[Weekly Discussion Thread] Scientists, what are the biggest misconceptions in your field?

fastparticles · 1 day

One of the biggest and most persistent: Quantum entanglement and nonlocality.

Its hard to blame people for not keeping it straight because its so subtle and tricky. One central question here is whether physics is nonlocal, but this framing turns out to be a little bit troublesome. Bell's theorem proves that, at least superficially, yes, you do have to accept that the physics manifestly necessitates an immediate connection across arbitrary distances. However, the nonlocality does not correspond to any physical variables you can ever influence. In other words, the non-locality is exclusively due to "nature's random number generator" which is why quantum physics never violates causality. One really common misconception is that this means some kind of superluminal communication is possible. It isnt. Another frustrating confusion is when people try to speculate about some physical mechanism that could affect the nonlocal collapse; it cannot be anything other than the basic rules of quantum mechanics. One way to emphasize this is that entangled states are a completely generic property of any composite quantum system, so clearly the only explanations that are possible are those that apply universally to all physical systems.

One way to think about it that I consider very helpful is to remember that its not actually possible to compare measurement results with your entangled "partner" until you classically communicate (i.e. sub-luminally). This act of exchanging measurement results classically should itself be considered a measurement; that is what the postulates of QM would dictate at least. This is not an interpretation-neutral statement, but it shows how QM be completely local without altering any of its predictions. (To hear one of physics's great minds arguing this point, here is Sidney Coleman.) To some extent, interpretational questions go beyond what can be experimentally adjudicated in principle, but the interpretational questions are also one of the main reasons that people care about this kind of experiment. They do radically constrain the options, and many that aren't quite killed are forced to be so contrived you may decide to kill them for yourself when you've assessed the evidence.

One more thing that many people miss: just like entanglement applies to any quantum system, there are also infinitely many incarnations of Bell's theorem. Many do not rely on inequalities like the original proof does, there are vastly more elegant and tangible ways to see that the results of Bell's theorem are completely inevitable.

fastparticles · 1 day

This is a fine slogan for an attitude, but its misleading. For one thing, when there is a noteworthy prediction or result in string theory, almost no one outside of the community ever hears about it or otherwise cares. For example, last summer there was a line of research based on a huge class of the physically viable scenarios that was used to predict a Higgs boson mass of "around 127 GeV". Its only a measured success, because the Higgs mass had a fairly narrow range, but these things are still important.

Its ludicrous to claim that string theory doesn't imply anything about what we see on accessible energy scales. Its true that its a difficult business because the predictions aren't sharply defined. *But people who suggest it predicts "everything" quite simply have no idea what they're talking about. *

There is a subtlety with string theory because it is on the one hand a framework of possible models; in that sense it is akin to "quantum field theory." If you know that reality is described by quantum field theory you know a lot of important things about how the world works, but in order to make definite predictions you need to have a specific model. However string theory is different and superior to QFT in that, fundamentally there is only one theory. All the different possibilities correspond to differences in physical parameters that can be changed by some processes. (besides some small number of discrete choices, like the asymptotics of spacetime).

All of the physically viable manifestations of string theory can be classified. They come in broad categories, each of which gives some rough predictions if you don't purposely try to fine-tune some contrived scenario. They especially can be classified into the compactification scenarios, with small extra dimensions, and scenarios where the extra dimensions are large, as in the "braneworlds". From the perspective of predictions for particle physics, the most important distinctions are whether SUSY is broken by gravity or gauge effects. SUSY hasn't been discovered right now, but there's still good reasons to think it could show up and if it does then there will be a lot of new opportunities opening up to test stringy predictions from the these different, relatively constrained possible scenarios. How SUSY is broken will be a huge clue to the correct high-energy theory, if we do find it.

The problem I find with the stance many people take is that it automatically precludes presenting any favorable evidence to string theory. Most of string theories successes are postdictions or retrodictions if you like, and its hard to see how it could have been very different based on where we are right now. The truth is, you have to be at least a little bit of an expert to really assess when the results are noteworthy. To mention one other really striking example, a pretty general class of F-theory compactifications can predict the CKM matrix almost exactly.. There is a pretty long list of ways that string theory indirectly informs and explains what we see. I dont mind when people interpret these things differently, but to claim that its been somehow engineered in order to do so is what is really preposterous.

String theory is at the edge of science for sure, but the endeavor to understand and test it absolutely is science. The people who claim otherwise are almost never very familiar with the work that is actually being done on the it. Even many physicists just seem to have absorbed a bunch of talking points and superficial, deceptive claims. If someone wants to say its its difficult, fine, that you dont care, fine, that you're convinced its wrong, fine. But to say it predicts nothing or that its not a theory or that its not physics is simply wrong.

fastparticles · 1 day

Quantum gravity is most certainly the most important aspect of physical understanding that has yet to be fully and definitively settled. The most commonly understood definition of "a theory of everything" is a description that unifies all of our quantum field theories that describe everything except gravity together with a consistent gravitational completion. If Ruiner is denying the existence, or possibility, of such a description then he's demonstrably wrong.

fastparticles · 1 day

and the reason why the whole "theory of everything" idea is just complete bullshit.

After a perfectly sensible explanation of renormalization, Im surprised to see such an abrupt veer into unsubstantiated conjecture. And really thats being much too kind. Unless you claim to adopt the most impractical (and useless) definition of a theory of everything. A scientifically positivist attitude isn't a license to deny the existence of nature operating in a specific, orderly way.

Evets616 · 2 days

As omg said, it comes down to two things: the radius and the strength of the magnetic field. The maximum energy should be directly proportional to those two things.

Your link says that the orbiting collider was going to have a circumference of 13,508 km which is almost exactly 500 times that of the LHC. So if we assume current B-field strength, the energy increase should be proportional to this factor, so that would translate into a maximum energy of 7,000 TeV.

A few months ago there was an interesting blog post about the future of accelerators, and in particular, about the likely upgrades of the LHC based on improved magnet technology, beyond the current 14 TeV design energy (see passage below). Assuming again a proportional increase, these magnets would then translate into a maximum energy for your orbiting collider of 16,500 Tev = 16.5 PeV.

Beyond that a higher energy upgrade is being planned that could push its energy up to 33 TeV. The magnets used in the LHC main ring today are based on superconducting niobium-titanium coils to generate magnetic fields of 8.5 tesla. Newer magnets could be built using niobium-tin to push the field up to 20 Tesla to more than double the energy. If they could revive the tunnel of the abandoned SSC collider in Texas and use niobium-tin magnets it would be possible to build a 100 TeV collider, but the cost would be enormous. The high-energy upgrade for the LHC is not foreseen before 2030 and anything beyond that is very distant. Realistically we must look to other methods for earlier advances.

Some basic collider math: http://www.hep.princeton.edu/~mcdonald/examples/lep.pdf

Evets616 · 2 days

Why the dig against Susskind? Everyone gets less sharp in their older years. We could list evidence all day, but thats not why scientists have things named after them...

hardcore_albacore · 2 days

FYI, $60 trillion is the approximate GDP of the earth, i.e. the value of the stuff produced in a year. Not the same as "all the money in the world", but its still an appropriate comparison to demonstrate how insane the demand is.

The "amount of money that exists" is pretty technical and subtle. The most standard definition for US currency is M2, of which there is currently about $10 trillion.

So the suit actually demands about 7 times the amount of US dollars in existence.

DarthSwag · 3 days

This is one of my favorite references: http://arxiv.org/abs/1012.3883

...but I guess that might be somewhat more than you want. :]

TheExiled · 4 days

No, thats not what I mean.

ImJulianAssange · 5 days

Antiwar doesn't report conspiracies. They report verifiable information. Feel free to post your favorite example proving me wrong.

TheExiled · 5 days

It agree that it is fairly advanced, but I don't know if I would consider it a good book. It covers a whole bunch of material in a very superficial way. At best it `paints the landscape'. If one wanted to learn the material covered at even a basic level additional sources would be needed.

I think this is simply reflective of the fact that its based on a physicist's priorities, not a mathematician's. I personally think its great and precisely because it conveys the subject matter efficiently without forcing me to become an expert mathematician, which I shouldnt need to do in order to understand the material well enough to apply it to physics.

ImJulianAssange · 6 days

If you didn't notice its written by a decades-long veteran of the CIA. Antiwar.com almost always does very solid, well-sourced reporting, even if their perspective is clear. Its infinitely better than the stenography practiced by the mainstream media outlets.

judehoffman · 7 days

From the article:

Established physics does not generally employ retrocausality.

Its a subtle issue but if you need to summarize, that sentence would be the right way.

isocliff · 10 days

That would seem to be the obvious thing to do. Apparently its because they're "equipment" or something, and nobody ever thought to change the dumb law making it nearly impossible.

tick_tock_clock · 10 days

I wholeheartedly agree with Scott's comment "you're a natural born theorist." And its a pleasure to have you ask this question in this way. I think I have some good tips for you.

So much of the beauty of all physics begins with, and is directly connected to, electromagnetism. And like Scott said, a lot of the intuitive, obvious beauty of E&M has to do with differential geometry. That is the natural setting for so much physics and math, and the insights are so unavoidable that everyone uses it without really knowing about it. To begin, you might want to just look at the wiki for differential forms, which mentions its incarnation in Maxwell's equations. One of the best free resources that helped me early on was this free textbook, specifically chapter 2. Even if you dont pick up every detail right away, pay attention to the basic properties of forms. Then Chapter 5 applies the ideas to electromagnetism.

Electromagnetism is also much more elegant with basic knowledge of special relativity. The E and B fields are not two objects but a single electromagnetic field tensor F (an antisymmetric 4x4 matrix has six free components). The electric (scalar) potential V, and the magnetic (vector) potential A, which defines B by B X A, are also one object. This object, which you can call the photon field or gauge field, is also called A but it carries a spacetime index in the sense of special relativity. This field is the source for the electromagnetic field tensor F, also called the gauge curvature form, meaning F is obtained by applying the exterior differential operator to A: F = dA. When you know all this stuff, writing Maxwell's equations in the usual vector-based way will seem just as crude as writing them all out component-wise. Heres a quick image summary of the proper way to organize them.

There are many ways differential geometry will streamline your understanding of EM. For example, Gauss's law (divergence theorem) and Ampere's law (Stokes' theorem) are both revealed to be special cases of a more general result that also goes by Stokes' theorem involving the exterior derivative (a kind of generalized curl). By far one of the most important facts to come out of this picture is that this operator always squares to zero, d² = 0. (for example the curl of a curl is zero, div of a div, etc). This matters because it means there is a symmetry; you're free to add any term to A that satisfies dA'=0 without changing any physics. This is gauge symmetry, and it is nothing less than the organizing principle for all physics, namely quantum field theory, gravity and string theory. What is most amazing about this fact is that when you study field theory, the gauge symmetry is actually revealed to be a consistency criterion for quantum spin-1 fields. So any other forces that could possibly exist must also obey curvature equations just like EM, and they do, with a slight generalization. So Maxwell's equations are not only beautiful but in a sense they are inevitable. And they are the door to a huge nexus of insights in physics and geometry.

Sorry for the length. But Im sure you understand this stuff excites me. ;] Hey you asked for high level applications. And btw if you want to buy an actual book this one might be great for your level.

TheCoreh · 10 days

"What I cannot create, I do not understand."

isocliff · 11 days

So much killing, nobody even bothers to notice if we're actually murdering veterans, apparently.

cowboyhugbees · 11 days

I love that comment. ;] Aint that the truth! Nice work all around. Thanks mate.

steve_bb · 11 days

Its horrifying that you think this is the moral standard thats relevant. You actually think this a legitimate moral argument? Wow.

God_Wills_It · 11 days

Yeah, the title is extremely funny because "teleportation" has a specific meaning which exclusively has to do with entanglement.

The word is clearly too dangerous for the headline-reading redditosphere and apparently the physorg writers too. And the problems are not just limited to the headline...

consorts · 11 days

Thanks for the TL;DR.

God_Wills_It · 11 days

Its pretty simple actually. In special relativity only the lightcones (past and future) can have a well-defined ordering that doesn't depend on the reference frame. That is really all you need to know. To make this a bit intuitive, you can look at this gif depicting Lorentz transformations. Remember that time runs vertically and space horizontally. You can see how generically points in the "sideways regions", i.e. those that are spacelike separated from you, can move from before you to after you or vice versa. This just follows from the fact that Lorentz transformations are nothing other than hyperbolic rotations.

So since there is no definite ordering of events that are spacelike separated, the simples interpretation of causal consistency is to simply say that causation only works into the forward lightcone. Quantum mechanically, there can be correlations between spacelike separated events, so its a bit more subtle, but overall the physics still prevents you from sending faster than light messages to preserve its consistency.

For the sake of argument, once you allow communication outside the lightcone, then from this point the message can be passed not only to a region that is spacelike-separated from you, but one that is strictly in your past. So cause and effect would be completely broken.

Edit: To spell it out as much as possible: 1) Lorentz transformations describe physically equivalent sequences of events. They are just an unphysical rotation of the coordinate system. 2) Any signal that goes just a tiny bit faster than light is traveling to points that are spacelike separated from you, outside the lightcone. Any point outside your lightcone can be rotated into your past. In fact it can be rotated arbitrarily close to your past lightcone. Thus any faster-than-light communication is already equivalent to pastwise communication in some sense. 3) The ability to communicate into your spacelike past automatically implies the ability to communicate to your strict past. Because the point you sent your message to in your spacelike past can then send messages to its spacelike past, which includes your timelike past. Therefore causal influences may only propagate into the forward lightcone if physics is to make any sense.

platypodes · 11 days

Yeah the whole fuzzball program is definitely an important aspect of our understanding of the puzzle, and a very worthy thing to bring up. They're newer results than the ones I linked in the other review, but provide somewhat more specific answers.

I never found that wiki article too helpful, I think this pdf has some more meaningful discussions: http://www.physics.ohio-state.edu/~mathur/faq2.pdf

I wouldn't describe it so much as a proposal but more like explicit stringy calculations showing the existence of solutions with the desired properties.

isocliff

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