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If the above assumption is true, is the space within atom (distance between nucleus and electron) stretched as well?

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If the above assumption is true, is the space within atom (distance between nucleus and electron) stretched as well?

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HallsofIvy

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Bill_K

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I agree, it's a misleading oversimplification of what really occurs. But unfortunately, so is "metric expansion"!The whole concept of space as a "fabric" that can be bent or stretched is often discussed on this forum. The consensus is that it is a totally useless concept with no real meaning.

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What is misleading about metric expansion? I've always seen it mentioned on this forum as a solid explanation.I agree, it's a misleading oversimplification of what really occurs. But unfortunately, so is "metric expansion"!

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timmdeeg

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In this context stretching doesn't mean creation of space, but most probably the enormous expansion of the universe by a factor > 10^30 (depending on the model) during the period of inflation. As was said already expansion should be understood as metric expansion.

If the above assumption is true, is the space within atom (distance between nucleus and electron) stretched as well?

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You would really do better to get your physics from somewhere other than pop-sci TV programs. Sometimes they get things right but they NEVER get everything right.

The "big bang" really has two meanings. First the "big bang singularity" and second the "big bang theory". The "singularity" is just the name for WHATEVER it was that happened before the big bang theory takes over. We don't know what that was. The big bang theory is a pretty well understood description of what happened AFTER the singularity, starting at about one Plank time after it.

So saying that

is fine if you mean that it is the space that existed AFTER the singularitythe space that we inhabit is the same space that existed at Big Bang

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No, spacing of objects below the level of galactic clusers (that is, galaxies, solar systems, atoms, etc) is not affected. I say AGAIN:

Google "metric expansion" and/or see the link in my signature.

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Space in and of itself is only geometric volume, it has no physical properties or energy to be warped, twisted stretched, etc. the statements curves space etc is misleading in that regard as it implies space has some separate property.

The geometric volume of space is filled with the existing energy mass contents of the universe as expansion occurs. So nothing is created, as space expands only the volume has changed

How particles and forces influence each other have mathematical geometric relations of influence, as the particles etc being measured occupy the volume of space, GR will use the term space-time curvature. Which describes how gravity influences the matter residing in space. (not that space itself has a property)

Universe geometry is the same in that the shape of the universe is a mathematical descriptive of the energy-density relations of all contributors,(matter,dark energy,gravity, etc) will have positive or negative pressure relations with one another, if the total energy-density is the same as or close to the critical density then the universe is flat. This is essentially a pressure distribution relation.

see here for more detail on Universe geometry

http://cosmology101.wikidot.com/universe-geometry p

page 2

http://cosmology101.wikidot.com/geometry-flrw-metric/

As expansion occurs there is simply more volume, the rate of expansion depends on the energy density relations as per above, energy-density of a type (radiation, matter, dark energy etc) has a corresponding energy-density to pressure relations is determined by its equation of state.

http://en.wikipedia.org/wiki/Equation_of_state_(cosmology)

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as to this question, in the early universe the temperatures was too high for atoms to form with stability, any atoms that did form would quickly decouple. Essentially all particles are in a state of thermal equilibrium. As the volume of space increases, the temperature drops in accordance to the ideal gas laws. So does the overall density. (atoms could not form until after inflation)

PV=nRT.

http://en.wikipedia.org/wiki/Ideal_gas_law

when the temperature drops enough different particles will drop out of thermal equilibrium. stable reactions of those particle species will start to form. However they drop out at different temperatures depending on which particle species etc. more details can be found in these two articles

http://arxiv.org/pdf/hep-th/0503203.pdf "Particle Physics and Inflationary Cosmology" by Andrei Linde

http://www.wiese.itp.unibe.ch/lectures/universe.pdf :" Particle Physics of the Early universe" by Uwe-Jens Wiese Thermodynamics, Big bang Nucleosynthesis

when you study cosmology in detail, it doesn't take long to realize that many of the metrics involved include the perfect fluid aspects and relations of thermodynamics in their equations. The FLRW metric and Einstein field equations included.

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by mysterious thing pulling on things you might be referring to the cosmological constant or dark energy. The energy-density of the cosmological constant is easily overpowered by the strong force and gravity. Its influence is only at extremely large scales, (such as the regions between galaxy clusters).

expansion only influences the regions of space not gravitationally bound or the strong force. Its energy density per volume is too small to overcome gravity or the strong force.

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.... You can generalized it that way. It just that the thing that drove the expansion of space is very diffuse in proportion to let say an atom. It doesn't have a continuous work against the other forces that affects or binds an atom but it can be interpreted this way. The accelerated expansion can have a very small constant, a negative force between electron and nucleus that makes an atom slightly bigger than an atom in a non-accelerating universe model. However, Dark energy is treated as constant vacuum energy and it would a appear that atom already as it is.

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"In physics, spacetime (also space–time, space time or space–time continuum) is any mathematical model that combines space and time into a single interwoven continuum".

In other words the warping is simply a mathematical descriptive used in GR to describe the geometric relations between gravity and matter.(including light paths,etc) Not space itself, GR does not state that space has a fabric or substance.

any form of physics deals with mathematical relations, even particle physics. Most of the equations used in particle physics are in actuality differential geometry equations.

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Drakkith

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Note that there is NO description of a fabric, sheet, or anything else analogous to a physical object. It's pure geometry.

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I know the Einstein GR equation is a tensor equation, and what tensors are. But GR must describe something physical , not just abstract differential geometry. If it changes the interaction of objects by changing the geometry of spacetime, then spacetime is something physical whose geometry

Note that there is NO description of a fabric, sheet, or anything else analogous to a physical object. It's pure geometry.

If GR is a theory of geometry, it belongs to math, not physics. This is the first time I've heard it described as a theory of geometry.

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Drakkith

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That depends on what "physical" means in this context, but I don't want to get into an argument over the meaning of words.I know the Einstein GR equation is a tensor equation, and what tensors are. But GR must describe something physical , not just abstract differential geometry. If it changes the interaction of objects by changing the geometry of spacetime, then spacetime is something physical whose geometrycanbe changed.

When I say that GR is a theory of geometry, I mean that it uses geometry to describe real, observable phenomena. The theory makes predictions that can be tested, and these tests have been verified. The theory accurately describes gravity, no one can argue this. As such, it is not a theory of math, it is a physics.If GR is a theory of geometry, it belongs to math, not physics. This is the first time I've heard it described as a theory of geometry.

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That depends on what "physical" means in this context, but I don't want to get into an argument over the meaning of words.

When I say that GR is a theory of geometry, I mean that it uses geometry to describe real, observable phenomena. The theory makes predictions that can be tested, and these tests have been verified. The theory accurately describes gravity, no one can argue this. As such, it is not a theory of math, it is a physics.

Physical means "stuff", matter and energy.

Hey, no argument from me that it makes predictions that have been verified. Eddington measured bending of light by the sun in what, 1919 or so, the orbit of Mercury was explained, and so on. Where we differ is the interpretation of some words. If you went back in time to 1 year after the BB, there would be a much smaller universe, I don't know what α(t) would have been. It got bigger, but not as in an explosion getting bigger. So something expanded.

You can go to numerous web sites about the metric expansion. Some agree with you, some with me, and some with neither. This is a case of "is to; is not".

I'm contributing nothing to this discussion, and am learning nothing, so will withdraw.

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Drakkith

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Then no, spacetime is not something physical since it isn't matter or energy.Physical means "stuff", matter and energy.

The universe wasn't smaller, it was more dense. That is, the distance between everything was much smaller than it is now. As the universe expanded the distance between objects increased. The reason the distance increased is explained in GR as being a result of geometry, not of something being stretched. The reason most places explain it as "space expanding" or "space stretching" is because it acts in a very similar manner as a surface being stretched out, with the increase in distance between two objects proportional to the distance between them. In other words, the further apart two objects are, the faster they recede from each other.If you went back in time to 1 year after the BB, there would be a much smaller universe, I don't know what α(t) would have been. It got bigger, but not as in an explosion getting bigger. So something expanded.What?

It's important to understand that just because expansion acts similar to a surface expanding or being stretched, does NOT mean that spacetime is literally expanding itself. It is simply a useful way to help visualize the expansion. A key difference between expanding space and an expanding surface is that the surface is embedded

I disagree. I think this is a case of most people being unable to understand differential geometry. There are a number of misconceptions about numerous scientific topics, including the expansion of space. Most of these misconceptions disappear when you look at the actual theories and the math behind them.You can go to numerous web sites about the metric expansion. Some agree with you, some with me, and some with neither. This is a case of "is to; is not".

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I agree with this fully, when you look at the mathematics behind any field of study, and I've studied a wide variety. (even though I seldom discuss many of them) they all boil down to mathematical relations of interactions of one form or anotherI disagree. I think this is a case of most people being unable to understand differential geometry. There are a number of misconceptions about numerous scientific topics, including the expansion of space. Most of these misconceptions disappear when you look at the actual theories and the math behind them.

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I agree with this fully, when you look at the mathematics behind any field of study, and I've studied a wide variety. (even though I seldom discuss many of them) they all boil down to mathematical relations of interactions of one form or another

...It's bit odd. Despite the math you can't take away the presence of form in any equation. Maybe it is something fundamental and no wonder anyone can easily get hooked to it.

BTW. The stretching/curving came from a mental picture of geometry in GR intepreted as lorentz transformed sheets of patched spacetime and the presence of stuff/energy curves that plane. It is not completely wrong to talk about fabric(frictionless) as a metaphor and a secondhand picture. Besides, It's the closest we have to a physical picture that explains a 'part' of the phenomenon.

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