expanding universe... but galaxies?

[juvilado]

hi, as Hubble noticed in the 20th century, galaxies are getting further from each other, as a result of the expanding universe. space itself isexpanding. my question is, as space itself is expanding and galaxies are located in space, are galaxies expanding too? is for instance the milky way getting wider?

[Shpaget]

On short time scales, no.

We're not quite sure what will happen in the future.

There are several hypothesis on what will happen, depending on what turns out to be true regarding the existence and density of dark energy.

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

Edited May 1, 2016 by Shpaget

[Camacha]

3 hours ago, juvilado said:

hi, as Hubble noticed in the 20th century, galaxies are getting further from each other, as a result of the expanding universe. space itself isexpanding. my question is, as space itself is expanding and galaxies are located in space, are galaxies expanding too? is for instance the milky way getting wider?

Gravity keeps things that are already close to each other together. Much later, things might fall apart.

Though, let us be honest, this is something that could easily have been answered by a simple Google search

[PB666]

The critical point about Dark Energy is that we know less about it than Dark Gravity. in fact the source and disposiotion is only visible at distance of 10 billion light years.

[K^2]

Size of a galaxy is function of its mass and angular momentum, neither of which change with space expansion. Hence the galaxies flying apart, rather than getting larger. This does mean that galaxies experience a type of stress from expansion, but all that's going to do is shift the equilibrium size a tiny bit.

[PB666]

1 hour ago, K^2 said:

Size of a galaxy is function of its mass and angular momentum, neither of which change with space expansion. Hence the galaxies flying apart, rather than getting larger. This does mean that galaxies experience a type of stress from expansion, but all that's going to do is shift the equilibrium size a tiny bit.

The only thing I would say about this is that if the universe slowing its expansion at a rate consistent with its gravity, then the effect on galaxies is minimal, because different each galxies motion is more dependent on local clusters and superclusters, and even so these are minimal compared to internal structures and proximal intergalactic dark matter. So that the intergalactic expansion of space-time should not have that much effect on the internal structure. 

The problem is dark energy, if dark energy acts in the vacuum of deep space the stretch is being born by dark matter in intergalactic space and again what goes on in galaxies and the internal motion, given the contribution of dark matter to the motion of galaxies we would be hard pressed to see its effect. If dark energy acts ubiquitously, a concept in and of itself is difficult to reconcile in a relativistally smooth manner, it is counteracting the force of gravity, then the graviational constant would have problems. For example, if you had a very dense body, like say Mercury, its gravitation constant would be much higher than a massive less dense onject like neptune. In addition it would completely counteract the affect of dark matter. 

This is all I want to say given so little known about dark energy, the effects could be inverse scalar on energy load and could have miniscule effects in dense energy space and overwhelming effects in massless space, but even here we are unaware of the scale. 

Rather than predicting any effects on galaxies I suggest we wait until at least some science comes in and addresses descrepancies. 

[Bill Phil]

Yes. But the amount over small lengths ( a hundred thousand light years is pretty small on the universe scale) is not very noticeable or large on human timescales. 

Like, if it expands by a factor of 1.00000001 in a hundred years then it won't get bigger by a single lightyear. But, over multiple billions of lightyears, the linear difference is much larger. These aren't actual numbers, though... Just an example. 2 times 2 is 4, but 2 times 8 is 16. The linear difference is very different.

[K^2]

8 hours ago, PB666 said:

So that the intergalactic expansion of space-time should not have that much effect on the internal structure. 

The problem is dark energy

The effect of dark energy is likewise minimal, simply because at galactic scale, acceleration is pretty much negligible. Yes, it'd be much harder for us to predict exactly what the impact of dark energy is, since we don't even really know how it's distributed for sure. But either way, it's not going to have a measurable effect on the structure of galaxies.

[NecroBones]

17 hours ago, juvilado said:

hi, as Hubble noticed in the 20th century, galaxies are getting further from each other, as a result of the expanding universe. space itself isexpanding. my question is, as space itself is expanding and galaxies are located in space, are galaxies expanding too? is for instance the milky way getting wider?

 

It's a great question. The answer is pretty much "no", galaxies aren't getting bigger due to the universe expanding. The short explanation is that within the confines of a galaxy, gravity is the dominant force, and expansion isn't happening. Between galaxies, in the large voids between clusters, "dark energy" is the dominant force, and the bulk of the expansion occurs there.

 

PBS Space Time answers this question here: (time index 9:23)

 

 

[Kertech]

as said above essentially no becuse gravity is stronger, however things do get weird if expansion occurs again (where growth occurs faster than the speed of light) where gravity (assumed to be transmitted at the speed of light) would either accelerate too (no change) or stay the same (an stuff will be stretched) but this is all very edge of field stuff and i don't know enough to really weigh in

[cubinator]

Hey, let's keep this on topic. It's an interesting question.

Because small objects like galaxies (wow, I just called galaxies small) are gravitationally bound, they won't be getting much bigger anytime soon. The closer you are to a massive object (like a galaxy or planet) the more it's gravity pulls on you. That's why most galaxies are not falling into each other unless they are very close (like Milky Way/Andromeda). Similarly, the expansion force is not very strong on objects that are held tightly together.

Imagine you are lying on your back on a sphere that is magically floating above the ground. A very large sphere would be quite comfortable to lie on, if it is many times larger than you. That is like what galaxies feel from the expansion force. If the sphere were smaller, it might be less comfortable, because the steeper curve pulls you down more. A sphere that was very small would hurt a lot! When you lie on your back on Earth's surface, can you tell it's round? Probably not. That's because you are so small compared to Earth that the amounts of it's circumference you encounter in daily life (unless you are an astronaut or something) are not large enough to show any noticeable amount of curvature.

It is theorized that if the expansion of the universe continues to accelerate, eventually the expansion force would overcome gravity and galaxies, then even stars and planets, and finally atoms until the universe was full of nothing but the most basic sub-atomic particles, which would continue to move away from each other until no two particles are in each others' observable universes, and then literally nothing would happen ever again. Or maybe there would be another Big Bang. We really don't know what will happen. But that would only occur in over 10¹⁰⁰ years, so we've got plenty of time.

To summarize, galaxies are not expanding significantly with the rest of the universe because they have strong gravity near them, and the expansion force isn't very strong over small distances.

I hope this helps explain your question! 

[Neriux]

Ok, your universe theories is great, but look at it as at bobble wave "speed of light effect". We can see light crossing our planet at this only moment, we cant travel to anywhere so our planet and moment its 1 second, its same like u doing photo. If universe started 13+ billions years ago, then we see middle not at starting point, starting point is outside of us 13+ billions light years away, behind our baks. And center what u seeing with "Houble" its what happened 13+ billions years before us. So center can be 1 milliard years long but for us its be just empty space. we can see just belt around us of our crosing time, light wawes from all around us. So your theories is sorry but bulexcrements, u cant jump in yesterdays train u cant even see it after it left station after reflected light moved from him away at 5 minutes from reaching horizon't.

And at same time if we moving faster than light, then we traveling back in time, and caching up light waves what even older. And even in this point to us center is empty buble of time, not because its empty but because his light long gone. Our universe probably microsecond at someone atom collider, and cosmos black because they not put there light.