think the kids understood why someone would give them a book for free just to hear whether they liked it, but then I’m not entirely sure I understand the review business myself.

In any case, my zero-effort review failed at the first hurdle, that being that the book is in English but the twins barely just read German. So “mommy, read!” it was. Except that of course reading wouldn’t have done because, a thousand hours of Peppa Pig notwithstanding, they don’t understand much English either.

I am telling you this so you can properly judge the circumstances under which this, cough, review was conducted. It was me translating English verse on the fly. Oh, yes, the book is in verse. Which you might find silly but I can attest, that seven year olds think it’s the best.

The translation problem was fairly easy to solve – I even managed a rhyme here and there – but the next problem wasn’t. Turns out that the book doesn’t have a plot. It is a series of pictures loosely connected to the text, but it has no storyline. At least I couldn’t find one. There’s a dog named “Hitch” which appears throughout the “Tiny Thinkers” series (so far three books), but the dog is not present on most pages. And even if it’s on the page, it’s not clear why or what it’s doing.

That absence of story was some disappointment. Not like first-graders are demanding when it comes to storytelling. “The dog stole the doodle and the cat found it” would have done. But no plot.

Ok, well, so I made up a plot. Something along the lines that everyone thought Richie was just crazy doing all the doodles but turned out he was a genius. No, I don’t plan making career with this.

The next problem I encountered is that the illustrations are as awesome as the text isn’t. They are professionally done cartoon-style drawings (four-fingered hands and all) with a lovely attention to detail. The particular headache they gave me is that in several images a girl appears and, naturally, my daughters were much more interested in who the girl is and what she is doing rather than what the boy’s squiggly lines have to do with tau neutrinos. Maybe Richie’s sister? The book leaves one guessing.

The final problem appeared on the concluding page, where we see an angry looking (female) math teacher reprimanding a very smug looking boy (we aren’t told who that is) for drawing doodles instead of paying attention to the teacher. The text says “If your teacher sees you doodling in class, and says those silly drawings won’t help you pass… You can explain that your doodle isn’t silly at all. It’s called a Feynman Diagram explaining things that are small.”

I wasn’t amused. Please understand. I have a degree. I can’t possibly tell my kids it’s ok to ignore their math teacher because maybe their drawings will one day revolutionize the world.

So I turned this into an explanation about how math isn’t merely about numbers and calculus, but more generally about relations that can, among others, be represented by drawings. I ended up giving a two-hour lecture on braid groups and set theory.

The book finishes with some biographical notes about Feynman.

On Amazon, the book is marked for Kindergardners, age 4-6. But to even make sense of the images, the children need to know what an atom is, what mathematics is, and what a microscope is. The text is even more demanding: It contains phrases like “quark and antiquark pair” and speaks of particles that repel or attract, and so on.

Because of this I’d have guessed the book is aimed at children age 7 to 10. Or maybe more specifically at children of physicists. Of course I don’t expect a picture book to actually explain how Feynman diagrams work, but the text in the book is so confused I can’t see how a child can make sense of it without an adult who actually knows that stuff.

At some point, for example, the text raises the impression that all particles pass through matter without interaction. “Things so small they pass right through walls!” You have to look at the illustration on the opposite page to figure out this refers only to neutrinos (which are not named in the text). If you don’t already know what neutrinos are, you’ll end up very confused which collisions the later pages refer to.

Another peculiar thing about the book is that besides the “doodles” it says pretty much nothing about Richard Feynman. Bongo drums appear here and there but are not mentioned in the text. A doodle-painted van can be spotted, but is only referred to in the biography. There is also what seems to be an illustration of Schrödinger’s cat experiment and later a “wanted” poster looking for the cat “dead or alive.” Cute, yes, but that too is disconnected from the text.

I got the impression the book is really aimed at children of physicists – or maybe just physicists themselves? – who can fill in the details. And no word of lock-picking!

As you can tell, I wasn’t excited. But then the book wasn’t for me. When I asked the girls for their impression, they said they liked the book because it’s “funny.” Further inquiry revealed that what’s funny about the book are the illustrations. There’s a dog walking through a bucket of paint, leaving behind footprints. That scored highly, let me tell you. There’s a car accident (a scattering event), an apple with a worm inside, and a family of mice living in a hole in the wall. There are also flying noodles and even I haven’t figured out what those are, which made them the funniest thing in the world ever, at least for what my children are concerned.

The book has a foreword by Lawrence Krauss, but since Krauss recently moved to the sinner’s corner, that might turn out to be more of a benefit for Krauss than for the book.

In summary, the illustrations are awesome, the explanations aren’t.

I feel like I should be grateful someone produces children’s books about physics at all. Then again I’m not grateful enough to settle for mediocrity.

Really, why anyone asks me to review books is beyond me.

Thursday, March 01, 2018

Who is crazy now? (In which I am stunned to encounter people who agree with me that naturalness is nonsense.)

I have new front teeth. Or rather, I have a new dentist who looked at the fixes and patches his colleagues left and said they’ve got to go. Time for crowns. Welcome to middle age.

After several hours of unpleasant short-range interactions with various drills, he puts on the crowns and hands me a mirror. “Have a look,” he says. “They’re tilted,” I say. He frowns, then asks me to turn my head this way and that way. “Open your mouth,” he says, “Close. Open.” He grabs my temples with a pair of tongs and holds a ruler to my nose. Then he calls the guy from the lab.

The lab guy shakes my hand. “What’s up?” he asks. “They crowns are tilted,” I say. He stares into my mouth. “They’re not,” he declares and explains he made them personally from several impressions and angle measurements and photos. He uses complicated words that I can’t parse. He calls for his lab mate, who confirms that the crowns are perfectly straight. It’s not the crowns, they say, it’s my face. My nose, I am told, isn’t in the middle between my pupils. I look into the mirror again, thinking “what-the-fuck,” saying “they’re tilted.”

Now three guys are staring at my teeth. “They’re not tilted,” one of them repeats. “Well,” I try a different take “They don’t have the same angle as they used to.” “Then they were tilted before,” one of them concludes. I contemplate the possibility that my teeth were misaligned all my life but no one ever told me. It seems very possible. Then again, if no one told me so far chances are no one ever will. “They’re tilted,” I insist.

The dentist still frowns. He calls for a colleague who appears promptly but clearly dismayed that her work routine was interrupted. I imagine a patient left behind, tubes and instruments hanging out of the mouth. “Smile,” she orders. I do. “Yes, tilted,” she speaks, turns around and leaves.

For a moment there, I felt like the participants in Asch’s famous 1951 experiment. Asch assigned volunteers to join a group of seven. The group was tasked with evaluations of simple images which they were told were vision tests. The volunteers did not know that the other members of the group had been given instructions to every once in a while all judge a longer of two lines as the shorter one, though the answer was clearly wrong. 75 percent of the trial participants went with the wrong majority opinion at least once.

I’d like to think if you’d put me among people who insisted the shorter line is the longer one, I’d agree with them too. I also wouldn’t drink the water, keep my back to the wall, and leave the room slowly while mumbling “Yes, you are right, yes, I see it clearly now.”

In reality, I’d probably conclude I’m crazy and then go write a book about it. Because that’s pretty much what happened.

For more than a decade I’ve tried to find out why so many high energy physicists believe that “natural” theories are more likely to be correct. “Naturalness,” here, is mathematical property of theories which physicists use to predict new particles or other observable consequences. Particle physicists’ widespread conviction that natural theories were preferable was the reason so many of them thought the Large Hadron Collider would see something new besides the Higgs boson: Supersymmetry, dark matter, extra dimensions, black holes, gravitons, or other exotic things.

Whenever I confessed to one of my colleagues I am skeptical that naturalness is a reliable guide, I was met with a combination of amusement and consternation. Most were nice. They explained things to me that I already knew. They didn’t answer my questions but insisted they did. Some gave up and walked away. Others got annoyed. Every once in a while someone told me I’m just stupid. All of them ignored me.

After each conversation I went and looked again at the papers and lecture notes and textbooks, but each time I arrived at the same conclusion, that naturalness is an argument from beauty, based on experience but with scant empirical evidence. For all I could tell, that a theory be natural was a wish not a prediction. I failed to see a reason for the LHC to honor this wish.

And it didn’t. The predictions for the LHC that were based on naturalness arguments did not come true. At least not so far, and we are nearing the end of new data. Gian-Francesco Giudice, head of the CERN theory division, recently rang in the post-naturalness era. Confusion reigns among particle physicists.

A few months have passed since Giudice’s paper. I am sitting at a conference in Aachen on naturalness and finetuning where I am scheduled to give my speech about how naturalness is a criterion of beauty, as prone to error as criteria of beauty have always been in the history of science. It’s a talk usually met with  befuddlement. Questions I get are mostly alterations of “Did you really just say what I thought you said?”

But this time it’s different. One day into the conference I notice that all I was about to say has already been said. The meeting, it seems, collected the world’s naturalness skeptics, a group of likeminded people I didn’t know exists. And they are getting more numerous by the day.

Most here agree that naturalness is not a reliable guide but a treacherous one, one that looks like it works until suddenly it doesn’t. And though we don’t agree on the reason why this guide failed just now and what to do about it, I’m not the crazy one any more. Several say they are looking forward to reading my book.

The crowns went back to the lab. Attempts at fixing them failed, and the lab remade them entirely. They’re straight now, and I am no longer afraid that smiling will reveal the holes between my teeth.