Does expansion exist on the micro level as well as the galactic level?

[Axuality]

Does expansion exist on the micro level as well as the galactic level?

I've never read about it, but it occurs to me that there can be no uniqueness about where the expansion of the universe exists.

I have to envision an atom as a 'kind' of solar system, and a molecule therefore as a 'kind' of galaxy, and an ore sample of this molecule as a galactic cluster. With this simplistic view in mind, it seems to me that the space between ALL particles, not just large objects, must be increasing- and frankly, that the particles themselves (since they are not "solid" objects, but rather consist of "smaller" entities (smaller expanding "universes")) must be expanding also.

Why have I read nothing of this? I'm not well-read admittedly.

By the way, if this were the case, wouldn't we feel the expansion of the physical object beneath our feet as a force pushing up against the bottom of our feet? Come to think of it, our feet would also be expanding down toward the ground, thereby creating some sort of feeling.

[Janus]

Expansion does not extend down to the microscopic level. In fact, it doesn't affect things smaller than clusters of galaxies. The reason for this is that the forces holding these objects together (gravity, electromagnetic and nuclear forces) are stronger than universal expansion.

[Axuality]

Expansion does not extend down to the microscopic level. In fact, it doesn't affect things smaller than clusters of galaxies. The reason for this is that the forces holding these objects together (gravity, electromagnetic and nuclear forces) are stronger than universal expansion.

Are we accepting that clusters of galaxies are expanding along with the space between them or not?

You implicitly say that stronger forces stop the expansion on levels smaller than clusters. You mean that these forces stop THINGS from moving.

When I stand on the surface of the earth, is it not said that I am accelerating at 32 ft/sec/sec, although I'm not MOVING toward or away from the center of the earth? Can there not be accleration or even expansion without movement?

It does not make intuitive sense to me that at some arbitrary level, expansion would no longer exist.

We may have to discover that at some relevant frame of reference, the forces of which you speak are not stronger than one another.

[Chronos]

In the present epoch, as Janus noted, it safe to say expansion does no operate at levels below intergalactic space. The future is less certain. Google on 'the big rip' for discussions.

[bwana]

...
It does not make intuitive sense to me that at some arbitrary level, expansion would no longer exist.

I agree and have puzzled about this contradiction as well. I explain it thusly:

Hubble parameter measures expansion of space and it is greater at increasing distances. Since these distances are HUGE and measured in light years, the information provided by these observations are VERY OLD. I conclude that the universe is no longer expanding since we do not see a hubble shift in our neighborhood, although we could detect it.

here is what i wrote:
http://physicsforums.com/showthread.php?t=335946
http://forums.anandtech.com/messageview.aspx?catid=50&threadid=2320348&enterthread=y

[Janus]

Are we accepting that clusters of galaxies are expanding along with the space between them or not?

You implicitly say that stronger forces stop the expansion on levels smaller than clusters. You mean that these forces stop THINGS from moving.

When I stand on the surface of the earth, is it not said that I am accelerating at 32 ft/sec/sec, although I'm not MOVING toward or away from the center of the earth? Can there not be accleration or even expansion without movement?

It does not make intuitive sense to me that at some arbitrary level, expansion would no longer exist.

We may have to discover that at some relevant frame of reference, the forces of which you speak are not stronger than one another.

The forces of which I speak all get stronger as the distance between the objects get closer together. The expansion of the universe does not. So yes, there is a boundary between expansion and nonexpansion. it is that point where galaxies are close enough for their mutual gravitational attraction is greater than their tendancy to move apart. Galaxy clusters do not expand because the individual galaxies are close enough to each other for gravity to hold them together. Galaxy clusters move apart because they are not close enough to each other.

An analogy: You are standing on a tile floor in your stocking feet. The floor has 1ft square tiles. The floor starts to expand (the 1 ft tiles eventually become 2 ft tiles, etc.)

You will see a person standing a few tiles away recede from you. (as the tiles expand, the distance between the center of the tiles increases. )

Now imagine a third person standing next to you, and you are holding hands. The person few tiles away will still recede from you, but the person standing next to won't. This is because your grip is stronger than the friction between both of your stockings and the floor. You are like two galaxies in a local cluster gravitationally bound to each other. The tiles still expand under your feet, you just don't move apart with them.

[bwana]

---

You are like two galaxies in a local cluster gravitationally bound to each other. The tiles still expand under your feet, you just don't move apart with them.

If gravity has this effect, then measurements of the hubble parameter in the vicinity of intense gravity wells (black hole, quasar,etc) should be 0. So, 2 galaxies that are very far away might have a certain redshift but a supermassive black hole next to a different galaxy in another part of the universe (but just as far away) should have much less redshift. Has this been seen?

[herbert]

Expansion does not extend down to the microscopic level. In fact, it doesn't affect things smaller than clusters of galaxies. The reason for this is that the forces holding these objects together (gravity, electromagnetic and nuclear forces) are stronger than universal expansion.

Whilst i appreciate that i am not at the high level of a PF mentor,

Surely the above cannot be correct.
If so how did inflation come about?
Space must expand at every level.
However, we have gravity too. this causes things to collapse.
There is a battle between expansion and gravity/electrical forces
On the microscopic, gravity and electromagnetic forces win and so whilst space itself expands the particles, planets etc don't.
One has to get far away and into what is called the 'Hubble flow' before expansion effects are greater than 'local effects'.
For instance the andromeda galaxy is close by and will eventually collide with our own. Gravity wins because the expansion effects are smaller that gravity effects.
BUT.... all space exapnds no matter on what scale.

[herbert]

If gravity has this effect, then measurements of the hubble parameter in the vicinity of intense gravity wells (black hole, quasar,etc) should be 0. So, 2 galaxies that are very far away might have a certain redshift but a supermassive black hole next to a different galaxy in another part of the universe (but just as far away) should have much less redshift. Has this been seen?
Intense gravity wells etc have gravitational redshift. this will be added on to cosmological redshift.
IE a photon of light escaping a black hole, gains lots of gravitational potential energy. Since E = hf, its energy reduces, frequency reduces wavelength increases.
Gravitationally redshifted.
Not zero.

[Chronos]

Gravitational redshift is a non contributor to H0. The vast majority of photons generated by black holes, etc., originate too far from the gravity well to be noticeably redshifted.

[PRDan4th]

If Newton were alive today and knew what we know, I think he would have added another term to his gravity equation. This would be a negative term (repulsive) and have a very very small constant times distance squared and perhaps independent on their masses. This term applies all the way from short distances to extremely long distances but is so small that it is not detectable at distances shorter than inter galactic distances. Perhaps something like:

F=G*(m1*m2)/r^2-R*r^2 and may have a m1*m2 relationship as well.

R would be the expansion or repulsive constant.

If this were the case at some distance the R term would balance the G term and gravity force F would be zero, beyond that distance expansion would overwhelm attraction.

Does this make any sense?

PRD

[herbert]

Gravitational redshift is a non contributor to H0. The vast majority of photons generated by black holes, etc., originate too far from the gravity well to be noticeably redshifted.

But surely one needs a 'standard candle' to determine Ho?
Cepheid variables work as do supernovae 1a.
Is there a standard candle black hole? ie a black hole that is equally bright (or dark????) no matter where it is in the universe?
Otherwise, surely it is not a matter of the photons 'not being noticeably redshifted' but that they just cannot be used?

[sylas]

Does expansion exist on the micro level as well as the galactic level?

No.

To a first approximation (and I must thank Wallace (http://www.physicsforums.com/member.php?u=51971) as a major help for my understanding this) expansion simply means that things are moving apart from each other. It isn't a force pushing things apart. The universe expands because things are moving apart from each other ... not the other way around.

That's the first approximation. The second approximation is that there are actually forces that act to slow down or to increase the rate at which things are moving.

Gravity works to pull things together, and hence to slow down expansion.

Dark energy works to push things apart, and hence to speed up expansion. As I understand it, "dark energy" is just a name we give for the apparent existence of something we don't really understand but which is the cause of expansion to be speeding up.

But on sufficiently small scales (a cluster of galaxies or less) you can just consider the nice simple model you are all used to, of a bunch of stuff moving around in space, and subject to gravity.

A galaxy isn't expanding, because its constituent parts are not moving apart from each other. No matter what motions you see elsewhere, the galaxy is all hanging together very nicely, and there is no particular "force" to counteract that, or to pull it apart. (Dark energy might in principle; but in the present epoch dark energy is far too weak to pull apart a galaxy or a galactic cluster.)

That's the bottom line. The only thing that might push things apart is a "dark energy", and what we infer about dark energy now is that it is way WAY too weak to matter at small scales. Apart from that, there's nothing at all about the expansion of space that would lead one to expect anything to be pulled apart, on any scale, unless it is already moving apart right now.

Cheers -- sylas

[herbert]

No.

To a first approximation (and I must thank Wallace (http://www.physicsforums.com/member.php?u=51971) as a major help for my understanding this) expansion simply means that things are moving apart from each other. It isn't a force pushing things apart. The universe expands because things are moving apart from each other ... not the other way around.


Don't think so, Space expands carrying all with it. The expansion we see now is just the dying embers of inflation and its scalar fields.
On top of that we have the peculiar motion of the heavenly bodies within it.
On the small scale, gravitational effects are far bigger than expansion of space effects so they dominate.
But on the large scale expansion effects dominate and things move away from each other.
Its a good thing that objects themselves don't get any bigger as otherwise we would not see the expansion.
If distances got bigger and our 'ruler' got bigger at the same rate then we would measure the distances as constant. Its like a thermometer. The only reason the mercury rises is that mercury expands but the glass doesn't (hardly). If everything expanded then the mercury level would stay the same.
Congratulations on the edit Sylas