@Comment 122 Schrodingers Cat

You are completely missing the point.

If you are on a rowing boat on a river that is moving at 1 mile per hour, you can easily make headway against the river by rowing at 4 miles per hour in the opposite direction. So just think of the river as space and the boat as the particles. The forces holding an atom together ( i.e the same size ) are vastly stronger....we are talkng quadrillions upon quadrillions of times stronger.....than any expansive force of the universe on that scale.

Just as the rowing boat moves through the flowing river against the current, so space simply flows through the particles of the nuclei as it ( the space ) expands. The effect is SO incredibly small that I don't think anyone has even measured it.....it's probably well beyond the limits of measurement.

No, everything does not expand in the same proportion.....because the expansion is an expansion relative to a fixed speed of light. There clearly has to be some fixed yardstick for change to have any meaning.

No,it is you who is missing the point.

Looking out of my window, I see stars, galaxies, by the millions. Huge, bigger than anyone can imagine, almost.

Did they begin that way? The big bang says no; they originated in a very, very small space indeed. So they must have expanded to reach their current humungous sizes. And my telescope must have expanded too, as must every other measuring instrument. Just as space itself has expanded.

The fact that there are internal forces at work, be it in a particle or in a galaxy, is utterly irrelevant to the argument. Of course the strong force is vastly bigger than the expansionary force, whatever that is. It is also vastly bigger than the force of gravity. But the strength, relative or absolute, of any of the four known forces has nothing whatever to do with the discussion.

As a layman, it seems clear to me by observation that the universe has expanded, that stars and galaxies have expanded along with it, and that you and I and all our measuring instruments have also expanded in synchrony with all the rest of it.

Can you not understand the conumdrum? If everything has expanded to the same degree, how is it possible to detect that expansion? And if the inner space of particles has not expanded, then how is it that you, me, stars and galaxies have become so large?

I have heard on this forum all sorts of 'explanations' from most learned folk, but little of it makes logical sense. Somone who should know better indicated that space was fixed and the apparent recession of the galaxies was the left-over velocity imparted by the big bang. Somone else called it a question of scale - a fishy answer if there ever was one! Someone even wrote that f = ma - a most unenlightenng contribution. Someone then said that it must be a mystery of the quantum. Yeah, right! Someone said it isn't space itself that's expanding, but it's the metric. Hmmm.

I raised what is, to me, a very genuine conumdrum. It appears that nobody here can provide a coherent answer, relaxing instead in the comfort of very dubious analogies.

Take yours. Suppose that you are indeed on a rowboat on a flowing river. Now double the size of EVERYTHING. You have no 'absolute' size to use as a yardstick, so how can you measure the fact that everything has expanded to twice the size?

In the case of lthe constant speed of light, I note that it is the frequency of the radiation that changes (red shift) due to cosmic expansion. Are you suggesting that we can use the wavelenght of a photon as a yardstick? Does light still the same constant velocity within the inner space of a particle?

I was really hoping for some informed opinion here, but it seems I am to be disappointed .... Ah well.

@Comment 118 Greeyman

Scale. It's a matter of scale. The expansion is only measurable at the intergalactic level. At lesser scales, motion of material within space is greater than the exapansion of the space between material. The background expansion is swamped by attractive forces (gravity, electromagnetic, et cetera).

At really fine scales the geometry of spacetime becomes ... weird. You have to stopo using general relativity to describe thing and start using quantum mechanics.

Do you mean that the expansion is only MEASURABLE at the intergalactic level, or that it is only REAL at that level?

Sure, it's easier to measure when there's lots of it, but I understand that EVERY point is receding from every other point (the dots on a balloon analogy.) The internal motions of material within space (your words) may well far exceed the cosmic expansion speed, but whatever those so-called motions are, you stretch space, you stretch the material, you increase the distance between any two points.

What has scale to do with it? Are you saying that it is real on one scale and not real on another?

@Comment 115 Schrodingers Cat

Comment 105 by Jollyroger

I would just like to add - it surely does not matter what holds particles together, the strong force, gluons, whatever. Why should the space within a particle be exempt from otherwise universal expansion? Does the strong force or whatever exactly balance the tendency to expand?

The short answer is....it isn't exempt. However, the expansion of space is a cumulative effect....similar to acceleration. Objects further away move away faster. It takes distances of light years for this effect to become noticeable....and on the scale of an atom the effect is absolutely miniscule.

That 'explanation' conflicts with every known fact. The expansion of the universe posits that every point moves apart from every other point. If you take ANY fixed point, then every other point appears to be moving away from you, the further, the faster. The fact that the effect is locally minuscule is neither here nor there - space should be expanding , so I'm told, an identical amount wherever you are. There is nothing cumulative about it at all, except that the more distant an object, the greater the recession speed and the easier it becomes to measure.

Elsewhere, somebody used the time-honoured expanding balloon analogy. Nothing wrong with that, but WHY don't the spots on the balloon expand exactly the same as the space between them?

But I'm glad to read that you believe that the 'inner space" of a particle is not exempt from cosmic expansion (my words). That is a point I made earlier. Because if the inner space of a particle is NOT exempt from the expansion, then EVERYTHING will expand in the same proportion and our ability to measure it will be precisely zero. That clearly does not happen.

@Comment 110 Geraint

Comment 111 by Greyman Comment 109 by Geraint :

I'm saying that the expansion of the Universe consists of the contents of the Universe moving apart. They only continue to move apart because there is no force between them strong enough to pull them back together.

No, it is the metric of space itself that is expanding. That's why it appears that distant galaxies are moving directly away, at a rate proportional to their distance, from ours.

Geraint - are you now saying that space is fixed and objects, such as galaxies, move apart because they received an initial push from the big bang (possibly augmented by dark matter etc)? That is the only conclusion I can reach from your balls and gravity analogy.

And I think it is absolutely wrong.

Now Greyman says it is the metric of space that is expanding. By metric I assume he means the unit of measurement, the yardstick that we use to define lengths, et.al.

So what is really expanding? Is it space itself, including our yardsticks but excluding 'material' objects such as particles, or is it only the space between such things as galaxies excluding our yardsticks and the inner space of particles?

I am genuinely confused, because the answers given so far are plain nonsensical.

Geraint again - if your balls and gravity analogy is correct, then Newton would be real proud of you and you certainly merit a Nobel. On the other hand, if Greyman is correct, then that leads again to my question, what is so special about the inner space of particles that allows them to ignore the expansion of the rest of the universe?

Is the universe expanding as observation would suggest? If so, why are some volumes (bound objects, I think you called them) exempt? Those bound objects are posited to consists almost entirely of space - so WHY doesn't that space expand the same as the external space?

@Comment 100 Geraint

I would just like to add - it surely does not matter what holds particles together, the strong force, gluons, whatever. Why should the space within a particle be exempt from otherwise universal expansion? Does the strong force or whatever exactly balance the tendency to expand?

What makes that inner space so special? And if we place such spaces end-to-end to form a rod - at what point does the agglomeration exhibit expansionist properties?