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Author Topic: Speed of gravity  (Read 2408 times)

Offline greeniemax

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Speed of gravity
« on: 29/03/2012 11:05:09 »
Gravity could be defined as field, now some people want to define as wave but I personally don't see it as wave as wave push rather than pull for no apparent reason.

Looking at the rate of expansion on two sides of universe the side where we are moving toward and side where we have moved from, if there is a difference.

Assuming our galaxy as i
Galaxy toward the middle (where we are expanding from) as a
Galaxy toward the event horizon (where we are expanding to) as b.

if rate of expansion = b>i>a than we know the expansion rate and find the speed of gravity.

In case there is no difference and all galaxies expanding at exactly same acceleration (which isn't possible) we could denote that gravity is instantaneous.

Thus difference in acceleration of different galaxies would give us the speed of gravity.

Comments please.


 

Offline imatfaal

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Re: Speed of gravity
« Reply #1 on: 29/03/2012 16:23:23 »
Unfo - we are moving away from everything (apart from our local cluster of Andromeda etc).  All other galaxies/clusters/superclusters are moving away from us and from each other - the only thing that is related to the speed of recession is the distance between the galaxies.  There is a search for any anisotropy in expansion rate - but I don't think any slightest hints have been found.  Most of the anisoptropy research is being done on the cmbr - which is yielding results; but not a centre/outer sort of thing, more a denser/lighter thing that could explain first clumping of primordial stars/galxies
 

Offline greeniemax

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Re: Speed of gravity
« Reply #2 on: 29/03/2012 22:34:32 »
Again the problem is also that even if we could see the expansion rate of galaxy that information comes to us at speed of light so even if gravity is faster it wouldn't work.

If you measure is slower than your objected being measured you'd get speed as good as light and never beyond it as all light related waves travel as fast as light.

hmm problem...
 

Offline greeniemax

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Re: Speed of gravity
« Reply #3 on: 30/03/2012 11:58:05 »
You know what Einstein was really smart (Of course he was), he selected the fastest thing we could sense or test.

Problem is that we can't find anything to block gravity like we could use it to get information from deep space, even find black holes as they have very high effect of gravity, though light can't escape it but gravity can.

So if gravity is a wave does it mean it a bigger u (initial speed) compared to light? (I don't believe gravity to be wave and people working on it in my opinion are just wasting money).

 

Online yor_on

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Re: Speed of gravity
« Reply #4 on: 30/03/2012 21:24:19 »
I don't see it as a wave Greenie. To me it becomes a 'deformation' of the geometry of SpaceTime, propagating at some position relative the observer. The only thing I expect different observers to agree on is that its 'speed' is no higher than 'c'. Even the expansion must follow that dictate. It's a real constant, for all observers, 'c'.
 

Online yor_on

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Re: Speed of gravity
« Reply #5 on: 30/03/2012 21:27:13 »
What I mean is that seen locally, any expansion of a vacuum/space must have a lower value than 'c'. Although as you add up all those localities, expanding the 'distance' will grow faster as more localities are added, as I think of it. I find it very hard to envision an expansion any other way.
 

Offline greeniemax

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Re: Speed of gravity
« Reply #6 on: 30/03/2012 22:28:21 »
Its an assumption, we cannot know now what is the speed of gravity as we do not have any kind of blocking material that would block gravity.

Why we need this blocking material? Because to look at a certain part of the universe you need to block the light or any kind of electromagnetic waves coming into the sensor, this is how you could concentrate on a given object to get its picture.

If we try to make a device that could see gravity it will be overwhelmed by gravity coming out of earth and sun, its possible to test such device when you take it out of solar system, where you could check the difference between the gravity of Earth as it moves and compare it to electromagnetic radiation coming out earth.

If they are same than we would know gravity travels at speed of light, but if changes in gravity is seen before light than gravity is faster, but frankly speaking I don't know if it would work because sensing would be too sensitive and gravity of the craft would be more than earth at that location. Secondly its lots of money wasted just to see what what is faster, when we can't even use gravity as we can't create it yet.

So as of right now we could assume anything we like but we haven't got a proof of any thing being true, light being slower than gravity or they being same speed.
 

Online yor_on

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Re: Speed of gravity
« Reply #7 on: 31/03/2012 08:06:53 »
'Gravity' is 'something' for sure, although I do not know what it is. In a SpaceTime picture it's a 3D geometry firstly, but how that geometry can be constructed? And then you have the added complication that the geometry as such is 'propagating' in the arrow of time.

If you could take a 'slice' out of it you would have a 'static' picture, but that's not how it works.
 

Offline greeniemax

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Re: Speed of gravity
« Reply #8 on: 31/03/2012 12:35:07 »
You see frankly speaking General Relativity gives good idea about how gravity works but it doesn't mean its the only picture or that is the way gravity is.

Without cosmological constant which Einstein called his "greatest mistake" it wouldn't work even outside our solar system, so its a great theory but isn't actual theory, theory is fine but problem is it simply assumes space to be empty, which apparently isn't true because of presence of dark matter. Now it could be that dark matter has some kind of resistances that works away from stars, as soon as dark matter comes close to a star it doesn't work anymore, thus it can have resistance on solar system as whole from outside but doesn't work inside it. Something like slowing it down from outside.
 

Online yor_on

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Re: Speed of gravity
« Reply #9 on: 03/04/2012 07:38:13 »
No Greenie, Einsteins theory of a geometry shaped by the metric of 'gravity' would work any which way.
Beautifully so :)

It's sad that so many higher educations doesn't teach relativity as it still is the best verified theory that exist. I keep meeting misunderstandings there. Why the cosmological constant was introduced was the question of how the universe was expected to behave, grow, stay the same, or shrink? Einstein thought the universe would be proofed to be static and so he needed something to stop 'gravity' from 'shrinking' the universe, as mass 'attracted' mass.  So he countermanded that force by inventing a constant that balanced it. Nowadays we expect the universe not only to expand, but also to accelerate that expansion.

The Cosmological Constant is a mathematical 'balance trick', still used.

"Recent observations are indicating that the cosmological constant should be brought back. Astronomers are finding that even when they include the maximum amount of dark matter allowed by the observations, there is not enough matter (luminous or dark) to flatten the universe---the universe is open with negative curvature if the cosmological constant is zero. The inflation theory predicts that the universe should be flat to very high precision. An extra energy called called dark energy is needed to make the universe curvature flat overall beyond what ordinary and dark matter can do. This dark energy is probably the cosmological constant (vacuum energy) described above. Recent observations of the cosmic microwave background show that the combined efforts of matter and dark energy flatten space as much as that predicted by inflation theory.

One major stumbling block in the theory of the cosmological constant is that quantum theory predicts that the total vacuum energy should be on the order of 10120 times larger than what is observed. The cosmological constant predicted from quantum theory would cause the universe to expand so fast that you would not be able to see your hand in front of your face because the light would not be able to reach your eyes! In reality we can see to billions of light years. Physicists are trying to figure out why there is such a big discrepancy between the quantum theory's prediction and observation. Some cosmologists are exploring the idea of a dark energy that varies with space and time called "quintessence"."

From Embellishments on the Big Bang.

You don't know why it is there but it 'must' be as your equations demands it, as some think. Then there are others trying other approaches for explaining why the universe acts as it does, but they are still all theoretical, as far as I know.

People tend to forget that, as when something becomes popular you will find a lot of physicists and laymen thinking in similar terms but if it is theoretical it still is, as any (honest) physicist will tell you. We're all human though, and sometimes we believe :)

I have a nice link to it. How Can Nothing Weigh Something?





« Last Edit: 03/04/2012 07:41:09 by yor_on »
 

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Re: Speed of gravity
« Reply #9 on: 03/04/2012 07:38:13 »

 

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