Duda Jarek

For both marine propeller and shooting e.g. free electron laser, indeed we don't control the details of individual particles, only their statistical behavior ... but still allowing to cause excitation of the target - by retarded EM wave. Applying T/CPT symmetry: reversing rotation of marine propeller, or reversing electron trajectory of free electron laser/synchrotron, the causation should reverse to causing deexcitation of target - by advanced EM wave ... with requirement that this target was initially excited, what is not true e.g. for most radio telescopes - preventing them from observation of advanced waves. Applying time symmetry to synchrotron:

Sure it seems highly suspicious that, among ~300 GM events, there was observed only single EM counterpart - including advanced waves into considerations could help explain. The current EM counterparts are retarded - being certain their non-existence when required, should indicate it was advanced GW (?) To have a chance to observe advanced EM counterparts, we would need telescopes with excited sensor - currently avoided by cooling.

Sure there is also statistics there, but stimulated - especially in superradiance, also in laser ... or wave behind marine propeller pushing or pulling energy from resonator is quite deterministic. For example white hole would emit, causing excitation in sensor of telescope. Applying T/CPT symmetry to this scenario, shouldn't black hole cause deexcitation of telescope sensor if prepared as excited? GR is solved by the least action principle - treating spacetime as 4D membrane minimizing tension as action - based on boundary conditions in both time directions. If there are e.g. orbiting supermassive black holes there, shouldn't distortions they create propagate in both directions of this 4D membrane? (for https://theconversation.com/to-map-the-vibration-of-the-universe-astronomers-built-a-detector-the-size-of-the-galaxy-244157 ) Solving GR by least action, QFT by Feynman ensembles is CPT symmetric, requires Einstein's block universe philosophy of time - that we travel through already found 4D solution ... e.g. in S-matrix: <psi_f | U | psi_i> with one amplitude coming from the past, second from the future, we multiply them e.g. in Born rule - allowing for very nonintuitive Bell violation.

Thermodynamics is for spontaneous emission, while here we are talking about stimulated. It is valuable to think about hydrodynamical analog: wave behind marine propeller carries energy, momentum and angular momentum - like photon. We can practically apply time symmetry - just reversing its rotation: getting pulling photon, causing deexcitation of target. Going to similar EM, we can analogously apply time symmetry to synchrotron radiation - just reversing electron trajectory, this way switching absorption and stimulated emission acting on target:

There is Feynman diagram photon exchange between coupled e.g. two electrons - current cooled EM receivers are focused on retarded: such that photon was emitted by target, absorbed by sensor ... for advanced you need CPT version of this diagram - reversed coupling: photon emitted by receiver, absorbed by target.

EM receivers are focused on absorption - of retarded wave. For advanced you need its time symmetric analog - receiver focused on emission, what requires its initial excitation ... usually avoided e.g. by cooling of radio telescope amplifier.

Sure, while being older than the age of the Universe would be a nice argument for advanced, luminosity distance is only one of 3 types of distances they are using, being only suggestion ... it is the last argument I have used, the remaining 3 are much stronger. The clearest would be certain lack of (retarded) EM counterpart when required - if excluding retarded, wouldn't we have to consider it was advanced? Such cases might be a matter of months now. What other ways could we use to distinguish retarded from advanced? Observing "too early to happen events" like with black hole mass gap seems such a way - could e.g. this 66 + 85 -> 142 merger be advanced wave? Then there are Timing Pulsar Arrays seeing vibrations of the Universe - claiming they require orbiting SMBH ... if retarded seem insufficient, couldn't they be also advanced? Any other arguments for/against advanced GW?

You have written that we are testing - if retarded vs advanced, how is it done? For GR there is used the least action principle. Gathered some more arguments. As the main source of gravitational wave events is just orbiting of e.g. two black holes, and evolving toward minus time orbiting remains orbiting, so using Euler-Lagrange toward minus time (t -> -t), or the least action principle, there should be generated similar waves - for us being advanced of similar chirp shape as retarded. LIGO just measures lengths - invariant to time symmetry, so should see both retarded and advanced waves. Therefore, maybe some of current ~300 events ( https://catalog.cardiffgravity.org/ ) could turn out advanced? Some arguments: - ultimate confirmation should be certain lack of (retarded) EM counterpart when required (e.g. neutron star merger), still only 1 per ~300 observed, leaving advanced wave possibility (?), - some events are believed to happen too early, like 66 + 85 -> 142 merger starting in 50-120 black hole Mass Gap, e.g. https://www.symmetrymagazine.org/ar...st-scale-could-explain-impossible-black-holes - advanced would have more time, - pulsar arrays show vibrations of the Universe requiring more than expected orbiting supermassive black holes - https://theconversation.com/to-map-...uilt-a-detector-the-size-of-the-galaxy-244157 - advanced could add them, - the largest observed luminosity distance is ~27Gly: twice the age of the Universe - maybe it is worth to consider advanced?

Sure, e.g. throwing a rock to a lake symmetric in equations, there appear asymmetries of solutions ... for physics we know many such asymmetries , like entropy gradient, emission asymmetry (e.g. circulating electron losing energy), tendency for black hole formation from direction of Big Bang. But solving physics by the least action(GR)/Feynman ensemble(QFT) using e.g. boundary conditions in Big Bang and Big Crunch, they seem very similar just hot soups - symmetric ways of solving from symmetric boundary conditions, shouldn't the solution be also symmetric? Reversing e.g. mentioned 3 asymmetries near Big Crunch, like in diagram above ( https://scienceforums.net/topic/140178-why-we-observe-only-retarded-gravitational-waves-not-advanced/#findComment-1304506 )? Both DESI observations and revisiting of supernova data (e.g. Sabine's https://www.youtube.com/watch?v=2VpP-qXuJMc ) suggest slowing down acceleration ... but sure Big Crunch is only hypothesis now, just convening to get intuitions - valuable also if it is not true. Least action GR is deterministic, but sure there is also QFT - solved e.g. by <psi_f |U| psi_i> S-matrix, also using boundary conditions in both time directions, between them assuming Feynman ensemble - e.g. of histories of Universe between Big Bang and Big Crunch. Returning to the topic, LIGO measures lengths - which are T/CPT invariant, so in theory should also see advances waves ... if only there are such events, scientists should test instead of assuming, but the big question is what to search for e.g. in LIGO data? Reversed chirps is just a first guess ... In contrast, EM receivers are rather focused on absorption - of retarded waves. For advanced would need to be sensitive for stimulated emission - requiring excitation of sensor, what is rarely used now.

So how would you like to solve general relativity for boundary conditions in Big Bang and Big Crunch? The standard universal answer seems: the least action principle, or Feynman ensemble for QFT. If so, what would be the difference between "hot soup" just after Big Bang and "hot soup" just before Big Crunch? - to make their surrounding very different: that one has tendency to form black holes, but the second doesn't?

Imagine there will be Big Crunch, so we can view the history of our eon as solution of the least action (GR)/Feynman ensemble(QFT) for boundary conditions in Big Bang and Big Crunch. In such solution evolve backward from Big Crunch - shouldn't there also be formed black holes? If they merge, for us they would generate advanced waves - should LIGO see them?

ps. diagram for such hypothetical advanced gravitational wave assuming Big Crunch: Diagra

Sure, I also suspect LIGO should see retarded and advanced waves as looking similar distortions of spacetime. However, there might be ways to distinguish observed events: separate confirmation e.g. visual - if based on retarded waves, their lack could indicate advances gravitational wave, chirp shape - backward evolving from Big Crunch, shouldn't its collisions have time-reversed chirp shape? Maybe it is worth to include such mirrored chirp shapes into their database they use for search?

KJW, CPT symmetry is in equations - that "running movie backward" e.g. evolving back from Big Crunch (+CP), the equations governing physics should be the same. Therefore, asymmetries cannot be in equations, need to be only in solution - like low entropy of Big Bang/Big Crunch - everything is localized, so entropy is low. Or emission asymmetry: that circulating electron now loses energy (gains in CPT) - seems because there is now more absorbers than emitters, but it can be reversed e.g. in tabletop particle accelerators using lasers ( https://newscenter.lbl.gov/2016/02/01/2-stage-laser-plasma-accelerator/ ), or applying CPT symmetry ... or maybe also in far future (?) Or there is now tendency to form black holes, which can collide - observed by LIGO ... but before Big Crunch shouldn't also this tendency be reversed? Could LIGO observe such advanced waves?

swansont, the big question is which boundary conditions? For Euler-Lagrange we use values and derivative to start evolution in one direction - usually toward future, but can also use it toward past by t -> -t. For the least action principle we use boundary conditions symmetrically from both directions. I haven't seen general relativity solved with Euler-Lagrange: "unrolling" 3D spacetime (?) Instead, they search for static 4D shape of spacetime satisfying least action equations - Einstein's block Universe, eternalism philosophy of time: https://en.wikipedia.org/wiki/Eternalism_(philosophy_of_time) And in such least action principle view, there are allowed closed timelike curves, but the found static 4D solution (we travel through) has already resolved all potential time paradoxes: https://en.wikipedia.org/wiki/Novikov_self-consistency_principle KJW, modern physics is believed to be CPT symmetric, so asymmetries like entropy gradient need to be properties of specific solution we live in, like throwing a rock to lake (symmetric in equations). E.g. LIGO rather mostly sees retarded waves, as "collisions from our past" seem more like in our solution, but maybe it also contains reversed (?) - e.g. assuming Big Crunch and evolving backward, getting black hole collisions this way for us would be "collisions from our future" with advanced waves - maybe LIGO could see, probably for time-reversed chirp shapes (?)

But isn't general relativity solved in time symmetric way like the least action principle? How would you like to restrict causality to uni-directional in such 4D block universe view? E.g. below black hole horizon time is switched with space, or even worse: Klein-botte-like wormhole ( https://en.wikipedia.org/wiki/Non-orientable_wormhole ) could in theory apply P or T symmetry to a rocket flying through it - how do you see causality there?

General relativity is rather solved in time symmetric way, like the least action principle condition in Einstein's field equations, what as in e.g. Wheeler-Feynman absorber theory requires symmetrically both retarded and advanced solutions. So why seems there are only considered retarded gravitational waves? Can we exclude being advanced wave for all observed events ( https://en.wikipedia.org/wiki/List_of_gravitational_wave_observations )? If not, should they use original chirp shapes, or maybe time reversed?

While your examples seem just reduced energy, time crystals are objects oscillating in the lowest energy state, which corresponds to kinetic energy so energy minimization usually kills it ... But somehow electron and neutrinos do it it - we should try to understand, and it seems to require negative terms in Hamiltonian - in perturbative approximation using negative energy virtual particles.

Seems we need negative Hamiltonian terms to explain why resting electron and neutrino are oscillating - making them https://en.wikipedia.org/wiki/Time_crystal , and such often automatically appear (e.g. https://arxiv.org/pdf/2501.04036 ) In effective descriptions they might need negative energy virtual particles, but are they also used as non-effective?

While special relativity says inertial mass is equivalent with energy, there are at least two more types of mass, for which equivalence seems not so certain - let me briefly summarize and ask for more arguments for/against their equivalence. Gravitational mass is hypothesized to be equal by equivalence principle, and gravitational interaction of antimatter now seems nearly certain to be the same (?) However, all these tests are for baryons and bulk matter made of them, for non-baryons I am aware only of this 1967 Witteborn, Fairbank test for electron - measuring maximal time for thermal electrons reaching upper electrode tmax=sqrt(2h/g), which turned out infinite, suggesting g=0. But later it was explained as due to gravitational charge gradient in shielding, so seems experimentally we still don't know (good slides). de Broglie clock, zitterbewegung - e.g. relativistic QM requires E=mc^2 for psi ~ exp(-iEt/hbar). For electron it was directly confirmed ( https://link.springer.com/article/10.1007/s10701-008-9225-1 ) by observing increased absorption of 81MeV electron beam when agreeing with spatial lattice of crystal, however, they got 0.28% disagreement. The same oscillation formula was used to introduce 3 masses based on neutrino oscillations, but experimental confirmation they are equivalent to energy seems quite difficult (maybe GERDA?) Are there some more arguments they are equal or not? Past and future experiments to improve the situation?

So you are saying that while circulating electron loses energy, circulating positron gains it? I think both are losing in our perspective, and both are gaining from CPT perspective. It can gain energy by synchrotron self-absorption, but it would need emitters in the past - which are rare now ... in contrast to absorbers in our future. In CPT perspective it is the opposite: more emitters than absorbers.

But as you have quoted “The CPT theorem says that CPT symmetry holds for all physical phenomena" ... So do you say "circulating charge" is outside of "all physical phenomena"? Or propose some understanding (I haven't seen in your posts)? I have proposed one: because there is more absorbers than emitters - do you agree, disagree (why?), or have a different understanding?

CPT symmetry says it doesn't matter if you look at circling charge forward or backward in time ... but it clearly depends in solution we live in. There is clear asymmetry we should understand ... and it seems essentially different than entropy asymmetry.

CPT symmetry is supposed to be in equations governing physics, so its violations need to be in solution. Indeed like entropy asymmetry ... but how would you like to conclude this emission asymmetry from it? I don't see how to do, looks like a different type of asymmetry - literally presence of more absorbers than emitters, reversed in CPT perspective.

Yes, it is called synchrotron self-absorption ... but the question is why emission is dominating in our perspective, but in CPT perspective absorption is dominating? Is it because of more absorbers than emitters? No, I am asking why against CPT symmetry: in our perspective circulating electron loses energy, but applying this symmetry it gains energy instead?