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 #56049 - 06/14/16 08:56 PM Vectors and time reversal. Bill S. Megastar Registered: 08/20/10 Posts: 3570 Loc: Essex, UK This thought experiment involves a friction-free snooker table, in a vacuum. The cue-ball is alone on the table, placed centrally on the balk cushion. At t=0 the cue strikes it, sending it straight up the table at constant velocity, v, with constant momentum, p. At t=1 it crosses the green spot.At t=2 it crosses the blue spot. At t=3 it arrives at the pink spot; at which point, time is reversed.It crosses the blue and green spots at t=2 and t=1, respectively. What happens to v and p, both are vectors, so at t=2 and t=1, in reversed time, the ball is travelling towards the balk cushion, but the vectors point away from it? _________________________ There never was nothing. Top
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 #56052 - 06/15/16 02:03 AM Re: Vectors and time reversal. paul Megastar Registered: 03/21/06 Posts: 4136 constant velocity? _________________________ 3/4 inch of dust build up on the moon in 4.527 billion years,LOL and QM is fantasy science. Top
 #56053 - 06/15/16 08:17 AM Re: Vectors and time reversal. [Re: paul] paul Megastar Registered: 03/21/06 Posts: 4136 the green , blue and pink spots are not lined up with each other.the 3 spots are not in a straight line so the ball would experience a change in velocity if it did cross the green spot and the blue spot and then it vectored to the pink spot.however you can buy more pink spots and place another pink spoton the table lined up with the other 2 spots and then they wouldall be in a straight line.or you could simply exchange the green spot with the brown spotin the OP if thats the way you do things. _________________________ 3/4 inch of dust build up on the moon in 4.527 billion years,LOL and QM is fantasy science. Top
 #56055 - 06/15/16 02:34 PM Re: Vectors and time reversal. Orac Megastar Registered: 05/20/11 Posts: 2819 Loc: Currently Illinois, USA Originally Posted By: Bill S.What happens to v and p, both are vectors, so at t=2 and t=1, in reversed time, the ball is travelling towards the balk cushion, but the vectors point away from it?Now place yourself at the other far end bounce cushion and time is always running backwards according to you even when you are waiting to strike the ball ... you may need to think about it for a second Time only goes the right way when the ball has bounced and is on it's way back.Bill S new word for the day to learn about => Hamiltonianhttps://en.wikipedia.org/wiki/Hamiltonian_mechanicsQuote:The time evolution of the system is uniquely defined by Hamilton's equationsYou have created a Hamiltonian description and it's just a mathematical description. The article even tells you how to deal with your vector descriptions and the physical meaning.Want me to prove to you that your description is completely meaningless ... pick up the ball somewhere in it's travels.So which way is your time running when I pick the ball up? Edited by Orac (06/15/16 02:37 PM) _________________________ I believe in "Evil, Bad, Ungodly fantasy science and maths", so I am undoubtedly wrong to you. Top
 #56057 - 06/15/16 05:57 PM Re: Vectors and time reversal. [Re: Orac] paul Megastar Registered: 03/21/06 Posts: 4136 oh , Im on orachnids ignore list ... LOL you may need to think about it for a second _________________________ 3/4 inch of dust build up on the moon in 4.527 billion years,LOL and QM is fantasy science. Top
 #56067 - 06/16/16 06:31 PM Re: Vectors and time reversal. Bill S. Megastar Registered: 08/20/10 Posts: 3570 Loc: Essex, UK Quote:At t=1 it crosses the green spot.Of course, that should have been the brown spot! Peter Ebdon plays snooker (very well) in spite of being colour blind; but even he would not put the green on that spot. _________________________ There never was nothing. Top
 #56068 - 06/16/16 07:42 PM Re: Vectors and time reversal. [Re: Orac] Bill S. Megastar Registered: 08/20/10 Posts: 3570 Loc: Essex, UK Quote:Now place yourself at the other far end bounce cushion and time is always running backwards according to you even when you are waiting to strike the ball ... you may need to think about it for a second I thought about it for a few seconds, but wherever I stand, time runs the same way. Thanks for the link. I understand that Roger Penrose's father tought him calculus the evening before he started it at school. It would take me a lot longer, and I don't have the time; so if there is something there that would enlighten me, it will need to be simplified. Lots! Quote:So which way is your time running when I pick the ball up?Same way it was before you picked it up. _________________________ There never was nothing. Top
 #56069 - 06/16/16 11:55 PM Re: Vectors and time reversal. paul Megastar Registered: 03/21/06 Posts: 4136 is this your thought experiment or someone elses?the reason Im asking is because if it were possible toreverse time then both v and p would be in the reversed direction.my reasoning on this is that when the ball strikes the cueat the balk cushion its momentum would be transferred intothe cue due to its v and mass.if the experiment is only referencing time as in a frame by frameevent such as a video that is stopped as the ball reaches the pink spot and then reversed frame by frame then in that case both v and p would still point the same way. _________________________ 3/4 inch of dust build up on the moon in 4.527 billion years,LOL and QM is fantasy science. Top
 #56072 - 06/17/16 12:10 PM Re: Vectors and time reversal. [Re: paul] Bill S. Megastar Registered: 08/20/10 Posts: 3570 Loc: Essex, UK Quote:the reason Im asking is because if it were possible toreverse time then both v and p would be in the reversed direction.For the sake of discussion, I'm accepting relativity. This means that t=2 (for example) is an immutable spacetime event. It cannot occur with v and p running R to L, then L to R. _________________________ There never was nothing. Top
 #56073 - 06/17/16 12:19 PM Re: Vectors and time reversal. [Re: Orac] Bill S. Megastar Registered: 08/20/10 Posts: 3570 Loc: Essex, UK Quote:Your experiment assumes you the observer are GOD and know exactly what is actually happening .. an impossibility for us mere mortals.This is more-or-less my starting point. There are too many impossibilities to allow physical time reversal to work. Or are there? Do we impose the "impossibilities" through our own maths and physics.BTW; I am "god"; so are you; but that's a whole different line of logic. _________________________ There never was nothing. Top
 #56074 - 06/17/16 12:26 PM Re: Vectors and time reversal. [Re: paul] Bill S. Megastar Registered: 08/20/10 Posts: 3570 Loc: Essex, UK Quote:is this your thought experiment or someone elses?It's my thought experiment, but I got the idea from somewhere. I'll let you know if/when I remember where, because I'm fairly sure there were other time related issues there as well.Yes - you are "god", too. Feels good, doesn't it? _________________________ There never was nothing. Top
 #56075 - 06/17/16 01:40 PM Re: Vectors and time reversal. paul Megastar Registered: 03/21/06 Posts: 4136 well if its about "spacetime" then I personally dont care.I just cant think of a valid reason to care.right , thats it. _________________________ 3/4 inch of dust build up on the moon in 4.527 billion years,LOL and QM is fantasy science. Top
 #56077 - 06/17/16 08:29 PM Re: Vectors and time reversal. [Re: paul] Bill S. Megastar Registered: 08/20/10 Posts: 3570 Loc: Essex, UK OK, forget about spacetime, if you wish. At t=2 the ball crosses the blue spot, R to L.At t=3 it arrives at the pink spot; at which point, time is reversed.At what time does the ball cross the blue spot, L to R? _________________________ There never was nothing. Top
 #56079 - 06/17/16 08:50 PM Re: Vectors and time reversal. paul Megastar Registered: 03/21/06 Posts: 4136 if time could be reversed then the measurements would also be reversed.t=2time is a measurement and nothing else.so its like using a measurement tape.measured out to t=3 then back to t=2why?because if time were forwarded again at the blue spotthen history would repeat in the same order.and the ball would once again approach the pink spotor t=3else if you advanced the time measurement to t=4as the ball crosses the blue spot thentime could not repeat if the time were forwarded at the blue spot because the next available time measurement would be t=5and only 3 units of time would have occured.t=1 t=2 and t=3 _________________________ 3/4 inch of dust build up on the moon in 4.527 billion years,LOL and QM is fantasy science. Top
 #56081 - 06/19/16 01:39 PM Re: Vectors and time reversal. Orac Megastar Registered: 05/20/11 Posts: 2819 Loc: Currently Illinois, USA Originally Posted By: Bill S.For the sake of discussion, I'm accepting relativity. This means that t=2 (for example) is an immutable spacetime event. It cannot occur with v and p running R to L, then L to R.immutable spacetime event???? ... in relativity? Really?Refresher ... Newtonian physics has immutable space and time events. Einstein wanted that feature in Relativity but he lost the argument and eventually worked it out that observers may see things differently.To be blunt unless you are god you can't even identify that the ball didn't just go past t2 and keep sailing on and you started observing it go backward ... in a nutshell you have no way to know your observation is "absolute" or "real". This goes back to the time problem at the event horizon and you wanting to make it real.You need to stop making things "real" and "immutable" just because you observe them. Go and read Einsteins train thought experiment.I can tell you from your setup I can't determine a thing, I don't have enough information. Edited by Orac (06/19/16 02:17 PM) _________________________ I believe in "Evil, Bad, Ungodly fantasy science and maths", so I am undoubtedly wrong to you. Top
 #56082 - 06/19/16 01:55 PM Re: Vectors and time reversal. Orac Megastar Registered: 05/20/11 Posts: 2819 Loc: Currently Illinois, USA Originally Posted By: Bill S.This is more-or-less my starting point. There are too many impossibilities to allow physical time reversal to work. Or are there? Do we impose the "impossibilities" through our own maths and physics.In your experiment there is no way to sort forward from backward time in your experiment, you haven't given me enough to sort that out.The biggest problem with your experiment is the result, which starts from an out there suggestion of a point at which time reverses.So to make the "result fit" I am thinking what motions could happen to "observe that", and more direct out there results would be things like enter a worm hole and come out at the same entry point but going backwards. You are constructing the far out idea of a point at which time could reverse so I assume I am allowed to put a wormhole there as time is going backwards. So I believe in worm holes no but nor do I believe in points at which time reverses.You need to have it clear in you mind when you talk of reversing time are you talking of really doing that or just reversing event order because the two things are not the same. Reversing event order is reasonably easy to do, reversing actual time not so much.Paul correctly worked the LOGIC fail, that you can't be talking about real actual time as you won't go backwards because through the same section of space you initially were going forward. So why didn't you go backwards when coming thru the same section of space originally.If this was your start point I think you need a new one Edited by Orac (06/19/16 02:26 PM) _________________________ I believe in "Evil, Bad, Ungodly fantasy science and maths", so I am undoubtedly wrong to you. Top
 #56084 - 06/20/16 09:16 AM Re: Vectors and time reversal. [Re: Orac] Bill S. Megastar Registered: 08/20/10 Posts: 3570 Loc: Essex, UK Quote: To be blunt unless you are god you can't even identify that the ball didn't just go past t2 and keep sailing on and you started observing it go backward ... in a nutshell you have no way to know your observation is "absolute" or "real".While this is all, undoubtedly, true; games of snooker are played, and they are subject to the laws of physics. If you apply your reasoning to the events of the macro-world, how would a player know what any ball was going to do? _________________________ There never was nothing. Top
 #56085 - 06/20/16 09:26 AM Re: Vectors and time reversal. [Re: Orac] Bill S. Megastar Registered: 08/20/10 Posts: 3570 Loc: Essex, UK Quote:If this was your start point I think you need a new one A tourist in Ireland stopped his car and asked a local man: “Could you direct me to Ballynanty?” The man thought for a moment, then said: “Ah, to be sure, if I was going to Ballynanty, I’d not start from here”. Edited by Bill S. (06/20/16 09:27 AM) _________________________ There never was nothing. Top
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