How are galaxies expanding along with space time?

[Phi for All]

5 minutes ago, Quantum321 said:

I did not imply we should throw out everything we have learned. Where did you get that?

I used the quote feature to highlight where you said the BB didn't explain some things so we were back where we started. That's ridiculous. All theories are in the process of improvement. The LCDM model the BB theory is base on is sound. There's no reason to think we have to go back to where we started.

[Strange]

Just now, Quantum321 said:

strange. " So, pretty much by definition, if the space (distance between them) expands then they get further apart. " Yes I know this is the prevailing explanation. But in my explanation of the three galaxies I don't see how space expansion between them should influence them at all.

This is the prevailing explanation because it works. 

[beecee]

33 minutes ago, Quantum321 said:

Thank you but I already understand the concepts of BB and what you are saying.

So you understand why expanding space is not moving around galaxies now?

[Strange]

4 hours ago, Quantum321 said:

It's interesting that the only was we have of measuring the speed of a galaxy is the Doppler shift.

It is important to note that it is not Doppler shift. If you try and interpret it as such, you get incorrect results.

[Quantum321]

Well, what I think is important to me and I contend that the standard model may be flawed. Just because space-time expands doesn't necessarily mean everything in space-time goes along with it.

Ok I have raised my questions and got some great answers. I think we have talked this out. Thanks to everyone for listening.

[Strange]

1 minute ago, Quantum321 said:

Well, what I think is important to me and I contend that the standard model may be flawed.

Then you would need some evidence, not just your lack of understanding.

[Quantum321]

WOW I am up to -24 now. I wonder how many of the scientists here have been briefed on some of the things I am talking about and choose to try to discredit me? I don't care...

[Phi for All]

14 minutes ago, Quantum321 said:

And I don't think I am being incredulous. I just have not heard any explanation as to how the galaxies  are accelerating their movements away. 

But this is exactly what the BB explains, so it's clear you don't understand it, therefore you think it's wrong, which leads you to argue from incredulousness, which is a big logical fallacy. You're basically saying, "It doesn't seem to me that this could be true, therefore it isn't. I'm not buying it." You aren't the first person to claim skepticism about something they don't understand.

[beecee]

44 minutes ago, Quantum321 said:

WOW I am up to -24 now. I wonder how many of the scientists here have been briefed on some of the things I am talking about and choose to try to discredit me? I don't care...

The observational evidence has discredited you. Space expands due to momentum from the BB: That spacetime expansion is nullified by gravity within galactic groups and walls....In empty space with little or no gravity, nothing stops space expanding due to the BB momentum: 

46 minutes ago, Quantum321 said:

Well, what I think is important to me and I contend that the standard model may be flawed. Just because space-time expands doesn't necessarily mean everything in space-time goes along with it.

Let's use the old balloon analogy with two or more dots painted on the surface...blow the balloon up, the skin [spacetime] expands and the dots [galaxies] appear to move apart....or the raisin loaf in an oven..... As the heat is applied, the dough [spacetime] expands...the raisins [galaxies] move apart. But the increasing separation between the dots/raisins/galaxies is not a Doppler effect [the dots/raisins/galaxies] actually moving apart themselves...It is a cosmological effect due to the balloon skin/dough/spacetime expanding.

 

5 hours ago, Quantum321 said:

Now I don't understand...if the BB is in question because there does not appear to a center from which everything is expanding then whats going on?

The BB is a theory of the evolution OF space and time [ as we know them] from a hot dense state...Everything, all of spacetime was packed to within the volume of an atomic nucleus...From that one can envisage that the BB happened everywhere at the same time. It did not occur IN spacetime.  The only center that is valid in cosmology is the center of one's observable universe.

Edited June 21, 2018 by beecee

[Mordred]

5 hours ago, Quantum321 said:

 

If there is no net force in any direction (which I agree with) Then why are to galaxies moving with the expansion of space? With all the conventional examples given here there isn't one that accurately describes whats happening in space. Raisins move because atoms push against atoms. Dots on a balloon because  they are anchored to the fabric of the balloon. There is no friction in space.

 

The volume between galaxy clusters increase this gives us the illusion of motion called recessive velocity via Hubbles law [latex] V={recessive}-H_0D[/latex] however this is what is called an apparent not a true velocity. In essence everything is in motion, gravity tries to contract matter etc but does not always succeed. Now lets look closer at everything is in motion. In expansion there is no inherent direction to that motion it has no net directional component. So atoms do act upon atoms etc, but not in any particular direction. Much like Brownian motion of an ideal gas. How this works is the evolution of the average density of matter. As more matter collapses to form galaxies the average density of matter on the global scale decreases, as this density decreases so does the average gravitational potential. This allows that Brownian type motion greater freedom to expand.

 The key formula is the critical density formula. This is the point where an expanding universe will stop expanding and then undergoes collapse. (Prior to discovery of the cosmological constant.).

Indeed radiation and matter is involved in expansion the cosmological constant describes why this expansion is in essence accelerating rather than slowing down as originally predicted. The FRW metric was rewritten to include lambda.

Here is the thing expansion has very little energy per cubic metre via calculations with the critical density formula this equates to roughly [latex] 7.0*10^{-10} [/latex] joules per cubic metre.

So locally to an LSS gravity easily overpowers this miniscule influence. Hence Galaxies themselves are unaffected by expansion.

 Be careful with the balloon or raisin analogy, it primary use is to describe how a homogeneous and isotropic expansion does not change any angles between dots or raisins and without any inherent directional average velocity.

Edited June 21, 2018 by Mordred

[beecee]

19 minutes ago, Mordred said:

 Be careful with the balloon or raisin analogy, it primary use is to describe how a homogeneous and isotropic expansion does not change any angles between dots or raisins and without any inherent directional average velocity.

Noted....All analogies have their limitations.

[swansont]

1 hour ago, Quantum321 said:

Well, what I think is important to me and I contend that the standard model may be flawed. Just because space-time expands doesn't necessarily mean everything in space-time goes along with it.

 

Space. Galaxies themselves are held together by gravity and don't expand. Everything in them, too.

[Quantum321]

Yes. I know that. I am referring to the entire galaxy. Why is it accelerating?

[swansont]

4 hours ago, Quantum321 said:

Oh I see so someone in the membership is not pleased with my thinking. I don't always accept the current dogma, its sad that other blindly do.

!

Moderator Note

This place is for science discussion. It's a science site. Curiosity is welcome. But ignorance-driven dissatisfaction? We'll help you with the ignorance part, but lose the attitude. 

 

4 minutes ago, Quantum321 said:

Yes. I know that. I am referring to the entire galaxy. Why is it accelerating?

It's not. 

[koti]

Well, I tried...

[Endy0816]

1 hour ago, Quantum321 said:

Yes. I know that. I am referring to the entire galaxy. Why is it accelerating?

Accelerating expansion of the Universe.

If the distance between galaxies* only ever doubled per second then you have a nice, constant rate.

But if it starts off being multiplied by 2, then 4,  then 16, you have an accelerating rate.

 

Basically galaxies* = stationary

distance between them all = increasingly increasing

 

*Note superclusters is more accurate. See Andromeda.

[Mordred]

1 hour ago, koti said:

Well, I tried...

 

 The topic is a bit difficult to grasp, with pop media's poor coverage being no help. It is often tricky for some to understand why the universe has accelerating expansion. Yet separate the laws of inertia from that descriptive. For some the expression the space is expanding between galaxies isn't sufficient.

 The difficulty however often lies with first understanding that in order to qualify as an acceleration one must apply a directional force. The OP has already stated he can accept this, one problem solved. The next hurdle is trying to explain how expansion works with the thermodynamic laws and the matter, radiation and cosmological terms. Unfortunately this step is a bit more difficult to grasp.  I recommend reading an article developed by someone who visited forums much like this one who later received his PH.D in Philosophies of Cosmology. His target audience is forum members so he kept the article as low math as possible.

Pay close attention to the difference between separation distance and those laws of inertia I mentioned.

http://tangentspace.info/docs/horizon.pdf :Inflation and the Cosmological Horizon by Brian Powell

lets start here then move into the fluid equations.

 

 

Edited June 22, 2018 by Mordred

[Markus Hanke]

9 hours ago, Quantum321 said:

I honestly don't think that galaxies would accelerate away from each other as a normal consequence of the nature of space-time.  You just don't get acceleration from the lack of a gravitational attraction. Sorry, but I just don't buy it...

As already explained in considerable detail - there is no proper acceleration. So you are not asked to buy into anything more than the validity of the law of gravity.

[Eise]

10 hours ago, Quantum321 said:

Well, what I think is important to me and I contend that the standard model may be flawed. Just because space-time expands doesn't necessarily mean everything in space-time goes along with it.

It seems to me that you see spacetime space as a fluid, as something in itself, that has influence on objects in it. Many physicists here already explained that this view on space is wrong. It it were true that galaxies are accelerating one would be able to measure the fictitious force caused by the acceleration. But we don't. Now you could think that therefore our galaxy is exactly in the middle of the universe, every other galaxy (except maybe the galaxies that belong to our cluster) recedes from us, so these would be able to measure acceleration. But that is against the idea of the cosmological principle, that we have no preferred place or orientation in the universe.

Spacetime is an abstraction of measuring of distances and periods, it is not a physical substance. So saying 'space expands' says nothing more than that distances become bigger. General Relativity can describe this without the idea that galaxies recede from each other due to some local forces. So spacetime does not exert any force on galaxies. Your understanding of space expansion is flawed.

[Eise]

Just found this in the Wikipedia entry of 'Spacetime':

Quote

 

Is spacetime really curved?
In Poincaré's conventionalist views, the essential criteria according to which one should select a Euclidean versus non-Euclidean geometry would be economy and simplicity. A realist would say that Einstein discovered spacetime to be non-Euclidean. A conventionalist would say that Einstein merely found it more convenient to use non-Euclidean geometry. The conventionalist would maintain that Einstein's analysis said nothing about what the geometry of spacetime really is.

Such being said,

1. Is it possible to represent general relativity in terms of flat spacetime?
2. Are there any situations where a flat spacetime interpretation of general relativity may be more convenient than the usual curved spacetime interpretation?
In response to the first question, a number of authors including Deser, Grishchuk, Rosen, Weinberg, etc. have provided various formulations of gravitation as a field in a flat manifold. Those theories are variously called "bi-metric gravitation", the "field-theoretical approach to general relativity", and so forth. Kip Thorne has provided a popular review of these theories.

The flat spacetime paradigm posits that matter creates a gravitational field that causes rulers to shrink when they are turned from circumferential orientation to radial, and that causes the ticking rates of clocks to dilate. The flat spacetime paradigm is fully equivalent to the curved spacetime paradigm in that they both represent the same physical phenomena. However, their mathematical formulations are entirely different. Working physicists routinely switch between using curved and flat spacetime techniques depending on the requirements of the problem. The flat spacetime paradigm turns out to be especially convenient when performing approximate calculations in weak fields. Hence, flat spacetime techniques will be used when solving gravitational wave problems, while curved spacetime techniques will be used in the analysis of black holes.

 

 

 

[geordief]

Is there any way it can be shown  from basic principles that global expansion must ** occur in the absence of gravity  and that the alternative where expansion or contraction do not occur  is completely unfeasible ?

In other  words is the only surprising thing about expansion that the  centre is apparently  everywhere ?(and this as a result of the universe  being  practically point like  in the past)

 

Was this point like origin thought perhaps to be a field like object of some kind  ?

 

**ie  aside from observational evidence.(was the whole idea of a static universe always  a non starter and simply entertained  for lack of real thought on the matter at the time?)

[Markus Hanke]

22 minutes ago, geordief said:

Is there any way it can be shown  from basic principles that global expansion must ** occur in the absence of gravity

Yes, the tendency to expand is already intrinsic in the FLRW solution to the Einstein equations. This is simply a natural consequence of laws of gravity. You would need to introduce a counter-mechanism to stop this from happening, such as an appropriate chosen cosmological constant.

22 minutes ago, geordief said:

and that the alternative where expansion or contraction do not occur  is completely unfeasible ?

It is not completely unfeasible - you can construct a “steady state” type of model by balancing out the observed average energy density of universe with an appropriately chosen cosmological constant. The trouble with this (apart from it not being what we actually observe) is that it is an extremely unstable configuration, like balancing a mountain on a needle - the cosmological constant would have to have an extraordinarily precise value, and even the slightest perturbation of that numerical value would destroy the balance. There is no known physical mechanism that could guarantee the stability of such a configuration, not even in principle; on the other hand, there are plenty of physical mechanisms that would introduce fluctuations in the value of that constant over time and space. So all considered, the “steady state” concept is not very physically feasible.

Edited June 22, 2018 by Markus Hanke

[Strange]

2 hours ago, geordief said:

Is there any way it can be shown  from basic principles that global expansion must ** occur in the absence of gravity  and that the alternative where expansion or contraction do not occur  is completely unfeasible ?

That was covered in the "Meaning of Einstein's Equations" link I provided earlier. 

[geordief]

1 hour ago, Strange said:

That was covered in the "Meaning of Einstein's Equations" link I provided earlier. 

I missed that**, but if GR is accepted as incomplete is expansion within its remit?Would a theory of quantum gravity  eventually have more to say on expansion (or am I thinking of inflation?)

 

**will look.

Edited June 22, 2018 by geordief

[Warped]

errr, pardon the interruption. The term used in Physics is "spacetime'" not "space-time"  Search "Einstein's Field Equations"