joigus

--StringJunky From:

That's a brilliant point. And kind of the direction I was trying to go when I pointed out on the thread about emergence that some apparently indisputably emergent concepts later appear as seemingly fundamental in another part of the theory, as if there was a POV-dependence that you cannot get rid of. I think this comment should be quoted in the other thread.

Since very early on I've thought Nature is superior to art (a little Socratic trick, as art is produced by humans, who are produced by Nature). Hands down it is. After all, she's had billions of years as a head start on whatever part of it we call art.

The way I understand it is like this: A phenomenon is emergent when it can be studied in terms of elementary parts and their relationships, while the phenomena to be explained are not present in the parts, appearing instead as a consequence of certain relationships between them. The example par excellence is pressure, which appears as a result of miriads of molecules hitting the walls of the container in so smooth and regular a way that all we experience is a consistent and continuously-varying resistance to reduce their volume if we try to push the system into a smaller volume. The idea that spacetime may ultimately be emergent appeared in physics in recent decades, in the form of commentary, rather than an actual proposal, I think. There are attempts to go in this direction, like loop quantum gravity, but I don't think it's any close to come to fruition. I quite agree with @studiot in that a standing difficulty, at least for me, is: What is the more fundamental thing of which time is a derived (another word for 'emergent') concept? Some people seem to think that considering time as made up of little chunks, discrete, is the big idea. Now, that's not how the concepts of pressure or temperature were arrived at. Pressure is not chunks of little pressure; temperature is not chunks of little temperature. Another problem I see is that sometimes we think we've understood a concept as emergent, or derived, only to find later a version of it that seems to resist such, shall we say, reductionistic approach. Examples of this are, IMO: 1) Negative pressure of the cosmological vacuum 2) Pressure and temperature* in black holes I don't think these can be considered just your garden-variety versions of pressure and temperature amenable to be understood in terms of 'little things doing their thing.' But who knows. All I can say for now is that it seems to me that any concept of emergent time that emerges (pun inevitable) is bound to be essentially different from being so in the same vein of temperature and pressure, ie, as 'little things doing their thing.' Something very really bold and beautiful seems necessary. I'm particularly interested in what @Eise and @Markus Hanke have to say about these matters. *Temperature is not just a feature of black holes, but also of any space-time horizons; even** horizons created by just picking a coordinate system (Rindler coordinates for flat spacetime). What about that?! **Not a typo for 'event'

It seems to be a semiclassical calculation, in which they've thrown in elements of quantum information theory. It's always a good thing that you can get confirmation of robust physical principles from approximate pictures of the physics. Thanks a lot.

I wouldn't worry too much about 'loan atoms'. Forget about atoms; they're pretty abstract thingies. The way they combine into macromolecules to form self-molecules, vs non-self molecules is far more significant. Whatever 'I' is, it's to do with information, and that's in how atoms hang out with each other, not in atom Sally meeting atom Tom. There are far fewer alien cells in your organism than there are self cells. Think about it. So, what's the big deal about 'foreign atoms'? There are 39 trillion non-self things living in you. I hope that doesn't give you nightmares, and I hope it helps.

Very much appreciated.

One language snippet that I've developed to try to explain this admittedly hard-to-understand concept is that quantum fields are instantiation devices. The analogy cannot be taken too far though, because, eg, instances of a program have and ID, while quanta haven't. You can insist on tagging them, but it's the wrong way to proceed... Perhaps there is no better way than getting your hands dirty with the maths, even at an elementary level, trying to express the field operators in the Fock representation: particle number 1, number 2, etc. Pretty soon the whole thing becomes a mess. Then you change the variables to the number representation: this many particles with state such and such. The way in which the equations get simpler hits you like a ton of bricks.

There is no such thing as this or that photon. Photons have no identity, so your question is meaningless. As are the questions, Where was the photon before the electron emitted it? Where is the photon after it's been absorbed? Etc. x-posted with Swansont.

+1. 🤣 Discussing it here would be good enough for me too.

As @exchemist said, inelastic collisions do not absolve you from complying with conservation of momentum. You need this momentum to come from an external source --wires, fields--, or be gained in exchange of exhaust momentum, as exchemist also pointed out at the very beginning of this thread. For whatever it's worth, I don't find anything of interest in the exposition seen so far.

Interesting... Thank you. I wasn't aware of gravastars.

I'm looking forward to that description. This swapping of the radial coordinate with the time coordinate is a general feature of horizons, though, AFAIK. Back in the sixties, Penrose and Hawking proved singularities to be an inevitable consequence of GR spacetimes, and formulated a conjecture of 'cosmic censorship', that there are no naked singularities ever; they're always hidden behind a horizon, with this funny swapping going on. But horizons appear from the POV of a far-away observer, from the POV of the free-falling observer nothing funny is going on. Looking at the maths, though, the falling observer is doomed. There is a point on their future worldline that means 'the end of space-time' for them. And it's in their future, because the coordinate that monitors time, from the perspective of the far-away observer (the one that carries the negative sign in the metric), is in their radial approach coordinate, rather than the 't' one that describes time outside. I know it's strange, but that's what the maths say. Even leaving aside the problem of evaporation, there are many problems with the Schwarzschild solution. An important one being that it is past-eternal. And astrophysical black holes presumably are not. Don't forget the Schwarzschild solution is static. The way you deal with that in GR is by directly deleting this freak eternal past, modelling a spherical shell of collapsing matter, and patching up the solutions à la Penrose. My approach to any physical problem is very mathematically-biased, but that's the only thing I can do with my toolkit. Yes, I am aware. But Laplace's 'black holes' were very different. Laplace realised that there can be objects that are capable of swallowing any light trying to escape from them, as a result of an escape-velocity calculation, but back then the speed of light was not considered to be the universal limit that today we know to be. From the Laplacian perspective, there's no problem in those photons being detected outside the 'horizon' if given proper initial data. They can't reach spatial infinity, that's all. Gravitational waves open up an invaluable tool to understand black-hole collisions and the like, but the physics community seems to agree that further theoretical clarification of what goes on in them is necessary. Are the words 'in them' even meaningful? In a way, all about a BH is coded in its surface. Some people like to think they are bridges to other space-times. My hunch is that they signal to a limitation of the description and that the interrelationship between gravity and gauge theory must be understood much better than it is today. Easier said than done, though.

The singularity of a BH lies in the future, rather than at the centre. So it's a time, not a position, from what I know. Now, you can call that the centre, for convenience, but it's a time, not a radius. Time and radius change roles when you cross the event horizon. That's what the maths says. What does that mean? I don't know. There are many things about black holes that I would like to understand better. Is the Schwarzschild black hole anything to go by, or is it just a freak of the equations of relativity for being so unrealistically simple? The only thing I can say is that theorists keep discussing them and the role they play in physics, including giant ones, microscopic ones that may exist, etc. There is no unanimous agreement about them. That's all I can say. The best thing about black holes is probably that they create conflict in our theories. I hope that means that research in black holes will usher in the next revolution in physics, but not much is certain about them except one thing: astrophysical black holes do exist.

I like this sentence. We should never underestimate the power of rephrasing the basics.

Love these tunes... There's something about waltz. And there's something about folk songs... Nightmarish tho.

Loved it.

It is not strictly necessary to excel at maths in order to have a good idea. Historically, Faraday was a perfect example of this.. Although it helps knowing your maths. But you need to understand how the ideas of physics relate to each other.

There is absolutely no significance whatsoever in the ratio between a kilo and a Coulomb. Same reason why the length of my nose divided by the mass of my head has no significance whatsoever. But I can define units o mass, length and time so that aforementioned ratio happens to be 9×109 or whatever other value I find convenient. Such is the nature of \( \varepsilon_0 \).

Bound state? You do have Yukawa couplings in the SM. Are you changing the SM? Your question isn't focused on what the Higgs field does? Can you 'hear' yourself? The Higgs field was summoned into physics because of what it does. Why else would we have a Higgs field? To make physics more spicy?

Saw it a couple of days ago. Almost spooky!

Force is related to momentum, and KE is a function of momentum: essentially (momentum)2/mass.

Really, really strange animal. Pink fairy armadillo, culotapado (hidden ass) or pichiciego (which I dare not translate). It has unique features among mammals, can use its tail and legs as a tripod, and its muscles reach the end of its extremities. https://en.wikipedia.org/wiki/Pink_fairy_armadillo

Maybe you don't see it this way, but everything I've seen so far upstream of this thread is help. You first need to understand what the Higgs field does in the standard model. The job description of the Higgs field is to provide mass for particles that, for some fundamental reason, shouldn't have one. The first class is gauge bosons that are found to be massive (W+, W-, and Z0 of the weak interaction). The other (quite important class) is charged fermions (not Majorana fermions, provided they exist). That includes quarks, and all leptons (electron, tau, muon...). It's not through strong coupling, as you've been told; it's through spontaneous symmetry breaking. In a manner of speaking, the particles get 'dressed' with a mass term. It's not at all like a coupling. How does your Gauss-law-based 'Higgs' do that? How does the symmetry get broken? How does it even work as a Higgs field? The Higgs field enters the physics through a potential, but it's a potential in the Higgs-field variable itself, not the space variable, as in Gauss' law. Etc. You need to understand basic physics. Let alone quantum field theory, and how the vacuum operates in that theory.

(my emphasis) SOL* * Smirking out loud