Possible matter being Created/Destroyed?

[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.

 

[Drakkith]

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.

Lets say I observe light from a galaxy moving away at exactly redshift z=0.1, and that light happens to go through a galaxy on the way to me. Is the galaxy I am observing the same distance as another galaxy who's redshift is also exactly z=0.1 who's light is not going through another galaxy before reaching me?

 

[Ich]

Lets say I observe light from a galaxy moving away at exactly redshift z=0.1, and that light happens to go through a galaxy on the way to me. Is the galaxy I am observing the same distance as another galaxy who's redshift is also exactly z=0.1 who's light is not going through another galaxy before reaching me?

The galaxy introduces some positive curvature, so I'd say that the distance in this direction is a little bit larger. See Shapiro delay.
But I don't see how this pertains to the discussion.

 

[Naty1]

ICH

Originally Posted by Ned Wright

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 do see what you mean...now...I think that's the best perspective...Thanks!

 

[Naty1]

Found it! the 'classic discussion from 2007:

Does Space Expand...[Wallace IS a cosmologist]

https://www.physicsforums.com/showthread.php?t=162727&highlight=current+flow&page=2

 

[Chronos]

The effect of cosmological expansion on the solar system is negligible. For discussion see http://arxiv.org/pdf/astro-ph/9803097v1.pdf

 

[jimpy]

hi Samuel99
it takes a lot of courage for you to post like this.I'm no expert by any means but there are a few issues worth you following up on here.
Firstly,in the case of the expanding accelerating universe then the observations that are made are all historic.
The most recent have just happened here.The rest are history.
So now I'll stick my neck out and we'll see what happens.
I think that the only location that the accelerating expansion of the universe is identifiable(is being the operative word)is here and now.
When we peer into the night sky we have a log of what happened in our yesterdays,right upto the beginning if we accept the idea that "The Big Bang"was an event that actually happened in our yesterdays.
Secondly I don't necessarily understand why 40 metres in 4000 light years is irrelevant.
I haven't been taught that rule.

It all depends on the significance of the variation.
Currently we are discussing here speculative possibilities which have widespread approval in the world of scientists.
The theories involved in your post are amongst the most complex ever advanced by mankind.
One of the first books in English relating to this area is "The Mathematical Theory of Relativity" by an Englishmen called Arthur Eddington" which was published in 1926 and is a second book of his about the theories of Albert Einstein.
It is called "The Mathematical Theory of Relativity"
A very important remark in the introduction to this work is as follows:
(he is discussing determining what length means when we exchange ideas)
"But to catalogue all the precautions and provisos in the operation of determining even so simple a thing as length is a task which we shirk.We might take refuge in the statement that the task though laborious is straightforward,and that the practical physicist knows the whole task without us writing it down for him."
It goes on from here,if you can get the book from your school library you can read the whole thing.It is on page 6 of the introduction.
I am impressed by your spirit,
Jimpy

 

[Ich]

The effect of cosmological expansion on the solar system is negligible. For discussion see http://arxiv.org/pdf/astro-ph/9803097v1.pdf

There's a discussion of this discussion here.

 

[Chronos]

Yes, my apologies, I noticed that after posting the link.

 

[Eimacman]

Universal expansion does have an effect. However, how that effect is felt depends on the binding energy/force and the kind of binding energy/force. Take an atom for example. It will not distort or deform at all because of universal expansion until the force of such expansion reaches parity with all the forces holding an atom together, Electromagnetic, Strong and Weak Nuclear, Electroweak etc. At that point the atom will suddenly come apart. Other binding energies/forces such as molecular bond strength, Vander Waals attraction, Gravitation, and so on will react according to their various properties. Any change caused by such expansion is significant if a sufficient amount of time passes, $10^{1000000}$ years for example.

Even then, any matter thus effected will only be changed into energy, and with entropy →∞ such energy will not most likely be useful.

 

[phinds]

Universal expansion does have an effect. However, how that effect is felt depends on the binding energy/force and the kind of binding energy/force. Take an atom for example. It will not distort or deform at all because of universal expansion until the force of such expansion reaches parity with all the forces holding an atom together, Electromagnetic, Strong and Weak Nuclear, Electroweak etc. At that point the atom will suddenly come apart. Other binding energies/forces such as molecular bond strength, Vander Waals attraction, Gravitation, and so on will react according to their various properties. Any change caused by such expansion is significant if a sufficient amount of time passes, $10^{1000000}$ years for example.

Even then, any matter thus effected will only be changed into energy, and with entropy →∞ such energy will not most likely be useful.

Can you provide any citation to a paper that shows that there is ANY expectation that "dark energy" will ever become strong enough to overcome those forces? I have never heard that before.