Gravity. Please knock this down

[mistermack]

With the river model, the idea must be that space is being annihilated, or at least compressed to near nothing, in a black hole.

If a black hole is has had a river of space flowing into it for ten billion years, that's a lot of space, in a small object. The idea that the Earth could be doing the same thing, on a much smaller scale, I don't think it's all that preposterous.

One thing I was wondering was what would this loss of space to stars, black holes and other matter actually do to the space that's left? Would it stretch it in some way, and if so, could it cause an apparent redshift?

[Strange]

6 minutes ago, mistermack said:

With the river model, the idea must be that space is being annihilated, or at least compressed to near nothing, in a black hole.

Space isn't "stuff" so it doesn't need to be annihilated or compressed. We are just talking about coordinates "flowing" into the black hole.

8 minutes ago, mistermack said:

One thing I was wondering was what would this loss of space to stars, black holes and other matter actually do to the space that's left? Would it stretch it in some way, and if so, could it cause an apparent redshift?

As the Gullstrand–Painlevé coordinates are exactly equivalent to Schwarzschild coordinates (or any of the other possible choices) it can't give results that are different from any other choice.

[mistermack]

Are you talking about the coordinates that describe a field?

[Strange]

3 minutes ago, mistermack said:

Are you talking about the coordinates that describe a field?

Yes. Space-time coordinates.

[mistermack]

So we're talking about a field that normally occupies a certain volume in remote space flowing into a black hole of relatively small volume or being annihilated? That's what I was picturing, anyway. Presumably space-time coordinates are describing something, even if it's not something in the sense of matter. I can't imagine a flow of mathematical coordinates, unrelated to anything.

[Strange]

3 minutes ago, mistermack said:

So we're talking about a field that normally occupies a certain volume in remote space

Well, the field IS space. (And time.)

3 minutes ago, mistermack said:

Presumably space-time coordinates are describing something, even if it's not something in the sense of matter.

Distances and times. Surprisingly.

 

BTW You might find John Baez's pages on the Einstein Field Equations helpful. They do go into the maths in a little detail but most bits are understandable even without fully understanding the maths.

http://math.ucr.edu/home/baez/einstein/

[mistermack]

So, with the metric expansion of space, distances are creeping up, with time. And in a black hole, distances are shrinking. 

So basically, my OP was suggesting that matter and energy could be causing distances to shrink, slightly, in their immediate vicinity. 

[Strange]

2 minutes ago, mistermack said:

So basically, my OP was suggesting that matter and energy could be causing distances to shrink, slightly, in their immediate vicinity. 

And that may be a valid interpretation. I don't know whether there is a general solution to the equations in those terms but as the Schwarzschild solution can be applied to a body like the Earth, as well as black holes, then there are at least some cases where it is valid.

P.S. The Baez pages explain why, in one case the equations describe expansion and in another they describe "attraction".

P.P.S. Remember Joan Baez? Cousins.

[mistermack]

18 minutes ago, Strange said:

P.P.S. Remember Joan Baez? Cousins.

Remarkable. 

There but for fortune . . . .

[mistermack]

The experiment I would like to see done, is to measure time dilation at the Earth's surface, for a stationary clock, and an identical clock  falling downwards at the Earth's escape velocity. If the "river" interpretation of GR was correct, you would expect the second clock to tick faster, when special relativity would have it ticking slower.

Would that be practical, or is there a problem with the concept? 

[Markus Hanke]

5 minutes ago, mistermack said:

the "river" interpretation of GR

There is not really any such thing. There is a waterfall analogy that is sometimes used to illustrate certain concepts of GR that would otherwise be difficult to explain without going deeply into the maths; but that is just an illustrative analogy. Unlike is arguably the case in quantum mechanics, there is no space for differing “interpretations” in GR.

[studiot]

1 hour ago, mistermack said:

falling downwards at the Earth's escape velocity

 

That's a clever trick an no mistake.

 

[swansont]

9 hours ago, mistermack said:

The experiment I would like to see done, is to measure time dilation at the Earth's surface, for a stationary clock, and an identical clock  falling downwards at the Earth's escape velocity. If the "river" interpretation of GR was correct, you would expect the second clock to tick faster, when special relativity would have it ticking slower.

Would that be practical, or is there a problem with the concept? 

Why at the escape velocity? That seems a pretty specific condition. What special thing happens at that speed? And at what position should it have that speed? (Atmosphere is going to prevent this happening over a path)

Why do you claim these two different predictions?

[mistermack]

1 minute ago, swansont said:

Why at the escape velocity? That seems a pretty specific condition. What special thing happens at that speed? And at what position should it have that speed? (Atmosphere is going to prevent this happening over a path)

Why do you claim these two different predictions?

We established on another thread some months ago that the time dilation on Earth's surface due to gravity is exactly the same as what would be caused by a downward flow of space time at the speed of the escape velocity. The formulas are identical. 

If there WERE a flow of space time into the Earth, at that speed, then by dropping a clock at the same speed, the clock should run faster. (I'm SUGGESTING this, not proposing it as a fact. ) I'm asking the question, could such an experiment be used to disprove the notion of a flow of space into a gravity well? I don't see why not.

[swansont]

1 hour ago, mistermack said:

We established on another thread some months ago that the time dilation on Earth's surface due to gravity is exactly the same as what would be caused by a downward flow of space time at the speed of the escape velocity. The formulas are identical. 

If there WERE a flow of space time into the Earth, at that speed, then by dropping a clock at the same speed, the clock should run faster. (I'm SUGGESTING this, not proposing it as a fact. ) I'm asking the question, could such an experiment be used to disprove the notion of a flow of space into a gravity well? I don't see why not.

So how does a rocket move downward at the escape velocity at the surface? This is a real experiment you are suggesting, not a thought experiment. Pretty safe to say it has not been done.

And why do you think there are two conflicting solutions? It sounds like you are proposing some new physics. This isn't the place to do that.

But consider just some generic rocket launch, with a parabolic trajectory. You could analyze that.

[mistermack]

1 hour ago, swansont said:

So how does a rocket move downward at the escape velocity at the surface? This is a real experiment you are suggesting, not a thought experiment. Pretty safe to say it has not been done.

And why do you think there are two conflicting solutions? It sounds like you are proposing some new physics. This isn't the place to do that.

But consider just some generic rocket launch, with a parabolic trajectory. You could analyze that.

Not a rocket with a clock. Maybe an isotope with a known characteristic frequency could be fired downwards and checked for how it compared to a stationary one? ( I'm just speculating ). 

Why two solutions? Well, if a river of space is passing downwards, then a stationary clock on the surface is moving at high speed relative to that space, and should be slowed. Whereas a clock co-moving with that space (ie stationary in that space) should run faster. According to time dilation due to motion through space.  

Whereas if the river model was wrong, then the surface clock is gravitationally slowed ( effectively the same) but the descending clock should be slowed even more, due to it's relative motion.

[Markus Hanke]

7 hours ago, mistermack said:

a flow of space time into the Earth

Such a concept does not make any physical or mathematical sense.

[mistermack]

5 hours ago, Markus Hanke said:

Such a concept does not make any physical or mathematical sense.

http://www.dailygalaxy.com/my_weblog/2014/06/gravitys-river-new-black-hole-theory-suggests-gravity-is-a-fluid-.html      

[swansont]

12 hours ago, mistermack said:

Not a rocket with a clock. Maybe an isotope with a known characteristic frequency could be fired downwards and checked for how it compared to a stationary one? ( I'm just speculating ). 

You can't do it with one atom of a radioactive isotope - one such atom is not a clock. Decay is stochastic. You would need a large number of them, with the correct (short) half-life, and somehow get them moving at the same speed. creating the short-lived isotope will be a huge technical barrier. OTOH, the muon measurement has been done, as well as gravity probe A. Both are consistent with relativity being correct.

This isn't speculations.

Quote

Why two solutions? Well, if a river of space is passing downwards, then a stationary clock on the surface is moving at high speed relative to that space, and should be slowed. Whereas a clock co-moving with that space (ie stationary in that space) should run faster. According to time dilation due to motion through space.  

Whereas if the river model was wrong, then the surface clock is gravitationally slowed ( effectively the same) but the descending clock should be slowed even more, due to it's relative motion.

If you have two possible answers, there must be two different equations, stemming from two different models. One of which is not relativity, making it moot for this discussion.

1 hour ago, mistermack said:

http://www.dailygalaxy.com/my_weblog/2014/06/gravitys-river-new-black-hole-theory-suggests-gravity-is-a-fluid-.html      

Gravity being modeled as a fluid ≠ spacetime is a river

[mistermack]

29 minutes ago, swansont said:

You can't do it with one atom of a radioactive isotope - one such atom is not a clock. Decay is stochastic. You would need a large number of them, with the correct (short) half-life, and somehow get them moving at the same speed. creating the short-lived isotope will be a huge technical barrier.

Atomic clocks are getting smaller all the time. If one could be designed for small size, rather than accuracy, you could possibly set it up. You don't need phenomenal accuracy, you just need to establish the difference between two, if any, and the direction of change. 

[Mordred]

Considering Swansont calibrates atomic clocks for a living it might be an idea to listen to him lol

[swansont]

17 minutes ago, Mordred said:

Considering Swansont calibrates atomic clocks for a living it might be an idea to listen to him lol

Builds.

also advises DARPA on their program to build small clocks.

I still don't understand why you need a specific speed for this experiment. So the gravitational effect and kinematic effect are the same size. That's not important. You still need a clock precise enough to measure some effect in order to confirm it - a stopwatch wouldn't do, for example, because it couldn't measure deviations unless they were huge. So there's no reason you couldn't apply equations to other conditions to do compare experiment and theory.

Unless the problem is that there is no other model, or some other impediment to predicting a specific result.

1 hour ago, mistermack said:

Atomic clocks are getting smaller all the time. If one could be designed for small size, rather than accuracy, you could possibly set it up. You don't need phenomenal accuracy, you just need to establish the difference between two, if any, and the direction of change. 

It's not clear to me why "phenomenal" accuracy isn't required. See above.

[mistermack]

1 hour ago, swansont said:

I still don't understand why you need a specific speed for this experiment.

You don't. But if you are testing the hypothesis that there is a flow of space downwards of approx 11km/sec then a clock moving downwards at 11 km/sec will be moving at the slowest possible speed in that flow. Anything slower or faster would give you motion in the flow. (if it exists) So 11 km/sec would give the greatest effect. It doesn't mean that it HAS to be that figure. Lesser speeds might still give a measurable effect, but higher speeds would be pointless.

1 hour ago, swansont said:

It's not clear to me why "phenomenal" accuracy isn't required. See above.

I was just pointing out that the numbers wouldn't be particularly important. You just need to discover if the clock runs slower, or faster, than the stationary clock.

[swansont]

2 hours ago, mistermack said:

You don't. But if you are testing the hypothesis that there is a flow of space downwards of approx 11km/sec then a clock moving downwards at 11 km/sec will be moving at the slowest possible speed in that flow. Anything slower or faster would give you motion in the flow. (if it exists) So 11 km/sec would give the greatest effect. It doesn't mean that it HAS to be that figure. Lesser speeds might still give a measurable effect, but higher speeds would be pointless.

I was just pointing out that the numbers wouldn't be particularly important. You just need to discover if the clock runs slower, or faster, than the stationary clock.

Then go ahead and analyze the experiments that have already been done. 

[Markus Hanke]

18 hours ago, mistermack said:

http://www.dailygalaxy.com/my_weblog/2014/06/gravitys-river-new-black-hole-theory-suggests-gravity-is-a-fluid-.html      

The gravity/fluid duality is not the same thing as the “flow of spacetime into the earth” comment I responded to. If you think about it carefully, you will realise quickly that spacetime is a completely static construct, in the sense that it is not embedded in any higher-dimensional manifold with additional dimensions of time. Spacetime is hence the totality of all events at all times, and therefore cannot in itself exhibit any dynamics. You can, however, use the idea of dynamics as an illustrative analogy in some situations, similar to the rubber sheet analogy - but it is always important to bear in mind that an analogy is not the same as the actual model.

I should also mention that the gravity/fluid duality never really made it into the mainstream, because the expected experimental evidence of gravitational turbulence has not been observed.