Starship Asterisk*

headscratcher wrote:If this particular aspect (gravity existing everywhere at the moment of creation, only changes propogating) of GR doesn't hold under a supplanting theory such as M theory (which says the membrane of spacetime that is distorted by gravity existed before gravity in which case the popping in of matter and gravity could be a change that could and would then have to propogate) then my model could still hold? With all due appreciation I am not confused by the common notion of the sun dissapearing. My model concerns appearing not disappearing. I appreciate that they can be very different physical events.

Standing on a platform Which may not exist, (Theory) And then saying because of that Theory, This further Theory may hold water. Does not tug my chain.

However, one or two, top scientists have had a good go, at understanding gravity, With not really getting to the bottom of it.

Me thinks, there must be a lot more than meets the eye, where gravity is concerned.

tc

Thanks for your reply. So l let me see if I've got this here.

When the model pops into existance the gravitational influence also pops in already connecting all matter.

The following model could be produced.

A lineup of stars and planet.

From left to right.

A star the size of our sun, 10 light minutes away a planet the size of the Earth, 20 light minutes away a very massive star, 30 light minutes away an even more massive star 30 degrees above the line of the other three objects. So star, planet, bigstar and big brother.

At the moment of creation the spherical planet will immediately develop tidal bulges, The star will accelerate towards bigstar and big brother, the planet will accelerate more towards bigstar and big brother, bigstar will accelerate even more toward big brother, up and out of line of star and planet.

Observing the planet we see the tidal bulges rise and know that there is somthing out there. No information is transfered because under GR the gravity is alread there. We see a bigger bulge on the side away from the small star but we don't know how big the stars are or how far away. The big bulge may be from a smaller star closer in. We also know that we are under acceleration because of the larger tidal bulge. 10 minutes later we see the small star. We then know that the stars we can't see are bigger and farther away. 20 minutes after creation we see bigstar and because it's been accelerating up we then see its change in position registered in the tidal bulge and we, already accelerating up due to big brother, accelerate up more because of the change in bigstar's change in position from original.

All this under GR.

If this particular aspect (gravity existing everywhere at the moment of creation, only changes propogating) of GR doesn't hold under a supplanting theory such as M theory (which says the membrane of spacetime that is distorted by gravity existed before gravity in which case the popping in of matter and gravity could be a change that could and would then have to propogate) then my model could still hold? With all due appreciation I am not confused by the common notion of the sun dissapearing. My model concerns appearing not disappearing. I appreciate that they can be very different physical events.

You mention that in my model the shift should be blue because the older stars are in a deeper gravity well. You didn't mention what might be expected as the light is traveling through a deepening gravity well. Not from shallow to deeper but from shallow to deeper and deepening as it travels.

headscratcher wrote:So I'm wrong about gravity crossing space at the speed of light? What is the physical nature of the information in gravity that does cross at the speed of light?

Changes in the gravity field propagate at speed c.

However, in your scenario, where the entire Universe is created at some t=0, insisting that the gravity field follows some rules as to its initial values everywhere is not the same as saying that some change in the field must have propagated from the sources to the various points in the field. A change that propagates means that the field "now" differs from the field "before", but if the universe was just created, there is no "before" to compare with, hence no change that we could say must have propagated from the sources.

One possible source of confusion here is that popular books about gravity like to say something like: if the Sun were to disappear this instant, it would be 9 minutes before the Earth stopped following its orbit around it. This is misleading, because the very same equations that tells us how fast gravity changes propagate also tells us that the Sun cannot simply just disappear. The field equations imply that energy is locally conserved; if the Sun were to disappear, it would have to go somewhere, and its mass would gravitate while on its way there.

Changes in the field propagate at speed c, but that does not mean that every conceivable kind of spatial variation in the field can exist.

So I'm wrong about gravity crossing space at the speed of light? What is the physical nature of the information in gravity that does cross at the speed of light?

There are some technical problems with making your model work. The equations of the general theory of relativity not only governs how spacetime evolves after you've started it; they also constrain which possible shapes a single instant-slice of spacetime can have, given what's in it. And, as far as I understand, GR does not allow a bunch of stars to have popped into bring without a fully-formed gravity field between them also popping into being. Otherwise the field equations must fail to hold locally somewhere between the stars, even though actual information has not yet had time to propagate.

But more importantly, your hypothesis yields the wrong sign for the redshift. In GR you can observe something deep down in a gravity well from a higher position, and it will appear redshifted. But your model leads to the opposite situation: We, now are under the influence of a lot of gravity, and observe distant galaxies as they looked when (according to your hypothesis) less gravity applied to them. That should mean that we're down in a gravity well, and those early, distant galaxies are close to its top. Therefore we should observe them blueshifted which is not what we do.

I guess that's a pretty wild claim. I'm not making such a claim. I was talking to a friend about an astronomy show a couple of weeks ago that got me thinking along a line that led to a strange conclusion regarding cosmological red shift. It's got me scratching my head. He said I could come here and see if I have some misunderstanding in the line of thought that led to the strange conclusion. I've been looking up the elements in books and online sources and still don't see the misunderstanding in the elements of the line of thought. I read a lot on my own about astronomy and physics. But I never went to college and there's only so much you can learn from reading.
I wouldn't know how to defend this strange conclusion as it's got me scratching my head. I'm sure I've got something wrong somewhere.

What I'd like to do is state my understanding of a list of elements that led to this strange conclusion and see if my understanding is the standard understanding of these elements. I'll start with a short list of what I think are some of the main elements that led to the strange conclusion. There is more to come. I'm not asking if these elements have been proven and my strange conclusion is not about the cause of these elements just if these descriptions illustrate the standard understanding of these elements.

1)

Matter, energy, space, time popped into existance. Doesn't matter if one came first or all happened at the same time just that matter, energy, gravity, space just popped into existance.

2)

Gravity crosses space at the speed of light. It does not cross instantaneously.

3) Clocks, time itself, time based events, in a high gravity field run faster or slower than in a low gravity field. A clock on the sun runs faster or slower than a clock on the Earth.

4)

Space near the surface of the sun due to higher gravity is different from space near the surface of the Earth.

5)

Objects far away appear to be in a more primitive state of galactic organization/evolution than near objects.


The Model

Taking the above list consider this. For convinience this model universe popped into existance as stars. It's infinite in extent but finite in age. Non expanding. Chaoticly distributed stars but on larger scale distribution differances average to uniformity. The cosmological principle applies. Everyone everywhere sees the same thing the same way.

So far it resembles our universe except for infinite in extent and non expanding.

We can expect that over time concentrations of stars organize into galaxies. The farther you look from any position the more primitive the evolution of these star groupings.

This is what we see in our universe.

Now consider;

Two stars right at the birth of this model. They are 4 light years apart. At that moment they have no influence on each other at all. They don't even exist for each other. They are outside of what Steven Hawking calls each other's light cones. They are glowing balls of hydrogen blazing happily away alone in the universe as far as physical influence on each other is concerned.

4 years later they come into each other's influence. They recieve each other's light and are influenced by each other's gravity. One day they are emitting light at the expected frequency of glowing hydrogen under the influence of the gravity of only themselves and the next they are emitting light under the influence of the gravity of themselves plus influence of the gravity of the other star.

Fast forward 15 billion years. Now our stars are emitting their light under the gravitational influence of gadzillions of stars, dust, black holes, dark matter etc. A light cone of stars of a volume 15 billion light years in radius.

We compare the light frequency from glowing hydrogen under the influence of all that gravity to the light frequency from glowing hydrogen from 15 billion light years distant stars that are under the influence of the gravity of the stars contained in a light cone volume of only a few hundred thousand light years radius.

The strange conclusion;
Shouldn't we expect there to be a differance in frequency? Even absent an expansion. Further, the light from distant stars is detected by matter under gravitational influence of 15 billion light years volume of stars. Also from the time it was emitted it has traveled through space undergoing this increasing gravitational influence.

We do see in our universe a differance in the frequency of light emitted by glowing hydrogen from distant stars compared to nearby stars. It's a red shift in frequency. Interpreted by us as caused by a Doppler shift due to the moving away of distant objects in an expanding universe.

Consider this also. Under the above model the light cone of our stars expands at the speed of light. There is already matter out there. So more matter is being added to the light cone of our stars all the time. At present the light cone encompases the matter of a volume of radius 15 billion light years. It took 15 billion years for the light cone to become this big. At some time in the future the volume of the light cone will be increasing by that much volume every year. Then every day. Then every second. Then every nanosecond. There is an accelerating increase in the volume and therefore the matter and gravity in the light cone of this model universe.

Interpreted as Doppler this accelerating increase in volume, mass and gravity, if resulting in an increase in the difference in the frequency of light from glowing matter in a massive light cone compared to a small light cone, would be interpreted as an acceleration of expansion.

Strange conclusion huh?