Will the LHC Smash Supersymmetry?

gbrumfiel writes "The Large Hadron Collider is just getting ready for its next big science run. One thing researchers hope it will find is evidence for supersymmetry, a theory that could help to unify fundamental forces and explain mysterious dark matter. But as Nature reports this week, the LHC has shown no signs of supersymmetry in data from last year's run. If super particles don't appear by 2012, then physicists might give up on the theory for good."

Comments

Naive Question

[Anonymous Coward]

Suppose they prove super-symmetry and find the Higgs Boson, what are we going to be able to do with it. Other than completing the theory, is there any practical use for this new found knowledge?

Genuine question, physics isn't my forté.

Thanks,

Re:Naive Question

[Rakshasa Taisab]

Pure research of this kind does not usually have any immediate applications that can be pointed to, so your question isn't exactly applicable. What we do know is that pure (or basic) research often enable progress in more practical oriented research.

Re:Naive Question

[TaoPhoenix]

Didn't we have the same "what use is this" question after that math story the other day? It's like a oblique troll that something is Useless Until Proven Useful.

General Theory of Truth: If something is true, something cool can be done with it. No exceptions. Politics don't count.

I agree *you* don't need this, but someone out there has to know this stuff.

Re:Naive Question

[darenw]

That's like going back in time and asking Coulomb or Volta about what applications their research would have.

"I don't know. Well, if you could make a small enough electrochemical cell to hide in your pocket, with wires you could shock people when you shake their hands, as a practical joke. Hee hee."

One way supersymmetry would be useful is at the theoretical level - it gives particle physicists another mathematical tool for predicting yet other kinds of particle to hunt for. It might help with understanding dark matter. When we know enough about space time matter and energy, my secret hope is we'll have insights for building faster than light insterstellar ships, or something else awesome.

Re:Naive Question

[Beelzebud]

I'm not sure anyone can give you a specific example but look at it this way: Know exactly how and why particles have mass, seems like a fairly fundamental thing to understand about the universe.

Re:Naive Question

[DeCappa]

What's the use of a new-born baby?

-Benjamin Franklin

Re:Naive Question

[AvitarX]

I bet it was more along the lines of "A Leyden jar that works more than once", or "Zombies!"

Re:Naive Question

[theMoleofProduction]

Once you find the Higgs there's a cut scene where God kicks in the door at Stephen Hawking's house, pistol-whips a nurse, and wheels Hawking away with a gun to his head. It fades to black and you see: "ACHIEVEMENT UNLOCKED: BOSON-NOVA!" The Level Up screen opens, you get to distribute skill points and pick a Level II perk, and then you move on to the next quest.

Re:Naive Question

[The_Wilschon]

Here's one possibility: All of our favorite science fiction stuff (things that would allow us to effectively have a galactic or even universal civilization) appears to be disallowed by special and general relativity. However, these things necessarily break down in some regard at the smallest (ie highest energy) scales. Understanding quantum gravity (if we can ever do so) will tell us just exactly how relativity breaks down at super high energies. It is possible that the particulars will show us a way to travel and communicate faster than light (think things like the Alcubierre bubble).

The LHC will probably not unlock the secrets of quantum gravity. However, understanding the lower energy phenomena like the mechanism for electroweak symmetry breaking, or supersymmetry (or technicolor, or a variety of other speculative theories) is a necessary step towards understanding quantum gravity. As such, I think that experiments like the LHC are vitally important to the extremely long term survival of the human species (we have to get off Earth and out of the solar system sometime within the next few billion years, at the very least).

As other posters have pointed out, this, along with all other speculative applications of what we learn from the LHC, are probably not going to be seen during our lifetimes.

Re:Naive Question

[MightyMartian]

Basic research rarely has obvious applications, and yet it pretty much lies at the heart of all technological advances. Guys screwing around in the 18th century with Leyden jars doing all kinds of interest parlor tricks probably looked pretty silly on the face of it, as well, and yet the ultimate value of these early experiments was enormous.

Re:Naive Question

[ObsessiveMathsFreak]

...and then you move on to the next quest.

Collect 8 top quarks and 3 anti-hydrogen atoms.

Re:Naive Question

[thesandtiger]

The troll in that thread was the idiot who didn't even read the summary where the answer to the question he had was given. In this case, I know I (and I assume the AC) genuinely want to understand what exactly this means because of a lack of understanding about physics.

The way I'd look at it is this:

If someone discovers a proof that P==NP, then even though we haven't found the practical solutions to some problems (factorization or whatever) yet, it means that there IS at least one "quick" solution. So, that basic knowledge has that potential practical application - even though we don't know how to do it yet we know it CAN be done, if this were so.

If someone discovers that super-symmetry or the Higgs is true or false, what does that mean? What practical applications, even in theory, would come from that discovery? I know that the basic research is important, but I'm curious as to what it might mean. Would we be able to then say "oh, hey, this means that even though we don't know how to do it, artificial gravity is possible" or time travel or whatever kind of thing?

Re:Naive Question

[John Hasler]

What we do know is that pure (or basic) research often enable progress in more practical oriented research.

Nuclear weapons, to be exact. Science brought politicians the bomb. They've been throwing money at physics ever since in hopes of something even better.

Re:Naive Question

[MobyDisk]

IANAP. There will be 1000 responses explaining why I am wrong. But every reply I've seen so far is "it might be useful for some undetermined future reason" which seems pretty weak. So at the risk of technical inaccuracy, here is my speculation:

The Higgs Boson is the particle that assigns mass to another particle. Once we understand it, it opens up a lot of questions and experiments:
- Can we create a Higgs Boson, thus creating artificial gravity? Tractor beams?
- Can we use them for signaling?
- Could we create gravity waves?
- Could we use them to store power?
- Could we create matter with no mass?

Re:Naive Question

[rgbatduke]

A more interesting question is what will happen if they don't prove supersymmetry and fail (once again) to find the Higgs Boson, and in fact find "nothing particularly interesting" (perhaps beyond insight into the quark-gluon plasma, which is already forthcoming) all the way out to its maximum energy across all experiments.

Lack of evidence is not evidence of lack, but it is worrisome. It leaves open the possibility that we are off on completely the wrong foot, that reality is really nothing like our models, and we might have to go looking for new physics to consistently explain things like particle mass and gravitation and cosmological deviations from gravitation currently wrapped up in the "dark matter/energy" hypotheses.

Come to think of it, we might learn just as much from failure as from success. As usual. Even if it is a very expensive failure, compared to the knowledge gleaned from it.

rgb

Re:Naive Question

[ironman_one]

Well, here is a story about a former Italian minister asking Alessandro Volta what "possible could be the benefit of electricity".( At he time electric appliances consisted of the " the Voltaic pile. A device able to give anyone a rather unpleasant chock but not much more.) Well, sad Volta, I relay don't know but sometime you might be able to tax it.

Re:Naive Question

[khallow]

Didn't we have the same "what use is this" question after that math story the other day? It's like a oblique troll that something is Useless Until Proven Useful.

I would use the term "truism" not "oblique troll". I consider the current tired slop, which passes for justification of science, to be abominable. If you do work in the sciences at the behest of someone else, I can only hope that you justify your work far better than what you did here. This is a reasonable question to ask and it is disturbing how frequently it is brushed off.

In the case of figuring out whether supersymmetry is a feature of the universe or not, it is worth noting that advancing fundamental theories of physics have helped us in the past. Quantum mechanics is the basis for the model of semiconductor physics which we have so successfully used to power wave after wave of computers. Relativity led to the discovery of fission, fusion, and a host of subtle effects that affect really precise atomic clocks. Quantum electrodynamics predicted the existence of anti-matter and explains free electron lasers.

Quantum Chromodynamics is the current state of the art. While I can't point to an invention enabled by the theory, the theory does an adequate job of modeling particle jets which are real phenomena experienced by anything which is exposed to very high energy cosmic rays. And it explains all the known particles that we have seen so far.

So justification #1, past success indicates likely future success.

As a result we have something like tens of thousands of people, who incidentally cost a lot to employ, exploring the boundaries of current physical theory. But they have a big problem, not a lot of observational evidence. This leads to justification #2, any new observations trim the thicket of theories and better focus this vast expenditure of society.

Third, it's not a primary target. Justification #3, it's a freebie that you might get from work that was going to be done anyway.

Fourth, we can already think of genuine applications. For example, if you can figure out how to reliably emit, steer, and intercept neutrinos, then you have a potential communication device which can operate through the Earth, even through the Sun. An obvious near future application of that is communication from a central point on Earth to deep sea subs (such as the US or Russia's submarine forces). It also provides a significant communication edge for high frequency traders. It's the only way someone on Earth could directly communicate with someone on the far side of the Moon (which always faces away from the Earth).

The reason this exercise is useful is because we have many ways to decide how to spend the money that gets spent on scientific output. Maybe it could be spent on other things of pressing urgency such as feeding children or marketing a business's existing product (depending where the money comes from). Even if you decide on a scientific expenditure, it is worth recalling that there are more than one possible destinations.

This is why it is important to have justification, one or more reasons why something is useful. Because someone has to decide what to try, even if it's left to the scientist with ideas rattling about in the skull.

Else, you might as well spend all that science money on me, Mr. Khallow. You'll get science (check!) and some really cool block parties, well, nation-scale parties. A bit more money might be spent on the parties than on the science, but that's ok. Science is being done. That's all that need concerns you.

Re:Naive Question

[bigsexyjoe]

The poster didn't argue that it wasn't useful. They asked if any immediate use is known. Not a dumb question, because often we can think of a specific application for new physics or math. For example, if someone solves does P=NP, we would care pretty fast. Sometimes we find the utility later, and sometimes nothing is found.

Re:Naive Question

[mjwx]

General Theory of Truth: If something is true, something cool can be done with it. No exceptions. Politics don't count.

No Politics do count, when a politician tells the truth something incredibly useful can be done with it. This has not been tested in some time however.

A validated theory is a stepping stone ...

[perpenso]

Suppose they prove super-symmetry and find the Higgs Boson, what are we going to be able to do with it. Other than completing the theory, is there any practical use for this new found knowledge? Genuine question, physics isn't my forté. Thanks,

A validated theory is, if nothing else, a stepping stone to an even more complete understanding. From better understanding comes new, or improved, tools. There is sometimes a time lag between discovery and practical application. Sometimes decades, sometimes a century or more. Consider nuclear fusion (what the sun is doing), potentially a safe and abundant source of power. Figuring out how to build and operate a fusion reactor will require understanding a few theories that were at one time merely theoretical with no practical application.

Re:A validated theory is a stepping stone ...

[thesandtiger]

The question then that I would have is "Why don't people who are trying to come up with practical applications act 'as if' the theory were true?"

I guess what I'm getting at (I'm not the AC who started this but I am also in a similar boat, understanding-wise) is: Right now it seems that most physicists THINK this theory is true. If that belief is validated, okay, great, they know they're on the right track, but aren't they already basing a lot of ideas for steps further down the line on the notion that this might be true? And, if that's the case, then aren't people coming up with, or at least thinking about, practical applications based on that assumption?

To me, it seems like the really interesting result would be if this assumption of super-symmetry (or anything else in a particular theory that is widely believed) doesn't actually prove true or doesn't behave like it has to for the theories to be true.

In case I'm being obtuse, I'll use an analogy:

When people were making rockets, they had some theories about what might happen in space, or what might be needed for the rocket to work, or what might happen to the people on a rocket, etc. They behaved "as if" those theories they had were true, or, at least, "as if" the most risky/dangerous versions of their theories were true and designed accordingly. So, they launched rockets, people were in them, and some of their theories panned out, some did not.

What could be built if these theories are true?

And, I am totally 100% behind the idea of learning stuff just to learn it - even if there isn't a practical application, understanding the universe is important.

Bleh, sorry, sick as a dog and on massive doses of NyQuil so I ramble.

high enough energy?

[Krau Ming]

*warning* semi-naive physics question here: does the LHC smash particles at a high enough velocity (or energy?) to definitively solve these problems? does the absence of a Higgs boson from the previous experiments disprove supersymmetry, or are we not smashing hard enough?

Re:high enough energy?

[spottedkangaroo]

I'm wondering the same thing. I think that they're looking for the "lightest super partner." Even one such partner would be evidence even if most of the partners were too heavy to show up in the LHC. But I don't really know how heavy any of them are.

Re:high enough energy?

[boristhespider]

No. We can never smash hard enough to disprove supersymmetry unless we find something that directly contradicts it. To put it another way, if all the LHC finds is a Higg's and expected results from the standard model, it doesn't actually disprove supersymmetry since any model of supersymmetry has so many parameters that you can tweak a few of them and lift the superpartners back up above the LHC's maximum energies. That is *always* going to be possible -- theoretically a limit would be if we had particle accelerators that reached the Planck energy and people would finally be saying "hang on, something's up here; we should be seeing quantum gravity by now and we're still not seeing the quarkinos", but in reality we're never getting to anything like an energy that would rule it out.

What's a lot more likely in my mind is that more physicists will begin to drop supersymmetry and look at something else that may actually have observable effects at "low" energies while otherwise the supersymmetry bandwagon will roll happily on with slightly more tightly-constrained parameters.

The hope is that the LHC not only doesn't see supersymmetry but *does* see something utterly unexpected. That's what I want from it. (Actually I want specifically no Higg's boson, and no supersymmetry.) Something unpredicted would rule out supersymmetry not least because any supersymmetric model that could account for it would be a posteriori -- constructed purely to do that and most likely grossly ugly as a result. By definition something unexpected is not a straight prediction of supersymmetric theories, and any model constructed purely to explain it will be under suspicion.

Before getting onto the next bit, the Higg's is not associated with supersymmetry, it's part of the standard model and doesn't require supersymmetry to exist. The Higg's is the last part of the standard model that is yet to be observed. They're different topics, and the LHC is hoped to shed light on both of them. As far as supersymmetry goes, the LHC was built basically to give us a pointer for where to go beyond the standard model and forms of supersymmetry are currently the most widely-favoured options.

The fear (at least my fear) is that the LHC will find nothing. Squat. No supersymmetry, nothing outwith the standard model -- but from my point of view, that it does find a Higg's. That would appear to add support to the standard model, which is a bit of a pain because the standard model's already broken since we *know* neutrinos have to have mass and fudging the standard model to put them in is pretty contrived.

However, not finding a Higg's at all would be brilliant -- so strictly speaking, the LHC finding *nothing at all* would be good. Because the Higg's should be within its capabilities and if it's not there there'll be a lot of head-scratching going on, and I always prefer things being rethought and reanalysed over mindlessly employing techniques chiefly developed in the 40s with QED and brought to fruition in the 70s with QCD and the electroweak theory.

But, in all fairness, I'm not a particle physicist, I'm a cosmologist.

Re:high enough energy?

[boristhespider]

most of them are pretty damn heavy. i believe the lsp is expected (from some models of supersymmetry) to show up in the lhc but it's easy enough to make sure it doesn't. if an lsp is found then at least part of the dark matter problem will be found, because that thing's basically stable and doesn't interact with us in any way.

warning: unfocused and off-topic rant ahead.

what's going to upset me is if an lsp is found (which i see as pretty unlikely, in all honesty) people are going to be shouting about how they've solved the dark matter problem -- they haven't, they've found that an lsp exists and is guaranteed to form *part* of the dark matter. there are plenty of other candidates and unfortunately i've been in physics long enough to realise that when there are about 15 or 20 candidates for something, most of them are there in some respect. i'll not be surprised if dark matter comprises of an lsp, massive neutrinos (we already *know* they're a dark matter, just not how significant they are if at all), relativistic corrections to the naive newtonian models of galaxies (galaxies are not living in flat space, they live in curved space which for spiral galaxies is cylindrical), a misapplication of the friedman equations in cosmology (the issue there being that they describe the universe "on average" and yet we haven't the faintest clue how that "average" is taken), and probably a host of other things i've forgotten and even others that have never been thought of yet.

Re:high enough energy?

[mangu]

But, in all fairness, I'm not a particle physicist, I'm a cosmologist.

What I want from cosmology is the same thing I want from the government: no inflation. A theory that needs a 78 orders of magnitude adjustment doesn't seem quite right to me.

Why not assume that the answer to the horizon problem is that under some circumstances FTL might exist? The problem with relativity is that it denies, in a somewhat dogmatic way, the existence of one absolute inertial reference, when we know there is at least one local reference that's "more inertial" than others because it's at rest with relation the the cosmic background.

In 1905 Ockham's razor was favorable to relativity because the microwave background wasn't known, but today we do know that it exists. Perhaps we have one reference where simultaneity can be defined in an absolute way, and the lack of simultaneity in other references is just an illusion caused by perspective. After all, there are many experiments demonstrating Bell's inequality that seem to indicate simultaneity in remote events.

It would seem to me that in the conditions shortly after the big bang there could exist conditions where some physical parameters were communicated instantaneously across the universe by quantum effects, this is at least no more unbelievable than cosmic inflation.

Re:high enough energy?

[boristhespider]

1: Pure phenomenology. No-one constructing inflationary models that I know of actually seriously believes that it's fundamental physics (at least, not after the second or third year of their PhD). What they *do* believe, frequently, is that the phenomenology can help guide a more fundamental theory. Personally I don't always agree with that; I think it can shroud a fundamental theory (in a similar vein to how cosmology is built on phenomenology that basically shrouds a very serious and neglected underlying issue).

Unless you're using the Higgs itself to drive inflation -- Guth's first model did this but it ran into problems with a graceful exit; it's recently been reawakened and re-examinded, though -- you're going to have a massive problem identifying an inflaton. We've not observed *any scalar fields whatsoever*. Even the Higgs remains elusive, though that might change in the near future. (Don't hold your breath.) So you immediately have a problem that what you're doing is specious. You can then either ground your inflaton in a well-reasoned model of high-energy physics or, and this is the standard approach, just invent a scalar field, call it the inflaton, and give it an arbitrary potential. So long as you make the potential flat enough that scalar field is an inflaton.

Basically it's phenomenology. But the people who do it are convinced it gives *suggestions* about what lies underneath, and in some ways they've got a point. Inflation works extremely well and it's standard to assume there was an inflationary epoch. You solve the horizon problem, the flatness problem and (if you believe in various GUTs) the monopole problem. (Basically -- why does the CMB look identical in opposite directions when the universe is too young for them to have ever interacted; why is the universe so fucking SMOOTH; and why do we not see any of these magnetic monopoles that GUTs produce in abundance?) Even more importantly, though, the quantum fluctuations of a scalar field coupled to gravity in the early universe produce tiny seeds that are basically exactly right. You can make models that get them exactly wrong but actually you have to work a bit; basic inflation made a prediction of those seeds, and when WMAP came along and looked at the CMB in unprecedented detail, it was dramatically confirmed. Basically those ripples had to be almost exactly Gaussian random, and "scale-invariant" meaning that the extremely large wavelengths were massively more powerful than the shorter wavelengths. That maps through to the formation of the CMB, when electrons condensed into protons to form hydrogen and light rays could suddenly free-stream carrying with them a photograph of the early universe. And it maps through even further, to the large-scale structure of galaxy clusters where we can look at those very same wavelengths. Much of a shift from those early imprints and that distribution is changed actually quite dramatically.

2: Dark matter is a big issue (well, duh). Basically "dark matter" is a catch-all term for whatever is causing rotation curves to deviate from the Newtonian prediction. I get irritated when people immediately assume it's a new exotic species of particle. I've put a couple of rants on this thread aimed at this kind of thing. My feeling is that dark matter in galaxies (and galaxy clusters) is made up of five or six different effects, *all* of which act as "dark matter", ie to flatten rotation curves: exotic particles perhaps, if supersymmetry is true; massive neutrinos since we now know that they are massive even if we don't know the mass, and neutrinos are so abundant that with *any* mass they form at least a dark matter even if it can't be the full dark matter (attributing the entire dark matter to massive neutrinos badly washes out structure on galaxy cluster scales); relativistic corrections coming from our naive assumptions that galaxies inhabit Minkowski (ie normal flat) space, since they don't, and that may -- *may* -- be able to account for up to roughly a tenth or more of spiral galaxies' dark matter; i

Re:high enough energy?

[boristhespider]

You can get Schroedinger's equation in a totally deterministic (if rather contrived) manner by taking a totally classical system and adding a modification to the potential. If you then take the momentum potential (or action, however you want to phrase it) and the density you can bundle them together as basically the phase and the amplitude of a wavevector that... solves the Schroedinger equation. Totally deterministic and totally indistinguishable from standard QM. It's also very ugly and is riddled with conceptual difficulties, not least how you go about second-quantising to get something like a field theory, but even so, it's a totally deterministic formulation of standard QM.

Also, as basically a gravity theorist, it pains me to say it but GR is less reliable than the Standard Model. We can test it down to maybe 0.1mm and up to Pluto's orbit and beyond that, nah. It's because gravity's so damned weak. The other forces are much stronger and much better probed, and electromagnetism is the best known of all. QED is still one of our best theories. The problem with taking that too far is that then people have a bad habit of assuming gravitons must form the basis of a successful quantum theory of gravity and throw out geometry altogether -- knowing all the time of course (because they know this shit much better than I) that GR is non renormalisable and you're doomed to failure going at it in anything like a typical way. That way leads to string theories and supergravities and 30 years of intensive maths with absolutely zero solid predictions. A nice alternative is loop quantum gravity, which takes a much more conservative approach, takes geometry seriously, finds a way of quantising spacetime without gravitons and 7 extra dimensions, and has absolutely zero solid predictions for about fifteen years less intensive study. Other alternatives are brilliant, and all of them have absolutely zero predictions, to my knowledge.

As for the black hole question, it's not answerable within "big bang cosmology" because GR would have broken down before you get to the point that all the matter is within its own event horizon. Before GR is at all valid (even assuming we could use it that early) you can't extrapolate. So there's no way of saying that a black hole would inevitably be there because there might not *be* black holes in quantum gravity and on those scales probably aren't. (QG is expected to wash out singularities in some manner, and we have no idea what it's gonna do to event horizons on such small scales but if you've, say, granulised spacetime in some manner you've immediately got quantised areas and volumes as in loop quantum gravity, and that puts limits on horizons.) But it's all speculation... as is saying that there'd be a black hole back then because that extrapolates GR well beyond its regime of validity.

I wouldn't say "it didn't, we live inside still". I've heard people suggest that (I've even seen a Creationist cosmology that used external coordinates to chart the interior of a Schwarzschild hole, put us bang in the centre on top of a singularity and then used gravitational time dilation to prove that the universe is only 6000 years old. No shit, he did it. Of course, it relies on using the wrong time coordinate and the wrong coordinate patch in general, and then assuming that the singularity on the event horizon is real -- it's not -- and then that we can live in the centre of those coordinates, but it was still a stroke of genius.) But I wouldn't. The geometry is weird if you believe the extended Scwarzschild solutions and it's even weirder if you think we live in a charged or rotating hole. I don't believe any of it. I don't really have any firm beliefs one way or another, in all honesty, but definitely not that we live inside some big black hole.

I think I've made my opinions about dark matter and dark energy fairly clear somewhere in these comments, three times I think :) They are band-aids, and very ugly ones at that. MOND is an interesting one. No-one, including Milg

Re:high enough energy?

[boristhespider]

I wrote a long reply to this and lost it by being an idiot :( Anyway, I said firstly to dig out a copy of Joao Magueijo's book which may or may not be called "Faster than the Speed of Light" which postulates a changing speed of light and lets you do away with inflation. I think a lot of people would be happy if we could do away with inflation completely, but anything that replaces it has to repeat its successes, which are many.

As for the CMB, it doesn't violate relativity, it's *predicted* by relativity. All it is is a thermal bath of photons left over from the big bang. If you put in a big bang cosmology, that's what you get out. It doesn't pick a physically preferred frame any more than saying "This is MY car and that's a preferred frame!" It is a preferred frame - it's the one you're observing from, but it's not physically preferred. GR is all about being able to look at things from any frame of reference -- that's how it wipes the force of gravity; it notes that it's as fictional as centrifugal force (which it is) and changes reference frames to study it properly. The CMB isn't an absolute inertial reference frame, it just happens to exist. It's not imposed on or by relativity, but if you use a Robertson-Walker solution and put any photons in it at all it's forced on you.

Also it might interest you to know that in the standard cosmological model (phenomenological as it is) we don't even lock ourselves to the CMB. We actually lock ourselves to CDM most of the time, or lock ourselves to some frame that makes gravity look as Newtonian as possible.

As for simultaneity and so on... well, GR is wrong. Unfortunate, but true. How wrong and in what way we don't know, but yes, there seem to be issues.

Re:high enough energy?

[Bootsy Collins]

I left cosmology ten years ago after the dreaded third postdoc, so I've no doubt I'm out of the loop on a lot of things. But still, I'm surprised by a lot of your post. There's a bunch I feel like agreeing with/disagreeing with/asking about, but I don't have the kind of years it must have taken you to write that to reply! So I'll just pick out a couple of things:

A priori there's no reason to actually connect the dark matter needed for galaxies and clusters with the dark matter employed in cosmology. Cosmology is based on the Friedman equations -- one saying how fast the universe expands and the other saying whether it's accelerating. The "dark matter" in cosmology is just a number that appears in these equations. Identifying it with the dark matter in clusters appears to make sense... but only if you believe the equations are seriously physically meaningful.

Sure, logically you can make that argument. But you have a strong hint, don't you, from the fact that the numbers seem to work out. You have a number of independent ways of getting at the dark matter in clusters of galaxies -- (M/L), the cluster baryon fraction, weak lensing, etc. -- which are fairly consistent with each other. (we'll ignore stuff like the luminosity/temperature/mass functions of clusters, which also seem consistent with everything I'm going to say, but introduce new assumptions about density fluctuations etc.) In the first two -- (M/L) and the baryon fraction -- your method for deriving Omega_matter doesn't depend on the Friedmann eqns, or even the Robertson-Walker metric. I then take that value for Omega_matter, the flatness result from WMAP, and get a value for Omega_lambda. Now I *have* introduced cosmology, because in looking at the power spectrum of temperature fluctuations on the surface of last scattering, my relation of angular scale to redshift depends on the RW metric. And maybe, as you say, those equations don't mean anything physical, so that value of Omega_lambda doesn't really mean anything. But if that's true, then why does the hypothetical universe described by those values of (Omega_matter, Omega_lambda) do so well with observations on a broad range of scales -- such the high-z supernova data or the morphology distribution of clusters at low redshift -- things that wouldn't have to be consistent with each other if the Friedmann equations were meaningless?

(snip) But all this is built on standard cosmology - the Friedman equations. And here's the rub: these describe the behaviour of the universe on average and come from assuming that the universe is composed of homogeneous and isotropic 3D slices. But the universe isn't homogeneous and isotropic! If it was we wouldn't be here. Instead we're like a loaf of wholemeal bread, filled with chasms and filaments.

From my (admittedly dated) experience, nobody ignores the large scale structure of the universe in arguing for homogeneity/isotropy. They argue instead that we converge to it as larger volumes are considered. The surface of last scattering gives you an opportunity to test this idea, and it doesn't seem crazy. And we've gotten a long, long way with the Robertson-Walker metric, the derivation of which is built on homogeneity and isotropy. Granted that there have been surprises in the application of the redshift-distance relation (derivable from the RW metric), such as the Type Ia SNe data that got the whole "dark energy" mess rolling (I've always wanted to slap Mike Turner for coining that phrase -- can't think of one I hate more); but I can't see how inhomogeneity-induced perturbations to the RW metric would manifest themselves on large scales exactly the opposite from how they manifest themselves on smaller scales, in the near vicinity of structures.

Re:high enough energy?

[kittylyst]

Bear in mind that SUSY was not intended to be a hack job. The Coleman-Mandula theorem is pretty definitive - if we want an abstraction that looks like QFT, then it has gravity, a gauge group (so in the real world SU(3) x SU(2) x U(1) at any energy scale we're ever likely to be able to detect / care about). SUSY is just the least messy way of extending symmetry in a way which doesn't violate Coleman-Mandula and which could provide constraints on the Higgs mass.

The original hope was that a) some existing particles would be found to be superpartners of other existing particles b) additional superpartners would be discovered relatively quickly.

That was all dashed hope, of course, but my point really is that SUSY didn't start off looking as bad as it does now. I never really believed in it, although some of the algebra was kind of pretty. Of course, having said that, I'll now be forced to eat my words (not for the first or last time), when the LHC finds a Higgs at the last gasp.

Re:Politics

[TaoPhoenix]

Sorry, I wasn't clear.

I meant that cool stuff "can be done". "Whether it will be done" is the whole other problem with the political side. Sometimes the "can be done" is pretty hard, and politicians hate hard stuff. "We can have a moon base in 20 years" - but only if we were so scared we stopped most of our petty squabbling to do it. Seriously, you engineer types out there, how hard is it really to get a quad-protected airtight building to the moon? Put it at some kind of shade-crossover point to use the solar power but not get totally fried.

The problem now is we have a Terrorist meme that will instantly shut down any planetary science because we have decided we can't trust anyone to be on the base without blowing it up.

No Higgs, no super symmetry, but a t-shirt

[sweetser]

That's my prediction, and my t-shirt: http://bit.ly/GEMtshirt

The idea: Maxwell's field theory is the best one we have, the basis of the standard model by swapping out the gauge groups. I figured out how to write the Lagrange density (every way energy can be exchanged inside a box) using quaternions. That is not so hard. Do you know how to factor (B^2 - E^2)? If so, then (Del A - (Del A)*)(A Del - (A Del)*) is the same thing, quaternion style. The quaternions cannot do gravity which involves totally symmetric changes in a metric. Therefore I used an even less popular algebra known by names such as the hypercomplex numbers or the Klein 4-group. Put that into the Lagrangian, which flips exactly half the signs. That makes my proposal for gravity.

Combine the EM quaternion rewrite with the hypercomplex gravity Lagrangian, but without that -(Del A)* thing which was subtracting away the gauge term. The gauge term is there in both the gravity and EM portion, but they wipe out each other, so gravity and EM apply to massive particles, but overall the Lagrangian is gauge invariant. The Higgs mechanism works via a clever solution. My unified standard model works via a clever Lagragian.

By the end of 2012, I will know if my t-shirt is wrong because the Higgs and/or supersymmetric particles are found, or my t-shirt is barking near the right tree.
Doug

Supporting material about the t-shirt
http://bit.ly/GEMIAPday1video
http://bit.ly/GEMIAPday1pdf

Re:That's what's wrong with Physics today

[Mr_Huber]

Er, they do realize that Kepler's laws do not apply to galaxies. They cannot, in fact, use Kepler's laws because they know quite well that the gravitational contribution of the stuff orbiting the center of mass is significant. That's why they use Newtonian physics in this situation. Our modern understanding of the evolution of spiral arms comes from this sort of analysis. They do not use Special or General relativity in this situation for two reasons. First is that the math is real hairy. Second, at these speeds and distances, it reduces down to good old Newtonian motion anyway.

As for Dark Matter, yes, there was a flash in the pan article a few years back about someone using General Relativity to analyze rotation curves and coming up with enough extra contribution to invalidate dark matter. The paper was up on ARXIV for about four hours before the first math errors were spotted and brought the whole thing crashing down. And even if that paper held, it wouldn't have explained results like the Bullet Cluster (http://en.wikipedia.org/wiki/Bullet_Cluster), where maps of particulate dark matter have been made. No modified gravity theory or assertions that dark matter goes away under SR or GR can explain those findings. Dark matter is real and we now have tools with which we can spot it. The trick is now to figure out what it is.

You seem to have a real misunderstanding of how physics, and all science, makes progress. Once we have theoretical models, they are, generally, perfect. A good theoretical model explains ALL available data, or it isn't a good model. Once we have a good model, the only way to improve it is to go actively looking for where it diverges from reality. Only with this new input, divergence from theoretical predictions, can models be refined, improved or even replaced.

That's why we're hunting the Higgs particle. Fact is, the Standard Model is slightly broken. Without a Higgs mechanism, predicted lepton mass does not conform with experiment. We have a gap right now, a discrepancy. We think we have a solution in the Higgs field. We could, I suppose, assume there's a Higgs field, pick one of the several variants and go with it. Or we could, you know, do some actual science and go looking for the thing and nail down its properties. Along the way, if we see some of the other things we're half expecting, super symmetry, discrepancies in gravity at the millimeter range, broken symmetries, energy leakage at high energies or anything else, so much the better.

The problem with science is not a lack of fundamentals. The problem is the theories are too damned good. Reality simply does not diverge from the theories unless we get into some really exotic conditions. Why do we need a superconducting particle collider with a diameter measured in kilometers? Because our models are frikkin' perfect for everything up to that. We know they're wrong. We know we can't reconcile GR with the Standard Model. But we won't know how to proceed until we can break either GR or the Standard Model. We don't know what piece of the puzzle is missing until we actually go and look at things.

Re:Politics

[ByOhTek]

The politicians are the Terrorists!

Remember kids, if you support a politician, a terrorist wins!

Good way to waste time

[Roger W Moore]

The question then that I would have is "Why don't people who are trying to come up with practical applications act 'as if' the theory were true?"

...because that would be a very good way to waste a lot of time. First question is "which theory" do you take to be true? Simple Standard Model Higgs or a Supersymmetric Higgs, or even a 2-higgs doublet model without supersymmetry? Next question is what is the mass of the Higgs bosons in your accepted theory? The problem with any unknown model is that there are free parameters which are unknown and so the phase space opens out so fast that it becomes impossible to concentrate any amount of effort on one particular area.

The other problem is that any effort may be completely wasted. For example Columbus set off to find a passage to India. Had you attempted to set up an Indian spice importing operation before he had returned you would have looked like a complete idiot.

To be precise...

[Kupfernigk]

I'm not even going to apologise for this pedantry, because I was at one time a member of the Royal Institution, before I foresook science for engineering.

In fact Faraday's joke was better than that, It was the Prime Minister (in those days called the First Lord of the Treasury, hence your confusion), and the Government had recently introduced some unpopular taxes. So Faraday's actual reply, "I know not, but I wager one day your Government will tax it" was doubly apposite.

The other one of these Victorian quotes is the response of the inventor of the dynamo when asked what use it was: "What use is a new-born baby?"

Utility is part of the plan

[Roger W Moore]

Physics at this level is like abstract mathematics: it exists for its own sake. Practical applications of this physics is like practical applications of number theory: just not in the plan.

Completely wrong. I don't know a single physicist who believes that. The reason we do what we do is because we are curious about the universe and want to find better ways to exploit it...but the first step in that is understanding. Practical applications are always part of the plan. The problem is that since we don't yet know the physics we don't yet know how to use it practically. 100 years ago "Physics at this level" was quantum mechanics which, since you are reading this article on a silicon based device, has turned out to be extremely useful. Of course absolutely nobody at the time could possibly have predicted the development of the integrated circuit from an understanding of quantum mechanics.

Even today early particle physics detector and accelerator technology is produced better medical imaging and treatment options. Just because we cannot imagine how today's discoveries will be used in 70-100 years form now does not mean that we don't fully expect them to be used for something.

Re:Utility is part of the plan

[mrsurb]

And of course number theory may have seemed useless at the time, but it turns out that useless things like factorising huge numbers into prime factors has practical applications for cryptography.

supersymmetry ain't...

[OldHawk777]

Observation problem: A particle in a field creates a field wave/state. There are not two *-particles. The *-particle/object is observed, or the *-wave/state is observed. A distant *-particle in the same field will show a wave/state relationship with the other particle, but never a particle relationship. Additionally, if the gravity field is uniquely interacting with another field (levity) as a pure gravity field bound by a pure levity field (or more fields) and/or localities/spots of varying strength single mesh-fields... well it could be interesting... %~P