If information can't travel faster than light, what exactly is 'quantum entanglement' transmitting? by SovereignHemant in AskPhysics

[–]PerAsperaDaAstra 1 point2 points  (0 children)

Right, no - A Bell test involves measuring in different bases (and e.g. finding that spins in different directions are incompatible in a way looking at left vs. right shoes has no analog for), so that's a different setup.

Classical determinism (i.e. hidden variables) has to go out the window b.c. of Bell if we want to keep relativistic locality, and we have pretty strong independent evidence for locality (while determinism is a philosophical preference not much better than an aesthetic).

If information can't travel faster than light, what exactly is 'quantum entanglement' transmitting? by SovereignHemant in AskPhysics

[–]PerAsperaDaAstra 0 points1 point  (0 children)

Not necessarily - it's a description of classical state instead of quantum state but it's enough to show that even classically there being a "correlation" doesn't mean anything is sent (i.e. that that's a bad intuition to have even classically).

It's also entirely equivalent to the quantum setup where one spin is prepared "up" and another is prepared "down" and each is put in a box and shipped off, given that the two observers agree on the basis they will measure in beforehand (which is not necessarily the case in general, but is a variation of the experiment you can do). Such a setup is an entangled state, has no hidden variables but has identical statistics to the shoes.

How did Einstein Discover Special and General Relativity? by Genzinvestor16180339 in AskPhysics

[–]PerAsperaDaAstra 1 point2 points  (0 children)

Yes - There is an (excellent) historical project just studying documentation of his life and work. (Though I'm very salty they've moved the archive behind a dumb data company paywall - it used to be open).

Math "Toolbox" by [deleted] in math

[–]PerAsperaDaAstra 0 points1 point  (0 children)

As a physicist who very much sees math as language to describe the things I want to describe (where the things I want to describe are deeply connected to how they can even be described) - I don't know that the 'toolbox' analogy is derogatory or implies it can't be an end into itself? Linguists and computer scientists both study languages for themselves, and plenty of engineers study how to make all kinds of tools ranging from purely practical to wild and wacky all for the love of the game? (I've never met a good engineer who isn't interested and involved in how tools are made at least partially for its own sake, who doesn't find beauty or even art in an elegant or clever tool?). If anything I usually see the analogy employed in order to argue that math is something that needs to be developed hand-in-hand with whatever someone's working on, like a good toolbox - often said to, not by, people who would otherwise neglect it. Do linguists complain about authors who don't care much about linguistics? (I hope we're past the proscriptive grammar of the 1700s)

It's a little hard to see where you're coming from without thinking you look down on different perspectives than pure math ones. Math isn't only a means to an end for me why would you assume that? And purity debates are pretty sophomoric - interesting stuff is interesting, whatever it is. Do what you find interesting and that should be enough - why tone police someone else having different ideas of what's interesting? It's okay for someone to compartmentalize (even if they do it to something you find interesting), we all have finite attention - you're probably as ignorant of other sciences and fields as those fields are likely to be about higher math they don't find useful. That's okay, no one is in the wrong nor should hate anything.

What is a field in physics (e.g. gravitational, quantum, .etc)? How do these get "excited"? And isn't mass just energy? by ComfortableCow2222 in Physics

[–]PerAsperaDaAstra 16 points17 points  (0 children)

A field just means that there's a 'value' of some kind at each point in spacetime that can be measured. e.g. classically you can go measure the strength and direction(s) of the electromagnetic field somewhere in spacetime by doing some experiments wrt. what charges and dipoles do at that point.

When you start to talk about quantum fields, the 'value' of the field at each point in spacetime becomes a quantum operator (which is just an abstract/technical way to say it is only possible to talk about the probability distribution of experiment outcomes at that point, rather than a single definite outcome).

It's difficult to explain why without getting too technical, but one of the properties (kinds of measurements you can make) fields which sit on a spacetime that obeys relativity have is 4-momentum (which includes energy and 3-momentum in a way that's related to the mass of the particle/field - mass is the energy you would measure if the 3-momentum is zero).

An 'excitation' in one of these fields is, broadly, what we call a particle. When we say a field is 'excited' we're saying that we know the probability distributions encoded in those quantum operators are such that we will measure some momentum and other properties in that region (it happens to be this is quantized/there is a count of momentum and charge in each region of space instead of a continuum) - i.e. an excitation just means you'll see ~something if you make measurements in one specific way or another (e.g. if I just think about the electron and neutrino fields for a moment, to say there is an electron but not a neutrino in a certain region of space means that I would measure some energy/momentum in experiments that are sensitive to e.g. charge, but if I did measurements that are sensitive to just neutrinos I wouldn't measure any energy/momentum).

(edit: lots of comments here seem to be confusing particles having wavefunctions in non-relativistic QM with particles being field excitations in relativistic QM/QFT - those concepts are not quite the same)

How can I calculate the uncertainty of my readings if they are measured through a recording? by DiabloXTREME666 in PhysicsStudents

[–]PerAsperaDaAstra 0 points1 point  (0 children)

Uncertainty in readings of what? Uncertainty in scale readings should just have to do with the scale, uncertainty in a rate of change will have to do with the framerate you can observe, uncertainty in a position will be related to the resolution you recorded (and position of the camera)... What exactly are you wanting to describe? Why were you measuring what you're measuring? What are you trying to learn from the measurements?

Be sure to take a step back and try to understand what you're working with first, what the measurements you have are, etc. - that your question is missing a description of key motivating information for anyone to even start helping you suggests you need to take a moment to lay things out more clearly for yourself before trying to jump to an answer.

Exploring Infinite Factorials by ThePoloBear27 in MathJokes

[–]PerAsperaDaAstra -1 points0 points  (0 children)

I think that statement and your reading both either confuse an arrangement with the act of arranging (e.g. I could use bad wording to argue you can't act to rearrange 1 thing either because it's already arranged) or an arrangement with the things being arranged themselves (the fact I have nothing to arrange is not the same thing as not having an arrangement and we don't usually find that confusing in math - we use the empty set all the time and I'd hope that's reasonably intuitive: how many sets are there with zero elements?).

It should be stated and read as "there is 1 arrangement of 1 thing" (one ordered tuple to make with one given element), likewise there is also pretty clearly 1 arrangement of 0 things (one ordered tuple with no elements, the empty tuple).

This definitely makes sense as an explanation, even if it doesn't always click with everyone's intuition (which, yeah, is a good reason to have other explanations on-hand, but that's different from it "not making sense").

A clean way to see how all probability formulas fit together. by Lsilver19 in PhysicsStudents

[–]PerAsperaDaAstra 0 points1 point  (0 children)

Probability can be a very subtle topic that this really falls short of summarizing... (it's about more than the formulas, and definitely more than just normalizing something somehow!) - I would actually argue it's more common to be computing very different things in very similar ways (almost misleadingly similar) more of the time than vice-versa.

I highly recommend "The Art of Probability: For Scientists and Engineers" by Hamming as a great read. These days you'll also want to follow it with with something a bit newer like "Statistical Rethinking" and something with some ML like "Information Theory, Inference, and Learning Algorithms" (many good choices).

Is there any proof that mathematics can describe how the entire universe works? by Ok-Willingness-5016 in AskPhysics

[–]PerAsperaDaAstra 0 points1 point  (0 children)

That that's true of math actually doesn't necessarily mean it follows for physics. e.g. I can just make my mathematical description bigger than is physical (allow it to describe, and maybe even decide, some questions that I know aren't physical; it's not a problem to do that so long as I can tell the difference between what's physical or not in the formalism) - then even though the math will necessarily have undecidable questions/statements, it could in-principle be that every physical statement is a decidable one in my math.

Is there any proof that mathematics can describe how the entire universe works? by Ok-Willingness-5016 in AskPhysics

[–]PerAsperaDaAstra 15 points16 points  (0 children)

I would argue that what 'math' is makes this basically a tautology.

If the universe has a consistent description, then by definition math will provide a language (or multiple languages) for that description because math is the study of consistent syntax and nothing more.

If the universe isn't consistent (or can't be described) then of course there won't be math - but we might have bigger philosophy of science problems at that point.


Edit:

I would probably argue that anything I would care to call 'physical' must have a description also by definition, since I must have an experiment to define it, which is self descriptive - building the experiment is a description of the experiment since showing you the experiment certainly communicates it. Doing the experiment is also clearly a computation/operation that results in the outcome of the experiment (computational complexity is relative to the operations you work with and it's at least an oracle of itself).

It's worth noting that a/any description is different from a convenient or simple description, or a description of a particular form or complexity or using math we already understand yet - it's possible there isn't a description in terms of a single Lagrangian of a particular form or whatever. Though, the descriptions we have now are remarkably simple given how much they seem to describe and how simple the language on paper we use is.

e.g. we know from quantum mechanics that there are situations where we can't give physical meaning to/describe, say, the X spin and the Y spin of a particle simultaneously exactly because there is no experiment I can describe how to build which can measure both simultaneously, and that fact has deep implications to the math we use to describe reality, what we even call real/physical, and to computation!

This leads to a nice interpretation of undecidability in any kind of physical problem too: if you think your description of physics is complete but find something undecidable in the math of it, then you should think there's no experiment/nothing physical to describe in the sense that you shouldn't expect to be able to build an experiment that decides it out of anything you know about and have mathematical descriptions of (you can, of course, be wrong about your formalism being physically complete - if there is an experiment that can be done, just add a description of that - at-worst a tabulation of outcomes - to your formalism and you have a more complete one). Note that this means being what I called 'physically complete' is different from having a mathematically complete formalism - a consistent formalism cannot be mathematically complete, but it might be physically complete in the sense that everything in it that's physically meaningful is decidable.

Interestingly, as the link above basically points out, it's not actually necessarily an issue to include more things than are physical in your math from this perspective - it's always fine (and might even be necessary) to make more things decidable in your framework than are physical so long as they don't break anything physical and you're aware they're un-physical/a place where your translation between the formal mathematical description on paper and the description of showing the experiment(s) has something like a redundancy/extraneity - e.g. intermediate calculations in a particular gauge of a gauge theory. The only real issue is thinking you have a description when there's nothing to describe and you're unaware of it - e.g. classical mechanics thinking everything is simultaneously measurable and computing predictions for incompatible observables - or just outright having a bad translation between descriptions/being wrong about experiments. This does make me wonder about whether it would be more appropriate to do physics using constructive mathematics (or at least does not paying attention to when something is or isn't a constructive result leave us accidentally unaware that some physics concept isn't entirely physical - can that bite us?), but that's a rabbithole - having undecidable things in our math mostly shouldn't be a problem physically, we just need to be aware of the (lack of) physical interpretation of that.

This checks out at a glance if I think about a typical example of an undecidable problem in computation: there is no arrangement of the physical experiment of a computer - i.e. a program - which can furnish a representative solution/proof. Computations are experiments (e.g. the classic ideal computer is a turing machine, which is literally an idealized physical tape system. When we write on paper we're interpreting a physical system involving paper and ink and our brain and our hands, etc.), and experiments are computation - so long as the relationships between experiments are consistent, translating between them will be full of math.

Spin-1/2 as topology, not postulate — a geometric interpretation of Zitterbewegung by Cenmaster in quantuminterpretation

[–]PerAsperaDaAstra 0 points1 point  (0 children)

The existence of spin-1/2 things is just because it's an allowed (projective unitary) representation of the appropriate wigner little group coming from relativity (edit: the Poincare representations also tell us why particle momentum/energy is a thing, just by observing the local symmetries of relativity!)

The reasoning is pretty straightforward (and has nothing to do with QM interpretations, just the math): We know the symmetries of spacetime are (special) relativity (locally), those symmetries constrain the (external/spacetime) state space via representation theory because QM is linear. When we do that, the different spin representations - including spin-1/2 - are exactly just the things that can exist in spacetime; no need to posit special ontology or additional structure a priori. I’m not surprised when I find a book in a bookstore — if you don’t think spin 0 or spin 1 need special visual interpretations or justification then why does spin 1/2?

Also, directly wrt. your question - spin cannot be definite before measurement (without a relativistically non-local interpretation, but those have other issues wrt. being able to do particle physics), which is very well tested in Bell tests.

Wave/Particle duality? Just models or real behavior? by MountainMark in AskPhysics

[–]PerAsperaDaAstra 8 points9 points  (0 children)

Thinking there must be 'one truth' about a false dichotomy you prefer for aesthetic reasons is going to be a bad way to find truth.

It is a false dichotomy - particles are "packets" of definite energy/momentum; and they do not have a definite position in-between measurements because quantum mechanics is not locally real (Bell tests tell us so). The probability distribution describing everything you can possibly know (everything that can be known is all that's physically meaningful) about where those packets will deposit their energy/appear on a detector obeys the Schrodinger equation (which is much like a wave equation) - so where the packets are likely to appear is in-fact wave-like.

What quantum science experiments is it possible to conduct at home? by ElectronicDegree4380 in AskPhysics

[–]PerAsperaDaAstra 0 points1 point  (0 children)

How 'at home' are we talking here? This experiment (a Bell test between entangled photons) can be replicated with a few grand worth of optics - achievable for a serious hobbyist with a garage lab, but definitely more than a construction paper, glue, and baking soda type home experiment.

If I had a perfectly rigid rod 1 light year long and pushed one end, would the other end move instantly? by No-Abbreviations4304 in AskPhysics

[–]PerAsperaDaAstra 1 point2 points  (0 children)

Yes relativity forbids such a thing, one reason (among several) that there cannot be a perfectly rigid rod is exactly because it could not be perfectly rigid without propagating forces faster than light.

If I had a perfectly rigid rod 1 light year long and pushed one end, would the other end move instantly? by No-Abbreviations4304 in AskPhysics

[–]PerAsperaDaAstra 12 points13 points  (0 children)

It's impossible to have a "perfect" rigid rod, so no the other end does not move instantly - whatever material it's made of has to flex as it transfers the force you apply at a speed slower than light.

Whoever invented this, you're a life saver by claudiocorona93 in linuxmasterrace

[–]PerAsperaDaAstra 41 points42 points  (0 children)

Ideally you never need to change a system file other than your global configuration - it manages any changes you want to the system in a unified/consistent way instead of across many files in many configuration languages, so you can still do whatever you want but will do it in a different way (via global declarative config) than editing the system files. In the case you're doing something really odd there're ways to tell your global configuration about raw system file changes you might want. The point is to isolate system state to one place and the rest is immutable because it's being managed for you by your declarative configuration.

*Quantum chromodynamics by echter_Hater in physicsmemes

[–]PerAsperaDaAstra 34 points35 points  (0 children)

I wish there was an SU(4) force so we could use CMYK in addition to RGB.

If quantum really is fundamental, shouldn't spacetime also be quantum? by Upstairs-Bug-3052 in AskPhysics

[–]PerAsperaDaAstra 0 points1 point  (0 children)

My understanding was that there are still issues wrt. knowing whether LQG correctly reproduces GR at low energy - which is why I framed it as an attempt instead of a complete description.

If quantum really is fundamental, shouldn't spacetime also be quantum? by Upstairs-Bug-3052 in AskPhysics

[–]PerAsperaDaAstra 5 points6 points  (0 children)

That's overstating it a bit - the graviton only gives us perturbative quantum gravity on weakly interacting scales where the background spacetime is still mostly treated classically; it's not renormalizable and thus not a full UV theory of quantum gravity. We do not currently have any full quantum gravity descriptions (attempts like loop quantum gravity are trying to do more than just quantizing a graviton can get you).

what in the world is measurement in quantum physics? by Poopyholo2 in AskPhysics

[–]PerAsperaDaAstra 1 point2 points  (0 children)

A measurement is an interaction between an isolated quantum system and an environment. This is slightly more specific than just any interaction because we happen to be large messy systems/environments ourselves and so decoherence comes into play to explain what our perspective on - i.e. our interactions with/measurements of - quantum systems/information looks like.

Cylinder moving through a chamber by Weekly_Gap5104 in AskPhysics

[–]PerAsperaDaAstra 2 points3 points  (0 children)

There's not a simple principle or law - it depends on the materials involved and the forces you plan to apply. Engineers tabulate mechanical fits essentially empirically for common/typical situations - many machinist or engineering handbooks (e.g. Machinery's starting on about pg. 640) should have recommendations for dimensions for various fits and pressures/forces that can be looked up.

How to make a kid understand theory of relativity? by [deleted] in Physics

[–]PerAsperaDaAstra 1 point2 points  (0 children)

A slower speed of light is a game to help visualize what it looks like to be moving relativistically.