geordief

That example occurred to me after I had asked the question. So the particles collide and as a result new particles result. Do they accelerate away from the region where the "parent" particle was? Or do they travel like a photon ,either at zero velocity or at c? If the latter then they don't accelerate and the acceleration as in "particle accelerator " is a classical process. That is why I put it in quotes.As "comparable" as possible ,I suppose. Are there any situations where a quantum system undergoes anything like what a classical system does when it is subject to accelerating forces? I think you are saying there aren't? Is it possible to treat a quantum particle (system?) classically? Does that introduce error?

Are there examples of how acceleration is treated in quantum theory? If a classical system is accelerated I have a picture of a wave traveling through the system like if you were to pull a string or push a rod. What happens in "comparable" situations when the systems are quantum? Does "acceleration" mean anything under those circumstances?

What is that supposed to mean ? Are "you" in a third frame of reference or in A's or B's?

In which frame of reference?

A cricket commentary as reported on a facebook account(the late Brian Johnson) "Sometimes, unintended humour can be the best. The late Brian Johnson was a star performer when on Test Match Special. He once remarked innocently, ‘the batsman’s Holding, the bowler’s Willey.’ When he realised his statement was hardly appropriate he had a fit of giggles. It still makes me smile. Not what he said, but his reaction to it" There was all this too (gaelic games commentaries of old) Legendary witty GAA commentator Mícheál O'Muircheartaigh is an active 93. Thanks to Ferghal McCarthy for these live gems. -Sean Óg Ó hAilpín: his father’s from Fermanagh, his mother’s from Fiji. Neither a hurling stronghold. -Anthony Lynch, the Cork corner-back, will be the last person to let you down – his people are undertakers. -The stopwatch has stopped. It’s up to God and the referee now. The referee is Pat Horan. God is God. - Brian Dooher is down injured. And while he is, I’ll tell ye a little story: I was in Times Square in New York last week, and I was missing the Championship back home. So I approached a newsstand and I said, “I suppose ye wouldn’t have The Kerryman, would ye?” To which, the Egyptian behind the counter turned to me and he said, “Do you want the North Kerry edition, or the South Kerry edition?” He had both – so I bought both. And Dooher is back on his feet… Colin Corkery on the 45 lets go with the right boot. It's over the bar. This man shouldn’t be playing football. He’s made an almost Lazarus-like recovery from a heart condition. Lazarus was a great man but he couldn’t kick points like Colin Corkery. Teddy McCarthy to Mick McCarthy, no relation, Mick McCarthy back to Teddy McCarthy, still no relation. I saw a few Sligo people at Mass in Gardiner Street this morning and the omens seem to be good for them. The priest was wearing the same colours as the Sligo jersey! 40 yards out on the Hogan Stand side of the field, Ciarán Whelan goes on a rampage… it’s a goal! So much for religion. He grabs the sliothar, he’s on the 50! He’s on the 40! He’s on the 30… he’s on the ground! Pat Fox out to the forty and grabs the sliothar. I bought a dog from his father last week. Fox turns and sprints for goal… the dog ran a great race last Tuesday in Limerick… Fox, to the 21, fires a shot – it goes to the left and wide… and the dog lost as well. In the first half, they played with the wind. In the second half, they played with the ball. 1-5 to 0-8… well, from Lapland to the Antarctic, that’s level scores in any man’s language. Pat Fox has it on his hurl and is motoring well now, but here comes Joe Rabbitte hot on his tail… I’ve seen it all now, a Rabbitte chasing a Fox around Croke Park. Here’s another I recall; " Jimmy Barry Murphy. Jimmy Barry Murphy. One of the ten. The ten who have won All Ireland Hurling and Football Senior Medals. He will be spoken of till the end of time”. Teddy looks at the ball, the ball looks at Teddy… Mike Houlihan for Limerick. He had his jaw broken by a kick from a bullock two months ago. He’s back now. ‘Twas some bullock that broke Mike Houlihan’s jaw!

Looking at it physically ,the light from P's nose recedes from him at c .He follows ,whilst outside the EH at <c You say he "catches up" with it .Is that because the light from his erstwhile nose radiates in all directions and so he "catches up" or "falls into" that part of the light that is not receding directly away from him but with a component back towards him?(which is red shifted?) If there was just one photon receding directly along his "line of site" he wouldn't even see it red shifted?

Very far from understanding this but can I ask ,if the up and down coordinates that apply outside the EH are replaced with future and past inside the EH what are the future and past coordinates that applied outside the EH replaced with inside the EH? Are there any spatial coordinates that apply inside the EH and can they be visualized? They wouldn't be flattened on the EH itself ,would they? (that's a wild ,desperate guess)

What about a small BH?

This seems a silly question ,but if two objects follow each other through the event horizon of a very large BH ,does the second object see the first object as it passes the EH? Even if the two are very close together... Alternatively would a Pinocchio lose the sight of the end of his nose first as he passes the threshold?

@iNow don't know .Everywhere? That would seem to be an answer in the spirit of "where is the centre of the universe ?" (answer : "everywhere") Do we know that black holes have "back holes" ,anyway? I thought we just knew as far as the event horizon and some have suggested all the matter could actually collect there -with there being nothing inside . Would the "back hole" be on the event horizon in that case? Obviously ,I know zilch about this Are you saying that the idea of the universe having an event horizon corresponding to what a black hole might is more or less a non starter ? Or maybe you were replying to someone else?

Is it at all possible that the observable universe is inside a black hole with the event horizon between the observable and the non observable regions?

Is there a limit to how large and how "undense" such an object can become? Less dense than the surrounding region ,for example?

We never got a breakdown**of covid mortality per hourly consumption of forms of social media vs mainstream medias vs party affiliation etc etc. ..by the looks of it. Hope we learned something from the Covid period **as suggested earlier in this thread.

Thanks.Probably a bit too hard for my brain to get around but I will accept it for now Not sure how it affects the point I was trying to make. Does it mean there isn't an unobservable universe beyond the observable universe? I think I found it here in physics stackexchange (by googling) https://physics.stackexchange.com/questions/552306/does-time-require-matter-to-exist#:~:text=In other words%2C GR states,without realistic physical initial conditions.

Don't really know what to think. But I don't think the observable universe is surrounded by a great void as in my understanding it is surrounded by "more of the same" but that we have no idea how much of this "more of the same" there or-or what it is doing. The only reason we don't see this "more of the same" is that it is receding from us faster than the speed of light and so has become invisible to us.

I am confused.Wouldn't it be extrinsic curvature if the boat fell off an imagined edge but intrinsic curvature if it just dropped out of view when it reached the horizon? Or does the light ray with which we see the boat disappear exist in an embedding 3rd dimension making the surface extrinsic after all?

Yes ,you draw a triangle on the flat water and measure the 3 angles. If they add up to 180 it is flat . Less and it is a positive curvature ;more and it is negative (like a saddle) And ,less obviously you can do the same in 3d(perhaps using a 2d surface embedded in the 3d in the same way) Not sure how you would do it in 4d spacetime.

OK .So can subsets of the physical universe (eg the solar system) be described as "local" or "global"? Does "local" only describe the model and not the physical objects it attempts to model? And are we talking about spacetime curvature or the topology of the physical (subsets of the) universe? I think I was talking about just topology in that last post(even if I used terminology that applies normally to spacetime curvature) ie is there such a thing as local topography versus global topography?

very distant= still local ? That wouldn't be evidence of a global topology, would it? The observable universe is still "local" isn't it? Does the maths you are referring to make any physical predictions or is it entirely " theoretical"? ("theoretical" in layman's speak)

How do we know that a global topology exists at all and that we don't just have a patchwork of local topologies?

Are there any physical models that do that with posited versions of an actual universe? Are there any models that picture such a universe "from a bird 's eye view"? Or is that just an illogical question to ask?(the "bird"/observer being part of the universe could not take a "bird's eye view" of itself as a part of the whole)

Can we populate the surface of that 2d model of a sphere with 3d objects of an imaginary universe which is posited to be edgeless and bounded? How would I see in the model that the objects were 3d if they were embedded in the 2d surface?

Is this a space with no time component? A space that is ready to be populated with objects? I think I am more familiar with a space that is created by objects reconfiguring themselves(in an overall expansionist way as per observations) I think that is the orthodox view even if I am not up to speed with it. It still seems difficult for me to imagine the 3d universe existing on the 2d surface of the sphere There doesn't seem to be room for the 3 dimensions. Is it just an analogy? And the universe is not hollowed out ,is it?)unless the "hollow" is somehow the past history-surely not that)

The difficulty I have is of picturing a topology for a universe that has no edge or boundary. It seems others don't have that problem or perhaps they have enough of a mathematical understanding of the possibilities that they don't need to have a mental picture Would I be right to think that a topology doesn't require any particular shape but it just describes the way parts of the whole connect with each other?

How many different kinds of topology are possible for the universe? Would these topologies depend on more than the spacetime curvature? Are they all expanding ,contacting ,steady state? Any other ways to distinguish between different candidate topologies?