Gravitational Time Dilation

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Here are Prof. Unruh's thoughts on the waterfall analogy:

Professor William Unruh said:

Analogies are not identities. Analogies have areas in which they they
reproduce the thing they are analogous to, and areas where they do not. An
elephant is not an ant, even though some of the ways they walk may well be
analogous.

The waterfall analogy is a good analogy when one looks at the propagation of
long wavelength waves-- they obey the same equations in the water and in the
spacetime. That does not mean that spacetime is a fluid, just as the analogy
between elephants and ants does not mean that ants have trunks, or weigh a
ton.

William G. Unruh
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Prof. Poisson was also kind to share his expert opinion:

Professor Eric Poisson said:
Hi Tashja,

Analogies can be useful in simplifying complicated
ideas, but they usually break down when one tries to
carry them too far or take them too seriously. The
waterfall analogy is useful, because it illustrates
how difficult it would be to maintain yourself at
a fixed position outside a black hole. But to use it
to suggest that "space falls inside the black hole"
is to push it too far. I don't even know what the
phrase is supposed to mean; observers fall inside
the black hole, not space.

Cheers!

Eric
_________________________________
Eric Poisson
Professor of Physics
University of Guelph
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Many thanks tashja - our patience amply rewarded as usual. Not 1 or 2 or 3 but 4 responses - echoes of a late-night TV commercial! So, I had to refresh memory and went back to #466 (Schmelzer) and #468 (myself). While I don't always agree with Eric Poisson, in this instance found his to-the-point blunt comments the most useful and accurate.
There was little to argue with re Prof. Hamilton's feed-back, and especially liked the last bit in response to OnlyMe re 'firewalls'.

Steve Carlip's second part reply was informative as to clarifying that 'inflow' is that 'marked' by free-falling observers (assumed to have free-fallen 'from infinity'). So I guess if such a free-faller could measure speed relative to static markers hovering at constant r, one could imagine it as being carried along 'on a river'. Nevertheless, some here who only pretend to understand physics, concluded space itself really flows into a BH. Poisson's remarks kills that idea stone dead.

The seeming legitimacy to actual 'space inflow' evidently is the idea that the BH 'singularity' acts as a bottomless sinkhole for space/spacetime itself. Hmm.... One big problem, in addition to those raised in #468: Exterior Schwarzschild metric is identical for a non-rotating BH or star of equal mass. But in the latter case, how can there be a river inflow? No convenient 'cosmic sinkhole' to just absorb the inflowing space. Does it bank up somehow and one either has zero 'river flow', or a reflected flow giving a counter-current flow that is net zero? In which case, one should be able to distinguish between the exterior metrics. Obviously not true, and space inflow as such makes no sense. It gets back to being a very limited analogy based on imagined flow speed of in-fallers relative to static hoverers. Nothing more.

Concerning W.Unruh's comments, I have some reservations. Is the analogy between waves propagating in flowing water and in a Schwarzschild spacetime really so good? I stand by point 1 in #468. Toward the end of second main para, p2 in last linked arXiv article there:
It is explicitly stated in general relativity that the local speed of light is always c, which implies that the speed of light along a finite distance is not necessarily c.
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The one-way average proper speeds, parallel to a 'g-field' are given on p7 by eqns. (12), (14) there. Note, the anisotropy in c enters as a term directly proportional to longitudinal displacement r between measurement points. Distinctly different to sound in a flowing fluid, where anisotropy has no such dependence. But please, tashja, one marathon round of replies here has been quite adequate to settle the main thing - space does not flow into 'BH's' or anything else for that matter.
 
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I had just given up on this poster Paddoboy.....Thanks to Tashja, this river thingie and photon floating like fish ultimately got clarified and well settled. The danger of latching on to analogy like ultimate truth could not have been better demonstrated. I am just afraid, he may come up with.... look this is what I said and 3 out of 4 professors are supporting my view !! That will make me go insane.
 
Q-reeus said:
. Nevertheless, some here who only pretend to understand physics, concluded space itself really flows into a BH. Poisson's remarks kills that idea stone dead.
.
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Obviously in your usual agenda driven state, you would be referring to me.
But since I have said at least three times that the river/waterfall analogy is just that, an analogy, your lengthy post just reflects the rantings of a blowhard, peddling untruths and lies.
And it appears the usual forum clown whose posts follows, is clinging to your coat tails reflecting the same untruths and lies.





RajeshTrivedi said:
I had just given up on this poster Paddoboy.....Thanks to Tashja, this river thingie and photon floating like fish ultimately got clarified and well settled. The danger of latching on to analogy like ultimate truth could not have been better demonstrated. I am just afraid, he may come up with.... look this is what I said and 3 out of 4 professors are supporting my view !! That will make me go insane.
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Are you a full quid rajesh?

I certainly hope you both have learnt something anyway, although I'm not totally convinced.
 
paddoboy said:
Thanks again tashja....
Obviously he confirms the photon heading directly radially away as I have been saying and as also confirmed by Professor Hamilton, but not keen on the water fall/river analogy.
That's more an individual taste thingy, and the Important bit is to realise it is just that...an analogy, and an analogy that has been supported by maths.
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post 446 which proves qreeus and rajesh are peddlers of untruth and lies, both because of agendas in my part in having certain threads moved to the fringe. Grudges are terrible things!
 
paddoboy said:
Are you a full quid rajesh?

I certainly hope you both have learnt something anyway, although I'm not totally convinced.
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You are forgetting, that long ago, I tried to put some sense in you about this river thingie, even James R attempted to clarify, but you as usual kept on clinging. Finally when QReeus and OnlyMe took up and Tashja got it from profs, that your stupidity got exposed that how you are trolling and harassing people without an iota of knowledge. Your other phantoms like singularity at Plancks' level, electron/proton/neutron getting stripped off by BH etc also will sooner go away. Just stay put and keep writing...thats what is required. More you speak/write faster you will be exposed.
 
There is a difference between fringe and alternative theory, which Paddoboy does not understand. It requires courage and understanding to come up with an alternative theory...No one has ever become great by finding fault or prostrating in front of establishment...which you do Paddoboy.

PS: I am not saying oppose for the sake of opposing, but there is something called rationality and logic. Some of the mainstream concepts, however prevalent they are, however well respected they are, ...they defy logic and common sense. There is no harm in thinking out of the box for the same. Thats how meaningful life moves, not by sycophancy.
 
RajeshTrivedi said:
You are forgetting, that long ago, I tried to put some sense in you about this river thingie, even James R attempted to clarify, but you as usual kept on clinging. Finally when QReeus and OnlyMe took up and Tashja got it from profs, that your stupidity got exposed that how you are trolling and harassing people without an iota of knowledge. Your other phantoms like singularity at Plancks' level, electron/proton/neutron getting stripped off by BH etc also will sooner go away. Just stay put and keep writing...thats what is required. More you speak/write faster you will be exposed.
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You are the last person to talk sense too anyone. You are a fraud with a totally rebuked hypothesis, and as I have just shown in post 610 re post 446, a liar to boot.
 
paddoboy said:
You are the last person to talk sense too anyone. You are a fraud with a totally rebuked hypothesis, and as I have just shown in post 610 re post 446, a liar to boot.
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Your post #446 is false Bravado, as I stated in my post #449. You tried to even snatch away the analogy from prof Hamilton as if Prof Hamilton seconded your opinion....Its ok, take some cold water bath.
 
RajeshTrivedi said:
There is a difference between fringe and alternative theory,
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You have never had a theory, alternative or otherwise. You have a discredited hypothesis that totally defies GR, despite the misleading statements you like to present to cover your nonsense.
RajeshTrivedi said:
PS: I am not saying oppose for the sake of opposing, but there is something called rationality and logic. Some of the mainstream concepts, however prevalent they are, however well respected they are, ...they defy logic and common sense. There is no harm in thinking out of the box for the same. Thats how meaningful life moves, not by sycophancy.
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You certainly are opposing for opposition sake, as has been shown in all your 8 or 9 threads, and the way they have been presented.
While there is nothing wrong in thinking outside the box, you do need evidence of some sort to validate it, and secondly, you need to be man enough to admit when you are wrong.
You fail on both counts.

Again, some questions you need to answer that you keep avoiding......


[1] If you do not accept BH's what do you have to explain the effects we see on spacetime and matter/energy? [BNS not accepted as they have been logically invalidated.
[2] Since according to GR it is impossible for any signal to travel from the center of a BH back out to the EH, how does a BH hold its shape, in light of the fact that you reject fossil fields and the nonlinearity of gravity/spacetime?
[3]Since you still seem to be insisting of the existence of your nonsense BNS, why don't you show some honesty, some intestinal fortitude and forget about your ego problem and post in the correct section?
[4] If the strong nuclear force is never surpassed as you say, how do you explain the complete disassembling of matter, sometimes even before crossing the EH.
[5]Have you ever heard of tidal gravitational effects?
[6] How do you explain the GR edict that tells us that when the Schwarzchild radius is reached, further collapse is compulsory.
[7]Why should anyone on this forum accept the "beliefs" and anti mainstream answers of a non professional person on the subject of BH cosmology, without you obtaining some reputable link to support your claims, such as I have done.
 
RajeshTrivedi said:
Your post #446 is false Bravado, as I stated in my post #449. You tried to even snatch away the analogy from prof Hamilton as if Prof Hamilton seconded your opinion....Its ok, take some cold water bath.
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:)
My post 446 states exactly what the Professors state....That the river/waterfall analogy is just that...a mathematically validated analogy that is very useful, which as usual you ignorantly rubbished.
Your Mother may think you are an Einstein, the world sees you as Donald Duck! Sorry ol chap!
 
You reframe or withdraw Q5 and Q7, then I will answer once again, all your questions. But you have to promise to this forum, that if you have any objection to my answeres then you will respond in your language, not some copy paste stuff.......Take the challenge ?
 
paddoboy said:
Obviously in your usual agenda driven state, you would be referring to me.
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It is you, as the raging buffoon who continually stirs up resentment unnecessarily, that has an unfortunately condoned Troll agenda.
But since I have said at least three times that the river/waterfall analogy is just that, an analogy, your lengthy post just reflects the rantings of a blowhard, peddling untruths and lies.
And it appears the usual forum clown whose posts follows, is clinging to your coat tails reflecting the same untruths and lies.
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Anyone is free to re-read your #448, #463, and decide what you were unquestioningly endorsing in full. As usual the SHOUTING bolded text gives clues. But let's see, I made key statements in #606 dealing with limitations of the river model, as also back in #468. Which ones do you challenge? I mean on a technically competent relevant basis.
 
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