How are galaxies expanding along with space time?

[Quantum321]

It's difficult for me to get my head around this. What force moves the galaxies along with space time? One would think that space time would just flow around the galaxies. Are galaxies moving with space time because of dark energy?

[Silvestru]

16 minutes ago, Quantum321 said:

It's difficult for me to get my head around this. What force moves the galaxies along with space time? One would think that space time would just flow around the galaxies. Are galaxies moving with space time because of dark energy?

Space-time is everything, including galaxies. I think there is a slight confusion in your understanding of spacetime so I will not attempt to answer your question. Please read the wiki article:

https://en.wikipedia.org/wiki/Spacetime

 

Quote

In physics, spacetime is any mathematical model that fuses the three dimensions of space and the one dimension of time into a single four-dimensional continuum

 

On the separate subject of why galaxies move, in summary there are 3 types of movement: they rotate, they interact with each other and they are are distancing themselves from each other.

The first two are due to gravity and the third is because:

Edited June 21, 2018 by Silvestru

[Markus Hanke]

It’s space that expands, not spacetime. This is an important distinction in this context.

The tendency for the spatial part of it to expand is intrinsic in this type of spacetime geometry; this means it’s a natural feature of this particular type of geometry. It requires no further cause or agent, other than the nonlinear law of gravity itself. This is somewhat analogous to shaving foam - once released from its spray can, it will have a natural tendency to expand, without the need for any external catalyst; this tendency is already intrinsic in its chemical composition and their physical properties.

The function of dark energy is only to regulate the rate at which the expansion happens - you can accelerate or decelerate the expansion over time, or - if its distribution is chosen in just the right manner - bring it to a halt. You can again liken that to shaving foam - its rate of expansion depends (assuming normal atmospheric pressure) on ambient temperature, just as the rate of metric expansion depends on the distribution of dark energy.

Quote

How are galaxies expanding along with space time?

They aren’t. What is expanding is only the space between them, so it’s the distance between galaxies that increases over time. In general, expansion happens only in regions that are not (or only very weakly) gravitationally bound; also, this expansion is noticeable only across very large scales, on the order of dozens of MPc and above.

Edited June 21, 2018 by Markus Hanke

[Quantum321]

Well, all of space is space time according to Einstein. My question is simple. Space is expanding. What force carries galaxies along with the expanding space. One would think that space would just flow around the galaxies. I know that atoms and molecules are locked together in galaxies and do not expand. I tried to look this up on the internet but no one addresses this question. 

Mr. Hanke " The tendency for the spatial part of it to expand is intrinsic in this type of spacetime geometry" This is where I have a problem. I look at this as an assumption.  What is the mechanism?

Edited June 21, 2018 by Quantum321

[Markus Hanke]

7 minutes ago, Quantum321 said:

Well, all of space is space time according to Einstein.

Space is a 3D hypersurface of simultaneity, for some fixed instant in time. Spacetime is the collection of all such hypersurfaces.

7 minutes ago, Quantum321 said:

What force carries galaxies along with the expanding space.

This question does not make sense, because there is no acceleration involved, so the galaxies do not “move” as a result of metric expansion. It’s only the empty space between the galaxies that expands. This phenomenon has to do with the geometry of spacetime, not with any mechanical forces.

7 minutes ago, Quantum321 said:

One would think that space would just flow around the galaxies.

I don’t know what you mean by this - space is not a medium, it doesn’t “flow”.

7 minutes ago, Quantum321 said:

I tried to look this up on the internet but no one addresses this question. 

That’s because the question does not make any sense in the context of physics.

Edited June 21, 2018 by Markus Hanke

[studiot]

4 minutes ago, Quantum321 said:

Well, all of space is space time according to Einstein. My question is simple. Space is expanding. What force carries galaxies along with the expanding space. One would think that space would just flow around the galaxies. I know that atoms and molecules are locked together in galaxies and do not expand. I tried to look this up on the internet but no one addresses this question. 

Well he didn't actually say that.

Space is a more wooly and general concept.

Spacetime is an artificial framework we use to measure with, just like the milestone or kilometer marking posts along the motorway.

The Universe is expanding, not our framework.

What is happening is that new pieces of 'space' are appearing/being isnerted between the existing ones.

These new pieces are identical to their older counterparts.

So the galaxies, milestones and kilometer posts stay the same, but just get further and further apart.

 

[Quantum321]

studiot

I understand that space is expanding using the process you described. But there is no friction in space. When space expands and encounters the atoms in a galaxy what pushes the atoms. Now I am sure you will say that in the current understanding of cosmological models that its intrinsic. But from a physical perspective I don't get it.

Let's look at it this way. Where ever I am in the universe everything appears to be moving away from everything else. There is no preferred place. So if space is expanding what why are the galaxies moving?

 

[Markus Hanke]

9 minutes ago, Quantum321 said:

What is the mechanism?

The mechanism would be the law of gravity itself. The macroscopic behaviour of galaxies etc across very large scales is taken to conform to the same law of gravity that also governs small scales, such as the motion of bodies in our solar system. We know from experiment and observation that this law (being the Einstein equations) is valid to a very high degree of accuracy on scales on the order of the solar system - from this, we extrapolate to larger scales, and the tendency to expand naturally emerges. So in essence, this tendency happens for the same reason why a rock falls towards the surface of the earth, when released somewhere high above. It’s a manifestation of gravity. 

15 minutes ago, Quantum321 said:

I look at this as an assumption.

It’s not so much an assumption as an extrapolation - it being that gravity works the same way on large scales as it does on small scales. If that extrapolation is accurate, then metric expansion naturally happens.

17 minutes ago, Quantum321 said:

This is where I have a problem.

Why is this a problem? We have no real reason to believe - as of yet - that gravity works differently on large scales than it does here in our neighbourhood. Of course, it is possible that gravity is scale-dependent - in fact, many alternative models of gravity have been developed over the past several decades that are based on precisely that possibility, so modern physics is definitely open to this idea. But the fact is also that none of these models have been able to match experiment and observation with the same degree of accuracy as General Relativity does. As “illogical” as standard cosmology may appear to the untrained eye (and I do grant you that it can appear that way), it is actually the simplest possible model to explain what we can observe. Most alternative models are very much more complicated, and require even more illogical assumptions.

[Quantum321]

Where is the gravity in space that interacts with the gravity of matter? Gravity is the weak and strong atomic forces. How does space interact with these forces?

[koti]

4 minutes ago, Quantum321 said:

Where is the gravity in space that interacts with the gravity of matter? Gravity is the weak and strong atomic forces. How does space interact with these forces?

Gravity is a seperate force from weak and strong interaction. The strong force holds matter together, the weak force causes radioactive decay and gravity is spacetime curvature under GR - 3 completely different forces/interactions. 

[Markus Hanke]

Just now, Quantum321 said:

Where is the gravity in space that interacts with the gravity of matter?

I don’t understand this question; can you explain a bit more?

1 minute ago, Quantum321 said:

Gravity is the weak and strong atomic forces.

No, gravity is distinct from the weak, strong and EM interactions. They are not the same thing, and function in very different ways.

2 minutes ago, Quantum321 said:

How does space interact with these forces?

Again, I am unsure what you mean by this. Space is not a separate entity in and of itself, and hence it does not “interact” with anything. It’s best understood as a background, a “stage” of you so will. I think a good way to look at space(time) is as a collection of events, and the relationships between these events are the geometry of spacetime.

On very small scales, as on atomic and subatomic levels, gravity plays almost no role at all under normal circumstances, since its coupling strength is very much weaker than any of the other interactions by many, many orders of magnitude. There are, however, scenarios where gravity becomes so strong that it cannot be neglected even on small scales (e.g. the interior region of black holes, or the very earliest times in the evolution of the universe) - but we are not currently able to describe such domains, because unlike the other three fundamental interactions, gravity cannot be straightforwardly quantised, since its nature is very different from the one of the other interactions. This is currently an area of very active and ongoing research.

[swansont]

26 minutes ago, Quantum321 said:

I understand that space is expanding using the process you described. But there is no friction in space. When space expands and encounters the atoms in a galaxy what pushes the atoms.

No, it doesn't push the atoms. Space expands, and two objects would tend to get further apart since there is more space between them. But there is no push.

The objects won't get further apart if they are bound together e.g. gravitationally

26 minutes ago, Quantum321 said:

Now I am sure you will say that in the current understanding of cosmological models that its intrinsic. But from a physical perspective I don't get it.

Let's look at it this way. Where ever I am in the universe everything appears to be moving away from everything else. There is no preferred place. So if space is expanding what why are the galaxies moving?

How would they not appear to move if you add space in between you and the galaxy you are observing?

[Quantum321]

Koti. No gravity is not a separate force. Gravity wave A is the strong nuclear force and gravity wave b is the weak force. Scientists have know this for some time now but keep it under wraps.

[Markus Hanke]

32 minutes ago, Quantum321 said:

When space expands and encounters the atoms in a galaxy what pushes the atoms.

Again, you need to remember that space is not any kind of mechanical medium, and that there is no motion involved, in the sense that no forces act on anything. If you were to attach an accelerometer to any of these galaxies, it would read exactly zero at all times, so there is no acceleration and hence no forces that act on anything. All that happens is that the distance between galaxies increases, because space there expands - so there is relative/apparent motion due to the increase in distances, but no local motion that involves forces or the transfer of energy. It’s purely a geometric phenomenon.

[studiot]

The milestones don't change, it's the numbers on them that change.

And since they are artificial constructs we can allow new ones to 'appear' without pushing the old ones.

[Markus Hanke]

Just now, Quantum321 said:

Koti. No gravity is not a separate force. Gravity wave A is the strong nuclear force and gravity wave b is the weak force. Scientists have know this for some time now but keep it under wraps.

This does not make any sense, I’m afraid.

[studiot]

1 minute ago, Quantum321 said:

Koti. No gravity is not a separate force. Gravity wave A is the strong nuclear force and gravity wave b is the weak force. Scientists have know this for some time now but keep it under wraps.

Koti is correct, although he could perhaps have expressed it better.

If this is the beginning of a conspiracy theory I am leaving the thread.

[Quantum321]

Swansont. " No, it doesn't push the atoms. Space expands, and two objects would tend to get further apart since there is more space between them. But there is no push. " This is exactly my problem. What physical properties are involved in "two objects would tend to get further apart since there is more space between them" Why would they? What force makes them get farther apart?

Markus Hanke

It makes perfect sense. There is no other force involved in gravity. It's not an undiscovered force. Do you honestly think that modern science could not detect a gravitational force if it existed?

I am not here to talk about gravity. I just can't accept the premise that matter will go with space as it expands. How could it do that without some mechanism to make it happen?

Edited June 21, 2018 by Quantum321

[Silvestru]

8 minutes ago, Quantum321 said:

Do you honestly think that modern science could not detect a gravitational force if it existed?

 

12 minutes ago, Quantum321 said:

No gravity is not a separate force. Gravity wave A is the strong nuclear force and gravity wave b is the weak force. Scientists have know this for some time now but keep it under wraps.

What experience, knowledge do you have on gravitational wave detection? 
Please move this thread to speculations/trash. I fear we will soon find out a new conspiracy theory.  

[studiot]

9 minutes ago, Quantum321 said:

I just can't accept the premise that matter will go with space as it expands.

Space doesn't 'go' anywhere. That is a false premise.

What would it move through?

 

[Markus Hanke]

14 minutes ago, Quantum321 said:

What force makes them get farther apart?

I think it is important that you actually read the replies you get on here, because otherwise you will just keep going in circles. As already explained, there is no force acting on the galaxies. There are no forces involved in any of this at all.

14 minutes ago, Quantum321 said:

There is no other force involved in gravity. It's not an undiscovered force. Do you honestly think that modern science could not detect a gravitational force if it existed?

Gravity is not a force - it’s a geometric property of spacetime. If you drop an accelerometer, it will read exactly zero at all times (you can try that out yourself at home), so as per F=ma, with a=0, there is no force. Yet it will still fall under the influence of gravity, and according to its rules.

Also, the weak/strong/EM interactions are not forces in the Newtonian sense either - they are interacting quantum fields. There are no mechanical forces involved anywhere in this. 

I think your basic problem is that you assume the universe and everything that is in it to be Newtonian (essentially the kind of physics you learn in high school) - but in reality it isn’t. Newtonian mechanics is just a highly simplified approximation that applies only under very limited circumstances. Even on comparatively small scales such as the solar system, Newtonian physics already fails miserably. Cosmology then is very far outside its domain of applicability. Trying to ask about what forces act on galaxies etc is hence largely meaningless, because the very concepts are essentially meaningless in the context of cosmology. There are other things at play here. 

All of this can very easily be understood in the framework of spacetime geometry - but if you do not acknowledge that as a valid concept (your own prerogative, of course), then there will be little point in this discussion.

Edited June 21, 2018 by Markus Hanke

[Quantum321]

I see I just received a demerit for telling the truth. OK.

" Space doesn't 'go' anywhere. That is a false premise. " I agree. Space it constantly being expanded through new space being generated as has been explained above. So you have space expanding..Why are galaxies moving along with the expanding space.

I am sorry. I have many posts in this thread I need to read. I know Einsteins equations explain all of this and this is what scientist have come to accept. It may be counter intuitive but something just doesn't set with me right.

Thanks to everyone for your comments.

Edited June 21, 2018 by Quantum321

[Silvestru]

1 minute ago, Quantum321 said:

So you have space expanding..Why are galaxies moving along with the expanding space.

 

Because the space between said galaxies is increasing.

[Quantum321]

29 minutes ago, Markus Hanke said:

Again, you need to remember that space is not any kind of mechanical medium, and that there is no motion involved, in the sense that no forces act on anything. If you were to attach an accelerometer to any of these galaxies, it would read exactly zero at all times, so there is no acceleration and hence no forces that act on anything. All that happens is that the distance between galaxies increases, because space there expands - so there is relative/apparent motion due to the increase in distances, but no local motion that involves forces or the transfer of energy. It’s purely a geometric phenomenon.

I hear you. Look at the Hubble constant. By definition galaxies are move away at an increasing rate based on parsec's of distance. "Moving away at an increasing rate" If you measure their rated of expansion from earth how can the accelerator read zero?

6 minutes ago, Silvestru said:

 

Yes I have also heard to raisins in the bread analogy. But that's not the same as galaxies and space.

[studiot]

1 minute ago, Quantum321 said:

1)

I see I just received a demerit for telling the truth. OK.

2)

" Space doesn't 'go' anywhere. That is a false premise. " I agree. Space it constantly being expanded through new space being generated as has been explained above. So you have space expanding..Why are galaxies moving along with the expanding space.

 

1) Nothing to do with me.

 

2) It is perhaps unfortunate that we don't have good words for this or that the words we have possess more than one meaning.
So selecting the wrong (inappropriate)  meaning for a word can result in a self contradictory meaningless statement.

 

We have the 'balloon analogy".

Like all analogies it is not an exact match so it has some properties in common with what we are modelling and some that are different.

This is OK just so long as we stick to the matching properties.

 

One property that does match is the process of inflating the balloon.

(It is regretable that one small section of scientists chose to hijak the word inflation to mean something entirely different)

But anyway imagaine the balloon partly inflated and we paint grid lines onto the surface with dots at each intersection.

Now let us inflate the balloon further.

We can easily observe several important facts that match what we see in the heavens.

1) The lines and dots are still attached to the same piece of balloon skin. They have not moved.

2) The balloon skin is still a continuous whole, it's just bigger.

3) New skin has appeared everywhere.

4) The lines and dots are now further apart as measured with our original tape measure.

 

Is there anything that troubles you about this?