The Raisin Bread Analogy Question

[phinds]

You came here with a question. An army of volunteer professionals has been happy to answer your question. You don't like the answer, so you argue it.

Indeed, I have acquired a reputation here for my patience with people who resist learning.

Julius Caesar, I want to most emphatically support BOTH part of what Dave just said. I have complimented him in the past on his incredible patience with people like you who seem steadfastly determined to be argumenative and to totally ignore all evidence and all explanations presented to them by folks who CLEARLY know far more that they do. Forum rules prohibit my telling you what I really think of you.

 

[marcus]

It is expanding into nothing - literally. 'Outside' the universe does not exist. The universe is not embedded in some pre-existing infinite emptiness...

Nothing? That does not seem logical. You might as well have said that a perpetual motion machine is possible. Something cannot expand into "Nothing".

My thought is that our universe is just one bubble amongst many bubbles within an ocean of something...something that is not "nothing".

Just realize that current models of the universe never say there is nothing, they simply don't require that there be anything to expand into...

Dave, Chronos and Drakkith are right. I think Julius is stubbornly not listening to them because he is misled by the English sentence "The universe expands."

To a many a layman, which is evidently what Julius is, "expanding universe" gives the wrong mental picture. Popularizers and science journalists should never have used that infectious phrase.

People should be told, instead, that distances expand, in our universe according to a definite largescale pattern.

The standard math model (different from the words and always-misleading analogies used to convey it to public) does not have a boundary. We have no evidence that a boundary exists, so we cannot justify including boundary in the model. So there is no OUTSIDE the universe---this is not even definable within the standard math model.*

All we know, or think we know, is this pattern of largescale distance expansion. It is predicted theoretically by the well-tested general law of changing geometry (gen. rel.) which tells us that large distances between points at rest relative to the average bulk matter HAVE to change. Distances HAVE to change according to a certain simple rule in order for the law to work, and expansion is one solution: uniform percentage rate. Furthermore that is what we observe! It not only comes out of the well-tested equations of geometric gravity, it is confirmed by what we see. And there is no boundary.

It would mess up the math and add unnecessary complication to add a boundary to the picture. Not only is one not needed, but it would be dishonest to pretend one without any evidence, and it would mess things up.

The verbal mistake was probably made in the 1930s or whenever the public was given the phrase "expanding universe". It evokes the image of being outside the U and the U having a definite boundary, like a piece of metal being heated and expanding. For unsophisticated listeners saying "it expands" inescapably calls up the idea of something with a definite shape expanding into the surroundings. That is not what the model says.

*There are alternative schemes which have boundary but lack supporting evidence, have not been thoroughly worked out, and are not used in normal cosmology work. One of the boundary-rich alternatives is the bubble picture you get in "eternal inflation" scenarios.
It's fine to speculate about such, but one can hardly say they are required logically

 

[DaveC426913]

A concise and elegant way of putting it.

"Distances within our universe are increasing."

 

[cepheid]

A concise and elegant way of putting it.

"Distances within our universe are increasing."

I said this too! It's buried in there, somewhere, honest!. Still, marcus probably was much more eloquent.

 

[bigmig]

I don't want to reinvigorate the arguments above but from a non-specialist viewpoint the question 'expanding into what' (and I really do appreciate the geometric nature of this and am comfortable with the extra space/space itself answer, I sort of prefer inflation) is the usual question, but rarely is it turned round to 'expanding out of what'. Which seems the logical corollary. And would warrant a similar answer I should think.
More significantly perhaps following this line of thought, does the math (which is beyond me) give any indication of how small a system can be and still maintain the situation that any 2 observers would 'see' themselves getting further apart? I realize we can only see the recession outside of bound systems usually spanning large distances.
However, within gravitationally bound systems I understand that 'inflation' is still present but has anyone deduced a lower limit to the size this operates at? I guess this would incline to the discreteness or otherwise of space at the smallest level - Planck size? So would the Planck size increase by continuum or up by energy levels. Bit of a thought experiment. The idea is that every observer sees themselves as the centre of inflation/distance increase, and centre implies points equidistant to either side, so how small can this system go, the Swartzchild limit?

 

[Drakkith]

Hmm, is it that gravity holds things together AGAINST expansion, or is it that once enough mass is in a volume of space the gravity simply causes expansion NOT to occur at all?

 

[bigmig]

Yes we know the inflation factor is much weaker than any other attraction even gravity and therefore, despite a small effect gravity holds systems more or less in Newtonian motion. What I struggle to conceptualize is how this spacial/distance inflation plays out as you move from intergalactic to interstellar and so on down to quantum scales.
I have read some work that attempts to rationalize continuity and discreteness at smaller scales by working with differentiable 'non-continuous' objects (but my understanding of this and the math is weak).
Despite the divergence of the math with everyday experience I think it still important that things should be reasonably explainable in terms of more familiar concepts.
Even though a 4th (or more) spatial dimension is unimaginable it is sort of conceptualisable with some practice and dumping preconceived notions, so is infinity etc. But at the end of the day, all this heavy physics has to explain what we see, perceive and expect at the human scale.
But the inflation of space where every 'observer' sees themselves as the centre, sort of 4th dimensional expansion - surface of hypershere etc, may not be what's happening at smaller scales.
Or as you say 'drakkith' does the interaction of matter/gravity with space change things. So if particles are introduced into space then the normal forces would resist a spatial inflation that is happening around them, or their presence negates the inflation. But if that's the case then it seems to me this variable inflation around matter would create a discontinuity/tension in space? I feel I'm barking up the wrong tree here and that's why I could do with a model. Help!