Physicists demonstrate new way to violate local causality
phys.org
phys.org
http://www.physics.umd.edu/courses/Phys270/Jenkins/Griffiths...
The simplest explanation of what measurement actually is, in a quantum sense, is that it's the act of entangling your brain with whatever amplitude configuration represents the experiment we're interested in looking at. Basically the amplitude goes from looking like "brain * (result A + result B)" to "brain A * result A + brain B * result B". Brain A at that point can't communicate in any meaningful way with brain B because there isn't any causal relationship between the two anymore, so in a sense the brain has "split" and this is what we call decoherence. But for brain A to suppose that brain B has vanished in a puff of smoke, that is to say to privilege brain A over brain B, needlessly complicates the theory. It is the same as saying that since you can't see a thing anymore, it must not exist, and trying to build an entire physics based around what happens after you close your eyes.
http://kantin.sabanciuniv.edu/sites/kantin.sabanciuniv.edu/f...
There are a lot of terms I do not fully understand in this article.
Can you recommend an application that would allow me to select for example the words "distant particles can be correlated in ways that are impossible for classical objects" and find out what lead to that discovery? Or what does "Bell inequality" really mean?
If not, are there recommended methods of understanding articles better?
I am thinking of this process:
- copy the article to a document
- find any words or sentences that you would like to understand better, highlight them in some colour e.g. red
- do some googling / wiki surfing or ask in HN or some kind of forums about them
- add sections after the paragraphs with highlights to explain the words or sentences
- recursion
- once satisfied, highlight the words in a different colour?
It does not feel good enough since it would be ~opening new tabs and~ make me go through a lot more effort than necessary, and it feels like I would be overwhelmed and give up eventually. If there is something that would make "understanding articles as easy as possible" then that would be amazing. I'll probably end up developing this myself...
Edit: was incorrect about opening new tabs
While you don't need new tabs to google a term with some addons, actual knowledge of the subject, even at a basic level, takes a lot more effort than opening tabs.
There's no magic bullet to learning.
Venkman: Ray, pretend for a moment that I don't know anything about metallurgy, engineering, or physics, and just tell me what the hell is going on.
Stantz: You never studied.
(Ghostbusters)
Just studying the principles -- e.g. reading an entry level Physics/QM book, would be better and more solid than surfing around, or asking for opinions on forums (which you couldn't evaluate anyway -- tons of bogus opinions in any kind of forum), or googling stuff.
Stuff like "Bell's inequality" are so basic that merely surfing and skimming wouldn't help (it would be all a kind of concept soup in the end). You can do that with more advanced notions.
https://www.youtube.com/watch?v=pyX8kQ-JzHI&list=PLQrxduI9Pd...
Yale Entry Level Physics Class: https://itunes.apple.com/us/itunes-u/physics-video/id3416518...
https://www.youtube.com/results?search_query=Yale+physics
MIT Quantum Physics: https://itunes.apple.com/us/itunes-u/quantum-physics-i/id887...
https://www.youtube.com/results?search_query=mit+quantum+mec...
quick google searches should yield more classes easily enough.
Some stuff is just hard to understand. You can make analogies, like talking about two people hiding a colored ball in their hand and one of them showing it later, but these are not truly helpful in really understanding the issue. For that you need a bit of math.
One physicist explained this really nicely, saying that because we live in the macroscopic world we have a certain kind of experience of it, and our gut feelings and intuitions are just wrong when applied to the microscopic world, and using math is just a way of avoiding these misconceptions, and after a while of doing that you will get a new "math intuition" of physics.
To demonstrate, ask a random person these questions:
If I stand on an airplane and jump, do I land where I started, further back, or further forward, relative to the plane?
if I whirl a ball on a string clockwise around my head and let go, does (neglecting vertical motion) the ball travel
A) curving counterclockwise B) curving clockwise C) in a straight line
I would say, that most people would answer correctly, that you would not land on the same place, but probably be blown away far backwards from air friction (even though they would just call it wind).
Example: literally the other reply to my comment. The notion of an "impeller" to continue uniform motion is Aristotelian, and it seems to coincide with a lot of people's intuition:
It also coincides with the kinds of experiment that people using Aristotelian physics are in a position to perform. See my comment about Carlo Rovelli's paper.
Losing contact with the ground has nothing to do with it. You don't need an "impeller" to continue uniform motion- see Newton's first law.
If you've ever taken a pee standing up on a plane, you'll notice that your pee doesn't veer rearward. You can juggle balls without losing them (you can try this in the back of a car). If you throw a ball forwards on a plane, it doesn't come back to you, and those carts that are rolled up and down the aisles aren't constantly trying to flee towards the back of the plane.
TL;DR Aristotle's physics lasted a long time because it works in the environment in which people used it.
I found:
- PBS Spacetime on YouTube is awesome
- Check out the double split experiment. It seems simple, but when you think about what getting interference patterns when only sending one particle at a time really means..
- Then when ready, the quantum eraser
- Bells inequality is a simple idea that proved the strange interpretation of the double split experiment was true, rather than a more mundane interpretation
Suppose you take the double slit (plate with two holes in it), and you start adding more holes. Of course the particle will go through all of them, but with less probability the further they are off-axis. We can also add more than one plate, and the particle will go through all possible combinations of holes with some probability. Now suppose we let the number of plates go to infinity, and then let the number of holes in each plate go to infinity. The particle still goes through all of the infinite combinations of holes, with less probability if the path is unlikely. But really, there is nothing left anymore between the particle source and the screen! There is just free space! So this path integral with the particle going sort-of-everyhere weighted by probability actually describes propagation through free space.
Keep in mind the double slit experiment is designed to illustrate the "effect" we observe, when we observe, is at least partially governed by the observation. Given certain interpretations, it can also have philosophical ramifications[1][2] for the existence of reality, self, and choice.
[1] https://en.wikipedia.org/wiki/Copenhagen_interpretation [2] https://en.wikipedia.org/wiki/Pilot_wave
Ugh. Please don't give more life to the meme of "spooky" quantum mechanics. It's mostly propagated by popular science outlets trying to make physics seem weirder than it is.
John Stewart Bell came up with with a theorem[1] that would be developed into experimental tests that showed what Einstein thought was an error in QM was actually observable. It's worth noting that closing all possible loopholes in experimental tests of Bell inequalities is difficult and elusive. The consensus is that QM is valid and entanglement does indeed exist, but there remains room for a tiny amount of doubt. Note: This is doubt the way scientists see it. i.e. A reason to perform further experiments. Theories can never be proven true, but teasing out every nuance and conceivable way in which they can be wrong, and testing them, is what makes theories accepted and useful. QM has stood up to enough tests that it's now a very well established theory. However, continuing to test QM is not useless. Searching for new ways in which well established theories can be wrong is how we found QM in the first place!
Note that QM does not say what, philosophically, entanglement is or explain the mechanism for how non-local correlations propagate. There are other theories that have attempted to explain this, but none have been successful so far in being both correct and, more importantly, testable.
There have been other inequalities experimentally tested in addition to Bell inequalities, such as Leggett inequalities[3]. To your understanding, these would not be interesting because they don't "teach us anything new". This is false. The question about QM and entanglement isn't as straight forward as a binary "yes it exists" vs "no it doesn't". There exist subtleties. Different inequalities have indeed enhanced our understanding of entanglement and proven useful in practical applications such as quantum computing and quantum cryptography. I haven't had time to dig into the work linked to here, but to dismiss it out of hand is not reasonable. The press release (to be taken with a grain of salt given the usual failings of science journalism) does suggest a novel approach that could be of practical use.
[1]https://en.wikipedia.org/wiki/EPR_paradox [2]https://en.wikipedia.org/wiki/Bell%27s_theorem [3]https://en.wikipedia.org/wiki/Leggett_inequality
The piece tells us "bilocal causality" is
> a concept that is related to the more standard local causality, except that it accounts for the precise way in which physical systems are initially generated.
and later references
> a new type of Bell inequality that accounts for the fact that the two sources of states used in the experiment are independent, the so-called bilocality assumption.
If, like me, you find this non-obvious, you may like to get some background from an earlier paper[2] (different authors) which has a seemingly less opaque description of bilocality than the phys.org article:
> Nowadays, fast progress towards advanced demonstrations of quantum communication networks, involving quantum repeaters [10] based on entanglement swappings [11] and quantum memories [12], are underway in many labs around the world. In these future quantum networks, several independent sources of entangled qubit pairs will distribute entanglement to partners who will then connect their neighbours by performing joint measurements on two (or more) qubits, each entangled with one neighbouring qubit, as illustrated for the simple case of three partners in Fig. 1. Such experiments have an interesting feature that has so far received little attention in previous works on nonlocality: the multipartite correlations between the measurement results at each site do not originate from a single multipartite entangled state, but from a series of bipartite entangled states that are initially independent and uncorrelated from each other; i.e., there is not a unique initial joint state (the analogue of λ in a locally causal model) that is responsible for the observed correlations, but these are instead created from smaller systems through joint measurements. [...]
1: https://www.google.com/search?q=%22bilocal+causality%22+-%22...
Leonard Susskind, Adam R. Brown, Ying Zhao
Quantum Complexity and Negative Curvature https://arxiv.org/abs/1608.02612
The Second Law of Quantum Complexity https://arxiv.org/abs/1701.01107
I believe there's a 5000 line genre buster just waiting to be written, using a simple SDF renderer and the wave equation. Please, someone beat me to it I have other things to write first.
Polygons are not allowed, only fields.
The structure of the argument is, "We stood up a strawman and knocked it down," which sounds pretty weak. Is bi-locality an inherently interesting property? Does all classical computation follow it? I don't know enough to know if I care, but press releases tend to oversell so my default stance has to be "No, I don't really care."
It rests on whether bi-locality is an empirically interesting property. And as it turns out there are some well-cited theoretical physics papers on the interest in this property for quantum networks [1], so it is likely that I am not the right audience for this press release, and a physicist might find this significantly more interesting.
[1]: https://scholar.google.com/scholar?q=bilocality+bell%27s+ine...
They used a new kind of locality and proved it was broken too. Interesting, but not groundbreaking.
Weaker than "I don't understand what the paper says, only read a high level layman summary, not sure even what what the experiment was for, but I'm gonna piss on it anyway"?
Even assuming what you already describe, the ability to show bi-locality as a new lower bound above which locality constraints apply, is very interesting, and nothing like a strawman.
It would only be a strawman if they claimed they violated locality in general.
That is, he was giving credit as respect to the researchers.
Come on. Parent was saying what it looked like to a layman, and then asking for someone to address that and ask what was actually going on. No need to "piss on [him]".
They took an prediction of existing theory that violates a weaker form of locality (i.e. demonstrated stronger non-locality), and realized it experimentally. They also didn't invent bilocality in any case.
To grasp the difference between the hard academic sciences and software development community, consider the differences between a telephone company and an astronomical observatory with a large telescope on a mountain top.
Many people here might be amateur enthusiasts, mixed with a handful of professional academic participants. Any award winning physicists hanging out here would be surprising.
That said, feel free to distinguish yourself by outshining everyone else. It would be a welcome addition.
I am an engineering grad with decade and a half of gap in physics education despite of my constant high level interest/familiarity. I can honestly say I have no idea what bi-local causality is which this article handwaves around in the first para. how can you expect people to debate this when they cant even cut open this basic 'black-box'.
Try to pick one or two comments that are wrong but not very wrong. Reply to them explaining the error(s). I like to add a Wikipedia link when available.
Ignore the very wrong comments. It's usually impossible to give a coherent reply. You only will get upset.
Also, to encourage a civil discussion try to upvote the grey comments unless they are offensive or extremely wrong.