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New LHC diboson excesses point to light SUSY

Guest blog by Tommaso Dorigo (CMS), a vocal SUSY denier who is starting to [verb] into his pants

Among the many more-or-less boring news from the ICHEP conference (International Conference on High Energy Physics), which is presently going on in Valencia (Spain), one bit today is sending good vibrations through the spine of many of the few phenomenologists who have chosen to remain faithful to the idea of Supersymmetry all the way to the bitter end. It is the excess of diboson events that ATLAS has just reported there. (See TRF on Thursday.)

\(W^\pm\) bosons are the massive particles discovered in 1983 by Carlo Rubbia at the CERN SppS collider. They govern weak interactions, the ones responsible for radioactive decays as well as for some of the processes going on in the stars' cores. \(W^\pm\) bosons can be produced in pairs through quite standard electroweak processes in particle collisions if the available energy is sufficiently high. And indeed, the pair production of \(W^\pm\) bosons has been studied since the late nineties at the Tevatron, at the LEP II collider, and then of course at the LHC.

The fact that the Higgs boson may decay into \(W^+W^-\) pairs is one extra motivation for studying these processes, but in earnest they are quite interesting by themselves. Already the sheer production rate of \(W^+W^-\) pairs at high energy is a topic on which one could write volumes – the cross section of the process would grow beyond what can be considered logical (the "unitarity bound") if there were no Higgs boson to damp down the rate. But let me stick to today's topic: SUSY!

It turns out that a paper titled "Stop the ambulance!" was submitted to the Arxiv just one week ago. (LM: It's really one month ago and there was also another equivalent paper posted simultaneously, see TRF on June 5th.) In it, authors Jong Soo Kim, Krzystof Rolbiecki, Kazuki Sakurai, and Jamie Tattersall argued that the rates of \(W^+W^-\) production published by ATLAS (in \(7\)-\(\text{TeV}\) collision data) and CMS (in \(7\)- and \(8\)-\(\text{TeV}\) collision data) are all above the Standard Model prediction, and went on to explain how a very simple SUSY model including light stop quarks, charginos, and neutralinos could fit the data much better than the Standard Model does.

The authors of 1406.0858 produced a fit of SM+simplified SUSY which has a maximum likelihood exceeding the SM one by 13.3 units – corresponding to an over 3-sigma preference of the data for the SUSY hypothesis. A first hint of Supersymmetry after all? The matter is serious, as the \(W^+W^-\) production process occurs in LHC collisions mainly by quark-antiquark annihilations, for which uncertainties are small. It is a very simple electroweak process and SM calculations just cannot be much off. But of course, with dozens of measurements of production rates by the LHC, finding one off cannot be too exciting, can it? Apparently, it can. In fact, the only missing piece given the LHC Run 1 data was the ATLAS \(8\)-\(\text{TeV}\) \(W^+W^-\) result. And it has just been shown at ICHEP: ATLAS measures the cross section at \[

\sigma(WW) = 71.4\pm7.5\,{\rm pb},

\] considerably higher than the theory prediction (\(57.3\,{\rm pb}\)) [For comparison, a year ago CMS published its measurement at \(8\TeV\) as \(\sigma(WW)=69.9\pm 6.9\,{\rm pb}\), using only a few inverse \({\rm fb}\) of \(8\TeV\) data; the result is more precise than the new ATLAS one, but it is systematics-dominated so it is unlikely to be improved soon]. A zoom-in view of the new ATLAS measurement is shown below.

Click to zoom in...

Artistic, isn't it? The grey bars are SM theory predictions, and the orange one is the new ATLAS measurement. Okay, yes, artistic maybe, but more interesting is the whole graph, which collects many different measurements by ATLAS. See below.

Click to zoom in...

The graph is busy, but you do not need to go through that whole list. The point is that we have some consistent deviations by the two LHC experiments with respect to the Standard Model; and a rather simple Supersymmetric scenario which appears to fit these deviations effectively. Even more significant is the fact that the model published by the SUSY phenomenologists came before the latest ATLAS result; so it is to some degree a "confirmation" of the picture drawn by the theorists. The graph below, taken from the preprint, is rather striking. It is a "temperature plot" showing the difference of the likelihood from the value of the best fit. Values close to zero are in red, and they indicate points of parameter space which give a good fit to the considered ATLAS and CMS measurements. On the horizontal axis you see the stop mass, on the vertical axis the neutralino mass. There is a nice band of red points around \(M_{\rm stop}=200\GeV\), \(M_{\rm neu}=150\GeV\) which is out of the current excluded regions of parameter space (lying below the black, yellow, and purple curves).

Click to zoom in...

Despite the inspiring graph and the red streak in non-excluded regions, the significance of the departures from SM rates is so far still too weak to claim anything, and yet, as I said above, some SUSY phenomenologists are not going to bed tonight, preferring to check their models than sleeping over it. What can I say... If they're roses, they will flourish. I very much hope they will, but I remain sceptical. It will be very interesting to see if ATLAS and CMS will make an effort to investigate more in detail the SUSY scenarios which would give exactly the observed excesses. Of course, the LHC SUSY searches are already extremely wide-range, but some corner of phase space might still be looked at in more detail... And needless to say, the \(13\)-\(\text{TeV}\) LHC run of 2015 is getting closer. So stay tuned for what could fizzle out or become the discovery of a young but already eventful century!

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reader kashyap vasavada said...

Very interesting blog Luboš! I agree with most of it. Scientific method has done well for some 500 years without bringing in philosophy, metaphysics or concept of God! I can get along very well with atheist theoretical physicists!! You may
take the attitude that physicists should make theoretical models (no matter how bizarre they look from intuitive point of view) and compare them with experimental results to see if they are right. As far as pragmatic physicists are concerned
that is the end. Thus metaphysics does not belong in the day to day study of physics. That is why I did not care for Sean Carroll’s view point on many world interpretation. Coming from Sean, it was doubly surprising because he attacks
openly religion and metaphysics! All the debates about decoherence are fine but splitting of the universe as a result of arbitrary action by human beings is just plainly too much! As I mentioned in my guest blog (which you were kind to publish) I am sympathetic to metaphysics in religious context but not in the physics context. On the other hand problems
do arise because we human beings are classical objects and our intuition is classical. So some people may want to understand the meaning of equations of theoretical physics. I can also understand why people like Weinberg (not a
religious person for sure) are not happy with any current interpretation of QM. You might say tough luck, get used to quantum world! Ok. Fine with me. But that
does bring in ideas close to metaphysics. That is the reason I am personally interested in debates about QM interpretations.
If at some future time, scientific method hits a brick wall and we cannot make any progress then we may have to reconsider. Obviously, I do not know if and when
that time will come!

reader Uncle Al said...

The vacuum is not exactly mirror-symmetric toward matter - by observation. SUSY can never be more than a parameterized curve fit plus residual that must be uniquely dialed in for its every applications. Newton was corrected by GR and QM. GR and QM cannot be unified until the vacuum is empirically described.

To prove: 2=3
4 - 10 = 9 - 15
Add 25/4 to both sides,
4 - 10 + 25/4 = 9 - 15 + 25/4
Write sides as complete squares,
(2 - 5/2)^2 = (3 - 5/2)^2
Take the square root of both sides
2 - 5/2 = 3 - 5/2,
add 5/2 to both sides

reader Kimmo Rouvari said...

I disagree (obviously) :-) and I'm actually very surprised by the fact that mainstream physics hasn't realized the underlying mechanism so far. It just resolves every fucking anomaly in physics!

QM emerges from ToEbi and that's a fact. Everyone who is capable of reading and understanding simple things surely agrees ;-) I dare you!

reader Luboš Motl said...

Dear Kimmo, there hasn't been any promising profound or unifying theory in physics since 1925 that would dare to change an epsilon about the postulates of quantum mechanics, and there won't be one in the future, either. Get used to it.

You may disagree but that's the last thing you can do about the facts I have stated - and pretty much rigorously proven. Do you realize that what you write makes no sense and there exists no conceivable evidence that could ever stand on your side?

The difference between a particular quantum theory and its classical counterpart is an increasing function of hbar. In quantum theory, hbar is nonzero. In classical physics, it is approximated by zero. The value of hbar has been measured - with the accuracy of one part in a billion, in fact - and it is not zero. The idea that the underlying laws are classical is therefore ruled out at 1 billion sigmas or so. The idea of a classical fundamental theory underlying the known phenomena is excluded and ludicrous beyond any imagination.

Note that I can really define hbar to be exactly what measures the difference between classical physics and quantum physics, in a very universal way, and I can still measure hbar defined in this way operationally. The measured nonzero Planck's constant really *does* imply that classical physics can never return again.

reader Dilaton said...

Ha, this is an astonishingly fair enough and enjoyable reading !

And as this site has a good anti-spam filter, not even the comments will upset me ;-)

(Uncle Al posting incoherent stuff I am used to by now, LOL)


reader Ron C. said...

Sorry this is OT, but I wanted to reach you and don't see any recent post on climate matters. Also sorry that this is a bit long, but I hope you will read and respond

You are probably aware of many blog discussions lately on the impacts of various adjustments upon the surface temperature records. In this context I only now discovered your excellent post of July 2011 analyzing HADCRUT3, neatly avoiding all the manipulations of historical data.

I have been referring to this in several places, and hope that people get your point. I think that if you updated this analysis with current HADCRUT3 data, it would be interesting to compare 3 years later. It would also make more people aware of this way of looking at surface temperatures.

Here is the comment I have been making elsewhere:

How about a statistical analysis of land surface termperatures where each site is treated as a distinct microclimate. I have always been uncomfortable with the adjusting, anomalizing and homogenizing of land surface temperature readings in order to get global mean temperatures and trends. Years ago I came upon Richard Wakefield’s work on Canadian stations in which he analyzed the trend longitudinally in each station, and then compared the trends. This approach respects the reality of distinct microclimates and reveals any more global patterns based upon similarities in the individual trends. It is actually the differences between microclimates that inform, so IMO averaging and homogenizing is the wrong way to go.

In Richard’s study he found that in most locations over the last 100 years, extreme Tmaxs (>+30C) were less frequent and extreme Tmins <-20C) were less frequent. Monthly Tmax was in a mild lower trend, while Tmin was strongly trending higher , resulting in a warming monthly average in most locations. Also, Winters were milder, Springs earlier and Autumns later. His conclusion: What's not to like?

Now I have found that in July 2011, Lubos Motl did a similar analysis of HADCRUT3. He worked with the raw data from 5000+ stations with an average history of 77 years. He calculated for each station the trend for each month of the year over the station lifetime. The results are revealing. The average station had a warming trend of +0.75C/century +/- 2.35C/century. That value is similar to other GMT calculations, but the variability shows how much homogenization there has been. In fact 30% of the 5000+ locations experienced cooling trends.


"If the rate of the warming in the coming 77 years or so were analogous to the previous 77 years, a given place XY would still have a 30% probability that it will cool down – judging by the linear regression – in those future 77 years! However, it's also conceivable that the noise is so substantial and the sensitivity is so low that once the weather stations add 100 years to their record, 70% of them will actually show a cooling trend.

Isn't it remarkable? There is nothing "global" about the warming we have seen in the recent century or so.The warming vs cooling depends on the place (as well as the month, as I mentioned) and the warming places only have a 2-to-1 majority while the cooling places are a sizable minority.

Of course, if you calculate the change of the global mean temperature, you get a positive sign – you had to get one of the signs because the exact zero result is infinitely unlikely. But the actual change of the global mean temperature in the last 77 years (in average) is so tiny that the place-dependent noise still safely beats the "global warming trend", yielding an ambiguous sign of the temperature trend that depends on the place."

reader Luboš Motl said...

Dear Dilaton, nice! Concerning Uncle, it's not incoherent. It's just the standard proof that 1+1=3, I like to present it, too. He just forgot the last step, to rewrite 2 as 1+1, so that one may actually prove 1+1=3. ;-)

reader JHardin said...


Wired just published an article promoting the pilot wave theory. Am I wrong but why do they do a macro-experiment to try and prove something on the quantum level? I like QM. The world is more interesting because of it.

reader Luboš Motl said...

Hi JHardin! Do you mean this?

I was just sent this very link by someone at Facebook - where I looked after a week.

reader PR Blondlot said...

Perhaps your understanding of quantum theory does not imply solipsism, but certainly a strange dualism.
One one hand you describe the 'material world' using operators and wave function(s) - on the other hand there are your 'observations' and your experiences.
The reason I this dualism is strange is of course that you also seem to belive that your brain, like any brain, is part of the 'material world' and at the same time the origin of your experiences.

reader Luboš Motl said...

Well, quantum mechanics is about "dualisms" of many kinds, it's really a fundamental principle of it, in certain interpretations.

At any rate, the very physical meaning of all the linear operators in QM is to predict the probabilities - from complex probability amplitudes which are effectively matrix elements of these operators - using the well-known rules. These two parts of the physical theory - operators and the rules for probabilities - are absolutely inseparable. Call it duality, megality, lumosity, whatever you want, but it's how Nature works and if you don't like it, it's your defect, not a defect of Nature.

reader giulio said...

Dear Lubos,

I am a young (graduate student) physicist, would you suggest me to pursuit the study of string theory (of which I know nothing at the day) or to join one of the new and fresh fields such as quantum computing?
I am not really concerned about the difficulty of the subject, I think that one can study anything, provided he has the will and passion to go through the process. What scares me is the possibility that theoretical physics is at a dead end and that it will be harder and harder in the future to get pleasure from doing research in it.

In addition, at what age did you start to study string theory?

reader Luboš Motl said...

Hi! You probably know what you like and what you're good at more accurately than I do, right?

Quantum computing is fun but it isn't really a fresh new subject. It really began in 1982 with Feynman's comments and the "elements" of the field have been around from 1925 and heavily discussed in the new form since the 1960s.

1982 is before the 11th person joined string theory during the 1984 First Superstring Revolution - so it may be fair to say that they're equally old fields.

reader kashyap vasavada said...

This is quite interesting. I have also heard that the present limit on Higgs width is roughly six times the SM width. So there is lot of room for exotic decays. Right?

reader Dilaton said...

Please do not listen to popular media channels, people who are not experts but have a personal agenda, books, blogs, etc throwing around anti-theoretical/fundamental physics tirades. Those journalists, or arrogantly their state of physics knowledge overreaching dilettants have no clue what they are talking about but feel entitled to pompously throwing around outragous far reaching negative claims about theoretical physics aniway, and should not be taken serious by anybody who is interested in fundamental physics.

It is better to listen to what good people who are real experts, such as for example the FPP winners, say and how they judge things such as the future of the field for example.

And here on TRF you are right too for patient introductions (but not dumbed down) to cool physics stuff, live reports about the newest developments in theoretical physics, correct judgements of new experimental results, important debunkings of nonsense, and a lot of fu ;-).

reader Luboš Motl said...

It's like saying that when your height is 1 meter and your bedroom has ceiling just 6 meters above the floor, there is not enough vertical room for your sex with your exotic partners.

reader jon said...

The key point is how Wigner's friend's subjective experience is explained for the time prior to being observed by Wigner. Wigner's friend will experience that time mentally just like any other, and yet the result that Wigner observes could be any of the possible outcomes. One can speculate about various possibilities about how it all happens, and perhaps some form of solipsism is true, but that's just philosophy for now.

reader Cliff said...

Exciting news that the excess is indeed continuing within the 8 TeV ATLAS data. I'll be very much looking forward to the 13 TeV run and I might even [verb] my pants in excitement as well (from purely positive emotions of course). ;]

How would the experts here quantify the significance of the discrepancy based on these different measurements?

reader Luboš Motl said...

One may prove all the statements that Wigner's friends had one of the sharp subjective experiences, that it was correlated with the observables describing the cat, and so on.

All material manifestations of his perceptions leave impact that may be (later) measured, and all these predictions agree.

If you mean some "really subjective" experience that has no measurable impact, it is subjective, so it is obviously not explained by any meaningful science used by other observers such as Wigner.

There is nothing else to explain here.

reader Kimmo Rouvari said...

I might better write a blog post of my own regarding what I consider classical and how QM emerges from ToEbi.

There is an experiment which proves my case totally right.

reader Edit_XYZ said...

"All material manifestations of his perceptions - e.g. Wigner's friend's
notes that he writes because that's how his brain is working or
programmed - leave impact that may be (later) measured, and all these
predictions agree with the observations that Wigner may make later."

Wigner's friend's notes that are the result of his observing the wave function collapsing into a measured state can very well disagree with Wigner's observations of the wave function later collapsing into a different measured state.

Unless you want to throw the probabilities calculated by quantum mechanical formalism to the garbage bin - in which case, quantum mechanics reduces to ~'everything is possible'.

Including the measured X seen by Wigner's friend spontaneously changing to to the measured X' seen by Wigner - despite the ridiculously low likelihood of this happening.

You don't prove that ~'quantum mechanics doesn't imply solipsism'

just by repeating this dictum accompanied by various ad personams, Lubos.

reader jon said...

Just because something is not measurable by science doesn't mean that it doesn't exist. QM cannot for example explain why one neural state gives rise to a color sensation and another gives rise to a sound sensation. That means QM is incomplete in regard to explaining that aspect of our experience.

reader Luboš Motl said...

Wigner's friend's notes that are the result of his observing the wave function collapsing into a measured state can very well disagree with Wigner's observations of the wave function later collapsing into a different measured state.

reader Luboš Motl said...

Dear Cliff, wow, a new reason to šit into your pants may have come a few minutes ago. "Dorigo's" CMS collaboration released

which concludes with a 2.5 sigma excess of flavor-violating decays of the Higgs.

Higgs shouldn't really measurably decay to mu-tau pairs at all because they're from different generations. But if the excess is interpreted as signal, it apparently does decay in this way in almost 1% of decays! Needless to say, flavor violation is a "prediction of generic enough SUSY models" even though it may in principle arise via different new physics, too.

reader Giotis said...

giulio, read also this before you decide:

reader Giotis said...


reader Dilaton said...

Oh yeah, cool :-)))

And it reminds me of something in another TRF post about F-uny LHC signals I want to check...

Have some troubles to find it, darn !

reader Edit_XYZ said...

You attribute the change between the measured X seen by Wigner's friend and the measured X' seen by Wigner to re-interference of the wave function after it was collapsed by Wigner's friend.

The problem is - it's trivially easy to conduct the experiment with both Wigner's friend and Wigner bring macroscopic; the wave function can collapse to X for Wigner's friend and to X' for Wigner as easily as always:

Wigner's friend, by using the quantum mechanical formalism (path integral, Heisenberg, Schrödinger) can calculate the probability of re-interference of the wave function after he collapsed it to be practically 0.
But, from Wigner's perspective, the wave function will interfere far more often than Wigner's friend's calculations allow. Indeed, the wave function will re-interfere as if Wigner's friend never collapsed it.

So - yes, you solved the contradiction, but you paid a very substantial price: for Wigner's friend, the quantum mechanical formalism gives wildly wrong predictions regarding the probability of re-interference of the wave-function.
In othe words, as I already said in my previous post, in order to solve the contradiction, you threw quantum mechanical formalism to the garbage bin, mr. 'shut up and calculate'.

reader tomandersen said...

The biggest reason for me why I think QM may be in trouble is the fact that Lubos spends a lot of time on it.

This was simply not needed a few years ago.

reader lukelea said...

I have a question. Lubos writes,

"Indeed, quantum mechanics isn't talking about the patterns in the "objective state of the world". It talks about patterns and regularities (expressed via conditional probabilities of many types) linking different pieces of knowledge about the state of objects. And this knowledge is intrinsically and unavoidably subjective at the fundamental level."

My question concerns Karl Popper's definition of a scientific or empirical fact as (as I recall) a sensory datum about which two or more (qualified) observers agree. I believe he used the term "inter-subjectivity" to cover these cases. They are distinguished from those cases that we call hallucinations, where there is no inter-subjective agreement.

Does Lubos agree with the importance of intersubjectivity when it comes to the "observables" with which quantum mechanics is concerned?

reader NikFromNYC said...

I have often wondered if the double slit experiment merely involved waves that then only appear as fixed points on a film screen simply because those waves can only excite a single molecule at a time, so the spread out wave gets sucked into a point only at the moment of being absorbed.

reader Sage Basil said...

some tard in /r/science with "High Energy Particle Physics | Quantum Field Theory" flair told me that

"Nope. Point particle is an artifact of a classical description.
Particles are described by quantum mechanical wave functions which give
their probability distribution in space. A 'point' particle merely has a
very tightly localized probability distribution (but not a true point)"

in response to my comment that point particles have infinite mass density, and then

"Point particle implies you know it's position exactly. That is
impossible. The wave function never collapses to a perfect point. Google
Heisenberg uncertainty principle"

in response to my comment that a probability distribution is not a mass distribution.

From what I can tell, this moron with less understanding than a bright high school student truly believes that he is a scientist. And since he has the flair, people pay attention to what he says.

Certainly, this misconception is the result of the 'waves not particles' slogan. But it doesn't matter what slogans are used, some people will understand, and others will recite the slogans and think that that is all there is to it.

It would be nice if credentials were not handed out like popcorn. That will not happen because politics, but ultimately, the cruel truth is that it doesn't matter what idiots think, except when they have political power, which they should not be trusted with, and in fact are not trusted with - instead, they are manipulated by politicians into pulling stunts like getting squished on the train tracks to stop nuclear power so that politicians can get power, money, and women for themselves.

reader Luboš Motl said...

If the probability of later interference is "practically zero", then the probability of a contradiction between Wigner and his friend is also "practically zero" because it's the damn same thing! You are just being dense.

reader Luboš Motl said...

You meant that the mankind's intelligence is in trouble, right?

Quantum mechanics is as flawless as it has been in the recent 89 years.

reader Luboš Motl said...

Dear Luke, it's a derivable fact that observers - different subjects - will agree about their measurements of pretty much macroscopic objects or observables.

But if they don't agree about something, like a description of a microscopic object, they just don't agree and it's demonstrably how Nature forces their descriptions to work.

I definitely disagree that "inter-subjectivity" which is just a milder code for "objectivity" is a "necessary prerequisite of science" or something like that. Popper was just another fucking confused philosopher so please don't try to sell his musings as something that scientists should be actually bound by.

reader Don said...

Wow! Thanks, Lubos, this explains a lot and is a very helpful follow up to your previous post on Many worlds pseudo science. This part summarized best for me:

"It was true because of a very simple and strong assumption that
classical physics made – namely that everything is fundamentally
described by "objective reality at each moment" that all observers have
to fundamentally agree about if they are accurate enough.

Quantum mechanics just refutes this assumption. "

Best, Don

reader Dilaton said...

Lumo does NOT spend time WORKING on QM to improve, repair, or whatever you call it, which is not needed and a waste time indeed. Even good engineers follow the guideline " Dont repair it if it is not broken" and QM is NOT broken...

But he spends a lot of time fighting vocal and arrogant anti-science zealots such as you for example, who have no clue what they are talking about, debunking nonsense that pops up even at places where only correct and serious physics is expected to appear (for example so-called peer-reviewed journals), and this was not needed a few years ago.

In fact Lumo is very generous and patient to let you comment here, I know that you are badly trolling about physics at other places in the internet too, so pleace appreciate this ;-)

reader anna v said...

A good incentive for the International Linear Collider and the LEP3. Sit on a higgs channel and measure cleanly everything.

reader lukelea said...

Then it is back to the drawing board for me. :)

reader NumCracker said...

Well, Written is an ET, so he needed much more time to get accustomed to live among us just before start working in our primitive scientific framework ;-)

reader farhad said...

Lubos can we say there is some interconnection "entanglement" between observers in universe that make it impossible that observation of two observer contradict together for example when someone observe a building destroyed or someone died this observation instantly change knowledge all other observer about it so when someone was observed dead someone else don't see it alive in his perception or some people don't see building destroyed and some others see it intact in their perception . ( if there is not a objective reality there must be some mechanism that allows all observers see a coherent reality )

reader Luboš Motl said...

Dear Farhad, apologies if I don't understand but to me, your comment sounds like *exactly* the same question that has been asked about 5,000 times.

An observer only learns about some fact - e.g. whether someone died or whether a building collapsed - when he measures it. It is useless for him to assume that there is a particular state of this observable if he hasn't actually measured it; and it's downright harmful for the validity of the predictions whenever the quantum effects - interference etc. - are still important.

Pretty much every pair of objects that have interacted in the past is entangled and entanglement guarantees correlations in pretty much any pair of quantities that may be measured on these two entangled objects. But the correlation only gets manifested when the results are measured. To replace the entangled state by a particular basis vector, like "up down" for two polarizations,before it is actually measured is wrong, wrong, wrong. The very word "entanglement" means that you cannot assume that such a reduction is possible before the measurement.

reader José Ignacio said...

Yes, but for this to happen the outside observer has to make evolve unitarily the physical system and the internal observer so that its previous measurement is deleted and replaced by that obtained the external observer. So when both observers can talk to each other they agree in the result of the measurement, because the internal observer has forgotten its previous measurement.

The explanation given in the Peres book is something so. Sorry if I cannot explain it better, I'm starting to read the book.

reader tommaso said...

Hi all,

(I tried to post here earlier but for some reason it did not go through)
I would not say I am a SUSY denier. I am rather a SUSY sceptic. I would be thrilled if we discovered that some realization of SUSY were what Nature chose for our Universe, just as anybody else, and probably more than most, as it would give me bread for the next fifty years (otherwise experimental HEP is bound to close soon). My problem is that I see the advantages of SUSY offset by a high implausibility of its hiding around an appearing endless string of corners. It fights my common sense, which is another way to say that the bayesian prior for the appeal of SUSY gets dumped a lot by the poor likelihoods it had to be multiplied by in the next umpteen years.


reader tomandersen said...

I agree - Luboš does not spend time repairing it, he for some reason spends time defending it. QM needs no repair, its still working fine.

Working fine is however not an indication that any theory is absolutely correct, or even that a new theory will not overturn it.

Working on a theory that everyone else 'knows' is a bad idea is often how science (and technology) move ahead. It's also usually a waste of time.

In this case Luboš has some good points (which don't convince me), but as he is well aware, its impossible to prove a theory right.

reader Luboš Motl said...

I know about that bug, don't know how to fix it, but know about some detail. Do some detailed observations and you will see that DISQUS sometimes adds the comment to the adjacent thread or blogpost. ;-) It is a systematic effect, so a whole wave of mis-addition of the same kind is likely.

Such problems may be contributed by the fact that the mobile version probably shows the number of "builtin Blogger comments" which are the same comment but they're being exported by DISQUS, if I remember well, so the export may be flawed.

Two weeks ago, my Sitemeter stopped working, and the new one doesn't add anything, either. It may be an even more serious bug although Google Analytics arguably shows more detailed data, mostly - I am not used to it.

reader Luboš Motl said...

Dear Tommaso, your negative arguments are illogical. They are upside down.

When an antelope is capable of hiding behind many corners, it may be annoying for the tiger (=you, if you don't get it) who is trying to eat the antelope. But it's surely a *positive* feature for the survival of the antelope, isn't it? SUSY is able to hide behind realistic corners which aren't obviously incompatible with the observations. That's a part of its viability. It is really representative of the corners. At least from some viewpoints, SUSY is representative of many other clever models of new physics one might invent. Those would also have to hide behind some previously unknown corners. SUSY is *already* doing that.

This illogic of yours must have something to do with the Popperian delusions which have propagated and which lead the laymen to dismiss a theory that has clever ways to hide from falsification or that is just daring to predict things that are true. Both such things are actually positive things for a theory. A theory is scientific when it talks about propositions that are in principle observable. SUSY clearly makes propositions that are highly nontrivial. Given these assumptions, whatever the theory does, say, or possess that improves its odds of survival is a *good* thing for the theory.

Check your numerous sign errors.

reader Anonymous said...

I have lost many friends for smoking pot. Now they are studying Loop quantum gravity, so keep your self far from marihuana!

reader Ly said...

Now protect win XP -

reader Dilaton said...


yes there are certainly things that could have been done to improve the trajectory or even switch path in my path integral of live (not 100% satisfied about the current intermediate state) ...

But you know, due to the nasty second law of thermodynamics it is sometimes difficult to even know which path to take and how to achieve it in advance ... ;-)


reader Dilaton said...

The new theory, which "improves" (generalises) quantum mechanics is called quantum field theory, but it does not "overthrow" but encompass it ... ;-)


reader Marcel van Velzen said...

“It is a very simple electroweak process and SM calculations just cannot be much off.” This is not telling the whole truth. Although the decay of the W can indeed be calculated very accurately in the SM, a serious discussion should also consider the uncertainties in the structure functions of the parton model or in other words the probability that a quark-antiquark collide inside two colliding protons. Are these so well-known (from maybe other processes) that they are irrelevant?

reader mr. critic said...

Fundamental probabilities sounds just lovely. Eliminates all the need for classical physics (which is boring). And they look like a result of the simple linear math of wave superpositions which explains all the "non-trivial" sides of quantum mechanics (which comes to my mind at least) like the uncertainty principle and the mutual interference between possible histories. But why call the wave function unobservable then? The "particle" is the wave function itself? No idea exactly how - It's not the common meaning of it - collection of data of some local region, which may not look like any function at all - but a perturbation of a universe-wide "sea" made of complex amplitudes.

Trying to observe the state of such sea by throwing stones in its water certainly will not allow you to know its objective state before the measurement. But there is a state and it's not the observer who creates a mini big bang while observing, i.e. a clean start of the evolution, right? You call the unknown a divinity? Ok by me, but try sending prayers toward it :)

I must confess, "modest level of solipsism" sounds pretty well. It gives room for the free will. But I'm not convinced. You know, without instrumental measurements even the classical world (the approximate one) is quite uncertain and subjective to the human brain. The lack of exact predictions of events (not probabilities) does not prove any level of solipsism - just our inability to have all the information about the wave structure.

reader Luboš Motl said...

We say that the wave function is not an observable and that it is not observable (without "an") because it is not observable!

There simply doesn't exist any apparatus that would measure, in a particular single repetition of a situation, something like psi(x,y,z). It is simply not possible. Not only the phase is unobservable - and the overall phase is unphysical. Even the absolute value is unobservable. An apparatus cannot even get an estimate.

Just try to think about it. If you're not completely hopeless, you will realize that one can't measure it.

According to quantum mechanics, and that's how Nature works. all observables - i.e. all quantities that can actually be measured by an apparatus - are given by a Hermitian linear operator.

Why don't you just try hard to learn the basics of modern physics? It's so wonderful and clear and your delusions are so breathtakingly pathetic.

reader tommaso said...

Dear Lubos,
funny, you politely ask me to publish a guest post on your blog concerning my view of the WW excess, and then tell me I should not express my opinion on SUSY. Oh well, coherence is not a virtue, is it ?
Anyway the antelope analogy is quite weak. Physicists have based their deductions on the apparent likelihood of phenomena (even in hypothesizing SUSY, through the naturalness argument!) for ages. It worked well until now, but for the existence of SUSY we should make an exception ?


reader Luboš Motl said...

Dear Tommaso, I asked you to blog post in order to show how SUSY deniers such as yourself are šitting to your pants.

I have never thought, not for one second, that it's appropriate for people like you to speculate about the probability of SUSY and similar questions. You know that very well. I don't have any incoherence whatsoever.

If you understood the very theory you tried to blog about, you would know that this is a hint that SUSY works in Nature and respects all the known rules of naturalness so your suggestion that it doesn't only highlights that you don't understand what you wrote about.

It's just a fact that corners are often natural. That's why antelopes hide there, too.

reader tommaso said...

Hi Marcel,
you are right - my text is not for insiders, and as such glosses over some details. I do believe that the PDF of q(x) and qbar(x) at x=0.03 or so is very well known, however, so I stand by my original statement, in a qualitative way. Of course one never ceases to learn, and NNNLO calculations may reveal striking differences and surprises, but again, the "scale" of these surprises can't be large.


reader tommaso said...

Lubos, your diarrhea of words is difficult to read. I don't think there's much to argue - when there is something to discuss your focus always shifts on why the other person is not qualified or how he or she is intrinsically stupid etcetera. It is fun for a while, but after a little bit you become just horribly boring. But you have your audience here so I guess you have to keep up to your standards... Good luck.


reader Dilaton said...

Hi Tommaso, what about admitting that you do not understand the explanations Lumo gave in the comments above, instead of disparaging them?

The SM Higgs was also quite "cornered" before it was finally discovered no?

Excluding large chunks of parameter space before something, such as low energy SUSY for example is discovered (if it is there, it does not have to be) is much more natural than being able to target the small correct region (maybe even a single point) in parameter space right from the start by an early lucky experimental shot. Also, nature gives a damn about what is easy to discover by humans and their technology, she/he/it does what she wants anyway ....

I rather like this blog post.

But I think too (as Lumo) that generally, the world would be much better if people who have not the appropriate technical/mathematical expertise in theoretical physics, would refrain from overreaching their state of knowledge by throwing around far reaching negative claims about the field and stop very vocally abusing popular media channels/books/blogs/ etc to amplify and their (to everybody in the know) unjustified claims.

reader jsc802 said...

That doesn't seem to stop you now does it, Dilaton?

I mean, Jesus Christ. The guy's job is to understand and experiment on the SUSY situation. He is allowed to have an opinion on it.

Luckily, I think Mr. Dorigo knows at heart that Lubos has a good heart and his knee jerk angry outbursts are just kind of unavoidable autistic tics that come with his personality.

reader Peter F. said...

Haha! I take it that this is your way of using illogic as a way of lamenting that "anything goes". :-)

This your 'proof' makes me start to think I am not completely mathematically wayward and maimed! %)))

reader Dilaton said...

His, as other experimenters job is to find signals for BSM physics, but the signals to look for are figured out by theorists and phenomenologists.

Experimenters do admirable good work but they neither have nor need a deep technical knowledge about HEP theory and it is not their job. So sorry no, Tommaso and other Experimentalists, and even less system administrators, high school teachers, teaching assistents, etc who are not even in the field of HEP, have absolutely no right to delude laypeople and scare physics students by throwing around unfounded dishonest negative claims about theoretical/fundamental physics. Sorry ;-)

Jesus Christ should help them to stick to their own job and learn some modesty.

reader Svik said...

How about postulating a new super force that keeps the hep parmeters fine tuned so as to avoid the need for Suzi and solves the qm vacum energy problem at the same time.

reader anon said...

Tommaso is a professional physicist since decades. Moreover, as a mere human being he is entitled to express any opinion he wants. Just like you do. Ah sorry. I forgot. You just parrot Motl (Lumo, for you) since years. Pay attention: your tongue well be fully consumed, soon or later.

reader anon said...

It is incredible how you pedantly copy exaclty all the expressions of Lubos. Do you I have any opinion of your own? I start thinking you are just Lubos in disguise. Lubos: it is not fair to post with 2 nicks..

reader Luboš Motl said...

Dear anon, if you learned how to state at least some things with the precision of mine, you would become a better human being, too.

It is really cute if an anonymous coward like you - preposterously - accuses someone of using wrong identities.

reader Dilaton said...

LOL I should probably take this as a compliment :-D

But be sure that everything I say and post here is my own personal opinion and way of thinking, and I am thankful to Lumo for offering a mostly troll free environment where theoretical physics topics and other things can be peacefully and scientifically discussed.

This guest post seems to attract a larger than usual amount of trolling spam, such as the comment I am replying too. The source of these spammers, who are also suckpuppeting and upvoting each other, is most probably to be found among Tommaso Dorigo's dubious friends who probably link to the above guest post to send us some spam and trolls...

reader jsc802 said...

You mention HEP-Experimenters but my guess is you'd feel the same way about anyone who is skeptical of SUSY or your favorite theory. Word of advice: just because you disagree with someone does not make them a stupid crackpot. For example, Lubos likes to talk a lot about the many worlds interpretation. Well, lots of smart physicists think we either have to go with MWI or search for hidden variables. Lubos likes to call both camps stupid crackpots. Now your list of stupid crackpots is getting longer. Is scott aaronson stupid? how about roger penrose? how about lenny susskind? The point is you should not think that everyone who disagrees with you is stupid and should be eliminated from the earth. Einstein would not approve of that attitube (but I guess he's a stupid crackpot).

My point about lubos personality is that it is endearing coming from him because he so obviously cannot help himself and it is just lubos being lubos. Plus he has a legitimate bone to pick with these people for being kicked out of academia. But hearing it from you is not quite so cute.

reader anna v said...

It is amusing that this long discussion which is really an ad hominem n the author is not about physics but for an analogy about putative new physics ! One should stop and think how much cultural and language misrepresentations play a role in interpreting such analogies.

Dilaton I take exception to your

"Experimenters do admirable good work but they neither have nor need a
deep technical knowledge about HEP theory and it is not their job. "

Good experimental physicists should have the mathematical background and have set successfully through courses or studied further the theoretical frameworks on which they experiment. They should be able to evaluate what they are passionately involved in studying spending decades of their life in the case of particle physics.

If this were not so, you would only get high level technicians and engineers overseen by theorists, and the failure of experiments would be guaranteed,

The same flame that turns a student to study physics should be burning in theorists and experimentalists for good physics to come out from this necessarily group work. Physicists talented with mathematics should turn into theorists and phenomenoligists and those talented with technical facility and data analysis into experimentalists, in an ideal world.

If I expect Susy to hold and string theory to be validated before I die :) is because of the appeal of the mathematical frame, that I do appreciate, even though I am by far unable to calculate a crossection from them.

But of course I think the arguments between particle physicists should not become confrontational, with fans who know little or nothing about physics, like a football game.

The data should talk and have the last word.

reader tommaso said...

Dear Dilaton,
I have held for six years a course in subnuclear particle physics at the University of Padova, for the masters course. I will restart soon, if you wish you can enroll -there is a significant part devoted to SUSY.
For the rest, criticism of what I can and can't know or do by commenters to the blog of a failed theoretical physicist are well below my attention threshold.


reader Luboš Motl said...

Dear Dilaton, if you had some important exchanges with Dorigo, please don't expect a reply here.

He tried to post a message so beyond the pale that he had to be instantly placed on the black list.

reader Morris said...

I've got what I think is a slightly unrelated question. Isn't space so large that we can safely conclude that at least some large groups of its points (for one example, possibly our solar system) have been repeated a few or many times?

reader Simon Phoenix said...

In the probably vain hope that I will not be banned after my first post I will try some flattery first. Excellent demolition of the inadequacies of the MWI, Lubos. I confess I've never quite understood why so many genuinely brilliant physicists subscribe to this nutty idea, or think that it provides any sort of 'explanation' of quantum measurement. I've always put this down to my own limitations as a physicist, so it's nice to see a robust and thorough exposition of the deficiencies of the MWI.
Having said that, I do think you're being a bit harsh on Everett's thesis as a whole. I think it contains some worthwhile insights (whether these insights are original is another question). The use of the Schmidt basis (an almost ubiquitous tool in quantum information theory these days), for example, is pretty cool as is the entropic uncertainty relation. Whilst I think results in information theory tend to be 'non-constructive' (Shannon's theorem, for example, tells us the limits on codes but not how to construct codes that achieve those limits) my own view is that they are perhaps a more fundamental perspective than other approaches. I like the notion that if we recover (classical) information about some observable we reduce our ability to extract information about a non-commuting observable - like the extraction of 'which-way' information, destroys our ability to extract 'phase' information. This kind of ties in with the notion that a measurement is made when classical information has been extracted.
Why do you think so many really good physicists (by really good I mean orders of magnitude more competent than me) subscribe to the MWI? It seems clearly deficient to me as an explanation of quantum measurement, and as a meta-physical position on 'reality' I think it's bordering on insane :-)

reader Luboš Motl said...

Dear Simon, sorry if I am harsh towards Everett's thesis but I don't see that your comment actually justifies that I am too harsh. For example:

I like the notion that if we recover (classical) information about some observable we reduce our ability to extract information about a non-commuting observable - like the extraction of 'which-way' information, destroys our ability to extract 'phase' information. This kind of ties in with the notion that a measurement is made when classical information has been extracted.

That's great but it was found by Bohr and Heisenberg in the 1920s, not in Everett's (much later) thesis that doesn't even articulate this thing - uncertainty or complementarity - correctly.

Perhaps the Schmidt basis is a seed to describe decoherence etc. but the mathematical part is due to, you know, Schmidt, while the physical application of the concept as shown by Everett isn't really right. Moreover, the essence of this decomposition has been intensely and explicitly discussed at least from the 1935 Schrödinger Cat thought experiment and I would insist that the Copenhagen school really knew all the right answers about the importance of the entanglement in picking the "useful basis" back in the 1920s. So Everett's "added value" is at most noise.

Good physicists - like Coleman who is a role model for that - often pay lip service to that thesis because they jumped on a bandwagon that turned Everett into a poster child of many correct concepts, like the fact that quantum mechanics applies equally to objects of all sizes, and so on, and no collapse ever occurs as a real process, and so on.

However, sociologically and historically, this is a completely wrong reason to favor Everett because the Copenhagen school *did* agree that there is no real physical processes that could be called the collapse - it's a change of the observer's knowledge expressed in the mathematical formalism of quantum mechanics - and on the contrary, Everett *did* really promote (non-existent) physical processes associated with the measurements, namely the splitting of the worlds after which his paradigm was really called.

So it's a mythology. Many physicists who are just fine and understand QM in a pragmatic, right, shut-up-and-calculate way, do say nice things about Everett because it has become a habit.

And then there are really confused people who don't get the point of quantum mechanics and its dependence on positivism/instrumentalism/subjectivism of the wave function at all.

reader Simon Phoenix said...

Thanks for the reply Lubos, food for thought there. It's a good reminder (which didn't really ought to be needed) about just how much the originators of QM really did 'grok' the issues.
There's been so much fuckwittery written about QM over the last 50 years, at least, that I really think anyone who writes about it should have to apply for some kind of licence to testify that they have at least read the first chapter of Dirac's text and some of the Bohr-Einstein debates lol!
I would describe myself as a mediocre physicist, at best, and so I wouldn't claim any deep 'understanding' of QM. The only way I can really make 'sense' of it all is to think about the state of 'knowledge' and how that changes. Operationally when I'm doing a calculation I think in terms of things being 'in' states and being projected into other states on measurement - but ultimately that's not a wholly consistent 'interpretational' perspective.
I think this is nicely illustrated with the GHZ state ~ |000> + |111> in which Alice has qubit 1 and Bob qubits 2 and 3. If Alice makes a measurement of spin-x then the state projection picture tells us that Bob's particles are projected into one of two maximally entangled states depending on the result of Alice's measurement.
The state that Bob ascribes to his 2 particles is, however, the density operator I/2 reflecting 1 bit of uncertainty. If Alice removes that uncertainty by sending Bob the value of the bit she measured then the density matrix Bob now ascribes is different - reflecting the change in the state of his knowledge.
Not telling you anything you don't already know I'm sure - but for me I think this example really emphasizes the role of our state of knowledge in all this.

reader Luboš Motl said...

Hi! Right, Dirac is a classic. Even though I didn't fully understand QM when I saw the book for the first time, I directly "felt" the firm foundations beneath me when I was reading it. It's so clear that the stuff is so deep and one must be very careful to avoid many naive mistakes - especially mistakes of talking about things that are physically meaningless. The "interpreters" of quantum mechanics are completely sloppy about all these conceptual things and they are proud about being sloppy!

I don't understand why you think that there is something problematic about the normal predictions for the GHZ state.

You have the GHZ state Psi. OK. You may adopt a global perspective. One may make many combinations of measurements in Alice's plus Bob's lab. Every Yes/No result of a measurement may be associated with a Hermitian projection operator, and the probability of any combination of results is the squared norm/length of the state

P1*P2* ... *Pn |Psi>

where P1 are the projection operators associated with the Yes/No measurements. For example, P = Jz/hbar+1/2 corresponds to the "Yes, the spin is up".

In this case, if you make two measurements, there are two projection operators acting in a product. Operators in Alice's lab commute with those in Bob's lab, a fact that is needed for locality.

You never have to talk about any "modification" or "collapse" of the state if you describe the whole system "globally". If you insist on talking about the B-degrees of freedom only, then indeed, if Bob trusts Alice's report about her measurement and he knows what the initial state for AB was, the GHZ state, then he may figure out what's the state for his own qubits and pretend that the Alice's qubits don't really exist beyond that.

But he doesn't have to "cut" his reasoning in this way. He may describe the whole system of the 3 qubits including Alice. In this whole physical system, he may prove that the state of Alice's mouth after she speaks is entangled with her measured qubits in a particular way, and he can make probabilistic predictions for the combinations of his measurements (of any kind) and for his measurement of Alice's mouth.

Because he may prove a particular entanglement between Alice's mouth and Alice's qubits, his listening to Alice is mathematically equivalent to the knowledge of Alice's qubits, and he may predict probabilities of different combinations of the results of any pairs of measurements in both labs using the standard and completely universal, unchanged rules of QM.

I don't know why people including you are so obsessed with "collapsing"{ the things all the time. Collapsing is just a method to simplify the calculation. It is never "fundamentally needed" for any physical reasoning.

reader Simon Phoenix said...

Lol! Yes indeed. Nice reply - totally agree. In much of the stuff I look at there is a natural 'cut' and so the reduced density operator perspective does make sense - but as you point out we can take a 'global' perspective which respects those universal unchanged rules of QM.
Obsessed with collapse? Lol! Yes probably - it's the way I originally learned QM and I guess it's kind of stuck as the way my head likes to work things out - but then I've also found in the past that the MWI helped me understand some beamsplitter problems more simply - and yet I think the MWI is madder than a box of frogs!
I also should point out an error in my previous reply - the density operator Bob ascribes before learning Alice's bit isn't (of course) the identity - but ~ |00><00| + |11><11|. Oops - sorry.
Thanks again for the reply - very illuminating and instructive

reader John McVirgo said...


Have you seen Everett's first draft of his thesis:

"Wave Mechanics Without Probability,"

This is the version that was passed to Bohr et al at Copenhagen. Bohr must have hit the roof from reading just the title.

reader Luboš Motl said...

Yes, I have, it's even worse than the final one. I am hitting the roof, too.

reader Trist said...

What about the preferred basis problem and Born rule?
Just wondering if you are one of those (as Carroll) who claim these issues are solved.

reader br said...

Hi Lubos,

Have you ever spoken to, or written to Sean Carroll about all this? Would it be worthwhile? He seems confident that decoherence answers most/all of the problems. I find the whole probability density splitting thing unimaginable, but I would expect Sean would agree with "The knowledge of the existence of interference of the state vector in quantum mechanics is the same thing as the knowledge that the world never fundamentally splits to two classical histories." As I vaguely pick up, the wavefunction of the multiverse remains in place, interfering with all the other multiverses quite happily, so there is never any true classical splitting. Not sure how that really is meant to work though...