Possible matter being Created/Destroyed?

[phinds]

The point is that cosmic expansion itself does not stop. Space itself is everywhere expanding, even here on earth. But as the Earth is bumped slightly father away from the sun due to cosmic expansion, it does not have the velocity to sustain a higher orbit, so it returns to its original distance from the sun. Shrink this bumping/returning process to an infinitesimal moment in time, and you see that the Earth never really moves outside its regular orbit. So it's not that the distance between the Earth and the sun is increasing due to cosmic expansion, but the amount is so small to be negligible. Rather, the distance between the Earth and the sun is not increasing due to cosmic expansion, despite space itself expanding around the earth. It's like the tablecloth being pulled from underneath the cups without upsetting them.

Are you sure about this? It has been my belief that "dark energy" EXISTS locally, but has absolutely no effect at all. Not "negligible", but ZERO.

 

[Drakkith]

The point is that cosmic expansion itself does not stop. Space itself is everywhere expanding, even here on earth. But as the Earth is bumped slightly father away from the sun due to cosmic expansion, it does not have the velocity to sustain a higher orbit, so it returns to its original distance from the sun. Shrink this bumping/returning process to an infinitesimal moment in time, and you see that the Earth never really moves outside its regular orbit. So it's not that the distance between the Earth and the sun is increasing due to cosmic expansion, but the amount is so small to be negligible. Rather, the distance between the Earth and the sun is not increasing due to cosmic expansion, despite space itself expanding around the earth. It's like the tablecloth being pulled from underneath the cups without upsetting them.

I'm not sure I see how this is any different than what I explained. The Earth isn't moving away from the Sun at all. Whether expansion simply doesn't happen, at all, within our solar system, or whether it takes place but is negligible and overpowered by gravity is beyond my ability to answer.

 

[Samuel99]

My understanding was that distances between objects in gravitationally-bound systems such as galaxies and solar systems are not increasing.

But they are increasing and we know this because of red shift. As galaxies move farther away from each other they appear to look redder in color.

 

[Naty1]

Drakkith posts:

I'm not sure I see how this is any different than what I explained.

but it is different and that's what I already posted.

chrisbaird captured what I meant in one short statement:

The point is that cosmic expansion itself does not stop.

The fact that gravitationally bound local systems may not move is not the measure of expanding space. Another way to think of it is that over billions of years, if nothing else changed, space would continue to expand but gravitationally bound local systems would not.

 

[phinds]

But they are increasing and we know this because of red shift. As galaxies move farther away from each other they appear to look redder in color.

You completely misunderstand. Try to get a grasp on "gravitationally bound systems" such as local clusters of galaxies.

Galaxies OUTSIDE gravitationally bound systems behave as you believe, but not ones inside which is what the statement was about.

 

[Ich]

Whether expansion simply doesn't happen, at all, within our solar system, or whether it takes place but is negligible and overpowered by gravity is beyond my ability to answer.

This is a purely philosophical point. Expansion in itself has no effect at all on local dynamics. The only thing you notice are the gravitational effects of local matter and energy (including DE). In an ideally homogeneous universe, these are proportional to \ddot a / a, the acceleration (or deceleration) of the expansion.

 

[Drakkith]

Couple of questions here.

1. If the distance between 2 objects is not increasing, due to normal gravitation, can you consider spacetime to be expanding between those objects?

2. Does the force of expansion cause the orbits of bound objects to be very slightly larger than they would be without expansion by opposing the forces holding them together?

 

[phinds]

Couple of questions here.

1. If the distance between 2 objects is not increasing, due to normal gravitation, can you consider spacetime to be expanding between those objects?

I don't see how you could, since it isn't

2. Does the force of expansion cause the orbits of bound objects to be very slightly larger than they would be without expansion by opposing the forces holding them together?

I don't see how that could be since if it DID happen, it would continue to increase, would it not, and then we would have evidence of it (and likely a lot of bad consequences). I mean, why would you assume that once expansion had an effect, it would just STOP having an effect?

 

[Ich]

1. If the distance between 2 objects is not increasing, due to normal gravitation, can you consider spacetime to be expanding between those objects?

Spacetime is never expanding. Space is expanding, and therefore "expansion" is just as coordinate dependent as "space". Wich means: you can consider space expanding there or not, it makes no difference.

2. Does the force of expansion cause the orbits of bound objects to be very slightly larger than they would be without expansion by opposing the forces holding them together?

There is no force of expansion.

 

[Drakkith]

Well, now I'm very confused again.

 

[Ich]

Why?

To be sure, I disagree with

I don't see how that could be since if it DID happen, it would continue to increase, would it not, and then we would have evidence of it (and likely a lot of bad consequences). I mean, why would you assume that once expansion had an effect, it would just STOP having an effect?

(wrong)

The fact that gravitationally bound local systems may not move is not the measure of expanding space. Another way to think of it is that over billions of years, if nothing else changed, space would continue to expand but gravitationally bound local systems would not.

(correct, but then: nothing is a measure of expanding space, except the things that are moving away from each other. If they aren't, well, what's the point of talking about expanding space?)

But as the Earth is bumped slightly father away from the sun due to cosmic expansion, it does not have the velocity to sustain a higher orbit, so it returns to its original distance from the sun.

(wrong)

 

[Drakkith]

Why?

Because this is a confusing topic.

 

[Ich]

Fair enough.

 

[Eimacman]

Greetings Drakkith:

I am also a little confused, perhaps I can dispel it.

The universe is expanding, this is shown by red-shift. No one can measure this directly because the instrumentality would be directly effected. Example if one tried using a ruler to measure the expansion of space the result would be nothing, being that the ruler would be "expanded" as well. This is due to the ruler being in space and being part of space.

The rate of expansion would be effected by gravitation, planets, star systems, clusters, galaxies, galaxy clusters, and so on; as well as any effects of dark-energy and dark-mater. The change of distance between Sol and Alpha Centari would increase because because of the expansion of space-time, but because of the local effects of the Milkyway's supermassive black hole, the combined gravitational effects of the stars as well as the gravitational effects of the halo of dark matter around the galaxy, would make such expansion possibly unreadable or very small.

The effects of such an expansion, if it is accelerating as current data suggests, all matter will eventually become unstable and decay into low energy photons spread across a cold universe. Matter would not have been destroyed only converted into energy, but so diffuse that it could never be used. This would be in the very very very distant future.

 

[Mark M]

No one can measure this directly because the instrumentality would be directly effected. Example if one tried using a ruler to measure the expansion of space the result would be nothing, being that the ruler would be "expanded" as well. This is due to the ruler being in space and being part of space.

Eimacman, this is incorrect. The space in between galaxies is growing, the objects within space are not.

 

[Eimacman]

Greetings Mark M:

Could you explain why an object would not be effected by the expansion of space-time, neglecting the local effects of gravitation?

 

[Mark M]

Greetings Mark M:

Could you explain why an object would not be effected by the expansion of space-time, neglecting the local effects of gravitation?

Eimacman, the expansion of space has absolutely no effect on an objects size. If it did, we wouldn't see any expansion - galaxies would simply grow with the expanding space.

 

[George Jones]

Greetings Mark M:

Could you explain why an object would not be effected by the expansion of space-time, neglecting the local effects of gravitation?

For an expansion on what Mark M said, see

http://arxiv.org/abs/gr-qc/0508052.

 

[afrinnover]

Sorry, I'm new comer, how to posting ?

 

[phinds]

This is a purely philosophical point. Expansion in itself has no effect at all on local dynamics.

I don't understand how this is a philosophical point. Either the expansion of the universe DOES have an effect on local scales or it DOES NOT have an effect. I see absolutely NOTHING about that that is philosophical.

Now, as to whether it MATTERS, I could agree that that's as much philosophical as factual since as I now understand it, if it DOES have an effect, it is negligible and will remain negligible in the solar system for the life of the sun.

Whether or not the effect would (if it exists) be negligible at a galactic scale I do not understand.

 

[Ich]

I don't understand how this is a philosophical point. Either the expansion of the universe DOES have an effect on local scales or it DOES NOT have an effect. I see absolutely NOTHING about that that is philosophical.

Right. But if it does not have an effect, the question whether space is expanding there or not is philosophical. And that's what I'm claiming. Have a look at Naty1's thread here.

 

[Chronos]

Conventional thinking is it has no effect. But, theoretically, it could have increased the size of the solar system by about 40 meters over the last 4.5 billion years - a bit less than expected merely due to radiative loss of solar mass over that same time frame.

 

[Drakkith]

Conventional thinking is it has no effect. But, theoretically, it could have increased the size of the solar system by about 40 meters over the last 4.5 billion years - a bit less than expected merely due to radiative loss of solar mass over that same time frame.

How would it cause the solar system to expand if gravity holds us to the Sun? I can understand how galaxies get carried away from each other, but they are not bound.

 

[Ich]

Conventional thinking is it has no effect. But, theoretically, it could have increased the size of the solar system by about 40 meters over the last 4.5 billion years [...]

What are you referring to?

 

[Naty1]

ICH: post #41

Originally Posted by Naty1

The fact that gravitationally bound local systems may not move is not the measure of expanding space. Another way to think of it is that over billions of years, if nothing else changed, space would continue to expand but gravitationally bound local systems would not.

(correct, but then: nothing is a measure of expanding space, except the things that are moving away from each other. If they aren't, well, what's the point of talking about expanding space?)

Not quite, if I understand your statement: sure, only intergalatic distances have measureable expansion of space. My perspective has so far been, and I may be way off base here, that a locally bound gravitational solar system does not inhibit space itself from expanding. [Unlike, for example, the balloon analogy where ALL space expansion moves massive objects.] In other words, we all agree, I think, that if our solar system were NOT present, it's empty space would expand infinitesimally in that volume; Maybe not by a measureable amount of course. Now we plop in a sun, some planets and moons there...will that stop space from expanding?? Is the presence of mass a glue that ties space together?? I have not so far thought so. [Does more curved space expand 'less' than more flat space??

 

[Ich]

Let me quote the FAQ right before the one you quoted:

Are galaxies really moving away from us or is space just expanding?

This depends on how you measure things, or your choice of coordinates. [...]

See what I mean? Expanding space and moving things are (at least locally) different descriptions of the same phenomenon. Just different coordinates. You can't decide which coordinate system is the correct one, as both are valid.

I think, that if our solar system were NOT present, it's empty space would expand infinitesimally in that volume

In a patch of empty space, you can easily use coordinates with H=70 km/s/km. Or you can use static coordinates. Both are valid descriptions of - nothing. It makes no difference observationally, so the question is a philosophical one.

 

[Drakkith]

In a patch of empty space, you can easily use coordinates with H=70 km/s/km. Or you can use static coordinates. Both are valid descriptions of - nothing. It makes no difference observationally, so the question is a philosophical one.

Would light passing through an area of space with or without something such as our solar system have it's wavelength stretched a tiny amount? Or how about while moving past or through a large galaxy?

 

[Eimacman]

Greetings George Jones:

That is the answer that I needed, I must study this further for my math is not as good as I would like.

Thank you.

Eimacman.

 

[Ich]

Would light passing through an area of space with or without something such as our solar system have it's wavelength stretched a tiny amount?

Depends on the observers you choose. If emitter and receiver are at rest wrt each other, there's no shift. If both are "comoving", i.e. moving away from each other according to the Hubble law, there is redshift, obviously.

In a "static space" description, the first observers don't move, and the second observers move away from each other.
In an "expanding space" description, the second observers don't move, and the first observers have a peculiar velocity that exactly cancels the cosmological redshift.

The results are the same in both descriptions.

 

[Chronos]

A photon approaching a gravitational field is blue shifted, as it exits that same gravitational field it is redshifted by exactly the same amount.