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The secret lives of long-lived particles
- jimmytidey 10y agoI'm really fascinated by the idea that physics might be completed in my lifetime. I know it's a naive point of view - people thought the same around 1900, just before quantum mechanics and special relativity were discovered. I also realise that CERN hasn't made the breakthrough researchers hoped for. But what if the idea of long-lived particles, or another theory, comes good? It reconciles the standard model with relativity and explains dark matter, and then... it's all over. The rest is tidying up details. Wouldn't that be the strangest time to be alive? I think some people would be disappointed, but I'd be thrilled.
- renox 10y ago>I'm really fascinated by the idea that physics might be completed in my lifetime. ? Unlikely, given the current situation where there isn't much real progress toward unification of QM and gravity..
- chriswarbo 10y agoI think it depends on how 'chaotic' new discoveries are. For example, discovering relativity helped us to explain the world as it already was; e.g. it explained the precession of Mercury's orbit, but Mercury's orbit was already precessing. On the other hand, since we discovered quantum mechanics, it's affected many aspects of the world. Many quantum effects only cause small deviations in measurements, similar to those of relativity, and naturally "average out" on the macro scale. Yet once we noticed them, we were able to amplify these effects, and now quantum devices like semiconductors are all over the place; even something mundane like the postal service now involves computers, and hence to be explained fully requires quantum mechanics. I can imagine a future where all of our discoveries are of the relativity kind; i.e. making more precise predictions of some measurements, and having little effect outside of those measurements (although relativity has certainly changed our perspective and interpretation of the universe!) I can also imagine a future where we discover some minor correction to a measurement, say a slight shift in the spectral lines of novae, which is explained via an effect we can harness and which will affect all manner of things in the way quantum physics has. For example, maybe the discrepancy is explained as a weak gravitational repulsion; or due to matter making short jumps through time; or some other phenomenon which affects natural systems in subtle ways, but which we can amplify artificially to have far reaching effects.
- XorNot 10y agohttp://www.nature.com/nature/journal/v436/n7047/full/436150a.html http://www.nature.com/nature/journal/v436/n7047/full/436150a... Nature publishes short sci-fi stories in each issue. This one is kind of amazing.
- chriswarbo 10y agoWell, it's a little amusing I suppose, but I don't see what makes it 'kind of amazing'. I never understood claims like "if there's no free will, why do anything?"; it doesn't matter whether something's deterministic or not, only whether it's predictable or not. The only non-BS form of "free will" I've come across is Wolfram's approach of computational irreducibility, where "I" am the computational process which calculates my behaviour. From that perspective, even if someone can predict my behaviour and choices with 100% accuracy, it's still "me" making those choices, since their model of me is just another instance of me. Everything else is just geocentric fairytales.
- AnimalMuppet 10y agoIf there's no free will, why do anything? Because I can't not do it, because I have no free will...
- XorNot 10y agoI like the hook of 1 second negative-time circuits being mass produced. So much so you can put them on keychains, buy them at a dollar shop, whatever. That's the thing you really need to imagine: a world filled with gadgets more common then iPhones, that do a very trivial bit of future prediction that massively undermines our entire perception of reality.
- teraflop 10y agoThere's a similar idea in Greg Egan's recent Orthogonal trilogy [1]. It's a fascinating series that explores a universe with different law of physics from our own, with the physical implications worked out in considerable detail. One of the more intriguing (although hand-wavy) ideas is that in this universe, it's fairly straightforward to construct a device to send information backwards in time -- but if you actually do so, social and technological progress will immediately grind to a halt, on purely thermodynamic grounds. The idea is that any information that you send back seems to "appear from nowhere" as part of a stable causal loop, and so the entropically-favored outcomes are the ones where as much of the information as possible is uninteresting. [1] http://www.gregegan.net/ORTHOGONAL/ORTHOGONAL.html http://www.gregegan.net/ORTHOGONAL/ORTHOGONAL.html
- saiya-jin 10y agowe might also find out that there is no real way to travel faster than light, bounding us to colonizing few nearby star systems at best (which might be utterly inhabitable without massive terraforming), a rather depressing thought.
- maze-le 10y ago> we might also find out that there is no real way to travel faster than light We don't need to find that out, we already know that
- bbctol 10y agoWell, there certainly seems to be no way for anything to move faster than light through spacetime. It's harder to rule out exotic matter or negative energy that could warp spacetime to (relatively) move an object faster than light.
- XorNot 10y agoOf course if computing power proceeds to its logical bounds, we'll have more then enough capacity to sustain thousands of personalities in substrate the same size as the human head. And once we're all immortal infomorphs, "time" - and thus distance, may end up having very different meanings to us. EDIT: Basically just go read Accelerando for a pretty good take on this whole idea (it's free online).
- nitrogen 10y agoAlso read Permutation City, Diaspora, and Schild's Ladder by Greg Egan. If you only read one, read Schild's Ladder.
- throwaway000002 10y ago> I'm really fascinated by the idea that physics might be completed in my lifetime. That's an unfortunate thought to be fascinated by. You should study some physics, instead of reading popular articles about it, or even what pre-eminent physicists say about their work. I can simply illustrate the situation by saying if a question Q eventually provides answer A, the a new question Q' arises: why A? You can tell yourself "it doesn't matter" but quite frankly, at the human scale, physics is already a done deal. Which only further illustrates why your thought is a bit naïve.
- jimmytidey 10y agoI certainly could read more, but I do have a degree in physics and philosophy. Certainly there will always be questions like: why something rather than nothing? However, if you have a (relatively) simple set of rules, like the standard model, which work in every context and (in principle) predicts all observable phenomena, it does seem like you've crossed some kind of threshold. An intellectual threshold - as you say it has limited practical implications. It would be a watershed like observing alien bacteria. You're not going to do much with it, but it seems to put you in touch with the cosmic. There might still be lots of emergent phenomena we don't fully understand, but we could still be confident that the underlying physics is totally understood. An example of this might be the Navier–Stokes equation - we don't fully understand it, but I don't think many people think that a complete understanding of why nature obeys this law will lead to any fundamentally new physics. It's certainly possible it's just questions all the way down, perhaps smaller and smaller structures will be observable at higher energies, but it's an open question. Another option is that we're close to bottoming out all of the complexity - and that's the possibility I find fascinating. I'm not envisioning a time when every possible question has been answered, instead I'm thinking of a time when any questions about fundamental physics will either have been answered or we can be satisfied that no empirical evidence will answer them. QM may already have hit this knowledge barrier. We know from Bell inequities there are no hidden variables, there is simply no empirical way to predict with certainty the state of a quantum system. We've hit the edge of the knowable. "Whereof one cannot speak, thereof one must be silent" - as Wittgenstein might have said about the situation. In defence of throwaway000002, when I talk with physicists about the idea that physics might be completed they mostly don't think it's likely. I don't think they subscribe to the questions all the way down model, instead they think we have a long way to go yet - though I think most researchers don't have clearly formed views on the subject.
- ISL 10y agoIt's questions all the way down. Even if we knew the complete theory of everything, the immediate question would become, "Why is the theory of everything the exact theory of everything?"
- deleted 10y ago[deleted]
- hleszek 10y agoBecause of the Anthropic principle !
- jimmytidey 10y agoConceivably, you could have empirical evidence for multiple universes, at which point the anthropic principle becomes a normal explanation. Until then, obvious it remains a bit of a non-explanation.
- platz 10y agoI hate the Anthropic principle.. it appears to be able to justify anything
- M_Grey 10y agoYou should hate anything that isn't testable and falsifiable, that's good hatred.
- platz 10y agoThanks!
- bertiewhykovich 10y agoWhy? What fundamental reason is there to reject the untestable and the unfalsifiable? At worst, these claims fall into an epistemological netherworld where they can neither be ascribed truth nor falsity -- at best they may be useful tools.
- M_Grey 10y agoWe're not even remotely close, but if it makes you feel any better, people have been speculating about an end to physics for... well... you're in centuries of good company at least.
- beevai142 10y agoCondensed-matter physics and chemistry have been "complete" in this sense since forever. You can write down on a small piece of paper the Hamiltonian of electrons interacting via electromagnetic forces with themselves and the atom nuclei. And that's pretty much it.
- Razengan 10y agoAs a complete layman trying to grok the physics of our reality's fundamentals, now and then during the occasional Wikipedia excursions, I get the feeling that there is no way there are only 3 physical dimensions, and that we as beings rooted in 3D may never be able to see the full picture first-hand. I think having visual eyesight also makes us heavily biased towards picturing everything as ultimately made up of discrete "particles," and as far as I can tell, our instruments are also limited by trying to distill the results of our experiments into visual images, which results in things like the "wave-particle duality" conundrum.
- cdumler 10y agoThis seems wrong to me. I know the LHC records total energy in and compares total energy out. Wouldn't any long lived particles would "appear" as areas of missing energy?
- ISL 10y agoYes, unless they appear as something you think you understand. In the specific case of this article, they're interested in particles that look a lot like a muon. The signature of a muon in a particle detector is that it leaves a charged track in the inner tracker, passes through the substantial mass of the electromagnetic calorimeter without saying much, and then goes pow in the muon detector (usually alternating plates of steel and detector). A long-lived particle could be quite similar; a charged track, a lot of nothing, and a decay in the muon tracker. Any particle that might roughly replicate the muon's signature might have hidden from existing searches for new physics. The proposal in the article is to cover the muon detector with higher-resolution trackers. If the "muon"'s decay doesn't conform to the standard plan, higher resolution would make it apparent. I'm not enough of an expert to know how sensitive this method is in comparison to other ways of hunting long-lived particles, but I have taken a class or two from one of the authors. If Lubatti's pitching the idea, it's worth thinking about.
- mattheww 10y agoAs you can imagine, the long-lived particles can have "any" lifetime. Since the lifetime is unknown, it makes sense to probe many lifetimes. The experiment being suggested by Lubatti and his collaborators probes lifetimes on the order of 10^5 - 10^7 m. There aren't strong constraints on this range, which can appear as missing energy in CMS or ATLAS (or not). CMS, ATLAS, and LHCb are giving constraints at 10^-6 to 10^2 m. Interestingly, the different experiments are probing mostly different ranges. To correct something in the grandparent (?) post, the LHC experiments do not know the incoming energy. Even though the beam energy is 6.5 TeV on 6.5 TeV, the collisions are only a fraction of that. We only know that the energy has to balance in the perpendicular direction. However, if a collision produces two invisible particles that balance each other, it would appear that there is no missing energy. In many of models, pair production of new particles is preferred, so if the particles are long-lived, they can be hard to find.
- grabcocque 10y agoSupersymmetry and String Theories. Two theories that are not even not even wrong. Their proponents dance and shift in the prevailing intellectual currents such that there's no possibility they could EVER be proven wrong. There's no null result, no complete experimental failure, that could ever possibly convince them they might, just might, have made an error.
- shepardrtc 10y agoI think you're trivializing the process through which these theories are created. This is incredibly difficult stuff. There is very, very difficult math involved and there are very difficult tests that have to be done with very expensive machines. These things aren't just made on a lark while have a pint or two one afternoon. And even while creating them, there is no guarantee that even if the math is correct that the theory is correct. Theorists know this. But they do it anyway because we need them to. Its hard work and they don't get enough recognition for it (aside from the few that make it on TV).
- effie 10y ago> But they do it anyway because we need them to. Its hard work and they don't get enough recognition for it (aside from the few that make it on TV). They certainly don't do it because "we need them to". That's not how theoretical physicists and mathematicians think. It's more of a quest for the holy grail for some and more of an interesting puzzle to solve for the others. That's why some of them just can't stop, even if it's overwhelmingly clear that we have no way to create and probe the extreme conditions where something new and unexpected that would guide the theory could happen. Just because the math is hard does not mean they should get more recognition for it - one should look at the fruits of the work for that. It's not wrong to get occupied with solving famous puzzles, but everything in proportion.
- bbctol 10y agoI'd say string theory has had more dancing proponents than supersymmetry by a long shot. Supersymmetry can be tested--that's what the LHC was for--and as the evidence mounts against it, proponents are right to change their theories.
- werkinprogress 10y agoInstall a 10 foot thick lead shield at the end of the detector and glue a $10 motion detector light to it. Problem solved. You're welcome, CERN.
- werkinprogress 10y ago> In the past, physicists assumed that new particles produced in particle collisions would decay immediately, almost precisely at their points of origin. But wouldn't missing energy be evident?
- krastanov 10y agoThe missing energy is evident indeed, but this is not the point. You usually use the missing energy as a proof of a neutral particle, not a fast decaying particle. And you can not say what that neutral particle was because you did not measure anything about it. More importantly, the particle we are considering, the one that decays really fast, near the origin, will decay into other particles, and those can be detected.
- werkinprogress 10y agoIf the new resultant particle(s) don't decay immediately near the collision why wouldn't their missing energy be evident?